Little is known of the separate effects of habitat fragmentation and degradation, which are typically confounded by habitat loss. We examined the separate effects of habitat availability, fragmentation, and degradation on the species richness and abundances of commensal species occupying coral colonies on Australia's Great Barrier Reef. Species richness, total abundance, and the abundances of the two most common commensals, a crab (Trapezia cymodoce) and a shrimp (Palaemonella sp.), increased with coral colony volume. However, relationships between coral colony volume and abundances of these two species differed. The minimum size of coral colonies inhabited by the shrimps was considerably smaller than that inhabited by the crabs. Furthermore, while abundances of these shrimps increased with colony volume, the crabs tended to occupy their hosts as male: female pairs. We manipulated two aspects of the habitat provided by these corals to their commensals. We fragmented habitats while controlling for habitat loss, and we degraded habitats by killing corals without affecting the physical structure of the habitat. Habitat degradation caused rapid declines in species richness, total abundance, and the abundances of the crab and shrimp species. While these declines were rapid they were not instantanceous, suggesting that some secondary degradation of these habitats caused these declines.Habitat fragmentation, on the other hand, had no effect on species richness, total abundance, or the abundance of the shrimp species. In contrast, abundances of trapezid crabs increased in response to fragmentation, most likely as a result of the liberation of space from territory holders that was then colonized by additional individuals. The patch sizes used in this study were considerably smaller than those used in many terrestrial fragmentation studies. Also, marine populations tend to be more open than terrestrial ones and composed of species with greater dispersal capabilities. Therefore, the application of these results to practical conservation problems will require extreme caution. Nevertheless, disentangling the effects of habitat fragmentation and degradation from habitat loss made effects of fragmentation per se visible. Because these results are novel, such effects of habitat fragmentation could be more widespread than is currently appreciated, and relevant to the development of new management tools for biological conservation.

No abstract

Zoos and public aquaria globally display numerous wild harvested, threatened species. To validate conservation credentials, displays are often associated with research projects, educational interpretation, or conservation-related activities. However, accompanying conservation benefits are rarely assessed. In this study, an approach to evaluate conservation benefits of captive wildlife experiences is modelled by assessing four Australian aquarium displays of the Critically Endangered largetooth sawfish Pristis pristis. Conservation impact scores were calculated for research, education, and conservation-related activities. In a novel approach, sawfish-related education (gaining knowledge, changing attitudes, and intentions to change behaviours) was evaluated using a before and after study design (n ¼ 2 229), and conservation impact scores were calculated using effect sizes. Although visitors to all aquariums demonstrated significant positive attitudinal changes, and at one site gained knowledge, no significant change in behavioural intentions were detected. Educational messages addressing attitudes and behaviours were mostly generalised and untargeted. Formative and ongoing evaluations are needed to develop and maintain targeted and relevant messages. With one exception, research projects and conservation activities were unlikely to contribute substantially to sawfish conservation due to limited support from the aquaria. We recommend that increased support is directed to projects that are targeted towards impactful conservation goals. ARTICLE HISTORY

1. Public aquaria globally display numerous threatened fish species captured from wild populations. Potential impacts of harvests are rarely evaluated despite the need for improved management and conservation practices. 2. Sawfishes (Family Pristiidae) are one of the world's most at-risk fish families. Most commonly displayed (30+ wild caught individuals) is the Critically Endangered largetooth sawfish, Pristis pristis. 3. Two Australian aquaria release captive P. pristis to the wild as they outgrow displays, intending to offset impacts of the original harvests. The fate of released sawfish is unknown. 4. Using acoustic telemetry, the behaviour (rates of movement, patterns of habitat use) and survival of aquarium released sawfish (n = 5) were compared to a control group of wild sawfish (n = 5). 5. Aquarium sawfish had reduced rates of movement, were more sedentary, and occupied smaller activity spaces than wild sawfish; but diel activity and habitat use patterns were similar. 6. Collectively, mortality was high. Two aquarium sawfish survived to the end of the monitoring period (391 days and 117 days, respectively), and no wild sawfish survived. The mean duration of survival for aquarium and wild sawfish was 157 and 58 days, respectively. 7. Whilst captivity affected behaviours, the lower mortality rates of aquarium sawfish indicates that releases may partially offset the impact of the original harvest. Further data are required to investigate potential long-term ecological impacts. 8. If P. pristis are to be used for aquarium displays, the best conservation outcomes could be achieved by harvesting in the first year of life when natural mortality is highest, followed by release into the freshwater reaches of the natal river where predation risk may be minimized. Size on release should be less than 2,800 mm total length to allow for migration from the river system as part of their natural life cycle.

Little is known of the separate effects of habitat fragmentation and degradation, which are typically confounded by habitat loss. We examined the separate effects of habitat availability, fragmentation, and degradation on the species richness and abundances of commensal species occupying coral colonies on Australia's Great Barrier Reef. Species richness, total abundance, and the abundances of the two most common commensals, a crab (Trapezia cymodoce) and a shrimp (Palaemonella sp.), increased with coral colony volume. However, relationships between coral colony volume and abundances of these two species differed. The minimum size of coral colonies inhabited by the shrimps was considerably smaller than that inhabited by the crabs. Furthermore, while abundances of these shrimps increased with colony volume, the crabs tended to occupy their hosts as male:female pairs. We manipulated two aspects of the habitat provided by these corals to their commensals. We fragmented habitats while controlling for habitat loss, and we degraded habitats by killing corals without affecting the physical structure of the habitat. Habitat degradation caused rapid declines in species richness, total abundance, and the abundances of the crab and shrimp species. While these declines were rapid they were not instantanceous, suggesting that some secondary degradation of these habitats caused these declines. Habitat fragmentation, on the other hand, had no effect on species richness, total abundance, or the abundance of the shrimp species. In contrast, abundances of trapezid crabs increased in response to fragmentation, most likely as a result of the liberation of space from territory holders that was then colonized by additional individuals. The patch sizes used in this study were considerably smaller than those used in many terrestrial fragmentation studies. Also, marine populations tend to be more open than terrestrial ones and composed of species with greater dispersal capabilities. Therefore, the application of these results to practical conservation problems will require extreme caution. Nevertheless, disentangling the effects of habitat fragmentation and degradation from habitat loss made effects of fragmentation per se visible. Because these results are novel, such effects of habitat fragmentation could be more widespread than is currently appreciated, and relevant to the development of new management tools for biological conservation.