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     

Contrasting rates of coral recovery and reassembly in coral communities on the Great Barrier Reef

Changes in the relative abundances of coral taxa during recovery from disturbance may cause shifts in essential ecological processes on coral reefs. Coral cover can return to pre-disturbance levels (coral recovery) without the assemblage returning to its previous composition (i.e., without reassembly). The processes underlying such changes are not well understood due to a scarcity of long-term studies with sufficient taxonomic resolution. We assessed the trajectories and time frames for coral recovery and reassembly of coral communities following disturbances, using modeled trajectories based on data from a broad spatial and temporal monitoring program. We studied coral communities at six reefs that suffered substantial coral loss and subsequently regained at least 50 % of their pre-disturbance coral cover. Five of the six communities regained their coral cover and the rates were remarkably consistent, taking 7–10 years. Four of the six communities reassembled to their pre-disturbance composition in 8–13 years. The coral communities at three of the reefs both regained coral cover and reassembled ten years. The trajectories of two communities suggested that they were unlikely to reassemble and the remaining community did not regain pre-disturbance coral cover. The communities that regained coral cover and reassembled had high relative abundance of tabulate Acropora spp. Coral communities of this composition appear likely to persist in a regime of pulse disturbances at intervals of ten years or more. Communities that failed to either regain coral cover or reassemble were in near-shore locations and had high relative abundance of Porites spp. and soft corals. Under current disturbance regimes, these communities are unlikely to re-establish their pre-disturbance community composition.     

Relationships between temperature, bleaching and white syndrome on the Great Barrier Reef

Coral bleaching and disease have often been hypothesized to be mutually reinforcing or co-occurring, but much of the research supporting this has only drawn an implicit connection through common environmental predictors. In this study, we examine whether an explicit relationship between white syndrome and bleaching exists using assemblage-level monitoring data from up to 112 sites on reef slopes spread throughout the Great Barrier Reef over 11 years of monitoring. None of the temperature metrics commonly used to predict mass bleaching performed strongly when applied to these data. Furthermore, the inclusion of bleaching as a predictor did not improve model skill over baseline models for predicting white syndrome. Similarly, the inclusion of white syndrome as a predictor did not improve models of bleaching. Evidence for spatial co-occurrence of bleaching and white syndrome at the assemblage level in this data set was also very weak. These results suggest the hypothesized relationship between bleaching and disease events may be weaker than previously thought, and more likely to be driven by common responses to environmental stressors, rather than directly facilitating one another.     

Disturbance and the dynamics of coral cover on the Great Barrier Reef (1995-2009)

Coral reef ecosystems worldwide are under pressure from chronic and acute stressors that threaten their continued existence. Most obvious among changes to reefs is loss of hard coral cover, but a precise multi-scale estimate of coral cover dynamics for the Great Barrier Reef (GBR) is currently lacking. Monitoring data collected annually from fixed sites at 47 reefs across 1300 km of the GBR indicate that overall regional coral cover was stable (averaging 29% and ranging from 23% to 33% cover across years) with no net decline between 1995 and 2009. Subregional trends (10-100 km) in hard coral were diverse with some being very dynamic and others changing little. Coral cover increased in six subregions and decreased in seven subregions. Persistent decline of corals occurred in one subregion for hard coral and Acroporidae and in four subregions in non-Acroporidae families. Change in Acroporidae accounted for 68% of change in hard coral. Crown-of-thorns starfish (Acanthaster planci) outbreaks and storm damage were responsible for more coral loss during this period than either bleaching or disease despite two mass bleaching events and an increase in the incidence of coral disease. While the limited data for the GBR prior to the 1980's suggests that coral cover was higher than in our survey, we found no evidence of consistent, system-wide decline in coral cover since 1995. Instead, fluctuations in coral cover at subregional scales (10-100 km), driven mostly by changes in fast-growing Acroporidae, occurred as a result of localized disturbance events and subsequent recovery.     

