The swarm dynamics of northern krill (Meganyctiphanes norvegica) and pteropods (Cavolinia inflexa) during vertical migration in the Ligurian Sea observed by an acoustic Doppler current profiler

A ship-mounted 153 kHz narrow-band ADCP and 1 m² MOCNESS were deployed between 16 and 24 Sept. 1997 in the Ligurian central zone (∼43°20′N 7°48′E). Results from both instruments showed that the zooplankton community performed vertical migrations that conformed to the classical pattern of ascent at dusk (∼18:30 h) and descent at dawn (∼06:30 h). Depth-discrete net samples between 0 and 500 m showed that the community was dominated by two species, the euphausiid Meganyctiphanes norvegica (Northern krill) and the pteropod Cavolinia inflexa, which migrated in separate discrete bands that were detectable by the ADCP. Information from the ADCP was used to estimate vertical migration speed in two ways: (i) from the trajectory of the back-scattering bands over time and (ii) from the Doppler-shift vertical velocity measured within depth zones at the corresponding time and depth of these bands. Estimates of the migration speed of C. inflexa were between 2 and 7 cm s⁻¹ upwards and between 4 and 7 cm s⁻¹ downwards. M. norvegica was estimated to migrate at speeds between 7 and 8 cm s⁻¹ upwards and over 11 cm s⁻¹ downwards. The consistently lower migration speeds estimated from Doppler measurements as compared with estimates obtained from measuring trajectories of back-scattering bands over time was believed to result from a methodological artefact. The Doppler measurements were nevertheless useful in a relative sense in revealing the relative speed of individuals within swarms. It was shown that individuals at the front of the upwardly migrating band of M. norvegica moved more slowly than those at the rear. These results illustrate the extra biological information that can be obtained by ADCPs compared with conventional echo-sounders.     

Microbial biomass and viral infections of heterotrophic prokaryotes in the sub-surface layer of the central Arctic Ocean

Seawater samples were collected for microbial analyses between 55 and 235 m depth across the Arctic Ocean during the SCICEX 97 expedition (03 September–02 October 1997) using a nuclear submarine as a research platform. Abundances of prokaryotes (range 0.043–0.47×10⁹ dm⁻³) and viruses (range 0.68–11×10⁹ dm⁻³) were correlated (r=0.66, n=150) with an average virus:prokaryote ratio of 26 (range 5–70). Biomass of prokaryotes integrated from 55 to 235 m ranged from 0.27 to 0.85 g C m⁻² exceeding that of phytoplankton (0.005–0.2 g C m⁻²) or viruses (0.02–0.05 g C m⁻²) over the same depth range by an order of magnitude on average. Using transmission electron microscopy (TEM), we estimated that 0.5% of the prokaryote community on average (range 0–1.4%) was visibly infected with viruses, which suggests that very little of prokaryotic secondary production was lost due to viral lysis. Intracellular viruses ranged from 5 to >200/cell, with an average apparent burst size of 45±38 (mean±s.d.; n=45). TEM also revealed the presence of putative metal-precipitating bacteria in 8 of 13 samples, which averaged 0.3% of the total prokaryote community (range 0–1%). If these prokaryotes are accessible to protistan grazers, the Fe and Mn associated with their capsules might be an important source of trace metals to the planktonic food web. After combining our abundance and mortality data with data from the literature, we conclude that the biomass of prokaryoplankton exceeds that of phytoplankton when averaged over the upper 250 m of the central Arctic Ocean and that the fate of this biomass is poorly understood.     

The role of crabs (Macrophthalmus japonicus) burrows on organic carbon cycle in estuarine tidal flat,Japan

