Pristine Coral Reefs Research Articles

The impact of space, host dissimilitude, and environment on prokaryotic communities of golf ball sponges

AbstractGolf ball sponges are small, sometimes inconspicuous, sponges. They can be found across a range of habitats varying from perturbed and pristine coral reefs to harbours and marine lakes and from the deep sea to shallow waters. They can be difficult to distinguish in the field and have presented some problems with taxonomists lumping and splitting species due to the difficulty in defining clear species boundaries. In the present study, we sampled golf ball sponges from Indo‐Pacific and Caribbean locations and used 16S gene amplicon sequencing to study their prokaryotic communities. We show that golf ball sponges harbour a wide variety of prokaryotic communities. Among the most prevalent operational taxonomic units (OTUs), several belonged to a range of taxa, including the bacterial AqS1 and EC94 groups, which have been associated with genes known to facilitate interactions between hosts and microbes. Certain host taxa were enriched with OTUs classified to the SAR202 clade of Chloroflexi. Our findings show that prokaryotic dissimilarity varied as a function of space (geographical distance) and host dissimilitude. The importance of space and host dissimilitude, however, varied depending on the data transformation with host dissimilitude a more important predictor of untransformed data whereas space was a more important predictor of log‐transformed data. Given that log‐transformation downscales the influence of abundant taxa, we interpret these results by the tendency of closely related host organisms to host similar sets of abundant symbiotic microorganisms; distantly sampled specimens, in contrast, tend to harbour less abundant prokaryotic microorganisms found in the surrounding environment (e.g., seawater or sediment).

Marine heatwaves impair the thermal refugia potential of marginal reefs in the northern South China Sea

Frequent marine heatwaves (MHWs), concurrent with climate warming, threaten global low-latitude, pristine coral reefs, leading to growing interest in identifying marginal coral reefs (relatively high-latitude and/or turbid reef environments) that can serve as thermal refugia from mass coral bleaching. However, the thermal refugia potential of marginal reefs remains controversial. We evaluated the thermal refugia potential of inshore reefs in the northern South China Sea (nSCS), a globally typical marginal reef system, by characterizing the long-term trend of MHW intensity and frequency and assessing thermal stress during a mass bleaching event in summer 2020. An unprecedented peak intensity of around 20 °C-weeks of cumulative heat stress, associated with a prolonged anomalous western Pacific subtropical high (WPSH) and weakened monsoon activity, induced record-breaking bleaching. The geographical variability of bleaching was strongly related to the extent of heat exposure and satellite-derived temperature anomalies. Under ongoing global warming, the frequency and intensity of MHWs over nSCS coral habitats show a markedly increasing trend, especially during the last decade. Intense MHWs and coral bleaching have already occurred throughout all El Niño-Southern Oscillation (ENSO) phases (e.g., 2010, 2015, and 2020). Climate change has pushed marginal coral reefs to or beyond the limits of their resilience, and frequent MHW events have amplified the increasing risk of thermal stress. There are no long-term thermal refugia for marginal reefs in the nSCS.

Observations of sharks (Elasmobranchii) at Europa Island, a remote marine protected area important for shark conservation in the southern Mozambique Channel

Sharks have declined worldwide and remote sanctuaries are becoming crucial for shark conservation. The southwest Indian Ocean is a hotspot of both terrestrial and marine biodiversity mostly impacted by anthropogenic damage. Sharks were observed during surveys performed from April to June 2013 in the virtually pristine coral reefs around Europa Island, a remote Marine Protected Area located in the southern Mozambique Channel. Observation events comprised 67 1-hour scientific dives between 5 – 35m depth and 7 snorkeling inspections, as well as 4 dinghy-based observations in the shallow lagoon. In a period of 24 days, 475 sharks were tallied. Carcharhinus galapagensis was most encountered and contributed 20% of the abundance during diving, followed by C. albimarginatus (10%). Both species were more abundant between 11-14h, and on the exposed sides of the island. Numbers of Sphyrna lewini were highest with 370 individuals windward and leeward, mostly schooling. S. lewini aggregations in the area are hypothesized to be attracted to the seamount archipelago offering favorable conditions for deep incursions and of which Europa Island forms part. C. amblyrhynchos, Galeocerdo cuvier and S. mokarran were uncommon, while there was an additional observation of Rhincodon typus. The lagoon of Europa was a nursery ground for C. melanopterus where it was the only species present. A total of 8 species was recorded, contributing to the shark diversity of 15 species reported from Europa since 1952 in the scientific and gray literature. Overall, with the occurrence of several species of apex predators in addition to that of R. typus, large schools of S. lewini, fair numbers of reef sharks and a nursery of C. melanopterus, Europa’s sharks constitute a significant reservoir of biodiversity, which contributes to preserve the functioning of the ecosystem. Our observations highlight the relevance of Europa Island for shark conservation and the need for shark-targeted management in the EEZ of both Europa and Bassas da India.

