Habitat preference in newly settled coral trout (Plectropomus leopardus, Serranidae)

 The densities of newly settled coral trout (Plectropomus leopardus, Pisces, Serranidae) were monitored in a variety of habitats on Green Reef in the Cairns section of the Great Barrier Reef to assess whether spatial patterns of recruitment are influenced by physical features of the substratum, and whether this species uses different habitats during its ontogeny. Surveys showed that small juveniles used sites that were significantly different from random and that these habitat associations changed as the fish grew larger. Specifically, coral trout recruited to level patches of rubble substrata >5 m² and subsequently shifted to high relief features. Densities of recruits were related to the amount of rubble substrata available. Accepted: 4 July 1996     

Spatial and temporal variation in predation on reef fishes by coral trout (Plectropomus leopardus,Serranidae)

The diet of coral trout Plectropomus leopardus (Serranidae) was studied over a two year period at One Tree Island, Great Barrier Reef, Australia. Rapid visual counts demonstrated that P. leopardus were most abundant on the reef slope habitat and inner edge of the enclosed lagoon. Few P. leopardus were found at sites from inner lagoon. It was hypothesized that diet would vary among habitats, times and size classes of coral trout. Ninety-two percent of P. leopardus that contained prey had consumed fish and 87% had only eaten fish. Many types of reef fish were taken by P. leopardus (e.g. Pomacentridae, Scaridae, Blenniidae and Labridae). Most pelagic prey (Clupeidae and Engraulididae) were taken on the reef slope, while some prey were solely or pimarily taken in the lagoon (e.g. Blenniidae and crustaceans). Most pelagic prey were taken on the reef slope in summer by P. leopardus>250 mm (SL). Plectropomus leopardus (<200 mm) from the lagoon had a higher proportion of invertebrates in the diet than fish from the reef slope. Plectropomus leopardus of all sizes ate small fish, while largest fish generally consumed largest prey (especially adult scarids and labrids). I argue that interactions among multiple species of prey and predators need more attention, because piscivores may respond to prey in different ways according to habitat type as well as the number and type of other prey types present. Furthermore, different sizes of fish (e.g. coral trout) may impact assemblages of prey in different ways.     

Reproduction of the inshore coral trout Plectropomus maculates (Perciformes: Serranidae) from the Central Great Barrier Reef, Australia

The reproductive biology of the serranid fish Plectropomus maculatus sampled from inshore waters of the Central Great Barrier Reef was studied based on histological analyses of gonad material. This species was shown to be a monandric protogynous hermaphrodite. The process of sex change foliowed the spawning period observed during September through November. Plectropomus: maculatus showed multiple spawning during this period. Sex change followed the usual protogynous mode with degeneration of ovarian germinal tissue accompanied by proliferation of male germinal tissue in the gonad. The sex structure of the sampled population was analysed based on age and size information. The size and age of first reproduction for females was 30.0cm s. L. and 2 years of age. The size and age of sex-transition was 35.4 cm s. L. and 4.4 years of age. The sex/size and sex/age relationships indicated that sex-change can occur over a broad range of sizes and ages. The sizes and age distributions of males and females P. maculates overlapped over 38% of the length range and over 42% of the maximum age observed.     

Effect of DNA extraction on ageing success in coral trout (Plectropomus leopardus) otoliths

To maximize the information commonly collected from otoliths, the effect of DNA extraction on the estimation of age with otoliths was evaluated by comparing sagittal otolith samples from common coral trout ( Plectropomus leopardus ) for clarity and ageing discrepancies in DNA-extracted and untreated control otoliths. The DNA extraction process had no significant effect, indicating that archived otoliths can be used as a source of DNA while retaining their utility for age estimation.     

Egg development, hatching and early life-history of Dissonus manteri (Copepoda), parasitic on the gills of coral trout, Plectropomus leopardus

The early life-history of Dissonus manteri differs markedly from that of Caligidae and from that of its congener Dissonus nudiventris. The uniseriate egg strings are of typical caligid form, but the stage hatching from the egg is a preecdysis nauplius which moults immediately to the copepodid. The empty naupliar cuticle remains tethered to the egg string by a pair of posterior threads which attach to the internal surface of the egg membrane. The duration of egg development is 112 h and the mean duration of hatching is 5.2 h at 25 degrees C. Aeration and water movement are important for successful hatching. Under these conditions, hatching success is 94.8%, but decreases to 48.4% in static water with no aeration. Mean survival time of the copepodid in the absence of a host is 41.4 h at 25 degrees C. The reduction of early free-living stages in the life-cycle and the high survival rate from egg to copepodid could be important in future coral trout aquaculture, since the potential for re-infection by this parasite is very high.     

