No-take Marine Reserves Research Articles

Year-Round Movements of Sooty Terns (Onychoprion fuscatus) Nesting Within One of the Atlantic’s Largest Marine Protected Areas

Seabirds are among the most threatened birds as a result of acute exposure to many anthropogenic threats. Their effective conservation requires a detailed understanding of how seabirds use marine habitats. Recently, one of the largest no-take marine reserves in the Atlantic was designated in tropical waters surrounding Ascension Island, on which the largest Atlantic population of sooty terns (Onychoprion fuscatus) breeds. Although they are the most abundant tropical seabird, they appear to have suffered marked population declines on Ascension Island as they have elsewhere. Here, we describe year-round movements and habitat use of male and female sooty terns between 2011 and 2015. On average, birds traveled 47,000 km during their 8 months of migration, during which they remained within 2,900 km of the island. They spent most of the day and night in flight, only touching down briefly on the ocean most likely to feed. Habitat suitability models successfully predicted foraging ranges of birds and their at-sea distributions varied considerably between seasons, years and sexes. Considerable variation in range overlap between birds and the new marine protected area (MPA) suggests that similar such studies of other marine taxa are urgently needed. The range of sooty terns mainly falls in the high seas outside of the new MPA, highlighting the very large areas that many oceanic seabirds forage across and the challenges their conservation present.

Using a difference-in-differences and synthetic control approach to investigate the socioeconomic impacts of Oregon's marine reserves

As Marine Protected Areas (MPAs) expand in size and number, it is critical that we understand how they are impacting local communities. However, social impact evaluations on MPAs are often conducted with limited data points before and after MPA implementation, which can weaken the reliability of their results. To address this gap, we collected longitudinal American Community Survey (ACS) socioeconomic data on coastal communities and counties adjacent to marine reserves in Oregon. Oregon has both limited-take MPAs and stricter no-take marine reserves. This study focused solely on the marine reserves. We compared treatment and control units before and after marine reserve implementation using both difference-in-differences (DID) and synthetic control approaches. Each approach yielded different results, potentially providing a more complete picture of marine reserve impacts and long-term trends while also highlighting the need to consider the variability of ACS data collected from small communities. The percent of the population employed in tourism-related industries was the only significant model in both the DID and synthetic control approaches. Tourism employment increased post marine reserve implementation more in communities adjacent to the marine reserves than in more distant coastal communities. This result could indicate that marine reserves are bringing more visitors to the coast, thereby increasing the need for a more tourism-based economy. However, this may not be the case since most coastal visitors are unaware of Oregon's marine reserves and fewer than 10% of business owners think the reserves have impacted their business. An alternative hypothesis is that the marine reserves were placed near communities with a prominent land-sea connection that were already shifting their economic base to focus more on tourism. This study contributes to the literature by demonstrating how secondary data sources can be used to aid in a more comprehensive MPA impact evaluation, how two different impact evaluation approaches (i.e., synthetic control and DID) can result in differing conclusions, and how the robust synthetic control approach can be easily applied to improve MPA impact evaluations. As one element of a large-scale assessment of marine reserve impacts, this study also broadens our understanding of underlying trends on the Oregon coast and how the recently implemented marine reserves may be impacting nearby communities.

Apo Island and Sumilon Island Marine Reserves and Beyond

As a response to the destruction of coral reef ecosystems, parts of the islands of Sumilon and Apo in Central Visayas were set up as No-Take Marine Reserves (NTMR) as a strategy of conservation for coral reef and associated marine systems by the Biology Department of Silliman University in 1974. Sumilon NTMR was managed by the University for 10 years (1974–1984) and Apo NTMR for 12 years (1982–1994). Beginning from 1983 to the present, Professor Garry R. Russ of James Cook University became Silliman’s collaborator. The two coral reef systems were monitored following the methodology in the Australia-ASEAN Project manual and the genetic parentage analysis. In our work on these two reserves, we obtained the cooperation local communities in the process of setting them up. The results of the nearly annual monitoring of these two NTMRs showed that over the years the fish biomass in the NTMRs increased and fish yields of fishers likewise increased over the years. There was also evidence that there was spillover of large sized fish and fish larvae from the NTMRs to other marine areas outside the protected areas. This movement is due to ocean currents in the study areas. The results of our experiments have been published in scientific journals showing the effectiveness of the marine reserve strategy. We have influenced many people throughout the country to set up more marine reserves in addition to our work in other parts of the Visayas and northern Mindanao.

