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Other Scientists

Ph.D. Student
Fieldwork Manager
Field Ops. Officer

Coral Reef Fish in the British Indian Ocean Territory

Principal Investigators
Other Scientists

Project Overview

Changes in reef fish communities affect their ecological interactions with other species and thus have important functional consequences at the ecosystem level.

Coral reef fishes are among the most conspicuous and diverse species group in the marine environment. They thrive in extremely dynamic environments and are, thus, strongly subjected to changes in abundance, community composition and biological traits through time. Nonetheless, coral reef fishes, like most of marine life nowadays, are directly or indirectly threatened by human activities. These anthropogenic threats are expected to have profound impacts on the coral reef fish communities of the British Indian Ocean Territory’s (BIOT) Marine Protected Area (MPA) in the coming years.

Firstly, the introduction of the invasive black rat has caused the crash of seabird populations on the islands it invaded. With the seabirds gone, the precious nutrient subsidies from their guano no longer percolates to fertilize adjacent reefs and support enhanced fish growth rates. Moreover, it is believed that the loss of these supplementary nutrients affected the resilience and recovery rate of benthic and fish communities in the face of other man-made stressors, such as climate change.

Secondly, the direct and illegal removal of sharks has a profound impact on the structure and function of reef food webs, expressed through ecological process such as a greatly diminished predation pressure on medium sized predators. Consequently, these impacts can cascade down trophic levels to the benthic community if, for instance, fish that feed on algae or corals change drastically in abundance or behavior. Such crashes or linked booms in communities can have further impacts on coral reef recovery and ultimately cause the ecosystem to crash.

Thirdly, anthropogenic climate change increases the frequency and severity of extreme weather events, such as abnormally high sea surface temperatures resulting with heat stress and the associated coral bleaching. Since most of the fishes rely on corals for food and structure, coral bleaching inevitably leads to changes in the abundance, and community structure of coral reef fishes.

Our project seeks to understand the status and resilience of the key communities of coral reef fishes that underpin the ecology of the BIOT MPA. Our team uses a multi-disciplinary approach that includes spatio-temporal monitoring of fish communities, experimental fieldwork, and laboratory analyses to address these pressing issues influencing the health of coral reefs and associated fish communities.

We have demonstrated the critical importance of seabird nutrient inputs for reef fish growth and biomass in BIOT, highlighting the importance of eradicating rats from tropical islands.

Nick Graham

Key Facts

95
underwater video surveys deployed
225
coral recruitment tiles installed
48%
greater biomass in fish communities next to rat-free islands

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