Foraging by Two Estuarine Fishes, Fundulus heteroclitus and Fundulus majalis, on Juvenile Asian Shore Crabs (Hemigrapsus sanguineus) in Western Long Island Sound Diane J. Brousseau & Anna E. Murphy & Nicole P. Enriquez & Kara Gibbons Received: 2 August 2007 / Revised: 2 October 2007 / Accepted: 2 October 2007 / Published online: 20 December 2007 # Coastal and Estuarine Research Federation 2007 Abstract The Asian shore crab, Hemigrapsus sanguineus, is a recent and particularly successful introduction to the east coast of the USA. Little research has been done on the utilization of Asian shore crabs for food by native species, a potential form of biocontrol. Over a 4-year period, we examined the gut contents of cogeners, Fundulus heteroclitus and Fundulus majalis, collected from two embayments in western Long Island Sound for the presence of juvenile H. sanguineus. Frequency (percent) of occurrence of food items in the guts of both species varied over year and study site. Asian shore crabs were consumed more often by F. heteroclitus than by F. majalis, but predation pressure by both species was low. Only 13% of F. heteroclitus and 7.7% of F. majalis found with food in their guts had ingested Asian shore crab remains. Of those, 1/3 had consumed whole crabs; the rest had only autotomized appendages in their guts. The mean carapace width of juvenile Asian shore crabs ingested by F. heteroclitus was 3.59±2.22 mm (N =33). Results of our study on killifish predation support the hypothesis that H. sanguienus abundance is partly explained by reduced impact of native predators (i.e., the “enemy release hypothesis”). Predation pressure of other potential enemies on both planktonic and benthic stages of the Asian shore crab must be investigated, however, to understand the full impact of predation on H. sanguineus population dynamics. Keywords Hemigrapsus sanguienus . Asian shore crab . Predation . Killifishes . Fundulus heteroclitus . Fundulus majalis Introduction Few marine invasions have been as successful as the introduction of the Asian shore crab, Hemigrapsus sanguineus, to the east coast of the USA. It was first observed in New Jersey in 1988 (Williams and McDermott 1990) and now ranges from Maine to North Carolina. In Long Island Sound, it has become the most abundant crab species of intertidal habitats where shelter from rock cover is available (Lohrer and Whitlatch 2002; Ahl and Moss 1999; Gerard et al. 1999). Most research to date has focused on the feeding ecology of this invader in attempts to determine potential impacts of this species on native biota (Gerard et al. 1999; Brousseau and Baglivo 2001, 2005; Lohrer and Whitlatch 2002; Boudreau and O’Connor 2003; Brousseau and Goldberg 2007). Little attention has been given to the utilization of Asian shore crabs for food by native species, a potential form of biocontrol. The common mummichog, Fundulus heteroclitus and its cogener Fundulus majalis, the striped killifish, occur in sheltered, coastal waters from Newfoundland to Florida and are among the most important fishes of east coast salt marshes (Able and Fahay 1998; Collette and Klein- MacPhee 2002). Fundulus heteroclitus is especially char- acteristic of upper regions of tidal marsh systems (Kneib 1986) whereas, F. majalis prefers higher salinity areas of estuaries and has been shown to frequent sandy beach habitats (Harvey 1998). Although both species are report- edly omnivorous, their diets differ because of different foraging locations. Fundulus heteroclitus frequently feeds on detritus, algae, and small crustaceans from marsh surfaces (Allen et al. 1994), whereas small clams and crustaceans living in sandy substrates often make up a large portion of the F. majalis diet (Steele et al. 1995; Harvey 1998). As these fish are active consumers of a wide variety Estuaries and Coasts: J CERF (2008) 31:144–151 DOI 10.1007/s12237-007-9006-7 D. J. Brousseau (*) : A. E. Murphy : N. P. Enriquez : K. Gibbons Biology Department, Fairfield University, Fairfield, CT 06824, USA e-mail: brousseau@mail.fairfield.edu