Crustacean Zooplankton Species Research Articles

Zooplankton Communities and Water Chemistry of Sudbury Area Lakes: Changes Related to pH Recovery

Temporal trends in pH, alkalinity, and crustacean zooplankton species richness and community composition were studied in 80 Sudbury area lakes sampled in 1971–76, 1981, and 1988–90. Alkalinity and pH have increased in recent years, but many of the study lakes remain quite acidic (modal pH 4.5–4.9). Species richness has also increased, on average, by 1.9 species/lake but is still low in many acid lakes relative to that in circumneutral lakes. Community composition differed among lakes of pH <5.0, 5.0–5.9, and ≥6.0, with some overlap between these groups because zooplankton recovery has lagged behind chemical recovery. Trajectories of community change in recovering acid lakes varied substantially in the early stages of recovery from highly acidic (pH <5.0) to moderately acidic pH (5.0–5.9). In contrast, trajectories in lakes recovered to pH ≥6.0 converged toward the community structure more typical of circumneutral lakes in the 1970's. This suggests that given sufficient time, zooplankton community structure of recovering lakes may approach that of circumneutral lakes.

Nutrient Element Limitation of Zooplankton Production

Freshwater crustacean zooplankton species show pronounced interspecific variability but approach intraspecific homeostasis in their stoichiometry. It is especially interesting that members of the dominating herbivores in freshwater systems, such as Daphnia species, show consistently high P:C ratios. Sestonic P:C ratios in epilimnetic waters are usually far below that encountered in the zooplankton, which suggests that grazers may approach a direct phosphorus limitation in many localities. This view was supported by a regional study of 47 lakes, in which most independent variables including phytoplankton biomass and chlorophyll were scarcely correlated with zooplankton biomass but particulate P (>0.45 μm) could explain a major part of the variance of zooplankton biomass. Of the various taxa, daphnids gave the best correlation with particulate P, cyclopids and rotifers the worst. These observations suggest that phytoplankton biomass per se may not be the major determinant of zooplankton biomass but that the nutritional status of phytoplankton (P cell quotas) rather than biomass in terms of carbon is most important, or that zooplankton suffer a direct P limitation in many lakes. The latter view is supported by model predictions given in this article. Also, both freshwater and marine copepod grazers could correspondingly be growth limited by an N:C ratio of ingested food that is too low The possibility of direct nutrient element limitation has wide implications for the regulation of herbivore production, competition, and overall cycling of nutrients in epilimnetic waters.

Predicting crustacean zooplankton species richness

Data from 66 North American lakes were collected to construct a model for predicting the number of crustacean zooplankton species expected in a lake. The chosen lakes have a range from 4 m* to 80 x lo9 m2 surface area, range from ultra-oligotrophic to hypereutrophic, and have zooplankton species lists based on several years of observation. The number of crustacean zooplankton species in a lake is significantly correlated with lake size, average rate of photosynthesis (parabolic function), and the number of lakes within 20 km. A multiple linear regression model, using these three independent variables, explains -75% of the variation in log species richness. Prediction of species richness was not enhanced by knowledge of lake depth, salinity, elevation, latitude, longitude, or distance to the nearest lake. The North American species-area curve is statistically different from and steeper than the corresponding European curve.

Recovery of Crustacean Zooplankton Species Richness in Sudbury Area Lakes following Water Quality Improvements

Temporal patterns in the species richness of crustacean zooplankton communities were assessed in eight Sudbury area lakes based on data collected between 1973 and 1986. Excluding a consistently nonacidic reference lake, the study lakes showed general reductions in acidity and trace metal concentrations during this period, related to reduced contaminant emissions from the Sudbury smelters. Despite water quality improvements, several of the study lakes continue to have low pH and elevated trace metal concentrations which have inhibited recovery of zooplankton species richness. However, in lakes with more favourable current pH and lower trace metal concentrations, substantial increases in the average species richness of crustacean plankton communities have occurred, apparently due to both invasion of new species and more frequent occurrence of existing species. These results clearly demonstrate that reductions in acid-forming emissions lead to both chemical and biological improvements in some aquatic systems.

Laboratory acidification of a crustacean zooplankton assemblage from a Rocky mountain subalpine lake (U.S.A.)

AbstractA laboratory acidification experiment was conducted with a Rocky Mountain zooplankton assemblage from a subalpine lake located downwind of energy development activities and significant sources of acid precursors. The objective of the study was to assess the relative effects of lowered pH (treatment pH 4.2 and 5.2, control pH 6.8) on the survival of different crustacean zoo‐plankton species under controlled conditions for extended periods (19 to 41 d). Analysis of variance (e.g., F = 4.55, p < 0.05) indicated statistically significant differences between controls and treatments (acid treatments contained fewer individuals than did controls) for all four species, and significant differences among species. Newman‐Keuls multiple range tests (e.g., q = 4.02, p < 0.025) demonstrated the following ranking of species sensitivity (high to low) to a lowered pH of 5.2: Daphnia rosea > Holopedium gibberum > Diaptomus lintoni > Cyclops sp. At pH 4.2, H. gibberum was significantly more tolerant than D. rosea and D. lintoni (q = 4.50, p < 0.025), but no other significant differences were apparent. The results agree generally with those of other published experiments and field surveys.

