Intraguild predatory interactions between the jellyfish <Emphasis Type="Italic">Cyanea capillata</Emphasis> and <Emphasis Type="Italic">Aurelia aurita</Emphasis>

While qualitative observations of jellyfish intraguild predation abound in the literature, there are only few rate measurements of these interactions. We quantified predation rates among two common jellyfish in northern boreal waters, Cyanea capillata and its prey Aurelia aurita, both of which also feed on crustacean zooplankton and fish larvae. A series of incubation experiments using a wide range of prey concentrations (0.38–3.8 m⁻³) in large containers (2.6 m³) was carried out. By replenishing the prey continuously as they were captured we maintained a nearly constant prey concentrations. Ingestion rates increased linearly up to prey concentrations of 1.92 m⁻³, yielding maximum clearance rates of ∼2.37 ± 0.39 m³ predator⁻¹ h⁻¹ for C. capillata predators 16 ± 2.3 cm in diameter. Mean ingestion rate at saturated prey concentrations (1.92–3.85 m⁻³) was 4.01 ± 0.78 prey predator⁻¹ h⁻¹. Behavioral observations suggested that predators did not alter their swimming behavior during meals, and thus that feeding rates were generally handling limited rather than encounter limited. Predators captured more prey than needed, and semi-digested prey was often discarded when fresh prey was encountered.     

Aerobic metabolic rates of swimming juvenile mako sharks, <Emphasis Type="Italic">Isurus oxyrinchus</Emphasis>

The shortfin mako shark, Isurus oxyrinchus, is a highly streamlined epipelagic predator that has several anatomical and physiological specializations hypothesized to increase aerobic swimming performance. A large swim-tunnel respirometer was used to measure oxygen consumption (MO₂) in juvenile mako sharks (swimming under controlled temperature and flow conditions) to test the hypothesis that the mako shark has an elevated maintenance metabolism when compared to other sharks of similar size swimming at the same water temperature. Specimen collections were conducted off the coast of southern California, USA (32.94°N and 117.37°W) in 2001-2002 at sea-surface temperatures of 16.0–21.0°C. Swimming MO₂ and tail beat frequency (TBF) were measured for nine mako sharks [77–107 cm in total length (TL) and 4.4 to 9.5 kg body mass] at speeds from 28 to 54 cm s⁻¹ (0.27–0.65 TL s⁻¹) and water temperatures of 16.5–19.5°C. Standard metabolic rate (SMR) was estimated from the extrapolation to 0-velocity of the linear regression through the LogMO₂ and swimming speed data. The estimated LogSMR (±SE) for the pooled data was 2.0937 ± 0.058 or 124 mg O₂ kg⁻¹ h⁻¹. The routine metabolic rate (RMR) calculated from seventeen MO₂ measurements from all specimens, at all test speeds was (mean ± SE) 344 ± 22 mg O₂ kg⁻¹h⁻¹ at 0.44 ± 0.03 TL s⁻¹. The maximum metabolic rate (MMR) measured for any one shark in this study was 541 mg O₂ kg⁻¹h⁻¹ at 54 cm s⁻¹ (0.65 TL s⁻¹). The mean (±SE) TBF for 39 observations of steady swimming at all test speeds was 1.00 ± 0.01 Hz, which agrees with field observations of 1.03 ± 0.03 Hz in four undisturbed free-swimming mako sharks observed during the same time period. These findings suggest that the estimate of SMR for juvenile makos is comparable to that recorded for other similar-sized, ram-ventilating shark species (when corrected for differences in experimental temperature). However, the mako RMR and MMR are apparently among the highest measured for any shark species.     

