Endemic fish species structuring oceanic intertidal reef assemblages

Abstract

Intertidal reef environments are facing a global crisis as climate changes are causing sea-level rise. Synergistically, other human-induced impacts (e.g., sewage, habitat loss) caused by concentration of human populations near the coast increase the natural vulnerability of intertidal ecosystems. However, the effect of these threats have long been neglected due, in part, to a limited knowledge of some aspects of intertidal fish ecology. We tested what are the main differences and drivers in fish assemblages structure between tidepools in three oceanic and three continental shelf (coastal) sites of the tropical southwestern Atlantic (Brazilian Province) using standardized sampling methods. Oceanic and coastal fish assemblages were distinctly structured at the trophic and composition levels. The noteworthy endemism species rate (38-44%) and high densities in oceanic sites are supported by resident species restricted to mid and high-shore tidepools where herbivores were the major trophic group. The coastal sites, on the other hand, were dominated by widely distributed and carnivore species. Physical (substrate type, pool height, subtidal distance and rock coverage), biological (sessile animal coverage) and chemical (salinity) parameters act as the driving forces influencing fish spatial occupancy. Here, clear evidences of high fish endemism and importance of endemics structuring oceanic communities may act as the last straw in favor of the conservation of oceanic intertidal reefs.

Figure 1

Fish endemism levels at oceanic sites for all reef fish fauna^,, and for intertidal fishes (present work).

Figure 2

Species contribution to assemblage similarity percentage (>80%) in density for each island. Endemic species (pictured) are Bathygobius brasiliensis, Stegastes rocasensis and Scartella itajobi in Rocas Atoll, B. brasiliensis, S. itajobi and S. rocasensis in Noronha and Entomacrodus sp., Stegastes fuscus trindadensis and Malacoctenus brunoi in Trindade. Map data ©2017 Google, edited and assembled in CorelDraw X5. Fish photos: R. Andrades, R. M. Macieira and J.-C. Joyeux.

Figure 3

Multidimensional scaling using fish density data in tidepools (N = 90) in regions (A) and sites (B).

Figure 4

Study sites in the southwestern Atlantic (left) and mean (+SE) fish density and biomass of the main trophic groups (CARN = carnivores, DETR = detritivores, HER = herbivores and OMNI = omnivores) in oceanic and coastal regions. Map data ©2017 Google, edited and assembled in CorelDraw X5.

Figure 5

Multivariate regression tree (MRT) analysis with the tree (top right) and principal component analysis (PCA) diagram for the tidepool fish species and environmental explanatory variables (bottom left). Dot color in PCA refers to MRT leaf color. MRT explanatory variables are Region (Oceanic and Coastal), Sessile animal coverage (AC), Subtidal distance (ST), Substrate (Carbonate = Carb and Non-carbonate = N-Carb), Rocky coverage (R), Pool height (H) and Salinity (S). Fish species shown in PCA are Abudefduf saxatilis (A.sax), Bathygobius brasiliensis (B.bra), Bathygobius soporator (B.sop), Bathygobius geminatus (B.gem), Entomacrodus sp. (E.sp.), Entomacrodus vomerinus (E.vom), Labrisomus nuchipinnis (L.nuc), Malacoctenus delalandii (M.del), Malacoctenus brunoi (M.bru), Omobranchus punctatus (O.pun), Ophioblennius trinitatis (O.tri), Scartella cristata (S.cri), Scartella itajobi (S.ita), Scartella poiti (S.poi), Starksia multilepis (S.mul), Stegastes fuscus trindadensis (S.f.tri), Stegastes rocasensis (S.roc), Thalassoma noronhanum (T.nor) and Tomicodon sp. (T.sp.).