Community structure across a large-scale ocean productivity gradient: Marine bird assemblages of the Southern Indian Ocean

Our objective was to understand how marine birds respond to oceanographic variability across the Southern Indian Ocean using data collected during an 16-day cruise (4–21 January 2003). We quantified concurrent water mass distributions, ocean productivity patterns, and seabird distributions across a heterogeneous pelagic ecosystem from subtropical to sub-Antarctic waters. We surveyed 5155 km and sighted 15,606 birds from 51 species, and used these data to investigate how seabirds respond to spatial variability in the structure and productivity of the ocean. We addressed two spatial scales: the structure of seabird communities across macro-mega scale (1000 s km) biogeographic domains, and their coarse-scale (10 s km) aggregation at hydrographic and bathymetric gradients. Both seabird density and species composition changed with latitudinal and onshore–offshore gradients in depth, water temperature, and chlorophyll-a concentration. The average seabird density increased across the subtropical convergence (STC) from 2.4 birds km⁻² in subtropical waters to 23.8 birds km⁻² in sub-Antarctic waters. The composition of the avifauna also differed across biogeographic domains. Prions (Pachyptila spp.) accounted for 57% of all sub-Antarctic birds, wedge-tailed shearwaters (Puffinus pacificus) accounted for 46% of all subtropical birds, and Indian Ocean yellow-nosed albatross (Thallasarche carteri) accounted for 32% of all birds in the STC. While surface feeders were the most abundant foraging guild across the study area, divers were disproportionately more numerous in the sub-Antarctic domain, and plungers were disproportionately more abundant in subtropical waters. Seabird densities were also higher within shallow shelf-slope regions, especially in sub-Antarctic waters, where large numbers of breeding seabirds concentrated. However, we did not find elevated seabird densities along the STC, suggesting that this broad frontal region is not a site of enhanced aggregation.     

Identifying biologically and physically special or unique sites for inclusion in the protected area design for the Great Barrier Reef Marine Park

A method to identify special and/or unique sites was developed when reviewing the zoning of the Great Barrier Reef Marine Park. Fifty-three (totalling approximately 10,445 km²) of 408 sites were identified as special or unique based on the amount, detail and nature of justification; geographic explicitness; type of information sources; number of independent sources; and national or international obligations. All but four special or unique sites increased in protection after the Zoning Plan was revised, increasing the area of no-take protection for all special or unique sites from 1614 km² (15.4%) to 4013 km² (38.4%).     

Mesoscale decrease of surface phosphate and associated phytoplankton dynamics in the vicinity of the subtropical South Pacific islands

Surface distributions of nutrients and phytoplankton were investigated in the vicinity of the subtropical South Pacific islands by using a continuous underway system with a highly sensitive nutrient analysis. A total of 17 transects, whose lengths ranged between 42 and 271 km, were sampled for continuous nutrient measurements. The study area was characterized by an overall depletion of nitrate+nitrite (<15 nM), but phosphate varied from 7 to 192 nM. The transects were grouped into 4 patterns according to distribution of phosphate concentrations. In 7 transects, a mesoscale decrease in phosphate occurred, coinciding with an elevation of in vivo chlorophyll fluorescence, which was accompanied by an increase in phytoplankton abundance as revealed by microscopy, flow cytometry, and accessory pigments. This mirror–image relationship between the phosphate concentration and phytoplankton abundance was most apparent on both a 99-km transect east of Tonga, where the phosphate concentration ranged from 17 to 125 nM, and on a 98-km transect west of Fiji, where the phosphate concentration ranged from 23 to 136 nM. Both these transects contained distinct blooms of Trichodesmium in areas with the lowest concentrations of phosphate. In other 2 transects, fluctuations in phosphate concentrations showed no distinct relationship with chlorophyll fluorescence. Other patterns that emerged included consistently high concentrations, ranging from 109 to 192 nM, in 5 transects and consistently low phosphate concentrations, ranging from 7 to 50 nM, in 3 transects. Abundance of Trichodesmium, Prochlorococcus, Synechococcus, and all accessory pigments examined tended to be higher in the low phosphate transects than in the high phosphate ones. In particular, Trichodesmium occurred in low phosphate water (<25 nM). There was no significant relationship between phosphate concentrations and nanoplanktonic unicellular cyanobacteria. Our observations suggest that surface phosphate decreases are associated with phytoplankton utilization of phosphate, and that nitrogen supply from Trichodesmium may contributes to this utilization.     

