Algal pigments in Southern Ocean abyssal foraminiferans indicate pelagobenthic coupling

Abstract

a b s t r a c tThe cytoplasm of four species of abyssal benthic foraminiferans from the Southern Ocean (around 511S; 121W and 501S; 391W) was analysed by High Performance Liquid Chromatography (HPLC) and found to contain large concentrations of algal pigments and their degradation products. The composition of the algal pigments in the foraminiferan cytoplasm reflected the plankton community at the surface. Some foraminiferans contained high ratios of chlorophyll a/degraded pigments because they were feeding on fresher phytodetritus. Other foraminiferans contained only degraded pigments which shows that they utilized degraded phytodetritus. The concentration of algal pigment and corresponding degradation products in the foraminiferan cytoplasm is much higher than in the surrounding sediment. It shows that the foraminiferans collect a diluted and sparse food resource and concentrate it as they build up their cytoplasm. This ability contributes to the understanding of the great quantitative success of foraminiferans in the deep sea. Benthic foraminiferans are a food source for many abyssal metazoans. They form a link between the degraded food resources, phytodetritus, back to the active metazoan food chains.

Indications for algae-degrading benthic microbial communities in deep-sea sediments along the Antarctic Polar Front

“…It was shown that benthic foraminiferans contained large amounts of fresh algal pigments at the sites influenced by bloom B and C, suggesting a quick transport of algal biomass to the deep sea (Cedhagen et al, 2014). We confirmed that bloom-derived POC indeed reached the seafloor likely within a short period of days to weeks by observing a pulse of organic matter in the form of fecal pellets around February 7th in the area of bloom B.…”

High particulate organic carbon export during the decline of a vast diatom bloom in the Atlantic sector of the Southern Ocean

“…5A and B). Indeed, a study by Cedhagen et al (2014) from the same cruise showed that abyssal benthic foraminifera at $ 4000 m were feeding on fresh phytodetritus. This indicates that at least part of the phytoplankton was transported to the seabed.…”

Are boundary conditions in surface productivity at the Southern Polar Front reflected in benthic activity?

“…Congruently, high surface concentration of Chl-a translated to increased densities and response of meiofauna (station 141; see data by Lins et al, 2014). At this station and further to the west in the SPF north of South Georgia, some foraminiferans were found to contain large amounts of pigments (Cedhagen et al, 2014) indicating immediate grazing of the freshly sedimented food pulse. Unfortunately, the EBS was lost at station 141, so that we lack macrofaunal data for this region.…”

“…However, this does not necessarily mean that coupling of the benthic communities to surface production does not occur in the SPF at all. On the one hand there are indications of tight linkages between surface primary productivity and meiofaunal densities as well as pigment uptake by foraminiferans (Lins et al, 2014;Cedhagen et al, 2014). On the other hand, high ratios of Si:C in sinking particles might reduce vertical POC fluxes and thus food supply for benthic organisms (Assmy et al, 2013).…”