Abstract
Oysters are a diverse group of marine bivalves that inhabit coastal systems of the world's oceans, providing a variety of ecosystem services, and represent a major socioeconomic resource. However, oyster reefs have become inevitably impacted from habitat destruction, overfishing, pollution and disease outbreaks that have pushed these structures to the break of extinction. In addition, the increased frequency of climate change related events promise to further challenge oyster species survival worldwide.Oysters' early embryonic development is likely the most vulnerable stage to climate change related stressors (e.g. salinity and temperature shifts) as well as to pollutants (e.g. arsenic), and therefore can represent the most important bottleneck that define populations' survival in a changing environment. In light of this, the present study aimed to assess two important oyster species, Crassostrea angulata and Crassostrea gigas embryo-larval development, under combinations of salinity (20, 26 and 33), temperature (20, 24 and 28 °C) and arsenic (As) exposure (0, 30, 60, 120, 240, 480, 960 and 1920 μg. As L−1), to infer on different oyster species capacity to cope with these environmental stressors under the eminent threat of climate change and increase of pollution worldwide.Results showed differences in each species range of salinity and temperature for successful embryonic development. For C angulata, embryo-larval development was successful at a narrower range of both salinity and temperature, compared to C. gigas.Overall, As induced higher toxicity to C. angulata embryos, with calculated EC50 values at least an order of magnitude lower than those calculated for C. gigas.The toxicity of As (measured as median effective concentration, EC50) showed to be influenced by both salinity and temperature in both species. Nonetheless, salinity had a greater influence on embryos' sensitivity to As. This pattern was mostly noticed for C. gigas, with lower salinity inducing higher sensitivity to As. Results were discussed considering the existing literature and suggest that C. angulata populations are likely to become more vulnerable under near future predictions for temperature rise, salinity shifts and pollution.
Highlights
Oyster reefs formed the dominant structural habitat in temperate estuarine systems of the world
Studies concerning this species teratogenesis date back to the 19th century, when the first trials on artificial fecundation of C. angulata were described for full salinity and 22 oC (Bouchon-Brandely, 1882), scarce information is available on the effects of varying salinity and temperature on this species embryonic development in laboratory conditions
Results further revealed that after 48 h no significant differences were observed among temperature levels at salinity 26 and 33 (Fig 4). These findings demonstrate that the arresting effect of As on C. gigas larvae development previously described is not permanent, because extending the exposure period to 48 h revealed higher frequencies of embryo-larval development completion (Supplementary table S2), which in turn resulted in similar toxicity effects to larvae exposed at different temperature levels at 48 h, unlike results obtained at 24 h for which temperature showed a higher effect
Summary
Oyster reefs formed the dominant structural habitat in temperate estuarine systems of the world. Oyster reefs render a variety of ecosystem services, including the formation of habitat structure for commercially important fish species, water quality improvement, shoreline defence against coastal erosion and carbon dioxide storage (Coen et al, 2007; Ridge et al, 2017; Fodrie et al, 2017; Grabowski et al, 2012). These ecosystems are globally threatened, and the majority are classified as functionally extinct (Beck et al, 2011). The comprehension of the factors influencing oysters’ environmental sensitivity can increase the background knowledge and the possibility to better protect and manage this important biological resource
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