Zooplankton Behavior Research Articles

Particulate matter distributions, chemistry and flux in the panama basin: response to environment forcing

Multidisciplinary studies of the particle cycle were carried out during two cruises in July–August and November–December 1979 at 5°N 82°W in the Panama Basin as part of the Sediment Trap Intercomparison Experiment (STIE) and Composition, Flux and Transfer Experiments (C-FATE). Measurements included: primary production; new production; hydrography; nutrient distributions; 12-kHz echo sounding; macrozooplankton biomass and group abundances; microzooplankton group abundances; vertical distributions, chemistry, and morphology of suspended and sinking particulate matter; and vertical particulate matter fluxes. Comparisons were made among particle fluxes determined by several means. Size distributions of fecal matter and fecal pellets determined on samples from the Large Volume in-situ Filtration System (LVFS) were used in settling models to calculate vertical particle fluxes. These results were compared with fluxes estimated from measurements of new production, with fluxes determined by short-term deployments of sediment traps in the upper 300m, and with fluxes recorded by moored time-series traps at 1268m. Previous C-FATE results had shown that the rates of primary production and new production are determined by the physical and chemical environment of the euphotic zone at this location. Results presented here indicate that new production and particle flux are in balance in the euphotic zone on the time scale of days. The data also demonstrate that particulate matter distributions, chemistry and fluxes in the water column extending from the euphotic zone to 1000m are closely related to rates of primary production and new production in the euphotic zone. Finally, the data show that the vertical particle flux gradient in the upper 1000m is determined by the instantaneous distributions, feeding activities, and migratory behaviour of zooplankton and fish present in the water column.

Lethal and sublethal effects of a molybdenum mine tailing on marine zooplankton: Mortality, respiration, feeding and swimming behavior in Calanus marshallae, Metridia pacifica and Euphausia pacifica

We report the laboratory survival, respiration, feeding and swimming behavior of zooplankton exposed to suspended tailing from a molybdenum mine that discharged into the Observatory Inlet fjord system in northern British Columbia. Test species were the copepods Calanus marshallae and Metridia pacifica and the euphausiid Euphausia pacifica. In the inlet, the discharge produced a turbid plume at intermediate depth and a near-bottom density flow down-slope into the deepest part of the fjord. The concentration of particles in the intermediate plume was always less than 15 mg liter −1 at 0·5 km from the outfall and declined with increasing distance. In toxicity experiments the lowest whole tailing solids concentration that produced a clear decrease in median survival time was 560 mg liter −1 for Euphausia pacifica at 112 h and Calanus marhallae at 464 h. All three test species ingested tailing particles. In several cases the presence of low tailing concentrations increased survival over that in filtered seawater. Oxygen consumption was affected at relatively low tailing concentration. The pattern of respiratory responses varied with species and nutritional condition. The swimming behavior of Calanus marshallae could be partitioned into five stereotypic patterns, of which one, “circles”, was associated with continuous feeding. ‘Circles’ was induced in Calanus when starved animals were fed a culture of the diatom Thalassiosira fluviatilis. ‘Circles’ was neither induced nor extinguished by the presence of tailing.

Measurements of acoustic correlation in the ocean with a high frequency echo-sounder

Measurements in a British Columbia fjord, using a high frequency echo-sounder, have provided the basis for inferring both mean and random components of scatterer motion at ranges up to 100 m. The measurements demonstrate the potential for a novel technique of flow speed measurement using an echo-sounder and show the way in which the random component of scatterer motion decorrelates the resulting signal. The results indicate decorrelation times of several seconds, illustrating the passive behaviour of the scatterers. This behaviour makes the scatterers ideal targets for remote sensing of flow properties and represents a limiting example of the conditions in which such measurements can be made. The measurements provide a new source of information relevant to the study of Zooplankton behaviour; in more active oceanographic conditions the relative motion of passive acoustic targets may also provide a basis for inferring the corresponding water motions and in particular, turbulence.