Perspectives on the impact of external risks on the future of dive tourism at a high latitude reef complex in the Indian Ocean Region

ABSTRACT South Africa's marine environment is rich in fauna and flora, and renowned for its pristine coral reefs. Yet, with various risks continuing to threaten the future of marine tourism in the Blue Economy, for how long can scuba diving tourism remain a popular marine recreational activity in the region? By means of a case study approach, this article aims to identify the range of domestic and international external risks impacting on dive tourism at a dive tourism hotspot at the iSimangaliso Wetland Park (iWP) in northern KwaZulu-Natal, South Africa. Results suggest that dive operators perceive external risks to be a significant threat to the future of their dive operations. Most pertinent are risks where domestic crime, political instability, depressed economic activity, access to dive tourism hotspots, and restrictive government regulations have impacted the dive tourism industry in the region.

Marine biodiversity of a pristine coral reef in French Polynesia

Understanding the natural state of coral reefs is paramount to evaluate the response of these ecosystems to local and global human impacts as well as management and conservation strategies. In French Polynesia, some islands are still pristine or uninhabited, such as Tupai atoll. Tupai has been uninhabited, with access to the lagoon prohibited since 2010. However, fishers from nearby islands often take from the outer reef slope at Tupai. Our marine biodiversity survey (coral, macro-invertebrates, and fish) conducted in 2019 highlighted a low density of commercial fish species and top-predators on the outer slope in comparison to the lagoon, where the top-predators represented 16% (of the density) of functional trophic groups. Our surveys also showed a high living coral cover (46%) on the outer slope of Tupai, perhaps due to the absence of both touristic sub-aquatic activities and local pollution from private and commercial activities. Overall, this initial scientific assessment of Tupai has granted an understanding of the spatial patterns of coral, macro-invertebrates, and fish assemblages in the absence of human impacts (i.e., in the lagoon), representing an ecological baseline that could inform conservation management strategies to ensure the preservation of coral reef ecosystem.

Assessing key ecosystem functions through soundscapes: A new perspective from coral reefs

Abstract The functioning of tropical coral reefs is imperilled by climate change, overfishing, and decreasing water quality. Maintaining their capacity to provide goods and services will critically depend on our ability to monitor their functioning at appropriate spatial and temporal scales. Given the constraints of traditional methods to respond to those needs, the potential of complementary tools such as Passive Acoustic Monitoring (PAM) is emerging. Coral reef soundscapes (i.e. ambient sound) encompass sounds produced by numerous organisms. Soundscape characteristics quantified by ecoacoustic indices have been found to reflect general ecosystem properties, such as diversity and abundance of fishes, and coral cover. The present study tested, on the virtually pristine coral reefs around Europa Island, South-West Indian Ocean, the capacity of acoustic indices to assess key ecosystem functions. Soundscapes were recorded during 2 h, and ecosystem functions were evaluated using video footage of the fish assemblages and underwater photogrammetry of the benthic landscapes. We found significant and strong correlations between six ecoacoustic indices and six key ecosystem functions, including habitat features and fish assemblage characteristics. The six ecoacoustic indices were representative of several combinations of frequency, amplitude and time analysis domains, highlighting the diversity of the functional information conveyed by soundscapes. Our findings reveal that a 2 h daytime recording on a coral reef could provide sufficient acoustic information to characterise major ecosystem functions of a site. This should facilitate the detection of functional disturbances at temporal and spatial scales adapted to the rapidity of upcoming climate changes. Our results also highlight the potential of ecoacoustics to bring novel and relevant insights in the functioning of ecosystems.

