Vertical and spatial distribution of the near-shore littoral meroplankton off the Bay of Blanes (NW Mediterranean Sea)

The total number of meroplankton larvae collected off the Bayof Blanes (NW Mediterranean) on 12 April 1995 ranged from 113to 203 ind. m^–3. Bivalve veligers were the most abundant,followed by polychaete larvae, among which those from the hesionids,spionids and nephtyds were dominant Larval abundances were higherin the deeper half of the water column and decreased just nearthe bottom, except in the shallowest confined site.     

Seasonal density dynamics and distribution of brachyuran crab larvae (Decapoda: Brachyura) in Amursky and Ussuriysky bays, Sea of Japan

The species composition, period of occurrence, density, and distribution of brachyuran crab larvae (Decapoda: Brachyura) in the Amursky and Ussuriysky bays (Sea of Japan) were studied in May–October 2007 and 2008. The larvae of this group were not numerous, with peak densities occurring in July at maximum water temperatures. The average brachyuran larvae density was up to 126.9 ind./m³ in Ussuriysky Bay and 68 ind./m³ in Amursky Bay; the contribution of Brachyura to all decapod larvae reached 80–90%. In Amursky Bay, the highest density of brachyuran larvae (up to 584 ind./m³) was observed along the western coast over depths to 20 m; in Ussuriysky Bay, the larval density was highest (up to 1817 ind./m³) in the shallowwater northern part and progressively decreased with depth. Larvae of 18 brachyuran species were found in plankton samples. In Amursky Bay, intertidal crab larvae of the genus Hemigrapsus dominated, Eriocheir japonica larvae were fairly numerous. Larvae of the pea crabs Pinnixa rathbuni and Tritodynamia rathbunae and zoeae of the bigtooth rock crab Glebocarcinus amphioetus were predominant in Ussuriysky Bay.     

The seasonal dynamics and distribution of burrowing shrimp larvae of the infraorders Gebiidea and Axiidea in Amursky and Ussuriysky Bays,the Sea of Japan

The species composition, period of occurrence, density, and distribution of the larvae of burrowing shrimp of the infraorders Gebiidea and Axiidea in Amursky and Ussuriysky bays (Sea of Japan) were studied in May–October 2008. Larvae of eight species of this group were found in plankton samples. The period of occurrence of larvae in the bays was longest in Upogebia major and Nihonotrypaea petalura (4 and 3 months, respectively). Zoeae of the rest of the species occurred in the plankton for no more than 2 months, indicating a single larval hatching during the reproductive season. The average density of gebiidean and axiidean larvae was low and reached the highest values (4 ind./m³) in June in Amursky Bay and in July in Ussuriysky Bay; their contribution to the total density of decapod larvae was not above 18%. In general, larvae of the family Upogebiidae dominated in Amursky Bay and larvae of the Callianassidae were predominant in Ussuriysky Bay. The zoeae of U. major (up to 37 ind./m³) and Nihonotrypaea makarovi (up to 46 ind./m³) were most numerous. Larvae of the family Axiidae were recorded only in very low numbers in both bays.     

Zooplankton life under the perennial Antarctic Sea ice

Zooplankton was collected during the drift on the USA-Russia Ice Station Weddell 1 in the western Weddell Sea. Stratified tows up to 1,000 m depths were performed under perennial ice at a distance of ca. 300 km from the marginal ice zone from March to May 1992. Seasonal abundance, developmental stage composition and vertical distribution in populations of large dominant calanoid copepod species were studied. The abundance of Calanoides acutus changed inconspicuously and averaged 1,260 ind. m^-2; its developmental stage composition was characterised by the dominance of copepodites V (CV) and hardly changed in the course of observations. Calanus propinquus was at most stations in fairly low abundance and was represented by CV and adults; at the latest stations, it was not found. Rhincalanus gigas was also scarce; III-IV stages were present, but the first of them only at the southernmost stations. In contrast to this species, in the relatively abundant population of Metridia gerlachei (1,370 ind. m^-2 on average), a new generation was observed. There was a clear deepening of the median depth of occurrence of the above three species from March to early May, while in late May a shifting to upper layers was observed which remained unexplained. The data obtained were compared to the data collected in the ice-open eastern part of the Weddell Sea in the corresponding season. It can be seen that the differences in populations dynamics of the four species under the perennial ice depends on their trophic mode, i.e. capability to store lipid reserves in summer and/or to feed in winter, and with food spectra.     