Feeding of Clausocalanids (Calanoida,Copepoda) on naturally occurring particles in the northern Gulf of Aqaba (Red Sea)

A total of 12 feeding experiments were conducted in the northern Gulf of Aqaba during spring (March/April) and autumn (September/October) 2002 at the Marine Science Station (MSS) in Aqaba. Females of three species of clausocalanids were selected: Clausocalanus farrani, C. furcatus and Ctenocalanus vanus. Natural occurring particle (NOP) larger than 5 μm were investigated as food source. The ambient chlorophyll a concentration at sampling depth (∼70 m) ranged between 0.15 and 1.00 μg chl a l⁻¹ and NOP concentrations ranged between 1.78 and 14.0 × 10³ cells l⁻¹ during the sampling periods. The division of particles into five size classes (5–10, 10–20, 20–50, 50–100 and >100 μm) revealed that most of the particles were found in the size classes below 50 μm (81–98%), while most of the natural occurring carbon (NOC) was concentrated in the size classes larger than 20 μm (70–95%). Ingestion rates were food density dependent rather than size dependent ranging between 0.02 and 1.65 × 10³ NOP ind⁻¹ day⁻¹ and 0.01 and 0.41 μg NOC ind⁻¹ day⁻¹, respectively, equivalent to a body carbon (BC) uptake between 0.4 and 51.8% BC day⁻¹. The share of the size classes to the total ingestion resembled in most cases the size class composition of the natural particle community.     

Developmental physiology of Antarctic asteroids with different life-history modes

Rates of respiration and protein synthesis were measured during embryonic and larval development of Antarctic asteroids with different life-history modes (non-feeding and feeding larvae: Acodontaster hodgsoni, Porania antarctica, Odontaster meridionalis). Patterns of respiration for these species all show an increase during embryogenesis, with subsequent maintenance of routine respiration (“starvation resistance”), even in the absence of food for ~4 months (O. meridionalis). Fractional rates of protein synthesis (i.e., rate per unit mass of whole-body protein content) in the Antarctic larvae are essentially identical to those of temperate species. Larvae of O. meridionalis had an average fractional synthesis rate of 0.52% ± 0.05 h⁻¹ at −1.0°C, which is comparable to the temperate asteroid Asterina miniata at 0.53% ± 0.14 h⁻¹ at 15°C. For embryos of the asteroids A. hodgsoni and P. antarctica, fractional rates of protein synthesis (~0.2% h⁻¹) also are comparable to those reported for embryos of temperate echinoderm species. While rates of synthesis are high, rates of protein deposition are relatively low (percent of protein synthesized that is retained for growth). During a ~4 month growth period for larvae of O. meridionalis, the average protein depositional efficiency was 5.2%. This contrasts with higher rates of depositional efficiency reported for similar developmental stages of temperate echinoderm species. The biological significance of maintaining high rates of macromolecular synthesis for species with low rates of cell division and low protein depositional efficiencies is intriguing in the context of understanding the mechanistic bases of extended life spans and dispersal potential in response to changing Antarctic environments.     

Diurnal cycle and kinetics of ammonium assimilation in the green alga <Emphasis Type="Italic">Ulva pertusa</Emphasis>

The kinetics of ammonium assimilation was investigated in Ulva pertusa (Chlorophyceae, Ulvales) from northeastern New Zealand. Ammonium assimilation exhibited Michaelis–Menten kinetics with a maximum rate of assimilation (V _max) of 54 ± 5 μmol g⁻¹ dry weight h⁻¹ and half-saturation constant (K _m) of 23 ± 8 μM. In contrast, values for ammonium uptake were considerably higher with a V _max of 316 ± 59 μmol g⁻¹ dry weight h⁻¹ and K _m of 135 ± 46 μM. At environmentally relevant ammonium concentrations (5 μM), assimilation accounted for most (70%) of the ammonium taken up. Darkness decreased the maximum rate of ammonium assimilation by 83%. We investigated the hypothesis that rates of biosynthetic processes are greater in the early part of the day in Ulva. Consistent with this hypothesis, the maximum rate of ammonium assimilation in U. pertusa peaked in the morning and coincided with low levels of the photosynthetic product sucrose, which peaked in the afternoon. There was a diurnal cycle in the rate of ammonium uptake and assimilation in light and dark, but the amplitude was much greater for assimilation than uptake. Moreover, our data suggest that net ammonium assimilation only occurs during the day in U. pertusa. We suggest that two major roles for diurnal cycles are minimisation of interspecific competition for resources and metabolic costs.     

