Number Of Copepods Research Articles

Seasonal changes in the abundance and biomass of copepods in the south-eastern Baltic Sea in 2010 and 2011.

BackgroundCopepods are major secondary producers in the World Ocean. They represent an important link between phytoplankton, microzooplankton and higher trophic levels such as fish. They are an important source of food for many fish species but also a significant producer of detritus. In the terms of the role they play in the marine food web, it is important to know how environmental variability affects the population of copepods.MethodsThe study of the zooplankton community in the south-eastern Baltic Sea conducted during a 24-month survey (from January 2010 to November 2011) resulted in the identification of 24 invertebrate species (10 copepods, seven cladocerans, four rotifers, one ctenophore, one larvacean, and one amphipod). Data were collected at two stations located in the open sea waters of the Gulf of Gdansk: the Gdansk Deep (P1) (54°50′N, 19°19′E) and in the western, inner part of the Gulf of Gdansk (P2) (54°32′N, 18°48.2′E). The vertical hauls were carried out with the use of two kinds of plankton nets with a mesh size of 100 µm: a Copenhagen net (in 2010), and a WP-2 net (in 2011).ResultsThe paper describes the seasonal changes in the abundance and biomass of copepods, taking into account the main Baltic calanoid copepod taxa (Acartia spp., Temora longicornis and Pseudocalanus sp.). They have usually represented the main component of zooplankton. The average number of copepods at the P1 Station during the study period of 2010 was 3,913 ind m−3(SD 2,572) and their number ranged from 1,184 ind m−3 (in winter) to 6,293 ind m−3(in spring). One year later, the average count of copepods was higher, at 11,723 ind m−3(SD 6,980), and it ranged from 2,351 ind m−3(in winter) to 18,307 ind m−3(in summer). Their average count at P2 Station in 2010 was 29,141 ind m−3, ranging from 3,330 ind m−3(in March) to 67,789 ind m−3(in May). The average count of copepods in 2011 was much lower at 17,883 ind m−3, and it ranged from 1,360 ind m−3 (in April) to 39,559 ind m−3 (in May).DiscussionThe environmental conditions of the pelagic habitat change in terms of both depth and distance from the shore. Although the qualitative (taxonomic) structure of zooplankton is almost identical to that of the coastal waters, the quantitative structure (abundance and biomass) changes quite significantly. The maximum values of zooplankton abundance and biomass were observed in the summer season, both in the Gdansk Deep and in the inner part of the Gulf of Gdansk. Copepods dominated in the composition of zooplankton for almost the entire time of the research duration. Quantitative composition of copepods at the P1 Station differed from the one at P2 Station due to the high abundance of Pseudocalanus sp. which prefers colder, more saline waters.

Diet Preferences of Small Fishes at Setiu Lagoon, Malaysia

This study aimed to investigate diet preferences of small fishes in a shallow coastal lagoon through analysis of their stomach contents.The 24 hours samplings was done during high tide at selected stations; mangrove areas and seagrass areas, both located at coastal lagoon of Setiu, Terengganu (N5o41.75’ E102o42’ to N5o 42.5’ E 102o41’). The small fishes were caught using seine nets (0.5 cm2), while the zooplanktons were collected using Kitahara zooplankton net (110 microns) then were preserved. All items found in the stomach were compared with the composition of the zooplanktons obtained from the water samples. During the sampling time, 10 species of small fishes were caught. There were higher number of fishes and zooplanktons caught from the seagrass areas than the mangrove areas. Nonetheless, diversity of zooplankton was higher in the mangroves. Overall, the number of harpacticoid was higher than all other food items found in the stomach of fishes caught from both areas despite the high number of calanoid copepods found in the lagoon

Induction of domoic acid production in diatoms—Types of grazers and diatoms are important