Economic valuation of the snapper recruitment effect from a well-established temperate no-take marine reserve on adjacent fisheries

The global exhaustion of marine fishery resources has triggered worldwide demands for sustainable utilization of marine resources and Ecosystem-Based Management (EBM). Marine Protected Areas (MPAs) are a long-term spatial management strategy in the EBM toolbox. MPAs demonstrate ecological and economic benefits. While MPAs’ ecological benefits are well researched, there are only a few studies that estimate the economic benefits of MPAs to the adjacent fisheries. Currently, methodologies for measuring the economic benefits flowing from MPAs are underdeveloped. Our research builds on a recent assessment of the economic contribution of a small, temperate, no-take marine reserve in New Zealand to rejuvenating depleted snapper (Sparidae: Chrysophrys auratus) stocks. Empirical evidence shows that 10.6% of newly settled juvenile snappers sampled up to 55 km outside of the MPA were the offspring of adult snappers from the MPA. This suggests a significant boost to the commercial fishery of $NZ 1.49 million catch landing value per annum and $NZ 3.21 million added from recreational fishing activity associated spending per annum. These values all come from the recruitment effects associated with one species, from only 0.08% of the marine space in the Hauraki Gulf, New Zealand. The economic valuation of this marine reserve’s snapper recruitment effect demonstrated $NZ 9.64 million in total spending accruing to recreational fishing per annum and $NZ 4.89 million in total output to commercial fisheries annually. This study is the first estimation of the economic valuation of the recruitment effects from a well-established temperate no-take MPA. It represents an important step forward for quantifying the economic benefits of marine reserves and how marine reserves could have positive influence on EBM and marine sustainability.

Successful parks for sharks: No-take marine reserve provides conservation benefits to endemic and threatened sharks off South Africa

Sharks are among the most threatened vertebrates on the planet. Marine protected areas (MPAs) have been widely established and promoted as a shark conservation tool. However, the geographic ranges of most imperiled shark species (endemic and threatened) fall outside the current global networks of MPAs, leaving the protective benefits of this tool questionable for the shark species of highest conservation concern. The Western Cape of South Africa is a hotspot for endemic and threatened shark species. Here, we examined the potential protective benefit of a no-take marine reserve (the De Hoop MPA) for imperiled shark species using baited remote underwater video stations (BRUVS). Eleven shark species were documented, with six of 11 species (55%) classified as threatened with extinction by the International Union for the Conservation of Nature. The composition of the shark assemblage was dominated by small to mid-sized species, including small endemics. Species-specific habitat preferences were identified, with all these habitats represented in the MPA. Frequency of occurrence and relative abundance of sharks on BRUVS were significantly higher inside the De Hoop MPA than outside. Both protected and commercially exploited sharks species exhibited higher relative abundance inside the MPA. Relative abundance also increased inside the MPA with increasing distance from the reserve boundaries. Our findings suggest that no-take MPAs can be an effective tool for protecting shark species of conservation concern, including threatened endemics, particularly if the MPA adequately incorporates their preferred habitats.

Development of reproductive potential in protogynous coral reef fishes within Philippine no-take marine reserves.

Empirical evidence for increases in the reproductive potential (egg output per unit area) of coral reef fish in no-take marine reserves (NTMRs) is sparse. Here, we inferred the development of reproductive potential in two species of protogynous reef fishes, Chlorurus bleekeri (Labridae: Scarinae) and Cephalopholis argus (Epinephelidae), inside and outside of Philippine NTMRs. We estimated key reproductive parameters and applied these to species-specific density and length data from 17 NTMRs (durations of protection 0-11 years) and paired fished sites (controls) in a space-for-time substitution approach. For C. argus, we also used density and length data collected almost annually over 29 years from a NTMR and an adjacent control at Apo Island. The results suggest that C. bleekeri can develop 6.0 times greater reproductive potential in NTMRs than controls after 11 years of protection, equivalent to approximately 582,000 more eggs produced 500 m-2 inside NTMRs. Enhancement of reproductive potential in C. argus was not evident after 11 years in the space-for-time substitution. At Apo Island NTMR, reproductive potential of C. argus increased approximately 6-fold over 29 years but NTMR/control ratios in reproductive potential decreased through time (from 3.2 to 2.4), probably due to spillover of C. argus from the NTMR to the control. C. argus was estimated to produce approximately 113,000 more eggs 500 m-2 inside Apo Island NTMR at the 29th year of protection. Ratios of reproductive potential between NTMR and controls in C. bleekeri and C. argus were often greater than corresponding ratios in density or biomass. The study underscores the importance of species-specific reproductive life history traits that drive variation in the development of larval fish subsidies that originate from NTMRs.

