Changes In Zooplankton Community Structure Research Articles

The influence of advection on zooplankton community composition in an Arctic fjord (Kongsfjorden, Svalbard)

A continuous, high-resolution time series of zooplankton and hydrographic data were collected from Kongsfjorden between April and September 2002 using a sediment trap and instrumentation deployed on a mooring. The time series has, for the first time, demonstrated the close relationship between water mass advection and changes in zooplankton community structure in Kongsfjorden. Zooplankton identified in the trap samples included 31 species/genera and seven higher taxa representing ubiquitous, boreal and Arctic biogeographic origins. Correspondence Analysis (CA) identified three phases of zooplankton community composition in 2002. Phase I, from 18 April to 29 May, consisted primarily of resident Calanus finmarchicus and Calanus glacialis stage CVI females. Phase II, from 30 May to 23 June, was dominated by meroplankton, Oikopleura cf. vanhoeffeni, C. finmarchicus early life stages (CI to CIII), Calanus hyperboreus and Themisto abyssorum. Phase III, from 4 July to 8 September, comprised C. finmarchicus (predominantly CV), C. glacialis CV, C. hyperboreus CIV and a greater diversity of other copepod species, in particular, increasing numbers of Oithona similis. Transition between the zooplankton community phases was abrupt and clearly associated with the advection of water masses into the fjord from the adjacent shelf. Peaks of the Arctic species C. glacialis, C. hyperboreus and T. abyssorum in late May were associated with a change in the dominant fjordic water mass from local Winter Cooled Water (WCW) to an influx of Arctic Water (ArW) from the coastal current. A temperature increase of 2.75 °C in the upper water column signified the transition from Phase II to Phase III with the dominant water mass changing from ArW to Atlantic Water (AW) from the West Spitsbergen Current.

Application of normalized biomass size spectra to laser optical plankton counter net intercomparisons of zooplankton distributions

The optical plankton counter (OPC) and recently the laser OPC (LOPC) have been used primarily in two measurement applications: (1) identification of specific zooplankton species and (2) changes in zooplankton community structure using size‐based spectral measurements. The normalized biomass size spectra (NBSS) are one representation of the size‐based approach. The present study is based on utilizing the NBSS to describe the conditions or characteristics of the zooplankton community that allow a reasonable intercomparison of net samples and LOPC measurements made simultaneously for data collected during two oceanographic cruises carried out in the Lower Estuary and the Gulf of St. Lawrence in spring 2001 and 2002, respectively. NBSS linear slopes <−0.7 indicate the presence of additional plankton material such as diatom aggregates and gelatinous material (present during or immediately following blooms) that are less present in nets and are not intercomparable with LOPC measurements. Conversely, slopes >−0.7, or more “blue water” conditions, indicate the potential for reasonable intercomparison of the two methods. This observation applies to smaller‐sized zooplankton such as copepodites of Calanus spp. with equivalent spherical diameter <900 μm. The measurement of larger Calanus spp. stages (IV–VI) did not seem affected by the presence of additional aggregates or gelatinous material and reasonable intercomparisons between LOPC and net were obtained for both sampling years. The LOPC signals produced by Calanus spp. (IV–VI) were larger and more easily separated.

Discriminating zooplankton assemblages in neritic and oceanic waters: A case for the northeast coast of India, Bay of Bengal

Zooplankton species distribution and abundance data at 17 locations in the inshore (10-30 m), shelf (50-200 m) and oceanic (2,500-2,800 m) regions off northeast India (Bay of Bengal) during January 1999-April 2001 revealed 112 taxa represented by 30 divergent groups. Copepods (58 species) dominated (87%) the population numerically. In general zooplankton diversity (Margalef richness d, Shannon-Wiener H', Pielou's evenness J') increased in the direction of the open sea relative to coastal locations with a concomitant decrease both in abundance (ind m(-3)) and biomass (dry mass m(-3)). Based on multivariate analyses, it was possible to distinguish the zooplankton community into different assemblages according to their location (e.g., inshore, shelf, oceanic) and seasonality. While Acrocalanus sp., Oithona sp., Corycaeus danae, Euterpina acutifrons, Paracalanus sp., and Acartia sp. were found characterizing the coastal locations, Oncaea venusta was the discriminating species for shelf waters. In oceanic areas, there was a clear dominance of Labidocera sp., Candacia sp., Euchaeta rimana, Centropages calaninus, Copilia mirabilis and Corycella gibbula. The investigations revealed that changes in zooplankton community structure across water bodies could be associated with differing salinity. During November 1999 (post-monsoon), when salinity in the coastal waters was relatively low (26-28.9 PSU), the zooplankton community consisted of mainly Acrocalanus sp., Salpa, Corycaeus danae, Oikopleura sp., Acartia sp., Evadne tergestina, and Creseis sp. In January 2000 (salinity 32.4-34.1), additionally Corycella gibbula, Labidocera sp., Centropages sp., Microsetella sp., Euterpina acutifrons, Canthocalanus pauper, and Oncaea venusta represented the population discriminating the assemblage from others. In May 2000 (pre-monsoon) when salinity was highest (34.7-35.3), Oithona sp., Paracalanus sp., and Acrocalanus gibber were found important. Chaetognaths formed a distinct group during this period. Results presented during this investigation are considered significant since no previous studies exist for this locale drawing comparisons of the kind made during this study between coastal and oceanic situations.