Life cycle of <Emphasis Type="Italic">Oithona</Emphasis> <Emphasis Type="Italic">similis</Emphasis> (Copepoda: Cyclopoida) in Kola Bay (Barents Sea)

The annual population dynamics (nauplii, old copepodites CIV–CV and adults) and seasonal variations in reproductive parameters of the cyclopoid copepod Oithona similis were investigated on the basis of the data 1999–2006 in Kola Bay, a large subarctic fjord in the Barents Sea. Population density of O. similis ranged from 110 to 9,630 ind m⁻³ and averaged 1,020 ± 336 ind m⁻³. The relative abundance of adults was high during winter (~60%). At the end of winter (mid-March), the population included a large percentage of later-stage copepodites (stage CIV 23% and stage CV 57%). There were two periods of mass spawning, in late June and September. Autumn and summer generations strongly differed in abundance, average prosome length (PL), clutch size (CS), egg diameter (D), egg production rates (EPR and SEPR) and female secondary production. Average PL decreased with increasing water temperature, while D and CS were strongly correlated with PL but unaffected by temperature. Annual average EPR and SEPR were 0.55 ± 0.18 eggs female⁻¹ day⁻¹ and 0.0011 ± 0.003 day⁻¹, respectively. Female secondary production averaged 0.8 ± 0.3 μg C m⁻³ day⁻¹ (range 0.001–3.58). There were positive relationships between abundance, EPR, SEPR, production and water temperatures. Reproductive parameters appeared to be controlled by hydrological factors and food conditions.     

Migration,distribution, and diving behavior of adult male loggerhead sea turtles (<Emphasis Type="Italic">Caretta caretta</Emphasis>) following dispersal from a major breeding aggregation in the Western North Atlantic

Sixteen satellite-tagged adult male loggerhead sea turtles (Caretta caretta) dispersed widely from an aggregation near Port Canaveral, Florida, USA (28°23′N, −80°32′W) after breeding. Northbound males migrated further (990 ± 303 km) than southbound males (577 ± 168 km) and transited more rapidly (median initial dive duration = 6 (IQR = 4–16) versus 19 (IQR = 10–31) min, respectively).. Migration occurred along a depth corridor (20–40 m) except where constricted by a narrow continental shelf width. Males foraged in areas 27 ± 41 km² day⁻¹ at locations <1–80 km from shore for 100.1 ± 60.6 days, with variability in foraging patterns not explained by turtle size or geography. Post-breeding dispersal patterns were similar to patterns reported for adult female loggerhead sea turtles in this region and adult male loggerhead sea turtles elsewhere in the northern hemisphere; however, foraging ground distributions were most similar to adult female loggerhead sea turtles in this region.     

How size relates to oxygen consumption,ammonia excretion,and ingestion rates in cold (<Emphasis Type="Italic">Enteroctopus megalocyathus</Emphasis>) and tropical (<Emphasis Type="Italic">Octopus maya</Emphasis>) octopus species

The scaling of metabolic rates with body mass is one of the best known and most studied characteristics of aquatic animals. Herein, we studied how size is related to oxygen consumption, ammonia excretion, and ingestion rates in tropical (Octopus maya) and cold-water (Enteroctopus megalocyathus) cephalopod species in an attempt to understand how size affects their metabolism. We also looked at how cephalopod metabolisms are modulated by temperature by constructing the relationship between metabolism and temperature for some benthic octopod species. Finally, we estimated the energy balance for O. maya and E. megalocyathus in order to validate the use of this information for aquaculture or fisheries management. In both species, oxygen consumption and ammonia excretion increased allometrically with increasing body weight (BW) expressed as Y = aBW ^b . For oxygen consumption, b was 0.71 and 0.69 for E. megalocyathus and O. maya, respectively, and for ammonia excretion it was 0.37 and 0.43. Both species had low O/N ratios, indicating an apparent dependence on protein energy. The mean ingestion rates for E. megalocyathus (3.1 ± 0.2% its BW day⁻¹) and O. maya (2.9 ± 0.5% its BW day⁻¹) indicate that voracity, which is characteristic of cephalopods, could be independent of species. The scope for growth (P = I − (H + U + R) estimated for E. megalocyathus was 28% higher than that observed in O. maya (320 vs. 249 kJ day⁻¹ kg⁻¹). Thus, cold-water cephalopod species could be more efficient than tropical species. The protein and respiratory metabolisms of O. maya, E. megalocyathus, and other octopod species are directly dependent on temperature. Our results offer complementary evidence that, as Clarke (2004) stated, the metabolic response (R and U) cannot be determined mechanistically by temperature, as previously proposed (Gillooly et al. 2002).     

