Diel changes in the particulate environment,feeding activity and digestive enzyme concentration in neritic zooplankton

Diel changes in the particulate environment and nutritional metabolism of neritic zooplankton were studied in the Bay of Villefranche-sur-mer (France) for 30 h during February. Although the survey was carried out over a period of negligible wind speed, the changes in the particle size spectra and species composition of the Zooplankton sampled suggested an abrupt and temporary oscillation in the water mass at the second sampling time. The rest of the 30-h period was characterized by gradual changes which usually returned to conditions close to, but different from, the starting ones. A clear diel rhythm was recorded for the biochemical composition of the phytoplankton, probably related to the periodicity of the photosynthetic metabolism.The feeding rate of Clausocalanus arcuicornis Giesbrecht, 1888, measured by gut fluorescence, also showed diel rhythmicity with maximum rate at night. Digestive enzyme activities were measured on the total Zooplankton population composed of five major species: Clausocalanus arcuicornis, Paracalanus sp., Calanus helgolandicus Claus, 1863, Acartia clausi Giesbrecht, 1889, and Oikopleura dioica Fol, 1859. The activities of the carbohydrases showed varying patterns of periodicity with one or two night maxima. The proteases showed a different pattern with acidic proteases peaking just before dawn and decreasing gradually during the day and no periodicity for trypsin-like activity. No association could be established between the enzyme changes and those of either the food supply or the species composition of the Zooplankton sampled, suggesting that both feeding and digestion diel rhythms are controlled by an internal clock. Influences of internal, external and experimental factors on the digestive enzyme activity rhythm are discussed. The resulting scheme of short term regulation was compared with that proposed earlier for medium term changes.     

Diel variation in body carotenoid content and feeding activity in marine zooplankton assemblages

The relationship between diel variation in body carotenoid contentand feeding activity of zooplankton from Los Angeles Harbor.California, was investigated during two time series of 24h and32h, in August 1983 and May 1984. Carotenoid levels varied significantly(t-test. p<0.01) during each time series, with peak levelsoccurring around midnight. Feeding activity also exhibited anight time peak during each experiment. The regression of carotenoidcontent on feeding activity explained 87% and 82% of the variancein either parameter in the August and May experiments respectively.However, the regression equations varied from one experimentto the next. Between-experiment differences in the relationbetween carotenoid content and feeding activity and in the meancarotenoid levels over each time series may be related to differencesin phytoplankton concentration and composition during each experiment.     

Diel variation of zooplankton in the tropical coral-reef water of Tioman Island,Malaysia

Zooplankton was sampled at 3-h intervals for a 48-h period from a coral reef of Tioman Island, Malaysia. It was size-fractionated into three size classes: 100–200, 200–335, and >335 μm using different sieves with different mesh sizes. Total zooplankton (>100 μm) abundance and biomass in the water column were high later at night (0300 h), not just after sunset as previously described in other studies. Only the largest size-fraction (>335 μm) of zooplankton significantly differed in biomass and abundance between day and night. The increase in the large zooplankton later in the night is suggested to be caused by the advection of pelagic species into the reef. This work has provided a measurement of the variation of zooplankton community over coral reef that can exist on a scale of hours.     

Study of color variation in the solitary ascidian Halocynthia roretzi, collected in the Inland Sea of Japan

In the vicinity of Yashiro Island in the Inland Sea of Japan, the solitary ascidian (tunicate) Halocynthia roretzi with tunics of various colors were collected. Samples of these animals were sorted into three groups on the basis of visual observation of tunic color. The red group includes animals with dark-red, light-red, or orange tunics. The pink group includes animals with tunic colors ranging between red and white. The white group includes only animals with completely white tunics. Animals in the white group lacked color internally, with the exception of the hepatopancreas and the gonads in breeding season; the epidermis and gill basket were white. In contrast, animals of both the red group and the pink group were colored internally, with red-orange epidermis and yellow gill basket. Alloreactivity was tested by mixed-hemocyte incubation between different animals belonging to the same color group and between animals belonging to different color groups. Alloreactivity between animals of the white group was 56.3%, between animals of the pink group was 60.0%, and between animals of the red group was 69.3%. The relatively high frequency of compatible combinations among the white animals is discussed.     

