Climate driven changes in recruitment success :linking long term trends in physical and biological parameters with larval abundance

Climate change is now recognized as having major impacts on the ecology of terrestrial, freshwater and marine systems with effects on a broad range of organisms across the globe. Increasing mean temperatures and greater variability in weather systems are having complex effects at the individual, community and ecosystem level. For example warmer weather has brought forward the timing of spring activities such as arrival of migrant birds and is affecting the geographical range of species as warm temperate species advance northwards and cold temperate and polar species retreat. At the community level, changes in assemblage composition have important implications for the way species interact and potentially for the functioning of whole ecosystems. In the marine realm the timing of the spring phytoplankton bloom has important implications for zooplankton and fish assemblages and indeed the whole marine food web. Changes in the timing of this bloom as a result of climate change have been demonstrated and shown to have significant effects on holoplanktonic organisms that spend their whole life in the plankton. However the implications of such changes to marine benthic organisms which live on the sea bed, through effects on their planktonic larvae are relatively unknown, but are likely to be extremely important. Intertidal barnacles have made a superb model organism for studies of larval transport and supply and are also sensitive indicators of climate change. Their larvae are also important components of coastal food webs. In the British Isles, barnacles are either boreal (northern) species which rely on a close match between larval release into the water column and timing of the spring phytoplankton bloom, and settle from the plankton in a pulse of relatively short duration, or lusitanean (southern) species which release multiple broods over an extended period of the summer. We will test the hypothesis that both sets of species will be affected by climate change but through different mechanisms acting at the larval stage, boreal species through changes in the match between larval release and the timing of phytoplankton blooms (match-mismatch) and lusitanean species through increases in sea water temperature. We will use the extensive long term planktonic datasets of the Sir Alister Hardy Foundation for Ocean Science (1950's to present) and Plymouth Marine Laboratory (1988 to present). We will extract data (through re-analysis of archived samples) on barnacle larval abundance around the British Isles in two key periods, spring and summer. The relationship between changes in larval abundance over the past 40 years and various biological (phytoplankton abundance, abundance of key diatom species) and physical (sea-surface temperature, North Atlantic Oscillation index) parameters will be examined using a number of statistical techniques. We will then determine how these relationships affect the recruitment success of barnacles (and ultimately adult abundance) to the shore, again using long term datasets (over 40 years) held by the MBA and the PI's (Jenkins and Hawkins). In this way we will improve our understanding of how hydroclimatic factors in the sea affect adult populations of benthic organisms through effects at the larval stage. Results will be used to extend further a model developed with colleagues at SAMS as part of a previous NERC grant to understand effects of climate change on adult populations of benthic organisms.