Horizontal patchiness in zooplankton populations in two Ontario kettle lakes

Horizontal distributions of zooplankton were investigated in two kettle lakes in southern Ontario. In Tory Lake a set of random samples at 1 m depth showed that Skistodiaptomus oregonensis and copepod nauplii were overdispersed (patchy). In Lake St. George a 20 point grid sampled at each of 0.5, 2, 4, and 6 m showed that Polyarthra spp., Keratella cochlearis, Asplanchna spp., Daphnia galeata mendotae, Bosmina longirostris, Eubosmina coregoni and copepod nauplii were all patchy in terms of both vertical and horizontal distributions. Contour diagrams showed that the patches tended to be comprised of unique groups of species. This was confirmed by principal components analysis which showed that Polyarthra spp. and K. cochlearis occurred together, that D. g. mendotae was found in a unispecies patch and that B. longirostris and E. coregoni were together. None of the zooplankton patches correlated with chlorophyll a measurements. A literature review suggests that there are four basic types of patches occurring in lakes and that there are at least 16 identifiable forces which might cause these distributions. The patch types are: I) large scale (> 1 km diameter), II) small scale, caused by wind-induced water movement, III) Langmuir circulation aggregations and IV) swarms, potentially caused by biotic factors.     

Multiscale patchiness of the calanoid copepod Temora longicornis in a turbulent coastal sea

We present evidence that intermittent variability in zooplanktonabundance can be characterized in terms of multifractals. A3-min-resolution time series of abundance in the calanoid copepodTemora longicornis, taken from a fixed mooring in the coastalwaters of the Eastern English Channel for 66 h, provided thedata for our analysis. The multifractal nature of the distributionof T. longicornis abundance appears to be very different fromthose of purely passive scalars (i.e. temperature and salinity),and also from phytoplankton biomass over a similar range ofscales in similar environments. Finally, we show that the multifractaldistribution of T. longicornis can be wholly described by threebasic parameters in the framework of universal multifractals,opening up very large perspectives for future modeling of pelagicecosystem structures and functions.     

Vesicle trafficking and cell surface membrane patchiness.

Membrane proteins and lipids often appear to be distributed in patches on the cell surface. These patches are often assumed to be membrane domains, arising from specific molecular associations. However, a computer simulation (Gheber and Edidin, 1999) shows that membrane patchiness may result from a combination of vesicle trafficking and dynamic barriers to lateral mobility. The simulation predicts that the steady-state patches of proteins and lipids seen on the cell surface will decay if vesicle trafficking is inhibited. To test this prediction, we compared the apparent sizes and intensities of patches of class I HLA molecules, integral membrane proteins, before and after inhibiting endocytic vesicle traffic from the cell surface, either by incubation in hypertonic medium or by expression of a dominant-negative mutant dynamin. As predicted by the simulation, the apparent sizes of HLA patches increased, whereas their intensities decreased after endocytosis and vesicle trafficking were inhibited.     

Factors affecting zooplankton feeding by the sea anemoneAiptasia pallida

Effects of various treatments on prey capture, prey ingestion and ingestion time of individualArtemia salina nauplii by the sea anemoneAiptasia pallida Verrill were studied in the laboratory. Exposure to crudeArtemia homogenate, 5 × 10^–4 M reduced glutathione or 5 × 10^–4 M proline significantly decreased the number ofArtemia that were captured and ingested but had no significant effect on the ingestion time of individualArtemia. Multiple captures increased the total ingestion time but decreased ingestion time per prey item. Results suggest that, under these conditions, the prey capture phase of zooplankton feeding was somewhat distinct from the ingestion phase since chemical stimuli that significantly reduced prey capture had no significant effect on ingestion time.     

Danger of zooplankton feeding: the fluid signal generated by ambush-feeding copepods

Zooplankton feed in any of three ways: they generate a feeding current while hovering, cruise through the water or are ambush feeders. Each mode generates different hydrodynamic disturbances and hence exposes the grazers differently to mechanosensory predators. Ambush feeders sink slowly and therefore perform occasional upward repositioning jumps. We quantified the fluid disturbance generated by repositioning jumps in a millimetre-sized copepod (Re ∼ 40). The kick of the swimming legs generates a viscous vortex ring in the wake; another ring of similar intensity but opposite rotation is formed around the decelerating copepod. A simple analytical model, that of an impulsive point force, properly describes the observed flow field as a function of the momentum of the copepod, including the translation of the vortex and its spatial extension and temporal decay. We show that the time-averaged fluid signal and the consequent predation risk is much less for an ambush-feeding than a cruising or hovering copepod for small individuals, while the reverse is true for individuals larger than about 1 mm. This makes inefficient ambush feeding feasible in small copepods, and is consistent with the observation that ambush-feeding copepods in the ocean are all small, while larger species invariably use hovering or cruising feeding strategies.     

