decussatus under climate change scenarios

We built a simulation model based on Dynamic Energy Budget theory (DEB) to assess the growth and reproductive potential of the native European clam Ruditapes decussatus and the introduced Manila clam Ruditapes philippinarum under current temperature and pH conditions in a Portuguese estuary and under those forecasted for the end of the 21st c. The climate change scenario RCP8.5 predicts temperature increase of 3 °C and a pH decrease of 0.4 units. The model was run under additional conditions of exposure to the emerging contaminant triclosan (TCS) and in the absence of this compound. The parameters of the DEB model were calibrated with the results of laboratory experiments complemented with data from the literature available for these two important commercial shellfish resources. For each species and experimental condition (eight combinations), we used data from the experiments to produce estimates for the key parameters controlling food intake flux, assimilation flux, somatic maintenance flux and energy at the initial simulation time. The results showed that the growth and reproductive potential of both species would be compromised under future climate conditions, but the effect of TCS exposure had a higher impact on the energy budget than forecasted temperature and pH variations. The egg production of R. philippinarum was projected to suffer a more marked reduction with exposure to TCS, regardless of the climatic factor, while the native R. decussatus appeared more resilient to environmental causes of stress. The results suggest a likely decrease in the rates of expansion of the introduced R. philippinarum in European waters, and negative effects on fisheries and aquaculture production of exposure to emerging contaminants (e.g., TCS) and climate change.

decussatus): evidence of species-specific toxicokinetics and DNA vulnerability

This study aims to assess and compare the kinetics (accumulation/elimination) of the marine biotoxins okadaic acid (OA) and dinophysistoxin-1 (DTX1), between native (Ruditapes decussatus) and invasive (Ruditapes philippinarum) clam species, and their genotoxic effects and DNA recover capacity after, exposure to toxic dinoflagellates Prorocentrum lima. Clams were fed with P. lima for 5 days and then to non-toxic algae (post-exposure) during other 5 days. Toxin concentrations determined in clams by LC-MS/MS were related with DNA damage and repair assessment through the comet and base excision repair (BER) assays, respectively. Differential accumulation patterns were observed between the invasive and native species. The invasive species consistently and progressively accumulated the toxins during the first 24 h of exposure, while the native clams showed drastic variations in the toxin accumulation. Nevertheless, at the end of a 5 days of exposure period, the native clams presented higher toxin concentrations, nearly reaching the legal regulatory limit for human consumption. In addition, native clams were vastly affected by OA and DTX1, presenting an increment in the DNA damage since the first day, with a correspondent increase in the repair activity. On the other hand, invasive clams were not affected by the dinoflagellate toxins, exhibiting only some signs of the challenge, namely an increase in the DNA repair mechanisms in the post-exposure period. Invasive clams R. philippinarum are better adapted to cope with harmful algal blooms and OA-group toxins than native species. These results may increase farming interest and may lead to new introductions of the invasive clams. In sympatry sites, exposure to OA-group toxins may unbalance clams species biomass and distribution as exposure to toxic dinoflagellates affects the native clams from cellular to a population level, representing a significant threat to development and maintenance of R. decussatus populations.

Biochemical performance of native and introduced clam species living in sympatry: The role of elements accumulation and partitioning

The present study reports metal and arsenic contamination in sediments, as well as element accumulation and partitioning in native (Ruditapes decussatus and Venerupis corrugata) and introduced (Ruditapes philippinarum) clam species living in sympatry at the Óbidos lagoon (Portugal). The biochemical performance and the human health risks derived from the consumption of these species are also discussed. The results obtained showed that R. decussatus was the most abundant species in all the sampling sites, revealing that the introduced clam has not yet supplanted the native species. The concentration of elements was higher in areas with higher Total Organic Matter (TOM) and fines content, being Chromium (Cr), Copper (Cu) and Lead (Pb) the most abundant metals. Clams from these areas showed the highest concentration of elements but the lowest bioaccumulation levels. Furthermore, except for As, higher concentration of elements was found in clams insoluble fraction, the less toxic fraction to the organisms. Due to the low contamination levels and because elements, except As, were mainly allocated to the insoluble fraction, clams presented similar biochemical parameters among distinct areas, with no significant oxidative stress induced. Furthermore, clams from the Óbidos lagoon represent a low health risk to human consumption since, except for As, their contamination levels were below the maximum permissible limits defined by international organizations.