Inference of past changes in zooplankton community structure and planktivorous fish abundance from sedimentary subfossils - a study of a coastal lake subjected to major fish kill incidents during the past century

To describe past changes in trophic structure, analyses were conducted of zooplankton (Cladocera, Rotifera) assemblages recovered in a 210 Pb dated sediment core from a shallow brackish lake exposed to several fish kill episodes during the 20 th century. A weighted-averaging zooplankton-based transfer function was applied to infer planktivorous fish densities (PL-CPUE) and to elucidate the potential of identify- ing fish kill incidents using sedimentary subfossils. The stratigraphical record showed a shift during the 20 th century. The cladoceran community structure changed from high abundance of macrophyte-associated taxa and chydorids, characteristic of clear water conditions, towards a community composed mainly by sediment-associated taxa, small-sized pelagic taxa as well as rotifers and chydorids, characteristic of eutrophic turbid conditions. Coinciding with these changes, the mean size of Daphnia ephippia decreased while inferred PL-CPUE increased. The results point towards progressive eutrophication with additional impact of salinity. Reduced temporal resolution of the sediment record made identification of fish kill incidents difficult. The indications of high fish planktivory and a decline in macrophyte abundance are consistent with anec- dotal observations of past fish investigations and contemporary data. The study dem- onstrates the usefulness of applying zooplankton subfossils to detect long-term changes in the trophic structure of brackish lakes in the past. In addition, it draws at- tention to the difficulties of using sediment records to highlight short-term events, such as fish kills, in shallow wind-impacted lakes.

Effects of fish stocking on the zooplankton community structure in a shallow lake in China

Abstract Changes in the zooplankton community structure in relation to fishery practices in Lake Donghu, Wuhan, China were examined. The number of Protozoa species increased slightly, whereas the number of rotifers and crustaceans decreased from the 1960s to the 1990s. The total annual average densities of zooplankton increased 15–20 times in the 1990s compared with the 1960s. This increase was largely attributed to Protozoa, which contributed 93.4% by number of the total zooplankton density in 1991. Cladoceran densities decreased markedly from 1987. Changes in densities of rotifers and copepods were not evident. Trends in zooplankton biomass were similar to density. Large changes in zooplankton community structure coincided with markedly changes in concentration of chlorophyll a and transparency in Lake Donghu in 1987. The year 1987 seems to be the threshold year when the zooplankton community structure changed considerably. These changes were related to continuously increasing fish stock biomass in the lake. It was suggested that fish stocking and fish biomass should be a better managed for improvement of the quality of the lake's environment.

Effects of a brief climatic event on zooplankton community structure and distribution in Arcachon Bay (France)

Short-term changes in zooplankton community structure and distribution in relation to changes in hydrological features were studied during summer in two distinct areas of Arcachon Bay (France) from July to September 1986. One sampling site was chosen in the northern part of the bay, influenced by oceanic inputs, and the other one in the south-eastern part of the bay, close to an estuarine zone, influenced by the River Leyre's inputs. Three different zooplankton assemblages were identified according to a temperature–salinity gradient: (i) an estuarine assemblage dominated by Acartia bifilosa and Acartia tonsa; (ii) an autochthonous assemblage composed of Acartia discaudata; and (iii) a coastal neritic one composed of Paracalanus parvus, Oncaea venusta and Penilia avirostris. All these latter assemblages remained stable during most part of the study period. However, a brief climatic event (storm event) occurred in mid-August and gave rise to a sharp decrease in temperatures along with significant changes in zooplankton structure and distributions in the bay. The estuarine community vanished and was replaced by the autochthonous community. In the northern part of the bay, the coastal neritic community succeeded the previously observed autochthonous community. The effect of this brief climatic event was durable since recovery time lasted two weeks with regard to hydrological features and zooplankton communities. In addition, the climatic event also had ecological consequences since it permitted spreading of planktonic organisms from small-localized areas throughout the bay.

