Complex patterns of population structure and recruitment of <Emphasis Type="Italic">Plectropomus leopardus</Emphasis> (Pisces: Epinephelidae) in the Indo-West Pacific: implications for fisheries management

Here the population genetic structure of an ecologically and economically important coral reef fish, the coral trout Plectropomus leopardus, is investigated in the context of contemporary and historical events. Coral trout were sampled from four regions (six locations) and partial mtDNA D-loop sequences identified six populations (Fst = 0.89209, P < 0.0001): Scott Reef and the Abrolhos Islands in west Australia; the Great Barrier Reef (GBR), represented by northern and southern GBR samples; New Caledonia and Taiwan, with Taiwan containing two genetic lineages. Furthermore, this study identified source and sink populations within and among regions. Specifically, the northern population in west Australia (Scott Reef) was identified, as the source for replenishment of the Abrolhos population, whilst New Caledonia was a source for recruitment to the GBR. Based on these insights from a single mtDNA marker, this study will facilitate the development of rational management plans for the conservation of P. leopardus populations and therefore mitigate the risk of population declines from anthropogenic influences.     

Temporal dynamics and plasticity in the cellular immune response of the sea fan coral, Gorgonia ventalina

The temporal dynamics of the invertebrate immune response often determines an organism’s success in responding to physiological stress, physical damage, and pathogens. To date, most immune challenge studies have been conducted under highly controlled laboratory conditions, with few attempts to study immune function in the wild. In this study, we characterized the temporal dynamics of the Caribbean sea fan, Gorgonia ventalina, cellular immune response [granular amoebocyte aggregation and prophenoloxidase (PPO) activation] to allogenic grafts in the laboratory and field using a clonally replicated design. Amoebocyte reaction time differed markedly between the lab (% amoebocyte surface area in tissue sections peaked at 2 days) and field (peak at 6 days). PPO activity decreased between 0 and 6 days after grafting in both ungrafted and grafted tissue, suggesting PPO is decoupled from other cellular components. The reaction norms of the fold induction in % amoebocyte area between disease-grafted and healthy-grafted tissue of each colony across time indicate high intercolony plasticity in cellular immune response. The plasticity between colonies was also evident in the magnitude of cellular immune response, ranging from a 0.88- to 1.60-fold increase in amoebocyte area between initial and 6 days for the disease-grafted tissue. With the demonstration of highly dynamic cnidarian cellular immune responses, our study expands understanding of the evolutionary ecology of metazoan immune defense mechanisms.     

Symbiont specificity and bleaching susceptibility among soft corals in the 1998 Great Barrier Reef mass coral bleaching event

Considerable variability in bleaching was observed within and among soft coral taxa in the order Alcyonacea (Octocorallia: Cnidaria) on the central Great Barrier Reef (GBR, latitude 18.2°–19.0°S, longitude 146.4°–147.3°E) during the 1998 mass coral bleaching event. In April 1998, during a period of high sea surface temperatures, tissue samples were taken from bleached and unbleached colonies representative of 17 soft coral genera. The genetic identities of intracellular dinoflagellates (Symbiodinium spp.) in these samples were analyzed using PCR-denaturing gradient gel electrophoresis fingerprinting analysis of the internal transcribed spacer regions 1 and 2. Alcyonaceans from the GBR exhibited a high level of symbiont specificity for Symbiodinium types mostly in clade C. A rare clade D type (D3) was associated only with Clavularia koellikeri, while Nephthea sp. hosted symbionts in clade B (B1n and B36). Homogenous Symbiodinium clade populations were detected in all but one colony. Colonies that appeared bleached possessed symbiont types that were genetically indistinguishable from those in nonbleached conspecifics. These data suggest that parameters other than the resident endosymbionts such as host identity and colony acclimatization are important in determining bleaching susceptibility among soft corals. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Algal overgrowth of alcyonacean soft corals

