Crustacean Zooplankton Community Research Articles

Changes in zooplankton and the phenology of the spiny water flea, <i>Bythotrephes</i>, following its invasion of Harp Lake, Ontario, Canada

The crustacean zooplankton community of Harp Lake, Ontario, Canada, has changed appreciably since the invasion by the spiny water flea, Bythotrephes. Crustacean species richness has declined, large-bodied Cladocera have replaced small-bodied ones, and there has been a downward trend in the total abundance of zooplankton because copepod abundance has remained stable while Cladoceran abundance has declined. Although the zooplankton community has now been stable for 4 years (1995–1998), the biology of the invader has changed dramatically. In particular, there have been 10-fold differences in the mean annual abundance of Bythotrephes in this 5-year period and substantial changes in the timing of population maxima. We attribute these changes to two factors: (i) transition from a summer to a fall switch from parthenogenesis to gametogenesis and (ii) interannual differences in the thickness of a warm, dark stratum in the lake. We hypothesize that this stratum provides a refuge for Bythotrephes from predation by lake herring, Coregonus artedii.

Rate of chitobiase degradation as a measure of development rate in planktonic Crustacea

We have developed a method to determine development time (molt rate) in both single and mixed populations of crustacean zooplankton based on turnover of the chitinolytic enzyme chitobiase in the ambient medium. We examined the relationship between body size and chitobiase activity released into the medium following molt in three freshwater cladoceran species, Ceriodaphnia spp., Daphnia pulex, and Daphnia magna. Chitobiase activity increased with body length, and a common relationship was observed among all three species (r2 = 0.82, p < 0.0001). Under steady-state conditions in laboratory cultures, the rate of decay of this enzyme in the medium was balanced by its rate of production by molting animals. The rate of decay of the enzyme in the absence of animals was therefore also its rate of production, which is a measure of the average rate of development of the crustacean zooplankton community. Development times for a D. magna culture (2×) and a Ceriodaphnia spp. - D. magna mixed culture were 65.4 vs. 62 h, 59 vs. 67 h, and 46.6 vs. 50 h, respectively, as measured by this "chitobiase method" versus conventional molt rate determinations.

Diatom and crustacean zooplankton communities, their seasonal variability and representation in the sediments of subarctic Lake Saanajärvi

Present and past diatom and crustacean zooplankton communities of subarctic Lake Saanajärvi in Finnish Lapland were studied with special emphasis on their representation in the sediment surface. Two years monitoring of the present state of the lake revealed it to be ultraoligotrophic with a biomass peak during autumn overturn. Chrysophytes and diatoms were the most abundant phytoplankton groups, with four species forming the main bulk of the crustacean zooplankton community. The comparison of the present plankton community with the species composition in the sediment surface showed that only some plankton groups are suitable for paleolimnological studies. The value of diatoms for paleolimnological studies was supported by the observation that all of the species recorded from various habitats in the lake were detectable in the sediment. In addition, some species (e.g. Cyclotella glomerata) that limnological sampling had not detected were found in the sediment record. Similarly, the zooplankton class Chydoridae and Daphnia hyalina species were equally or better represented in the sediment than in the water column. On the other hand, the sediment trap and core evidence of the whole crustacean zooplankton community suggested many zooplankton species have little or no significance in paleolimnological studies. For example the two dominant copepod species, Eudiaptomus graciloides and Cyclops abyssorum, were not detectable in sediment trap samples. These findings indicate that only a small fraction of the living biota are preserved in the sediments, and this should be taken into account when drawing conclusions based on the detection of just one such species group.

Composition, biomass and potential grazing impact of the crustacean and pelagic tunicates in the northern Humboldt Current area off Chile:differences between El Niño and non-El Niño years

