Noise limits to low-light vision: Thermal noise in the retinae of rockfish (genus Sebastes)

Thermal noise caused by temperature-induced rhodopsin isomerizations may set limits to low-light visual sensitivity in ectothermic organisms. I examine low-light absolute sensitivity in congeneric nearshore fishes within the genus Sebastes to determine: whether low-light sensitivity is affected by environmentally relevant temperature changes, and, if so, whether sensitivity levels acclimate to compensate for changes in sensitivity resulting from changes in ambient temperature, and, last, how changes in low-light visual sensitivity translate into changes in organisms' ecological interactions.; This study is based on measurement of absolute dark-adapted visual thresholds from intact fish determined using an in situ electroretinogram (ERG) in black, blue, olive, and kelp rockfish. For all species, 10°C increase in temperature yields a 10-fold increase in the threshold stimulus irradiance. Activation energy (Ea) of the process underlying temperature dependence of absolute sensitivity is estimated from the Arrhenius relationship for rates of rhodopsin isomerizations/rod/second at thresholds. The revealed Ea is 36+/-3 kcal/mol, within the literature range for rhodopsin isomerization. However, while temperature dependence of absolute sensitivity for all species is similar, sensitivity levels differ between black and blue rockfish, and kelp and olive rockfish. This correlates with reported diel activity patterns. Nocturnal species (olive and kelp) have greater visual sensitivity than diurnal congeners. I suggest that visual sensitivity structures diel activity patterns in this rockfish community. Potential acclimation to long-term temperature change (days to weeks) was tested by acclimating blue rockfish to 7, 13 and 18°C. Threshold sensitivity was measured subsequent to thermal acclimation treatments. No effect of acclimation treatment was found. Ecological significance of varying retinal sensitivity was examined using computational models of submarine light environments to determine how changes in threshold sensitivity translate into visual activity window durations. The model predicts that seasonal temperature changes (∼4° C) have little ecological impact, but greater changes in temperature will affect visual activity windows. Visual activity window durations are compared between diurnal and nocturnal species. The greater sensitivity of nocturnal species translates into a 3-5 hour advantage in daily visual activity window over diurnal congeners. Additionally, rockfish community diel activity patterns are predicted to be sensitive to increasing light pollution.