Osprey Reef Research Articles

Response of reef corals and fish at Osprey Reef to a thermal anomaly across a 30 m depth gradient

Coral bleaching causes coral mortality that has knock-on effects on reef ecosystems, including reductions of some fish species. However, the extent of coral bleaching varies considerably among habitats. For example, deeper areas of reefs typically bleach less than areas in the shallows. However, rates of coral mortality at depth and the knock-on effects on other reef species are rarely documented. Here, we quantified the extent of coral bleaching and resulting mortality following a marine heat wave at Osprey Reef in the Coral Sea, Australia, along a depth gradient from 2 to 30 m. We also quantified the response of the associated reef fish assemblages. We found taxon-specific patterns in both bleaching and mortality, with some taxa bleaching less at depth, some bleached most at intermediate depths, and others exibiting no difference among depths. Similarly, bleaching-induced mortality varied among taxa and with depth. However, in the more abundant taxa (e.g. Acropora, Montipora and Porites), mortality was lower at greater depths. Reef fish assemblage structure had not changed 1 yr after bleaching. The relatively high incidence of bleaching at depth compared to other studies is likely due to high light penetration in the clear waters of the Coral Sea, suggesting corals in these habitats have a higher risk of bleaching during thermal anomalies. Nonetheless, corals capable of living in deeper waters appear more likely to have persisted through this severe bleaching event, while the fish assemblage did not change in response to the loss of live coral cover.

Nautilus: biology, systematics, and paleobiology as viewed from 2015

The natural history of the nautilid genus Nautilus, composed of a controversial number of extinct and extant species, has been the subject of scientific scrutiny for centuries. While a great research effort lasting from the mid-1970s to 1990s contributed vast amounts of new information concerning the evolutionary history, current diversity, mode of life, and ecological position in its habitats took place, since that time there has been far less concentrated research, and most of that has concerned the diversity and genetic distance of isolated populations using genetic techniques. In spite of the reprinting of one of the two 1987 books examining aspects of Nautilus biology, the only new field-based work on Nautilus until recently has been the important, Ph.D. thesis conducted by Andrew Dunstan on the isolated, seamount inhabiting nautiluses living on Osprey Reef, Australia. In this contribution we attempt to integrate Dunstan’s important new work with other, post-2010 research so as to update our current understanding of the evolutionary history (based on fossil as well as modern genetic work), characteristic habitats, mode of life, and physiology so as to give a 2015 perspective on those aspects of the natural history of Nautilus that are of paleobiological relevance.

Spatial patterns in the distribution of benthic assemblages across a large depth gradient in the Coral Sea, Australia

The Queensland Plateau in the Coral Sea off north-eastern Australia supports numerous submerged and emergent reefs. Osprey Reef is an emergent reef at the northern tip of the plateau ~1500 m in elevation. Over such a large depth gradient, a wide range of abiotic factors (e.g., light, temperature, substratum etc.) are likely to influence benthic zonation. Despite the importance of understanding the biodiversity of Australia’s Coral Sea, there is a lack of biological information on deep-water habitats below diving depths. Here, we used a deep-water ROV transect to capture video, still photos and live samples over a depth range spanning 92 to 787 m at North Horn on Osprey Reef. Video analysis, combined with bathymetry data, was used to identify the zones of geomorphology and the benthic assemblages along the depth gradient. There were marked changes in the geomorphology and the substrate along this depth gradient which likely influence the associated benthos. Cluster analysis indicated five benthic assemblage groups, which showed clear zonation patterns and were generally predictable based on the depth and sedimentary environment. These results are the first quantitative observations to such depths and confirm that the waters of the Coral Sea support diverse benthic assemblages, ranging from shallow-water coral reefs to mesophotic coral ecosystems, to deep-water azooxanthellate corals and sponge gardens. The knowledge provided by our study can inform management plans for the Coral Sea Commonwealth Marine Reserve that incorporate the deeper reef habitats and help to minimise future damage to these marine ecosystems.

