Abstract

Dispersion of larvae in currents around estuaries and complex coastlines has been a major gap in our understanding of the coherence of marine protected areas and the potential of invasive species to invade. Tidal currents can be dynamic and energetic and larvae of otherwise sedentary species can swim vertically in synchronicity with tides or in response to their environment. Such swimming in shallow tidal waters can dramatically impact dispersion. We use three elements to model the dispersion of manila clam larvae in Poole Harbour; 1) Experimental evidence related to this species in its native habitat which includes field surveys and laboratory studies of swimming and other behaviour, 2) field surveys of the recent history of patterns of distribution within Poole Harbour, and 3) industrial scale hydrodynamic models of water movement originally intended for harbour development applications. These are combined in an individual based model of manila clam larvae within the harbour and the adjacent English Channel. The objective is to answer simple conservation and management questions such as whether it is possible that larvae seeded inside Poole harbour could invade along the coast to the next suitable habitat, and if it is likely to have formed a self sustaining population within the harbour, and if there is a network of invasion within the harbour. The manila clam in Poole Harbour is an interesting and topical example of an invasive species, as it is at its northernmost edge of its range here, it is a commercially exploited species, and its abundance appears to be steadily expanding in Poole harbour over the last 20 years. Our models show some surprising results and since we have created video output, the main findings are accessible to non specialists and specialists alike.