Dynamique de la population de moule verte Perna viridis et réponse au dinoflagellé toxique Karenia brevis : application de la théorie du budget d'énergie dynamique pour évaluer les tendances d'évolution de la population

Abstract : Worldwide, introductions of exotic species to new regions is of rising concern which can lead to catastrophic ecosystem alterations through competition with native species and disruption in energy flow.Perna viridis is a recently introduced bivalve species to US coastal waters and has vigorously spread throughout the southeastern US. However, little information regarding population structure and response to local environmental factors has been reported. Red tide blooms formed by the toxic dinoflagellate Karenia brevis are frequent along the Gulf coast of Florida and as a recently introduced species, it is unclear what tolerance P. viridis has toward these events and associated brevetoxins (PbTx). Further, as an invasive species ecological concerns have risen regarding potential for spread and competition with native bivalve species, particularly the eastern oyster Crassostrea virginica.This study aimed to characterize the population dynamics of established P. viridis populations and their response to naturally occurring K. brevis blooms. This was completed through monitoring of growth, mortality, juvenile recruitment, gametogenesis and biochemical composition (protein, glycogen and lipid) throughout a three year monitoring period to evaluate the effects of K. brevis blooms. Additionally, tissue PbTx concentrations were analyzed to determine uptake, accumulation and elimination rates. Data collected from the field and information reported in the literature were used to create a functional DEB model to predict individual growth and reproduction of P. viridis under environmentally realistic conditions.Prior to onset of the first K. brevis bloom event, P. viridis showed rapid growth rates (6 – 11 mm month-1) and high survival (mortality <1%). However, during K. brevis blooms growth rate dropped significantly and bioaccumulation of PbTx in the soft tissue was observed. High tissue PbTx concentrations persisted long after bloom dissipation and high rates of mortality ensued, severely reducing population densities. PbTx in mussels nearly doubled that of oysters sampled during the same time and remained above the regulatory limit for significantly longer, 2 ½ weeks and 16 weeks, respectively.Biochemical composition and reproduction appeared unaffected, exhibiting year round gametogenesis with a partial, intermittent spawning strategy and stability in reserves. A lack of significant seasonal cycles in biochemical composition suggests sufficient food and energy availability to support the observed year round gametogenesis. While continuous spawning capabilities were evident two major peaks in spawning and recruitment were observed (spring and fall), suggesting reduced fertilization and / or larval development and survival due to the presence of K. brevis and associated ichthyotoxins and hemolysins.These results indicate that while high tissue PbTx concentrations may lead to reduced growth in P. viridis, gametogenesis is not inhibited, allowing the population to survive K. brevis bloom exposure and reproduce, even while individual mortality was high. Prolonged bioconcentration of PbTx may lead to increased threat of post bloom trophic transfer, resulting in negative impacts on other important fisheries and higher food web implications. While it cannot be conclusively determined that the cause of reduced growth, survival and recruitment is due to red tide events, the parallels observed suggest that K. brevis is an important factor in the drastic changes in population structure.Through the work presented here, population dynamics of locally established P. viridis populations were characterized through monthly monitoring and the development of a DEB model to accurately predict the growth and reproduction under dynamic environmental conditions. This work aims to synthesize our knowledge on the individual bioenergetics of P. viridis and to aid in understand population dynamics and potential for competition with local C. virginica [...]
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Katherine Mcfarland. Dynamique de la population de moule verte Perna viridis et réponse au dinoflagellé toxique Karenia brevis : application de la théorie du budget d'énergie dynamique pour évaluer les tendances d'évolution de la population. Ecosystems. Université de Bretagne occidentale - Brest, 2015. English. ⟨NNT : 2015BRES0022⟩. ⟨tel-02294585⟩

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