The genetic structure of Nautilus pompilius populations surrounding Australia and the Philippines.

Understanding the distribution of genetic diversity in exploited species is fundamental to successful conservation. Genetic structure and the degree of gene flow among populations must be assessed to design appropriate strategies to prevent the loss of distinct populations. The cephalopod Nautilus pompilius is fished unsustainably in the Philippines for the ornamental shell trade and has limited legislative protection, despite the species' recent dramatic decline in the region. Here, we use 14 microsatellite markers to evaluate the population structure of N.pompilius around Australia and the Philippines. Despite their relative geographical proximity, Great Barrier Reef individuals are genetically isolated from Osprey Reef and Shark Reef in the Coral Sea (FST =0.312, 0.229, respectively). Conversely, despite the larger geographical distances between the Philippines and west Australian reefs, samples display a small degree of genetic structure (FST =0.015). Demographic scenarios modelled using approximate Bayesian computation analysis indicate that this limited divergence is not due to contemporary gene flow between the Philippines and west Australia. Instead, present-day genetic similarity can be explained by very limited genetic drift that has occurred due to large average effective population sizes that persisted at both locations following their separation. The lack of connectivity among populations suggests that immigrants from west Australia would not facilitate natural recolonization if Philippine populations were fished to extinction. These data help to rectify the paucity of information on the species' biology currently inhibiting their conservation classification. Understanding population structure can allow us to facilitate sustainable harvesting, thereby preserving the diversity of genetically distinct stocks.

Early Life History of Alatina cf. moseri Populations from Australia and Hawaii with Implications for Taxonomy (Cubozoa: Carybdeida, Alatinidae)

The early life stages of the cubomedusa Alatina cf. moseri from Osprey Reef (North Queensland, Australia) and Waikiki (Oahu, Hawaii) were studied using laboratory-based culturing conditions. Spawning populations from both regions were observed with reliable periodicity allowing polyp cultures from these locations to be collected and established under laboratory conditions. The polyps of this species were successfully reared from spawning adults. Polyps of Alatina cf. moseri were cultured at temperatures of 23–28°C, developed up to 19 tentacles and reached up to 1.70 mm in height. The balloon-shaped hypostomes possessed 4 well-defined lips. The polyps increased their numbers by means of formation of either sedentary polyp buds or creeping-polyp buds, which attached after 2–3 days. Metamorphosis occurred at temperatures of 25–28°C. Development of polyps and medusae were achieved for the first time within the genus Alatina and allowed comparisons of early life history between these and other species of the Carybdeida families. The metamorphosis and young medusa of this genus showed characters that differed distinctly from those noted for other Carybdeida species, but are very similar to the one described from Puerto Rico by Arneson and Cutress in 1976 for Alatina sp. (named by them Carybdea alata). Based on this evidence, the discrepancies in original specimen descriptions and the previous genetic comparisons, we support the suggestion that the two previously described species of Alatina from Australia and Hawaii (Alatina mordens and Alatina moseri) appear to represent artificial taxonomic units and may in fact be the same as the original Carybdea alata species named from Puerto Rico. Further taxonomic studies are desperately needed in order to clarify the various species and description discrepancies that exist within this newly proposed genus.

Evidence of mimicry of gelatinous zooplankton by anguilliform leptocephali for predator avoidance

Leptocephali are the transparent larvae of eels and their relatives, whose laterally compressed bodies contain gelatinous material. Although abundant throughout the world’s oceans, leptocephali are rarely observed in their natural environment. Video recordings of leptocephali in surface waters at night at Osprey Reef in the Coral Sea revealed that 6 of 21 larvae filmed displayed a distinct shape-change behavior of curling up into fully or partially coiled shapes. Their transparency and gelatinous consistency results in the coiled leptocephali resembling the typical body shapes and consistency of gelatinous zooplankton such as jellyfish, ctenophores, siphonophores, and salps. Due to either stinging defenses or low food value, many fishes avoid consuming gelatinous zooplankton, so the curling behavior in response to threatening situations may result in mimicry of these organisms. This could provide leptocephali with higher survival rates compared with flight from pelagic predators that are close enough to detect them.