Temporal and spatial variation of coastal zooplankton in the Baltic Sea

When analysing temporal variation monthly mean abundances of zooplankton sampled at a eoastal station in the northern Baltic Sea between 1976 and 1988 showed the lowest between-year variation in the summers The coefficients of variation were estimated at 50% for rotifers in June. 70% for cladocerans in August and between 30 and 50% for different copepodite stages in August Moreover in the summers, all dominating zooplankton groups were abundant Estimates of yearly biomass or production of zooplankton must, however, be based on frequent sampling during the whole year because of large differences between months in zooplankton composition and abundance
In 1989. spatial variation was analyzed by sampling zooplankton on three occasions along a 9 8 km transect with 15 stations, 700 m apart All taxonomic/life-stage groupings of zooplankton were heterogeneously distributed Geostatistical analysis did not give a definite answer to what the minimum distance between stations should be to obtain independent samples but indicated that 700 to 1400 m would be sufficient in most cases For most of the zooplankton groupings the coefficients of variation in the sampled area were estimated at 20-40% on all sampling occasions     

Seasonal variation in the species composition of tintinnid cilates in Hiroshima Bay, the Seto Inland Sea of Japan

Seasonal changes in the species composition of tintinnid ciliateswere examined based on time-series samples taken at 2 week intervalsover a 3 year period in Hiroshima Bay, the Seto Inland Sea ofJapan. The maximum abundance of total tintinnids over the entireperiod was 5.7 x 10³ indi viduals l^– Among 32 speciesidentified, a consistent seasonal occurrence was recognizedin 22 species. The relationships between various environmentalfactors and the abundance of each species of tintinnids wereanalyzed using principal component analysis From this analysis,the abundance of many tintinnids was revealed to be associatedwith temperature, the <20 µm size fraction of chlorophylla and water column stability, but not with the <20 µmsize fraction of chlorophyll a, nor with salinity. From theseresults, tintinnid species were divided into five associationtypes: species whose abundance increased with increasing temperature,decreasing temperature, nanophytoplankton abundance, increasingwater column mixing, or increasing water stratification coupledwith low temperature.     

Diel vertical migration of zooplankton in the Northeast Atlantic

Acoustic Doppler current profiler (ADCP) data collected duringAugust–September 1991 reveal the diel migration of zooplanktonin the northeast Atlantic (50–60     

Abundance and diversity of surface zooplankton in the Gulf of Aqaba, Red Sea, Egypt

Surface zooplankton were studied in Egyptian coastal watersof the Gulf of Aqaba, from bimonthly samples from July 1994to May 1995. Species diversity, numerical abundance and dynamicswere analysed for each taxon, at six sites, inside three Protectorates.A total of 62 taxa and species were identified. At all sites,copepods were predominant in the standing crop with an averageof 1945 ind. M^–3 and formed {small tilde}75.5%, numerically,of the total zooplankton community. The meroplanktonic larvaeoccupied the second rank and they constituted {small tilde}19.7%of the total zooplankton. Seasonally, the main peak of zooplanktonabundance was recorded in winter (January) with an average of3510 ind. M^–3 while September was characterized by thelowest density (1906 ind. m^–3 The relatively higher diversityvalues were recorded at Ras Mohammed Protectorate and a progressivedecline in diversity was observed northward.     

Carbon and nitrogen content of Noctiluca scintillans in the Seto Inland Sea, Japan