Advances in Ecological Studies on Zooplankton

Advances in ecological stuides on zooplankton were reviewed based on the published papers and authors' studies. Contents include long-term ecology, dynamics changes of zooplankton, predation ecology and effects of environmental factors such as temperature, food resources on zooplankton. Long-term studies on zooplankton are very important to understand changes of ecosystem, especially those driven by slow processes, rare or episodic events and highly variable, stable or complex processes. The major objectives of long-term investigations are to provide reliable estimates of base-line variation, to detect long-term trends in the mean level of base-line, to detect rare events and to provide information for meaningful, testable hypotheses. A lot of research results demonstrated that changes in zooplankton community structure were determined largely by fish in the water bodies, with high stocking rate of planktivorous fish, and also by predation of invertebrate animals such as some copepods. Water temperature, food resources etc. may cause a stable zooplankton community. Among the freshwater zooplankton community, Daphnia and Cyclops vicinus may be the key groups. Because Daphnia plays a key role in the top-down control of phytoplankton, and C. vicinus are key factors in aquatic food chain during the period of their maximum abundance. In addition, several research topics such as molecule biology of zooplankton, zooplankton ecology of the surface microlayer, influence of engineering water conservancy project on ecosystem and zooplankton, and batch culture of zooplankton were discusses.

Annual and Seasonal Changes in Zooplankton Community Structure of Lake Kawaguchi, Japan.

Annual and seasonal changes in the community structure of metazoan plankton in Lake Kawaguchi were studied from April 1993 to December 1995. Sixteen taxa of rotifer, 4 taxa of cladoceran and 5 taxa of copepods were identified in this study. Among zooplankton species, Kellicottia longispina, Synchaeta stylata, Bosmina longirostris, and Daphnia galeata were found abundantly. Copepod species were grouped into Cyclopoida. A comparison of the present with previous studies indicates that some cladoceran species, Bosmina fatalis and Bosminopsis deitersi, have vanished altogether. It may be concluded that the structure of the zooplankton community in this lake has changed remarkably in recent years.

ASPECTS OF COMPARATIVE PLANKTON ECOLOGY IN CASCADING MGENI RIVER RESERVOIRS (MIDMAR, ALBERT FALLS, AND NAGLE): AN OVERVIEW

Summary An overview of a three year study of abundance, community structure and succession of zooplankton and phytoplankton in relation to physical limnological conditions in Lakes Midmar and Albert Falls is presented, along with findings on zooplankton from a nine month study of Lake Nagle. Physical stability increased between Midmar (mean summer N2 = 6.55 × 104 s2) and Albert Falls (N2 = 8.70 × 104 s2), in line with elevations in water temperature. Phytoplankton richness and diversity was similar in these reservoirs, although zooplankton species richness increased downstream. Abundance levels of both phyto- and zoo-plankton were broadly comparable in these two reservoirs. In Midmar and Albert Falls, overall mean (± SD) chlorophyll levels were 3.60 ± 1.54 and 3.41 ± 1.41 μg 11, with corresponding overall average zooplankton standing stocks of 0.85 and 0.76 g m2 dry mass, dropping to 0.54 g m2 in Nagle (for which spring to midsummer data are missing). Ruderal and colonist phytoplankters were persistently dominant both in Midmar and Albert Falls, in keeping with the continuous (if incomplete) mixing patterns evident in these reservoirs. Few stress tolerant algae occurred. The summer ruderal assemblage was unexpectedly dominated by diatoms in the physically more stable conditions of Albert Falls, but not Midmar. Mean zooplankton grazer-induced instantaneous mortality rates for planktonic algae for the whole study were estimated (by regression predictions) as 0.17 d1 in both lakes. Phytoplankton was not studied in Nagle. Changes in zooplankton community structure between Midmar and Nagle largely involved progressive increases in the contribution of smaller-bodied cladocerans (comprising both sequentially smaller species of Daphnia (D. pulex, D. longispina, D. laevis), and additional genera such as Diaphanosoma, Ceriodapnia, Moina and Bosmina). As with a parallel progressive switch between Metadiaptomus meridianus and Tropodiaptomus spectabilis over this series of reservoirs, (and the temporal separation of “co-existing” populations in Albert Falls), which has been shown experimentally to be strongly temperature-linked, changes in absolute temperature are implicated as a primary causal factor in the shifts in cladoceran species composition. Temporal occurrences of these species also indicate the primacy of temperature.