A large flux of particulate matter in the deep Japan Trench observed just after the 1994 Sanriku-Oki earthquake

Three time-series sediment traps were deployed in the Japan Trench at 40°26′N, 144°28′E, from October 1994 to May 1995. The depths were approximately 1, 4.2 and 6.8 km and the water depth was 7150 m. There were large mass fluxes in spring at 1 and 4.2 km depths, whereas increased fluxes appeared from 27 December 1994 to 29 January 1995, at 4.2 and 6.8 km depths. The 1994 Sanriku-Oki earthquake (M_w=7.7) occurred on 28 December 1994, at 40°27′N, 143°43′E, adjacent to the study site. Distinct increases in non-biogenic material were observed at both 4.2 and 6.8 km just after the earthquake; the material seems to have originated from the surface sediments, though differing Mn/Al of particulate materials at the two depths imply a difference in their source areas. Analysis indicates that the main part of the increased particulate fluxes at 6.8 km depth derived from the sediment on the eastern slope of the Japan Trench.     

Kinetic study reveals weak Fe-binding ligand,which affects the solubility of Fe in the Scheldt estuary

The chemistry of dissolved Fe(III) was studied in the Scheldt estuary (The Netherlands). Two discrete size fractions of the dissolved bulk (< 0.2 μm and < 1 kDa) were considered at three salinities (S = 26, 10 and 0.3).Within the upper estuary, where fresh river water meets seawater, the dissolved Fe concentration decreases steeply with increasing salinity, for the fraction < 0.2 μm from 536 nM at S = 0.3 to 104 nM at S = 10 and for the fraction < 1 kDa from 102 nM to 36 nM Fe. Further downstream, in the middle and lower estuary, this decrease in the Fe concentration continues, but is far less pronounced. For all samples, the traditionally recognised dissolved strong organic Fe-binding ligand concentrations are lower than the dissolved Fe concentrations.Characteristics of dissolved Fe-binding ligands were determined by observing kinetic interactions with adsorptive cathodic stripping voltammetry. From these kinetic experiments we concluded that apart from the well-known strong Fe-binding organic ligands (L, logK′ = 19–22) also weak Fe-binding ligands (P) existed with an α value (binding potential = K′ · [P]) varying between 10^11.1 and 10^11.9. The presence of this relatively weak ligand explained the high concentrations of labile Fe present in both size fractions in the estuary. This weak ligand can retard or prevent a direct precipitation after an extra input of Fe.The dissociation rate constants of the weak ligand varied between 0.5 × 10^− 4 and 4.3 × 10^− 4 s^− 1. The rate constants of the strong organic ligand varied between k_d = 1.5 × 10^− 3–17 × 10^− 2 s^− 1 and k_f = 2.2 × 10⁸–2.7 × 10⁹ M^− 1 s^− 1. The dissociation rate constant of freshly amorphous Fe-hydroxide was found to be between 4.3 × 10^− 4 and 3.7 × 10^− 3 s^− 1, more labile or equal to the values found by Rose and Waite [Rose, A.L., Waite, T.D., 2003a. Kinetics of hydrolysis and precipitation of ferric iron in seawater. Environ. Sci. Technol., 37, 3897–3903.] for freshly precipitated Fe in seawater.Kinetic rate constants of Fe with the ligand TAC (2-(2-Thiazolylazo)-p-cresol) were also determined. The formation rate constant of Fe(TAC)₂ varied between 0.1 × 10⁸ and 3.6 × 10⁸ M^− 1 s^− 1, the dissociation rate constant between 0.2 × 10^− 5 and 17 × 10^− 5 s^− 1 for both S = 26 and S = 10. The conditional stability constant of Fe(TAC)₂ (β_Fe(TAC)2′) varied between 22 and 23.4 for S = 10 and S = 26 more or less equal to that known from the literature (logβ_Fe(TAC)2′ = 22.4; [Croot, P.L., Johansson, M., 2000. Determination of iron speciation by cathodic stripping voltammetry in seawater using the competing ligand 2-(2-Thiazolylazo)-p-cresol (TAC). Electroanalysis, 12, 565–576.]). However, at S = 0.3 the logβ_Fe(TAC)2′ was 25.3, three orders of magnitude higher. Apparently the application of TAC to samples of low salinity can only be done when the correct β_Fe(TAC)2′ is known.     