Feeding behaviour of the sea cucumber <Emphasis Type="Italic">Cucumaria frondosa</Emphasis> (Echinodermata: Holothuroidea) in the laboratory and the field: relationships between tentacle insertion rate,flow speed,and ingestion

The sea cucumber, Cucumaria frondosa, is a benthic suspension feeder that captures food particles on its tentacles and then inserts them into its mouth one at a time. Previous studies have suggested that tentacle insertion rate (TIR) could be a useful indicator of food intake. The present study determined whether flow velocity affects TIR and whether TIR is a good indicator of ingestion. Video observations of sea cucumbers in Passamaquoddy Bay (45°01.70N, 66°55.74W) in August 1995 showed that TIRs increased with velocities up to 55 cm s⁻¹ and decreased steadily at flows above that up to 130 cm s⁻¹. In October 2006, laboratory flume studies were carried out on specimens collected from the same site in the previous August. Temperature and salinity (12°C and 32) in the flume were the same as in the field at the time of collection. There was high individual variation in feeding behavior at free-stream velocities of 4–40 cm s⁻¹ and TIR was independent of flow. As the number of tentacle insertions increased in the flume experiments, the amount of chloropigments in the digestive tracts of the sea cucumbers also increased. This suggests that TIR, which can be measured non-intrusively using remote video techniques, could be a good indicator of feeding behavior and ingestion in C. frondosa.     

Trophic role of small cyclopoid copepod nauplii in the microbial food web: a case study in the coastal upwelling system off central Chile

Copepod grazing impact on planktonic communities has commonly been underestimated due to the lack of information on naupliar feeding behaviour and ingestion rates. That is particularly true for small cyclopoid copepods, whose nauplii are mainly in the microzooplankton size range (<200 μm). The trophic role of Oithona spp. nauplii was investigated off Concepción (central Chile, ~36°S) during the highly productive upwelling season, when maximum abundances of these nauplii were expected. Diet composition, ingestion rates, and food-type preferences were assessed through grazing experiments with different size fractions of natural planktonic assemblages (<3, <20, <100, and <125 μm) and cultures of the nanoflagellate Isochrysis galbana. When the Oithona spp. nauplii were offered a wide range of size fractions as food (pico- to microplankton), they mostly ingested small (2–5 μm) nanoflagellates (5–63 × 10³ cells nauplius⁻¹ day⁻¹). No ingestion on microplankton was detected, and picoplankton was mainly ingested when it was the only food available. Daily carbon (C) uptake by the nauplii ranged between 28 and 775 ng C nauplius⁻¹, representing an overall mean of 378% of their body C. Our relatively high ingestion rate estimates can be explained by methodological constraints in previous studies on naupliar feeding, including those dealing with “over-crowding” and “edge” effects. Overall, the grazing impact of the Oithona spp. nauplii on the prey C standing stocks amounts up to 21% (average = 13%) for picoplankton and 54% (average = 28%) for nanoplankton. These estimates imply that the nauplii of the most dominant cyclopoid copepods exert a significant control on the abundances of nanoplankton assemblages and, thereby, represent an important trophic link between the classical and microbial food webs in this coastal upwelling system.     

