MEPS 207:155-169 (2000)  -  doi:10.3354/meps207155

ABSTRACT: A series of field and laboratory experiments examined the factors that control fish-assemblage structure in barrier islands ponds on the Eastern Shore of Virginia. We investigated why surf-zone fishes, which are introduced to the island ponds during periodic wash-over events, are unable to persist for extended periods. We simulated over-wash events by collecting fishes from the shallow surf-zone and introducing them into 0.56 m² field enclosures. During summer months, surf-zone fishes typically died within 24 h. Levels of dissolved oxygen and temperature frequently exceeded the tolerance limits of the surf-zone fishes (demonstrated in a series of laboratory experiments), suggesting that these variables were responsible for fish mortality. In non-summer months, when dissolved oxygen and temperature stresses were ameliorated, surf-zone fishes could survive for months in the ponds. We conducted field-enclosure experiments at 3 fish densities in order to evaluate the survival and condition of a common surf-zone fish, Membras martinica (the rough silverside): (1) 8 M. martinica (14 fish m^-2), (2) 16 M. martinica (28 fish m^-2), and (3) 8 M. martinica + 8 Fundulus heteroclitus (28 fish m^-2). After approximately 1 mo during the spring, fall and winter, survival and condition of fishes in Treatments 2 and 3 were significantly reduced, suggesting that biological interactions were an important cause of surf-zone fish mortality. A temporal environmental stress gradient may result in seasonally varying importance of abiotic and biotic structuring factors.

KEY WORDS: Marsh pond · Fish · Competition · Seasonal · Dissolved oxygen · Community structure · Barrier Island · Virginia