Submerged Aquatic Vegetation
Continued from Habitats and Plant Communities page…
The benthic macroflora exhibit considerable temporal and spatial variation. Only a few species are common year-round due to the sensitivity of most of the plants to changes in solar radiation and water temperature. Species diversity peaks in late spring, and is lowest in late summer. Although the community composition varies greatly during the year, the dominant species persist.
Many of the benthic macroalgae are unattached to any substrate, and drift along the bottom. Sea lettuce (Ulva lactuca) is consistently one of the most abundant macroalgal species in the estuary. Sea lettuce provides food and shelter for some fauna, but may grow excessively in nutrient-enriched areas, causing problems such as hypoxia, smothering of fauna, and lowered aesthethic value. Areas with reduced circulation (e.g., dead-end canals) are particularly prone to the buildup of sea lettuce. In some estuaries (e.g., Delaware inland bays), excess sea lettuce is harvested to reduce impacts on water quality.
Vascular plants occur along the shallow margins of the estuary in waters less than 1 m in depth. Eelgrass (Zostera marina) is the dominant seagrass species in Barnegat Bay, forming dense beds (particularly on sandflats) along the backside of the barrier island system. Widgeon grass (Ruppia maritima) is of secondary importance, also attaining highest concentrations on the eastern sand flats. Locally dense beds of sago pondweed (Potamogeton pectinatus) appear north of Toms River, with lesser quantities of horned pondweed (Zannichellia palustris), widgeon grass, and eelgrass.
The occurrence of SAV species in the estuary strongly depends on environmental conditions. Each species has its own requirements for and tolerances of physical characteristics, such as temperature, salinity, sediment composition, water velocity, and turbidity. Vascular plants compete with each other and with algae for light, space, and nutrients. The abundance of vascular plants is a function in part of the amount of seeds set the previous year and the successful germination of the seeds. Annuals that grow from rhizomes and tubers (e.g., horned pondweed) may reappear in the same location year after year. The temporal and spatial shifts of SAVs in the Barnegat Bay ecosystem likely result from naturally-occurring cycles (Loveland et al., 1984), although anthropogenic activities such as dredging, nutrient loading, boating, and the use of personal watercraft may be detrimental.
Disease is responsible for significant declines of seagrasses during certain years. For example, McClain and McHale (1997) showed that wasting disease, presumably caused by the protist Labyrinthula zosterae, destroyed about 400 ha of eelgrass beds in Barnegat Bay in 1995. Less disease and SAV destruction occurred in 1996, although as much as 50% of eelgrass leaves exhibited wasting disease at this time.
SAVs have several functional roles in the Barnegat Bay estuarine ecosystem. They provide a substantial amount of primary production for the Barnegat Bay estuary, and serve as critically important habitat for benthic epifauna and infauna. Some organisms graze on SAV (e.g., gastropods, fish, ducks, muskrats). Some benthic macrovegetation (e.g., Zostera marina) also represent valuable spawning, nursery, and feeding grounds for finfish populations in the estuary. They likewise stabilize the benthic habitat by baffling waves and currents and mitigating substrate erosion.
This is an excerpt from the “Scientific Characterization of the Barnegat Bay-Little Egg Harbor Estuary and Watershed,” Chapter 6 (2001).