Behaviour of pelagic larvae of four coral-reef fish species in the ocean and an atoll lagoon

In-situ behaviour of settlement-stage larvae (10-30 mm) of four coral-reef fishes - Acanthurus triostegus, Chromis viridis, Neoniphon argenteus and Ptereleotris sp. - differed between lagoon and ocean at Rangiroa Atoll, Tuamotu Islands, French Polynesia. Divers released 130 larvae individually in midwater, and recorded larval swimming speed, depth and direction. All species swam faster than average currents, and C. viridis swam faster in the lagoon than in the ocean. Vertical distribution behaviour of all species differed between ocean and lagoon, generally by larvae swimming deeper in the ocean. Nearly all individual larvae swam directionally. Within a species, distribution of average bearings of individual larvae was not directional, nor did it differ between ocean and lagoon. Larvae detected predators 3-6 m away, and stopped or changed depth or direction to avoid them. We therefore reject the 'simplifying assumptions' that reef-fish larvae are passive or that their behaviour is independent of location. Behavioural flexibility of settlement-stage reef-fish larvae has implications for dispersal, retention and population connectivity. This constitutes the first report of larval reef-fish behaviour in the open ocean. However, in the ocean, many larvae descended rapidly below safe diving depth, and adult remoras interfered, making in-situ study of larval behaviour difficult.     

Observations on Calanus glacialis eggs under the spring sea ice in the Barents Sea

During a spring cruise to the ice-covered Barents Sea in May 1997, high concentrations of Calanus glacialis eggs were found below the pack ice. Maximum abundance was 5,900 eggs m^-3 directly at the ice-water interface. Vertical distribution in the water column showed a decrease with depth, indicating positive buoyancy of the eggs. The possible role of the under-ice habitat as a nursery ground for C. glacialis is suggested.     

Distribution of Calanus species in Kongsfjorden, a glacial fjord in Svalbard

The distribution of Calanus species was investigated in Kongsfjordenin summer of 1996 and 1997. In both years Calanus finmarchicusand Calanus glacialis dominated, although the boreal C. finmarchicuswas more abundant than the Arctic C. glacialis in 1997. Thiscoincided with a 2°C higher water temperature at 50 m in1997, indicating stronger influence of Atlantic origin waterthat year. Advected Calanus finmarchicus occurred in deep andsubsurface layers of the outer fjord in 1996 (200 ind. m^-3,mainly CIII). A less abundant local population aggregated insurface layers of the inner fjord (100 ind. m^-3). Similarly,advected C. finmarchicus occurred in subsurface layers in 1997(446 ind. m^-3, mainly CIII and CIV) and a local population insurface layers (183 ind. m^-3, mainly CI). Calanus glacialisin 1996 aggregated as CII and CIII in the deep layers of theouter fjord (272 ind. m^-3), whereas CIII–CV were abundant(216 ind. m^-3) in cold surface waters of the inner fjord. In1997 C. glacialis (mostly CIII–CV) was more abundant inthe outer than in the inner part of the fjord (40 and 192 ind.m^-3, respectively). Within Kongsfjorden, Calanus finmarchicusneeds one year to complete its life cycle, whereas Calanus glacialisneeds two. Calanus hyperboreus seems to be an expatriate inthe fjord system.     

Pelagic larvae of benthic invertebrates of the Vostok Bay,peter the great bay,Sea of Japan: Composition,phenology, and population dynamics

For the first time, year round and long-term seasonal research on the composition, phenology, and population dynamics of pelagic larvae of bottom invertebrates were conducted in the Vostok Bay of the Sea of Japan. Larvae of 98 taxa of various ranks were found. The larvae of bivalves and polychaetes were the most diverse. The larvae of bottom invertebrates occurred in plankton year-round. Their density was at its minimum in January (less than 100 ind./m³), and its maximum from June to November (more than 1000 ind./m³). The larvae of polychaetes dominated in the autumn and winter seasons, whereas bivalve and gastropod larvae dominated in the spring and summer seasons. It was shown that the proportion of pollution tolerant meroplankton larvae of the Polydora and Pseudopolydora genera was high in the Vostok Bay, and could indirectly indicate increasing anthropogenic pressure in the area.     

