Atoll Research Articles

Evolution of the Late Miocene atoll systems offshore Xisha Islands

Modern atolls have been studied systematically and thoroughly in the South China Sea. However, the knowledge of a paleo-atoll and related sedimentary system is very limited. Here we used the newly acquired high resolution 2D seismic data, and discovered three late Miocene atoll systems in the offshore Xisha Islands for the first time. We named them atoll system A, B, C, respectively. These three atoll systems, all developed on the horsts dominated by normal fault, consist mainly of atoll reefs, patch reefs, fore-reef slope deposits, and lagoons. On the basis of the interpreted sequence stratigraphic framework and the identification of fore-reef slope deposits, we suggested only the atoll system A continued to grow until Quaternary, and both of atoll system B and C had been drowned in Pliocene. In late Miocene, the atoll systems in the study area were most developed, either in magnitude or in maturity, which indicated late Miocene was the most flourishing period of reef builders, and this was in accordance with the drilling result of ODP Leg 184 in the South China Sea. Pliocene was an important reef drowning period in the study area, and both atoll systems B and C were drowned and hemipelagic deposits prevailed gradually. Quaternary was another reef drowning period in the study area, two large atoll reefs grown on the atoll system A were finally drowned, and hemipelagic deposits begun to drape and fill the palaeo-atoll systems. The growth and drowning of atolls are controlled mainly by tectonic subsidence in long term, but global eustatic can impact it in short term also.

PT-path reconstruction via unraveling of peculiar zoning pattern in atoll shaped garnets via image assisted analysis: an example from the Santa Lucia del Mela garnet micaschists (northeastern Sicily-Italy)

Garnet micaschists nearby Santa Lucia del Mela - Peloritani Mountains (North-eastern Sicily, Italy), were studied by integrating information obtained from petrographic and image-assisted analyses of mineral phase compositions by using X-ray maps and thermodynamic modeling. These rocks are characterized by the presence of atoll garnets, and preserve a continuous array of textures from pristine garnets, through peninsula or island textures, to atoll textures. Completely substituted garnets represent the final stage of the process. These textures result from the metamorphic evolution of the rocks, consisting of two main stages of recrystallization-deformation events. The sequence of mineral parageneses associated to successive deformation events is as follows: early D1 is characterized by the assemblage wm1 + chl1 + bt1 + pl1 + grt1 + qtz + ilm + ap; late D1 by grt2 + wm2 + chl2+ bt2 + pl2 + qtz + ilm + ap + hem; D2 (associated to garnet core transformation) by grt3 + bt3 + pl3 + wm3 + qtz + chl3 + ilm. On the basis of textural observations and mineral parageneses, the atoll formation is related to the substitution of garnet cores during the D2 stage, with the consumption of garnet cores (grt1) and production of new garnet rim (grt3) with wm, bi, qtz and pl. The recognition of the different stages of garnet growth and associated parageneses has been obtained using image analysis coupled with compositional maps, performed via multivariate statistical analysis of four selected X-Ray map arrays. Following the textural and mineral-chemical analyses, PT conditions associated to the three recrystallisation stages have been determined via pseudosection computations. Results indicate that the analyzed rock-types have recorded a clock-wise PT trajectory during the Variscan orogeny, defined by a prograde evolution, in amphibolite facies conditions, preserved in relic garnet cores, followed by an initial decompressional evolution toward lower amphibolite facies conditions associated to a partial heating. During this last stage the multi stadial atollization process took place, retrogradely evolving toward a green-schist facies conditions, constrained through the compositions of the pseodomorphyc mineral aggregates gradually substituting previously formed garnets.

The influence of repetitive thermal stresses on the dominance of reef-building Acropora spp. (Scleractinia) on coral reefs of the Maldive Islands

The distribution and size-age structure of Acropora corals were studied in two Maldivian atolls that differ in their geographic position and sea surface temperature regimes. The frequency and strength of thermal anomalies for the last 2 decades had a significant influence on the abundance, mortality rates, and age structures of acroporid communities. The long-term temperature amplitude was higher and the maxima were more pronounced in the northernmost Ihavandippolu Atoll than those in the equatorial South Huvadhoo Atoll. These differences resulted in a 10.4% mean cover of Acropora at Ihavandippolu Atoll, whereas the Acropora cover in the South Huvadhoo Atoll reached 59.5%. In the northern atoll, the coral mortality rate after the 2010 thermal anomaly was 3 times higher than that in the southern atoll. Younger acroporid colonies (up to 2 years old) dominated the northern atoll reefs, while the southern atoll showed a high proportion of older mature colonies. In both atolls, healthy table colonies of Acropora cytherea with a disk diameter greater than 2 m were observed that apparently survived three thermal anomalies since 1998. The mechanisms of acclimatization of Acropora and the prospects for its dominance in the Maldives under changing environmental conditions are discussed.

