DOI: 10.5061/dryad.63xsj3v5c
title: Greater functional similarity in mobile compared to sessile assemblages colonizing artificial coastal habitats

description: Among anthropogenic habitats built in the marine environment, floating and
 non-floating structures can be colonized by distinct assemblages. However,
 there is little knowledge whether these differences are also reflected in
 the functional structure. This study compared the functional diversity of
 sessile and mobile invertebrate assemblages that settle over 3 months on
 floating vs. non-floating artificial habitats, in two Chilean ports. Using
 morphological, trophic, behavioral, and life history traits, we found
 differences between mobile and sessile assemblages regarding the effect of
 the type of habitat on the functional diversity. Compared to sessile
 assemblages, a greater functional similarity was observed for mobile
 assemblages, which suggests that their dispersal capacity enables them to
 balance the reduced connectivity between settlement structures. No traits,
 prevailing or selected in one or the other habitat type, were however
 clearly identified; a result warranting further studies focusing on more
 advanced stages of community development.
description: cf. Figueroa NN, Brante A, Viard F, Leclerc J-C (2021) Greater
 functional similarity in mobile compared to sessile assemblages colonizing
 artificial coastal habitats. Marine Pollution Bulletin 172:112844; DOI:
 10.1016/j.marpolbul.2021.112844
 <em>Study area</em> The study area
 comprised two ports (separated by 30 linear km) of the Biobío Region,
 Chile: San Vicente (36.7591ºS, 73.1551ºW) and Coliumo (36.5377ºS,
 72.9571ºW). As a sidenote, San Vicente is open to international trade,
 while Coliumo is only open to regional traffic (see Leclerc et al. 2018,
 2020b), although maritime traffic was not the scope of our study. These
 two ports are located in two different bays (San Vicente and Coliumo bays)
 characterized by distinct biotic compositions in either natural (e.g. for
 intertidal mollusks; Aldea and Valdovinos, 2005) and artificial habitats,
 although little is known regarding soft sediment habitats in ports (but
 see Leclerc et al. 2018 for rapid assessment surveys of conspicuous taxa).
 Both ports present various types of artificial habitats that are part of
 the coastal infrastructure, and which were categorized for this study as:
 (1) non-floating habitats: those attached to the docks by rigid steel
 foundations/pillars and in direct contact with the benthos; and (2)
 floating habitats: comprising longlines or buoys that remain in the water
 column with a weaker, less prominent link to the
 benthos.<br><br><em>Dataset overview, study design,
 sampling and species identification</em> Our
 study capitalized on the sampling carried out between March and June,
 2017, by Leclerc et al. (2020b), who focused on sessile assemblages. In
 brief, the sampling consisted of the deployment of a series of 15 cm x 15
 cm black polypropylene settlement plates, arranged in structures
 (experimental units) held by PVC tubes (for details, see Leclerc et al.
 2020b). The plates were used to have a standardized substrate (surface and
 material) and new available surface area (which is a main limiting
 resource, e.g. Sellheim et al. 2010) to be colonized by sessile and mobile
 taxa (flora and invertebrates). In each of the study
 ports and on the two types of habitats (floating vs. non-floating), two
 experimental units bearing plates were placed vertically, separated by 20
 m to 50 m, and at approximately 3 m to 4 m depth. In the non-floating
 habitats of both ports, these were placed on the pillars of the pier,
 while in floating habitats they were attached to buoys (San Vicente) or
 longline (Coliumo) by ropes. Four plates per experimental unit were
 removed three months after installation, which is sufficient time for the
 settlement and growth of the sessile and mobile assemblages to take place
 on the plates (see Leclerc and Viard 2018, Sellheim et al. 2010). The
 plates were individually transferred underwater in polypropylene rubble
 bags (mesh size &lt; 0.5 mm) to minimize the loss of the mobile fauna
 and were kept for 4 h in a tank with seawater until they were processed in
 the laboratory. <br>In the laboratory, sessile (Leclerc et al.
 2020b) and mobile taxa (this study) were identified under a dissecting
 microscope at the lowest possible taxonomic level. The abundance of the
 sessile taxa was estimated as the coverage at 100 intersection points in
 an area of 120 cm × 120 cm, as detailed in Leclerc et al. (2020b), while
 the abundance of the mobile taxa was estimated by counting the number of
 individuals per plate. The mobile fauna was sampled, after the
 identification of the sessile taxa, by washing the plate using a 500 µm
 mesh sieve. The samples were preserved in 95 % EtOH for later
 identification. Most mobile taxa were identified morphologically to the
 genus or family level due to a lack of taxonomic literature for the South
 East Pacific taxa of many abundant groups (e.g.,
 amphipods).<br><br><em>Functional traits
 categorization</em> After identification, the
 sessile and mobile taxa were classified according to several functional
 traits related to their life history, behavior, and feeding habits. In
 this work, sessile taxa were considered to be those species with no or low
 mobility, those considered as habitat formers, and those which, after
 their settlement, do not migrate between plates. Their functional traits
 were subdivided into different modalities as proposed by Bremner et al.
 (2003) and Beauchard et al. (2017). The information on life history traits
 of the individual taxa was extracted from different online sources, such
 as GBIF, NEMESIS, NIMPIS, MarLIN, NAS, MSIP, BIOTIC and Polytraits, as
 well as bibliographic sources. Each trait was categorized into three to
 five modalities (e.g., the trait “Larval development” was given three
 modalities: pelagic planktotrophic, pelagic lecithotrophic or direct
 benthic) obtaining a total of 11 traits and 46 modalities of traits, as
 detailed in Table 1. The affinity of each taxon with the modalities of
 each trait was assigned so that the "total affinity" of each
 trait equaled 1 (Chevenet et al. 1994). This fuzzy coding allows a taxon
 to display modalities of a trait to different degrees (Chevenet et al.
 1994). When information about a particular trait in a taxon could not be
 obtained, the affinity value of a similar taxon within its taxonomic group
 (genus or family, whichever is closest available) was used as a proxy,
 however only whenever variations of the trait within the taxonomic group
 chosen had not been reported. Otherwise, an equal affinity value was
 assigned for all modalities of that trait for the taxon.
 Functional trait data were analyzed separately for each
 assemblage (mobile vs. sessile). From the trait matrix (“Traits-taxon
 matrix”) of the sessile and mobile assemblages, respectively, an analysis
 of biological traits was performed (BTA; Bremner et al. 2003, 2006). This
 was based on combining this matrix with the taxa abundance matrix
 ("Taxon-plate matrix") by means of a canonical scalar product
 that transforms and weights the scores (between 0 and 1 following the
 fuzzy coding) of each trait modality by the abundance of each taxon. This
 procedure allowed for the generation of a functional trait abundance
 matrix ("Traits-plate matrix"), on which the subsequent
 functional structure analyses were based.
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