# A Common Terminology to Unify Research and Conservation of Coralline Algae and the Habitats They Create

Victor L. Jardim, Jacques Grall, M. Beatriz Barros-Barreto, Anaëlle Bizien, Thomas Benoit, Juan C. Braga, Juliet Brodie, Thomas Burel, Andrea Cabrito, Guillermo Diaz-Pulido, et al.

<figure><img src="image_1.png" /></figure>

To cite this version:

Victor L. Jardim, Jacques Grall, M. Beatriz Barros-Barreto, Anaëlle Bizien, Thomas Benoit, et al. A Common Terminology to Unify Research and Conservation of Coralline Algae and the Habitats They Create. Aquatic Conservation: Marine and Freshwater Ecosystems, 2025, 35 (3), 10.1002/aqc.70121. hal-05018044

HAL Id: hal-05018044

https://hal.univ-brest.fr/hal-05018044v1

Submitted on 3 Apr 2025

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_2.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
<figure><img src="image_3.png" /></figure>

PERSPECTIVE

OPEN ACCESS

# A Common Terminology to Unify Research and Conservation of Coralline Algae and the Habitats They Create

Victor L. Jardim¹ ID | Jacques Grall¹,² ID | M. Beatriz Barros-Barreto³ ID | Anaëlle Bizien² | Thomas Benoit⁴ |
Juan C. Braga⁵ | Juliet Brodie⁶ ID | Thomas Burel¹ ID | Andrea Cabrito⁷ | Guillermo Diaz-Pulido⁸ ID | Patrick Gagnon⁹ |
Jason M. Hall-Spencer¹⁰,¹¹ | Mathieu Helias¹²,¹³ | Paulo Antunes Horta¹⁴ ID | Siddhi Joshi¹⁵ | Nick A. Kamenos¹⁵,¹⁶ |
Regina Kolzenburg¹⁵ ID | Erik C. Krieger¹⁷,¹⁸ | Erwann Legrand¹⁹ ID | Tessa M. Page²⁰ ID | Viviana Peña²¹ |
Federica Ragazzola²²,²³ | Lina M. Rasmusson²⁴ ID | Francesco Rendina²⁵ | Nadine Schubert²⁶ ID | João Silva²⁶ |
Frederico T. S. Tâmega²⁷ ID | Adeline Tauran²⁸ | Heidi L. Burdett¹⁵,¹⁶ ID

¹Université de Brest, CNRS, IRD, Ifremer, LEMAR, IUEM, Plouzané, France | ²UAR 3113, Observatoire Marin, Université de Brest, Plouzané, France | ³Department of Botany, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil | ⁴Ifremer, Centre de Bretagne, DYNECO, Laboratory of Coastal Benthic Ecology, Plouzané, France | ⁵Departamento de Estratigrafia y Paleontología, Universidad de Granada, Granada, Spain | ⁶Natural History Museum, Research, London, UK | ⁷Institut de Ciències del Mar (ICM), CSIC, Barcelona, Spain | ⁸School of Environment and Science, Coastal & Marine Research Centre, Griffith University, Nathan, Queensland, Australia | ⁹Department of Ocean Sciences, Ocean Sciences Centre, Memorial University of Newfoundland, St. John's, Newfoundland and Labrador, Canada | ¹⁰School of Biological and Marine Sciences, University of Plymouth, Plymouth, UK | ¹¹Shimoda Marine Research Center, University of Tsukuba, Shimoda, Japan | ¹²Conservatoire National des Arts et Métiers, INTECHMER, Cherbourg-en-Cotentin, France | ¹³Normandie Université, UNICAEN, Laboratoire des Sciences Appliquées de Cherbourg, Cherbourg-en-Cotentin, France | ¹⁴Departamento de Botânica, Universidade Federal de Santa Catarina, Florianópolis, Brazil | ¹⁵Umeå Marine Sciences Centre, Umeå University, Umeå, Sweden | ¹⁶Department of Ecology & Environmental Science, Umeå University, Umeå, Sweden | ¹⁷Red Sea Research Center, King Abdullah University of Science and Technology, Thuwal, Saudi Arabia | ¹⁸School of Biological Sciences, Victoria University of Wellington, Wellington, New Zealand | ¹⁹Institute of Marine Research, Bergen, Norway | ²⁰School of Ocean and Earth Science, University of Southampton, National Oceanography Centre Southampton, Southampton, UK | ²¹Facultad de Ciencias, BIOCOST Research Group, A Coruña, Spain | ²²Genoa Marine Center, Stazione Zoologica Anton Dohrn, Villa del Principe, Genoa, Italy | ²³National Biodiversity Future Center (NBFC), Palermo, Italy | ²⁴Department of Biological and Environmental Sciences, University of Gothenburg, Gothenburg, Sweden | ²⁵Department of Science and Technology, Laboratory of Marine Ecology, Centro Direzionale, University of Naples Parthenope, Naples, Italy | ²⁶Centre of Marine Sciences (CCMAR/CIMAR LA), Campus de Gambelas, Universidade do Algarve, Faro, Portugal | ²⁷Departamento de Biotecnologia Marinha, Instituto de Estudos do Mar Almirante Paulo Moreira (IEAPM), Arraial do Cabo, Brazil | ²⁸Université de Bordeaux, CNRS, Bordeaux INP, EPOC, UMR 5805, Station Marine d'Arcachon, Pessac, France

**Correspondence:** Victor L. Jardim (victor.leitejardim@univ-brest.fr)

**Received:** 11 June 2024 | **Revised:** 4 March 2025 | **Accepted:** 7 March 2025

**Funding:** This work was supported by Wiley.

**Keywords:** algal ridges | carbonate crust | CCA | coral-algal reefs | coralligenous | coralline algae | linguistic uncertainty | maerl | rhodolith | typology

## ABSTRACT

Linguistic uncertainty is a prime source of uncertainty pervading ecology and conservation. Coralline algae are a widespread and diverse group of calcifying red macroalgae that underpin coastal ecosystem function and service provision. Recent increasing interest in coralline algae in the scientific literature has revealed a diverse but confusing terminology at organism to habitat scales. Coralline algal research and conservation are international and multidisciplinary, so there are geographic and disciplinary imbalances in research and conservation efforts. To reach consensus and reduce uncertainty, we propose a unified terminology. We review trends in cultural and scientific use of coralline algal terms and propose a system based on six morphologies: (1) attached, (2) free-living geniculate, (3) encrusting and free-living nongeniculate coralline algae, the latter either being (4)

This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

© 2025 The Author(s). *Aquatic Conservation: Marine and Freshwater Ecosystems* published by John Wiley & Sons Ltd.
nucleated or (5) non-nucleated thalli or (6) fragments. We take inspiration from other coastal systems that have achieved consensus through umbrella terms, such as ‘coral’ and ‘kelp’, to accelerate global progress in coralline algal research and conservation. We characterise 14 coralline algae–dominated habitat global types, falling within seven functional groups, four biomes and four realms: (1) freshwater coralline streams; (2) coralline tide pools; (3) intertidal coralline rims and (4) turf; (5) coralline sea caves; (6) coral–algal reefs; (7) algal ridges; (8) coralligenous reefs; subtidal (9) carbonate crusts, (10) coralline barrens and (11) turf; and (12) articulith, (13) maerl and (14) rhodolith beds, which fall into the coralline algal bed functional group. We hope this unified terminology promotes data comparison, enables cross-boundary and cross-sector sharing of best practices, develops capacity for meta-analyses and improves conservation strategies.

# 1 | Introduction

A subject with strong cultural, scientific and/or socio-economic connections is usually associated with a high diversity of terms to describe it, because language and human cognition and perception are deeply intertwined (Drew 2005; Klemfuss et al. 2012; Thierry 2016). Similarly, the stronger the connections of a people to a species or group of species, the higher the number of words to describe them (Drew 2005). This pattern can also be seen in scientific language. However, while a diverse terminology can enable specific descriptions, it can also hinder broader scientific understanding of the subject. This is due to increasing uncertainty (Kéfi et al. 2019; Kovalenko et al. 2012), where there is a lack of a unique and complete understanding of a subject. Uncertainty can arise from contrasting multiple knowledge—distinct but equally valid views (Brugnach et al. 2008). Linguistic uncertainty has been identified as one of the main classes of uncertainty that impairs ecological knowledge and effective conservation strategies (Regan et al. 2002; Kujala et al. 2013).

Coralline algae are a highly diversified, globally distributed group of red calcifying macroalgae (Corallinophycidae, Rhodophyta) that thrive in marine and locally in freshwater environments under a wide range of conditions (Johansen 1981; Žuljević et al. 2016). Following pioneering taxonomy-driven work at the end of the 19th century (Foslie 1894; Woelkerling et al. 2005; Woelkerling 2008), coralline algae have received increasing attention in the scientific literature (Figure 1). This interest came from the recognition of their global importance for coastal ecosystem function, service provision and biogeochemical cycling, their sensitivity to projected environmental change and their value in palaeoecological records (McCoy and Kamenos 2015). Similarly, given the biological resources provided by the habitats these coralline algae create, there is increasing concern related to their exploitation (Grall and Hall-Spencer 2003; Riosmena-Rodríguez 2017; Berchez 2022; Mógor et al. 2021; Ramos et al. 2023). Such recognition is driving conservation efforts, with coralline algae being increasingly included in marine management frameworks around the world (European Commission et al. 2016; Keith, Fragkopolou, et al. 2022; Brodie et al. 2023; Axelsson 2023).

As a consequence of increasing recognition and the unmatched morphological diversity of the group, the terminology used for coralline algae and the habitats they form has also become diverse, sometimes leading to linguistic uncertainty (McCoy and Kamenos 2015). The European Red List of Habitats (European Commission et al. 2016) exemplifies this

linguistic uncertainty in coralline algal science and conservation. This document alone has 11 names for coralline algal habitats and includes numerous others in which coralline algae are notable components (Figure 2; Table S1). Among the terms used, some are polysemic (have multiple meanings) and context dependent, while some are synonymous. This linguistic uncertainty has the potential to lead to misunderstandings among researchers, decision-makers and other stakeholders, transcending into policy-making (Norton 1998; Milner-Gulland and Shea 2017) and public engagement (Vigliano Relva and Jung 2021).

Coralline algal research and conservation are inherently international and disciplinarily diverse due to the worldwide distribution and the diversity of the algal group. This leads to local and regional scale variations in priorities: Coralline algal research disciplines are not evenly developed worldwide (Rendina et al. 2022) and conservation efforts depend on local pressures and stakeholders (Keith, Ferrer-Paris, et al. 2022). Here, we highlight the importance of unification and community consensus as a tool for contextualisation, to ensure readers understand the meaning of a term (Crump et al. 1999). We review how coralline algal terminology has evolved since the 18th century at organism and habitat levels, identifying long-term trends in cultural and scientific usages of these terms and proposing a unified typology for coralline algal habitats, providing authors with terms that can make communication about these algae more efficient. We hope this will help advance coralline algal research and conservation by (1) facilitating observational and experimental data comparisons; (2) enabling cross-boundary and cross-sector sharing of technique developments, best practices and conservation strategies; and (3) improving meta-analyses, as synonyms can be missed in published literature leading to skewed results (Hodges 2008; Stroud et al. 2015; Cira et al. 2019).

# 2 | Facilitating Progress in Coralline Algal Research and Conservation Worldwide

A unified terminology for coralline algal habitats may foster better international research collaboration, accelerating the advancement of coralline algal research frontiers and base conservation strategies on a more coherent foundation. In other coastal systems, this has been achieved—‘coral’, ‘kelp’, ‘seagrass’ and ‘mangrove’ are umbrella terms for 10s–1000s of species with high intravariability, and all have similarly simple habitat terms. The cohesive terminology and grouping of such diverse habitats has facilitated their international recognition within research,
<figure><img src="image_4.png" /><figcaption>**FIGURE 1** | Scopus search for publications containing coralline algal terms in the title, abstract or keywords from 1970 to 2023. (A) Search terms: 'coralline alga*' OR 'coralline red alga*' OR 'coralligene*' OR 'coralligenous' OR 'maerl*' OR 'rhodolite*' OR 'rhodolith*'. Total number of publications = 3713. Total and individual term trends are shown—note that one publication may contain more than one term. (B) Number of single-country publications containing the terms (maerl*) or rhodolith ('rhodolith*' OR 'rhodolite*'), showing the 10 most productive countries to illustrate regional and global trends, created with the 'bibliometrix' R package (Aria and Cuccurullo 2017; R Core Team 2024).</figcaption></figure>

conservation and more widely, with numerous examples of global datasets and assessments (Hamilton and Casey 2016; Krumhansl et al. 2016; McKenzie et al. 2020; Sully et al. 2019; van Katwijk et al. 2016; van Woesik and Kratochwill 2022). Recognition for the importance of coralline algal research lags far behind—we believe due in part to the disparate terminology used at organism to habitat levels. Similarly, global datasets for coralline algae and the habitats they form are lacking, despite increasing academic attention (Figure 1).

Ecosystem conservation and management is typically implemented through local action, which may lead to both epistemic and linguistic uncertainty when aggregated at larger scales (Box 1; Keith, Ferrer-Paris, et al. 2022). However, international and interdisciplinary studies, which depend on a coordinated scientific community, enable cross-comparisons between baseline knowledge, ecological status and conservation efforts and help share successful policies and protect coralline algal habitats globally (Wilson et al. 2004; Brodie 2009; Tuya et al. 2023). Scaling-up local ecological data helps global conservation (Agardy 2005; Edgar et al. 2016, 2014; Rowland et al. 2020) and is needed for coralline algal conservation as at present, this is a data-deficient topic (Ferrigno et al. 2023; McCoy and Kamenos 2015; van der Heijden

and Kamenos 2015; Rendina et al. 2022; Ferrigno et al. 2023). Addressing linguistic uncertainty will help resolve this and better set conservation objectives (Milner-Gulland and Shea 2017).

