I am a molecular ecologist working at the interface of coral reef ecology, fishery science and population genetics. My research is best described as the molecular ecology and evolution of coral reefs, with emphasis on the population dynamics of coral reef fishes including: the dispersal ecology and recruitment dynamics of larval fishes, the reproductive success of adult fishes, and the role of hybridisation in speciation.
The principal application of my research to date has been in understanding patterns of dispersal for marine fishes, which is relevant to the optimal design of networks of marine protected areas. I have developed and applied molecular tools to resolve patterns of larval dispersal for coral reef fishes at a scale ranging from tens of metres to hundreds of kilometres. As a molecular ecologist I bring a unique perspective and a unique set of tools to resolve current issues in spatial management of marine ecosystems.
Theme 1: Dispersal ecology and recruitment dynamics of larval fishes
Networks of no-take marine reserves are widely advocated as a means to conserve biodiversity and manage coastal fisheries. Reserves not only deliver rapid and long-term benefits within their boundaries, they also provide a broader framework that augments the resilience of coral reef ecosystems. Understanding the level of demographic connectivity between discreet populations is essential to determine a network’s efficacy to supplement fisheries and protect biodiversity. In theory, the larger biomass of exploited fishes within reserves, and higher reproductive capacity, increase recruitment to nearby populations due to larval export, and connectivity between reserves support stable populations. However, for large exploited fishes, it has been seemingly impossible to determine where the larvae from populations within reserves go or assess the relative importance of the supply of juveniles from reserves. One of the major challenges is identifying methods that can be applied to large species at the scale at which reserve networks have been implemented.
My doctoral research, under the supervision of Prof. Geoffrey Jones (JCU), Prof. Garry Russ (JCU) and Dr Serge Planes (EPHE), focused on the role of no-take marine protected areas for marine conservation and fishery management. I developed and applied methods of genetic parentage analysis to track the dispersal of juvenile fish for two exploited coral reef fishes in a network of no-take marine protected areas of the Great Barrier Reef Marine Park (Harrison et al. 2012 – Current Biology). It is the first study to demonstrate that marine protected areas can export fish larvae beyond their boundaries, enhancing local recruitment in fished areas and connecting populations inside marine protected areas.
Theme 2: The reproductive success of adult fishes
It is now widely appreciated that, for many exploited fishes, establishing no-take marine reserves can lead to higher densities and larger average fish size inside reserves. Networks of marine reserves continue to be designed and implemented on the basis that reserves play an important role, not only in the long–term conservation of fish populations within their boundaries, but also in sustaining fish stocks in areas open to fishing. This has recently been supported by new genetic studies that show juveniles sourced from reserves can be retained in natal reserves, exported to fished areas and exchanged among reserves. However, the effectiveness of reserves in sustaining populations assumes that they provide a consistent source of juvenile recruitment over time. In addition, reserves will be most effective if the larger fish that accumulate inside reserves make a disproportionate contribution to the supply of juveniles. The relatively new application of genetic parentage analysis to large exploited marine fishes provides a means to determine when, where and from whom the juveniles from reserves originate.
Theme 3: The role of hybridisation in speciation
It has long been considered that hybrid zones serve as ‘natural laboratories’ to investigate evolutionary processes such as selection, adaptation and speciation. However, marine ecosystems offer few barriers to gene flow and hybrid zones have only ever been described in isolated places where biogeographic regions collide. How these species maintain evolutionary boundaries in the face of such widespread hybridisation is somewhat of a ‘paradox’.
Under the biological species concept, in which species are reproductively isolated, inter-specific hybrids should be an extremely rare occurrence. In reality, the evolutionary boundaries between species are permeable and best estimates indicate that 1 to 10% of all animal species and up to 25% of plant species hybridise with at least one other species in the wild. What then, are the mechanisms that maintain species boundaries in the face of on-going gene flow and allow for hybrid speciation?
Theme 4: COTS connectivity
Population outbreaks of coral-eating crown-of-thorns starfish (CoTS), Acanthaster cf. planci, are a leading cause of coral cover losses throughout the Indo-Pacific region. A lack of understanding of the potential triggers and spread of outbreaks remains a major challenge for management interventions that aim to control active outbreaks or prevent future outbreaks from occurring.Inferring the source and spread of outbreaks of crown-of-thorns starfish (CoTS) provides not only information about the demographic and ecological factors contributing to these outbreaks, but also information on how best to monitor reefs for future outbreaks and curtail their spread.
Theme 5: Coral Reef Ecology and Conservation in the Coral Sea
Coral reefs are periodically subjected to acute (e.g storms) and chronic (e.g. fishing) disturbances that can take decades to recover from. The potential to rebound from such events will depend on the level of protection they have been afforded and crucially, the degree of connectivity with neighbouring reefs. Today, a growing human population is encroaching on marine environments leading to dramatic shifts in coral cover and species composition, which undermines their potential for recovery. The pervasive degradation of the world’s coral reefs underscores the need for solutions that promote the recovery potential of these ephemeral ecosystems.