Sea Star Acanthaster Planci Research Articles

Taste attractivity of tropical echinoderms for barramundi Lates calcarifer

Fish meal has become the suppressing factor for fish feed development. The current practice of using forage fish as the protein source in fish feed is not sustainable and is one of the major bottlenecks in the aquaculture industry. Numerous researchers have aimed to find newer, less expensive, and more widely available sources of protein, such as food industry by-products and other local raw materials. Echinoderms (sea stars, sea urchins, and sea cucumbers) are common and abundant in marine shallow and intertidal areas, but only some of them are harvested and cultivated. An experiment was conducted with barramundi Lates calcarifer juveniles (7–9 cm total length) to examine the taste attractivity of several echinoderm species, including the pest crown-of-thorns sea star Acanthaster planci, which devastated live coral reefs during population outbreaks. Feeding behavior that accompanies fishes' responses to agar pellets flavored with hydrophilic extracts of echinoderms was evaluated. It was found that extracts of 5 out of 6 species (sea stars Linckia laevigata, A. planci, Culcita novaeguineae, Fromia milleporella, holothurian Holothuria atra) had an aversive taste for barramundi. In contrast, extract of sea urchin Diadema setosum was highly palatable. The barramundi repeatedly grasped the pellet with an aversive taste before rejecting it. Palatable pellets were swallowed after a single grasp but were retained in the fishes' mouth much longer than less palatable ones. Pellets having a size about 5% of the fish's body length (4 mm) were often fragmented by fish during intraoral processing. Fragmentation of pellets correlates negatively with pellet retention time but positively with repeated grasps performed. The present study has shown that most of the echinoderms examined are unpalatable for barramundi and the use of these animals as an ingredient in barramundi feed is not recommended.

Monitoring and assessing a 2-year outbreak of the corallivorous seastar Acanthaster planci in Ari Atoll, Republic of Maldives.

Outbreaks of the corallivorous crown-of-thorns seastars have received increasing attention due to their negative impacts on coral reefs in the Indo-Pacific Ocean. However, outbreaks in remote and dislocated islands are still poorly understood. This study aims to begin filling informational gaps regarding outbreaks of Acanthaster planci in the remote islands of the central Ari Atoll, Republic of Maldives. The population of A. planci was monitored during three periods over 2years (2015-2016) to evaluate variations in abundance and to characterise size structure and feeding behaviour. The outbreak appeared to be severe and active throughout the entire study period. The size structure analysis revealed a multimodal distribution dominated by individuals between 20 and 30cm, suggesting that the outbreak may have resulted from a few nearby mass spawning events. Additionally, the most abundant live coral was Porites, which was also the most consumed genus; however, the electivity index showed a preference for corals of the genera Favites and Pavona. Finally, we also highlighted the need for more geographically extended surveys to better understand local patterns regarding outbreaks of A. planci in the Republic of Maldives.

Bias associated with the detectability of the coral-eating pest crown-of-thorns seastar and implications for reef management.

Outbreaks of the predator crown-of-thorns seastar (COTS) Acanthaster planci cause widespread coral mortality across the Indo-Pacific. Like many marine invertebrates, COTS is a nocturnal species whose cryptic behaviour during the day can affect its detectability, particularly in structurally complex reef habitats that provide many refuges for benthic creatures. We performed extensive day and night surveys of COTS populations in coral reef habitats showing differing levels of structural complexity and COTS abundance. We tested whether estimations of COTS density varied between day and night observations, and if the differences were related to changes in COTS abundance, reef structural complexity and the spatial scale of observation. Estimations of COTS density were on average 27% higher at night than during the day. Differences in COTS detection varied with changing seastar abundance but not reef structural complexity or scale of observation. Underestimation of COTS abundance in daytime was significant for a broad seastar density range, thus potentially affecting most outbreak events. Our study suggests that portions of COTS populations can be undetected during conventional surveys and control campaigns, which are exclusively conducted by day, and significantly affect the trajectory of coral reefs. Accounting for bias in COTS detection can strengthen coral reef management broadly.

The role of vision for navigation in the crown-of-thorns seastar, Acanthaster planci.

