Population dynamics of Pomphorhynchus bulbocolli in Gammarus pseudolimnaeus

The population dynamics of larval Pomphorhynchus bulbocolli were studied in the amphipod intermediate host, Gammarus pseudolimnaeus. Amphipods were collected monthly from April 1982 to March 1983 from a study site at the West Fork of Drake's Creek, Simpson Co., Kentucky. The number of infected amphipods per m2 was lowest (0.6) in May and highest (27.3) in November. A total of 2,502 amphipods was examined; 1,575 (62.9%) were infected with P. bulbocolli. Infection intensity ranged from 1 to 12 with a mean of 1.83 +/- 0.03. Single and multiple worm infections were found in 800 (50.8%) and 775 (49.2%) amphipods, respectively. Female amphipods had higher prevalence and intensity of infections than males but differences were not significant. Prevalence in the monthly samples was lowest in May (5.1%) and highest in October (88.1%). The monthly mean intensity of infection was lowest in July (1.10 +/- 0.04) and highest in November (2.02 +/- 0.08). Amphipods in length classes 3 through 15 were infected with P. bulbocolli. In late summer and fall, amphipods in all length classes were infected, while in late winter and spring only large amphipods were infected. Recruitment of P. bulbocolli into amphipods was seasonal and the total infrapopulation within an amphipod was usually acquired at one time. There was little correlation between size and number of larvae present.     

Seasonal changes of macrozooplankton and Benthic Boundary Layer macrofauna from the Bay of Saint-Brieuc (western English Channel)

The macrozooplankton and Benthic Boundary Layer (BBL) macrofauna over a coarse sand and pebble community in the Bay of Saint-Brieuc (western English Channel) were sampled with a WP2 zooplankton net and with a modified MACER-GIROQ suprabenthic sledge, respectively, from February 1994 to November 1995. One hundred and sixty-four species were collected in 44 suprabenthic sledge hauls and 19 taxa in 30 zooplankton net hauls. In the water column, appendicularians and cnidarians dominated, while, in the BBL, holoplanktonic amphipods, chaetognaths, amphipods and mysids dominated the fauna; among them Apherusa spp., Sagitta setosa Muller, Anchialina agilis (Sars), Sirella clausii Sars and Eusirus longipes Boeck were the dominant species. The density and biomass of the BBL macrozooplankton were lower than those of the macrozooplankton in the water column. The density and biomass of suprabenthos remained a low throughout the year. In the water column, density and biomass of macrozooplankton showed a maximum in spring and remained low from autumn to winter; conversely, in the BBL, the density and biomass of both macrozooplankton and suprabenthos were higher from summer to autumn. The change in abundance of both BBL and pelagic taxa was seasonal. Some species were primarily sampled in the water column (appendicularians, cladocerans and cnidarians), while others were preferentially found at the BBL (suprabenthic species, holoplanktonic amphipods and cephalopods). A third group was collected throughout the water column (chaetognaths and fish larvae).      

Patterns of macroinvertebrate abundance in inland saline wetlands: a trophic analysis

We used stable isotopes and gut-content analysis to compare trophic relations of macroinvertebrates between two types of saline wetlands in the Laramie Basin, Wyoming, USA. Amphipods (Hyallela azteca), chironomid larvae, and predatory insects (mainly Zygopteran larvae) occurred in both wetland types. However, in oligosaline wetlands (0.5–5‰ total dissolved solids) amphipods were dominant, whereas in mesosaline wetlands (5–18‰) amphipods were scarce and chironomid larvae and predatory insects were much more abundant. Salinity alone seemed inadequate to explain these differences, so we examined trophic interactions to address three main questions: (1) why are predatory insects more abundant in mesosaline wetlands, (2) why are chironomid larvae less abundant in oligosaline wetlands, and (3) why are amphipods uncommon in mesosaline wetlands? Zygopteran larvae ate mainly chironomid larvae and zooplankton, and did not eat amphipods; chironomid larvae were an average 93 dry mass of zygopteran intake. Guts of amphipods contained no animal parts and little vascular plant tissue, but rather mainly amorphous detritus. Chironomid larvae ate amorphous detritus as well as diatoms. There is potential for competition between amphipods and chironomids, but the nature of amorphous detritus in these wetlands needs further study. Because amphipods appear unavailable as prey for predatory insects, top-down impacts on chironomid larvae may be greater in oligosaline than in mesosaline wetlands. Our results suggest that (1) predatory zygopteran larvae and hemipterans are more abundant in mesosaline wetlands due to more abundant chironomid prey, (2) chironomids are less common in oligosaline wetlands because of both competition with amphipods and greater per capita consumption by predatory insects, and (3) amphipods are scarce in mesosaline wetlands because, lacking a resting stage and mode of direct dispersal, they do not cope well with extremes created by hydrologic instability in mesosaline wetlands. These mechanisms may apply to wetlands in other regions where similar patterns of invertebrate community structure have been reported.     