Deep sea mining's future effects on Fiji's tourism industry: A contingent behaviour study

Pristine coral reefs possess a tremendous potential for contributing to tourism and economic development. This is especially important for Fiji given their tourism economy's reliance on diving and coastal activities. Understanding divers’ perceptions of coral reefs and environmental issues is, therefore, paramount to sustaining the tourism industry. Despite the importance of coral reefs to the Fijian tourism sector, the Fijian Government has granted exploration licenses to mining companies to assess the viability of deep sea mining (DSM) activities in Fiji's seas. There is concern that DSM may negatively impact reef-related tourism due to tourists’ perception that DSM activities degrades Fiji's coral reefs. This study conducts a contingent behaviour survey to explore how tourists’ expectations of DSM will affect their future travel decisions and subsequently influence overall tourism demand in Fiji. Our findings show that divers and snorkelers demonstrate a high willingness to return to Fiji in the future, based on their previous travel experience, but that they would significantly reduce their future visits if DSM was to take place in Fiji. These results contribute to our understanding of the potential trade-offs between DSM and reef-related tourism and give some preliminary estimates of the potential economic consequences of the Fijian Government allowing DSM within their territorial waters.

Meta-mass shift chemical profiling of metabolomes from coral reefs

Untargeted metabolomics of environmental samples routinely detects thousands of small molecules, the vast majority of which cannot be identified. Meta-mass shift chemical (MeMSChem) profiling was developed to identify mass differences between related molecules using molecular networks. This approach illuminates metabolome-wide relationships between molecules and the putative chemical groups that differentiate them (e.g., H2, CH2, COCH2). MeMSChem profiling was used to analyze a publicly available metabolomic dataset of coral, algal, and fungal mat holobionts (i.e., the host and its associated microbes and viruses) sampled from some of Earth's most remote and pristine coral reefs. Each type of holobiont had distinct mass shift profiles, even when the analysis was restricted to molecules found in all samples. This result suggests that holobionts modify the same molecules in different ways and offers insights into the generation of molecular diversity. Three genera of stony corals had distinct patterns of molecular relatedness despite their high degree of taxonomic relatedness. MeMSChem profiles also partially differentiated between individuals, suggesting that every coral reef holobiont is a potential source of novel chemical diversity.

Resetting predator baselines in coral reef ecosystems

What did coral reef ecosystems look like before human impacts became pervasive? Early efforts to reconstruct baselines resulted in the controversial suggestion that pristine coral reefs have inverted trophic pyramids, with disproportionally large top predator biomass. The validity of the coral reef inverted trophic pyramid has been questioned, but until now, was not resolved empirically. We use data from an eight-year tag-recapture program with spatially explicit, capture-recapture models to re-examine the population size and density of a key top predator at Palmyra atoll, the same location that inspired the idea of inverted trophic biomass pyramids in coral reef ecosystems. Given that animal movement is suspected to have significantly biased early biomass estimates of highly mobile top predators, we focused our reassessment on the most mobile and most abundant predator at Palmyra, the grey reef shark (Carcharhinus amblyrhynchos). We estimated a density of 21.3 (95% CI 17.8, 24.7) grey reef sharks/km2, which is an order of magnitude lower than the estimates that suggested an inverted trophic pyramid. Our results indicate that the trophic structure of an unexploited reef fish community is not inverted, and that even healthy top predator populations may be considerably smaller, and more precarious, than previously thought.

Spatiotemporal Assessment of CO2\u2013Carbonic Acid System Dynamics in a Pristine Coral Reef Ecosystem, French Frigate Shoals, Northwestern Hawaiian Islands

Observations of surface seawater fugacity of carbon dioxide (fCO2) and pH were collected over a period of several days at French Frigate Shoals (FFS) in the Northwestern Hawaiian Islands (NWHI) in order to gain an understanding of the natural spatiotemporal variability of the marine inorganic carbon system in a pristine coral reef ecosystem. These data show clear island-to-open ocean gradients in fCO2 and total alkalinity that can be measured 10–20 km offshore, indicating that metabolic processes influence the CO2–carbonic acid system over large areas of ocean surrounding FFS and by implication the islands and atolls of the NWHI. The magnitude and extent of this spatial gradient may be driven by a combination of physical and biogeochemical processes including reef water residence time, hydrodynamic forcing of currents and tidal flow, and metabolic processes that occur both on the reef and within the lagoon.

