Vertical distribution and nocturnal migration of Nyctiphanes couchi (Crustacea: Euphausiacea) in relation to the summer thermocline in the Celtic Sea

Vertical distributions and nocturnal migrations of the developmental stages of Nyctiphanes couchi (Bell) in relation to the summer thermocline in the Celtic Sea, 25 to 26 August 1982, have been investigated using the Longhurst-Hardy Plankton Recorder (LHPR). The vertical distributions of the metanauplii and adult females suggest that N. couchi liberates its young within the euphotic zone as mature metanauplii which, in a matter of hours, moult into the first feeding stage (Calyptopis I). The ascent migration by adult females took a maximum of 3 h (17.10 to 20.05 hrs) and had an amplitude of 50m (54 to 4 m) from below to above the thermocline. A 7C° thermocline occurred between 20 to 30 m in these profiles. The nocturnal migrations by the females were for the purpose of breeding as well as feeding within the euphotic zone and were not influenced by the presence of the thermocline. The majority of the calyptopes and furciliae remained above the thermocline over the sampling period. The post-larval males and females migrated; their vertical distributions showed a pattern similar to those of the adult females. The larger the developmental stage, the deeper was the mode of its vertical distribution. The zooplankton dry weight in the profiles ranged from 3.74 to 6.91 g per haul (=1.85 to 3.45 g C m^-2, 0 to 100 m). The euphausiids represented 35% of total zooplankton dry weight and their migrations removed a large percentage of the total zooplankton biomass from the euphotic zone for 18 h d^-1. Such a large displacement of biomass would have a major impact on the biological interactions within the ecosystem.     

Vertical distribution of Calanus finmarchicus and C. helgolandicus in relation to the development of the seasonal thermocline in the Celtic Sea

The geographical distribution and annual mean abundance of Calanus finmarchicus (Gunnerus) and C. helgolandicus (Claus) in the northern North Atlantic Ocean were shown in relation to the seasonal and annual fluctuations of abundance of the species in the Celtic Sea from 1960 to 1981. These congeneric copepods, although showing allopatric distributions over most of their geographical range, have sympatric distributions in the Celtic Sea where they dominate the dry weight biomass of the plankton throughout the year. The two species respond differently to the development of the seasonal thermocline and halocline by taking up different vertical distributions in the water column. C. finmarchicus occurred in the colder, more saline water below the thermocline, while C. helgolandicus occurred in the warmer, less saline water above the thermocline. This behaviour is postulated as a mechanism by which these morphologically similar copepods more fully exploit the resources of their temporally and spatially heterogeneous environment and also minimise interspecific competition. The species have the same foraging techniques and are able to exploit the same size spectrum of particulates. The vertical depth strata in which the populations are found for most of the year in the Celtic Sea means that both species exploit the diatom bloom in early spring but, thereafter, C. helgolandicus grazes on the daily production of the autotrophs in the euphotic zone while C. finmarchicus, below the thermocline, has to rely for its food on sedimenting particulates (whole cells, detritus and faecal material). The isolating mechanisms whereby these two populations partition the habitat in the Celtic Sea are discussed.     

Vertical distribution of zooplankton glutamate dehydrogenase in relation to chlorophyll in the vicinity of the Nantucket Shoals

The vertical distributions of chlorophyll, and zooplankton glutamate dehydrogenase (GDH) and respiratory electron transport system (ETS) activities were measured at five stations in the vicinity of the Nantucket Shoals using a submersible pump-profiling system. Distinctly lower zooplankton GDH activities and chlorophyll concentrations were found at a station showing little vertical stratification as compared to the other stations where vertical stratification was more pronounced. Maximum GDH activity was observed at or immediately above the chlorophyll maximum at the stratified stations. Respiration to excretion (O:N) ratios determined from the enzyme data were lowest in or just above the chlorphyll maximum, suggesting proteolytic catabolism at those depths. Both features had previously been observed in the oligotrophic Gulf of Mexico. Ammonium excretion determined from GDH activity was estimated to provide 20 to 40% of the total algal nitrogen requirement.Bigelow Laboratory Contribution No. 82016     

Vertical distribution,and seasonal and diurnal migration of Calanus helgolandicus in the Celtic Sea