A multi-disciplinary research program was conducted in the northern Humboldt Current System in a 80 X 80 nautical n7ile area off Antofagasta, northern Chile (23 S) on 3 occasions: before the 1997/98 El Nirio event (January 1997), and dunng the onset and maximum penods of the event (July 1997 and January 1998, respectively). As a part of this program, the trophodynamic role of pe lag~c tunlcates (salps and appendiculanans), as well as the crustacean zooplankton, divided into 3 size classes (large[euphauslids], medium[large calanoid copepods] and small-size animals [small calanoid and cyclopoid copepods]) were assessed One of the most conspicuous physical processes was the deepenlng of the thermocline during the El Nirio event, which in turn led to suppression of nutrient enrichment by upwelling events and low chlorophyll a (chl a ) concentrations in the study area. Chl a and particulate organlc carbon (POC) values were hlgher near the coast, and coastaWoceanic gradients were greater m the case of chl a. High chl a (100 to 160 mg m-') and POC ( l 1 to 17 g m-2) concentrations were usually found associated with bays and/or capes w~thin 40 nautical miles of the coast. In contrast, oceanic areas showed low concentrations throughout the study. Small calanoid and cyclopoid copepods represented only a minor fraction of the total crustacean zooplankton carbon (4 to 20%), although they often accounted for a relatively large portion of the total ingestion (26 to 68%) of the crustacean zooplankton community. Euphausiids represented a large fraction of total crustacean zooplankton carbon (28 to 73 %), and accounted for between 5 and 61 % of total crustacean zooplankton grazing. Ingestion rate as a percentage of body carbon was negatively correlated with animal size, varying between 4 % in euphausiids (17 mm) and 123% in small calanoid copepods (0.8 to 1.7 mm). A companson of estimated daily respiration rates and daily carbon ingestion rates indicated that ingestion of phytoplankton would have exceeded respiratory demands for both large and small calanoid copepods during all 3 sampling periods. In contrast, ingestion of phytoplankton failed to account for the respiratory needs of the euphausiids. This, together with microscopical observations, led to the conclusion that euphausiids utilised other sources of carbon such as detritus, microand mesozooplankton in addition to phytoplankton. Crustacean zooplankton showed a s~gnificant grazing impact, removing from 10 to 34 % of primary production (PP). Salps of the species Salpa fuslformis were present in dense aggregates that could have removed up to 60% of PP during January 1997. On average, the grazing impact of this specles was approximately one-half (16%) that of the whole crustacean zooplankton community combined (34 %). We did not find any significant difference in zooplankton biomass between January 1997 (nonEl Nino) and January 1998 (El Nino), with average biomasses of 24.6 and 21.4 mg dry wt m- respectively. There was, however, a shift in the size spectrum of crustacean zooplankton towards small-sized copepods between January 1997 (60 mg C m-') and January 1998 (186 mg C m-2)

Rate of chitobiase degradation as a measure of development rate in planktonic Crustacea

We have developed a method to determine development time (molt rate) in both single and mixed populations of crustacean zooplankton based on turnover of the chitinolytic enzyme chitobiase in the ambient medium. We examined the relationship between body size and chitobiase activity released into the medium following molt in three freshwater cladoceran species, Ceriodaphnia spp., Daphnia pulex, and Daphnia magna. Chitobiase activity increased with body length, and a common relationship was observed among all three species (r2 = 0.82, p < 0.0001). Under steady-state conditions in laboratory cultures, the rate of decay of this enzyme in the medium was balanced by its rate of production by molting animals. The rate of decay of the enzyme in the absence of animals was therefore also its rate of production, which is a measure of the average rate of development of the crustacean zooplankton community. Development times for a D. magna culture (2×) and a Ceriodaphnia spp. - D. magna mixed culture were 65.4 vs. 62 h, 59 vs. 67 h, and 46.6 vs. 50 h, respectively, as measured by this "chitobiase method" versus conventional molt rate determinations.

Crustacean zooplankton communities in a New Zealand lake during four decades of trophic change

Lake Rotorua is a eutrophic polymictic lake in the centre of the North Island, New Zealand. Three studies of its crustacean zooplankton, in 1955–56, 1967–69, and 1994–95 have been made. Despite increased eutrophication since the first study, species composition has not changed: the calanoid copepod, Calamoecia lucasi, dominates for much of the year and Bosmina cf. meridionalis and Cerio‐daphnia cf. dubia are the only limnetic cladocerans. Comparison of their annual cycles in abundance between the studies show little regularity in the seasonal patterns, suggesting that stochastic events, such as storms, may be the most important controlling factors through their effects on food levels.

Biological Recover y from Lake Acidification: Zooplankton Communities as a Model of Patterns and Processes

Knowledge of the recovery of aquatic communities from lake acidification is limited. Data from studies of crustacean zooplankton communities, however, do reveal some of the major mechanisms important in the biological recovery process. Important influences on recovery include factors related to habitat quality and the ability of organisms to colonize. During recovery, existing species and colonists from internal and external sources interact to form a new community. The relative roles of internal and external influences remain poorly understood. Four general community types can be identified as possible outcomes of the recovery process: the original community, a normal alternate community, a community limited by dispersal, and a community limited by biological resistance. Empirical data indicate that, given suitable water quality, about a decade is sufficient to permit substantial recovery of zooplankton communities if there are no severe physical or biological barriers to restructuring.

