Respiration rate and cost of swimming for Antarctic krill,<Emphasis Type="Italic"> Euphausia superba</Emphasis>, in large groups in the laboratory

Constructing realistic energy budgets for Antarctic krill, Euphausia superba, is hampered by the lack of data on the metabolic costs associated with swimming. In this study respiration rates and pleopod beating rates were measured at six current speeds. Pleopod beating rates increased linearly with current speed, reaching a maximum of 6 beats s^–1 at 17 cm s^–1. There was a concomitant linear increase in respiration rate, from 1.8 mg O₂ g_D^–1 h^–1 at 3 cm s^–1 to 8.0 mg O₂ g_D^–1 h^–1 at 17 cm s^–1. The size of the group tested (50, 100 and 300 krill) did not have a significant effect on pleopod beating rates or oxygen consumption (ANCOVA, F=0.264; P>0.05). The cost of transport reached a maximum of 75 J g^–1 km^–1 at 5 cm s^–1, and then decreased with increasing current speed to 29 J g^–1 km^–1. When considered in light of energy budgets for E. superba, these data indicate that the cost of swimming could account for up to 73% of total daily metabolic expenditure during early summer.Communicated by G.F. Humphrey, Sydney     

Life in a warm deep sea: routine activity and burst swimming performance of the shrimp<Emphasis Type="Italic"> Acanthephyra eximia</Emphasis> in the abyssal Mediterranean

Measurements of routine swimming speed, tail-flip escape responses, and oxygen consumptions were made of the deep-sea shrimp Acanthephyra eximia using autonomous landers in the Rhodos Basin at depths of up to 4,400 m and temperatures of 13–14.5°C. Routine swimming speeds at 4,200 m averaged 0.18 m s^–1 or 3.09 body lengths s^–1, approximately double those of functionally similar oceanic scavengers. During escape responses peak accelerations of 23 m s^–2 or 630.6 body lengths s^–2 were recorded, with animals reaching speeds of 1.61 m s^–1 or 34.8 body lengths s^–2. When compared to shallow-water decapods at similar temperatures these values are low for a lightly calcified shrimp such as A. eximia despite a maximum muscle mass specific power output of 90.0 W kg^–1. A preliminary oxygen consumption measurement indicated similar rates to those of oceanic crustacean scavengers and shallower-living Mediterranean crustaceans once size and temperature had been taken into account. These animals appear to have high routine swimming speeds but low burst muscle performances. This suite of traits can be accounted for by high competition for limited resources in the eastern Mediterranean, but low selective pressure for burst swimming due to reductions in predator pressure.Communicated by J.P. Thorpe, Port Erin     

Behavior and growth ofMercenaria mercenaria during simulated storm events

Experiments were conducted in April–August 1989 on juvenileMercenaria mercenaria (L.) in an oscillatory water tunnel to simulate resuspension of bottom sediments by waves and to determine the effects of shortterm storm events on particle ingestion, pseudofeces production, and shell growth. Juveniles (mean length = 19.2 mm) were subjected to identical concentrations of algae in both low-flow, gentle waves (maximum velocity = 7 cm s^–1) and high-velocity storm waves (maximum velocity = 22 cm s^–1). Suspended sediment levels reached 193 mg 1^–1 at 1 cm above the bed during storms. Shell growth decreased by a maximum of 38% during the storm when levels of phytoplankton were high (average cell concentration = 43 × 10⁶ cells 1^–1), and by 18% when phytoplankton levels were low (av cell conc = 6 × 10⁶ cells 1^–1). Orientation of clam siphons was not related to flow direction. Significantly more pseudofeces were produced when the clams were subjected to increased sediment resuspension under waves, and in troughs of sand ripples. The size of sediment grains ingested did not vary significantly among the flow treatments. The decrease in shell growth during storms may be due to a reduction in filtration rate coupled with a decrease in net energy gained from filtration due to costs of pseudofeces production. The magnitude of the decrease seems to be related to concentration of algae, water temperature, age of clams and sediment transport mode (bed load or suspended load). Thus, the interpretation of growth increments must be made in the context of these environmental variables.     