The objective of this study is to elucidate the burrow structure and to clarify the role of burrows in material cycle in the tidal flat. In our work, we focused on the dominant species in muddy tidal flat, crab Macrophthalmus japonicus.Burrow structure of Macrophthalmus japonicus was investigated on a Katsuura river tidal flat in Tokushima prefecture, Japan, using in situ resin casting. Sampling was conducted in August 2006, and a total of 48 burrow casts were obtained. Burrows consisted mainly of J-shaped structures (98%) while the rest belonged to U-shaped structures (2%). The maximum measured burrow volume was 120 cm³ and wall surface area was 224 cm², while maximum burrow length and depth were 23.2 cm and 16.5 cm, respectively. Burrow volume and surface area were strongly correlated with carapace width of M. japonicus. Investigation of the individual number of M. japonicus in 13 quadrats (50 × 50 × 20 cm) was conducted using 2 mm sieve. The number of M. japonicus was 15–31 ind./m². Using cohort analysis we estimated that surface area of burrows was 0.07–0.15 m²/m².CO₂ emission rate was measured at the surface sediment during the period from June to December 2008. Results varied from 13.8 ± 2.2 to 49.4 ± 3.2 mg CO₂/m²/h, and organic carbon decomposition was 3.8 ± 0.6–13.5 ± 0.9 mg C/m²/h. This leads the increase of organic carbon decomposition by 1.1 times, because of the expansion of the tidal flat surface area by burrowing activity. Organic carbon decomposition in burrow walls therefore contributed to organic matter decomposition in the tidal flat. These results indicated that in situ activities of Macrophthalmus japonicus significantly influence the material cycle and it is important to consider the existence of burrow in order to understand the fluxes of materials and to evaluate the purification function of the tidal flat.     

Picophytoplankton in the equatorial Pacific: vertical distributions in the warm pool and in the high nutrient low chlorophyll conditions

Abundance distribution and cellular characteristics of picophytoplankton were studied in two distinct regions of the equatorial Pacific: the western warm pool (0°, 167°E), where oligotrophic conditions prevail, and the equatorial upwelling at 150°W characterized by high-nutrient low-chlorophyll (HNLC) conditions. The study was done in September–October 1994 during abnormally warm conditions. Populations of Prochlorococcus, orange fluorescing Synechococcus and picoeukaryotes were enumerated by flow cytometry. Pigment concentrations were studied by spectrofluorometry. In the warm pool, Prochlorococcus were clearly the dominant organisms in terms of cell abundance, estimated carbon biomass and measured pigment concentration. Integrated concentrations of Prochlorococcus, Synechococcus and picoeukaryotes were 1.5×10¹³, 1.3×10¹¹ and 1.5×10¹¹ cells m⁻², respectively. Integrated estimated carbon biomass of picophytoplankton was 1 g m⁻², and the respective contributions of each group to the biomass were 69, 3 and 28%. In the HNLC waters, Prochlorococcus cells were slightly less numerous than in the warm pool, whereas the other groups were several times more abundant (from 3 to 5 times). Abundance of Prochlorococcus, Synechococcus and picoeukaryotes were 1.2×10¹³, 6.2×10¹¹ and 5.1×10¹¹ cells m⁻², respectively. The integrated biomass was 1.9 g C m⁻². Prochlorococcus was again the dominant group in terms of abundance and biomass (chlorophyll, carbon); the respective contributions of each group to the carbon biomass were 58, 7 and 35%. In the warm pool the total chlorophyll biomass was 28 mg m⁻², 57% of which was divinyl chlorophyll a. In the HNLC waters, the total chlorophyll biomass was 38 mg m⁻², 44% of which was divinyl chlorophyll a. Estimates of Prochlorococcus, Synechococcus and picoeukaryotes cell size were made in both hydrological conditions.     

Seasonal patterns in the fish and epibenthic crustaceans community of an intertidal zone with particular reference to the population dynamics of plaice and brown shrimp

The intertidal zone of a sandy beach located on the French coast of the Eastern Channel, was sampled during spring and summer 2000 to analyse the community structure of fish and epibenthic crustaceans. The presence of many juvenile fish (mainly O-group) and crustaceans indicated the important role played by the intertidal zone as a nursery ground. The brown shrimp, Crangon crangon and O-group plaice, Pleuronectes platessa are the two most abundant species of the intertidal ecosystem.Plaice settlement period extended from mid-March to early June. Over the survey period, densities increased to maximum numbers of about 27 ind. 10 m⁻² in mid-April. In the following week, density rapidly decreased due to mortality and migration into deeper waters. The mortality was attributed mainly to predation by brown shrimp (C. crangon) and to a lesser extent by the shore crab (Carcinus maenas). The mean size of 0-group plaice increased from 19 mm in mid-April to 58 mm in July. Growth of juvenile 0-group plaice is described by an exponential equation: total length (TL, mm) = 12.602 e^{0.022 (post-settlement age)}. Post-settlement growth rates, estimated by otolith microstructure analysis, were 0.38 mm d⁻¹ for plaice ≤30 mm and 0.61 mm d⁻¹ for plaice >30 mm. Settlement of juvenile brown shrimp started in mid-April, peaked in early June (93 ind. 10 m⁻²) and continued with fluctuating intensity throughout the summer. Growth rate of juvenile C. crangon, estimated after the settlement peak, was 0.163 mm d⁻¹. Growth conditions of juvenile plaice and C. crangon were analysed by comparing estimated growth in the field with predicted maximum growth according to temperature-growth rate models from experimental studies of growth with unlimited food supply. For plaice, the estimated growth rate was lower (plaice ≤30 mm) but similar (plaice >30 mm) to the predicted maximum growth suggesting a food limitation only for newly settled individual. The observed increase in mean length of juvenile C. crangon was lower than the maximum possible growth. The function of the intertidal zone in the early juvenile stages of marine species is discussed.     

