J. H. Choat

Influence of tidally induced fronts and Langmuir circulations on distribution and movements of presettlement fishes around a coral reef

The slicks of tidally induced fronts and Langmuir circulations were studied near Bowden Reef, Great Barrier Reef, in December 1987. There were two components to the study: (1) a description of physical oceanography adjacent to the reef; (2) sampling for planktonic organisms, designs being stratified according to hydrology. Tidal fronts extended 1 to 2 km from the reef outside the lagoon. Fish of a variety of developmental forms and zooplankton were most abundant in slicks of fronts. Sixteen to 81% of fish that were captured were presettlement reef-fishes. There was an unclear relationship between the presence of slicks of Langmuir circulations and abundance of fish in the lagoon. This relationship was largely because well developed atherinids and recently hatched pomacentrids showed no predictable relationship with the presence of windrows. Jellyfish,Aurelia aurita, were found in extremely high concentrations in the slicks of Langmuir circulations; small carangids were associated with jellyfish. Movements of fronts were influenced by the tide and wind. In some conditions we observed fronts to change position as the tide reversed direction. Fronts that were orientated offshore (1 to 2 km), were observed to rotate and align with the reef. Because of a “halo” of oceanographic features such as tidal fronts, the reef may be a larger target for presettlement fishes than its topography would suggest. It is argued that some organisms are advected into slicks, while others respond to high concentrations of zooplanktonic food and remain in slicks. Localised oceanographic features may also affect the settlement patterns of fishes on reefs.

Influence of season, ontogeny and tide on the diet of the temperate marine herbivorous fish Odax pullus (Odacidae)

The diet of the temperate marine herbivorous fish Odax pullus (Pisces: Odacidae) was examined using gut-content analysis followed by principal-component analysis and analysis of variance. Fish were collected near Leigh, on the northeast coast of New Zealand, from February 1983 to September 1984. The data were categorised by size of fish, season, and state of tide. A major ontogenetic shift in diet was observed. Juveniles fed on animal material (crustaceans and gastropods), epiphytic rhodophytes, and some phaeophyte material. Adults fed almost exclusively on two phaeophyte taxa, the laminarian Ecklonia radiata and the fucoid Carpophyllum spp. Dietary selection was evident at the level of particular plant components; the diet of larger fish in spring samples was dominated by fucoid reproductive receptacles. There was no direct evidence of a tidal influence on diet composition of O. pullus, although the relative proportions of E. radiata and Carpophyllum spp. ingested by adult fish appeared to vary with tidal state. The volume of gut contents varied seasonally for all size classes, although the timing of peak annual food intake varied among size classes. Tidal state did not influence the volume of the gut contents. The ontogenetic and seasonal trends evident in the diet of O. pullus appeared to be related to a number of factors including relative gut length, gonad development, ontogenetic changes in feeding anatomy and seasonal changes in algal composition.

The likelihood of extinction of iconic and dominant herbivores and detritivores of coral reefs: the parrotfishes and surgeonfishes

Parrotfishes and surgeonfishes perform important functional roles in the dynamics of coral reef systems. This is a consequence of their varied feeding behaviors ranging from targeted consumption of living plant material (primarily surgeonfishes) to feeding on detrital aggregates that are either scraped from the reef surface or excavated from the deeper reef substratum (primarily parrotfishes). Increased fishing pressure and widespread habitat destruction have led to population declines for several species of these two groups. Species-specific data on global distribution, population status, life history characteristics, and major threats were compiled for each of the 179 known species of parrotfishes and surgeonfishes to determine the likelihood of extinction of each species under the Categories and Criteria of the IUCN Red List of Threatened Species. Due in part to the extensive distributions of most species and the life history traits exhibited in these two families, only three (1.7%) of the species are listed at an elevated risk of global extinction. The majority of the parrotfishes and surgeonfishes (86%) are listed as Least Concern, 10% are listed as Data Deficient and 1% are listed as Near Threatened. The risk of localized extinction, however, is higher in some areas, particularly in the Coral Triangle region. The relatively low proportion of species globally listed in threatened Categories is highly encouraging, and some conservation successes are attributed to concentrated conservation efforts. However, with the growing realization of mans profound impact on the planet, conservation actions such as improved marine reserve networks, more stringent fishing regulations, and continued monitoring of the population status at the species and community levels are imperative for the prevention of species loss in these groups of important and iconic coral reef fishes.