An increasing number of studies proposing unified terminologies to resolve language uncertainty in ecology often resort to trait-based and functional approaches (Bellwood et al. 2024; Ellison 2019; Keith, Ferrer-Paris, et al. 2022; Streit and Bellwood 2023). Here, we review the terms used for coralline algae and propose a unified typology at first the organism and then the habitat level. We then define coralline algae-dominated habitats based on the International Union for Conservation of Nature (IUCN) Global Ecosystem Typology (GET) (Keith, Ferrer-Paris, et al. 2022).

### 3 | The Emergence of a Diverse Terminology

All orders within the Corallinophycidae (Phylum: Rhodophyta), except the Rhodogorgonales, fall under the umbrella term 'coralline algae'—almost all of which have extensive calcification in the cell walls (Jeong et al. 2021). The Rhodogorgonales have a very different calcification process and a gorgonian-like filamentous morphology (Fredericq and Norris 1995). The
<figure><img src="image_5.png" /><figcaption>**FIGURE 2** | Coralline algae in the European Red List of Habitats (European Commission et al. 2016). (A) The number of habitats where coralline algae are in the habitat name (n=11) or are listed as a notable component in the habitat description (n=22) and (B) the current conservation status of coralline algal-associated habitats across the Mediterranean, Black Sea and Atlantic regions. Further information on each habitat is provided in Table S1.</figcaption></figure>

coralline algae are divided into two groups based on morphology (Figure 3): geniculate (erect fronds with uncalcified segments known as genicula) and nongeniculate (thalli lacking uncalcified segments). However, this morphological division is not reflected in their phylogeny. The order Corallinales has both geniculate and nongeniculate taxa, sometimes in a single genus, assuming evolutionary reversals of some taxa to theancestral, nongeniculate state (Hind et al. 2018). Nongeniculate coralline algae can have a free-living or encrusting morphology, the latter being flat or with branch-like protuberances (Irvine and Chamberlain 1994). Some species are exclusively encrusting, while others can be found both free-living or encrusting (Hernandez-Kantun et al. 2016).

Besides the presence of genicula, coralline algae present great morphological and functional diversity. They greatly vary in size, thickness and shape, varying from (small) to (large). The group also presents several life strategies: parasitic, semiedophytic, epilithic, epiphytic, epizoic or live as epibionts on man-made surfaces such as glass, plastic and metal (Adey and Sperapani 1971; Adey and Macintyre 1973; Harvey et al. 2005; Dean et al. 2015; McCoy and Kamenos 2015). This diversity is thought to be at least partially due to the presence of secondary pits and vegetative cell fusions that allow the translocation of photosynthates to living cells beneath photosynthetic tissues, allowing lateral growth (Steneck 1983, 1986). The morphological and functional diversity of the group has contributed to the proliferation of terms used to describe coralline algae.

**3.1 | Free-Living Nongeniculate Coralline Algae**

Free-living, nodule forming, nongeniculate coralline algae have been documented since the mid-18th century (e.g., Linnaeus 1758; Ellis and Solander 1786), although they were

thought to be animals that looked like plants (zoophytes) until Philippi (1837) identified them as photosynthetic organisms. Initially classified as *Millepora* hydrocorals (Ellis and Solander 1786; Pallas 1766) and later as *Nullipora* zoophytes (Lamarck 1801), they were then identified as coralline algae of the genera *Lithothamnion* Heydrich and *Lithophyllum* Philippi, in the mid-late 1800s (Wiegmann 1837; Chauvin 1842; Foslie 1894). Since then, multiple terms have arisen from both traditional and scientific ecological knowledge, with varying consensus over their interchangeability such as coatings, nodules, maerl, rhodoliths, rhodolites or rhodoids; there are at least 12 terms used in the academic literature for free-living coralline algae (Riosmena-Rodríguez 2017).

For example, in the early 20th century the Breton word maerl (*maërl*, in French) started gaining popularity in the scientific community (Lemoine 1910), although it had been used for centuries by Celtic and French people in reference to the coralline algae exploited for soil treatment—as a variant of ‘marne’ the word for calcareous rocks (Augris and Berthou 1990). The terms ‘maerl’ and ‘maerl beds’ have been historically used for unattached coralline algal habitats created by *L. corallioides* (P.Crouan & H.Crouan) P. Crouan & H. Crouan, *Boreolithothamnion glaciale* (Kjellman) P.W.Gabrielson, Maneveldt, Hughey & V. Peña (previously *Lithothamnion glaciale*) and *P. calcareum* (Pallas) W.H.Adey & D.L.McKibbin ex Woelkering & L.M.Irvine in the Northeast (NE) Atlantic and subarctic seas (Cabioch 1969; Adey and Macintyre 1973; Barbera et al. 2003; Wilson et al. 2004; Hinojosa-Arango et al. 2009; Peña et al. 2014; Jenkins et al. 2021). These species often lack a nucleus, the main reason why many now consider only such forms as maerl (sensu stricto). At least 13 different maerl-forming species have been identified in the NE Atlantic with many different growth forms (Peña et al. 2013, 2021; Pardo et al. 2014; Qui-Minet et al. 2021; Helias and Burel 2023). The term maerl sensu lato has sometimes been
**Box 1. Rhodolith/maerl beds: a tale of detrimental linguistic uncertainty in conservation efforts and how human connection may improve it**

An example of linguistic uncertainty affecting conservation is a lack of cohesion on free-living non-geniculate coralline algae terminology. The European Red List of Habitats (Table S1) uses the term ‘maerl beds’ for the Atlantic but “rhodolith beds” for the Mediterranean, although both are defined as “sedimentary bottoms characterised by any morphology and species of unattached non-geniculate calcareous red algae” (European Commission et al., 2016). Curiously, *Lithothamnion corallioides* and *Phymatolithon calcareum*, typically associated with the term ‘maerl’ in the Atlantic, are explicitly listed in the European Red List as the main species found in “Mediterranean rhodolith beds”. The latest OSPAR commission Benthic Habitats report recognises maerl beds as threatened and/or in decline, but does not consider rhodolith beds (OSPAR, 2023).

While maerl beds in the Atlantic are recognised as Endangered or Vulnerable, Mediterranean rhodolith beds are considered ‘data deficient’ on the European Red List of Habitats (European Commission et al., 2016), despite extensive research conducted on Mediterranean coralline algal beds (Jacquotte, 1962; Pérès and Picard, 1964; Basso, 1998; Barbera et al., 2003; Bordehore et al., 2003; Ordines and Massutí, 2009; Sciberras et al., 2009; Sanz-Lázaro et al., 2011; Barberá et al., 2012; Micallef et al., 2012; Savini et al., 2012; Martin et al., 2014). Therefore, linguistic uncertainty is probably partly responsible for the ‘data deficient’ status. Indeed, Mediterranean coralline algal beds may be facing even more extreme conditions than those in the Atlantic zone and may deserve a higher conservative status (Rindi et al., 2019).

Besides baseline scientific knowledge, the deep historical roots and cultural connections humans have with the ocean cannot be overstated and might be reflected on the different levels of protection given to coralline algal beds worldwide (Poe et al., 2013; Bennett, 2019). For instance, the term ‘maerl’ has an important historical and cultural heritage value in many places in the North Atlantic, especially in Brittany, France. A local festival called ‘La fête du maërl’ takes place every four years in Plougastel-Daoulas in the Bay of Brest, attracting more than 5000 people with art exhibits, traditional dancing and historical re-enactments to remember those who extracted coralline algae for a living, and to raise awareness of the ecological and socioeconomic importance of these habitats (Friant and Marie, 2010; Péron and Marie, 2010; Noisette, 2013).

used to include nucleated growth forms of unattached coralline algae and the habitats they form in the Mediterranean (Barberá et al. 2017) and NE Atlantic (Axelsson 2023).

In the second half of the 20th century, the terms rhodolith and rhodolith beds were first introduced to describe ‘unattached aggregations of calcareous red algae’ (Barnes et al. 1970, 1971). This broad definition could, therefore, include free-living thalli of noncoralline calcifying red algae such as Peyssonneliaceae (subcl. Rhodymeniophycidae) species (Buchbinder and Halley 1985). However, these other calcifying red algae are usually associated with corallines and are seldom the dominant nodule-forming component, with exceptions in transition zones (Ballesteros 1994; Basso 2012; Bianchi and Morri 2025; V. A. Bracchi, Bazziacalupo, et al. 2022; Deinhart et al. 2022).

The terms rhodolite and rhodoid were also proposed at the time (Bosellini and Ginsburg 1971; Peryt 1983), but because these had previously been used to describe a variety of red garnets and other coated grains, they were discarded for coralline algal nodules (Adey and Macintyre 1973; Ginsburg and Bosellini 1973). Since then, rhodolith has become the most widely used term for free-living nongeniculate coralline algae (Rendina et al. 2022) except in Europe, where maerl is more commonly used (Figure 1B). Although the first definitions of rhodolith sensu lato did not distinguish among nucleated and non-nucleated nodular calcifying red algal growths, Steneck (1986) only considers those that grow around a nucleus as rhodoliths sensu stricto. Nucleated nodules can also be further classified based on the relative contribution of the coralline algal component to the whole nodule structure into coatings (< 50%) or rhodoliths
<figure><img src="image_6.png" /><figcaption>**FIGURE 3** | Proposed morphological organismal typology for coralline algae. Note that rhodolith and maerl both have historically been given both strict and broad definitions. Rhodolith sensu stricto only includes nucleated nodules, while maerl sensu stricto includes only non-nucleated forms. While rhodolith sensu lato includes only nodular forms, maerl sensu lato also includes nonnodular fragments. Here, we present historical uses so that authors can be specific about which morphotypes are referred to when using any of the terms. The represented morphologies are examples of the variety in growth forms. Arrows represent reproductive strategies that enable shifts between different types: Attached algae can grow into free-living forms, while free-living reproductive forms can produce spores that will grow into attached forms.</figcaption></figure>

(> 50%) (Steneck 1983; Basso 1998). The nucleus can be of biotic or abiotic origin, and nucleated rhodoliths can be composed of one or several thalli, often with multiple species on individual nodules (Riosmena-Rodríguez 2017). There is growing use of rhodoliths sensu lato as a general term for coralline algal nodules, particularly those with nuclei, while maerl sensu stricto remains the term commonly used for non-nucleated free-living nongeniculate coralline algae (Foster 2001; Arnold et al. 2021; Bélanger and Gagnon 2023).

Subclassifications have been created to reflect the morphological diversity of free-living nongeniculate coralline algae and introduce a rich terminology that can be source of linguistic uncertainty. For instance, both Bosence (1983) and Basso (1998) proposed the term ‘boxwork’ for different types of nodules. Bosence (1983) distinguished them in three classes: branching, columnar and laminar, with the latter being divided into concentric and nonconcentric nodules (boxwork). Basso (1998) proposed three classes: boxwork rhodoliths (large, multispecific, laminar to columnar nucleated nodules with multiple voids), *prâlines* (small, monospecific, laminar, branching or columnar nucleated nodules) and unattached branches (small, monospecific, unattached non-nucleated branches). Although useful to describe specific morphologies, when using subclassifications, authors should be explicit about their meanings to avoid confusion.

## 3.2 | Encrusting Nongeniculate Coralline Algae

Much like free-living forms of nongeniculate coralline algae, descriptions of encrusting forms date back to the 1700s. Pérès and Picard (1964) provide a wealth of information on the variety of habitats these algae can form and an evocative variety of French terms used to describe these habitats. The term crustose coralline algae became popular at the end of the 20th

century, when it was initially used as a synonym for nongeniculate coralline algae (Adey and Macintyre 1973; Bosence 1983; Steneck 1986). Nowadays, crustose coralline algae usually refers to encrusting (sessile) nongeniculate corallines only (McCoy and Kamenos 2015), although free-living forms are sometimes also referred to as crustose coralline algae (Amado-Filho et al. 2012; Pereira-Filho et al. 2012; V. Bracchi, Caronni, et al. 2022; Rebelo et al. 2022). This ambiguity is understandable since many encrusting species may grow on mobile substrata (biogenic, lithic or man-made) to create nucleated free-living specimens (Foster 2001). The term ‘crustose’ can also be misleading as many nongeniculate species have calcified upright branches (Woelkerling et al. 2005). Additionally, many geniculate species can be confused with encrusting nongeniculate species in early development stages, as they present a nongeniculate basal crust preceding the formation of upright geniculate fronds (Irvine and Chamberlain 1994).

Much of the diversity of terms regarding encrusting nongeniculate coralline algae stems from the wide variety of habitats that they form. These include coralline algal rims, buttresses, platforms, cornices and *trottoirs*, coralline algal-dominated tide pools and sea caves, coral-algal reefs, coralline algal carbonate crusts (or cor-stromes) and coralligenous reefs, the latter also being known as coralligenous assemblages, formations, concretions, coralligène or simply coralligenous (Marion 1883). The similarities and differences among these habitats are discussed below, in the habitat typology section.

## 3.3 | Geniculate Coralline Algae

Geniculate coralline algae were first described as zoophytes in the 18th century (Linnaeus 1758). The name comes from their genicula, an uncalcified, joint-like cell structure, separating two intergenicula, the calcified segments of the upright
fronds usually developed from a nongeniculate basal disc. The term genicula was initially employed for *Equisetum* plants (Blackstone 1746), then for Cnidarians by Linnaeus (1758) and Ellis and Solander (1786), and was subsequently applied to corallines (Harvey 1847).

