Fish populations in the Western Indian Ocean are boosted by the movement and exchange of water between different parts of the ocean, research led by the University of Oxford has found.

Particularly affected by this water movement, known as oceanographic connectivity, are herbivorous reef fish groups, which are vital to coral reef resilience.

Researchers said the findings suggest policymakers should consider connectivity when deciding on conservation areas.

The study also pinpointed sea surface temperature and chlorophyll levels as significant factors influencing reef fish distribution and abundance in the Western Indian Ocean.

Laura Warmuth, the lead author from the Department of Biology at the University of Oxford, said: "It was striking that herbivorous fish, which are critical to reef resilience, were particularly strongly impacted by ocean connectivity.

"Efficient conservation area prioritisation should include connectivity for decision making regarding marine protected area management across country borders.

"This is particularly relevant in the human-pressured Western Indian Ocean region, where annual bleaching is predicted on most coral reefs by mid-century, even under optimistic climate change scenarios."

In the Western Indian Ocean, small-scale fisheries contribute up to 99 per cent of protein intake and provide around 82 per cent of household income, making coastal communities highly dependent on reefs for food security.

While sea surface temperatures are rising around the world, temperatures in the Indian Ocean are increasing faster than other tropical oceans.

Fish diversity is central to reef resilience, providing several key services to reefs by their different feeding patterns such as feeding on algae which can compete with corals.

The research team developed a metric of proportional oceanographic connectivity to integrate this element into ecological models, revealing medium connectivity levels were generally associated with higher fish abundances.

However, high connectivity could have adverse effects, such as increased dispersal of pollutants or invasive species, but may help with larvae dispersal.

Professor Mike Bonsall, senior author from the University of Oxford's Department of Biology, said: "It is really imperative that decision-makers responsible for marine planning understand how ocean patterns and environmental factors affect reef fish across the food chain.

"Our work emphasises how crucial this link is between ocean currents and fish ecology for understanding the broader impact of environmental change and fishing regulations on sensitive coral reef fish systems."

The researchers plan to continue their work by exploring the impacts of human activities on reef fish abundance and biomass in the Western Indian Ocean, as well as how predicted changes in environmental and oceanographic factors under different climate change scenarios will affect fish abundances and distributions.