The Wicked Problem of China's Disappearing Coral Reefs

We examined the development of coral reef science and the policies, institutions, and governance frameworks for management of coral reefs in China in order to highlight the wicked problem of preserving reefs while simultaneously promoting human development and nation building. China and other sovereign states in the region are experiencing unprecedented economic expansion, rapid population growth, mass migration, widespread coastal development, and loss of habitat. We analyzed a large, fragmented literature on the condition of coral reefs in China and the disputed territories of the South China Sea. We found that coral abundance has declined by at least 80% over the past 30 years on coastal fringing reefs along the Chinese mainland and adjoining Hainan Island. On offshore atolls and archipelagos claimed by 6 countries in the South China Sea, coral cover has declined from an average of >60% to around 20% within the past 10–15 years. Climate change has affected these reefs far less than coastal development, pollution, overfishing, and destructive fishing practices. Ironically, these widespread declines in the condition of reefs are unfolding as China's research and reef‐management capacity are rapidly expanding. Before the loss of corals becomes irreversible, governance of China's coastal reefs could be improved by increasing public awareness of declining ecosystem services, by providing financial support for training of reef scientists and managers, by improving monitoring of coral reef dynamics and condition to better inform policy development, and by enforcing existing regulations that could protect coral reefs. In the South China Sea, changes in policy and legal frameworks, refinement of governance structures, and cooperation among neighboring countries are urgently needed to develop cooperative management of contested offshore reefs. El Problema Malvado de la Desaparición de los Arrecifes de Coral en China     

Spatial and temporal variation in coral recruitment on the Great Barrier Reef: Implications for dispersal hypotheses

Over 15 000 coral recruits were counted on settlement plates from three mid-shelf reefs and six fringing reefs in the northern section of the Great Barrier Reef during two summers (1986 and 1987) and one winter (1987). The density of coral recruits on some settlement plates from a fringing reef was up to 4.88 cm^–2, the highest value ever reported. Mean density of recruits was greater on fringing reefs (81.1 recruits/settlement plate) than on mid-shelf reefs (15.6 recruits/settlement plate), but there was greater spatial variation in abundance of recruits between the fringing reef sites. Other differences between the mid-shelf reefs and the fringing reefs were that different taxa were dominant, and that settlement orientation differed, with mid-shelf recruits settling preferentially on horizontally oriented surfaces and fringingreef recruits preferring vertical surfaces. Of the three midshelf reefs, Green Island reef recorded the highest recruitment rate for each of the two summers, despite having a depauperate adult coral population following predation by the asteroidAcanthaster planci. This suggests that coral larvae frequently travel between reefs. In contrast with an earlier study, there was no consistent difference in abundance of recruits between forereef and backreef locations. Overall, the results indicated great spatial variation in the availability of coral larvae, both on the scale of whole reefs and within-reef habitats.     

Diversity,abundance, and distribution of reef sharks on outer-shelf reefs of the Great Barrier Reef,Australia

Quantifying the distribution and habitat use of sharks is critical for understanding their ecological role and for establishing appropriate conservation and management regimes. On coral reefs, particularly the Great Barrier Reef (GBR), little is known regarding the distribution of sharks across major reef habitat types. In this study, we surveyed shark populations across outer-shelf reefs of the GBR in order to determine the diversity, abundance, and distribution of reef sharks across three major coral reef habitats: (1) the reef slope, (2) the back reef and (3) the reef flat. Model selection revealed that habitat was the principal factor influencing shark distribution and abundance. Specifically, overall shark abundance and diversity were significantly higher on the reef slope (and to a lesser degree, the back reef) than the reef flat. This confirms that shark populations are not homogeneously distributed across coral reefs. Thus, the results presented herein have important implications for shark population assessments. In addition, our results highlight the potential importance of the reef slope, with high levels of live coral cover and structural complexity, for sustaining reef shark populations. As this habitat is highly susceptible to disturbance events, this study provides a useful context for predicting and understanding how environmental degradation may influence reef shark populations in the future.     