The Corallinales is the only order of coralline algae with geniculate species (Walker et al. 2009). The presence of genicula was long considered the most important character for taxonomic distinction (Johansen 1981). However, the presence of genicula is a derived character that has arisen in the descendants of nongeniculate coralline algae multiple times (Aguirre et al. 2010; Peña et al. 2020). Hind et al. (2018) also suggest that evolutionary reversals have occurred within the subfamily Corallinoideae, twice within the geniculate genus *Bossiella* P.C. Silva.

The genicula development pattern differs from one genus to another, either through the development of uncalcified cells (apical growth for the Metagoniolithoideae or subapical growth for the genus *Lithothrix* Gray) and/or by decalcification (important in Lithophylloideae) (McCoy et al. 2023). The genicula grant these algae some degree of physical flexibility and were initially called *articulis* by Linnaeus—hence the popularity of the alternative term ‘articulated coralline algae’ (Johansen 1981).

Geniculate taxa are usually epilithic and typically occur in the intertidal and subtidal zones from polar to tropical environments (Stewart 1982; Kelaher et al. 2001), although species can also be epiphytic or epizoic. They are often strongly attached by crustose or stoloniferous holdfasts, which can be extensive and sometimes confused for an encrusting nongeniculate coralline algae base (Brodie et al. 2013). Some geniculate corallines can be free-living and create extensive habitats similar to free-living nongeniculate coralline algae beds—these understudied growth forms have been recently named ‘articuliths’ (Tâmega et al. 2017, 2021).

## 3.4 | Creating International Cohesion Through a Unified Typology

As coralline algal science and interest from conservation and policy sectors have grown, the diversity of terms used to describe these algae and their associated habitats has also increased. Although a diversity of terms enables specificity in organismal/habitat descriptions, the definition of terms and the extent of ‘interchangeability’ between terms is not internationally consistent, creating uncertainty. Adoption of specific terms (and rejection or delineation of others), namely, in policy documents, creates uncertainty and places coralline algal habitats at greater risk of inadequate protection measures.

## 4 | Proposed Organismal Typology

Some terms, such as crustose coralline algae and nongeniculate coralline algae, have been used interchangeably when they designate organisms with different life histories and ecological functions. On the other hand, organisms with similar traits and functions have been named differently on cultural and morphological bases, as in the case of the free-living nongeniculate

coralline algae. Informed by both terminology history and morphological differentiation (discussed above), we propose a unified organismal typology (Box 2 and Figure 3).

In this typology, coralline algae are initially distinguished by their structural morphology, leading to the categorisation of geniculate and nongeniculate forms. The mode of attachment is then used to further differentiate these forms. This includes attached and free-living geniculate forms, as well as encrusting (sessile) and free-living nongeniculate forms. Free-living nongeniculate types can be nodules or fragments—the latter having only one long axis (Figure 3). Encrusting nongeniculate forms may have branches which, when detached, can become free-living fragments or non-nucleated nodules—referred to as ‘maerl’ in the strictest sense. The broader term ‘maerl’ can encompass all free-living forms, including nucleated and non-nucleated nodules and fragments. Conversely, the term ‘rhodolith’ in its broadest sense and following the original definition by Barnes et al. (1971) may include noncoralline calcifying red algae and encompasses all free-living nodules, while in its strictest sense, it specifically refers only to nucleated nodules of free-living nongeniculate coralline algae. Importantly, we do not prescribe authors necessarily use the terms sensu lato and sensu stricto when referring to maerl or rhodoliths, but instead, advocate authors are explicit about which type of coralline algae is being referred to (nucleated nodules, non-nucleated nodules or fragments) whenever they use one term or the other—as many definitions exist.

## 5 | Proposed Habitat Typology

International cohesion among coralline terminology might be even more important at the habitat level for conservation and management. When different terms are employed to habitats with similar ecological traits and functions, dissimilar protection levels might be applied (Kujala et al. 2013). In this sense, a functional approach could be an effective alternative basis for a unified terminology (Hattam et al. 2021; Streit and Bellwood 2023). Many coralline algal species can be considered multi-influence engineers, as they can affect several biotic and abiotic processes and resultant ecosystem functions (Byers 2022). Therefore, we propose a unified morphofunctional habitat typology in which we describe and group coralline algae—dominated habitats following the IUCN's GET (global-ecosystems.org). The GET units are based on (1) ecosystem functions and ecological processes, (2) their characteristic biota, (3) conceptual consistency throughout the whole biosphere, (4) a scalable structure, (5) spatially explicit units and (6) descriptive parsimony (Keith, Ferrer-Paris, et al. 2022).

### 5.1 | IUCN's Global Typology

The GET has three upper hierarchical levels (Figure 4): 11 realms (Level 1), including atmospheric (which is taken into account but has no lower hierarchical units), freshwater, marine, terrestrial, subterranean and six transitional realms not relevant here; 25 functional biomes (Level 2); and 110 functional groups (Level 3). Biomes are components of a realm with similar ecosystem structure and one or a few common major ecological drivers
Box 2. Coralline algae organismal typology and definition key

<table><tr><td>Coralline algae</td><td>1</td></tr><tr><td>Geniculate</td><td>2</td></tr><tr><td>Attached</td><td>3</td></tr><tr><td>Free-living</td><td>4</td></tr><tr><td>Non-geniculate</td><td>5</td></tr><tr><td>Encrusting</td><td>6</td></tr><tr><td>Free-living</td><td>7</td></tr><tr><td>Fragment<sup>a,b</sup></td><td>8</td></tr><tr><td>Nodule</td><td>9</td></tr><tr><td>Nucleated<sup>c,d</sup></td><td>10</td></tr><tr><td>Non-nucleated<sup>a,b,d</sup></td><td>11</td></tr></table>

1. Calcifying benthic red algae within the Corallinophycidae (exc. Rhodogorgonales, Rhodophyta)

2. Corallinales species with calcified frond segments separated by genicula (uncalcified cells)

3. Geniculate coralline algae attached to substrata by crustose or stoloniferous holdfasts

4. Geniculate coralline algae living unattached in nodular forms known as articuliths

5. Fully calcified coralline algae lacking genicula

6. Non-geniculate coralline algae attached to substrata, also known as Crustose Coralline Algae

7. Non-geniculate coralline algae living unattached as fragments or nodules

8. Fragments of branching encrusting and free-living non-geniculate coralline algae

9. Nodular growths of free-living non-geniculate coralline algae

10. Free-living non-geniculate coralline algae growing as nodules over a biogenic or abiotic nucleus.

11. Free-living non-geniculate coralline algae growing in nodular forms from unattached fragments

a. Maerl sensu stricto. Includes non-nucleated nodules of free-living non-geniculate coralline algae and fragments of branching non-geniculate coralline algae

b. Maerl sensu lato. Includes all free-living non-geniculate coralline algae.

c. Rhodolith sensu stricto. Includes nucleated nodules of free-living non-geniculate coralline algae.

d. Rhodolith sensu lato. Includes all nodules of non-geniculate coralline algae and other non-coralline calcareous red algae of the presence of nuclei.

and functions. Functional groups are similar systems within a biome that share common ecological drivers and present similar biotic traits. Functional groups can be further divided into three bottom hierarchical levels: regional subgroups (Level 4), global types (Level 5) and subglobal types (Level 6). Level 4 units are based on ecoregions and are not applied here because many regions are data deficient for coralline algae (European Commission et al. 2016; Rendina et al. 2022; Brodie et al. 2023). Lower Levels 5 and 6 are independent of Level 4 and have a bottom-up hierarchy. Global types (Level 5) are defined by the

aggregation of subglobal types (Level 6, regional expressions of functional groups) based on compositional resemblance. Global types grouped into the same functional group share similar ecological processes, drivers and services but present different biotic composition.

Level 6 units are regional expressions of functional groups that are explicitly linked to local knowledge and are aggregated based on subglobal classifications. Aggregation of subglobal units to broader global units (Level 5) is based on compositional
<figure><img src="image_7.png" /></figure>

**FIGURE 4** | Simplified IUCN's Global Ecosystem Typology (GET) showing only the realms containing coralline algal habitats. There are three upper hierarchical levels: 1—realms, 2—biomes and 3—functional groups. Level 3 levels can be further divided into 4—regional subgroups, 5—global types and 6—subglobal types. Four core realms represent major components of the biosphere: terrestrial, freshwater, marine and subterranean (the atmospheric realm is also taken into account but has no lower level units). Six additional transitional realms are defined as combinations of the four core realms. Core realms are coloured, while transitional realms are grey. Whenever a unit presents more than four lower levels, dashed lines are used to represent them. Lower levels of a single unit at each upper level are shown to simplify the diagram. Arrows indicate top-down (black) and bottom-up (red) structures. F = freshwater; M = marine; S = subterranean; T = terrestrial. Adapted from Keith, Ferrer-Paris, et al. (2022). Unit names are shown in Figure 5.

resemblance and is necessary to address uncertainty from contrasting multiple knowledge (Brugnach et al. 2008; Keith, Ferrer-Paris, et al. 2022). Therefore, under the post-2020 Global Biodiversity Framework, the IUCN's Red List Index of Ecosystems (RLIE) is used to inform the IUCN's Red List of Ecosystems and takes GET into account (Bland et al. 2019; Nicholson et al. 2021). The RLIE summarises the risk status and trends of ecosystems and can be reported at national or global levels and disaggregated by ecosystem type, using the GET (Rowland et al. 2020).

We characterise a nonexhaustive list of 10 coralline algae—dominated global types, falling within seven IUCN functional groups, four biomes and four realms (Figure 5). The global types we propose are based on subglobal habitats (GET Level 6) and grouped based on the main coralline algae morphologies (cf. Box 2 and Figure 3) and their compositional and functional resemblances.

## 5.2 | The Freshwater Realm (F)

In the freshwater realm (F), classified under the rivers and streams biome (F1) and the permanent upland streams functional group (F1.1), a unique encrusting nongeniculate coralline algae habitat has been documented in the Cetina river karst watershed in Croatia (Žuljević et al. 2016; Koletić et al. 2020). It is formed by *Pneophyllum cetinaensis*, the only known freshwater member of the Corallinales, colonising every hard substratum available as well as roots and mollusc shells (Žuljević et al. 2016;

Necchi and Vis 2021). No studies have yet investigated the role of this coralline algae freshwater habitat on shaping associated assemblages. Unfortunately, this habitat is under strong human pressures, as the river crosses two cities and has several hydroelectric power plants, dams and artificial lakes along its course (Žuljević et al. 2016).

## 5.3 | The Marine–Terrestrial Transitional Realm (MT)

In the marine–terrestrial transitional realm (MT), three coralline global types are identified, all included in the shorelines biome and rocky shorelines functional group (MT1.1). Geniculate coralline algae can be a dominant part of rocky shoreline habitats. They are autogenic ecosystem engineers, forming turf that provides shelter to well-developed macrofaunal and macroalgal communities (Stewart 1982; Grahame and Hanna 1989; Kelaher et al. 2001; Nelson 2009). However, they are increasingly at threat from rising seawater water temperature, marine heatwaves and ocean acidification (Brodie et al. 2014; Williamson et al. 2014; Rendina et al. 2019; Kolzenburg et al. 2021).

Encrusting nongeniculate coralline algae may also be the main habitat-forming species in rocky shorelines, forming coralline algae-coated tide pools or intertidal encrusting coralline algae rims depending on their position in the shoreline and spatial organisation. Tide pools dominated by encrusting nongeniculate coralline algae can be found up to the upper intertidal zone,
<figure><img src="image_8.png" /><figcaption>**FIGURE 5** | Coralline algae-associated habitat nomenclature and typology, following the IUCN's Global Ecosystem Typology. New global types are proposed here, based on functional and compositional resemblances among subglobal types. Recommended habitat names are proposed as global types for consistency within the coralline algae community. Superscript numbers represent the dominant morphotypes of habitat-forming coralline algae, as described in Figure 3: 1 = encrusting nongeniculate coralline algae; 2 = attached geniculate coralline algae; 3 = free-living geniculate coralline algae nodules; 4 = free-living nongeniculate coralline algae nodules and fragments; 5 = free-living calcifying coralline algae nodules (including noncoralline species). Exemplary habitat photographs: MT1.1 = intertidal coralline turf, Brittany, France (credit: Victor L. Jardim); SM1.3 = coralline algae sea cave, Brittany France (credit: Jacques Grall); M1.3 = coral-algal reef, Great Barrier Reef, Australia (credit: Tessa Page); M1.5 = corallige-nous reef, Sorrento, Italy (credit: Francesco Rendina); M1.10 (from top to bottom) = articulith bed, Rio de Janeiro, Brazil (credit: Frederico Tamega), Carraroe maerl beach composed mostly of nongeniculate coralline algae fragments, County Galway, Ireland (credit: Siddhi Joshi) and rhodolith bed Capri, Italy (credit: Francesco Rendina).</figcaption></figure>

making them environmentally variable habitats characterised by distinct seasonal and diurnal cycles (Legrand et al. 2018) and intense biotic pressures, such as grazing (Steneck et al. 1991; Wai and Williams 2006). Coralline algae-dominated tide pools are usually dominated by a few species of encrusting non-geniculate coralline species (Wai and Williams 2006; Dorey et al. 2023). Although tide pools usually present low diversity of

associated organisms when compared to subtidal communities, they are more diverse than the surrounding emergent rock habitats (Firth et al. 2014).

Intertidal encrusting nongeniculate coralline algae rims are formed through the coalescence of numerous coralline algae thalli on vertical or subvertical rocky surfaces (Verlaque 2010).
Coralline algae rims usually present a porous upper layer of living coralline algae over dead algae, an intermediate hardened multilayered sedimentary matrix with filled-up interstices and a highly colonised lower eroded matrix of dead crustose coralline algae (Pezzolesi et al. 2017). These habitats, also known as *trottoirs* in the Mediterranean, are understudied and face numerous threats, namely, sea-level rise, human mechanical impact and pollution, which grants them Vulnerable status on the European Red List of Habitats (European Commission et al. 2016; Blanfuné et al. 2023).

