Ocean acidification effects in the early life-stages of summer flounder, Paralichthys dentatus.

The limited available evidence about effects of high CO₂ and acidification of our oceans on fish suggests that effects will differ across fish species, be subtle, and interact with other stressors. An experimental framework was implemented that includes the use of (1) multiple marine fish species of relevance to the northeastern USA that differ in their ecologies including spawning season and habitat; (2) a wide yet realistic range of environmental conditions (i.e., concurrent manipulation of CO₂ levels and water temperatures), and (3) a diverse set of response variables related to fish sensitivity to elevated CO₂ levels, water temperatures, and their interactions. This report is on an array of early life-history responses of summer flounder (Paralichthys dentatus), an ecologically and economically important flatfish of this region, to a wide range of pH and CO₂ levels. Survival of summer flounder embryos was reduced by 50% below local ambient conditions (7.8 pH, 775ppmpCO₂) when maintained at the intermediate conditions (7.4 pH, 1860ppmpCO₂), and by 75% below local ambient when maintained at the most acidic conditions tested (7.1 pH, 4715ppmpCO₂). This pattern of reduced survival of embryos at higher CO₂ levels was consistent among three females used as sources of embryos. Sizes and shapes of larvae were altered by elevated CO₂ levels with longer larvae in more acidic waters. This pattern of longer larvae was evident at hatching (although longer hatchlings had less energy reserves) to midway through the larval period. Larvae from the most acidic conditions initiated metamorphosis at earlier ages and smaller sizes than those from more moderate and ambient conditions. Tissue damage was evident in older larvae (age 14 to 28 d post-hatching) from both elevated CO₂ levels. Damage included liver sinusoid dilation, focal hyper-plasia on the epithelium, separation of the trunk muscle bundles, and dilation of the liver sinusoids and central veins. Cranial-facial features were affected by CO₂ levels that changed with ages of larvae. Skeletal elements of larvae from ambient CO₂ environments were comparable or smaller than those from elevated CO₂ environments when younger (14d and 21 d post-hatching) but larger at older ages (28 d). The degree of impairment in the early life-stages of summer flounder due to elevated CO₂ levels suggests that this species will be challenged by ocean acidification in the near future. Further experimental comparative studies on marine fish are warranted in order to identify the species, life-stages, ecologies, and responses that are most sensitive to increased levels of CO₂ and acidity in near-future ocean waters, and a strategy is proposed for achieving these goals. [ABSTRACT FROM AUTHOR]