Comparison of whole animal costs of protein synthesis among polar and temperate populations of the same species of gammarid amphipod

Contrasting responses to salinity and future ocean acidification in arctic populations of the amphipod Gammarus setosus

Climate change is leading to alterations in salinity and carbonate chemistry in arctic/sub-arctic marine ecosystems. We examined three nominal populations of the circumpolar arctic/subarctic amphipod, Gammarus setosus, along a salinity gradient in the Kongsfjorden-Krossfjorden area of Svalbard. Field and laboratory experiments assessed physiological (haemolymph osmolality and gill Na⁺/K⁺-ATPase activity, NKA) and energetic responses (metabolic rates, MO₂, and Cellular Energy Allocation, CEA). In the field, all populations had similar osmregulatory capacities and MO₂, but lower-salinity populations had lower CEA. Reduced salinity (S = 23) and elevated pCO₂ (~1000 μatm) in the laboratory for one month increased gill NKA activities and reduced CEA in all populations, but increased MO₂ in the higher-salinity population. Elevated pCO₂ did not interact with salinity and had no effect on NKA activities or CEA, but reduced MO₂ in all populations. Reduced CEA in lower-rather than higher-salinity populations may have longer term effects on other energy demanding processes (growth and reproduction).

Experimental investigation of tidal and freshwater influence on Symbiodiniaceae abundance in Anthopleura elegantissima

The San Francisco Bay outflow creates a tidally influenced low-salinity plume that affects adjacent coastal sites. In the study region, Anthopleura elegantissima (Cnidaria; Anthozoa) hosts a single symbiont, the dinoflagellate Breviolum muscatinei. Salinity, temperature, and aerial stress induce a bleaching response similar to corals where symbionts are expelled, causing further energetic stress. Using field observations of environmental conditions and symbiont abundance at sites on a gradient of exposure to estuarine outflow, along with a fully crossed multifactorial lab experiment, we tested for changes in symbiont abundance in response to various combinations of three stressors. Lab experiments were designed to mimic short term outflow events with low salinity, high temperature, and aerial exposure treatments. The lab aerial exposure treatment was a statistically significant factor in suppressing symbiont repopulation (ANOVA, p = .017). In the field, symbiont density decreased with increasing tidal height at the site closest to freshwater outflow (ANOVA, p = .007), suggesting that aerial exposure may affect symbiont density more than sea surface temperature and salinity. Unanticipated documentation of survival in 9 months of sand burial and subsequent repopulation of symbionts is reported as a six-month extension to past observations, exemplifying strong tolerance to environmental insult in this Cnidarian mutualism. The study of this symbiosis is useful in examining predicted changes in ocean conditions in tidepool communities and considering relative sources of stress.

Effect of protein synthesis inhibitor cycloheximide on starvation, fasting and feeding oxygen consumption in juvenile spiny lobster Sagmariasus verreauxi

Metabolism in aquatic ectotherms evaluated by oxygen consumption rates reflects energetic costs including those associated with protein synthesis. Metabolism is influenced by nutritional status governed by feeding, nutrient intake and quality, and time without food. However, little is understood about contribution of protein synthesis to crustacean energy metabolism. This study is the first using a protein synthesis inhibitor cycloheximide to research contribution of cycloheximide-sensitive protein synthesis to decapod crustacean metabolism. Juvenile Sagmariasus verreauxi were subject to five treatments: 2-day fasted lobsters sham injected with saline; 2-day fasted lobsters injected with cycloheximide; 10-day starved lobsters injected with cycloheximide; post-prandial lobsters fed with squid Nototodarus sloanii with no further treatment; and post-prandial lobsters injected with cycloheximide. Standard and routine metabolic rates in starved lobsters were reduced by 32% and 41%, respectively, compared to fasted lobsters, demonstrating metabolic downregulation with starvation. Oxygen consumption rates of fasted and starved lobsters following cycloheximide injection were reduced by 29% and 13%, respectively, demonstrating protein synthesis represents only a minor component of energy metabolism in unfed lobsters. Oxygen consumption rate of fed lobsters was reduced by 96% following cycloheximide injection, demonstrating protein synthesis in decapods contributes a major proportion of specific dynamic action (SDA). SDA in decapods is predominantly a post-absorptive process likely related to somatic growth. This work extends previously limited knowledge on contribution of protein synthesis to crustacean metabolism, which is crucial to explore the relationship between nutritional status and diet quality and how this will affect growth potential in aquaculture species.