Aspects of water column primary productivity in the Chukchi Sea during summer

Measurements of primary productivity, chlorophyll a, incident solar radiation, phosphate-P, silicate-Si, nitrate-N, nitrite-N, ammonium-N, temperature and salinity were made in the Marginal Ice Zone of the Chukchi Sea in summer 1974. Low to moderate levels of primary productivity (0.07 to 0.97 g C m^-2 half-day^-1) were observed; primary productivity exceeded 3 g C m^-2 half-day^-1 at two stations. Surface primary productivity was nitrogen-limited at most stations. Mean chlorophyll a concentration in the photic zone varied from 0.4 to 17.8 mg m^-3. Higher concentrations and significant subsurface accumulation of chlorophyll a, reaching 40 mg m^-3, were observed in July at stations near the ice-edge than those in open water. No chlorophyll maximum was noted in September, when values ranged from 0.4 to 2.2 mg m^-3. It is postulated that the contribution of sea-ice algae to the total chlorophyll content can be substantial, but that the stay of these cells in the water column may not be long. Non-linear regression estimates from solar radiation and chlorophyll-specific primary productivity data showed a maximal photosynthetic rate of 18 mg C mg chlorophyll a ^-1 half-day^-1, an optimal light intensity of 54 langleys half-day^-1, and markedly reduced primary productivity at moderately higher light intensities. These features indicate that phytoplankton was shade-adapted.     

In situ net primary productivity and photosynthesis of Antarctic sea ice algal, phytoplankton and benthic algal communities

Primary production at Antarctic coastal sites is contributed from sea ice algae, phytoplankton and benthic algae. Oxygen microelectrodes were used to estimate sea ice and benthic primary production at several sites around Casey, a coastal area in eastern Antarctica. Maximum oxygen export from sea ice was 0.95 mmol O₂ m⁻² h⁻¹ (~11.7 mg C m⁻² h⁻¹) while from the sediment it was 6.08 mmol O₂ m⁻² h⁻¹ (~70.8 mg C m⁻² h⁻¹). When the ice was present O₂ export from the benthos was either low or negative. Sea ice algae assimilation rates were up to 3.77 mg C (mg Chl-a)⁻¹ h⁻¹ while those from the benthos were up to 1.53 mg C (mg Chl-a)⁻¹ h⁻¹. The contribution of the major components of primary productivity was assessed using fluorometric techniques. When the ice was present approximately 55–65% of total daily primary production occurred in the sea ice with the remainder unequally partitioned between the sediment and the water column. When the ice was absent, the benthos contributed nearly 90% of the primary production.     

Differences in productivities between the Great Australian Bight and the Gulf of Carpentaria,Australia, in summer

Phytoplankton standing crop (chlorophyll a) and primary productivity were recorded, and zooplankton biomass was estimated in the two large bays of Australia, the Great Australian Bight on the south coast (December, 1965) and the Gulf of Carpentaria on the north coast (December, 1968). In the Gulf of Carpentaria, the phytoplankton standing crop (average, 27.3 mg chlorophyll a m^-2) and primary productivity (average, 133.1 mg C m^-2 h^-1), as well as zooplankton biomass (average, 305.3 mg wet weight m^-3) are much higher than in the Great Australian Bight (12.1 mg chlorophyll a m^-2, 18.2 mg C m^-2 h^-1, 7.1 mg wet weight m^-3, respectively). The unexpectedly low productivity values in the Great Australian Bight are attributable to environmental conditions of this bay, which obtains neither replenishment of nutrients from the land nor receives upwelling of deep water.     

Community metabolism of intertidal flats in the Ems-Dollard estuary

To obtain an insight into the flux of carbon through intertidal sediments of the Ems-Dollard estuary, the annual cycles of gross benthic primary production and community respiration were measured at six stations, together with a set of environmental parameters. In a stepwise multiple regression analysis it was shown that temperature alone and temperature plus viable bacteria explained 50 and 70% respectively of the observed variation in community respiration. Other variables, including the rate of primary production and amount of organic carbon in the sediment were less important. The rate of primary production could not be fitted adequately into a multiple regression equation. The annual values of community respiration (177–794 gO₂·m^-2·yr^-1) and primary production (82–628 gO₂·m^-2·yr^-1) were within the range of published values. except for one station in the vicinity of a wastewater outfall, which had an extreme production (average 984 gO₂·m^-2·yr^-1). At four stations, annual community respiration exceeded primary production by 40%. It is concluded that the main carbon flux within the sediment, from CO₂ to benthic primary producers, to benthic consumers and from there to CO₂ again,was completed within a month or so, leaving untouched the large bulk of organic matter within the sediment. Possible effects of wastewater discharges on community metabolism are discussed.Publication No. 43 of the project Biological Research in the Ems-Dollard Estuary     