The vertical distribution and migration (seasonal, diel and ontogenetic) of Calanus helgolandicus are described from the shallow (100 m) shelf-seas to the south-west of the British Isles. In 1978 and 1979, the overwintering population of C. helgolandicus consisted primarily of Stage V copepodites and adults. By late winter/early spring the copepodites had moulted to adult females (>90%), which matured and bred the first cohorts of the year, prior to onset of the spring phytoplankton bloom in April/May. C. helgolandicus reached a peak of numerical abundance in August of 20x10³ copepodites m^-2 (over the depth range sampled -0 to 70 m), which was 200 times the population in winter. The seasonal peak of abundance occurred 4 mo after the peak of the bloom of phytoplankton in spring. The yearly development of the copepod was not always out of phase with the diatom bloom, as seen when the data from 1978 was placed in the context of a longer time-series collected at 10 m over 22 yr (1960–1981, inclusive). Large vertical migrations were observed in the younger copepodites (CI and II) in May from below to above the thermocline. In the remainder of the year, the CI and CII stages behaved differently and were located above the thermocline within the euphotic zone. The largest vertical displacements of biomass were seen in the summer months due to the migrations of the CV stages and adults, which had developed from the spring cohorts. It was contended that the seasonal and vertical migrations of C. helgolandicus are part of a more complex pattern of inherent behavior than has been reported previously and that, however difficult this is to discern in the natural populations, it always expresses itself.     

Vertical distribution,diurnal and seasonal migration of copepods in Saronic Bay,Greece

The problem of vertical distribution and the movements of copepods was studied from several plankton samples collected by vertical hauls in the Saronic Bay, Greece during two cruises (8 to 17 August and 21 November to 1 December, 1969). The species, whose vertical movements were analyzed, were divided into 3 groups: (1) Those which perform diurnal vertical migration (generally psychrophilic species found in summer samples in deeper layers and in reduced numbers). In autumn, the number of specimens is generally increased and many individuals reach the surface at night. From surface hauls it is known that these species abound in night surface hauls during the cold period. (2) Those species which execute a seasonal vertical migration. These, too are, in general, psychrophilic and found in summer in the deep water layers. In autumn, the population of the upper layers increases. From surface hauls it is known that these species abound in day and night surface samples. (3) Copepods which remained at the surface layer in both seasons of our cruises. These species are thermophilic and are absent from surface hauls during the cold period.     

Copepod photobehavior in a simulated natural light environment and its relation to nocturnal vertical migration

To investigate the roles of light in initiating, controlling and directing nocturnal vertical migration, photoresponses of the adult, female copepod Acartia tonsa Dana were measured under simulated natural underwater light conditions using a video system. Copepods were adapted to a range of background light levels and tested with the following stimuli: absolute quantal intensity, absolute change in quantal intensity and relative (%) change in quantal intensity. The stimulus initiating vertical movements was relative change in quantal intensity, while responsiveness was controlled by the level of light adaptation. A. tonsa swam upward in response to decreases. Response with minimal stimulation occurred at an adaptation intensity close to that in the copepod's natural habitat at the time of the migratory ascent (near the bottom of the Newport River estuary, North Carolina, near sunset). Analysis of the angles of upward movement showed that light is not a directional cue. Relative increases in intensity resulted in sinking, with minimal stimulation required at an adaptation intensity close to that in the field when the migratory descent occurs near sunrise. These results offer a reasonable explanation of how light cues may shape nocturnal vertical migratory patterns.     

Microplankton of the Gulf of Elat: Aspects of seasonal and bathymetric distribution

