Grazing on diatoms by harpacticoid copepods: species-specific density-dependent uptake and microbial gardening

Abstract

Four common intertidal harpacticoid species (Paramphiascella fulvofasciata, Tigriopus brevicornis, Nitocra spinipes and Harpacticus obscurus) were offered pelagic diatoms (Phaeodactylum tricornutum) as food in laboratory experiments. To ensure generality we used copepod species originating from diverse habitats with different ecological characteristics. The diatoms were enriched in the stable carbon 13 C isotope to facilitate tracing in the harpacticoids. Uptake of diatoms was clearly species-specific and in general P. fulvofasciata was more efficient than the other species. We found significant uptake by 24 h of incubation for T. brevicornis. From 24 h onwards we found an increase for all 3 species. Species had similar δ 13 C values before and after starvation, indicating that labeled material was efficiently assimilated in their tissues. We tested whether diatom assimilation is density-dependent and this was true for 2 species (N. spinipes and P. fulvofasciata) but not for the semi-pelagic T. brevicornis. Finally, a positive effect of faecal pellets on food uptake for the less mobile species was shown, indicating that microbial gardening occurs within benthic harpacticoids as it does for several other crustacean species.

Does sediment grain size affect diatom grazing by harpacticoid copepods?

“…As a consequence, a functional interpretation of feeding mechanisms of both harpacticoids remains highly speculative. A further generalisation of our results towards a larger group of harpacticoids would be inappropriate in view of our limited knowledge on the ecology of the test organisms and our Wrst indications towards species-speciWc grazing behaviour (De Troch et al, 2005). The technique of tracing diatom uptake by means of stable isotopes oVers an adequate approach to unravel the feeding ecology of harpacticoid copepods.…”

“…The duration of the experiment was based on the outcome of an earlier experiment to test the temporal uptake of diatoms by harpacticoids. It was shown that after 4 days (96 h) a stable, measurable 13 C enrichment could be traced (De Troch et al, 2005).…”

“…The former reaching sizes of 0.66-0.8 mm and a carbon content of 14.7 § 0.4 g C, the latter reaching sizes up to 0.83 mm and a carbon content of 15.6 § 0.6 g C (De Troch et al, 2005). There is no detailed information available on the range of sedimentary conditions the species can tolerate under Weld conditions.…”

“…In order to reveal the basic energy Xows of benthic ecosystems, most to all studies involved laboratory experiments with cultured harpacticoid copepods reared on a variety of food sources, e.g., microalgae (Carman & Thistle, 1985;De Troch, Steinarsdóttir, Chepurnov, & Ólafsson, 2005), protozoans (Rieper & Flotow, 1981), bacteria (Rieper, 1978(Rieper, , 1982 and Xesh (Fetcher, Thistle, Arlt, Suderman, & Vopel, 2004;Guidi, 1984;Lopez, 1982;Seifried & Dürbaum, 2000). The laboratory lay-out however, imposes strong constraints on the extrapolation of the resulting data to Weld situations.…”

Selective predation by a harpacticoid copepod on ciliates in phytotelmata: a laboratory experiment

“…Marine harpacticoid copepods have been shown to consume a wide range of food sources, including bacteria, exopolymer substances, microalgae, flagellates, ciliates, fungi and yeasts (Rieper & Flotow, 1981;Hicks & Coull, 1983;Rieper, 1985). Most studies have focused on harpacticoids as consumers of diatoms and/ or bacteria, demonstrating some degree of selectivity in their feeding (Chepurnov, 1987;Perlmutter & Meyer, 1991;De Troch et al, 2005Wyckmans et al, 2007). Although significant ontogenetic changes in copepod size, morphology and behaviour must inevitably lead to diet shifts, in most feeding studies only the adult copepods were taken into consideration.…”