Distribution Of Zooplankton Biomass Research Articles

Vertical distribution of size-fractions in the zooplankton community in Lindåspollene, Western Norway. l. Seasonal variations

Abstract Zooplankton were collected in depth strata separated by 2 to 5 m. The samples were divided into five size-classes: > 1000 μm. 500–1000 μm, 250–500 μm. 125–250 μm, 60-125 μm, During spring and autumn there were maxima in the total biomass. about four times higher than during summer. At the time of biomass maxima, the total biomass showed a bimodal vertical distribution, with maxima in the upper and the lower part of the water column. The upper maximum was located between the surface and the base of the thermocline, the lower in the oxycline. During summer, when the total biomass was low. the vertical pattern diminished. The same trends were observed in 1983 in all size-classes, except for the > 1000-μm size-class. This size-class had a single biomass maximum during summer, located in the upper part of the water column. Seasonal variation in vertical distribution and in depth-integrated biomass increased from the smaller towards the larger size-classes. Relations between the vertical distribution of zooplankton biomass and other biotic and abiotic factors are discussed.

Experimental evaluation of effects of zooplankton biomass and size distribution on algal biomass and productivity in three nutrient-limited lakes

Experimental evaluation of effects of zooplankton biomass and size distribution on algal biomass and productivity in three nutrient-limited lakes

Horizontal and vertical distribution of zooplankton biomass in the southern Benguela, May 1983

Zooplankton was sampled over four depth ranges with an obliquely towed, multiple, opening-closing RMT-1 × 6 net in May 1983 during an anchovy recruitment survey in the southern Benguela. This sampler allowed animals ranging in size from small copepods (> 200 μm diameter) to large euphausiids (> 3 500 μm diameter) to be collected quantitatively over the whole water column on the continental shelf. The stratification of biomass estimates into different layers is a significant improvement over existing data in the southern Benguela region. The discovery of subsurface peaks in the vertical distribution of zooplankton biomass at night allowed estimation of the zooplankton standing stock with more confidence than previously. The horizontal distributions of zooplankton biomass are, in general, consistent with patterns previously observed in the southern Benguela. Copepods were dominant inshore, whereas larger organisms such as euphausiids, chaetognaths and hyperiid amphipods were dominant farther offshore. The difference in the patterns of vertical distribution between inshore and offshore zooplankters is discussed in relation to predation pressure and population maintenance.

Net-zooplankton biomass of the Adriatic Sea

On the basis of 1 107 plankton samples collected during 1971–1981 in the different parts of the Adriatic Sea, the horizontal distribution of net zooplankton biomass, expressed as dry weight and ash-free dry weight, is discussed. The northern Adriatic combined with the Gulf of Trieste usually had the highest standing crop of zooplankton. Biomass in other regions was lower and more uniform. In general, the highest zooplankton stocks came from the shallow regions close to the coast where the sources of enrichment from the land (fresh water inflow, land drainage. “pollution” where it exists) and the shallow sediments are the highest. We believe the elevated zooplankton biomass encountered in the north Adriatic to be due to proliferation of tolerant non-selective feeding zooplankton species, such as copepods, which can use detritus as a major fraction of their diet. The northern Adriatic is rich in living and non-living suspended particles throughout the year and can thus maintain high zooplankton biomass. This conclusion is probably valid for similar regions of the Mediterranean Sea.

Vertical distribution of zooplankton biomass and species in northeastern Baffin Bay related to temperature and salinity

Vertical distributions of various species and stages of zooplankton at different times of the day were determined by stratified sampling with the BIONESS in northeastern Baffin Bay during early August. The water column was divided into an upper subarctic zone (>0° C, salinity 0° C, salinity 34‰). The upper subarctic zone was dominated by two species of pteropod molluscs; the lower subarctic water was dominated by the copepods, Calanus finmarchicus, C. glacialis and C. hyperboreus whose copepodite stages showed depth distributions that were different from one another, with the copepodite stage 5 and adult females generally shallower than the younger stages. All stages of all Calanus species were in the zone of primary production (10 to 50 m) while the copepods Pseudocalanus, Metridia and Oithona were generally found below this zone. Only C. finmarchicus and C. glacialis showed evidence of diurnal migration, migrating to the surface waters when the sun was at its lowest position on the horizon (i.e. at 0100 h).

Seasonal Changes in Net Phytoplankton of the West-Central North Sea

INTRODUCTIONIn 1976 the Fisheries Laboratory, Lowestoft, carried out 13 plankton sampling cruises off the north-east coast of England. They spanned the months February-November. From these cruises Harding et al. (1978) described the distributions of surface chlorophyll and nutrients and the production offish eggs and larvae. Reynolds (1978) described in more detail the distributions of chlorophyll and phaeopigments throughout the year, and Horwood (1982) detailed the distribution of zooplankton biomass. This study presents the species composition of the algae from a small region of the survey area illustrated in Fig. 1.