Tectonic subsidence provides insight into possible coral reef futures under rapid sea-level rise

Sea-level rise will change environmental conditions on coral reef flats, which comprise extensive habitats in shallow tropical seas and support a wealth of ecosystem services. Rapid relative sea-level rise of 0.6 m over a relatively pristine coral reef in Solomon Islands, caused by a subduction earthquake in April 2007, generated a unique opportunity to examine in situ coral reef response to relative sea-level rise of the magnitude (but not the rate) anticipated by 2100. Extent of live coral was measured from satellite imagery in 2003, 2006, 2009 and 2012. Ecological data were obtained from microatolls and ecological surveys in May 2013. The reef was sampled at 12 locations where dense live hard coral remained absent, remained present or changed from absent to present following subsidence. Ecological data (substratum depth, live coral canopy depth, coral canopy height, substratum suitability, recruitment, diversity and Acropora presence) were measured at each location to identify factors associated with coral response to relative sea-level rise. Vertical and horizontal proliferation of coral occurred following subsidence. Lateral expansion of live coral, accomplished primarily by branching Acropora spp., resulted in lower diversity in regions which changed composition from pavement to dense live coral following subsidence. Of the ecological factors measured, biotic factors were more influential than abiotic factors; species identity was the most important factor in determining which regions of the reef responded to rapid sea-level rise. On relatively pristine reef flats under present climatic conditions, rapid relative sea-level rise generated an opportunity for hard coral to proliferate. However, the species assemblage of the existing reef was important in determining response to sea-level change, by providing previously bare substrate with a source of new coral colonies. Degraded reefs with altered species composition and slower coral growth rates may be less able to respond to climate change-induced sea-level changes.

Connectivity in grey reef sharks (Carcharhinus amblyrhynchos) determined using empirical and simulated genetic data.

Grey reef sharks (Carcharhinus amblyrhynchos) can be one of the numerically dominant high order predators on pristine coral reefs, yet their numbers have declined even in the highly regulated Australian Great Barrier Reef (GBR) Marine Park. Knowledge of both large scale and fine scale genetic connectivity of grey reef sharks is essential for their effective management, but no genetic data are yet available. We investigated grey reef shark genetic structure in the GBR across a 1200 km latitudinal gradient, comparing empirical data with models simulating different levels of migration. The empirical data did not reveal any genetic structuring along the entire latitudinal gradient sampled, suggesting regular widespread dispersal and gene flow of the species throughout most of the GBR. Our simulated datasets indicate that even with substantial migrations (up to 25% of individuals migrating between neighboring reefs) both large scale genetic structure and genotypic spatial autocorrelation at the reef scale were maintained. We suggest that present migration rates therefore exceed this level. These findings have important implications regarding the effectiveness of networks of spatially discontinuous Marine Protected Areas to protect reef sharks.

Evidence for overfishing on pristine coral reefs: reconstructing coastal catches in the Australian Indian Ocean Territories

The fisheries statistics systems of many countries are performing poorly, often failing to report on small-scale catches, particularly from subsistence and recreational fisheries. These deficiencies, which lead to the underestimation of catches, are particularly evident in overseas territories of developed countries. This study is an attempt to remedy this for the years 1950–2010 for the Australia Indian Ocean Territories, an area from which little reporting is done. The results suggest that the Cocos (Keeling) Islands had a catch of approximately 80 t·year−1 in the 1950s (essentially subsistence based), which increased, starting in the mid-1980s to reach 250 t·year−1 in recent years, mainly due to the introduction of recreational and later commercial fishing, with signs of overexploitation since 2000. The coastal catch from Christmas Island was tentatively assessed as being higher (40–70 t·year−1) in the 1950s and 1960s than in the 2000s (<30 t·year−1). Fisheries managers in these areas should focus on determining primary target species and their vulnerability to overfishing, as well as developing island specific recreational fishing management plans.

Unsustainable Land-Based Source Pollution in a Climate of Change: A Roadblock to the Conservation and Recovery of Elkhorn Coral &amp;lt;i&amp;gt;Acropora palmata&amp;lt;/i&amp;gt; (Lamarck 1816)