Selection on fish personality differs between a no-take marine reserve and fished areas.

Marine reserves can protect fish populations by increasing abundance and body size, but less is known about the effect of protection on fish behaviour. We looked for individual consistency in movement behaviours of sea trout in the marine habitat using acoustic telemetry to investigate whether they represent personality traits and if so, do they affect survival in relation to protection offered by a marine reserve. Home range size had a repeatability of 0.21, suggesting that it represents a personality trait, while mean swimming depth, activity and diurnal vertical migration were not repeatable movement behaviours. The effect of home range size on survival differed depending on the proportion of time fish spent in the reserve, where individuals spending more time in the reserve experienced a decrease in survival with larger home ranges while individuals spending little time in the reserve experienced an increase in survival with larger home ranges. We suggest that the diversity of fish home range sizes could be preserved by establishing networks of marine reserves encompassing different habitat types, ensuring both a heterogeneity in environmental conditions and fishing pressure.

Partially protected areas as a management tool on inshore reefs

Partially Protected Areas (PPAs) are a widely-used management tool, yet comparatively little is known about their effectiveness compared to more commonly studied No-Take Marine Reserves (NTMRs). Here, we examine the efficacy of two kinds of PPAs (with and without spearfishing) within the Great Barrier Reef Marine Park (GBRMP) that are subject to a range of fishing limitations, and assess their utility as a marine park zoning and fisheries management tool. Fish abundance, size, and habitat composition were compared inside PPAs and NTMRs on inshore reefs of the central GBR. Fish abundances were lower inside PPAs relative to adjacent NTMRs for primary fishing targets, with no detectable effects for secondary targets and non-targets, or for species richness. Fish assemblages differed amongst zones, but these variations were minor compared to regional variations in species composition. Partially Protected Areas supported 46%–69% of the relative abundance of total primary targets compared to adjacent NTMRs, with no evident increase in abundance in zones where spearfishing was prohibited. There were no reductions in the size of two key target species: coral trout (Plectropomus spp.) and stripey snapper (Lutjanus carponotatus) inside PPAs, and only stripey snapper had significant reductions in abundance inside PPAs compared to NTMRS. Habitat and biophysical characteristics (especially topographic complexity) were strong drivers of fish abundance, but the relative influence of zone was greater for target species compared to non-targets. This study provides novel data on PPAs and highlights their utility as a spatial management tool in contributing to conservation and fisheries management goals.

Minimum size limits and the reproductive value of numerous, young, mature female fish.

Fisheries management relies on various catch and effort controls to preserve spawning stock biomass and maximize sustainable yields while limiting fishery impacts on marine ecosystems. These include species-specific minimum or maximum size limits to protect either small non-reproductive subadults, a portion of reproductively mature adults, or large highly fecund individuals. Protecting size classes of mature fish is expected to yield a viable source of larvae for replenishing populations and reduce the risk of recruitment overfishing, yet size-specific recruitment contributions have rarely been assessed empirically. Here, we apply genetic parentage analysis to measure the reproductive success of a size-structured population of a commercially important species of coral grouper (Plectropomus maculatus-Serranidae) in no-take marine reserves (NTMRs) in the Great Barrier Reef Marine Park, Australia. Although the per capita reproductive success of individual fish increases rapidly with body length, the numerous young mature female fish, below the minimum size limit (MSL) (38 cm total length), were responsible for generating disproportionately large contributions (36%) towards larval replenishment of both fished and reserve reefs. Our findings indicate that MSLs are an effective harvest control measure to safeguard a portion of the spawning stock biomass for coral grouper and supplement recruitment subsidies assured from NTMRs.

