Climate-driven changes in the recruitment success of marine invertebrates : the role of food supply and temperature

• Main Author: Griffith, Katherine
• Published: Bangor University 2013
• Subjects: 577.7
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.613449

Current trends indicate that key events in the life cycle of marine organisms (e.g. spawning, reproduction, larval release) are taking place earlier in the season in response to global warming associated with climate change. Specific changes in the phenology (i.e. the timing of these life cycle events) of planktonic organisms suggest that responses to climate change are not consistent for all functional groups in the pelagic community. As a result, the tight synchrony that exists between pulses of production of larvae and their food sources could be disrupted; this may cause a decline in survival and affect recruitment levels into a population. Marine invertebrates with complex life cycles from temperate‐cold regions may be particularly sensitive to changes in food availability and temperature as, during the larval phase, many of these species are strongly dependent on seasonal peaks of pelagic food sources. The degree to which mismatches between the timing of larval development and seasonal peaks of planktonic production may influence recruitment success of a species is unknown, and may vary depending on species life‐history. Intertidal barnacles are widely distributed and ecologically important species which serve as a good model species to investigate the impact of potential shifts in food and temperature associated with climate change. Semibalanus balanoides is boreal species which synchronously releases its larvae once a year to coincide with the spring phytoplankton bloom. In contrast, Austrominius modestus is a lusitanean species which releases multiple broods over a much longer period of time, with larval production at its peak during the summer months when food supply is lower. These two contrasting species are ideal models to use in a comparative study aimed at understanding the effects of food limitation and temperature on the recruitment success of marine invertebrates. In this study, I focused on the combined effects of food limitation and temperature on larval performance of S. balanoides and A. modestus. Firstly, I examined whether a reduction in available food at different temperature conditions would have an impact on the recruitment success of either species. This approach was to assess if there were any differences between species responses to potential low food environments and also explored whether changes in temperature could exacerbate any larval responses to low food. I also evaluated the responses of both species to temporal mismatches, simulating food availability as consequence of larval release occurring before or after peaks in food abundance, to identify whether the timing of food availability during larval development was important for recruitment success. Following this, I concentrated on identifying the mechanisms by which these two species may differ in their responses to food limitation and temperature. Here, the tolerance of both species to starvation at different temperatures was examined and the elemental composition of the energy reserves they have upon hatching was assessed to identify any differences that may exist between the species. Finally, I focused on the ingestion rates of both species to see whether they exhibit any differences in their feeding rates in response to a range of food concentrations at different temperatures. A partial energy budget for larvae was also estimated to evaluate if species differed in their capabilities to use food for growth, development and maintenance in different food/temperature environments. Results showed that the timing and abundance of food sources were critical for the recruitment success of S. balanoides and less important for A. modestus. A temperature of 15oC was sub‐optimal for S. balanoides and tended to increase the negative effects of food limitation. Both food limitation and temperature had strong effects on naupliar mortality and cyprid settlement success rates for S. balanoides and, thus, were important in determining the supply and quality of settlers to a population. When compared to A. modestus, the poorer performance of S. balanoides could not be explained by differences in initial energy reserves or starvation tolerance immediately after hatching as these were comparable between the two species. Considerable differences were observed in the ingestion rates of both species during the early stages and suggested that differences in mass specific feeding rates may be linked to the better performance of A. modestus in food limited environments. In summary, results suggest that recruitment success of S. balanoides would be particularly vulnerable to mismatches of larval pulses with their food sources, particularly at higher temperatures, due to the strong effects of these factors on larval supply and larval quality. In contrast, even under food limited conditions, moderate increases in temperature should not result in strong negative consequences for A. modestus. Work presented here highlights that species‐specific responses to climate‐driven changes in the environment may profoundly affect the abundance and distribution of marine invertebrate species with complex life cycles, through direct and interactive effects of these changes on larval mortality and settlement success.