Delivery and assessment of small island developments

This paper reports on an aspect of continual research into small island hotel and resort development. Inputted are crucial elements of a consequential literature review linked to an appropriately selected building project case study. The analysis of existing research relevant to the topic correlated concerns fl owing from trends of rising tourist numbers set against demands for more unique locations. Concurrently, the main focus of this paper is evaluation of the planning, design, construction and operation of a new tourism resort located on an uninhabited coral atoll identifi ed and considered predicted and actual performance outcomes. Signifi cantly, this 5-year investigation critically reviewed measurable responses to ecological pressures. These were noted in the processes of assessment during and following an initial independent international third-party certifi cation organization’s auditor using a process-based development framework tool. A major driver for the research is the shared aim of several stakeholders involved in associated ‘in time’ studies. This is to ascertain the veracity of specifi c environmental, social and economic measures when implemented by resort developers and an associated facility management companies. Most actions of these parties are primarily a response to increasing emblematic relevance and exacting government-driven policies. However, many also view broader company (CSR) and community aspirations as factors crucial to the delivering of project sustainability. A primary objective of the broader research programme has involved the engendering of links between theory and practical implementation of sustainable development principles with the reality of development. Another and equally pragmatic consideration was to show and evaluate the use of process tools by those engaged in the planning, design, construction and eventual operation of hotel and resort developments. This activity is to determine their propensity to using performance framework models targeted at achieving sustainable development and improved ecological outcomes.

Mapping bottom depth and albedo in coastal waters of the South China Sea islands and reefs using Landsat TM and ETM+ data

Optical models for the retrieval of shallow water bottom depth and albedo using multispectral data usually require in situ water depth data to tune the model parameters. In the South China Sea (SCS), however, such in situ data are often lacking or obsolete (perhaps from half a century ago) for most coastal waters around its islands and reefs. Here, we combine multispectral data collected by MODIS and Landsat to estimate bottom depth and albedo for four coral reef regions in the SCS, with results partially validated by some scarce in situ data. The waters in these remote regions are oligotrophic whose optical properties can be well derived from Moderate Resolution Imaging Spectroradiometer (MODIS) measurements when the waters are optically deep. The MODIS-derived optical properties are used to estimate the water column attenuation to the Landsat measurements over shallow waters, thus eliminating the requirement of model tuning using field measured water depths. The model is applied to four Landsat Thematic Mapper (TM) and Enhanced Thematic Mapper Plus (ETM+) images covering Pratas Atoll, Woody Island, Scarborough Shoal, and North Danger Reefs. The retrieved bathymetry around Pratas Atoll and North Danger Reefs are validated with some in situ data between 1 and 25 m. The relative difference and root mean square difference between the two measurements were 17% and 1.6 m, for Pratas Atoll and 11% and 1.1 m for North Danger Reefs, respectively. These results suggest that the approach developed here may be extended to other shallow, clear waters in the SCS.

Consequences of a government-controlled agricultural price increase on fishing and the coral reef ecosystem in the republic of kiribati.

BackgroundEconomic development policies may have important economic and ecological consequences beyond the sector they target. Understanding these consequences is important to improving these policies and finding opportunities to align economic development with natural resource conservation. These issues are of particular interest to governments and non-governmental organizations that have new mandates to pursue multiple benefits. In this case study, we examined the direct and indirect economic and ecological effects of an increase in the government-controlled price for the primary agricultural product in the Republic of Kiribati, Central Pacific.Methods/Principal FindingsWe conducted household surveys and underwater visual surveys of the coral reef to examine how the government increase in the price of copra directly affected copra labor and indirectly affected fishing and the coral reef ecosystem. The islands of Kiribati are coral reef atolls and the majority of households participate in copra agriculture and fishing on the coral reefs. Our household survey data suggest that the 30% increase in the price of copra resulted in a 32% increase in copra labor and a 38% increase in fishing labor. Households with the largest amount of land in coconut production increased copra labor the most and households with the smallest amount of land in coconut production increased fishing the most. Our ecological data suggests that increased fishing labor may result in a 20% decrease in fish stocks and 4% decrease in coral reef-builders.Conclusions/SignificanceWe provide empirical evidence to suggest that the government increase in the copra price in Kiribati had unexpected and indirect economic and ecological consequences. In this case, the economic development policy was not in alignment with conservation. These results emphasize the importance of accounting for differences in household capital and taking a systems approach to policy design and evaluation, as advocated by sustainable livelihood and ecosystem-based management frameworks.