Enhanced particle-feeding capacity of corals on turbid reefs (Great Barrier Reef, Australia)

Reef corals occur across a wide range of habitats, from offshore clear waters to nearshore sediment-laden environments. This study tests the hypothesis that corals from turbid nearshore areas have greater capacity to utilise suspended sediment as a food source than conspecifics from less turbid and midshelf areas. The hypothesis was tested on two common and widespread coral species on the Great Barrier Reef (Pocillopora damicornis and Acropora millepora). The particle clearance rates of samples from more turbid reefs were two-fourfold those of conspecifics from less turbid and midshelf reefs. Rates of sediment ingestion were generally a linear function of sediment load indicating no significant saturation within the concentration range of 1–30 mg dry weight l⁻¹. Estimated assimilation efficiency of particulate ¹⁴C varied between 50 and 80%, and was maximised for midshelf A. millepora at the lowest sediment concentration, suggesting that heterotrophy is more efficient in oligotrophic habitats. Based on feeding-response curves, assimilation efficiencies, and published records of ambient particle concentrations, representatives of these species on turbid inshore reefs are 10–20 times more heterotrophic on suspended sediment than their conspecifics on less turbid and midshelf reefs. Accepted: 7 September 1999     

Local variation in herbivore feeding activity on an inshore reef of the Great Barrier Reef

Threats to coral reefs may be manifested through an increase in macroalgae. Across the globe, phase-shifts from coral to macroalgal dominance have been reported from the Caribbean, Indian and Pacific Oceans. While the Great Barrier Reef (GBR) is in relatively good condition, inshore reefs may exhibit over 50% macroalgal cover. However, our understanding of the processes preventing the macroalgal expansion remains uncertain. Using a remote video bioassay approach, this study quantified herbivory in three bays along the leeward margin of Orpheus Island. Despite significant with-in bay variation in herbivory there was no detectable statistical difference in the rates of herbivory among bays. Furthermore, of the 45 herbivore species recorded from the island, only three played a significant role in bioassay removal, Siganus canaliculatus, Siganus javus and Kyphosus vaigiensis, with only one species predominating in each bay. Reefs of the GBR may therefore be more vulnerable than previously thought, with the removal of macroalgae depending on just a few species, which exhibit considerable spatial variability in their feeding behaviour.     

Linkages between coral assemblages and coral proxies of terrestrial exposure along a cross-shelf gradient on the southern Great Barrier Reef

Coral core records, combined with measurements of coral community structure, were used to assess the long-term impact of multiple environmental stressors on reef assemblages along an environmental gradient. Multiple proxies (luminescent lines, Ba/Ca, δ¹⁵N) that reflect different environmental conditions (freshwater discharge, sediment delivery to the nearshore, nutrient availability and transformations) were measured in Porites coral cores collected from nearshore reefs at increasing distance from the intensively agricultural region of Mackay (Queensland, Australia). The corals provide a record (1968–2002) of the frequency and intensity of exposure to terrestrial runoff and fertilizer-derived nitrogen and were used to assess how the present-day coral community composition may have been influenced by flood-related disturbance. Reefs closest to the mainland (5–32 km offshore) were characterized by low hard coral cover (≤10%), with no significant differences among locations. Distinct annual luminescent lines and elevated Ba/Ca values (4.98 ± 0.63 μmol mol⁻¹; mean ± SD) in the most inshore corals (Round Top Island; 5 km offshore) indicated chronic, sub-annual exposure to freshwater and resuspended terrestrial sediment that may have historically prevented reef formation. By contrast, corals from Keswick Island (32 km offshore) indicated episodic, high-magnitude exposure to Pioneer River discharge during extreme flood events (e.g., 1974, 1991), with strongly luminescent lines and substantially enriched coral skeletal δ¹⁵N (12–14‰). The reef assemblages at Keswick and St. Bees islands were categorically different from all other locations, with high fleshy macroalgal cover (80.1 ± 7.2% and 62.7 ± 7.1%, respective mean ± SE) overgrowing dead reef matrix. Coral records from Scawfell Island (51 km offshore) indicated little exposure to Pioneer catchment influence: all locations from Scawfell and further offshore had total hard and soft coral cover comparable to largely undisturbed nearshore to middle shelf reefs of the southern Great Barrier Reef.     