Relative influence of environmental factors and fishing on coral reef fish assemblages.

Understanding whether assemblages of species respond more strongly to bottom-up (availability of trophic resources or habitats) or top-down (predation pressure) processes is important for effective management of resources and ecosystems. We determined the relative influence of environmental factors and predation by humans in shaping the density, biomass, and species richness of 4 medium-bodied (10-40 cm total length [TL]) coral reef fish groups targeted by fishers (mesopredators, planktivores, grazer and detritivores, and scrapers) and the density of 2 groups not targeted by fishers (invertivores, small fish ≤10 cm TL) in the central Philippines. Boosted regression trees were used to model the response of each fish group to 21 predictor variables: 13 habitat variables, 5 island variables, and 3 fishing variables (no-take marine reserve [NTMR] presence or absence, NTMR size, and NTMR age). Targeted and nontargeted fish groups responded most strongly to habitat variables, then island variables. Fishing (NTMR) variables generally had less influence on fish groups. Of the habitat variables, live hard coral cover, structural complexity or habitat complexity index, and depth had the greatest effects on density, biomass, and species richness of targeted fish groups and on the density of nontargeted fishes. Of the island variables, proximity to the nearest river and island elevation had the most influence on fish groups. The NTMRs affected only fishes targeted by fishers; NTMR size positively correlated with density, biomass, and species richness of targeted fishes, particularly mesopredatory, and grazing and detritivorous fishes. Importantly, NTMRs as small as 15 ha positively affected medium-bodied fishes. This finding provides reassurance for regions that have invested in small-scale community-managed NTMRs. However, management strategies that integrate sound coastal land-use practices to conserve adjacent reef fish habitat, strategic NTMR placement, and establishment of larger NTMRs will be crucial for maintaining biodiversity and fisheries.

Spatial ecology of Norway lobster Nephrops norvegicus in Mediterranean deep-water environments: implications for designing no-take marine reserves

The Norway lobsterNephrops norvegicusis one of the most important marine resources for European fisheries. However, overfishing has caused the stocks to decline over the last decades, particularly in the Mediterranean Sea. The implementation of no-take marine reserves could change these current trends, thus achieving a more sustainable fishery. The effectiveness of no-take reserves depends on optimal size design, and because of this, new behavioural data on the spatial ecology of the species are of pivotal importance. Here, for the first time, we investigated the spatial movements and daily activity patterns of Norway lobster in a deep-water (315-475 m depth) no-take marine reserve of 10 km2in the continental slope of the northwestern Mediterranean Sea, by combining acoustic tracking and tagging-recapture procedures. The results revealed the territorial behaviour of Norway lobster, centred in small exclusive individual areas where most displacements took place at midday. We found that once settled in a place, their home ranges reached approximate sizes of 17.75 to 736.25 m2, suggesting that no-take marine areas focussed on recovering Norway lobster populations do not require large extents to be effective. Tag-recapture data indicated minimal spillover of biomass, implying that Norway lobsters are site settled and do not perform large movements. Future studies on larval spread and recruitment would be necessary to focus on the possible spillover benefit for fisheries. The acoustic telemetry system used in the present experiment effectively revealed the range of movement of individuals, and thus represents a promising monitoring tool to assess no-take marine reserve sizes and reciprocal spacing for deep-water demersal resources.

Morphological sexual maturity of the marine crab Xanthodius parvulus at the State Marine Park Laje de Santos, São Paulo, Brazil

ABSTRACT The marine crab Xanthodius parvulus (Fabricius, 1793) is naturally distributed in the Western Atlantic, being commonly found in the northeastern Brazilian coast. However, this species has been also recorded in the southeastern coast, especially in São Paulo State, on islands located close to harbors, which are becoming a place of occurrence for exotic species. This study aimed to estimate the morphological sexual maturity (relative growth) of X. parvulus the functional biological patterns of the species in a No-take marine reserve. The crabs were sampled at the Marine State Park of Laje de Santos, an important protected area from São Paulo that is located close to the largest Brazilian harbor, Santos, using an artificial substrate and active search methods (scuba diving). The morphological sexual maturity of females was estimated in 7.28 mm, according to the Abdomen Width vs. Carapace Width relationship, while for males this value was 8.83 mm based on the Gonopod Length vs. Carapace Width relationship, the females presented an increase in abdominal growth, even during the mature stage in order to achieve higher reproductive success, since the abdominal structure is used to protect the embryos. The Gonopod Length vs. Carapace Width relationship showed that males copulate with different sized females, since a non-exaggerated growth of the gonopods keeps them adequate to the size of the female genital pore, i.e., juveniles exhibited negative allometry and adults presented isometry. Thus, estimating the size of the sexual maturity of a species requires the development of a model to acknowledge its biological and reproductive pattern, being an important tool to increase the knowledge about the behavior of this species and one of the parameters to evaluate its conservation status.

