ライブラリー Annual Energy Outlook 2000

Author Posting. © Oceanography Society, 2007. This article is posted here by permission of Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 20, 3 (2007): 22-39.

/pdf/larval-transport-and-dispersal-in-the-coastal-ocean-and-3ltd4lbhh0.pdf

Larval transport and dispersal in the coastal ocean and consequences for population connectivity

Management and conservation can be greatly informed by considering explicitly how environmental factors influence population genetic structure. Using simulated larval dispersal estimates based on ocean current observations, we demonstrate how explicit consideration of frequency of exchange of larvae among sites via ocean advection can fundamentally change the interpretation of empirical population genetic structuring as compared with conventional spatial genetic analyses. Both frequency of larval exchange and empirical genetic difference were uncorrelated with Euclidean distance between sites. When transformed into relative oceanographic distances and integrated into a genetic isolation-by-distance framework, however, the frequency of larval exchange explained nearly 50 per cent of the variance in empirical genetic differences among sites over scales of tens of kilometres. Explanatory power was strongest when we considered effects of multiple generations of larval dispersal via intermediary locations on the long-term probability of exchange between sites. Our results uncover meaningful spatial patterning to population genetic structuring that corresponds with ocean circulation. This study advances our ability to interpret population structure from complex genetic data characteristic of high gene flow species, validates recent advances in oceanographic approaches for assessing larval dispersal and represents a novel approach to characterize population connectivity at small spatial scales germane to conservation and fisheries management.

/pdf/ocean-currents-help-explain-population-genetic-structure-41f902crez.pdf

Ocean currents help explain population genetic structure

Marine plastic debris floating on the ocean surface is a major environmental problem. However, its distribution in the ocean is poorly mapped, and most of the plastic waste estimated to have entered the ocean from land is unaccounted for. Better understanding of how plastic debris is transported from coastal and marine sources is crucial to quantify and close the global inventory of marine plastics, which in turn represents critical information for mitigation or policy strategies. At the same time, plastic is a unique tracer that provides an opportunity to learn more about the physics and dynamics of our ocean across multiple scales, from the Ekman convergence in basin-scale gyres to individual waves in the surfzone. In this review, we comprehensively discuss what is known about the different processes that govern the transport of floating marine plastic debris in both the open ocean and the coastal zones, based on the published literature and referring to insights from neighbouring fields such as oil spill dispersion, marine safety recovery, plankton connectivity, and others. We discuss how measurements of marine plastics (both in situ and in the laboratory), remote sensing, and numerical simulations can elucidate these processes and their interactions across spatio-temporal scales.

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The physical oceanography of the transport of floating marine debris

A pelagic larval stage is found in nearly all demersal marine teleost fishes, and it is during this pelagic stage that the geographic scale of dispersal is determined. Marine biologists have long made a simplifying assumption that behaviour of larvae--with the possible exception of vertical distribution--has negligible influence on larval dispersal. Because advection by currents can take place over huge scales during a pelagic larval stage that typically lasts for several days to several weeks, this simplifying assumption leads to the conclusion that populations of marine demersal fishes operate over, and are connected over, similar huge scales. This conclusion has major implications for our perception of how marine fish populations operate and for our management of them. Recent (and some older) behavioural research-reviewed here-reveals that for a substantial portion of the pelagic larval stage of perciform fishes, the simplifying assumption is invalid. Near settlement, and for a considerable portion of the pelagic stage prior to that, larvae of many fish species are capable of swimming at speeds faster than mean ambient currents over long periods, travelling tens of kilometres. Only the smallest larvae of perciform fishes swim in an energetically costly viscous hydrodynamic environment (i.e., low Reynolds number). Vertical distribution is under strong behavioural control from the time of hatching, if not before, and can have a decisive, if indirect, influence on dispersal trajectories. Larvae of some species avoid currents by occupying the epibenthic boundary layer. Larvae are able to swim directionally in the pelagic environment, with some species apparently orientating relative to the sun and others to settlement sites. These abilities develop relatively early, and ontogenetic changes in orientation are seemingly common. Larvae of some species can use sound to navigate, and others can use odour to find settlement habitat, at least over small scales. Other senses may also be important to orientation. Larvae are highly aware of their environment and of potential predators, and some school during the pelagic larval stage. Larvae are selective about where they settle at both meso and micro scales, and settlement is strongly influenced by interactions with resident fishes. Most of these behaviours are flexible; for example, swimming speeds and depth may vary among locations, and speed may vary with swimming direction. In direct tests, these behaviours result in dispersal different from that predicted by currents alone. Work with both tropical and temperate species shows that these behaviours begin to be significant relatively early in larval development, but much more needs to be learned about the ontogeny of behaviour and sensory abilities in larvae of marine fishes. As a preliminary rule of thumb, behaviour must be taken into account in considerations of dispersal after the preflexion stage, and vertical distribution behaviour can influence dispersal from hatching. Larvae of perciform fishes are close to being planktonic at the start of the pelagic period and are clearly nektonic at its end, and for a substantial period prior to that. All these things differ among species. Larvae of clupeiform, gadiform and pleuronectiform fishes may be less capable behaviourally than perciform fishes, but this remains to be confirmed. Clearly, these behaviours, along with hydrography, must be included in modelling dispersal and retention and may provide explanations for recent demonstrations of self-recruitment in marine fish populations. Current work is directed at understanding the ontogeny of the gradual transition from planktonic to nektonic behaviour. Although it is clear that larvae of perciform fishes have the ability to strongly influence their dispersal trajectories, it is less clear whether or how these abilities are applied.

