Degradation of coastal water quality in the form of low dissolved oxygen levels (hypoxia) can harm biodiversity, ecosystem function, and human wellbeing. Extreme hypoxic conditions along the coast, leading to what are often referred to as "dead zones," are known primarily from temperate regions. However, little is known about the potential threat of hypoxia in the tropics, even though the known risk factors, including eutrophication and elevated temperatures, are common. Here we document an unprecedented hypoxic event on the Caribbean coast of Panama and assess the risk of dead zones to coral reefs worldwide. The event caused coral bleaching and massive mortality of corals and other reef-associated organisms, but observed shifts in community structure combined with laboratory experiments revealed that not all coral species are equally sensitive to hypoxia. Analyses of global databases showed that coral reefs are associated with more than half of the known tropical dead zones worldwide, with >10% of all coral reefs at elevated risk for hypoxia based on local and global risk factors. Hypoxic events in the tropics and associated mortality events have likely been underreported, perhaps by an order of magnitude, because of the lack of local scientific capacity for their detection. Monitoring and management plans for coral reef resilience should incorporate the growing threat of coastal hypoxia and include support for increased detection and research capacity.biodiversity | coral bleaching | dissolved oxygen | hypoxia | water quality

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The mode of development in marine invertebrates is believed to have consequences for dispersal, gene flow, geographic range, and speciation and extinction rates. The factors responsible for among-species differences in mode of development are not well understood and patterns of variation in mode of development have not been documented for many groups. I present a compiled data set of developmental characters for 78 species of calyptraeid gastropods: 53 Crepidula, 9 Calyptraea, 11 Crucibulum and 5 other species. Analysis of this data set shows that egg-and hatching-size distributions are strongly positively skewed. As expected, egg size correlates with hatching size and time to hatching in species without nurse eggs. Egg size is not significantly different between species with planktotrophic development and species with direct development with nurse eggs. Hatching size of direct developers with and without nurse eggs do not differ. Developmental characters do not vary with adult body size among species. There are strong latitudinal effects in mode of development, the frequency of planktotrophic species decreases with increasing latitude while the proportion of direct developers increases. There is also a striking latitudinal pattern in the occurrence of nurse eggs; almost all species with nurse eggs occur in the southern hemisphere. These latitudinal patterns do not appear to be explained by sea surface temperature. Comparisons with other gastropods for which similar compilations are available show a striking difference between heterobranchs (opisthobranchs and pulmonates) and caenogastropods in developmental characteristics.KEY WORDS: Larvae · Invertebrate development · Crepidula · Crucibulum · Calyptraea Resale or republication not permitted without written consent of the publisher

The mode of development of marine invertebrates is thought to influence levels of population structure and the location of species range endpoints via differences in dispersal ability. To examine these effects, populations of three sympatric clades of sedentary, marine gastropods in the genus Crepidula were sampled along the Atlantic and Gulf coasts of North America. A haplotype tree was constructed for each clade based on 640 bp sequences of mitochondrial cytochrome oxidase c subunit I. Examination of the tree topology, and AMOVA analysis show that species with direct development (those hatching as benthic juveniles) have higher levels of population structure than do species with planktonic development. Both species in the direct-developing C. convexa clade have high levels of geographical differentiation, with most populations representing a discrete clade of haplotypes. The planktotrophic species C. fomicata contains two major haplotype clades, both of which include samples from throughout the Atlantic coast. In this species there is no geographical differentiation among haplotypes but AMOVA analysis detects a small but statistically significant level of geographical structure. The population structure within the C. plana species complex appears also to vary with mode of development: C. atrasolea, a direct-developing species, has higher levels of population structure than does C. depressa, a sympatric planktotrophic species. The coincident occurrence of range endpoints and genetic breaks along the east coast of Florida in both direct-developing species and species with planktonic development indicates that this biogeographic break is not due to development-specific mechanisms such as hydrographic effects on larval recruitment.