Coral reefs all over the Indo-Pacific suffer from substantial damage caused by the crown-of-thorns seastar Acanthaster planci, a voracious predator that moves on and between reefs to seek out its coral prey. Chemoreception is thought to guide A. planci. As vision was recently introduced as another sense involved in seastar navigation, we investigated the potential role of vision for navigation in A. planci. We estimated the spatial resolution and visual field of the compound eye using histological sections and morphometric measurements. Field experiments in a semi-controlled environment revealed that vision in A. planci aids in finding reef structures at a distance of at least 5 m, whereas chemoreception seems to be effective only at very short distances. Hence, vision outweighs chemoreception at intermediate distances. A. planci might use vision to navigate between reef structures and to locate coral prey, therefore improving foraging efficiency, especially when multidirectional currents and omnipresent chemical cues on the reef hamper chemoreception.

Larval phenotypic plasticity in the boom-and-bust crown-of-thorns seastar, Acanthaster planci

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 539:179-189 (2015) - DOI: https://doi.org/10.3354/meps11495 Larval phenotypic plasticity in the boom-and-bust crown-of-thorns seastar, Acanthaster planci Kennedy Wolfe1,*, Alexia Graba-Landry2, Symon A. Dworjanyn2, Maria Byrne1,3 1School of Medical Sciences, The University of Sydney, Sydney, NSW 2006, Australia 2National Marine Science Centre, Southern Cross University, Coffs Harbour, NSW 2450, Australia 3School of Biological Sciences, The University of Sydney, Sydney, NSW 2006, Australia *Corresponding author: kennedy.wolfe@sydney.edu.au ABSTRACT: Many echinoderm larvae exhibit phenotypic plasticity: a change in phenotype in response to environmental food levels. We investigated phenotypic plasticity in the larvae of the crown-of-thorns seastar Acanthaster planci, an opportunistic boom-and-bust species with larvae that have a strong response to food conditions. The increased predation pressure resulting from outbreaks (population explosions) of A. planci is deleterious to coral reefs, but the link between population outbreaks and larval ecology is poorly understood. We hypothesised that the larvae of A. planci would have a different morphological profile in the oligotrophic conditions typical of tropical waters than in the eutrophic conditions associated with increased nutrients. We predicted that larvae reared in low food conditions would increase their ciliated band length to enhance feeding potential. Larvae were fed algal concentrations representing starvation (0 cells ml-1), low food (oligotrophic; 1000 cells ml-1), high food (eutrophic; 10000 cells ml-1) or excessive food (100000 cells ml-1) conditions. A phenotypic response was evident. Larvae in the 2 high food treatments had a shorter ciliated band length relative to body size. Conversely, larvae in the starvation and low food treatments had longer ciliated bands relative to body size, a change that would enhance particle capture capacity and facilitate larval success. This plastic response of the larvae of A. planci could have flow-on effects to adult populations, potentially facilitating population outbreaks. KEY WORDS: Asteroidea · Bipinnaria · COTS · Feeding larvae · Nutrients Full text in pdf format PreviousNextCite this article as: Wolfe K, Graba-Landry A, Dworjanyn SA, Byrne M (2015) Larval phenotypic plasticity in the boom-and-bust crown-of-thorns seastar, Acanthaster planci. Mar Ecol Prog Ser 539:179-189. https://doi.org/10.3354/meps11495 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 539. Online publication date: November 12, 2015 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2015 Inter-Research.

Lime Juice and Vinegar Injections as a Cheap and Natural Alternative to Control COTS Outbreaks.