Are larvae of demersal fishes plankton or nekton

The potential impacts of climate change on marine planktonic ecosystems remain difficult to predict. Climate forcing can alter nutrient availability and preda- tor community composition, and here we show that these shifts may dramatically alter plankton trophic structure, size distributions and biomass. We modeled phytoplank- ton and zooplankton as a highly resolved size spectrum with size-dependent nutrient uptake and predation and analyzed the model both as a size spectrum and as a food web. Model results identified 2 distinct regimes defined by the average zooplankton feeding preferences. Regime I communities, where planktonic predators are specialists or large relative to prey, had low omnivory, many top predators, low connectance and relatively flat size spec- tra. Regime II communities, where predators are general- ists or small relative to prey, had a high degree of om- nivory, no top predators, high connectance and steep size spectra. Model ecosystems with generalist predators had lower size diversity, smaller plankton and gappier size distributions than ecosystems with specialist predators. Nutrient availability had little influence on trophic struc- ture but strongly impacted size structure and biomass. Most surprisingly, phytoplankton biomass sometimes de- creased with added nutrients if predators were small rela- tive to prey, implying that both predators and nutrients mediate shifts between bottom-up and top-down control. Based on our synthesized estimates of size-selective feed- ing parameters, we infer that size and trophic structure should be strongly affected by abundances of generalist, bloom-forming taxa such as salps and jellyfish, many of which are responsive to ocean temperature. Size-selective feeding fundamentally affects community structure and is a likely mechanism of change in planktonic ecosystems where community composition varies with temperature.

/pdf/plankton-community-properties-determined-by-nutrients-and-1dobsbma7o.pdf

Plankton community properties determined by nutrients and size-selective feeding

Larvae of coastal gastropods sink in turbulence and may use nearshore turbulence as an initial settlement cue. Our objective was to quantify the relationship between turbulence and the proportion of sinking larvae for competent mud snail veligers (Ilyanassa obsoleta). We exposed larvae to a range of field-relevant turbulence conditions ( «5 8.1 3 10 23 to 2.7 3 10 0 cm 2 s 23 ) in a grid-stirred tank, holding other factors constant. We used a video plankton recorder to record larval movements in still water and in turbulence. Larval trajectories and velocity measurements were extracted using video-image analysis. We also measured turbulent flow velocities independently, using laser Doppler velocimetry. To interpret empirical measurements in terms of larval behavior, we developed a threecomponent, normal mixture model for vertical velocity distributions of larvae in turbulence. The model was fitted to observed larval velocities by maximum likelihood, to estimate the proportions of sinking, hovering, and swimming larvae. Over the range of turbulence intensities found in typical coastal habitats, the proportion of sinking larvae increased exponentially (r 2 5 0.89) with the log of the turbulence dissipation rate. The net mean behavioral velocity of the larvae shifted from positive to negative when the dissipation rate reached ;10 21 cm 2 s 23 . By sinking when they enter turbulent, shallow water, competent larvae could improve their chances of settling in favorable coastal habitats. Very little is known about how larval behavior in the plankton affects patterns of larval supply and settlement of benthic invertebrates. Much work has been done to describe larval behavior during the exploration of substrates, when larvae can sometimes select settlement sites over small scales (millimeters to centimeters). Less progress has been made on understanding the behavioral contribution while larvae are transported through the water column to benthic habitats. Under some hydrodynamic conditions, larvae could settle more successfully if they responded to waterborne cues by sinking toward the benthos. If the swimming velocity and gravitational sinking velocity differ by a factor of two or more, behavioral changes can significantly affect larval sink1

