Shallow water as a refuge habitat for fish and crustaceans in non- vegetated estuaries: an example from Chesapeake Bay

Abstract

In the Rhode River, in the absence of submerged aquatic vegetation (SAV), inter- and intraspecific size segregation occurred by depth from May-October. Small species (Palaemonetes pugio, Crangon septemspinosa, Fundulus heteroclitus, F. majalis, Rhithropanopeus harrisii, Apeltes quadracus, Gobiosoma bosci) were most abundant at depths <70cm. The proportion of small individuals decreased significantly with depth for seven of eight species, with C. septemspinosa the exception. These distributional patterns were related to depth-dependent predation risk. Large species (Callinectes sapidus, Leiostomus xanthurus and Micropogonias undulatus), predators of some of the small species, were often most abundant in deep water (>70cm). In field experiments, mortality of tethered P. pugio (30-35mm), small P. heteroclitus (40-50mm), and small C. sapidus (30-70mm) increased significantly with depth. Predation risk was apparently size-dependent, creating the observed intra-and interspecific size differences among depth zones. For C. septemspinosa, burial may modify this size-dependency and create the absence of intraspecific size increase with depth. Historically, P. pugio and Fundulus spp. were not restricted to shallow waters and were abundant in deeper SAV beds, which provided a structural refuge from predators. Since the recent demise of SAV in Chesapeake Bay, many small species have shifted their distributions and now utilize shallow water as an alternate refuge habitat. -from Authors