Daily feeding rates in herbivorous labroid fishes

Estimates of daily feeding rates were obtained for two groups of herbivorous labroid fishes, one confined to cold water and the other to tropical reef environments. These were the family Odacidae, represented by Odax pullus from New Zealand waters, (Goat Island Bay: Latitude 36° South; on the northeastern coast of New Zealand) and the family Scaridae, represented by Scarus rivulatus, S. schlegeli and S. sordidus from the northern Great Barrier Reef (Lizard Island; a mid-shelf reef at 14° South latitude). Observations on the odacid were made in 1984 and in 1992, and on the scarids in 1984 and 1988. O. pullus displayed a diurnal feeding pattern in which the rates (expressed as bites min-1) are greatest early in the day. The mean combined feeding rate for three size groups (juveniles, subadults and adults) peaked (average of 2.9 bites) from 06.00 to 08.00 hrs and declined fourfold to a combined average of 0.7 bites min-1 by midday. The greatest mean feeding rate recorded was 3.7 bites min-1, with an overall mean of 1.8 bites min-1. For subadults and adults there were consistent trends in feeding, with subadults feeding at a greater rate than adults and both groups displaying a decline in feeding rate during the day. The change in feeding rate with time of day was statistically significant in both groups. The pattern for juvenile O. pullus was different from that in the two larger size groups in that juveniles did not show a uniform decline in feeding with time of day. For scarids, the daily feeding rate varied by site, but the pattern was similar for all species, characterised by initial low rates increasing to higher but variable levels by midday. The influence of both site of feeding and time of day on feeding rate was confirmed by analysis. The overall mean values for each species were 20.1 bites min-1 for S. rivulatus, 19.7 bites min-1 for S. schlegeli and 14.9 bites min-1 for S. sordidus. For scarids, the peak feeding rates varied from 19.3 to 32.8 bites min-1, with overall rates from 14.9 to 21.1 bites min-1. Estimates of activity and movement patterns during feeding were obtained for O. pullus. Distance moved per unit time was highly variable, 0.1 to 47.5 m min-1, with a mean of 8.5 m min-1 (SD=9.9). Trends in movement among sexes and size classes were obscured by the variable movement patterns of individual fishes.

Hybridization of reef fishes at the Indo-Pacific biogeographic barrier: a case study

Hybridization is recognized as an important source of genetic variation. In some reef fishes, including the Acanthuridae, hybridization has been detected due to intermediate colouration. This study used a molecular genetic approach to investigate hybridization in two Acanthurid species: Acanthurus leucosternon and Acanthurus nigricans, which have Indian and Pacific Ocean distributions respectively and are sympatric in the eastern Indian Ocean. In this area a putatitve hybrid, Acanthurus cf. leucosternon has been recognized based on intermediate colouration and restriction to the sympatric region of otherwise allopatric putative parental species. This study aimed to test this hypothesis using genetic tools. The three species were sampled from Cocos (Keeling) and Christmas Islands, the biogeographic boundary where many Indian and Pacific Ocean biota meet. Representatives from allopatric populations of both parental species and outgroups were also sampled. Mitochondrial COI and intron 1 of the nuclear ribosomal protein S7 were sequenced from 13 and 30 specimens respectively. Although sample sizes in this study are relatively small and more genetic data, including an extended phylogeographic sampling, is required to further evaluate these findings, the COI results support hybrid origins of Acanthurus cf. leucosternon, but S7 data are inconclusive due to the possibility of incomplete lineage sorting. The fourfold more abundant Acanthurus nigricans is most often the maternal parent. Inter-fertile hybrids apparently backcross with rare Acanthurus leucosternon males, transferring Acanthurus nigricans mitochondria to this species. These results suggest that Acanthurus leucosternon may eventually be lost from these islands, due to their relative rarity and introgressive hybridization.

Sexual development and reproductive demography of the green humphead parrotfish (Bolbometopon muricatum) in the Solomon Islands

An investigation of the reproductive biology of the green humphead parrotfish (Bolbometopon muricatum) from three areas in the Western Province of the Solomon Islands revealed that B. muricatum exhibits several features that differ from the pattern of reproductive development observed in most parrotfishes. Unlike most parrotfishes, histological evidence suggests that the sexual pattern of B. muricatum is essentially gonochoristic with high incidences of anatomical but non-functional hermaphroditism. B. muricatum also differs from other parrotfishes in that all males pass through an immature female (or bisexual) phase as demonstrated by all adult testis retaining the ex-ovarian lumen and peripheral sperm sinuses in the gonad wall. However, a protogynous diandric reproductive strategy cannot be excluded given that sampling may have missed transitional individuals. Marked variation in the demography of male B. muricatum between the three locations examined is considered to reflect variation in historical fishing effort.