The Adaptive Significance of Calanoid Copepod Pigmentation: A Comparative and Experimental Analysis

A two-part study was undertaken to investigate the adaptive value of carotenoid pig- mentation to calanoid copepods and the costs in terms of visually selective predation. A comparative survey of copepod populations documented the distribution of pigmented forms and suggested the importance of water temperature, lake depth, and elevation to copepod pigmentation. Estimates of photodamaging irradiance and yearly temperature regime were constructed from the primary survey variables and compared for their correlation with copepod pigmentation. Yearly temperature regime is directly related to elevation and is most important in explaining variation in copepod pigmentation. Copepods are most darkly pigmented in the coldest lakes. Phytoplankton pigment concentration is not limiting to the pigmentation of calanoid copepods. Laboratory experiments demonstrated that carotenoid pigments can be photoprotective to calanoid copepods exposed to strong sunlight, yet field experiments failed to demonstrate photodamage when copepods were allowed to migrate vertically in enclosures. Respirometry experiments have shown that pigmented copepods respire faster in the light than in the dark, while unpigmented copepods do not. This metabolic facilitation by light helps to explain literature accounts of the sunlight-related behavior of pigmented zooplankton. Laboratory and field experiments with predators confirmed that vertebrate predators select pig- mented calanoid copepods, but that common invertebrate predators are not visually selective. Trout are highly visually selective predators. Although salamanders are visually selective in laboratory enclosures, they are inefficient at capturing calanoid copepods in nature. Pigments are adaptive to calanoid copepods because they facilitate a metabolic increase and provide photoprotection when the animals are illuminated. Pigments are rarely found in the zooplank- ton, however, because zooplankton are continuously exposed to predation by visually selective pred- ators. In cold environments with short growing seasons, as at high elevations, the advantages of pigmentation at least partially outweigh the costs in terms of selective predation, thus shifting the balance in favor of pigmentation.

A laboratory method for studying zooplankton swimming behaviors

A laboratory method is presented for studying zooplankton swimming behaviors such as phototaxis and photokinesis. The method attempts to standardize laboratory conditions and to minimize the effects of several phenomena which modify zooplankton behavior. The role of angular light distribution in zooplankton behavior is discussed, and an apparatus which simulates a natural underwater light environment is described. The procedure minimizes the fluctuations in zooplankton swimming speed and vertical distribution that are caused by large light stimuli, noise, food deprivation, endogenous rhythms, and other factors. The experimental animals were viewed remotely with the aid of a light amplifier and video camera. A mathematical equation and computer program for calculating three-dimensional swimming speeds of zooplankton from video recordings are described in detail.

Diel migration patterns of demersal reef zooplankton

Demersal zooplankton reside in or near the reef substrata and usually migrate into the water column at night. There is no single pulse of migratory activity. The zooplankton rise at variable rates throughout the night, with a peak activity usually during the second hour after sunset. This temporal pattern is a reflection of the behavior of the dominant (80–90% of night samples) cyclopoid, Oithona colcarva Bowman. Not all zooplankton taxa exhibit the same diel migratory patterns. Harpacticoids, another Oithona sp., copepod nauplii, barnacle nauplii, and appendicularians are most abundant during the day. Isopods show a peak of activity also during the second hour after sunset while polychaetes are most abundant during the first hour. The behavior of the other groups studied (the cyclopoid Corycaeus sp., other cyclopoids, ostracods, amphipods, tanaids, decapods, mysids, and chaetognaths) was less easily defined. The migration of many species in a pulse during the period of least planktivore activity and migration during the day of small species and juvenile members of larger species suggests that visual predators have an important influence on the migratory behavior of reef zooplankton.

The Distribution of Particulate Organic Carbon in the Oceans: Ecological Implications

AbstractDistribution of participate organic carbon (POC) in the oceans appears to be in the form of small “clouds” high in POC superimposed on lower background values typical of depth and water mass. The background values display an exponential decrease with depth. Samples taken at close intervals, both vertical and horizontal, suggest that the extent of these clouds in water below the photic zone must be less than a meter in any dimension. The concentration of POC in the clouds is of the same order as that found in surface waters. Feeding behaviour of the larger zooplankton may involve active searching for these patches; the organisms should be examined for evidences of mechanisms for finding patches. The maximum distance between patches, even in deeper water, must be of the order of a few tens of meters.

