Helene Marsh

Corneal avascularity is due to soluble VEGF receptor-1.

Corneal avascularity—the absence of blood vessels in the cornea—is required for optical clarity and optimal vision, and has led to the cornea being widely used for validating pro- and anti-angiogenic therapeutic strategies for many disorders. But the molecular underpinnings of the avascular phenotype have until now remained obscure and are all the more remarkable given the presence in the cornea of vascular endothelial growth factor (VEGF)-A, a potent stimulator of angiogenesis, and the proximity of the cornea to vascularized tissues. Here we show that the cornea expresses soluble VEGF receptor-1 (sVEGFR-1; also known as sflt-1) and that suppression of this endogenous VEGF-A trap by neutralizing antibodies, RNA interference or Cre-lox-mediated gene disruption abolishes corneal avascularity in mice. The spontaneously vascularized corneas of corn1 and Pax6+/- mice and Pax6+/- patients with aniridia are deficient in sflt-1, and recombinant sflt-1 administration restores corneal avascularity in corn1 and Pax6+/- mice. Manatees, the only known creatures uniformly to have vascularized corneas, do not express sflt-1, whereas the avascular corneas of dugongs, also members of the order Sirenia, elephants, the closest extant terrestrial phylogenetic relatives of manatees, and other marine mammals (dolphins and whales) contain sflt-1, indicating that it has a crucial, evolutionarily conserved role. The recognition that sflt-1 is essential for preserving the avascular ambit of the cornea can rationally guide its use as a platform for angiogenic modulators, supports its use in treating neovascular diseases, and might provide insight into the immunological privilege of the cornea.

Adaptive management of the Great Barrier Reef: A globally significant demonstration of the benefits of networks of marine reserves

The Great Barrier Reef (GBR) provides a globally significant demonstration of the effectiveness of large-scale networks of marine reserves in contributing to integrated, adaptive management. Comprehensive review of available evidence shows major, rapid benefits of no-take areas for targeted fish and sharks, in both reef and nonreef habitats, with potential benefits for fisheries as well as biodiversity conservation. Large, mobile species like sharks benefit less than smaller, site-attached fish. Critically, reserves also appear to benefit overall ecosystem health and resilience: outbreaks of coral-eating, crown-of-thorns starfish appear less frequent on no-take reefs, which consequently have higher abundance of coral, the very foundation of reef ecosystems. Effective marine reserves require regular review of compliance: fish abundances in no-entry zones suggest that even no-take zones may be significantly depleted due to poaching. Spatial analyses comparing zoning with seabed biodiversity or dugong distributions illustrate significant benefits from application of best-practice conservation principles in data-poor situations. Increases in the marine reserve network in 2004 affected fishers, but preliminary economic analysis suggests considerable net benefits, in terms of protecting environmental and tourism values. Relative to the revenue generated by reef tourism, current expenditure on protection is minor. Recent implementation of an Outlook Report provides regular, formal review of environmental condition and management and links to policy responses, key aspects of adaptive management. Given the major threat posed by climate change, the expanded network of marine reserves provides a critical and cost-effective contribution to enhancing the resilience of the Great Barrier Reef.

SPATIAL SCALE, SPECIES DIVERSITY, AND HABITAT STRUCTURE: SMALL MAMMALS IN AUSTRALIAN TROPICAL RAIN FOREST

We investigated patterns of mammal assemblage structure on the Atherton Tableland in the Wet Tropics biogeographic region of northeastern Australia. We used live trapping and quantitative estimates of stratified vegetation density to examine the relationships between the structure of the mammal assemblage and habitat structure over three nested spatial scales across a natural vegetation gradient from rain forest to dry, open forest. The narrow transition zone enabled us to examine the relationships between mammal assemblage structure and habitat structure while minimizing the confounding effects of distance, climate, and biogeographic history. The structure of the mammal assemblages was closely related to vegetation structure across and within habitats, and over all spatial scales examined. Vegetation complexity and heterogeneity both influenced assemblage structure, but the relationships varied with spatial scale. Species richness was highest in the open forest and decreased across the gradient into the rain forest. Point diversity was only weakly explained by vegetation structure, whereas >80% of the variation in species richness at the local scale could be explained by vegetation structure. Local-scale species richness of ground-dwelling mammals was mostly a product of the spatial variability in assemblage structure (β diversity), which was associated with the spatial variability in vegetation structure. Local-scale habitat heterogeneity thus promoted local-scale species richness via the close ecological interaction between mammals and habitat structure. The multiscale approach used here, and the nesting of spatial variability in within-habitat vegetation structure, enabled us to demonstrate the scale-dependent effects of spatial habitat heterogeneity and complexity on the structure and diversity of the small-mammal assemblage.