Phytoplankton community structure and primary production in small intertidal estuarine-bay ecosystem (eastern English Channel,France)

From May 2002 to October 2003, a fortnightly sampling programme was conducted in a restricted macrotidal ecosystem in the English Channel, the Baie des Veys (France). Three sets of data were obtained: (1) physico-chemical parameters, (2) phytoplankton community structure illustrated by species composition, biovolume and diversity, and (3) primary production and photosynthetic parameters via P versus E curves. The aim of this study was to investigate the temporal variations of primary production and photosynthetic parameters in this bay and to highlight the potential links with phytoplankton community structure. The highest level of daily depth-integrated primary production Pz (0.02–1.43 g C m⁻² d⁻¹) and the highest maximum photosynthetic rate P ^B _max (0.39–8.48 mg C mg chl a ⁻¹ h⁻¹) and maximum light utilization coefficient α^B [0.002–0.119 mg C mg chl a ⁻¹ h⁻¹ (μmol photons m⁻² s⁻¹)] were measured from July to September. Species succession was determined based on biomass data obtained from cell density and biovolume measurements. The bay was dominated by 11 diatoms throughout the year. However, a Phaeocystis globosa bloom (up to 25 mg chl a m⁻³, 2.5 × 10⁶ cells l⁻¹) was observed each year during the spring diatom bloom, but timing and intensity varied interannually. Annual variation of primary production was due to nutrient limitation, light climate and water temperature. The seasonal pattern of microalgal succession, with regular changes in composition, biovolume and diversity, influenced the physico-chemical and biological characteristics of the environment (especially nutrient stocks in the bay) and thus primary production. Consequently, investigation of phytoplankton community structure is important for developing the understanding of ecosystem functioning, as it plays a major role in the dynamics of primary production.     

Contrasting life histories and secondary production of populations of Munnopsurus atlanticus (Isopoda: Asellota) from two bathyal areas of the NE Atlantic and the NW Mediterranean

The isopod Munnopsurus atlanticus occupies bathyal depths in both the Bay of Biscay (NE Atlantic; between 383 and 1022 m) and in the Catalan Sea (Northwestern Mediterranean; between 389 and 1859 m). The species was dominant in both assemblages, reaching bathymetric peaks of abundance on the upper part of the continental slope (400 m depth) in the Bay of Biscay and at ˜600 m in the Catalan Sea. Both the Atlantic and the Mediterranean populations are bivoltines. Demographic analysis of the Bay of Biscay population revealed the production of two generations per year with different potential longevity (5 mo for G₁ and 11 mo for G₂). The mean cohort-production interval (CPI) was estimated at 8 mo, and results of the demographic analysis were also used to estimate production for the Catalan Sea populations. Mean annual density (D) and biomass (B) were higher in the Bay of Biscay (D = 356.7 individuals 100 m⁻²; B = 0.803 mg dry wt m⁻² yr⁻¹) than in the Mediterranean (D = 16.3 individuals 100 m⁻²; B = 0.078 mg dry wt m⁻² yr⁻¹). Also, mean annual production was an order of magnitude higher in the Atlantic (between 4.063 and 4.812 mg dry wt 100 m⁻² yr⁻¹ depending on the method used) than in the Catalan Sea (between 0.346 and 0.519 mg dry wt 100 m⁻² yr⁻¹). M. atlanticus feeds on a wide variety of benthic and pelagic food sources. In both study areas, phytodetritus was not important in the diet of M. atlanticus. In contrast, gut-content data suggested an indirect coupling with phytoplankton production in both areas via foraminiferans. The life history and the recorded production are considered in respect to both the dynamics and levels of primary production and the total mass flux in the respective study areas. Differences in the secondary production of both populations seemed to be more consistently explained by differences in total mass flux than by differences in the primary production levels; this is also consistent with the variety of food sources exploited by M. atlanticus. Received: 22 February 1999 / Accepted: 3 February 2000     

Plankton of the fladen ground during FLEX 76 II. Population dynamics and production of Thysanoessa inermis (Crustacea: Euphausiacea)

