The role of phototrophic sulfur bacteria as food for meiobenthic harpacticoid copepods inhabiting eutrophic coastal lagoons

Abstract

Laboratory experiments were undertaken using Amonardia normani and Schizopera cf compacta, two meiobenthic harpacticoid copepods commonly found in coastal lagoons . The first experiments were designed to determine if the phototrophic sulfur bacteria Chromatium gracile can be ingested by these copepods and at what concentrations . Egestion rate was used as an index of feeding rate. The response of the egestion rate, expressed in numbers of faecal pellets produced by copepod per day, as a function of bacterial concentration followed the functional model . A . normani attained constant feeding rates from the bacterial concentration of 1 x 107 cells ml -1 (5 jig C ml -1 ) onwards, S. cf. compacta attained constant feeding rates from 2 .6 x 107 cells ml -1 (13 pg C ml -1 ) onwards. The faecal pellet volume changed significantly (p<0 .05) between food concentrations for A . normani but not for S. cf. compacta (p>0.05) . In order to investigate the effect of the phototrophic bacterial diet on the population dynamics of A . normani three groups of nauplii were maintained at 2 x 107 cells ml -1 and observed every day. The mortality of these nauplii was very high compared to those maintained on a diatom diet (Nitzschia constricta) ; only in one of the groups did some copepodites develop but no adults were ever observed. Adults fed on bacteria did not have different (p>0.05) survival rates compared to those fed on diatoms, nevertheless, the number of nauplii produced was significantly less (p<0 .05) on the bacterial diet. These results lead us to suggest that although the phototrophic sulfur bacteria (Chromatium gracile) can be ingested by both copepod species it cannot sustain the full development of the A. normani population . Thus, a bloom of phototrophic sulfur bacteria does not seem to be a favourable situation for opportunistic benthic copepods to colonize eutrophic coastal lagoons after a dystrophic crisis .

Eutrophication gradients in coastal lagoons as exemplified by the Bassin d'Arcachon and the �tang du Pr�vost

“…Recent studies have shown very high bacterial productivity in coastal lagoons (references in Torreton, 1991) but few describe accurately the interrelationships between such biomass and the consumers in the water column and benthos (Gophen et al ., 1974 ;Caumette et al ., 1983 ;Rieper, 1982 ;Carman & Thistle, 1985 ;Decho & Castenholz, 1986 ;Souza-Santos et al ., 1996) . Fenchel & Jorgensen (1977) calculated that bacteria in the detritic food chain provided between 60-80% of the diet of the meiofauna .…”

Substrate-dependent bacterivory by intertidal benthic copepods

“…The work of Rieper (1978) formed a baseline study for the role of bacterivory by copepods. Later on, Souza- Santos et al (1996Santos et al ( , 1999 underlined the role of bacteria associ ated with diatoms to rear copepods and the use of bacteria as a potential food source. Harpacticoid copepods are rich in polyunsaturated fatty acids such as EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) which are essential to their consumers (e.g., juvenile fish) and which they probably largely obtain from consumption of diatoms or other 'high-quality' food sources such as PUFA-rich dinoflagellates (Veloza et al 2006;Chen et al 2012).…”