## 5.4 | The Subterranean-Marine Transitional Real (SM)

In the subterranean-marine transitional real (SM), sea caves (SM1.3) are special refuge habitats acting as biodiversity reservoirs (Bussotti et al. 2006; Gerovasileiou and Bianchi 2021). They are formed in a variety of rock types and can include biogenic habitats dominated by encrusting nongeniculate coralline algae (Adey and Vassar 1975; Gerovasileiou and Bianchi 2021). Sea caves have strong biotic zonation due to gradients in light and hydrography, with low-light communities dominated by coralline algae in cave entrances (Guido et al. 2019; Gerovasileiou and Bianchi 2021). Although highly diverse, sea caves are considered low resilient habitats and face many threats, including invasive species, global change and local human impacts (Tillin 2015; Gerovasileiou and Bianchi 2021).

## 5.5 | The Marine Realm (M)

In the marine realm (M), we identify six global habitat types in which coralline algae are the main biogenic component, all of them in the marine shelf (M1) biome. In photic coral reefs (M1.3), encrusting nongeniculate coralline algae dominate forming coral-algal reefs. Tropical coral-algal reefs (also known as algal reefs) form thick, mostly calcified frameworks of coralline algal crusts, corals, foraminifera, vermetids, serpulids and boring organisms (Littler 1973; Adey 1978, 1998). Encrusting nongeniculate coralline algae can characterise both inshore and fringing reefs, as well as mid and outer-shelf reefs, and thick coralline algal crusts are often more abundant in outer-shelf reefs (Dean et al. 2015). In the tropics, encrusting nongeniculate coralline algae often dominate the windward most exposed crests of reefs, sometimes accounting for up to 90% of the composition of reef crests, creating algal ridges (Adey and McKibbin 1970; Adey 1998). Coralline algae can contribute more than corals to coral reef carbonate production in some reefs (Cornwall et al. 2023). The Taoyuan Algal Reef (Taiwan) is the largest known subtropical intertidal algal reef; it spans over 27km on a tidal flat and is approximately 4m thick (Liou et al. 2017; Zhan et al. 2022). It is thought to harbour high coralline algal endemism and overall diversity but is threatened by coastal development and industrial waste run-off (Kuo et al. 2020; Heard et al. 2021; Chen et al. 2022; Zhan et al. 2022). All tropical coral reefs assessed on the IUCN's Red List of Habitats are either endangered or critically endangered (Bland et al. 2019, 2017). Their conservation status is primarily based on increased frequency and severity of warming-induced coral bleaching events (Hughes et al. 2017; Sully et al. 2019; Andrello et al. 2022). The

impacts of warming on tropical coralline algae per se are varied, but overall, encrusting nongeniculate coralline algae seem less sensitive to warming stress than scleractinian corals (Cornwall et al. 2022). However, the impacts of global change and human activities on coralline algae need to be better understood and integrated when discussing the vulnerability of coralline algal habitats (Kuffner et al. 2008; Diaz-Pulido et al. 2012; Webster et al. 2013; Cornwall et al. 2017; Heard et al. 2021; Kluibenschedl et al. 2023).

Coralline algae are the deepest known macroalgae and have been found at 268-m depth (Littler et al. 1985), with encrusting nongeniculate coralline algae often being the dominant component of photo-limited marine animal forests (M1.5), forming coralligenous reefs. Coralligenous reefs (also known as coraligenous assemblages, formations, concretions or simply coraligenous) are typical mesophotic habitats of the Mediterranean Sea (Ballesteros 2006). They are among some of the best studied coralline algal habitats (Ferrigno et al. 2023) and were first described by Marion (1883). The term comes from the French word *coralligène*, which means ‘coral maker’, and is used to describe coralline algae dominated hard bottom communities (Basso et al. 2022). Coralligenous reefs are usually characterised by several layers of encrusting nongeniculate coralline algae (from a few centimetres to several metres thickness) over several kilometres on either rocky walls in the intertidal or subhorizontal sedimentary or rocky substrata in the subtidal, occurring at depths of over 150 m (Bosence 1983; Basso et al. 2022).

Subtidal rocky reefs (M1.6) are often dominated by coralline algae in the photic zone. In Subarctic and Arctic regions, encrusting nongeniculate coralline algae coat most subtidal rocky surfaces and can form thick carbonate crusts (or cor-stromes) that can be as thick as 0.5m. Coralline algal carbonate crusts occur both in the Atlantic and Pacific ocean basins and may be composed of different taxa, although *Clathromorphum* Foslie and *Boreolithothamnion* species are the most abundant (Adey et al. 2013). In the Arctic, these carbonate crusts may be extremely long-lived, with *Clathromorphum* specimens aged up to 1200 years BP (Adey et al. 2015). This, in combination with their capacity to incorporate certain elements and isotopes in their band-like growth structures, can be useful for biogeochemical analyses and paleoclimate reconstructions (Adey et al. 2013; Halfar et al. 2013; Gould et al. 2022). Carbonate crusts are highly diverse habitats, harbouring macrobenthic communities as diverse as those found in surrounding habitats dominated by canopy macroalgae (Chenelot et al. 2011).

Similarly, encrusting nongeniculate coralline algae are the main biogenic components of subtidal rocky reef habitats usually known as ‘urchin barrens’. These often-extensive habitats are distributed worldwide and emerge from a stable-state shift from structurally complex, macroalgae-dominated seascapes (such as kelp forests) to expanses of coralline-encrusted rock due to intense sea urchin grazing (Filbee-Dexter and Scheibling 2014). Even after the drivers of sea urchin outbreaks subside, these barrens often persist, sometimes maintained by other grazers such as limpets (Melis et al. 2019; Piazzi et al. 2016). While often associated with a loss of key ecosystem functions (Eger et al. 2024), coralline barrens are not devoid of life. They support diverse assemblages of benthic mega-invertebrates and can present
structurally complex nongeniculate coralline species that pro-
vide habitat for a variety of organisms (Agnetta et al. 2024;
Ramos et al. 2025).

Geniculate coralline algae are also major colonisers of rocky
shores, forming coralline turfs. This habitat can be found
worldwide across diverse environments, ranging from polar to
tropical regions (Nelson 2009). Geniculate coralline algal turf
habitats are characterised by the dense aggregation of genic-
ulate fronds, forming cohesive mats that can reach heights of
up to 15 cm (Connell et al. 2014). Their thalli, composed of stiff
branches, provide a substratum for the attachment of numer-
ous epiphytes (Soltan et al. 2001) while their three-dimensional
structure fosters a high diversity of organisms, particularly small
invertebrates (Kelaher and Castilla 2005; Berthelsen et al. 2014;
Marchini et al. 2019; Ragazzola et al. 2021).

Finally, the IUCN GET recognises 'Rhodolith/Maerl beds' (M1.10) (Keith, Fragkopolou, et al. 2022). These coralline algal beds are aggregations of alive and dead free-living nongeniculate coralline algae that cover extensive benthic areas (Riosmena-Rodríguez 2017) and are common in fossil deposits (Aguirre et al. 2017). They are distributed worldwide and have a wide-depth range from intertidal to mesophotic zones (Davies et al. 2004; Wilson and Blake 2011; Pereira-Filho et al. 2012; Basso et al. 2016; Veras et al. 2020; Pierri et al. 2024). Here, we propose that FEG M1.10 is renamed as coralline algal beds—also including articu-lith beds (formed by geniculate coralline algal nodules) and remov-ing linguistic uncertainty related to different morphotypes and locations. In the global typology, GET M1.10 is defined as benthic carbonate systems dominated by free-living, slow-growing, long-lived coralline algae covering 30%–100% of the seafloor within the beds, providing autochthonous energy to the system. In the GET definition, only nongeniculate coralline algae are included; how-ever, the ecosystem properties, resources, ambient environmental conditions, disturbance regimes and biotic interactions used to define them could also be applied to free-living geniculate coral-line algae (Keith, Fragkopolou, et al. 2022). For instance, rhodolith and maerl beds are grouped on the basis of moderate productiv-ity (Martin et al. 2005; Riosmena-Rodríguez 2017; Qui-Minet et al. 2022), high associated biodiversity (Peña et al. 2014; Boyé et al. 2019; Helias and Burel 2023) and high structural complexity (Jardim et al. 2022; Bélanger and Gagnon 2023; Cabrito et al. 2024). Although understudied and possibly rare, articulith beds probably share most of these characteristics, are formed through similar processes and face similar pressures (Tâmega et al. 2017, 2021). Little is known, however, about the durability of the structure of articuliths, which may not be as long-lasting as the thalli formed by nongeniculate corallines—although closely packed thalli can protect geniculate corallines from breakage, a feature that may be enhanced in articuliths (Martone and Denny 2008a, 2008b).

6 | Conclusion

Inconsistent definitions can lead to ecological uncertainty and
variable conservation policies for habitats with similar traits,
functions and services and facing similar anthropic pressures.
We have suggested a consistent set of terms to describe coralline
algae and coralline algal habitats to help put them into a global
context to support local actions and decision-making (Keith,

Ferrer-Paris, et al. 2022). We highlight the importance of clar-
ifying uncertain terms and simplifying dichotomies through
contextualisation when using polysemic or synonymous terms.
We resolve, in an integrative and adaptive way, a long-lasting
debate on the use of the terms ‘maerl’ and ‘rhodolith’ through
the umbrella term ‘coralline algal beds’ and explicit definitions
that allow established terms in local and global scientific and
management frameworks to coexist without creating uncer-
tainty. Language is adaptative and ever-changing, and while
a diverse coralline algal terminology reflects the widespread
distribution and growing scientific and conservation relevance
of the group, authors must have a contextualisation tool to sim-
plify and clarify the terms they use. In this context, we urge
the scientific community to adopt a more cohesive terminology
for coralline algae, to improve scientific progression and inter-
national collaborations and to facilitate conservation, public
understanding and stakeholder engagement.

Acknowledgements

We thank Elsevier and Aquatic Conservation: Freshwater and Marine Ecosystems for sponsoring the 7th International Coralline Algae Meeting, in which the terminology of coralline algae was discussed. We also thank Dr Guilherme H. Pereira-Filho and Dr Ricardo Bahia for their insights and feedback on the final manuscript.

Conflicts of Interest

The authors declare no conflicts of interest.

Data Availability Statement

Data sharing is not applicable to this article as no new data were created or analysed in this study.

References

Adey, W. H. 1978. "Algal Ridges of the Caribbean Sea and West Indies." *Phycologia* 17: 361-367. https://doi.org/10.2216/i0031-8884-17-4-361.1

Adey, W. H. 1998. "Coral Reefs: Algal Structured and Mediated Ecosystems in Shallow, Turbulent, Alkaline Waters." *Journal of Phycology* 34: 393-406.

Adey, W. H., J. Halfar, and B. Williams. 2013. "The Coralline Genus *Clathromorphum* Foslie emend. Adey: Biological, Physiological, and Ecological Factors Controlling Carbonate Production in an Arctic-Subarctic Climate Archive." *Smithsonian Contributions to the Marine Sciences* 40: 1-41. https://doi.org/10.5479/si.1943667X.40.1

Adey, W. H., J. J. Hernandez-Kantun, G. Johnson, and P. W. Gabrielson. 2015. "DNA Sequencing, Anatomy, and Calcification Patterns Support a Monophyletic, Subarctic, Carbonate Reef-Forming Clathromorphum (Hapalidiaceae, Corallinales, Rhodophyta)." *Journal of Phycology* 51: 189-203. https://doi.org/10.1111/jpy.12266.

Adey, W. H., and I. G. Macintyre. 1973. "Crustose Coralline Algae: A Re-Evaluation in the Geological Sciences." *GSA Bulletin* 84: 883-904. https://doi.org/10.1130/0016-7606(1973)84<883:CCAARI>2.0.CO;2.

Adey, W. H., and D. L. McKibbin. 1970. "Studies on the Maerl Species *Phymatolithon calcareum* (Pallas) nov. comb. and *Lithothamnium coraloides* Crouan in the Ria de Vigo." *Botanica Marina* 13: 100-106. https://doi.org/10.1515/botm.1970.13.2.100.

Adey, W. H., and C. P. Sperapani. 1971. "The Biology of *Kvaleya epilaeve*, a New Parasitic Genus and Species of Corallinaceae." *Phycologia* 10: 29-42. https://doi.org/10.2216/i0031-8884-10-1-29.1.
Adey, W. H., and J. M. Vassar. 1975. "Colonization, Succession and Growth Rates of Tropical Crustose Coralline Algae (Rhodophyta, Cryptonemiales)." *Phycologia* 14: 55-69. https://doi.org/10.2216/i0031-8884-14-2-55.1.

Agardy, T. 2005. "Global Marine Conservation Policy Versus Site-Level Implementation: The Mismatch of Scale and Its Implications." *Marine Ecology Progress Series* 300: 242-248.

Agnetta, D., C. Bonaviri, F. Badalamenti, F. Di Trapani, and P. Gianguzza. 2024. "Coralline Barrens and Benthic Mega-Invertebrates: An Intimate Connection." *Marine Environmental Research* 199: 106579. https://doi.org/10.1016/j.marenvres.2024.106579.

Aguirre, J., J. C. Braga, and D. Bassi. 2017. "Rhodoliths and Rhodolith Beds in the Rock Record." In *Rhodolith/Maërl Beds: A Global Perspective, Coastal Research Library*, edited by R. Riosmena-Rodríguez, W. Nelson, and J. Aguirre, 105-138. Springer International Publishing. https://doi.org/10.1007/978-3-319-29315-8_5.