Estimating Animal Abundance in Heterogeneous Environments: An Application to Aerial Surveys for Dugongs

Abstract The probability of detecting an animal in a sampled area during a survey consists of 2 components: 1) the probability of an animal being available for detection (availability), which can be highly variable in heterogeneous environments; and 2) the probability of an animal being detected, conditional on its being available for detection (perception). Many surveys only estimate the latter probability because modeling the availability process requires information collected external to the survey. We illustrate estimation of both probabilities in an application to aerial surveys of dugongs (Dugong dugon) in Northern Australian coastal waters where water clarity varies greatly over relatively small spatial scales. Using artificial dugong models and timed depth recorders deployed on 15 wild dugongs to obtain dive profiles, we carried out experiments to determine zones of detectability for dugongs at the range of depths, turbidities, and sea states that spanned the environmental heterogeneity encountered on dugong surveys. Resulting probability estimates were heterogeneous and dependent on the measured conditions. To estimate perception probability, we used a tandem team of 2 observers on either side of the aircraft. This permitted fitting generalized Lincoln–Petersen models with Program MARK. We then used the generalized Horvitz–Thompson estimator, based on the overall detection probability for each individual dugong, to generate population estimates. We also developed a new simulation-based method for estimating standard errors and confidence intervals. We contrast absolute abundance estimates of dugongs in the Torres Strait and Northern Great Barrier Reef regions using both the new and original approaches (Marsh and Sinclair 1989a). For Torres Strait, the new method produced a substantially smaller estimate (11,956 vs. 14,106 dugongs) and a very much smaller standard error (1,189 vs. 2,314 dugongs), whereas the new method produced slightly larger estimates (mean 9,855 vs. 9,193 dugongs, standard error 1,184 vs. 917 dugongs) for the Northern Great Barrier Reef survey.

Key Questions in Marine Megafauna Movement Ecology

It is a golden age for animal movement studies and so an opportune time to assess priorities for future work. We assembled 40 experts to identify key questions in this field, focussing on marine megafauna, which include a broad range of birds, mammals, reptiles, and fish. Research on these taxa has both underpinned many of the recent technical developments and led to fundamental discoveries in the field. We show that the questions have broad applicability to other taxa, including terrestrial animals, flying insects, and swimming invertebrates, and, as such, this exercise provides a useful roadmap for targeted deployments and data syntheses that should advance the field of movement ecology.

The Indo-Pacific Humpback Dolphin, Sousa chinensis (Osbeck, 1765), in Australian Waters: a Summary of current knowledge

Indo-Pacific humpback dolphins (Sousa chinensis) occur in the coastal northern waters of Australia from approximately the Queensland – New South Wales border (31°27primeS, 152°55primeE) to Ningaloo Reef (22°17primeS, 113°48primeE) in Western Australia. Due to their coastal, estuarine distribution, Indo-Pacific humpback dolphins are particularly vulnerable to several human activities in and adjacent to coastal areas. At present, it is not possible to assess the population status of humpback dolphins in Australian waters because information on their biology and ecology is limited. The sparse data available for selected areas indicate that humpback dolphins occur in discrete, geographically localized populations and are susceptible to anthropogenic threats (e.g., incidental captures in gill nets). The conservation of humpback dolphins in Australias northern coastline will depend on the maintenance of high-quality habitat in areas that are already under some protection, the identification of critical habitats, the inclusion of these habitats in the rezoning initiatives of protected areas, and the reduction of conservation threats. Precautionary measures should be adopted while further work on abundance estimates, population structure, and levels of human-caused mortality are carried out on a wider scale in Australian waters.