Grazers can induce toxin (domoic acid, DA) production in diatoms. The toxic response has been observed in two species of Pseudo-nitzschia and was induced by Calanus copepods. In this study, interactions between diatoms and copepods were further explored using different species of diatoms and copepods. All herbivorous copepods induced toxin production, whereas exposure to carnivorous copepods did not. In line with this, increasing the number of herbivorous copepods resulted in even higher toxin production. The induced response is thus only elicited by copepods that pose a real threat to the responding cells, which supports that the induced toxin production in diatoms evolved as an inducible defense.The cellular toxin content in Pseudo-nitzschia was positively correlated to the concentration of a group of specific polar lipids called copepodamides that are excreted by the copepods. This suggests that copepodamides are the chemical cues responsible for triggering the toxin production. Carnivorous copepods were found to produce less or no copepodamides.Among the diatoms exposed to grazing herbivorous copepods, only two of six species of Pseudo-nitzschia and none of the Nitzschia or Fragilariopsis strains responded by producing DA, indicating that not all Pseudo-nitzschia species/strains are able to produce DA, and that different diatom species might have different strategies for coping with grazing pressure. Growth rate was negatively correlated to cellular domoic acid content indicating an allocation cost associated with toxin production. Long-term grazing experiments showed higher mortality rates of grazers fed toxic diatoms, supporting the hypothesis that DA production is an induced defense mechanism.

Differential bioaccumulation of mercury by zooplankton taxa in a mercury-contaminated reservoir Guizhou China

Mercury (Hg) contamination in aquatic systems remains a global concern with the biomagnification of methylmercury (MeHg) through primary consumers (zooplankton) to fish and humans. In this study, total mercury (THg) and MeHg concentrations were analyzed in zooplankton collected from Baihua reservoir (Guizhou Province, China). Our results demonstrated that THg and MeHg concentrations were strongly correlated to zooplankton community and biomass composition. The THg concentration was significantly higher in micro-zooplankton compared to meso-zooplankton and macro-zooplankton, and MeHg concentration increased significantly as body size increased. Hg increases in zooplankton were influenced by the numbers of calanoid copepods and Daphnia present relative to phytoplankton and zooplankton biomass. Many zooplankton taxa in the three size-fractions were affected by THg exposure. The biomasses of Bosmina longirostris, Thermocyclops brevifurcatus, Asplanchna priodonta and Cyclops vicinus vicinus were positively correlated with Hg accumulation, while Daphnia hyalina, and Phyllodiaptomus tunguidus had a negative association. THg and MeHg bioaccumulation factors were correlated with phosphorus and total nitrogen concentration, zooplankton biomass, and chlorophyll-a concentration. Phosphorus loading was associated with increased THg and MeHg accumulation in the zooplankton highlighting biomagification with eutrophication. Chlorophyll-a levels were not correlated to THg and MeHg accumulation in zooplankton when phytoplankton densities were >107 cells L−1 and chlorophyll-a concentrations <9 μgL−1. This finding contradicts the idea of MeHg biodilution with increased algae biomass. However, changes in the phytoplankton species and biomass altered the availability of food for zooplankton, particularly micro-zooplankton and macro-zooplankton. Ultimately, the bioaccumulation of MeHg and THg across lower trophic levels was based more on the availability of preferred food resources than on total biological productivity.

Relationship between seasonal dynamics in zooplankton density and Ergasilus infection in two reservoirs

Ergasilosis is a common parasitic disease of fish caused by species of the family Ergasilidae. During the fish growing season, parasitic abundance (including developmental stages) changes in relation to zooplankton development. In this study, we evaluated the seasonal dynamics of ergasilosis in relation to zooplankton development at two reservoirs (Hubenov, Koryčany) in the Morava River Basin (Czech Republic). Samples of fish and zooplankton were obtained at monthly intervals between April and October 2014. In total, 189 fish of 11 species were caught using electrofishing and seine nets. Overall, epidemiological characteristics were higher in the Hubenov reservoir, which also hosted higher numbers of pelagic Copepods. Hubenov also supported a higher number of predatory fish species, which presumably helped to reduce the number of zooplanktonophagic cyprinids. Our results suggest that each reservoir represents a unique ecosystem with its own pattern of ergasilosis seasonal development. Differences between reservoirs are closely related to zooplankton development, which is in turn affected by the fish stock in each reservoir. As the nauplius and copepod stages of arthropods form part of the zooplankton assemblage, they will be found at highest numbers in reservoirs where predatory fish suppress zooplanktonophagic fish species. We suggest to analyse zooplankton with the determination of the genusErgasilus.