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.     

Diet overlaps and feeding relationships between the year classes in the yellow perch (Perca flavescens)

Synopsis A comparative study of the diets of five year classes of perch in Lake Opinicon showed Year class 0 to be mainly Cladocera feeders, the Year class 11 to take a diversified range of insect larvae, whereas from Year class V onwards Anisoptera nymphs, decapods, and fish dominated the diet. Sizes of the dominant food items changed strikingly with growth, prey weights of 0.1, 0.5–1.0, and 100–250 mg predominating in these three age groupings. There were marked month to month changes in types and proportions of different prey consumed.Overall and month to month feeding overlaps between consecutive year classes were considerable, most values ranging from 0.68–1.0 by the Levins formula. However, diet overlap dropped sharply with increasing age gap.Month to month dietary changes and year class differences were interpreted relative to benthic invertebrate abundance cycles. Months of increased diet overlap were characteristically those when favored prey types peaked, thereby simultaneously attracting several year classes to them. Hence increased diet. overlap is not necessarily an indicator of increased intraspecific competition.Habitat differences between the year classes of perch in Lake Opinicon were partial and concerned mainly the smaller, and larger, fish relative to those in the middle size range.     

Large-scale spatial variability in bioerosion of experimental coral substrates on the Great Barrier Reef (Australia): importance of microborers

To study the effects of terrigenous inputs on rates of bioerosion by grazers and micro- and macroborers, two inshore sites, one mid-shelf site, two outer barrier sites, and one site located in the Coral Sea were selected along a cross-shelf transect (200 km from onshore to offshore) on the northern Great Barrier Reef. At each site, two grids were firmly attached to the substrate on which replicate experimental blocks, cut from live colonies of Porites sp., were laid in order to study the intra-site bioerosion variability as well as the variation between sites. After 1 year of exposure, rates of bioerosion were estimated using petrographic sections, scanning electron microscopy, and image analysis. Sites differed significantly. The lowest rates were found at the inshore sites (0.46ǂ.14 kg CaCO₃ m^-2 year^-1), while the highest rates were found at the outer barrier sites (3.6ǂ.52). The pattern of bioerosion exhibited at these six sites varied also, mainly due to different levels of bioerosion by grazers and microborers. Rates of macrobioerosion were low. We suggest that this was due to varying levels of terrigenous inputs, hydrographic patterns, and interactions between agents of bioerosion.     

Assessing loss of coral cover on the Great Barrier Reef: A response to Hughes et al. (2011)

Hughes et al. (Coral Reefs, 2011, in press) challenge our interpretations of the changes in coral cover observed on the Great Barrier Reef (GBR) between 1986 and 2004 (Sweatman et al. in Coral Reefs 30:521–531, 2011). They question whether we can accurately assign all causes of coral loss; we contend that this makes no difference to the observed changes. They defend the validity of historical data on coral cover from before the start of systematic large-scale monitoring and conclude that coral cover has been declining since at least 1960, but we find no trend in the early data. We remain convinced that combining data collected at different spatial scales (quadrats and transects in the past mixed with more recent whole-reef averages from manta tows) are likely to overestimate decline, because whole-reef averages will very rarely reach the high cover values that can occur at the quadrat scale. Hughes et al. (Coral Reefs, 2011, in press) state that we dismiss runoff as a cause of ecosystem degradation; we defend our interpretations and dispute some of their examples. In summary, we stand by our conclusion that coral cover on the GBR declined in the period 1986–2004 but through localised and unsynchronised changes that included recovery.     