披山岛海区浮游动物种类组成及数量分布特点

根据2007年披山岛海区春季和夏季2个季度浮游动物调查资料,分析和研究了浙江省玉环县披山岛海区浮游动物种类组成和数量分布特点.结果表明:浮游动物共有18种,属3门12属,其中桡足类的种类最多,占总种数的72.22%;主要优势种为中华哲水蚤(Calanus sinicus)、瘦拟哲水蚤(Paracalanus gracilis)、针刺拟哲水蚤(Paracalanus aculeatus)和红小毛猛水蚤(Microsetella rosea).浮游动物的平均丰度及生物量均为春季比夏季高,春季的平均丰度为6.55×103个/m3,夏季为6.13×103个/m3;春季的平均生物量为216.49 mg/m3,夏季为98.26 mg/m3.桡足类的生物量占浮游动物总量的75.97%～97.55%,是决定披山岛浮游动物数量分布和变动的主要成分.与历史资料和邻近海域相比较,披山岛海区生物量与其接近或大于东海各海域.春、夏两季生物多样性(H′)有显著性差异(P<0.05),春季具有较高的生物多样性,且远海的生物多样性大于近海.     

Distribution of surface zooplankton and seabirds across the Southern Ocean

Surface zooplankton and seabird densities and community composition in the Atlantic (between Cape Town and Sanae) and Pacific (between New Zealand and the Ross Sea) sectors of the Southern Ocean are described and related to oceanographic features. Samples were collected during two return voyages aboard the MV Benjamin Bowring as part of the Transglobe Expedition (1979–1981). High abundances of surface zooplankton and seabirds were consistently observed within the main frontal systems of the Southern Ocean. Generally, on a mesoscale significant correlations between surface temperature and the distribution of zooplankton or seabirds were observed. On a macroscale, the geographical positions of the zooplankton and seabird communities coincided with specific water masses. The results of this study suggest that appropriate food availability rather than water temperature is important for the determination of seabird distribution. The ecological importance of the recently described frontal zone associated with the northern boundary of the maximum winter expansion of sea ice is confirmed by biological data obtained in this study.     

Mechanical properties of the surface of the sea urchin egg at fertilization and during cleavage

1. 1. Changes in stiffness of the cell surface at fertilization and during cleavage in sea urchin eggs were determined by the magnetic particle method.

2. 2. The stiffness of the cell surface increased at fertilization, reached a maximum after about 1.5 min, then decreased and reached a minimum about 4 min after insemination, followed by a gradual increase, in the eggs of Temnopleurus toreumaticus at 25.5 to 26.5 °C.

3. 3. The stiffness of the cell surface increased during the diaster stage, reached a maximum 2 to 3 min before the onset of cleavage, then decreased to a minimum about 1 min before the onset of cleavage, increased again, reached a maximum during cleavage and then diminished, in the eggs of Temnopleurus toreumaticus at 25.5 to 26.5 °C. A similar stiffness change was observed in the eggs of Hemicentrotus pulcherrimus at 17 to 19 °C, occurring almost in parallel in both the equatorial and polar surfaces.

     

The price of patchiness

Patchy distribution of animals, on a large or small scale, is a common phenomenon. Various explanations have been given for this spatial and temporal heterogeneity, but in many cases the causes are obscure. Patchy distribution of zooplankton is not understood and was not even expected in the fast turbulent currents of the well mixed tidal channels of the Wadden Sea. This patchiness is shown here for a number of plankton species. Methods commonly used for monitoring plankton usually neglect the fact of patchy distribution, and thus results suffer. Interpretation of such data can be highly misleading, particularly when used to assess the environmental status of an area: an overestimate or underestimate of population density may be the result. Sound quantitative data can only be obtained by making great efforts in terms of work and money. The costs entailed by such studies must be valued accordingly. Presented at the VI International Wadden Sea Symposium (Biologische Anstalt Helgoland, Wattenmeerstation Sylt, D-2282 List, FRG, 1–4 November 1988)     

Immunological evidence for the localization of sialoglycosphingolipids at the cell surface of sea urchin spermatozoa.

