Despite the importance of coastal ecosystems for the global carbon budgets, knowledge of their carbon storage capacity and the factors driving variability in storage capacity is still limited. Here we provide an estimate on the magnitude and variability of carbon stocks within a widely distributed marine foundation species throughout its distribution area in temperate Northern Hemisphere. We sampled 54 eelgrass (Zostera marina) meadows, spread across eight ocean margins and 36° of latitude, to determine abiotic and biotic factors influencing organic carbon (Corg) stocks in Zostera marina sediments. The Corg stocks (integrated over 25‐cm depth) showed a large variability and ranged from 318 to 26,523 g C/m2 with an average of 2,721 g C/m2. The projected Corg stocks obtained by extrapolating over the top 1 m of sediment ranged between 23.1 and 351.7 Mg C/ha, which is in line with estimates for other seagrasses and other blue carbon ecosystems. Most of the variation in Corg stocks was explained by five environmental variables (sediment mud content, dry density and degree of sorting, and salinity and water depth), while plant attributes such as biomass and shoot density were less important to Corg stocks. Carbon isotopic signatures indicated that at most sites <50% of the sediment carbon is derived from seagrass, which is lower than reported previously for seagrass meadows. The high spatial carbon storage variability urges caution in extrapolating carbon storage capacity between geographical areas as well as within and between seagrass species.

The reproductive pattern of R. exoculata was also examined by dissection and direct measurement of oocytes from females collected in September 1994 and November 2004, providing the first comparison of reproductive development in samples from different months for this species. There was no significant difference in oocyte size-frequency distributions of females collected in these samples, indicating a lack of seasonal reproduction in R. exoculata. INTRODUCTIONHydrothermal vents are highly dynamic, heterogeneous and ultimately ephemeral deep-sea environments. Vent organisms can experience variations in the temperature and chemistry of their environment on the timescale of seconds as a result of turbulent mixing of hydrothermal fluids and ambient seawater, typically overlaid on longer-period tidal variations. On longer timescales, volcanic events at mid-ocean ridges can disturb vent communities directly, while tectonic events can disrupt the subsurface plumbing of hydrothermal systems. As a consequence of the local variations in hydrothermal activity that result from such processes, temporal variation has been noted in the composition, abundance and distribution of megafauna at vents on subannual to interannual timescales.Hydrothermal vent communities were discovered in the eastern Pacific in the late 1970s and the longest ecological time-series are therefore available from those sites. Interannual variation has been noted in the distribution and abundance of megafauna at 13°N on the East Pacific Rise, related to an interruption in hydrothermal activity (Desbruyères, 1998).Expeditions to 9°N have recorded the early stages of vent community development following a volcanic eruption in 1991 that destroyed part of an established community, while community composition and venting patterns at 21°N demonstrate temporal stability at a decadal scale (Desbruyères, 1998). Meanwhile on the Galapagos Rift, decadal-scale variation has been noted in the vent community at Rose Garden despite an apparent lack of fluctuations in venting over the period of visits (Desbruyères, 1998), implying ecological change mediated by biological interactions.Hydrothermal vent communities were first observed on the Mid-Atlantic Ridge in 1985 (Rona et al., 1986) and ecological studies of Mid-Atlantic vent communities have therefore lagged behind those of their eastern Pacific counterparts. At shallow (<2000 m) vent sites close to the Azores, long-term monitoring of communities dominated by the mussel Bathymodilus azoricus is underway, but there have been few studies of temporal variation at deeper vent systems further south on the Mid-Atlantic Ridge. Interannual temporal variation has been examined in faunal distributions at Broken Spur vent field (Copley et al., 1997) and subannual variation investigated at the TAG hydrothermal mound before and after drilling by the Ocean Drilling Program in 1995 (Copley et al., 1999). Anecdotal observations suggest interannual stability in community composition at the TAG hydrothermal mound (Gebruk et al., 19...

Abstract. Latitudinal gradients in species interactions are widely cited as potential causes or consequences of global patterns of biodiversity. However, mechanistic studies documenting changes in interactions across broad geographic ranges are limited. We surveyed predation intensity on common prey (live amphipods and gastropods) in communities of eelgrass (Zostera marina) at 48 sites across its Northern Hemisphere range, encompassing over 37°of latitude and four continental coastlines. Predation on amphipods declined with latitude on all coasts but declined more strongly along western ocean margins where temperature gradients are steeper. Whereas in situ water temperature at the time of the experiments was uncorrelated with predation, mean annual temperature strongly positively predicted predation, suggesting a more complex mechanism than simply increased metabolic activity at the time of predation. This large-scale biogeographic pattern was modified by local habitat characteristics; predation declined with higher shoot density both among and within sites. Predation rates on gastropods, by contrast, were uniformly low and varied little among sites. The high replication and geographic extent of our study not only provides additional evidence to support biogeographic variation in predation intensity, but also insight into the mechanisms that relate temperature and biogeographic gradients in species interactions.