Graham J. Edgar

One-third of reef-building corals face elevated extinction risk from climate change and local impacts

The conservation status of 845 zooxanthellate reef-building coral species was assessed by using International Union for Conservation of Nature Red List Criteria. Of the 704 species that could be assigned conservation status, 32.8% are in categories with elevated risk of extinction. Declines in abundance are associated with bleaching and diseases driven by elevated sea surface temperatures, with extinction risk further exacerbated by local-scale anthropogenic disturbances. The proportion of corals threatened with extinction has increased dramatically in recent decades and exceeds that of most terrestrial groups. The Caribbean has the largest proportion of corals in high extinction risk categories, whereas the Coral Triangle (western Pacific) has the highest proportion of species in all categories of elevated extinction risk. Our results emphasize the widespread plight of coral reefs and the urgent need to enact conservation measures.

Global conservation outcomes depend on marine protected areas with five key features

In line with global targets agreed under the Convention on Biological Diversity, the number of marine protected areas (MPAs) is increasing rapidly, yet socio-economic benefits generated by MPAs remain difficult to predict and under debate. MPAs often fail to reach their full potential as a consequence of factors such as illegal harvesting, regulations that legally allow detrimental harvesting, or emigration of animals outside boundaries because of continuous habitat or inadequate size of reserve. Here we show that the conservation benefits of 87 MPAs investigated worldwide increase exponentially with the accumulation of five key features: no take, well enforced, old (>10 years), large (>100 km2), and isolated by deep water or sand. Using effective MPAs with four or five key features as an unfished standard, comparisons of underwater survey data from effective MPAs with predictions based on survey data from fished coasts indicate that total fish biomass has declined about two-thirds from historical baselines as a result of fishing. Effective MPAs also had twice as many large (>250 mm total length) fish species per transect, five times more large fish biomass, and fourteen times more shark biomass than fished areas. Most (59%) of the MPAs studied had only one or two key features and were not ecologically distinguishable from fished sites. Our results show that global conservation targets based on area alone will not optimize protection of marine biodiversity. More emphasis is needed on better MPA design, durable management and compliance to ensure that MPAs achieve their desired conservation value.

Oyster Reefs at Risk and Recommendations for Conservation, Restoration, and Management

Native oyster reefs once dominated many estuaries, ecologically and economically. Centuries of resource extraction exacerbated by coastal degradation have pushed oyster reefs to the brink of functional extinction worldwide. We examined the condition of oyster reefs across 144 bays and 44 ecoregions; our comparisons of past with present abundances indicate that more than 90% of them have been lost in bays (70%) and ecoregions (63%). In many bays, more than 99% of oyster reefs have been lost and are functionally extinct. Overall, we estimate that 85% of oyster reefs have been lost globally. Most of the worlds remaining wild capture of native oysters (> 75%) comes from just five ecoregions in North America, yet the condition of reefs in these ecoregions is poor at best, except in the Gulf of Mexico. We identify many cost-effective solutions for conservation, restoration, and the management of fisheries and nonnative species that could reverse these oyster losses and restore reef ecosystem services.

Effects of the declaration of marine reserves on Tasmanian reef fishes, invertebrates and plants

The reef biota in four Tasmanian marine reserves and at associated unprotected reference sites was investigated over a 6-year period following protection from fishing. The largest reserve at Maria Island (7 km coastline length) proved the most effective at achieving species conservation and resource enhancement. The number of fish, invertebrate and algal species, the densities of large fishes (>325 mm length), bastard trumpeter (Latridopsis forsteri) and rock lobsters (Jasus edwardsii), and the mean size of blue-throated wrasse (Notolabrus tetricus) and abalone (Haliotis rubra), all increased significantly within the Maria Island reserve relative to external reference sites. Increases of an order of magnitude in the biomass of rock lobsters and two orders of magnitude in the abundance of trumpeter were particularly noticeable. Small abalone declined in density within the reserve, while large abalone became more numerous. The effectiveness of marine reserves corresponded with reserve size. Changes in species richness of fishes, invertebrates or plants were not detected in any of the three smaller reserves, other than an increase in number of fish species greater than 325 mm size within the Tinderbox marine reserve (2 km reserve length). Although patterns were partly obscured by the low power of statistical tests, trends were generally evident at the Tinderbox reserve for increasing densities of large fishes and rock lobsters, and for increases in the mean size of rock lobsters, abalone and blue-throated wrasse. Most of these trends were not apparent in the reserves with small reef areas at Governor Island (1 km reserve length) and Ninepin Point (1 km length). Rock lobsters above the legal size limit nevertheless became abundant in all reserves by the end of the study while remaining rare outside. Indirect changes to reef assemblages were also detected following the declaration of the Maria Island marine reserve. Accompanying the increase in macroalgal species richness was a change in predominant plant species from Cystophora retroflexa to Ecklonia radiata. Results of this study provide the first clear evidence that shallow Tasmanian reef ecosystems are overfished, and that unfished coastal ecosystems differ substantially from those where fishing occurs. The most noticeable changes caused by fishing were the virtual elimination of net-susceptible and heavily targeted species, which may otherwise be common, plus indirect changes to algal communities. We suggest that ecosystem change associated with fishing of shallow coastal reefs may be a widespread phenomenon worldwide.

