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...
The feeding behavior and diet in nature are described for two species of chaetognaths in an open ocean community. Sagitta elegans lives and feeds primarily in the upper water column (0–25 m) and the vertical distribution of this species may be explained primarily by its requirement of high prey densities. Eukrohnia hamata apparently needs less food and is found mainly below the mixed layer with a vertical distribution restricted by temperature. The same prey species, those with the highest densities at Station “P,” make up the diet of both chaetognaths, although Eukrohnia eats significantly more small prey. The major prey of juvenile chaetognaths (numerical frequency) are small cyclopoid copepods, a group frequently overlooked in plankton surveys. These species also comprise 41% of the diet of older chaetognaths, which prey in addition on stage V copepodites of the largest copepods. It is suggested that the development of larval chaetognaths depends on abundant, small prey but that older chaetognaths can handle prey of a very wide spectrum of sizes.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.