Abstract
Climate changes are projected to alter the structure and function of marine ecosystems, and
these environmental changes can be amplified in polar regions. Understanding the response of
marine species to altered environmental conditions is an expanding field of research as near
future scenarios predict changes to an array of key biological factors including temperature,
pH and salinity, which will affect species physiology, biochemistry and life history traits. The
Antarctic sea star, Odontaster validus is a keystone species and opportunistic predator in the
nearshore shallow Antarctic marine benthos. Its biology is relatively well understood making
it a useful sentinel species to explore the impacts of environmental changes, such responses to
Southern Ocean warming and the potential for acclimation.
This thesis uses three measures of physiological fitness over 10 months to experimentally
explore the acclimation capacity of O. validus to ocean warming. To examine this, adult O.
validus were acclimated to five temperature treatments (0°C, 1°C, 2°C, 3°C, 4°C). At 3-month
intervals, O. validus were sampled for respiration, morphometrics and oxidative stress markers.
Of the three measures of physiological fitness, none showed any evidence of acclimation or
recovery over time. Temperature significantly increased respiration, antioxidant enzyme
activity and levels of oxidative damage markers across almost all treatment. O. validus pyloric
caecum, a nutrient storage organ, were larger in the 3°C treatment compared to others. The
metabolic scaling rate and reproductive gonadosomatic tissue were also not affected by
temperature in this study. These responses suggest that whilst O. validus is able to
metabolically adjust to increased temperatures, physiological acclimation is not achieved (i.e.
return to physiological activity over time, that is the same as the ambient states).
The implications for O. validus survival in warmer conditions require more investigation,
particularly the capacity to maintain key functions such as growth and reproduction in
increased temperatures, the sensitivity of early life history stages and the potential pressure of
invasive competitors caused by range shifts.