Pelagic larvae of bivalve mollusks and polychaetes in winter plankton of the Kara Sea

Quantitative zooplankton samples were obtained by vertical tows with a Juday plankton net, in the southern Kara Sea, from November 28 to December 11, 2005 (by an expedition of the Murmansk Marine Biological Institute KSC RAS aboard the nuclear ice-breaker “Soviet Union”). The most abundant meroplankton forms were juveniles of Bivalvia and larvae of Polychaeta (the maximum abundances were 106.2 ind/m³ and 7.5 ind/m³, respectively). The results are discussed in relation to changes in the thermal regime of the Arctic Ocean observed during the recent decades.     

Mesozooplankton community structure in the Southern Ocean upstream of the Prince Edward Islands

A meso-scale oceanographic grid survey was conducted during the first cruise of the Marion Offshore Ecosystem Variability Study in the upstream region of the Prince Edward Islands in austral autumn (April/May) 2001. Mesozooplankton samples, collected using a Bongo net (fitted with 200-µm and 300-µm mesh nets), were separated into three size fractions, 200-500 µm, 500-1,000 µm, 1,000-2,000 µm, by reverse filtration. Total surface (depth<5 m) chlorophyll-a concentration during the study ranged between 0.11 and 0.34 µg l^-1 and was always dominated by picophytoplankton (0.45-2.0 µm). Total mesozooplankton abundance and biomass during the survey ranged between 49 and 1,512 ind. m^-3 and between 0.7 and 25 mg Dwt. m^-3, respectively. Throughout the survey, the 200 to 500 µm class numerically dominated the mesozooplankton community, with an average of ~69% (SD=ᆠ.3%). The dominant species in the 200- to 500-µm size fraction were the copepods, Oithona similis, Calanus simillimus and Metridia lucens, and the pteropod, Limacina retroversa. However, in terms of biomass, the 1,000- to 2,000-µm group was predominant, with dry weight values constituting an average of ~66% (SD=ᆞ.2%). The most well-represented species in this group were the carnivorous Euphausia vallentini, Thysanoessa vicina, Sagitta gazellae and Eukrohnia hamata. Three distinct groupings of stations were identified by numerical analysis. The different station groupings identified reflect changes in the relative contributions of the dominant species, as opposed to the presence/absence of species.     

Carnivorous feeding and respiration of the Arctic under-ice amphipod Gammarus wilkitzkii

. The dominant Arctic under-ice amphipod Gammarus wilkitzkii consumes a wide range of food items. The carnivorous feeding activity and energy budget of this large species were studied using three different approaches. Maximum potential ingestion rates I_max estimated from an allometric function taken from the literature and based on body mass were 2.1ǂ.4% of body carbon day^-1. Based on respiration measurements, the specific ingestion rates required to meet metabolic demands were lower (1.4ǂ.4% of body carbon day^-1). Feeding experiments, in which co-occurring pelagic calanoid (Calanus hyperboreus) or sympagic harpacticoid (Halectinosoma sp.) copepods were offered as prey, yielded actual ingestion rates of 8.0LJ.6% of body carbon day^-1 and 0.1ǂ.1% of body carbon day^-1, respectively. These results indicate that predatory feeding on pelagic copepods may constitute an important food source for G. wilkitzkii. Abundances of G. wilkitzkii at the ice underside (median: 1.6 ind. m^-2), Calanus spp. in the upper metre below the ice (2.6 ind. m^-3), and Halectinosoma sp. in the lowermost 2-3 cm of the ice (393.5 ind. m^-2) were determined from several multi-year pack-ice floes in the northern Greenland Sea and Fram Strait. Potential predation impact of G. wilkitzkii was estimated by combining information on ingestion rates with population densities. It was very high on Calanus spp. in the under-ice water layer (61.5% of the under-ice standing stock day^-1), but comparatively low on Halectinosoma sp. in the bottom of the ice (3.8% of standing stock day^-1). The observation of G. wilkitzkii preying on pelagic copepods in the under-ice water layer represents a hitherto unknown but obviously significant process and a new direction in the cryo-pelagic coupling in the Arctic marine ecosystem.     