Global human footprint on the linkage between biodiversity and ecosystem functioning in reef fishes.

A global survey of reef fishes shows that the consequences of biodiversity loss are greater than previously anticipated as ecosystem functioning remained unsaturated with the addition of new species. Additionally, reefs worldwide, particularly those most diverse, are highly vulnerable to human impacts that are widespread and likely to worsen due to ongoing coastal overpopulation.

Global patterns in the impact of marine herbivores on benthic primary producers

Despite the importance of consumers in structuring communities, and the widespread assumption that consumption is strongest at low latitudes, empirical tests for global scale patterns in the magnitude of consumer impacts are limited. In marine systems, the long tradition of experimentally excluding herbivores in their natural environments allows consumer impacts to be quantified on global scales using consistent methodology. We present a quantitative synthesis of 613 marine herbivore exclusion experiments to test the influence of consumer traits, producer traits and the environment on the strength of herbivore impacts on benthic producers. Across the globe, marine herbivores profoundly reduced producer abundance (by 68% on average), with strongest effects in rocky intertidal habitats and the weakest effects on habitats dominated by vascular plants. Unexpectedly, we found little or no influence of latitude or mean annual water temperature. Instead, herbivore impacts differed most consistently among producer taxonomic and morphological groups. Our results show that grazing impacts on plant abundance are better predicted by producer traits than by large-scale variation in habitat or mean temperature, and that there is a previously unrecognised degree of phylogenetic conservatism in producer susceptibility to consumption.

The influence of plant structure on the species richness, biomass and secondary production of macrofaunal assemblages associated with Western Australian seagrass beds

Abstract Considerable differences were found in the species of macrofauna present at Cliff Head and Seven Mile Beach, two coastal seagrass-dominated sites with differing wave exposure in Western Australia. The differences in the faunas between sites were generally much greater than differences between the various habitats within each site. The species richnesses of the faunal assemblages in different seagrass habitats nevertheless followed consistent patterns at both sites, with rankings of habitats from species richest to poorest as: turf, Amphibolis frond, Posidonia, Halophila/Heterozostera, Amphibolis rhizome, detached macrophyte and unvegetated sediments. The faunas associated with artificial seagrass clumps placed in three habitats at each site showed similar patterns of species richness, with significant differences between habitats and between sites but with no site—habitat interaction. Only one environmental factor, the diversity of food resources, was found to correspond with these patterns of faunal species richness. Macrofaunal abundance, biomass and production were all much greater in vegetated than unvegetated habitats. These faunal parameters nevertheless varied greatly between habitats and between sites. Amongst the vegetated habitats, estimated annual secondary production was highest in theAmphibolis rhizome (47.2 g AFDW · m−2 · yr−1) and least in the Halophila/Heterozoslera (24.3 g AFDW · m−2 · yr −1) habitats at Cliff Head. The converse situation was found at Seven Mile Beach, with the Halophila/Heterozostera habitat (42.2 g AFDW · m−2 · yr−1) having nearly four times the estimated macrofaunal production of the Amphibolis rhizome habitat (11.7 g AFDW · m−2 · yr−1). These differences between sites are explained by reference to the distribution of plant debris bound at the sediment surface. Similar relationships between secondary production, the biomass of debris and the biomass of live plant material were independently formulated for the two sites, with the general equation for both sites being P = 13.8 + 0.22 · D + 0.039 · S (n = 12, r2 = 0.61) where P is annual macrofaunal production (g · m−2 · yr−1), D is the mean biomass of debris (g· m−2) and S is the mean biomass of live plant material (g · m−1). Neither the biomass of seagrass rhizomes nor the biomass of drifting debris were significantly correlated with secondary production.

Integrating abundance and functional traits reveals new global hotspots of fish diversity