Seasonality in Polyps of a Tropical Cubozoan: A latina nr mordens

A latina nr mordens have been located in large predictable spawning aggregations near Osprey Reef in the Coral Sea eight to ten days after a full moon; however, polyps have never been located in-situ. The polyp stage contributes to the abundance of medusae through asexual reproduction and metamorphosis, and may influence the periodicity of medusae by metamorphosis of the polyp. To elucidate the relationship between medusae periodicity and polyp ecology, polyps were exposed to thermal and osmotic treatments in order to determine the theoretical environmental limits to their distribution. Maximum fecundity occurred in thermal treatments of 21 to 25ºC and the theoretical minimum thermal requirement for population stability was approximately 17ºC. Polyps were also exposed to five feeding regimes and fecundity was found to be positively correlated with feeding frequency. Thermal and osmotic variations did not induce metamorphosis in this species, however, reduced food did. The implications of asexual reproduction and cues for metamorphosis in relation to population dynamics of this species are discussed.

Molecular Evidence Shows Low Species Diversity of Coral-Associated Hydroids in Acropora Corals

A novel symbiosis between scleractinians and hydroids (Zanclea spp.) was recently discovered using taxonomic approaches for hydroid species identification. In this study, we address the question whether this is a species-specific symbiosis or a cosmopolitan association between Zanclea and its coral hosts. Three molecular markers, including mitochondrial 16S and nuclear 28S ribosomal genes, and internal transcribed spacer (ITS), were utilized to examine the existence of Zanclea species from 14 Acropora species and 4 other Acroporidae genera including 142 coral samples collected from reefs in Kenting and the Penghu Islands, Taiwan, Togian Island, Indonesia, and Osprey Reef and Orpheus Island on the Great Barrier Reef, Australia. Molecular phylogenetic analyses of the 16S and 28S genes showed that Acropora-associated Zanclea was monophyletic, but the genus Zanclea was not. Analysis of the ITS, and 16S and 28S genes showed either identical or extremely low genetic diversity (with mean pairwise distances of 0.009 and 0.006 base substitutions per site for the 16S and 28S genes, respectively) among Zanclea spp. collected from diverse Acropora hosts in different geographic locations, suggesting that a cosmopolitan and probably genus-specific association occurs between Zanclea hydroids and their coral hosts.

The Untethered Remotely Operated Vehicle PICASSO-1 and Its Deployment From Chartered Dive Vessels for Deep Sea Surveys Off Okinawa, Japan, and Osprey Reef, Coral Sea, Australia

AbstractThe untethered remotely operated vehicle (uROV) PICASSO-1, which is controlled in real time from a surface support vessel via a Φ0.9 mm fiber optic cable, is capable of dives to 1,000-m depth at a duration of up to 6 h and yet is deployable from ships of sizes as low as 17 tonnes. The vehicle was developed at the Japan Agency for Marine-Earth Science and Technology, has carried out 63 dives to date, and is now operable by a team of four biologists and one technician. PICASSO-1 can collect video (HDTV × 1, NTSC × 3) and environmental information (depth, temperature, salinity, dissolved oxygen concentration, fluorescence [chlorophyll a proxy], turbidity) concurrently, and this is output with vehicle heading, camera zoom, and other vital statistics via Ethernet. Acoustically obtained vehicle position information, deck and control room video, and sound data streams are also output via Ethernet, and the whole dive is recorded in a synchronous fashion on a logging/playback system that enables dives to be re-enacted in their entirety to facilitate analyses back in the laboratory. Operations have been successfully carried out overseas using a chartered dive boat, and the system represents a leap forward for exploration of the oceans to significant depths but at relatively low cost and with no loss in data quality.

