The biological and physical processes contributing to planktonic thin layer dynamics were examined in a multidisciplinary study conducted in East Sound, Washington, USA between June 10 and June 25, 1998. The temporal and spatial scales characteristic of thin layers were determined using a nested sampling strategy utilizing 4 major types of platforms: (1) an array of 3 moored acoustical instrument packages and 2 moored optical instrument packages that recorded distributions and intensities of thin layers; (2) additional stationary instrumentation deployed outside the array comprised of meteorological stations, wave-tide gauges, and thermistor chains; (3) a research vessel anchored 150 m outside the western edge of the array; (4) 2 mobile vessels performing basin-wide surveys to define the spatial extent of thin layers and the physical hydrography of the Sound. We observed numerous occurrences of thin layers that contained locally enhanced concentrations of material; many of the layers persisted for intervals of several hours to a few days. More than one persistent thin layer may be present at any one time, and these spatially distinct thin layers often contain distinct plankton assemblages. The results suggest that the species or populations comprising each distinct thin layer have responded to different sets of biological and/or physical processes. The existence and persistence of planktonic thin layers generates extensive biological heterogeneity in the water column and may be important in maintaining species diversity and overall community structure.

Although bioluminescence (BL) in the open ocean has been extensively studied, coastal BL remains poorly understood due, in large degree, to a lack of BL instrumentation appropriate to measure the fine-scale biological and physical complexity of the coastal regime. As a contribution toward understanding coastal BL, we developed the Multipurpose Bioluminescence Bathyphotometer (MBBP). This compact, self-contained bathyphotometer (BP) was designed to function in a variety of deployment modes, including conventional shipboard profilers, towed platforms, autonomous underwater vehicles (AUVs), and profiling moorings. In all configurations, the instrument preserves signal structure at centimeter to meter scale resolution, the scale at which higher-flow instruments might disturb thin layers and other fine-scale water column features. In the MBBP, seawater is conveyed with minimal premeasurement excitation into a light-baffled stimulation and measurement chamber at a continuously measured flow rate of 350 to 400 mL s -1. A photomultiplier tube (PMT) records light from bioluminescent organisms after they are mechanically stimulated at the chamber entrance by a high-velocity impeller. Calibration and test protocols were developed to determine BL stimulation efficiency and MBBP measurement characteristics. To illustrate the capabilities of the MBBP to resolve the fine-scale structure of the BL community, measurements from two coastal environments are presented.

Electrophysiological techniques have been applied to monitoring sensory discharges from the first antennae of calanoid copepods. Extracellular nerve impulse traffic from both mechanoreceptors and putative chemoreceptors has been recorded. The first antennae of some, but not all, calanoid groups possess "giant" mechano receptive axons generating very large (mV) extracellular signals. There are two such giant antennal mechano receptors (GAMs) innervating setae of each distal tip. These are sensitive to small (< 10 nm) controlled hydrodynamic disturbances, including abrupt displacements and sinusoidal vibrations with frequencies up to and exceeding 2 kHz. Behavioral studies show that escape "jumps"can be triggered in Labidocera madurae by the same types of disturbances. Sensitivities as low as 4 nm were observed at frequencies of ca. 900 Hz. Behavioral sensitivities are similar to those measured physiologically and suggest that firing of the GAMs is capable of triggering escape behavior, perhaps even with a single nerve impulse.

a b s t r a c tEcosystem function will in large part be determined by functional groups present in biological communities. The simplest distinction with respect to functional groups of an ecosystem is the differentiation between primary and secondary producers. A challenge thus far has been to examine these groups simultaneously with sufficient temporal and spatial resolution for observations to be relevant to the scales of change in coastal oceans. This study takes advantage of general differences in the bioluminescence flash kinetics between planktonic dinoflagellates and zooplankton to measure relative abundances of the two groups within the same-time space volume. This novel approach for distinguishing these general classifications using a single sensor is validated using fluorescence data and exclusion experiments. The approach is then applied to data collected from an autonomous underwater vehicle surveying 4500 km in Monterey Bay and San Luis Obispo Bay, CA during the summers of [2002][2003][2004]. The approach also reveals that identifying trophic interaction between the two planktonic communities may also be possible.

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