The carbon and nitrogen content of Noctiluca scintillans cellsfrom the Seto Inland Sea, Japan was investigated in order toestimate its biomass in natural samples. The carbon contentof N.scintillans ranged from 123 to 627 ng C cell^–1 witha mean value of 353 ng C cell^–1, or 1.12 to 2.67 fg Cµm^–3 with a mean value of 1.98 fg C µm^–3.The nitrogen content ranged from 36.0 to 232 ng N cell^–1with a mean value of 131 ng N cell^–1, or 0.499 to 0.910fg N µm^–3 with a mean value of 0.694 fg N µm^–3.Total cell carbon and nitrogen increased but the carbon andnitrogen per cell volume decreased with increasing cell volume.The C/N ratio of the cells ranged from 2.3 to 4.4, which wasrelatively low compared with the Redfield ratio. The carbonand nitrogen content was extremely low (91.2 ng C cell^–1,41.8 ng N cell^–1) for starved cells, whereas it was extremelyhigh (528 ng C cell^–1, 205 ng N cell^–1) for cellswhich had ingested the large diatom, Coscinodiscus wailesii.Our results suggest that the carbon and nitrogen content ofN.scintillans varies depending on its physiological conditionand the type of food that it has recently consumed.     

Diel variation in feeding rate and prey composition of herring and mackerel in the southern Gulf of St Lawrence

Diel feeding patterns of herring Clupea harengus and mackerel Scomber scombrus in the southern Gulf of St Lawrence were examined based on samples obtained by midwater trawling between 19 and 26 June 2001. Within 3 h time periods, stomach contents tended to be more similar between fish from the same tow than between fish from different tows. Thus, in contrast to previous diet studies, which have used individual fish stomachs as independent observations, tow was used as the experimental unit in statistical analyses in this study. Diel patterns in stomach fullness were identified using generalized additive models. Two peaks in stomach fullness occurred for herring, one in the morning and the other in the evening. Mackerel showed an increase in feeding intensity throughout the day with a peak in mid‐afternoon. The diel changes in stomach contents suggested rapid gastric evacuation rates for both species, especially for herring. The estimate of the instantaneous evacuation rate for herring was twice that for mackerel. Calanus copepods (mainly C. hyperboreus ), fishes (mainly capelin Mallotus villosus ) and euphausiids were the main prey found in the stomachs of both species. Calanus copepods dominated the diet of herring regardless of time period. They also dominated the diet of mackerel during the late afternoon, evening and night while fishes and euphausiids were dominant during the morning and early afternoon. These diel patterns emphasize the need for sampling throughout the day and night in order to estimate ration and diet composition for bioenergetic and ecosystem models.     

The role of zooplankton in the functioning of the Taganrog Gulf ecosystem in the Sea of Azov

The taxonomic composition, distribution of biomass and seasonal variability of zooplankton were studied in various areas of the Taganrog Gulf of the Sea of Azov. The structural-functional transformation of zooplankton was analyzed for ecosystems of various levels of organization (the hypereutrophic central and eutrophic western parts). Unusually strong water blooming caused by cyanobacteria and the pressure of predatory comb jelly results in the elimination of zooplankton, the simplification of the trophic web, and the loss of the ecosystem’s capacity for biotic self-purification. The considerable participation of microzooplankton, especially that of tintiniids, in the metabolism of the Taganrog Gulf ecosystem is one of the important features of its sustainable functioning.     

Biomass, feeding and production of Noctiluca scintillans in the Seto Inland Sea, Japan

The abundance and biomass of the large heterotrophic dinoflagellateNoctiluca scintillans, together with the changes in its potentialprey items, were monitored in the Seto Inland Sea, Japan, duringsummer 1997 (17 July-11 August). Growth and grazing rates ofNscintillans fed natural plankton populations were also measuredeight and seven times, respectively, during the survey period.The abundance and biomass of N scintillans averaged over thewater column (19 m) were in the range 1–345 cells 1^–1(temporalaverage = 93 cell1^–1) and 0.1–49.6 µg C l^–1(temporalaverage = 13.8 µg C l^–1; three times higher thanthat of calanoid copepods during the same period). Noctilucascintillans populations followed the changes in phytoplankton:N.scintillans biomass was increasing during the period of diatomblooms and was at a plateau or decreasing during periods oflow chlorophyll a. The growth rates of N.scintillans (µ)were also consistent with the wax and wane of the N.scintillanspopulation: N.scintillans showed highest growth rates duringdiatom blooms. A simple relationship between µ and chlorophylla concentration was established, and the production of N.scintillanswas estimated using this relationship and the measured biomass.The estimated production averaged over the water column wasin the range >0.1–5.2 µg C l^–1 day^–1(temporalaverage = 1.4 µg C l^–1 day^–1; 64% of the productionof calanoid copepods during the same period). Diatom clearancerates by N.scintillans were in the range 0.10–0.35 mlcell^–1 day^–1, and the phytoplankton population clearanceby N.scintillans was >12% day^–1. Thus, although thefeeding pressure of N.scintillans on phytoplankton standingstock was low, N.scintillans was an important member of themesozooplank-ton in terms of biomass and production in the SetoInland Sea during summer.     