Diel variations of the bathymetric distribution of zooplankton groups and biomass in Cap-Ferret Canyon,France

The bathymetric distribution, abundance and diel vertical migrations (DVM) of zooplankton were investigated along the axis of the Cap-Ferret Canyon (Bay of Biscay, French Atlantic coast) by a consecutive series of synchronous net hauls that sampled the whole water column (0–2000 m in depth) during a diel cycle. The distribution of appendicularians (maximum 189 individuals m⁻³), cladocerans (maximum 287 individuals m⁻³), copepods (copepods<4 mm, maximum 773 individuals m⁻³, copepods>4 mm, maximum 13 individuals m⁻³), ostracods (maximum 8 individuals m⁻³), siphonophores (maximum >2 individuals m⁻³) and peracarids (maximum >600 individuals 1000 m⁻³) were analysed and represented by isoline diagrams. The biomass of total zooplankton (maximum 18419 μg C m⁻³, 3780 μg N m⁻³) and large copepods (>4 mm maximum 2256 μg C m⁻³, 425 μg N m⁻³) also were determined. Vertical migration was absent or affected only the epipelagic zone for appendicularians, cladocerans, small copepods and siphonophores. Average amplitude of vertical migration was about 400–500 m for ostracods, some hyperiids and mysids, and large copepods, which were often present in the epipelagic, mesopelagic, and bathypelagic zones. Large copepods can constitute more than 80% of the biomass corresponding to total zooplankton. They may play an important role in the active vertical transfer of carbon and nitrogen.     

Twenty-nine months of geomorphic change in upper Monterey Canyon (2002–2005)

Time serial multibeam bathymetry is used to evaluate geomorphic trends and submarine processes in the upper 4 km of Monterey Canyon, California. Seven high-resolution bathymetric surveys conducted between September 2002 to February 2005 show that the upper canyon axis and head grew in volume 1 000 000 m³ ± 700 000 m³, at an average annual rate of 400 000 m³/a ± 300 000 m³/a through lateral erosion and vertical incision. This net loss of substrate during the 29-month period is parsed between local erosion of 1 400 000 m³ and local deposition of 350 000 m³. A submarine landslide with a scar void volume of 70 000 m³ and debris pile of 52 000 m³ occurred between March 2003 and September 2004. During the subsequent months until February 2005, the slide scar grew 40% in volume while the debris pile shrank by 80%. The canyon-head rim adjacent to Moss Landing Harbor prograded seaward and retreated shoreward significantly (up to 50 m) during the study suggesting frequent episodes of sediment build up and subsequent down-canyon failure. A large field of sand waves located in the channel axis was completely reworked in each time series except for a 24 h period where no wave crest movement was noted, and a 32 day period where up-canyon migration of approximately 7 m was recorded in the northern tributary.     

Time-series observation of POC fluxes estimated from 234Th in the northwestern North Pacific

Time-series measurements of ²³⁴Th activities and particulate organic carbon (POC) concentrations were made at time-series stations (K1, K2, K3, and KNOT) in the northwestern North Pacific from October 2002 to August 2004. Seasonal changes in POC export fluxes from the surface layer (∼100 m) were estimated using ²³⁴Th as a tracer. POC fluxes varied seasonally from approximately 0 to 180 mg C m⁻² d⁻¹ and were higher in spring–summer than in autumn–winter. The export ratio (e-ratio) ranged from 6% to 55% and was also higher in spring–summer. Annual POC fluxes were estimated to be 31 g C m⁻² y⁻¹ in the subarctic region (station K2) and 23 g C m⁻² y⁻¹ in the region between the subarctic and subtropical gyres (station K3). POC fluxes and e-ratios in the northwestern North Pacific were much higher than those in most other oceans. The annual POC flux corresponded to 69% of annual new production estimated from the seasonal difference of the nutrient in the Western Subarctic Gyre (45 g C m⁻² y⁻¹). These results indicate that much of the organic carbon assimilated in the surface layer of the northwestern North Pacific is transferred to the deep ocean in particulate form. Our conclusions support previous reports that diatoms play an important role in the biological pump.     

