Nitrogen regeneration during the degradation of several amino acids by plankton communities collected near Halifax,Nova Scotia,Canada

Nitrogen regeneration accompanying the bacterial degradation of a variety of amino acids supplied at 10.0 M to samples of coastal plankton communities collected near Halifax, Nova Scotia, Canada was examined. A lag period characterized by a low rate of amino acid uptake and ammonia release was typically followed by a dramatic increase in the rates of uptake and ammonia release. The duration of the lag period varied with the amino acid tested. The ratio of the final ammonia concentration to the nitrogen supplied as amino acid was taken as the regeneration ratio. This value varied from 0.58 to 0.86 for L-arginine and 0.38 to 1.17 for the other amino acids tested, with an average value of 0.74. The presence of inorganic fixed nitrogen at 10.0 M had no effect on the degradation of L-arginine. Other organic compounds supplied at 10.0 M decreased the lag period for L-arginine uptake and degradation. Glucose supplied at 50.0 M decreased the nitrogen regeneration ratio, but did not further decrease the lag for L-arginine degradation. Carbon respiration ratios for L-arginine, L-glutamate, and L-lysine were 0.70, 0.68, and 0.65 when the nitrogen regeneration ratios were 0.86, 0.38, and 0.77, respectively.     

Relationship between phytoplankton cell size and the rate of orthophosphate uptake: in situ observations of an estuarine population

Orthophosphate uptake by a natural estuarine phytoplankton population was estimated using two methods: (1) ³²P uptake experiments in which filters of different pore sizes were used to separate plankton size-fractions; (2) ³³P autoradiography of phytoplankton cells. Results of the first method showed that plankton cells larger than 5 m were responsible for 2% of the total orthophosphate uptake rate. 98% of the total uptake rate occurred in plankton composed mostly of bacteria, which passed the 5 m screen and were retained by the 0.45 m pore-size filter. There was no orthophosphate absorption by particulates in a biologically inhibited control containing iodoacetic acid. Orthophosphate uptake rates of individual phytoplankton species were obtained using ³³P autoradiography. The sum of these individual rates was very close to the estimated rate of uptake by particulates larger than 5 m in the ³²P labelling experiment. Generally, smaller cells were found to have a faster uptake rate per m³ biomass than larger cells. Although the nannoplankton constituted only about 21% of the total algal biomass, the rate of phosphate uptake by the nannoplankton was 75% of the total phytoplankton uptake rate. Results of the plankton autoradiography showed that the phosphate uptake rate per unit biomass is a power function of the surface: volume ratio of a cell; the relationship is expressed by the equation Y=2x10^-11 X ^1.7, where Y is gP m^-3 h^-1 and X is the surface: volume ratio. These results lend support to the hypothesis that smaller cells have a competitive advantage by having faster nutrient uptake rates.     

Nutrients and biomass distribution in the Gulf of Aqaba (Elat), Red Sea

The distribution of phosphate, nitrate and silicate values obtained from 300 samples and of biomass determined by displacement volume in about 1,900 vertical plankton hauls (65, 200 and 330 m) collected from 8 oceanographic station during 1974–1975 in the Gulf of Aqaba (Elat) are summarized and illustrated by crosssections. Generally, the Gulf is poor in nutrients and the data indicate that it is filled with upper (150 m) Red Sea waters, flowing in over the sill of Tiran. Nutrient content of the upper and deep waters immediately outside the sill are well within the known range of those in the northern Red Sea. Biomass values are relatively low in the Gulf are generally similar to those reported from the northern Red Sea. Both nutrients and biomass values display seasonal and bathymetric variations in the Gulf and outside the sill.     

