Building baseline knowledge of mesophotic ecosystems in Ascension Island MPA

Expanding knowledge and training to improve conservation of the island's ecosystems
Ascension Island with black durgon triggerfish

Building baseline knowledge of mesophotic ecosystems in Ascension Island MPA

Expanding knowledge and training to improve conservation of the island's ecosystems
Title: Building baseline knowledge of mesophotic ecosystems in Ascension Island Marine Protected Area (MPA)
Funding amount: £375,153
Location: Ascension Island
Dates: 1 April 2024 – 31 March 2026
University of Plymouth PIs: Professor Kerry Howell, Dr Philip Hosegood
 

Overview

Ascension Island Government (AIG) aspires to deliver ecosystem-scale, evidence-based management. However, the biodiversity and physical environment beyond diver depths (>99% of the MPA) is poorly understood, compromising efforts to effectively manage fisheries, quantify carbon sequestration and assess threats. 
This project aims to provide baseline knowledge of mesophotic ecosystems (30–300 m), thus improving their conservation, including incorporation of predicted climate change induced shifts in their distribution into management plans. The emphasis on training will also build on-island capacity for long-term monitoring and management.

This project represents another effort to simultaneously address crucial scientific issues, in this case the distribution, diversity and abundance of deeper coral reefs that remain unexplored and poorly understood, especially their oceanographic drivers, whilst building local capacity to take ownership of the challenge.

By providing the tools and training to continue investigations beyond the project lifetime, we are empowering the local scientific community to face the challenges of climate change on the marine ecosystem head-on.

Philip HosegoodDr Philip Hosegood
Associate Professor in Physical Oceanography

Objectives

Working in collaboration with the AIG Conservation and Fisheries Directorate (AIGCFD), this project will: 
  1. Deliver baseline oceanographic and biological data on the mesophotic ecosystems of the Ascension Island MPA
  2. Build capacity for on-island long-term monitoring of the MPA
  3. Serve as a model that can be ported to other UKOTs.
Researchers deploying mooring for echosounder equipment in the Ascension Island MPA
Submerged echosounder equipment with sharks in the Ascension Island MPA
Letting out the line on submerged echosounded equipment in the Ascension Island MPA

Context of the issue

The AIG is committed to making its MPA an international exemplar of evidence-based ocean management. While the AIG Conservation and Fisheries Directorate (AIGCFD) has developed the capacity to monitor shallow marine biodiversity, current survey efforts are largely confined to the upper 30 m – driven by sampling practicality rather than ecological boundaries. 
Historically, surveying beyond diver depths required costly equipment and large research vessels, but advances in marine technology have now removed many of these barriers. The mesophotic zone is a critical component of the marine ecosystem, supporting lower trophic levels and key life stages of fish species important to local fisheries. However, limited knowledge of habitats and species distributions below 30 m constrains stock assessments, weakens management effectiveness, and undermines planning in the face of climate change. As a result, improving understanding of mesophotic communities is identified as a major priority in the Ascension Island MPA (AIMPA) Management Plan and its Monitoring, Evaluation and Research Strategy.
Modelling and limited towed camera surveys conducted during the Blue Belt-sponsored Discovery Cruise in November 2022 indicate the presence of deep-water coral and other carbon-sequestering communities within Ascension’s mesophotic zone. These habitats remain unmapped and unstudied, preventing assessment of their role in climate change mitigation and limiting the ability to monitor their vulnerability to climate impacts. Without this information, AIG cannot produce accurate blue carbon assessments or develop effective climate adaptation strategies, both of which are also key objectives in the AIMPA Management Plan and Monitoring, Evaluation and Research Strategy.

How the project addresses the issue

The project aims to achieve its objectives as follows:
Objective 1
Existing AIGCFD research conducted by the University indicates distinct oceanographic conditions on the island's east and west coasts, so surveys will use a replicated, side-stratified design across two seasons, with deployments from an AIG vessel. Transects will be stratified by depth and habitat using existing high-resolution multibeam data. Oceanographic moorings equipped with current meters and temperature and water-property sensors will be deployed along transects to resolve thermocline dynamics, the primary control on mesophotic ecosystems. Initial baseline surveys using specialised equipment will enable high-resolution characterisation of the thermal regime, which can subsequently be monitored using proxy indicators (e.g., temperature variability) with AIG-owned equipment. Hydrophone recordings at each transect will assess rockhind grouper presence and abundance.
Objective 2
Four AIGCFD staff will receive end-to-end training in mesophotic survey design, equipment deployment, and data management/analysis, delivered by experienced University of Plymouth partners. Camera systems and temperature sensors will remain on the island after project completion.
Objective 3
During the second field campaign, three knowledge exchange fellows from St Helena, Turks and Caicos, and Gibraltar will join the AIGCFD team for training. Together, they will assess how the methodology can be adapted to their territories, ensuring it is transferable across UKOT contexts.
 
 
 

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