Evolutionary history of the butterflyfishes (f: Chaetodontidae) and the rise of coral feeding fishes

Of the 5000 fish species on coral reefs, corals dominate the diet of just 41 species. Most (61%) belong to a single family, the butterflyfishes (Chaetodontidae). We examine the evolutionary origins of chaetodontid corallivory using a new molecular phylogeny incorporating all 11 genera. A 1759‐bp sequence of nuclear (S7I1 and ETS2) and mitochondrial (cytochrome b) data yielded a fully resolved tree with strong support for all major nodes. A chronogram, constructed using Bayesian inference with multiple parametric priors, and recent ecological data reveal that corallivory has arisen at least five times over a period of 12 Ma, from 15.7 to 3 Ma. A move onto coral reefs in the Miocene foreshadowed rapid cladogenesis within Chaetodon and the origins of corallivory, coinciding with a global reorganization of coral reefs and the expansion of fast‐growing corals. This historical association underpins the sensitivity of specific butterflyfish clades to global coral decline.     

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.     

Epifaunal community structure in Acropora spp. (Scleractinia) on the Great Barrier Reef: implications of coral morphology and habitat complexity

The role of microhabitat in structuring epifaunal communities on four corals of varying morphology in the genus Acropora (A. millepora, A. hyacinthus, A. pulchra, A. formosa) was determined on two fringing reefs in the central Great Barrier Reef. Greater abundance and species richness of epifauna on tightly branched coral species in comparison to their rarity or absence on open-branched species suggests that protection afforded by complex habitats is important in structuring coral epifaunal communities. Within species, neither total colony space nor live surface area of corals was correlated with either the abundance or species richness of associated epifauna. However, space between branches significantly affected the size of Tetralia crabs associated with different coral species. Patterns in the size distribution of Tetralia on two species of Acropora suggest that crabs select coral hosts according to branch spacing, changing host species as they grow larger.     

The feeding behaviour of caterpillars (Manduca sexta) on tobacco and on artificial diet

ABSTRACT. Feeding behaviour of fifth instar tobacco hornworm caterpillars, Manduca sexta (Johansen) (Lepidoptera; Sphingidae), eating tobacco or artificial diet, is quantitatively described. The insects grow at the same rate on both foods. There is no daily rhythm of feeding behaviour. For most insects, feeding on either food occurs in bouts with the lengths of interfeed gaps and of feeding bouts appearing to be distributed randomly. However, in many insects there is a strong correlation between the length of a feeding period and that of the preceding non-feeding period.
The proportion of time spent feeding on tobacco is much greater than on artificial diet. On tobacco, feeding periods are separated by shorter interfeed gaps than on the artificial diet, while the rate of bout initiation is similar on either food.
On both tobacco and artificial diet, the proportion of time spent feeding increases as the fifth stadium proceeds. This is due to both longer feeding bouts and shorter gaps. The rate of food acquisition within bouts does not change during the stadium.     

The ecology of the visual pigments of snappers (Lutjanidae) on the Great Barrier Reef

The visual pigments in the retinal photoreceptors of 12 species of snappers of the genus Lutjanus (Teleostei; Perciformes; Lutjanidae) were measured by microspectrophotometry. All the species were caught on the Great Barrier Reef (Australia) but differ in the colour of the water in which they live. Some live in the clear blue water of the outer reef, some in the greener water of the middle and inshore reefs and some in the more heavily stained mangrove and estuarine water. All the species had double cones, each member of the pair containing a different visual pigment. Using Baker's and Smith's (1982) model to predict the spectral distribution of ambient light from chlorophyll and dissolved organic matter it was found that the absorption spectra of the visual pigments in the double cones were close to those that confer the maximum sensitivity in the different water types. Single cones contained a blue or violet-sensitive visual pigment. The visual pigments in the rods showed little variation, their wavelength of maximum absorption always being in the region 489–502 nm.Abbreviations DOC dissolved organic carbon - DOM dissolved organic material - MSP microspectrophotometry deceased     

Macroalgae, nutrients and phase shifts on coral reefs: scientific issues and management consequences for the Great Barrier Reef