Samples taken in the northern North Sea with the Continuous Plankton Recorder (CPR), the Undulating Oceanographic Recorder (UOR) and the Longhurst-Hardy Plankton Recorder (LHPR) during the Fladen Ground Experiment in 1976 (FLEX 76) are used to describe the vertical distribution and population dynamics of Thysanoessa inermis (Krøyer) and to provide estimates of the production and carbon budget of the population from 19th March to 3 June 1976. Spawning occurred in late April and early May, in near synchronisation with the start of the spring bloom of phytoplankton. Eggs, nauplii and calyptopes reached maximum abundance in succession, and furciliae were numerous when sampling ceased in early June. Adults increased in length from a mean of 12.1 mm in mid-March to 17.5 mm in early June and the estimated production was 2.40 mg m^-3 over the 74 d period. Total carbon ingested by the population of T. inermis was estimated to be 10 mg C m^-2 d^-1 in the upper 100m which was only 1.5% of the daily primary production of 0.68 gC m^-2 measured over the FLEX period 26 March to 4 June 1976. The grazing by T. inermis on the phytoplankton population was assumed to have little effect on the control and depletion of the spring phytoplankton bloom during FLEX 77.JOSDAP Contribution No. 50     

Diel variation of bacterial productivity in seagrass (Zostera capricorni) beds measured by rate of thymidine incorporation into DNA

Diurnal variations occurred in bacterial growth rates in the sediment and water column associated with seagrass (mainly Zostera capricorni Aschers) beds in Moreton Bay, Queensland, Australia. Studies were carried out in March and June 1981. Cell production rates increased by 5- to 10-fold during the morning and decreased during the afternoon. No nocturnal variation was observed. Daily bacterial cell production rate in the aerobic zones of the seagrass bed was estimated to be 43 mg C m^-2. A minimum of 100 mg C m^-2 d^-1 would be required to support the bacterial production. This represents about 10% of net primary production. The incorporation of tritiated thymidine into DNA was used to measure bacterial growth. The validity of the method is discussed.     

Production primaire pélagique de l'Etang de Berre en 1977 et 1978. Comparaison avec le milieu marin (Méditerranée nord-occidentale)

Measurements of primary production and photosynthetic efficiency were carried out in the brackish lake “Etang de Berre” near Marseilles (France), which is diluted by the Durance River, and in the area of Carry-le-Rouet (Mediterranean Sea) about 25 km off the Rhône River outlet. Primary production (¹⁴C) estimations were made in Etang de Berre from December 1977 to November 1978. The carbon uptake rates ranged between 38 and 1 091 mg C m^-3 d^-1, with an average surface value of 256 mg; water-column carbon-uptake rates ranged between 240 and 2 310 mg C m^-2 d^-1, with an average of 810, representing 290 g C m^-2 per year and 45 000 tons per year of photosynthetized carbon for the whole lake. Gross photosynthetic production measured by the method of Ryther was studied over a 2 yr period. The values obtained from marine water (Carry-le-Rouet) ranged from 23 to 2 337 mg C m^-2 d^-1, with a weighted average of 319, representing about 110 g C m^-2 per year. The values in brackish water (Etang de Berre) ranged from 14 to 1 778 mg C m^-2 d^-1, with a weighted average of 682, representing 250 g C m^-2 per year and 38 400 tons per year of photosynthesized carbon for the whole lake. The values derived from both methods of primary production measurements are approximately similar. Net production (computed from biomass estimations by Utermöhl's method) was compared with gross photosynthetic production. The net production in marine water did not display significant variations: most values were usually near zero. On the other hand, net production in brackish water exhibited a number of clear variations compared with concentrations of gross photosynthetic production during the whole 2 yr period. This large difference between estimations of gross and net production may be due to grazing, which is high in Etang de Berre, but slower and more constant in seawater. The ratios of primary production: chlorophyll a and gross photosynthetic production: biomass were also studied. In Etang de Berre, the former ratio ranges between 0.57 and 3.75, with an average of 1.44; this is similar to previously reported values. The ratio gross production: biomass in Etang de Berre varies between 0.3 and 4.2, with an average of 1.27, also confirming previous data. The very high values calculated for marine waters in the present study may result from an under-estimation of biomass.     