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

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

Behaviour that influences dispersal and connectivity in the small,young larvae of a reef fish

Determining the scale of larval dispersal and population connectivity in demersal fishes is a major challenge in marine ecology. Historically, considerations of larval dispersal have ignored the possible contributions of larval behaviour, but we show here that even young, small larvae have swimming, orientation and vertical positioning capabilities that can strongly influence dispersal outcomes. Using young (11–15 days), relatively poorly developed (8–10 mm), larvae of the pomacentrid damselfish, Amblyglyphidodon curacao (identified using mitochondrial DNA), we studied behaviour relevant to dispersal in the laboratory and sea on windward and leeward sides of Lizard Island, Great Barrier Reef. Behaviour varied little with size over the narrow size range examined. Critical speed was 27.5 ± 1.0 cm s⁻¹ (30.9 BL s⁻¹), and in situ speed was 13.6 ± 0.6 cm s⁻¹. Fastest individuals were 44.6 and 25.0 cm s⁻¹, for critical and in situ speeds, respectively. In situ speed was about 50% of critical speed and equalled mean current speed. Unfed larvae swam 172 ± 29 h at 8–10 cm s⁻¹ (52.0 ± 8.6 km), and lost 25% wet weight over that time. Vertical distribution differed between locations: modal depth was 2.5–5.0 and 10.0–12.5 m at leeward and windward sites, respectively. Over 80% of 71 larvae observed in situ had directional swimming trajectories. Larvae avoided NW bearings, with an overall mean SE swimming direction, regardless of the direction to nearest settlement habitat. Larvae made smaller changes between sequential bearings of swimming direction when swimming SE than in other directions, making it more likely they would continue to swim SE. When swimming NW, 62% of turns were left (more than in other directions), which would quickly result in swimming direction changing away from NW. This demonstrates the larvae knew the direction in which they were swimming and provides insight into how they achieved SE swimming direction. Although the cues used for orientation are unclear, some possibilities seemingly can be eliminated. Thus, A. curacao larvae near Lizard Island, on average swam into the average current at a speed equivalent to it, could do this for many hours, and chose different depths in different locations. These behaviours will strongly influence dispersal, and are similar to behaviour of other settlement-stage pomacentrid larvae that are older and larger.     

Automated method for the determination of total arsenic and selenium in natural and drinking water by HG-AAS

A multicommutated flow system was designed and evaluated for the determination of total arsenic and selenium by Hydride Generation Atomic Absorption Spectrometry (HG-AAS). It was applied to the determination of arsenic and selenium in samples of natural and drinking water. Detection limits were 0.46 and 0.08 μg l⁻¹ for arsenic and selenium, respectively; sampling frequency was 120 samples h⁻¹ for arsenic and 160 samples h⁻¹ for selenium. Linear ranges found were 1.54–10 μg l⁻¹ (R = 0.999) for arsenic and 0.27–27 μg l⁻¹ (R = 0.999) for selenium. Accuracy was evaluated by spiking various water samples and using a reference material. Recoveries were in the range 95–116%. Analytical precision (s _r (%), n = 10) was 6% for both elements. Compared with the Standard Methods, APHA, 3114B manual method, the system consumes at least 10 times less sample per determination, and the quantities of acid and reducing agent used are significantly lower with a reduction in the generation of pollutants and waste. As an additional advantage, the system is very fast, efficient and environmentally friendly for monitoring total arsenic and selenium levels in waters.     

Mobilization of arsenic and other trace elements of health concern in groundwater from the Salí River Basin, Tucumán Province, Argentina