Colonies of the soft coral Lobophytum pauciflorum (Ehrenberg, 1834) (Coelenterata: Octocorallia: Alcyonacea: Alcyoniidae), some of which were heavily overgrown by the algae Ceranium flaccidum (Kuetzing) Ardissone and Enteromorpha sp., and other minor epizoites, were collected at Taylor Reef (17°50S; 146°35E) in the Great Barrier Reef. Overgrown colonies contained the diterpene 2-epi-sarcophytoxide as the major secondary metabolite, while conspecific colonies with clean polyparies contained two diterpenes in approximately equal amounts: 14-hydroxycembra-1,3,7,11-tetraene and 15-hydroxycembra-1,3,7,11-tetraene. By contrast, twenty conspecific pairs of overgrown and clean colonies of other alcyoniid soft corals collected from Pelorus Channel, Palm Island Group (18°34S; 146°29E), showed no chemical differences within in the pairs. Cultures of a common species of Ceramium [C. codii (Richards) Mazoyer] were incubated with different concentrations of nine soft-coral-derived diterpenes and significant algal growth inhibition was observed in many cases. It appears that terpenoids from soft coral may contribute to the lack of epizoic organisms on soft-coral polyparies.     

Variation in colony geometry modulates internal light levels in branching corals, <Emphasis Type="Italic">Acropora humilis</Emphasis> and <Emphasis Type="Italic">Stylophora pistillata</Emphasis>

Colonial photosynthetic marine organisms often exhibit morphological phenotypic plasticity. Where such plasticity leads to an improved balance between rates of photosynthesis and maintenance costs, it is likely to have adaptive significance. To explore whether such phenotypic plasticity leads to more favourable within-colony irradiance for reef-building branching corals, this relationship was investigated for two coral species Acropora humilis and Stylophora pistillata, along a depth gradient representing light habitats ranging from 500 to 25 μmol photons m⁻² s⁻¹, during 2006 at Heron Island, Great Barrier Reef (23.44°S, 151.91°E). In the present study changes in flow-modulated mass transfer co-varied with light as a function of depth. In low-light (deep) habitats, branch spacing (colony openness) in A. humilis and S. pistillata was 40–50% greater than for conspecifics in high-light environments. Also, branches of A. humilis in deep water were 40–60% shorter than in shallow water. Phenotypic changes in these two variables lead to steeper within-colony light attenuation resulting in 38% higher mean internal irradiance (at the tissue surface) in deep colonies compared to shallow colonies. The pattern of branch spacing was similar for S. pistillata, but this species displayed an alternate strategy with respect to branch length: shade adapted deep and cave colonies developed longer and thinner branches, allowing access to higher mass transfer and irradiance. Corals in cave habitats allowed 20% more irradiance compared to colonies found in the deep, and had a 47% greater proportion of irradiance compared to colonies in the shallow high-light environment. Such phenotypic regulation of internal light levels on branch surfaces partly explains the broad light niches of many branching coral species. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Fecundity of red coral <Emphasis Type="Italic">Corallium rubrum</Emphasis> (L.) populations inhabiting in contrasting environmental conditions in the NW Mediterranean

In this study, we examined the variability and potential patterns of fecundity in the precious Mediterranean red coral Corallium rubrum (L. 1758). A total of 12 populations were selected from the NW Mediterranean Sea. We used a hierarchical sampling design to explore fecundity patterns associated with different environmental conditions found in different cave zones (entrance vs. interior), depths (15–22 vs. 39–42 m), and geographic locations (Côte Bleue vs. Calanques). Overall, 240 apical tips from colonies (10 male + 10 female colonies per population) were analyzed. Fecundity ranged between 1.0 ± 0.7 and 3.2 ± 2.3 mature gonads per polyp in female colonies and between 2.5 ± 1.6 and 6.9 ± 2.5 mature gonads per polyp in male colonies. The fecundity of red coral varied significantly for populations dwelling in different cave zones and geographic areas but not for the examined depths. Our results contribute to the knowledge of red coral fecundity in populations not yet studied in the NW Mediterranean and elucidate significant variability in fecundity within different environmental conditions. The information on coral fecundity can contribute to the development of management and conservation plans for red coral populations.     