Outbreaks of the corallivorous crown-of-thorns seastar Acanthaster planci (COTS) represent one of the greatest disturbances to coral reef ecosystems in the Indo-Pacific, affecting not only coral reefs but also the coastal communities which rely on their resources. While injection approaches are increasingly used in an attempt to control COTS densities, most of them display severe drawbacks including logistical challenges, high residual environmental impacts or low cost-effectiveness. We tested a new alternative control method based upon acidic injections of cheap, 100% natural products. We investigated the lethal doses, intra- and inter-specific disease transmission and immune responses of COTS when injected with fresh lime juice (extracted from local Citrus arantifolia) and white spirit vinegar. High COTS mortality was achieved with small volumes: 10–20 ml per seastar induced death in 89%/97% of injected specimens after an average 34.3 h/29.8 h for lime juice and vinegar respectively. Highest efficiency was reached for both solutions with double shots of (2 × 10 ml) in two different areas on the body: 100% mortality occurred within 12–24 h, which is similar or faster compared with other current injection methods. Multiple immune measures suggested that death was very likely caused by pH stress from the acidic solutions rather than a bacterial infection. Contagion to either conspecifics or a variety of other reef species was not observed, even at COTS densities 15 times higher than the highest naturally reported. 10 to 20 l lime juice/vinegar could kill up to a thousand COTS at a cost of less than 0.05 USD per specimen; no permits or special handling procedures are required. We conclude that injections of lime juice and vinegar offer great advantages when compared to current best practises and constitute a cheap and natural option for all reefs affected by COTS.

Juvenile Trapezia spp. crabs can increase juvenile host coral survival by protection from predation

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 515:151-159 (2014) - DOI: https://doi.org/10.3354/meps10970 Juvenile Trapezia spp. crabs can increase juvenile host coral survival by protection from predation H. Rouzé1,2,*, G. Lecellier1,2,3, S. C. Mills2,4, S. Planes1,2, V. Berteaux-Lecellier1,2, H. Stewart1,5 1CRIOBE USR 3278 CNRS-EPHE-UPVD, BP 1013, Moorea, 98729 French Polynesia 2Laboratoire d’Excellence ‘CORAIL’, 58 avenue Paul Alduy, 66860 Perpignan, France 3Université de Versailles-Saint Quentin, 55 Avenue de Paris, Versailles Cedex, France 4CRIOBE USR 3278 CNRS-EPHE-UPVD, 58 Avenue Paul Alduy, 66860 Perpignan Cedex, France 5Department of Fisheries and Oceans Canada, 4160 Marine Drive, West Vancouver, British Columbia V7V 1N6, Canada *Corresponding author: heloise.rouze@gmail.com ABSTRACT:Adult crabs are known to play critical roles in the survival of their adult coral hosts, but little is known of the mutualism between juvenile crabs (≤0.5 cm) and their juvenile hosts. Field and laboratory experiments both demonstrated that the presence of juvenile crabs of the genus Trapezia in young host Pocillopora corals (2 to 3 cm diameter) increased coral survival by 32% and reduced consumption by the corallivorous seastar Acanthaster planci. These experiments also showed that juvenile Trapezia were not effective at deterring predation by another common predatory seastar, Culcita novaeguineae. Finally, our work highlights that the defensive ability of symbiotic crabs may be genus-specific, as juvenile Tetralia spp. crabs, obligate symbionts of Acropora spp., displayed no protection against either A. planci or C. novaeguineae. KEY WORDS: Juvenile · Trapeziid · Corals · Acanthaster planci · Culcita novaeguineae · Mutualism · Predation · Defence Full text in pdf format PreviousNextCite this article as: Rouzé H, Lecellier G, Mills SC, Planes S, Berteaux-Lecellier V, Stewart H (2014) Juvenile Trapezia spp. crabs can increase juvenile host coral survival by protection from predation. Mar Ecol Prog Ser 515:151-159. https://doi.org/10.3354/meps10970 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 515. Online publication date: November 18, 2014 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2014 Inter-Research.

Correction: Impacts of Ocean Acidification on Early Life-History Stages and Settlement of the Coral-Eating Sea Star Acanthaster planci

Correction: Impacts of Ocean Acidification on Early Life-History Stages and Settlement of the Coral-Eating Sea Star Acanthaster planci

The thermal tolerance of crown-of-thorns (Acanthaster planci) embryos and bipinnaria larvae: implications for spatial and temporal variation in adult populations

