ABSTRACT
Ophiothrix fragilis is an efficient suspension-feeder which dominates the pebble community in the English Channel. In the Dover Strait, its density can exceed 2000 ind.m−2 and its mean biomass (ash free dry weight) is 210 g.m−2. Previous studies showed the influence of such a dense population on exchange (i.e. ammonia release) at the water-sediment interface.
The nutritional efficiency of O. fragilis was measured under controlled hyrodynamic conditions. Between 1000 and 1300 ophiurids were put in a tank containing 340 litres of sea water. They were fed with a culture of Skeletonema costatum. Initial particle concentrations were between 3 and 19 µg Chl.a.1−1. The current speed remained stable during the experiments (≈ 8 cm.s−1), it allowed the ophiurids to maintain a typical suspension-feeding behaviour.
The nutrition N of ophiurids (in µg Chl.a.ind−1.h−1) appeared to be more related to the chlorophyll a flux F (i.e. chlorophyll a concentration x current speed, in mg Chl.a.m−2.s−1) than to the chlorophyll a concentration only. The logistic model best expressed the individual nutrition as a function of the chlorophyll a flux : https://www.w3.org/1998/Math/MathML"> N=1 .45/(1+26 .18e -4 .80F ), ? ? n=84, ? r 2 =0 .86 https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003077831/4587b5e2-7fda-4069-ad30-2ed116eb75db/content/eqn93_1_B.tif" xmlns:xlink="https://www.w3.org/1999/xlink"/>
Using the mean density of the population in the Dover Strait (≈ 1500 ind.m−2), we calculated theoretical transfers of chlorophyll a from the water to the population ranging from 1.92 to 52 mg.m−2.d−1.