The localization of sialoglycosphingolipids in the plasma membrane of sea urchin spermatozoa was studied by employing immunological methods including immunolysis of liposomal model membranes. The antibodies produced against these complex lipids were found to agglutinate various sea urchin spermatozoa differently. Both species differences and species similarities in the agglutination were found in spermatozoa of the echinoderm, the sea urchin and the starfish. The agglutination of the sea urchin spermatozoa was inhibited specifically by ceratain carbohydrates. Only a limited number of molecular species of sialoglycosphingolipid were localized at the surface of the plasma membrane of sea urchin spermatozoa cells. Moreover, topographical differences were found in the localization of the sialoglycosphingolipids at the cell surface of spermatozoa.     

Pelagic sea snakes dehydrate at sea

Secondarily marine vertebrates are thought to live independently of fresh water. Here, we demonstrate a paradigm shift for the widely distributed pelagic sea snake, Hydrophis (Pelamis) platurus, which dehydrates at sea and spends a significant part of its life in a dehydrated state corresponding to seasonal drought. Snakes that are captured following prolonged periods without rainfall have lower body water content, lower body condition and increased tendencies to drink fresh water than do snakes that are captured following seasonal periods of high rainfall. These animals do not drink seawater and must rehydrate by drinking from a freshwater lens that forms on the ocean surface during heavy precipitation. The new data based on field studies indicate unequivocally that this marine vertebrate dehydrates at sea where individuals may live in a dehydrated state for possibly six to seven months at a time. This information provides new insights for understanding water requirements of sea snakes, reasons for recent declines and extinctions of sea snakes and more accurate prediction for how changing patterns of precipitation might affect these and other secondarily marine vertebrates living in tropical oceans.     

Barium spikes are generated in the spines of the sea urchin Diadema antillarum

In the presence of calcium, Ba2+ ions, at concentrations as low as 1-2 mM, block the action potentials (a.p.'s) elicited by the electrical stimulation of the primary spines of Diadema antillarum. Lower concentrations of barium (0.1 mM) potentiate the a.p.'s recorded from spines equilibrated with Ca-Free artificial sea water (ASW). Exposure of the spines to a saturated solution of EDTA in Ca-free, unbuffered ASW reversibly blocks their electrical activity. Spines blocked by EDTA continue to generate a.p.'s following their equilibration with Ca-free ASW containing 1 mM of Ba2+ ions. The time course of the a.p.'s recorded from spines equilibrated with normal ASW is only slightly affected by the combined action of 15 mM of tetraethylammonium (TEA) and 5 mM of 4-aminopyridine (4-AP). In contrast, the duration of the a.p.'s recorded from spines blocked by EDTA and placed in 1 mM barium is markedly increased by the combined actions of TEA and 4-AP at the above concentrations. We conclude that the Ca-channels of the neurites present in Diadema spines are not, at least qualitatively, an exception with regard to their permeation by Ba2+. The blocking action of low concentrations of these ions, particularly in the presence of calcium, may be explained by the extremely high surface to volume ratio prevailing in neurites with a diameter of only less than 0.1-0.3 micron.     

Restless gossamers: antibody clearance by hydrodynamic flow forces generated at the surface of motile trypanosome parasites

Trypanosomes evade antibody-mediated lysis via antigenic variation and rapid antibody removal from their cell surface. Recently, in Cell, Engstler et al. (2007) have discovered the mechanism for antibody clearance. Hydrodynamic forces generated by trypanosome swimming create a current, causing surface-bound antibodies to act as "molecular sails." Consequently, they are swept to the cell posterior, internalized via the flagellar-pocket, and degraded. Hydrodynamic sorting is a novel biological process, possibly applicable in other contexts.     

Solar and lunar rhythms in the occurrence of Astronesthes niger (Pisces) at the sea surface

Abstract

The mesopelagic fish Astronesthes niger concentrates in the uppermost centimeters of the sea when both sun and moon are below the horizon. Probability of positive catches increases towards the times of lower culmination of sun and moon and perhaps is highest when both culminations are about synchronous. Positive catches were made only when the moon was near its first or third quarter, but this might be somewhat influenced by the material which was not evenly distributed in relation to moonphases. It is assumed that A. niger needs moonlight for vertical migration, but avoids the surface during illumination.     

