Primary production of phytoplankton and chlorophyll a in the southeast Barents Sea in August-September 1998

A study was performed from August 11 to September 3, 1998 in the Pechora Sea, which covered the shallow-water southeastern Barents Sea. Chlorophyll a concentration in the surface layer (C_chls) ranged from 0.08 to 1.15 mg/m**3, while primary production in the water column (C_phs) Varied from 17 to 170 mg C/m**2/day, aver. 75 mg C/m**2/day. Transition from central deep-water (60-190 m) parts of the sea to coastal shallow-water (15-30 m) parts was accompanied by increase of average C_chls values 2.4 times (from 0.21 to 0.51 mg/m**3) and decrease in average C_phs 1.6 times (from 95 to 58 mg C/m**2/day); the latter, in turn, resulted from decrease in thickness of the photosynthetic layer (H_ph) from 55 to 12 m and its relative transparency (H) from 17 to 4 m. This sharp change in H value and absence of a positive feedback between C_chls and C_phs were most probably related to rapid increase in the role of yellow substance and suspended matter in absorption of solar radiation in coastal waters. In sea areas with depths greater than 30 m a deep chlorophyll maximum was observed; at most of stations it located in the 20-35 m deep layer during illumination in photosynthetic active radiation range comprising 0.8-1.5% of its surface value. Parameters of photosynthetic light curves in these regions indicate participation of shade-adapted flora in formation of the deep chlorophyll maximum. In coastal waters characterized by a relatively uniform chlorophyll distribution over the water column no light adaptation of phytoplankton to efficient utilization of low irradiation for photosynthesis was encountered. Thus, a conclusion was made that combination of extremely low values of C_phs and H_ph makes the pelagic ecosystem of the Pechora Sea coastal regions very sensitive to anthropogenic impacts that may increase water turbidity.

Seawater carbonate chemistry, calcification, primary production and respiration of a temperate rhodolith Lithothamnion corallioides in a laboratory experiment

Coralline algae are considered among the most sensitive species to near future ocean acidification. We tested the effects of elevated pCO2 on the metabolism of the free-living coralline alga Lithothamnion corallioides ("maerl") and the interactions with changes in temperature. Specimens were collected in North Brittany (France) and grown for 3 months at pCO2 of 380 (ambient pCO2), 550, 750, and 1000 µatm (elevated pCO2) and at successive temperatures of 10°C (ambient temperature in winter), 16°C (ambient temperature in summer), and 19°C (ambient temperature in summer +3°C). At each temperature, gross primary production, respiration (oxygen flux), and calcification (alkalinity flux) rates were assessed in the light and dark. Pigments were determined by HPLC. Chl a, carotene, and zeaxanthin were the three major pigments found in L. corallioides thalli. Elevated pCO2 did not affect pigment content while temperature slightly decreased zeaxanthin and carotene content at 10°C. Gross production was not affected by temperature but was significantly affected by pCO2 with an increase between 380 and 550 µatm. Light, dark, and diel (24 h) calcification rates strongly decreased with increasing pCO2 regardless of the temperature. Although elevated pCO2 only slightly affected gross production in L. corallioides, diel net calcification was reduced by up to 80% under the 1,000 µatm treatment. Our findings suggested that near future levels of CO2 will have profound consequences for carbon and carbonate budgets in rhodolith beds and for the sustainability of these habitats.