Lipid content of some Caribbean corals in relation to depth and light

Three procedures for the extraction of coral lipids were compared and a rapid and effective method for future use is suggested. This method was used to measure the lipid content of the branching coral Porites porites (Pallas) and the massive corals Montastrea annularis (Ellis and Solander) and Siderastrea siderea (Ellis and Solander) during July and August 1991. P. porites and M. annularis were sampled on two fringing reefs, each characterised by different water quality affecting light transmission, and at depths of down to 30 m on a barrier reef on the west coast of the island. m. annularis contained, on average, 29% of dry weight as lipid, and there were no significant differences in lipid levels between corals sampled on either fringing reef at 3 and 6 m, or between fringing reefs and the barrier reef at 13, 20 or 30 m depth. Five samples were also taken from a single massive colony of S. siderea at 3 m on a fringing reef and at 13, 20 and 30 m depth on the barrier reef. Values for lipid ranged from 26 to 35% of dry tissue weight. P. porites from 3 and 6 m depth on both fringing reefs contained the same amount of lipid (11% of dry tissue weight). However, at 13 m depth on the barrier reef this coral contained significantly less lipid (8.5% of dry tissue weight). This difference may be attributable to a higher nutritional intake by P. porites on the fringing reefs.     

Appraisal of visual assessments of habitat complexity and benthic composition on coral reefs

Visual assessments of topographic habitat structure and benthos on coral reefs were appraised using quantitative data collected from 16 replicate surveys within each of 21 sites on Seychelles reefs. Results from visual assessments of reef benthos were similar to those obtained using techniques frequently used to assess benthic complexity and composition. Visual estimates of habitat topography were correlated with rugosity, reef height and holes of 10–70 cm diameter, whilst visual estimates of benthic composition were very similar to those obtained from line intercept transects. Visual estimates of topography correlated strongly with species richness of fish communities and explained 42% of the variation in these data. The relationship between visual estimates of topography and species richness is strongest with fish 10–30 cm total length (TL), abundance of fish within this size category also correlating positively with topographic visual assessments. Visual techniques are prone to observer bias, however with regular training they can be used to quickly provide a reliable and effective means of assessing habitat complexity and benthos on coral reefs.     

Effects of eutrophication on reef-building corals

Seven fringing reef complexes were chosen along the leeward coast (west) of Barbados to study the effects of eutrophication processes upon the scleractinian coral assemblages. The structure of scleractinian coral communities was studied along an eutrophication gradient with a quantitative sampling method (line transect) in terms of species composition, zonation and diversity patterns. On the basis of these data the fringing reefs were divided into three ecological zones: back reef, reef flat, and spur and groove. Statistically discernible and biologically significant differences in scleractinian coral community structure, benthic algal cover and Diadema antillarum Philippi densities were recorded among the seven fringing reefs. High correlations between environmental variables and biotic patterns indicate that the effects of eutrophication processes (nutrient enrichment, sedimentation, turbidity, toxicity and bacterial activity) were directly and/or indirectly affecting the community structure of scleractinian coral assemblages. In general, species diversity was most sensitive in delineating among-reef, and among-zone, differences, which were attributed to intensification of eutrophication processes. Porites astreoides Lamarck, P. porites (Pallas), Siderastrea radians (Pallas), and Agaricia agaricites (Linnaeus) were the most abundant coral species in the polluted southern reefs. The absence and/or low abundance of coral species previously characterized as well adapted to high turbidity and sedimentation [i.e. Montastrea cavernosa Linnaeus, Meandrina meandrites (Linnaeus)] indicate that eutrophication processes may adversely affect these species. It is suggested that sediment rejection abilities, combined with feeding and reproductive strategies, are the primary biological processes of scleractinian corals through which eutrophication processes directly and/or indirectly affect the structure of coral communities.     

ReefBahia, an integrated GIS approach for coral reef conservation in Bahia, Brazil

Coral reefs around the world are facing serious threats. These fragile ecosystems are in need for conservation. The coastal state of Bahia hosts the most extensive and richest area of coral reefs in the South Atlantic Ocean. Assessment, planning and management of coral reef ecosystems are particularly challenging tasks. This work shows how the creation of a GIS improves the process of management, monitoring and conservation of the Bahian reef environments The initial data input started by the vectorization of 1) bathymetric data from the Bureau of Hydrography and Navigation (DHN), 2) shoreline and mangrove areas from Landsat 7 ETM + images, 3) near surface reefs from Quickbird images, and 4) coastal and marine protected areas of federal, state and local administrations. Geological, physical, biological and social information was then included in order to create a suitable marine GIS for conservation aims. The data includes information on sediment granulometry and transport patterns, rocky substrate outcrops, sea surface temperature, wave direction, rain precipitation, major contributing river discharge, artisanal fishery, benthic cover and bleaching data. ReefBahia GIS has provided essential information for a better understanding of coral reefs of the state of Bahia geological and ecological characteristics such as mapping, representation, connectivity and biodiversity of coral reefs, geological facies, Quaternary sedimentation, numeric modeling of wave refraction and monitoring of bleaching events.     