Impacts of cyclone Hamish at One Tree Reef: integrating environmental and benthic habitat data

The southern Great Barrier Reef (GBR), a region that rarely experiences cyclones, was impacted by tropical cyclone (TC) Hamish in March 2009. We documented on-reef physical and habitat conditions before, during and after the cyclone at One Tree Reef (OTR) using data from environmental sensor instrumentation and benthic surveys. Over 5 years of monitoring, ocean mooring data revealed that OTR experienced large swells (4–8 m) of short duration (10–20 min) not associated with a cyclone in the area. These swells may have contributed to the physical disturbance of benthic biota and decline in coral cover recorded prior to and after TC Hamish. During the cyclone, OTR sustained southeasterly gale force winds (>61.2 km h⁻¹) for 18.5 h and swells >6 m in height for 4 h. Benthic surveys of exposed sites documented a 20% drop in live coral cover, 30% increase in filamentous algae cover and the presence of dislodged corals and rubble after the storm. Leeward sites were largely unaffected by the cyclone. Benthic cover did not change in the lagoon sites. Significant rubble movement and infill of the lagoon occurred. Two years after the cyclone, algal cover remained high and laminar corals had not recovered. Total coral cover at impacted sites had continued to decline. Environmental conditions and habitat surveys supported Puotinen’s (Int J Geogr Inf Sci 21:97–120, 2007) model for cyclone conditions that cause reef destruction. While TC Hamish had a major impact on the reef, change in benthic cover over several years was due to multiple stressors. This on-reef scale integration of physical and biological data provided a rare opportunity to assess impacts of a major storm and other disturbances, showing the importance of considering multiple stressors (short-lived and sustained) in assessing change to reef habitats.     

Reproduction,recruitment and fragmentation in nine sympatric species of the coral genus Acropora

Multispecies assemblages of the coral genus Acropora occur commonly throughout the Indo-Pacific Ocean. Nine species from such an assemblage comprising 41 species of Acropora, at Big Broadhurst Reef on the Great Barrier Reef, were studied during 1981–1983. Similarities and differences in reproductive modes and timing, oocyte dimensions and fecundity, recruitment by larvae and by fragments, and mortality were recorded. All species had an annual gametogenic cycle, were simultaneous hermaphrodites, and had the same arrangement of gonads in polyps. In six species, most colonies released gametes on the same night of the year, in early summer, during a mass spawning event involving many coral genera. A seventh species had colonies spawning at this as well as other times of the year. Another species spawned in late summer, and gametes were not observed to mature in the last species. Eggs were very large (601 to 728 m geometric mean diameter) and fecundity of polyps low, compared with other corals; no reduction in oocyte numbers occurred during oogenesis. Reef-flat species had slightly bigger and fewer eggs than reef-slope species. All species recruited by larvae, but four also multiplied by fragmentation, either year-round or during occasional rough weather. Yearround fragmenters had few larval recruits; non-fragmenters had many, and a rough-weather fragmenter had an intermediate number of larval recruits. It was concluded that larval recruitment largely determined species composition, and that reduced larval recruitment was responsible for sparse distribution of fragmenting species. Subsequent mortality in some species and increase by fragmentation in others probably determined relative abundances.     

Survey of deep-dwelling red coral (<Emphasis Type="Italic">Corallium rubrum</Emphasis>) populations at Cap de Creus (NW Mediterranean)

The distribution and population structure of the eurybathic gorgonian Corallium rubrum were studied off Cap de Creus (Costa Brava, Northwestern Mediterranean Sea). Red coral is endemic to the Mediterranean Sea and the adjacent NE Atlantic coast, where it has been over exploited for centuries. This study presents, the first quantitative data on the spatial distribution and structure of a population extending between 50 (common SCUBA limits) and 230 m depth, and compared it with shallow populations previously studied in the same area. Different remotely operated vehicles (ROV) and two methodological approaches were employed during four cruises between 2002 and 2006: 1-Extensive surveys: sea to coast transects in which red coral density and patch frequency were recorded; 2-Intensive surveys, in which parameters describing colony morphology were recorded. Most of the hard substrate between 50 and 85 m depth was inhabited by red coral colonies, showing a patch frequency of 8.3 ± 7.9 SD patches per 100 m-transect (total transect area: 34 m²), and within-patch colony densities of 16–376 colonies m⁻² (mean of 43 ± 53 colonies m⁻²). Below 120 m depth red coral was less abundant, and rather than forming dense patches as in shallow water, isolated colonies were more common. The population structure differed between sites that are easily accessible to red coral fishermen, and remote ones (both at similar depth, 60–80 m), as colonies in easily accessible locations were smaller in height and diameter, and showed a less developed branching pattern. At shallower locations (10–50 m depth) the population structure was significantly different from those at deeper locations, due to the heavy harvesting pressure they are exposed to in the shallows. Twenty-five to forty-six percentage of the deeper colonies were taller than 6 cm, while only 7–16% of the shallow water colonies exceeded 6 cm colony height. Forty-six to seventy-nine percentage of the colonies in deeper waters were large enough to be legally harvested, while only 9–20% of the shallow water colonies met the 7 mm legal basal diameter to be collected. The branching pattern was also better developed in deeper colonies, as up to 16% of the colonies showed fourth order branches, compared to less than 1% of the shallow water colonies (of which 96% consisted of only one single branch). The results thus confirm that C. rubrum populations above 50 m depth are exposed to a higher harvesting intensity than deeper populations in the same area.     