Morphodynamic characterization of beaches on a Pacific atoll island: Tetiaroa, French Polynesia

Jeanson, M., Anthony, E.J., Etienne, S., Dolique, F., 2014. Morphodynamic characterization of beaches on a Pacific atoll island: Tetiaroa, French Polynesia. In: Green, A.N. and Cooper, J.A.G. (eds.), Proceedings 13th International Coastal Symposium (Durban, South Africa), Journal of Coastal Research, Special Issue No. 70, pp. 176–181, ISSN 0749-0208.Beach profile types and wave characteristics were monitored in April 2013 on the small islet of Onetahi in the south Pacific coral reef atoll of Tetiaroa, French Polynesia, with the aim of characterizing atoll islet beach morphodynamics. Twelve beach profiles were each surveyed using a theodolite, and water levels and wave characteristics measured over four semi-diurnal tidal cycles using four miniature pressure sensors deployed in the subtidal zone. Water levels corresponded to a very narrow microtidal range (~0.2 m). Wave heights were extremely low throughout (<0.15 m), and spectral decomposition showed a mix between gravity and infragravity energy. The latter dominant at high water, whereas energy was virtually nil at low tide. The wave characteristics, which reflect significant filtering of large Pacific waves by the atoll reef, were not in phase with the intertidal beach morphology. These were interpreted as largely inherited from differential exposure to higher-energy events that occasionally impacted the atoll, notably Cyclone Oli in February 2010. Sand aprons in the lagoon, moving from the eastern to the southern and ultimately the western shores of the island in response to wave pumping, locally enhance build-up of the lower beach where shoreline orientation changes. Confrontation of these observations with long-term islet shoreline trends identified by Le Cozannet et al. (2013) suggests that high-energy event-scale changes and daily background beach cosmetic changes associated with subtidal sand apron mobility, and intertidal swash reworking during the narrow tidal excursion are embedded in long-term morphological stability likely hinged on sand circulation around the islet.

Spatial discordance in fish, coral, and sponge assemblages across a Caribbean atoll reef gradient

AbstractCertain biodiversity patterns on coral reefs are generally consistent but we still lack fundamental insight into how assemblages vary across spatially heterogeneous reef systems. We compared fish, coral, and sponge assemblages across a symmetrical physiographical gradient (windward forereef, lagoon patch reef, leeward forereef) of the Glover's Reef atoll, Belize. Species richness of fishes and corals was highest in the deep habitat (15 m) on the windward forereef. Sponges were diverse and abundant on both deep windward and leeward forereefs but not on the exposed shallow (5 m) windward forereef. Fish and benthic assemblages were relatively distinct in each reef zone, with the lagoon patch reef communities consisting of a combination of leeward and windward species. Nevertheless, there were no clear patterns in community similarity matrices of fish and benthic assemblages, suggesting that overall coral and sponge assemblages had weak or no direct association with patterns in fish assemblages. A closer examination of fish trophic groups indicated that planktivores and predators were predictably associated with depth, whereas herbivores were associated with shallow protected reefs. None was specifically associated with spatial location along the atoll gradient. These patterns of diversity distribution are important for identifying spatial conservation priorities. A Marine Protected Area (MPA) at Glover's Reef encompasses substantial windward forereef and patch reef habitats. A much lesser extent of protection is afforded the leeward forereef that supports faunal assemblages that are unique and productive, if not as diverse as the windward forereef. Isolated coral atolls can serve as ideal systems to study spatial heterogeneity and biodiversity patterns, but more experimental studies are needed to reveal the mechanistic processes underlying these patterns.

