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Investigating functional redundancy versus complementarity in Hawaiian herbivorous coral reef fishes

Parrotfish photo courtesy of the Hawaii Division of Aquatic Resources

Parrotfish photo courtesy of the Hawaii Division of Aquatic Resources

TitleInvestigating functional redundancy versus complementarity in Hawaiian herbivorous coral reef fishes
Publication TypeJournal Article
Year of Publication2016
AuthorsKelly E.LA, Eynaud Y., Clements S.M, Gleason M., Sparks R.T, Williams I.D, Smith JE
Date Published2016/12
Type of ArticleArticle
ISBN Number0029-8549
Accession NumberWOS:000386070800021
Keywordsassemblages; bioerosion; community structure; competition; Complementarity; diversity; ecological implications; ecosystem; Functional guild; Functional redundancy; herbivore; productivity; selectivity; sparisoma-viride; status; Trophic

Patterns of species resource use provide insight into the functional roles of species and thus their ecological significance within a community. The functional role of herbivorous fishes on coral reefs has been defined through a variety of methods, but from a grazing perspective, less is known about the species-specific preferences of herbivores on different groups of reef algae and the extent of dietary overlap across an herbivore community. Here, we quantified patterns of redundancy and complementarity in a highly diverse community of herbivores at a reef on Maui, Hawaii, USA. First, we tracked fish foraging behavior in situ to record bite rate and type of substrate bitten. Second, we examined gut contents of select herbivorous fishes to determine consumption at a finer scale. Finally, we placed foraging behavior in the context of resource availability to determine how fish selected substrate type. All species predominantly (73-100 %) foraged on turf algae, though there were differences among the types of macroalgae and other substrates bitten. Increased resolution via gut content analysis showed the composition of turf algae consumed by fishes differed across herbivore species. Consideration of foraging behavior by substrate availability revealed 50 % of herbivores selected for turf as opposed to other substrate types, but overall, there were variable foraging portfolios across all species. Through these three methods of investigation, we found higher complementarity among herbivorous fishes than would be revealed using a single metric. These results suggest differences across species in the herbivore "rain of bites" that graze and shape benthic community composition.

Short TitleOecologia

Our work demonstrates that individual species within a single herbivore community have different consumption patterns on a reef and are selecting for different types of available algae despite initial appearances of high functional redundancy. In situ observation combined with gut content analysis allowed us to differentiate within and between species’ bite rates and substrates bitten within a given reef context. Thus, we are able to quantify the “rain of bites” (Hamilton et al. 2014) across a reefscape, with resolution to macroalgae genera and turf algae functional form. This detailed view of the herbivore community helps to inform how individual herbivores influence benthic community structure based on community algal composition, although importantly, the ecological fate of these bites has different implications. Increasing functional complementarity with additional ecological metrics emphasizes the importance of diverse herbivore communities for reef ecosystem function.

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