Seasonality of coral reproduction in the Dampier Archipelago,northern Western Australia

Coral spawning in Western Australia (WA) occurs predominantly in the austral autumn in contrast to the Great Barrier Reef (GBR) on Australia’s east coast where most spawning occurs in spring. Recent work, however, suggests a second spawning period in northern WA with at least 16 Acropora spp spawning in spring or early summer. This discovery has initiated a re-examination of reproductive seasonality in northern WA, particularly on inshore reefs adjacent to large development projects, such as the site of this study in Mermaid Sound, in the Dampier Archipelago. Three locally abundant taxa, Porites spp, Pavona decussata and Turbinaria mesenterina were sampled monthly from September 2006 to May 2007 to determine sexuality, the mode of reproduction and the time of gamete maturity. All three taxa were gonochoric broadcast spawners. Porites spp. colonies were mature in November and December, P. decussata in March and April. In contrast, most colonies of T. mesenterina contained mature gametes for up to 5 months beginning in November, suggesting either individuals are releasing gametes on multiple occasions, or they retain mature gametes for more than 1 month. Field surveys to determine the reproductive status of the remaining coral assemblage were conducted prior to the full moon in October 2006 and March 2007. Only four species contained mature gametes in October 2006. In contrast, 55 species contained mature gametes in March 2007. We conclude that the major spawning season of corals on shallow-inshore reefs in the Dampier Archipelago is autumn, although taxa that spawn in spring and summer include Porites spp., Acropora spp. and possibly T. mesenterina that are numerically dominant at many of these sites. Consequently, management initiatives to limit the exposure of coral spawn to stressors associated with coastal development may be required in up to five months per year.     

Longitudinal variations of coral reef features in the Marine National Park,Gulf of Kachchh

The Gulf of Kachchh is characterised by a strong tidal variation and the reef communities are capable of higher exposure time during negative tides. About 11 sites located along the Marine National Park (MNP) from west to east were studied for assessing the present status of live coral cover along with other life-form categories. In the present study, the maximum live coral cover was recorded in Pirotan Island, followed by Laku Point, Mithapur and Boriya reef. Multivariate analyses such as Principal Component Analysis and Correspondence Analysis supported that the contribution of live coral cover was more towards Pirotan Island whereas the contribution of coral species cover was more towards Laku Point. Bray-Curtis cluster analysis categorized all the study sites into four major clusters with 78 % similarity based on life-form categories. Among them, two clusters from western region (one forming site from Mithapur Reef to Lakku Point and another one forming from Ashaba Gugar Reef to Dabdaba Island), the third one combines the western and eastern regions (Boriya Reef to Kalubar Island), the fourth one comprises the eastern region (Narara Reef to Sikka), and one outlier Pirotan Island. Based on coral species cover, two major clusters with 55 % similarity were formed. Among them, one cluster was formed from Pirotan Island to Kalubar Island in the eastern side of MNP and the second one comprised the western region of MNP (Boriya Reef to Laku Point), and one outlier Mithapur Reef. Thirty one species of live corals belonging to 8 families and 18 genera were recorded in the Marine National Park itself during the study period.     

