The significance of large motile predators in controlling the distribution and abundance of the macrobenthic invertebrates within the sediments (the infauna) in a shallow subtidal sand community was tested using manipulative field experiments. The blue crab (Callinectes sapidus) and 2 species of bottom—feeding fishes, spot (Leiostomus xanthurus) and hogchoker (Trinectes maculatus), were either excluded from or confined to small areas using wire mesh cages. Callinectes and Leiostomus effectively reduced infaunal desnities; Trinectes did not. The infauna responded to decreased predation with a large increase in density and diversity within 2 mo. The large population increases were exhibited by opportunistic species, which are considered to be most subject to predaton. Species whos populations where least affected by predation were those species which live deep in or quickly retract into the sediment. These species thus avoid predation and were generally the dominat species in the natural community. For species whose density increased greatly in exclosures, recruitment was by planktonic larvae and growth was very rapid, individuals grwoing to maturity in only a few months. Densities of all infaunal species increased in exclosures, suggesting that their population densities under natural conditions are not controlled by competitive interactions. In community, infaunal population sizes are limited by predation and not by food or space. Severe predation pressure and physical disturbances, particulary sediment instability, keep population levels far below the carrying capacity of the environment. Severe predation, and the rapid growth, short generation times, and rapid turnover rates of constituent populations suggest that such infaunal communities, despite a low standing crop, are an important food source for predator species important to man.

No abstract

Salt marshes of the Indian River Lagoon, Florida (USA) were once p.'olif]c producers of mosquitoes. Mosquitoes lay their eggs on the infrequently-flooded high marsh surface when the soil surface is exposed. The eggs hatch when the high marsh is flooded by the inflequent high tides or summer rains. To control mosquito production, most of the salt marshes (over 16,200 ha) were impounded by the early 1970s. Flooding, usually by pumping water from the Lagoon, effectively controlled mosquitoes.However, impounding had a profoundly negative impact on the wetland plant, fish, and invertebrate communities. Isolation fiom the Lagoon cut off aquatic access by transient estuarine species that used the wetlands for feeding or as nursery area. In one study, the number of fish species dropped fl'om 16 to 5 alter impounding Wetland vegetation within some impoundments was totally eliminated: other impoundments developed into freshwater systems.When tidal exchange is restored through hydrologic connection, usually by culverts installed through the perimeter dike, recovery to more natural conditions is often rapid. In one impoundment where wetland vegetation was totally eliminated, recovery of salt-tolerant plants began ahnost immediately. In another, cover of salt-tolerant plants increased 1,056% in less than 3 years. Fisheries species that benefitted the most were snook, ladyfish, and striped intlllet. Over 1,500 juvenile snook were captured in a single 3-hr flood-tide culvert trap as they attempted to migrate into an impoundment. The zooplankton community rapidly returned to the more typical marsh-Lagoon community. Water quality and sediment sulfides returned to typical marsh values. Overall, reconnection enhances natural productivity and diversity, although water quality in the perimeter ditch, an artifact of dike construction, remains problematic.Earlier experiments demonstrated that flooding only during the summer mosquito breeding season provided as effective mosquito control as year-round flooding. In standard management, the impoundment is flooded in summer, then left open to the Lagoon through culverts the rest of" the year. Culverts are typically opened when the thll sea level rise first floods the high marsh. Impoundment reconnection is being implemented by a multi-agency partnership. The total reconnected area is expected to reach 9,454 ha by the end of 1998, representing 60% of the impounded wetlands in the entire IRk system. One stumbling block is private ownership of many of the remaining isolated impoundments.-" Uni\ersity of Florida, IFAS. Journal Series No. R-05201. ; Itarbor Branch Contribution Number II52. 94 VOLUSIA t IR ~Mkk Merritt r Island ! i. BR Impounded Wetlands in the Indian River Lagoon 9 Impoundments _ land Water KILOMETERS 0 6.43 12.8

No abstract

The role of vegetative seagrass fragments as a dispersal and recruitment mechanism has received little attention. Research on the potential of vegetative fragments as a dispersal mechanism can help us better understand the ability of seagrass beds to recover from disturbance events, to recruit into new areas, and to survive over long periods. The objectives of this study were to (1) determine the viability of vegetative fragments of Halodule wrightii and Halophila johnsonii as a function of time after removal from sediment, (2) determine whether season of collection affects the fragments' recruitment potential, (3) determine if the source of fragments of H. johnsonii affects viability, (4) determine how long fragments float, and (5) determine the frequency of fragment settlement and rooting vs. time. Mesocosm experiments with plants collected from Indian River Lagoon, Florida demonstrated that fragments of H. wrightii remain viable during spring for up to 4 wk with a marked decline in survival after 2 wk of drifting. Fall plants had a shorter period of viability with only 5% of fragments remaining viable by Week 2. Although the source location of the fragments did not influence viability for H. johnsonii, day and season were highly significant for viability, with spring plants remaining viable for up to 4 d and fall plants remaining viable for twice as long. The short viability of H. johnsonii illustrates the importance of rapid settlement when uprooted from a source bed, limiting dispersal to short distances. H. wrightii appears to maintain its viability for a longer period of time, indicating that this species may be able to utilize fragments as a dispersal mechanism over longer distances. The vegetative fragments of both H. wrightii and H. johnsonii had the ability to settle and root in mesocosms, demonstrating that fragmentation is a viable mechanism for dispersal and recruitment for these species.