Residency and Spatial Use by Reef Sharks of an Isolated Seamount and Its Implications for Conservation

Although marine protected areas (MPAs) are a common conservation strategy, these areas are often designed with little prior knowledge of the spatial behaviour of the species they are designed to protect. Currently, the Coral Sea area and its seamounts (north-east Australia) are under review to determine if MPAs are warranted. The protection of sharks at these seamounts should be an integral component of conservation plans. Therefore, knowledge on the spatial ecology of sharks at the Coral Sea seamounts is essential for the appropriate implementation of management and conservation plans. Acoustic telemetry was used to determine residency, site fidelity and spatial use of three shark species at Osprey Reef: whitetip reef sharks Triaenodon obesus, grey reef sharks Carcharhinus amblyrhynchos and silvertip sharks Carcharhinus albimarginatus. Most individuals showed year round residency at Osprey Reef, although five of the 49 individuals tagged moved to the neighbouring Shark Reef (∼14 km away) and one grey reef shark completed a round trip of ∼250 km to the Great Barrier Reef. Additionally, individuals of white tip and grey reef sharks showed strong site fidelity to the areas they were tagged, and there was low spatial overlap between groups of sharks tagged at different locations. Spatial use at Osprey Reef by adult sharks is generally restricted to the north-west corner. The high residency and limited spatial use of Osprey Reef suggests that reef sharks would be highly vulnerable to targeted fishing pressure and that MPAs incorporating no-take of sharks would be effective in protecting reef shark populations at Osprey and Shark Reef.

Erratum to: Precious coral and rock sponge gardens on the deep aphotic fore-reef of Osprey Reef (Coral Sea, Australia)

During the course of video/still image analysis, some pictures unfortunately appear to have been mixed up. The coral colonies shown in Fig. 1 have not been sampled, and their identity is not confirmed. However, numerous Corallium sp. colonies were found at the same site in greater depth (602–627 m), as shown in Fig. S1 (attached), and their identity was confirmed by DNA barcoding. We would like to emphasize that the main message of our Reef Site article, the first discovery of precious corals on the aphotic reef slope of Osprey Reef, is still unchanged. We thank Rob Beaman (JCU) for pointing this out to us and Sarah Adolf (LMU) for assistance with DNA barcoding.

Precious coral and rock sponge gardens on the deep aphotic fore-reef of Osprey Reef (Coral Sea, Australia)

Precious coral and rock sponge gardens on the deep aphotic fore-reef of Osprey Reef (Coral Sea, Australia)

Variation in depth of whitetip reef sharks: does provisioning ecotourism change their behaviour?

In the dive tourism industry, shark provisioning has become increasingly popular in many places around the world. It is therefore important to determine the impacts that provisioning may have on shark behaviour. In this study, eight adult whitetip reef sharks Triaenodon obesus were tagged with time-depth recorders at Osprey Reef in the Coral Sea, Australia. Tags collected time and depth data every 30 s. The absolute change in depth over 5-min blocks was considered as a proxy for vertical activity level. Daily variations in vertical activity levels were analysed to determine the effects of time of day on whitetip reef shark behaviour. This was done for days when dive boats were absent from the area, and for days when dive boats were present, conducting shark provisioning. Vertical activity levels varied between day and night, and with the presence of boats. In natural conditions (no boats present), sharks remained at more constant depths during the day, while at night animals continuously moved up and down the water column, showing that whitetip reef sharks are nocturnally active. When boats were present, however, there were also long periods of vertical activity during the day. If resting periods during the day are important for energy budgets, then shark provisioning may affect their health. So, if this behaviour alteration occurs frequently, e.g., daily, this has the potential to have significant negative effects on the animals’ metabolic rates, net energy gain and overall health, reproduction and fitness.