Effects of region,demography, and protection from fishing on batch fecundity of common coral trout (Plectropomus leopardus)

Batch fecundity of female Plectropomus leopardus, a coral reef fish targeted by commercial and recreational fishing, was compared between reefs open to fishing and reefs within no-take marine reserves within three regions of the Great Barrier Reef (GBR), Australia. Length, weight, and age had positive effects on batch fecundity of spawners from northern and central reefs but negligible effects on spawners from southern reefs. Females were least fecund for a given length, weight, and age in the southern GBR. Batch fecundity of a 500-mm fork length female was 430 % greater on central reefs and 207 % greater on northern reefs than on southern reefs. The effects of length and age on batch fecundity did not differ significantly between reserve and fished reefs in any region, but weight-specific fecundity was 100 % greater for large 2.0 kg females on reserve reefs compared with fished reefs in the central GBR. We hypothesize that regional variation in batch fecundity is likely driven by water temperature and prey availability. Significant regional variation in batch fecundity highlights the need for understanding spatial variation in reproductive output where single conservation or fishery management strategies cover large, potentially diverse, spatial scales.     

Spatiotemporal patterns of coral disease prevalence on Heron Island,Great Barrier Reef,Australia

Despite increasing research effort on coral diseases, little is known about factors driving disease dynamics on the Great Barrier Reef (GBR). This is the first study to investigate the temporal patterns of coral disease prevalence and potential drivers of disease around Heron Island, in the southern Capricorn Bunker sector of the GBR. Surveys were conducted in two austral summers and three winters between November 2007 and August 2009 on six sites around the island. Six diseases were detected: brown band syndrome (BrB), growth anomalies (GA), ulcerative white spots (UWS), white syndrome (WS), skeletal eroding band disease (SEB) and black band disease (BBD). The lowest overall mean disease prevalence was 1.87 ± 0.75% (mean ± SE) in November 2007 and the highest 4.22 ± 1.72% in August 2008. There was evidence of seasonality for two diseases: BrB and UWS. This is the first study to report a higher prevalence of BrB in the winter. BrB had a prevalence of 3.29 ± 0.58% in August 2008 and 1.53 ± 0.28% in August 2009, while UWS was the most common syndrome in the summer with a prevalence of 1.12 ± 0.31% in November 2007 and 2.67 ± 0.52% prevalence in January 2008. The prevalence of GAs and SEB did not depend on the season, although the prevalence of GAs increased throughout the study period. WS had a slightly higher prevalence in the summer, but its overall prevalence was low (<0.5%). Sites with high abundance of staghorn Acropora and Montipora were characterised by the highest disease prevalence (12% of Acropora and 3.3% of Montipora species were diseased respectively). These results highlight the correlations between coral disease prevalence, seasonally varying environmental parameters and coral community composition. Given that diseases are likely to reduce the resilience of corals, seasonal patterns in disease prevalence deserve further research.     

Contrasting patterns of genetic structure in two species of the coral trout Plectropomus (Serranidae) from east and west Australia: introgressive hybridisation or ancestral polymorphisms

Inter-specific genetic relationships among regional populations of two species of grouper (Plectropomus maculatus and Plectropomus leopardus) were examined using mitochondrial and nuclear markers. mtDNA revealed contrasting regional inter-specific patterns whilst nuclear markers revealed contrasting patterns among markers, irrespective of region. In eastern Australia (EA) the species form a single mtDNA lineage, but the two species are reciprocally monophyletic in Western Australia (WA). This supports previous evidence for hybridisation between these species on the east coast. WA P. leopardus forms a sister relationship with the EA P. leopardus-maculatus clade while WA P. maculatus is more basal and sister to the P. leopardus lineages, indicating mtDNA does not suffer from incomplete lineage sorting for these species. In contrast, one of three nuclear markers (locus 7-90TG) differentiated the species into two reciprocally monophyletic clades, with no evidence of hybridisation or ancestral polymorphism. The remaining two nuclear markers (2-22 and ETS-2) did not separate these two species, while distinguishing other plectropomid species, suggesting incomplete lineage sorting at these nuclear loci. These results together with coalescence analyses suggest that P. leopardus females have hybridised historically with P. maculatus males and that P. maculatus mitochondria were displaced through introgressive hybridisation and fixation in the P. maculatus founder population on the Great Barrier Reef. The contrasting regional patterns of mtDNA structure may be attributed to Quaternary sea-level changes and shelf width differences driving different reef configurations on each coast. These reef configurations have provided opportunities for local scale interaction and reproduction among species on the narrower EA continental shelves, but not on the broader WA continental shelves.     

