Substrate rugosity and temperature matters: patterns of benthic diversity at tropical intertidal reefs in the SW Atlantic

Abstract

Modeling and forecasting ocean ecosystems in a changing world will require advances in observational efforts to monitor marine biodiversity. One of the observational challenges in coastal reef ecosystems is to quantify benthic and climate interactions which are key to community dynamics across habitats. Habitat complexity (i.e., substrate rugosity) on intertidal reefs can be an important variable explaining benthic diversity and taxa composition, but the association between substrate and seasonal variability is poorly understood on lateritic reefs in the South Atlantic. We asked if benthic assemblages on intertidal reefs with distinct substrate rugosity would follow similar seasonal patterns of succession following meteo-oceanographic variability in a tropical coastal area of Brazil. We combined an innovative 3D imaging for measuring substrate rugosity with satellite monitoring to monitor spatio-temporal patterns of benthic assemblages. The dataset included monthly in situ surveys of substrate cover and taxon diversity and richness, temporal variability in meteo-oceanographic conditions, and reef structural complexity from four sites on the Eastern Marine Ecoregion of Brazil. Additionally, correlation coefficients between temperature and both benthic diversity and community composition from one year of monitoring were used to project biodiversity trends under future warming scenarios. Our results revealed that benthic diversity and composition on intertidal reefs are strongly regulated by surface rugosity and sea surface temperatures, which control the dominance of macroalgae or corals. Intertidal reef biodiversity was positively correlated with reef rugosity which supports previous assertions of higher regional intertidal diversity on lateritic reefs that offer increased substrate complexity. Predicted warming temperatures in the Eastern Marine Ecoregion of Brazil will likely lead to a dominance of macroalgae taxa over the lateritic reefs and lower overall benthic diversity. Our findings indicate that rugosity is not only a useful tool for biodiversity mapping in reef intertidal ecosystems but also that spatial differences in rugosity would lead to very distinct biogeographic and temporal patterns. This study offers a unique baseline of benthic biodiversity on coastal marine habitats that is complementary to worldwide efforts to improve monitoring and management of coastal reefs.

Taxonomic and functional diversity of benthic macrofauna associated with rhodolith beds in SE Brazil

“…Our study support that rhodolith beds have a higher macrofaunal abundance and are home to a more diverse and distinct set of benthic taxa when compared to the underlying sediments, supporting our first hypothesis that these habitats may increase local and regional biodiversity. Our results are thus similar to previous assessments of the effects of rhodolith beds on benthic assemblages (Carvalho, Loiola & Barros, 2017;Gabara et al, 2018), and reveal similar ecological processes of substrate complexity governing benthic ecosystems observed in other coastal marine habitats (Archambault & Bourget, 1996;Mazzuco, Stelzer & Bernardino, 2020). We also observed that spatial heterogeneity in rhodolith nodules density and in the underlying sediments contribute to maintaining a greater species diversity and a higher dissimilarity in species composition between rhodolith and sedimentary habitats.…”

Reef Larval Recruitment in Response to Seascape Dynamics in the SW Atlantic

“…Seascape patterns provided several insights about potential larval mechanisms in the studied tropical rocky reef communities. The Seascapes revealed a lower recruitment rate in rocky reefs during warmer and higher nutrient conditions, which suggests that expected warmer temperatures would decrease recruitment success in this region [40,41]. Seascape analysis also revealed that intrusions of meteorological cold fronts change the coastal oceanography to subtropical conditions and likely promote rapid increases in recruitment through increased larval supply and dissolved nutrients.…”

“…This is a tropical region with an average air temperature of 25ºC that has experienced significant warming trends during the last four decades [39]. The coastal zone is characterized by sparce intertidal lateritic reefs with abundant macroalgal and rhodolith beds [41]. Coastal oceanographic conditions are typically influenced by E-NE winds from the South Atlantic high-pressure system, strong internal tidal currents, and E-SE wave swells [62,63].…”

“…The study was carried at a Brazilian LTER site (HCES) on the coastal SW Atlantic in a marine protected area located in the Eastern Brazil Marine Ecoregion. This region has experienced significant warming trends during the last four decades (1970-2010; [39]) and previous work indicated that larval recruitment and adult intertidal reef assemblages in this region are vulnerable to periods of high sea temperatures [40,41].…”

“…Using the LTER HCES dataset from that represents regional recruitment trends [40,41], we quantified recruitment across multiple temporal scales (years, seasons, and months) for several reef invertebrate species. We then tested the association between recruitment patterns (abundance and composition of species) and Seascapes, identifying the Seascape classes that were key to recruitment variability.…”