Live adult oysters and biofilms were separated experimentally as potential sources of waterborne chemical inducers of settlement in oyster larvae (Crassostrea virginica). Bacteria films growing on external shell surfaces were removed by mechanical agitation and chemical oxidation. This technique removed >99% of the viable bacteria without disrupting the normal production of metabolites by the oysters, measured as the weight-specific production of ammonium and dissolved organic carbon (DOC). In comparison to the external biofilms, microfloral abundances in oyster tissues and on internal shell surfaces were numerically insignificant ({le}0.1% of total). Biofilms growing on aged shell material without the living oyster served as a source of bacteria metabolites. Metabolites released in particle-free, artificial seawater (ASW) medium by biofilms and by adult oysters (lacking biofilms) were tested for effects on larval behavior, relative to ASW (control). The larvae were exposed to solutions in a Plexiglas[R] microcosm (30 ml capacity). Locomotory responses were video recorded under infrared illumination, then subjected to computer-video motion analysis. Oyster larvae responded similarly to waterborne substances released both from adult conspecifics and from biofilms. The responses included: larvae rapidly swimming vertically downward in the water column; their horizontal swimming speed then slowed while their rate of turning increased, which focused activity near the bottom; and finally, the larvae contacted the bottom and attached with their foot, indicating settlement. Further analysis demonstrates that the settlement-inducing compounds of each source have a molecular weight between 500 and 1000.

Planktonic oyster larvae (Crassostreu virginica) respond behaviorally to waterborne chemical cues and rapidly settle on substratum. "Settlement" is defined here as attachment of the larval foot to the substrate. Although a topic of considerable research for the past 50 yr, the identity of these cues remains unresolved. We provide four lines of experimental evidence all pointing to the singular identity of these substances. First, molecular-weight fractionations of seawater used to bathe adult oysters (with intact biofilms) were bioassayed, indicating the presence of waterborne settlement inducers between 500 and 1,000 Da. The inducers were degraded by proteases but not by carbohydrases or by lipase. Of several proteases we applied, only those cleaving basic amino acids (lysine and arginine) from the C-terminal and arginase (an enzyme condensing arginine at the C-terminal to ornithine) eliminated settlement-inducing activity. Second, trypsin hydrolysates of casein were significantly more effective in causing larval settlement than products of either acid or pronase hydrolysis of this protein. Third, a tri-peptide having arginine at the C-terminal, glycyl-glycyl+arginine (hereafter referred to as GGR), evoked settlement at a concentration as low as lo-lo M. Dose-response curves for GGR and for the active fraction (500-1,000 Da) of oyster bath water were essentially identical. Fourth, tests of 21 free amino acids identified only lysine and arginine as settlement cues. Larval settlers were far more sensitive to arginine than lysine but significantly less sensitive to arginine than to peptides with arginine at the C-terminal.Our combined results are all consistent in identifying low-molecular-weight peptides with arginine at the C-terminal as the natural, water-soluble cues inducing oyster settlement.

No abstract

Particulate matter concentration (PM, often referred to as total suspended solids [TSS]) is an important parameter in the evaluation of water quality. Several optical measurements used to provide an estimate of water turbidity have also been used to estimate PM, among them light transmission, backscattering, and side-scattering. Here we analyze such measurements performed by the Alliance for Coastal Technologies (ACT) at various coastal locations to establish whether a given optical method performs better than others for the estimation of PM. All the technologies were found to perform well, predicting PM within less than 55% relative difference for 95% of samples (n = 85, four locations). Backscattering performed best as a predictor of PM, predicting PM with less than 37% relative difference for 95% of samples. The correlation coefficient (R) was between 0.96 and 0.98 for all methods with PM data ranging between 1.2 to 82.4 g m -3. In addition, co-located measurements of backscattering and attenuation improves PM prediction and provides compositional information about the suspended particles; when their ratio is high, the bulk particulate matter is dominated by inorganic material while when low, dominated by organic material.

The development of phosphate sensors suitable for long-term in situ deployments in natural waters, is essential to improve our understanding of the distribution, fluxes, and biogeochemical role of this key nutrient in a changing ocean. Here, we describe the optimization of the molybdenum blue method for in situ work using a lab-on-chip (LOC) analyzer and evaluate its performance in the laboratory and at two contrasting field sites. The in situ performance of the LOC sensor is evaluated using hourly time-series data from a 56-day trial in Southampton Water (UK), as well as a month-long deployment in the subtropical oligotrophic waters of Kaneohe Bay (Hawaii, USA). In Kaneohe Bay, where phosphate concentrations were characteristic of the dry season (0.13 ± 0.03 µM, n = 704), the in situ sensor accuracy was 16 ± 12% and a potential diurnal cycle in phosphate concentrations was observed. In Southampton Water, the sensor data (1.02 ± 0.40 µM, n = 1,267) were accurate to ±0.10 µM relative to discrete reference samples. Hourly in situ monitoring revealed striking tidal and storm derived fluctuations in phosphate concentrations in Southampton Water that would not have been captured via discrete sampling. We show the impact of storms on phosphate concentrations in Southampton Water is modulated by the spring-neap tidal cycle and that the 10-fold decline in phosphate concentrations observed during the later stages of the deployment was consistent with the timing of a spring phytoplankton bloom in the English Channel. Under controlled laboratory conditions in a 250 L tank, the sensor demonstrated an accuracy and precision better than 10% irrespective of the salinity (0-30), turbidity (0-100 NTU), colored dissolved organic matter (CDOM) concentration (0-10 mg/L), and temperature Grand et al.In situ Lab-On-Chip Phosphate Sensor (5-20 • C) of the water (0.3-13 µM phosphate) being analyzed. This work demonstrates that the LOC technology is mature enough to quantify the influence of stochastic events on nutrient budgets and to elucidate the role of phosphate in regulating phytoplankton productivity and community composition in estuarine and coastal regimes.