Fluid flow reconstruction in karstified Panormide platform limestones (north-central Sicily): Implications for hydrocarbon prospectivity in the Sicilian fold and thrust belt

Diagenetic analysis based on field and petrographic observations, isotope and microthermometric data was used to reconstruct the fluid flow history of the Cretaceous shallow water limestones from the Panormide platform exposed in north-central Sicily. Analysis focused on diagenetic products in cavities and dissolution enlarged fractures of the karstified limestones that occur just below a regional unconformity. The fluid flow history could be broken down into five stages that were linked to the kinematic and burial history of the region. (1) Petrography (zoned cathodoluminescence and speleothem textures) and stable isotopes (6.5 < δ¹⁸O_V-PDB < ?3.5‰ and 0 < δ¹³C_V-PDB < ?14‰) indicate that the earliest calcite phase was associated with karstification during emergence of the platform. Limestone dissolution at this stage is important with regard to possible reservoir creation in the Panormide palaeogeographic domain. (2) Fine-grained micrite sedimentation, dated as latest Cretaceous by nannopalaeontology and its ⁸⁷Sr/⁸⁶Sr isotope ratio (0.7078), marks replacement by marine fluids during subsequent submergence of the karstified platform. (3) The following calcite cement was still precipitated by marine-derived fluids (?7.0 < δ¹⁸O_V-PDB < ?5.0‰ and ?3.0 < δ¹³C_V-PDB < 0.5‰/T_m = ?2 to ?5 °C), but at increasingly higher temperatures (T_h = 60–120 °C). This has been interpreted as precipitation during Oligocene foredeep burial. (4) Hot (T_h = 130–180 °C), low saline (T_m < ?2.5 °C) fluids with increasingly higher calculated δ¹⁸O_SMOW signatures (+6 to +14‰) subsequently invaded the karst system. These fluids most likely migrated during fold and thrust belt development. The low salinity and relatively high δ¹⁸O_SMOW signatures of the fluids are interpreted to be the result of clay dewatering reactions. The presence of bitumen and associated fluorite with hydrocarbon inclusions at this stage in the paragenesis constrains the timing of oil migration in the region. (5) Finally, high saline fluids with elevated ⁸⁷Sr/⁸⁶Sr (0.7095–0.7105) signatures invaded the karst system. This last fluid flow event was possibly coeval with localized dolomitization and calcite cementation along high-angle faults of Pliocene age, as suggested by identical radiogenic signatures of these diagenetic products.     

Automated high resolution determination of the trace elements iron and aluminium in the surface ocean using a towed Fish coupled to flow injection analysis

A towed surface sampling device coupled to two automated flow injection analysis (FIA) systems is described. The towed system permits uncontaminated sampling of seawater from research vessels while underway at full speed. Coupling the sampler to the FIA systems permits automatic determination of Al and Fe in surface waters at natural levels at 5 min intervals, equivalent to ∼1.5 km spacing at a ship speed of 10 knots (5 m s⁻¹). Results from the tropical Atlantic indicate significant (50%) variation in concentrations of both Al and Fe on space scales of less than 90 km. The combined system facilitates surface mapping of large regions of the ocean for dissolved Al and Fe, thus identifying the sites and magnitude of eolian deposition to the surface ocean. In combination with the determination of nutrients and other biological parameters this permits the investigation of the role that eolian deposition plays in modifying surface water biogeochemical cycles.     

