Global warming impairs stock-recruitment dynamics of corals.

Changes in disturbance regimes due to climate change are increasingly challenging the capacity of ecosystems to absorb recurrent shocks and reassemble afterwards, escalating the risk of widespread ecological collapse of current ecosystems and the emergence of novel assemblages1-3. In marine systems, the production of larvae and recruitment of functionally important species are fundamental processes for rebuilding depleted adult populations, maintaining resilience and avoiding regime shifts in the face of rising environmental pressures4,5. Here we document a regional-scale shift in stock-recruitment relationships of corals along the Great Barrier Reef-the world's largest coral reef system-following unprecedented back-to-back mass bleaching events caused by global warming. As a consequence of mass mortality of adult brood stock in 2016 and 2017 owing to heat stress6, the amount of larval recruitment declined in 2018 by 89% compared to historical levels. For the first time, brooding pocilloporids replaced spawning acroporids as the dominant taxon in the depleted recruitment pool. The collapse in stock-recruitment relationships indicates that the low resistance of adult brood stocks to repeated episodes of coral bleaching is inexorably tied to an impaired capacity for recovery, which highlights the multifaceted processes that underlie the global decline of coral reefs. The extent to which the Great Barrier Reef will be able to recover from the collapse in stock-recruitment relationships remains uncertain, given the projected increased frequency of extreme climate events over the next two decades7.

Global biodiversity patterns of benthic marine algae.

Species richness patterns are remarkably similar across many marine taxa, yet explanations of how such patterns are generated and maintained are conflicting. I use published occurrence data to identify previously masked latitudinal and longitudinal diversity gradients for all genera of benthic marine macroalgae and for species in the Order Bryopsidales. I also quantify the size, location, and overlap of macroalgal geographic ranges to determine how the observed richness patterns are generated. Algal genera exhibit an inverse latitudinal gradient, with biodiversity hotspots in temperate regions, while bryopsidalean species reach peak diversity in the tropics. The geographic distribution of range locations results in distinct clusters of range mid-points. In particular, widespread taxa are centered within tight latitudinal and longitudinal bands in the middle of the Indo-Pacific and Atlantic Oceans while small-ranged taxa are clustered in peripheral locations, suggesting that variation in speciation and extinction are important drivers of algal diversity patterns. Hypotheses about factors that regulate diversity contain underlying assumptions about the size and location of geographic ranges, in addition to predictions as to why species numbers will differ among regions. Yet these assumptions are rarely considered in assessing the validity of the prevailing hypotheses. I assess a suite of hypotheses, suggested to explain patterns of marine diversity, by comparing algal-richness patterns in combination with the size and location of algal geographic ranges, to the richness and range locations predicted by these hypotheses. In particular, the results implicate habitat areas and ocean currents as the most plausible drivers of observed diversity patterns.