Unpacking the Problem of Benthic Cyanobacterial Mats on Tropical Coral Reefs. (APSF 22021)

APSF 22021 | Amount: $41,888 | Project Leader: Amanda Ford | Project Period:

A project undertaken at The University of the South Pacific Fiji, and supervised by Dr Amanda Ford.

Tropical coral reefs are being fundamentally altered by climate change impacts and local anthropogenic stressors. Widespread ecosystem shifts characterised by losses of hard corals and emerging dominance of alternative groups threaten the continued provision of ecosystem services to millions of humans. Understanding the dynamics of these alternative taxa that threaten the health and resilience of coral-dominated systems is thus imperative. While macroalgae have received the bulk of attention for dominating shifted or degraded reefs, this project aims to investigate the ecology of one microbial group that has received little research attention but is increasingly causing concern at reef locations worldwide: benthic cyanobacterial mats (BCMs).

Benthic Cyanobacterial Mat

BCMs grow as a filamentous ‘carpet’ over sand, hard substrate, or living organisms such as corals or algae which can consequently die. In the last decade, BCM coverage exceeding 50% has been reported from multiple locations, including reefs in the Pacific Island region. Limited temporal and spatial data has precluded detailed exploration into the factors that facilitate BCM proliferation, but declining water quality and elevated temperatures are expected to be primarily responsible, similar to freshwater cyanobacterial blooms which are better studied. BCMs are becoming increasingly prevalent across Fiji, also perplexingly at remote and otherwise pristine areas, and for the first time have been observed to persist through the cold season. 

Drivers of BCM abundance are thus complex and understudied, deeming management interventions challenging. Furthermore, once BCMs are established, a myriad of self-perpetuating feedback cycles are hypothesised to reinforce reef decline. Additionally, cyanobacteria can produce many toxins, and neurotoxins in benthic cyanobacteria have been linked to a sickness that manifests very similarly to ciguatera fish poisoning, therefore suggesting there may be implications for human health.

Reef Surveys

To address these issues, this project has four main objectives: 

(1) Analyze survey data from reefs across Fiji to generate baseline data on the spatial distribution of BCMs and to determine how BCM cover relates to environmental features and other benthic attributes. 

(2) Perform regular fine-scale surveys at Fiji’s Coral Coast and consistently record environmental conditions to generate data on temporal dynamics of BCMs on a set of inshore reefs, and record the different morphological features, growth dynamics, and toxicity of the common BCM types. 

(3) Assess how the most prevalent BCMs impact reef fish herbivory functions to determine whether they affect critical ecosystem processes. 

(4) Test the competition dynamics between BCMs and local coral species with different morphologies and how this links to BCM toxicity and composition.