Diel changes in phytoplankton photosynthetic efficiency in Brackish waters

From 18 to 23 September 1974, investigations on the diel changes in phytoplankton were carried out in the Baltic Sea. Every 4 h, water samples were collected from 2 and 15 m, and PO₄, chlorophyll a, temperature, salinity, pH, phytoplankton composition and phytoplankton light photosynthesis relationship were determined. Continuous measurements of surface irradiance and some estimations of zooplankton were also made. P ^B (photosynthesis per unit chlorophyll a at low light levels of 2·10^-2 cal cm^-2 min^-1) revealed only random variation during the sampling period, i.e., 1.0 to 1.6 mg C (mg chlorophyll a)^-1 h^-1. P _m ^B (Light-saturated photosynthesis per unit of chlorophyll a) displayed pronounced diel fluctuations with the highest value of about 6 mg C (mg chlorophyll a)^-1 h^-1 around noon, and the lowest value of about 2.5 mg C (mg chlorophyll a)^-1 h^-1 during the night, during which latter period the value of P _m ^B was more or less constant. Reasons for the diel fluctuations are discussed, and an equation which describes these fluctuations is proposed. Using this equation, the daily phytoplankton production estimated in incubators by a previously described method can be corrected for the time of day at which samples are collected.     

Direct measurement of dissolved organic carbon release by phytoplankton and incorporation by microheterotrophs

It is now possible to divide particulate primary production into algal and heterotrophic components without physical separation. This depends on two innovations, the introduction of isotope in the form of labelled dissolved product(s) of primary production and the employment of a data analysis specifically designed for tracer kinetic incorporation experiments. The ¹⁴C technique described by Steemann Nielsen (1952) is inapplicable in the analyses of certain classes of systems and kinetic tracer incorporation experiments must be employed instead. We show that measurement of PDOC production rate requires such kinetic tracer analyses. Measurements made in the laboratory on water taken from 2 m depth in South West Arm of the Port Hacking estuary showed that: (1) the steady-state rate of PDOC production was 0.10 to 0.13 mg C.m^-3.h^-1; (2) the rate of PDOC incorporation into microheterotroph particulate organic carbon was 0.10 to 0.12 mg C.m^-3.h^-1; (3) the rate at which PDOC was respired to CO₂ was 0.001 to 0.003 mg C.m^-3.h^-1. (4) the PDOC makes up only about 0.1% of the total dissolved organic carbon. The size class of particles associated with PDOC production differed from the size class responsible for uptake of PDOC. More than 50% of the PDOC production was associated with particles having a nominal diameter range of 20 to 63 m, while this fraction was responsible for <10% of the incorporation.     

Modelling the growth and harvest yield of the giant kelp Macrocystis pyrifera

The giant kelp Macrocystis pyrifera is one of the largest and fastest growing seaweeds and is dominant over large areas of the west coast of North America. A model of its growth has been developed which describes plant biomass and production over the course of a year as a function of environmental parameters which affect the light flux. Such parameters include water clarity, spacing between plants, bottom depth, latitude, harvesting activity, and photosynthetic response (P _max and I _k ). Model results for a standard set of conditions (latitude 33°N, 3 m plant spacing, water absorbance of 0.115 m^-1 and 12 m depth) yield a peak daily gross production of almost 6 g C m^-2 d^-1, peak daily net production of almost 3 g C m^-2 d^-1, and a peak specific growth rate of about 0.022 d^-1. Annual gross production for this case is 1 567 g C m^-2 yr^-1; annual net production is 537 g C m^-2 yr^-1. These values are comparable to those from field measurements. Size and timing of biomass and production peaks are affected by changes in the parameters describing the light field, with peaks usually occurring later in the year for more adverse circumstances. Inhigher latitudes, the seasonal variation is so extreme that the plant could not last the year at 53° N in 12 m of water, although it is able to survive the year in shallower water. Harvesting has severe effects on biomass and production. Model results suggest that light limitation is a very important constraint on kelp growth that should not be overlooked. This implies that differences in parameters describing two environments must be considered when comparing results obtained at different locales.     

