The Future For Reef Fish Research Onthe

Given the diversity of the fishes and the ecological complexity of the GBR, there are a multitude of novel research issues to follow up. Much of what we hear about the GBR concerns issues of habitat disturbance and loss and the consequences of overfishing. These are legitimate issues and the global picture of the status of coral reefs demonstrates that although the GBR is relatively healthy, the consequences of natural and anthropogenic disturbances can be manifested very quickly. The most effective way to evaluate the potential influences of disturbance and exploitation is through an understanding of the biology of the organisms themselves. Reef animals, and especially the fishes, vary in the way they respond to stress and environmental change. It is difficult to generalise from one group to another and the best approach is to understand the biological mechanisms, both evolutionary and ecological, that underlies the way different groups respond to change.

We identify three areas of future studies of GBR fishes that will yield the type of information discussed above. This list is not exhaustive or prioritised, but it captures some of the excitement of ongoing reef fish research.

Depth distributions of reef fishes. How deep does the GBR go? Using baited video cameras it is now possible to obtain visual samples of the diversity of reef fishes to a depth of 200 m, below the level of active coral growth. These surveys have revealed that a number of species

BOX 28.4 GENETIC STRUCTURE OF PLECTROPOMUS POPULATIONS

The genetic structure of Plectropomus on the east and west coasts of Australia. The diagram represents a phylogenetic tree based on molecular sequences from the D-loop region of the mitochondrial (mt) genome of P. leopardus and P. maculatus collected from the tropical coasts of eastern and western Australia. Sequences from P. laevis constitute an outgroup. The colours represent mt sequences characteristic of each species (blue, P. leopardus; green, P. maculatus).

Plectropomus leopardus sequences grouped as a single clade (A), with populations from the two coasts occurring as two genetically distinct sister clades. Plectropomus maculatus populations from the west coast form a distinct clade (B). However, on the east coast P. leopardus and P. maculatus do not separate into species-specific clades and are genetically indistinguishable with the mitochondrial marker used in this study. The failure of the mitochondrial marker to distinguish the two species is attributable to interspecific hybridisation between these species on the GBR. The structure of the phylogenetic tree is strongly supported in ML and Bayesian analyses. Further details of this study are provided in L. van Herwerden et al. (2006). Molecular Phylogenetics and Evolution, 41, 420-435.

P. leopardus Western Australia

P. leopardus P. maculatus GBR

A P. leopardus

Clade B P. maculatus Clade

P. leopardus P. maculatus GBR

P. maculatus Western Australia

A P. leopardus

Clade B P. maculatus Clade

P. maculatus Western Australia

P. laevis GBR

Figure 28.8 Genetic structure of Plectropomus populations. (Image: L. van Herwerden, JCU.)

that were considered to be shallow water fishes extend to 100 m depth. This work requires a reevaluation of the habitat association for some common reef species and also identifies species that are able to extend their depth range in response to shallow water disturbances, such as sudden increases in temperature or fishing effects.

Genetic analysis of population structures. Is there a consistent genetic signature associated with the very recent colonisation of the GBR by reef fishes including further examples of hybridisation between related species? Surveys of reef fish genetic structure are also important with respect to the detection of 'cryptic' species. However, this carries with it an important caveat;

it is unwise to use a genetic criterion such as differences in mitochondrial sequences to differentiate fish species, as the Plectropomus example shows. Two things are essential for the confirmation of cryptic species. At least two lines of evidence such as morphological and/or structural distinctions as well as genetic differences are required. More importantly, it is critical to have the capacity to correctly identify reef fishes in the field. This capacity is being eroded as taxonomic research in our museums winds down. Collecting tissues from reef fishes for such schemes as the Barcode of Life without proper taxonomic quality control is a recipe for disaster.

Multi-scale analysis of life history features. After a slow start, there are a number of study programs investigating the age-based life history features of coral reef fishes using age information extracted from reef fish otoliths. This is important for a number of reasons, including the analysis of stock structure. Many species of reef fish show significant differences in growth and mortality rates between localities. This is very conspicuous in GBR fishes. Such studies are valuable when linked to analyses of genetic structure over the same scale as it provides insights into the mechanisms underlying spatial differences in demography. Preliminary work suggests that reef fishes show great plasticity with respect to growth rates, reproductive outputs and age-structure, but it is unclear to what extent this has a genetic basis. When examined on a broader geographic scale, GBR reef fishes show some unique demographic features including far greater life spans than those in adjacent reef systems although the significance of this is not clear at present.

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