Deep-sea species diversity: Does it have a characteristic scale?

Dispersion patterns and species diversities of deep-sea macrobenthos were examined for evidence that diversity-controlling processes operate predominantly on any one of several spatial scales. Identification of such scales, if any, would aid in the identification of the diversity-regulating processes themselves. The specific hypothesis that species diversity is independent of scale and location within the deep sea was tested with replicated..

Developing Tools to Evaluate Spawning & Fertilization Dynamics of the Giant Sea Scallop — Phase II: Field Trials in Experimental Populations

Objective 1 — Sperm advection-diffusion model: Develop a two-dimensional spatial model to predict the concentration o f sperm and effective range of fertilization in a sperm plume at varying distances from a source population of spawning males under scenarios of synchronous and asynchronous spawning. Objective 2 — Fertilization assays in field populations: Conduct a time series of fertilization assays over experimental populations of scallops to (a) further develop the methodology to assess ambient sperm loads in scallop populations over the course of the spawning season, (b) compare model predictions about spatial patterns of sperm concentration and fertilization generated in Objective 1 to field observations on experimental populations, (c) determine the influence of differences in the sperm plume arising from two experimental populations spanning a ten-fold difference in male density, and (d) conduct laboratory flume experiments to evaluate potential biases introduced by Nitex egg baskets to estimates of absolute and relative rates of fertilization

Effects of bivalve siphonal currents on the settlement of inert particles and larvae

Dye studies in a flume revealed that the strong exhalent siphonal current of an individual cockle, Clinocardium nuttallii, behaved much like a cylinder held in the flow, shedding vortices downstream. The inhalent flow was much slower and more diffuse, its effects being limited to the lowermost few centimeters above the bottom. Flume experiments with inert particles having settling velocities similar to those of polychaete larvae revealed that the vortex shedding from the excurrent jet led to variability in deposition of the particles a few centimeters downstream of the jet, and that neither the jet nor the incurrent flow substantially changed the mean number of particles depositing per unit area of bed. Field observations within a few days after settlement of Hobsonia florida, an ampharetid polychaete, using ecologically similar but nonplanktonically recruiting oligochaetes as an internal control, showed similarly enhanced variability in recruitment within a few centimeters of the siphon of resident Mya arenaria (soft-shelled clam). We could find no evidence that isolated clams impede settlement in their immediate surroundings and found, instead, some indication of local settlement being enhanced by the flow convergence toward the incurrent siphon. We thus suggest that any negative influence of suspension-feeding bivalves upon settlement is a larger-scale phenomenon caused by depletion of recruits through the integrated filtering activities of individuals upstream of the settlement site. Hence manipulation of bivalve density in small plots may not be very informative regarding influences upon larval settlement

Hadal community structure: Implications from the Aleutian Trench

A 0.25-m2 box core from the Aleutian Trench (50°58.0\u27N, 171°37.5\u27W) was used to generate hypotheses concerning the regulation of benthic community structure in oceanic trenches. High food supply and the concentrating effects of trench topography are suggested by the unexpectedly high standing crop (1272 individuals of macrofaunal taxa m2) and by the feeding modes of the captured polychaetes...

CMG Collaborative Research: Interactions of Phytoplankton with Dissipative Vortices

The aim of this project is to develop coordinated laboratory experiments and computational models to address a fundamental question in oceanography concerning magnitudes and mechanisms of turbulence effects on phytoplankton and other particles at the spatial scale of individual organisms. The importance of external energy in the form of turbulence in determining relative success of different kinds of phytoplankton dates to the seminal analysis of Munk and Riley (1952) and Margalef (1978). Margalef\u27s mandala asserts that high nutrient concentrations and turbulence intensities favor dominance by diatoms, whereas low values favor non-red-tide dinoflagellates. Subsequent work has revealed a wide spectrum of turbulence effects among species of dinoflagellates, including growth stimulation. The physicochemical mechanisms that govern these effects largely remain to be determined, however.Through iteration between innovative numerical models and experiments, the investigators will close a growing gap between textbook understanding of turbulent flows and understanding of consequences for suspended organisms and particles. Models and experiments have used one-dimensional shear to assess turbulence effects at the level of single cells and chains. Effects of fluid straining on concentration fields and cell rotation have been predicted, and effects on cell growth and motion, documented. Current understanding of turbulence, however, places greater emphasis on vorticity, gradients in vorticity and vortices at dissipation scales experienced by individual phytoplankton cells. We propose to develop a framework for both numerical and analog evaluation of effects that cells experience from being in and near viscous-scale vortices, that capture effects of vorticity as well as fluid deformation, evolution of concentration fields, and fluid-structure interactions. Roles of vorticity and gradients in vorticity in determining cell motions and thereby shaping concentration fields have been underappreciated, partly because a signature feature of turbulence, i.e., vortex stretching, is impossible in the two-dimensional flows that so far have been used as theoretical models and the primary basis of analog devices.Numerical approaches will use two simplified models of small-scale vortex structure and evolution, the Burgers vortex and the Lundgren stretched-spiral vortex, giving particular attention to diffusion of vorticity within and away from both. Both decaying and equilibrium vortices will be explored. Models of cells and chains of cells will be based on shapes and flexural stiffnesses of actual cells and chains. Each will be placed successively at a range of positions within and near a vortex and will be fully coupled mechanically to the fluid. Behaviors of interest are cell and chain translation, rotation and deformation and their feedbacks to local velocity and vorticity fields that could be used by grazers to locate a cell. Also to be modeled is the diffusion of scalars (nutrients with cell as sink or metabolites with cell as source), allowing calculation of diffusive fluxes for nutrient acquisition and prediction of chemical fields used by grazers. The investigators will further take advantage of their existing models of flow around flagella to include motile dinoflagellates in the modeling and measurement scheme.Analog experiments will exploit the fact that flows near Kolmogorov scale are dominated by viscosity, just as in earlier Couette experiments, but will incorporate realistic, 3D time variation. Borrowing from a burgeoning variety of geometries used in microfluidics, the investigators will construct a variety of small devices that utilize shed vortex streets, mild jets and cavity flows to match deformation rates, vorticities and gradients in them that produce interesting effects on phytoplankton in their numerical models of vortices. These analogs will be used to test the model predictions and to pose new questions of the models.Broader impacts: Results for phytoplankton extend easily to other important phenomena such as diffusion of attractants from eggs spawned in a turbulent environment (e.g., by abalone and other benthic invertebrates) and corresponding sperm swimming capabilities. They have implications for other important encounter processes such as particle coagulation and sedimentation, hydrosol filtration, and predator-prey interactions. This new approach provides both a natural bridge from larger-scale, direct numerical simulation (DNS) models of turbulence to these individual-scale effects of turbulence and a logical path to parameterizing these effects in larger-scale fluid dynamic models.Turbulence intensity is one of the parameters most likely to be influenced by climate change, and the investigators will work closely with the Center for Ocean Sciences Education Excellence Ocean Systems (COSEE-OS) that has chosen oceans under climate change as its major focus. They will also build on their history of providing teaching and outreach materials in biomechanics at low Reynolds numbers for graduate students, undergraduates and high-school teachers. They will complement both of these efforts with professionally produced, evocative visual animations of the important phenomena that they identify for incorporation into the COSEE-OS website