Seasonal influences on size-fractionated chlorophyll a concentrations and primary production in the north-west Indian Ocean

Chlorophyll a (chl a) concentrations and primary production by the 0.2–2, 2–18 and >18 μm phytoplankton size-fractions were estimated along a transect in the NW Indian Ocean extending from the coast of Oman to 8°N 68°E during the late SW monsoon and autumn intermonsoonal seasons in 1994. Primary production was estimated using the ¹⁴C technique with either in situ or simulated in situ incubations. During the late monsoon season, maximal chl a and production values were recorded in the coastal upwelling zone with values of 69 mg m^-2 and 3800 mg C m^-2 d^-1, respectively. The maxima, which were distributed patchily in this region, were dominated by the >18 μm size-fraction. Over the remainder of the transect chl a concentrations and production averaged 30 mg m^-2 and 1500 mg C m^-2 d^-1, respectively, with approximately equal contributions by the three size-fractions in the case of chl a at the majority of stations, but in general, with a maximum in production in the 0.2–2 μm fraction. Immediately following cessation of the SW monsoon wind, chl a and production values over the northern part of the transect decreased to values similar to those over the southern part of the transect at the time of the SW monsoon, with the contributions by the three size-fractions being approximately equal. During the following intermonsoonal season, both chl a concentrations and production across the section were dominated by the 0.2–2 μm size-fraction, with average chl a and production values of the order of 20 mg m^-2 and 750 mg C m^-2 d^-1, respectively. Considerable variation in production values, however, was exhibited across the transect. A clearly defined subsurface chl a maximum was only recorded at the southernmost stations of the transect in oligotrophic waters: the feature did not develop universally across the transect during the intermonsoon.     

Organic matter budget in the Southeast Atlantic continental margin close to the Congo Canyon: In situ measurements of sediment oxygen consumption

A study of organic carbon mineralization from the Congo continental shelf to the abyssal plain through the Congo submarine channel and Angola Margin was undertaken using in situ measurements of sediment oxygen demand as a tracer of benthic carbon recycling. Two measurement techniques were coupled on a single autonomous platform: in situ benthic chambers and microelectrodes, which provided total and diffusive oxygen uptake as well as oxygen microdistributions in porewaters. In addition, sediment trap fluxes, sediment composition (Org-C, Tot-N, CaCO₃, porosity) and radionuclide profiles provided measurements of, respectively input fluxes and burial rate of organic and inorganic compounds.The in situ results show that the oxygen consumption on this margin close to the Congo River is high with values of total oxygen uptake (TOU) of 4±0.6, 3.6±0.5 mmol m⁻² d⁻¹ at 1300 and 3100 m depth, respectively, and between 1.9±0.3 and 2.4±0.2 mmol m⁻² d⁻¹ at 4000 m depth. Diffusive oxygen uptakes (DOU) were 2.8±1.1, 2.3±0.8, 0.8±0.3 and 1.2±0.1 mmol m⁻² d⁻¹, respectively at the same depths. The magnitude of the oxygen demands on the slope is correlated with water depth but is not correlated with the proximity of the submarine channel–levee system, which indicates that cross-slope transport processes are active over the entire margin. Comparison of the vertical flux of organic carbon with its mineralization and burial reveal that this lateral input is very important since the sum of recycling and burial in the sediments is 5–8 times larger than the vertical flux recorded in traps.Transfer of material from the Congo River occurs through turbidity currents channelled in the Congo valley, which are subsequently deposited in the Lobe zone in the Congo fan below 4800 m. Ship board measurements of oxygen profiles indicate large mineralization rates of organic carbon in this zone, which agrees with the high organic carbon content (3%) and the large sedimentation rate (19 mm y⁻¹) found on this site. The Lobe region could receive as high as 19 mol C m⁻² y⁻¹, 1/3 being mineralized and 2/3 being buried and could constitute the largest depocenter of organic carbon in the South Atlantic.     

