Dominant Crustacean Research Articles

Importance of artificial high flows in maintaining the ecological integrity of a regulated river

Artificial high flows attempt to simulate natural flood pulses in flow-regulated rivers with the intent to improve their ecological integrity. The long-term use of such high flow events have shown beneficial ecological effects on various rivers globally. However, such responses are often non-linear and characterized by underlying feedback mechanisms among ecosystem components. The question arises as to what happens when such high flow releases are disrupted or even discontinued. Here, we used the long-term (22 years) monitoring dataset from the river Spöl to examine whether discontinuation (2016–2021) of the flood program (annual artificial high flows from 2000 to 2016) resulted in the ecological degradation of the river. We used monitoring data of physico-chemistry, periphyton, benthic organic matter, macroinvertebrates and fish (brown trout, Salmo trutta fario L.) in the analysis. The flood program had no long-term effect on water physico-chemistry with most parameters showing typical variations associated with season and inter-annual weather patterns. The floods were effective at mobilizing bed sediments that reduced periphyton biomass and benthic organic matter following each flood. Increases in periphyton biomass and benthic organic matter occurred between floods, but both parameters showed no significant increase with discontinuation of the flood program. Floods reduced macroinvertebrate densities, but with density increases occurring between floods. The pulsed disturbances, and the progressive change in the habitat template, resulted in shifts in community assembly by reducing densities of Gammarus fossarum, a dominant crustacean, which allowed other taxa to colonize the system. Macroinvertebrate densities remained low after discontinuation of the floods, although G. fossarum densities have increased substantially while other taxa, especially some stoneflies, remained low in abundance. Notably, community assembly returned to a pre-flood composition with discontinuation of the floods. The abundance of brown trout increased substantially during the flood program but returned to low pre-flood numbers with discontinuation of the floods. We conclude that the flood program was beneficial to the ecology of the river Spöl and discontinuation of the floods resulted in degradation of the system after a relatively short lag period. However, the system showed high resilience to an earlier perturbation, a sediment spill in 2013, suggesting a rapid positive response by biota with resumption of the flood program.

Stomach content analysis of young Russell's oarfish (Regalecus russelii) from Taiwan, and a report on an unusual case of predation.

In this study, we analyzed the stomach content of two individuals of rare, young Russell's oarfish, Regalecus russelii, from Taiwan. One of them was captured alive along with larval fish and crustaceans by a stow net from the shallow waters (15-18m deep) of the Tamsui River mouth. A total of 38 individuals of larval fish belonging to three species (86.4% of all prey) and 6 individuals of crustaceans belonging to three species were found in the Russell's oarfish specimen's stomach. Among the prey, the Japanese anchovy (Engraulis japonicus) was the most dominant fish species, accounting for 44.7% of all fishes; and luciferids were the most dominant crustaceans, accounting for 66.7% of all crustaceans. All the prey fish were sandy or a mixture of sandy and muddy sediment dwellers. The luciferids and Japanese anchovies are characterized by having diel vertical migration behavior. Based on the sampling information and biological characteristics of the fish larvae and crustaceans, we conjectured that the abundance of these prey when they moved up to the upper layer of the Tamsui River mouth at nighttime had attracted the young Russell's oarfish to hunt there. In addition, we speculated that it might be easier for the vertical-swimming Russell's oarfish to hunt a large number of luciferids assembled in the upper layer of the water by its particular posture or angle of view.