Virulence of Corynosoma constrictum (Acanthocephala: Polymorphidae) in Hyalella azteca (Amphipoda) throughout parasite ontogeny

Development and growth of parasites depend on resources provided by the host and the parasite's ability to use them. Identifying specific costs incurred by the host provides insight for assessment of parasite energy budgets, which differ among taxa and ontogenetic stages. Data from this study were analyzed using an accelerated failure-time model with intensity as a covariate. Results indicated significantly reduced survival of amphipods, Hyalella azteca, infected with the acanthocephalan Corynosoma constrictum compared with uninfected controls. Male and female amphipod survivorship and infection intensity did not differ; however, amphipods with high-intensity infections (> 16 larvae) died earlier compared with amphipods with low-intensity infections (< 3 larvae). The majority of infected amphipods died between 12 and 24 days postexposure, a period of rapid larval development. It is hypothesized that host death may be due either to an increase in overall larval nutritional demands or to parasite-mediated depletion of a specific host substance. Results from this study suggest that developing C. constrictum satisfies energy requirements by depriving amphipod hosts of resources normally used for somatic growth and maintenance.     

Distribution of pelagic larvae of benthic marine invertebrates in the Bellingshausen Sea

During November and December 1992, plankton samples were collected using a ring net of mesh size 200 m vertically hauled through a 600 m water column, at five stations along a transect running north from the Allison Peninsula in the Bellingshausen Sea. Three stations were located over the continental shelf; two of these were ice bound, whilst the third was at the ice edge. Two other stations were in deeper, ice-free water. Sixteen different larval and juvenile types were found representing seven phyla: Echinodermata, Nemertea, Coelenterata, Mollusca, Annelida, Arthropoda and Bryozoa, of which the first two were the most abundant. Larval numbers and types decreased with distance offshore and away from permanent sea ice. The presence of many stages of nemertean larval development within a short time scale, in an area where developmental tends to be slow, suggests that reproduction occurs over an extended period and that the larvae have a long planktonic phase. The increased size of later developmental stages of the nemertean larvae indicates they obtain nutrition within the water column during winter, when little particulate food is present.     

Seasonal changes in feeding and relative condition factors of Arctic grayling (<Emphasis Type="Italic">Thymallus arcticus</Emphasis>) in a stretch of the middle reaches of the Yenisei River

The seasonal dynamics of feeding spectra and diet of Arctic graying in a stretch of the middle reaches of the Yenisei River (from the dam of the Krasnoyarsk HPP to the mouth of the Kan River) was studied in 2009–2013. Its connection with the food-supply state and fish growth has been traced. It has been shown that the intensity of fish feeding is relatively stable throughout the year, despite significant fluctuations in zoobenthos biomass. The contribution of groups dominating in diet (amphipods and larvae of caddisflies) changes depending on the month. Amphipods prevail in the diet of fish during the period from June to October and caddisflies prevail in the winter and spring months. Among caddisflies, selective feeding on a small species, Apatania crymophila, has been revealed. The change of the primary diet component during the summer period corresponds to a sharp increase in the coefficients of relative condition factors with a peak in August–September. It has been assumed that changes in the ratio of weight and linear sizes of fish are associated not only with an increase in the water temperature, but also with the grayling switching to the consumption of amphipods with a higher nutrition value.     