Annual biomass and production of the oceanic copepod community off Discovery Bay,Jamaica

Monthly samples were collected in oceanic waters off Discovery Bay, Jamaica, in 60- and 200-m vertical hauls, using 200- and 64-m mesh plankton nets, from June 1989 to July 1991. Length-weight regressions were derived for twelve genera of copepods (R²=0.79 to 0.97). For eight occasions spanning the study period, biomass estimates generated from these length-weight regressions differed by only 3% from direct weight determinations. The mean ash content of copepods was 7.1%, and the energy density was 20.8 kJ g^-1 ash-free dry weight (AFDW). Mean annual biomass of the total copepod community in the upper 60 m was 1.83 mg AFDW m^-3 (range 1.14 to 2.89 mg AFDW m^-3), and for the 200-m water column was 0.96 mg AFDW m^-3 (range 0.12 to 1.99 mg AFDW m^-3). Estimates of generation times for five common taxa ranged from 16.1 to 33.4 d. None of the taxa investigated displayed isochronal development; in general, stage duration increased in later copepodite stages. Weight increments showed a significant decrease in later copepodite stages, but with strong reversal of the trend from stage 5 to adult female in most species. Daily specific growth rates also declined in later copepodite stages, and ranged from 1.49 d^-1 in stage 1–2 Paracalanus/Clausocalanus spp. to 0.04 in stage 5-female of Oithona plumifera. Progressive food limitation of somatic copepodite growth and egg production is postulated. Naupliar production was 50.4 to 59.5% of copepodite production, and egg production was 35.1 to 27.7% of copepodite production in the 60-and 200-m water columns, respectively. Total annual copepod production, including copepodites, nauplii, eggs and exuviae, was 160 kJ m^-2 yr^-1 for the upper 60 m and 304 kJ m^-2 yr^-1 for the upper 200 m. Secondary production of the copepod community in oceanic waters off Discovery Bay approaches 50% of the corresponding value in tropical neritic waters.     

Seasonal composition of meroplankton and holoplankton in the Bristol Channel

A decreasing gradation in the plankton standing stock of the Bristol Channel was observed from the seaward section to the inner, less saline, reaches. Two sub-regions of our survey, the North Outer Channel (NOC) and the Inner Channel (IC), represented the extremes of this gradient and were selected for detailed comparison. The integrated zooplankton biomass, over the 307 d sampling period (4 November 1973 to 6 September 1974), was 2 475 mg C m^-3 (266 mg C m^-2 d^-1) in the NOC and 335 mg C m^-3 (20 mg C m^-2 d^-1) in the IC. The omnivorous plankton accounted for 76% of the standing stock in the NOC and 89% in the IC, of which 58 and 23% were meroplankton and 39 and 71% were holoplankton, respectively; the remainder was unassigned. The majority of the meroplankton in both subregions was decapod larvae and adults, whereas the holoplankton biomass was dominated in the NOC by copepods (89%) and in the IC by mysids (57%), mainly Schistomyzis spiritus. Centropages hamatus was the most abundant copepod species in the NOC and accounted for 32% of the total holoplankton omnivore standing stock. In the NOC and IC, the carnivorous plankton accounted for 24 and 11% of the total plankton biomass, respectively. In the two sub-regions, 20 and 21% of the carnivores were meroplanktonic (primarily larvae of sprats and pilchards), while the holoplankton carnivores contributed 75 and 74% to the NOC and IC, respectively (Sagitta elegans, Pleurobrachia pileus). S. elegans dominated the holoplankton carnivore biomass for the majority of the year and accounted for 96% in the NOC and 60% in the IC. The integrated total particulate carbon over the 307 d period was 200 g C m^-3 (6 600 g C m^-2) in the NOC and 838 g C m^-3 (15 084 g C m^-2) in the IC. The annual primary production ranged from 164.9 g C m^-2 yr^-1 in the Outer Channel (North and South) to 6.8 g C m^-2 yr^-1 in the IC. The zooplankton biomass reached a maximum in July. The total particulate carbon (TPC) in July was 400 mg C m^-3 in the NOC of which ca. 78 mg C m^-3 were phytoplankton and ca. 21 mg C m^-3 were zooplankton; these values compare favourably with those found in the adjoining Celtic Sea. In the IC, the TPC was 2 800 mg C m^-3, of which ca. 107 mg C m^-3 were phytoplankton and 2.8 mg C m^-3 were zooplankton. From the low primary production estimates for the IC it can be concluded that the majority of the chlorophyll, like the TPC, was allochthonous in origin. Furthermore it is suggested that zooplankton plays a minor role in this estuarine ecosystem and is not the main consumer of the suspended particulate carbon; the benthic filter-feeding communities are presumed to fulfill this role in the Bristol Channel.     