Preliminary Studies on the Occurrence and Abundance of Zooplankton Major Taxa in Keamari, Karachi- Backwaters

A preliminary study was conducted on the occurrence and abundance of zooplankton in the Karachi backwaters. Zooplankton sampling was conducted on monthly basis and the study was carried out on the basis of three seasons including pre-monsoon (January to May), monsoon (June to September) and post-monsoon (October to December) from a permanent station Napier Mole bridge (24o50’34’’.90 N, 66o59’17’’.55 E) during June 1996 to May 1998. The hydrographic parameters including air temperature (oC), water temperature (oC), salinity (ppt), dissolved oxygen (mg/L), pH, and transparency (cm) were recorded. Total 14 groups of zooplankton were recorded; hydromedusae, copepoda, mysids, amphipoda, acetes, lucifer, chaetognath, penaeid pl, caridean pl, zoea, megalopa, squilla larvae, fish larvae, fish eggs and others. Pre-monsoon season shows highest number of individuals and copepods were found to be the dominant group in all seasons. Zooplankton diversity, equitability and margalef index were measured seasonally. Highest shannon – wiener diversity index H' = (1.83), equitability E= (0.69) and margalef species richness Index d= (1.37) were measured in post-monsoon season. Statistical analysis (ANOVA) was performed in between seasons and zooplanktonic groups. No significant difference (at P&gt;0.05, 0.148) was observed between zooplankton and seasons.

Diet composition and feeding habits of larval Pacific bluefin tuna Thunnus orientalis in the Sea of Japan: integrated morphological and metagenetic analysis

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 583:211-226 (2017) - DOI: https://doi.org/10.3354/meps12341 Diet composition and feeding habits of larval Pacific bluefin tuna Thunnus orientalis in the Sea of Japan: integrated morphological and metagenetic analysis Taketoshi Kodama1,*, Junya Hirai2,7, Saori Tamura1, Takashi Takahashi3, Yosuke Tanaka4,8, Taiki Ishihara5, Atsushi Tawa5, Haruyuki Morimoto1, Seiji Ohshimo5,6 1Japan Sea National Fisheries Research Institute, Japan Fisheries Research and Education Agency, Suido-cho, Chuo, Niigata 951-8121, Japan 2National Research Institute of Fisheries Science, Japan Fisheries Research and Education Agency, Fukuura, Kanazawa, Yokohama, Kanagawa 236-8648, Japan 3Joetsu Environmental Science Center, Shimo-monzen, Joetsu, Niigata 942-0063, Japan 4Amami Laboratory, Seikai National Fisheries Research Institute, Japan Fisheries Research and Education Agency, Sakiyamahara, Hyo, Setouchi-cho, Oshima, Kagoshima 894-2414, Japan 5National Research Institute of Far Seas Fisheries, Japan Fisheries Research and Education Agency, Orido, Shimizu, Shizuoka 424-8633, Japan 6Seikai National Fisheries Research Institute, Japan Fisheries Research and Education Agency, Taira-machi, Nagasaki 851-2213, Japan 7Present address: Atmosphere and Ocean Research Institute, The University of Tokyo, Kashiwanoha, Kashiwa, Chiba 277-8564, Japan 8Present address: Tohoku National Fisheries Research Institute, Japan Fisheries Research and Education Agency, Sakiyama, Miyako, Iwate 027-0097, Japan *Corresponding author: takekodama@affrc.go.jp ABSTRACT: Diet compositions of larval Pacific bluefin tuna (PBT) Thunnus orientalis caught in the Sea of Japan during the summers of 2011-2015 were investigated using both microscopic (n = 149) and metagenetic (n = 120) methods to determine the species’ prey and feeding habits. The microscopic analysis revealed that prey abundance in gut contents ranged from 0-10 ind. larva-1 (mean ± SD: 0.89 ± 1.5 ind. larva-1, including larvae with empty guts), which was low, similar to levels for larval bluefin tunas in other seas except the Mediterranean. The cladoceran family Podonidae (Podon spp. and Evadne spp.) represented the most abundant prey (0.73 ± 1.4 ind. larva-1) observed microscopically. Metagenetic analysis of the 18S V9 region detected a taxonomically wide range of prey. In addition to Podonidae, morphologically unidentified taxa were detected as major prey, including Copepoda (Paracalanus parvus s.l. and Labidocera sp.), Appendicularia (Oikopleura spp.), and Doliolida (Doliolum sp.). Compared with plankton communities in the sea, the proportions of Oikopleura spp. and Podonidae in the guts of the larvae were high, indicating that PBT larvae fed on them selectively. Although copepods were abundant in the sea, PBT larvae only consumed a small number of them. The ability of copepods to escape predation is higher than that of Oikopleura spp. and Podonidae, and the guts of the PBT larvae generally contained a low number of copepods considering their abundance and size in the region. This study successfully characterized the prey of PBT larvae in the Sea of Japan, and showed that they were unable to exploit the abundance of copepods, a fact which may lead to high larval mortality. KEY WORDS: Pacific bluefin tuna · Larval feeding habits · Larval trophic ecology · Diet composition · Zooplankton · 18S rDNA · Metagenomics · Trophic selectivity Full text in pdf format Supplementary material PreviousNextCite this article as: Kodama T, Hirai J, Tamura S, Takahashi T and others (2017) Diet composition and feeding habits of larval Pacific bluefin tuna Thunnus orientalis in the Sea of Japan: integrated morphological and metagenetic analysis. Mar Ecol Prog Ser 583:211-226. https://doi.org/10.3354/meps12341 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 583. Online publication date: November 16, 2017 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2017 Inter-Research.

