Lipid class dynamics and storage depots in juvenile weakfish Cynoscion regalis and their application to condition assessment.

Lipid class dynamics, the pattern of change in the primary form and location of lipid stores and their relationship with standard length (L(S) ), were investigated in collections of young-of-the-year weakfish Cynoscion regalis for the purpose of determining the utility of this analysis as an indication of condition. The separation of total lipids into individual classes and the analysis of potential storage depots revealed the general patterns of lipid class dynamics and energy storage in C. regalis during their period of juvenile estuarine residency. Phospholipid and cholesterol exhibited moderate but variable (8·1-40·0 and 1·3-21·5 mg g(-1) , respectively) concentrations across the entire juvenile period and were the predominant lipid classes in juveniles <100 mm L(S) , while wax ester concentrations were low (c. 1 mg g(-1) ) and exhibited the least amount of variability among lipid classes. Triacylglycerols (TAG) and free fatty acids (FFA) exhibited similar dynamics, with relatively low concentrations (<15 mg g(-1) ) in individuals ≤100 mm L(S) . In larger juveniles both TAG and FFA concentrations generally increased rapidly, though there was considerable variability in both measures (0·0-199·7 and 0·0-49·7 mg g(-1) , respectively). Increasing levels of lipids, primarily in the form of TAG, with size indicated an accumulation of energy reserves with growth, thus providing an indication of individual condition for larger juveniles. Separate analysis of liver, viscera and the remaining carcass indicated that liver and viscera did not represent a significant depot of TAG reserves. Analysis of samples derived from whole juvenile C. regalis thus provided an accurate estimate of energy reserves.

Downscaling global ocean climate models improves estimates of exposure regimes in coastal environments.

Climate change is expected to warm, deoxygenate, and acidify ocean waters. Global climate models (GCMs) predict future conditions at large spatial scales, and these predictions are then often used to parameterize laboratory experiments designed to assess biological and ecological responses to future change. However, nearshore ecosystems are affected by a range of physical processes such as tides, local winds, and surface and internal waves, causing local variability in conditions that often exceeds global climate models. Predictions of future climatic conditions at local scales, the most relevant to ecological responses, are largely lacking. To fill this critical gap, we developed a 2D implementation of the Regional Ocean Modeling System (ROMS) to downscale global climate predictions across all Representative Concentration Pathway (RCP) scenarios to smaller spatial scales, in this case the scale of a temperate reef in the northeastern Pacific. To assess the potential biological impacts of local climate variability, we then used the results from different climate scenarios to estimate how climate change may affect the survival, growth, and fertilization of a representative marine benthic invertebrate, the red abalone Haliotis rufescens, to a highly varying multi-stressor environment. We found that high frequency variability in temperature, dissolved oxygen (DO), and pH increases as pCO2 increases in the atmosphere. Extreme temperature and pH conditions are generally not expected until RCP 4.5 or greater, while frequent exposure to low DO is already occurring. In the nearshore environment simulation, strong RCP scenarios can affect red abalone growth as well as reduce fertilization during extreme conditions when compared to global scale simulations.

Is global climate change influencing the overwintering distribution of weakfish Cynoscion regalis?

The pattern of stable isotope signatures in a sub-sample of 67 juvenile weakfish Cynoscion regalis, captured at the mouth of the Christina River, 113 km upstream of the mouth of Delaware Bay (U.S.A) in the autumn of 2000, suggested that they resided at the location since recruitment. The possibility that young C. regalis departed from the generally characteristic life-history pattern of marine migrants at this latitude, i.e. emigrating offshore with the adults in autumn was bolstered by the collection of 69 individuals during the winters of 2000-2006 from the travelling screens of a power plant located at river kilometre 88 including an 118 mm total length juvenile captured in mid-February 2006.