Seasonal fluctuations of vagile benthos in the uppermost sublittoral of a maritime Antarctic fjord

Quantitative samples of benthos were taken on a stony beach in the maritime Antarctic (Admiralty Bay, King George Island, South Shetland Islands) during a complete annual cycle. The sampled habitat consisted of cobbles lying on sand and gravel in the fringe between the littoral and sublittoral zones; samples were always taken at low tide just below the water line. In this habitat, abundant macroalgal detritus was observed between stones. This stony beach appeared to be very rich in vagile fauna settled between and under stones. Macrobenthos consisted mainly of amphipods (ca. 85% of total number), gastropods (11%) and nemerteans (3%). The abundance of whole macrofauna ranged to over 50,000 ind. m^-2 and its biomass over 600 g m^-2 (FW). Seven species of Amphipoda and four species of Gastropoda were found. Amphipoda were dominated by Gondogeneia antarctica (over 70% of all amphipods) and Paramoera edouardi (over 20%), whereas among gastropods Laevilitorina antarctica prevailed (over 70%). Unexpectedly high abundance and biomass of Amphipoda were observed in the first half of winter (May/July), surpassing otherwise important summer amphipod abundance. The probable reason for this phenomenon could be high autumn abundance of decaying algae on the beach in the tidal zone, providing detritus that is probably the main food source for Amphipoda.     

Distribution, species composition, and dynamics of echinoderm larvae in an area of the Tumen River Estuary and of the Far East State Marine Reserve

Species composition, distribution, and density dynamics of echinoderm larvae were determined based on four samples taken at 28 stations in the summer-autumn season of 1997 in an area adjacent to the Tumen River Estuary and to the Far East State Marine Reserve. Larvae of nine species were recorded. The larvae ofOphiura sarsi (up to 9600 ind./m³) and ofEchinocardium cordatum (2058 ind./m³) were dominant in terms of density. The echinoderm larvae mostly appeared in the upper water layer (0–15 m). The study area can be divided into two sites based on the density and species composition of echinoderm larvae: the first to the south of Furugel'ma Island, where the density and species number were low, and the second to the north of Furugel'ma Island, where these parameters had higher values.     

Field deposition of Bt transgenic corn pollen: lethal effects on the monarch butterfly

We present the first evidence that transgenic Bacillus thuringiensis (Bt) corn pollen naturally deposited on Asclepias syriaca; common milkweed, in a corn field causes significant mortality of Danaus plexippus L. (Lepidoptera: Danaidae) larvae. Larvae feeding for 48 h on A. syriaca plants naturally dusted with pollen from Bt corn plants suffered significantly higher rates of mortality at 48 h (20Dž%) compared to larvae feeding on leaves with no pollen (3Dž%), or feeding on leaves with non-Bt pollen (0%). Mortality at 120 h of D. plexippus larvae exposed to 135 pollen grains/cm² of transgenic pollen for 48 h ranged from 37 to 70%. We found no sub-lethal effects on D. plexippus adults reared from larvae that survived a 48-h exposure to three concentrations of Bt pollen. Based on our quantification of the wind dispersal of this pollen beyond the edges of agricultural fields, we predict that the effects of transgenic pollen on D. plexippus may be observed at least 10 m from transgenic field borders. However, the highest larval mortality will likely occur on A. syriaca plants in corn fields or within 3 m of the edge of a transgenic corn field. We conclude that the ecological effects of transgenic insecticidal crops need to be evaluated more fully before they are planted over extensive areas.     