Export fluxes of particulate organic carbon in the Chukchi Sea: A comparative study using 234Th/238U disequilibria and drifting sediment traps

Large-volume sampling of ²³⁴Th and drifting sediment trap deployments were conducted as part of the 2004 Western Arctic Shelf–Basin Interactions (SBI) spring (May 15–June 23) and summer (July 17–August 26) process cruises in the Chukchi Sea. Measurements of ²³⁴Th and particulate organic carbon (POC) export fluxes were obtained at five stations during the spring cruise and four stations during the summer cruise along Barrow Canyon (BC) and along a parallel shelf-to-basin transect from East Hanna Shoal (EHS) to the Canada Basin. ²³⁴Th and POC fluxes obtained with in situ pumps and drifting sediment traps agreed to within a factor of 2 for 70% of the measurements. POC export fluxes measured with in situ pumps at 50 m along BC were similar in spring and summer (average = 14.0 ± 8.0 mmol C m^− 2 day^− 1 and 16.5 ± 6.5 mmol C m^− 2 day^− 1, respectively), but increased from spring to summer at the EHS transect (average = 1.9 ± 1.1 mmol C m^− 2 day^− 1 and 19.5 ± 3.3 mmol C m^− 2 day^− 1, respectively). POC fluxes measured with sediment traps at 50 m along BC were also similar in both seasons (31.3 ± 9.3 mmol C m^− 2 day^− 1 and 29.1 ± 14.2 mmol C m^− 2 day^− 1, respectively), but were approximately twice as high as POC fluxes measured with in situ pumps. Sediment trap POC fluxes measured along the EHS transect also increased from spring to summer (3.0 ± 1.9 mmol C m^− 2 day^− 1 and 13.0 ± 6.4 mmol C m^− 2 day^− 1, respectively), and these fluxes were similar to the POC fluxes obtained with in situ pumps. Discrepancies in POC export fluxes measured using in situ pumps and sediment traps may be reasonably explained by differences in the estimated POC/²³⁴Th ratios that arise from differences between the techniques, such as time-scale of measurement and size and composition of the collected particles. Despite this variability, in situ pump and sediment trap-derived POC fluxes were only significantly different at a highly productive station in BC during the spring.     

Contrasting life-histories,secondary production,and trophic structure of Peracarid assemblages of the bathyal suprabenthos from the Bay of Biscay (NE Atlantic) and the Catalan Sea (NW Mediterranean)

The life-histories and the secondary production of four dominant peracarid crustaceans (the mysids Boreomysis arctica and Parapseudomma calloplura, the amphipod Rhachotropis caeca, and the isopod Ilyarachna longicornis) in bathyal depths of the Bay of Biscay (NE Atlantic; between 383 and 420 m) and the Catalan Sea (Northwestern Mediterranean; between 389 and 1355 m) were established. Both the Atlantic and the Mediterranean populations of the major part of the target-species had two generations/year with mean cohort-production intervals (CPI) ranging from 5.5 mo for Ilyarachna longicornis to 6.3 mo for Parapseudomma calloplura. The Hynes method showed secondary production to vary in the Bay of Biscay between 0.113 mg DW m⁻² yr⁻¹ for I. longirostris and 3.069 mg DW m⁻² yr⁻¹ for P. calloplura, with P/B ratios between 4.57 (I. longirostris) and 7.93 (Boreomysis arctica). In the Catalan Sea, production varied between 0.286 mg DW m⁻² yr⁻¹ for I. longirostris and 1.096 mg DW m⁻² yr⁻¹ for P. calloplura, with P/B between 5.72 (I. longirostris) and 6.66 (P. calloplura). Application of two different empiric models to the whole peracarid assemblage gave similar levels of secondary production in both study areas (between 29.26 and 32.14 mgDWm⁻² yr⁻¹ in the Bay of Biscay; between 26.23 and 26.54 mg DW m⁻² yr⁻¹ in the Catalan Sea). From the analysis of gut contents of 22 species the dominant species in each study area were assigned to two basic trophic levels, detritus feeders and predators. Also, cumulative curves of dominance showed high diversity (low dominance) for peracarid assemblages distributed at mid-bathyal depths (524–693 m) both in the Bay of Biscay off Arcachon and in the Catalan Sea off Barcelona. We also discuss and compare, both within and between areas, how environmental features may explain the observed diversity patterns, the trophic structure, and the production results obtained for the suprabenthos assemblages.     

