Based on the belief that marine larvae, which can spend days to months in the planktonic stage, could be transported considerable distances by ocean currents, it has long been assumed that populations of coastal species with a planktonic larval stage are demographically open and highly ''connected.'' Such assumptions about the connectivity of coastal populations govern approaches to managing marine resources and shape our fundamental understanding of population dynamics and evolution, yet are rarely tested directly due to the small size and high mortality of marine larvae in a physically complex environment. Here, we document a successful application of elemental fingerprinting as a tracking tool to determine sources of settled invertebrates and show that coastal mussel larvae, previously thought to be highly dispersed, can be retained within 20 -30 km of their natal origin. We compare two closely related and co-occurring species, Mytilus californianus and Mytilus galloprovincialis, and determine that, despite expected similarities, they exhibit substantially different connectivity patterns. Our use of an in situ larval culturing technique overcomes the previous challenge of applying microchemical tracking methods to species with completely planktonic development. The exchange of larvae and resulting connectivities among marine populations have fundamental consequences for the evolution and ecology of species and for the management of coastal resources.elemental fingerprinting ͉ in situ larval culturing ͉ larval retention ͉ larval transport ͉ Mytilus

Rapid population growth and coastal development are primary drivers of marine habitat degradation. Although shoreline hardening or armoring (the addition of concrete structures such as seawalls, jetties, and groins), a byproduct of development, can accelerate erosion and loss of beaches and tidal wetlands, it is a common practice globally. Here, we provide the first estimate of shoreline hardening along US Pacific, Atlantic, and Gulf of Mexico coasts and predict where future armoring may result in tidal wetland loss if coastal management practices remain unchanged. Our analysis indicates that 22 842 km of continental US shoreline -approximately 14% of the total US coastline -has been armored. We also consider how socioeconomic and physical factors relate to the pervasiveness of shoreline armoring and show that housing density, gross domestic product, storms, and wave height are positively correlated with hardening. Over 50% of South Atlantic and Gulf of Mexico coasts are fringed with tidal wetlands that could be threatened by future hardening, based on projected population growth, storm frequency, and an absence of coastal development restrictions.

In the high-salinity seaward portions of estuaries, oysters seek refuge from predation, competition and disease in intertidal areas 1,2 , but this sanctuary will be lost if vertical reef accretion cannot keep pace with sea-level rise (SLR). Oyster-reef abundance has already declined ∼85% globally over the past 100 years, mainly from over harvesting 3,4 , making any additional losses due to SLR cause for concern. Before any assessment of reef response to accelerated SLR can be made, direct measures of reef growth are necessary. Here, we present direct measurements of intertidal oyster-reef growth from cores and terrestrial lidar-derived digital elevation models. On the basis of our measurements collected within a mid-Atlantic estuary over a 15-year period, we developed a globally testable empirical model of intertidal oyster-reef accretion. We show that previous estimates of vertical reef growth, based on radiocarbon dates and bathymetric maps 5,6 , may be greater than one order of magnitude too slow. The intertidal reefs we studied should be able to keep up with any future accelerated rate of SLR (ref. 7) and may even benefit from the additional subaqueous space allowing extended vertical accretion.Oyster-reef communities (Crassostrea virginica) provide numerous ecosystem services, including production of oysters, water filtration 8,9 , provision of habitat for fishes and crustaceans 10 , shoreline stabilization 11,12 , and maintenance of estuarine-water alkalinity 13 . In the face of natural and anthropogenic stressors, such as harvesting, degrading water quality, increasing rates of SLR, warming, disease, ocean acidification, and parasitism, reef habitats and associated services are becoming unsustainable. Loss of these reefs in estuaries that otherwise lack alternative hard substrates is a global problem 4 . SLR, in particular, threatens oyster reefs in the high-salinity seaward portions of estuaries because there, oysters seek refuge from biofouling (space competition), predation and disease in intertidal areas 1,2 . The importance of the intertidal area to individual oyster growth in lower estuaries is apparent from experimental work that has shown intertidal oysters grow 34% faster and exhibit an order of magnitude less fouling (percentage cover) than subtidal oysters 14 . Constructed subtidal reefs in no-harvest sanctuaries (North Carolina, USA) were also found to have few, if any, live oysters (mean density of 0-92 live oysters m −2 ) after six years in euhaline waters, whereas intertidal reefs faired significantly better (200-225 live oysters m −2 ; ref. 15). Restoration is a common mitigation option for historic oyster-reef loss, but project success with accelerating SLR will depend on a reef 's ability to maintain an intertidal position. Model simulations presume that reef-accretion rates cannot exceed the rate of SLR, but parameterizations are not verified with direct measures of reef-scale growth 16,17 . Without direct measures of reef-scale growth, our ability to assess restoration and conservation ...

Global temperatures are rising, and are expected to produce a poleward shift in the distribution of many organisms. We quantified changes in fish assemblages within seagrass meadows of the northern Gulf of Mexico (GOM) between the 1970s and 2006-2007, and observed changes consistent with this forecast. During 2006-2007 we sampled seagrass meadows using the same gears and methods previously employed by R. J. Livingston in coastal waters of northwest Florida throughout the 1970s. Comparisons between datasets revealed numerous additions to the fish fauna during 2006-2007 that were completely absent in the 1970s, including: Lutjanus synagris (lane snapper), Epinephelus morio (red grouper), Chaetodon ocellatus (spotfin butterflyfish), Mycteroperca sp (grouper, non gag), Centropristis philadelphica (rock sea bass), Fistularia tabacaria (bluespotted cornetfish), Ocyurus chrysurus (yellowtail snapper), Thalassoma bifasciatum (bluehead wrasse), Abudefduf saxatilis (sergeant major), Acanthuridae spp. (surgeonfishes) and Sparisoma viride (stoplight parrotfish). Several other species showed large increases in abundance during the interval between 1979 and 2006, including Mycteroperca microlepis (gag grouper, up $ 200 Â ), Lutjanus griseus (gray snapper, up $ 105 Â ), and Nicholsina usta (emerald parrotfish, up $ 22 Â ).All of these are tropical or subtropical species that now make up a greater percentage of seagrass-associated fish assemblages in the northern GOM than in the past. Additionally, we observed regional increases in air and sea surface temperatures (43 1C) during the $ 30 years that separate Livingston's samples and ours that correlate with northern shifts in the distribution of warm-water fishes. Documenting these range shifts is a critical first step in investigating the consequences of global warming for endemic marine communities and fishery production in the northern GOM.