Larval niche selection and evening exposure enhance adoption of a predacious social parasite, Maculinea arion (large blue butterfly), by Myrmica ants

Larvae of the butterfly genus Maculinea feed briefly on a foodplant before being adopted as social parasites into Myrmica ant nests. Each Maculinea species typically survives only with a single Myrmica species, yet the eggs are laid across the overlapping territories of 3-5 Myrmica species and several other ants. The ability of Maculinea arion - a 'predatory' species of Maculinea - to influence its adoption into host Myrmica colonies was studied for the first time in the field. Some earlier reports, involving captive non-host ants, suggested that larvae of the predatory Maculinea follow ant trails into host nests or wander some distance from their foodplant before being discovered and (after a long interaction) carried away by Myrmica foragers. No dispersal from foodplants occurred in wild Maculinea arion larvae. Instead, they increased by >100-fold their probability of being discovered and adopted by Myrmica spp., rather than by ants of other genera, by exposing themselves in the micro-niche occupied by Myrmica foragers at their time of day of peak foraging. Despite a complex, hour-long interaction with Myrmica workers before being carried to the nest, Maculinea arion did not enhance its adoption by host species of Myrmica. Eggs were laid without bias in Myrmica sabuleti (host) and Myrmica scabrinodis (non-host) territories; larval survival on Thymus was the same in both ants' territories; larvae waited to be found beneath their foodplant rather than seek their host; Myrmica sabuleti and Myrmica scabrinodis foraged in the same vertical and temporal niches, and had the same probability of discovering larvae; both ants behaved identically after finding larvae and took the same time to adopt them; and the ratio of wild larvae taken into Myrmica sabuleti or Myrmica scabrinodis nests was the same as the distribution between these ants of Thymus, eggs and pre-adoption larvae.     

Water content, hydraulic conductivity, and ice formation in winter stems of Pinus contorta: a TDR case study

Stem water content, ice fraction, and losses in xylem conductivity were monitored from November 1996 to October 1997 in an even-aged stand of Pinus contorta (lodgepole pine) near Potlatch, Idaho, USA. A time domain reflectometry (TDR) probe was used to continuously monitor stem water contents and ice fractions. Stem sapwood water contents measured with TDR were not different from water contents measured gravimetrically. The liquid water content of stems ranged from 0.70 m³ m^-3 to 0.20 m³ m^-3 associated with freezing and thawing of the wood tissue. Ice fraction of the stem varied from 0-75% during the winter suggesting liquid water was always present even at ambient temperatures below -20°C. Shoot xylem tensions decreased through the winter to a minimum of ca. -1.4 MPa in February then increased to -0.4 MPa in May. Shoot xylem tensions decreased during the growing season reaching -1.7 MPa by September. Annually, low shoot water potentials were not correlated to decreases in stem hydraulic conductivity. Xylem conductivity decreased due to cavitation through the winter and was 70% of summer values by March. Decreases in xylem conductivity were correlated to low shoot water potentials and cumulative freezing and thawing events within the xylem. Xylem conductivity increased to pre-winter values by May and no reductions in xylem conductivity were observed during the growing season.     

Pelagic larvae of bivalve mollusks of Amursky Bay,Sea of Japan

Larvae of 63 Bivalvia taxa were found in Amursky Bay. Of these, 47 were identified to the species level. Larvae of 55 taxa were found throughout the bay. The highest species diversity was recorded in the northeastern part and in the center of the southern part of the bay, as well as at the exit from it. Larvae of Mactra chinensis, Mytilus coruscus, Crassostrea gigas, Teredo navalis, Mya japonica, and Mysella ventricosa were widely distributed in the bay. The maximum numbers of species were observed in July and September. A comparison of species lists using the set-theory method showed that the species complexes typical of different parts of Amursky Bay are formed under the influence of the Razdolnaya River runoff flow from the north and marine waters coming from the south. The mean density of larvae during the observation period was 1100 specimens/m³ in the northern and 735 specimens/m³ in the southern part of the bay. The highest density of larvae in Amursky Bay was observed at the end of June, the beginning of July, and in September; the minimal larval density occurred in April, May, and August. While the species diversity was similarly high, the density of larvae was significantly higher in Amursky Bay than in the nearby Ussuriisky Bay.     

