Vertical distribution of fish larvae in the Great Barrier Reef Lagoon,Australia

To investigate the natural defenses of Antarctic marine organisms against exposure to ultraviolet (UV) radiation (280 to 320 nm), 57 species (1 fish, 48 invertebrates, and 8 algae) were collected during austral spring 1988 in the vicinity of Palmer Station (Anvers Island, Antarctic Peninsula) and were analyzed for the presence of mycosporine-like amino acids (MAAs), compounds that absorb UV radiation and may provide shielding from these biologically hazardous wavelengths. Nearly 90% of the 57 species examined contained MAAs, and eight specific MAA compounds were identified. Seven of these (palythine, porphyra-334, shinorine, mycosporineglycine, palythene, asterina-330, and palythinol) have been observed previously in marine organisms from temperate and tropical latitudes. A new MAA, mycosporineglycine: valine, was found in the Antarctic fish and in 38 of the invertebrate species examined. This study confirms widespread occurrence of MAAs in Antarctic marine organisms and suggests that these species have some degree of natural biochemical protection from UV exposure.Contribution No. 502 from the Australian Institute of Marine Science     

Cross-shelf distribution of copepods and fish larvae across the central Great Barrier Reef

The distribution of total dry weight of zooplankton, copepod numbers and ichthyoplankton across the outer continental shelf in the central Great Barrier Reef was examined at bi-weekly intervals for three months over summer of 1983. Copepods were sampled (236 m net) within 10 m of the surface and within 10 m of the bottom. Mean densities in surface waters decreased markedly from the mid-shelf to outer shelf and the Coral Sea, but no cross-shelf gradient occurred in the bottom-water. Densities of copepods on the mid-shelf (surface and bottom waters) and in bottom-waters of the outer shelf were typically ca. 400 m^–3. Significantly lower densities (ca. 100 m^–3) occurred in surface waters of the outer shelf, except during outbursts of Acartia australis, when densities in these waters differed little from those elsewhere on the shelf. In oceanic waters, 10 km from the outer shelf station, copepod densities in surface waters were ca. 40 m^–3. Four of the five most abundant copepod taxa in surface waters, Paracalanus spp., Eucalanus crassus, Acrocalanus gracilis and Canthocalanus pauper, tended to be most abundant at the mid-shelf end of the transect. Acartia australis was sporadically very abundant in surface waters of the outer shelf, as was Paracalanus spp. in bottom-water of the outer shelf. An assemblage of Coral Sea species of copepod occurred in bottom-water of the outer shelf during two major intrusions, but not at other times. Densities of all common species varied considerably between cruises. Maximum densities of all common species except A. australis tended to be associated with diatom blooms linked to intrusions but a bloom did not necessarily mean all common species were abundant. Fish larvae included both reef and non-reef taxa, with reef taxa predominating on the outer shelf (approx 2:1 in density of individuals) and non-reef taxa dominating in nearshore samples (approx 2:1). Nine of the ten most abundant taxa analysed showed highly significant variation in numbers among stations and all but one of these also exhibited significant station x cruise interactions. Interactions generally reflected changes in the rank importance of adjacent stations from one cruise to the next or lack of any significant cross-shelf variation on some cruises where overall abundance of the taxa was low.     

Coral-spawn slicks in the Great Barrier Reef: preliminary observations

Aerial surveys and surface samples in the spring of 1985, showed that slicks of coral eggs and embryos (coral spawn) formed in large numbers within and between reefs in the Central Great Barrier Reef Region. Coral-spawn slicks appeared on the days immediately following the annual mass multispecific spawning of reef corals. They were white or pink in colour, and were often highly elongate in form extending up to 5 km in length, and 10 m in width. Over 99% of each slick sampled during the surveys consisted of dead eggs, embryos and their breakdown products, which formed dense, highly viscous patches readily recognizable during aerial surveys. Despite the low proportion of live material, the slicks contained high concentrations of live embryos (15 to 230 per litre) which were over two orders of magnitude greater than concentrations in adjacent water masses. The distinctive colour, shape and texture of the coral-spawn slicks generally distinguished them from slicks formed by blooms of the blue-green alga Oscillatoria erythraea, which also occur commonly in the region. Many of the slicks were closely associated with surface oceanographic features, such as fronts between water parcels, and wakes and eddies behind reefs. Although more detailed sampling and surveys are required, these results suggest that it may be possible to track the movements of coral embryos and larvae directly for the first one or two days following mass spawning, and indirectly thereafter by monitoring other surface features.     