To understand the role of sea temperature on the population biology of the crown-of-thorns sea star Acanthaster planci, the thermal window for embryonic and larval development was investigated. In two experiments, the response of embryos and larvae across 12 temperatures from 19.4 to 36.5 °C was quantified as the percentage of individuals reaching cleavage stage embryos, blastula, gastrula, early-bipinnaria, late-bipinnaria larvae or abnormal. Measurements were made at 7 times up to 72 h post-fertilisation, with the morphometrics of larvae measured in the 72-h sample. Acanthaster planci developed at temperatures between 19.4 and 33.2 °C, with a thermal window for development to the late-bipinnaria stage between 25.6 and 31.6 °C. Development rate, normal development and larval size were optimal at 28.7 °C, with development rates remaining relatively constant up to 31.6 °C. Rates of abnormality increased steadily (early embryonic stages) above 28.7 °C and was 100 % at temperatures approaching 33 °C. These experiments provide a more detailed insight into the response of A. planci developmental stages to temperature. The present day distribution of the species in eastern Australia overlap with the optimal thermal window for development to the late-bipinnaria stage (≈25–32 °C), implying a role of temperature in controlling population distributions and abundances. Despite this, short- or long-term temperature increases may not be a major modulator of the crown-of-thorns recruitment success, population dynamics and distribution in the future as no significant change in development rates, larval survival and growth occurred within this thermal window. Therefore, moderate (1–2 °C) increases in sea temperatures caused by El Nino or near-future ocean warming may not drive an increase in developmental and settlement success. Indeed, without any acclimation to warmer temperatures expected under near-future warming (+2 to 4 °C), climate change could ultimately reduce larval survival due to elevated mortality above the optimal development temperature.

Impacts of Ocean Acidification on Early Life-History Stages and Settlement of the Coral-Eating Sea Star Acanthaster planci

Coral reefs are marine biodiversity hotspots, but their existence is threatened by global change and local pressures such as land-runoff and overfishing. Population explosions of coral-eating crown of thorns sea stars (COTS) are a major contributor to recent decline in coral cover on the Great Barrier Reef. Here, we investigate how projected near-future ocean acidification (OA) conditions can affect early life history stages of COTS, by investigating important milestones including sperm motility, fertilisation rates, and larval development and settlement. OA (increased pCO2 to 900–1200 µatm pCO2) significantly reduced sperm motility and, to a lesser extent, velocity, which strongly reduced fertilization rates at environmentally relevant sperm concentrations. Normal development of 10 d old larvae was significantly lower under elevated pCO2 but larval size was not significantly different between treatments. Settlement of COTS larvae was significantly reduced on crustose coralline algae (known settlement inducers of COTS) that had been exposed to OA conditions for 85 d prior to settlement assays. Effect size analyses illustrated that reduced settlement may be the largest bottleneck for overall juvenile production. Results indicate that reductions in fertilisation and settlement success alone would reduce COTS population replenishment by over 50%. However, it is unlikely that this effect is sufficient to provide respite for corals from other negative anthropogenic impacts and direct stress from OA and warming on corals.

Trichodermaerin, a New Diterpenoid Lactone from the Marine Fungus Trichoderma erinaceum Associated with the Sea Star Acanthaster planci

Trichodermaerin (1), a novel diterpenoid lactone, together with the known compound, harziandione (2) were isolated from the culture broth of the fungus Trichoderma erinaceum associated with the sea star Acanthaster planci. Their structures were determined by analysis of the NMR and MS data. 1 was the Baeyer-Villiger monooxygenase catalyzed oxidation product of 2. Compound 2 did not show cytotoxic activities against various cancer cell lines.

Predator crown-of-thorns starfish (Acanthaster planci) outbreak, mass mortality of corals, and cascading effects on reef fish and benthic communities.

Outbreaks of the coral-killing seastar Acanthaster planci are intense disturbances that can decimate coral reefs. These events consist of the emergence of large swarms of the predatory seastar that feed on reef-building corals, often leading to widespread devastation of coral populations. While cyclic occurrences of such outbreaks are reported from many tropical reefs throughout the Indo-Pacific, their causes are hotly debated, and the spatio-temporal dynamics of the outbreaks and impacts to reef communities remain unclear. Based on observations of a recent event around the island of Moorea, French Polynesia, we show that Acanthaster outbreaks are methodic, slow-paced, and diffusive biological disturbances. Acanthaster outbreaks on insular reef systems like Moorea's appear to originate from restricted areas confined to the ocean-exposed base of reefs. Elevated Acanthaster densities then progressively spread to adjacent and shallower locations by migrations of seastars in aggregative waves that eventually affect the entire reef system. The directional migration across reefs appears to be a search for prey as reef portions affected by dense seastar aggregations are rapidly depleted of living corals and subsequently left behind. Coral decline on impacted reefs occurs by the sequential consumption of species in the order of Acanthaster feeding preferences. Acanthaster outbreaks thus result in predictable alteration of the coral community structure. The outbreak we report here is among the most intense and devastating ever reported. Using a hierarchical, multi-scale approach, we also show how sessile benthic communities and resident coral-feeding fish assemblages were subsequently affected by the decline of corals. By elucidating the processes involved in an Acanthaster outbreak, our study contributes to comprehending this widespread disturbance and should thus benefit targeted management actions for coral reef ecosystems.

