| Summary: | <p>Marine plastic pollution and coral vulnerability may appear unrelated, but both problems rely on the dispersal of buoyant particles (plastic fragments and coral larvae) through ocean currents. Understanding their dispersal is vital for marine management and conservation, critical during a time of major environmental change. Through a series of Lagrangian studies, we investigate and contribute solutions to these twin problems, with a focus on the western Indian Ocean.</p>
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<p>Using global Lagrangian simulations incorporating ocean currents, waves and winds, we find that much of the plastic debris beaching at remote islands in the western Indian Ocean likely drifted from the northern and eastern Indian Ocean. However, a substantial proportion at some islands may have been discarded from ships transiting the Indian Ocean and local fishing activity. Monsoonal winds play an important role in determining the seasonality of debris accumulation, facilitating targeted clean-up efforts.</p>
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<p>We run a regional ocean simulation, generating almost three decades of validated surface current predictions for the tropical southwestern Indian Ocean at 2 km resolution. We couple this simulation with a larval dispersal model, predicting the potential connectivity between all shallow-water coral reefs in the region. The temporal variability of connectivity is dominated by high-frequency, stochastic variability introduced by ocean currents, limiting what we can usefully infer about short-term connectivity between remote reefs.</p>
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<p>Ocean currents play an important role in explaining regional biogeography and population genetics, with well-connected clusters of reefs along the coasts of Kenya and Tanzania, and within the northern Mozambique Channel. The Chagos Archipelago, whilst geographically isolated, still exchanges significant numbers of larvae with the rest of the southwestern Indian Ocean. However, integrating modelled connectivity into an eco-evolutionary model suggests that the rate of environmental change, rather than connectivity, may dominate the response of coral reefs to warming over the 21st Century.</p>
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