Chronic eutrophication and turbidity are critical detrimental factors impacting coral reef ecosystems, adversely affecting their ecological functions, services, benefits, and resilience across multiple spatial scales and over prolonged periods of time. Inadequate land use practices and lack of appropriate sewage treatment can adversely contribute to increase land-based source pollution (LBSP) impacts in coastal waters and to magnify impacts by sea surface warming trends associated to climate change. Fringing coral reefs off Vega Baja, Puerto Rico, support extensive remnant patches of Elkhorn coral Acropora palmata (Lamarck 1816), which was listed in 2006 as a threatened species under the US Endangered Species Act. Chronic impacts by LBSP have significantly affected local downstream fringing reefs. We characterized the spatial extent of a water quality stress gradient across 12 reefs along the Vega Baja coast through monthly measurements of multiple physico-chemical parameters. Most parameters, particularly PO4, , chlorophyll-a, and the concentration of optical brighteners (OABs), showed a statistically significant increase (PERMANOVA, p 4, , and chlorophyll-a, exceeded recommended concentrations for coral reef ecosystems by factors of 7 - 50 times, 600 - 1240 times, and 17 - 83 times, respectively, depending on the source of the effluents and the distance from sewage pollution sources. Also, water turbidity exceeded 4 - 10 times the recommended value for pristine coral reefs. Coral reefs showed significant decline in close proximity to the polluted zone, showing a significantly different benthic community structure (PERMANOVA, p i.e., macroalgae, algal turf) and bare substrate. Percent coral cover and abundance of A. palmata, showed a significant increase with distance. Coral species richness, species diversity index, and the variance in taxonomic distinctness were very low on reef patches adjacent to the polluted zone, increased at a moderate distance with increasing coral cover and co-existence of multiple species, and declined far from the pollution source due to dominance exerted by A. palmata. This study suggests that chronic LBSP resulted in a major decline of one of the largest and most dense remnant stands of A. palmata across the northeastern Caribbean and that nutrient and chlorophyll-a concentrations were unsustainable for coral reefs. This situation requires immediate solution to prevent further damage to these unprecedented resources. It further suggests that chronic LBSP may synergistically magnify sea-surface warming impacts driving corals to an increased state of risk in face of forecasted climate change impacts. Actions to mitigate and adapt to climate change impacts on coral reefs must require a priori controls of LBSP to be effective.

Infaunal biodiversity patterns from Carnarvon Shelf (Ningaloo Reef), Western Australia

Infauna are important in many ecological processes but have been rarely considered in biodiversity assessments of coral reefs and surrounding areas. We surveyed infaunal assemblages and associated environmental factors (depth, seabed reflectance, sediment characteristics) in three areas (Mandu, Point Cloates, Gnaraloo) along the Carnarvon Shelf, Western Australia. This region supports Ningaloo Reef, a relatively pristine coral reef protected by the Ningaloo Marine Park and a Commonwealth marine reserve. Macrofauna were sampled with a Smith-McIntyre grab and sieved through 500 µm. A total of 423 species and 4036 individuals was recorded from 145 grabs, with infauna accounting for 67% of species and 78% of individuals. Rare species (≤2 individuals per species) represented 42% of the total assemblage. Assemblages were significantly different among all three areas, with the most distinct recorded from the southern-most area (Gnaraloo). Although assemblages varied significantly with depth and sediment composition (mud and gravel), these relationships were weak. Results from the current study broadly quantify macrofaunal diversity in the region and identify potential spatial and environmental patterns which will help inform future marine management plans, including the provision of baseline information to assess the efficacy of protected areas in soft-sediment habitats adjacent to coral reefs.

Status and community-based conservation of marine turtles in the northern Querimbas Islands (Mozambique)

AbstractSituated in the northernmost part of Mozambique, the northern Querimbas Islands support some of the most diverse and pristine coral reefs in the Western Indian Ocean. The community-based turtle conservation programme that we developed on Vamizi Island has facilitated the identification and protection of a key nesting site for the green marine turtle Chelonia mydas in Mozambique, with a mean of 122 nests per year. The area is also used by nesting female and immature hawksbill turtles Eretmochelys imbricata. Nesting activity of green turtles was observed all year round, with a peak in the summer (February–March). Incubation periods of this species showed seasonal fluctuations inversely correlated with air temperature. Hatching success was high (87%) when nests were not lost through tidal overwash and erosion, which affected nearly 40% of all nests in 2007. Using satellite tracking of four green turtles nesting on Vamizi we identified foraging grounds in marine protected areas in Kenya, Tanzania and north-west Madagascar. Migratory routes of two individuals along the East African coast were generally neritic and all passed through the waters of multiple nations and as many as six marine conservation areas, emphasizing the importance of regional cooperation. Awareness programmes were also conducted with resource users, and the development of a community-based management system triggered the creation of a marine sanctuary by the local community.