Effect of temperature on the escape responses of larval herring,Clupea harengus

Herring (Clupea harengus L.) larvae from spring and autumn spawning stocks were reared at different constant temperatures from 5° to 17 °C. At equivalent developmental stages, the spring larvae were longer than the autumn larvae and the larvae reared at low temperatures were longer than those reared at high temperatures. At hatching and at the end of the yolk-sac stage, the larvae were induced, by a probe, to make C-start escape responses, which were recorded and analysed using a high-speed video recording at 400 frames s^-1. The response was rapid and of short duration. The tailbeat frequency and swimming speed were measured during the burst of swimming following the C-start at different test temperatures and in larvae with different temperature histories. The tail-beat frequency was strongly temperature-dependent, rising from 19 Hz at 5 °C to 37 Hz at 17 °C with no effect of temperature history, season or developmental stage. The burst-swimming speed ranged at hatching from 75 to 90 mm s^-1 at 5 °C to 110 to 160 mm s^-1 at 17 °C and at yolk resorption from 90–115 mm s^-1 at 5 °C to 175–190 mm s^-1 at 17 °C. The longer, spring-spawned larvae swam faster than the shorter autumn-spawned larvae. When the swimming speeds were expressed as body lengths (L) s^-1, these differences disappeared. Larvae swam from 7–9 L s^-1 at 5 °C to 15–20 L s^-1 at 17 °C at hatching, and from 8–9 L s^-1 at 5 °C to 15–17 L s^-1 at 17 °C at yolk resorption. There was, however, a significantly faster specific swimming speed by the larvae reared at 12 °C in spring 1991.Honorary Research Fellow of the Scottish Association for Marine ScienceUnfortunately, Karen Fretwell was drowned in an accident on 9 January 1993     

Respiration,photosynthesis and carbon metabolism in planktonic ciliates

Release of¹⁴C-labelled carbon dioxide from uniformly labelled cells was used to measure respiration by individual ciliates in 2-h incubations in 1989 and 1990. In a strictly heterotrophic ciliate,Strobilidium spiralis (Leegaard, 1915), release of labelled carbon dioxide was equivalent to ca. 2.8% of cell C h^–1 at 20°C, and there was no difference between rates in the dark and light. In the chloroplast-retaining ciliatesLaboea strobila Lohmann, 1908,Strombidium conicum (Lohmann, 1908) Wulff, 1919 andStrombidium capitatum (Leegaard, 1915) Kahl, 1932, release of labelled carbon dioxide was less in the light than in the dark in experiments done at 15°C. InL. strobila release of radiolabel as carbon dioxide was equivalent to ca. 2.4% of cell C h^–1 in the dark but ca. 1% at 50µE m^–2 s^–1, an irradiance limiting to photosynthesis. InS. conicum release of radiolabel as carbon dioxide was equivalent to ca. 4.4% of cell C h^–1 in the dark, but at an irradiance saturating to photosynthesis (250 to 300µE m^–2 s^–1) there was no detectable release of labelled carbon dioxide. InS. capitatum release of radiolabel as carbon dioxide was equivalent to ca. 4.3% of cell C h^–1 in the dark but at an irradiance saturating to photosynthesis was ca. 2.4% of cell C h^–1. These data, combined with data from photosynthetic uptake experiments, indicate that¹⁴C uptake underestimates the total benefit of photosynthesis by 50% or more in chloroplastretaining ciliates.Contribution no. 7510 from the Woods Hole Oceanographic Institution     

Ultrasonic tracking of Greenland sharks,<Emphasis Type="Italic"> Somniosus microcephalus</Emphasis>, under Arctic ice

