Oceanographic drivers of ecosystem variability in the Chagos archipelago

Conservation strategies for biodiversity hotspots and safe havens in a changing climate
Reef manta ray

Oceanographic drivers of ecosystem variability in the Chagos archipelago

Conservation strategies for biodiversity hotspots and safe havens in a changing climate
Title: Oceanographic drivers of ecosystem variability in the Chagos archipelago: Conservation strategies for biodiversity hotspots and safe Havens in a changing climate
Funded by: Garfield Weston Foundation, Bertarelli Foundation 
Funding amount: £2,683,000
Location: Chagos Archipelago, British Indian Ocean Territory
Dates: 1 November 2019 – 31 March 2026
Project partners: Manta Trust
University of Plymouth PI: Dr Philip Hosegood 
University of Plymouth staff: Professor Kerry Howell, Professor Martin Attrill, Dr Clare Embling, Dr Nicola Foster, Dr Joanna Harris, Dr Clara Diaz, Dr Ted Robinson, Danni Eager, Peter Ganderton, Vasyl Vlasenko, Nataliya Stashchuk
 

Overview

The marine environment is under increasing threat from human activities and climate change, requiring urgent improvements in conservation management strategies. 
Approaches to conserving the marine environment have traditionally been based on single scientific disciplines, usually purely biological approaches, with little or no attention given to the role of physical processes such as ocean currents. Such simplistic approaches cannot explain how ecosystems evolve. For example, existing basic theories explaining why animals aggregate in 'hotspots' fail to stand up in practice. 
To address this challenge, this project's interdisciplinary team of oceanographers, marine biologists, hydrographic surveyors and biogeochemists is developing a new understanding of how tropical marine ecosystems function that accounts for the complex relationship between the ocean's physical features and the animals that live in it.
Our research uses the Chagos Archipelago in the British Indian Ocean Territory (BIOT), a 640,000 km2 marine protected area (MPA), as a planetary-scale laboratory to learn how a thriving marine ecosystem develops in its natural state. We have identified key oceanographic processes and interactions occurring throughout this ecological 'hotspot', from microscopic phytoplankton to top predators such as sharks. Our work targets the pivotal roles played in the BIOT ecosystem by seamounts, deep mesophotic reefs, and regional changes in oceanographic conditions. This work sits within the wider programme of research, conservation and communication delivered in the BIOT through the Bertarelli Programme in Marine Science.

Based in the Chagos Archipelago – one of the last near-pristine marine ecosystems remaining on the planet – this project represents an enormous opportunity to understand how the tropical marine ecosystem functions without the influence of humans.

Over three research cruises, challenged by the COVID-19 pandemic that imposed enormous practical and logistical challenges, we have made huge strides in understanding how deep coral reefs function and respond to changes in the prevailing oceanographic regime, the fundamental behaviour of reef manta ray, and the distribution and response of fish communities throughout the region, with wide ranging impacts on how tropical ecosystems can be understood and managed elsewhere.