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.     

Reef size and isolation determine the temporal stability of coral reef fish populations

Temporal variance in species abundance, a potential driver of extinction, is linked to mean abundance through Taylor's power law, the empirical observation of a linear log-log relationship with a slope between 1 and 2 for most species. Here we test the idea that the slope of Taylor's power law can vary both among species and spatially as a function of habitat area and isolation. We used the world's most extensive database of coral reef fish communities comprising a 15-year series of fish abundances on 43 reefs of Australia's Great Barrier Reef. Greater temporal variances were observed at small and isolated reefs, and lower variances at large and connected ones. The combination of reef area and isolation was associated with an even greater effect on temporal variances, indicating strong empirical support for the idea that populations on small and isolated reefs will succumb more frequently to local extinction via higher temporal variability, resulting in lower resilience at the community level. Based on these relationships, we constructed a regional predictive map of the dynamic fragility of coral reef fish assemblages on the Great Barrier Reef.     

Migration,habitat use,and competition among mobile corals (Scleractinia: Fungiidae) in the Gulf of Eilat,Red Sea

We examined the impact of seven species of mobile mushroom corals (Fungiidae) on the community structure of sheltered reef slopes in terms of their patterns of migration, habitat use and competition with other benthic organisms. On fringing reefs at Eilat, Red Sea, polyps detached at 1 to 6 cm length, and grew to 11–55 cm length. Attached mushroom corals were oriented vertically in reef cavities. Detached corals migrated downward on the reef slope and onto rubble or soft substratum at the reef base, at 29 to 71 cmyr^–1. Mobility decreased with corallum size and extent of undersurface ornamentation. In aquaria, small corals righted themselves and migrated up to 6 cm d^–1 by nocturnally inflating and pushing their tissues against the substratum. Autonomous coral behavior and storm-generated water motion appeared to account for most fungiid mobility at Eilat. Mushroom corals did not damage each other upon contact, even in multi-species aggregations, but unilaterally damaged non-fungiid scleractinian corals. Their dominance during contact interactions retards overgrowth by larger attached scleractinians, and mobility allows them to colonize soft substrata not accessible to most other reef corals.     

Multi-scale marine biodiversity patterns inferred efficiently from habitat image processing

Cost-effective proxies of biodiversity and species abundance, applicable across a range of spatial scales, are needed for setting conservation priorities and planning action. We outline a rapid, efficient, and low-cost measure of spectral signal from digital habitat images that, being an effective proxy for habitat complexity, correlates with species diversity and requires little image processing or interpretation. We validated this method for coral reefs of the Great Barrier Reef (GBR), Australia, across a range of spatial scales (1 m to 10 km), using digital photographs of benthic communities at the transect scale and high-resolution Landsat satellite images at the reef scale. We calculated an index of image-derived spatial heterogeneity, the mean information gain (MIG), for each scale and related it to univariate (species richness and total abundance summed across species) and multivariate (species abundance matrix) measures of fish community structure, using two techniques that account for the hierarchical structure of the data: hierarchical (mixed-effect) linear models and distance-based partial redundancy analysis. Over the length and breadth of the GBR, MIG alone explained up to 29% of deviance in fish species richness, 33% in total fish abundance, and 25% in fish community structure at multiple scales, thus demonstrating the possibility of easily and rapidly exploiting spatial information contained in digital images to complement existing methods for inferring diversity and abundance patterns among fish communities. Thus, the spectral signal of unprocessed remotely sensed images provides an efficient and low-cost way to optimize the design of surveys used in conservation planning. In data-sparse situations, this simple approach also offers a viable method for rapid assessment of potential local biodiversity, particularly where there is little local capacity in terms of skills or resources for mounting in-depth biodiversity surveys.     

Effect of Macroalgal Expansion and Marine Protected Areas on Coral Recovery Following a Climatic Disturbance