Distribution and abundance of fish larvae off the coast of West Pakistan

The material was collected during 4 different cruises on the shelf off the coast of W. Pakistan in November–December, 1964 and in March, 1967 and 1968. The hydrography as well as the zooplankton-biomass distribution are briefly described. A total of 5777 larval fish were taken in 33 positive vertical hauls by an Indian Ocean Standard Net. The number of larvae in positive hauls ranged from 2 to 1262 larvae haul-1. The most productive area of the ichthyoplankton was the waters south of Karachi, covered during the “Machera Cruise”, where 828 to 1262 larvae haul-1 were obtained. The larvae were identified to species, genera or family. Sardinella sindensis (specific identification uncertain) larvae dominated in abundance. The other abundant larvae belonged to Benthosema spp., Amentum commersonii, Vinciguerria spp. and Diaphus spp. Larval distributions and abundances are described. Aggregation and spawning of adult Sardinella (sindensis) in the waters off the coast of W. Pakistan in November/December, 1964, are discussed. Presumably, the waters south of Karachi represent good feeding grounds for s. (sindensis) larvae. Displacement volume, length and weight relationships of various larval size groups have been studied and a high rate of larval mortality (at a length of 5.0 to 8.5 mm) observed.

Acid-iron waste as a factor affecting the distribution and abundance of zooplankton in the New York Bight: I. Laboratory studies on the effects of acid waste on copepods

Laboratory experiments were conducted using three species of copepods to study the effects acid-iron wastes might have on zooplankton. Individuals of Calanus finmarchicus, Temora longicornis and Pseudocalanus sp. were maintained in bottles containing varying dilutions of acid wastes in sea water or control sea water solutions for 24 to 48 hours to examine survival of adults exposed to high concentrations of waste. They were also maintained for time periods up to 18 days to ascertain effects on reproduction and survival of young. In addition, individuals of C. finmarchicus were transferred through a series of increasing dilutions of acid wastes and into filtered sea water to simulate the short-term effects of acid waste concentrations in the wake of a discharging barge. Substantial mortality of adults of the above three copepods occurred at concentrations of acid waste producing pH's of approximately 6·5 and lower. However, this mortality is not indicative of mortality in the field as these concentrations and pH values exist for only a short time (less than 3 min) due to rapid mixing of the acid waste with sea water. Individuals maintained in buffered acid wastes of comparable dilutions showed no mortality, while individuals maintained in test media using sulfuric acid in place of acid waste showed high mortalities at pH's of 5·5 or less. Thus, acidity of test solutions may be a principal cause of copepod mortality rather than some toxic component of the waste material. Inhibition of reproduction and deleterious effects on survival of young were observed in experiments of 18 days duration at concentrations of acid wastes which do not in fact persist for such periods on the acid grounds. No mortality was observed when C. finmarchicus was transferred through acid waste dilutions with pH values and time periods comparable to those they would encounter on the acid grounds during discharge of acid wastes. Acid waste discharges, therefore, did not appear to be responsible for the large variations in zooplankton biomass previously observed in the survey area since mortality of species due to short term exposure to high concentrations of waste appears small and little effect on adults or larval forms at great dilutions could be demonstrated. Although the average biomass from the acid grounds was 30% less than that from the adjacent control area, this difference could not be directly linked to the toxicity of acid-iron waste. The spatial pattern of biomass variations and the results from the initial laboratory toxicity studies suggested the difference was probably due to a transitory large scale patchiness of zooplankton. We have conducted further laboratory studies on the effects of acid wastes on copepod species that occur in the area where acid waste is discharged. The results of these experiments are reported here. We have also counted the zooplankton samples collected at the time of our synoptic field sampling survey of the acid waste dumping site and a nearby control area. The analysis of these data and the implications to the observed distribution of zooplankton biomass and to monitoring studies are presented in the succeeding paper (Wiebe et al., 1973).

Ecological Studies on New Zealand Lacustrine Zooplankton with Special Reference to Boeckella propinqua Sars (Copepoda: Calanoida)

A study was made of the zooplankton of a small, warm monomictic, closed, alkaline lake. This was located on Mayor Island, an offshore island of the North Island of New Zealand. Morphometric, thermometric, and chemical aspects of this lake are discussed. The vertical distribution of the zooplankton was investigated by the vertical hauling of a closing net and by the horizontal towing of a Clarke Bumpus sampler. The vertical distribution of zooplankton biomass and of the different planktonic crustacean species at different times of the year is discussed. When thermal stratification was well developed, all crustacean and rotatorian species had a very sharply defined lower limit between the upper limit of the metalimnion and the thermocline; minimal population densities existed some distance above this lower limit. A reversed diurnal vertical migration is reported for Daphnia carinata and the mature males of Boeckella propinqua. The following investigations and findings refer to Boeckella propinqua: the vertical distribution of four population components (CI-V, C VI male, male, C VI female, female , and C VI female, female, with eggs) at different times of the year is discussed; departure of sex ratio from 1 : 1 is reported; cyclic seasonal changes, which correlated inversely with temperature during part of the year, occurred in mean length and mean number of eggs in sacs; mean egg number also correlated with mean body length; considerable simultaneous interpopulational variation in mean egg number was found; length measurements of adults from November surface collections showed a bimodal distribution, and at the same time vertical variation occurred in the nature of size-frequency distributions-in both sexes the upper mode was progressively diminished with increasing depth and finally eliminated; in these November collections the percentage of lower modal females with eggs was much smaller than that for upper modal ones; when surface collections showed unimodal size distributions there appeared to be no vertical variation in size-frequency distributions; variation in the lobulation of the last metasomal segment of females is mentioned; the occurrence of a cestode cysticercoid stage in male and female stages CV and VI, and parasitic castration of C VI male, male, is reported. General observations are made on the Rotatoria and the vertical distribution of Filinia longiseta is dealt with. Comparisons are made between the zooplankton of a number of mainland lakes and that of the Mayor Island lake.