Varying reef shark abundance trends inside a marine reserve: evidence of a Caribbean reef shark decline

Spatial comparisons of reef shark abundance inside and outside marine protected areas (MPAs) are common and generally report positive MPA effects, yet few studies have tracked abundance trends over long time periods. This is problematic because inside:outside comparisons at a single point in time cannot evaluate whether populations are declining. In Belize, the Caribbean reef shark Carcharhinus perezi is one of the most fished shark species and is more abundant inside MPAs. Although the relative abundance of C. perezi was stable inside Glover’s Reef Marine Reserve (GRMR) from 2001 to 2013, using standard baited remote underwater video station surveys, we document a decline in relative abundance inside the no-take marine reserve from 2009 to 2019. We used a negative binomial generalized linear model and model averaging to test the effect of year, depth, and water temperature on C. perezi and nurse shark Ginglymostoma cirratum relative abundance. While model-averaged results indicated a C. perezi decline, G. cirratum remained stable from 2009 to 2019. We hypothesize that the C. perezi decline is a result of fishing along the edge of GRMR, while G. cirratum stability is related to their behavior and nationwide protection. Given the dynamic nature of fisheries regulations, economic pressures, and site-specific environmental conditions, our results emphasize the need for standardized long-term monitoring of reef sharks inside and around MPAs globally.

Effects of marine reserves on predator-prey interactions in central California kelp forests

Marine reserves are often designed to increase density, biomass, size structure, and biodiversity by prohibiting extractive activities. However, the recovery of predators following the establishment of marine reserves and the consequent cessation of fishing may have indirect negative effects on prey populations by increasing prey mortality. We coupled field surveys with empirical predation assays (i.e. tethering experiments) inside and outside of 3 no-take marine reserves in kelp forests along the central California coast to quantify the strength of interactions between predatory fishes and their crustacean prey. Results indicated elevated densities and biomass of invertebrate predators inside marine reserves compared to nearby fished sites, but no significant differences in prey densities. The increased abundance of predators inside marine reserves translated to a significant increase in mortality of 2 species of decapod crustaceans, the dock shrimpPandalus danaeand the cryptic kelp crabPugettia richii, in tethering experiments. Shrimp mortality rates were 4.6 times greater, while crab mortality rates were 7 times greater inside reserves. For both prey species, the time to 50% mortality was negatively associated with the density and biomass of invertebrate predators (i.e. higher mortality rates where predators were more abundant). Video analyses indicated that macro-invertivore fishes arrived 2 times faster to tethering arrays at sites inside marine reserves and began attacking tethered prey more rapidly. The results indicate that marine reserves can have direct and indirect effects on predators and their prey, respectively, and highlight the importance of considering species interactions in making management decisions.

Effects of cooperation and different characteristics of Marine Protected Areas in a simulated small-scale fishery