Composition of the near-reef zooplankton at Heron Reef,Great Barrier Reef

Using a light trap, zooplankton was sampled at three stations at Heron Reef, Great Barrier Reef: (a) a typical patch reef in the Heron lagoon, (b) a site in 8 m water on the southern slope of Heron reef, and (c) a station approximately 300 m south of (b), in the open water of the channel between Heron and Wistari reefs. Samples were taken at the surface and on the substratum at the lagoon and reef-slope stations, and at 3 to 6 m depth at the open-water station. A total of 114 taxa, many recognized as species, were distinguished in the samples. Pronounced differences existed in abundance, diversity, and taxonomic composition of the samples obtained at different stations. Less pronounced differences existed between surface and substratum samples from the same station. Near-reef samples were more similar to one another than to open-water samples. Decapod larvae, amphipods, and cumaceans were all abundant in near-reef samples and very rare in open-water samples. Forams, isopods, mysids and polychaetes were common in near-reef samples, and rare or absent in open-water samples. Copepods were abundant in all samples but the near-reef samples contained predominantly different species than did samples from the open water. The near-reef fauna included 66 taxa which did not occur in open-water samples. Many of these were epibenthic rather than strictly planktonic in behaviour.     

Zooplankton community structure and water flow in the lee of Helix Reef (Great Barrier Reef, Australia)

To investigate which physical processes contribute most in moulding zooplankton community structure in the waters close to coral reefs, light traps moored in a grid pattern were used to collect zooplankton from the sea surface at 16 stations on the downstream side of Helix Reef during three time periods (2100-2200, 2400-0100, and 0300-0400 hours) over three consecutive nights covering the new moon period in January 1992. Two distinct zooplankton communities were present: a community composed primarily of reef-resident, demersal plankton immediately to the south of the reef in an area of reduced flushing, and a community containing coastal and shelf-seas taxa at the more exposed sites in the open flow field. The fauna composition at a number of exposed stations was as rich as that at sheltered stations both in terms of number of taxa and diversity indices but was almost an order of magnitude less abundant. The reef-resident, demersal plankton community was dominated by gammarid amphipods, mysids, and polychaetes, whereas only transient, meroplanktonic forms such as echinoderm and echinopluteus larvae and shelf-seas, holoplanktonic forms such as doliolids and larvaceans were significantly more abundant in the exposed community. Zooplankton associations were apparently formed by a combination of hydrodynamic processes, spatial and temporal distribution patterns of individual taxa, specific behaviours of certain taxa, and the interactions among taxa at different trophic levels.     

Effects of herbivory on zonation of Sargassum spp. within fringing reefs of the central Great Barrier Reef

A combination of small-scale transplants and herbivore exclusion was used to test the importance of herbivory, physiological tolerance limits, and recruitment and dispersal in regulating the distribution and abundance of the genus Sargassum on two nearshore fringing reefs of the central Great Barrier Reef, during 1992/1993. Sargassum (predominantly S. oligocystum and S. tenerrimum) were transplanted from reef-flat zones where they normally grow, to a seaward coral zone where they are not normally found. At Great Palm Island, coral-zone transplants only survived if protected from herbivores. At Brook Island, survival of uncaged coral-zone transplants was more variable but not significantly lower than plants returned to the Sargassum zone. Thus herbivory may be a major cause of the zonation patterns of adult Sargassum on these fringing reefs, but the importance of this factor varies between and within reefs. Since protected Sargassum survived and grew for up to 6 mo in the coral zone, the adult algae are not physiologically limited by any physical or chemical differences between zones. However, Sargassum recruitment to the coral zone was very low (mean 2.7 recruits m⁻² over 13 mo), and was not significantly affected by herbivores. Since rates of herbivory were relatively slow, effective exclusion of Sargassum from the coral zone by herbivores may depend on low recruitment of the algae. In a broader context, the distribution of Sargassum may depend on the combined spatial patterns of herbivory and recruitment. Received: 24 January 1997 / Accepted: 12 May 1997     