Beach development on an uplifted coral atoll: Niue, south west Pacific

Niue is an uplifted coral atoll in the south western Pacific characterised by erosional terraces on its coastal margin. Beaches are found around the island located in pockets at the rear of erosional shore platforms. The beaches in Niue are <100m long, <25m wide and generally less than 0.5m thick. The beaches sit on top of an abrasion ramp that dips seaward at a similar angle to the beach. The morphology, stability and sedimentology of these beaches are investigated through laser surveying, aerial photo analysis and petrographic techniques. Surveying was undertaken in 2008 and 2010 with data compared to previous work conducted in the 1990s in order to assess the controls on sediment deposition on uplifted coral atolls. There is a high potential for sediment transport on the island. The beaches are entirely removed during tropical cyclone events and even under calm conditions sediment is mobile. The restriction of beaches to pockets along the rocky coast suggests that these areas temporally interrupt sediment transport allowing beaches to form. All the beaches are composed of a typical chlorozoan assemblage of carbonate grains dominated by coral (20–50%), coralline algae (18%) and foraminifera (up to 81%). These sediments are produced on the platforms in the immediate vicinity of the beaches with little longshore transport between embayments being evident. The close relationship between source and depositional zones, combined with the high transport potential across the platforms indicates that the beaches are highly vulnerable to any change in either energy conditions or sediment supply.

Architecture, development and geological control of the Xisha carbonate platforms, northwestern South China Sea

Newly acquired seismic data allow improved understanding of the architecture and evolution of isolated carbonate platforms on the continental slope of the northern South China Sea. The Xisha carbonate platforms were initiated on a basement high, the Xisha Uplift, in the early Miocene and have remained active up to the present. Their distribution is limited to pre-existing localized, fault-bounded blocks within the Xisha Uplift so individual platforms were small in size at the beginning of the Miocene. However, during the middle Miocene, the platform carbonate factories flourished across an extensive area with 55,900 km(2). The platforms began to backstep in response to a relative sea-level rise in the late Miocene. Platform-edge reefs, patch reefs, pinnacle reefs, atoll reefs and horseshoe reefs, all developed on various platforms. The distribution of platform carbonates shrank significantly during Pliocene-Quaternary time to isolated carbonate platforms, represented today by Xuande Atoll and Yongle Atoll. Tectonics and eustasy were the two main controls on platform development. Tectonics controlled both the initial topography for reef growth and the distribution of platforms, including those that survived the drowning event associated with the late Miocene rapid relative sea-level rise. Eustasy controlled high-frequency carbonate sequence development Crown Copyright (C) 2014 Published by Elsevier B.V. All rights reserved.

Recovery of Missing Explanatory Notes of the First Geological Map of Funafuti Atoll, 1904

Funafuti atoll in the central Pacific was the site of the first deep drilling into a coral atoll. Drilling was carried out during three expeditions in 1896–98, sponsored by the Royal Society, London. Its purpose was purely scientific: to test Charles Darwin’s theory of coral atoll formation. Surface geological investigations were also undertaken during the second expedition in 1897, and detailed maps, descriptions and explanatory notes on the 32 islands located on the atoll rim were prepared for publication in the Royal Society’s report on The Atoll of Funafuti, published in 1904. However, not all of the island descriptions and explanatory notes that accompanied the final 63 page text and 14 map sheets on the geology of Funafuti Atoll were included in the published work, although this appears not to have been noticed by the volume’s editor, Professor T.G. Bonney in London, or by the authors T.W. Edgeworth David and George Sweet in Australia. Lacking are descriptions of the islands on Funafuti’s northern and northwestern rim as well as the explanatory notes to accompany five of the 14 map sheets. Searches were undertaken through archives of the expedition in the United Kingdom and Australia in an attempt to uncover the ‘missing’ material. This archival search met with partial success in the Sir Edgeworth David Papers at Sydney University where a draft manuscript containing ‘explanatory notes’ on seven islands and five of the 14 map sheets was uncovered. These notes are transcribed in an annex to the present report. The reasons behind the omission of this material in the final publication are not clear, though the archival documentation does provide a fascinating insight into the difficulties associated with scientific expedition publications at the end of the nineteenth century, when editors and authors were separated by large time and space differences, several contributors were involved in map, note and text preparation, and drafts of chapters and illustrations were transported in hard-copy over long distances, such as from Australia to the United Kingdom, as was the case of the Funafuti report.