Six Greenland sharks, Somniosus microcephalus (Bloch and Schneider, 1801), 190–355 cm fork length, were tracked under land-fast sea ice off northern Baffin Island (73.2°N; 85.3°W) between 16 and 28 May 1999, using ultrasonic telemetry. The sharks were tracked continuously for periods of 5.5–13.0 h, with the tracks of two individuals lasting 31.4 and 42.8 h, respectively, each with an interval when the track was lost. Several sharks dove after release and moved along the ocean bottom for the duration of the tracking period, while others varied their movements regarding course and depth. Two sharks made repeated visits to within 11 m of the ice–water interface from deeper water. The tracked sharks exhibited no apparent depth or temperature preferences, and pooled data indicated that sharks remained deep during the morning and gradually moved into shallower depths through the afternoon and night. Rates of descent (average=0.099 m s^–1) were significantly greater than rates of ascent (average=0.058 m s^–1) for all sharks, and the average rate of horizontal movement over ground was estimated as 0.215 m s^–1. Based on the movements of tracked sharks and information contained in the literature, S. microcephalus may prey on seals in areas covered by land-fast sea ice.Communicated by J.P. Grassle, New Brunswick     

Photosynthetic performance of Laminaria solidungula measured in situ in the Alaskan High Arctic

Photosynthetic performance in the kelp Laminaria solidungula J. Agardh was examined from photosynthesis irradiance (P-I) parameters calculated from in situ ¹⁴C uptake experiments, using whole plants in the Stefansson Sound Boulder Patch, Alaskan Beaufort Sea, in August 1986. Rates of carbon fixation were determined from meristematic, basal blade, and second blade tissue in young and adult sporophytes. Differences in saturating irradiance (I _k, measured as photosynthetically active radiation, PAR), photosynthetic capacity (P _max), and relative quantum efficiency () were observed both between young and adult plants and between different tissue types. I _k was lowest in meristematic tissue (20 to 30 E m^–2 s^–1) for both young and adult plants, but consistently 8 to 10 E m^–2 s^–1 higher in young plants compared to adults in all three tissues. Average I _k for non-meristematic tissue in adult plants was 38 E m^–2 s^–1. Under saturating irradiances, young and adult plants exhibited similar rates of carbon fixation on an area basis, but under light limitation, fixation rates were highest in adult plants for all tissues. P _max was generally highest in the basal blade and lowest in meristematic tissue. Photosynthetic efficiency () ranged between 0.016 and 0.027 mol C cm^–2 h^–1/E m^–2 s^–1, and was highest in meristematic tissue. The relatively lower I _k and higher exhibited by L. solidungula in comparison to other kelp species are distinct adaptations to the near absence of light during the eight-month ice-covered period and in summer when water turbidity is high. Continuous measurement of in situ quantum irradiance made in summer showed that maximum PAR can be less than 12 E m^–2 s^–1 for several days when high wind velocities increase water turbulence and decrease water transparency.The Univeristy of Texas Marine Science Institute Contribution No. 695     

Seasonal and depth related variation in the photosynthesis–irradiance response of<Emphasis Type="Italic"> Ecklonia radiata</Emphasis> (Phaeophyta,Laminariales) at West Island,South Australia

The photosynthesis–irradiance response of Ecklonia radiata (C. Agardh) J. Agardh, a common kelp in the temperate southern hemisphere, was investigated in situ throughout the year and across a depth profile at West Island, South Australia. Temperature and irradiance environment altered throughout the year, varying at 3 m between 14–20°C and 279–705 mol photons m^–2 s^–1. Photosynthetic capacity (P_m) varied throughout the year between 177–278 mol O₂ g^–1 dry wt h^–1 at 3 m and 133–348 mol O₂ g^–1 dry wt h^–1 at 10 m. The irradiance required for sub-saturation of photosynthesis (E_k) varied between 97–152 and 81–142 mol photons m^–2 s^–1 for 3 m and 10 m respectively, and the respiration rate varied between 15–36 and 13–20 mol O₂ g^–1 dry wt h^–1 for 3 m and 10 m. A clear seasonal change in photokinetic parameters was detected and provided strong evidence for a seasonal acclimation response. During winter an increase in the efficiency of light utilisation at low irradiance () was accompanied by a decrease in both E_k and that required for photosynthetic compensation. P_m also increased during the winter and autumn months and respiratory requirements decreased. These changes enable E. radiata to display an optimal photosynthetic performance throughout the year despite significant changes in the surrounding environment.Communicated by P.W. Sammarco, Chauvin     