Regulation of Pigment Sedimentation by Photo-Oxidation and Herbivore Grazing

Reversed-phase high pressure liquid chromatography was used to show that algal carotenoid sedimentation is regulated by photo-oxidation and herbivore grazing in three unproductive, north-temperate lakes. Comparison of algal carotenoid and biovolume standing stocks revealed that carotenoid concentrations in epilimnetic waters were influenced by nonplanktonic inputs of pigments as well as phytoplankton community composition. Sediment traps did not record weekly events in the water column. Pigments that were incorporated in zooplankton feces and sank rapidly (e.g. alioxanthm and pheophorbide a) were overrepresented in trap material relative to epilimnetic pigment standing stocks. Differential decay of pigments in traps could not account for this observed bias. Chlorophyll mass–balance budgets corroborated the important influence of grazing by large-bodied zooplankton on pigment sedimentation. Interannual differences in pigment sedimentation were caused by changes in zooplankton community structure and the vertical zonation of phytoplankton communities. In the absence of fecal transportation, photo-oxidation destroyed carotenoids prior to their sedimentation from the photic zone. Therefore, sedimentary carotenoid composition is regulated by loss processes as well as changes in algal community composition.

Seasonal patterns of grazing and nutrient limitation of phytoplankton in a eutrophic lake

Observations and experiments on zooplankton grazing and nutrient (N and P) limitation of phytoplankton of Lake Mendota, Wisconsin, revealed that the relative strength of the two factors varied markedly during the seasonal succession of phytoplankton. Furthermore, seasonal changes in grazing and nutrient limitation were caused not only by seasonal changes in zooplankton community structure and nutrient availability but also by changes in phytoplankton community structure, which led to changes in edibility to zooplankton. The spring phytoplankton bloom of diatoms and small flagellates was highly vulnerable to grazing by both cyclopoid copepods and Daphnia, although Daphnia had a much stronger effect. Increased Daphnia grazing in late spring resulted in low phytoplankton biomass (the clear‐water period) and a phytoplankton community dominated by colonial green algae — taxa vulnerable to grazing by Daphnia but not other zooplankton. Nutrients (N and P) did not limit phytoplankton growth during the spring bloom or the clear‐water period. After the clear‐water period, the summer phytoplankton community was dominated by blue‐greens and Ceratium. Grazing effects by both Daphnia and copepods were low in summer, while nutrient limitation (both N and P) became severe. Reduced grazing impacts in summer may have resulted from prior intense grazing impacts, which led to dominance of grazing‐resistant taxa. These results suggest that seasonal variation in the strength of grazing and nutrient controls in eutrophic lakes results from changes in zooplankton biomass and community structure, nutrient availability, and phytoplankton community structure interacting to determine phytoplankton seasonal succession.

Effects of grazing by Daphnia on algal carotenoids: Implications for paleolimnology

Reverse-phase thin layer chromatography was used to quantify algal carotenoid degradation resulting from grazing by Daphnia magna in suspensions of lyophilized Oscillatoria utermohlii, O. limnetica, Anabaena flos-aquae and Synechococcus sp. Three samples were removed every 24 h from 0 h to 144 h and the carotenoid, carbon and nitrogen content of the remaining algal-fecal mixture was determined. Grazing by Daphnia reduced carotenoid concentrations by 30%–80% after 144 h, with myxoxanthophyll being the most labile pigment in experiments with filamentous cyanophytes. However, as a group, the carotenoids were more resistant to the combined effects of grazing by Daphnia and bacterial action than were particulate algal carbon (78% to 82% lost by 144 h) or nitrogen (86%–90%) during the period in which easily digestible material remained. The maximal extent of carotenoid enrichment relative to particulate carbon ranged from 150% to 300% of initial pigment concentrations but declined with repeated coprophagy. On the basis of these results and published pigment budgets, we conclude both that fecal transportation of pigments may be an important determinant of carotenoid accumulation rates and that carotenoid stratigraphies should record predator-mediated changes in zooplankton community structure, especially in oligotrophic conditions.

Predator driven changes in community structure.

The zooplankton community of a small pond changed markedly with temporal variation in predation pressure. Long term changes in zooplankton community structure occurred following the replacement of planktivorous fish by phantom midge (Chaoborus americanus) larvae as the predominant predator of zooplankton. The interannual changes following the establishment of Chaoborus included the apparent or near extinction, of species ill adapted to the new predation pressure and the successful colonization of well adapted species. Seasonal changes in the species composition and size distribution of the zooplankton community correlate with temporal variation in predation intensity associated with temperature-activity patterns of the predator or changes in the stage structure of the predator population.

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.