Journal of Experimental Marine Biology and Ecology 252 2000 57–74
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Experimental study of suspension-feeding activity in the ¨
serpulid polychaete Ditrupa arietina O.F. Muller
ˆ ´
Esther Jordana, Jean-Claude Duchene, Franc¸ois Charles , Antoine Gremare, Jean-Michel Amouroux
´ Observatoire Oceanologique de Banyuls
, CNRS UMR 7621, BP 44, F-66651, Banyuls-sur-Mer Cedex, France
Received 23 March 1999; received in revised form 23 May 2000; accepted 31 May 2000
Abstract
As time spent feeding can be an index of the feeding intensity, we attempted to describe the filtering activity in the suspension-feeding polychaete Ditrupa arietina. This description was based
on the detection of the opening of the gill-crown by an automated image analysis system. The common pattern of activity could be described as the succession of filtering events and resting
periods of which the number and the mean duration differed greatly from one worm to another. Filtering activity in D
. arietina was neither a continuous process nor even a process having a particular rhythm. Within a same batch of worms, total filtration durations could represent between
12.5 and 87.5 of the total experimental time. Despite a strong inter-individual variability, our results showed the existence of pronounced seasonal variations in the activity of the gill-crown. In
May, worms spent less than 25 of time feeding compared to more than 50 during the rest of year. These temporal changes appeared to result from the physiological state of the worms
reproductive period and ageing at the time of the experiment.
2000 Elsevier Science B.V. All
rights reserved.
Keywords : Suspension-feeding; Polychaete; Image analysis; Ditrupa arietina
1. Introduction
The serpulid polychaete Ditrupa arietina has recently increased all along the north ´
western coasts of the Mediterranean Sea Gremare et al., 1998a,b. The abundances
2
reported, up to 3000 individuals ind m , and the wide geographical distribution
Corresponding author. E-mail address
: charlesarago.obs-banyuls.fr F. Charles. 0022-0981 00 – see front matter
2000 Elsevier Science B.V. All rights reserved.
P I I : S 0 0 2 2 - 0 9 8 1 0 0 0 0 2 3 1 - 8
58 E
. Jordana et al. J. Exp. Mar. Biol. Ecol. 252 2000 57 –74
suggest that through processes such as nutrition, this species affects the functioning of the coastal benthic ecosystem in this region.
As for all the other serpulids Jorgensen, 1966, D . arietina is a suspension feeder.
Therefore, through the benthic trophic network, one of its major impacts concerns the removal of particles from the water mass overlaying the sediment. Quantitative
information about the filtration and clearance rates in suspension-feeding polychaetes remains rather scarce. One commonly held belief is that this group of suspension-feeders
processes small water volumes and is generally less efficient than other suspension- feeding Dales, 1957. Consequently suspension-feeding polychaetes have more or less
been considered as organisms relying on environmental factors to get the energy they need Merz, 1984. More recently, the ecological role of suspension-feeding in
polychaetes has been demonstrated in some systems Merz, 1984; Davies et al., 1989; Riisgard et al., 1996. Moreover, suspension-feeding polychaetes are described as highly
efficient suspension-clearers, relying on very dilute food resources to live and grow Riisgard and Ivarsson, 1990. Laboratory experiments, especially those conducted to
assess physiological performances e.g. filtration, clearance, and oxygen consumption rates of suspension feeders, were often run on isolated specimens Shumway et al.,
1988; Riisgard and Ivarsson, 1990. Consequently, values measured generally corre- spond to the greatest performance rates of the organisms. Extrapolation of such values to
determine, for instance, the global feeding pressure of a natural population of worms requires knowledge of the average time actually spent feeding by each individual.
In suspension feeders, the intensity of feeding basically depends on filtering capacity and filtering activity i.e. time spent pumping; Foster-Smith, 1976. Such a parameter
sometimes may be affected by factors which that induce co-ordinated responses and even rhythm of activity Leonard, 1989; Sanford et al., 1994; Vedel et al., 1994; Achituv
and Yamaguchi, 1997; Thorin et al., 1998. The assessment of the feeding activity at different time scales and under various environmental conditions is thus essential for
extrapolating feeding rates clearance and ingestion rates to the field.
The aim of the present study is to describe the filtering activity of the serpulid Ditrupa arietina. This description is based on the utilisation of an automated video system that
tracks the opening of the gill fan e.g. indicating that worms were processing water. We looked i for temporal changes in the filtration behaviour of worms from different
populations, and ii at the effect of variations in environmental factors on the filtering activity.
2. Material and methods