 Degradation of coral reefs often involves a “phase shift” from abundant coral to abundant macroalgae. This paper critically reviews the roles of nutrient increases in such phase shifts. I conclude that nutrient overloads can contribute to reef degradation, but that they are unlikely to lead to phase shifts simply by enhancing algal growth rates and hence allowing overgrowth of corals, unless herbivory is unusually or artificially low. Concentrations of dissolved inorganic nutrients are poor indicators of reef status, and the concept of a simple threshold concentration that indicates eutrophication has little validity. I discuss the significance and consequences of these assessments for reef management, focusing on the Great Barrier Reef, and conclude with some specific recommendations, including protection of herbivorous fishes, minimisation of terrestrial runoff, and protection of coastal reefs. Accepted: 13 August 1999     

Ten microsatellite loci for the reef‐building coral Acropora millepora (Cnidaria,Scleractinia) from the Great Barrier Reef,Australia

Here we present nine novel, polymorphic microsatellite loci developed for the scleractinian coral Acropora millepora (Acroporidae) from the Great Barrier Reef. In addition, we have assessed the specificity and polymorphism of five microsatellite loci previously developed for a Caribbean congener and one locus developed for an Indo‐Pacific congener. Only one of the latter six loci produced reliable results, yielding a total of 10 polymorphic microsatellite loci for A. millepora. Variability was tested on 20–23 individuals from a single population, plus another ～10 individuals from each of three different populations, resulting in five to 20 alleles per locus.     

Defensive strategies of soft corals (Coelenterata: Octocorallia) of the Great Barrier Reef

Summary The relationship between ichthyotoxicity and predation-related defensive functional morphology was examined in alcyonacean soft corals of the central and northern regions of the Great Barrier Reef (GBR), Australia. Approximately 170 specimens were assessed encompassing a number of genera within three families: 1) the Alcyoniidae (Lobophytum, Sarcophytum, Sinularia, Cladiella, Parerythropodium, and Alcyonium); 2) Neptheidae (Lemnalia, Paralemnalia, Capnella, Lithophyton, Nephthea, Dendronephthya, Scleronephthya, and Stereonephthya), and 3) Xeniidae (Anthelia, Efflatounaria, Cespitularia, Heteroxenia, and Xenia). Ichthyotoxicity data were derived from earlier studies which used Gambusia affinis Baird and Girard (Vertebrata, Pisces) as a test organism. These data were compared to morphological data collected from specimens in the field and laboratory. Three sets of statistical analyses were performed, each considering a progressively narrower group of taxa. The first included 68 specimens and considered 16 morphological characters in each, falling into the general categories of gross colony form, colony texture, presence of mucus, colony color, polyp retractility, and sclerite morphology and distribution. These were tested for independence against ichthyotoxicity data. The second set of analyses involved a more restricted morphological data set derived from 28 species of Sinularia in combination with 28 species within the Nephtheidae, comparing them to their respective toxicity ranks. The third analysis considered the previous two taxonomic groups separately in relation to their toxicity levels.The attempt to consider many morphological characters in a taxonomically diverse collection did not reveal any general association in the Alcyonacea between defensive morphology and toxicity, and those associations which did emerge were clearly erroneous. The second analysis, considering only Sinularia spp. and nephtheids, demonstrated a negative association between ichthyotoxicity and the morphological characters of a) polypary armament, b) microarmament of the individual polyp, and c) strong mineralization of the coenenchyme. The third analysis revealed that the negative association found between toxicity and the first two characters was derived entirely from the nephtheids while the association detected between toxicity and the third character was restricted to Sinularia. It is concluded that a relationship between toxicity and morphology can be demonstrated, but it is heavily dependent upon which specific morphological characters are being considered and at what level of taxonomic resolution the analysis is being performed. An approach utilizing many characters over many taxa is unlikely to yield significant, reliable, or meaningful results.Australian Institute of Marine Science Contribution Number 383