Energy performance evaluation of fishing vessels by fuel mass flow measuring system

A new fuel consumption monitoring system was set up for research purpose in order to evaluate the energy performance of fishing vessels under different operating conditions. The system has been tested on two semi-pelagic pair trawlers in the Adriatic Sea with an engine power of around 900 kW, and with length overall of around 30 m. Both vessels work with a gear of similar design and size, the differences between the two vessels are in the propeller design and the hull material: the first with a controllable pitch propeller (CPP) and a metal hull, the second with a fixed pitch propeller (FPP) and a wooden hull. The fuel monitoring system conceived at CNR-ISMAR Ancona (Italy) consists of two mass flow sensors, one multichannel recorder and one GPS data logger. The working time duration, the vessel speed, the total fuel consumption and the instant fuel rate were logged by the system. A typical commercial round trip for a semi-pelagic trawler consists of several fishing operations (steaming, trawling sailing, etc.). Fuel consumption rate and vessel speed data were used to identify energy performance under different vessel-operating conditions. The highest fuel demands were during the trawling (130 l/h at 4.4 kn) and the steaming (100–130 l/h at 11 kn) phases. Fuel savings of up to 15% could be obtained by reducing the navigation speed of half a knot.     

Compositional and fluorescence characteristics of the giant diatom Ethmodiscus along a 3000 km transect (28°N) in the central North Pacific gyre

The giant diatom Ethmodiscus was examined along an east–west transect at 28–30°N during 2002 and 2003 to determine if abundance, chemical composition or physiological status of this largest of diatoms varied on the scale of 100's–1000's of km in North Pacific gyre. Abundance ranged from <0.1–>2.0 cells m⁻³ and supported the notion of an abundance mosaic reported previously. However, there was only minimal support for the relationship between abundance and nutrient concentration at 125 m reported previously. Cellular chlorophyll varied little along the transect (7.3–10.9 ng chl cell⁻¹) except at the westernmost station. Cellular N and P quotas co-varied 3–4.5 fold (mean=50.8±3.7 and 3.7±0.8 nmol N and P cell⁻¹) and yielded N:P ratios that closely clustered around the Redfield ratio (average=14.6±1.1). Only low levels of chlorophyll-normalized alkaline phosphatase (APase) activity were observed (0.4–2.5 nmol P μg chl⁻¹ h⁻¹) with APase activity lower than that in either the bulk water, or co-occurring Trichodesmium spp. and Pyrocystis noctiluca. The active fluorescence parameter F_v:F_m, a property sensitive to Fe stress, was uniformly high at all stations (average=0.73±0.04 for 2003, and 0.69±0.05 for 2002), indicating sufficient Fe for optimum photosynthetic competence. These results contrasted sharply with results from Rhizosolenia mats reported along the same transect where there was a significant decline westward in F_v:F_m. Both ferredoxin (Fd) and flavodoxin accumulated in cells of Ethmodiscus, resulting in Fd Index values of<0.6. Iron cell quotas ranged from 0.7–5.1 pmol Fe cell⁻¹. When normalized to cytoplasmic volume, the Fe μm⁻³ was comparable to that of Escherichia coli. We note that the disproportionate contribution of the vacuole (with its high organic content) to total volume typical of large diatoms is a potentially significant source of error in Fe:C ratios and suggest that Fe should be normalized to cytoplasmic volume whenever possible to permit valid intercomparisons between studies. The composition, F_v:F_m data and Fe:C ratio suggest a relatively uniform population experiencing little N, P or Fe stress. The uncoupling of the Fd Index from these measures is consistent with previous findings showing that the expression of flavodoxin can be characterized as an early stress response and that its accumulation is not necessarily correlated with physiological deficit. Ethmodiscus appears to be well adapted to some of the most oligotrophic waters in the ocean. Because it is an important sedimentary marker, the biology of living Ethmodiscus provides insights into the source of extensive Ethmodiscus oozes. Mass sedimentation after frontal accumulation has been suggested as a source for these oozes. Our data contain no evidence that the flux is linked directly to Fe, N or P stress.     

Geometry and migration characteristics of bedforms under waves and currents: Part 2: Ripples superimposed on sandwaves

This paper presents results of a series of detailed measurements of geometric and migrating characteristics of ripples superimposed upon sandwaves under the action of combined waves and currents. Velocity measurements within the fluid, surface wave characteristics and 3D mapping of the bottom were recorded with an Acoustic Doppler Velocimeter (ADV), an acoustic water level sensor and a 32 composite element array of sub-aquatic acoustic sensors, respectively. Bottom records were statistically analyzed to obtain height, length and migration rates of ripples. Experiments examined ripple heights and wavelengths for the mobility factors (as defined in Eq. (4)) and the Reynolds wave number within the ranges 10 < ψ < 88 and 16 × 10³ < Re_w < 5 × 10⁵, respectively. Measured values were compared with laboratory and field data together with semi-empirical and analytical formulae from the literature. Good correlation was obtained when plotting measured ripple length and length in dimensionless form as a function of the Reynolds wave number Re_w. Under a given hydraulic condition, it was observed that ripples with different geometric characteristics may coexist at different locations over the sandwave. Ripple steepness is presented as a function of the Shields parameter although characterized with rather large scatter. Finally, average ripple migration speed is presented as a function of the Shields parameter and the mobility number.     