Disturbance plays an important role in structuring marine ecosystems, and there is a need to understand how conservation practices, such as the designation of Marine Protected Areas (MPAs), facilitate postdisturbance recovery. We evaluated the association of MPAs, herbivorous fish biomass, substrate type, postdisturbance coral cover, and change in macroalgal cover with coral recovery on the fringing reefs of the inner Seychelle islands, where coral mortality after a 1998 bleaching event was extensive. We visually estimated benthic cover and fish biomass at 9 sites in MPAs where fishing is banned and at 12 sites where fishing is permitted in 1994, 2005, 2008, and 2011. We used analysis of variance to examine spatial and temporal variations in coral cover and generalized additive models to identify relations between coral recovery and the aforementioned factors that may promote recovery. Coral recovery occurred on all substrate types, but it was highly variable among sites and times. Between 2005 and 2011 the increase in coral cover averaged 1%/year across 21 sites, and the maximum increase was 4%/year. However, mean coral cover across the study area (14%) remained at half of 1994 levels (28%). Sites within MPAs had faster rates of coral recovery than sites in fished areas only where cover of macroalgae was low and had not increased over time. In MPAs where macroalgae cover expanded since 1998 there was no recovery. Where coral was recovering on granite reefs there was a shift in relative prevalence of colony life‐form from branching to encrusting species. This simplification of reef structure may affect associated reef fauna even if predisturbance levels of coral cover are attained. Efecto de la Expansión de Macroalgas y Áreas Marinas Protegidas sobre la Recuperación de Coral Después de una Perturbación Climática     

Modelling coral reef ecosystems with limited observational data

Ecosystem models represent potentially powerful tools for coral reef ecosystem managers. They can provide insight into ecosystem dynamics not achievable through alternative means allowing coral reef managers to assess the potential outcome of any given management decision. One of the main limitations in the applicability of ecosystem models is that they often require detailed empirical data and this can restrict their applicability to ecosystems that are either currently well studied or have the resources available to collect the required data. This study describes the development of a coral reef ecosystem model that can be calibrated to an ecosystem with limited empirical data. Based on the assumption that coral reef ecological structure is generic across all tropical coral reefs and that the magnitude of the interactions between ecological components is reef specific, the dynamics of the ecosystem can be replicated based on limited empirical data. The model successfully replicated the dynamics of three individual reef systems including an inshore and oceanic reef within the Great Barrier Reef and a Caribbean reef system. It highlighted the importance of understanding the specific dynamics of a given reef and that a positive management intervention in one system may result in a negative outcome for another. The model was also used to assess the importance of various interactions within coral reef ecosystems. It identified the interactions between hard corals and other non-algal benthic components as being an important (but currently understudied) facet of coral reef ecology. The development of this modelling approach provides access to ecosystem modelling tools for coral reef managers previously excluded due to a lack of resources or technical expertise.     

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.     

Using Coral Disease Prevalence to Assess the Effects of Concentrating Tourism Activities on Offshore Reefs in a Tropical Marine Park

Abstract: Concentrating tourism activities can be an effective way to closely manage high‐use parks and minimize the extent of the effects of visitors on plants and animals, although considerable investment in permanent tourism facilities may be required. On coral reefs, a variety of human‐related disturbances have been associated with elevated levels of coral disease, but the effects of reef‐based tourist facilities (e.g., permanent offshore visitor platforms) on coral health have not been assessed. In partnership with reef managers and the tourism industry, we tested the effectiveness of concentrating tourism activities as a strategy for managing tourism on coral reefs. We compared prevalence of brown band disease, white syndromes, black band disease, skeletal eroding band, and growth anomalies among reefs with and without permanent tourism platforms within the Great Barrier Reef Marine Park. Coral diseases were 15 times more prevalent at reefs with offshore tourism platforms than at nearby reefs without platforms. The maximum prevalence and maximum number of cases of each disease type were recorded at reefs with permanently moored tourism platforms. Diseases affected 10 coral genera from 7 families at reefs with platforms and 4 coral genera from 3 families at reefs without platforms. The greatest number of disease cases occurred within the spatially dominant acroporid corals, which exhibited 18‐fold greater disease prevalence at reefs with platforms than at reefs without platforms. Neither the percent cover of acroporids nor overall coral cover differed significantly between reefs with and without platforms, which suggests that neither factor was responsible for the elevated levels of disease. Identifying how tourism activities and platforms facilitate coral disease in marine parks will help ensure ongoing conservation of coral assemblages and tourism.     

