Testing for Resistance of Pelagic Marine Copepods to a Toxic Dinoflagellate

With few exceptions, the evolutionary consequences of harmful algae to grazers in aquatic systems remain unexplored. To examine both the ecological and evolutionary consequences of harmful algae on marine zooplankton, we used a two-fold approach. In the first approach, we examined the life history responses of two geographically separate Acartia hudsonica (Copepoda Calanoida) populations reared on diets containing the toxic dinoflagellate Alexandrium fundyense . One copepod population was from a region, Casco Bay, Maine, USA, that has experienced recurrent blooms of highly toxic Alexandrium spp. for decades; whereas the other population from Great Bay, New Jersey, USA, has never been exposed to toxic Alexandrium blooms. The life history experiment demonstrated that when the copepod population from New Jersey was reared on a diet containing toxic A. fundyense it exhibited lower somatic growth, size at maturity, egg production and survival than the same population reared on a diet without toxic A. fundyense . In contrast, toxic A. fundyense did not affect the life-history traits of the Maine population. Fitness, finite population growth rate (λ), was significantly reduced in the New Jersey population, but not in the Maine population. These results are consistent with the hypothesis of local adaptation (resistance) of the historically exposed copepod population to the toxic dinoflagellate. In the second approach, we further tested the resistance hypothesis with a laboratory genetic selection experiment with the naïve New Jersey copepod population exposed to a diet containing toxic A. fundyense. This experiment demonstrated that the ingestion and egg production of adult females of naïve copepods fed A. fundyense improved after three generations of being reared on a diet containing the toxic dinoflagellate. The results of the present study have important implications for understanding how grazer populations may respond to the introduction of toxic algae to their environment, and suggest that grazer resistance may be a feedback mechanism that may lead to bloom control

Comparison of the Functional and Numerical Responses of Resistant versus Non-resistant Populations of the Copepod Acartia Hudsonica Fed the Toxic Dinoflagellate Alexandrium Tamarense

The functional and numerical responses of grazers are key pieces of information in predicting and modeling predator–prey interactions. It has been demonstrated that exposure to toxic algae can lead to evolved resistance in grazer populations. However, the influence of resistance on the functional and numerical response of grazers has not been studied to date. Here, we compared the functional and numerical responses of populations of the copepod Acartia hudsonica that vary in their degree of resistance to the toxic dinoflagellate Alexandrium tamarense. In common environment experiments carried out after populations had been grown under identical conditions for several generations, female copepods were offered solutions containing different concentrations of either toxic A. tamarense or the non-toxic green flagellate Tetraselmis sp. ranging from ∼25 to 500 μgC L−1, and ingestion and egg production rates were measured. Throughout most of the range of concentrations of the toxic diet, copepod populations that had been historically exposed to toxic blooms of Alexandrium exhibited significantly higher ingestion and egg production rates than populations that had little or no exposure to these blooms. In contrast, there were no significant differences between populations in ingestion or egg production for the non-toxic diet. Hence, the between population differences in functional and numerical response to A. tamarense were indeed related to resistance. We suggest that the effect of grazer toxin resistance should be incorporated in models of predator and toxic prey interactions. The potential effects of grazer toxin resistance in the development and control of Alexandrium blooms are illustrated here with a simple simulation exercise

Multimodel inference to quantify the relative importance of abiotic factors in the population dynamics of marine zooplankton

The effect of multiple stressors on marine ecosystems remains poorly understood and most of the knowledge available is related to phytoplankton. To partly address this knowledge gap, we tested if combining multimodel inference with generalized additive modelling could quantify the relative contribution of environmental variables on the population dynamics of a zooplankton species in the Belgian part of the North Sea. Hence, we have quantified the relative contribution of oceanographic variables (e.g. water temperature, salinity, nutrient concentrations, and chlorophyll a concentrations) and anthropogenic chemicals (i.e. polychlorinated biphenyls) to the density of Acartia clausi. We found that models with water temperature and chlorophyll a concentration explained ca. 73% of the population density of the marine copepod. Multimodel inference in combination with regression-based models are a generic way to disentangle and quantify multiple stressor-induced changes in marine ecosystems. Future-oriented simulations of copepod densities suggested increased copepod densities under predicted environmental changes