Mesozooplankton Distribution in Kavaratti Atoll, Lakshadweep Archipelago, South West Coast of India with Special Reference to Calanoid Copepods

Lakshadweep archipelago is a group of coral Islands on the West coast of the Arabian Sea. It is one among the unique coral atolls in India that are well known for several species of fishes and other biotic resources. Seasonal variation in mesozooplankton, particularly of copepod abundance and distribution in the inner and outer lagoon of Kavaratti atoll were studied during April 2013 (premonsoon), September 2013 (monsoon) and January 2014 (postmonsoon). Copepods were the most dominant taxa in all the stations and seasons, that accounted 44.15 to 85.97% of the total mesozooplankton abundance. Ostracoda (premonsoon), crustacean larvae (monsoon) and chaetognaths (postmonsoon) formed the abundant groups in the respective seasons. Mesozooplankton community in the study area exhibits temporal variation corresponding to the variation in abiotic parameters therefore can be used as potential indicators of water quality. Calanoid copepods formed the dominant taxa during monsoon and postmonsoon, while cyclopoid copepods dominated during premonsoon. Among the copepods, species of the family Candacidae, Calanidae, Pontellidae, Temoridae, Psuedodiaptomidae, Centropagidae and Oithonidae were predominant. The ten species of calanoids

Long-distance dispersal of the coconut palm by migration within the coral atoll ecosystem

The location of the original home of the coconut palm, Cocos nucifera, and the extent of its natural dispersal are not known. Proponents of a South American origin must explain why it is not indigenous there and why it shows greatest diversity in southern Asia. Conversely, proponents of an Asian origin must explain why there are no Asian Cocoseae and why the closest botanical relative to Cocos is in South America. Both hypotheses share the common problems of how, when, where and in what directions long-distance dispersal occurred. These difficulties are resolved by accepting that C. nucifera originated and dispersed by populating emerging islands of the coral atoll ecosystem, where establishment conditions impose high selection pressures for survival. When lifted by wave action onto virtually sterile, soilless coralline rocks just above sea level and exposed to the full impact of the sun, seednuts must germinate, root and establish vigorous populations. The cavity within the nut augments the buoyancy provided by the thick husk, which in turn protects the embryo and, by delaying germination, simultaneously extends viability while floating and provides a moisture-retentive rooting medium for the young seedling. These adaptations allow coconuts to disperse widely through the coral atoll ecosystem. The monthly production of fruit and the long floating duration ensure that viable seednuts are always available in the lagoon to replace those destroyed by hurricanes and tsunamis, or to populate newly emerged coral atolls elsewhere. Long-distance dispersal is secondary, because it was the spontaneous, independent migration of coral polyps on a prolonged geological time scale that generated new coral atolls in new areas where the coconuts would be amongst the earliest inhabitants. The coconut palm became an intermittent, itinerant, pioneer endemic there, and also on suitable beaches on volcanic or large islands and continental coastlines.

Diet Reconstruction and Resource Partitioning of a Caribbean Marine Mesopredator Using Stable Isotope Bayesian Modelling

The trophic ecology of epibenthic mesopredators is not well understood in terms of prey partitioning with sympatric elasmobranchs or their effects on prey communities, yet the importance of omnivores in community trophic dynamics is being increasingly realised. This study used stable isotope analysis of 15N and 13C to model diet composition of wild southern stingrays Dasyatis americana and compare trophic niche space to nurse sharks Ginglymostoma cirratum and Caribbean reef sharks Carcharhinus perezi on Glovers Reef Atoll, Belize. Bayesian stable isotope mixing models were used to investigate prey choice as well as viable Diet-Tissue Discrimination Factors for use with stingrays. Stingray δ15N values showed the greatest variation and a positive relationship with size, with an isotopic niche width approximately twice that of sympatric species. Shark species exhibited comparatively restricted δ15N values and greater δ13C variation, with very little overlap of stingray niche space. Mixing models suggest bivalves and annelids are proportionally more important prey in the stingray diet than crustaceans and teleosts at Glovers Reef, in contrast to all but one published diet study using stomach contents from other locations. Incorporating gut contents information from the literature, we suggest diet-tissue discrimination factors values of Δ15N ≊ 2.7‰ and Δ13C ≊ 0.9‰ for stingrays in the absence of validation experiments. The wide trophic niche and lower trophic level exhibited by stingrays compared to sympatric sharks supports their putative role as important base stabilisers in benthic systems, with the potential to absorb trophic perturbations through numerous opportunistic prey interactions.