The components of 4 major groups of microplankton were identified and their numerical abundance determined in net samples collected at depth intervals down to 600 m at a permanent station off the H. Steinitz Marine Biological Laboratory, Elat. The samples analyzed were collected once a fortnight over a period of 1 year beginning in June 1974. The groups studied were the Cyanophyta, Bacillariophyta and Pyrrhophyta of the phytoplankton and the Tintinnina of the microzooplankton. The pattern of vertical distribution of the phytoplankton as a whole showed a general decrease in cell numbers with increasing depth. The blue-green algae, consisting mainly of Trichodesmium sp. trichomes, were confined primarily to the upper 100 m. The diatoms were unevenly distributed, with one species, a minute centric diatom, Thalassiosira subtilis, associated with a massive bloom during March 1975 between 300 and 400 m. The peridinians, the group with the largest number of species, included forms which were evenly distributed throughout the whole water column and forms limited either to the upper or deeper water strata in accordance with their light intensity preferences. The mass occurrence of newly-emerged dinoflagellate cysts of Pyrophacus horologicum, a weakly-armoured dinoflagellate, in the 200 to 300 m depth interval during April 1975, suggests that reproductive processes in dinoflagellates may also be light-controlled. The tintinnids, like the phytoplankton groups, were most abundant in the upper 100 m with a gradual decrease in numbers of individuals, though not in species, in the deeper water strata. The overall yearly pattern of microplankton distribution indicates 3 peaks: late fall and early summer peaks consisting primarily of blue-green algae and one in early spring consisting of several species of diatoms and peridinians and of species of tintinnids which thrive in the same niches as the phytoplankton. Both phytoplankton and tintinnid production was lowest during the summer months.     

深圳湾浮游动物的群落结构及季节变化

2008年2月、5月、8月和11月分别对深圳湾浮游动物进行了周年的季节调查,结果共检出浮游动物38种和浮游幼体13类,其中原生动物2种,腔肠动物4种,介形类1种,桡足类22种,软甲类3种,毛颚类3种,被囊类1种,多毛类2种,浮游幼体（包括仔鱼）13类。年均丰度和生物量分别为406.7 ind.m-3和764.0 mg.m-3,高峰均位于夏季,低谷分别位于冬、春季。种类数（包括浮游幼虫）秋季最多为43种,夏季次之为30种,冬季最少仅23种。主要优势种为太平洋纺锤水蚤Acartia pacifica、刺尾纺锤水蚤Acartia spinicauda、短角长腹剑水蚤Oithona brevicornis、双生水母Diphyes chamissonis、卡玛拉水母Malagazzia carolinae、蔓足类幼体和桡足幼体等。多样性指数和均匀度年均值分别为2.568和0.526。回归分析表明浮游动物丰度和生物量与各环境因子之间存在明显的相关性,但有季节变化。     

Vertical distribution and migration of fishes of the lower mesopelagic zone off Oregon

An exceptionally large midwater trawl (50 m² mouth area) with 5 opening and closing codends was towed horizontally in the lower mesopelagic zone at depths of 500, 650, 800 and 1000 m off Oregon (USA) from 1–6 September, 1978. In comparison to more conventional trawls, ours collected more fish, including rare species and large individuals of common species. Comparison of collections made by day and by night revealed that 12 of the 15 most common species probably migrated vertically. Bathylagus milleri evidently migrates from 650 m during the day to 500 m at night. Cyclothone acclinidens and C. atraria were more abundant by night than by day at 800 m, possibly due to an upward migration from deeper depths at night. C. pseudopallida, C. signata, Chauliodus macouni, Tactostoma macropus and Stenobrachius leucopsarus were more abundant by day than by night at 500 m, suggesting that they migrated out of this depth horizon at night. Lampanyctus regalis, and large individuals of B. pacificus were more abundant by night than by day at 500 m, possibly because they migrated upward from near 650 m. Many species exhibited trends of increasing or decreasing size with depth, and several species showed changes in migratory behavior with size. For example, only small (<240 mm) T. macropus migrated vertically, whereas only large (>110 mm) B. pacificus appeared to migrate. Depths of maximum abundance of congeneric species were usually separated. B. milleri and B. pacificus had similar distributions by day, but the former was shallower at night. S. leucopsarus tended to live shallower than S. nannochir both day and night. Congeners always occurring at the same depth were Cyclothone pseudopallida and C. signata (both most abundant at 500 m) and C. acclinidens and C. atraria (both most abundant at 800 m).     

Relation of fish larvae and zooplankton biomass in the Gulf of Aden

This study is based on zooplankton samples collected in the upper 50 m by the F.R.V. Manihine in the Gulf of Aden during October–November, 1966 and February–March, 1967. Generally, the displacement volume of zooplankton varied between 20 and 67 ml/m². Some higher values, up to 100 ml/m², were also observed. The number of larval fish in positive hauls ranged from 2 to 282 larvae/m². An inverse relationship between the number of larval fish and the accompanying volume of zooplankton was noted. This relationship is discussed. It is hypothesized that larval mortality due to predation in the Gulf of Aden during the northeast monsoon (November, February and March) was very high.     