Observations on the incidence and seasonal fluctuations of certain crustacean larvae in the plankton of the South-West Coast of India

The seasonal fluctuations in the incidence of planktonic organisms and the larval forms of certain crustaceans such as crabs, barnacles and post larvae of prawns in the plankton of the south-west coast of India have been followed for a period of three years from 1963. South-west monsoon period is the least productive period for zooplankton in this area. Brachyuran zoeae, post larvae of prawns and barnacle nauplii occur in the plankton throughout the year with distinct peaks for different groups. The zoeae ofUca annulipes occur in the plankton from September to May with a peak during November–December. The zoeae ofPortunus pelagicus are present in the plankton from September to June and their abundance is in February–March. The post larvae ofMetapenaeus affinis are found in the inshore plankton from November to June with the peak in March. The nauplii ofBalanus amphitrite communis occur in the plankton in all the months of the year, the peak incidence has been during November January. The zoeae ofU. annulipes are found to tolerate better the medium saline conditions. Of the ecological factors, salinity of the ambient water and the availability of planktonic food for the larvae seem to influence the seasonal fluctuations of these crustacean larvae in this locality.     

Occurrence and body size changes of drifting land-locked Ryukyu-ayu Plecoglossus altivelis ryukyuensis larvae in the San-numata River, Okinawa-jima Island, Japan

The occurrence and body size of drifting land-locked Ryukyu-ayu, Plecoglossus altivelis ryukyuensis, larvae were investigated in the San-numata River, Okinawa-jima Island from November 2000 to March 2001. The water temperature in the river fluctuated from 13.8 to 17.9°C during the sampling period. The drifting larvae occurred from mid-December to mid-March with an estimated spawning peak during late November and early December. The notochord length of the drifting larvae ranged from 4.9 to 6.7 mm (5.7 ± 0.3 mm, mean ± SD), and became longer as the spawning months progressed. These results imply that the land-locked population possesses the same maturation attributes as the original amphidromous population.     

GRAY WHALE (ESCHRICHTIUS ROBUSTUS) HABITAT UTILIZATION AND PREY SPECIES OFF VANCOUVER ISLAND, B. C.

Habitat utilization and prey species of Vancouver Island gray whales were investigated by (1) summarizing 26 yr of distribution and feeding data and (2) conducting intensive observations in Clayoquot Sound, Vancouver Island, from 1989 to 1996. Whale distribution and movements were monitored from March to November through systematic boat surveys and whale-watch sighting programs. Prey species were collected by suction hose and plankton net or determined through analysis of fecal samples. Gray whales utilized virtually all of the southern west coast of Vancouver Island over the 26-yr observation period. Distribution, prey species, and feeding behavior showed marked variability during any one season and between years. Some feeding areas were used on an annual basis, others with >10-yr intervals between use. Feeding occurred in shallow sand or mud bays, eel grass beds, kelp beds, in the open water column, and at the surface. Young whales appeared to utilize habitat and prey species differently than adults. Main prey species included herring eggs/larvae ( Clupea harengus pallasi ), crab larvae ( Cancer magister megalops, Pachycbeles spp. zoea), mysids ( Holmesimysis sculpta, Neomysis rayii, Acanthomysis spp.), amphipods ( Ampelisca spp., Atylus borealis ), and ghost shrimp ( Callianassa californiensis ). The definition and relative importance of specific feeding grounds and the study of human impacts on this population are complicated by its broad and variable use of habitat and prey species.     

The effect of early and late hatching on the escape response of walleye pollock (Theragra chalcogramma) larvae

Hatching of fish eggs fertilized at the same time occurs overa period of several days. Differences in the escape responseof fish larvae during the hatching period have not hithertobeen studied. In this study, the escape response of walleyepollock (Theragra chalcogramma) larvae over the hatching periodwas examined. Escape speed, response to multiple touches witha fine probe, response to water currents generated by a predatorand predation by euphausiids (Thysanoessa inermis) and amphipods(Pleusirus secorrus) were measured in the laboratory. Otolithmeasurements of field-collected larvae support a broad hatchingperiod for walleye pollock eggs in the sea similar to that observedin the laboratory. The escape response of walleye pollock larvaewas affected by rank in the order of hatching, thus with respectto predation, hatching order may affect the survival of larvaein the sea. Early hatching larvae were smaller, less sensitiveto tactile stimulation, had a slower, weaker escape responseand higher laboratory rates of predation mortality than thosethat hatched later.     