The Salí River Basin in north-west Argentina (7,000 km²) is composed of a sequence of Tertiary and Quaternary loess deposits, which have been substantially reworked by fluvial and aeolian processes. As with other areas of the Chaco-Pampean Plain, groundwater in the basin suffers a range of chemical quality problems, including arsenic (concentrations in the range of 12.2–1,660 μg L⁻¹), fluoride (50–8,740 μg L⁻¹), boron (34.0–9,550 μg L⁻¹), vanadium (30.7–300 μg L⁻¹) and uranium (0.03–125 μg L⁻¹). Shallow groundwater (depths up to 15 m) has particularly high concentrations of these elements. Exceedances above WHO (2011) guideline values are 100% for As, 35% for B, 21% for U and 17% for F. Concentrations in deep (>200 m) and artesian groundwater in the basin are also often high, though less extreme than at shallow depths. The waters are oxidizing, with often high bicarbonate concentrations (50.0–1,260 mg L⁻¹) and pH (6.28–9.24). The ultimate sources of these trace elements are the volcanic components of the loess deposits, although sorption reactions involving secondary Al and Fe oxides also regulate the distribution and mobility of trace elements in the aquifers. In addition, concentrations of chromium lie in range of 79.4–232 μg L⁻¹ in shallow groundwater, 129–250 μg L⁻¹ in deep groundwater and 110–218 μg L⁻¹ in artesian groundwater. All exceed the WHO guideline value of 50 μg L⁻¹. Their origin is likely to be predominantly geogenic, present as chromate in the ambient oxic and alkaline aquifer conditions.     

Feeding ecology and energetics of the Antarctic chaetognaths Eukrohnia hamata, E. bathypelagica and E. bathyantarctica

Ecological and physiological studies focused on dietary preferences, lipid biochemistry and energetics within the three Antarctic chaetognaths Eukrohnia hamata, E. bathypelagica and E. bathyantarctica from meso- and bathypelagic depths. Eukrohnia hamata and E. bathypelagica respired 0.15 μL O₂ mg dry mass (DM)⁻¹ h⁻¹, which translates to an average metabolic loss of only <1.1% of body carbon per day. Lipid storage was not substantial in E. bathypelagica (mean 11.5 ± 6.5% DM) and E. bathyantarctica (mean 15.4 ± 4.1% DM) during summer and winter, suggesting year-round feeding of these predators mainly on copepods. In E. bathypelagica, total fatty acids were dominated by the fatty acids 16:0, 20:5(n-3) and 22:6(n-3) and in E. bathyantarctica also by 18:1(n-9), a fatty acid usually found in storage lipids. Only the latter species was characterized by significant amounts of wax esters, consisting largely of the common fatty alcohols 16:0, 20:1(n-9) and the unusual fatty alcohol isomer 22:1(n-9).     

Microsensor studies of photosynthesis and respiration in the symbiotic foraminifer Orbulina universa

Oxygen and pH microelectrodes were used to investigate the microenvironment of the planktonic foraminifer Orbulina universa and its dinoflagellate endosymbionts. A diffusive boundary layer surrounds the foraminiferal shell and limits the O₂ and proton transport from the shell to the ambient seawater and vice versa. Due to symbiont photosynthesis, high O₂ concentrations of up to 206% air saturation and a pH of up to 8.8, i.e. 0.5 pH units above ambient seawater, were measured at the shell surface of the foraminifer at saturating irradiances. The respiration of the host–symbiont system in darkness decreased the O₂ concentration at the shell surface to <70% of the oxygen content in the surrounding air-saturated water. The pH at the shell surface dropped to 7.9 in darkness. We measured a mean gross photosynthetic rate of 8.5 ± 4.0 nmol O₂ h⁻¹ foraminifer⁻¹. The net photosynthesis averaged 5.3 ± 2.7 nmol O₂ h⁻¹. In the light, the calculated respiration rates reached 3.9 ± 1.9 nmol O₂h⁻¹, whereas the dark respiration rates were significantly lower (1.7 ± 0.7 nmol O₂ h⁻¹). Experimental light–dark cycles demonstrated a very dynamic response of the symbionts to changing light conditions. Gross photosynthesis versus scalar irradiance curves (P vs E _o curves) showed light saturation irradiances (E _k) of 75 and 137 μmol photons m⁻² s⁻¹ in two O. universa specimens, respectively. No inhibition of photosynthesis was observed at irradiance levels up to 700 μmol photons m⁻² s⁻¹. The light compensation point of the symbiotic association was 50 μmol photons m⁻² s⁻¹. Radial profile measurements of scalar irradiance (E _o) inside the foraminifera showed a slight increase at the shell surface up to 105% of the incident irradiance (E _d). Received: 26 January 1998 / Accepted: 11 April 1998     