Marine fisheries are a critically important source of food, nutrition, and employment for millions of people. As the global population increases, new and expanding pressures are created on fish resources. Marine Protected Areas (MPAs) have been widely promoted as valuable tools for rebuilding or maintaining fish stocks around the world. The success of MPAs, however, widely depends on their particular configuration and management and their effectiveness is often object of contentious debates in both scientific and political arenas. Since fisheries management is a collective action problem, some forms of human cooperation in terms of fishing behaviour can lead to sustainable fisheries and can represent, in theory, a complementary or even an alternative approach to the establishment of no-take marine reserves. We present here a new Agent-Based Model (ABM) that captures the main characteristics of an idealised small-scale fishery. We then use the model to investigate the combined effects of different fishing strategies (expressed by a cooperative trait associated to fishing effort) and various configurations of no-take reserves (including presence or absence of MPA, size of MPA, age of MPA, i.e. time elapsed since its establisment, and distance between two MPAs) on fish abundance and catch under an overfishing regime. Our results show that high cooperation without an MPA can be as effective as lower levels of cooperation combined with an MPA in maintaining fish stocks and catches at relatively high levels. The mobility of our fish agents implies that, contrary to current belief, these results may not be limited to sedentary species. We also found that the greatest impacts on fish abundance and catch are produced by the size of an MPA and the time elapsed since its establishment. Furthermore, the distance between two MPAs has no significant effect, regardless of the cooperation levels characterising the fishing agents. Despite its simplicity, the ABM presented here provides insights on the most plausible effects that combinations of different MPA designs and human cooperation strategies can produce on overexploited small-scale fisheries. When appropriately adapted with a realistic, fishery-specific parameterisation, this model can constitute a valuable tool for evaluating the impact of different resource management strategies. We make the model available as open-source software with the aims of fostering reproducibility, transparency, and flow of ideas.

Beyond protection: Fisheries co-benefits of no-take marine reserves

Overfishing and other anthropogenic impacts to ocean ecosystems have motivated widespread implementation of no-take marine reserves to protect biodiversity and fished resources. Fully protected marine reserves now comprise approximately 2.5% of the ocean and calls for enhanced protections abound. The benefits to marine biodiversity within reserve borders are clear, yet the contributions beyond borders remain the subject of continued scholarship. In this article, six co-benefits of marine reserves for fisheries are explored. Broadly, the six co-benefits fall within two categories 1) use of reserves as tools to adaptively learn, promote resiliency, and manage marine resources, especially in the face of a changing climate and 2) use of reserves to provide credit against uncertainty in management and sustainability criteria. Broader understanding and consideration of the benefits of marine reserves can further policy discussions and deepen conversations regarding social, ecological, and economic tradeoffs of implementing marine reserves.

Coral cover a stronger driver of reef fish trophic biomass than fishing.

An influential paradigm in coral reef ecology is that fishing causes trophic cascades through reef fish assemblages, resulting in reduced herbivory and thus benthic phase shifts from coral to algal dominance. Few long‐term field tests exist of how fishing affects the trophic structure of coral reef fish assemblages, and how such changes affect the benthos. Alternatively, benthic change itself may drive the trophic structure of reef fish assemblages. Reef fish trophic structure and benthic cover were quantified almost annually from 1983 to 2014 at two small Philippine islands (Apo, Sumilon). At each island a No‐Take Marine Reserve (NTMR) site and a site open to subsistence reef fishing were monitored. Thirteen trophic groups were identified. Large planktivores often accounted for >50% of assemblage biomass. Significant NTMR effects were detected at each island for total fish biomass, but for only 2 of 13 trophic components: generalist large predators and large planktivores. Fishing‐induced changes in biomass of these components had no effect on live hard coral (HC) cover. In contrast, HC cover affected biomass of 11 of 13 trophic components significantly. Positive associations with HC cover were detected for total fish biomass, generalist large predators, piscivores, obligate coral feeders, large planktivores, and small planktivores. Negative associations with HC cover were detected for large benthic foragers, detritivores, excavators, scrapers, and sand feeders. These associations of fish biomass to HC cover were most clear when environmental disturbances (e.g., coral bleaching, typhoons) reduced HC cover, often quickly (1–2 yr), and when HC recovered, often slowly (5–10 yr). As HC cover changed, the biomass of 11 trophic components of the fish assemblage changed. Benthic and fish assemblages were distinct at all sites from the outset, remaining so for 31 yr, despite differences in fishing pressure and disturbance history. HC cover alone explained ~30% of the variability in reef fish trophic structure, whereas fishing alone explained 24%. Furthermore, HC cover affected more trophic groups more strongly than fishing. Management of coral reefs must include measures to maintain coral reef habitats, not just measures to reduce fishing by NTMRs.

A connectivity portfolio effect stabilizes marine reserve performance.