A note on the development of the thermocline in temperate lakes

An exact solution has been obtained for a non-linear partial differential equation governing the vertical transport of heat in a lake. The equation, derived and analyzed numerically by Sundaram and Rehm (1971, 1973) is based on a balance between thermal buoyany forces and wind induced turbulence. The exact solution displays the qualitative features of the numerical solution and its representation of the seasonal descent of the thermocline is accurate.     

Vertical distribution and diurnal migration of some Cyclopoida (Copepoda) in the tropical region of the Pacific Ocean

The material was collected in the western equatorial part of the Pacific Ocean at a 24 h station on December 21 to 23, 1968. Collections were made by means of 2 Juday nets from 2 winches simultaneously. A series of hauls was made at 2 h intervals. The vertical distribution of 17 Cyclopoida species, belonging to 3 families (Oithonidae, Oncaeidae and Corycaeidae) was studied. From 0 to 300 m, the absolute number of Cyclopoida individuals was practically constant throughout the 24 h period. The bulk of the species performed no diurnal vertical migration, or migrated with low intensity in the usual way (i.e. moved upward at night and downward during the day). Only 2 Oncaeidae species performed significant diuranl vertical migration. No reversed migration in Cyclopoida was discovered. To characterize the vertical distribution of Cyclopoida, the distribution of the cores of populations (abundancies between 25 and 75%) was examined. During the 24 h period, the cores of populations of various Cyclopoida species were found at different depths; this steplike distribution was not disturbed in migrating species. The cores of populations differed both with habitat depth and time of ascent of the migrating species to the surface layer. This peculiarity, probably, tends to lessen the intensity of food competition between Cyclopoida species with similar nutritional habits.     

Continuous plankton records: relationships between species of phytoplankton and zooplankton in the seasonal cycle

Seasonal fluctuations in abundance and their geographical variations in the north-east Atlantic Ocean and the North Sea for 49 taxa of both phytoplankton and zooplankton have been studied by multivariate techniques. Most of the observed variability in both seasonal and geographical fluctuations in abundance can be attributed to differences between the taxa with respect to population growth rates modulated by temperature coupled with the distribution of overwintering stocks, with the overall pattern also influenced by the timing of the establishment and breakdown of vertical stability in the water column. The observations indicate that for any species, the similarity between its seasonal cycles in the various areas, which represent a wide range of hydrographic regimes, is appreciably greater than any differences induced by interaction between the species in any particular area.     

Surface zooplankton dynamics and community structure in the Gulf of Aqaba (Eilat), Red Sea

Winter and summer zooplankton maxima were observed on both near-reef and offshore sampling sites in the northern part of the Gulf of Aqaba, with summer maxima smaller than those of winter and more characterized by larval forms. Near-reef zooplankton biomass was generally several times greater than that observed 2 km offshore. During 1987, a near-reef maximum of 155 ind. or 12.2 g wet biomass m^–3 was observed in March, while 103 ind. or 8.5 g wet biomass m^–3 was observed in July. In the same year, 2 km offshore a maximum of 53 ind. or 2.5 g wet biomass m^–3 was observed in February, while a maximum of 33 ind. or 0.5 g wet biomass m^–3 was noted in July. The following year, 1988, the near-reef zooplankton abundances were little changed, but offshore zooplankton abundances were much higher (317 m^–3). During 1987, the dominant winter (March) forms near the reef were gammarid amphipods, at maximum concentrations of 100 ind. m^–3, where the summer (July) maximum was composed primarily of mysids (34 m^–3), gammarid amphipods (30 m^–3), and fish eggs (24 m^–3). The offshore winter zooplankton fauna was characterized by copepods and appendicularians, each at a maximum concentrations of ca 13 ind. m^–3, while the summer maximum was dominated by brachyuran zoea (31 m^–3). Though the 1988, winter near-reef zooplankton community compositions were similar to those of 1987, the offshore zooplankton fauna was dominated by ostracods, which were relatively rare in previous years. Preliminary data suggests that holoplanktonic forms like chaetognaths, copepods and appendicularians, at an offshore site exhibit different patterns of vertical migration than those near the reef. This different behavior may result from different species compositions of these taxa or from high concentrations of pseudoplanktonic bentho-neritic peracarid crustaceans.Please address correspondence and reprint requests to T. Echelman, Marine Science Research Center, State University of New York, Stony Brook, New York 11794-5000, USA     

