An ecosystem model of the Prince Edward Island archipelago

A model of an ecosystem provides a useful tool for the exploration of management options to achieve desired objectives. With the move to a more holistic approach to marine resource management, ecosystem models and the indicators that can be derived using them, are providing a means to move away from single species management and allow for the ecosystem effects of population dynamics to be explored. This work describes the construction of an ecosystem model of the Prince Edward archipelago. The archipelago consists of two islands, Marion and Prince Edward, which are situated southeast of the southern tip of Africa at 46°46′S, 37°51′E. The islands are host to millions of seabirds and seals that use the islands as a refuge for breeding and moulting. Using the Ecopath software, the ecosystem is described across three separate decades (1960s, 1980s, 2000s). All trophic links are described based on the rich published literature that exists for the islands. Local survey data for population estimates and trophic linkages were sourced for defining and quantifying the food web. The system is summarised into 37 functional groups which include 4 primary producer groups at the lower trophic spectrum, and 14 land based top predator groups (seals and seabirds) representing the majority of the higher trophic levels. Two detrital groups are included. The food web is compared across the three time periods with transfer efficiencies declining for the higher trophic levels through time, suggesting a decline in energetic coupling between groups. Comparison of the PEI ecosystem with eight other modeled sub Antarctic/Antarctic systems showed the ecosystem size (as measured in total biomass throughput per year, year−1) to be lower than all other systems and was found to be most similar to the Kerguelen Islands for the ecological metrics assessed. Future research priorities are highlighted based on an assessment of data availability, data gaps and sensitivity testing. The construction of this model provides a much needed tool for the advancement of management for the archipelago, which have both fisheries and conservation concerns.