The seasonal succession of zooplankton in the Southern Ocean south of Australia,part II: The Sub-Antarctic to Polar Frontal Zones

Between October 2001 and March 2002 six transects were completed at monthly intervals in the Sub-Antarctic Zone (SAZ) and Inter-Sub-Antarctic Front Zone (ISAFZ)/Polar Frontal Zone (PFZ) in the Southern Ocean south of Australia. Zooplankton were collected with a Continuous Plankton Recorder and NORPAC net and multivariate analysis was used to analyse the seasonal succession of communities. Despite strong, seasonally consistent, biogeographic differences between the SAZ and ISAFZ/PFZ, community structure in all zones was dominated by a suite of common taxa. These included the ubiquitous Oithona similis, foraminiferans and appendicularians (Core taxa), occurring in >97% of samples and contributing an average of 75% to total sample abundance, and Calanus simillimus, Rhincalanus gigas, Ctenocalanus citer, Clausocalanus brevipes, Clausocalanus laticeps, Oithona frigida, Limacina spp. and chaetognaths (Summer taxa), present in >57% of samples and occurring at seasonally high densities. Because of the dominance of the Core and Summer taxa, the seasonal succession was most clearly evident as a change in zooplankton densities. In October densities averaged <15 ind m⁻³, rising to 52 ind m⁻³ (max=92 ind m⁻³) in November, and subsequently increasing slowly through to January (ave=115 ind m⁻³; max=255 ind m⁻³). Densities peaked abruptly in February (ave=634 ind m⁻³; max=1593 ind m⁻³), and remained relatively high in March (ave=193 ind m⁻³; max=789 ind m⁻³). A latitudinal lag in seasonal development was observed with peak densities occurring first in the SAZ (February) and then in the ISAFZ/PFZ (March). The seasonal community succession was strongly influenced by species population cycles. The role of zooplankton in biogeochemical cycling in the SAZ and ISAFZ/PFZ was discussed in the light of past sediment trap data collected from the study area.     

Basin-scale variability of phytoplankton biomass,production and growth in the Atlantic Ocean

The latitudinal distributions of phytoplankton biomass, composition and production in the Atlantic Ocean were determined along a 10,000-km transect from 50°N to 50°S in October 1995, May 1996 and October 1996. Highest levels of euphotic layer-integrated chlorophyll a (Chl a) concentration (75–125 mg Chl m⁻²) were found in North Atlantic temperate waters and in the upwelling region off NW Africa, whereas typical Chl a concentrations in oligotrophic waters ranged from 20 to 40 mg Chl m⁻². The estimated concentration of surface phytoplankton carbon (C) biomass was 5–15 mg C m⁻² in the oligotrophic regions and increased over 40 mg C m⁻² in richer areas. The deep chlorophyll maximum did not seem to constitute a biomass or productivity maximum, but resulted mainly from an increase in the Chl a to C ratio and represented a relatively small contribution to total integrated productivity. Primary production rates varied from 50 mg C m⁻² d⁻¹ at the central gyres to 500–1000 mg C m⁻² d⁻¹ in upwelling and higher latitude regions, where faster growth rates (μ) of phytoplankton (>0.5 d⁻¹) were also measured. In oligotrophic waters, microalgal growth was consistently slow [surface μ averaged 0.21±0.02 d⁻¹ (mean±SE)], representing <20% of maximum expected growth. These results argue against the view that the subtropical gyres are characterized by high phytoplankton turnover rates. The latitudinal variations in μ were inversely correlated to the changes in the depth of the nitracline and positively correlated to those of the integrated nitrate concentration, supporting the case for the role of nutrients in controlling the large-scale distribution of phytoplankton growth rates. We observed a large degree of temporal variability in the phytoplankton dynamics in the oligotrophic regions: productivity and growth rates varied in excess of 8-fold, whereas microalgal biomass remained relatively constant. The observed spatial and temporal variability in the biomass specific rate of photosynthesis is at least three times larger than currently assumed in most satellite-based models of global productivity.     

Submarine groundwater discharge (SGD) as a main nutrient source for benthic and water-column primary production in a large intertidal environment of the Yellow Sea

The biogeochemistry and magnitude of submarine groundwater discharge (SGD) was investigated in one of the largest tidal flat ecosystems worldwide, along the Yellow Sea coast. A representative semi-enclosed embayment located in the south eastern Yellow Sea, Hampyeong Bay, was chosen for this purpose. Groundwater and seawater samples were collected in three seasons (May, July, and September) and analyzed for Ra isotopes, nutrients, and photosynthetic pigments. The biogeochemistry of SGD was strongly influenced by tidal oscillations and seasonal precipitation changes and switched from a brackish, nutrient-enriched regime in May and July to an exclusively saline regime, with lower nutrient concentrations, in September. SGD magnitudes, calculated by using a ²²⁶Ra mass balance model, were 0.14 m³ m^? 2 d^? 1 in May and 0.35 m³ m^? 2 d^? 1 in September. A nutrient mass balance was established for the two campaigns, which suggests that SGD causes the flushing of substantial amounts of pore water nutrients into this embayment; because of SGD, the embayment acts as a source of dissolved inorganic silicates (DSi) that are transported to the open ocean. Potential C fixation rates derived from this nutrient mass balance were compared with two different models for water-column phytoplankton productivity based on water-column Chl a and local irradiation levels. The Chl a-based models generally showed lower C fixation rates than the nutrient-based mass balance, indicating removal of up to 70% of the nutrients by other primary producers, such as benthic algae. During monsoon season, when benthic algal biomass is high and nutrient fluxes are substantial due to a terrestrial component, SGD — driven benthic primary production could play a significant role in this large tidal flat ecosystem.     

