DOI: 10.5068/d1h98v
title: Data for: Functional trait variability supports the use of mean trait values and identifies tradeoffs for marine macroalgae

description: Trait-based ecology (TBE) has proven useful in the terrestrial realm and
 beyond for collapsing ecological complexity into traits that can be
 compared and generalized across species and scales. However, TBE for
 marine macroalgae is still in its infancy, motivating research to build
 the foundation of macroalgal TBE by leveraging lessons learned from other
 systems. Our objectives were to evaluate the utility of mean trait values
 (MTVs) across species, to explore the potential for intraspecific trait
 variability, and to identify macroalgal ecological strategies by
 clustering species with similar traits and testing for bivariate
 relationships between traits. To accomplish this, we measured thallus
 toughness, a trait associated with resistance to herbivory, and tensile
 strength, a trait associated with resistance to physical disturbance, in
 eight tropical macroalgal species across up to seven sites where they were
 found around Moorea, French Polynesia. We found interspecific trait
 variation generally exceeded intraspecific variation across species.
 Further, MTV within species varied across sites, suggesting future
 research should focus on whether these traits are influenced by
 site-specific differences in biotic and abiotic drivers. Species grouped
 into three clusters representing different ecological strategies: species
 that were defended against herbivores but not strong, species that were
 strong but not defended, and species that were neither. Intraspecific
 Standardized Major Axis regressions revealed five species exhibited
 significant or marginally significant positive relationships between these
 two traits, suggesting trait syndromes within species. Only one species
 exhibited a significant intraspecific tradeoff, as indicated by a negative
 regression slope. Synthesis: Our results point to three key takeaways that
 should provide a foundation to rapidly advance development of TBE for
 macroalgae in the future. First, our evidence supports the use of MTVs for
 macroalgae. Second, we identified significant spatial variability in
 macroalgal traits may indicate an ability to respond to shifting
 environmental drivers. Third, measuring even a few traits can be a
 powerful tool to identify different ecological strategies to resist
 disturbances such as herbivory and removal by wave action.  We
 hope these novel findings motivate future research into a wider suite of
 macroalgal traits, functions, and strategies to further develop
 trait-based approaches for marine macroalgae.
description: <em>Approaches</em> Our overall
 approach was to measure MTV and the associated variance of two functional
 traits for eight common species of coral reef macroalgae across seven
 fringing reef sites in Moorea, French Polynesia. To maximize our
 probability of capturing a wide range of interspecific variation, we chose
 a diverse set of commonly occurring algal species while to maximize our
 probability of capturing a wide range of intraspecific variability, we
 collected these algae at a diverse set of fringing reefs. We aimed to
 determine if MTV differs between species as well as within species across
 sites. Next, we identified ecological strategies used by clusters of
 species that could be used to resistant either herbivory or physical
 disturbance. Finally, we assessed the nature of bivariate trait
 relationships for individuals within each species.
 <em>Study system</em>  We
 conducted our study on fringing reefs of Moorea, a high volcanic island in
 the Society Islands archipelago of French Polynesia in the South Pacific.
 Moorea is approximately 18 kilometers northwest of Tahiti. We targeted
 fringing reefs for our study because, while variable, macroalgae are
 generally abundant on these reef types around Moorea.
 We chose seven fringing reef sites with abundant and diverse
 macroalgae. From easternmost to westernmost, sites included Temae (TE),
 Maharepa (MA), Gump (GU), Green Marker (GM), Hilton (HI), Sailing School
 East (SSE), and Sailing School West (SSW). While all sites were fringing
 reefs, they varied in their continuity (continuous vs. patch reef) and
 exposure to wind and waves (within a bay with anthropogenic influences or
 along the more exposed open shore), which we reasoned maximized our
 likelihood of capturing each algal species’ potential for intraspecific
 trait variation. Temae, Maharepa, and Hilton likely experience the highest
 water movement as they are on the more exposed northern or eastern shore.
