Vertical segregation of holoplanktonic molluscs in the epipelagic layer, southern Gulf of Mexico

Abstract

The small-scale vertical distribution of five genera of holoplanktonic molluscs inhabiting the upper oceanic layer (0-105 m) was analysed to test whether evident distribution patterns could be attributed to habitat partitioning. Zooplankton samples were taken over neritic waters during the day and night using a 505-lm multiple closing net at five levels (0-6, 6-12, 12-18, 45-55 and 95-105 m) of the water column. Flowmeters were placed in each net to estimate the amount of filtered water. From the 55,654 identifiable specimens of holoplanktonic molluscs, only 6.2 % were in juvenile stage, and Cavolinia, Diacavolinia, Diacria, Oxygyrus and Clio were the most abundant genera. Adults of these genera comprised 3 % of the total abundance. The abundance data were examined using a spatial segregation index, and its significance was tested with null model methods based on Monte Carlo randomizations. Results indicated that adults showed a much more overlapped distribution in the water column than the in the earlier stages. Indeed, juveniles of Cavolinia, Diacavolinia and Oxygyrus were mainly found in the 0-18-m layer, whereas Diacria and Clio were recorded in the 45-105-m stratum. Null model arguments revealed a significant vertical segregation among them. Potential ecological factors involve preferential spawning areas of adults, avoidance of competition for feeding and spatial resources, use of visual capabilities in searching prey, brood protection and avoidance of strong turbulence conditions.

Changes in Red Snapper Diet and Trophic Ecology Following the Deepwater Horizon Oil Spill

“…However, nothing in their morphology would suggest they are able to strain or even pick zooplankton from the water column. Instead, they likely forage on swarms of plankton, such as pteropods or hyperiid amphipods (Fenwick 1978;Sanvicente-Añorve et al 2013), when available. The phenomenon of Red Snapper subsidizing their diet with zooplankton was described previously by Ouzts and Szedlmayer (2003) and McCawley and Cowan (2007) for fish sampled at artificial reefs off Alabama in the northern Gulf of Mexico.…”

Zooplankton summer composition in the southern Gulf of Mexico with emphasis on salp and hyperiid amphipod assemblages

“…The zooplankton assemblage of the deep basins of the GOM is dominated in both abundance and biomass by calanoid copepods followed by euphausiids and chaetognaths (Hopkins, 1982; Suárez-Morales et al ., 2009; Rowe, 2017). However, some low-abundance taxa, such as cnidarians and pelagic tunicates, bloom under favourable conditions and may occasionally dominate the zooplankton (Esnal, 1979; Suarez-Morales et al ., 2002; Flores-Coto et al ., 2010; Sanvicente-Añorve et al ., 2013; Martell-Hernández et al ., 2014; Färber Lorda et al ., 2019). These blooms are frequently associated with the occurrence of other diverse taxa (Schabetsberger et al ., 2003; Gasca et al ., 2009).…”