Large Reef Fish Research Articles

Do tabular corals constitute keystone structures for fishes on coral reefs?

This study examined the changes in community composition of reef fishes by experimentally manipulating the availability of shelter provided by tabular structures on a mid-shelf reef on the Great Barrier Reef. At locations where access to tabular corals (Acropora hyacinthus and Acropora cytherea) was excluded, a rapid and sustained reduction in the abundance of large reef fishes occurred. At locations where tabular structure was added, the abundance and diversity of large reef fishes increased and the abundance of small reef fishes tended to decrease, although over a longer time frame. Based on their response to changes in the availability of tabular structures, nine families of large reef fishes were separated into three categories; designated as obligate, facultative or non-structure users. This relationship may relate to the particular ecological demands of each family, including avoidance of predation and ultraviolet radiation, access to feeding areas and reef navigation. This study highlights the importance of tabular corals for large reef fishes in shallow reef environments and provides a possible mechanism for local changes in the abundance of reef fishes following loss of structural complexity on coral reefs. Keystone structures have a distinct structure and disproportionate effect on their ecosystem relative to their abundance, as such the result of this study suggests tabular corals may constitute keystone structures on shallow coral reefs.

Fishing down the largest coral reef fish species

Studies on remote, uninhabited, near-pristine reefs have revealed surprisingly large populations of large reef fish. Locations such as the northwestern Hawaiian Islands, northern Marianas Islands, Line Islands, U.S. remote Pacific Islands, Cocos-Keeling Atoll and Chagos archipelago have much higher reef fish biomass than islands and reefs near people. Much of the high biomass of most remote reef fish communities lies in the largest species, such as sharks, bumphead parrots, giant trevally, and humphead wrasse. Some, such as sharks and giant trevally, are apex predators, but others such as bumphead parrots and humphead wrasse, are not. At many locations, decreases in large reef fish species have been attributed to fishing. Fishing is well known to remove the largest fish first, and a quantitative measure of vulnerability to fishing indicates that large reef fish species are much more vulnerable to fishing than small fish. The removal of large reef fish by fishing parallels the extinction of terrestrial megafauna by early humans. However large reef fish have great value for various ecological roles and for reef tourism.

Cleaner fish coloration decreases predation risk in aggressive fangblenny mimics

Mimicry systems can be classified by the nature of fitness benefits obtained by the mimic, namely increased mating opportunities (reproductive), increased foraging potential (aggressive), or reduced predation risk (protective). However, there is increasing evidence that mimicry categories are not mutually exclusive and mimics can obtain benefits from more than 1 category. Here, I provide evidence that an aggressive mimic, the bluestriped fangblenny Plagiotremus rhinorhynchos, also benefits from reduced predation risk by resembling the juvenile cleaner wrasse Labroides dimidiatus, which are thought to be relatively immune from predation due to the mutualistic nature of cleanerclient interactions. Instead of removing ectoparasites from larger reef fish, bluestriped fangblennies approach and attack reef fish removing scales and dermal tissue. Fangblennies can switch between their mimic and nonmimic coloration within 510min, depending on whether their model (the cleaner wrasse) is present or absent. I found that mimic fangblennies increased their risk-taking behavior toward potential predators compared with nonmimic fangblennies. Mimics were also more likely to attack other reef fish in the presence of predators compared with nonmimics. Animals should only increase risk-taking behavior when they perceive the threat of predation to be low. Therefore, this study provides important evidence that cleaner coloration provides protection from predation to both cleaner fish and their mimics, and the benefits of aggressive mimicry of cleaner wrasse have to be reevaluated in the light of these data.

The effect of coral morphology on shelter selection by coral reef fishes

While the loss of structural complexity causes declines in coral reef fish diversity, the processes leading to this decline are largely unexplained. To explore the role of coral morphology in providing shelter for fishes, tabular, branching and massive corals were filmed with video cameras and their usage by large reef fishes compared. Tabular corals were utilised more than the other two morphologies, with at least triple the abundance, biomass and residence times of large fishes. The preference of coral reef fishes for specific structural traits of tabular corals was also examined using artificial structural units. This experimental component showed that large reef fishes preferred opaque rather than translucent canopies. It appears that large fishes cue to tabular corals because of the concealment and/or shade provided. It is suggested that a loss of tabular corals as a result of climate change would have significant ecological impacts for the coral reef fishes that use these structures for shelter.

Site fidelity and activity patterns of a humphead wrasse, Cheilinus undulatus (Labridae), as determined by acoustic telemetry

This study examines the short-term site fidelity, the home range size and the activity patterns of one specimen of the emblematic and threatened humphead wrasse, Chelinus undulatus. Four omnidirectional hydrophones were deployed for 7 months in the mooring area of Laregnere marine reserve (New Caledonia). The hydrophone network covered 50 ha. The monitored fish was caught in the study site and surgically implanted with an ultrasonic transmitter. The fish displayed a regular diurnal rhythm during 25 days before leaving the area. Different patterns of spatial use were identified. The temporal succession of these patterns indicates that the minimum distance covered by the fish every day ranged between 20 and 200 m. Its home range was at least 5 ha. A decrease of the detection was observed before the departure of the fish. This decrease coincided with the beginning of the reproduction period in New Caledonia and supports the hypothesis of a fish departure for the reproductive event. Despite the survey of only one specimen, the home range and movement calculated using acoustic telemetry are different in scale than the reported scuba-based visual estimations. Such information is essential for the development of management policies and conservation measures of large reef fish species highly vulnerable to disturbance and fishing pressure.