Diel vertical migration of the marine copepod<Emphasis Type="Italic"> Calanopia americana</Emphasis>. II. Proximate role of exogenous light cues and endogenous rhythms

The marine copepod Calanopia americana Dahl undergoes twilight diel vertical migration (DVM) in the Newport River estuary, North Carolina, USA, in synchrony with the light:dark cycle. Copepods ascend to the surface at sunset, descend to the bottom around midnight, and make a second ascent and descent before sunrise. Behavioral assays with C. americana in the laboratory during fall 2002/2003 and summer 2004 investigated aspects of three hypotheses for the proximate role of light in DVM: (1) preferendum hypothesis (absolute irradiance), (2) rate of change hypothesis (relative rates of irradiance change), and (3) endogenous rhythm hypothesis. Results suggest that C. americana responds to exogenous light cues consistent with its DVM pattern; changes in absolute irradiance evoked swimming responses that would result in an ascent at sunset and descent at sunrise, while relative rates of irradiance decrease at sunset (–0.0046 s^–1) evoked an ascent response, and relative rates of irradiance increase at sunrise (0.0042 s^–1) evoked a descent response. Furthermore, C. americana expressed an endogenous rhythm in vertical migration that was positively correlated with field observations of twilight DVM. Collectively, these results indicate that both exogenous light cues and endogenous rhythms play a proximate role in twilight DVM of C. americana, providing redundancy in the causes of its vertical migration.Communicated by J.P. Grassle, New Brunswick     

Growth pattern andβ-dimethylsulphoniopropionate (DMSP) content of green macroalgae at different irradiances

Growth rates and intracellular-dimethylsulphoniopropionate (DMSP) concentrations of five green algal species collected from different geographic regions in 1986 and 1989 were determined under four photon flux rates. InUlothrix implexa, U. subflaccida andAcrosiphonia arcta from Antarctica, growth was light-saturated at lower irradiances than in temperateUlva rigida from Southern Chile andBlidingia minima from Germany. The DMSP content ofUlothrix implexa, A. arcta andUlva rigida was directly correlated with the light factor: with increasing irradiance, algal DMSP level increased. In contrast, inUlothrix subflaccida andB. minima DMSP concentrations gradually decreased up to a photon flux rate of 30µmol m^–2 s^–1, then increased markedly under the highest photon flux rate tested. In non-growing, dark-incubatedA. arcta DMSP content was reduced by 35%, while the DMSP pool of all other species remained unchanged, at the level of pre-culture conditions. Under full darkness all plants exhibited a significantly higher DMSP concentration compared with algae grown at low photon flux rates of 2 to 30µmol m^–2 s^–1. These data show a correlation between growth pattern and DMSP biosynthesis, and may point to a species-specific minimum amount of light energy necessary for DMSP accumulation.Contribution no. 302 of the Alfred Wegener Institute of Polar and Marine Research     

Experimental Study of Gas-Liquid Interfacial Properties in a Stepped Cascade Flow