Philip HosegoodDr Philip Hosegood
Associate Professor in Physical Oceanography

Objectives

Our overall aim is to develop strategies for conserving the marine environment that accounts for the complex relationship between the biological and physical regimes. The specific environments we focus on in this project are those in greatest and most urgent need of conservation measures. 
1. Make detailed observations of seamounts to ensure findings contribute to their preservation
Many seamounts have been overexploited to the point of ecosystem collapse because of the enormously diverse range, and disproportionate abundance, of marine life that aggregates over and around them. Of specific interest is the importance of seamounts and atolls to shark populations; our previous research in the BIOT has demonstrated that seamounts act as magnets to dense aggregations of fish and sharks due to the currents that evolve over the seamount summit. We need to further test this hypothesis with targeted and appropriately designed observations to ensure that our findings contribute towards the designation of seamounts as no-take areas that offer adequate protection.
2. Investigate the sensitivity of mesophotic reef-based species to environmental stressors
Secondly, mesophotic coral reefs exist in the twilight zone between depths of 30–150 m. While these ecosystems have traditionally been studied to investigate their role as refugia for shallow-water reefs (they reside in cooler water thought to enable them to largely avoid disturbances that impact shallow corals), they are biologically and ecologically significant ecosystems in their own right, with high levels of biodiversity, including unique, rare and endemic species, that require protection. 
With the growing acceptance that surface corals may become extinct within the next 50 years as increases in sea surface temperature continue unabated, mesophotic coral ecosystems will be required to provide the critical role played by shallow reefs in tropical ecosystems, including fisheries resources, coastal protection, nutrient recycling and carbon sinks. However, due to mesophotic reefs being below the depth to which divers traditionally reach, we currently know very little about the species and communities that reside there and their sensitivity to environmental stressors such as temperature.
3. Develop conservation strategies for reef manta rays
We are undertaking the most comprehensive research to date of the reef manta ray subpopulation resident at Egmont in the BIOT. Reef manta rays are commonly exploited for their cartilaginous gill plates, which fetch a high price, particularly in Southeast Asia, where they are erroneously thought to have medicinal properties. With catastrophic declines of up to 92% in some regions, the rays are now listed as vulnerable to extinction on the IUCN’s Red List of Threatened Species. 
Measures to protect manta rays are hindered by an incomplete knowledge of how they use environmental cues to determine where and when they forage, often in dense aggregations that render them especially vulnerable to exploitation. The conservation strategies we are developing will provide a cornerstone of measures designed to protect these charismatic animals but, equally, will contribute to equivalent efforts for other large marine animals.
Researcher swimming with a manta ray
Hamerhead shark swimming above coral
Research team in the Chagos archipelago
Research vessel recovering instruments at sea in Chagos archipelago

Context of the issue

The climate emergency has continued at pace, with recent reports suggesting that we are on course for the 'worst-case' climate scenario due to anthropogenic emissions. Human exploitation has directly resulted in the reduction of wildlife populations by two-thirds in less than 50 years and a dramatic decline in biodiversity. 
Alongside the fundamental changes in weather patterns arising from climate change that impact numerous aspects of society, increased pressure from a growing human population has seen an increase in the demand for natural resources. Within this global context, the role played by the marine environment, and the threat faced by organisms living in it, are becoming increasingly prominent and urgent. 
Coral communities and the regional ecosystems that depend on their existence face collapse as sea temperatures rise, plastic pollution is making its way into the food chain through the consumption of fish that have ingested it, and fish stocks are continually placed under intolerable pressure to provide food, with illegal fishing in particular dramatically increasing over the past few years. Conservation strategies based on accurate scientific understanding that accounts for the rapidly evolving climate are urgently needed to mitigate human impacts and to identify the habitats and organisms in greatest need of protection.

How the project addresses the issue

This multidisciplinary project aims to develop conservation strategies that have global relevance in this rapidly evolving era, both societally and climate-related. While direct action aimed at mitigating habitat loss and degradation (e.g. attempts to repopulate surface coral reefs in the Great Barrier Reef) is important, especially in educating the younger generation on the challenges we must increasingly face, these measures often fail to address the cause of the problem. 
In this project, we are identifying why and how critical habitats and animals are suffering so that we can contribute to the design of appropriate conservation measures that reduce – or, if necessary, account for – the scale of the impact rather than compensating for the damage after it has happened. 
Barriers to achieving this often arise from scientific disciplines operating in isolation; to address this, we are underpinning studies of the mesophotic coral community (which, at between 30–150 m depth, is thought to avoid the warm surface waters that cause bleaching), fish biomass distribution, and manta behaviour with physical oceanographic measurements. The combination of scientific disciplines is crucial; our recent discoveries demonstrate that all marine organisms respond rapidly to subtle changes in the physical environment, such as currents and water properties.
 
 
 

Centre for Coastal and Ocean Processes and Engineering (C-COPE)

C-COPE brings together strength areas from across the University's Faculty of Science and Engineering with a research focus on the physical and chemical processes in coastal, ocean and marine environments, and their human impacts.
The Centre's sphere of interest stretches from the head of tidal estuaries to the bottom of the ocean, and includes the disciplines of physical oceanography, marine biogeochemistry, coastal engineering and marine geology.
 
Tuvalu Tepuka atoll