Kenneth L. Webb

Nitrogen Fixation in a Coral Reef Community

Algal reef flats at Enewetak Atoll, Marshall Islands, fix atmospheric nitrogen at rates comparable to those in managed agriculture. The dominant nitrogen fixer appears to be the blue-green alga Calothrix crustacea. Since this nutrient enrichment contributes to the high productivity of adjacent coral reefs and undoubtedly to atoll lagoons, it is recommended that the algal reef flats receive increased conservation priority.

Amino acid flux in an estuary.

Dissolved organic matter in York River estuary included 38 micrograms of free amino acids per liter. The highest concentrations were of glycine, serine, and ornithine. Of the 14 amino acids studied for uptake by planktonic bacteria, glycine, methionine, and serine had the greatest flux rates. The total amino acid flux represented from 1 to 10 percent of the daily photosynthetic carbon fixation.

Photosynthetic temperature acclimation in two coexisting seagrasses, Zostera marina L. and Ruppia maritima L.

Abstract The physiological responses to temperature were investigated in two coexisting seagrasses, Zostera marina L. and Ruppia maritima L. sensu lato from the lower Chesapeake Bay, Virginia. Seven plant collections were made from March to July, 1983 at ambient temperatures of 8–30°C. Both species maintained relatively constant fresh: dry weight ratios and chlorophyll a : b ratios over the five-month period. Total chlorophyll content remained constant in Z. marina while that of R. maritima doubled from March to July. P max values for both species increased with increasing temperature and declined at temperatures above 19 and 23°C ( Z. marina and R. maritima , respectively). P max values were significantly higher for R. maritima compared to Z. marina at temperatures above 19°C. Both short-term (laboratory) and long-term (in situ) responses to temperature regimes affected estimates of the photosynthetic capacity of both species. Thus, temperature histories of experimental material should be carefully considered when interpreting temperature effects on photosynthesis. This study provides support of the hypothesis that seasonal community dynamics of Z. marina and R. maritima in Chesapeake Bay are regulated in part by different responses to light and temperature.

Nutritional mode of several non-pigmented microflagellates from the York River estuary, Virginia☆

Five species of non-pigmented microflagellates (3–10 μ m). isolated from the York River estuary, Virginia, U.S.A., were successfully cultured. All five microflagellates were shown, by feeding experiments and electron microscopy, to ingest live bacteria. These same microflagellates were not capable of utilizing 11 organic substrates at concentrations to 0.75 mg · 1−1. We propose that the normal nutritional mode of the marine microflagellates tested is to ingest bacteria rather than dissolved organic matter or a combination thereof.

Polyunsaturated fatty acids and neutral lipids in developing larvae of the oyster,Crassostrea virginica

The fatty acid composition of oyster larvae at various stages, as well as of the algal diet, were determined by gas liquid chromatography (GC). Saturated fatty acids are the major fatty acid components in all larval stages and account for 34–62%, 30–35% and 35–81% of the neutral, polar and total lipids of algal-fed larvae respectively. Weight percentage of saturated fatty acid in “starved” larvae was consistently higher (63–81%) during the whole period. The total polyunsaturated fatty acids were higher in the polar lipids than in the neutral lipids. The concentration of the ω3 fatty acids also was comparatively higher in the polar lipids than in the neutral lipids. In the total and neutral lipid fractions, the weight percentage of polyunsaturated and ω3 fatty acids was higher in the eyed than in the pre-eyed (pediveliger) larvae. Eicosapentaenoic acid (20∶5ω3) and 22∶6ω3 were not detected in lipids of “starved” and young larvae. There was an accumulation of 20∶5ω3, 22∶6ω3, and total ω3 fatty acids in the older larvae. Lipid classes were separated by thin layer chromatography (TLC). There was no qualitative change in lipid composition during larval development, but a marked increased of triacylglycerol in larvae up to the stage of maturation in algae-fed larvae.