Gas-liquid interface measurements were conducted in a strongly turbulent free-surface flow (i.e., stepped cascade). Local void fractions, bubble count rates, bubble size distributions and gas-liquid interface areas were measured simultaneously in the air-water flow region using resistivity probes. The results highlight the air-water mass transfer potential of a stepped cascade with measured specific interface area over 650 m^–1 and depth-average specific area up to 310 m^–1. A comparison between single-tip and double-tip resistivity probes suggests that simple robust single-tip probes may provide accurate, although conservative, gas-liquid interfacial properties. The latter device may be used in the field and in prototype plants. Notation a = specific interface area (m^–1); a _mean = depth-average specific interface area (m^–1): a _mean=frac1Y ₉₀limits sup> Y ₉₀ sup ₀(1–C)dy; C = local void fraction; C _gas = dissolved gas concentration (kg m^–3); C _mean = depth-average mean air concentration defined as: C _mean=1–d/Y ₉₀; C _s = saturation concentration (kg m^–3); D = dimensionless air bubble diffusivity (defined by [1]); d = equivalent clear-water flow depth (m): d=limits sup> Y ₉₀ sup ₀(1–C) dy; d_ab = air bubble diameter (m); d_c = critical flow depth (m); for a rectangular channel: d _c=sqrt[3]q _w ²/g; F = air bubble count rate (Hz); F _max = maximum bubble count rate (Hz), often observed for C=50%; g = gravity acceleration (m s^–2); h = step height (m); K _L = liquid film coefficient (m s^–1); K = integration constant defined as: K=tanh ^–1 sqrt0.1)+(2D)^–1 [1]; L = chute length (m); N = velocity distribution exponent; ———– ^*Corresponding author, E-mail: h.chanson@mailbox.uq.edu.au Q _w = water discharge (m³ s^–1); q _w = water discharge per unit width m² s^–1); t = time (s); V = local velocity (m s^–1); V _c = critical flow velocity (m s^–1); for a rectangular channel: V _c=sqrt[3]q _w g V _max = maximum air-water velocity (m s^–1); V ₉₀ = characteristic air-water velocity (m s^–1) where C = 90%; W = channel width (m); x = longitudinal distance (m) measured along the flow direction (i.e., parallel to the pseudo-bottom formed by the step edges); y = distance (m) normal to the pseudo-bottom formed by the step edges; Y₉₀ = characteristic distance (m) where C=0.90; Y ₉₈ = characteristic distance (m) where C=0.98; = slope of pseudo-bottom by the step edges; = diameter (m).     

Photosynthetic characteristics of Prochloron sp./ascidian symbioses

The prokaryotic green alga Prochloron sp. (Prochlorophyta) is found in symbiotic association with colonial didemnid ascidians that inhabit warm tropical waters in a broad range of light environments. We sought to determine the light-adaptation features of this alga in relation to the natural light environments in which the symbioses are found, and to characterize the temperature sensitivity of photosynthesis and respiration of Prochloron sp. in order to assess its physiological role in the productivity and distribution of the symbiosis. Colonies of the host ascidian Lissoclinum patella were collected from exposed and shaded habitats in a shallow lagoon in Palau, West Caroline Islands, during February and March, 1983. Some colonies from the two light habitats were maintained under conditions of high light (2 200 E m^–2 s^–1) and low light (400 E m^–2 s^–1) in running seawater tanks. The environments were characterized in terms of daily light quantum fluxes, daily periods of light-saturated photosynthesis (H_sat), and photon flux density levels. Prochloron sp. cells were isolated from the hosts and examined for their photosynthesis vs irradiance relationships, respiration, pigment content and photosynthetic unit features. In addition, daily P:R ratios, photosynthetic quotients, carbon balances and photosynthetic carbon release were also characterized. It was found that Prochloron sp. cells from low-light colonies possessed lower chlorophyll a/b ratios, larger photosynthetic units sizes based on both reaction I and reaction II, similar numbers of reaction center I and reaction center II per cell, lower respiration levels, and lower P_max values than cells from high-light colonies. Cells isolated from low-light colonies showed photoinhibition of P_max at photon flux densities above 800 E m^–2 s^–1. However, because the host tissue attenuates about 60 to 80% of the incident irradiance, it is unlikely that these cells are normally photoinhibited in hospite. Collectively, the light-adaptation features of Prochloron sp. were more similar to those of eukaryotic algae and vascular plant chloroplasts than to those of cyanobacteria, and the responses were more sensitive to the daily flux of photosynthetic quantum than to photon flux density per se. Calculation of daily minimum carbon balances indicated that, though high-light cells had daily P:R ratios of 1.0 compared to 4.6 for low-light cells, the cells from the two different light environments showed nearly identical daily carbon gains. Cells isolated from high-light colonies released between 15 and 20% of their photosynthetically-fixed carbon, levels sufficient to be important in the nutrition of the host. Q₁₀ responses of photosynthesis and respiration in Prochloron sp. cells exposed briefly (15–45 min) to temperatures between 15° and 45°C revealed a discontinuity in the photosynthetic response at the ambient growth temperatures. The photosynthetic rates were found to be more than twice as sensitive to temperatures below ambient (Q₁₀=3.47) than to temperatures above ambient (Q₁₀=1.47). The Q₁₀ for respiration was constant (Q₁₀=1.66) over the temperature range examined. It appears that the photosynthetic temperature sensitivity of Prochloron sp. may restrict its distribution to warmer tropical waters. The ecological implications of these findings are discussed in relation to published data on other symbiotic systems and free-living algae.     