Plankton of the fladen ground during FLEX 76 III. Vertical distribution,population dynamics and production of Calanus finmarchicus (Crustacea: Copepoda)

Samples taken in the northern North Sea with the Continuous Plankton Recorder (CPR), the Undulating Oceanographic Recorder (UOR), the Longhurst Hardy Plankton Recorder (LHPR) and by our colleagues from other participating Institutes during the Fladen Ground Experiment (FLEX 76) were used to describe the vertical distribution and population dynamics of Calanus finmarchicus (Gunnerus) and to provide estimates of the production and carbon budget of the population from 19 March to 3 June, 1976. Total production of the 19 March to 3 June, 1976. Total production of the nauplii and copepodite stages (including adults), during the exponential growth phase in May, was estimated to be in the range of 0.49 to 0.91 g C m^-2 d^-1 or 29.0 to 55 g dry wt m^-2 (14.5 to 27.8 g C m^-2) for the three successive 10 d periods in May. Two gross growth efficiencies (K ₁) (20 and 34%), together with the lower value of C. finmarchicus production, were used to calculate the gross ingestion levels of algae as 2.45 and 1.44 g C m^-2 d^-1 (73.5 and 43.2 g C m^-2 over the May period). These ingestion levels, together with the algae ingested by other zooplankton species, are greater than the estimated total phytoplankton production of 45.9 g C m^-2 over the FLEX period. A number of factors are discussed which could explain the discrepancies between the production estimates. One suggestion is that the vertical distribution of the development stages of this herbivorous copepod and their diel and ontogenetic migration patterns enable it to efficiently exploit its food source. Data from the FLEX experiment indicated that the depletion of nutrients limited the size of the spring bloom, but that it was the grazing pressure exerted by C. finmarchicus which was responsible for the control and depletion of the phytoplankton in the spring of 1976 in the northern North Sea.JONSDAP Contribution No. 51     

Primary production of Posidonia oceanica in the Mediterranean Basin

Primary production of the marine phanerogam Posidonia oceanica (Linnaeus) Delile was measured by lepidochronological analyses at 22 sites in the Mediterranean Sea (Corsica, France, Italy, Sardinia and Turkey), between 1983 and 1992, to determine spatial and temporal variations. Leaf production (blade and sheath) ranged from 310 to 1 540 mg dry wt shoot^–1 yr^–1, depending on site and depth. Rhizome production ranged from 24 to 120 mg dry wt shoot^–1 yr^–1 (6% of average leaf production). At some sites the results obtained by lepidochronological analysis were consistent with earlier results obtained by classic methods (e.g. leaf-marking). While primary production per shoot (mg dry wt shoot^–1 yr^–1) displayed no significant differences between sites, primary production of the P. oceanica meadow (g dry wt m^–2 yr^–1) decreased with increasing depth at all sites studied. This decrease correlated with reduced density of the meadow (number of shoots per m²) with increasing depth. Past primary production was also extrapolated at three sites at the island of Ischia (Italy) for a period of 5 yr in order to determine interannual variations over a period of several years. While major variations were recorded for the surface stations (5 and 10 m depth), production remained stable at the deepest station (20 m depth). Given the large geographical scale of the study (location, depth range), it would appear that while P. oceanica production remains considerable, the values recorded in the literature on the basis of classical analyses (surface stations) represent maxima, and cannot be generalised for meadows as a whole.     

Photosynthesis and amelioration of desiccation in the intertidal saccate alga Colpomenia peregrina

Rates of gross photosynthesis for the intertidal saccate alga Colpomenia peregrina (Sauv.) Hamel were determined under submersed and emersed conditions. Maximal photosynthetic rates were lower than for most seaweeds but comparable with other saccate members of the genus. By fitting the data to a hyperbolic tangent function, maximal photosynthetic rates were estimated to be 5.29 mmol CO₂ m^-2 h^-1 under submersed conditions and 2.06 mmol CO₂ m^-2 h^-1 under emersed conditions. I_k for submersed thalli was 69.1 E m^-2 s^-1, wherea for emersed thalli it was 149.0 E m^-2 s^-1, or 2.2 times higher. At low tide in the field and under saturating irradiance, carbon from seawater retained within the thallus cavity was assimilated at 0.9 mmol CO₂ m^-2 h^-1. In the laboratory under emersed conditions, carbon from this source was taken up at 0.6 mmol CO₂ m^-2 h^-1 at 20°C and at 0.34 mmol CO₂ m^-2 h^-1. Retained seawater also greatly reduced drying under desiccating conditions. Experimental thalli from which seawater had been removed lost thallus water continuously throughout the drying period (120 min). On the other hand, control, thalli lost water for the first 15 min, after which no further water loss occurred. At the termination of the experiment, control thalli had lost 7.2% of their water, whereas experimental thalli had lost 39.2%. Desiccation affected the emersed photosynthetic rate of experimental and control thalli. Emersed photosynthetic rates for thalli dried for 15 min were higher than for fullyhydrated thalli. However, emersed photosynthesis of thalli dried for longer than 15 min was lower than fully-hydrated rates and was directly related to percent water loss. Utilizing data from this study, a model was constructed to determine total photosynthetic production of C. peregrina over a single daylight period. From these calculations it was determined that emersed photosynthesis can increase daily photosynthetic production of C. peregrina by 50%.     