Latitudinal species diversity and density of cryptic crustacean (Brachyura and Anomura) in micro-habitat Autonomous Reef Monitoring Structures across Kepulauan Seribu, Indonesia

Abstract. Hazeri G, Rahayu DL, Subhan B, Sembiring A, Anggoro AW, Ghozali AT, Madduppa HH. 2019. Latitudinal species diversity and density of cryptic crustacean (Brachyura and Anomura) in micro-habitat Autonomous Reef Monitoring Structures across Kepulauan Seribu, Indonesia. Biodiversitas 20: 1466-1474. Kepulauan Seribu is located in the north of Jakarta and has historically been affected by anthropogenic activities. Based on its anthropogenic pressure, the archipelago is divided latitudinally into three main parts; the southern part, is a collection of islands located closest to Jakarta Bay and characterized by poor water quality, large sediment and pollutant inputs from nearby rivers, the central and north part that possesses a better water quality. Brachyura and Anomura are dominant crustacean groups in the ocean, which inhabited areas from littoral zone to the deep sea. However, its diversity and abundance are relatively understudied especially in the area where anthropogenic pressure is severe like Kepulauan Seribu. The ARMS (Autonomous Reef Monitoring Structure) is a standardized monitoring method systematically designed for observing indications of organism’s biodiversity in units of time. This research was conducted by employing ARMS as a standardize monitoring procedure to catalog and provide census of Crustaceans (Brachyuran and Anomuran) distributed across the archipelago. All crustacean inhabiting each unit of ARMS were collected and identified. Species diversity was then evaluated to see whether gradient in anthropogenic pressure has a direct impact on species composition and abundance. A total of 24 ARMS units were deployed from 2013 to 2016, located in three zones: south (9), central (9) and north (6) of Kepulauan Seribu. This study identified 17 species from 8 different families of Brachyura and 11 Anomura species from 4 different families from all sites. However, low available identification references for Indonesian crustacean made some specimen were identified only up to family level. The highest species diversity of Brachyura was recorded from family Xanthidae, followed by Portunidae and Pilumnidae, while in Anomura was in Porcellanidae, followed by Paguridae, Galatheidae, and Diogenidae. The high species diversity and density of brachyurans and anomurans were recorded in the central zone. This research infers that the species diversity of Crustaceans (Brachyura dan Anomura) seems dependent on the environmental quality, but most likely all crustacean species depend on the availability of habitat structure.

Metatrancriptomic analysis from the Hepatopancreas of adult white leg shrimp (Litopenaeus vannamei)

White leg shrimp (Litopenaeus vannamei) is a widely cultured shellfish in coastal areas of the Pacific and is considered one of the dominant crustaceans in aquaculture, globally. There is currently no information regarding the functional role of the microbiome of L. vannamei. In this study Next Generation Sequencing techniques were used to generate the metatranscriptome of the hepatopancreas from adult individuals of this species. The functional role of the microbiome showed that the most represented bacterial phylum consisted of Proteobacteria, Firmicutes and Actinobacteria, in which several bacterial classes produce different sets of hydrolytic enzymes. The most represented functions in the microbiome were related to the metabolism of proteins, amino acids, carbohydrates and lipids. These systems were also highly represented in L. vannamei. This response suggests that the nutrient absorption involves the joint participation of the host and the microbiome. A similar behavior was observed in abiotic stress related genes in L. vannamei and the microbial communities. There was a high representation in both systems, suggesting that the host-microbiome has adapted to the environmental fluctuations. Pathogens were found in this study in low titers, which are common in marine organisms; and several mechanisms that participate in the pathogenic response of L. vannamei were identified such as: proteolytic enzymes and cell communication mechanisms. Over a thousand genic microbial products were identified in the metatranscriptome of L. vannamei including the presence of several genes related to metabolic functions, stress and antibiotic resistance. This study provides evidence of the microbiome interactions in L. vannamei during the culture of this species and the different factors that could affect the microbial composition and gene expression.

