Each month, a selected blog from Lizard Island Reef Research Foundation (LIRRF) is featured at the AM. LIRRF supports scientific research & education at the AM’s Lizard Island Research Station on the Great Barrier Reef. For this month, we feature: The functioning of future coral reefs.

Lizard Island epitomises the plight of Anthropocene coral reefs as it has been subjected to a growing number and escalating intensity of disturbances in recent years, especially cyclones and bleaching events. However, despite these disturbances pushing coral cover to very low levels around Lizard Island (Fig. 1a-c) there has been some recovery (Fig. 1d-f). The overarching aim of my research project is to explore how these disturbed and recovering coral reefs function, and how they can provide an insight into the functioning of future reef states. To address this aim, a major objective of my fellowship has been to build on a time series of photo-quadrats that were first established in early 2016, immediately prior to the widescale bleaching event that impacted Lizard Island in that year. The same photo-quadrats have been re-sampled at regular intervals since then, and by adding to this dataset I can assess where and how corals are recovering. In addition, I have been exploring how a variety of factors shape the functioning of these reefs, with a particular focus on the sediments trapped within the algal turfs which often typify disturbed reefs (Fig 1c, d).

Photographs showing the loss of hard and soft corals between February 2016 and January 2018

Figure 1. Photographs showing the loss of hard and soft corals between February 2016 and January 2018 at one of my study sites in the lagoon due to coral bleaching (a-c) and the recovery of Acropora cover between January 2018 and January 2021 (d-f) at one of my sites between Palfrey and South Island. Grey arrows denote when quadrats were photographed, while thermometers denote bleaching events (note bleaching in 2020 and 2021 was relatively mild).

Image: Sterling Tebbett
© Sterling Tebbett

Unfortunately, due to ongoing disruptions from Covid-19 in 2021 my first trip in the 2021 calendar year was delayed by several months. However, at the end of August I successfully completed a 7-day trip to Lizard Island to retrieve 43 current meters and 5 pressure sensors which had been deployed around Lizard Island since February 2021. The data from these instruments should be key to understanding how hydrodynamics influence coral recovery and recruitment around Lizard Island. In addition, I am lucky enough to be writing this progress report from Lizard Island where I am half-way through a 28-day trip. As of today, my assistants and I have re-photographed 298 of 445 quadrats spread across 19 transects around Lizard Island (Fig. 2a). In addition, we have been quantifying the interactions between algal turf sediments and herbivorous fishes at Lizard Island and adjacent reefs through video deployments and the collection of algal turf sediment samples as well as commenced re-deployment of current meters and pressure sensors.

After my fellowship trip in January/February 2021, I extracted and analysed the data from the photo-quadrats. In doing so, I revealed that from 2018 to 2021 there were significant increases (>600%) in coral cover on two semi-exposed reefs and that this was associated with substantial recruitment of Acropora corals (Figs 1, 2). Interestingly, these rates of coral cover regeneration rank amongst some of the highest reported in the literature. However, fourteen lagoonal and back reef locations exhibited virtually no recovery nor Acropora recruitment (Fig. 2). Despite examining a suite of potential explanatory variables there were no clear explanations for this discrepancy in Acropora recruitment rates, although further exploration of hydrodynamic drivers may hold the key. Overall, these results suggest that some recovery is possible immediately after severe cumulative disturbances on reefs, although this recovery is highly spatially heterogenous, and some reefs may fail to recover significantly before the next major disturbance. Importantly, I have now published the results of this research as a scientific article in Marine Environmental Research titled “Spatial patchiness in change, recruitment, and recovery on coral reefs at Lizard Island following consecutive bleaching events”. In addition, I was able to collaborate with Juliano Morais, a fellow PhD student in the Research Hub for Coral Reef Ecosystem Functions, who also utilised these photo-quadrats for another scientific article published in Scientific Reports titled “Dangerous demographics in post-bleach corals reveal boom-bust versus protracted declines”.

I am very thankful that the funding provided by The Ian Potter Foundation has given me the opportunity to see, as well as document, how reefs around Lizard Island are changing following disturbance, especially the remarkable capacity for Acropora cover to regenerate in some situations. I believe the insights I have gained from spending this time on the reefs around Lizard Island will be invaluable in shaping my research and career going forward.

By Sterling Tebbett | PhD student at James Cook University and 2020 Ian Potter Doctoral Fellow at Lizard Island. Read more about him in the post Changing Reefs.

To view the original blog and more LIRS blogs, please go to: https://lirrf.org/the-functioning-of-future-coral-reefs-fishes-sediments-and-productivity/

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