Novel Sorbicillin Analogues from the Marine Fungus Trichoderma sp. Associated with the Seastar Acanthaster Planci

Two novel sorbicillinoid analogues, (4'Z)-sorbicillin (1) and (2S)-2,3-dihydro-7-hydroxy-6-methyl-2-[(E)-prop-1-enyl]-chroman-4-one (2), together with three known compounds, (2S)-2,3-dihydro-7-hydroxy-6,8-dimethyl-2-[(E)-prop-1-enyl]-chroman-4-one (3), sorbicillin (4), and 2',3'-dihydrosorbicillin (5), were isolated from the culture broth of the fungus Trichoderma sp. associated with the seastar Acanthaster planci. Their structures were determined by analysis of the NMR and MS data. Compound I was the first example with a Z-configuration of the C-4'/C-5' double bond in the sorbyl side chain. Compounds 2 and 3 were uncommon monomeric sorbicillinoids with a cyclic sorbyl chain. 2, 3 and 5 showed moderate cytotoxic activities against various cancer cell lines.

Acanthaster planci Outbreak: Decline in Coral Health, Coral Size Structure Modification and Consequences for Obligate Decapod Assemblages

Although benthic motile invertebrate communities encompass the vast majority of coral reef diversity, their response to habitat modification has been poorly studied. A variety of benthic species, particularly decapods, provide benefits to their coral host enabling them to cope with environmental stressors, and as a result benefit the overall diversity of coral-associated species. However, little is known about how invertebrate assemblages associated with corals will be affected by global perturbations, (either directly or indirectly via their coral host) or their consequences for ecosystem resilience. Analysis of a ten year dataset reveals that the greatest perturbation at Moorea over this time was an outbreak of the corallivorous sea star Acanthaster planci from 2006 to 2009 impacting habitat health, availability and size structure of Pocillopora spp. populations and highlights a positive relationship between coral head size and survival. We then present the results of a mensurative study in 2009 conducted at the end of the perturbation (A. planci outbreak) describing how coral-decapod communities change with percent coral mortality for a selected coral species, Pocillopora eydouxi. The loss of coral tissue as a consequence of A. planci consumption led to an increase in rarefied total species diversity, but caused drastic modifications in community composition driven by a shift from coral obligate to non-obligate decapod species. Our study highlights that larger corals left with live tissue in 2009, formed a restricted habitat where coral obligate decapods, including mutualists, could subsist. We conclude that the size structure of Pocillopora populations at the time of an A. planci outbreak may greatly condition the magnitude of coral mortality as well as the persistence of local populations of obligate decapods.

Coral growth on three reefs: development of recovery benchmarks using a space for time approach

This 14-year study (1989–2003) develops recovery benchmarks based on a period of very strong coral recovery in Acropora-dominated assemblages on the Great Barrier Reef (GBR) following major setbacks from the predatory sea-star Acanthaster planci in the early 1980s. A space for time approach was used in developing the benchmarks, made possible by the choice of three study reefs (Green Island, Feather Reef and Rib Reef), spread along 3 degrees of latitude (300 km) of the GBR. The sea-star outbreaks progressed north to south, causing death of corals that reached maximum levels in the years 1980 (Green), 1982 (Feather) and 1984 (Rib). The reefs were initially surveyed in 1989, 1990, 1993 and 1994, which represent recovery years 5–14 in the space for time protocol. Benchmark trajectories for coral abundance, colony sizes, coral cover and diversity were plotted against nominal recovery time (years 5–14) and defined as non-linear functions. A single survey of the same three reefs was conducted in 2003, when the reefs were nominally 1, 3 and 5 years into a second recovery period, following further Acanthaster impacts and coincident coral bleaching events around the turn of the century. The 2003 coral cover was marginally above the benchmark trajectory, but colony density (colonies.m−2) was an order of magnitude lower than the benchmark, and size structure was biased toward larger colonies that survived the turn of the century disturbances. The under-representation of small size classes in 2003 suggests that mass recruitment of corals had been suppressed, reflecting low regional coral abundance and depression of coral fecundity by recent bleaching events. The marginally higher cover and large colonies of 2003 were thus indicative of a depleted and aging assemblage not yet rejuvenated by a strong cohort of recruits.