Calcium concentration in leaf litter affects the abundance and survival of crustaceans in streams draining warm–temperate forests

Summary Stream ecosystems receive large quantities of nutrients from terrestrial ecosystems that influence community dynamics. However, few studies have investigated the effects of subsidiary calcium, an essential element of animals, on stream ecosystems. We focused on differences in calcium concentrations of leaf litter between tree species. In particular, litter of Japanese cedar (Cryptomeria japonica) has a higher concentration of calcium than other taxa, and the tree is planted in many parts of Japan. Therefore, we predicted that a C. japonica plantation would affect the supply of subsidiary calcium to stream ecosystems. We compared calcium concentration of leaf litters, soils, stream water and stream benthic invertebrates sampled at nine sites in catchments composed of cedar plantations, evergreen broad‐leaved forest and clear‐cut areas. In addition, we placed 10 Gammarus nipponensis in each of 10 nylon cages in the nine streams and after one month surveyed the number of surviving individuals. Calcium concentration in stream water and soil, and the density and survival of the dominant crustacean (Gammarus nipponensis) were significantly higher at sites dominated by C. japonica compared with other forest types. Furthermore, invertebrate community composition was correlated with total calcium and nitrate in stream water, indicating that terrestrial vegetation can affect stream invertebrate communities, particularly crustaceans.

Feeding ecology and trophic position of a Mediterranean endemic ray: consistency between sexes, maturity stages and seasons

The study of trophic ecology of marine predators is crucial to better understand the ecological factors that condition their role within marine ecosystems. Here we investigated the trophic habits and position of a Mediterranean endemic predator, the starry ray, Raja asterias. Specifically, we quantified the diet composition of this endemic ray in a highly exploited area of the NW Mediterranean, and we evaluated the effects of sex, maturity-stage and season on its feeding habits. Our results revealed that the starry ray is a predator of crustaceans (crabs and shrimps), and to a lower extent on teleosts, molluscs and polychaetes. This species has a high trophic position within its food web and feeds mainly on crabs (mainly Liocarcinus depurator and Goneplax rhomboides), independent of their sex, maturity-stage or season. The great importance of crabs in the diet of starry ray may be due to the fact that crabs are the dominant crustaceans in terms of biomass and abundance in the area where starry rays were collected, thus allowing them to exploit the most abundant food resource. Since the starry ray has shown a progressive decline on the catch, further research is needed to analyse the main drivers of starry ray dynamics in the Western Mediterranean Sea. Our results present important new data that will allow us to further explore the population dynamics of starry rays and the role of crustacean availability and fishing activity.

Dominant intertidal crustacean and gastropod species in Qeshm Island, Iran, northern Persian Gulf

Qeshm Island is the largest island of the Persian Gulf. It is located in the north-eastern part, near the Strait of Hormuz, which connects the Persian Gulf with the Gulf of Oman. Between 2007 and 2010 by support of the Persian Gulf Biotechnology Research Center a collection of the two most dominant macrobenthic fauna groups (Gastropoda and Crustacea) was gathered around the island. A total of 28 intertidal stations were investigated, including four basic habitat types (rocky, sandy, mud flats and mangrove forests), which resulted in a large diversity of species encountered. The present report provides a summary of the collected taxa. A total of 123 taxa belonging to Crustacea and Gastropoda are recorded in the present study. Identification of the species up to the lowest possible level was attempted; about 88% were identified up to species level. In total, 109 species have been identified. Rocky sites were the most diverse intertidal habitats in the island.

Harmful algae are not harmful to everyone

Seagrasses reduce sediment erosion, filter land-derived pollutants, and provide living space for numerous invertebrates, but seagrasses are increasingly threatened by bloom-forming macroalgae. We tested for density-dependent effects of the macroalga Gracilaria comosa on the seagrass Halophila ovalis and its associated invertebrates in a subtidal field experiment, in the Swan River estuary (in Perth, Western Australia). G. comosa had significant negative effects on H. ovalis, reducing leaf densities by 20 and 40% when exposed to 0.7 and 1.4kgalgalwetweightm−2, respectively. By contrast, seagrass-associated invertebrates were positively affected by Gracilaria; taxonomic richness and densities of dominant crustacean and mollusc species increased with algal addition. More specifically, densities of surface dwelling gastropods, that utilize a 2-dimensional habitat, were saturated at 0.7kgalgalwetweightm−2, whereas densities of interstitial isopods and amphipods, that utilize a 3-dimensional habitat, had highest densities at 1.4kgalgalwetweightm−2. A non-native ecosystem engineer, the bioturbating gastropod Batillaria australis, dominated the surface dwelling mollusc community, and this invader was strongly facilitated by algal additions, being 5 times more abundant under algal mats compared to control plots. If the Swan River becomes more nutrient polluted and subsequently more algal dominated, then this ubiquitous invader may proliferate further, with difficult-to-predict system-wide ecological and biogeochemical consequences. We conclude that, in our experiment, ‘harmful algae’ inhibited the seagrass itself but facilitated most seagrass-associated invertebrates.