The western boundary current in the Bransfield Strait,Antarctica

The Bransfield Strait west of the Antarctic Peninsula has been considered as a highly productive region for all trophic levels from primary production, to zooplankton aggregations, especially krill, to birds and mammals. The western boundary current, referred to as the Bransfield Current, plays an important role in determining the transport and retention of biota in the Bransfield Strait. Following the study of surface current characteristics in the strait using 39 tracks of mixed-layer drifters deployed between 1988 and 1990, a high-resolution transect of temperature, salinity and current measurements crossing the Bransfield Current was conducted between 13 and 14 March 2004, for understanding its horizontal and vertical structure and dynamics. The results from current, temperature and salinity measurements using a vessel mounted narrow band acoustic doppler current profiler and conductivity–temperature–depth (CTD) sensors revealed the magnitude of this current of approximately 50 cm/s within a horizontal distance of 15 km associated with a narrow and deep density front 4–6 km wide and 500 m deep. The comparison between the direct current measurements and the geostrophic current estimates from the density field implies that the Bransfield Current is geostrophically balanced. The mechanism forming this current is explored with Sverdrup dynamics. Results indicate that the negative wind stress curl and β-effect lead to a southwestward transport in the Bransfield Strait. When this transport is restricted by land and shelves, a narrow western boundary current is formed.     

The role of combined laser scanning and video techniques in monitoring wave-by-wave swash zone processes

Simulating swash zone morphodynamics remains one of the major weaknesses of beach evolution models. One of the reasons is the limited availability of data on morphological changes at the temporal scales of individual swash events. This paper sets out to present a new hybrid system, consisting of 2D/3D laser scanners and several video cameras, which was designed to monitor swash zone topographic change on a wave-by-wave basis. A methodology is proposed consisting of sensor calibration and several data processing steps, allowing a fusion of different sensors. Such an approach can improve the performance of several field/laboratory, optical technique applications for nearshore hydro- and morpho-dynamic measurements. Digital Elevation Models from a 3D scanner were used in the extrinsic camera calibration procedure and reduced the geo-rectification errors from 0.035 m < RMSE < 0.071 m to 0.008 m < RMSE < 0.013 m. The 2D scanner provided instantaneous measurements of the water and dry beach surface elevation along a 10 m cross-shore section, and comparison with ultrasonic sensor measurements resulted in RMS errors within the 1.7 cm < RMSE < 3.2 cm range. The combination of 2D scanner and video data (i) reduced geo-rectification errors by more than one order of magnitude; and (ii) made 2D laser point cloud processing easier and more robust. The hybrid monitoring system recorded the morphological change of a replenished beach-face on a wave-by-wave basis, during large-scale, physical modeling experiments and the observations showed that individual swash events could result in elevation changes up to dz = ± 10 cm. The sediment transport direction and intensity of the monitored swash events was relatively balanced and sediment transport rates ranged between − 3.5 kg m^− 1 s^− 1 > Q_t > 3.5 kg m^− 1 s^− 1. Extreme transport swash events became rarer as the morphology was reaching equilibrium.     

