Recent deep-sea nematodes and agglutinated foraminifera select specific grains and bioclasts from their environments: Ecological implications

The high-latitude regions are known for a diverse array of benthic meiofauna, yet our understanding of these communities remains limited, particularly in the deep ocean. This study aims to assess the variability and adaptation of nematodes and agglutinated foraminifera in the modern sediments of the Southern Pacific Ocean at >3500 m water depth. Seawater and sediment slurry from the first piston cores (i.e., mudline samples) from International Ocean Discovery Program Sites U1539, U1540, U1541, and U1543 were analyzed for Rose Bengal stained nematode and agglutinated benthic foraminifera. During the microscopic study seven nematode specimens belonging to the genus Desmoscolex, with 16–17, 36 or 38 main rings were found. Scanning electron microscopy study suggest that one morphotype with 17 main rings used only coccoliths of the species Calcidiscus leptoporus while the other specimens used fine-grained siliciclastic material on their concretion ring. Besides nematodes, a few benthic agglutinated foraminifera specimens exclusively used a single species of planktic foraminifera (Globoconella inflata) and/or robust coccoliths, in addition to other fine-grained siliciclastic material, for their test construction. These patterns appear to be highly selective. Specimens of the same benthic nematode Desmoscolex genus and agglutinated foraminifera that have diverse grain types show that these specimens can adapt to their environments, choose specific grains as per their preference, and have no relationship with the grain/particle abundance. This study of Desmoscolex and agglutinated foraminifera species suggests low to moderate organic matter flux and increased ventilation in the abyssal depth of the Southern Pacific Ocean.