Aguirre, J., F. Perfectti, and J. C. Braga. 2010. "Integrating Phylogeny, Molecular Clocks, and the Fossil Record in the Evolution of Coralline Algae (Corallinales and Sporolithales, Rhodophyta)." *Paleobiology* 36: 519-533. https://doi.org/10.1666/09041.1.

Amado-Filho, G. M., G. H. Pereira-Filho, R. G. Bahia, D. P. Abrantes, P. C. Veras, and Z. Matheus. 2012. "Occurrence and Distribution of Rhodolith Beds on the Fernando de Noronha Archipelago of Brazil." *Aquatic Botany* 101: 41-45. https://doi.org/10.1016/j.aquabot.2012.03.016.

Andrello, M., E. S. Darling, A. Wenger, A. F. Suárez-Castro, S. Gelfand, and G. N. Ahmadia. 2022. "A Global Map of Human Pressures on Tropical Coral Reefs." *Conservation Letters* 15: e12858. https://doi.org/10.1111/conl.12858.

Aria, M., and C. Cuccurullo. 2017. "Bibliometrix: An R-Tool for Comprehensive Science Mapping Analysis." *Journal of Informetrics* 11: 959-975. https://doi.org/10.1016/j.joi.2017.08.007.

Arnold, C., D. Bélanger, and P. Gagnon. 2021. "Growth Resilience of Subarctic Rhodoliths (*Lithothamnion glaciale*, Rhodophyta) to Chronic Low Sea Temperature and Irradiance." *Journal of Phycology* 58: 251-266. https://doi.org/10.1111/jpy.13231.

Augris, C., and P. Berthou. 1990. "Les Gisements de Maërl en Bretagne (Report)."

Axelsson, M. B. 2023. *A Categorisation System for Maerl Bed Habitats in England, NERR123*. Natural England.

Ballesteros, E. 1994. "The Deep-Water Peysonnelia Beds From the Balearic Islands (Western Mediterranean)." *Marine Ecology* 15: 233-253. https://doi.org/10.1111/j.1439-0485.1994.tb00055.x.

Ballesteros, E. 2006. "Mediterranean Coralligenous Assemblages: A Synthesis of Present Knowledge." *Oceanography and Marine Biology: An Annual Review* 48: 123-195.

Barbera, C., C. Bordehore, J. A. Borg, et al. 2003. "Conservation and Management of Northeast Atlantic and Mediterranean Maerl Beds." *Aquatic Conservation: Marine and Freshwater Ecosystems* 13: S65-S76. https://doi.org/10.1002/aqc.569.

Barberá, C., S. Mallol, A. Vergés, M. Cabanellas-Reboredo, D. Díaz, and R. Goñi. 2017. "Maerl Beds Inside and Outside a 25-Year-Old No-Take Area." *Marine Ecology Progress Series* 572: 77-90. https://doi.org/10.3354/meps12110.

Barberá, C., J. Moranta, F. Ordines, et al. 2012. "Biodiversity and Habitat Mapping of Menorca Channel (Western Mediterranean): Implications for Conservation." *Biodiversity and Conservation* 21: 701-728. https://doi.org/10.1007/s10531-011-0210-1.

Barnes, J., D. J. Bellamy, D. J. Jones, et al. 1971. "Morphology and Ecology of the Reef Front of Aldabra." *Symposia of the Zoological Society of London* 28: 87-114.

Barnes, J., D. J. Bellamy, D. J. Jones, B. A. Whitton, E. Drew, and J. Lythgoe. 1970. "Sublittoral Reef Phenomena of Aldabra." *Nature* 225: 268-269. https://doi.org/10.1038/225268a0.

Basso, D. 1998. "Deep Rhodolith Distribution in the Pontian Islands, Italy: A Model for the Paleocology of a Temperate Sea." *Palaeogeography, Palaeoclimatology, Palaeoecology* 137: 173-187. https://doi.org/10.1016/S0031-0182(97)00099-0.

Basso, D. 2012. "Carbonate Production by Calcareous Red Algae and Global Change." *Geodiversitas* 34: 13-33. https://doi.org/10.5252/g2012n1a2.

Basso, D., L. Babbini, S. Kaleb, V. A. Bracchi, and A. Falace. 2016. *Monitoring Deep Mediterranean Rhodolith Beds, Aquatic Conservation: Marine and Freshwater Ecosystems*. John Wiley and Sons Ltd. https://doi.org/10.1002/aqc.2586.

Basso, D., V. A. Bracchi, P. Bazzicalupo, M. Martini, F. Maspero, and G. Bavestrello. 2022. "Living Coralligenous as Geo-Historical Structure Built by Coralline Algae." *Frontiers in Earth Science* 10: 961632.

Bélanger, D., and P. Gagnon. 2023. "Spatiotemporal Variability in Subarctic *Lithothamnion glaciale* Rhodolith Bed Structural Complexity and Macrofaunal Diversity." *Diversity* 15: 774. https://doi.org/10.3390/d15060774.

Bellwood, D., S. Brandl, M. McWilliam, R. Streit, H. Yan, and S. Tebbett. 2024. "Studying Functions on Coral Reefs: Past Perspectives, Current Conundrums, and Future Potential." *Coral Reefs* 43: 281-297. https://doi.org/10.1007/s00338-024-02474-z.

Bennett, N. J. 2019. "Marine Social Science for the Peopled Seas." *Coastal Management* 47: 244-252. https://doi.org/10.1080/08920753.2019.1564958.

Berchez, F. 2022. "Brazil: Heed Price of Marine Mining for an Alternative Fertilizer." *Nature* 607: 239. https://doi.org/10.1038/d41586-022-01890-x.

Berthelsen, A., J. Hewitt, and R. Taylor. 2014. "Coralline Turf-Associated Fauna Are Affected More by Spatial Variability Than by Host Species Identity." *Marine Biodiversity* 45: 689-699. https://doi.org/10.1007/s12526-014-0270-z.

Bianchi, C. N., and C. Morri. 2025. "Different Rhodolith Assemblages Host Distinct Associated Species but Similar Ecological Groups: A Case Study in NW Mediterranean Sea." *Aquatic Botany* 196: 103826. https://doi.org/10.1016/j.aquabot.2024.103826.

Blackstone, J. 1746. *Specimen Botanicum quo Plantarum Plurium Rariorum Angliae Indigenarum Loci Natales Illustrantur*. Typis Gulielmi Faden. https://doi.org/10.5962/bhl title.106704.

Bland, L. M., E. Nicholson, R. M. Miller, et al. 2019. "Impacts of the IUCN Red List of Ecosystems on Conservation Policy and Practice." *Conservation Letters* 12: e12666. https://doi.org/10.1111/conl.12666.

Bland, L. M., T. J. Regan, M. N. Dinh, et al. 2017. "Using Multiple Lines of Evidence to Assess the Risk of Ecosystem Collapse." *Proceedings of the Royal Society B: Biological Sciences* 284: 20170660. https://doi.org/10.1098/rspb.2017.0660.

Blanfuné, A., C.-F. Boudouresque, M. Verlaque, A. Minne, F. Noisette, and T. Thibaut. 2023. "Impact of Sea Level Rise on the Mediterranean *Lithophyllum byssoides* Rims." *Scientific Reports* 13: 10577. https://doi.org/10.1038/s41598-023-37110-3.

Bordehore, C., A. A. Ramos-Esplá, and R. Riosmena-Rodríguez. 2003. "Comparative Study of Two Maerl Beds With Different Otter Trawling History, Southeast Iberian Peninsula." *Aquatic Conservation: Marine and Freshwater Ecosystems* 13: S43-S54. https://doi.org/10.1002/aqc.567.

Bosellini, A., and R. N. Ginsburg. 1971. "Form and Internal Structure of Recent Algal Nodules (Rhodolites) From Bermuda." *Journal of Geology* 79: 669-682.
Bosence, D. W. J. 1983. "Coralline Algal Reef Frameworks." *Journal of the Geological Society* 140: 365-376. https://doi.org/10.1144/gsjgs.140.3.0365.

Boyé, A., É. Thiébaut, J. Grall, et al. 2019. "Trait-Based Approach to Monitoring Marine Benthic Data Along 500 km of Coastline." *Diversity and Distributions* 25: 1879-1896. https://doi.org/10.1111/ddi.12987.

Bracchi, V., S. Caronni, A. Meroni, et al. 2022. "Morphostructural Characterization of the Heterogeneous Rhodolith Bed at the Marine Protected Area "Capo Carbonara" (Italy) and Hydrodynamics." *Diversity* 14: 51. https://doi.org/10.3390/d14010051.

Bracchi, V. A., P. Bazzicalupo, L. Fallati, et al. 2022. "The Main Builders of Mediterranean Coralligenous: 2D and 3D Quantitative Approaches for Its Identification." *Frontiers in Earth Science* 10: 910522.

Brodie, J., R. H. Walker, C. Williamson, and L. M. Irvine. 2013. "Epitypification and Redescription of *Corallina officinalis* L., the Type of the Genus, and *C. elongata* Ellis et Solander (Corallinales, Rhodophyta)." *Cryptogamie Algologie* 34: 49-56.

Brodie, J., J. Wilbraham, C. Maggs, et al. 2023. "Red List for British Seaweeds: Evaluating the IUCN Methodology for Non-Standard Marine Organisms." *Biodiversity and Conservation* 32: 1-19. https://doi.org/10.1007/s10531-023-02649-0.

Brodie, J., C. J. Williamson, D. A. Smale, et al. 2014. "The Future of the Northeast Atlantic Benthic Flora in a High CO₂ World." *Ecology and Evolution* 4: 2787-2798. https://doi.org/10.1002/ece3.1105.

Brodie, J. F. 2009. "Is Research Effort Allocated Efficiently for Conservation? Felidae as a Global Case Study." *Biodiversity and Conservation* 18: 2927-2939. https://doi.org/10.1007/s10531-009-9617-3.

Brugnach, M., A. Dewulf, C. Pahl-Wostl, and T. Taillieu. 2008. "Toward a Relational Concept of Uncertainty: About Knowing Too Little, Knowing Too Differently, and Accepting Not to Know." *Ecology and Society* 13: 30. https://doi.org/10.5751/ES-02616-130230.

Buchbinder, B., and R. B. Halley. 1985. "Occurrence and Preservation of Eocene Squamariacean and Coralline Rhodoliths: Eua, Tonga." In *Paleoalgology*, edited by D. F. Toomey and M. H. Nitecki, 248-256. Springer. https://doi.org/10.1007/978-3-642-70355-3_19.

Bussotti, S., A. Terlizzi, S. Fraschetti, G. Belmonte, and F. Boero. 2006. "Spatial and Temporal Variability of Sessile Benthos in Shallow Mediterranean Marine Caves." *Marine Ecology Progress Series* 325: 109-119. https://doi.org/10.3354/meps325109.

Byers, J. E. 2022. "Using Ecosystem Engineers to Enhance Multiple Ecosystem Processes." *Functional Ecology* 38: 22-36. https://doi.org/10.1111/1365-2435.14130.

Cabioch, J. 1969. "Les Fonds de Maërl de la Baie de Morlaix et Leur Peuplement Végétal." *Cahiers de Biologie Marine* 10: 139-161.

Cabrito, A., S. de Juan, H. Hinz, and F. Maynou. 2024. "Morphological Insights Into the Three-Dimensional Complexity of Rhodolith Beds." *Marine Biology* 171: 127. https://doi.org/10.1007/s00227-024-04437-y.

Chauvin, J. F. 1842. *Recherches sur l'Organisation, la Fructification et la Classification de Plusieurs Genres d'Algues: Avec la Description de Quelques Espèces Inédites on peu Connues: Essai d'une Répartition des Polypiers Calcifères de Lamouroux Dans la Classe des Algues.* Éditeur non Identifié.

Chen, M.-H., Y.-Y. Huang, B.-Y. Huang, et al. 2022. "Historical Connectivity and Demography of the Ferocious Reef Crab, *Eriphia ferox* (Crustacea; Eriphiidae), Demonstrate That Taoyuan Algal Reef Is an Essential Population Source Along the East Taiwan Strait." *Frontiers in Marine Science* 8: 799989. https://doi.org/10.3389/fmars.2021.799989.

Chenelot, H., S. C. Jewett, and M. K. Hoberg. 2011. "Macrobenthos of the Nearshore Aleutian Archipelago, With Emphasis on Invertebrates Associated With *Clathromorphum nerostratum* (Rhodophyta, Corallinaceae)." *Marine Biodiversity* 41: 413-424. https://doi.org/10.1007/s12526-010-0071-y.

Cira, T. M., K. Quick, and R. C. Venette. 2019. "Watch Your Language: Consequences of Linguistic Uncertainty for Insect Management." *American Entomologist* 65: 258-267. https://doi.org/10.1093/ae/tmz068.

Connell, S. D., M. S. Foster, and L. Airoldi. 2014. "What Are Algal Turfs? Towards a Better Description of Turfs." *Marine Ecology Progress Series* 495: 299-307. https://doi.org/10.3354/meps10513.

Cornwall, C., J. Carlot, O. Branson, et al. 2023. "Crustose Coralline Algae Can Contribute More Than Corals to Coral Reef Carbonate Production." *Communications Earth & Environment* 4: 105. https://doi.org/10.1038/s43247-023-00766-w.

Cornwall, C. E., S. Comeau, and M. T. McCulloch. 2017. "Coralline Algae Elevate pH at the Site of Calcification Under Ocean Acidification." *Global Change Biology* 23: 4245-4256. https://doi.org/10.1111/gcb.13673.

