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We demonstrate the presence of significant differentiation in development rate, adult body length, and stomatic growth rate in the estuarine harpacticoid copepod Scottolana canadensis (Willey) collected from a broad range of latitudes (27°—43° N) and reared in the laboratory for several generations under the same conditions (15 g salts per 1000 g seawater, and 15°, 20°, 25°, or 28°C). The changing pattern of differential growth with increased temperature suggests local adaptation to maximize scope for growth under prevailing temperatures conditions; northern—derived individuals grew faster at low but not at high temperatures.

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Aureococcus anophagefferens is a picoplankionic alga that since 1985 has bloomed in coastal embayments of the western mid‐Atlantic, ranging from Narragansett Bay, Rhode Island, to Barnegat Bay, New Jersey, with greatest incidence of recurrence in Long Island bays, New York. Blooms of this small alga, referred to as “brown tide,” can persist for several months during late spring and summer at densities in excess of 1.0×106 cells ml−1. They are not associated with anomalous chlorophyll a, dissolved oxygen, or inorganic macronutrient (N, P) levels. Meterologically induced reduced flushing rates, elevated salinities, and delivery of micronutrients (e.g. iron) from the watershed have been implicated in bloom initiation. Brown tides have had severe detrimental effects on the benthos, especially eelgrass (Zostera marina) and suspension‐feeding bivalves, including bay scallops (Argopecten irradians) and blue mussels (Mytilus edulis). Adult bivalves experience sublethal effects (e.g. inhibition of clearance rates) at Aureococcus concentrations as low as ∼2×105 cells ml−1 and mortalities at ∼106 cells ml−1, attributed to toxicity of this microalga. Impacts of brown tide on zooplankton are less clear, but reduced egg production rates of copepods and reduced population growth rates of ciliates are documented at higher brown tide concentrations (≥1.0×106 cells ml−1). We summarize the state of knowledge about the physical, chemical, and biological factors that may contribute to brown tide initiation, maintenance, and decline and assess its ecological effects.

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We studied the effects of attached peritrich ciliates on the fitness of natural populations of Acartia hudsonica (Pinhey) in Stony Brook Harbor, Long Island Sound. Ciliate infection occurred during late spring, and ciliate load (No. ind.-') was not related to copepod age, stage, or body size. Simulated in situ experiments conducted throughout the period of abundance of A. hudsonica showed that egg production rate (No. d-l) was positively correlated to ambient water temperature, but negatively correlated to ciliate load. Salinity and the concentration of total or >8-10 pm Chl a were not significant in explaining the variation in egg production rate. Egg hatching success (O/o) was not influenced by the infection status (presence or absence) of the female. Infected nauplii had lower survival rates (d-l) compared to uninfected nauplii, but their developmental rates (molts d -I) were not significantly different. Significantly slower average sinking rates were found for infected adults compared to uninfected adults. Slower sinking rates for infected copepods may have been due to an increase in surface area which increased drag. Infected adults with slower sinking rates may be more susceptible to predation. Our findings show that peritrich ciliates can play a role in the seasonal decline and future recruitment of A. hudsonica.

Three experiments were carried out in 300 l mesocosms using natural seawater from the Peconic Bays ecosystem, Long Island, New York, to examine the ability of the northern quahog Mercenaria mercenaria to prevent blooms of the brown tide alga Aureococcus anophagefferens. Nutrient enrichment and mixing of the mesocosms was conducted according to previous methods that we have employed to induce brown tides. Treatments with and without clams were examined. Abundances of A. anophagefferens increased dramatically during 8 to 9 d experiments in mesocosms without bivalves (average peak abundances > 600 000 cells ml -1). The brown tide alga constituted > 50% of the total phytoplankton biomass in these mesocosms by the end of the experiment. In contrast, algae in mesocosms with high abundances of clams did not develop brown tides and A. anophagefferens abundances in these mesocosms were 2 orders of magnitude lower. Bivalves not only prevented a buildup of total phytoplankton biomass but also prevented the shift in phytoplankton species composition to dominance by A. anophagefferens observed in treatments without clams. Experiments to test the efficacy of different abundances of clams for preventing blooms of A. anophagefferens demonstrated that population clearance rates by clams of approximately 40% of the mesocosm volume d -1 were sufficient to prevent the buildup of phytoplankton biomass and net population growth of the brown tide alga under the environmental conditions and nutrient enrichment that we employed. This turnover rate by suspension-feeding bivalves is similar to the same magnitude of bivalve filtration pressure estimated for Great South Bay, Long Island more than 2 decades ago, prior to the outbreak of brown tides. We conclude that the feeding activities of northern quahogs in shallow bays can exert considerable control on total phytoplankton biomass in the overlying water column, and specifically on the ability of A. anophagefferens to dominate the phytoplankton assemblage and form brown tides.

The identification and enumeration of microorganismal species in natural aquatic assemblages is an essential prerequisite for ecological studies of these populations. The ability to distinguish between closely related taxa is especially critical when these species pose health and environmental risks. Traditionally, protistan species (microalgae and protozoa) have been identified morphologically and enumerated by using light or electron microscopy. Light microscopy (bright field, phase, and differential interference contrast) has been used to identify many protists that possess distinct morphological features, whereas electron microscopy has been used effectively for many small algae and protozoa (e.g., cell sizes of Յ10 m). Protists typically have been counted by epifluorescence microscopy (25) or by using settling techniques and inverted light microscopy (30).Unfortunately, these approaches have significant disadvantages for ecological studies in which it is necessary to identify and count small protists in large numbers of samples in a timely manner. Morphological features that are relevant for species identification are not always easy to discern by methods that are most commonly used for enumeration. For example, transmitted and epifluorescence microscopy do not allow visualization of morphological features that are pertinent for species identifications of many small protists (e.g., striations on frustules of diatoms or body scales on chrysomonads that can be observed only by electron microscopy). In addition, microscopic analyses generally are time-consuming, and the processing of large numbers of samples that are typical in ecological surveys and experiments may require weeks or months to complete. In order to circumvent these shortcomings, new approaches based in modern immunology and genetics have emerged that are able to provide rapid and accurate identification and enumeration of microbial species.Immunological approaches for identifying and enumerating marine microalgae have become commonplace within the last two decades. These methods and their ecological applications for the identification of phytoplankton have been summarized (19,31). Both polyclonal antibodies (PAbs) and monoclonal antibodies (MAbs) have been developed for use by microbial ecologists. Immunological probes have proven useful for identifying species of cyanobacteria (10), raphidophytes (29), dinoflagellates (22), pelagophytes (3, 21), and other minute algal taxa (11,24) and even for distinguishing between toxic and nontoxic strains of harmful algae (6). An added advantage of this approach is that these methods often can be converted to formats that are significantly more rapid than routine microscopical counts (32).Aureococcus anophagefferens is a pelagophyte alga that typifies the difficulties of accurately identifying and enumerating small protistan species in natural water samples. The alga is minute (ϳ2 to 4 m in diameter) and spherical, lacks flagella and body scales, and has few other features that might easily distinguish it ...