Marine population structure and dynamics

Understanding processes affecting the population dynamics of marine organisms involves work across the School integrating research in ecology, biogeochemistry and hydrodynamics using a variety of taxa, ranging from seabirds to fish to a range of benthic invertebrates, including non-native species.

1. Connectivity

The extent to which marine populations are connected is a fundamental parameter determining their dynamics, genetic diversity, spread of disease and resilience to human exploitation.

We are using chemical tags, i.e the stable isotopic and trace element composition of scales and otoliths, as a means to study connectivity and movement patterns of marine and freshwater fishes. Recent work (McCarthy) has determined whether different nursery grounds for European plaice Pleuronectes platessa possess distinctive microchemical signatures. We have also used stable isotope chemistry to examine the degree of connectivity between sea bass in south, mid and north wales, and used both the stable isotopic and microchemical composition of scales and otoliths to determine stream of origin for brown trout Salmo trutta in freshwater. The Celtic Sea Trout Project has built on this work to examine the movement patterns of sea trout in the Irish Sea to inform trans-national management plans.

Work on population connectivity integrates the work of hydrodynamic modellers (Robins, Neill) and ecologists (Gimenez, Jenkins, Mahlam) in the School. The majority of marine benthic invertebrates have a larval stage in their life cycle and hence the level of connectivity between local populations is determined by larval transport. Hydrodynamic modelling is a powerful tool to understand and predict patterns of connectivity. Biophysical modelling of larval dispersal in the Irish Sea has shown the importance of release location and larval behaviour in driving patterns of connectivity. This modelling approach is being extended to understand how changes in the baroclinic (density-driven) and wind-driven currents with climate change will affect connectivity patterns and the consequences of regional extinction in populations which are weakly connected.

2. Larval ecology and Recruitment dynamics

The environmental conditions experienced by larvae may affect recruitment through density-mediated effects, i.e. through changes in the number of larvae reaching the benthic habitat (the settlement rate) and trait-mediated effects, i.e. through changes in larval traits (e.g. growth rate) that affect juvenile survival ( see marine life histories). Density-mediated effects have been studied extensively within the framework of supply-side ecology. However, our understanding of trait-mediated effects, especially on how they operate under field conditions, is less advanced. Work by Gimenez and Jenkins focuses on trait mediated effects through experimental determination of how environmentally driven variation in growth and body size affects juvenile survival and recruitment. This work has examined spatial and temporal variation in larval traits over a hierarchy of spatial scales across the west coast of Scotland and combined lab and field manipulations to examine the consequences of trait variation. The intention is that such studies lead to an integrative theory of recruitment, where individual level processes are integrated into population level models.

3. Population biology of marine vertebrates

Marine top predators are important components of coastal and oceanic food webs widely and are recognised as important indicators of ecosystem condition and functioning. Worldwide marine top predator populations are experiencing a multitude of pressures including direct and indirect anthropogenic influences. Monitoring of marine top predator populations provides useful data but often fails to capture the underlying demographic and behavioural changes that are accountable for observed population-level change (Cordes).

We use of long-term individual-based studies of marine top predators. This includes harbour seals and bottle-nose dolphins to explore the demographic and behavioural responses to environmental change and a variety of anthropogenic activities.