Variation in the population biology of stripey bass Lutjanus carponotatus within and between two island groups on the Great Barrier Reef

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 243:191-207 (2002) - doi:10.3354/meps243191 Variation in the population biology of stripey bass Lutjanus carponotatus within and between two island groups on the Great Barrier Reef Jacob P. Kritzer* School of Marine Biology & Aquaculture and CRC Reef Research Centre, James Cook University, Townsville, Queensland 4810, Australia *Present address: Department of Biological Sciences, University of Windsor, Windsor, Ontario N9B 3P4, Canada. Email: kritzer@uwindsor.ca ABSTRACT: Density, population structure, mortality and growth of Lutjanus carponotatus on the Great Barrier Reef were compared on 2 spatial scales: between the Lizard and Palm Island groups and among 4 locations within the Palm group. The mean density at the Palm group was approximately 7 times that of the Lizard group. There were 2-fold differences in density within the Palm group, but strong statistical signals were not detected due to high variability in the data. Differences in size structures and asymptotic body sizes between the island groups were pronounced, and smaller differences were also evident within the Palm group. While age structures were similar among Palm group locations and lacked anomalous peaks, a series of strong cohorts at older age classes at the Lizard group suggests greater recruitment variability there during the past 2 decades. Variability in mortality did not increase with scale, as larger differences existed within the Palm group than between it and the Lizard group. The population traits estimated in this study were used in conjunction with reef area data to generate estimates of abundance and biomass, the values of which illustrate how multiple population traits interact to ultimately determine population size and reproductive potential. Multi-scale studies that examine a variety of aspects of population biology are rare for large reef fish, but are needed to identify which traits are likely to exhibit variation on which spatial scales. KEY WORDS: Coral reef fish · Demography · Spatial variation · Growth · Mortality Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 243. Online publication date: November 13, 2002 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2002 Inter-Research.

Atypichthys strigatus (Pisces: Scorpididae): An opportunistic planktivore that responds to benthic disturbances and cleans other fishes

Abstract Atypichthys strigatus (Günther) were abundant on temperate reefs in New South Wales, Australia. Dietary analyses indicated that they feed primarily on plankton, but also consume benthic organisms. Initial observations suggested thai A. strigatus respond to disturbances of the substratum for the purpose of feeding. The substratum in barrens and kelp habitats was experimentally disturbed to examine the response by A. strigatus. Significantly more A. strigatus were found in disturbed areas than in undisturbed areas and their feeding rate was greater in disturbed areas. The response by A. strigatus to disturbance was the same in barrens and kelp habitats, although there was a more marked response in the barrens habitat. Atypichthys strigatus also responded to natural disturbance by large reef fishes (e.g. Achoerodus viridis: Labridae). Furthermore, A. strigatus of a broad range of sizes (25–90 mm standard length) were observed cleaning other reef fishes. The behavioural flexibility of A. strigatus probably leads to increased feeding opportunities, and hence increased foraging success, for the fish. Moreover, it raises questions about the accuracy of partitioning fish species according to one trophic group.

Distribution and abundance of fish in a rocky reef environment at the subantarctic Auckland Islands, New Zealand

The distribution and abundance of fish in a rocky reef environment were investigated at the subantarctic Auckland Islands of New Zealand, in June 1986. Fish were counted in transects and specimens were taken. The diversity and abundance of species of large reef fish was low; a total of eight species were observed. Most fish were benthic carnivores. These findings are similar to studies of reef fish in subantarctic waters of Chile. Large differences in species composition were found among locations at the Auckland Islands. The number of species and their abundance was highest near exposed headlands. Few fish were found on reefs at more sheltered inlets. At most locations the nototheniids Paranotothenia angustata and P. microlepidota ranked first in abundance at deep and shallow sites. There were some species that showed differences in abundance with depth. Highest abundance of Bovichthys variegatus, Latridopsis cilaris, Latris lineata and Pseudolabrus cinctus were in deep water on reefs. Large numbers of juvenile P. microlepidota were found only in shallow water. No depth related patterns were found for P. angustata and Mendosoma lineatum. Specimens, other than those counted in transects, were also collected. There were small fish, 4 species of tripterygiids, 1 gobiescocid and 2 syngnathids. The Auckland Islands had closer zoogeographic affinities with islands of temperate and subantarctic New Zealand than with other landmasses of the westwind drift. Although most fish found at the Auckland Islands are found also in temperature New Zealand, the converse of this pattern was not found. The proportional representation of species and trophic groups differed markedly between these regions.

Estimating length frequency distributions of large reef fish underwater

We describe the training of divers to recognise and remove bias in estimating lengths of fish underwater. Divers were asked to allocate objects, from a population (N=50) with a known length frequency distribution, to ten 100 mm size classes. Observed and expected distributions were then compared and the divers informed of their errors. Training continued until divers consistently produced length frequency distributions that were not significantly different from the expected distribution (α=0.8) by the one sample Kolmogorov-Smirnov (K-S) test. Divers were trained in five trials, but after six months they had lost all their ability and had to be retrained. Three trained divers observing the “same” population of the large reef fish Plectropomus leopardus (Serranidae) produced length frequency distributions that were not significantly different (P>0.1) on 67% of occasions. Data collected by divers can be used to detect small but real differences in length frequency distributions of populations when analysed using the two sample K-S test. We suggest a means of determining within site variation in length frequency relative to between site variation.