The alphaBbetaC integrin is expressed on the surface of the sea urchin egg and removed at fertilization

Integrins are expressed on the surface of some vertebrate eggs where they are thought to have a role in fertilization. The objective of this study is to determine if integrins are expressed on sea urchin eggs. The alphaB and betaC subunits were cloned using the homology polymerase chain reaction. Monoclonal and polyclonal antibodies were developed against bacterially expressed fragments of the extracellular domains of the betaC subunit and the alphaB subunit. As well, a monoclonal antibody was developed against a synthesized peptide corresponding to part of the cytoplasmic domain of betaC. Analysis of biotinylated egg cortex extracts immunoprecipitated with either anti-betaC or anti-alphaB yields bands of 130 and 225 kDa. Immunoblots confirm that betaC is part of the complex immunoprecipitated with anti-alphaB. Confocal immunofluorescence and immunogold electron microscopy show that betaC is present on the surface of the unfertilized egg at the tips of microvilli and in cortical granules. During the cortical reaction, immunoreactivity with antibodies to the extracellular domains of betaC and alphaB disappears from the egg surface, and microvillar casts on the fertilization envelope become immunoreactive. With antibodies to the cytoplasmic domain of betaC, immunoreactivity is lost from the surface of the egg, but the fertilization envelope does not immediately become immunoreactive. In immunoblots of egg cortex there are immunoreactive bands of the predicted sizes for alphaB and betaC. However, in fertilization envelopes, a second band that is slightly lower in molecular weight is also present. Eggs fertilized in the presence of soybean trypsin inhibitor have elongated microvilli that remain bound to the elevating fertilization envelope and immunoreactive to anti-betaC antibodies. Eggs fertilized in the presence of an ovoperoxidase inhibitor, 3-amino-1,2,4-triazole, have a patchy distribution of betaC immunoreactivity in fertilization envelopes. Together, these data suggest that alphaBbetaC integrins are expressed on the surface of unfertilized eggs and, during the cortical reaction, the extracellular domains are cleaved by proteases and cross-linked into the fertilization envelope by ovoperoxidase. The alphaBbetaC integrin receptors may have several potential functions prior to their removal at fertilization, including attachment of the vitelline envelope to the egg surface and anchoring the cortical cytoskeleton.     

Earlier nesting by loggerhead sea turtles following sea surface warming

The onset of spring, noted by the timing of wildlife migratory and breeding behaviors, has been occurring earlier over the past few decades. Here, we examine 15 years of loggerhead sea turtle, Caretta caretta, nesting patterns along a 40.5 km beach on Florida's Atlantic coast. This small section of beach is considered to be the most important nesting area for this threatened species in the western hemisphere. From 1989 to 2003, the annual number of nests fluctuated between 13 000 and 25 000 without a conspicuous trend; however, based on a regression analysis, the median nesting date became earlier by roughly 10 days. The Julian day of median nesting was significantly correlated with near‐shore, May sea surface temperatures that warmed an average of 0.8°C over this period. This marine example from warm temperate/subtropical waters represents another response of nature to recent climate trends.     

Phytoplankton dynamics in relation to hydrography, nutrients and zooplankton at the onset of sea ice formation in the eastern Weddell Sea (Antarctica)

The quantitative and qualitative distribution of phytoplankton was investigated along five North–South transects in the eastern Weddell Sea during the transition from late autumn to winter. Relationships with the regional hydrography, progressing sea ice coverage, nutrient distribution and zooplankton are discussed and compared with data from other seasons. To the north of the Antarctic Slope Front (ASF) a remnant temperature minimum layer was found above the primary pycnocline throughout summer. Surface waters had not entirely acquired typical winter characteristics. While temperature was already in the winter range, this was not the case for salinity. Highest biomass of phytoplankton, with the exception of the first transect, was found in the region adjoining the ASF to the north. Absolute chlorophyll a (Chl a) concentrations dropped from 0.35 to 0.19 g l^–1 . Nutrient pools exhibited a replenishing tendency. Ammonium concentrations were high (0.75–2 mol l^–1), indicating extensive heterotrophic activity. The phytoplankton in the ASF region was dominated by nanoflagellates, particularly Phaeocystis spp.. North of the ASF the abundance of diatoms increased, with Fragilariopsis spp., F. cylindrus and Thalassiosira spp. dominating. Community structure varied both due to hydrographical conditions and the advancing ice edge. The phytoplankton assemblage formed during late autumn were very similar to the ones found in early spring. A POC/PON ratio close to Redfield, decreasing POC concentration and a high phaeophytin/Chl a ratio, as well as a high abundance of mesozooplankton indicated that a strong grazing pressure was exerted on the phytoplankton community. A comparison between primary production (PP) in the water column and the sea ice showed a shift of the major portion of PP into the ice during the period of investigation.