Comparative demography of commercially important parrotfish species from Micronesia

Fishery-independent sampling was used to determine growth patterns, life span, mortality rates and timing of maturation and sex change in 12 common parrotfishes (Labridae: tribe Scarinae) from five genera (Calotomus, Cetoscarus, Chlorurus, Hipposcarus and Scarus) in Micronesia. Interspecific variation in life-history traits was explored using multivariate analysis. All species displayed strong sex-specific patterns of length-at-age among which males reached larger asymptotic lengths. There was a high level of correlation among life-history traits across species. Relationships between length-based and age-based variables were weakest, with a tenuous link between maximum body size and life span. Cluster analysis based on similarities among life-history traits demonstrated that species were significantly grouped at two major levels. The first grouping was driven by length-based variables (lengths at maturity and sex change and maximum length) and separated the small- and large-bodied species. Within these, species were grouped by age-based variables (age at maturity, mortality and life span). Groupings based on demographic and life-history features were independent of phylogenetic relationships at the given taxonomic level. The results reiterate that body size is an important characteristic differentiating species, but interspecific variation in age-based traits complicates its use as a life-history proxy. Detailed life-history metrics should facilitate future quantitative assessments of vulnerability to overexploitation in multispecies fisheries.

Spawning Aggregations in Reef Fishes; Ecological and Evolutionary Processes

What factors have been important in the evolution of reef fish spawning aggregations? Surprisingly, basic biological features such as size, trophic ecology and anatomy are more predictive than life history features. As long as the different groups (Resident and Transient aggregators) shared basic properties of body size, nutritional ecology and anatomy they manifest similar spawning behaviours regardless of whether they are protogynous or gonochoristic, exhibit short or long generation times or have slow or fast population turnover rates. A critical element in the evolution of spawning aggregations is proposed to be the rapid advection of eggs and larvae away from the reef environment. In addition the timing of spawning episodes may be linked to specific seasonal and climatic features of the ocean environment, a variant of the match/mismatch hypothesis developed to explain spawning patterns in clupeoid fishes. Neither larval retention nor broad dispersal are seen as critical elements in the evolution of spawning aggregations. It is hypothesized that differences in aggregate spawning patterns and their underlying processes will occur in the Pacific and Atlantic oceans, a reflection of the different histories, oceanic environments and habitat structures of these two ocean basins.

Cytology of terminally differentiated Epulopiscium mother cells.

Epulopiscium sp. type B, a member of the Firmicutes, is a large (up to 300 microm), cigar-shaped bacterial symbiont of surgeonfish that propagates itself by forming multiple intracellular offspring. This unusual form of reproduction is an apparent modification of a developmental program used by some Firmicutes to produce an endospore. At the onset of offspring formation, the Epulopiscium cell divides at both poles. The polar cells are engulfed by the larger mother cell and grow within the mother cell. At the final stages of development, the Epulopiscium mother cell lyses. Here we describe changes in Epulopiscium cell structure, focusing on mother cell DNA replication and cell death. DNA replication was examined by labeling cells with the nucleotide analog bromodeoxyuridine. As expected, DNA replication occurs in the developing offspring. However, well after passage of genetic information from parent to offspring is complete, DNA within the mother cell continues to replicate. Using fluorescence microscopy, we found that near the end of the offspring growth cycle, mother cell DNA disintegrates. The mother cell membrane and wall deteriorate as well. DNA replication within this terminally differentiated cell indicates the importance of mother cell nucleoids in cell maintenance and the development of offspring. The synchronized timing of mother cell deterioration within a population suggests that the Epulopiscium mother cell undergoes a programmed cell death. The programmed death of the mother cell may allow for the timely release of resources accumulated in the mother cell to provide nutrients to populations of these intestinal microbes and their host.

Refined bomb radiocarbon dating of two iconic fishes of the Great Barrier Reef

Refinements to the methodology of bomb radiocarbon dating made it possible to validate age estimates of the humphead wrasse (Cheilinus undulatus) and bumphead parrotfish (Bolbometopon muricatum). Age for these species has been estimated from presumed annual growth zones in otoliths at ,30 and ,40 years respectively. The validity of these estimates was tested using bomb radiocarbon dating on the small and fragile otoliths of these species, and provided an opportunity to refine the method using advanced technologies. A regional D 14 C reference record from hermatypic coral cores from the Great Barrier Reef was assembled and D 14 C measurements from extracted otolith cores of adult otoliths were successful. Validated ages supported the accuracy of growth zone derived ages using sectioned sagittal otoliths. Additional keywords: Australia, Bolbometopon muricatum, bumphead parrotfish, carbon-14, Cheilinus undulatus, humphead wrasse, Labridae, micromilling, otolith.