Free amino acid composition of the soft-shell clam Mya arenaria in relation to salinity of the medium☆

Abstract 1. 1. Individuals of the soft-shelled clam Mya arenaria were transferred from a salinity of 20‰ to a graded series of salinities from 2 to 30‰. 2. 2. Total ninhydrin positive substances (NPS) in adductor muscle extracts determined periodically with time after transfer to a 5‰ medium indicated a 48-hr acclimation period. 3. 3. NPS measurements after 48 hr in each respective medium showed a linear relationship between NPS in adductor muscle and salinity. 4. 4. Ion exchange chromatography of muscle extracts of animals kept in the respective media for 5 days indicated that changes in glycine and alanine are largely responsible for the linear relatioship between NPS and salinity.

Nutrient and oxygen redistribution during a spring neap tidal cycle in a temperature estuary.

Spring tidal currents produce homogeneous water columns in a number of estuaries that are moderately stratified during neap tides. In the York River estuary, this destratification redistributes ammonium and phosphate regenerated by the benthos as well as oxygen from the surface. This redistribution has significant implications for nutrient cycles, organism distributions, and the management of estuaries.

The effect of temperature of salinity-induced changes in the free amino acid pool of Mya arenaria☆

Abstract 1. 1. The accumulation of free amino acid (FAA) and ninhydrinpositive substance (NPS) in the adductor muscle of Mya arenaria in response to an increased salinity was not linear with time. 2. 2. Three components in the process of NPS and FAA accumulation are proposed: (1) a fast component active during the first 24 hr, (2) a slow component effective from 36 hr and (3) a taurine component effective during the time lag between the fast and slow components. 3. 3. The increase in the alanine concentration accouted for 80–90 per cent of the observed increase in NPS concentration. 4. 4. The high correlation between the decrease in the concentration of aspartic acid and the increase in the concentration of alanine indicates a direct relationship in the formation of alanine from aspartic acid. It is suggested that aspartic acid undergoes a decarboxylation forming alanine. 5. 5. The rate-temperature functions of NPS accumulation for warm- and cold-acclimated M. arenaria did not conform to standard patterns described for warms- and cold-acclimated poikilotherms.

Salinity-Induced Changes in the Alanine and Aspartic Aminotransferase Activity in Three Marine Bivalve Molluscs

AbstractSalinity-induced increase in alanine concentration of gill tissue of Mya arenaria and Spisula solidissima is correlated with increased alanine aminotransferase activity during the first day of osmotic stress due to salinity increase. Both responses are lacking in Mercenaria mercenaria. Metabolic pathways for alanine accumulation appear similar to those described for invertebrate facultative anaerobiosis.

THE SIGNIFICANCE OF UREA FOR PHYTOPLANKTON NUTRITION IN THE YORK RIVER, VIRGINIA

ABSTRACT The rate of 14 C-urea utilization was measured concurrently with in situ 14 CO 2 productivity measurements during four 24 hour stations at the mouth of the York River estuary between July and November, 1974. After two hour incubations, the 14 C from urea was recovered from both the CO 2 and particulate phases. Particulate utilization represented 10-55% of the total. Mean utilization rates ranged from 4 ng-at urea N dm −3 h −1 in November to 175 ng-at dm −3 h −1 in July. Mean urea-N concentrations ranged from 1.1 to 1.6 μg-at dm −3 . Phytoplankton were considered to be principally responsible for utilization of urea because the process was light dependent and subject to inhibition by both DCMU and avidin. Atomic ratios of C:urea-N (productivity/urea-N utilization) ranged from 10 to 170, indicating that at times urea supplied most of the nitrogen required by the phytoplankton. A rectangular hyperbola adequately describes the relationship between light intensity and both 14 CO 2 and urea utilization. However, urea utilization was saturated at lower light intensities than photosynthesis, resulting in a higher C:N ratio near the surface than deeper in the euphotic zone. The nanophytoplankton (passing a 15 μm sieve) were responsible for about 80% of both productivity and urea utilization.