Makeely Blandford has completed her final report for studies undertaken at the Australian Museum’s Lizard Island Research Station. The project was supported by the Gough Family Doctoral Fellowship, and over three summers, five field trips were conducted. The aim of her research was to examine the independent and interactive effects of habitat fragmentation and habitat loss on fish populations.
Coral reefs are one of the world’s most biodiverse ecosystems that support a diverse array of marine life. Unfortunately, coral reefs are also under threat due to a variety of factors such as climate change, disease, and declining water quality. Outbreaks of crown of thorns starfish add to the stressors resulting in the death of large tracts of coral and the subsequent fragmentation of reefs. As coral habitats decline and fragment, it can have a significant impact on the fish populations that depend on them. Despite this, there have been relatively few studies on the effects of habitat fragmentation on reef fish populations.
While numerous studies have quantified the effects of coral (i.e., habitat) loss on coral reef fishes, very few have considered how habitat fragmentation affects reef fish populations and assemblages. This PhD research investigated how the fragmentation of coral reef habitats influences the structure of reef fish communities. Specifically, in a series of experimental and observational field studies, this project studied the effect of coral habitat patch size, spatial separation and arrangement on the recruitment, persistence, growth and composition of reef fish assemblages inhabiting the reefs surrounding Lizard Island.
Makeely’s research found that the effects of habitat fragmentation on fish populations are highly context-specific and depend on various factors such as spatial and temporal scales, the composition and size of habitats, and stocking density of fish communities. The research highlighted that spatial separation is an important factor in structuring coral reef fish assemblages on natural habitat patches. Specifically, a rapid increase in fish density and species richness was observed when natural habitat patches were over ten meters from the next closest reef. However, this finding only relates to established fish assemblages on natural patch reefs.
To investigate the effects of habitat fragmentation on the critical life-stage of coral reef fish immediately following settlement, experimental studies were conducted using habitat clusters constructed from live branching coral adjacent to shallow lagoonal reef, and settlement-stage common coral reef damselfish collected in light traps. The persistence of damselfish, as well as any fish that recruited naturally to the clusters, were recorded to investigate the effects of habitat fragmentation on reef fishes. The research found that spatial separation did not affect the persistence of early post-settlement damselfish on experimental patches over eight days, nor did spatial separation affect the natural settlement of coral reef fishes over fourteen days. However, a reduction in the overall spatial extent of habitat (as a proxy for habitat loss) was directly related to the abundance and species richness of recently settled fish.
Furthermore, the number and size of patches did affect the early post-settlement persistence of the damselfish, Pomacentrus amboinensis, with persistence significantly reduced on experimental reef clusters with moderate levels of fragmentation compared to those with no fragmentation and high fragmentation. These results suggest that the effects of habitat fragmentation on coral reef fishes are context-specific and depend on the degree and nature of the fragmentation, precluding generalizations across spatial and temporal scales. Similar variation in terrestrial ecosystems has led to considerable debate regarding the importance of habitat fragmentation in conservation, and the results of this research could help inform appropriate management strategies for coral reefs.
Given the ongoing and accelerating decline of coral reefs, this body of work supports existing assertions that reduction in the spatial extent of habitats, and specifically, coral loss, is detrimental to coral reef fish assemblages. However, effects of habitat loss may be conflated with habitat fragmentation, and further work is needed to understand the interactions between these processes.
Makeely is grateful for the opportunity afforded her by the Gough Family Doctoral Fellowship. “My contribution to scientific understanding, presented in my PhD thesis and published works, would not have been possible without the support of this fellowship and I am most appreciative to have had the opportunity to conduct timely and important research on reef fishes of the Great Barrier Reef at such a world-class research station.”
By Tony Le Deux based on Makeely Blandford’s final report