Distribution,abundance, and substrate preferences of demersal reef zooplankton at Lizard Island Lagoon,Great Barrier Reef

Demersal zooplankton, those plankton which hide within reef sediments during the day but emerge to swim freely over the reef at night, were sampled quantitatively using emergence traps planced over the substrate at Lizard Island Lagoon, Great Barrier Reef. Densities of zooplankton emerging at night from 6 substrate types (fine, medium, and coarse sand, rubble, living coral and reef rock) and from 5 reef zones (seaward face, reef flat, lagoon, back reef, and sand flat) were determined. A large population of nocturnal plankton including cumaceans, mysids, ostracods, shrimp, isopods, amphipods, crustacean larvae, polychaetes, foraminiferans and copepods are resident members of the reef community at Lizard Island. The mean density of plankton emerging throughout the reef was 2510±388 (standard error) zooplankton/m² of substrate. Biomass averaged 66.2±5.4 mg ash-free dry weight/m² of substrate. Demersal zooplankton exhibited significant preferences for substrate types and reef zones. The highest mean density of zooplankton emerged from coral (11,264±1952 zooplankton/m²) while the lowest emerged from reef rock (840±106 zooplankton/m²). The density of demersal plankton was six times greater on the face than in any other zone, averaging 7900±1501 zooplankton/m². Copepods dominated samples collected over living coral and rubble while foraminiferans, ostracods and decapod larvae were most abundant from sand. Plankton collected with nets at night correlated only qualitatively with plankton collected in emergence traps from the same location. Although abundant, demersal plankton were not numerous enough to meet the metabolic needs of all corals at Lizard Island Lagoon. Demersal plankton appear especially adapted to avoid fish predation. The predator-avoidance strategies of demersal plankton and maintenance of position on the reef are discussed. Our results indicate that much of the zooplankton over coral reefs actually lives on the reef itself and that previous studies using standard net sampling techniques have greatly underestimated plankton abundance over coral reefs.     

Rates of nitrogen fixation on coral reefs across the continental shelf of the central Great Barrier Reef

This study was undertaken in 1981 to determine whether there were major variations in potential rates of nitrogen fixation on apparently bare coralline substrate from reefs across the continental shelf of the central Great Barrier Reef. Nitrogen fixation, measured as rates of ethylene production (nmol cm^-2h^-1), was significantly lower on substrata from two inner-shelf reefs, (0.46 and 1.07) than on two middle-shelf reefs (2.10 and 2.97) and on two outer-shelf reefs (3.20 and 3.81). By contrast, algal biomass (mg cm^-2) on experimental substrate was significantly higher on inner-shelf reefs (80.8 and 59.4) than on middleshelf (27.1 and 23.8) and outer-shelf reefs (26.4 and 22.4). The rate of nitrogen fixation was positively correlated with the proportion of bare substratum and significantly higher concentrations of dissolved inorganic nitrogen were found in waters over the reefs than in water flowing onto those reefs. The abundance of algal-grazing fishes was reported previously to be significantly lower on inner-shelf reefs. It is suggested that this cross-shelf variation in the activity of algal-grazing fishes may be a determinant of the observed cross-shelf variations in potential nitrogen fixation.Contribution No. 233 from the Australian Institute of Marine Science     

The distribution of herbivorous fishes on the Great Barrier Reef

The composition and functionality of ecologically important herbivorous fish assemblages were examined throughout much of Australia’s Great Barrier Reef (GBR). Diversity and abundance of surgeonfishes (Acanthuridae), parrotfishes (Labridae) and rabbitfishes (Siganidae) were strongly associated with position on the continental shelf, whilst effects of latitude were weaker and inconsistent. Species distributions varied considerably amongst taxonomic groups; parrotfishes were mostly widespread whilst distributions of surgeonfishes were often restricted. Most inshore environments supported depauperate herbivore assemblages dominated by different taxa and functional groups compared with assemblages in offshore environments. There were also strong cross-shelf transitions in the main taxa performing each functional role. Overall, this study show that the functional contributions of herbivorous fish assemblages to important ecosystem processes and the contributing taxa vary considerably amongst different GBR environments. Additionally, the two most numerically dominant herbivores actively select detritus, not algae, supporting increasing evidence for the importance of detritus in coral reef ecology.     