Species richness has dominated our view of global biodiversity patterns for centuries. The dominance of this paradigm is reflected in the focus by ecologists and conservation managers on richness and associated occurrence-based measures for understanding drivers of broad-scale diversity patterns and as a biological basis for management. However, this is changing rapidly, as it is now recognized that not only the number of species but the species present, their phenotypes and the number of individuals of each species are critical in determining the nature and strength of the relationships between species diversity and a range of ecological functions (such as biomass production and nutrient cycling). Integrating these measures should provide a more relevant representation of global biodiversity patterns in terms of ecological functions than that provided by simple species counts. Here we provide comparisons of a traditional global biodiversity distribution measure based on richness with metrics that incorporate species abundances and functional traits. We use data from standardized quantitative surveys of 2,473 marine reef fish species at 1,844 sites, spanning 133 degrees of latitude from all ocean basins, to identify new diversity hotspots in some temperate regions and the tropical eastern Pacific Ocean. These relate to high diversity of functional traits amongst individuals in the community (calculated using Rao’s Q), and differ from previously reported patterns in functional diversity and richness for terrestrial animals, which emphasize species-rich tropical regions only. There is a global trend for greater evenness in the number of individuals of each species, across the reef fish species observed at sites (‘community evenness’), at higher latitudes. This contributes to the distribution of functional diversity hotspots and contrasts with well-known latitudinal gradients in richness. Our findings suggest that the contribution of species diversity to a range of ecosystem functions varies over large scales, and imply that in tropical regions, which have higher numbers of species, each species contributes proportionally less to community-level ecological processes on average than species in temperate regions. Metrics of ecological function usefully complement metrics of species diversity in conservation management, including when identifying planning priorities and when tracking changes to biodiversity values.

The production and trophic ecology of shallow-water fish assemblages in southern Australia II. Diets of fishes and trophic relationships between fishes and benthos at Western Port, Victoria

A total of 5113 fishes belonging to 91 species was collected from seagrass and unvegetated habitats at Western Port for dietary analysis between August 1989 and November 1990, with 720 animals having empty guts. None of the common species was found to have a highly specialised diet. Crustaceans were the dominant component in the diets of the majority (69%) of the 88 species with non-empty guts, with five species (a girellid, a mugilid, a monacanthid and two gobiids) consuming large amounts of algal material, and only one species [the garfish Hyporhamphus melanochir (Valenciennes)] ingesting seagrass in any quantity. In general, dietary differences between juveniles and adults of a species were as great as dietary differences between fish belonging to different species when at the same body size. Amongst the crustacean feeders, diets generally changed from predominantly copepods to predominantly peracarids (amphipods, isopods and mysids) at ≈0.1 g wet body weight, and from predominantly peracarids to predominantly crabs and shrimps at ≈100 g. Across the range of species examined, there was a close relationship between the size of ingested prey and fish biomass. Prey length averaged 7.5% of predator length. The dominant species in gillnet catches, the mullet Aldrichetta forsteri (Cuvier & Valenciennes), possessed an unusual diet because prey were smaller than for other fishes of the same body size and large quantities of algal material were also consumed. Similar trophic pathways leading to fishes were found in different habitats, with the major linkages being from benthic microalgae and detritus through epifaunal crustaceans to the smaller fishes. The major predators of small fishes were locally-resident species, the rock flathead Platycephalus laevigatus Cuvier & Valenciennes in seagrass beds and the sand flathead Platycephalus bassensis Cuvier & Valenciennes at unvegetated sites. Crustaceans supplied most of the dietary intake for the small fish communities at all sites, with molluscs and polychaetes also important but supplying >25% of food consumed at only two sites. When daily rates of consumption were compared with daily production of food, the production of crustaceans >1 mm sieve size was calculated to be all consumed by fish. The production of the non-crustacean benthos was an order of magnitude higher than that consumed by fish predators. These results indicate that the availability of high quality crustacean prey may limit the production of fishes, and that fishes are likely to compete diffusively for crustacean prey. Additional support for this hypothesis is provided by the observations that the condition of seagrass-associated fish declined, and mortality rates were high, during the autumn season when total fish consumption could not be supported by crustacean production.

The conservation significance of estuaries: a classification of Tasmanian estuaries using ecological, physical and demographic attributes as a case study

Estuaries arguably represent the most anthropogenically-degraded habitat-type on earth, with few estuaries in temperate and tropical regions existing in a near pristine state. Conservation of estuarine biodiversity requires recognition that different estuary types are subjected to particular types and levels of human impact. To protect assemblages associated with all estuary types in Tasmania, Australia, the conservation significance of the 111 large- and moderate-size estuaries in the island state were assessed by firstly categorising estuaries into nine groups on the basis of similarities in physical attributes. These attributes were quantified using GIS maps of estuaries and their catchments and field-collected data, with separation of groups primarily reflecting presence of a seaward barrier, tidal range, salinity, estuary size and river runoff. The adequacy of the physical groups as surrogates for biological patterns was assessed by comparison with data on the distribution of 390 macrobenthic invertebrate taxa in 48 Tasmanian estuaries and 101 beach-seined fish species in 75 estuaries. Multivariate analyses indicated that six of the nine estuarine groups based on physical data were useful for categorising biological relationships between estuaries, but that three groups required modification to prove more biologically meaningful. Within each of the estuarine groups, human population, landuse and land tenure data were used to assess the level of anthropogenic disturbance to each estuary, and the estuary with least disturbance in each group assigned highest conservation significance. Recommendations have been made to create a comprehensive system of estuarine protected areas by legislating to protect species within the nine representative estuaries of highest conservation significance, plus an additional estuary with exceptional species richness. Such a system of protected areas should conserve the range of estuarine biodiversity with minimal disruption to existing estuary users.