The complete mitochondrial genome sequence of Euphausia pacifica (Malacostraca: Euphausiacea) reveals a novel gene order and unusual tandem repeats

Euphausiid krill are dominant organisms in the zooplankton population and play a central role in marine ecosystems. Euphausia pacifica (Malacostraca: Euphausiacea) is one of the most important and dominant crustaceans in the North Pacific Ocean. In this paper, we described the gene content, organization, and codon usage of the E. pacifica mitochondrial genome. The mitochondrial genome of E. pacifica is 16 898 bp in length and contains a standard set of 13 protein-coding genes, 2 ribosomal RNA genes, and 22 transfer RNA genes. Translocation of three transfer RNAs (trnL(1), trnL(2), and trnW) was found in the E. pacifica mitochondrial genome when comparing with the pancrustacean ground pattern. The rate of K(a)/K(s) in 13 protein-coding genes among three krill is much less than 1, which indicates a strong purifying selection within this group. The largest noncoding region in the E. pacifica mitochondrial genome contains one section with tandem repeats (4.7 x 154 bp), which are the largest tandem repeats found in malacostracan mitochondrial genomes so far. All analyses based on nucleotide and amino acid data strongly support the monophyly of Stomatopoda, Penaeidae, Caridea, Brachyura, and Euphausiacea. The Bayesian analysis of nucleotide and amino acid datasets strongly supports the close relationship between Euphausiacea and Decapoda, which confirms traditional findings. The maximum likelihood analysis based on amino acid data strongly supports the close relationship between Euphausiacea and Penaeidae, which destroys the monophyly of Decapoda.

Prevalence of Colacium vesiculosum (Colaciales: Euglenophyceae) on planktonic crustaceans in a subtropical shallow lake of Argentina

Colacium vesiculosum (Euglenophyceae) is an epibiont common on planktonic microcrustaceans of continental waters. The interaction between epibionts and substrate organisms is not very well known, particularly in subtropical environments of South America. In the present work, we analyzed the prevalence, density, biomass and attachment sites of C. vesiculosum on planktonic microcrustaceans from Paiva Lake, a subtropical lake of Argentina. With the aim to evaluate whether epibionts affect the filtering rates of Notodiaptomus spiniger, the dominant planktonic crustacean, we carried out bioassays using phytoplankton < 53 microm. Crustaceans were sampled using a PVC tube (1.2m long and 10cm in diameter), filtering 50L of water through a 53 microm-mesh. Microcrustaceans were counted in Bogorov chambers under a stereoscopic microscope. The infested organisms were separated and observed with a photonic microscope to determine density and biovolume of epibionts, by analyzing their distribution on the exoskeleton. The prevalence of C. vesiculosum was higher in adult crustaceans than in their larvae and juveniles. The most infested group was that of calanoid copepods, related to their high density. The attachment sites on the exoskeleton were found to be the portions of the body which have a higher probability of encounter with epibionts during locomotion and feeding, i.e., antennae and thoracic legs in copepods, and thoracic legs and postabdomen in cladocerans. The similar values found in the filtering rate of infested and uninfested individuals of N. spiniger and the constant prevalence (< 40%) of epibiont algae, suggest that C. vesiculosum does not condition the life of planktonic crustaceans of Paiva Lake.