Total,chemical and biological oxygen consumption of the sediments in Lindåspollence,Western Norway

Measurements of total, chemical and biological oxygen consumption were made at 5 stations situated between 22 and 35 m in Lindåspollene, Norway. The results from each station did not reveal any clear seasonal variation, but the pooled data showed highest values in September, and lowest in January. Problems concerning interpretion of results of biological and chemical O₂ consumption obtained by a poisoning technique (using formaldehyde) are discussed. The time-weighted mean of the annual total O₂ consumption based on all stations was 10.67 ml m^-2 h^-1 or 92.2 l m^-2 year^-1. This corresponds to a consumption of 34.5g C m^-2 year^-1 (respiratory quotient=0.7), or 34 to 37% of the net annual primary production of phytoplankton.     

Production of tropical copepods in Kingston Harbour, Jamaica: the importance of small species

The copepod community observed during an 18-month period at the mouth of eutrophic Kingston Harbour, Jamaica, was dominated by small species of Parvocalanus, Temora, Oithona, and Corycaeus. Mean copepod biomass was 22.1 mg AFDW m⁻³ (331 mg m⁻²). Annual production was 1679 kJ m⁻², partitioned as 174 kJ m⁻² naupliar, 936 kJ m⁻² copepodite, 475 kJ m⁻² egg and 93 kJ m⁻² exuvial production. All nauplii, most copepodites and many adults, equivalent to half of the biomass and production, were missed by a standard 200-μm plankton net, emphasizing the importance of nauplii and small species in secondary production estimates. The evidence suggests that growth rates and production are generally not food limited, and we speculate that size-selective predation shapes the structure of the harbour community. Biomass and production are higher than previous estimates for tropical coastal waters, but comparable to other eutrophic tropical embayments and many productive temperate ecosystems. Far from being regions of low productivity, tropical zooplankton communities may have significant production and deserve greater research attention than they currently receive. Received: 19 September 1997 / Accepted: 21 October 1997     

Primary production and environmental factors in an oligotrophic biome in the Aegean Sea

The rate of the primary production of the phytoplankton community in the Petalion Gulf, Aegean Sea, was studied from January 1970 to May 1971, at a station situated at approximately Latitude 37°54N; Longitude 24°11E. A variety of physical and chemical parameters such as chlorophyll, primary nutrients (N,P,Si), temperature, salinity, oxygen and light penetration were also studied simultaneously. The rate of the gross primary production varied from 40 to 200 mg C m^-2 day^-1, with a mean value of 90 mg C m^-2 day^-1. The annual gross primary production was calculated to be 33 g C m^-2, which is the minimum known value in the Aegean and Mediterranean Seas. Maximum production was found at the depth of 20 m on the average, mainly due to high light intensities. Petalion Gulf supports a small photosynthetic biomass, as indicated by the low seasonal values of chlorophyll a (0.01 to 0.18 mg m^-2), the highest values being found in the summer. The low production rate noted may have been due to the low nutrient concentrations found: N, 0.04 to 0.32 g-at/1; P, 0.00 to 0.15 g-at/1; Si, 0.45 to 2.25 g-at/1. It is suggested that inorganic phosphorus and nitrogen may alternate in limiting primary production rates in these oligotrophic waters. The temperate waters of the Petalion Gulf are stratified in summer (15.5° to 24.7°C) and well-mixed in winter (12.9° to 15.0°C); they are oxygen-saturated throughout the year, and of high transparency, with 86 m depth for the euphotic zone on the average yearly. The Petalion Gulf is therefore characterized as a typical oligotrophic biome in the Aegean and Eastern Mediterranean Seas.