Box jellyfish may eat up the oceans

As the oceans become more acidic, box jellyfish may start eating a lot more. Their greedy appetites could have a huge impact on marine ecosystems. To find out, Edd Hammill of Utah State University and his colleagues collected copepods and one of their predators, the box jellyfish Carybdea rastoni, from the waters around Australia. They kept the plankton in tanks containing either ambient seawater or seawater acidified at levels predicted for 2100, then added box jellyfish to half of each set of tanks. After 10 days, they counted what survived. Both acidification and box jellyfish reduced the number of copepods, but the two together caused 27 per cent more deaths than the sum of the two individually. The jellyfish were eating more: they ate nearly 37 per cent of copepods in the ambient seawater tanks, but almost 83 per cent in the acidified water

Ocean acidification causes no detectable effect on swimming activity and body size in a common copepod

Ocean acidification can impair an animal’s physiological performance and energetically demanding activities such as swimming. Behavioural abnormalities and changed activity in response to ocean acidification are reported in fish and crustacean species. We studied swimming activity in the calanoid copepod Pseudocalanus acuspes in response to near-future ocean acidification. Water and copepods were sampled from ten mesocosms deployed on the Swedish west coast. The experiments were conducted on animals reared in the mesocosms for 2 months during spring. Copepods were filmed after long-term (chronic) high-CO2, and after 20 h acute exposure to CO2. There was no significant effect of CO2 on copepods in chronic high-CO2, nor significant effect after the 20 h acute exposure. In addition, we measured prosome length from a large number of adult copepods, but no effect of acidification on body size was found. In this study, P. acuspes did not show sensitivity to near-future pCO2 levels. Even if a number of papers suggest that copepods seem robust to future ocean acidification, interaction between multiple stress factors, such as elevated temperature, hypoxia and salinity changes may impair a copepod’s ability to resist lowered pH.