Spatial, temporal and habitat-related variation in the abundance of large predatory fish at One Tree Reef, Australia

 Patterns of abundance of large piscivorous fish (>200 mm TL) were documented at two spatial and four temporal scales within the main lagoon of One Tree Reef on Australia’s Great Barrier Reef. Grouper (Serranidae), snapper (Lutjanidae) and wrasses (Labridae) were the most abundant large piscivores. On a large scale (hundreds of metres), patterns of predator abundance were consistently greater on the inner edge than centre of the lagoon over a range of temporal scales: days, weeks, months and years. On a small spatial scale (tens of metres), the abundance of large predatory fish was patchy. At both spatial scales, fish were consistently aggregated in particular areas and associated with specific structural features of the reef habitat. Predator abundance was high where live corals were predominant and the topography was more complex. Hence, predation pressure and its potential effects on the distribution and abundance of prey populations, both in time and space, may vary greatly within lagoonal environments. Accepted: 25 May 1997     

Spatio-temporal variation in coral recruitment at different scales on Heron Reef, southern Great Barrier Reef

 Recruitment of scleractinian corals on settlement plates at Heron Island, Great Barrier Reef, was examined over four years (September 1991–September 1995) to quantify spatio-temporal patterns at different scales and to assess post settlement mortality. Recruitment was dominated by pocilloporid corals which accounted for 80.1% of the 8627 spat counted, whereas non-isoporan acroporids represented only 16.4%. Poritids, faviids and isoporan acroporids rarely recruited to the plates (3.5%), despite their obvious abundance as adults on the reef. Recruitment patterns on the plates indicate strong space-time interactions as evidenced by patchy recruitment of both pocilloporid and acroporid spat. Interactions were found between space (on the scale of 10² m, i.e. sites within zones, and 10¹ m, i.e. racks within sites) and time (on the scale of years) for pocilloporids and between space (on the scale of 10³ m, i.e. zones, and 10² m) and time (on the scale of years) for acroporids. Post-recruitment mortality of acroporid spat in the period 3–10 months after their major spawning was dependent on their initial recruitment density, but pocilloporid mortality was either independent of initial recruitment density or, more likely, obscured by additional recruitment of pocilloporids to plates between late February and September. High rates of recruitment and growth by other sessile organisms, particularly bryozoans and oysters, appear to result in increased post-recruitment mortality and limit recruitment of scleractinian corals on settlement plates. The work reinforces an emerging picture that coral recruitment patterns are determined by mechanisms that manifest over a large range of spatial scales. Accepted: 1 September 1997     

Temporal variation in the diet of a coral reef piscivore (Pisces: Serranidae) was not seasonal

Seasonal and smaller scale temporal variations in the diet of the large predatory grouper Plectropomus leopardus were examined on the central Great Barrier Reef, Australia. In 5 months over a 2-year period, 742 P. leopardus (₅ cm standard length) were collected for stomach content analysis. Despite intensive sampling, identified prey were spread over 20 families and much of the dietary variation was considered to be stochastic. Most aspects of the diet of P. leopardus did not vary seasonally. Frequency, rates of feeding, and proportion of fish consumed were consistent throughout the study. Size of fish prey did not vary significantly between seasons. Pomacentridae, Caesionidae, Scaridae, and Labridae were four of the five most important prey families consumed and did not vary seasonally in the diet. Prey in the other family, the small-sized schooling Clupeidae, were consumed sporadically among months with no seasonal patterns. One less common prey family variedseasonally in the diet; Synodontidae, which are small voracious predators of fish recruits, were consumed by P. leopardus more in summer than winter. Although the diet of P. leopardus is not influenced by the seasonal influx of small fishes recruiting to reefs, these large piscivores may indirectly improve recruit survival by consuming small and abundant predators of new recruits.     

Patterns of recruitment and microhabitat associations for three predatory coral reef fishes on the southern Great Barrier Reef, Australia

This study examined recruitment patterns and microhabitat associations for three carnivorous fishes, Plectropomus maculatus, Lutjanus carponotatus and Epinephelus quoyanus, at the Keppel Islands, southern Great Barrier Reef, Australia. Habitat selectivity was highest for recruits that were found mostly with corymbose Acropora, predominantly on patches of live coral located over loose substrates (sand). Adults were more commonly associated with tabular Acropora. The proportion of P. maculatus (72 %) found with live corals was higher than for L. carponotatus (68 %) and E. quoyanus (44 %). Densities of recruits were highly variable among locations, but this was only partly related to availability of preferred microhabitats. Our findings demonstrate that at least some carnivorous reef fishes, especially during early life-history stages, strongly associate with live corals. Such species will be highly sensitive to increasing degradation of coral reef habitats.     