The influence of the south-west monsoon upon the nutrient biogeochemistry of the Arabian Sea

Variations in the nutrient concentrations were studied during two cruises to the Arabian Sea. The situation towards the end of the southwest monsoon season (September/October 1994) was compared with the inter-monsoonal season during November and December 1994. Underway surface transects showed the influence of an upwelling system during the first cruise with deep, colder, nutrient-rich water being advected into the surface mixed layer. During the southwesterly monsoon there was an area of coastal Ekman upwelling, bringing colder water (24.2°C) into the surface waters of the coastal margin. Further offshore at about 350 km there was an area of Ekman upwelling, as a result of wind-stress curl, north of the Findlater Jet axis; this area also had cooler surface water (24.6°C). Further offshore (>1000 km) the average surface temperatures increased to >27°C. These waters were oligotrophic with no evidence of the upwelling effects observed further inshore. In the upwelling regions nutrient concentrations in the close inshore coastal zone were elevated (NO₃=18 μmol l^-1, PO₄=1.48 μmol l^-1); higher concentrations also were measured at the region of offshore upwelling off the shelf, with a maximum nitrate concentration of 12.5 μmol l^-1 and a maximum phosphate concentration of 1.2 μmol l^-1. Nitrate and phosphate concentrations decreased with increasing distance offshore to the oligotrophic waters beyond 1400 km, where typical nitrate concentrations were 35.0 nmol l^-1 (0.035 μmol l^-1) in the surface mixed layer. A CTD section from the coastal shelf, to 1650 km offshore to the oligotrophic waters, clearly showed that during the monsoon season, upwelling is one of the major influences upon the nutrient concentrations in the surface waters of the Arabian Sea off the coast of Oman. Productivity of the water column was enhanced to a distance of over 800 km offshore. During the intermonsoon period a stable surface mixed layer was established, with a well-defined thermocline and nitracline. Surface temperature was between 26.8 and 27.4°C for the entire transect from the coast to 1650 km offshore. Nitrate concentrations were typically between 2.0 and 0.4 μmol l^-1 for the transect, to about 1200 km where the waters became oligotrophic, and nitrate concentrations were then typically 8–12 nmol l^-1. Ammonia concentrations for the oligotrophic waters were typically 130 nmol l^-1, and are reported for the first time in the Indian Ocean. The nitrogen/phosphorus (N/P) ratios suggest that phytoplankton production was potentially nitrogen-limited in all the surface waters of the Arabian Sea, with the greatest nitrogen limitation during the intermonsoon period.     

ScotMap: Participatory mapping of inshore fishing activity to inform marine spatial planning in Scotland

A detailed understanding of fishing activity in Scottish waters is required to inform marine spatial planning. Larger fishing vessels are fitted with Vessel Monitoring Systems (VMS) offering spatial information on fishing activity. VMS does not cover smaller vessels (under 15 m), which fish predominantly in inshore waters where the competition for space is often greatest. To improve knowledge of the distribution of fishing activity and value of fisheries in Scotland's inshore waters, Marine Scotland conducted a participatory fisheries mapping project, known as ScotMap. The data were collected during face-to-face interviews with 1090 fishermen of Scottish registered commercial fishing vessels under 15 m in overall length and relate to fishing activity for the period 2007–2011. Interviewees were asked to identify the areas in which they fish, estimate the contribution these areas make to vessel earnings, and to provide associated information. The majority of interviews relate to creel fishing. The data collected were aggregated to provide mapped outputs of the monetary value, relative importance to fishermen and the usage of the seas around Scotland (number of fishing vessels and number of crew). ScotMap outputs provide information on the locations of inshore fishing activities and the economic importance of different sea areas at a much higher spatial resolution than was previously possible. Outputs have informed marine policy development, provide a valuable resource for marine spatial planning in Scotland and illustrate how participatory mapping can generate useful resources on the location and importance of inshore fishing areas.     

Hydrolytic ectoenzyme activity associated with suspended and sinking organic particles within the anoxic Cariaco Basin

