Browsing by Author "Ng, Terence P. T."
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- Cheating the locals: invasive mussels steal and benefit from the cooling effect of indigenous musselsPublication . Lathlean, Justin A.; Seuront, Laurent; McQuaid, Christopher D.; Ng, Terence P. T.; Zardi, Gerardo I.; Nicastro, Katy RThe indigenous South African mussel Perna perna gapes during periods of aerial exposure to maintain aerobic respiration. This behaviour has no effect on the body temperatures of isolated individuals, but when surrounded by conspecifics, beneficial cooling effects of gaping emerge. It is uncertain, however, whether the presence of the invasive mussel Mytilus galloprovincialis limits the ability of P. perna for collective thermoregulation. We investigated whether varying densities of P. perna and M. galloprovincialis influences the thermal properties of both natural and artificial mussel beds during periods of emersion. Using infrared thermography, body temperatures of P. perna within mixed artificial beds were shown to increase faster and reach higher temperatures than individuals in conspecific beds, indicating that the presence of M. galloprovincialis limits the group cooling effects of gaping. In contrast, body temperatures of M. galloprovincialis within mixed artificial mussel beds increased slower and exhibited lower temperatures than for individuals in beds comprised entirely of M. galloprovincialis. Interestingly, differences in bed temperatures and heating rates were largely dependent on the size of mussels, with beds comprised of larger individuals experiencing less thermal stress irrespective of species composition. The small-scale patterns of thermal stress detected within manipulated beds were not observed within naturally occurring mixed mussel beds. We propose that small-scale differences in topography, size-structure, mussel bed size and the presence of organisms encrusting the mussel shells mask the effects of gaping behaviour within natural mussel beds. Nevertheless, the results from our manipulative experiment indicate that the invasive species M. galloprovincialis steals thermal properties as well as resources from the indigenous mussel P. perna. This may have significant implications for predicting how the co-existence of these two species may change as global temperatures continue to rise.
- Size and position (sometimes) matter: small-scale patterns of heat stress associated with two co-occurring mussels with different thermoregulatory behaviourPublication . Lathlean, Justin A.; Seuront, Laurent; McQuaid, Christopher D.; Ng, Terence P. T.; Zardi, Gerardo I.; Nicastro, Katy RHeat-related mass mortalities and local extinctions are expected to rise as the frequency, duration, and intensity of extreme heat events increase due to climate change, particularly in the case of sessile or sedentary species that cannot relocate. Little is known, however, of how biotic factors, such as the size and non-motile behaviour of individuals, contribute to small-scale variation in susceptibility to heat-related mortality during such events. We used infrared thermography to investigate how manipulated mussel bed size and the size structure of individuals within beds influence small-scale variability in the body temperatures of two intertidal mussel species with different thermoregulatory behaviours (gaping vs. non-gaping) during simulated extreme heat conditions. At times, body temperatures of small individuals reached higher temperatures than large individuals, irrespective of mussel bed size, though this was more apparent for the non-gaping species. Average body temperatures and heating rates of individuals within large mussel beds were generally greater than for individuals within small mussel beds, irrespective of species or individual size. This pattern seems to reflect an effect of the greater circumference/ area ratio for small mussel beds as individuals on the windward side of all beds displayed convective cooling and body temperatures 3-5 degrees C cooler than those on the leeward side. Such high levels of inter-individual variability in body temperatures at small spatial scales suggest the need for a greater appreciation and inclusion of biotic factors in assessing susceptibility of populations to climate change.