Prosorhynchine trematodes (Digenea: Bucephalidae) from epinephelines (Perciformes: Serranidae) on the Great Barrier Reef,Australia

Six new species of bucephalid trematodes from the prosorhynchine bucephalid genera Prosorhynchus Odhner, 1905 and Neidhartia Nagaty, 1937 are reported from the epinepheline genera Cephalopholis, Cromileptes, Epinephelus and Variola on the Great Barrier Reef, Australia. Two species of Prosorhynchus and one of Neidhartia are reported from Epinephelus spp., P. jexi n. sp. from E. quoyanus, P. lafii n. sp. from E. fuscoguttatus and N. epinepheli n. sp. from E. maculatus. The other three new species are P. robertsthomsoni n. sp. from Cephalopholis argus, C. cyanostigma and C. miniata, P. conorjonesi n. sp. from Cromileptes altivelis, and P. milleri n. sp. from Variola louti. Extensive examinations of other piscivorous fish species from the Great Barrier Reef have not revealed these six bucephalid species, which appear to be restricted at least to the host genera from which they are reported here.     

Habitat associations of juvenile fish at Ningaloo Reef, Western Australia: the importance of coral and algae

Habitat specificity plays a pivotal role in forming community patterns in coral reef fishes, yet considerable uncertainty remains as to the extent of this selectivity, particularly among newly settled recruits. Here we quantified habitat specificity of juvenile coral reef fish at three ecological levels; algal meadows vs. coral reefs, live vs. dead coral and among different coral morphologies. In total, 6979 individuals from 11 families and 56 species were censused along Ningaloo Reef, Western Australia. Juvenile fishes exhibited divergence in habitat use and specialization among species and at all study scales. Despite the close proximity of coral reef and algal meadows (10's of metres) 25 species were unique to coral reef habitats, and seven to algal meadows. Of the seven unique to algal meadows, several species are known to occupy coral reef habitat as adults, suggesting possible ontogenetic shifts in habitat use. Selectivity between live and dead coral was found to be species-specific. In particular, juvenile scarids were found predominantly on the skeletons of dead coral whereas many damsel and butterfly fishes were closely associated with live coral habitat. Among the coral dependent species, coral morphology played a key role in juvenile distribution. Corymbose corals supported a disproportionate number of coral species and individuals relative to their availability, whereas less complex shapes (i.e. massive & encrusting) were rarely used by juvenile fish. Habitat specialisation by juvenile species of ecological and fisheries importance, for a variety of habitat types, argues strongly for the careful conservation and management of multiple habitat types within marine parks, and indicates that the current emphasis on planning conservation using representative habitat areas is warranted. Furthermore, the close association of many juvenile fish with corals susceptible to climate change related disturbances suggests that identifying and protecting reefs resilient to this should be a conservation priority.     

Responses of coral and fish assemblages to a severe but short-lived tropical cyclone on the Great Barrier Reef,Australia

Changes in reef assemblages of corals and fishes following a tropical cyclone were assessed using data sets from (1) manta tow surveys of entire reef perimeters and (2) intensive surveys of specific sites, across 11 reefs lying close to the cyclone's track. Only one of the reefs experienced an obvious and immediate decline in mean coral cover (from 24 to 8%) due to the cyclone. The abundance and species richness of adult damselfish assemblages on intensive survey sites at this reef were not affected in the short term (6-8 weeks), despite the removal of 48% of living hard coral. Assemblages of adult fishes showed a similar lack of response at three other reefs where no significant habitat changes had occurred. Eleven to twelve months later, the total abundance of damselfishes had decreased substantially at eight of the sampled reefs, while the abundance of larger mobile fishes remained stable. We infer that the effects on coral assemblages reflect the short duration and orientation of the cyclone, the history of exposure to wave energy (influencing life-form structure and therefore degree of fragility), and the degree of consolidation of the reef matrix. The lack of short-term effects of the cyclone on adult fishes shows that these fishes can endure periods of intense underwater turbulence. The lack of change in damselfish assemblages weeks after loss of coral cover implies that this resource was not limiting adult fish densities. The reasons for widespread decreases in damselfish numbers 11-12 months after the cyclone are unknown.     

