C. Brock Woodson

Chemically mediated competition between microbes and animals: microbes as consumers in food webs.

Microbes are known to affect ecosystems and communities as decomposers, pathogens, and mutualists. However, they also may function as classic consumers and competitors with animals if they chemically deter larger consumers from using rich food-falls such as carrion, fruits, and seeds that can represent critical windfalls to both microbes and animals. Microbes often use chemicals (i.e., antibiotics) to compete against other microbes. Thus using chemicals against larger competitors might be expected and could redirect significant energy subsidies from upper trophic levels to the detrital pathway. When we baited traps in a coastal marine ecosystem with fresh vs. microbe-laden fish carrion, fresh carrion attracted 2.6 times as many animals per trap as microbe-laden carrion. This resulted from fresh carrion being found more frequently and from attracting more animals when found. Microbe-laden carrion was four times more likely to be uncolonized by large consumers than was fresh carrion. In the lab, the most common animal found in our traps (the stone crab Menippe mercenaria) ate fresh carrion 2.4 times more frequently than microbe-laden carrion. Bacteria-removal experiments and feeding bioassays using organic extracts of microbe-laden carrion showed that bacteria produced noxious chemicals that deterred animal consumers. Thus bacteria compete with large animal scavengers by rendering carcasses chemically repugnant. Because food-fall resources such as carrion are major food subsidies in many ecosystems, chemically mediated competition between microbes and animals could be an important, common, but underappreciated interaction within many communities.

Stratified turbulence in the nearshore coastal ocean: Dynamics and evolution in the presence of internal bores

High-frequency measurements of stratified turbulence throughout the water column were collected over a 2 week period in the nearshore environment of southern Monterey Bay, CA, using a cabled observatory system and an underwater turbulence flux tower. The tower contained a vertical array of acoustic Doppler velocimeters and fast-response conductivity-temperature sensors, providing a nearly continuous data set of turbulent velocity and density fluctuations and a unique look into the stratified turbulence field. The evolution of various turbulence quantities and direct measurements of the vertical turbulent diffusivity is examined in the presence of nearshore internal bores, both in the near-bed region and in the stratified interior. We show that individual bores can drive substantial changes in local turbulence and mixing dynamics, with considerable differences between the leading and trailing edges of the bores. Using direct observations of the flux Richardson number, our measurements confirm previous observations that show the highest mixing efficiencies (Γ) occurring in regions of buoyancy-controlled turbulence. Parameterizations of the flux Richardson number as a function of the turbulence activity number are also presented. Finally, we demonstrate that the commonly used assumption of a constant mixing efficiency (Γ = 0.2) for calculating turbulent diffusivities leads to significant overestimates compared to diffusivity values calculated using the directly measured mixing efficiency. Implications of the results are discussed.

Ocean fronts drive marine fishery production and biogeochemical cycling

Significance Fronts in the ocean act as oases in a fluid desert that are not fully accounted for in climate or fisheries model projections. Fronts act to increase production by channeling nutrients through multiple trophic levels, including commercially important fishes and marine mammals, and enhance carbon export to the deep ocean. Fronts consequently have immense effects on the ocean, from base of the food chain up through the dinner table and mediation of global climate change. Here we show how fronts can be incorporated into current models, using a technique from fluid dynamics to improve both climate and fisheries models. Long-term changes in nutrient supply and primary production reportedly foreshadow substantial declines in global marine fishery production. These declines combined with current overfishing, habitat degradation, and pollution paint a grim picture for the future of marine fisheries and ecosystems. However, current models forecasting such declines do not account for the effects of ocean fronts as biogeochemical hotspots. Here we apply a fundamental technique from fluid dynamics to an ecosystem model to show how fronts increase total ecosystem biomass, explain fishery production, cause regime shifts, and contribute significantly to global biogeochemical budgets by channeling nutrients through alternate trophic pathways. We then illustrate how ocean fronts affect fishery abundance and yield, using long-term records of anchovy–sardine regimes and salmon abundances in the California Current. These results elucidate the fundamental importance of biophysical coupling as a driver of bottom–up vs. top–down regulation and high productivity in marine ecosystems.

Spatiotemporal Variation in Cross-Shelf Exchange across the Inner Shelf of Monterey Bay, California

AbstractCross-shelf exchange resulting from wind- and wave-driven flows across the inner shelf has been the focus of a considerable body of work. This contribution extends recent analyses to the central California coastline using 5-yr of moored current observations. Acoustic Doppler Current Profiler (ADCP) data from stations across the Monterey Bay (two in the northern bay and one in the southern bay), in water depths of ~20 m, showed net offshore transport throughout the year. For the northern bay sites, cross-shelf exchange was dominated by Ekman transport driven by along-shelf diurnal sea breezes during the upwelling season. Intense stratification in the northern bay leads to very shallow observed Ekman layers (~5–8 m), and consequently no overlap between bottom and surface Ekman layers within a few hundred meters of the coast. The total transport is less than predicted by theory consistent with models of shallow-water Ekman transport. The observed transport (~42% of full Ekman transport) is shown to b...