Continuous plankton records: The occurrence of apostome ciliates (Protozoa) on Euphausiacea in the North Atlantic Ocean and North Sea

The phoronts (resting cysts) of apostome ciliates have been recorded on Euphausia hemigibba, E. krohni, Meganyctiphanes norvegica, Nematoscelis megalops, Nyctiphanes couchi, Thysanoessa gregaria, T. inermis, T. longicaudata and T. raschi taken in the Continuous Plankton Recorder Survey of the North Atlantic Ocean and the North Sea. Variations in the percentage of host euphausiids infested by apostomes have been studied in relation to species, geography, body size and season. The percentage infestation was found to be related mainly to the body size of the hosts. The apostomes are believed to be species that develop either in the exuviae discarded exoskeletons or corpses of the euphausiids, or in the digestive systems of predators of the euphausiids.     

Contribution of moulting and eggs to secondary production in Nyctiphanes australis (Crustacea: Euphausiacea)

This study was designed to assess the contribution of moulting and eggs to production of the euphausiid Nyctiphanes australis G. O. Sars. For this purpose, live specimens were collected from Storm Bay, south-eastern Tasmania, between August and December 1981, while preserved samples, collected between February 1980 and February 1981, were also examined. The intermoult period of N. australis increased exponentially with increase in body length and weight. Larvae moulted approximately every 2.5 to 3 d and adults every 4 to 5 d at 15°C. A decrease in temperature from 15° to 10°C resulted in the intermoult period almost doubling. The mean weight of exuviae produced represented nearly 6% of the body dry weight of the individual. Continuous maturation of ova was observed, with an individual female capable of releasing a total of 1 100 eggs in a lifetime. These are deposited as a series of batches into a pair of external ovisacs every 30 d. The size of the batch of eggs was dependent on the size of the female. Moulting of euphausiids forms a significant contribution of organic matter to detrital food webs. A value of 42.01 mg m^-3 yr^-1 was obtained for the production of exuviae. Egg production was calculated to be between 1.41 and 4.22 mg m^-3 yr^-1. Production and mean annual biomass of N. australis was previously calculated as 78.29 mg m^-3 yr^-1 and 5.39 mg m^-3, respectively. Thus, the total production integrated for the whole of Storm Bay was 125 mg m^-3 yr^-1 or 2 309 tonnes dry wt yr^-1, representing an overall P:B ratio of 23.1.     

Release of dissolved organic carbon from the estuarine intertidal macroalga Enteromorpha prolifera

The estuarine macroalga Enteromorpha prolifera was collected from Coos Bay, Oregon, USA during 1981, and its release of photosynthate as dissolved organic carbon (DOC) was studied using ¹⁴C as a tracer. During photosynthesis in 30 S sea water, with a fixation rate averaging 7.37 mg C g^-1 dry wt h^-1, release ranged from 0.13 to 0.57 mg C g^-1 dry wt h^-1 and from 1.65 to 6.23% of total fixed carbon. Release of DOC appears to be linear with time over 3 h. As exposed algae become increasingly desiccated, their photosynthetic rates decline dramatically, but upon reimmersion the highly desiccated algae lose a larger fraction of their fixed carbon than the slightly desiccated algae. This loss comes in a pulse release of DOC over the initial 15 min, followed by declining release rates. The pulse loss due to rainfall is 5 times greater than that due to tidal resubmergence, and may briefly exceed the prior photosynthetic rate. Although lowering the salinity from 30 to 5 does not substantially alter photosynthetic rates, it does increase the DOC release range up to 1.02 mg C g^-1 dry wt h^-1 and 16.10% of fixed carbon. Heterotrophic microbes from the algal habitat readily use the available DOC at about 15% h^-1.     

