Meiofauna in Rhodolith Beds on the Continental Shelf of the Potiguar Basin (Brazil)

Abstract

In continental shelves of tropical areas, ecological studies on meiofauna are scarce and most studies were mainly based on a single sampling event or limited spatial design. Along the Potiguar Basin continental shelf, carbonate sediments, produced by calcareous algae (rhodoliths) and corals, dominate. The ecology of rhodolith beds has been the subject of relatively few studies despite this ecosystem being under strong pressure due to its large economic potential, especially in poorly known tropical areas, and because of global climate change that will likely have a profound impact on crustose coralline species. In the Potiguar Basin, oil spill hazards should also be considered as potential sources of stress due to its history of oil and gas exploration in both onshore and offshore areas. This study focuses on the spatial and temporal patterns of meiofauna communities and their relationship to natural variables. Four campaigns were conducted. Three replicates at four isobaths (5, 10, 20 and 50 m) were sampled, in which 20 stations, each at a distance of 20 km, were positioned, totaling five transects (T1–T5). For each of the Nematoda, Copepoda, and Tardigrada groups, which together accounted for more than 88% of total meiofauna abundance during each campaign, up to 100 individuals per replicate, when available, were identified to the lowest taxonomic level. Three hundred and twenty one lower taxa (species and genera) were identified, with an overall average density of almost 700 ind.cm⁻². The data indicate that the Potiguar Basin benthos has one of the most diverse meiofauna communities ever sampled, with densities falling within the ranges of similar continental shelf environments. Considering spatial variation, a large part of the meiofauna community variability was clearly related to the presence of the Açu incised valley. Despite the importance of spatial factors, which would suggest sediment parameters as the most important, our analysis indicated that ecological interactions may have the same importance in this eco-engineered system. Temporal variation was particularly evident in the density trend. We hypothesize that the much lower meiofauna densities observed during the 2014 campaigns were the result of a very strong seawater warming event during 2010, associated with the ENSO of 2009–2010, and a subsequent strong reduction in precipitation over several years, due to an anomalously northward position of the ITCZ. This hypothesis predicts that as climate change continues, there will be widespread modifications in the structure and functioning of meiofauna communities in rhodolith beds.