Effect of monsoonal climate on sulfate reduction in coastal sediments of the central Great Barrier Reef lagoon

Rates of sulfate reduction were measured during the spring dry and summer wet seasons of 1992 in shallow coastal sediments of the central Great Barrier Reef lagoon. In the dry season, sulfate reduction rates, integrated to 18–20 cm depth, ranged from 23.8 to 30.8 mmol S m^-2 d^-1. In the wet season, heavy monsoonal rains and wind-induced waves caused severe disturbance of sediments leading to less anoxic conditions, and to a 2- to 3-fold decline in rates of sulfate reduction (10.2 to 12.8 mmol S m^-2 d^-1). The percentage of reduced ³⁵S recovered as acid-volatile sulfide (% AVS_red) ranged from 15.8 to 44.9% in spring, and was significantly reduced at each station in summer (range 14.5 to 31.4%). An analysis of variance indicated that seasonality accounted for 31.5% of the total variance in total rates of sulfate reduction, with only 7.5% of the variance accounted for by depth into the sediment; there were no station differences. In both seasons, there were no clear patterns in the proportion of radiolabel incorporated into the AVS and chromium-reducible sulfur (CRS) pools with depth into the sediment. These results are contrary to the seasonal patterns and pathways of sulfate reduction in temperate coastal sediments.     

High genetic variability in a population of Tridacna maxima from the Great Barrier Reef

A population of the bivalve mollusk Tridacna maxima (Röding) from Hron Island, Great Barrier Reef, Australia, was studied by gel electrophoresis, and proved to be highly variable genetically, with an average heterozygosity of about 22%. This compares closely with a population of T. maxima from Enewetak (Eniwetok) Atoll, with an average heterozygosity of about 20%, very high for marine organisms. Enewetak Atoll was the site of a series of nuclear tests. The Heron Island study verifies that the high variability is natural, and supports the hypothesis that species from trophically stable environments tend to be highly variable genetically.     

Locomotion performance of green turtle hatchlings from the Heron Island Rookery,Great Barrier Reef

Locomotion performance plays a vital role in determining hatchling green turtle Chelonia mydas survival in the first few hours after emerging from their nests as hatchlings crawl and swim the gauntlet of predators before reaching the relative safety of the open ocean. Previous laboratory based constant incubation experiments found incubation temperature to influence the size and swimming performance of hatchling green turtles. Here we examine the morphology and crawling and swimming performance of hatchling green turtles as they emerge from nests on Heron Island rookery in the southern Great Barrier Reef to test the hypothesis that nest temperature in the field can influence these attributes. We found inter-nest differences in hatchling mass and dimensions, and that hatchling mass was not correlated with nest temperature. However, hatchlings from warmer nests had smaller carapace dimensions than hatchlings from cool nests suggesting that more yolk was converted to hatchling tissue during embryonic development in cool nests. There was considerable intra- and inter-nest variation in both crawling and swimming performance of hatchlings. Hatchlings from cool nests tended to be faster crawlers than hatchlings from warm nests, but the thrust produced during swimming was not correlated with nest temperature. During the 4 h swimming trial, hatchlings swimming effort decreased significantly during the first 3 h but swimming effort remained relatively constant for the last 1 h. Individual hatchling crawling and swimming performances were not correlated with each other. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Synchronous spawnings of 105 scleractinian coral species on the Great Barrier Reef

