The distribution and apparent habitat preferences of the common mummichog (Fundulus heteroclitus) in southwestern Spain were examined during summer-fall 1996.This introduced species was more or less continuously distributed along the Atlantic coast of Spain, being more abundant in sites near the coastline (usually < 10 km inland), mainly in four extensive marshes. The species preferred marsh-related mesohabitats, such as salt lagoons, salt marsh fish ponds and marsh channels, both natural and manmodified. F. heteroclitus was mostly found at salinities > 25. It was the most frequently captured fish species, occurring at 81 of the 272 sites sampled; their frequency of occurrence was almost twice that of the second ranked species (Gambusia holbrooki).However in over 80 % of cases, F. heteroclitus was found alone or with only one sympatric fish species, which usually belonged to a group composed of Gobius niger, mugilids, Anguilla anguilla, Blennius sp., Lebias ibera, Pomatoschistus sp. and Dicentrarchus labrax. Finally, we discuss the origin and dispersal of mummichog in the Iberian peninsula and the potential effects of this species on native fish populations.
IntroductionThe mummichog, Fundulus heteroclitus, is an exceptionally wide ranging cyprinodontid fish. It naturally occurs along the east coast of North America from south-western Newfoundland to northeastern Florida. This species is ubiquitous in North American East Coast salt marshes, being mostly found in sheltered coastal waters. Although occasionally it inhabits freshwater habitats, the species is best known from the tidal salt marsh, a fluctuating physical environment for which mummichogs are well adapted due to considerable plasticity in their ecological requirements (Kneib, 1986).The first records of F. heteroclitus in the Iberian Peninsula are dated between 1973-1976(Hernando, 1975Coelho et al., 1976). However, the precise date and location of the species' introduction still remains unclear. Although there have been studies describing its life-history pattern (Arias & Drake, 1986;Drake et al., 1987;Fernández-Delgado, 1989) and density , 1989 little is known about the role of F. heteroclitus in this new European habitat. The introduction of exotic species can have a negative effect on the functioning of native ecosystems (Dowling & Childs, 1992;Barlow et al., 1987;Richardson & Whoriskey, 1992). It is suspected that mummichogs may have already negatively affected some native endemic species like the endangered Lebias ibera.This study describes the detailed distribution and abundance of F. heteroclitus along the coast of southwestern Spain. Also we document their habitat preferences, including the composition of the fish assemblages found in those habitats. Finally, we discuss the potential causes of the observed pattern of mummichog distribution and the effects of this species on native fish populations.
Methods
Study areaThis study was carried out in an area near the coast in the provinces of Huelva, Sevilla and Cádiz (southwestern Spain) (Figure1)....