Cornwall, C. E., B. P. Harvey, S. Comeau, et al. 2022. "Understanding Coralline Algal Responses to Ocean Acidification: Meta-Analysis and Synthesis." *Global Change Biology* 28: 362-374. https://doi.org/10.1111/gcb.15899.

Crump, N. S., E. J. Cother, and G. J. Ash. 1999. "Clarifying the Nomenclature in Microbial Weed Control." *Biocontrol Science and Technology* 9: 89-97. https://doi.org/10.1080/09583159929947.

Davies, P. J., J. C. Braga, M. Lund, and J. M. Webster. 2004. "Holocene Deep Water Algal Buildups on the Eastern Australian Shelf." *PALAIOS* 19: 598-609.

Dean, A., R. Steneck, D. Tager, and J. Pandolfi. 2015. "Distribution, Abundance and Diversity of Crustose Coralline Algae on the Great Barrier Reef." *Coral Reefs* 34: 581-594. https://doi.org/10.1007/s00338-015-1263-5.

Deinhart, M., M. S. Mills, and T. Schils. 2022. "Community Assessment of Crustose Calcifying Red Algae as Coral Recruitment Substrates." *PLoS ONE* 17: e0271438. https://doi.org/10.1371/journal.pone.0271438.

Diaz-Pulido, G., K. R. N. Anthony, D. I. Kline, S. Dove, and O. Hoegh-Guldberg. 2012. "Interactions Between Ocean Acidification and Warming on the Mortality and Dissolution of Coralline Algae." *Journal of Phycology* 48: 32-39. https://doi.org/10.1111/j.1529-8817.2011.01084.x.

Dorey, N., S. Martin, and L. Kwiatkowski. 2023. "Ocean Acidification Enhances Primary Productivity and Nocturnal Carbonate Dissolution in Intertidal Rock Pools." *Biogeosciences* 20: 4289-4306. https://doi.org/10.5194/bg-20-4289-2023.

Drew, J. A. 2005. "Use of Traditional Ecological Knowledge in Marine Conservation." *Conservation Biology* 19: 1286-1293. https://doi.org/10.1111/j.1523-1739.2005.00158.x.

Edgar, G. J., A. E. Bates, T. J. Bird, et al. 2016. "New Approaches to Marine Conservation Through the Scaling Up of Ecological Data." *Annual Review of Marine Science* 8: 435-461. https://doi.org/10.1146/annurev-marine-122414-033921.

Edgar, G. J., R. D. Stuart-Smith, T. J. Willis, et al. 2014. "Global Conservation Outcomes Depend on Marine Protected Areas With Five Key Features." *Nature* 506: 216-220. https://doi.org/10.1038/natur e13022.

Eger, A. M., C. O. Blain, A. L. Brown, S. S. W. Chan, K. I. Miller, and A. Vergés. 2024. "Kelp Forests Versus Urchin Barrens: A Comparison of Ecosystem Functions and Services Provided by Two Alternative Stable Marine Habitats." *Proceedings of the Royal Society B: Biological Sciences* 291: 20241539. https://doi.org/10.1098/rspb.2024.1539.

Ellis, J., and D. C. Solander. 1786. *The Natural History of Many Curious and Uncommon Zoophytes: Collected From Various Parts of the Globe.* B. White and Son.

Ellison, A. M. 2019. "Foundation Species, Non-Trophic Interactions, and the Value of Being Common." *iScience* 13: 254-268. https://doi.org/10.1016/j.isci.2019.02.020.
European Commission, Directorate-General for Environment, J. R. Rodwell, et al. 2016. *European Red List of Habitats. Part 1, Marine Habitats*. Publications Office of the European Union. https://doi.org/10.2779/032638.

Ferrigno, F., F. Rendina, R. Sandulli, and G. Russo. 2023. "Corallogenous Assemblages: Research Status and Trends of a Key Mediterranean Biodiversity Hotspot Through Bibliometric Analysis." *Ecological Questions* 35: 1-32. https://doi.org/10.12775/EQ.2024.002.

Filbee-Dexter, K., and R. E. Scheible. 2014. "Sea Urchin Barrens as Alternative Stable States of Collapsed Kelp Ecosystems." *Marine Ecology Progress Series* 495: 1-25. https://doi.org/10.3354/meps10573.

Firth, L. B., M. Schofield, F. J. White, M. W. Skov, and S. J. Hawkins. 2014. "Biodiversity in Intertidal Rock Pools: Informing Engineering Criteria for Artificial Habitat Enhancement in the Built Environment." *Marine Environmental Research: Special Issue: Managing Biodiversity in a Changing Ocean* 102: 122-130. https://doi.org/10.1016/j.marenvres.2014.03.016.

Foslie, M. 1894. *The Norwegian Forms of Lithothamnion*. Royal Norwegian Society of Sciences and Letters.

Foster, M. S. 2001. "Rhodoliths: Between Rocks and Soft Places." *Journal of Phycology* 37: 659-667. https://doi.org/10.1046/j.1529-8817.2001.00195.x.

Fredericq, S., and J. Norris. 1995. "A New Order (Rhodogorgonales) and Family (Rhodogorgonaceae) of Red Algae Composed of Two Tropical Calciferous Genera, *Renouxia* gen. nov. and *Rhodogorgon*." *Cryptogamic Botany* 5: 316-331.

Friant, G., and G. Marie. 2010. "Diagnostic sur le Patrimoine Maritime Culturel Immatériel des Communes Littorales du Parc Naturel Marin d'Iroise."

Gerovasileiou, V., and C. Bianchi. 2021. "Mediterranean Marine Caves: A Synthesis of Current Knowledge." *Oceanography and Marine Biology* 59: 1-88.

Ginsburg, R. N., and A. Bosellini. 1973. "Form and Internal Structure of Recent Algal Nodules (Rhodolites) From Bermuda: A Reply." *Journal of Geology* 81: 239. https://doi.org/10.1086/627843.

Gould, J., J. Halfar, W. H. Adey, and J. B. Ries. 2022. "Growth as a Function of Sea Ice Cover, Light and Temperature in the Arctic/ Subarctic Coralline *C. compactum*: A Year-Long In Situ Experiment in the High Arctic." *Frontiers in Marine Science* 9: 900033.

Grahame, J., and F. S. Hanna. 1989. "Factors Affecting the Distribution of the Epiphytic Fauna of *Corallina officinalls* (L.) on an Exposed Rocky Shore." *Ophelia* 30: 113-129. https://doi.org/10.1080/00785326.1989.10430839.

Grall, J., and J. M. Hall-Spencer. 2003. "Problems Facing Maerl Conservation in Brittany." *Aquatic Conservation: Marine and Freshwater Ecosystems* 13: S55-S64. https://doi.org/10.1002/aqc.568.

Guido, A., V. Gerovasileiou, F. Russo, et al. 2019. "Composition and Biostratiny of Sponge-Rich Biogenic Crusts in Submarine Caves (Aegean Sea, Eastern Mediterranean)." *Palaeogeography Palaeoclimatology Palaeoecology* 534: 109338. https://doi.org/10.1016/j.palaeo.2019.109338.

Halfar, J., W. H. Adey, A. Kronz, S. Hetzinger, E. Edinger, and W. W. Fitzhugh. 2013. "Arctic Sea-Ice Decline Archived by Multicentury Annual-Resolution Record From Crustose Coralline Algal Proxy." *Proceedings of the National Academy of Sciences* 110: 19737-19741. https://doi.org/10.1073/pnas.1313775110.

Hamilton, S. E., and D. Casey. 2016. "Creation of a High Spatio-Temporal Resolution Global Database of Continuous Mangrove Forest Cover for the 21st Century (CGMFC-21)." *Global Ecology and Biogeography* 25: 729-738. https://doi.org/10.1111/geb.12449.

Harvey, A., W. Woelkerling, T. Farr, K. Neill, and W. Nelson. 2005. *Coralline Algae of Central New Zealand an Identification Guide to Common "Crustose" Species*. 57th ed. NIWA.

Harvey, W. H. 1847. *Nereis australis, or Algae of the Southern Ocean: Being Figures and Descriptions of Marine Plants, Collected on the Shores of the Cape of Good Hope, the Extra-Tropical Australian Colonies, Tasmania, New Zealand, and the Antarctic Regions*. Herbarium of the Dublin University.

Hattam, C., S. Broszeit, O. Langmead, et al. 2021. "A Matrix Approach to Tropical Marine Ecosystem Service Assessments in South East Asia." *Ecosystem Services* 51: 101346. https://doi.org/10.1016/j.ecoser.2021.101346.

Heard, J., W.-C. Tung, Y.-D. Pei, et al. 2021. "Coastal Development Threatens Datan Area Supporting Greatest Fish Diversity at Taoyuan Algal Reef, Northwestern Taiwan." *Aquatic Conservation: Marine and Freshwater Ecosystems* 31: 590-604. https://doi.org/10.1002/aqc.3477.

Helias, M., and T. Burel. 2023. *Maerl-Associated Macroalgae in the Bay of Brest (Brittany, France)*. Vol. 53, 14. Marine Biodiversity. https://doi.org/10.1007/s12526-022-01322-z.

Hernandez-Kantun, J. J., J. M. Hall-Spencer, J. Grall, et al. 2016. "North Atlantic Rhodolith Beds." *Rhodolith/Maërl Beds: A Global Perspective*: 265-279. https://doi.org/10.1007/978-3-319-29315-8_10.

Hind, K. R., P. W. Gabrielson, C. Jensen, and P. T. Martone. 2018. "Evolutionary Reversals in Bossiella (Corallinales, Rhodophyta): First Report of a Coralline Genus With Both Geniculate and Nongeniculate Species." *Journal of Phycology* 54: 788-798. https://doi.org/10.1111/jpy.12788.

Hinojosa-Arango, G., C. A. Maggs, and M. P. Johnson. 2009. "Like a Rolling Stone: The Mobility of Maerl (Corallinaceae) and the Neutrality of the Associated Assemblages." *Ecology* 90: 517-528. https://doi.org/10.1890/07-2110.1.

Hodges, K. E. 2008. "Defining the Problem: Terminology and Progress in Ecology." *Frontiers in Ecology and the Environment* 6: 35-42. https://doi.org/10.1890/060108.

Hughes, T. P., J. T. Kerry, M. Álvarez-Noriega, et al. 2017. "Global Warming and Recurrent Mass Bleaching of Corals." *Nature* 543: 373-377. https://doi.org/10.1038/nature21707.

Irvine, L. M., and Y. M. Chamberlain. 1994. *Seaweeds of the British Isles, Volume 1 Rhodophyta, Part 2B. Corallinales, Hildenbrandiales*. Natural History Museum.

Jacquotte, R. 1962. "Etude des Fonds de Maërl de Méditerranée." *Recueils des Travaux de la Station Marine d'Endoume* 26: 141-216.

Jardim, V. L., O. Gauthier, C. Toumi, and J. Grall. 2022. "Quantifying Maerl (Rhodolith) Habitat Complexity Along an Environmental Gradient at Regional Scale in the Northeast Atlantic." *Marine Environmental Research* 181: 105768. https://doi.org/10.1016/j.marenvres.2022.105768.

Jenkins, T., M.-L. Guillemin, C. Simon Nutbrown, H. Burdett, J. Stevens, and V. Peña. 2021. "Whole Genome Genotyping Reveals Discrete Genetic Diversity in North-East Atlantic Maerl Beds." *Evolutionary Applications* 14: 1558-1571. https://doi.org/10.1111/eva.13219.

Jeong, S. Y., W. A. Nelson, J. E. Sutherland, et al. 2021. "Corallinapetrales and Corallinapetraceae: A New Order and Family of Coralline Red Algae Including *Corallinapetra gabrielii* comb. nov." *Journal of Phycology* 57: 849-862. https://doi.org/10.1111/jpy.13115.

Johansen, H. W. 1981. *Coralline Algae: A First Synthesis*. CRC Press.

Kéfi, S., V. Domínguez-García, I. Donohue, C. Fontaine, E. Thébault, and V. Dakos. 2019. "Advancing Our Understanding of Ecological
Stability.” *Ecology Letters* 22: 1349–1356. https://doi.org/10.1111/ele.13340.

Keith, D. A., J. R. Ferrer-Paris, E. Nicholson, et al. 2022. "A Function-Based Typology for Earth's Ecosystems." *Nature* 610: 513–518. https://doi.org/10.1038/s41586-022-05318-4.

Keith, D. A., E. Fragkopolou, J. Assis, and N. Schubert. 2022. "M1.10 Rhodolith/Maërl Beds." In *A Function-Based Typology for Earth's Ecosystems*—*Appendix S4*. The IUCN Global Ecosystem Typology v2.1: Descriptive Profiles for Biomes and Ecosystem Functional Groups. Nature.

Kelaher, B. P., and J. C. Castilla. 2005. "Habitat Characteristics Influence Macrofaunal Communities in Coralline Turf More Than Mesoscale Coastal Upwelling on the Coast of Northern Chile." *Estuarine, Coastal and Shelf Science* 63: 155–165. https://doi.org/10.1016/j.ecss.2004.10.017.

Kelaher, B. P., M. G. Chapman, and A. J. Underwood. 2001. "Spatial Patterns of Diverse Macrofaunal Assemblages in Coralline Turf and Their Associations With Environmental Variables." *Journal of the Marine Biological Association of the United Kingdom* 81: 917–930. https://doi.org/10.1017/S0025315401004842.

Klemfuss, N., B. Prinzmetal, and R. Ivry. 2012. "How Does Language Change Perception: A Cautionary Note." *Frontiers in Psychology* 3: 78.

