On filament width in oceanic plankton distributions

A plankton patch deformed by diffusion, straining flow and biologicalgrowth is demonstrated to have a minimum width, /, which ispurely a function of the effective diffusivity, , and the strainrate, .     

Patterns and drivers of vertical movements of the large fishes of the epipelagic

Reviews in Fish Biology and Fisheries - Large epipelagic fishes (>?30 kg maximum size) are known to display a variety of patterns of vertical movement. Although advances in...     

Diets and feeding selectivity among the epipelagic copepod community near South Georgia in summer

During the austral midsummers of 1989/1990 and 1990/1991, seven grazing experiments were undertaken near South Georgia. The copepods spanned 3 orders of magnitude in body mass, from young copepodids of small pseudocalanids to adult females of Rhincalanus gigas. Incubations were in natural sea-water and feeding rates were determined by microscope counts of food items (size range 7–1200 m). Daily rations of the smallest copepods were up to 120% body carbon per day. These high rations contrast with values of less than 10% for large copepods (older copepodids of Calanoides acutus and R. gigas). All sizes of copepods could ingest the full size spectrum of measured particles. However, maximum filtration rates of small copepods were on cells <100 m whereas the large grazers cleared the largest cells (usually long diatoms) at maximum rates. Motile, non-diatom taxa (mainly heterotrophic, aloricate dinoflagellates and ciliates) did not appear to have been eaten in preference to diatoms of similar size, but their abundance and high calorific value meant that they comprised a median of 43% of carbon intake across the experiments. These motile, mainly <50 m cells were of a suitable size for ingestion by small copepods and consequently featured more prominently in their diets. The ability of small copepods to feed heavily on cells <50 m, before, during or after blooms, may be important in their life cycles, leading to reduced competition with their larger relatives.     

The paddlefish rostrum functions as an electrosensory antenna in plankton feeding

A novel electrosensory function is presented for the large, plankton-feeding, freshwater paddlefish, Polyodon spathula, along with a hypothesis which accounts for the distinctive, elongated rostrum of this unusual fish. Behavioural experiments conducted in the ''dark'' (under infrared illumination), to eliminate vision, show that paddlefish efficiently capture planktonic prey to distances up to 80–90 mm. They make feeding strikes at dipole electrodes in response to weak low-frequency electrical currents. Fish also avoid metal obstacles placed in the water, again in the dark. Electrophysiological experiments confirm that the Lorenzinian ampullae of paddlefish are sensitive to weak, low-frequency electrical signals, and demonstrate unequivocally that they respond to the very small electrical signals generated by their natural zooplankton prey (Daphnia sp.). We propose that the rostrum constitutes the biological equivalent of an electrical antenna, enabling the fish to accurately detect and capture its planktonic food in turbid river environments where vision is severely limited. The electrical sensitivity of paddlefish to metallic substrates may interfere with their migrations through locks and dams.     

Growth of dominant zooplankton species feeding on plankton microflora in Lake Shira

Batch cultures and continuous flow cultures were used to study the growth rates of zooplankton species from Shira lake, the rotifer Brachionus plicatilis Muller and calanoid copepod Arctodiaptomus salinus Daday, which were fed on phytoplankton and bacterioplankton from the lake. Analyses of the birth and survival rates were used to demonstrate that the lake phytoplankton, consisting mostly of cyanobacteria and diatomaceous algae, is inadequotes for optimal realisation of the reproductive potential of B. plicatilis when compared with the bacterial diet. The study revealed that the kinetic growth characteristics of the two zooplankters were similar: B. plicatilis r _max, 0.120 d^–1; S ₀, 0.253; and K _s, 0.114 mg dry mass l^–1; and for A. salinus r _max, 0.129 d^–1; S ₀, 0.240; and K _s, 0.171 mg dry mass l^–1. Fluctuations in natural food concentration reduced the growth rate of both species. Even though the threshold concentration of food for B. plicatilis and A. salinus were quite similar, the copepods were less sensitive to food limitation.     

A review of cnidarians and ctenophores feeding on competitors in the plankton

Predation among pelagic cnidarians and ctenophores is reviewed. The diets of semaeostome scyphomedusae and hydromedusae commonly include other gelatinous zooplanktivores. However, few species of siphonophores and ctenophores are known to consume other gelatinous species. Most of these species can be said to exhibit intraguild predation, since they consume species that potentially compete with them for food. In addition, some hydromedusan and ctenophore species may consume other gelatinous zooplanktivores exclusively. Characteristics of cnidarians and ctenophores as predators and as prey of other gelatinous species are discussed.     

