The influence of stochastic temperature fluctuations in shaping the physiological performance of the California mussel, Mytilus californianus.

Climate change is forecasted to increase temperature variability and stochasticity. Most of our understanding of thermal physiology of intertidal organisms has come from laboratory experiments that acclimate organisms to submerged conditions and steady-state increases in temperatures. For organisms experiencing the ebb and flow of tides with unpredictable low tide aerial temperatures, the reliability of reported tolerances and thus predicted responses to climate change requires incorporation of environmental complexity into empirical studies. Using the mussel Mytilus californianus, our study examined how stochasticity of the thermal regime influences physiological performance. Mussels were acclimated to either submerged conditions or a tidal cycle that included either predictable, unpredictable or no thermal stress during daytime low tide. Physiological performance was measured through anaerobic metabolism, energy stores and cellular stress mechanisms just before low tide, and cardiac responses during a thermal ramp. Both air exposure and stochasticity of temperature change were important in determining thermal performance. Glycogen content was highest in the mussels from the unpredictable treatment, but there was no difference in the expression of heat shock proteins between thermal treatments, suggesting that mussels prioritise energy reserves to deal with unpredictable low tide conditions. Mussels exposed to fluctuating thermal regimes had lower gill anaerobic metabolism, which could reflect increased metabolic capacity. Our results suggest that although thermal magnitude plays an important role in shaping physiological performance, other key elements of the intertidal environment complexity such as stochasticity, thermal variability and thermal history are also important considerations for determining how species will respond to climate warming.

Acclimation to tidal conditions alters the physiological responses of the green shore crab, Carcinus maenas, to subsequent emersion.

Animals inhabiting the intertidal zone are exposed to abrupt changes in environmental conditions associated with the rise and fall of the tide. For convenience, the majority of laboratory studies on intertidal organisms have acclimated individuals to permanently submerged conditions in seawater tanks. In this study, green shore crabs, Carcinus maenas, were acclimated to either a simulated tidal regime of continuous emersion-immersion ('tidal') or to permanently submerged conditions ('non-tidal') to assess their physiological responses to subsequent emersion. Tidal crabs exhibited an endogenous rhythm of oxygen consumption during continuous submersion with lower oxygen consumption during periods of anticipated emersion, which was not detected in non-tidal crabs. During emersion, tidal crabs were able to buffer apparent changes in acid-base balance and exhibited no change in venous pH, whereas non-tidal crabs developed an acidosis associated with a rise in lactate levels. These results indicate that tidal crabs were better able to sustain aerobic metabolism and had lower metabolic costs during emersion than non-tidal crabs. It is likely that the elevated levels of haemocyanin exhibited by tidal crabs allowed them to maintain oxygen transport and buffer pH changes during emersion. This suggests that acclimation of C. maenas to submerged conditions results in a loss of important physiological mechanisms that enable it to tolerate emersion. The results of this study show that caution must be taken when acclimating intertidal organisms to submerged conditions in the laboratory, as it may abolish important physiological responses and adaptations that are critical to their performance when exposed to air.

PelagiCam: a novel underwater imaging system with computer vision for semi-automated monitoring of mobile marine fauna at offshore structures.

Engineered structures in the open ocean are becoming more frequent with the expansion of the marine renewable energy industry and offshore marine aquaculture. Floating engineered structures function as artificial patch reefs providing novel and relatively stable habitat structure not otherwise available in the pelagic water column. The enhanced physical structure can increase local biodiversity and benefit fisheries yet can also facilitate the spread of invasive species. Clear evidence of any ecological consequences will inform the design and placement of structures to either minimise negative impacts or enhance ecosystem restoration. The development of rapid, cost-effective and reliable remote underwater monitoring methods is crucial to supporting evidence-based decision-making by planning authorities and developers when assessing environmental risks and benefits of offshore structures. A novel, un-baited midwater video system, PelagiCam, with motion-detection software (MotionMeerkat) for semi-automated monitoring of mobile marine fauna, was developed and tested on the UK's largest offshore rope-cultured mussel farm in Lyme Bay, southwest England. PelagiCam recorded Atlantic horse mackerel (Trachurus trachurus), garfish (Belone belone) and two species of jellyfish (Chrysaora hysoscella and Rhizostoma pulmo) in open water close to the floating farm structure. The software successfully distinguished video frames where fishes were present versus absent. The PelagiCam system provides a cost-effective remote monitoring tool to streamline biological data acquisition in impact assessments of offshore floating structures. With the rise of sophisticated artificial intelligence for object recognition, the integration of computer vision techniques should receive more attention in marine ecology and has great potential to revolutionise marine biological monitoring.

Patterns of heart rate and cardiac pausing in unrestrained resting decapod crustaceans.

Measurement of heart rate (HR) has been used as an important physiological indicator in a broad range of taxa. In the present study HR patterns were measured in five species of unrestrained, resting decapod crustaceans. In addition to variation in HR among individuals, it was also very variable within an individual animal. While some of this variation was related to activity, there was also a non-locomotory component. Unstressed, resting crabs exhibited intermittent heart activity, whereas HR in stressed crabs was more stable, suggesting differential control of HR in resting crabs. Once the animals settled in the experimental apparatus they exhibited regular and extended cardiac pauses (acardia) of 15-300-s duration. As with HR, there was a significant variation in the frequency and length of acardic events, which were only observed in inactive crabs. Regaining of HR, following a period of acardia, was characterized by small adjustments in position and movement of the mouthparts. This rhythmic pattern, and the fact that entry into and out of acardia was not instantaneous, suggested that these events were related to release of neurohormones and their subsequent degradation in the system, rather than direct neural control of the heart. Because HR was variable and interrupted by regular periods of acardia, caution is recommended when calculating baseline levels of HR, or using HR alone as an indicator of physiological stress. Incorporating a coefficient of variation for HR and/or measuring the periods of acardia may be a more reliable indicator of physiological stress in decapod crustaceans.