Possible causes of temporal fluctuations in primary production of the microphytobenthos in the Danish Wadden Sea

The effects of prior exposure to unlabelled naphthalene on the processes of uptake, tissue distribution and elimination of [1-¹⁴C] naphthalene by mussels (Mytilus edulis) were examined. Mussels collected from Whitsand Bay (S. W. England) in October 1980 were either held unexposed or exposed to unlabelled naphthalene (0.5 μg 1^?1) for 4 wk, prior to receiving a 4 h pulse of [1-¹⁴C] naphthalene in the medium (7 μg 1^?1). After 4 h exposure to [1-¹⁴C] naphthalene, the major tissues (digestive gland, gills, kidneys, mantle and remaining tissue) showed exponential depuration curves which could be resolved into two statistically significant components. The kinetics of elimination and the biological half-times of [1-¹⁴C] naphthalene in the tissues were determined. Mussels pre-exposed to unlabelled naphthalene had a significantly higher rate of elimination of [1-¹⁴C] naphthalene from the gills and kidneys. These results indicate that the toxicant, naphthalene, is actively excreted from the body by the gills and kidneys and the process is enhanced by prior exposure to the toxicant.     

Values of net compensation irradiation and their dependence on photosynthetic efficiency and respiration in marine unicellular algae

Daily compensation irradiation for net photosynthetic rates (ΣI _comp) of Skeletonema costatum (Greville) Cleve, Chaetoceros ceratosporum Ostenfeld, Nitzschia sp., Thalassiosira nordenskiöldii Cleve, and Chroomonas salina (Wislouch) Butcher were measured during 1979 to obtain values for use in ecological models describing compensation and critical depths of marine phytoplankton. Batch cultures of these unicellular algae were exposed to temperatures and photoperiods varying from 6° to 15°C and 8.4 to 16.0 h, conditions typical of surface water in Saanich Inlet, a fjord in Vancouver Island, British Columbia, Canada. Results obtained with S. costatum and T. nordenskiöldii provided estimates of ΣI _comp varying between 1.8 and 13 J cm^-2 d^-1, from which a mean value of 7.0 J cm^-2 d^-1 was calculated for use in ecological models with neritic phytoplankton. No seasonal variation in compensation irradiation was noted because photosynthetic efficiencies, which increased as division rates increased, were balanced by respiration rates, which increased as temperature increased. Results obtained with Chaetoceros ceratosporum, Nitzschia sp., and Chroomonas salina were difficult to interpret, because respiration rates were stimulated and depressed by light, respectively, for the first two species and the last one. This light effect was greatest when cells grew under conditions of low temperature and short photoperiod. Also, under winter and spring conditions, cells of Nitzschia sp. appeared to fix CO₂ in the dark and with low irradiances by mechanisms other than photosynthesis.     

Colonization of meiobenthos in oil-contaminated subtidal sands in the lower Chesapeake Bay

In-situ manipulative experiments were conducted over a 3-month period (May–August 1980) to examine the rate at which meiobenthos colonizes oiled and untreated azoic fine sands at a shallow subtidal site in the lower York River, Virginia. Three concentrations of fresh Prudhoe Bay crude oil were added to sediments: 100, 2 500 and 10000 mg oil kg^-1 dry wt sediment. Untreated azoic and natural sediments served as controls. Within 16 d, meiofauna densities in all treatments were comparable to natural populations in surface oxidized sediments, but densities fluctuated greatly during the remainder of the sampling period. Nematodes slowly colonized the subsurface anoxic sediments below the redox potential discontinuity (RPD); some less common species did not significantly recover below the RPD in the two more heavily oiled treatments. Analysis of nematode community composition by reciprocal averaging ordination and numerical classification revealed generally lower abundances, but no distinct differences, in species composition in the oiled substrates as compared to untreated and natural community controls. Ordination of sequential samples suggested that the nematode species assemblages in the untreated controls fully recovered from these small-scale disturbances by 90 d. Life history characteritics and frequent tidal transport combine to make estuarine meiobenthos highly resilient following disturbance. Contrary to prior recolonization studies, a successional sequence was found for the colonizing nematodes which may be analogous to models of macrobenthic colonization (e.g. McCall, 1975). The comesomatid nematode Sabatieria pulchra, which is frequently dominant in polluted sediments, colonized relatively late in the experiment. Consequently, stress resistance and resilience may not be as coincident in meiofauna as in macrofauna because of differences in factors affecting their dispersal.