Macrofauna bentónica asociada a bancos ostrícolas en las lagunas costeras Carmen, Machona y Mecoacán, Tabasco, México

Oyster beds have an important impact on coastal ecosystems. In this work, samplings were done during the dry, the rainy and the ?North wind? seasons, in eight oyster reefs at the Lagoons of Mecoacán, Carmen and Machona, in Tabasco, Mexico. The a diversity was calculated with the Shannon-Wiener, Simpson and Margalef indexes. An Analysis of Variance was done to evaluate if there was a difference in the average of the indexes at each reef in every season, verifying the assumptions of normality and variance homogeneity. In the case of mollusk richness, we found 13 families, 13 genera and 15 species of gastropods, as well as 8 families, 10 genera and 11 species of bivalves. Seven families, 11 genera and 12 species of crustaceans were recorded. In the case of mollusks, the highest average value of species richness was recorded during the dry season, in Puente de Ostión reef (DMg= 13.6), whereas in the case of species diversity, the highest average value was recorded during the ?North wind? season, at Largo (H? = 0.77). The dominant mollusks during the three seasons were Ischadium recurvum, Isognomon alatus and Crepidula plana. In the case of crustaceans, the highest average value, both in species richness and diversity, was recorded during the rainy season (DMg= 15.50, H? = 1.15) at Pinzón reef. The dominant crustaceans were Balanus eburneus, Balanus improvisus, Eurypanopeus depressus and Petrolishtes armatus.

Biological identifications through DNA barcodes: the case of the Crustacea

The ability of a 650 base pair section of the mitochondrial cytochrome c oxidase I (COI) gene to provide species-level identifications has been demonstrated for large taxonomic assemblages of animals such as insects, birds, and fishes, but not for the subphylum Crustacea, one of the most diverse groups of arthropods. In this study, we test the ability of COI to provide identifications in this group, examining two disparate levels in the taxonomic hierarchy — orders and species. The first phase of our study involved the development of a sequence profile for 23 dominant crustacean orders, based upon the analysis of 150 species, each belonging to a different family. The COI amino acid data placed these taxa into cohesive assemblages whose membership coincided with currently accepted boundaries at the order, superorder, and subclass levels. Species-level resolution was subsequently examined in an assemblage of Decapoda and in representatives of the genera Daphnia (Cladocera) and Gammarus (Amphipoda). These studies revealed that levels of nucleotide sequence divergence were from 19 to 48 times greater between congeneric species than between individuals of a species. We conclude that sequence variation in the COI barcode region will be very effective for discriminating species of Crustacea.

Spatio-temporal variations in the diversity and abundance of commercially important Decapoda and Stomatopoda in subtropical Hong Kong waters

In subtropical Hong Kong, western waters (WW) are strongly influenced by the freshwater input from the Pearl River estuary, especially during summer monsoon, whereas eastern waters (EW) are predominantly influenced by oceanic currents throughout the year. Such hydrographical differences may lead to spatio-temporal differences in biodiversity of benthic communities. This study investigated the diversity and abundance of commercially important decapods and stomatopods in EW (i.e. Tolo Harbour and Channel) and WW (i.e. Tuen Mun and Lantau Island) of Hong Kong using monthly trawl surveys (August 2003–May 2005). In total, 22 decapod and nine stomatopod species were recorded. The penaeid Metapenaeopsis sp. and stomatopod Oratosquillina interrupta were the most abundant and dominant crustaceans in EW and WW, respectively. Both univariate and multivariate analyses showed that WW supported significantly higher abundance, biomass and diversity of crustaceans than EW, although there were significant between-site and within-site variations in community structure. Higher abundance and biomass of crustaceans were recorded in summer than winter. Such spatio-temporal variations could be explained by differences in the hydrography, environmental conditions and anthropogenic impacts between the two areas. Temporal patterns in the abundance–biomass comparison curves and negative W-statistics suggest that the communities have been highly disturbed in both areas, probably due to anthropogenic activities such as bottom trawling and marine pollution.