Effects of Acid Mine Drainage on the Estuarine Food Web, Britannia Beach, Howe Sound, British Columbia, Canada

We investigated the effects of acid mine drainage (AMD) from Britannia Creek, BC, Canada, a stream contaminated by an abandoned copper mine, on the estuarine food web. Near the mouth of Britannia Creek, sediments and the water contained high concentrations of dissolved copper and the waters were highly acidic. Relative to a reference location, rockweed (Fucus gardneriSilva) cover was reduced, phytoplankton biomass was lower, chironomid larvae were less abundant, and fewer gammarid amphipods colonized basket traps. Laboratory toxicity tests confirmed that sediments and water from the lower reaches of Britannia Creek and its estuary were highly toxic to midge larvae (Chironomus tentansFabricius), the marine amphipod (Eohaustorius washingtonianusThorsteinson) and also impaired fertilization of sand dollars (Dendraster excentricusEschscholtz). Analyses of stomach contents of chum salmon fry (Oncorhynchus ketaWalbaum) indicated that they preferred to feed on chironomid larvae and gammarid amphipods at Britannia Creek estuary but these two taxa were less abundant at Britannia Creek estuary relative to the reference location. AMD from Britannia Mine disrupted the structure and function of the intertidal ecosystem resulting in loss of food production for fish including chum salmon fry and other species.     

Size matters: predation of fish eggs and larvae by native and invasive amphipods

Invasive predators can have dramatic impacts on invaded communities. Extreme declines in macroinvertebrate populations often follow killer shrimp (Dikerogammarus villosus) invasions. There are concerns over similar impacts on fish through predation of eggs and larvae, but these remain poorly quantified. We compare the predatory impact of invasive and native amphipods (D. villosus and Gammarus pulex) on fish eggs and larvae (ghost carp Cyprinus carpio and brown trout Salmo trutta) in the laboratory. We use size-matched amphipods, as well as larger D. villosus reflecting natural sizes. We quantify functional responses, and electivity amongst eggs or larvae and alternative food items (invertebrate, plant and decaying leaf). D. villosus, especially large individuals, were more likely than G. pulex to kill trout larvae. However, the magnitude of predation was low (seldom more than one larva killed over 48 h). Trout eggs were very rarely killed. In contrast, carp eggs and larvae were readily killed and consumed by all amphipod groups. Large D. villosus had maximum feeding rates 1.6–2.0 times higher than the smaller amphipods, whose functional responses did not differ. In electivity experiments with carp eggs, large D. villosus consumed the most eggs and the most food in total. However, in experiments with larvae, consumption did not differ between amphipod groups. Overall, our data suggest D. villosus will have a greater predatory impact on fish populations than G. pulex, primarily due to its larger size. Higher invader abundance could amplify this difference. The additional predatory pressure could reduce recruitment into fish populations.     

Studies on the biology of Chaoborus flavicans (Meigen) (Diptera: Chaoboridae) in a fish-free eutrophic pond,Japan

Population dynamics of Chaoborus flavicans larvae of various instars was studied from November 1986 to December 1987 in a eutrophic, fish-free pond, Japan. First and 2nd instar larvae were observed from late April to late October, indicating a reproductive period of about half a year. C. flavicans overwintered in the 4th instar larvae. In water column samples, total density of all instars was 680–23680 m^-2, and pupal density 0–2600 m^-2; larvae of the 1st, 2nd, and 3rd instars showed 5–6 density peaks in 1987, suggesting that 5–6 generations occur during a year (peaks of the 4th instar larvae were not clear, probably due to their longer development than those of younger instars). In sediment samples, no 1st and 2nd instar larvae were found, 3rd instar larvae were found occasionally but density of the 4th instar larvae was 280–18600 m^-2, and pupal density varied between 0–502 m^-2. Fouth instar larvae accumulated in sediment in the cold season and in the water column in the warm season; high temperature and low oxygen concentration were the most important factors limiting the distribution of larvae in the sediment in summer in the NIES pond. The dry weight of total C. flavicans larvae was 0.08–4.2 g m^-2 in sediment samples and 24–599 μg l^-1 (0.10–2.40 g m^-2) in water column samples. Comparisons of maximum densities in the NIES pond in different years and in waters of different trophic status show that density is generally higher in eutrophic than in oligotrophic habitats. This revised version was published online in July 2006 with corrections to the Cover Date.     