https://aslopubs.onlinelibrary.wiley.com/doi/pdf/10.4319/lo.2004.49.6.1937

Sinking behavior of gastropod larvae (Ilyanassa obsoleta) in turbulence

SUMMARY Oyster larvae ( Crassostrea virginica ) could enhance their settlement success by moving toward the seafloor in the strong turbulence associated with coastal habitats. We characterized the behavior of individual oyster larvae in grid-generated turbulence by measuring larval velocities and flow velocities simultaneously using infrared particle image velocimetry. We estimated larval behavioral velocities and propulsive forces as functions of the kinetic energy dissipation rate e, strain rate γ, vorticity ξ and acceleration α. In calm water most larvae had near-zero vertical velocities despite propelling themselves upward (swimming). In stronger turbulence all larvae used more propulsive force, but relative to the larval axis, larvae propelled themselves downward (diving) instead of upward more frequently and more forcefully. Vertical velocity magnitudes of both swimmers and divers increased with turbulence, but the swimming velocity leveled off as larvae were rotated away from their stable, velum-up orientation in strong turbulence. Diving speeds rose steadily with turbulence intensity to several times the terminal fall velocity in still water. Rapid dives may require a switch from ciliary swimming to another propulsive mode such as flapping the velum, which would become energetically efficient at the intermediate Reynolds numbers attained by larvae in strong turbulence. We expected larvae to respond to spatial or temporal velocity gradients, but although the diving frequency changed abruptly at a threshold acceleration, the variation in propulsive force and behavioral velocity was best explained by the dissipation rate. Downward propulsion could enhance oyster larval settlement by raising the probability of larval contact with oyster reef patches.

/pdf/active-downward-propulsion-by-oyster-larvae-in-turbulence-4avc1w2t8l.pdf

Active downward propulsion by oyster larvae in turbulence.

Intertidal gastropod larvae retract their vela and sink in strong turbulence, and this behavior potentially increases settlement in turbulent coastal habitats. We incorporated turbulence-induced sinking behavior of mud snail larvae (Ilyanassa obsoleta) in a vertical advection-diffusion model to characterize behavioral effects on larval supply and settlement in a tidal channel. Throughout flood and ebb tides, larvae that sink in turbulence have higher near-bed concentrations than passive larvae. This high supply of larvae enables behaving larvae to settle more successfully than passive larvae in strong currents characteristic of tidal inlets. Unlike passive larvae, those that sink in turbulence settle more successfully in stronger currents than in weaker ones and would concentrate their settlement in energetic tidal zones. Turbulence-mediated behavior may give intertidal larvae a greater ability to select habitats and may reduce larval mortality rates due to settlement failure.

https://aslopubs.onlinelibrary.wiley.com/doi/pdf/10.4319/lo.2007.52.3.1156

Effects of turbulence‐mediated larval behavior on larval supply and settlement in tidal currents

http://science.whoi.edu/labs/pinedalab/PDFdocs/Tapia,Pineda_et_al.PDF

Heidi L. Fuchs

Papers

Plankton community properties determined by nutrients and size-selective feeding

Sinking behavior of gastropod larvae (Ilyanassa obsoleta) in turbulence

Active downward propulsion by oyster larvae in turbulence.

Effects of turbulence‐mediated larval behavior on larval supply and settlement in tidal currents

High-frequency observations of wind-forced onshore transport at a coastal site in Baja California