Re‐Creating Missing Population Baselines for Pacific Reef Sharks

SummarySharks and other large predators are scarce on most coral reefs, but studies of their historical ecology provide qualitative evidence that predators were once numerous in these ecosystems. Quantifying density of sharks in the absence of humans (baseline) is, however, hindered by a paucity of pertinent time-series data. Recently researchers have used underwater visual surveys, primarily of limited spatial extent or nonstandard design, to infer negative associations between reef shark abundance and human populations. We analyzed data from 1607 towed-diver surveys (>1 ha transects surveyed by observers towed behind a boat) conducted at 46 reefs in the central-western Pacific Ocean, reefs that included some of the world's most pristine coral reefs. Estimates of shark density from towed-diver surveys were substantially lower (<10%) than published estimates from surveys along small transects (<0.02 ha), which is not consistent with inverted biomass pyramids (predator biomass greater than prey biomass) reported by other researchers for pristine reefs. We examined the relation between the density of reef sharks observed in towed-diver surveys and human population in models that accounted for the influence of oceanic primary productivity, sea surface temperature, reef area, and reef physical complexity. We used these models to estimate the density of sharks in the absence of humans. Densities of gray reef sharks (Carcharhinus amblyrhynchos), whitetip reef sharks (Triaenodon obesus), and the group “all reef sharks” increased substantially as human population decreased and as primary productivity and minimum sea surface temperature (or reef area, which was highly correlated with temperature) increased. Simulated baseline densities of reef sharks under the absence of humans were 1.1–2.4/ha for the main Hawaiian Islands, 1.2–2.4/ha for inhabited islands of American Samoa, and 0.9–2.1/ha for inhabited islands in the Mariana Archipelago, which suggests that density of reef sharks has declined to 3–10% of baseline levels in these areas.ResumenLos tiburones y otros depredadores mayores son escasos en la mayoría de los arrecifes de coral, pero estudios de su ecología histórica proporcionan evidencia cualitativa de que los depredadores una vez fueron numerosos en estos ecosistemas. Sin embargo, la cuantificación de la densidad de tiburones en ausencia de humanos (línea de base) es obstaculizada por la falta de datos de series de tiempo pertinentes. Recientemente, los investigadores han utilizado muestreos visuales submarinos, de extensión espacial limitada o de diseño no estándar, para inferir asociaciones negativas entre la abundancia de tiburones de arrecife y las poblaciones humanas. Analizamos datos de 1607 muestreos por remolque de buzos (transectos >1ha muestreados por observadores remolcados por una lancha) realizados en 46 arrecifes en el Océano Pacífico centro-occidental, arrecifes que incluyeron algunos de los más prístinos del mundo. Las estimaciones de densidad de tiburones fue sustancialmente menor (<10%) que estimaciones publicadas a partir de muestreos a lo largo de transectos pequeños (<0.02 ha), lo cual no es consistente con las pirámides de biomasa invertidas (la biomasa de depredadores es mayor que la biomasa de presas) reportadas para arrecifes prístinos por otros autores. Examinamos la relación entre la densidad de tiburones de arrecife observados en los muestreos por remolque de buzos y la población humana en modelos y consideramos la influencia de la productividad oceánica primaria, la temperatura de la superficie del mar, la superficie del arrecife y su complejidad física. Utilizamos estos modelos para estimar la densidad de tiburones en ausencia de humanos. Las densidades de Carcharhinus amblyrhynchos, Triaenodon obesus y el grupo de “tiburones estrictamente arrecifales” incrementó sustancialmente a medida que disminuyó la población humana y que incrementó la productividad primaria y la temperatura de la superficie del mar (o superficie del arrecife, que estaba altamente correlacionada con la temperatura. Las densidades basales simuladas de tiburones arrecifales en ausencia de humanos fueron 1.1–2.4/ha para las Islas Hawaianas, 1.2–2.4/ha en islas deshabitadas de Samoa Americana y 0.9–2.1/ha e islas deshabitadas del Archipiélago Mariana, lo que sugiere que la densidad de tiburones arrecifales ha declinado entre 3 -10% en relación con los niveles basales en esas áreas.