Production of atmospheric sulfur by oceanic plankton: biogeochemical, ecological and evolutionary links

Biological production of the volatile compound dimethylsulfide in the ocean is the main natural source of tropospheric sulfur on a global scale, with important consequences for the radiative balance of the Earth. In the late 1980s, a Gaian feedback link between marine phytoplankton and climate through the release of atmospheric sulfur was hypothesized. However, the idea of microalgae producing a substance that could regulate climate has been criticized on the basis of its evolutionary feasibility. Recent advances have shown that volatile sulfur is a result of ecological interactions and transformation processes through planktonic food webs. It is, therefore, not only phytoplankton biomass, taxonomy or activity, but also food-web structure and dynamics that drive the oceanic production of atmospheric sulfur. Accordingly, the viewpoint on the ecological and evolutionary basis of this amazing marine biota-atmosphere link is changing.     

Distribution and feeding of chaetognaths in the epipelagic zone of the Lazarev Sea (Antarctica) during austral summer

This study seeks to determine the effects of local hydrography on the distribution, abundance and feeding of chaetognaths in the Lazarev Sea, an area strongly controlled by physical processes which has been held responsible for initiating the Weddell Polynya. Zooplankton samples were taken at 39 stations on four transects located between 6°W and 3°E and from 60°S to 70°S between surface and 350 m. The dominant species, Eukrohnia hamata, accounted for 86.5% of all chaetognaths, followed by Sagitta gazellae (8.1%) and Sagitta marri (5.4%). These three species showed distinct vertical and horizontal distribution patterns. While E. hamata and S. marri had maximum abundances below 250 m depth, S. gazellae showed a narrow distribution band in the upper 150 m depth. The distribution pattern was strongly modified at the Greenwich meridian with an upward transport of a high abundance of deep dwelling organisms (S. marri and E. hamata) and a displacement of S. gazellae to the surface, likely coupled with the rise of the warm, saline halo around the Maud Rise. Small copepods were the main prey of all three chaetognath species. Feeding rates (FR) varied among species and depth. Sagitta marri showed the highest FR with 0.38 prey d⁻¹, followed by S. gazellae and E. hamata (0.22 and 0.07 prey d⁻¹). Feeding rates were usually highest in the 25–80-m stratum. Size distribution and maturity of E. hamata revealed a dominance of small and immature organisms along all depths and stations, suggesting that this area might be acting as an important source of recently spawned organisms to the surface.     

Comparison of plankton intake by Indian carp fingerlings under different feeding conditions

The influence of different culture systems on the amount of plankton consumed by fingerlings of three carp species (Labeo rohita, Catla catla and Cirrhinus mrigala) was examined in outdoor culture tanks during a 90 day growing period. The fish were raised under two basically different feeding conditions: (a) fed with allochthonous live plankton; (b) fed with plankton grown autochthonously in the fish growing tanks fertilized with manures. Both feeding regimes were compared with control groups. It was found that the plankton intake for carp held in the live food system was significantly higher than with the manured and control systems. Related to maximum intake, maximum abundance of plankton in the live food system was a consequence of improved water quality expressed in terms of lower values of BOD and COD and higher values of DO and pH; this was conducive to fast reproduction of some of the zooplankton which constituted the major food items for the test carp, as well as to the regular exogenous introduction of live plankton. The ingestion of plankton was found to be related to carp body weight raised to the power b. The exponent b ranged from 0.29 to 0.93 during the 90-day growing period.     

Patterns of respiration in Locusta migratoria nymphs when feeding

Flow‐through respirometry was used to investigate patterns of respiration of fifth‐instar Locusta migratoria L. nymphs fed a chemically defined, synthetic food. Each animal was recorded for up to 2.7 h, during which they had access to food and water ad libitum, and at least one meal was taken. The start of feeding was coincident with a sudden and rapid rise in respiration. Both carbon dioxide (CO₂) production and oxygen (O₂) consumption rose, the traces for the two gasses showing a high degree of alignment. The end of a meal correlated with a sudden and rapid decrease in respiratory rate towards resting levels. When feeding was interrupted by an intra‐meal pause, respiratory rate tended to drop marginally and then stabilize, before rising rapidly upon the resumption of feeding within the meal. Maximal rates of respiration during feeding represented a 3–4‐fold increase over those at rest. Walking and climbing within the chamber were not associated with any noticeable change in respiratory rate above baseline. When locusts were quiescent between feeding episodes, respiration was steady and continuous, rather than discontinuous. Possible causes for large changes in respiration during feeding are discussed.     

