Assessing Water-Quality with Submersed Aquatic Vegetation

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The phenotypic plasticity and performance of two growth-forms of Caulerpa racemosa (Forsskal) J. Agardh, one found in estuarine conditions, the other growing in a coastal reef environment was studied in laboratory culture. There was no change in the morphology of either growth-form when cultured through a range of salinity (10—40%o) and light (20—140 μEm-2s-1) conditions.

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The relative importance of nitrogen (N) and phosphorus (P) limitation for growth and biomass accumulation in an estuarine population of eelgrass (Zostera marina L.) was examined by in situ additions of nitrogen (+N), phosphorus (+P) and nitrogen plus phosphorus (+N+P) to sediments at low and high loading rates. Nitrogen treatments resulted in no significant increases in leaf tissue N levels and only a small increase in the N content of root plus rhizome tissues.

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We determined feeding rates of the hydromedusan Nemopsis bachei L. Agassiz in the mesohaline region of Chesapeake Bay, USA during the spring of 1989 and 1990 from gut contents, digestion rates and abundances of medusae and zooplankton. The medusae consumed primarily copepodites of Acartia tonsa, selecting against naupliar stages.

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The effects of daily light period on diurnal growth patterns of a green macroalga [Caulerpa cupressoides v. lycopodium f. elegans (J. Agardh) Weber-van Bosse] and a seagrass (Halophila decipiens Ostenfeld) were investigated in Salt River submarine canyon in the US Virgin Islands in summer 1984. The daily light period, in which quantum irradiance exceeded the light saturation point for photosynthesis of the macroalga and seagrass, was manipulated in situ using lamps and shades.

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Seagrasses, along with all other marine primary producers, are generally considered to be nitrogen limited. Now experimental enrichments of the tropical seagrass Syringodium filiforme Kütz. show that phosphorus, rather than nitrogen, can be the primary limiting nutrient in a marine carbonate environment. Phosphorus enrichment of carbonate sediments resulted in dramatic increases in seagrass growth, biomass, and tissue phosphorus composition.

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Shoot density, Leaf production, Rhizome/root production, Chlorophyll content

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For the past 4 summers (1985–1988), the microalga Aureococcus anophagefferens bloomed in Long Island embayments, causing large scale perturbations in water column dynamics. The “brown tide” algal blooms brought about significant changes in the benthic community as well. The high cell densities (>109 l-1) of A. anophagefferens significantly increased light absorption in the water column (Cosper et al., 1987), and reduced the light available to plants living on the bottom of the embayments.

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The first appearance of the “brown tide” in the early summer of 1985 was over a wide geographic range along the northeast coast of the United States in non-contiguous bodies of water: Narragansett Bay, Rhode Island, and Long Island embayments in New York as well as Barnegat Bay in New Jersey (Fig.1) (Nuzzi and Waters, 1989; Olsen, 1989; Sieburth et al., 1988; Sieburth and Johnson, 1989; Smayda and Villareal, 1989).

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Water motion effects on metabolism of a common reef-building coral, Acropora formosa Dana, were studied utilizing laboratory incubations. Net photosynthesis and respiration were significantly reduced (≈ 25% lower) in unstirred conditions compared with stirred conditions. Dark calcification was reduced by ≈60% in unstirred conditions. Light-enhanced calcification appeared to be reduced by ≈ 25% in unstirred conditions; however, this effect was not statistically significant.

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