Annual abundance and biomass of aloricate ciliates in tropical neritic waters off Kingston,Jamaica

The daily abundance of aloricate ciliates at Lime Cay, Jamaica, a shallow neritic site, ranged from 29 to 118 × 10⁶ m^–2 (0.97 to 3.93 × 10⁶ m^–3) between November 1985 and November 1986. Biomass was converted to kilojoules (1 kcal=4.1855 kJ) assuming 42% carbon, 20.15 kJ (g dry wt)^–1, and 20% cell shrinkage. Biomass ranged from 0.40 to 3.00 kJ m^–2 (13.3 to 100 J m^–3; 0.28 to 2.08µg C l^–1) with an annual mean of 1.11 kJ m^–2 (36.8 J m^–3; 0.764µg C l^–1). Nanociliates (<20µm equivalent spherical diameter, ESD) dominated abundance, but microciliates (> 20µm ESD) dominated biomass.Strombidium, Strobilidium, Tontonia andLaboea species were conspicuous taxa. Annual production estimates of the aloricate assemblage, based on literature growth rates, ranged from 404 kJ m^–2 yr^–1 (37 J m^–3 d^–1) to 1614 kJ m^–2 yr^–1 (147 J m^–3 d^–1). A compromise estimate of 689 kJ m^–2 yr^–1 (i.e., 63 J m^–3 d^–1) is comparable to other estimates from tropical and subtropical regions. A model of annual energy flow through 11 planktonic compartments suggests the total ciliate assemblage (aloricates and tintinnines) to be as productive as metazoan herbivores and metazoan carnivores.     

Reaction times and force production during escape behavior of a calanoid copepod, Undinula vulgaris

Effective escape behavior contributes to the success of copepods in planktonic communities. The kinematics of escape were studied in tethered Undinulavulgaris (Calanoida) by analyzing the timing and magnitude of their power strokes to a precisely controlled, sudden mechanical perturbation in the surrounding water. Copepods responded with rapid swims to water velocities of 36 to 86 μm s⁻¹. Reaction times were under 2.5 ms following stimulus onset. The time course of force exerted was complex, but reproducible from stimulus to stimulus. Multiple power strokes (“kicks”) were frequently observed in response to single stimuli. Time intervals of 5 ms were observed between the end of one escape kick and the beginning of the next. U. vulgaris developed maximum forces of 40 to over 100 dynes (dyn) during a rapid swim. The behavioral reaction times and intervals between multiple responses observed in this calanoid are among the shortest reported in aquatic invertebrates. Received: 25 November 1997 / Accepted: 8 October 1998     

Diurnal gut pigment rhythm and metabolic rate of<Emphasis Type="Italic"> Calanus euxinus</Emphasis> in the Black Sea