Near-bottom zooplankton aggregations in Kongsfjorden: implications for pelago–benthic coupling

Near-bottom zooplankton communities have rarely been studied despite numerous reports of high zooplankton concentrations, probably due to methodological constraints. In Kongsfjorden, Svalbard, the near-bottom layer was studied for the first time by combining daytime deployments of a remotely operated vehicle (ROV), the optical zooplankton sensor moored on-sight key species investigation (MOKI), and Tucker trawl sampling. ROV data from the fjord entrance and the inner fjord showed high near-bottom abundances of euphausiids with a mean concentration of 17.3 ± 3.5 n × 100 m−3. With the MOKI system, we observed varying numbers of euphausiids, amphipods, chaetognaths, and copepods on the seafloor at six stations. Light-induced zooplankton swarms reached densities in the order of 90,000 (euphausiids), 120,000 (amphipods), and 470,000 ind m−3 (chaetognaths), whereas older copepodids of Calanus hyperboreus and C. glacialis did not respond to light. They were abundant at the seafloor and 5 and 15 m above and showed maximum abundance of 65,000 ind m−3. Tucker trawl data provided an overview of the seasonal vertical distribution of euphausiids. The most abundant species Thysanoessa inermis reached near-bottom concentrations of 270 ind m−3. Regional distribution was neither related to depth nor to location in the fjord. The taxa observed were all part of the pelagic community. Our observations suggest the presence of near-bottom macrozooplankton also in other regions and challenge the current view of bentho–pelagic coupling. Neglecting this community may cause severe underestimates of the stock of pelagic zooplankton, especially predatory species, which link secondary production with higher trophic levels.

Terrestrial dissolved organic carbon subsidizes estuarine zooplankton: An in situ mesocosm study

Freshwater inflows play an important role in delivering dissolved organic carbon (DOC) to estuaries. Episodic inputs of DOC may support increased bacterial production. However, the role of DOC in supporting zooplankton production is widely debated. To evaluate this role we performed an in situ mesocosm experiment in the Bega River estuary, Australia. We added a DOC leachate derived from terrestrial vegetation to 400 L mesocosm bags as treatments of +1.5, +3, and +16 mg C L−1 and monitored changes in carbon, nitrogen, phosphorus, bacteria, chlorophyll a (Chl a), and zooplankton over 22 d. Bacterial biomass peaked at day 2 and was highest in the +16 mg C L−1 treatment. Chl a was not significantly different between treatments. Mesozooplankton was dominated by copepodites of Gladioferens pectinatus and Sulcanus conflictus between days 5–9 and by adults between days 9–15. Significantly higher numbers of copepods were present in the +16 treatment followed by the +3 mg C L−1 treatment compared with the controls. Stable carbon isotope signatures of copepods in the +16 mg C L−1 treatment were significantly different from the control and showed leachate carbon supported between 29.3% and 55.8% of copepod biomass. These results suggest that the impact of allochthonous DOC loading events on estuarine zooplankton occurs over short periods, and that the magnitude of response is, in part, controlled by the quantity of bioavailable DOC loaded to the system. Our findings underscore the importance of microbial dynamics stimulated by DOC loading events from freshwater inflows as a trophic path in estuarine food webs.

Seasonal copepod lipid pump promotes carbon sequestration in the deep North Atlantic

Estimates of carbon flux to the deep oceans are essential for our understanding of global carbon budgets. Sinking of detrital material ("biological pump") is usually thought to be the main biological component of this flux. Here, we identify an additional biological mechanism, the seasonal "lipid pump," which is highly efficient at sequestering carbon into the deep ocean. It involves the vertical transport and metabolism of carbon rich lipids by overwintering zooplankton. We show that one species, the copepod Calanus finmarchicus overwintering in the North Atlantic, sequesters an amount of carbon equivalent to the sinking flux of detrital material. The efficiency of the lipid pump derives from a near-complete decoupling between nutrient and carbon cycling—a "lipid shunt," and its direct transport of carbon through the mesopelagic zone to below the permanent thermocline with very little attenuation. Inclusion of the lipid pump almost doubles the previous estimates of deep-ocean carbon sequestration by biological processes in the North Atlantic.