First evidence of gender-related differences in immune parameters of the clam Ruditapes philippinarum (Mollusca, Bivalvia)

For the first time, gender-related differences in some important functional parameters of haemocytes from the clam Ruditapes philippinarum have been studied. Clams were collected during the pre-spawning phase, when sex can be distinguished by microscopic observation of gonadal smears, in order to ascertain whether the two sexes reach the stressful spawning period with different degrees of immunosurveillance. Total haemocyte count (THC), haemocyte size frequency distribution, capability of haemocytes to assume the vital dye neutral red (NR, indicative of endocytotic activity), lysozyme-like and acid phosphatase activities in both haemocyte lysate (HL) and cell-free haemolymph (CFH), and superoxide dismutase (SOD) and catalase (CAT) activities in HL were all evaluated. No differences in THC values were found between the two sexes, but differing haemocyte size frequency distributions were observed: the fraction of larger haemocytes (7–9 μm diameter, 200 fl volume) was markedly increased in females and that of smaller haemocytes (<5 μm diameter, <200 fl volume) markedly increased in males. Interestingly, when haemocytes were observed under the light microscope, a significantly higher percentage of granulocytes was found in haemolymph from females, compared with that of males. Significantly increased NR uptake was recorded in female haemocytes. No significant variation in lysozyme-like activity was observed in HL, whereas in CFH, enzyme activity was significantly higher in females. HL acid phosphatase activity was significantly higher in males with respect to females; no significant variations in enzyme activity were observed in CFH. HL SOD and CAT activities were significantly higher in females than in males. Overall, on the basis of the cell parameters studied here, gender-related differences in immune parameters were found in R. philippinarum, indicating that females have more active haemocytes than males during the pre-spawning period.     

In situ thermal dynamics of shallow water corals is affected by tidal patterns and irradiance

We studied the diel variation of in situ coral temperature, irradiance and photosynthetic performance of hemispherical colonies of Porites lobata and branching colonies of Porites cylindrica during different bulk water temperature and tidal scenarios on the shallow reef flat of Heron Island, Great Barrier Reef, Australia. Our study presents in situ evidence that coral tissue surface temperatures can exceed that of the surrounding water under environmental conditions typically occurring during low tide in shallow reef or lagoon environments. Such heating may be a regular occurrence on shallow reef flats, triggered by the combined effects of high irradiance and low water flow characteristic of low Spring tides. At these times, solar heating of corals coincides with times of maximum water temperature and high irradiance, where the slow flow and consequent thick boundary layers impede heat exchange between corals and the surrounding water. Despite similar light-absorbing properties, the heating effect was more pronounced for the hemispherical P. lobata than for the branching P. cylindrica. This is consistent with previous laboratory experiments showing the evidence of interspecific variation in coral thermal environment and may result from morphologically influenced variation in convective heat transfer and/or thermal properties of the skeleton. Maximum coral surface warming did not coincide with maximum irradiance, but with maximum water temperature, well into the low-tide period with extremely low water flow in the partially drained reef flat, just prior to flushing by the rising tide. The timing of low tide thus influences the thermal exposure and photophysiological performance of corals, and the timing of tidally driven coral surface warming could potentially have different physiological impacts in the morning or in the afternoon.     

Using three-dimensional surface area to compare the growth of two Pocilloporid coral species

Many facets of coral research require coral colony surface area estimates. This study developed a relationship between the two-dimensional (2D) projected area and the three-dimensional (3D) whole colony surface area for two commonly studied Indo-Pacific coral species: Pocillopora damicornis and Stylophora pistillata. The surface index function was used to measure the growth of colonies in situ around Heron reef on the southern Great Barrier Reef. The results show that while growth between the two species was not significantly different when measured in two dimensions, the 3D area showed significantly different growth rates with S. pistillata growing at almost double the rate of P. damicornis. The study demonstrates that it is possible to make reliable estimates of the 3D surface area of entire colonies of these complex branching coral species, using the plan view of the coral and a pre-determined surface index function. In addition, this study shows that the 3D surface area provides a more useful measure of colony growth than the traditional methods of either 2D area or longest dimension.     