Ontogenetic changes in the diet of the sandbar shark, Carcharhinus plumbeus, in lower Chesapeake Bay and Virginia (USA) coastal waters

This study describes the diet of the sandbar shark, Carcharhinus plumbeus, highlighting differences in diet within various regions of the Virginia (USA) nursery area, as well as ontogenetic changes in diet. Stomach samples were obtained in 2001 and 2002 from 232 sharks caught by gillnets or longlines. Historical data from the Virginia Institute of Marine Science (VIMS) Shark Ecology Program were also analyzed. Ontogenetic changes in diet were evident, with crustacean prey decreasing in frequency with increasing shark size, and elasmobranch prey importance increasing with increasing shark size. Whereas previous research in Chincoteague Bay, VA showed the blue crab, Callinectes sapidus, was the dominant crustacean in sandbar shark diet, the mantis shrimp, Squilla empusa, dominated the crustacean portion of the diet in this study. Differences in diet of sharks were observed among locations within the study area. Small juveniles (≤80 cm precaudal length) in the lower Chesapeake Bay ate more fishes, whereas Eastern Shore juveniles ate more crustaceans. Crustacean prey items varied among locations along the Eastern Shore, with more portunid crabs consumed in waters near Wachapreague and more mantis shrimp consumed near Sand Shoal Inlet. Our study showed that Carcharhinus plumbeus is a generalist predator and is thus unlikely to strongly impact the population of any particular prey species, and in turn is not likely to be strongly affected by fluctuations in abundance of a single prey species.

Eel parasite diversity and intermediate host abundance in the River Rhine, Germany.

European eels (Anguilla anguilla) from 2 sampling sites on the Rhine river (near Karlsruhe and near Worms) were investigated with respect to their parasite communities. Nine different metazoan species were found to live in and on the eels. The highest number of species was recorded from the intestine, which contained up to 6 different helminths. Among these, acanthocephalans were the most prevalent worms with the eel-specific parasite Paratenuisentis ambiguus as the dominant species of the intestinal component communities at both sites. Comparing the intestinal parasites from eels caught near Karlsruhe with those from Worms, the acanthocephalans showed a significantly lower abundance at Worms. A significantly lower mean number of intestinal helminth species as well as a significantly lower Brillouin's Index was found at Worms compared with Karlsruhe. This difference could be related to the abundance of the respective intermediate crustacean hosts. At the sampling site Worms the amphipod Corophium curvispinum was the dominant crustacean. Additionally, only the isopod Jaera istri and the amphipod Dikerogammarus villosus were found. All these crustacean species have only recently colonized the Rhine river system via the Main-Danube canal, built in the early 1990s. They are not known to act as intermediate hosts for any of the acanthocephalans found in the eels. The site near Karlsruhe exhibited a higher crustacean diversity, including Asellus aquaticus and different species of the genus Gammarus, which are all known intermediate hosts for the acanthocephalans found. Therefore, changes of eel parasite diversity can be correlated with the appearance of invading crustacean species (neozoans).

Experimental and Field Studies of Mesocyclops notius (Copepoda: Cyclopoida) from a Subtropical Chinese Lake, Lake Donghu