In situ oxygen microelectrode measurements of bottom-ice algal production in McMurdo Sound, Antarctica

In-situ estimates of fast-ice algal productivity at Cape Evans, McMurdo Sound, in 1999 were lower than at the same site in previous years. Under-ice irradiance was between 0 and 8 µmol photons m^-2 s^-1; the ice was between 1.9 and 2.0 m thick and the algal biomass averaged 150 mg chl a m^-2, although values as high as 378 mg chl a m^-2 were recorded. Production on 11 and 12 November was between 0.053 and 1.474 mg C m^-2 h^-1. When the data from 11 November were fitted to a hyperbolic tangent function, a multilinear regression gave estimates for P_max of 0.571 nmol O₂ cm^-2 s^-1, an ! of 0.167 nmol O₂ cm^-2 s^-1 µmol^-1 photons m^-2 s^-1 and an E_k of 3.419 µmol photons m^-2 s^-1. A P_max of 2.674 nmol O₂ cm^-2 s^-1, an ! of 0.275 nmol O₂ cm^-2 s^-1 µmol^-1 photons m^-2 s^-1, r of 0.305 nmol O₂ cm^-2 s^-1 and an E_k of 9.724 µmol^-1 photons m^-2 s^-1 were estimated from the 12 November data. The sea-ice algal community was principally comprised of Nitzschia stellata, Entomoneis kjellmanii and Berkeleya adeliensis. Other taxa present included N. lecointei, Fragilariopsis spp., Navicula glaciei, Pleurosigma spp. and Amphora spp. Variations in the method for estimating the thickness of the diffusive boundary layer were not found to significantly affect the measurements of oxygen flux. However, the inability to accurately measure fine-scale variations in biomass is thought to contribute to the scatter of the P versus E data.     

Distribution patterns of Baltic herring larvae, Clupea harengus L., in the coastal waters off Helsinki, Finland

Changes in the spatial distribution of Baltic herring larvaethrough time were investigated in the waters off Helsinki, thenorthern Baltic Sea. The average larval densities were comparableto the relatively low levels (mean around 2 larvae m^–2)found in other studies in the Gulf of Finland. In shallow baysvirtually no herring larvae were found in early June. In lateJune and early July the densities of larvae longer than 10 mmincreased to 1–4 larvae m^–2 in shallow areas (depth<2 m), i.e. to levels higher than those recorded in deeperwaters. In combination with data on the size distributions ofthe larvae, these observations suggest that a significant proportionof the herring larvae are found in shallow water after the yolksac stage. We conclude that shallow coastal waters are potentiallyimportant nursery areas for herring larvae and that this featureof herring larval biology should be taken into account in planningsampling programs for larval herring.     

Trophodynamics of the plankton community at Dogger Bank: predatory impact by larval fish

The trophodynamics of a coastal plankton community were studied,focusing on fish larvae and their copepod prey. The major objectiveswere to describe distributional overlap and evaluate the predatoryimpact by larval fish. The study was carried out across DoggerBank in the North Sea, August-September 1991. Sampling transectscrossed tidal fronts off the Bank and plankton at all trophiclevels showed peak abundance within frontal zones. Also Verticallythere was a significant overlap in distributional patterns ofthe plankton. Seven species of fish larvae were abundant, ofthese sprat (Sprattus sprattus) dominated. The abundance ofone group of fish larvae peaked in the shallow water close tothe Bank, whereas other species, including sprat, were foundin deeper water. Prey preference and predation pressure of fishlarvae were assessed using information on prey sizes and growthrates of larvae and the copepod prey. We estimated larval removalof preferred prey sizes to 3–4% day^–1, counterbalancedby a 3–7% day^–1' replenishment from copepod productionand growth. Additional predation pressure on copepods by aninvertebrate predator was estimated to 1–3%day^–1.In conclusion, the dynamics of fish larvae and other zooplankterswere closely linked. At peak abundances of fish larvae (>35mg dry weight m^–2), the accumulated predation on specificsize ranges of copepods, exerted by larvae and other predators,could exceed the ability of copepod replenishment and intra-/interspecificcompetition among predators might take place.