Co-occurrence of copepods and dissolved free amino acids in shelf sea waters

Abstract

The vertical distribution of chlorophyll a, copepods, dissolved free amino acid concentration and the fixation of a4C by phytoplankton were monitored in the springs of 1983, 1987 and 1988 in the Ushant front region, shelf edge of the Celtic Sea and central Irish Sea, respectively. In each area, two stations characterized by mixed and stratified water conditions were compared. Vertical distributions of amino acids coincided with the distribution of copepods. A positive and significant correlation was found between the abudance of copepods and the concentration of amino acids dissolved in seawater. A negative and significant correlation was found between chlorophyll a and the concentration of amino acids. Enrichment of amino acids (_> 20 to 500 nM 1-t at specific depths) due to aspartic and glutamic acids, glutamine and ornithine, was assumed to reflect copepod feeding activity and faecal production. At these depths, the natural concentration and diversity of amino acids, including aspartic acid, glutamic acid, asparagine, serine, histidine, glutamine, arginine, threonine, glycine, alanine, tyrosine, valine, phenylalanine, ornithine and lysine, were high enough and in the correct proportions for triggering feeding and swimming and swarming behavior of copepods, as well as their remote detection of food at the micro-and meso-scales (1 to 10 m). This accumulation of amino acids also constitutes a potential additional source of organic nitrogen for bacteria and phytoplankton.

The fluid physics of signal perception by mate-tracking copepods

“…Taking the neurophysiological detection threshold for the amino acid, serine, determined with electroantennograms to be around 10 79 M (¢gure 7), the original concentration could be back-calculated to 4.5 Â10 79 for the patch or 10 78 M for the plume. However, as behavioural thresholds are most commonly 1^3 orders of magnitude greater than physiological thresholds (Derby & Atema 1988), a more conservative approach would be to assume that the lower limits of detection are in the order of 10 77 M so that the concentration released by the female can be at a level of 10 76 M. In either case, these concentrations are still well within estimates for concentrations released by zooplankton or around swarms, or found to stimulate swarming behaviour (10 73 to 10 78 M: Williams & Muir 1981;Poulet & Ouellet 1982;Wheeler 1983;Poulet et al 1991). Thus, production of an amino acid odour trail may be possible, although we cannot rule out the existence of more speci¢c signal molecules from other chemical classes.…”

“…Instead, we used literature values for the concentration of amino acids, a possible stimulant (Poulet & Martin-Jezequel 1983;Poulet & Ouellet 1982;Poulet et al 1986). The background concentration of amino acids in seawater is 10 710 M, a concentration of 10 76 M has been found to elicit swarming behaviour in copepods, and an intracelluar concentration can be 10 73 M (McCarthy & Goldman 1979;Wheeler 1983;Carlucci et al 1986;Poulet & Ouellet 1982;Poulet et al 1991). We suggest that the concentration in the thin trail of a single copepod's wake is 10 75 M. The concentration in the thick wake of a slowly swimming, hovering copepod can be two orders of magnitude less or 5 Â10 78 M. Because a hovering copepod swims at half the speed of a cruising copepod, the concentration of amino acids accumulating over the same period may be doubled.…”

“…Zooplankters are attracted by the scent of algae and can swarm in a phytoplankton patch (Poulet et al 1991;Williamson 1981;Tiselius et al 1993). They can synchronize their vertical migratory pattern and aggregate in a common isolume, at a common location in a temperature gradient, at the pycnocline in a density gradient, or nutricline in a nutrient gradient (Wright et al 1980;Mackas et al 1985;Hamner 1988;Ambler et al 1991).…”

Fates of diatom carbon and trace elements by the grazing of a marine copepod

“…Direct experimental evidence also demonstrates the damage to phytoplankton cells under certain grazing situations (Conover 1966, Martin et al 1970, Corner et al 1972. The importance of DOM production can also be evaluated by comparing bacterial production with the presence of both phytoplankton and zooplankton or phytoplankton alone, or by directly measuring the production of DOM during zooplankton grazing (Lampert 1978, Williams & Poulet 1986, Roman et al 1988, Poulet et al 1991, Peduzzi & Herndl 1992, Kamjunke & Zehrer 1999. However, direct evidence of inefficient feeding as a potential source for DOM production is not clearly established in these studies, because other biological processes, such as exudation by phytoplankton cells, excretion by zooplankton and release from egested fecal pellets, may all contribute to the total DOM production during relatively long incubation periods.…”

Characteristics of the chemical plume behind a sinking particle in a turbulent water column

“…Using observed background concentrations (e.g. Poulet et al 1991, Suttle et al 1991, and observed responses by copepod (Yen et al 1998) and bacteria (Carlucci et al 1986, Atema 1988, Suttle et al 1991, estimated a value of 4 × 10 -11 mol cm -3 (40 nM), while Jackson & Kiørboe 2004) used a value of 3 × 10 -11 mol cm -3 (30 nM). Plume properties.…”