Distribution,habitat preferences and behaviour of the critically endangered Maltese top-shell <Emphasis Type="Italic">Gibbula nivosa</Emphasis> (Gastropoda: Trochidae)

The Maltese top-shell, Gibbula nivosa Adams 1851, is a critically endangered marine trochid gastropod endemic to the Maltese Islands (central Mediterranean). Previously unrecorded live since 1981, rediscovery of this species in 2006 has enabled the collection of basic biological data for the first time, based on a population in Sliema Creek. The field distribution and habitat preferences of G. nivosa were investigated via stratified random sampling, while aspects of its behaviour were studied through laboratory experiments. Gibbula nivosa occurred primarily in near-homogeneous or homogeneous infralittoral cobble/pebble beds, at an overall density of 17.6 ± 25.0 SD individuals m⁻²; however, large spatial and temporal variations in abundance were recorded. The snails did not exhibit gregarious behaviour and the slightly clumped dispersion pattern noted in the field appeared to result from patchiness of the habitat. Recruitment was observed in post-summer months, which, together with data on shell-size distributions, suggests that G. nivosa spawns in early summer and attains adult size (maximum shell width ~9 mm) in less than 1 year. Gibbula nivosa showed a circadian activity pattern with nocturnal foraging involving indiscriminate ingestion of particles browsed off the substratum; observations on responses to four potential predators suggest that nocturnal activity may have evolved in response to diurnal predation. Historical records of snail occurrence and the present study suggest that population declines of G. nivosa in the past were probably related to habitat alteration as a result of anthropogenic pressure.     

Spring sea ice photosynthesis,primary productivity and biomass distribution in eastern Antarctica, 2002–2004

While it is known that Antarctic sea ice biomass and productivity are highly variable over small spatial and temporal scales, there have been very few measurements from eastern Antarctic. Here we attempt to quantify the biomass and productivity and relate patterns of variability to sea ice latitude ice thickness and vertical distribution. Sea ice algal biomass in spring in 2002, 2003 and 2004 was low, in the range 0.01–8.41 mg Chl a m⁻², with a mean and standard deviation of 2.08 ± 1.74 mg Chl a m⁻² (n = 199). An increased concentration of algae at the bottom of the ice was most pronounced in thicker ice. There was little evidence to suggest that there was a gradient of biomass distribution with latitude. Maximum in situ production in 2002 was approximately 2.6 mg C m⁻² h⁻¹ with assimilation numbers of 0.73 mg C (mg Chl a)⁻¹ h⁻¹. Assimilation numbers determined by the ¹⁴C incubations in 2002 varied between 0.031 and 0.457 mg C (mg Chl a)⁻¹ h⁻¹. Maximum fluorescence quantum yields of the incubated ice samples in 2002 were 0.470 ± 0.041 with E _k indices between 19 and 44 μmol photons m⁻² s⁻¹. These findings are consistent with the shade-adapted character of ice algal communities. In 2004 maximum in situ production was 5.9 mg C m⁻² h⁻¹ with an assimilation number of 5.4 mg C (mg Chl a)⁻¹ h⁻¹. Sea ice biomass increased with ice thickness but showed no correlation with latitude or the time the ice was collected. Forty-four percent of the biomass was located in bottom communities and these were more commonly found in thicker ice. Surface communities were uncommon.     

Clearance rates of the great scallop (<Emphasis Type="Italic">Pecten maximus</Emphasis>) and blue mussel (<Emphasis Type="Italic">Mytilus edulis</Emphasis>) at low natural seston concentrations