Well-managed and enforced no-take marine reserves generate important larval subsidies to neighboring habitats and thereby contribute to the long-term sustainability of fisheries. However, larval dispersal patterns are variable, which leads to temporal fluctuations in the contribution of a single reserve to the replenishment of local populations. Identifying management strategies that mitigate the uncertainty in larval supply will help ensure the stability of recruitment dynamics and minimize the volatility in fishery catches. Here, we use genetic parentage analysis to show extreme variability in both the dispersal patterns and recruitment contribution of four individual marine reserves across six discrete recruitment cohorts for coral grouper (Plectropomus maculatus) on the Great Barrier Reef. Together, however, the asynchronous contributions from multiple reserves create temporal stability in recruitment via a connectivity portfolio effect. This dampening effect reduces the variability in larval supply from individual reserves by a factor of 1.8, which effectively halves the uncertainty in the recruitment contribution of individual reserves. Thus, not only does the network of four marine reserves generate valuable larval subsidies to neighboring habitats, the aggregate effect of individual reserves mitigates temporal fluctuations in dispersal patterns and the replenishment of local populations. Our results indicate that small networks of marine reserves yield previously unrecognized stabilizing benefits that ensure a consistent larval supply to replenish exploited fish stocks.

Environmental disturbance events drive declines in juvenile wrasse biomass on inshore coral reefs of the Great Barrier Reef

Environmental disturbances and fishing are well known drivers of coral reef fish population size, length-frequency, and assemblage structure. However, few studies have partitioned the spatial and temporal impacts of multiple disturbance events and long-term no-take marine reserve (NTMR) protection on the biomass of juvenile and adult reef-fishes based on the known size of sexual maturity. Here, we document responses in the biomass of juvenile and adult wrasses (Labridae) Hemigymnus melapterus, H. fasciatus, Cheilinus fasciatus, and Oxycheilinus digramma, to environmental disturbance events, NTMR protection, and predator density on inshore fringing coral reefs at the Palm and Whitsunday Island groups, Great Barrier Reef (GBR), Australia from 2007 to 2018 (12 years). The biomass of juvenile and adult wrasses on inshore GBR reefs were driven predominantly by benthic habitat associations, rather than by NTMR protection or density of wrasse predators (Plectropomus spp.). Despite similar species-specific associations of juvenile and adult wrasses with benthic cover, juvenile wrasse biomass consistently declined following coral bleaching and cyclone events. Conversely, adult wrasses had variable responses to disturbance events, including some increases in biomass. Disturbance-mediated declines in the biomass of juvenile wrasses are likely to generate ongoing reductions in the abundance of these species on inshore GBR reefs. Our findings provide further evidence that habitat loss impacts a range of coral reef fishes beyond those that are directly reliant upon live coral. Shifts in assemblage structure, loss of biodiversity, and reductions in fishery productivity will become increasingly apparent in coral reef ecosystems if anthropogenic global warming continues unabated.

Comparative demography of commercially important species of coral grouper, Plectropomus leopardus and P. laevis, from Australia's great barrier reef and Coral Sea marine parks.

Understanding the spatial and environmental variation in demographic processes of fisheries target species, such as coral grouper (Genus: Plectropomus), is important for establishing effective management and conservation strategies. Herein we compare the demography of Plectropomus leopardus and P. laevis between Australia's Great Barrier Reef Marine Park (GBRMP), which has been subject to sustained and extensive fishing pressure, and the oceanic atolls of Australia's Coral Sea Marine Park (CSMP), where there is very limited fishing for reef fishes. Coral grouper length-at-age data from contemporary and historical otolith collections across 9.4 degrees of latitude showed little difference in lifetime growth between GBRMP and CSMP regions. Plectropomus laevis populations in GBRMP reefs had significantly higher rates of total mortality than populations in the CSMP. Mean maximum lengths and mean maximum ages of P. laevis were also smaller in the GBRMP than in the CSMP, even when considering populations sampled within GBRMP no-take marine reserves (NTMRs). Plectropomus leopardus, individuals were on average smaller on fished reefs than NTMRs in the GBRMP, but all other aspects of demography were broadly similar between regions despite the negligible levels of fishing pressure in the CSMP. Similarities between regions in growth profiles and length-at-age comparisons of P. laevis and P. leopardus suggest that the environmental differences between the CSMP and the GBRMP may not have significant impacts on lifetime growth. Our results show that fishing may have influenced the demography of coral grouper on the GBR, particularly for the slower growing and longer lived species, P. laevis.