The vertical distribution, diel gut pigment content and oxygen consumption of Calanus euxinus were studied in April and September 1995 in the Black Sea. Gut pigment content of C. euxinus females was associated with diel vertical migration of the individuals, and it varied with depth and time. Highest gut pigment content was observed during the nighttime, when females were in the chlorophyll a (chl a) rich surface waters, but significant feeding also occurred in the deep layer. Gut pigment content throughout the water column varied from 0.8 to 22.0 ng pigment female^–1 in April and from 0.2 to 21 ng pigment female^–1 in September 1995. From the diel vertical migration pattern, it was estimated that female C. euxinus spend 7.5 h day^–1 in April and 10.5 h day^–1 in September in the chl a rich surface waters. Daily consumption by female C. euxinus in chl a rich surface waters was estimated by taking into account the feeding duration and gut pigment concentrations. Daily carbon rations of female C. euxinus, derived from herbivorous feeding in the euphotic zone, ranged from 6% to 11% of their body carbon weight in April and from 15% to 35% in September. Oxygen consumption rates of female and copepodite stage V (CV) C. euxinus were measured at different temperatures and at different oxygen concentrations. Oxygen consumption rates at oxygen-saturated concentration ranged from an average of 0.67 g O₂ mg^–1 dry weight (DW) h^–1 at 5°C to 2.1 g O₂ mg^–1 DW h^–1 at 23°C for females, and ranged from 0.48 g O₂ mg^–1 DW h^–1 at 5°C to 1.5 g O₂ mg^–1 DW h^–1 at 23°C for CVs. The rate of oxygen consumption at 16°C varied from 0.62 g O₂ mg^–1 DW h^–1 at 0.65 mg O₂ l^–1 to 1.57 g O₂ mg^–1 DW h^–1 at 4.35 mg O₂ l^–1 for CVs, and from 0.74 g O₂ mg^–1 DW h^–1 at 0.57 mg O₂ l^–1 to 2.24 g O₂ mg^–1 DW h^–1 at 4.37 mg O₂ l^–1 for females. From the oxygen consumption rates, daily requirements for the routine metabolism of females were estimated, and our results indicate that the herbivorous daily ration was sufficient to meet the routine metabolic requirements of female C. euxinus in April and September in the Black Sea.Communicated by O. Kinne, Oldendorf/Luhe     

Initial contact,exploration and attachment of barnacle (Balanus amphitrite) cyprids settling in flow

Settlement responses of barnacle (Balanus amphitrite) cyprids to boundary-layer flows were examined in laboratory flume-experiments. The leading-edge configuration of flat plates was altered in order to manipulate flows without changing surface topography or freestream velocity. Settlement along the plates correlated strongly with downstream gradients in shear stress. Analyses of video images taken during the experiments indicate that cyprids first contact plates in regions where plate-ward advection is high, and subsequent exploratory movement along the plate is oriented with flow direction at the plate surface. After exploration, cyprids reject a surface more frequently in a fast flow (10 cm s^–1 freestream velocity) than in a slow flow (5 cm s^–1), but rejection occurs in shear stresses well below the threshold that would prevent attachment and exploration. A higher rejection rate does not result in lower settlement, however, since contact rate is higher in fast than slow flows. The movement of cyprids in flow thus appears to be a passive transport process during the initial contact stage of settlement, but an active behavioral response to flow direction and shear stress during later stages of exploration and attachment.     

Feeding and swimming of lysianassid amphipods in a shallow cold-water bay

The potential for dispersal by lysianassid amphipods and their localization to carrion in a shallow cold-water bay in the Middle Saint Lawrence Estuary were assessed by means of endobenthic sampling, SCUBA observations, measures of swimming speeds, and by exposure of bait (50–100 g of fish) in traps. Seventy-five to 99.9% of animals attracted to traps were lysianassid amphipods belonging to five species. Lysianassid species were spatially segregated in the Bay at low tide but all were more or less dispersed at high tide. Second cohortAnonyx sarsi Steele and Brunel,Boeckosimus edwardsi andOnisimus littoralis (Krøyer) were more dispersed than the small first cohort individuals. Second cohortA. sarsi were crawlers or low (0–0.5 m off the bottom) suprabenthic swimmers in the day, but upper (0.5–2 m) suprabenthic swimmers at night. In contrast, first cohortA. sarsi were crawlers or low suprabenthic swimmers day-and-night, whileOrchomenella pinguis (Boeck) followed this swimming pattern at night but were generally akinetic in the day. Mean swimming speeds ofA. sarsi (13.6 cm s^-1) andOn. littoralis (12.1 cm s^-1) were 2 to 3 times greater than those ofOr. pinguis (7.4 cm s^-1) andPsammonyx nobilis (Stimpson) (4.4 cm s^-1). Catchability coefficients (i.e. ratio number of individuals per trap:endobenthic abundance) were 74 (A. sarsi), 8 (On. littoralis), 7 (Or. pinguis), and 0.7 (P. nobolis) m² of bottom. Gut content analysis indicated thatA. sarsi fed mostly on large carrion, whileOn. littoralis were markedly opportunistic, andOr. pinguis andP. nobilis relied on detritus, algae, and small crustaceans.     