Reproductive biology of the planktonic copepod Paracalanus sp. in the Inland Sea of Japan

Egg production of the planktonic copepod Paracalanus sp. wasinvestigated both in the laboratory and in the Inland Sea ofJapan. Its spawning varied daily, but not always, being highestduring the night or around dawn. The egg size was correlatedpositively with female body size. Under food-satiated laboratoryconditions, the specific egg production rate increased exponentiallywith an increase of temperature from 5.0 to 17.5°C, beyondwhich the rate decreased. However, the egg production rate ofthe natural population did not decrease up to     

Detection of marine birnavirus genome in zooplankton collected from the Uwa Sea,Japan

Marine birnaviruses (MABVs) infect a wide range of fish and shellfish, yet their mode of transmission is still unclear. To determine whether marine plankton serve as a vector for MABVs, we examined plankton collected from the Uwa Sea, Japan. The phytoplankton and zooplankton were collected monthly, at depths of 0 and 40 m, from May to November 2001. Detection of the MABV genome was carried out using 2-step PCR and virus isolation. Viral genome was detected in zooplankton collected at 0 m depth in September and at 40 m depth in November. The virus could not be isolated in the PCR-positive samples. These results suggest that zooplankton may act as a vector of MABVs, although the infective and/or accumulated virus titer in zooplankton was low.     

Diel patterns of UVBR-induced DNA damage in picoplankton size fractions from the Gulf of Aqaba,Red Sea

This study focuses on the impact of natural levels of UVBR (ultraviolet-B radiation: 280 to 315 nm) on bacterio- and phytoplankton (<10 mm) from the Gulf of Aqaba, Red Sea. Incident biologically effective doses (BEDs) and attenuation of biologically effective radiation in the water column were measured using a DNA biodosimeter. UVBR-induced DNA damage was measured as cyclobutane pyrimidine dimers (CPDs), using an antibody directed to CPDs followed by chemiluminescent detection. Depth profiles of DNA damage were determined in two plankton size fractions (0.2 to 0.8 mm and 0.8 to 10 mm) collected down to 50 m depth. Furthermore, accumulation and removal of CPDs were monitored in surface plankton samples during several daily cycles. Small plankton (plankton <10 mm) composition was determined by flow cytometry. The plankton community in the Gulf of Aqaba was dominated by nonphototrophic bacteria and the free-living prochlorophyte Prochlorococcus spp. (<0.8 mm). In general, no DNA damage could be detected in dosimeter DNA below 15 m. In contrast, DNA damage (up to 124 CPD Mnucl-1) could be detected in all bacterio- and phytoplankton samples. DNA damage accumulated throughout the day, indicating that plankton in the Gulf of Aqaba undergo UVBR stress via CPD induction. Although the numbers of CPDs decreased during darkness, both size fractions showed some residual DNA damage at the end of the night. This suggests that dark repair processes did not remove all CPDs, or that part of the plankton community was incapable of repair at all. CPD levels in the two size fractions showed no significant differences in situ. During full solar radiation exposures (samples incubated in bags), more CPDs were detected in the smaller (0.2 to 0.8 mm) size fraction as compared to the larger (0.8 to 10 mm) size fraction. In these experiments, initial plankton composition was significantly different from the field samples. This implies that a shift in the population structure or irradiance conditions can lead to a significant change in UVBR sensitivity. In conclusion, the results show that the picoplankton-dominated phyto- and bacterioplankton communities in the clear surface waters from the Gulf of Aqaba undergo UVBR stress. Repair pathways are not sufficient to eliminate damage during or after UVBR exposure hours, suggesting photomortality as a potential loss parameter of the plankton community.     