Patterns in the life histories and feeding strategies of British macrolepidoptera

Temperate Lepidoptera typically have life cycles of a year or less. The time available to feed and attain a suitable state for reproduction might thus constrain potential life-history patterns, and species characteristics such as adult size, overwintering stage, first month of larval feeding and feeding specificity may only occur in particular combinations. Several studies have documented correlates of feeding ecology which suggest this is indeed the case. We use data for more than 900 British macrolepidoptera to establish relationships among several ecological and life-history variables to determine whether only particular combinations can occur. Few patterns of feeding characteristics predicted in the literature are observed. Distinct, consistent life-history syndromes cannot be defined; almost any combination of the life-history characteristics we looked at can occur. So long as it is possible to fit in with timing constraints at certain critical times of year, there seems to be a great deal of flexibility in how the rest of the time can be filled. However, several broad and potentially interesting patterns still emerge. Polyphagous species are larger than specialists; the month in which species start to feed inlinked to both their overwintering stage and the growth form of the plant they feed upon; and there are no species overwintering in the egg stage and having two broods per year.     

The discovery of an Antarctic epipelagic medusan in the Mediterranean

A single specimen of the Antarctic anthomedusan Russellia mirabilisKramp 1957 has recently been collected in the AlboránSea. This is the first record for an Antarctic epipelagic organismin the Mediterranean Sea. Transport in the ballast water ofa cargo ship seems the most plausible mechanism for explainingthis rare occurrence. However, an alternative hypothesis isexplored involving a possibly complex medusan life cycle togetherwith the role of Antarctic (Intermediate and Bottom) water asdispersal mechanisms.     

Patterns of the quantitative distribution of plankton heterotrophic flagellates in the high-mountain Lake Sevan (Armenia)

Patterns of the quantitative development and spatial distribution of heterotrophic flagellates have been studied in Lake Sevan (Armenia). The abundance and biomass of flagellates is lower in summer than in autumn, but on the whole these parameters correspond to the quantitative parameters in oligotrophic lakes. Differences in the vertical and horizontal distribution of flagellates have been found during summer stratification and autumn homothermy.     

The landward distribution of oceanic plankton and micronekton over the west Florida continental shelf as related to their vertical distribution

The landward distributions of 69 plankton and 92 micronektonspecies over the west Florida continental shelf were examinedin relation to their vertical distribution in the eastern Gulfof Mexico. Using linear and power-curve regressions, it wasfound that extent of landward occurrence is significantly correlatedwith bottom topography in terms of bottom depth and distancefrom the open Gulf. Epipelagic plankton species were distributedconsiderable distances across the shelf whereas the mesopdagicshrimp and fish species were not found landward of slope stations.Possible factors affecting landward distribution, such as currents,vertical migration patterns, and predation, are discussed.     

Predation,cover, and convergent evolution in epipelagic oceans

The factor of most importance to the structure of epipelagic oceanic communities is the absence of cover and the inability to hide from predators in surface waters during the day (Elton, 1939). Visual predation in an environment devoid of cover has resulted in convergent evolution into only six modal adaptive patterns. Large, fast, visual predators roam the water, 1) alone or in 2) schools, and they eat anything of appropriate size that they see. Prey escape only by dint of 3) very small size, 4) invisibility due to tissue transparency, 5) diurnal vertical migration, or by 6) exploitation of the sea surface. The sensory ecology and physiology of zooplankton are different from that of all other animal categories in all other habitats. Epipelagic zooplankton are either extremely small animals, with small and structurally simple sense organs, or they are large, with gelatinous, transparent bodies which often lack sense organs.     

Patterns in feeding: a behavioural analysis using Locusta migratoria nymphs

ABSTRACT. Feeding patterns of Locusta migratoria L. nymphs, kept under LD 12:12 at 30°C with ample food, were analysed over the first 6 days of the fifth instar. A number of differences were found between the light and dark phases. (1) More was eaten during the light than the dark, with the differences becoming progressively larger over the 6 days. (2) During light phases most insects showed an increasing tendency to feed with time since the last meal, while in the dark the probability of starting to feed remained constant. (3) There was little variation in feeding patterns within the light phase, but marked changes occurred within the dark phase, feeding declining to a low level in the last 4h. The amount eaten during a meal was regulated similarly in the light and dark, with time rather than amount eaten being of paramount importance in terminating a meal. The time when feeding started was somewhat influenced by the size of the preceding meal, but once feeding began meal size was largely independent of the preceding meal. The importance of food quality in determining the pattern of feeding is discussed.     

