Research Progress in Area 1 方向 ( 一 ) 課題進展 87 Abstract Coral reefs are vitally important to the health and security of at least 500 million people but are globally threatened by a range of stressors. Ocean warming and increasingly frequent pan-tropical bleaching events have emerged as the principal threat, and human nutrient loading from land and large-scale deoxygenation of the ocean may also be of great concern for reef survival. However, understanding how reef ecosystems function and respond to changes in the surrounding ocean and climate have been hampered by the paucity of data sets linking environmental dynamics with ecological responses. The goal of this work is to gather in-situ environmental data over benthic habitats occurring across oceanic gradients, including the strong oceanic-estuarine gradient around Hong Kong, in order to identify the key drivers of coral community health, especially stress and mortality events, and ecological responses to environmental change. Research Activities and Progress • Two seasons of field work completed around Hong Kong (winter and summer), involving extensive sampling and analysis of water, sediments and organisms, and the deployment of equipment for characterizing the local coral reef gradient; • Pilot experiments across Hong Kong’s marine environmental-urbanisation gradient using a Gradient Factor apparatus and seawater carbonate chemistry analyses to demonstrate links between community composition and changes in net ecosystem production and calcification rates over benthic habitats; • Carried out research raining of students including via an oversubscribed Undergraduate Research Opportunities Project (UROP). Key Findings • Cryptic diversity can explain hidden differences in bleaching susceptibility in corals across environmental gradients; • Cryptic diversity supports niche differentiation in reef corals, with internal-wave exposure driving cryptic species distributions across depth gradients; • Marine heatwave severity, and coral bleaching mortality, across depth gradients can be paradoxical based on regional surface conditions due to the impact of mesoscale eddies on sea level, thermocline depths, and thus internal-wave cooling. Research Output Publication 2 Trained personnel 8 Environmental Drivers of Coral Reef Health across Oceanic Gradients Prof. Alex S.J. Wyatt The Hong Kong University of Science and Technology Fig 1. Niche differentiation in cryptic Pocillopora spp. Across coral reef depth gradients (Johntson, Wyatt et al., in press, Coral Reefs).
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