Early spring bloom phytoplankton-nutrient dynamics at the Celtic Sea Shelf Edge

Phytoplankton production was measured at the shelf edge region of the Celtic Sea in April/May 1994 at the beginning of the spring bloom. Size fractionated ¹⁴C uptake experiments showed that phytoplankton >2 μm dominated the bloom although, in the period immediately before the increase in phytoplankton biomass, picophytoplankton (<2 μm) was responsible for up to 42% of the production; in these late winter conditions, chlorophyll concentrations were generally <0.7 μg l^-1 and primary production was ca. 70 mmol C m^-2 d^-1. As the spring bloom developed, phytoplankton production rates of 120 mmol C m^-2 d^-1 were measured. Chlorophyll concentration increased to >2 μg l^-1 as a result of growth of larger phytoplankton, including diatoms, with large numbers of Nitzschia, Thalassionema and Chaetoceros dominating the assemblage. Picophytoplankton production declined as the spring bloom progressed. Nutrient concentrations were not depleted during the sampling period, and NO^-₃ concentrations were >6 μmol l^-1. Nutrient assimilation rates were measured at the same time as primary production was estimated. Before the development of any substantial phytoplankton biomass, the uptake rates for ammonium and nitrate were very similar, with f-ratios ranging from 0.5 to 0.6. Assimilation of ammonium remained relatively constant after the onset of stratification and bloom development, but nitrate uptake increased by a factor of 2 or more, resulting in f-ratios >0.8. There was significant phosphate uptake in the dark, which was generally ca. 50% of the rate in the light. The C : N : P assimilation ratios changed as the bloom developed; in the pre-bloom situation, when small phytoplankton cells dominated the assemblage, the C : N assimilation ratio was variable, with some stations having ratios less than (ca 2.5), and some higher than (ca. 9), the Redfield ratio. The most actively growing assemblages had N : P ratios close to the Redfield ratio, but the C : N ratios were consistently lower. New production was found to be closely correlated with the size of the species making up the phytoplankton assemblage, and high f ratios were measured when larger phytoplankton dominated the assemblage.     

Home range and diel behavior of the ballan wrasse,Labrus bergylta,determined by acoustic telemetry

Effective fisheries management needs to consider spatial behavior in addition to more traditional aspects of population dynamics. Acoustic telemetry has been extensively used to provide information on fish movements over different temporal and spatial scales. Here, we used a fixed-receiver array to examine the movement patterns of Labrus bergylta Ascanius 1767, a species highly targeted by the artisanal fleet of Galicia, NW Spain. Data from 25 individuals was assessed for a period of 71 days between September and November 2011 in the Galician Atlantic Islands Maritime-Terrestrial National Park. Fish were present within the monitored area more than 92% of the monitored time. The estimated size of individual home ranges, i.e. the area where fish spent most of their time, was small. The total minimum convex polygons area based on all the estimated positions was 0.133 ± 0.072 km², whereas the home range size estimated using a 95% kernel distribution of the estimated positions was 0.091 ± 0.031 km². The core area (50% kernel) was 0.019 ± 0.006 km². L. bergylta exhibited different patterns of movement in the day versus the night, with 92% of the fish detected more frequently and traveling longer distances during the daytime. In addition, 76% of the fish displayed a larger home range during the day versus during the night. The linearity index was less than 0.005 for all fish suggesting random movements but within a relatively small area, and the volume of intersection index between consecutive daily home ranges was 0.75 ± 0.13, suggesting high site fidelity. The small home range and the sedentary behavior of L. bergylta highlight the potential use of small MPAs as a management tool to ensure a sustainable fishery for this important species.     