Patterns of pollen feeding and habitat preference among Heliconius species

Abstract 1. The ecological circumstances that precipitate speciation remain poorly understood. Here, a community of Heliconius butterflies in lowland Panama was studied to investigate patterns of pollen use, and more specifically the ecological changes associated with the recent divergence of Heliconius melpomene (Linnaeus) and H. cydno (Doubleday).
2. Considering the seven commonest Heliconius species in the community, 32 types of pollen or spore were encountered in pollen loads but only five pollen species were common. Systematic exploitation of pollen was therefore confined to a small proportion of the flowers visited.
3. Most of the variation in pollen load composition between individuals was explained by differences in collecting locality. The exception was Psiguria , which was used in all habitats by the melpomene / hecale clade far more than by the erato / sapho clade. This may suggest an ancestral switch within Heliconius towards increased reliance on Psiguria pollen.
4. Heliconius cydno and H. melpomene differed significantly in pollen load composition for three of the five most commonly collected pollen species. This is most probably explained by differences in habitat preference; H. melpomene and its co-mimic H. erato are found in open habitat while H. cydno and its co-mimic H. sapho are found in closed-canopy forest.
5. As melpomene and cydno are known to hybridise occasionally, such differences in adult microhabitat contribute to pre-mating isolation. Habitat divergence between H. cydno and H. melpomene , which is associated with changes in mimicry, must have played a role in their recent speciation.     

Distribution of cephalopods in the upper epipelagic northwestern Bering Sea in autumn

In the northwestern Bering Sea in autumn, the epipelagic cephalopod community was represented by the boreal fauna, and was found to be composed of three families and nine species of the order Teuthida: Gonatidae (Berryteuthis magister, Boreoteuthis borealis, Gonatopsis japonicus, Gonatus madokai, Gonatus kamtschaticus, Gonatus onyx, and Gonatus pyros), Chiroteuthidae (Chiroteuthis calyx) and Onychoteuthidae (Onychoteuthis borealijaponica). Two pelagic gonatid species (B. borealis and G. kamtschaticus) dominated the cephalopod community in the upper 50 m. The distribution patterns of B. borealis and G. onyx were associated with diel vertical migrations of these squid. The distribution of two distinct size groups of G. kamtschaticus suggested ontogenetic migration of larger squid to deeper layers, and adds to previous data suggesting that this species may be a heterogeneous assemblage. Demersal B. magister rarely occurred in the surface waters. The occurrence of maturing O. borealijaponica in the southern marine area indicated that these were occasional seasonal migrants from the ocean. The occurrence of juvenile C. calyx suggested that these squid may conduct vertical forage migrations from deep waters to the surface layers.     

Environmental conditions and compositions of plankton and nekton in the epipelagic zone of the northwestern Pacific Ocean in summer 2009, the year of the largest spawning migration of pink and Chum Salmon

The distribution of temperature, salinity, phytoplankton, zooplankton, and nekton, including Pink Salmon and Chum Salmon, is analyzed based on the data from a complex survey conducted in the upper epipelagic zone of the northwestern Pacific Ocean in June–July 2009. An estimate of water transfer, plankton biomass (by size fractions and taxonomic groups), and biomass and abundance of nekton is made. The water circulation pattern was notable for the “compressed” state of the Western Subarctic Gyre. Copepods predominated in zooplankton (60.8% biomass), and Pacific Salmon dominated in the nekton. The ratio of the plankton biomass to the nekton biomass in various biostatistical areas varied from 23.9 to 195.1 (mean 46.7). It was found that the nekton biomass in the area of the spreading subarctic waters reaches its maximum in the summer months and that in the area of subtropical waters reaches its maximum in the fall. In the upper 30-meter layer, the biomass of fish and squid rose during the night to 2.92 million tons, or 1.6 times as much, due to mesopelagic migrants. The nekton communities of the upper epipelagic of the northwestern Pacific Ocean functioned normally, providing a high level of biological and fish productivity.