Influence of sea-level rise on freshwater lenses of different atoll island sizes and lens resilience to storm-induced salinization

Human populations inhabiting remote coral atoll islands in the tropical Pacific Ocean rely heavily on thin unconfined fresh groundwater lenses (FWLs) as their main natural source of potable water. Potential threats to the continuing viability of atoll FWLs may be associated with eustatic sea-level rise (SLR), but little is known about the influence of SLR on the FWLs of different atoll island sizes and the resilience of FWLs to salinization caused by storm-induced wave washover of low-lying land. Here, numerical modelling is carried out to generate steady-state FWL configurations at three chosen island sizes (400, 600 and 800 m widths), upon which a 40 cm SLR scenario is imposed, followed by transient simulations to assess saline damage and recovery over a 1-year period after a storm washover event on a 600 m wide island. Two different approaches are tested for taking into account the existence of a freshwater swamp, formed where a topographic depression exposes the central region of a FWL above the ground surface. These ‘groundwater window’ and ‘specified flux’ approaches yield similar results, implying that complex integrated surface and groundwater modelling may be unnecessary to develop realistic models of FWL configuration where central freshwater swamps exist. Thereafter, steady-state solutions indicate how FWL dimensions are not related in a linear manner to atoll island size, such that smaller islands develop much more restricted lenses than larger islands. Partly in consequence, smaller FWLs display greater potential for disturbance by SLR, while larger and more robust FWLs may show more resilience. Results from simulation of saline damage caused by storm washover produce a somewhat counterintuitive finding: in a post-SLR situation it is apparent that FWL vulnerability to washover salinization may actually be reduced, owing to the thinner layer of unsaturated substrate lying above the water table (i.e. FWL surface), into which saline water can infiltrate and accumulate during a storm washover event.

Seismic stratigraphy of the Blue Hole (Lighthouse Reef, Belize), a late Holocene climate and storm archive

Abstract Five seismic units may be identified in the ~ 8 m thick Holocene sediment package at the bottom of the Blue Hole, a 120 m deep sinkhole located in the atoll lagoon of Lighthouse Reef, Belize. These units may be correlated with the succession of an existing 5.85-m-long sediment core that reaches back to 1.385 kyrs BP. The identification of seismic units is based on the fact that uniform, fine-grained background sediments show weak reflections while alternating background and coarser-grained event (storm) beds exhibit strong reflections in the seismic profiles. The main source of sediments is the marginal atoll reef and adjacent lagoon area to the east and north. Northeasterly winds and storms transport sediment into the Blue Hole, as seen in the eastward increase in sediment thickness, i.e., the eastward shallowing of the Blue Hole. Previous assumptions of much thicker Holocene sediment packages in the Blue Hole could not be confirmed. So far, close to 6-m-long cores were retrieved from the Blue Hole but the base of the sedimentary succession remains to be recovered. The nature of the basal sediments is unknown but mid-Holocene and possibly older, Pleistocene sinkhole deposits can be expected. The number of event beds identified in the Blue Hole (n = 37) during a 1.385 kyr-long period and the number of cyclones listed in historical databases suggest that only strong hurricanes (categories 4 and 5) left event beds in the Blue Hole sedimentary succession. Storm beds are numerous during 1.3–0.9 kyrs BP and 0.8–0.5 kyrs BP.

Fish Tales: Local fishing in the Kingdom of Tonga

In the small island developing state of Tonga, an archipelago of 176 coral atolls scattered across 664,853 square kilometres of the South Pacific Ocean, power and resourcing differentials dictate which people are permitted to be commercial fishermen and what groups do the subsistence kind, customary fishing. A handful of Native Tongans engage in commercial exporting. The tuna industry is dominated by foreign vessels, by foreign countries, that can afford the state fishing license and the operation costs.&#x0D; The Government of Tonga has confined coastal communities to customary fishing as the sustainable development model, a solution beset with tension. There is resource scarcity of inshore fishing stock. When local fishermen are denied access to deep sea commercial fishing their chances at exporting and making profit are limited, tempting some to poach undersized stock and pressure the government to remove conservation sanctions on species at risk of depletion. What options for livelihood from the sea do coastal communities have? Related to this, what tensions emerge between the Tongan state and coastal communities wanting to be included in the commercial fishing industry?

