The relative contributions to organic matter production and the interactions between submerged vascular plants and their associated microalgae assemblages were investigated in seagrass communities characteristic of the lower Chesapeake Bay. The studies were conducted in three parts; the first compared production and respiration of the major autotrophic components in adjacent seagrass communities dominated by Zostera marina and Ruppia maritima, respectively. Annual production for the two communities differed; in the Z. marina area microalgal (i.e. phytoplankton and benthic microalgae) production dominated during the summer months, whereas in the R. maritima area, the macrophyte-epiphyte complex dominated throughout the growing season. Both areas exhibited high annual gross production rates (1580 gC m('-2) in the Z. marina area and 1000 gC m('-2) in the R. maritima area) of which the microalgae accounted for 45% and 36% in the two communities respectively. The ratio of net production to dark respiration (P/R) exceeded 1.0 for each of the components, suggesting export and/or burial of carbon from the system. The second series of studies investigated specific interactions between Z. marina and its epiphytic microalgae. Two sites were examined, where previous observations had been made of differing epiphytic colonization patterns. The two seagrass ecosystems differed markedly in epiphytic abundance, community structure, and productivity and respiration of the epiphytic complex. Based on gross morphological characteristics of the seagrass host, differences in nutrient conditions could exist at the two sites, where the hypothetically enriched site coincided with a flourishing epiphytic community. Effects of nutrient enrichment and light reduction on epiphytic growth were examined directly in the third phase of this study using controlled microcosm experiments. Both nutrient enrichment and light reduction led to enhanced epiphytic productivity and biomass, as well as increased light attenuation associated with epiphytic growth. Direct reduction in ambient light also stimulated epiphytic production relative to that of the seagrass host. Reduced abundance of plant leaves in the nutrient enriched systems perhaps indicated some signs of stress to Z. marina. This study suggests that nutrient enrichment and light reduction in the water column could increase epiphytic growth and production, possibly at the expense of the macrophyte.

The oxygen metabolism and exchange of nutrients between sediment and water were studied on a submerged sandy shoal in the York River, Virginia from March to December 1983. Particular emphasis was placed on the variability in metabolic estimates over different time scales. Variation in oxygen metabolism was examined over the photoperiod, between successive sampling days, between tidal condition (mid-day high vs. low tide), and among seasons. Morning NP was significantly greater than afternoon NP over the study. Mean hourly NP and R were significantly different between successive days in 4 of 6 tests, and 2 of 6 tests respectively. R was significantly higher on days with mid-day low tides (noon (+OR-) 2 hours). Mean hourly NP was 49% greater on days with mid-day low tides and R was 70% greater. Hourly NP and R were significantly different among seasons. R peaked in summer and NP in fall. Plots of mean hourly NP and R by month were made using all data for a given month and compared to plots made by randomly selecting a single measurement for each month. The latter plots are based on 12 data points, the former on 185 points. The two types of plots produced very similar annual rate estimates but differed radically in their depiction of seasonal changes. Within dark domes, hourly fluxes of ammonium and phosphate ranged from -21 (uptake) to 364 ug-at N m('-2) and -3 to 76 ug-at P m('-2). Nitrate + nitrite fluxes were generally small and erratic, comprising an average of only 15% of the total dissolved inorganic nitrogen flow. Releases of ammonium and phosphate peaked in summer, were an exponential function of temperature, and a linear function of respiration. Average ammonium release within transparent domes was only 25% of the average release in the dark domes, but phosphate fluxes were nearly identical to those in the dark domes. Nitrate + nitrite fluxes comprised an average of 17% of the total dissolved inorganic nitrogen flux of the transparent domes. Ammonium fluxes were significantly different between dome treatments, fluxes of the other nutrients were not significantly different.

Early life histories of alewife (Alosa pseudoharengus) and blueback herring (A. aestivalis), collectively known as river herring, are poorly documented for Chesapeake Bay populations. Improved knowledge of these early life histories potentially will aid fisheries, habitat and resource management. Investigations were conducted following two lines. First, alewife and blueback herring larvae reared from eggs were used to investigate methods for species identification and to validate the otolith increment method for age determination. Blueback herring larvae hatched from naturally-spawned eggs were reared to age 24 d. Alewife and blueback herring larvae hatched from artificially-spawned eggs were reared to age 32 d and age 37 d. Alewife larvae exhibited paired melanophores laterally along the notochord starting at about 15 mm SL, contracted xanthophores dorsally on the head, and lacked xanthochrome at the caudal fin base. Blueback herring exhibited one or two melanophores dorsally on the notochord starting at about 11 mm SL, relatively large xanthophores dorsally on the head, and xanthochrome at the caudal fin base. Other pigment variation was found. Estimated deposition of otolith increments was 1.16 and 0.90 increment d&\sp{lcub}-1{rcub}& for blueback herring larvae and 0.90 increment d&\sp{lcub}-1{rcub}& for alewife larvae. Increment enumeration was affected by otolith microstructure appearance, but estimated deposition did not differ statistically from one increment d&\sp{lcub}-1{rcub}&. Second, larval river herring distributions, abundances, growth rates, and hatch dates in the Pamunkey River tidal freshwater reach were analyzed. Distributions and abundances of zooplankton prey for river herring larvae were also analyzed. High abundances in two tidal creeks suggested that larvae occur in these areas from about late April to about mid-May. Larval river herring growth, pooled across seasons, was faster in the tidal creeks, 0.46 mm d&\sp{lcub}-1{rcub}&, than the mainstem river, 0.34 mm d&\sp{lcub}-1{rcub}&. Faster growth in the tidal creeks may increase survival by reducing the larval stage duration. Older larvae, pooled across habitats, grew faster than younger larvae, 0.59 mm d&\sp{lcub}-1{rcub}& and 0.35 mm d&\sp{lcub}-1{rcub}&. Larvae with relatively earlier hatch dates were associated primarily with the mainstem river while larvae with relatively later hatch dates were associated primarily with the tidal creeks. Zooplankton abundances were higher in the tidal creeks than the mainstem river.

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