Latitudinal Differentiation in the Effects of the Toxic Dinoflagellate Alexandrium spp. on the Feeding and Reproduction of Populations of the Copepod Acartia Hudsonica

Blooms of the dinoflagellate Alexandrium spp. increase in their frequency, toxicity and historical presence with increasing latitude from New Jersey (USA) to the Gaspé peninsula (Canada). Biogeographic variation in these blooms results in differential exposure of geographically separate copepod populations to toxic Alexandrium. We hypothesize that the ability of copepods to feed and reproduce on toxic Alexandrium should be higher in copepods from regions that are frequently exposed to toxic Alexandrium blooms. We tested this hypothesis with factorial common environment experiments in which female adults of the copepod Acartia hudsonica from five separate populations ranging from New Jersey to New Brunswick were fed toxic and non-toxic strains of Alexandrium, and the non-toxic flagellate Tetraselmis sp. Consistent with the hypothesis, when fed toxic Alexandrium we observed significantly higher ingestion and egg production rates in the copepods historically exposed to toxic Alexandrium blooms relative to copepods from regions in which Alexandrium is rare or absent. Such differences among copepod populations were not observed when copepods were fed non-toxic Alexandrium or Tetraselmis sp. These results were also supported by assays in which copepods from populations both historically exposed and naı̈ve to toxic Alexandrium blooms were fed mixtures of toxic Alexandrium and Tetraselmis sp. Two-week long experiments demonstrated that when copepods from populations naı̈ve to toxic Alexandrium were fed a toxic strain of Alexandrium they failed to acclimate, such that their ingestion rates remained low throughout the entire two-week period. The differences observed among populations suggest that local adaptation of populations of A. hudsonica from Massachusetts (USA) to New Brunswick (Canada) has occurred, such that some populations are resistant to toxic Alexandrium

Morphological types and seasonal variation in eggs of zooplankton species from bottom sediments in Bahia Blanca Estuary, Argentina

Resting egg production is a survival mechanism in zooplankton species against adverse environmental conditions. Egg accumulation in the upper layer of the bottom sediments is fundamental to the resurgence of the populations of these species when conditions become more favourable. Rotifers, such as Synchaeta sp. and planktonic copepods such as Acartia tonsa and Eurytemora americana are commonly found in Bahía Blanca Estuary and they produce resting eggs. We studied eggs isolated from samples of bottom sediments obtained from two sites located within the inner part of Bahía Blanca Estuary (Cuatreros Port and Ing. White Port). The aims of our work were to describe the morphological types of eggs found in bottom sediments; to try to identify to which species they belong; to corroborate the identity of some of them by means of incubations; and to determine either the spatial or seasonal presence of morphological types according to the sampling site. Sediment samples were collected from Cuatreros Port on a monthly basis from January to December 2003 and samples from Ing. White Port were collected from the area close to the industrial zone only in April 2004. All samples were treated following the sugar flotation method of Onbé. The eggs were observed under stereomicroscope and light microscope. Besides, incubation experiments with eggs were sometimes carried out. Five morphological types of eggs (type A, B, C, D and E) were found in the sediments from Cuatreros Port whereas three types of eggs were found at Ing. White Port (F, G and H). Of the 8 morphological types of eggs found in this study, only those of the rotifer Synchaeta sp. in Cuatreros Port and the copepod A. tonsa in the two sampling sites were confirmed to be respectively diapausal and “delayed -hatching”. As regards the seasonal variation of the eggs found in the sediments from Cuatreros Port and the active forms of the populations of Synchaeta sp. and A. tonsa, our study confirms the presence of eggs in the sediment either in periods of time during which no active forms have been previously reported in the plankton or in periods of time during which only some active forms have been reported at very low densities. Concerning the spatial variation at Ing.White Port, the differences in the presence of eggs across the sampling areas may be due to sediment modifications produced by anthropic impact, where industrial effluents are discharged.Fil: Diodato, Soledad Lorena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; ArgentinaFil: Berasategui, Anabela Anhi. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; ArgentinaFil: Hoffmeyer, Monica Susana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; Argentina. Universidad Tecnológica Nacional; Argentin