Observational data on the effects of infection by the copepod Salmincola californiensis on the short- and long-term viability of juvenile Chinook salmon (Oncorhynchus tshawytscha) implanted with telemetry tags

Fish movements are often studied using radio or acoustic tags assuming the handling and tagging procedures have little effect on the behavior of the animal. Indeed, many studies provide guidelines for acceptable methods. However, these studies generally assume the fish are otherwise healthy but this may not always be the case. One example is the infection of juvenile salmon in the western USA by the naturally-occurring parasitic copepod Salmincola californiensis, for which little is known about the effects on results from tagged animals. We report on observational data from juvenile Chinook salmon (Oncorhynchus tshawytscha) surgically implanted with telemetry tags relative to the numbers of S. californiensis within their branchial cavities and on their bodies to determine if the intensity of infection resulted in differences in mortality shortly after tagging or post-release activity in a reservoir over a period of about 4 months. The data indicate a negative effect of copepods in the branchial cavities on short-term mortality (within 24 h of tagging) and suggest negative effects on movements after release into the reservoir. Short-term mortalities were infrequent and, due to the observational nature of the data, few tagged fish had more than three copepods in their branchial cavities, although surveys of fish in the reservoir indicate much greater infection intensities are common. Copepod numbers on the body did not appear to be associated with short-term mortality or movements after release. The number of copepods on the body was unrelated to the number within the branchial cavities, indicating site-specific counts are needed to assess the infection. Infection with Salmincola californiensis is common in juvenile Chinook salmon in western USA reservoirs and may affect the viability of fish used in studies of telemetered animals. Our limited assessment suggests infection by Salmincola californiensis affects the short-term morality of tagged fish and may affect long-term viability of tagged fish after release; however, the intensity of infection in the sample population did not represent the source population due to the observational nature of the data. We suggest these results warrant further study into the effects of infection by Salmincola californiensis on the results obtained through active telemetry and perhaps other methods requiring handling of infected fish.

New evidence for the involvement of Paracartia grani (Copepoda, Calanoida) in the life cycle of Marteilia refringens (Paramyxea)

The dynamics of the protozoan parasite Marteilia refringens was studied in Thau lagoon, an important French shellfish site, for 1year in three potential hosts: the Mediterranean mussel Mytilus galloprovincialis (Mytiliidae), the grooved carpet shell Ruditapes decussatus (Veneriidae) and the copepod Paracartia grani (Acartiidae). Parasite DNA was detected by PCR in R. decussatus. In situ hybridisation showed necrotic cells of M. refringens in the digestive epithelia of some R. decussatus suggesting the non-involvement of this species in the parasite life cycle. In contrast, the detection of M. refringens in mussels using PCR appeared bimodal with two peaks in spring and autumn. Histological observations of PCR-positive mussels revealed the presence of different parasite stages including mature sporangia in spring and autumn. These results suggest that the parasite has two cycles per year in the Thau lagoon and that mussels release parasites into the water column during these two periods. Moreover, PCR detection of the parasite in the copepodid stages of P. grani between June and November supports the hypothesis of the transmission of the parasite from mussels to copepods and conversely. In situ hybridisation performed on copepodites showed labeling in some sections. Unusual M. refringens cells were observed in the digestive tract and the gonad from the third copepodid stage, suggesting that the parasite could infect a copepod by ingestion and be released through the gonad. This hypothesis is supported by the PCR detection of parasite DNA in copepod eggs from PCR-positive females, which suggests that eggs could contribute to the parasite spreading in the water and could allow overwintering of M. refringens. Finally, in order to understand the interactions between mussels and copepods, mussel retention efficiency (number of copepods retained by a mussel) was measured for all P. grani developmental stages. Results showed that all copepod stages could contribute to the transmission of the parasite, especially eggs and nauplii which were retained by up to 90%.

