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Herbivore management is an important tool for resilience-based approaches to coral reef conservation, and evidence-based science is needed to enact successful management. We synthesized data from multiple monitoring programs in Hawai'i to measure herbivore biomass and benthic condition over a 10-year period preceding any major coral bleaching. We analysed data from 20 242 transects alongside data on 27 biophysical and human drivers and found herbivore biomass was highly variable throughout Hawai'i, with high values in remote locations and the lowest values near population centres. Both human and biophysical drivers explained variation in herbivore biomass, and among the human drivers both fishing and land-based pollution had negative effects on biomass. We also found evidence that herbivore functional group biomass is strongly linked to benthic condition, and that benthic condition is sensitive to changes in herbivore biomass associated with fishing. We show that when herbivore biomass is below 80% of potential biomass, benthic condition is predicted to decline. We also show that a range of management actions, including area-specific fisheries regulations and gear restrictions, can increase parrotfish biomass. Together, these results provide lines of evidence to support managing herbivores as an effective strategy for maintaining or bolstering reef resilience in a changing climate. [ABSTRACT FROM AUTHOR]

Protection mutualists display territorial behaviors, which also act as protective services for their host species. These territorial behaviors may inhibit the ability of other organisms to use the habitat provided by the host species. Coral guard crabs (Trapeziidae) and snapping shrimps (Alpheidae) form a guild of protection mutualists that aggressively defend their obligate host corals from predators. Here, we investigate how these protection mutualists affect the colonization and/or establishment of the community associated with the host coral. We found that Trapezia intermedia and Alpheus lottini both had species‐specific effects on the probability of colonization. Alpheus lottini inhibited recruitment by conspecifics, but did not affect the settlement of Trapezia spp. T. intermedia did not affect recruitment by Trapezia spp. or Alpheus spp. Both T. intermedia and A. lottini limited colonization by some other decapod species, including xanthid and portunid crabs. The presence of protection mutualists affected the trajectory of communities associated with host corals such that the initial presence of protection mutualists explained 20% of variation in community composition six‐months later. The communities on corals with protection mutualists had similar richness but lower beta‐diversity than control corals after six months. Host response to protection mutualists was mixed. Over the two‐month colonization study when the mutualist treatments were maintained and colonizing species were removed, host corals with both protection mutualists had lower growth rates than control corals or corals with only T. intermedia; however, coral growth did not differ between treatments over the six‐month establishment study when community trajectories were followed without interference. [ABSTRACT FROM AUTHOR]

The extent to which populations persist under environmental stress depends on the reproductive output of individuals that survive the stress. In coral systems, corals bleach in response to stress from elevated water temperature. However, little is known of the extent to which thermal stress impairs the reproductive capacity of the survivors over the following years, limiting the capacity to predict how populations will persist in the Anthropocene.Using histology to quantify the abundance and size of oocytes and spermaries per polyp, we tested how bleaching impairs the reproductive response of the coral Pocillopora meandrina over two reproductive seasons following the 2015 mass bleaching event in the Hawaiian Islands.We found that smaller colonies not only had a greater probability of bleaching but also suffered greater reproductive impacts over a longer time. In contrast, larger colonies generated comparable reproductive output regardless of bleaching severity, although bleached colonies generated smaller oocytes the year after bleaching.These results show that reproductive impacts of bleaching are more complex and size‐specific than commonly assumed. Therefore, estimates of bleaching mortality may underestimate the true impact of thermal stress on populations, especially as populations lose larger individuals from repeated and co‐occurring stressors. A free Plain Language Summary can be found within the Supporting Information of this article. [ABSTRACT FROM AUTHOR]

Most of the diversity on coral reefs is in the cryptofauna, the hidden organisms that inhabit the interstitial spaces of corals and other habitat-forming benthos. However, little is known about the patterns and drivers of diversity in cryptofauna. We investigated how the cryptofaunal community associated with the branching coral Pocillopora meandrina varies across spatial scales and environmental gradients. We performed nondestructive visual surveys of the cryptofaunal community on 751 P. meandrina colonies around the island of O‘ahu (30-73 colonies per site, 3-6 sites per region, five regions). We identified 91 species, including 48 fishes and 43 invertebrates. Most of these species were observed rarely, with only 19 species occurring on greater than 5% of surveyed colonies. Variation in community abundance and species richness was greatest at the scale of the coral colony and lowest at the site scale. Abundance and species richness increased with increasing colony size and maximum wave height, and decreased with increasing surface chlorophyll-a. In an analysis of species-specific responses, colony size, wave height, and chlorophyll-a were significant drivers of occurrence. Depth and percent live coral tissue were also identified as important correlates for community composition with distinct responses across taxa. Analyzing species-specific responses to environmental gradients documented a unique pattern for the guard crab Trapezia intermedia, which had a higher probability of occurring on smaller colonies (in contrast to 18 other common taxa). The results of a principal coordinates analysis on community composition and a co-occurrence analysis further supported T. intermedia as having a unique distribution across colonies, even in comparison with four other Trapezia species. Overall, these patterns emphasize the importance of host coral characteristics (i.e., colony size and percent live tissue) and physical characteristics of the surrounding habitat (i.e., wave energy, chlorophyll-a, and depth) in structuring cryptofaunal communities and characterize species-specific responses to environmental gradients. [ABSTRACT FROM AUTHOR]

Coral colonies regularly suffer tissue damage from natural and anthropogenic sources. The resultant wounds can decrease colony fitness and act as sources of infection or algal overgrowth. By systematically breaking branches on 54 Pocillopora meandrina colonies and following in situ tissue regeneration (April–August 2017), variation in the wound recovery process was investigated within colonies, among colonies, and across four sites on O'ahu, Hawai'i. Ninety-five percent of all wounds healed, with an average healing time of 42 days. Average healing time was not different between initial and subsequent wounds. The relative importance of intrinsic factors, extrinsic factors, and disturbance history for the wound repair process was examined. Previous colony stressors, i.e., percent live coral tissue and bleaching history, were not correlated with wound healing time. These results indicate that wound repair is a priority for P. meandrina. Colony size and depth were significantly correlated with wound healing time: larger colonies healed 14 days faster than smaller colonies, and deeper colonies healed 25 days slower than shallower colonies. These findings support the hypothesis that larger colonies have more energy available for tissue regeneration. The observation of longer healing times for deeper colonies is likely driven by extrinsic factors that vary with depth, including temperature, wave energy, and irradiance. Overall, we show that wound healing in P. meandrina is physiologically resilient to previous stressors, but is affected by both colony size and depth. Understanding drivers of variation in regenerative processes for corals is critical for predicting coral population recovery after disturbances. [ABSTRACT FROM AUTHOR]