Kluibenschedl, A., C. Cornwall, W. Nelson, M. Lamare, D. Pritchard, and C. Hepburn. 2023. "Interactive Effects of Ocean Acidification and Water Flow on Growth and Recruitment of Early Successional Coralline Algal Communities." *Phycologia* 62: 637–647. https://doi.org/10.1080/00318884.2023.2272776.

Koletić, N., A. Alegro, A. Rimac, N. Vuković, and V. Šegota. 2020. "Catalogue of Croatian Freshwater Rhodophytes." *Phytotaxa* 434: 151–169. https://doi.org/10.11646/phytotaxa.434.2.2.

Kolzenburg, R., F. D'Amore, S. McCoy, and F. Ragazzola. 2021. "Marginal Populations Show Physiological Adaptations and Resilience to Future Climatic Changes Across a North Atlantic Distribution." *Environmental and Experimental Botany* 188: 104522. https://doi.org/10.1016/j.envexpbot.2021.104522.

Kovalenko, K. E., S. M. Thomaz, and D. M. Warfe. 2012. "Habitat Complexity: Approaches and Future Directions." *Hydrobiologia* 685: 1–17. https://doi.org/10.1007/s10750-011-0974-z.

Krumhansl, K. A., D. K. Okamoto, A. Rassweiler, et al. 2016. "Global Patterns of Kelp Forest Change Over the Past Half-Century." *Proceedings of the National Academy of Sciences* 113: 13785–13790. https://doi.org/10.1073/pnas.1606102113.

Kuffner, I. B., A. J. Andersson, P. L. Jokiel, K. S. Rodgers, and F. T. Mackenzie. 2008. "Decreased Abundance of Crustose Coralline Algae due to Ocean Acidification." *Nature Geoscience* 1: 114–117. https://doi.org/10.1038/ngeo100.

Kujala, H., M. A. Burgman, and A. Moilanen. 2013. "Treatment of Uncertainty in Conservation Under Climate Change." *Conservation Letters* 6: 73–85. https://doi.org/10.1111/j.1755-263X.2012.00299.x.

Kuo, C.-Y., S. Keshavmurthy, A. Chung, et al. 2020. "Demographic Census Confirms a Stable Population of the Critically-Endangered Caryophyllid Coral *Polycathus chaishanensis* (Scleractinia; Caryophyllidae) in the Datan Algal Reef, Taiwan." *Scientific Reports* 10: 10585. https://doi.org/10.1038/s41598-020-67653-8.

Lamarck, J. B. P. A. D. 1801. *Système des Animaux Sans Vertèbres, ou, Tableau Général des Classes, des Ordres et des Genres de ces Animaux : Présentant Leurs Caractères Essentiels et Leur Distribution, d'Après la Considération de Leurs Rapports Naturels et de Leur Organisation, et Suivant l'Arrangement Établi Dans les Galeries du Muséum d'Hist. Naturelle, Parmi Leurs Dépouilles Conservées : Précédé du Discours d'Ouverture du Cours de Zoologie, Donné Dans le Muséum National d'Histoire Naturelle l'An 8 de la République. Muséum National d'Histoire Naturelle*. https://doi.org/10.5962/bhl title.116650.

Legrand, E., P. Riera, O. Bohner, et al. 2018. "Impact of Ocean Acidification and Warming on the Productivity of a Rock Pool Community." *Marine Environmental Research* 136: 78–88. https://doi.org/10.1016/j.marenvres.2018.02.010.

Lemoine, P. 1910. "Essai de classification des Mélobésiées basée sur la structure anatomique." *Bulletin de la Société Botanique de France* 57, no. 5: 323–331.

Linnaeus, C. 1758. *Systema Naturae per Regna Tria Naturae: Secundum Classes, Ordines, Genera, Species, cum Characteribus, Differentiis, Synonymis, Locis*. Holmiae, Impensis Direct. Laurentii Salvii. https://doi.org/10.5962/bhl title.542.

Liou, C.-Y., S.-Y. Yang, and C. A. Chen. 2017. "Unprecedented Calcareous Algal Reefs in Northern Taiwan Merit High Conservation Priority." *Coral Reefs* 36: 1253. https://doi.org/10.1007/s00338-017-1619-0.

Littler, M. M. 1973. "The Population and Community Structure of Hawaiian Fringing-Reef Crustose Corallinaceae (Rhodophyta, Cryptonemiales)." *Journal of Experimental Marine Biology and Ecology* 11: 103–120. https://doi.org/10.1016/0022-0981(73)90050-6.

Littler, M. M., D. S. Littler, S. M. Blair, and J. N. Norris. 1985. "Deepest Known Plant Life Discovered on an Uncharted Seamount." *Science* 227: 57–59. https://doi.org/10.1126/science.227.4682.57.

Marchini, A., F. Ragazzola, C. Vasapollo, et al. 2019. "Intertidal Mediterranean Coralline Algae Habitat Is Expecting a Shift Toward a Reduced Growth and a Simplified Associated Fauna Under Climate Change." *Frontiers in Marine Science* 6: 106. https://doi.org/10.3389/fmars.2019.00106.

Marion, A. F. 1883. *Esquisse d'Une Topographie Zoologique du Golfe de Marseille*. Cayer et cie.

Martin, C. S., M. Giannoulaki, F. De Leo, et al. 2014. "Coralligenous and Maërl Habitats: Predictive Modelling to Identify Their Spatial Distributions Across the Mediterranean Sea." *Scientific Reports* 4: 5073. https://doi.org/10.1038/srep05073.

Martin, S., J. Clavier, J.-M. Guarini, et al. 2005. "Comparison of *Zostera marina* and Maerl Community Metabolism." *Aquatic Botany* 83: 161–174. https://doi.org/10.1016/j.aquabot.2005.06.002.

Martone, P. T., and M. W. Denny. 2008a. "To Break a Coralline: Mechanical Constraints on the Size and Survival of a Wave-Swept Seaweed." *Journal of Experimental Biology* 211: 3433–3441. https://doi.org/10.1242/jeb.020495.

Martone, P. T., and M. W. Denny. 2008b. "To Bend a Coralline: Effect of Joint Morphology on Flexibility and Stress Amplification in an Articulated Calcified Seaweed." *Journal of Experimental Biology* 211: 3421–3432. https://doi.org/10.1242/jeb.020479.

McCoy, S., and N. Kamenos. 2015. "Coralline Algae (Rhodophyta) in a Changing World: Integrating Ecological, Physiological, and Geochemical Responses to Global Change." *Journal of Phycology* 51: 6–24. https://doi.org/10.1111/jpy.12262.

McCoy, S., C. M. Pueschel, C. E. Cornwall, et al. 2023. "Calcification in the Coralline Red Algae: A Synthesis." *Phycologia* 62: 648–666. https://doi.org/10.1080/00318884.2023.2285673.

McKenzie, L. J., L. M. Nordlund, B. L. Jones, L. C. Cullen-Unsworth, C. Roelfsema, and R. K. F. Unsworth. 2020. "The Global Distribution of Seagrass Meadows." *Environmental Research Letters* 15: 074041. https://doi.org/10.1088/1748-9326/ab7d06.

Melis, R., G. Ceccherelli, L. Piazzi, and M. Rustici. 2019. "Macroalgal Forests and Sea Urchin Barrens: Structural Complexity Loss, Fisheries Exploitation and Catastrophic Regime Shifts." *Ecological Complexity* 37: 32–37. https://doi.org/10.1016/j.ecocom.2018.12.005.

Micallef, A., T. P. Le Bas, V. A. I. Huvenne, P. Blondel, V. Hühnerbach, and A. Deidun. 2012. "A Multi-Method Approach for Benthic Habitat Mapping of Shallow Coastal Areas With High-Resolution Multibeam
Data.” *Continental Shelf Research* 39–40: 14–26. https://doi.org/10.1016/j.csr.2012.03.008.

Milner-Gulland, E. J., and K. Shea. 2017. "Embracing Uncertainty in Applied Ecology." *Journal of Applied Ecology* 54: 2063–2068. https://doi.org/10.1111/1365-2664.12887.

Mógor, Á., J. Amatussi, G. Mogor, and L. Gemin. 2021. "Biostimulant Action of *Lithothamnium* sp. Promoting Growth, Yield, and Biochemical and Chemical Changes on Onion." *Journal of Applied Phycology* 33: 1905–1913. https://doi.org/10.1007/s10811-021-02394-3.

Necchi, O., Jr., and M. L. Vis. 2021. "Subphylum Eurhodophytina, Classes Bangiophyceae and Florideophyceae, Subclasses Corallinophycidae, Hildenbrandiophycidae, and Rhodymeniophycidae." In *Freshwater Red Algae: Phylogeny, Taxonomy and Biogeography*, edited by M. L. Vis and O. Necchi Jr., 57–94. Springer International Publishing. https://doi.org/10.1007/978-3-030-83970-3_3.

Nelson, W. A. 2009. "Calcified Macroalgae—Critical to Coastal Ecosystems and Vulnerable to Change: A Review." *Marine and Freshwater Research* 60: 787–801. https://doi.org/10.1071/MF08335.

Nicholson, E., K. E. Watermeyer, J. A. Rowland, et al. 2021. "Scientific Foundations for an Ecosystem Goal, Milestones and Indicators for the Post-2020 Global Biodiversity Framework." *Nature Ecology & Evolution* 5: 1338–1349. https://doi.org/10.1038/s41559-021-01538-5.

Noisette, F. 2013. *Impacts de l'Acidification des Océans sur les Organismes Benthiques Calcifiants des Milieux côtiers Tempérés*. PhD Thesis. Université Pierre et Marie Curie—Paris VI.

Norton, B. G. 1998. "Improving Ecological Communication: The Role of Ecologists in Environmental Policy Formation." *Ecological Applications* 8: 350–364. https://doi.org/10.1890/1051-0761(1998)008[0350:IECTRO]2.0.CO;2.

Ordines, F., and E. Massuti. 2009. "Relationships Between Macro-Epibenthic Communities and Fish on the Shelf Grounds of the Western Mediterranean." *Aquatic Conservation: Marine and Freshwater Ecosystems* 19: 370–383. https://doi.org/10.1002/aqc.969.

OSPAR. 2023. "Benthic Habitats Thematic Assessment." In *OSPAR, 2023: Quality Status Report 2023*. OSPAR Commission.

Pallas, P. S. 1766. *Elenchus Zoophytorum Sistens Generum Adumbrationes Generaliores et Specierum Cognitarum Succintas Descriptiones, cum Selectis Auctorum Synonymis*. Apud Petrum van Cleef.

Pardo, C., L. Lopez, V. Peña, et al. 2014. "A Multilocus Species Delimitation Reveals a Striking Number of Species of Coralline Algae Forming Maerl in the OSPAR Maritime Area." *PLoS ONE* 9: e104073. https://doi.org/10.1371/journal.pone.0104073.

Peña, V., I. Bárbara, J. Grall, C. A. Maggs, and J. M. Hall-Spencer. 2014. "The Diversity of Seaweeds on Maerl in the NE Atlantic." *Marine Biodiversity* 44: 533–551. https://doi.org/10.1007/s12526-014-0214-7.

Peña, V., R. Barreiro, J. Hall-Spencer, and J. Grall. 2013. "*Lithophyllum* spp. Form Unusual Maerl Beds in the North East Atlantic: The Case Study of *L. fasciculatum* (Lamarck) Foslie, 1898, in Brittany." *An aod—Les Cahiers Naturalistes de l'Observatoire Marin* II, no. 2: 11–21.

Peña, V., D. Bélanger, P. Gagnon, et al. 2021. "Lithothamnion (Hapalidiales, Rhodophyta) in the Changing Arctic and Subarctic: DNA Sequencing of Type and Recent Specimens Provides a Systematics Foundation*." *European Journal of Phycology* 56: 468–493. https://doi.org/10.1080/09670262.2021.1880643.

Peña, V., C. Vieira, J. C. Braga, et al. 2020. "Radiation of the Coralline Red Algae (Corallinophycidae, Rhodophyta) Crown Group as Inferred From a Multilocus Time-Calibrated Phylogeny." *Molecular Phylogenetics and Evolution* 150: 106845. https://doi.org/10.1016/j.ympev.2020.106845.

Pereira-Filho, G. H., G. M. Amado-Filho, R. L. De Moura, et al. 2012. "Extensive Rhodolith Beds Cover the Summits of Southwestern Atlantic

Ocean Seamounts." *Journal of Coastal Research* 28: 261–269. https://doi.org/10.2112/11T-00007.1.

Pérès, J.-M., and J. Picard. 1964. *Nouveau Manuel de Bionomie Benthique de la mer Méditerranée*. Station Marine d'Endoume.

Péron, F., and G. Marie. 2010. *Atlas du Patrimoine Maritime du Finistère. Le Télégramme*.

Peryt, T. M. 1983. "Classification of Coated Grains." In *Coated Grains*, edited by T. M. Peryt, 3–6. Springer. https://doi.org/10.1007/978-3-642-68869-0_1.

Pezzolesi, L., A. Falace, S. Kaleb, J. Hernandez-Kantun, C. Ferrano, and F. Rindi. 2017. "Genetic and Morphological Variation in an Ecosystem Engineer, *Lithophyllum byssoides* (Corallinales, Rhodophyta)." *Journal of Phycology* 53: 146–160. https://doi.org/10.1111/jpy.12488.

Philippi, R. A. 1837. "Beweis, Dass die Nulliporen Pflanzen Sind." *Archiv für Naturgeschichte* 3: 387–393. pl. 9, figs 2–6.

Piazzi, L., F. Bulleri, and G. Ceccherelli. 2016. "Limpets Compensate Sea Urchin Decline and Enhance the Stability of Rocky Subtidal Barrens." *Marine Environmental Research* 115: 49–55. https://doi.org/10.1016/j.marenvres.2016.01.009.