 In addition, a portion of Temae’s backreef was filled to create the
 airport, resulting in substantial wave driven current (pers. obs.). In
 contrast, Gump, Sailing School East, and Sailing School West are located
 within bays and are likely more enriched with nutrients due to greater
 proximity and exposure to local agricultural land (Clausing et al., 2016;
 De’ath & Fabricius 2010). Finally, herbivory pressure is generally
 higher at Maharepa and Hilton compared to sites within the bays (Bergman
 et al., 2016). Temae is an MPA and appears to have abundant herbivorous
 fish communities (pers. obs.); however, we could not find any formal
 surveys. <em>Algal
 collection</em> We collected eight macroalgal
 species from each of our seven sites where they were available and noted
 the life cycle type. If possible, we also noted the generation ID of the
 thallus collected as ploidy has been shown to influence algal responses to
 environmental drivers in some cases (see Krueger-Hadfield 2020; Table 1)
 and therefore may influence trait distributions four brown algae (class
 Phaeophyceae) Dictyota bartayresiana (Dictyotales), Padina boryana
 (Dictyotales; lightly calcified), Sargassum pacificum (Fucales), and
 Turbinaria ornata (Fucales), three red algae (division Rhodophyta)
 Acanthophora spicifera (Ceramiales), Amansia rhodantha (Ceramiales), and
 Galaxaura divaricata (Nemaliales; heavily calcified), and one green alga
 (division Chlorophyta) Halimeda opuntia (Bryopsidales; heavily calcified).
 D. bartayresiana, P. boryana, and A. spicifera tend to occur in more
 sheltered habitats (Guiry & Guiry 2022) and can be found in many
 fringing reef habitats in Moorea (pers. obs.). A. rhodantha, G.
 divaricata, H. opuntia, T. ornata, and S. pacificum can occur in sheltered
 areas to more high-energy, exposed areas of the reef, with T. ornata and
 S. pacificum the only species able to persist on the high-energy reef
 crest. H. opuntia, A. spicifera, T. ornata, S. pacificum are able to
 reproduce asexually via fragmentation (Kilar & McLachlan 1986;
 Walters et al., 2002), and some studies suggest species in the Dictyota
 genus are capable of reproduction via fragmentation as well (Herren et
 al., 2006). From each site, approximately 15 whole,
 macroscopic thalli that appeared healthy (no decay visible) for each
 species were haphazardly collected via snorkel at approximately 1- to 2-m
 depth. Although our target was n=10, extra thalli were collected in case
 trait measurements needed to be repeated (see below). Macroalgae were
 collected and tested the same day between April 21 and May 15, 2019,
 usually completing approximately one site per day. All collected algal
 thalli were immediately transported back to the UC Berkeley Gump South
 Pacific Research Station and placed in an outdoor flow-through water
 table. Using ambient seawater, thalli were cleaned of sediment and
 associated organisms and processed within approximately six hours of
 collection. <em>Thallus
 toughness</em>  To measure thallus toughness
 (“weight to penetrate”) for each species from each site, we attempted to
 collected similar-sized individuals for each species and sampled blades or
 tissue from the middle of each thallus (where applicable, see below), as
 all of the collected algal species exhibit apical growth. Using this
 location across all species maximized our ability to achieve a
 representative average for thallus toughness as it limited sampling tissue
 that may differ in toughness due to differences in age. For example, for
 more simple growth forms that were primarily blade-like (D. bartayresiana
 and P. boryana) or mainly composed of branches without distinct stipes (A.
 spicifera, G. divaricata, and H. opuntia), we sampled tissue from the
 blade or branch in the middle of each thallus. For more complex growth
 forms with distinct stipes and blades (S. pacificum, T. ornata) or a
 midrib (A. rhodantha), we sampled individual blades from the middle of
 each thallus and tested the middle of each blade (avoiding the midrib for
 A. rhodantha). Despite our best attempts to minimize variation in trait
 values due to algal age/size, it is possible that sites could differ in
 age of the algal communities (i.e., sites with new algal growth vs. no new
 growth), which would contribute to inter-site trait variation.
 To measure thallus toughness for each species, we secured each
 algal subsample below a penetrometer so the needle of the penetrometer
 gently rested on the surface of the thallus (adapted from Duffy &
 Hay 1991; Bittick et al., 2016; Ryznar et al., 2021). Then, we
 sequentially added weight to the penetrometer until the needle just
 pierced the thallus surface. This was repeated for 10 different replicate
 thalli for each species at each site. <em>Thallus
 tensile strength</em>  To measure thallus tensile
 strength (“weight to break”), we used 10 whole replicate thalli (apex
 through holdfast) of similar sizes for each species from each site. The
 basal end at the holdfast (where one was apparent) of each thallus was
 secured to a spring scale while the apical end was pulled until the
 thallus broke. The force (weight) required to break the thallus was used
 as a measure of tensile strength. Data were discarded if the thallus broke
 where it was secured at the base or where it was being pulled near the
 apical end.