English

&nbsp; Fish parasitology is an indispensable tool in aquatic health studies and a basic understanding of richness of a community parasitism in many localities is essential for instituting control. Many copepod parasites are ecto-parasites which negatively affect the appearance and reduced production of species of economically important fish, both from the wild and fish farms, thus making them difficult to market. In this study, copepod parasitic investigation was carried out in gills of 856 fish mugilidae (Mugil cephalus and Liza falcipinnis) in three stations (Ganvie, Djdje and Zogbo) of Lac Nokoue lagoon. In the three stations, three species of parasitic copepod were found: Nipergasilus bora, Ergasilus latus and Ergasilus lizae. The highest total percentage copepod prevalence was found in Ganvie (86.23%) and the least in Djdje (63.14%). There is significant difference (P&lt;0.05) in the rate of infestation of L. falcipinnis at Djdje than the other two stations, where as M. cephalus shows no significant difference in the rate of infestation in the three stations. The research reveals higher number of parasite copepods during the rainy season. &nbsp; &nbsp; Key words: Copepod parasites, Mugilidae fish, Lac Nokoue Lagoon.

Validation of a sandwich hybridization assay for marine copepod detection

The sandwich hybridization assay (SHA) is a rapid and robust RNA detection method for identifying and quantifying planktonic organisms in marine samples. Although tests for taxonomic specificity with pure cultures of target organisms yield encouraging results, the inevitable presence of non-target organisms in environmental samples might confound qualitative and quantitative aspects of the assay. This study examined the sensitivity of SHA to detect known quantities of cultured Tigriopus californicus (Copepoda: Podoplea) in environmental samples that contained naturally occurring copepods, other organisms, and unknown chemical backgrounds. SHA reliably detected culture-raised T. californicus in addition to naturally occurring podoplean copepods. Additionally, cultured Pseudo-nitzschia australis (Bacillariophyceae: Bacillariales), a harmful bloom-forming algal species typically found in water samples from the Monterey Bay, California, slightly enhanced SHA detection of T. californicus. Because SHA detects total RNA, factors that regulate RNA content within individuals may confound inferences about the number of copepods in a sample. Body size, physiological state, life-history stage, and gravidity of females all affected detectable levels of RNA in T. californicus individuals. For zooplankton taxa with complex life histories, the translation of molecular counts to quantities of individuals remains challenging.

Connectivity and complexity of floodplain habitats govern zooplankton dynamics in a large temperate river system

Summary Large river–floodplain systems are characterised by seasonal flow variability. High flows lead to hydrological connection between the main channel and inundated off‐channel lakes, wetlands and floodplains, which provide essential habitats for riverine biota. We tested the following hypotheses: (i) that crustacean zooplankton are more abundant in connected lentic habitats such as riverine lakes and wetlands and have a different community composition compared with the main channel and (ii) that vegetation structure will moderate abundances of crustacean zooplankton in the lower reaches of the Waikato River, New Zealand. Zooplankton densities in main channel inflows and inundated floodplains showed clear seasonal changes, with cladoceran and copepod abundance peaks occurring in the majority of sites 2–3 weeks following the peak spring discharges (coinciding with the retreat of water from floodplains into the main channel). Mean densities of zooplankton were highest in the inflows originating from riverine lakes (10–20 ind. L−1) where rotifers were dominant. We recorded significantly higher abundances of copepods in peat bog and swamp wetland inflows (c. 5 ind. L−1) relative to the main river channel and riverine lake inflows (0.1–1 ind. L−1). Some lake inflows also had high numbers of cladocerans (5–10 ind. L−1). Inundated floodplains displayed heterogeneity in zooplankton community composition in relation to their structural complexity. Flooded forest accommodated higher numbers of copepods (c. 8 ind. L−1) and cladocerans (c. 17 ind. L−1) than flooded grassland, where zooplankton assemblages resembled those in the main river channel and were characterised by dominance of rotifers and low overall zooplankton densities (1–2 ind. L−1). Our results suggest that seasonal flow and flood pulses, which determine the degree of connectivity of the main channel with the floodplain and off‐channel habitats, govern zooplankton densities and community structure in this large temperate river. Furthermore, the structural complexity of floodplain habitats may play an important role in enhancing riverine zooplankton diversity. We postulate that the post‐flood peak of large‐bodied cladocerans and copepods might have historically played an important role in the provision of food for juvenile fish such as migrating Galaxiidae.