Improved Estimation of the Dry Weight of Holopedium gibberum (Crustacea, Cladocera) Using Clutch Size, a Body Fat Index, and Lake Water Total Phosphorus Concentration

Holopedium gibberum is one of the most important species of crustacean zooplankton in Canadian Shield lakes, yet satisfactory length–weight relationships (LWR's) have not been constructed from North American populations. In this report we show that, despite assertions to the contrary, weights of individual H. gibberum can be successfully predicted from body length (L) of animals measured in a nonanaesthetized, relaxed position. We use a relationship between postabdomen length and L to show that LWR's of Ontario and Scandinavian populations of H. gibberum differ. As such differences among lakes are the rule and not the exception, it is not safe to assume that published LWR's for zooplankton are widely applicable. Consideration of clutch size (CS) and a body fat index (BFI) in addition to L significantly improved estimates of the dry weight of Holopedium from Plastic Lake in central Ontario. This model provided more accurate estimates of Holopedium dry weight in 29 test lakes than the simple LWR, i.e. it had wider applicability. Predicted weights in the test lakes were further improved by consideration of lake water total phosphorus concentrations.

The influence of individual variation on length-biomass regressions in three crustacean zooplankton species

Length-biomass regressions were established for the cladoceran Bosmina longispina maritima and for the copepods Euryremora affinis hirundoides and Limnocalanus macrurus , all common in the Baltic Sea. Biomass was analysed as individual organic carbon content. For Bosmina , length was a weak estimator of biomass; only 51% of the variation in carbon content was explained by length. For pre-adult stages of copepods length was a rather good estimator of biomass. For Euryremora nauplii. the length-carbon relationship was best described by linear equations (r 2 was between 0.49 and 0.69), and for copepodite stages (CI-V) by exponential functions (r 2 = 0.81). The regressions for two different sampling areas (Baltic proper and Bothnian Bay) did not show statistically significant differences. Among the copepodites (CI-V) of Limnocalanus there was a linear relationship between length and carbon content (r 2 = 0.76). In both copepod species there was no or a weak correlation between length and biomass among adults.

Comparative role of salps and other zooplankton in the cycling and transport of selected elements and natural radionuclides in Mediterranean waters

Salps, salp fecal pellets and other zooplankton species were analyzed for a suite of elements and natural radionuclides to assess their role in the biogeochemical cycling of nuclides in oceanic waters. The nuclide/Al ratios in organisms normalized to the same ratio in crustal rock indicated that Ca, Sr, Zn, Cu, U,210Po, and210Pb are enriched in the organisms. The concentrations of Fe, Al, Th isotopes and210Pb in salps and fecal pellets were about an order of magnitude higher than those in salps, whereas Ca, Cu, Zn, Mn and Po were higher by factors of about 2–5. Fluxes via salp defecation were higher than those which have been measured in crustacean zooplankton species, a result primarily due to the high defecation rates characteristic of salps. High nuclide levels in salp fecal pellets coupled with high defecation rates and presumed high salp biomass in many areas underscore the importance of these indiscriminate filter feeders in packaging and transporting to depth particulate-associated nuclides in surface waters.

Seasonal and short term fluctuations in zooplankton abundance in tropical Lake Malawi1

A growing body of data documents seasonal variations in the abundance of tropical zooplankton populations, in contrast to persistent impressions that these populations are stable in size and in age structure. Four of the six most common crustacean zooplankton species in southern Lake Malawi exhibited seasonal changes in population size over a period of 2.5 years. Seasonal trends were repeated between years, but both seasonal and annual patterns in zooplankton abundance were confounded by short term fluctuations in population size. These short term fluctuations represented demographic changes and could not be dismissed as sampling error. As a result, patterns of zooplankton abundance varied considerably between years, and no one year’s data accurately described the dynamics of zooplankton in this tropical lake.

Bioaccumulation and Effects of Cadmium and Zinc in a Lake Michigan Plankton Community

We conducted four in situ experiments in the southern basin of Lake Michigan to determine the responses of the plankton community to additions of cadmium (3 μg/L) and zinc (15, 30, 60, and 90 μg/L) as well as the bioaccumulation of zinc by different species of crustacean zooplankton. Total cadmium and zinc concentrations in treated enclosures (accounting for pretreatment lakewater concentrations of ~ 20 ng Cd and ~ 1 μg Zn per litre) were calculated from measurements of 109Cd and 65Zn with known specific activities.Zinc significantly reduced zooplankton populations and several other properties of community structure and function at concentrations much lower than those previously reported to be toxic to zooplankton and well below the levels established for protection of freshwater life. Zinc additions as low as 15 μg/L significantly reduced chlorophyll a, primary productivity, dissolved oxygen, specific zooplankton populations, zooplankton species diversity, and community similarity within 2 wk. Populations of several zooplankton species were severely reduced by 15 μg/L; for example, the population of the rotifer Conochilus unicornis was reduced to less than 1% of that in controls. Secondary, indirect effects included significant increases of a few populations, including Bosmina longirostris and Keratella cochlearis, for zinc additions of 15 and 30 μg/L. Most of the populations and community properties that we measured showed somewhat different percentage reductions in response to a given zinc addition at different times, but their relative (rank) values at different times were similar. Specific zooplankton populations were more sensitive to zinc than community similarity indices, and species diversity indices were relatively insensitive. Bioaccumulation of zinc by different species of crustaceans increased with added zinc but showed few significant differences among species. The small differences among species could, nevertheless, partially account for some of the observed changes in zooplankton community structure.