Uptake of picophytoplankton,bacterioplankton and virioplankton by a fringing coral reef community (Ningaloo Reef,Australia)

We examined the importance of picoplankton and virioplankton to reef trophodynamics at Ningaloo Reef, (north-western Australia), in May and November 2008. Picophytoplankton (Prochlorococcus, Synechococcus and picoeukaryotes), bacterioplankton (inclusive of bacteria and Archaea), virioplankton and chlorophyll a (Chl a) were measured at five stations following the consistent wave-driven unidirectional mean flow path of seawater across the reef and into the lagoon. Prochlorococcus, Synechococcus, picoeukaryotes and bacterioplankton were depleted to similar levels (~40% on average) over the fore reef, reef crest and reef flat (=‘active reef’), with negligible uptake occurring over the sandy bottom lagoon. Depletion of virioplankton also occurred but to more variable levels. Highest uptake rates, m, of picoplankton occurred over the reef crest, while uptake coefficients, S (independent of cell concentration), were similarly scaled over the reef zones, indicating no preferential uptake of any one group. Collectively, picophytoplankton, bacterioplankton and virioplankton accounted for the uptake of 29 mmol C m⁻² day⁻¹, with Synechococcus contributing the highest proportion of the removed C. Picoplankton and virioplankton accounted for 1–5 mmol N m⁻² day⁻¹ of the removed N, with bacterioplankton estimated to be a highly rich source of N. Results indicate the importance of ocean–reef interactions and the dependence of certain reef organisms on picoplanktonic supply for reef-level biogeochemistry processes.     

The cercaria of Galactosomum bearupi Pearson, 1973 (Trematoda: Heterophyidae) at Heron and Masthead Islands,Great Barrier Reef,Australia

Magnacercous cercariae, all morphologically identical but with different coloured tails, were found naturally infecting the intertidal prosobranch gastropod Clypeomorus batillariaeformis Habe & Kosuge (Cerithiidae) at Heron and Masthead Islands. Several species of coral-dwelling fishes were exposed to magnacercous cercariae. Active ingestion by the fish, followed by the complete development of the metacercaria in the optic lobes, occurred in Pomacentrus molluccensis Bleeker, but not in Dascyllus aruanus (L.), where development stopped short after encystment. All cercariae turned out to belong to the same species, Galactosomum bearupi Pearson, 1973. Natural infections of G. bearupi metacercariae were found in eight species of fish at Heron Island: Pomacentrus molluccensis, P. wardi Whitley, P. bankanensis Bleeker, P. flavicauda Whitley, Stegastes cf. fasciolatus (Ogilby), Sillago maculata Quoy & Gaimard, S. cf. ciliata Cuvier and Crenimugil crenilabris (Forsskål). This represents the fourth account of the cercaria of a species of Galactosomum.     

The role of the predatory trahira (Pisces: Erythrinidae) in structuring fish assemblages in lakes of a Neotropical floodplain

We performed an experimental manipulation of trahira Hoplias aff. malabaricus in a series of isolated lakes of the upper Paraná River floodplain to evaluate its short-term impact on the structure of fish assemblages. The effects of trahira density (treatment groups: addition, removal, and reference) in two habitat categories (open and macrophyte-covered areas) on attributes of the fish assemblage structure were evaluated (using rm-ANOVA) over 120 days. Reductions in species richness were recorded in all assemblages and were more pronounced at the end of the experiment within macrophyte-covered areas of the lakes where H. aff. malabaricus was removed. In these lakes, the number of fish was also significantly smaller and evenness was significantly higher than in those in which trahira were added or maintained at natural densities. The increase of the relative abundance of all size classes over the first 60 days on the assemblages where trahira was present, and the decrease of the small-sized fish where trahira was absent contributed to the lack of pronounced alterations in total biomass. The absence of the predator from its preferred habitat was found to negatively affect the less abundant species, which seemed to be highly sensitive to the effects of interspecific competition among prey species. In addition to the well-known effects of hydrological seasonality, the role played by native predators might be important in determining the persistence of local species in the fish assemblages of Neotropical floodplains.     

Copepoda associated with the coral Gardineroseris planulata (Dana) on the Great Barrier Reef,northeastern Australia

Three new lichomolgid copepods associated with the scleractinian Gardineroseris planulata (Dana) are described: Sociellus torus, n. gen., n. sp., characterized by a 2-segmented endopod in leg 3 and the lack of an inner seta on the first segment of the endopod in legs 1–3; Odontomolgus pumilus, n. sp., of very small size and having a much elongated free segment in leg 5 of the female; and Paramolgus ampullaceus, n. sp., distinguished by the bottle-shaped genital segment of the female. In addition, the harpacticoid Alteuthellopsis corallina Humes, 1981, is reported from this coral. With the inclusion of 3 species of the poecilostomatoid genus Xarifia already described (Humes, 1985) there are now 7 species of copepods known to be associated with Gardineroseris planulata on the Great Barrier Reef.