Benthic Invertebrate Responses to Size and Density Manipulations of the Common Mummichog, Fundulus Heteroclitus, in an Intertidal Salt Marsh

Abstract

Most studies of the effects of predation on the organization and structure of prey communities have ignored predator population size structure and density. In the present investigation, we designed a series of field experiments to test the effects of these predator population properties on the intertidal benthic invertebrates of a salt marsh. The common mummichog, Fudulus heteroclitus, was the primary predator in our experiments. Three size—classes of mummichogs (small, 40—50) mm Total Length [TL]: medium, 50—69 mm TL; large >70 mm TL) were maintained at each of three densities (1, 2 and 4 fish/m2) in 10—m2 enclosures on the salt marsh. Water—filled pits were included in each cage as low—tide refuges for the fish. Each fish treatment combination was replicated three times. In addition, there were three uncaged 10—m2 plots (open controls) and three caged plots from which Fundulus were excluded (closed controls). Three cylindrical core samples (0.005 m2) were extracted from the sediment to a depth of 10 cm in each of the 33 experimental plots 1, 4, and 10 mo after initiation of the experiment in June 1978. Densities of the small, surface—dwelling invertebrates which make up most of the benthic community (Manayunkia aestuarina, Streblospio benedicti, Leptochelia rapax, ostracods, hydrobiid snails, and Gemma gemma) were highest in enclosures containing large fish, and lowest in closed controls and in enclosures containing small fish. Intermediate invertebrate densities occurred in enclosures containing medium—sized mumichogs. The effects of fish size were enhanced at high fish densities (2—4 fish/m2), although fish density alone had little effect on invertebrate abundance. We considered several hypotheses that could explain the findings. Small epibenthic predators—disturbers like the grass shrimp, Palemonetes pugio, were commonly observed in the experimental enclosures. The gut contents of fish taken from enclosures indicated that the shrimp were ingested only by medium and large size—classes of F. heteroclitus. We suggest that infaunal densities increased in response to the control of small epibenthic predator—disturbers (i.e., P. pugio) by the larger F. heteroclitus.

Can Thin-lipped Mullet Directly Exploit the Primary and Detritic Production of European Macrotidal Salt Marshes?

“…Despite very short submersion periods, mullets filter and ingest large quantities of sediment, and concentrate and assimilate organic matter produced by these coastal wetlands, which therefore act as important feeding areas for these species and other exploiting fish species (Laffaille et al, 2001). Although organic matter exportation from salt marshes to sea water by physical vectors such as tidal currents can be significant (Teal, 1962;Nixon, 1980;Gordon & Cranford, 1994), export of organic matter from salt marshes is facilitated by trophic migration of aquatic fauna (Kneib & Stiven, 1982;Kneib, 1987;Lefeuvre et al, 1999) Only a few fish species are able to assimilate salt marsh primary production directly; which is the case for the clupeid Brevoortia patronus in the United States (Deegan et al, 1990) and Liza spp. in Europe.…”

Guild structure and foraging impact of blue crabs and epibenthic fish in a sub-estuary of Chesapeake Bay

“…In soft-bottom ecosystems like the Rhode River subestuary, predator-prey interactions are particularly complex (sensu Carpenter & Kitchell 1988) because these communities are dominated by guilds of rather generalized predators capable of switching among diverse prey, and because they usually lack a single competitively dominant prey species capable of monopolizing resources (Reise 1978, Virnstein 1980, Kneib & Stiven 1982, Ambrose 1984, Commito & Ambrose 1985 . That is, while predation is often the prevailing control of community structure, a single keystone-like species occurs rarely if at all (Peterson 1979, Levinton 1982.…”

Importance of predatory infauna in marine soft-sediment communities

“…It is becoming apparent that complex trophic interactions occur in infaunal communities (e.g. Commito 1982, Kneib & Stiven 1982, Ambrose 1984b, Commito & Shrader 1985. However, untd it is demonstrated that epibenthic predators take infaunal predators preferentially and that infaunal predators significantly affect nonpredatory infauna, a 2-level model of epibenthic predators and infauna should have primacy as the best general description of marine soft-sediment communities.…”