Drivers of biodiversity associated with rhodolith beds from euphotic and mesophotic zones: insights for management and conservation

Ecologically important marine ecosystems should be identified and protected, as is the case of the poorly known SW Atlantic rhodolith beds. Understanding the main variables predicting biodiversity patterns is essential for determining priority areas for conservation. Here, we analyzed the macroinvertebrate associated with rhodoliths from euphotic and mesophotic zones from the Fernando de Noronha Archipelago investigating the drivers of diversity distribution in this habitat. Rhodoliths were sampled and vagile macroinvertebrates (>500 μm) were classified and quantified. We verified that estimated density of organisms associated with rhodoliths in the euphotic zone was 17 % greater than the mesophotic zone. The communities along depth zones show dissimilarities, suggesting that both environments are ecologically distinct. Comparisons with other ecosystems revealed that rhodolith beds have similar diversity of macroinvertebrates. We also found that four of the six tested variables predicted 85 % of the variability observed in the vagile macroinvertebrate community (i.e. average diameter, depth, biomass of macroalgae and density of rhodoliths in the bed). These variables should be taken into account in future research in modeling the biodiversity associated with the rhodolith beds. This is especially relevant in the SW Atlantic where the rhodolith beds seem to harbor an associated biodiversity greater than previous works had indicated, moreover, they represent one of the main ecosystems that are often superimposed with mining activities1813743CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ2017/22273-

Population dynamics and secondary production of Euzonus furciferus Ehlers (Polychaeta, Opheliidae) in an exposed sandy beach of Southern Brazil Dinâmica populacional e produção secundaria de Euzonus furciferus Ehlers (Polychaeta, Opheliidae) numa praia exposta do sul do Brasil

The distribution, population dynamics and secondary production of the polychaete Euzonus furciferus was studied in Atami Beach (Southern Brazil), from February 1992 to March 1993. Euzonus furciferus Ehlers, 1897 is the only deposit feeder species of the upper intertidal region. The organisms were present in the sandy beach all over the year, concentrated in a narrow band, and reaching maximal densities of 3,029 individuals m-2. Peaks of abundance occurred in September 1992, with a mean of 681.8 individuals m-2. Recruitment occurred in winter, with a peak in July. Mean annual biomass was estimated in 0.218 gAFDW m-2, with a total annual production of 0.466 gAFDW m-2 y-1, giving a P/B ratio of 2.13 y-1. Similar values were found for a filter-feeder polychaete inhabiting the same beach, suggesting that general food disposability of each particular environment is more important for production than the trophic strategic employed by those organisms exploring this environment.<br>A dinâmica populacional e a produção secundária do poliqueta Euzonus furciferus foi estudada em uma praia arenosa exposta do sul do Brasil. O estudo foi realizado na praia de Atami, de fevereiro de 1992 a março de 1993. Euzonus furciferus Ehlers, 1897 é a única espécie comedora de depósito da região superior do intermareal. Os organismos foram encontrados na praia ao longo de todo o ano, concentrados em uma estreita faixa, e alcançando densidades máximas de 3.029 indivíduos.m-2. Picos de abundância ocorreram em setembro de 1992, com uma média de 681,8 indivíduos.m-2. O recrutamento ocorreu no inverno, com um pico em julho. A biomassa média anual foi estimada em 0,218 gPSLC m-2, com uma produção anual total de 0,466 gPSLC m-2ano-1, e com uma razão P/B de 2,13 ano-1. Valores similares foram encontrados para um poliqueta filtrador existentes na mesma praia, sugerindo que a disponibilidade geral de alimento para cada ambiente particular é mais importante para a produção do que a estratégia trófica empregada pelos organismos que exploram este ambiente