Global Conservation Potential in Coral Reef Halos: Consistency over Space, Time, and Ecosystems Worldwide.

AbstractHalos around coral reefs are landscape-scale patterns arising from multispecies interactions that collectively structure reefscapes over many thousands of square kilometers. First described in the 1960s, halos are known from a handful of locations and continue to captivate scientists. What remains unknown is how globally widespread, persistent, and dynamic halos are. We examined satellite imagery of reefs globally, coupled with in situ field observations, to show that halos are a globally ubiquitous, persistent, yet dynamic ecological phenomenon spanning vastly different systems. We further document the previously undescribed presence of halos outside the tropics surrounding seagrass "reefs" and highlight the temporal scales over which coral reef halos change, merge, and persist. Specifically, we show that halos can change in size over relatively short temporal scales of months, despite persisting over decades. In doing so, we document patterns suggesting that additional biophysical mechanisms than previously assumed may shape halos. Understanding the full suite of mechanisms governing halo formation and maintenance may enable us to use them as proxies for species interactions. Given the global extent of halos, their role in affecting sedimentary carbon storage, and their relationship with marine reserve existence and maturity, they may ultimately serve as globally relevant indicators of coral reef ecosystem functioning and health.

Changes in local free-living parasite populations in response to cleaner manipulation over 12 years.

Predation on parasites is an important ecological process, but few experimental studies have examined the long-term impacts on the prey. Cleaner fish prey upon large numbers and selectively feed on the larger individuals of the ectoparasitic stage of gnathiid isopods. Removal of cleaner fish Labroides dimidiatus for 1.5-12.5 years negatively affects coral reef fishes, but the mechanism is unclear. A reduction in local parasite populations or the size of individual parasites would benefit all susceptible fishes. We tested whether cleaner presence reduces local gnathiid populations using 18 patch-reefs distributed between two sites (both at Lizard Island, Great Barrier Reef) which were maintained cleaner-free or undisturbed for 12 years. Using emergence traps (1 m2), free-living gnathiid stages were sampled before and after cleaner fish were removed during the day and night, up to 11 times over the course of the experiment. There were effects of the removal in the predicted direction, driven largely by the response at one site over the other involving 200% more gnathiids, but manifested only in the daytime sampling after 4 months. There was also a main effect (36%) for the shared sample dates at both sites after 12 years. Gnathiid size occasionally differed with cleaner presence, but in no consistent way over time. Contrary to our predictions, changes in free-living gnathiid population numbers and their size structure rarely reflected the changes in fish populations and individuals observed on cleaner-free reefs. Therefore, evidence that this predator alone regulates gnathiids remains limited, suggesting other contributing processes are involved.

Engaging recreational fishers in management and conservation: global case studies.

Globally, the number of recreational fishers is sizeable and increasing in many countries. Associated with this trend is the potential for negative impacts on fish stocks through exploitation or management measures such as stocking and introduction of non-native fishes. Nevertheless, recreational fishers can be instrumental in successful fisheries conservation through active involvement in, or initiation of, conservation projects to reduce both direct and external stressors contributing to fishery declines. Understanding fishers' concerns for sustained access to the resource and developing methods for their meaningful participation can have positive impacts on conservation efforts. We examined a suite of case studies that demonstrate successful involvement of recreational fishers in conservation and management activities that span developed and developing countries, temperate and tropical regions, marine and freshwater systems, and open- and closed-access fisheries. To illustrate potential benefits and challenges of involving recreational fishers in fisheries management and conservation, we examined the socioeconomic and ecological contexts of each case study. We devised a conceptual framework for the engagement of recreational fishers that targets particular types of involvement (enforcement, advocacy, conservation, management design [type and location], research, and monitoring) on the basis of degree of stakeholder stewardship, scale of the fishery, and source of impacts (internal or external). These activities can be enhanced by incorporating local knowledge and traditions, taking advantage of leadership and regional networks, and creating collaborations among various stakeholder groups, scientists, and agencies to maximize the probability of recreational fisher involvement and project success.