Non-selective predator – the versatile diet of Amur sleeper (Perccottus glenii Dybowski, 1877) in the Vistula River (Poland), a newly invaded ecosystem

The Amur sleeper diet spectrum was investigated in addition to its spatial, seasonal and size-related changes, in order to predict which groups of native prey would be most affected by this exotic predator that has rapidly invaded many Eastern and Central European inland waters in recent decades. In total, 527 Perccottus glenii individuals were collected in four sites in the Włocławski Reservoir (the Vistula River, Baltic basin, Poland). Altogether 50 food categories were identified, including crustaceans, insects, molluscs, annelids, araneids, fishes and amphibians. Most of them were associated with aquatic vegetation, indicating that the Amur sleeper collects its prey from the submerged plants rather than directly from the bottom sediments. Amphipods and chironomid larvae, supplemented by zygopteran larvae and molluscs, composed the main forage base in all studied sites, although their importance was varied. The diet composition differed among P. glenii size-groups. Significant variation was found in numeric abundance of amphipods, chironomid larvae, fish and zygopteran larvae (Kruskal–Wallis P < 0.01). Seasonal changes in the diet were also observed whereby in spring and summer, dipteran larvae and amphipods were prevalent food items; the importance of molluscs and zygopteran larvae increased considerably in September; and fish showed the highest occurrence in June, July and August. The broad diet spectrum of the Amur sleeper indicates that it is a non-selective, opportunistic predator and that several taxonomic groups of native hydrofauna as well as macroinvetebrates and fish may be affected by its presence. The highly flexible feeding strategy undoubtedly favours Amur sleeper expansion in invaded watersheds.     

Population dynamics and parasitation of planktonic and epibenthic crustaceans in the Baltic Schlei fjord

The planktonic and epibenthic crustacean fauna from two sites of the brackish Schlei fjord, Northern Germany, was investigated over a six-month period. Calanoid and cyclopoid copepods were more abundant in lower salinities, whereas, benthic decapods, isopods and amphipods prevailed in the site of higher salinity. Cestodan larvae were found only in spring which may be due to the timing of the respective life-cycles. Parasites of benthic crustaceans, mostly digenean metacercariae but also cestodans, acanthocephalans and nematodes, appeared from spring to late summer. Decreasing salinities caused lower intensities of the most abundant parasite,Maritrema subdolum; only the true brackish-water species among the hosts were more heavily infested than those found in higher salinities. The correlation of parasite size and host size at infestation became apparent. Therefore,Crangon crangon is an optimal host for the largePodocotyle atomon metacercariae. Coevolutive trends between some hosts and parasites are made evident.     

Zooplankton inputs and outputs in the saltmarsh at Towra Point, Australia

The contribution made by saltmarsh to the production of estuarine zooplankton was examined through a comparison of inputs and outputs of tidal water at a site on Towra Point, NSW, Australia. Saltmarsh proved to be a net exporter of crab and gastropod larvae, although it functioned as a sink for copepods and amphipods. Further, the highest density of zooplankton in estuarine nearshore habitats (saltmarsh, mangrove, seagrass, and open water) during a high tide event was found in the saltmarsh. The presence of high concentrations of zooplankton, predominantly crab and gastropod larvae, in the saltmarsh and lesser extent in the mangrove represents a source of food for estuarine fish.     

Effect of Acanthocephala infection on the reproductive potential of crustacean intermediate hosts

The effect of a naturally acquired infection by three acanthocephalan parasites Dentitruncus truttae, Echinorhynchus truttae, and Polymorphus minutus on the reproductive potential of their intermediate host, Echinogammarus tibaldii (Amphipoda) from Lake Piediluco (Centre of Italy) was assessed. During May 2007, 1135 amphipods were collected from two different samplings and examined for larval helminths. Forty-five amphipods were infected and of those, 16 were infected with D. truttae (intensity = 1-3 larvae), 15 with E. truttae (intensity = 1-2 larvae), and 14 with P. minutus (intensity = 1 larva). The sex ratio was nearly 1:1 in all examined amphipods. One female infected with D. truttae contained six eggs in the brood pouch and another female infected with E. truttae contained five eggs. However, none of the eight female amphipods harbouring P. minutus larva contained eggs in their brood pouch. Uninfected females of the same size and body length as that of the infected females contained between 20 and 32 eggs. No acanthocephalan species were found to co-occur.     

