James Cook University

About: James Cook University is a education organization based out in Townsville, Queensland, Australia. It is known for research contribution in the topics: Population & Coral reef. The organization has 9101 authors who have published 27750 publications receiving 1032608 citations. The organization is also known as: JCU.

Interspecific competition and coexistence in a guild of coral-dwelling fishes

Abstract: We investigated the effects of interspecific competition on abundance, habitat partitioning, and coexistence of six closely related species of gobies (genus Gobiodon) that inhabit a range of acroporid coral species at Lizard Island, Great Barrier Reef. After documenting the extent of overlap in habitat use among pairs of species in the field, we used a combination of field and laboratory experiments to investigate the relationship between these patterns and the occurrence of interspecific competition. Experiments in aquaria tested the ability of five of the species to compete against G. histrio, the apparent competitive dominant, including the effects of body size and prior residency. A manipulative field experiment, in which abundance of G. histrio was reduced, tested whether competition with this species limits the abundance of the other five species. Two species competed for space with G. histrio in the field, yet overlap in habitat use with G. histrio was high for one of these species (G. axillaris) and low for the other (G. brochus). In aquaria, G. axillaris and G. histrio preferred the same species of coral and had equivalent, size-based, competitive abilities. The coexistence of G. axillaris and G. histrio at the scale of 10’s metres on the reef can thus be explained by a competitive lottery model. However, differential distributions of these two species across the reef flat and reef crest suggests that resource partitioning or habitat selection at larger spatial scales are also important to their coexistence. In aquaria, G. brochus was an inferior competitor to G. histrio and could only gain access to the preferred species of coral through an advantage in body size or prior residency. Low overlap in habitat use between G. brochus and G. histrio in the field appears to result from niche shifts by the subordinate competitor only, indicating coexistence via an included niche model. The field experiment indicated that the other three other species did not compete for space with G. histrio, and these species exhibited either low (G. rivulatus) or high (G. quinquestrigatus and G. unicolor) overlap in habitat use with G. histrio. Experiments in aquaria demonstrated that G. rivulatus and G. histrio did not compete because they preferred different species of coral. In contrast, G. unicolor and G. histrio exhibited high overlap in habitat use but did not compete because they were able to co-habit the same coral colonies without affecting each other. In aquaria, G. quinquestrigatus and G. histrio preferred the same coral species and G. quinquestrigatus was an inferior competitor, so these species were expected to compete for space in the field. In a field recolonization experiment, coral colonies previously occupied by G. quinquestrigatus were rarely recolonized by G. histrio, indicating that these species coexist because they use different types of coral colonies in the field. The study demonstrates that there is no single relationship between overlap in resource use and the occurrence of interspecific competition, even among closely related species, and that species within a guild can coexist by a diversity of mechanisms.

Importance of live coral habitat for reef fishes

Abstract: Live corals are the key habitat forming organisms on coral reefs, contributing to both biological and physical structure. Understanding the importance of corals for reef fishes is, however, restricted to a few key families of fishes, whereas it is likely that a vast number of fish species will be adversely affected by the loss of live corals. This study used data from published literature together with independent field based surveys to quantify the range of reef fish species that use live coral habitats. A total of 320 species from 39 families use live coral habitats, accounting for approximately 8 % of all reef fishes. Many of the fishes reported to use live corals are from the families Pomacentridae (68 spp.) and Gobiidae (44 spp.) and most (66 %) are either planktivores or omnivores. 126 species of fish associate with corals as juveniles, although many of these fishes have no apparent affiliation with coral as adults, suggesting an ontogenetic shift in coral reliance. Collectively, reef fishes have been reported to use at least 93 species of coral, mainly from the genus Acropora and Porities and associate predominantly with branching growth forms. Some fish associate with a single coral species, whilst others can be found on more than 20 different species of coral indicating there is considerable variation in habitat specialisation among coral associated fish species. The large number of fishes that rely on coral highlights that habitat degradation and coral loss will have significant consequences for biodiversity and productivity of reef fish assemblages.

Genetic Divergence across Habitats in the Widespread Coral Seriatopora hystrix and Its Associated Symbiodinium

Abstract: Background: Coral reefs are hotspots of biodiversity, yet processes of diversification in these ecosystems are poorly understood. The environmental heterogeneity of coral reef environments could be an important contributor to diversification, however, evidence supporting ecological speciation in corals is sparse. Here, we present data from a widespread coral species that reveals a strong association of host and symbiont lineages with specific habitats, consistent with distinct, sympatric gene pools that are maintained through ecologically-based selection. Methodology/Principal Findings: Populations of a common brooding coral, Seriatopora hystrix, were sampled from three adjacent reef habitats (spanning a ~30 m depth range) at three locations on the Great Barrier Reef (n = 336). The populations were assessed for genetic structure using a combination of mitochondrial (putative control region) and nuclear (three microsatellites) markers for the coral host, and the ITS2 region of the ribosomal DNA for the algal symbionts (Symbiodinium). Our results show concordant genetic partitioning of both the coral host and its symbionts across the different habitats, independent of sampling location. Conclusions/Significance: This study demonstrates that coral populations and their associated symbionts can be highly structured across habitats on a single reef. Coral populations from adjacent habitats were found to be genetically isolated from each other, whereas genetic similarity was maintained across similar habitat types at different locations. The most parsimonious explanation for the observed genetic partitioning across habitats is that adaptation to the local environment has caused ecological divergence of distinct genetic groups within S. hystrix.