Seasonal refugia, shoreward thermal amplification, and metapopulation dynamics of the ctenophore Mnemiopsis leidyi in Narragansett Bay, Rhode Island

Abstract

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...

Invasive ctenophore Mnemiopsis leidyi in Norway

“…At comparable salinities, M. leidyi is in its native range encountered at temperatures ranging from 0 to .308C (reviewed in Haraldsson et al, 2013). In Narragansett Bay, live M. leidyi have even been observed under ice in below freezing temperatures (Costello et al, 2006). Winter minimum temperatures at the hydrographical stations along the Norwegian coast were consistently higher when deeper in the water column ( Figure 5), suggesting M. leidyi could also find refuge from cold temperatures by overwintering at depth.…”

“…Mnemiopsis leidyi exhibits pronounced source -sink dynamics with local extinctions at less favourable locations combined with repeated annual re-colonization from adjacent seed areas in both its native and introduced ranges (Purcell et al, 2001;Costello et al, 2006Costello et al, , 2012Bolte et al, 2013). During the non-reproductive period, advective losses can result in the disappearance of M. leidyi from large areas (Costello et al, 2006(Costello et al, , 2012.…”

“…During the non-reproductive period, advective losses can result in the disappearance of M. leidyi from large areas (Costello et al, 2006(Costello et al, , 2012. Successful overwintering takes place in regions with low water exchange, which allows the populations to persist over winter (Costello et al, 2006(Costello et al, , 2012.…”

“…Within its native range in Narragansett Bay, M. leidyi overwinter in shallow inshore retention areas (Costello et al, 2006;Beaulieu et al, 2013). Protected inner fjords or polls (offshoot of a fjord with a narrow entrance and a shallow sill) with limited water exchange could also provide a suitable habitat for the establishment of permanent populations in Norway.…”

Predator-induced vertical behavior of a ctenophore

“…Agassiz, 1865) persists in high numbers during the summer to winter, both in its native range along the American Atlantic coasts (Costello et al, 2006;2012) and in invaded habitats like the Black and Caspian Seas (Vinogradov et al, 2005), the North Sea (Riisgård et al, 2007), the Baltic Sea (Javidpour et al, 2009), and the Mediterranean Sea (Fuentes et al, 2010). The recent invasions of northern European waters have stimulated heightened interest in the role of M. leidyi as a competitor and predator of crustacean zooplankton, fish eggs, and larvae (e.g., Colin et al, 2010;Jaspers et al, 2011).…”