Long-term trends in the abundance and community structure of coastal zooplankton in the southern Benguela system, 1951–1996

Long-term trends in the abundance and species composition of zooplankton are described. These trends are based on retrospective analysis of zooplankton samples collected in the St Helena Bay area off the South African west coast since the development of the pelagic fishery in the 1950s. Samples were selected from seven sampling programmes (1951–1967, 1974, 1978, 1983, 1984, 1987 and 1988–1996) that monitored the main commercial fishing grounds during peak recruitment (March–June). Abundance data are presented for size-based taxonomic groups, which include cyclopoid and small, medium and large calanoid copepods, cladocerans, euphausiids, amphipods, chaetognaths and pelagic tunicates. Despite discontinuity in the time-series and the use of different samplers, all taxa showed a significant long-term increase in their abundance by at least one order of magnitude between 1951 and 1996. Total zooplankton abundance increased from 4.2×103 to 7.2×105 ind·m−2 over the same period. Multiple regression analysis of the log-transformed data indicates size-based differential rates of increase in population levels among the crustacean size classes, with a maximum rate in cyclopoids (slope = 0.052) and a minimum rate in euphausiids (slope = 0.035). This resulted in a significant shift through time in the crustacean zooplankton community structure, which may reflect differential size-selective predation during periods of anchovy Engraulis capensis or sardine Sardinops sagax dominance. The observed long-term increase in zooplankton abundance could be a response to a long-term decrease in predation pressure following decreases in stocks of pelagic fish, which in turn could be caused by increased predation by top predators. Another mechanism contributing to the long-term increase in zooplankton is the observed long-term intensification of coastal upwelling, which could enhance primary and secondary production, and increase advective input of zooplankton populations into the study area and augment their retention.

Effects of invading vendace (Coregonus albula L.) on species composition and body size in two zooplankton communities of the Pasvik River System, northern Norway

Species composition and body-size distribution were studied in the crustacean zooplankton communities of two limnologically similar lake localities situated 50 km apart in the Pasvik River System, northern Norway. A recent invasion and successive downstream expansion of vendace (Coregonus albula), a specialized zooplanktivorous fish, allowed comparisons between sites with different predation pressures. Vendace had established a high population density and was the dominant fish species in the pelagic of the upper locality, but had just invaded the lower locality with a small number of individuals. Whitefish (Coregonus lavaretus), a closely related but less specialized zooplanktivore species, dominated the native fish community of both lakes. The zooplankton community of the upper locality was dominated in June and August by Bosmina longirostris, the smallest zooplankton species represented in the water course, and in September by Daphnia cristata. The lower locality was dominated by the larger Holopedium gibberum and Eudiaptomus graciloides in June, by D.cristata in August, and by D.cristata and B.longirostris in September. The mean body size of the three most abundant cladoceran species was significantly smaller in the upper locality, compared to the lower locality. It was concluded that the invasion and establishment of a dense vendace population in the upper locality had increased the predation pressure in the pelagic, resulting in a reduction of body size and a shift towards smaller species in the zooplankton community.

Changes in the crustacean zooplankton community of Harp Lake, Canada, following invasion by Bythotrephes cederstrœmi

1. Detecting the impacts of invading Bythotrephes cederstrœmi (Crustacea, Onychopoda, Cercopagididae) on zooplankton in North American lakes has been hampered by the brevity of pre‐invasion data, and by the difficulty of distinguishing the effects of the invader from other stresses. The data from Harp Lake in Ontario, Canada, circumvent these difficulties. Bythotrephes appeared in the lake in 1993. There is a 15‐year pre‐invasion data set, and no significant complicating concurrent stresses.2. The species composition and the size structure of the crustacean zooplankton community of Harp Lake changed after the invasion. Several small species either declined dramatically in abundance (e.g. Bosmina longirostris, Tropocyclops extensus) or disappeared (Chydorus sphaericus, Diaphanosoma birgei, Bosmina (Neobosmina) tubicen). In contrast the abundance of the larger cladocerans Holopedium gibberum and Daphnia galeata mendotae and the hypolimnetic copepod Leptodiaptomus sicilis increased. Several univariate and all multivariate summarizations of zooplankton abundance, biomass and size structure highlighted the uniqueness of the post‐invasion community.3. The alterations in the zooplankton community could not be attributed to changes in lake acidity, thermal regimes, penetration by ultraviolet light, nutrient status, fish stocking or the abundances of native invertebrate predators, but they were correlated with Bythotrephes abundance, both within and among years. Hence, we hypothesize that the invasion by Bythotrephes has significantly altered the crustacean zooplankton community of Harp Lake.

