People and ecosystems

Understanding of the links between coral reef ecosystems, the goods and services they provide to people, and the wellbeing of human societies.


Ecosystem dynamics: past, present and future

Examining the multi-scale dynamics of reefs, from population dynamics to macroevolution


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Advancing the fundamental understanding of the key processes underpinning reef resilience.

Coral Bleaching

Coral Bleaching

Coral Reef Studies

From 2005 to 2022, the main node of the ARC Centre of Excellence for Coral Reef Studies was headquartered at James Cook University in Townsville, Queensland (Australia)

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Coral reef mesopredator trophodynamics in response to reef condition


Wednesday, 1st March, 9:00 to 10:00 hrs

Building 19, Room 106, JCU Townsville Campus
Tessa Hempson
Tessa Hempson

Abstract. Mesopredators represent an important component of coral reef ecosystems, both economically, supporting large reef fisheries, and ecologically, as potentially important drivers of reef trophodynamics.  The lack of knowledge of how this functional group is affected by reef degradation and benthic community shifts and how this influences their role in the food web is cause for concern, particularly given the widespread threats facing coral reefs. This thesis aims to address this important research gap by focusing on four key implications of habitat degradation for mesopredators and their role in coral reef trophodynamics. First, stable isotope techniques demonstrated that piscivorous mesopredators can alter their diets to adapt to changing prey availability following disturbance. Second, mesopredators occupied an altered trophic niche on regime-shifted reefs, with decreased energy stores in their livers, indicating a loss of condition. Next, using a long-term data set documenting regime-shift and recovery following bleaching, trophic pyramid structure demonstrated that while all reefs experienced an initial increase in relative biomass in base trophic levels, and a decrease in mid trophic levels, regime-shifted reefs developed a concave structure, while recovering reefs showed broad mid trophic level representation in the long term. Finally, using a meso-scale patch reef experiment to examine the effects of predicted climate-driven changes in coral assemblages, as reefs become dominated by more thermally tolerant, less complex coral species, fish communities become less diverse, and more strongly impacted by mesopredators. Sublethal effects (e.g. reduced growth rates, fecundity and condition) of altered trophodynamics may not be evident in the short term, but in the long term may cause unexpected population declines in long-lived mesopredator species. This thesis offers valuable insight into the effects of habitat degradation on coral reef mesopredators, which can support reef fisheries management and conservation of this ecologically and economically important group.

Biography. Tessa grew up on a farm in the savannas and escarpment forests of South Africa, an environment that instilled in her a passion for ecology from a young age.  After a year in Tasmania as a Rotary Scholar, she began her undergraduate studies via correspondence with the University of South Africa (UNISA) while travelling and working in SCUBA diving. In 2003 she returned to South Africa to complete her BSc. in Botany and Zoology at the University of Cape Town (UCT), followed by a BSc. Hons in Zoology, a field course in the Kruger National Park with the Organisation for Tropical Studies (OTS) and a MSc. in Conservation Biology from the same university. Her study subjects ranged from the impacts of elephants on savanna vegetation and bat community ecology to upwelling system dynamics, crinoid symbionts and the effects of dynamite fishing on coral reefs in Tanzania. Since graduating she has worked as a conservation manager for the Sustainable Seas Trust (SST), sailed the South American coast, volunteered as a researcher on the Aldabra Atoll World Heritage Site in the Seychelles and managed diving and marine logistics on Vamizi Island in the Quirimbas Archipelago of Mozambique, before deciding it was time to fulfil a lifetime aspiration of pursuing a PhD in coral reef ecology at James Cook University; supervised by, Prof Nicholas Graham, Dr Aaron MacNeil, Dr Andrew Hoey, Prof Geoff Jones, and Dr Glenn Almany.


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