Scale-Dependent Dispersion within the Stratified Interior on the Shelf of Northern Monterey Bay

AbstractAutonomous underwater vehicle measurements are used to quantify lateral dispersion of a continuously released Rhodamine WT dye plume within the stratified interior of shelf waters in northern Monterey Bay, California. The along-shelf evolution of the plume’s cross-shelf (lateral) width provides evidence for scale-dependent dispersion following the 4/3 law, as previously observed in both surface and bottom layers. The lateral dispersion coefficient is observed to grow to 0.5 m2 s−1 at a distance of 700 m downstream of the dye source. The role of shear and associated intermittent turbulent mixing within the stratified interior is investigated as a driving mechanism for lateral dispersion. Using measurements of time-varying temperature and horizontal velocities, both an analytical shear-flow dispersion model and a particle-tracking model generate estimates of the lateral dispersion that agree with the field-measured 4/3 law of dispersion, without explicit appeal to any assumed turbulence structure.

Effects of current and future coastal upwelling conditions on the fertilization success of the red abalone (Haliotis rufescens)

&NA; Acidification, deoxygenation, and warming are escalating changes in coastal waters throughout the world ocean, with potentially severe consequences for marine life and ocean‐based economies. To examine the influence of these oceanographic changes on a key biological process, we measured the effects of current and expected future conditions in the California Current Large Marine Ecosystem on the fertilization success of the red abalone (Haliotis rufescens). Laboratory experiments were used to assess abalone fertilization success during simultaneous exposure to various levels of seawater pH (gradient from 7.95 to 7.2), dissolved oxygen (DO) (˜60 and 180 &mgr;m.kg SW) and temperature (9, 13, and 18 °C). Fertilization success declined continuously with decreasing pH but dropped precipitously below a threshold near pH 7.55 in cool (9 °C—upwelling) to average (13 °C) seawater temperatures. Variation in DO had a negligible effect on fertilization. In contrast, warmer waters (18 °C) often associated with El Niño Southern Oscillation conditions in central California acted antagonistically with decreasing pH, largely reducing the strong negative influence below the pH threshold. Experimental approaches that examine the interactive effects of multiple environmental drivers and also strive to characterize the functional response of organisms along gradients in environmental change are becoming increasingly important in advancing our understanding of the real‐world consequences of changing ocean conditions.

A novel coupled fluid-behavior model for simulating dynamic huddle formation

A coupled numerical model is developed to examine aggregative behavior in instances where the behavior not only responds to the environment, but the environment responds to the behavior such as fish schooling and penguin huddling. In the coupled model, the full Navier-Stokes equations are solved for the wind field using a finite difference method (FDM), and coupled to a smoothed particle hydrodynamics (SPH) model adapted to simulate animal behavior (penguins are individual particles in the SPH). We use the model to examine the dynamics of penguin huddling as a purely individual fitness maximizing behavior. SPH is a mesh-free Lagrangian method driven by local interactions between neighboring fluid particles and their environment allowing particles to act as free ranging ‘animals’ unconstrained by a computational grid that implicitly interact with one another (a critical element of aggregative behavior). The coupled model is recomputed simultaneously as the huddle evolves over time to update individual particle positions, redefine the properties of the developing huddle (i.e., shape and density), and adjust the wind field flowing through and around the dynamic huddle. This study shows the ability of a coupled model to predict the dynamic properties of penguin huddling, to quantify biometrics of individual particle “penguins”, and to confirm communal penguin huddling behavior as an individualistic behavior.

A unifying theory for top-heavy ecosystem structure in the ocean

Size generally dictates metabolic requirements, trophic level, and consequently, ecosystem structure, where inefficient energy transfer leads to bottom-heavy ecosystem structure and biomass decreases as individual size (or trophic level) increases. However, many animals deviate from simple size-based predictions by either adopting generalist predatory behavior, or feeding lower in the trophic web than predicted from their size. Here we show that generalist predatory behavior and lower trophic feeding at large body size increase overall biomass and shift ecosystems from a bottom-heavy pyramid to a top-heavy hourglass shape, with the most biomass accounted for by the largest animals. These effects could be especially dramatic in the ocean, where primary producers are the smallest components of the ecosystem. This approach makes it possible to explore and predict, in the past and in the future, the structure of ocean ecosystems without biomass extraction and other impacts.Evidence of inverted trophic pyramids in marine food webs has been enigmatic owing to lack of theoretical support. Here, Woodson et al. use metabolic and size-spectra theory to show that inverted pyramids are possible when food webs have generalist predators and consumers with large body sizes.

Connecting Flow over Complex Terrain to Hydrodynamic Roughness on a Coral Reef

AbstractFlow over complex terrain causes stress on the bottom leading to drag, turbulence, and formation of a boundary layer. But despite the importance of the hydrodynamic roughness scale z0 in pr...