Movements and Habitat-Use of Loggerhead Sea Turtles in the Northern Gulf of Mexico during the Reproductive Period

Nesting strategies and use of important in-water habitats for far-ranging marine turtles can be determined using satellite telemetry. Because of a lack of information on habitat-use by marine turtles in the northern Gulf of Mexico, we used satellite transmitters in 2010 through 2012 to track movements of 39 adult female breeding loggerhead turtles (Caretta caretta) tagged on nesting beaches at three sites in Florida and Alabama. During the nesting season, recaptured turtles emerged to nest 1 to 5 times, with mean distance between emergences of 27.5 km; however, several turtles nested on beaches separated by ∼250 km within a single season. Mean total distances traveled throughout inter-nesting periods for all turtles was 1422.0±930.8 km. In-water inter-nesting sites, delineated using 50% kernel density estimation (KDE), were located a mean distance of 33.0 km from land, in water with mean depth of −31.6 m; other in-water inter-nesting sites, delineated using minimum convex polygon (MCP) approach, were located a mean 13.8 km from land and in water with a mean depth of −15.8 m. Mean size of in-water inter-nesting habitats were 61.9 km² (50% KDEs, n = 10) and 741.4 km² (MCPs, n = 30); these areas overlapped significantly with trawling and oil and gas extraction activities. Abundance estimates for this nesting subpopulation may be inaccurate in light of how much spread there is between nests of the same individual. Further, our results also have consequences for critical habitat designations for northern Gulf loggerheads, as protection of one nesting beach would not encompass the entire range used by turtles during breeding seasons.     

Annual sediment respiration in estuarine sandy intertidal flats in the Seto Inland Sea, Japan

To quantify organic matter mineralization at estuarine intertidal flats, we measured in situ sediment respiration rates using an infrared gas analyzer in estuarine sandy intertidal flats located in the northwestern Seto Inland Sea, Japan. In situ sediment respiration rates showed spatial and seasonal variations, and the mean of the rates is 38.8 mg CO₂-C m⁻² h⁻¹ in summer. In situ sediment respiration rates changed significantly with sediment temperature at the study sites (r ² = 0.70, p < 0.05), although we did not detect any significant correlations between the rates and sediment characteristics. We prepared a model for estimating the annual sediment respiration based on the in situ sediment respiration rates and their temperature coefficient (Q ₁₀ = 1.8). The annual sediment respiration was estimated to be 92 g CO₂-C m⁻² year⁻¹. The total amount of organic carbon mineralization for the entire estuarine intertidal flats through sediment respiration (43 t C year⁻¹) is equivalent to approximately 25% of the annual organic carbon load supplied from the river basin of the estuary.     

Biology of the swimming acorn worm Glandiceps hacksi from the Seto Inland Sea of Japan

The enteropneust hemichordate Glandiceps hacksi inhabits the muddy bottoms of the intertidal to subtidal zones of Koguno-shima Island, located in the central part of the Seto Inland Sea of Japan. Monthly collections from October 2005 to September 2007 revealed that their spawning occurs once a year, in the latter half of May. Parameters such as density and sex ratio, as well as the type of sediment, were also examined. Worm behavior and type of burrows revealed that G. hacksi are infaunal burrowers. Autotomy and regeneration of their posterior regions, and swimming behavior were also observed in an aquarium environment. This is the first comprehensive study on the biology of G. hacksi, the swimming acorn worm.     

Clinal variation at aspartate aminotransferase-2 in spotted seatrout,Cynoscion nebulosus (Cuvier), inhabiting the north-western Gulf of Mexico

Clinal variation was observed at the aspartate aminotransferase-2 (AAT-2) locus in the marine fish Cynoscion nebulosus (Cuvier) inhabiting the bays and estuaries of the Texas and northern Mexico Gulf coasts. Frequency of the AAT-2(80) allele increased from 0.9% at Sabine Lake, Texas to 17.1% at Rio Soto La Marina, Mexico. A statistically significant correlation existed in the frequency of this allele with degrees north latitude and west longitude. This information, if properly incorporated into a comprehensive enhancement programme, could facilitate supplemental stocking success.