Using time-depth-light recorders to measure light levels experienced by a diving marine mammal

Acoustic telemetry was used to track vertical and horizontal movement patterns and to monitor the stomach temperatures of seven juvenile shortfin mako sharks (Isurus oxyrinchus Rafinesque) in the Southern California Bight from July to November 2002. Makos (80–145 cm fork length, FL) were attracted to the tracking vessel, where they were fed a mackerel containing an acoustic transmitter that reported temperature and pressure. Tracks ranged from 6.8–45.4 h. Collectively, the mako sharks spent 80% of the track record at 0–12 m, 15% at 12–24 m, and 5% at depths >24 m. The average horizontal swimming speed was 2.3 km h^–1 or 0.55 FLs s^–1, and the greatest distance traveled was 145 km in 45.4 h. For the six tracks >21 h, there was a positive correlation between body size and maximum depth. Makos used more of the water column during daylight hours. Mean stomach temperature was 3.8±1.5°C above ambient, and body size was positively correlated with both maximum and average stomach temperature. Stomach content analyses of four makos captured at the end of tracking verified the occurrence of feeding events as indicated by changes in stomach temperature.Electronic Supplementary Material Supplementary material is available in the online version of this article at Communicated by J.P. Grassle, New Brunswick     

Feeding responses of the tentaculate deposit-feederEupolymnia nebulosa (Annelida: Polychaeta): Influence of sexual maturity

Feeding responses of the tentaculate depositfeeding polychaeteEupolymnia nebulosa (Montagu) were studied by measuring rates of uptake of three different¹⁴C-labelled diatoms (unialgal cultures ofNavicula incerta Grunow,Nitzschia acicularis Wm Smith, andNitzschia sp.). Worms used during this study were collected in the harbor of Port-Vendre (Western Mediterranean) during August 1986 (immature worms) and December 1987 (mature worms). Uptake rates were affected both by the length of the experiments and by the nature of the food offered. The highest rate of uptake (2.98 10^–4 mg ashfree dry wt of algae mg^–1 dry wt of worms h^–1) was obtained during short-term experiments (4 h) with the smallest diatom (Nitzschia sp.). The lowest rate of uptake (0.21 10^–4 mg ash-free dry wt of algae mg^–1 dry wt of worms h^–1) was also obtained withNitzschia sp., but for a long-term (48 h) experiment. There was no significant difference between rates of uptake of immature and mature worms.     

Uptake of dissolved organics by marine bacteria as a function of fluid motion

A mass transfer analysis predicts that fluid motion can increase the assimilation of dissolved organics by attached compared to free-living microorganisms under certain conditions. To test this we examined the effect of advective flow and fluid shear on the uptake of model compounds (leucine and glucose) by natural assemblages of heterotrophic bacteria, collected from Roosevelt Inlet, Delaware Bay (USA), in 1989. We found that [³H]leucine uptake by cells held in fluid moving at 20 to 70 m d^–1 was eight times larger than uptake by cells at a velocity of 3 m d^–1. This effect was only observed at low leucine concentrations (ca. 1 nM), when uptake was likely not saturated. When we added leucine at concentrations expected to saturate leucine uptake (ca. 11 nM), fluid motion past cells did not affect uptake. Fluid flow past bacteria did not increase [³H]glucose uptake, and laminar shear rates of 0.5 to 2.1 s^–1 did not increase either glucose or leucine uptake by suspended bacteria. These results indicate that fluid motion increases bacterial uptake of certain lowmolecular-weight dissolved organics only when the microorganism exists in an advective flow field. As predicted from a mass transfer model, fluid shear rates in natural systems are too low to affect bacterial uptake of such compounds.