Three lines of evidence to link outbreaks of the crown-of-thorns seastar Acanthaster planci to the release of larval food limitation

Population outbreaks of the coral-eating crown-of-thorns seastar, Acanthaster planci, continue to kill more coral on Indo-Pacific coral reefs than other disturbances, but the causes of these outbreaks have not been resolved. In this study, we combine (1) results from laboratory experiments where larvae were reared on natural phytoplankton, (2) large-scale and long-term field data of river floods, chlorophyll concentrations and A. planci outbreaks on the Great Barrier Reef (GBR), and (3) results from A. planci—coral population model simulations that investigated the relationship between the frequency of outbreaks and larval food availability. The experiments show that the odds of A. planci larvae completing development increases ~8-fold with every doubling of chlorophyll concentrations up to 3 μg l−1. Field data and the population model show that river floods and regional differences in phytoplankton availability are strongly related to spatial and temporal patterns in A. planci outbreaks on the GBR. The model also shows that, given plausible historic increases in river nutrient loads over the last 200 years, the frequency of A. planci outbreaks on the GBR has likely increased from one in 50–80 years to one every 15 years, and that current coral cover of reefs in the central GBR may be 30–40% of its potential value. This study adds new and strong empirical support to the hypothesis that primary A. planci outbreaks are predominantly controlled by phytoplankton availability.

Pedicellariae of the crown-of-thorns sea star Acanthaster planci are not an effective defence against fouling

This study focused on the speculative role of the pedicellariae of the sea star Acanthaster planci in fouling control, as quantitative measurements showed that this species is free of any macro-fouling organisms. The morphology and distribution of its pedicellariae were measured to determine if larvae or propagules of fouling organisms could settle between pedicellariae without being in their physical range. The elementary and straight pedicellariae of A. planci had a mean length of 0.7 mm and a mean distance of 2.6 mm. The total number of pedicellariae was proportional to the estimated surface area of A. planci. To determine how pedicellariae respond to tactile stimulation, pedicellariae were stimulated by touching either inner, outer or basal sites of pedicellariae with a hypodermic needle. Pedicellariae closed rapidly on touch and closed for significantly longer when touched at their inner sites (8.9 s) than outer (6.7 s) and basal (7.9 s) sites. Settling larvae were simulated by dropping silica beads (size: 50.2, 181.5, 255.7 and 510.7 µm, density: 2.5 g ml-1) and zirconium/silica beads (size: 191.2 and 507.6 µm, density: 3.7 g ml-1) over the pedicellariae. The percentage of responding pedicellariae increased proportionally with increasing size of the silica beads. However, the percentage also increased when zirconium/silica beads of similar size but higher density were used, demonstrating that the mass, not size, of the beads was the main driving factor for the closure of pedicellariae. Pedicellariae were also stimulated by placing larvae of the bryozoan Bugula neritina (250 µm) and fragments of the alga Chrysocystis fragilis (150-1000 µm) over the pedicellariae. However, the response of the pedicellariae to the larvae of B. neritina was consistently low and none of the pedicellariae responded to the fragments of C. fragilis. These results demonstrate that for A. planci pedicellariae offer little or no defence against fouling.

