Solveig I Bühring

Enhanced benthic activity in sandy sublittoral sediments: Evidence from 13C tracer experiments

Abstract In situ and on-board pulse-chase experiments were carried out on a sublittoral fine sand in the German Bight (southern North Sea) to investigate the hypothesis that sandy sediments are highly active and have fast turnover rates. To test this hypothesis, we conducted a series of experiments where we investigated the pathway of settling particulate organic carbon through the benthic food web. The diatom Ditylum brightwellii was labelled with the stable carbon isotope 13C and injected into incubation chambers. On-board incubations lasted 12, 30 and 132 h, while the in situ experiment was incubated for 32 h. The study revealed a stepwise short-term processing of a phytoplankton bloom settling on a sandy sediment. After the 12 h incubation, the largest fraction of recovered carbon was in the bacteria (62%), but after longer incubation times (30 and 32 h in situ) the macrofauna gained more importance (15 and 48%, respectively), until after 132 h the greatest fraction was mineralized to CO2 (44%). Our findings show the rapid impact of the benthic sand community on a settling phytoplankton bloom and the great importance of bacteria in the first steps of algal carbon processing.

Are Rhodophyceae a dietary component for deep-sea holothurians?

Eicosatetraenoic acid (20:4(n-6)), a polyunsaturated fatty acid (PUFA), was found in deep-sea holothurians at a depth of nearly 5000 m in the temperate north-east Atlantic. It has been suggested that deep-sea animals may be able to synthesize this compound de novo . Since this fatty acid is typical of Rhodophyceae, which has previously been found incorporated in gelatinous material captured in the deep sea, an alternative origin of this fatty acid in the deep-sea holothurians is proposed.