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

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

A geological perspective on the degradation and conservation of western Atlantic coral reefs

Continuing coral‐reef degradation in the western Atlantic is resulting in loss of ecological and geologic functions of reefs. With the goal of assisting resource managers and stewards of reefs in setting and measuring progress toward realistic goals for coral‐reef conservation and restoration, we examined reef degradation in this region from a geological perspective. The importance of ecosystem services provided by coral reefs—as breakwaters that dissipate wave energy and protect shorelines and as providers of habitat for innumerable species—cannot be overstated. However, the few coral species responsible for reef building in the western Atlantic during the last approximately 1.5 million years are not thriving in the 21st century. These species are highly sensitive to abrupt temperature extremes, prone to disease infection, and have low sexual reproductive potential. Their vulnerability and the low functional redundancy of branching corals have led to the low resilience of western Atlantic reef ecosystems. The decrease in live coral cover over the last 50 years highlights the need for study of relict (senescent) reefs, which, from the perspective of coastline protection and habitat structure, may be just as important to conserve as the living coral veneer. Research is needed to characterize the geological processes of bioerosion, reef cementation, and sediment transport as they relate to modern‐day changes in reef elevation. For example, although parrotfish remove nuisance macroalgae, possibly promoting coral recruitment, they will not save Atlantic reefs from geological degradation. In fact, these fish are quickly nibbling away significant quantities of Holocene reef framework. The question of how different biota covering dead reefs affect framework resistance to biological and physical erosion needs to be addressed. Monitoring and managing reefs with respect to physical resilience, in addition to ecological resilience, could optimize the expenditure of resources in conserving Atlantic reefs and the services they provide.     

A spatial model of growth and competition strategies in coral communities

A discrete spatial simulation model is developed to investigate the type and intensity of biological and physical factors influencing the structure of coral communities. The model represents reproduction, growth, and interspecific competition by coral colonies in terms of “ownership” of space in a plot of reef habitat. Using data for several eastern Pacific coral species, the model reproduces observed changes in species composition and diversity during coral community development. Model results suggest that during early successional stages, or in areas that are frequently disturbed, larval colonization and rapid growth are more important than dominance achieved by extracoelenteric digestion or by growing over another coral in acquiring and maintaining possession of reef substrate. In mature communities that remain undisturbed, dominance is the best competitive strategy. Although the model was developed to study natural and man-induced changes in the community dynamics of coral reefs, it could be adapted to study other sessile organisms where spatial pattern is an important influence on the frequency and outcome of biological interactions.     

Surface area in ecological analysis: Quantification of benthic coral-reef algae

The surface area of organisms and substrata is shown to be a significant ecological parameter because of its functional importance in the system. Quantification of surface area can be of particular value in morphologically complex environments such as coral reefs. The amount of surface in a reef habitat can be estimated by direct measurements and theoretical approximations, using a surface index (SI) for the amount of surface increase over that of a similarly bounded plane. SI values for a section of the British Honduran barrier reef ranged up to 15 in the reef-crest area at scales significant to macro-organisms. By combining substrate-area measurements with estimates of percent coverage of the major benthic algal components, a reef transect with a horizontal area of 300 m² was shown to have over 300 m² covered by benthic macroalgae. The potential for the further development of surface estimation techniques is discussed.     

Slow Growth and Lack of Recovery in Overfished Holothurians on the Great Barrier Reef: Evidence from DNA Fingerprints and Repeated Large-Scale Surveys

Abstract:  Commercially fished holothurians have important functions in nutrient recycling, which increases the benthic productivity of coral reef ecosystems. Thus, removal of these animals through fishing may reduce the overall productivity of affected coral reefs. To investigate the potential for recovery of overfished holothurian (  Holothuria nobilis ) stocks on the Great Barrier Reef (GBR), we (1) conducted field surveys on 23 reefs after fishery closure, (2) modeled total virgin biomass and compared it with the total amount fished, and (3) estimated individual growth rates with a DNA fingerprinting technique. Two years after fishery closure, no recovery of H. nobilis stocks on reefs previously open to fishing was observed. Densities on reefs protected from fishing since the onset of the fishery in the mid 1980s remained about four times higher than on fished reefs. Based on density estimates and geographic information system data on the habitat area of each reef, we calculated that the virgin biomass (in the main fished area between 12° and 19°S) was about 5500 t and is now about 2500 t. The reduction is on the same order of magnitude as the total amount fished until 1999 (approximately 2500 t). The DNA analysis of repeated samples on three locations indicated high recapture rates of fingerprinted and released individuals of H. nobilis . Fitting growth curves with Francis's growth function indicated that medium-sized individuals (1 kg) grew 35–533 g /year, whereas large animals (2.5 kg) consistently shrank. Small animals (<500 g) were rarely observed. In combination, these data indicate that production of H. nobilis stocks is very low, presumably with low mortality, low recruitment, and slow individual growth rates. Consistent with anecdotal evidence, recovery of H. nobilis stocks on the GBR may take several decades, and we suggest a highly conservative management plan to protect both the stocks and the ecosystem.