Recovery of crustacean zooplankton communities from acid and metal contamination: comparing manipulated and reference lakes

En comparant les changements survenus a long terme dans les communautes de crustaces zooplanctoniques de trois lacs experimentalement chaules situes pres des usines metallurgiques de Sudbury (Ontario) avec des valeurs temporelles et spatiales mesurees dans des lacs de reference situes a distance de Sudbury, nous (i) demontrons l'utilite des lacs de reference dans l'etude de la restauration d'un bassin lacustre, (ii) comparons des indicateurs de restauration univaries et multivaires et (iii) determinons si la rapidite de la restauration depend de la gravite de la pollution acide et metallique. Les lacs de reference nous ont permis d'etablir des objectifs de restauration ainsi que des normes de variabilite interannuelle. La performance des mesures univariees comme indicateurs de deterioration et de restauration peut etre representee comme suit: richesse = diversite > uniformite > abondance. Nous avons obtenu les valeurs multivariees en mettant en relation les donnees recueillies a Sudbury et les resultats d'une analyse des correspondances appliquee aux donnees de reference spatiales. Les approches univariee et multivariee se sont revelees d'une sensibilite egale avec les mesures relatives a la presence des especes; toutefois, c'est avec les mesures multivariees incluant l'abondance relative des taxons que nous avons obtenu la meilleure performance d'ensemble. Les deux lacs les plus acides (pH de 4,5) n'etaient pas restaures 15 ans apres la neutralisation, mais le zooplancton du lac Nelson, le moins acide (pH de 5,7) des lacs experimentaux etait completement restaure 10 ans apres le chaulage. Ces resultats laissent esperer que, si les mesures internationales de reduction des emissions de SO 2 avaient pour effet de renverser l'acidification, le zooplancton serait restaure dans les milliers de lacs moyennement acidifies de l'Amerique du Nord.

Recovery of crustacean zooplankton communities from acid and metal contamination: comparing manipulated and reference lakes

Recovery of crustacean zooplankton communities from acid and metal contamination: comparing manipulated and reference lakes

Changes in the pelagic crustacean zooplankton of high-boreal Island Lake, Saskatchewan, associated with uranium mining

Island Lake, Saskatchewan, has become eutrophic, subsaline (salinity between 0.5 and 3.0 g I(-1)) and contaminated with several metals over the last decade. In this study, the crustacean zooplankton community in the lake in early summer 1989 is compared to the community during the early summers of the baseline years 1978 and 1979, based on archived environmental impact assessment samples. Community composition has changed, probably because of salinization and perhaps, to a lesser extent, eutrophication. Calanoid copepods have disappeared, while the numbers of species of cyclopoid copepods and cladocerans have increased. Ceriodaphnia reticulata, present in 1988 only, was more numerous than any other species during all three years. Densities of all other species were very low in 1989, which has led to lower diversity (Simpsons Index). Predation by Chaoborus probably contributed to the low abundances in 1989. The characteristics of the zooplankton community in 1989 were very similar to those of zooplankton in culturally acidified lakes, and indicate that Island Lake is in poor health. The success of Ceriodaphnia, a standard toxicity bioassay genus, is noteworthy under such contaminated conditions. While the taxonomic changes are obvious, the zooplankton data are limited; therefore causes can only be inferred. The study demonstrates the need for more and better ecosystem-specific biological information in order to do environmental impact assessments, in this case for mining in the north.

Crustacean Zooplankton Communities and Lake Morphometry in Precambrian Shield Lakes

To investigate relationships between crustacean zooplankton communities and lake morphometry we sampled 60 near-neutral Precambrian Shield lakes, including many small, shallow lakes. Morphometry-related patterns in the distributions of many zooplankton species were evident. Lake depth determined the occurrence of hypolimnetic species, and lake depth, lake area, and watershed area were positively related to the species richness of zooplankton communities. Among lakes with fish, deeper (maximum depth &gt;8 m) lakes were characterized by greater species richness, higher abundances of a number of species including Daphnia pulex, Daphnia galeata mendotae, Daphnia dubia, and Diacyclops bicuspidatus thomasi, and lower abundances of Leptodiaptomus minutus, than shallower (maximum depth &lt;8 m) lakes. Increased predation pressure by small fish species in smaller, shallower lakes probably influenced the observed species distributions. Lakes inferred to be fishless based on the presence of Chaoborus americanus typically had relatively high abundances of D. pulex, Diaphanosoma brachyurum, and Aglaodiaptomus leptopus, and absences of D. g. mendotae and D. birgei, patterns attributable to intense invertebrate predation on zooplankton.

