The lobate ctenophore Mnemiopsis leidyi occurs throughout Narragansett Bay, Rhode Island, during warm summer months but is often undetectable in the central portion of the bay during winter months. During 2 yr of weekly sampling, we found that M. leidyi populations in a shallow embayment, Greenwich Cove, either overwintered or were only briefly absent during winter. The Greenwich Cove population reproduced weeks earlier and reached higher average and peak population concentrations than open-bay populations. Shallow embayment populations such as that in Greenwich Cove probably serve as source populations that inoculate the main region of the bay by advective transport in the spring months. We propose that earlier occurrences of M. leidyi during recent years are due to amplification of pulsed spring warming events that permit early reproduction in the shallow embayments that serve as source regions for M. leidyi in Narragansett Bay. We further suggest that the source-sink perspective we describe is relevant not only to Narragansett Bay but other temperate regions of the world persistently occupied by M. leidyi.The importance of Mnemiopsis leidyi as a planktonic predator has been documented by a large body of research on its feeding capabilities (Kremer 1975;Reeve et al. 1978;Waggett and Costello 1999) and trophic impacts (Kremer 1979;Shiganova et al. 2001;Sullivan et al. 2001). These predatory capabilities underlie the importance of recent range expansion patterns for M. leidyi. Invasion of regions outside its historical distributions have resulted in dramatic planktonic community alterations in regions such as the Black Sea (Shiganova et al. 2003) and Sea of Azov (Studenikina et al. 1991). Although perhaps less acclaimed than these spatial range expansions, records of temporal range expansion within its endemic range can also cause important changes in planktonic community dynamics (Sullivan et al. unpubl. data). For example, within Narragansett Bay, peak occurrence of M. leidyi has shifted approximately 2 months earlier than the historic mean (Sullivan et al. 2001). However, the historically dominant summer copepod, Acartia tonsa, has not experienced a similar phenological shift, with the result that the seasonal timing of predator (M. leidyi) and prey (A. tonsa) overlap differently than during the past. One result of this change is that A. tonsa has been almost eliminated from the plankton during recent summers in Narragansett Bay as a result of predation pressure from M. leidyi (Sullivan et al. unpubl. data). The long-term trophic consequences of near removal of copepods from Narragansett Bay during summer months, historically a period of high copepod abundance, are not yet clear. However, there is evidence of reduction in numbers of some species of larval fish in recent years (Keller et al. 1999) and increases in summer values of chlorophyll a (Chl a) (Sullivan et al. unpubl. data).Despite the potentially important consequences of phenological shifts by M. leidyi, the mechanisms underlying M. leidyi...

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Grazing by the overbite clam Corbula amurensis (formerly known as Potamocorbula) may be the cause of substantial declines in phytoplankton biomass and zooplankton in the San Francisco Estuary (SFE) following its introduction in 1986. While grazing rates have been examined on bacteria, phytoplankton, and copepod nauplii, the consumption of protistan microzooplankton by C. amurensis has not previously been measured. In this study, laboratory feeding experiments revealed that C. amurensis cleared 0.5 l ind-1 h-1 of microzooplankton (ciliates) and 0.2 l ind-1 h-1 of chlorophyll (chl) a. Despite the higher clearance rate on microzooplankton, clams obtained more of their carbon from phytoplankton, which dominated the prey assemblage on most dates. When the measured clearance rates are extrapolated to field populations of clams, fractional loss rates (50 to 90% d-1) exceed the population growth capacity of microzooplankton. Although microzooplankton may not be a major component of the diet of these clams, C. amurensis may further alter food web dynamics through consumption of this important trophic intermediary, thus disrupting this link from bacteria and phytoplankton to higher trophic levels.

In most aquatic ecosystems, copepod nauplii outnumber all other mesozooplankton. Although thousands of studies have examined feeding by later life history stages, the feeding habits of nauplii are poorly known. We offered conspecific adult and naupliar stages of the current-feeding calanoid copepod Pseudodiaptomus marinus and the ambush-feeding cyclopoid copepod Oithona davisae 14 species of phytoplankton from various functional and taxonomic groups that spanned a wide size range. Using a novel epifluorescence microscopy method, we calculated an index of gut pigment for copepods fed each phytoplankton species. We also measured adult and naupliar feeding rates on three species of phytoplankton: the cryptomonad Rhodomonas salina, the prasinophyte Tetraselmis suecica, and the diatom Thalassiosira pseudonana, by an improved gut fluorescence method using a microplate reader. Despite their smaller size, weaker swimming and sensory capabilities, and rudimentary feeding apparatus, nauplii fed on a large range of cell sizes and were capable of consuming many of the same phytoplankton as adults.

There is a need for more information on the relationship between diseases and fluctuations of wild populations of marine animals. In the case of Callinectes sapidus reovirus 1 (CsRV1, also known as RLV), there is a lack of baseline information on range, prevalence and outbreaks, from which to develop an understanding of population‐level impacts. An RT‐qPCR assay was developed that is capable of detecting 10 copies of the CsRV1 genome. In collaboration with state, federal and academic partners, blue crabs were collected from sites throughout the north‐eastern United States to assess the northern range of this pathogen. In addition, archived crab samples from the Chesapeake Bay were assessed for CsRV1 by RT‐qPCR and histology. PCR‐based assessments indicate that CsRV1 was present at all but one site. Prevalence of CsRV1 as assessed by RT‐qPCR was highly variable between locations, and CsRV1 prevalence varied between years at a given location. Mean CsRV1 prevalence as assessed by RT‐qPCR was >15% each year, and peak prevalence was 79%. The wide geographic range and highly variable prevalence of CsRV1 indicate that more study is needed to understand CsRV1 dynamics and the role the virus plays in blue crab natural mortality.