Repression of fecundity in the neritic copepod Acartia clausi exposed to the toxic dinoflagellate Alexandrium lusitanicum:relationship between feeding and egg production

Abstract

The effect of the saxitoxin-producing dinoflagellate Alexandrium lusitanicum on the reproductive success of the calanoid copepod Acartia clausi was examined in the laboratory. Experiments were carried out to investigate the functional response of feeding and fecundity of copepod females at increasing concentrations (200 to 1600 pg C I-') of either the toxic A. lusitanicum or the nontoxic Rhodomonas baltica as food sources. Additional expenments were performed to determine if prolonged exposure to A. luatanlcum affects copepod survival and fecundity. Results demonstrate that A. clausj fed on toxic cells at high rates without lethal effects and was able to produce eggs. Survival of females was similar with both diets. Depending on the food source, different functional responses were found. Feeding and fecundity of A. clausi on a diet of R. baltica followed simultaneously a typical satiation response. Fecundity was high and attained maximal rates of 32 to 36 eggs female-' d-'. In contrast, functional responses of ingestion and fecundity by A. clausi fed on A. lusjtanicum were not closely associated. Whereas feeding rates increased linearily with increasing food concentrations, egg production was llmited and stayed constant at 16 to 20 eggs female-' d-' over the range of food concentrations offered. The comparison of calculated gross growth efficiencies for females feeding on both algae indicated an inefficient utilization of ingested toxic food. High feeding rates on toxic A. lusitanicum suggest that saxitoxins do not act as allelopathic chemicals against grazing in A. clausi. Nevertheless, fecundity was adversely affected. It is suggested that ingested toxins probably interfere with digestive processes or cause an enhanced energy expenditure due to detoxiflcation because copepods could cope with toxic algae. As a result, less energy is available and this might explain the reduced fecundity in females

Grazing of the dinoflagellate Noctiluca scintillans on the paralytic toxin-producing dinoflagellate Gymnodinium catenatum: Does grazing eliminate cells during a bloom?

“…This means that when copepods feed on toxic cells, some of the assimilated energy is used to eliminate or manage toxins and less energy is channeled into egg production (Dutz 1998). This is consistent with our observations of N. scintillans shedding its cytoplasmic membrane after ingesting toxic cells for several days.…”

Effect of microalgal food on the sex reversal of Hippolyte inermis (Crustacea: Decapoda)

“…The average size of females in the DFC treatment, however, was smaller than the size of females in all the other treatments. Therefore, the development of a female gonad may require energies which slow the normal growth process (Dutz 1998).…”

“…Diatoms have been demonstrated to influence the ecology and the life cycle of other crustaceans , Dutz 1998. Egg production and hatching success in individuals of the copepod Centropages typicus decreased when diatoms were fed to adult females .…”

Distinctly different behavioral responses of a copepod, Temora longicornis , to different strains of toxic dinoflagellates, Alexandrium spp.

“…Some studies have demonstrated reduced growth and egg production rates (Colin and Dam, 2007;Dutz, 1998;Guisande et al, 2002;Roncalli et al, 2016;Sopanen et al, 2011;Teegarden et al, 2008) or elevated mortality (Avery et al, 2008;Sopanen et al, 2011) in copepods exposed to toxic algae compared to control algae. Such responses may be mediated by the behaviors considered above that both lead to reduced prey ingestion, or by the regurgitation of consumed algae, as described here for T. longicornis feeding on A. tamarense Alex2.…”

“…Paralytic shellfish toxins are sodium-ion channel blockers that can cause potent neurotoxic syndromes in humans as well as fish, seabirds and marine mammals (Cembella, 1998;Turner and Tester, 1997;Turner, 2014). Reported effects on copepods offered PST-containing Alexandrium spp., however, range from none to adverse effects on ingestion rate, egg production, egg hatching and offspring development duration (Dutz, 1998;Frangopulos et al, 2000;Guisande et al, 2002). These variations in responses are not related to the overall toxicity of the cells (Teegarden et al, 2008) and raises the question of whether or not the PSP toxins actually function as a grazer deterrents.…”