Zooplankton spatial patterns in two lakes with contrasting fish community structure

Horizontal and temporal patterns in crustacean zooplankton communities were analyzed in two small, oligotrophic lakes which were morphologically and chemically similar, but had contrasting fish communities. Ranger Lake was dominated by two bass species and the planktivores numbered 1200 ind. ha−1. There were significant differences in the distribution of zooplankton taxa and size classes between sampling stations. In Ranger Lake, the smallest size classes were more abundant at the deeper stations and the larger individuals were more abundant at the shallower stations. In Mouse Lake, the smaller individuals were more common at the shallow stations and the larger individuals were more common at the deeper stations. These differences suggest medium scale patterns induced by vectorial forces, but modified by species specific migration patterns. We tested the hypothesis that horizontal heterogeneity should be influenced by planktivore density and found that none of the taxa showed significant between-lake differences in the variance-mean regressions. We also tested the hypothesis that larger taxa should be more heterogeneous and we found that cladocerans were more heterogeneous than copepods and nauplii. In terms of sampling methodology our data suggest that the between-station variability was so high that a single mid-lake sample would certainly lead to completely unacceptable errors in the estimation of population densities and biomasses.

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 &lt;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 &lt;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.

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.

Relationship between feeding of blueback herring and the zooplankton community of a Texas reservoir

Following the introduction of blueback herring (Alosa aestivalis), we examined herring food habits and the crustacean zooplankton community in Lake Theo, a 30-hectare reservoir located on a tributary of the Red River in north Texas. Prior to the introduction in spring, 1982, the reservoir contained an established fish community dominated by centrarchids. Blueback herring stomachs and zooplankton were sampled quarterly from summer, 1982 through winter, 1985. Cladocerans accounted for 89.4% of the zooplankton consumed by herring. Median lengths of cladocerans and copepods in the herring diet were significantly greater than those in the reservoir. No appreciable changes in lengths of cladocerans and copepods in the reservoir were observed after blueback herring introduction, but the zooplankton community shifted from cladoceran to copepod domination.

Zooplankton Dynamics in a Great Lakes Coastal Marsh

The zooplankton ecology of coastal marshes of the Laurentian Great Lakes is virtually unknown, although these systems are believed to perform important functions in the overall Great Lakes ecosystem. Thus, the composition and seasonal dynamics of the crustacean zooplankton communities of a riverine coastal marsh and the adjoining wave zone of Lake Erie were compared over 13 months. The open waters of the marsh upstream possessed a zooplankton community distinctly different from that in the wave zone, in terms of both the species composition and the population dynamics of some shared species. The downstream end of the marsh possessed a transitional zooplankton community which shared species with both the upstream marsh and wave zone communities and which had intermediate abundances of most species common to both habitats. A small summer storm runoff event briefly disrupted the development of several zooplankton populations in the marsh. Further studies are needed to identify the important factors which influence the marsh zooplankton ecology. Preliminary evidence indicates that the factors probably include planktivory by fishes and Chaoborus, aquatic macrophyte beds, a chemical and chlorophyll gradient from upstream to the lake, persistent high suspended sediments, and the flushing action of storm runoff events.

Creating conditions for changes in prey community structure by Chaoborus spp. in a lake in Sweden

In Lake G»rdsjon (Southwest Sweden), liming as an experimental improvement of living conditions for pelagic algae, resulted in a significant increase of algal biomass and a reduction of mean cell size. The algal development was beneficial for small sized filter feeding zooplankton, particularly rotifers, which showed a significant increase. The increase in abundance of small sized zooplankton created better food conditions for the smaller instars, and thus a much better overall survival of Chaoborus larvae. The resulting, 6–7 times larger population of Chaoborus larvae significantly changed the structure of the crustacean zooplankton community. Bosmina coregoni, the fastest swimmer of the crustacean species suffered most and was strongly reduced by the increased predation from Chaoborus. The share of cladocerans decreased, while copepods increased in importance.