Ectohydrolase activities of suspended microbiota were compared to those associated with sinking particles (sed-POM) retrieved from sediment traps deployed in the permanently anoxic Cariaco Basin. In shore-based assays, activities of aminopeptidase, β-glucosidase, chitinase and alkaline phosphatase were measured in samples obtained from oxic and anoxic depths using MUF- and MCA-labeled fluorogenic substrate analogs. Hydrolysis potentials for these enzymes in the seston varied widely over the nine cruises sampled (8 Nov 1996–3 May 2000) and among depths (15–1265 m); from <10 to over 1600 nM d^?1 hydrolysate released, generally co-varying with one another and with suspended particulate organic carbon (POC) and particulate nitrogen (PN). Hydrolytic potentials, prokaryotic abundances and POC/PN concentrations in sinking debris were 400–1.3×10⁷ times higher than in comparable volumes of seawater. However when normalized to PN, hydrolytic potentials in sediment trap samples were not demonstrably higher than in Niskin bottle samples. We estimate that PN pools in sediment trap samples were turned over 2–1400 times (medians=7–26x) slower by hydrolysis than were suspended PN pools. Median prokaryotic growth rates (divisions d^?1) in sinking debris were also ～150 times slower than for bacterioplankton. Hydrolytic potentials in surface oxic waters were generally faster than in underlying anoxic waters on a volumetric basis (nM hydrolysate d^?1), but were not significantly (p>0.05) different when normalized to PN or prokaryote abundances. Alkaline phosphatase was consistently the most active ectohydrolase in both sample types, suggesting that Cariaco Basin assemblages were adapted to decomposing phosphate esters in organic polymers. However, phosphorus limitation was not evident from nutrient inventories in the water column. Results support the hypothesis that efficiencies of polymer hydrolysis in anoxic waters are not inherently lower than in oxic waters.     

Population ecology and habitat preferences of juvenile flounder Platichthys flesus (Actinopterygii: Pleuronectidae) in a temperate estuary

The European flounder Platichthys flesus is a widely distributed epibenthic species and an important component of demersal fish assemblages in the European Atlantic coastal waters. In Portuguese estuaries, this species reaches high densities, especially in Minho estuary (NW Iberian Peninsula, Europe), potentially playing an important role in the system's ecology. In this context, the population structure, production and the habitat use of juvenile P. flesus were investigated. Sampling took place monthly, from February 2009 until July 2010 along the entire estuarine gradient (5 sampling stations distributed in the first 29 km from the river mouth, with S1 located near the river mouth, S2 inside a salt marsh, S3 in a salinity transition zone, while S4 and S5 were located in the upper estuary). Flounder's density varied significantly among sampling stations and seasons (two-way PERMANOVA: p < 0.001), with the majority of the individuals being found during the spring (30.1%) and in S3 and S4 (72.6%). Males and females presented an even distribution, with a higher proportion of males observed during summer. Fish length also differed among sampling stations and seasons (two-way PERMANOVA: p < 0.001), with larger fishes being found in S1 during the autumn (168.50 ± 59.50 mm) and the smallest in S4 during the spring (33.80 ± 3.12 mm). Size classes associated differently with environmental variables, with larger juveniles being more abundant in the downstream areas of the estuary, whereas smaller juveniles were related to higher water temperatures, suggesting a habitat segregation of P. flesus of different sizes. The fish condition of P. flesus in Minho estuary was higher than in other systems, probably due to the dominance of juveniles on the population. Also, the densities found in this estuary were up to 32 times higher than in other locations, suggesting that Minho estuary is an important nursery area for the species. The estimated secondary production of P. flesus was lower than previous studies acknowledged in the system (0.037 g.WWm^− 2.year^− 1), indicating that the production estimates of this species in estuaries can vary considerably depending on of several factors such as the sampling year and strategy, population and fish size.     

Effects of mesoscale phytoplankton variability on the copepods Neocalanus flemingeri and N. plumchrus in the coastal Gulf of Alaska

The copepods Neocalanus flemingeri and N. plumchrus are major components of the mesozooplankton on the shelf of the Gulf of Alaska, where they feed, grow and develop during April–June, the period encompassing the spring phytoplankton bloom. Satellite imagery indicates high mesoscale variability in phytoplankton concentration during this time. Because copepod ingestion is related to food concentration, we hypothesized that phytoplankton ingestion by N. flemingeri and N. plumchrus would vary in response to mesoscale variability of phytoplankton. We proposed that copepods on the inner shelf, where the phytoplankton bloom is most pronounced, would be larger and have more lipid stores than animals collected from the outer shelf, where phytoplankton concentrations are typically low. Shipboard feeding experiments with both copepods were done in spring of 2001 and 2003 using natural water as food medium. Chlorophyll concentration ranged widely, between 0.32 and 11.44 μg l⁻¹ and ingestion rates varied accordingly, between 6.0 and 627.0 ng chl cop⁻¹ d⁻¹. At chlorophyll concentrations<0.50 μg l⁻¹, ingestion is always low, <40 ng cop⁻¹ d⁻¹. Intermediate ingestion rates were observed at chlorophyll concentrations between 0.5 and 1.5 μg l⁻¹, and maximum rates at chlorophyll concentrations>1.5 μg l⁻¹. Application of these feeding rates to the phytoplankton distribution on the shelf allowed locations and time periods of low, intermediate and high daily feeding to be calculated for 2001 and 2003. A detailed cross-shelf survey of body size and lipid store in these copepods, however, indicated they were indistinguishable regardless of collection site. Although the daily ingestion of phytoplankton by N. flemingeri and N. plumchrus varied widely because of mesoscale variability in phytoplankton, these daily differences did not result in differences in final body size or lipid storage of these copepods. These copepods efficiently dealt with small and mesoscale variations in their food environment such that mesoscale structure in phytoplankton did not affect their final body size.     