MODELING FISH BIOMASS STRUCTURE AT NEAR PRISTINE CORAL REEFS AND DEGRADATION BY FISHING

Inverted biomass pyramids (IBPs) seem to be extremely rare in natural communities. Until recently, the only examples have been in freshwater and marine planktonic communities. In 2002 and 2008, investigators documented inverted biomass pyramids for nearly pristine coral reef ecosystems within the NW Hawaiian islands and the Line Islands, where apex predator abundance comprises up to 85% of the fish biomass. Large predator:prey biomass ratio seems to be a signature of nearly pristine coral reefs. While the mechanism responsible for the IBP for homogeneously mixed planktonic communities seems to be well understood, this mechanism is not strictly applicable to nearly pristine coral reefs where much of the prey use coral as refuge and are inaccessible to the predators. We construct a mathematical model with an explicit refuge to illustrate a new biologically plausible mechanism that can explain stable IBPs in nearly pristine coral reefs. New modeling components include a refuge of explicit size, a refuge size dependent functional response, and refuge size dependent prey growth rate. Utilizing realistic life history parameters of coral reef fishes, our model exhibits a stable inverted biomass pyramid. We prove that all fishing decreases the biomass ratio and sufficiently strong fishing transforms the inverted biomass pyramid to be bottom heavy. Finally we use our model to test the conjecture that pristine coral reefs will rebound faster from environmental shocks and find that it is not always true.

The Lagoon at Caroline/Millennium Atoll, Republic of Kiribati: Natural History of a Nearly Pristine Ecosystem

A series of surveys were carried out to characterize the physical and biological parameters of the Millennium Atoll lagoon during a research expedition in April of 2009. Millennium is a remote coral atoll in the Central Pacific belonging to the Republic of Kiribati, and a member of the Southern Line Islands chain. The atoll is among the few remaining coral reef ecosystems that are relatively pristine. The lagoon is highly enclosed, and was characterized by reticulate patch and line reefs throughout the center of the lagoon as well as perimeter reefs around the rim of the atoll. The depth reached a maximum of 33.3 m in the central region of the lagoon, and averaged between 8.8 and 13.7 m in most of the pools. The deepest areas were found to harbor large platforms of Favia matthaii, which presumably provided a base upon which the dominant corals (Acropora spp.) grew to form the reticulate reef structure. The benthic algal communities consisted mainly of crustose coralline algae (CCA), microfilamentous turf algae and isolated patches of Halimeda spp. and Caulerpa spp. Fish species richness in the lagoon was half of that observed on the adjacent fore reef. The lagoon is likely an important nursery habitat for a number of important fisheries species including the blacktip reef shark and Napoleon wrasse, which are heavily exploited elsewhere around the world but were common in the lagoon at Millennium. The lagoon also supports an abundance of giant clams (Tridacna maxima). Millennium lagoon provides an excellent reference of a relatively undisturbed coral atoll. As with most coral reefs around the world, the lagoon communities of Millennium may be threatened by climate change and associated warming, acidification and sea level rise, as well as sporadic local resource exploitation which is difficult to monitor and enforce because of the atoll's remote location. While the remote nature of Millennium has allowed it to remain one of the few nearly pristine coral reef ecosystems in the world, it is imperative that this ecosystem receives protection so that it may survive for future generations.

Benthic Composition of a Healthy Subtropical Reef: Baseline Species-Level Cover, with an Emphasis on Algae, in the Northwestern Hawaiian Islands

The Northwestern Hawaiian Islands (NWHI) are considered to be among the most pristine coral reef ecosystems remaining on the planet. These reefs naturally contain a high percent cover of algal functional groups with relatively low coral abundance and exhibit thriving fish communities dominated by top predators. Despite their highly protected status, these reefs are at risk from both direct and indirect anthropogenic sources. This study provides the first comprehensive data on percent coverage of algae, coral, and non-coral invertebrates at the species level, and investigates spatial diversity patterns across the archipelago to document benthic communities before further environmental changes occur in response to global warming and ocean acidification. Monitoring studies show that non-calcified macroalgae cover a greater percentage of substrate than corals on many high latitude reef sites. Forereef habitats in atoll systems often contain high abundances of the green macroalga Microdictyon setchellianum and the brown macroalga Lobophora variegata, yet these organisms were uncommon in forereefs of non-atoll systems. Species of the brown macroalgal genera Padina, Sargassum, and Stypopodium and the red macroalgal genus Laurencia became increasingly common in the two northernmost atolls of the island chain but were uncommon components of more southerly islands. Conversely, the scleractinian coral Porites lobata was common on forereefs at southern islands but less common at northern islands. Currently accepted paradigms of what constitutes a “healthy” reef may not apply to the subtropical NWHI, and metrics used to gauge reef health (e.g., high coral cover) need to be reevaluated.