Arachidonic acid and α-linolenic acid, feeding attractants for the crown-of-thorns sea star Acanthaster planci, from the sea urchin Toxopneustes pileolus

In the tropical zones of the Indo-Pacific Oceans, the crown-of-thorns sea star Acanthaster planci, as the predator of corals, destroys coral reefs. We recently found that viscera of the sea urchin Toxopneustes pileolus produced a feeding attractant for this sea star. Using our simple bioassay system, we isolated arachidonic acid and α-linolenic acid as feeding attractants from T. pileolus. This is the first report about the sea star A. planci being attracted to unsaturated fatty acids. Interestingly, other unsaturated fatty acids such as eicosapentaenoic acid, docosahexaenoic acid and linoleic acid showed no activity. Our preliminary experiments indicated that these attractants have an attractive effect for the sea star both in the aquarium and in the sea. We anticipated that these attractants could be used to control A. planci. In addition, we verified the existence of arachidonic acid in the coral as one of the feeding attractants.

A REGIONAL MODEL TO PREDICT CORAL POPULATION DYNAMICS IN RESPONSE TO EL NIÑO–SOUTHERN OSCILLATION

The objective of this paper was to modify an existing size-structured pop- ulation model for the coral Gardineroseris planulata developed from field measurements at the Uva Island reef, Panama, for use at the regional scale (Tropical Eastern Pacific). The modified model can be used to aid in prediction of changes in coral population dynamics in response to ENSO events of different frequency and magnitude. The earlier model incorporates coral growth, predation by the sea star Acanthaster planci, and mortality associated with El Ninio-Southern Oscillation (ENSO) events. The regional model was modified from the earlier local version by extending the coral growth-temperature rela- tionship to include the lower temperatures observed in areas of strong seasonal upwelling. In addition, ENSO-associated mortality was modified by incorporating a dynamic function that relates partial mortality of corals in different size classes to the rate of temperature change during an ENSO event. This function is based on data from three reef areas (Uva Island and the Pearl Islands, Panama, and the Galapagos Islands, Ecuador), which represent a regional gradient from an area characterized by relatively high annual temperature with low variability to areas with lower annual temperature subject to seasonal upwelling. Model predictions of coral population size structure in different areas agreed with field obser- vations. Predictions for coral recovery after an ENSO event were most accurate for the Uva Island population and least accurate for the Galapaigos Islands population. We also tested the effect of various ENSO frequencies on the size structure of the coral population. Increasing ENSO frequency in the upwelling area resulted in an increase in the proportion of small colonies, while the same increase in ENSO frequency in the thermally stable reef area had little effect on the population. Sensitivity analysis suggested that more accurate estimates of growth of the smallest and largest colonies in upwelling areas as well as predation on intermediate-size colonies are important to improve predictive capability.

Sperm Diffusion Models and In Situ Confirmation of Long-Distance Fertilization in the Free-Spawning Asteroid Acanthaster planci.

This study was undertaken to compare fertilization rates of the sea star Acanthaster planci that were predicted using sperm diffusion models with those that were determined under natural conditions in the field. During experimentally induced spawnings, measured fertilization rates for broadcast eggs were high. More than 70% of the eggs were fertilized at distances as great as 8 m downstream from a single spawning male starfish, and more than 20% were fertilized at separations of more than 60 m. Fertilization was still measurable, at 5.8%, 100 m downstream. Lateral diffusion of sperm away from the axis of flow produced fertilization rates of 13.8% at 8 m normal to the flow and 32 m downstream. The large volumes of sperm released by male A. planci are the primary cause of high rates of fertilization for eggs derived from widely spaced individuals. Models of sperm diffusion using high sperm release rates such as those found in this starfish accurately confirmed the fertilization rates measured in situ for two populations of A. planci with widely differing rates of sperm release. We observed some changes in starfish density and degree of aggregation in the study population for spawning periods during two spawning seasons, though these were not striking. High levels of aggregation may not be necessary for fertilization success in this starfish, due to the potential for long-distance fertilization and the probability that, for any spawning starfish, the total number of zygotes formed will be greater at some distance from the point of spawning. Although fertilization rates in areas distant from the sperm source were relatively low, the total area for potential gamete encounters is much greater and may make a large contribution to net fertilization. We predict that other behaviors, such as migration to shallow water, commonly associated with spawning in A. planci and other marine invertebrates will have measurable impacts on fertilization success. The potential for high levels of fertilization in A. planci was realized during natural spawnings. Fertilization rates as high as 99% were recorded when levels of spawning synchrony were high.