Zooplankton distribution across Fram Strait in autumn: Are small copepods and protozooplankton important?

We investigated zooplankton distribution in September 2006/2007 at eight stations across Fram Strait in contrasting water masses ranging from cold Polar water to warm Atlantic water. Our main objectives were: (1) to describe the plankton community in the upper 200 m during autumn, and (2) to investigate the importance of small-sized copepods and protozooplankton in an arctic ecosystem when the majority of the large Calanus species had entered diapause. We sampled both with a WP-2 net and Go-Flo bottle and show that small copepods <1 mm are significantly undersampled using a WP-2 net with 90 μm mesh.Small copepods and protozooplankton made a significant contribution both in terms of abundance and total zooplankton biomass at all stations in September, when the large calanoid copepods had left the upper 200 m. The dominating group in the upper 60 m at all stations was Oithona spp. nauplii and their daily estimated grazing potential on the <10 μm phytoplankton ranged from 0.1% to 82% of the standing stock. Both Oithona copepodites and nauplii biomass showed a significantly positive relation with temperature, but not with potential food. Heterotrophic protozooplankton, on the other hand, were most likely bottom-up regulated by the availability of phytoplankton <10 μm. We hypothesise that Oithona nauplii and protozooplankton compete for food and conclude that there was a strong link between the zooplankton community and the microbial food web in Fram Strait.     

Metazoan meiofauna within the oxygen-minimum zone off Chile: Results of the 2001-PUCK expedition

A quantitative study of metazoan meiofauna was carried out at continental shelf and slope stations affected by the oxygen-minimum zone in the eastern South Pacific off Chile. Densities of meiobenthos at the investigated stations off Antofagasta (22°S), Concepción (36°S), and Chiloé (42°S) ranged from 1282.1 to 8847.8 ind 10 cm⁻². Oxygen deficiency led only to average abundances, despite higher food availability and freshness at the corresponding sites. Sediment organic carbon, chlorophyll-a, and phaeopigment contents were used as measures of the input from water-column primary production, which accumulated at the oxygen-minimum zone stations. The highest abundances were found at a station with an oxygen content of 0.79 mL L⁻¹, which was slightly elevated from what is defined as oxygen minimum (0.5 mL L⁻¹). The most oxygenated site yielded the lowest densities. Meiofauna assemblages became more diverse with increasing bottom-water oxygenation, whereas nematodes were the most abundant taxon at every station, followed by annelids, copepods, and nauplii.     

Field and laboratory studies on the effect of particle size and composition on optical backscattering measurements in hydrothermal plumes

We describe the performance of an inexpensive but highly sensitive light backscattering sensor (LBSS) suitable for use in deep-sea waters, where particle concentrations are typically <∼0.1 mg/l. Laboratory calibrations using aluminosilicate particles and latex spheres show that the concentration-normalized backscattering of the LBSS, K_bs, is greatest for particles with a diameter close to the wavelength of light emitted by the LBSS (0.88 μm), declining by more than a factor of five for particles <0.1 μm or >10 μm. Field studies indicate that in hydrothermal plumes dominated by fine-grained metal precipitates the 95% confidence interval for predicting mass concentration with an LBSS ranges from ±0.004 mg/l for 0.03 mg/l suspensions to ±0.008 mg/l at 0.12 mg/l. Comparisons among a group of 19 LBSSs found between-instrument variability to reach 70%, but normalizing the raw data using a laboratory calibration procedure reduced the maximum variability to ∼8%.