. Isotopic niche analysis reveals the low functional redundancy of herviborous fish in unprotected reef of the Abrolhos bank (Bahia Brazil)

MANOELA LELIS; JAVIER CIANCIO; CARLOS HACKRADT; FABIANA FELIX HACKRADT; ITALO LIMA

Congreso; CRS 2021 - 14th International Coral Reef Symposium; 2021

The present studyinvestigated the amplitude and overlap of the isotopic niche of fiveherbivorous fish(HF) species in two reefs with different levels ofanthropogenic impact, with the aim to understandtheir relevance for theresilience of coral reefs. We hypothesize that species of the familiesAcanthuridaeand Scaridae outside the MPAs present greater niche amplitudes (trophicplasticity) andless niche overlap (redundancy), due to less interspecificcompetition, compared to inside MPAs. Weuse the stable isotope analyses ofcarbon and nitrogen (isotopic niche) as a proxy for the variation oftheecological niche in both environments. We also compared populationcharacteristics such asabundance, biomass, and the total length of HF speciesamong protected and unprotectedenvironments via underwater sensus. The studywas developed in two reefs in the Abrolhos Bank, anextension of the continentalshelf in eastern brazilian coast. This region is considered the most diversecoralreef systems from South Atlantic Ocean. For the isotopic analysis, fish werecaptured by scubadivers with a landing net and fragments of dorsal muscle wereextracted with a punch, from sixindividuals of five species (A. chirurgus, A.bahianus, A. coeruleus, Sp. axillare, and Sc. trispinosus) inboth locations,during January and February 2019. The trophic structure of the two communities(protectedand unprotected) were described using Layman's adapted metrics and estimatedfrom aBayesian approach. Underwater visual census showed that only A. coeruleusis significantly lessabundant outside the MPA, while biomass and body lengthwas reduced for Sc. trispinosus and A.Coeruleus in the unprotected reef. Allspecies, except Sp. axillare, had greater amplitudes of niche andisotopic nicheoverlap in the protected area. A. chirurgus showed the largest isotopic niche,and themost specialized (smaller niche) was Sp. axillare, both within the MPA.The small and unique isotopicniche found in Sp. axillare indicates that thespecies may have a unique function in the removal ofcertain algae. We foundclear differences in the isotopic niche of the five HF species, even in specieswithinthe same functional group. Suggesting the HF community has low functionalredundancy, beingeven less redundant outside the MPA. These results are awarning and alert us about a possiblereduction in the resilience capacity ofthe unprotected reef at Abrolhos Bank