New resource axes for deposit feeders?

Recent work on selectivity in deposit feeders has focused on the importance of particle size. In field experiments with exotic sediments of known characteristics (glass beads), we demonstrate that selective ingestion in a multitentaculate, surface deposit feeding ampharetid polychaete depends upon particle specific gravities and surface textures. The degree of selectivity for specific gravity is shown to be dependent upon worm size...

Cross-phyletic patterns of particle selection by deposit feeders

In controlled laboratory experiments using a wide array of exotic sediments of known characteristics (glass and plastic beads) we studied the mechanical, evolutionarily-fixed component of particle selection for ingestion in 5 surface and 6 subsurface deposit feeders, from 3 phyla (Annelida, Mollusca and Arthropoda). Three species were nonselective within all or part of the 3-324 μm particle size range tested, while the remaining 8 species exhibited unimodal patterns of size selection, peaking near 6 μm. In addition, the surface deposit feeders displayed a strong preference for particles of low specific gravity. Particle selection in tube construction by the polychaetes followed similar but weaker trends. Initial particle gathering into the mantle cavities of the bivalves by inertial suction or adhesion to mucus-covered appendages appeared nonselective

Hands-on Oceanography. Settling of Particles in Aquatic Environments Low Reynolds Numbers

The purpose of this activity is to familiarize students with how a particle’s size, shape and orientation affects its settling at low Reynolds numbers. This activity can also be used to teach statistical skills (e.g., replication of measurements, propagation of error, type I vs. type II regressions)

Adhesive-based selection by a tentacle-feeding polychaete for particle size, shape and bacterial coating in silt and sand

We tested particle selection by a surface deposit-feeding, tentaculate spionid polychaete, Pseudopolydora kempi japonica Imajima and Hartman. In experiments with peroxide-cleaned, sizegraded but otherwise natural silts and sands, individual worms showed peak preference for particles 80-99 μm in diameter, compared with previous (Self and Jumars, 1988) documentation of peak preference for particles of 7 μm in experiments conducted with plastic and glass beads. These results imply that microtektites will not in general be good tracers of mixing of mineral grains of comparable size. Animals exhibited statistically significant but not marked differences in size selectivity for subrounded versus subangular grain shapes; the size preference peak was broader in subangular grains, for which orientation of the grain can alter probabilities of both contact and retention. When one size class of grains was coated with the bacterium Halomonas halodurans (ATCC 29686), animals in general showed enhanced selection (relative to controls with no food value on any size class) of that size and smaller grains, even though these smaller grains lacked food value. Greatest selection, however, generally occurred for the coated size class. Results from inclusion of glass beads in some of the experiments and from separate experiments with tentacle analogs imply that this selective capability may be largely passive and mechanical. Natural grains, due to surface texture, have more surface area for adhesive contact than do smooth glass beads so that larger grains than beads are retained. Bacteria-coated grains, in turn, appear to be picked up preferentially due to adhesion with the bacterial coating; petroleum jelly-coated microscope slides also succeed in selective retention of the size class that is bacterially coated. Substantial selection by adhesive-utilizing deposit feeders apparently can be achieved without investment in complex, time- and energy-consuming sensory systems and behaviors. Experiments with natural grains showed notably more scatter than prior experiments with glass beads, but this difference is consistent with the mechanism. For nonspherical particles, both contact and retention depend on orientation as well as size

Sediment destabilization by animal tubes

Laboratory flume ex periments we re conducted in order to test the influence on sediment e rodibility of varying densities of the tube-building polychaete worm Owenia fusiformis. Experiments were performed on isolated individuals, in order to measure approximate spatial limits of isolated tube effects, and on arrays of individuals at densities reported previously to be associated with stable beds...