Following observations of mass spawning of hermatypic corals on the Great Barrier Reef in 1981 and 1982, spawning dates were successfully predicted and documented at five reefs on the Central and Northern Great Barrier Reef in 1983. During the predicted times, 105 species from 36 genera and 11 families were observed to spawn. Of these, 15 species were shown to have an annual gametogenic cycle. All but two of the species observed during mass spawnings shed gametes which underwent external fertilization and development. Synchronous spawning was observed both within and between the five reefs studied, which were separated by as much as 5° of latitude (500 km) or almost a quarter of the length of the Great Barrier Reef. The mass spawning of corals took place on only a few nights of the year, between the full and lastquarter moon in late spring. Maturation of gametes coincided with rapidly rising spring sea temperatures. Lunar and diel cycles may provide cues for the synchronization of gamete release in these species. The hour and night on which the greatest number of species and individuals spawned coincided with low-amplitude tides. Multispecific synchronous spawning, or mass spawning, of scleractinian and some alcyonacean corals represents a phenomenon which is, so far, unique in both marine and terrestrial communities.     

Sperm ultrastructure of the giant clam Tridacna maxima (Tridacnidae: Bivalvia: Mollusca) from the Great Barrier Reef

Using transmission electron microscopy, spermatozoa from a member of the Tridacnidae, or giant clams, are described for the first time and compared with spermatozoa of other bivalves, especially other heterodonts. The acrosomal vesicle of Tridacna maxima (Röding, 1798) is short (0.37?μm), blunt-conical, and exhibits a prominent basal ring. A narrow apical elaboration of the nucleus, the nuclear peg, projects deep into the basal invagination of the acrosomal vesicle. Aside from this specialization, the nucleus is a solid elongate-cylindrical structure (7.66?μm) that exhibits several small irregular lacunae. Four or occasionally three round-ovate mitochondria surround a pair of orthogonally-arranged, triplet-substructure centrioles. The proximal centriole is connected to a small indentation of the nuclear base by a thin layer of granular pericentriolar material, whereas the distal centriole is anchored to the plasma membrane by nine terminally-forked satellite fibres. The 9?+?2 pattern axoneme of the tail is continuous with the distal centriole. Comparison with other bivalves indicates a very close relationship between tridacnids and cardiids based on sperm ultrastructure. Specifically, the presence of a nuclear peg links Tridacna spp. with the cardiid genus Cerastoderma, but further information on the many unstudied genera is required to test the exact nature of this relationship. The sperm ultrastructure provides additional support for the recently proposed hypothesis that the Tridacnidae may be no more than a specialized subfamily of the Cardiidae.     

Uptake and clearance of diesel alkanes from sediments by the Great Barrier Reef gastropod Strombus luhuanus

Sediments from the reef flat at Heron Island, Great Barrier Reef, were treated with known amounts of diesel and the uptake and clearance characteristics of the diesel n-alkanes by the gastropod Strombus luhuanus, in the field and aquaria, were measured. In each case, the uptake curve was unusual in that the concentration, expressed in terms of wet weight, reached a maxima within 24 h and then declined to relatively low levels. The maximum concentrations reached were below that in the sediments. Within the range investigated, the alkanes exhibited a substantial decline in the uptake rate-constant with increasing carbon number, tricosane exhibiting approximately 25% of the uptake rate-constant of dodecane. On the other hand, persistence, measured as the half-life, showed an increase with carbon number. Dodecane had a half life of 0.6 d and octadecane one of 2.2 d.     

Vertical profiles of bacterial abundance,productivity and growth rates in coastal sediments of the central Great Barrier Reef lagoon

Vertical patterns of bacterial densities, productivity and specific growth rates in coastal muds, quartz sands and muddy sands of the central Great Barrier Reef lagoon were examined in summer (February) and autumn (May) 1988. Variations in these parameters with station location, sediment depth and season were complex, exhibiting significant main and interaction effects in most instances. Some trends were apparent despite the large and complex variations. Bacterial densities did not vary seasonally, ranging from 2.9 to 38.1×10⁹ cells g^-1 dry wt, averaged over sediment depth (0 to 20 cm) and seasons. Trend analysis revealed that densities decreased with increasing sediment depth. Bacterial production (tritiated thymidine incorporation into DNA) was high, ranging from 0.4 to 5.7 gCm^-2 d^-1 (integrated over 10 cm depth), as were specific growth rates (grand mean, =0.25 d^-1; range=0.004 to 1.3 d^-1). Both were generally higher in summer than in autumn. Vertical profiles of productivity and specific growth rates revealed actively growing bacterial assemblages down to 20 cm depth. Factors which may account for these very abundant and productive communities are: (1) subsurface accumulations of detritus exported from adjacent mangrove forests, and (2) physical disturbance from tidal scouring and severe climate (e.g. cyclones, wet-season floods). Disturbance events occur frequently enough to inhibit the development of highly sulphidic conditions, but stimulate production of bacterial types (aerobes, fermenters) capable of incorporating labelled thymidine into their DNA.     