This paper reports experimental and field studies on the cyclopoid Mesocyclops notius from subtropical Lake Donghu close to the Yangtze river. Mesocyclops notius, a dominant crustacean Zooplankter throughout tropical Australia, was previously considered to be endemic to Australia, but recently, Mesocyclops leuckarti in Lake Donghu was re-identified as M. notius. Laboratory culture experiments were conducted to reveal the effect of temperature (15, 20, 25 and 30 degreesC) on the development, growth and reproduction of M. notius. Temperature was inversely related to development times of eggs, nauplii and copepodites, body length and physiological longevity of adults, and brood size. Body length and physiological longevity of females were greater than those of males at the same temperature. No reproduction took place at 15 degreesC. Production and seasonal cycles of M. notius during 1980-1982 were studied at two sampling stations of Lake Donghu. At the mid-lake station, the annual production and production/biomass (P/B) ratio of M. notius varied between 6.0 and 18.0 g dry wt m(-2) year(-1) and 74.6 and 95.5, respectively. Mesocyclops notius reached their highest density peaks in the warm months (July-October), with a maximum density of 1256 individuals l(-1) at a littoral site. No reproduction and recruitment by AL notius took place during the cold months (December March) when the temperature of the lake water was < 15 degreesC. Mesocyclops notius were more abundant at a littoral station than at a pelagic station, possibly due to different food availability. The higher male:female sex ratio of M. notius at the littoral station was most likely caused by size-selective fish predation on larger females.

Long-term changes in crustacean zooplankton and water quality in a shallow, eutrophic Chinese lake densely stocked with fish

From surveys made in 1962–1963, 1973–1974, 1979–1996 at two Stations in Lake Donghu, a shallow eutrophic water body near Wuhan, P. R. China, the authors, derive long-term changes in species composition, standing crop and body-size of planktonic crustaceans. The species number decreased from the 1960s to the 1990s. The cladocerans dropped from 46 (1960s) to 26 (1980s) to 13 (1990s); the copepods decreased from 14 (1960s) to 10 (1980s) to 7 (1990s). From the mid-1980s on, the dominant crustaceans also changed: Daphnia hyalina and D. carinata ssp. were replaced by Moina micrura and Diaphanosoma brachyurum at Stations 1 and 2, respectively; Cyclops vicinus replaced Mesocyclops leuckarti.

The Feeding Ecology of the Cyclopoid Copepod Diacy clops thomasi in Lake Ontario

Diacyclops thomasi is the dominant crustacean zooplanhton in Lake Ontario, making up much of the mesozooplankton biomass. However, the role of Diacyclops in the food-web dynamics of Lake Ontario is relatively unexplored. The feeding ecology of Diacyclops in Lake Ontario was examined by predator manipulation experiments, performed monthly from April 1991 until September 1991. Diacyclops consumed a variety of food items including: a mixotrophic dinoflagellate ( Gymnodinium helveticum); ciliates (choreotrichines); and other protozoans (heliozoans). Prey items were generally microplankton-sized (15–100 μm), motile, and without any hard external covering. Diacyclops had no effect on non-motile algae, small flagellates (<15 μm), or on organisms with tests or loricas. Keratella cochlearis, a loricate rotifer, was the most abundant rotifer through most of the stratification period but was not consumed by Diacyclops. However, we present evidence that Diacyclops preys on the eggs of this species without consuming the females to which the eggs are attached. Our results indicate that adult Diacyclops are selective omnivores in the pelagic food chain of Lake Ontario.

The zooplankton story of humic Lake Skjervatjern during whole catchment acidification

Major trends in macrozooplankton development were monitored in humic lake Skjervatjern from 1988 to 1994. No changes were detected following division into an acidified basin (A) and reference basin (B) in 1989. Acidification was initiated in autumn 1990. During the summer of 1991, there was a normal development of zooplankton in the B-basin, while an initial increase and subsequent collapse of the dominant crustacean Holopedium occurred in the A-basin. Here, total zooplankton biomass dropped from a July maximum of 72 μg C L −1 to a September minimum of less than 4 μg C L −1. Holopedium remained dominant in the B-basin, while it was absent from the A-basin during the following years. The zooplankton perturbations occurred in spite of marginal changes in pH and Al-concentrations. Survival tests did not reveal any acute toxicity of the acidified water, nor did climatic variables offer any explanation for the zooplankton changes. There were pronounced oscillations in phytoplankton biomass and species composition. Measured grazing rates indicated that these oscillations were not caused by macrozooplankton grazing, while disappearance of key phytoplankton species, notably Oocystis, apparently contributed to the zooplankton decline.

Thermal effects

Thermal effects