Biochemical composition of crustacean zooplankton from the eastern Gulf of Mexico

Water, protein, lipid, and ash, were measured in 38 species of crustacean zooplankton (1 decapod, 1 mysid, 12 euphausiids, and 24 copepods) found in the upper 1000 m in the eastern Gulf of Mexico. Deeper-living species had higher water and lower protein contents; lipid levels were highest in species found at mid-depths (500–550 m). Within vertically migrating genera, lipid and water contents were generally low. Deeper-living non-migratory genera had high water contents. Based on present results and literature values for unassayed groups, the standing stocks of zooplankton in terms of calories were highest at 30–50 m during the day and at 15 m at night, and decreased exponentially with depth. The high lipid levels of two mesopelagic species contribute to a secondary peak of zooplanktonic caloric content at 550 m. This results in an average caloric density here that is 1.5 times higher than in individual animals at the surface. While zooplankton populations at this depth are sparse, energy content per individual prey item can be high.

Length-Dry Weight Relationships of Some Freshwater Zooplanktona

Abstract Biomass of zooplankton can be estimated from the relation between length and weight by measuring the appropriate dimension of length on individual zooplankton. Length-dry weight relationships for 15 species of freshwater crustacean zooplankton collected from the Connecticut River were determined. Length-weight equations can be used to rapidly determine the biomass of zooplankton species when it is impractical to directly measure their weights.

Midsummer Crustacean Zooplankton Communities in Acid-Stressed Lakes

The distribution of limnetic crustacean zooplankton species and species associations in 47 industrially acidified lakes of the La Cloche Mountains, Ontario, are examined. pH, which ranged from 3.8 to 7.0, and to a lesser extent lake area and depth are the major determinants of the structure of these communities. Mesocyclops edax, Cyclops bicuspidatus thomasi, Diaptomus minutus, Holopedium gibberum, Diaphanosoma leuchtenbergianum, and Bosmina sp. were common species which occurred over the entire pH range. Tropocyclops prasinus mexicanus, Epischura lacustris, Diaptomus oregonensis, Leptodora kindtii, Daphnia galeata mendotae, D. retrocurva, D. ambigua, and D. longiremis plus some other rare species making a total of 64% of all species found never or rarely occurred below pH 5.0. Polyphemus pediculus, Daphnia catawba, and D. pulicaria were found primarily in lakes with low pH. An increase in the complexity of the zooplankton communities with increasing pH was evident. Above pH 5.0 the communities contained 9–16 species with three or four dominant species; in lakes with pH 5.0 or less the communities comprised one to seven species with only one or two dominants. Compared with relatively unspoiled lakes of similar morphometry in northwestern Ontario (ELA lakes) the La Cloche lakes have unusually simple zooplankton associations, particularly the very acidic lakes. Recurrent group analysis of the La Cloche and ELA lakes indicated that they were both characterized by a single major recurrent group of six species, five of which were common to the two areas. In the La Cloche lakes the group of six species occurred most frequently in lakes with pH above 5.0 although it maintained its integrity even down to pH 5.0. It is concluded that pH has a great effect on these zooplankton communities, primarily in lakes with pH below 5.0 where many species are completely eliminated and even tolerant species become progressively rarer until in some lakes a single species (D. minutus) remains.

Photosynthetically Elevated pH as a Factor in Zooplankton Mortality in Nutrient Enriched Ponds

During a nutrient enrichment study of eight small ponds, the mortality of crustacean zooplankton species was investigated using a life table technique. There was close agreement between high pH values and the disappearance of crustacean zooplankton in four of the highly fertilized ponds. Pond water containing phytoplankton was toxic to the dominant Ceriodaphnia reticulata, yet pond phytoplankton isolated from pond water and resuspended in chlorinated tap water supported excellent growth of C. reticulata. Millipore—filtered pond water was not toxic. Analysis of chemical changes occurring in pond water with filtration showed a slight decrease in pH as the only significant alteration that is directly related to zooplankton mortality. The existence of such a pH mortality factor was demonstrated by testing the survivorship of newborn. C. reticulata in artificially adjusted pH treatments. A change from pH 10.8 to 11.2 radically altered the survivorship. Other hypothesis to explain the disappearance of C. reticulata–predation, starvation, allelophathic chemicals–are discounted. It is suggested that the one reported case of allelopathy between a green alga and a cladoceran, that reported by Ryther (1954), may instead have been partly a pH mortality factor. It is further suggested that in culturally enriched waters of low buffering capacity such a pH mortality factor may be common. In such lakes and ponds the quality of the water deteriorate due to the loss of the zooplankton.