Variations in structure of estuarine fish communities in relation to abundance of submersed vascular plants

Abstract

Fish communities and other ecological variables were sampled for 6 mo (May to October) in successive years (1979, 1980) at vegetated and non-vegetated areas in 2 distinctively different littoral zones (an open bay and a protected cove) of mid-salinity Chesapeake Bay, USA. Fish abundance, biomass and species richness were h~gher in vegetated areas at both sites, and were significantly correlated with macrophyte biomass Diel patterns of fish abundance varied, but highest catches generally occurred at dusk or at night. At one sampling site fish assemblages were dominated by smaller individuals in the vegetated area, suggesting an attraction of juveniles to macrophyte beds for food or refuge from predation. Larger piscivorous fish, which were also caught in greater numbers in vegetated areas, may have been attracted there by higher densities of forage fish. At the cove site the biomass of Paleomonetes sp. was comparable to that of the fish community towards the end of the plant growing season. Benthic infauna were also more abundant in vegetated areas at both sites, and stomach analyses indicated these organisms to be the dominant food resources for common fishes. Diets were generally non-selective in non-vegetated areas while highly selective for epiphytic fauna in macrophyte beds. Fish stomachs were also significantly fuller in vegetated areas, indicating generally greater feeding success. Fish production varied among major species but was higher overall at vegetated areas, following the seasonal patterns of primary production. Most of the differences in fish production between areas were attributable to higher instantaneous growth rates rather than higher biomass. It appears that the greater abundance and species richness of fish assemblages in vegetated areas of this region of Chesapeake Bay resulted from the attractiveness of these habitats as rich sources of preferred foods.

Why do juvenile fish utilise mangrove habitats?

“…In most fish species, like those in this study, there appears to be a strong association between small individuals and vegetated habitats with larger size classes moving to less vegetated habitats (Werner et al, 1983a;Mittelbach, 1984;Thayer et al, 1987;Lubbers et al, 1990;Laegdsgaard, 1996) with concomitant shifts in diet (Keast, 1978;Stoner, 1982;Lubbers et al, 1990;Laegdsgaard, 1996). For many fish species, increase in size confers an ability to feed on larger food items and a decreased vulnerability to predators (Vince et al, 1976;Mittelbach, 1981Mittelbach, , 1986Werner et al, 1983a,b;Jones, 1984;Power, 1984;Ebeling and Laur, 1985;Archambault and Feller, 1991).…”

“…four-times the number of juvenile fish when compared with either unfouled stakes or no structure. Many forms of vegetation allow for accumulation of small invertebrates (Stoner, 1982;Robertson, 1984;Lubbers et al, 1990;Schneider and Mann, 1991) that are an important food of many juvenile fish species. The epiphytic algae on mangrove pneumatophores accumulate an assemblage of Fig.…”

“…Many vegetated areas are a rich source of invertebrates (Harrington and Harrington, 1961;Stoner, 1982;Heck Jr. and Thoman, 1984;Orth et al, 1984;Bell and Westoby, 1986;Lubbers et al, 1990) that are suitable prey for small planktivorous fish. However, if the vegetation is too dense, fish may be hampered in their capture of prey, so that intermediate levels of structure of some seagrass and marsh plants effects the most profitable food returns (Vince et al, 1976;Crowder and Cooper, 1982;Stoner, 1982).…”

Effects of watershed and estuarine characteristics on the abundance of submerged aquatic vegetation in Chesapeake Bay subestuaries

“…SAV provides habitat for shellfish and fish, supplies food for waterfowl and marsh mammals, absorbs excess nutrients, and helps control shoreline erosion (Lubbers et al 1990). In the late 1960s and early 1970s, there was a dramatic Bay-wide decline in SAV abundance (Orth and Moore 1983) that was closely related to the deterioration of water quality (Kemp et al 2004).…”

Habitat requirements for submerged aquatic vegetation in Chesapeake Bay: Water quality, light regime, and physical-chemical factors

“…Losses of SAV beds are of particular concern because these plants create rich habitat and food for animals, supporting growth of diverse waterfowl, fish, and invertebrate populations (Lubbers et al 1990;Heck et al 1995). Seagrass and SAV communities also significantly modulate key biogeochemical (Caffrey and Kemp 1990), physical (Rybicki et al 1997;Koch and Gust 1999), and sedimentological (Fonseca et al 1982;Ward et al 1984) processes.…”