Effects of temperature, salinity, and predators on mortality of and colonization by the invasive hydrozoan Moerisia lyonsi

Abstract

The successful invasion of non-indigeneous species depends on initial colonization as well as establishing a self-maintaining population. The invasive hydrozoan Moerisia lyonsi (Boulenger, 1908), possibly originating from low-salinity waters in the Black Sea and Middle East regions, has become established in low-salinity waters in several estuaries of North America, including Chesapeake Bay. The effects of temperature and salinity on mortality of M. lyonsi polyps were examined in the laboratory in February 2001 in the presence of abundant food. The polyps of M. lyonsi were directly transferred from 20°C and 10 salinity to one of 45 combinations of temperature (10–29°C) and salinity (1–40). Polyp mortality within 7 days occurred only in low-temperature treatments with salinities of 35–40. Surviving polyps reproduced asexually in salinities of 1–40 at 20–29°C, and in salinities of 1–25 at 15°C, but not in any salinities at 10°C. The greatest asexual reproduction rates, an index for population survival potential, occurred at salinities of 5–20. Survival and reproduction of M. lyonsi over such broad temperature and salinity ranges indicate that M. lyonsi may colonize and establish populations throughout the Chesapeake Bay; however, M. lyonsi medusae were reported only at salinities <9.3 there. This discrepancy may be due to the effects of predators. The scyphomedusan Chrysaora quinquecirrha (Desor, 1848), but not the ctenophore Mnemiopsis leidyi (A. Agassiz, 1865) consumed M. lyonsi medusae in laboratory experiments in August–September 2001. Populations of M. lyonsi do not appear to be limited by temperature and salinity conditions; however, their distribution in Chesapeake Bay may be restricted to low salinities not inhabited by predators.