Great scallop, Pecten maximus, and blue mussel, Mytilus edulis, clearance rate (CR) responses to low natural seston concentrations were investigated in the laboratory to study (1) short-term CR variations in individual bivalves exposed to a single low seston diet, and (2) seasonal variations in average CR responses of bivalve cohorts to natural environmental variations. On a short temporal scale, mean CR response of both species to 0.06 μg L⁻¹ chlorophyll a (Chl a) and 0.23 mg L⁻¹ suspended particulate matter (SPM) remained constant despite large intra-individual fluctuations in CR. In the seasonal study, cohorts of each species were exposed to four seston treatments consisting of ambient and diluted natural seston that ranged in mean concentration from 0.15 to 0.43 mg L⁻¹ SPM, 0.01 to 0.88 μg L⁻¹ Chl a, 36 to 131 μg L⁻¹ particulate organic carbon and 0.019 to 0.330 mm³ L⁻¹ particle volume. Although food abundance in all treatments was low, the nutritional quality of the seston was relatively high (e.g., mean particulate organic content ranged from 68 to 75%). Under these low seston conditions, a high percentage of P. maximus (81–98%) and M. edulis (67–97%) actively cleared particles at mean rates between 9 and 12 and between 4 and 6 L g⁻¹ h⁻¹, respectively. For both species, minimum mean CR values were obtained for animals exposed to the lowest seston concentrations. Within treatments, P. maximus showed a greater degree of seasonality in CR than M. edulis, which fed at a relatively constant rate despite seasonal changes in food and temperature. P. maximus showed a non-linear CR response to increasing Chl a levels, with rates increasing to a maximum at approximately 0.4 μg L⁻¹ Chl a and then decreasing as food quantity continued to increase. Mean CR of M. edulis also peaked at a similar concentration, but remained high and stable as the food supply continued to increase and as temperatures varied between 4.6 and 19.6°C. The results show that P. maximus and M. edulis from a low seston environment, do not stop suspension-feeding at very low seston quantities; a result that contradicts previous conclusions on the suspension-feeding behavior of bivalve mollusks and which is pertinent to interpreting the biogeographic distribution of bivalve mollusks and site suitability for aquaculture.     

Diet and seasonal prey capture rates in the Mediterranean red coral (Corallium rubrum L.)

Gorgonians are passive suspension feeders, contributing significantly to the energy flow of littoral ecosystems. More than in active suspension feeders (such as bivalves, ascidians and sponges) their prey capture is affected by spatial and temporal prey distribution and water movement. Corallium rubrum is a characteristic gorgonian of Mediterranean sublittoral hard bottom communities. This study found a high variability in the annual cycle of prey capture rate, prey size and ingested biomass, compared to other Mediterranean gorgonians. Detrital particulate organic matter (POM) was found throughout the year in the polyp guts and constituted the main proportion of the diet (25–44%). Crustacean fragments and copepods (14–46%) accounted for the second major proportion, while invertebrate eggs (9–15%) and phytoplankton (8–11%) constituted the smallest part of the diet. To verify the importance of detrital POM in the energy input of this precious octocoral species, in situ experiments were carried out during the winter–spring period. The results confirm the importance of detrital POM as the main source of food for C. rubrum [0.13±0.04 μg C polyp⁻¹ h⁻¹ (mean±SD)]. This study also compares the prey capture rates of two colony size classes and two depth strata: Within the same patch, small colonies (<6 cm height) captured significantly more prey per polyp (0.038±0.09 prey polyp⁻¹ h⁻¹) than larger colonies (>10 cm high) (0.026±0.097 prey polyp⁻¹ h⁻¹) and showed a higher proportion of polyps containing prey (17% compared to 10%). Comparing colonies of similar size (<6 cm height) revealed that the colonies situated at 40 m depth captured significantly more prey (0.038±0.09 prey polyp⁻¹ h⁻¹) than the ones at 20 m (0.025±0.11 prey polyp⁻¹ h⁻¹). One pulse of copepods was recorded that constituted 16% of all captured prey during the 15-month period studied in one of the sampled populations. The data suggest that the variability of hydrodynamic processes may have a higher influence on the feeding rate than seasonal changes in the seston composition. The carbon ingestion combined with data on the density of the exploited population results in 0.4–9.6 mg C m⁻² day⁻¹. The grazing impact of current, heavily exploited and small-sized populations is comparable to that of larger Mediterranean gorgonians, suggesting that unexploited red coral populations may have a high impact compared with other passive suspension feeders.