Bethan Lang - AIMS@JCU

Bethan Lang

bethan.lang@my.jcu.edu.au

PhD
ARC Centre of Excellence Coral Reef Studies

Bethan Lang

bethan.lang@my.jcu.edu.au

PhD
ARC Centre of Excellence Coral Reef Studies
The effect of ocean warming on the behaviour and physiology of crown-of-thorns starfish (CoTS, Acanthaster cf. solaris), and impacts on prey corals.

Bethan grew up in the UK, where she completed her BSc (hons) degree in Biology at Oxford Brookes University, before commencing an MSc in Ecology, Evolution and Conservation at Imperial College London. She first became fascinated by the infamous crown-of-thorns starfish (CoTS) while completing her undergraduate project on their distribution and feeding habits in the Wakatobi Marine National Park in Indonesia. Bethan is now studying for a PhD under the supervision of Prof. Morgan Pratchett (primary), Prof. Andrew Hoey, Dr. Sven Uthicke (AIMS), Dr Jennifer Donelson and Dr. Ciemon Caballes in the ARC Centre of Excellence for Coral Reef Studies, investigating the effect of ocean warming on CoTS, and interactions with their coral prey. She hopes that her work will aid our understanding of the future population dynamics of the starfish, and the threat they may pose to the reef under further climate change.

The effect of ocean warming on the behaviour and physiology of crown-of-thorns starfish (CoTS, Acanthaster cf. solaris), and impacts on prey corals.

2019 to 2022

Project Description

The combined threats of CoTS outbreaks and temperature-induced coral bleaching are reducing the resilience of the Great Barrier Reef. However, little is known about how CoTS populations may fare in a warmer ocean, and how interactions with their thermosensitive coral prey may change. This project seeks to determine:
1) The effect of acute thermal exposure on the performance of CoTS
2) The effect of prolonged thermal exposure on the performance of CoTS
3) The thermal preferences of CoTS
4) The effect of coral health and coral cover on the feeding behaviour and condition of CoTS, and the density and distribution of their populations.

Project Importance

This project is of high importance, considering that CoTS and climate change are two of the greatest threats to the Great Barrier Reef. Understanding the effect of warming, and changes in quantity and quality of coral prey on CoTS, will aid predictions regarding their future population density and distribution, and the cumulative or synergistic threats they may pose to the reef under further climate change.

Project Methods

A summary of methods for the four chapters of this project are as follows:
1) The effect of acute thermal exposure on CoTS performance was established using intermittent-flow respirometry in order to measure the oxygen consumption rate (proxy for metabolic rate) over a wide temperature range. In addition, a mechanistic understanding of the observed organism level responses was gained by using a spectrophotometer to measure the activity of enzymes that are proxies for aerobic and anaerobic metabolism in CoTS tissue samples, over a similarly wide thermal range.
2) The effect of prolonged thermal exposure on CoTS performance was established by exposing starfish to four different thermal regimes, and assessing righting time (proxy for neuromuscular coordination), movement rate, oxygen consumption rate (again using intermittent-flow respirometry) and mortality, at various timepoints.
3) The thermal preferences of CoTS will be established using a y maze, where water at various temperatures will be fed into the maze at different points, creating a thermal gradient. CoTS movement within the maze will be monitored to determine temperature preference.
4) To establish the relationship between CoTS and their coral prey in a warmer ocean, CoTS will be exposed to healthy and bleached corals in the laboratory, and feeding preferences and rates will be established. Furthermore, field surveys will be conducted in bleaching and non-bleaching years, to establish how coral health and cover impacts on the condition, density and distribution of CoTS populations on the Great Barrier Reef.

Project Results

It has been discovered that CoTS are highly thermosensitive. In acute temperature studies, CoTS metabolism became depressed between 33-35C, with larger starfish being more sensitive to extreme temperatures. This observation is supported by the fact that at a similar temperature, activity of Citrate synthase (proxy for aerobic capacity) becomes negligible. Lactate dehydrogenase (proxy for anaerobic capacity) on the other hand, increases with temperature, and is extremely high at the temperature range that metabolic depression is observed at the organism level. This indicates that this reduced metabolic rate at extreme temperatures is largely a consequence of this switch to unsustainable anaerobic metabolism. In the prolonged thermal exposure studies, CoTS in the most extreme thermal treatment (end-point temperature of 32C) had a significantly higher probability of mortality. This may be explained in part by the slight metabolic depression observed in starfish from this treatment. Furthermore, a reduction in the average movement rate was observed in the most extreme temperature treatment, between the third week, when the water temperature was 30C, and the final week, when the end-point temperature of 32C was reached, indicating a possible effect of temperature on locomotion.

Keywords

Behaviour,
Biochemistry,
Climate change,
Controlled Environment,
Coral reefs,
Corals,
Crown of Thorn Starfish,
Distribution,
Echinoderms,
Ecology,
Field based,
Interaction,
Manipulative experiments,
Ocean warming,
Physiology,
Quantitative marine science,
Temporal change

Supervised By:

Sven Uthicke (AIMS)

Morgan Pratchett (JCU)

Andrew Hoey (ARC Centre of Excellence Coral Reef Studies)

Ciemon Caballes (ARC Centre of Excellence Coral Reef Studies)

Jennifer Donelson (ARC Centre of Excellence Coral Reef Studies)