Steps in the construction of underwater coral nursery, an essential component in reef restoration acts

Many coral reefs worldwide are rapidly declining, but efficient restoration techniques are not yet available. Here, we evaluate methodologies for reef restoration based on the “gardening concept”. A floating mid-water prototype nursery was placed at 6 m depth (14 m above sea-bottom) within the nutrient-enriched environment of a fish farm (Eilat, Red Sea). Ten colonies from five branching coral species provided 6,813 fragments (0.5–3 cm height). The fragments, each attached to a plastic pin, were inserted into plastic nets that were tied to a rope-net floating nursery. After 144 nursery days, only 13.1% of the fragments died and 21.2% were detached by mechanical forces. Small colonies ready for transplantation developed within 144–200 days. Ramets’ ecological volumes increased 13–46 folds and their heights by a factor of 3.5. After 306 days, the ecological volumes of the colonies increased 147–163 fold as compared to original volumes (revealing a daily growth rate constant of 1.67% during the first 5–10 months) and height values by a factor of six. Building and maintenance costs of the nursery were low. This nursery prototype demonstrates the feasibility of the coral “gardening concept” by fulfilling several important needs, namely, mass production of coral colonies at low costs, high survivorship, fast growth, short nursery phase and improved methodologies for handling farmed colonies.     

Predators selectively graze reproductive structures in a clonal marine organism

Although the fitness consequences of herbivory on terrestrial plants have been extensively studied, considerably less is known about how partial predation impacts the fitness of clonal marine organisms. The trophic role of Caribbean parrotfish on coral reefs is complex: while these fish are important herbivores, as corallivores (consumers of live coral tissue), they selectively graze specific species and colonies of reef-building corals. Though the benefits of parrotfish herbivory for reef resilience and conservation are well documented, the negative consequences of parrotfish grazing for coral reproductive fitness have not been previously determined. We examined recently grazed colonies of Montastraea annularis corals to determine whether grazing was positively associated with coral reproductive effort. We measured gonad number, egg number and size, and proportional reproductive allocation for grazed and intact coral colonies 2–5 days prior to their annual spawning time. We found that parrotfish selectively grazed coral polyps with high total reproductive effort (number of gonads), providing the first evidence that parrotfish selectively target specific tissue areas within a single coral colony. The removal of polyps with high reproductive effort has direct adverse affects on coral fitness, with additional indirect implications for colony growth and survival. We conclude that chronic grazing by parrotfishes has negative fitness consequences for reef-building corals, and by extension, reef ecosystems.     

Coral mortality following extreme low tides and high solar radiation

Extreme tidal events are one of the most predictable natural disturbances in marine benthic habitats and are important determinants of zonation patterns in intertidal benthic communities. On coral reefs, spring low tides are recurrent disturbances, but are rarely reported to cause mass mortality. However, in years when extremely low tides coincide with high noon irradiances, they have the potential to cause widespread damage. Here, we report on such an event on a fringing coral reef in the central Great Barrier Reef (Australia) in September 2005. Visual surveys of colony mortality and bleaching status of more than 13,000 corals at 14 reef sites indicated that most coral taxa at wave-protected sites were severely affected by the event. Between 40 and 75% of colonies in the major coral taxa (Acropora, Porites, Faviidae, Mussidae and Pocilloporidae) were either bleached or suffered partial mortality. In contrast, corals at wave-exposed sites were largely unaffected (<1% of the corals were bleached), as periodic washing by waves prevented desiccation. Surveys along a 1–9 m depth gradient indicated that high coral mortality was confined to the tidal zone. However, 20–30% of faviid colonies were bleached throughout the depth range, suggesting that the increase in benthic irradiances during extreme low tides caused light stress in deeper water. Analyses of an 8-year dataset of tidal records for the area indicated that the combination of extended periods of aerial exposure and high irradiances occurs during May–September in most years, but that the event in September 2005 was the most severe. We argue that extreme low-tide, high-irradiance events are important structuring forces of intertidal coral reef communities, and can be as damaging as thermal stress events. Importantly, they occur at a time of year when risks from thermal stress, cyclones and monsoon-associated river run-off are minimal.     