Zoning,a fundamental cornerstone of effective Marine Spatial Planning: lessons learnt from the Great Barrier Reef,Australia

The Great Barrier Reef Marine Park was established to provide for conservation and ecologically sustainable multiple use of 344,400 km² of a large marine ecosystem. Management is based on multiple use, with zoning as a fundamental component of marine spatial planning. The legislative framework, including a specific Act and Regulations, address the objectives of ecosystem-based, integrated management of human uses and impacts consistent with best contemporary understanding of biological diversity. Zoning is one of a suite of management tools that include other spatial and temporal management tools and non-spatial measures including public education, community engagement, codes of environmental best practice, industry partnerships and economic instruments. The first section of the Great Barrier Reef Marine Park came into operation in 1981 and the most recent zoning came into operation in mid 2004. The paper discusses some common misunderstandings about zoning and identifies lessons that appear relevant for others addressing management and use of marine ecosystems and natural resources.     

The use of clear-water non-estuarine mangroves by reef fishes on the Great Barrier Reef

Within the tropics, mangroves and coral reefs represent highly productive biomes. Although these habitats are often within close proximity, the role and importance of mangrove habitats for reef fish species remains unclear. Throughout the Indo-Pacific, reef fish species appear to have few links with estuarine mangrove habitats. In contrast, clear-water non-estuarine mangrove habitats throughout the Caribbean support many reef fish species and may be fundamental for sustaining reef fish populations. But how important are clear-water non-estuarine mangroves for reef fishes within the Indo-Pacific? Using visual surveys during diurnal high tide, the fish assemblages inhabiting clear-water mangrove and adjacent reef habitats of Orpheus Island, Great Barrier Reef, were recorded. Of the 188 species of fishes that were recorded, only 38 were observed to inhabit both habitats. Of these, only eight were observed more than five times within each habitat. These observations provide little indication that the clear-water mangroves are an important habitat for reef fish species. In addition, although based on just a 3-month survey period, we found little evidence to suggest that these areas are important nurseries for reef fish species. The clear-water mangroves of Orpheus Island may, however, provide an additional foraging area for the few reef fish species that were observed to utilize these habitats during high tide. The difference in the importance of clear-water mangroves for reef fishes within this study compared with clear-water mangrove counterparts within the Caribbean is surprising. Although only preliminary, our observations would support suggestions that the patterns reflect the different hydrological characteristics and evolutionary histories of these two biogeographic regions.     

Occurrence and characteristics of unusual protistan symbionts from surgeonfishes (Acanthuridae) of the Great Barrier Reef,Australia

The occurrence of unusual symbiotic microorganisms was examined in the intestines of a range of fish from the Great Barrier Reef, Australia. The fish taxa examined included 26 species of the family Acanthuridae, as well as representatives of phylogenetically related and herbivorous taxa. The microorganisms, referred to as protists, were only found in herbivorous and detritivorous members of the Acanthuridae. Protists were not found in planktivorous acanthurids, nor in any members of the families Kyphosidae, Pomacentridae, Scaridae, Zanclidae, Siganidae and Bleniidae we examined. In addition, protists were absent from the herbivorous acanthurids A. xanthopterus and A. nigricans. A range of protist forms, characterized by differences in size (8 to 417 m), shape and mode of cell division (daughter-cell production and binary fission), was observed. The occurrence of these forms appeared to be correlated with host feedingecology. Large forms (>100 m) of the protists were only found in acanthurids which fed over hard-reef substrata. Smaller forms were found in sand-grazing and detritivorous species. One of the protist forms appears identical to protists previously reported from Red Sea acanthurids.