Vertical distributions of euphausiids and fish in relation to light intensity in the Northeastern Atlantic

The relationship between the vertical distributions of euphausiids and fish and light intensity has been studied directly by using a photometer in conjunction with an acoustically controlled rectangular midwater trawl. Samples were taken at a position centered on 47°N; 17°W on 15 and 16 May 1978. Five species of euphausiid and six species of fish have been analysed, both groups contained migrant and non-migrant species. The population of each of these species occurred throughout a light regime spanning at least three orders of magnitude of intensity; none of them was restricted to, or followed, and isolume. There were no sexual or size differences in the distributions of the euphausiids, but the population of Argyropelecus hemigymnus was probably stratified during the day, with smaller individuals occurring shallower than large ones. The results are discussed in relation to previous observations and to the theories of photic regulation of distributions and migrations.     

Photosynthetic rates of benthic marine algae in relation to light intensity and seasonal variations

The effect of light intensity on rate of photosynthesis was measured at irregular intervals over a 12-month period for 22 benthic marine algae in the western Baltic Sea. In most species photosynthesis (mg O₂·g dry weight^-1·h^-1) was highest in spring and summer, corresponding to the seasonal growth pattern of the algae. In winter all the species showed adaptation of the light compensation point. Highest productivity was shown by algae which are: short-lived annual species rather than perennials, eulittoral rather than sublittoral, and which possess sheet-like or filamentous thalli rather than coarsely branched forms. These factors are clearly inter-related.This research was carried out while one of us (R.J.K.) was an Alexander von Humboldt fellow at the University of Kiel, and is part of the programme Sonderforschungsbereich 95, Wechselwirkung Meer-Meeresboden, Universität Kiel.     

Vertical movement of the littoral fringe periwinkle Nodilittorina exigua in relation to wave height

The relationship between daily vertical distribution of the littoral fringe periwinkle Nodilittorina exigua and daily wave height was investigated at Shirahama, Japan (33°42N; 135°21E) daily, from May 1981 to August 1982. The positions of the snails on a cliff shore were high when the wave-reach was high, and ascended with increasing height of the wave-reach. The snails moved a long distance upwards in late summer, when typhoon swells occurred, and moved gradually downwards again in autumn, parallel to decreasing wave-reach. They displayed more active vertical movement in warmer seasons of the year and this activity was not positively correlated with the frequency of wetting. Downward migration in autumn ensured frequent and constant immersion. Taken in conjunction with results in the literature, the present study emphasizes the adaptive significance of vertical movement by N. exigua in the littoral-fringe environment.     

Spring and autumn spatial distribution of zooplankton carbon requirement across the Mediterranean Sea

Zooplankton represents a key contributor to the ocean biological pump through its consumption of sinking and suspended carbon. A specific and highly sensitive method to evaluate zooplankton carbon requirement from the sinking flux is through the estimation of the activity of the electron transport system. The present study was carried out from samplings in 2006, and it was focused on the spatial 200–0?m zooplankton carbon demand across 24 sampling stations, along the Mediterranean Sea, from the island of Crete to the Strait of Gibraltar. Its potential day/night variability was evaluated. The zooplankton composition, abundance and biomass were investigated. The carbon demand per unit zooplankton biomass indicates geographical and diel differences among the sampling stations. A higher mean carbon demand was seen for the western Mediterranean with respect to the eastern Mediterranean, which can be justified through the observed ratio of gelatinous:crustacean taxa and the water temperatures recorded. Higher carbon demand was measured in samples collected during the dark hours. The relation to the presence and abundance of actively migrating euphausiids and copepods was discussed. A comparison with data from another of our study carried out in the same study area but in another seasonal period was done.