The effects of the water soluble fractions of No. 2 fuel oil on the survival and behaviour of coastal and oceanic zooplankton

Acute effects of water-soluble fractions (WSF) of No. 2 fuel oil both coastal and oceanic zooplankton were studied and their LC 50 for various exposure times (1 to 72 h) compared. Coastal zooplankton seemed to be more resistant to the WSF than oceanic zooplankton. This difference was probably caused mainly by the dissimilar species composition of the two zooplankton populations under investigation. The evidence from this study indicates that, on a species or taxon basis, there are some species in coastal waters more vulnerable to oils than among oceanic zooplankton and it is strongly recommended that further studies of the tolerance of both populations to various petroleum hydrocarbons be carried out at the same time. A vital staining method was used to distinguish the dead from the immobile forms. Expected variations both in the curves of mortality compared with time and in the curves of mortality compared with concentration of oil are explained and a possible method to decrease variability is suggested. Change of behaviour of coastal zooplankton due to the WSF of No. 2 fuel oil was also observed during the first hour of exposure.

The Vertical Migration Behaviour of Estuarine Plankton

A series of investigations on the vertical migration behaviour of estuarine zooplankton have been carried out in recent years. Several of these investigations have been carried out in collaboration with other zoologists and the detailed findings are being published separately. The work is reviewed here and an attempt is made to draw some general conclusions regarding the behaviour patterns observed. Attention is concentrated particularly on the behaviour of the copepod Pseudodiaptomus, Aspects investigated include behaviour in the field under natural conditions, light reactions and swimming speeds in the laboratory, reactions to layers of low salinity water, the role of endogenous rhythm in this behaviour and the significance of these behaviour patterns to the organisms.

Biochemical studies on the production of marine zooplankton.

Summary1. Phytoplanktonic algae vary in their value as food for zooplankton and no single algal food can meet the full nutritional needs of zooplanktonic animals. Perhaps this is because optimal amounts of essential micronutrients are not all present in any one alga. The dietary requirements of planktonic Crustacea, as far as they are known, bear some resemblance to those of vertebrates.2. The proteins of phytoplankton are similar in amino acid composition to those of zooplankton. This circumstance should favour efficient synthesis of protein by the animal, for assuming amino acids are all released in the gut and absorbed at approximately the same rate, they will be presented to the tissues in roughly the right relative amounts for protein formation.3. Zooplankton are able to alter the characteristics of the fatty acids present in their diet by elongating the carbon chain length and by increasing the degree of unsaturation.4. Measurements of phosphorus and nitrogen excretion indicate that zooplankton are metabolically very active. Some of the very high rates of phosphorus excretion are questioned and it is suggested that some portion of the phosphorus compounds liberated by zooplankton have passed straight through the gut without being assimilated. It is unlikely that all forms of organically bound phosphorus are equally rapidly assimilated and turned over by zooplankton.5. Estimates of the rate of ammonia excretion by zooplankton differ markedly. This may be a matter of size/surface area of the animals concerned—smaller animals excreting more rapidly than larger animals. It has been claimed that a‐amino nitrogen is released in considerable quantities by zooplankton but the evidence is not yet compelling.6. There is considerable disagreement on the efficiency of food assimilation and conversion by zooplankton. One view is that irrespective of the quantity of phyto‐plankton ingested assimilation is uniformly high. The opposing view holds that when rapid ingestion of phytoplankton occurs the percentage assimilated falls. More information on the feeding behaviour of zooplankton and on the physiology of their digestive processes is required before this controversy can be satisfactorily resolved.

Effect of Low-salinity Water on the Vertical Migration of Estuarine Plankton

PLANKTON in estuaries is frequently exposed to water of different salinities in layers at different levels, with less dense low-salinity water at the surface1. The effects of such salinity layers on the behaviour and distribution of zooplankton have been considered by a number of workers, including in recent years Harder2, Banse3 and Lance4.