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Abstract Persistent shifts to undesired ecological states, such as shifts from coral to macroalgae, are becoming more common. This highlights the need to understand processes that can help restore affected ecosystems. Herbivory on coral reefs is widely recognized as a key interaction that can keep macroalgae from outcompeting coral. Most attention has been on the role ‘grazing’ herbivores play in preventing the establishment of macroalgae, while less research has focused on the role of ‘browsers’ in extirpating macroalgae. Here we explored patterns, environmental correlates and state shift consequences of spatial co-variation in grazing and browsing functions of herbivorous fishes. Grazing and browsing rates were not highly correlated across 20 lagoon sites in Moorea, French Polynesia, but did cluster into 3 (of 4) combinations of high and low consumption rates (no site had low grazing but high browsing). Consumption rates were not correlated with grazer or browser fish biomass, but both were predicted by specific environmental variables. Experiments revealed that reversibility of a macroalgal state shift was strongly related to spatial variation in browsing intensity. Our findings provide insights and simple diagnostic tools regarding heterogeneity in top-down forcing that influences the vulnerability to and reversibility of shifts to macroalgae on coral reefs. 

The data included in this data package were collected in the lagoon of Moorea, French Polynesia. Data on coral mortality were collected in July 2019. Data on nitrogen content (%N) in the long-lived brown macroalga Turbinaria ornata were collected during six sampling campaigns between January 2016 and May 2021 to characterize nitrogen availability at each site. Data on seawater temperatures at six LTER sites in the back reef were collected from 2005-2019, but temperature loggers at two sites (LTER 1 and LTER 6) only recorded partial ocean temperature records during the heatwave from 2018-2019. We used our entire time series (spanning from 2005 to 2018) of temperature across our four long-term sites for which we have data in 2019 to predict ocean temperature data for LTER 1 and LTER 6 in 2019. These data were used for analyses in the manuscript entitled "Effects of nitrogen enrichment on coral mortality depend on the intensity of heat stress". 

Ecosystem responses to disturbance depend on the nature of the perturbation and the ecological legacies left behind, making it critical to understand how climate‐driven changes in disturbance regimes modify resilience properties of ecosystems. For coral reefs, recent increases in severe marine heat waves now co‐occur with powerful storms, the historic agent of disturbance. While storms kill coral and remove their skeletons, heat waves bleach and kill corals but leave their skeletons intact. Here, we explored how the material legacy of dead coral skeletons modifies two key ecological processes that underpin coral reef resilience: the ability of herbivores to control macroalgae (spatial competitors of corals), and the replenishment of new coral colonies. Our findings, grounded by a major bleaching event at our long‐term study locale, revealed that the presence of structurally complex dead skeletons reduced grazing on turf algae by ~80%. For macroalgae, browsing was reduced by >40% on less preferred (unpalatable) taxa, but only by ~10% on more preferred taxa. This enabled unpalatable macroalgae to reach ~45% cover in 2 years. By contrast, herbivores prevented macroalgae from becoming established on adjacent reefs that lacked skeletons. Manipulation of unpalatable macroalgae revealed that the cover reached after 1 year (~20%) reduced recruitment of corals by 50%. The effect of skeletons on juvenile coral growth was contingent on the timing of settlement relative to the disturbance. If corals settled directly after bleaching (before macroalgae colonized), dead skeletons enhanced colony growth by 34%, but this benefit was lost if corals colonized dead skeletons a year after the disturbance once macroalgae had proliferated. These findings underscore how a material legacy from a changing disturbance regime can alter ecosystem resilience properties by disrupting key trophic and competitive interactions that shape post‐disturbance community dynamics. 

Small-scale fisheries provide seafood for billions of people and are one of the largest employers in many coastal communities. Those households engaged in these fisheries who maintain diverse income sources are generally thought to be better prepared to cope with social or ecological perturbations such as the crises presented by the COVID-19 pandemic. One outcome of the COVID-19 crisis was the collapse of international tourism after many nations instituted strict border controls to slow the virus’s spread, severely impacting coastal communities that depend on tourism-related employment. This research assessed the effects of COVID-19-induced collapse of tourism on small-scale coral reef fishers and households in Moorea, French Polynesia. Ninety-five households were surveyed about their livelihoods, fishing, demographics, and income-generating occupations before and after the lockdown. Shifts in fish biomass were evaluated using time series data collected through underwater visual surveys, and roadside fish vendors were surveyed to assess fish sales. Results showed that after tourism employment evaporated more Moorea households began fishing to boost their incomes and food security. However, the increase in fishing pressure showed no appreciable decline in the biomass of fishable species. The households responsible for the increased fishing activities were those who were working in the tourism economy prior to the pandemic and subsequently lost their jobs. Households that combined fishing with construction or other stable sectors showed greater abilities to cope, while those combining fishing with tourism were heavily impacted. Importantly, results showed that those households devoted solely to fishing managed the crisis adeptly due to their superior fishing skills and ecological knowledge. This pattern suggests that not all forms of household livelihood diversification confer equal advantages and that resource-dependent households are not necessarily intrinsically less resilient. More generally, it is argued that we should be cautious when promoting livelihood diversification as a blanket solution to decrease household vulnerability, and that ecological knowledge diversity is underappreciated. 