Vertical Distribution and Migration Patterns of Nautilus pompilius

Vertical depth migrations into shallower waters at night by the chambered cephalopod Nautilus were first hypothesized early in the early 20th Century. Subsequent studies have supported the hypothesis that Nautilus spend daytime hours at depth and only ascend to around 200 m at night. Here we challenge this idea of a universal Nautilus behavior. Ultrasonic telemetry techniques were employed to track eleven specimens of Nautilus pompilius for variable times ranging from one to 78 days at Osprey Reef, Coral Sea, Australia. To supplement these observations, six remotely operated vehicle (ROV) dives were conducted at the same location to provide 29 hours of observations from 100 to 800 meter depths which sighted an additional 48 individuals, including five juveniles, all deeper than 489 m. The resulting data suggest virtually continuous, nightly movement between depths of 130 to 700 m, with daytime behavior split between either virtual stasis in the relatively shallow 160–225 m depths or active foraging in depths between 489 to 700 m. The findings also extend the known habitable depth range of Nautilus to 700 m, demonstrate juvenile distribution within the same habitat as adults and document daytime feeding behavior. These data support a hypothesis that, contrary to previously observed diurnal patterns of shallower at night than day, more complex vertical movement patterns may exist in at least this, and perhaps all other Nautilus populations. These are most likely dictated by optimal feeding substrate, avoidance of daytime visual predators, requirements for resting periods at 200 m to regain neutral buoyancy, upper temperature limits of around 25°C and implosion depths of 800 m. The slope, terrain and biological community of the various geographically separated Nautilus populations may provide different permutations and combinations of the above factors resulting in preferred vertical movement strategies most suited for each population.

Nautilus pompilius Life History and Demographics at the Osprey Reef Seamount, Coral Sea, Australia

Nautiloids are the subject of speculation as to their threatened status arising from the impacts of targeted fishing for the ornamental shell market. Life history knowledge is essential to understand the susceptibility of this group to overfishing and to the instigation of management frameworks. This study provides a comprehensive insight into the life of Nautilus in the wild. At Osprey Reef from 1998–2008, trapping for Nautilus was conducted on 354 occasions, with 2460 individuals of one species, Nautilus pompilius, captured and 247 individuals recaptured. Baited remote underwater video systems (BRUVS) were deployed on 15 occasions and six remotely operated vehicle (ROV) dives from 100–800 m were conducted to record Nautilus presence and behavior. Maturity, sex and size data were recorded, while measurements of recaptured individuals allowed estimation of growth rates to maturity, and longevity beyond maturity. We found sexual dimorphism in size at maturity (males: 131.9±SD = 2.6 mm; females: 118.9±7.5 mm shell diameter) in a population dominated by mature individuals (58%). Mean growth rates of 15 immature recaptured animals were 0.061±0.023 mm day−1 resulting in an estimate of around 15.5 years to maturation. Recaptures of mature animals after five years provide evidence of a lifespan exceeding 20 years. Juvenile Nautilus pompilius feeding behavior was recorded for the first time within the same depth range (200–610 m) as adults. Our results provide strong evidence of a K-selected life history for Nautilus from a detailed study of a ‘closed’ wild population. In conjunction with population size and density estimates established for the Osprey Reef Nautilus, this work allows calculations for sustainable catch and provides mechanisms to extrapolate these findings to other extant nautiloid populations (Nautilus and Allonautilus spp.) throughout the Indo-Pacific.