Zooplankton associated with the oxygen minimum zone system in the northern upwelling region of Chile during March 2000

Zooplankton in the coastal upwelling region off northern Chile may play a significant biogeochemical role by promoting carbon flux into the subsurface OMZ (oxygen minimum zone). This work identifies the dominant zooplankton species inhabiting the area influenced by the OMZ in March 2000 off Iquique (20°S, northern Chile). Abundance and vertical distribution studies revealed 17 copepod and 9 euphausiid species distributed between the surface and 600 m at four stations sampled both by day and by night. Some abundant species remained in the well-oxygenated upper layer (30 m), with no evidence of diel vertical migration, apparently restricted by a shallow (40–60 m) oxycline. Other species, however, were found closely associated with the OMZ. The large-sized copepod Eucalanus inermis was found below the oxycline and performed diel vertical migrations into the OMZ, whereas the very abundant Euphausia mucronata performed extensive diel vertical migrations between the surface waters and the core of the OMZ (200 m), even crossing it. A complete assessment of copepods and euphausiids revealed that the whole sampled water column (0–600 m) is occupied by distinct species having well-defined habitats, some of them within the OMZ. Ontogenetic migrations were evident in Eucalanidae and E. mucronata. Estimates of species biomass showed a substantial (>75% of total zooplankton biomass) daily exchange of C between the photic layer and the OMZ. Both E. inermis and E. mucronata can actively exchange about 37.8 g C m⁻² d⁻¹ between the upper well-oxygenated (0–60 m) layer and the deeper (60–600 m) OMZ layer. This migrant biomass may contribute about 7.2 g C m⁻² d⁻¹ to the OMZ system through respiration, mortality, and production of fecal pellets within the OMZ. This movement of zooplankton in and out of the OMZ, mainly as a result of the migratory behavior of E. mucronata, suggests a very efficient mechanism for introducing large amounts of freshly produced carbon into the OMZ system and should, therefore, be considered when establishing C budgets for coastal upwelling systems.     

Xanthophyll cycling in Phaeocystis globosa and Thalassiosira sp.: a possible mechanism for species succession

The ability of phytoplankton species to initiate photo-protective mechanisms and the rates by which they do so have been suggested to be partly responsible for species succession. To examine whether this is also true in the case of diatom spring blooms preceding Phaeocystis globosa, cultures of P. globosa and Thalassiosira sp. were investigated under controlled laboratory conditions for differences in their xanthophyll cycling rates and abilities. It was found that P. globosa exhibited active and rapid xanthophyll cycling when cultures photoacclimated to 10, 50 and 100 μmol quanta m⁻² s⁻¹, were shifted to 150 and 250 μmol quanta m⁻² s⁻¹. The early spring diatom Thalassiosira only exhibited xanthophyll cycling when acclimated to 10 μmol quanta m⁻² s⁻¹. P. globosa always exhibited faster xanthophyll cycling rates than Thalassiosira, giving P. globosa a possible competitive edge over Thalassiosira sp. It was also found that the magnitude of xanthophyll cycling correlates with the intensity of light changes during the one-hour xanthophyll cycling experiments, and thus may be regarded as related to photoacclimation.     

Air–sea CO2 fluxes in the north-eastern shelf of the Gulf of Cádiz (southwest Iberian Peninsula)

An intra-annual investigation of the fugacity of CO₂ (fCO₂) has been conducted in surface waters of the north-eastern shelf of the Gulf of Cádiz (SW Iberian Peninsula) in four cruises made in 2006 and 2007. Intra-annual variability of fCO₂ was assessed and is discussed in terms of mixing, temperature and biology. In the study area of the shelf, thermodynamic control over fCO₂ predominates from early May to late November, and this is opposite and similar in magnitude to the net biological effect. However, biological control over fCO₂ predominates during winter. The results suggest that surface waters in the coastal area are under-saturated with respect to atmospheric CO₂ during most of the year; therefore they represent a sink for atmospheric CO₂ between November and May (? 1.0 mmol m^? 2 day^? 1), but a weak source in June (1.3 mmol m^? 2 day^? 1). In contrast, the coastal ecosystems studied (the lower estuary of Guadalquivir Estuary and Bay of Cádiz) acted as a weak sink for atmospheric CO₂ during February (? 1.3 mmol m^? 2 day^? 1) and as a source between May and November (2.6 mmol m^? 2 day^? 1). The resulting mean annual CO₂ flux in the north-eastern shelf of the Gulf of Cádiz was ? 0.07 mol m^? 2 year^? 1 (? 0.2 mmol m^? 2 day^? 1), indicating that the area acts as a net sink on an annual basis.