Behaviorally Mediated Larval Transport in Upwelling Systems

Highly advective upwelling systems along the western margins of continents are widely believed to transport larvae far offshore in surface currents resulting in larval wastage, limited recruitment, and increased population connectivity. However, suites of larval behaviors effectively mediate interspecific differences in the extent of cross-shelf migrations between nearshore adult habitats and offshore larval habitats. Interspecific differences in behavior determining whether larvae complete development in estuaries or migrate to the continental shelf are evident in large estuaries, but they sometimes may be disrupted by turbulent tidal flow or the absence of a low-salinity cue in shallow, low-flow estuaries, which are widespread in upwelling systems. Larvae of most species on the continental shelf complete development in the coastal boundary layer of reduced flow, whereas other species migrate to the mid- or outer shelf depending on how much time is spent in surface currents. These migrations are maintained across latitudinal differences in the strength and persistence of upwelling, in upwelling jets at headlands, over upwelling-relaxation cycles, and among years of varying upwelling intensity. Incorporating larval behaviors into numerical models demonstrates that larvae recruit closer to home and in higher numbers than when larvae disperse passively or remain in surface currents.

Patterns of Microbially Driven Carbon Cycling in the Ocean: Links between Extracellular Enzymes and Microbial Communities

Heterotrophic microbial communities play a central role in the marine carbon cycle. They are active in nearly all known environments, from the surface to the deep ocean, in the sediments, and from the equator to the Poles. In order to process complex organic matter, these communities produce extracellular enzymes of the correct structural specificity to hydrolyze substrates to sizes sufficiently small for uptake. Extracellular enzymatic hydrolysis thus initiates heterotrophic carbon cycling. Our knowledge of the enzymatic capabilities of microbial communities in the ocean is still underdeveloped. Recent studies, however, suggest that there may be large-scale patterns of enzymatic function in the ocean, patterns of community function that may be connected to emerging patterns of microbial community composition. Here I review some of these large-scale contrasts in microbial enzyme activities, between high-latitude and temperate surface ocean waters, contrasts between inshore and offshore waters, changes with depth gradients in the ocean, and contrasts between the water column and underlying sediments. These contrasting patterns are set in the context of recent studies of microbial communities and patterns of microbial biogeography. Focusing on microbial community function as well as composition and potential should yield clearer understanding of the factors driving carbon cycling in the ocean.