Aerial surveys and the potential biological removal technique indicate that the Torres Strait dugong fishery is unsustainable

The globally significant dugong population of Torres Strait supports an important indigenous fishery for meat and oil. The fishery is protected by the Torres Strait Treaty between Australia and Papua New Guinea. A time series of aerial survey estimates from 1987–2001 confirms that there is considerable temporal variability in the size of the dugong population in the region and adds to a growing body of evidence from other aerial surveys and satellite tracking that dugongs undertake large-scale movements associated with temporal and spatial changes in the distribution of their seagrass food. The magnitude of these effects on both the size of the population and the catch cannot be disaggregated from the effects of population depletion from overharvesting. The Potential Biological Removal method was used in conjunction with the aerial survey data to estimate sustainable anthropogenic mortality from all causes for a range of empirically-derived estimates of dugong life-history parameters. These estimates of a sustainable harvest are so far below the current harvest that it must be unsustainable. Governments should heed the Islanders’ requests for assistance in implementing co-management of the fishery as a matter of urgency.

HISTORICAL MARINE POPULATION ESTIMATES: TRIGGERS OR TARGETS FOR CONSERVATION? THE DUGONG CASE STUDY

Recent studies have estimated the historical abundance of large marine vertebrates to determine potential targets for conservation. We evaluated this approach using 1990s aerial survey estimates of dugong abundance and an estimate of the decline in dugong numbers since the 1960s based on changes in the catch per unit effort of dugong bycatch in a government shark control program on the east coast of Queensland, Australia. This analysis indicated that the catch rate of dugongs caught in shark nets, at six locations between latitudes 16.5° S and 28° S, declined at an average of 8.7% per year between 1962 and 1999. This represents a decline to 3.1% of initial catch rates over the sampling period. If the changes in the populations sampled by the shark nets and aerial surveys were equivalent, this result suggests that the region supported 72 000 dugongs in the early 1960s compared with an estimated 4220 dugongs in the mid-1990s. The seagrass habitat in the region is currently insufficient to support 72 000 dug...

Unsustainable harvest of dugongs in Torres Strait and Cape York (Australia) waters: two case studies using population viability analysis

A significant proportion of the world’s remaining dugongs (Dugong dugon) occur off northern Australia where they face various anthropogenic impacts. Here, we investigate the viability of two dugong meta-populations under varying regimes of indigenous hunting. We construct population viability analyses (PVAs) using the computer package VORTEX and published estimates of population sizes and hunting rates. In Torres Strait between Cape York and New Guinea, our models predict severe and imminent reductions in dugong numbers. Our ‘optimistic’ and ‘pessimistic’ models suggest median times for quasi-extinction of 123 and 42 years, respectively. Extinction probabilities are also high for eastern Cape York Peninsula. We demonstrate the inadequacy of reserves when harvest rates in neighbouring areas are high, identify the maximum harvest rates for meta-population stability and emphasise the urgent need for indigenous community involvement in management to establish sustainable rates of dugong harvest in these regions.

The unusual metal status of the dugong Dugon dugon

Using atomic absorption spectroscopy, exceptionally high concentrations of iron (778 to 82,363 μg g+1 dry weight) and zinc (219 to 4,183 μg g+1 dry weight) were detected in the livers of Dugong dugon (Müller) from north Queensland compared with reported values for other marine mammals from other areas of the world. Levels of copper (9.1 to 608 μg g+1 dry weight), cadmium (<0.1 to 59 μg g+1 dry weight), cobalt (0.5 to 72 μg g+1 dry weight) and silver (0.2 to 39 μg g+1 dry weight) in the liver, and cadmium (0.2 to 209 μg g+1 dry weight) in the kidney were also relatively high in several samples, whilst concentrations of nickel, lead and chromium were consistently below the limits of detection in all tissues. Manganese concentrations, in all tissues examined, were generally comparable with those reported from other marine mammals. Tissue concentrations of a number of metals varied with the age of the dugong. Levels of iron, zinc, cadmium and cobalt in the liver zinc and cadmium in the kidney, and iron in the muscle were significantly positively correlated with age. Copper and manganese in both liver and kidney were negatively correlated with age. Large deposits of the iron-rich pigment, haemosiderin, the quantity of which also tended to increase with age, was a conspicuous feature of the livers of all the post-natal dugongs examined histologically. It seems unlikely that the unusual metal status of the dugong reflects anthropogenic activities, since many individuals were collected in remote areas far from major sites of urbanization and industrialization. Seagrasses, the major food of dugongs, were collected from various north Queensland dugong habitat-areas and analysed. Very high concentrations of iron but low levels of copper were detected. The significance of such dietary imbalances and their possible influence on the metal status of the dugong were therefore considered.