Comparison of sampling methods for semipelagic animals in two deep basins of Lake Saimaa

The efficiency of different methods for sampling semipelagic animals was compared in the deep basins of Lake Paasivesi and Lake Puruvesi of the complex Lake Saimaa, Finland, during 1990–92. Certain semipelagic animals, such as Mysis relicta, amphipods and larvae of Chaoborus fiavicans, are important bioindicators of water and benthic quality. However, owing to their high mobility and vertical migrations they are difficult to sample quantitatively with traditional benthic methods. The equipment used for sampling was comprised of:

1. Vertical nets (0.56 and 0.13 m²) placed on the bottom for 5 minutes or 12 hours and hauled up vertically.
2. Plexiglass traps placed on the bottom for 12–14 hours.
3. Mysis-trawl hauled horizontally c. 250–300 metres on the bottom.
4. Ekman-grab.

In 1992, parallel samples were taken with vertically hauled nets (12 h and plexiglass traps baited with fish or liver or provided with a chemical light. Large vertically hauled nets were the most efficient equipment for catching Gammaracanthus lacustris, M. relicta and larvae of Ch. flavicans whilst baited or lighted nets were less effective. Lighted plexiglass traps were most effective in catching Pallasea quadrispinosa and water mites, but baited and control traps sampled inefficiently. The trawl sampled M. relicta and P. quadrispinosa relatively well, but was less efficient in sampling other groups. The Ekman-grab was effective only for sampling Monoporeia affinis. The semipelagic community differed between the studied basins. The dominant semipelagic animals in the humic, deep L. Paasivesi were M. relicta, amphipods and larvae of Ch. flavicans whilst the number of water mites was low in the catches. In the shallower, clear-water L. Puruvesi the densities of crustaceans and Chaoborus-larvae were low whilst some water mites, such as Piona pusilla, occurred in high numbers. Nocturnal sampling was more effective, especially for M. relicta.     

A light trap to collect krill and other micronektonic and planktonic animals under the Antarctic coastal fast ice

Summary Under the Antarctic coastal fast ice a light trap proved to be promising device for collecting not only planktonic animals, but also micronektonic animals like krill which have been rarely collected with tow nets. Sampling was conducted at night from May through November, 1984 in Kitano-ura Cove off the East Ongul Island in Lützow-Holm Bay. Design of the gear and the sampling procedure are described. A total of 37 samplings were made that resulted in the collection of seven species of copepods, eight species of amphipods, three forms of notothenid fish larvae, two species each of euphausiids and polychaetes, and one species each of mysid, cumacean, isopod and tanaid crustaceans. All were collected in satisfactory condition for laboratory experiments. During the winter Euphasia superba was found to be benthopelagic and it probably feeds on detritus on the sea floor at about 40 m depth under the ice.JARE-25 Biology Contribution No.1     

Carotenoids, photoprotection and food web links in Lake Baikal

1. Carotenoids were extracted from macrophytes, sponges, amphipods, fish stomachs, fish livers, fish ovaries and zooplankton in samples collected from various depths in Lake Baikal. 2. Acetone extracts from macrophytes showed a ratio of absorption at wavelengths of 430 and 665 nm consistently in the range 2.1–2.5. Sponges from very shallow water (1.5m) showed a similar ratio, but a sponge from 25m gave a ratio of 6.6, indicating a reduction in the concentration of chlorophyll relative to carotenoids. 3. Extracts from amphipods gave some support for the photoprotection hypothesis, with lower concentrations of carotenoids in amphipods from the deepest water. 4. Some fish took high concentrations of carotenoids into their stomachs, but the concentrations found in their Livers and ovaries were very much lower. Fish appear to be one of the carotenoid sinks in Lake Baikal. 5. Plankton samples showed an apparent inversion, with the highest concentration of carotenoid in the deepest sample, but this was a result of the sinking into deep water of the filamentous diatom Melosira.