Abstract Mounting evidence suggests that fishing can be a major driver of coral‐to‐macroalgae regime shifts on tropical reefs. In many small‐scale coral reef fisheries, fishers target herbivorous fishes, which can weaken coral resilience via reduced herbivory on macroalgae that then outcompete corals. Previous models that explored the effects of harvesting herbivores revealed hysteresis in the herbivory–benthic state relationship that results in bistability of coral‐ and macroalgae‐dominated states over some levels of fishing pressure, which has been supported by empirical evidence. However, past models have not accounted for the functional differences among herbivores or how fisher selectivity for different herbivore functional groups may alter the benthic dynamics and resilience. Here, we use a dynamic model that links differential fishing on two key herbivore functional groups to the outcome of competitive dynamics between coral and macroalgae. We show that reef state depends not only on the level of fishing but also on the types of herbivores targeted by fishers. Selectively fishing browsing herbivores that are capable of consuming mature macroalgae (e.g., unicornfish) increases precariousness of the coral state by moving the system close to the coral‐to‐macroalgae tipping point. By contrast, selectively harvesting grazing herbivores that are only capable of preventing macroalgae from becoming established (e.g., parrotfishes) can increase catch yields substantially more before the tipping point is reached. However, this lower precariousness with increasing fishing effort comes at the cost of increasing the range of fishing effort over which coral and macroalgae are bistable; increasing hysteresis makes a regime shift triggered by a disturbance more difficult or impractical to reverse. Our results suggest that management strategies for small‐scale coral reef fisheries should consider how functional differences among harvested herbivores coupled with fisher selectivity influence benthic dynamics in light of the trade‐off between tipping point precariousness and coral recovery dynamics following large disturbances. 

With marine heat waves increasing in intensity and frequency due to climate change, it is important to understand how thermal disturbances will alter coral reef ecosystems since stony corals are highly susceptible to mortality from thermally-induced, mass bleaching events. In Moorea, French Polynesia, we evaluated the response and fate of coral following a major thermal stress event in 2019 that caused a substantial amount of branching coral (predominantly Pocillopora ) to bleach and die. We investigated whether Pocillopora colonies that occurred within territorial gardens protected by the farmerfish Stegastes nigricans were less susceptible to or survived bleaching better than Pocillopora on adjacent, undefended substrate. Bleaching prevalence (proportion of the sampled colonies affected) and severity (proportion of a colony’s tissue that bleached), which were quantified for >1,100 colonies shortly after they bleached, did not differ between colonies within or outside of defended gardens. By contrast, the fates of 399 focal colonies followed for one year revealed that a bleached coral within a garden was a third less likely to suffer complete colony death and about twice as likely to recover to its pre-bleaching cover of living tissue compared to Pocillopora outside of a farmerfish garden. Our findings indicate that while residing in a farmerfish garden may not reduce the bleaching susceptibility of a coral to thermal stress, it does help buffer a bleached coral against severe outcomes. This oasis effect of farmerfish gardens, where survival and recovery of thermally-damaged corals are enhanced, is another mechanism that helps explain why large Pocillopora colonies are disproportionately more abundant in farmerfish territories than elsewhere in the lagoons of Moorea, despite gardens being relatively uncommon. As such, some farmerfishes may have an increasingly important role in maintaining the resilience of branching corals as the frequency and intensity of marine heat waves continue to increase. 

Abstract Surveying coastal systems to estimate distribution and abundance of fish and benthic organisms is labor‐intensive, often resulting in spatially limited data that are difficult to scale up to an entire reef or island. We developed a method that leverages the automation of a machine learning platform, CoralNet, to efficiently and cost‐effectively allow a single observer to simultaneously generate georeferenced data on abundances of fish and benthic taxa over large areas in shallow coastal environments. Briefly, a researcher conducts a fish survey while snorkeling on the surface and towing a float equipped with a handheld GPS and a downward‐facing GoPro, passively taking ~ 10 photographs per meter of benthos. Photographs and surveys are later georeferenced and photographs are automatically annotated by CoralNet. We found that this method provides similar biomass and density values for common fishes as traditional scuba‐based fish counts on fixed transects, with the advantage of covering a larger area. Our CoralNet validation determined that while photographs automatically annotated by CoralNet are less accurate than photographs annotated by humans at the level of a single image, the automated approach provides comparable or better estimations of the percent cover of the benthic substrates at the level of a minute of survey (~ 50 m²of reef) due to the volume of photographs that can be automatically annotated, providing greater spatial coverage of the site. This method can be used in a variety of shallow systems and is particularly advantageous when spatially explicit data or surveys of large spatial extents are necessary.