Effects of Mosquitofish, Gambusia affinis, on Channel Catfish, Ictalurus puncatatus, Production Ponds

AbstractMosquitofish, Gambusia sp., have been spread throughout the world to biologically control mosquitoes. However, the fish has gained a reputation as an invasive species and has been implicated in displacing native aquatic species. Gambusia affinis are native to the southeastern United States and commonly occur in commercial channel catfish, Ictalurus punctatus, production ponds. We investigated effects of mosquitofish presence on zooplankton populations, water quality, disease occurrence, and fish production in experimental ponds. There were no differences between ponds with or without mosquitofish in numbers of calanoid copepods, cyclopoid copepods, total copepods, Bosmina sp., Ceriodaphnia sp., Moina sp., Daphnia sp., or total cladocerans. There were also no differences in copepod and cladoceran sizes. Copepod nauplii were more numerous during the summer months in ponds with mosquitofish. There were no differences in water quality variables (soluble reactive phosphorus, nitrate, nitrite, ammonia, total nitrogen, total phosphorus, pH) or phytoplankton density between ponds stocked with and without mosquitofish. Catfish production and disease occurrence were also similar between ponds with and without mosquitofish. Although mosquitofish may cause problems when stocked outside their native range, there does not appear to be any adverse effects of mosquitofish presence in catfish production ponds.

Mass culture and offspring production of marine harpacticoid copepod Tisbe biminiensis

The aim of the present study was to develop mass culture techniques for the copepod Tisbe biminiensis Volkmann-Rocco, 1973. Copepod culture was carried out in transparent plastic boxes (32 × 47 × 14.5 cm) containing 4.5 L of filtered aerated seawater at room temperature (28 to 32 °C) and a salinity value of 35‰. The copepods were fed daily with commercially available ornamental fish food (Alcon Basic®) and every other day following water exchange with 500 mL of one of the following diatoms: Phaeodactylum tricornutum or Thalassiosira fluviatilis. In all experiments, the number of copepods was estimated by sub-sampling. Offspring harvesting once a week and the presence of sediments on the bottom did not affect population growth. The harvesting of T. biminiensis from the 5 L cultures produced a mean of 28,000 nauplii and copepodites L −1 day −1 over a 130-day period using relatively simple culture techniques. Population abundance recuperated four days following offspring harvesting. The present study indicates that good results were achieved in the mass culture of T. biminiensis. The improvement of these techniques combined with biochemical composition studies can enable the future use of T. biminiensis as live food for marine larvae.

Size-differential feeding in Pinna nobilis L. (Mollusca: Bivalvia): Exploitation of detritus, phytoplankton and zooplankton

The endangered fan shell Pinna nobilis is a large bivalve mollusc (<120 cm shell length) endemic to the Mediterranean that lives one-third buried in soft substrata, generally in shallow coastal waters. We hypothesised that P. nobilis of different sizes would ingest different food sources, because small fan shells will inhale material from closer to the substratum than do large fan shells. We studied stomach contents and faeces of 18 fan shells, 6 small (mean 23.0 cm length), 6 medium-sized (mean 41.5 cm length) and 6 large (mean 62.7 cm length) living in a small area of a low-energy coastal detritic bottom characterised by mud, sand and macroalgae at Mali Ston Bay, Croatia. We found that all P. nobilis ingested copious quantities of undetermined detritus (probably at least 95% of ingested material), phytoplankton, micro and mesozooplankton and pollen grains. Large P. nobilis stomach contents showed a preponderance of water column calanoid copepods, while small fan shells had higher numbers of bivalve larvae. All fan shells took in high numbers of harpacticoid copepods that are benthonic, feeding on microbial communities of detritus and benthic vegetation. There was also a significant selection of phytoplankton species, some apparently occurring between inhalation and ingestion. The stomach contents of small P. nobilis had a higher organic matter content than either medium-sized or large fan shells; this indicated that small fan shells ingested detritus of higher organic content than did larger P. nobilis. As the faeces of all P. nobilis had similar organic matter content, this also indicates higher assimilation efficiencies in small fan shells. The demonstration of differential dietary selectivity by different sized animals has implications for future trophic studies of this endangered species. This study also provides the first demonstration of predation on zooplankton by P. nobilis.