Pierri, C., C. Longo, A. Falace, et al. 2024. "Invertebrate Diversity Associated With a Shallow Rhodolith Bed in the Mediterranean Sea (Mar Piccolo of Taranto, South-East Italy)." *Aquatic Conservation: Marine and Freshwater Ecosystems* 34: e4054. https://doi.org/10.1002/aqc.4054.

Poe, M., K. Norman, and P. Levin. 2013. "Cultural Dimensions of Socioecological Systems: Key Connections and Guiding Principles for Conservation in Coastal Environments." *Conservation Letters* 7: 166–175. https://doi.org/10.1111/conl.12068.

Qui-Minet, Z. N., D. Davoult, J. Grall, et al. 2021. "Physiology of Maerl Algae: Comparison of Inter- and Intraspecies Variations." *Journal of Phycology* 57: 831–848. https://doi.org/10.1111/jpy.13119.

Qui-Minet, Z. N., D. Davoult, J. Grall, and S. Martin. 2022. "The Relative Contribution of Fleshy Epiphytic Macroalgae to the Production of Temperate Maerl (Rhodolith) Beds." *Marine Ecology Progress Series* 693: 69–82. https://doi.org/10.3354/meps14089.

R Core Team. 2024. *R: A Language and Environment for Statistical Computing*. R Foundation for Statistical Computing.

Ragazzola, F., A. Marchini, M. Adani, et al. 2021. "An Intertidal Life: Combined Effects of Acidification and Winter Heatwaves on a Coralline Alga (*Ellisolandia elongata*) and Its Associated Invertebrate Community." *Marine Environmental Research* 169: 105342. https://doi.org/10.1016/j.marenvres.2021.105342.

Ramos, D. A. E., J. Del Rio, J. Peñas, and J. C. Braga. 2025. "An Unusual Protuberant *Lithophyllum* sp. From Southern Spain Increases Structural Complexity in Urchin Barrens." *Aquatic Conservation: Marine and Freshwater Ecosystems* 35: e70090. https://doi.org/10.1002/aqc.70090.

Ramos, E. P., T. R. Ferreira, D. B. de Aguiar, F. L. Alves, and S. Dousseau-Arantes. 2023. "*Lithothamnion* sp. as Biostimulant in Plant Cultivation." *Pesquisa Agropecuária Tropical* 53: e76273. https://doi.org/10.1590/1983-40632023v5376273.

Rebelo, A. C., S. Teichert, V. Bracchi, M. Rasser, and D. Basso. 2022. "Editorial: Crustose Coralline Red Algae Frameworks and Rhodoliths: Past and Present." *Frontiers in Earth Science* 10: 1090091. https://doi.org/10.3389/feart.2022.1090091.

Regan, H. M., M. Colyvan, and M. A. Burgman. 2002. "A Taxonomy and Treatment of Uncertainty for Ecology and Conservation Biology." *Ecological Applications* 12: 618–628. https://doi.org/10.1890/1051-0761(2002)012[0618:ATATOU]2.0.CO;2.

Rendina, F., P. J. Bouchet, L. Appolloni, et al. 2019. "Physiological Response of the Coralline Alga *Corallina officinalis* L. to Both Predicted Long-Term Increases in Temperature and Short-Term Heatwave
Events.” *Marine Environmental Research* 150: 104764. https://doi.org/
10.1016/j.marenvres.2019.104764.

Rendina, F., E. Buonocore, A. C. di Montanara, and G. F. Russo. 2022.
"The Scientific Research on Rhodolith Beds: A Review Through
Bibliometric Network Analysis." *Ecological Informatics* 70: 101738.
https://doi.org/10.1016/j.ecoinf.2022.101738.

Rindi, F., J. C. Braga, S. Martin, et al. 2019. "Coralline Algae in a Changing Mediterranean Sea: How Can We Predict Their Future, if We Do Not Know Their Present?" *Frontiers in Marine Science* 6: 723. https://doi.org/10.3389/fmars.2019.00723.

Riosmena-Rodríguez, R. 2017. "Natural History of Rhodolith/Maërl Beds: Their Role in Near-Shore Biodiversity and Management." In *Rhodolith/Maërl Beds: A Global Perspective, Coastal Research Library*, edited by R. Riosmena-Rodríguez, W. Nelson, and J. Aguirre, 3-26. Springer International Publishing. https://doi.org/10.1007/978-3-319-29315-8_1.

Rowland, J. A., L. M. Bland, D. A. Keith, et al. 2020. "Ecosystem Indices to Support Global Biodiversity Conservation." *Conservation Letters* 13: e12680. https://doi.org/10.1111/conl.12680.

Sanz-Lázaro, C., M. D. Belando, L. Marín-Guirao, F. Navarrete-Mier, and A. Marín. 2011. "Relationship Between Sedimentation Rates and Benthic Impact on Maërl Beds Derived From Fish Farming in the Mediterranean." *Marine Environmental Research* 71: 22-30. https://doi.org/10.1016/j.marenvres.2010.09.005.

Savini, A., D. Basso, V. A. Bracchi, C. Corselli, and M. Pennetta. 2012.
"Maerl-Bed Mapping and Carbonate Quantification on Submerged
Terraces Offshore the Cilento Peninsula (Tyrrhenian Sea, Italy)."
*Geodiversitas* 34: 77-98. https://doi.org/10.5252/g2012n1a5.

Sciberras, M., M. Rizzo, J. R. Mifsud, et al. 2009. "Habitat Structure and Biological Characteristics of a Maerl Bed Off the Northeastern Coast of the Maltese Islands (Central Mediterranean)." *Marine Biodiversity* 39: 251-264. https://doi.org/10.1007/s12526-009-0017-4.

Soltan, D., M. Verlaque, C. François Boudouresque, and P. Francour. 2001. "Changes in Macroalgal Communities in the Vicinity of a Mediterranean Sewage Outfall After the Setting Up of a Treatment Plant." *Marine Pollution Bulletin* 42: 59-70. https://doi.org/10.1016/S0025-326X(00)00116-8.

Steneck, R., S. Hacker, and M. Dethier. 1991. "Mechanisms of Competitive Dominance Between Crustose Coralline Algae: An Herbivore-Mediated Competitive Reversal." *Ecology* 72: 938-950. https://doi.org/10.2307/1940595.

Steneck, R. S. 1983. "Escalating Herbivory and Resulting Adaptive Trends in Calcareous Algal Crusts." *Paleobiology* 9: 44-61. https://doi.org/10.1017/S0094837300007375.

Steneck, R. S. 1986. "The Ecology of Coralline Algal Crusts: Convergent Patterns and Adaptative Strategies." *Annual Review of Ecology and Systematics* 17: 273-303. https://doi.org/10.1146/annurev.es.17.110186.001421.

Stewart, J. G. 1982. "Anchor Species and Epiphytes in Intertidal Algal Turf." *Pacific Science* 36, no. 1: 45-59.

Streit, R. P., and D. R. Bellwood. 2023. "To Harness Traits for Ecology, Let's Abandon 'Functionality'." *Trends in Ecology & Evolution* 38: 402-411. https://doi.org/10.1016/j.tree.2022.11.009.

Stroud, J. T., M. R. Bush, M. C. Ladd, R. J. Nowicki, A. A. Shantz, and J. Sweatman. 2015. "Is a Community Still a Community? Reviewing Definitions of Key Terms in Community Ecology." *Ecology and Evolution* 5: 4757-4765. https://doi.org/10.1002/ece3.1651.

Sully, S., D. E. Burkepile, M. K. Donovan, G. Hodgson, and R. van Woesik. 2019. "A Global Analysis of Coral Bleaching Over the Past Two Decades." *Nature Communications* 10: 1264. https://doi.org/10.1038/s41467-019-09238-2.

Tâmega, F. T., G. H. H. Perna, P. Spotorno-Oliveira, R. Riosmena-Rodríguez, and J. E. de Gonçalves. 2017. "A Unique Free-Living Geniculate Coralline Algal Bed Formation." *Marine Biodiversity* 47: 373-374. https://doi.org/10.1007/s12526-016-0487-0.

Tâmega, F. T., B. N. Torrano-Silva, M. C. Oliveira, et al. 2021.
"Identification of 'Articuliths' in a Unique Algal Bed Formation
From Brazil and Description of *Jania cabista* sp. nov. (Corallinales,
Rhodophyta)." *Phycologia* 60: 283-302. https://doi.org/10.1080/00318
884.2021.1916279.

Thierry, G. 2016. "Neurolinguistic Relativity: How Language Flexes Human Perception and Cognition." *Language Learning* 66: 690-713. https://doi.org/10.1111/lang.12186.

Tillin, H. 2015. "Foliose Seaweeds and Coralline Crusts in Surge Gully Entrances." In *Marine Life Information Network: Biology and Sensitivity Key Information Reviews [Online]*, edited by H. Tyler-Walters and K. Hiscock. Marine Biological Association of the United Kingdom.

Tuya, F., N. Schubert, J. Aguirre, et al. 2023. "Levelling-Up Rhodolith-Bed Science to Address Global-Scale Conservation Challenges." *Science of the Total Environment* 892: 164818. https://doi.org/10.1016/j.scitenv.2023.164818.

van der Heijden, L. H., and N. A. Kamenos. 2015. "Reviews and Syntheses: Calculating the Global Contribution of Coralline Algae to Total Carbon Burial." *Biogeosciences* 12: 6429-6441. https://doi.org/10.5194 bg-12-6429-2015.

van Katwijk, M. M., A. Thorhaug, N. Marbà, et al. 2016. "Global Analysis of Seagrass Restoration: The Importance of Large-Scale Planting." *Journal of Applied Ecology* 53: 567-578. https://doi.org/10.1111/1365-2664.12562.

van Woesik, R., and C. Kratochwill. 2022. "A Global Coral-Bleaching Database, 1980-2020." *Scientific Data* 9: 20. https://doi.org/10.1038/s41597-022-01121-y.

Veras, P., I. Pierozzi-Jr, J. B. Lino, et al. 2020. "Drivers of Biodiversity Associated With Rhodolith Beds From Euphotic and Mesophotic Zones: Insights for Management and Conservation." *Perspectives in Ecology and Conservation* 18: 37-43. https://doi.org/10.1016/j.pecon.2019.12.003.

Verlaque, M. 2010. "Field Methods to Analyse the Condition of Mediterranean *Lithophyllum byssoides* (Lamarck) Foslie Rims." *Scientific Reports of Port-Cros National Park* 24: 185-196.

Vigliano Relva, J., and J. Jung. 2021. "Through the Eyes of Another: Using a Narrative Lens to Navigate Complex Social-Ecological Systems and to Embrace Multiple Ways of Knowing." *Frontiers in Marine Science* 8: 678796.

Wai, T.-C., and G. A. Williams. 2006. "Effect of Grazing on Coralline Algae in Seasonal, Tropical, Low-Shore Rock Pools: Spatio-Temporal Variation in Settlement and Persistence." *Marine Ecology Progress Series* 326: 99-113. https://doi.org/10.3354/meps326099.

Walker, R., J. Brodie, S. Russell, L. Irvine, and S. Orfanidis. 2009.
"Biodiversity of Coralline Algae in the Northeastern Atlantic Including
*Corallina caespitosa* sp. nov. (Corallinoideae, Rhodophyta)." *Journal
of Phycology* 45: 287-297. https://doi.org/10.1111/j.1529-8817.2008.
00637.x.

Webster, N. S., S. Uthicke, E. S. Botté, F. Flores, and A. P. Negri. 2013. "Ocean Acidification Reduces Induction of Coral Settlement by Crustose Coralline Algae." *Global Change Biology* 19: 303-315. https://doi.org/10.1111/gcb.12008.

Wiegmann, F. A. 1837. *Archiv für Naturgeschichte*. 3rd ed. Nicolai'schen Buchhandlung.

Williamson, C. J., J. Najorka, R. Perkins, M. L. Yallop, and J. Brodie. 2014. "Skeletal Mineralogy of Geniculate Corallines: Providing Context for Climate Change and Ocean Acidification Research." *Marine Ecology Progress Series* 513: 71-84. https://doi.org/10.3354/meps10929.
Wilson, B., and S. Blake. 2011. "Notes on the Origins and Biogeomorphology of Montgomery Reef, Kimberley, Western Australia." *Journal of the Royal Society of Western Australia* 94: 107-119.

Wilson, S., C. Blake, J. A. Berges, and C. A. Maggs. 2004. "Environmental Tolerances of Free-Living Coralline Algae (Maerl): Implications for European Marine Conservation." *Biological Conservation* 120: 279-289. https://doi.org/10.1016/j.biocon.2004.03.001.

Woelkerling, W. J. 2008. *The Coralline Red Algal Herbarium of Mikael Foslie and Its Impact on Scientific Research*. Vol. 16. Gunneria 79.

Woelkerling, W. J., G. Gustavsen, H. Myklebost, T. Prestø, and S. Såstad. 2005. *The Coralline Red Algal Herbarium of Mikael Foslie: Revised Catalogue With Analyses*. Gunneria 77.

Zhan, S. H., L. Chen, C.-P. Liao, et al. 2022. "Geographic Distance, Sedimentation, and Substrate Shape Cryptic Crustose Coralline Algal Assemblages in the World's Largest Subtropical Intertidal Algal Reef." *Molecular Ecology* 31: 3056-3071. https://doi.org/10.1111/mec.16455.

Žuljević, A., S. Kaleb, V. Peña, et al. 2016. "First Freshwater Coralline Alga and the Role of Local Features in a Major Biome Transition." *Scientific Reports* 6: 19642. https://doi.org/10.1038/srep19642.

## Supporting Information

Additional supporting information can be found online in the Supporting Information section.