Coral reefs benefit from reduced land-sea impacts under ocean warming.

Coral reef ecosystems are being fundamentally restructured by local human impacts and climate-driven marine heatwaves that trigger mass coral bleaching and mortality1. Reducing local impacts can increase reef resistance to and recovery from bleaching2. However, resource managers lack clear advice on targeted actions that best support coral reefs under climate change3 and sector-based governance means most land- and sea-based management efforts remain siloed4. Here we combine surveys of reef change with a unique 20-year time series of land-sea human impacts that encompassed an unprecedented marine heatwave in Hawai'i. Reefs with increased herbivorous fish populations and reduced land-based impacts, such as wastewater pollution and urban runoff, had positive coral cover trajectories predisturbance. These reefs also experienced a modest reduction in coral mortality following severe heat stress compared to reefs with reduced fish populations and enhanced land-based impacts. Scenario modelling indicated that simultaneously reducing land-sea human impacts results in a three- to sixfold greater probability of a reef having high reef-builder cover four years postdisturbance than if either occurred in isolation. International efforts to protect 30% of Earth's land and ocean ecosystems by 2030 are underway5. Our results reveal that integrated land-sea management could help achieve coastal ocean conservation goals and provide coral reefs with the best opportunity to persist in our changing climate.

Effectiveness of surrogate taxa in the design of coral reef reserve systems in the Indo-Pacific.

Implementing systematically designed reserve systems is crucial to slowing the global decline of coral reef health and diversity. Yet, the paucity of spatial data for most coral reef taxa often requires conservation planners to design reserve systems based only on a subset of taxonomic groups as surrogates for all other taxa. In terrestrial systems the validity of surrogates for reserve design is established by testing for cross-taxon congruence (similarities in spatial patterns of species richness), but this concept has rarely been examined in the marine environment. We tested the suitability of taxa as conservation representation surrogates of coral reef species richness across the Indo-Pacific, based on species lists of fishes, corals, and mollusks from 167 sites. First, we tested the relevance of cross-taxon congruence patterns to predict these surrogacy patterns. We determined congruence between taxonomic groups by conducting a correlation analysis of dissimilarity values between pairs of sites. We then evaluated how well each taxonomic group represented the other groups in a marine reserve system selected by a greedy reserve-selection algorithm relative to reserve systems selected by chance. No taxonomic group we examined was a reliable surrogate for the other groups such that site selection based on that group always represented other taxa significantly better than random selection of sites. Sites selected based on hard corals represented the other taxonomic groups in a reserve system worse than randomly selected sites. Although we found high cross-taxon congruence between fishes and corals and between corals and mollusks, for some regions cross-taxon congruence was not always a reliable indicator of the ability of one taxonomic group to efficiently represent another in a reserve system. We concluded that in Indo-Pacific coral reef ecosystems one can only be sure that a target taxon is efficiently represented in a reserve system when data on that taxon are used to select a reserve system.

Rapid assessment of stony coral richness and condition on Saba Bank, Netherlands Antilles.

The benthic habitats of Saba Bank (17 degrees 25'N, 63 degrees 30'W) are at risk from maritime traffic, especially oil tankers (e.g., anchoring). To mitigate this risk, information is needed on the biodiversity and location of habitats to develop a zone use plan. A rapid survey to document the biodiversity of macro-algae, sponges, corals and fishes was conducted. Here we report on the richness and condition of stony coral species at 18 select sites, and we test for the effects of bottom type, depth, and distance from platform edge. Species richness was visually assessed by roving scuba diver with voucher specimens of each species collected. Coral tissue was examined for bleaching and diseases. Thirty-three coral species were documented. There were no significant differences in coral composition among bottom types or depth classes (ANOSIM, P>0.05). There was a significant difference between sites (ANOSIM, P<0.05) near and far from the platform edge. The number of coral species observed ranged from zero and one in algal dominated habitats to 23 at a reef habitat on the southern edge of the Bank. Five reef sites had stands of Acropora cervicornis, a critically endangered species on the IUCN redlist. Bleaching was evident at 82% of the sites assessed with 43 colonies bleached. Only three coral colonies were observed to have disease. Combining our findings with that of other studies, a total of 43 species have been documented from Saba Bank. The coral assemblage on the bank is representative and typical of those found elsewhere in the Caribbean. Although our findings will help develop effective protection, more information is needed on Saba Bank to create a comprehensive zone use plan. Nevertheless, immediate action is warranted to protect the diverse coral reef habitats documented here, especially those containing A. cervicornis.