Nautilus at Risk – Estimating Population Size and Demography of Nautilus pompilius

The low fecundity, late maturity, long gestation and long life span of Nautilus suggest that this species is vulnerable to over-exploitation. Demand from the ornamental shell trade has contributed to their rapid decline in localized populations. More data from wild populations are needed to design management plans which ensure Nautilus persistence. We used a variety of techniques including capture-mark-recapture, baited remote underwater video systems, ultrasonic telemetry and remotely operated vehicles to estimate population size, growth rates, distribution and demographic characteristics of an unexploited Nautilus pompilius population at Osprey Reef (Coral Sea, Australia). We estimated a small and dispersed population of between 844 and 4467 individuals (14.6–77.4 km−2) dominated by males (83∶17 male∶female) and comprised of few juveniles (<10%).These results provide the first Nautilid population and density estimates which are essential elements for long-term management of populations via sustainable catch models. Results from baited remote underwater video systems provide confidence for their more widespread use to assess efficiently the size and density of exploited and unexploited Nautilus populations worldwide.

In situ observation of Denise’s pygmy seahorse Hippocampus denise associated with a gorgonian coral Annella reticulata at Osprey Reef, Australia

Hippocampus denise, one of the world's smallest seahorses, was described from Indonesia and appears to be relatively widespread in the West Pacific (Lourie and Randall 2003). The widespread occurrence of this species has been recorded in books, dive magazines and on the internet (e.g. Kuiter 2000), and recently the occurrence of this species was reported from Holmes Reef (Coral Sea) based on samples collected, together with gorgonians Villogorgia sp. from a depth of ~100 m (Foster et al. 2012). Biological and ecological data on this species are, however, very limited as well as in situ observations of this species at such great depths. Underwater observations using a high-definition video camera on the untethered remotely operated vehicle, PICASSO-1, enabled us to confirm the occurrence of this species at Osprey Reef, a Coral Sea atoll in Australian waters, the first in situ record from this isolated oceanic reef.

Live-Aboard Dive Boats in the Great Barrier Reef: Regional Economic Impact and the Relative Values of Their Target Marine Species

Using data collected from more than 1,000 tourists on live-aboard dive boats operating in the Cairns/Cooktown management area of the Great Barrier Reef, this paper estimates the regional economic impact of that live-aboard industry. It also uses a subset of these data (247 respondents) to investigate some of the relative ‘values’ of key marine species seen on the trips that included the Coral Sea location of Osprey Reef and which targeted multiple species of wildlife. The authors find that (i) each year, the live-aboard dive boats are directly responsible for generating at least AU$16 million worth of income in the Cairns/Port Douglas region; (ii) visitors participating in different types of trips gain their highest levels of ‘satisfaction’ from interacting with different types of species; and (iii) visitors to Osprey Reef would be willing to pay more for a ‘guaranteed’ sighting of sharks than they would for a ‘guaranteed’ sighting of large fish, marine turtles or a ‘wide variety of species’.

Nautilus pompilius fishing and population decline in the Philippines: A comparison with an unexploited Australian Nautilus population

Baseline capture and mark-and-release studies of Nautilus pompilius conducted at Osprey Reef, Coral Sea, Australia reveal that this unexploited population is stable from a catch per unit effort (CPUE) basis over 12 years. In contrast, data from a detailed interview questionnaire of N. pompilius fishers and traders in Palawan, Philippines highlight a fishery that is unsustainable. The results from the Philippines show up to 80% declines in reported CPUE from 1980 to the present, fewer than three Nautilus generations, which can be attributed to fishing pressure. This is evidence for N. pompilius (and by ecological association, other Nautilus species) to be assessed as ‘endangered’ in the IUCN (International Union for Conservation of Nature) Red List. Questionnaire responses suggested there is no cultural or historical relevance of Nautilus fishing to local communities and the fishery only provides approximately 10–20 years of economic return before becoming non-viable. Identification of new Nautilus fishing sites and training of locals by buyers from distant depleted fishing areas illustrate how the value and demand for Nautilus shells generates fishing pressure.

Cover Caption

Cover description: A diver hovering in clear water over Osprey Reef, Great Barrier Reef, Australia. Diving fees can help capture some of the willingness to pay for diving in marine protected areas (MPAs), but an excessive reliance on tourism for funding MPA management could expose coral reefs to damages. Photo by Leah Gerber.