Depth-dependent responses to solar ultraviolet radiation and oxidative stress in the zooxanthellate coral Acropora microphthalma

Colonies of Acropora microphthalma (Verrill 1869) were transferred from depths of 2 to 3, 10, 20, and 30 m to UV-transparent and UV-opaque respirometry chambers placed at 1 m depth at Bowl Reef, Great Barrier Reef, in March 1989. Peak rates of photosynthesis in colonies originating at 2 and 10 m were unaffected by solar ultraviolet (UV) radiation at 1 m, whereas photosynthesis showed 30 and 38% inhibition in colonies transferred from 20 and 30 m, respectively. This differential sensitivity of corals to UV radiation was consistent with the five- to tenfold higher concentrations of UV-absorbing, mycosporine-like amino acids (MAAs, putative defenses against UV) in 2- and 10-m colonies compared with 20- and 30-m colonies. Photosynthesis in zooxanthellae freshly isolated from 2- and 10-m corals, however, was inhibited by UV, indicating that the host's tissues, which contain 95% of the total MAAs in corals at these depths, are the first line of defense against solar UV and provide protection to their endosymbiotic algae. The general bathymetric decline in the activities of the antioxidant enzyme superoxide dismutase (SOD) in the host, and SOD, catalase, and ascorbate peroxidase in the zooxanthellae, is related to the decrease in potential for photooxidative stress with increasing depth.     

Population structure, growth and recruitment of the euryalinid brittle-star Astrobrachion constrictum (Echinodermata: Ophiuroidea) in Doubtful Sound, Fiordland, New Zealand

The euryalinid brittle-star (snake star) Astrobrachion constrictum (Farquhar) lives coiled around the branches of black coral (Antipathes fiordensis) colonies. Twenty-two vertical transects, 10 m wide by 30 m deep, were swum in Doubtful Sound over a 2.5 yr period from 1993 to 1995. Numbers, disc diameters and colour morphotypes of brittle-stars inhabiting coral colonies were recorded. 36.3% of the coral colonies >200 mm tall (n = 292) hosted ≥1 Astrobrachion constrictum (range 0 to 12). Overall, the population was patchily distributed on the available coral habitat. The dark red colour morphotype of A. constrictum was most common (87%, n = 279) followed by the yellow, striped, and then spotted varieties. The population was comprised mainly of large (≥10 mm disc diam) individuals, and juveniles were rarely encountered, indicating low rates of recruitment or a high mortality of recruits. Disc-diameter data gathered from this and previous studies indicated that growth in A. constrictum is initially rapid, with individuals reaching a disc diameter of 15 mm in ≃2.5 yr; growth decreases with age, as in other deep-sea ophiuroids. Growth rate within years, however, was not constant, with faster growth in the spring/summer. Maximum size for A. constrictum is reached in ≃8 yr at ˜23 mm disc diam. Anecdotal evidence indicates that A. constrictum may not be confined solely to black coral colonies. Received: 25 September 1996 / Accepted: 16 October 1996     

The basics of acidification: baseline variability of pH on Australian coral reefs

Ocean acidification is one of the key threats facing coral reef ecosystems, but there are few estimates of spatial and temporal variability in pH among reef habitats. The present study documents levels of spatial variability in pH among coral reef habitats (9 to 10), among locations separated by 100’s km of latitude and between east (Great Barrier Reef, GBR) and west (Ningaloo Reef) coasts of Australia. Differences were found in pH between inshore and offshore waters along Ningaloo Reef (means 8.45, 8.53, respectively). Replicate assessments here ranged from 8.22 to 8.64. On the GBR, the range of values over all habitats and replicates was 0.39 pH units (7.98 to 8.37). There were minor but significant differences of 0.05 pH units between 5 consecutive days for habitats on average. Highest pH was recorded in filamentous algal beds maintained by the damselfish Dischistodus perspicillatus. Lowest pH was found in water extracted from sand-dwelling goby holes. While there were marked changes in pH over a 48-h sampling period among 4 habitats at Lizard Island (GBR), there was little evidence of a diel trend. Understanding how pH varies at scales that are relevant to organisms that live on shallow coral reefs is crucial for the design and interpretation of experiments that test the effects on organisms of the changes in water chemistry predicted to affect oceans in the future.