Coral communities of the remote atoll reefs in the Nansha Islands, southern South China Sea

During the months of May and June in the year 2007, a survey was conducted regarding coral reef communities in the remote atolls (Zhubi Reef and Meiji Reef) of Nansha Islands, southern South China Sea. The goals of the survey were to: (1) for the first time, compile a scleractinian coral check-list; (2) estimate the total richness, coral cover, and growth forms of the community; and (3) describe preliminary patterns of community structure according to geomorphological units. Findings of this survey revealed a total of 120 species of scleractinia belonging to 40 genera, while the average coral cover was 21 %, ranging from less than 10 % to higher than 50 %. Branching and massive corals were also found to be the most important growth forms of the whole coral community, while Acropora, Montipora, and Porites were the three dominant genera in the overall region, with their contributions to total coral cover measuring 21, 22, and 23 %, respectively. Overall, coral communities of the Nansha Islands were in a relative healthy condition with high species diversity and coral cover. Spatial pattern of coral communities existed among various geomorphological units. Mean coral cover was highest in the patch reef within the lagoon, followed by the fore reef slope, reef flat, and lagoon slope. The greatest contributors to total coral cover were branching Acropora (45 %) in the lagoon slope, branching Montipora (44 %) in the reef flat, and massive Porites (51 %) in the patch reef. Coral cover in the fore reef revealed a greater range of genera than in other habitats. The leeward fore reef slope had higher coral cover (> 50 %) when compared with the windward slope (< 10 %). The coral communities of the inner reef flat were characterized by higher coral cover (27 %) and dominant branching Montipora corals, while lower coral cover (4 %) was dominated by Psammocora with massive growth forms on the outer reef flat. Destructive fishing and coral bleaching were two major threats to coral communities in the study area.

Population density estimation of southern stingraysDasyatis americanaon a Caribbean atoll using distance sampling

ABSTRACTThe southern stingrayDasyatis americanais a benthic mesopredator found in varying densities throughout Caribbean shallow reef systems, yet despite its increasing inclusion in fisheries, many aspects of its population ecology are still unknown.Belt transects and distance sampling techniques were used to estimate seasonal abundance of an unexploited, isolated population of southern stingrays in lagoon and forereef habitats at Glovers Reef Atoll, Belize.Southern stingrays were the most abundant elasmobranch in both shallow lagoon margin (&lt; 5 m) and shallow forereef (&lt; 15 m) habitats in all sampling seasons. Lagoon density showed no seasonal variation and was estimated at 245 (95% CI 226–265) individuals per km2.Forereef sampling indicated lower densities compared with the lagoon habitat, as well as seasonality with a significantly lower stingray density in November of 25 (16–37) compared with either of the April surveys of 100 (71–141) and 78 (53–116). Total population size for all lagoon habitat was estimated as ~8400 stingrays (7700–9100, 4%CV).This is the first study known to utilize distance sampling techniques on benthic elasmobranchs. Absolute estimates of population density are crucial in wildlife management and will be an important tool in tracking community and trophic dynamics in affected systems of declining top predators, particularly in species devoid of natural identifying marks.Copyright © 2012 John Wiley &amp; Sons, Ltd.

Modeling causal structures

The Lotka–Volterra predator-prey-model is a widely known example of model-based science. Here we reexamine Vito Volterra’s and Umberto D’Ancona’s original publications on the model, and in particular their methodological reflections. On this basis we develop several ideas pertaining to the philosophical debate on the scientific practice of modeling. First, we show that Volterra and D’Ancona chose modeling because the problem in hand could not be approached by more direct methods such as causal inference. This suggests a philosophically insightful motivation for choosing the strategy of modeling. Second, we show that the development of the model follows a trajectory from a “how possibly” to a “how actually” model. We discuss how and to what extent Volterra and D’Ancona were able to advance their model along that trajectory. It turns out they were unable to establish that their model was fully applicable to any system. Third, we consider another instance of model-based science: Darwin’s model of the origin and distribution of coral atolls in the Pacific Ocean. Darwin argued more successfully that his model faithfully represents the causal structure of the target system, and hence that it is a “how actually” model.