Densities Of Nauplii Research Articles

Growth, survival, and myogenic gene expression in the post-larvae of Colossoma macropomum provisioned with Artemia nauplii.

Artemia nauplii are widely used as fish larvae feed due to its beneficial nutritional characteristics for larval development; however, efficient feeding strategies are needed to balance its high costs. Therefore, we evaluated the effects of different densities of Artemia nauplii (100, 250, 500, 750, and 1000 nauplii/post-larvae) on the growth, survival, water quality, and myogenic gene expression of tambaqui (Colossoma macropomum) post-larvae cultivated in a recirculating aquaculture system. After 2weeks of trial, there was a significant decrease in dissolved oxygen concentration with the increase in nauplii density, but it did not interfere with larval performance and survival. In the first week, larvae fed with fewer than 500 nauplii/post-larvae presented slower growth, while in the second week, larvae fed with 1000 nauplii/post-larvae had the highest final weight and length. Regression analysis suggests that the optimum feeding density of Artemia nauplii during the first week is 411 nauplii/post-larvae, while for the second week, the growth increased proportionally to the feeding densities. The relative expression of the myod, myog, and mstn genes was higher in larvae fed with fewer than 500 nauplii/post-larvae. Although low-growing larvae showed increased expression of myod and myog genes, responsible for muscle hyperplasia and hypertrophy, respectively, mstn expression may have played a significant inhibitory role in larval development. Further research is needed to better determine the effects of the live food on the zootechnical performance and the expression of the myogenic genes in the initial phase of the life cycle of the tambaqui post-larvae.

How many generations does Epischura baikalensis (Copepoda, Calanoida) have in Lake Baikal?

Abstract Epischura baikalensis Sars is a dominant pelagic species of the Lake Baikal zooplankton. We empirically determined the duration of the development of Epischura from field data, as it is not possible to determine this experimentally. Based on our data, we conclude that the central pelagic food web of metazoan species in Lake Baikal has not two, as was previously accepted, but three generations during a year and each lasts not 6 but instead 3 to 4 months. The life cycle of the species also possibly includes a 3-months long winter embryonic diapause, starting in November and ending in late February with the start of the under-ice algae bloom. The high nauplii density in spring is not the result of high adult density, suggesting the presence of resting eggs in the E. baikalensis life cycle. We also found a large morphological difference between the pelagic eggs of the species in the winter and in the summertime. The possible participation of diatom algal toxins in the regulation of the seasonal dynamics of their main consumer in Lake Baikal, similar to those known in marine ecosystems, is discussed. The population dynamics in a year with relatively low diatom algae density show four peaks of reproduction, i.e., in February, June, September, and December. In years with significant (more than 15 000 cells/l) diatom blooming we found mass mortality of E. baikalensis juveniles in the plankton, with only two clear peaks of nauplii density. A negative correlation was found between the number of population density peaks for E. baikalensis and the spring-blooming of diatom algae.

Relationships between the daily growth rate of Japanese anchovy Engraulis japonicus larvae and environmental factors in Osaka Bay, Seto Inland Sea, Japan

Seasonal changes in the growth rate of larval Japanese anchovy Engraulis japonicus collected by shirasu seine net boats in Osaka Bay in 2008 were estimated using otolith daily growth increments to examine the effects of environmental factors. Larval anchovy were caught from May to November. The range in standard length (SL) of the larval anchovy was 10–35 mm, and larvae of SL 20–25 mm dominated numerically, accounting for more than 40% of all anchovy larvae. Daily growth rates for the last five days before catch increased from May to July, decreased or were stagnant in August and September, increased again in October, and decreased in November. Seawater temperature and density of copepod nauplii were correlated with the daily growth rate. In this study, the relationship between growth rate and temperature showed a skewed dome shape, with an optimum temperature for growth of around 23 °C. These results in summer of 2008 suggest that the growth rate of Japanese anchovy increased with increasing temperature for temperatures < 23 °C, but growth was limited by prey availability and/or other factors, such as low dissolved oxygen, at higher temperatures. Recent environmental improvements in nutrient inputs to Osaka Bay are discussed in relation to larval growth rate.

Stress of life at the ocean’s surface: Latitudinal patterns of UV sunscreens in plankton across the Atlantic

The near-surface layer of the ocean is a habitat in which plankton are subjected to very different stresses to those in deeper layers. These include high turbulence and illumination, allowing increased visibility to predators, and exposure to harmful UV radiation. To provide insights into stress caused by UV, we examined the occurrence of protective UV-absorbing compounds called mycosporine-like amino acids (MAAs) in seston and zooplankton along an Atlantic Meridional Transect (AMT) between 45°S and 50°N. Seston contained most MAAs per unit phytoplankton carbon in the northern Atlantic gyre and equatorial region and this coincided with distribution of the nitrogen fixing cyanobacterium Trichodesmium spp. and increased UV transparency but not irradiance. Asterina-330 was the most abundant MAA in the seston. MAAs were detected in a third of the zooplankton tested and these taxa varied greatly both in the amount and diversity of the MAAs that they contained with copepods in temperate regions containing highest concentration of MAAs. Most commonly found MAAs in zooplankton were palythine and shinorine. Juvenile copepods were found not to contain any MAAs. We determined abundance and richness of zooplankton inhabiting the top 50cm of the ocean. Zooplankton abundance and genera richness was low in the surface waters in contrast to the dome-shaped latitudinal trend in genera richness commonly found from depth-integrated zooplankton sampling. The lack of any measurable MAA compounds in nauplii across the whole transect was concomitant with their severe (3–6-fold) reduction in nauplii densities in the near-surface layer, as compared to the underlying water column. Overall we suggest that the UV stress on life near the surface, particularly in the warmer, oligotrophic and brightly-lit low latitudes, imposes radically different pressures on zooplankton communities compared to the rest of the epipelagic.

A method of estimating in situ salmon louse nauplii production at fish farms

Abundance and depth distribution of planktonic sea lice were investigated in rela- tion to hydrodynamics and diurnal solar insolation at a salmon farm in Sundalagið, Faroe Islands. Plankton surveys were conducted by surface tows with a plankton net around the farm and by using a plankton pump at 1, 4 and 6 m depth in a fish cage. The entire sample content was investigated under a stereomicroscope and sea lice were identified. Sea lice of the species Lepeophtheirus salmonis and Caligus elongatus were present at the farm. Nauplii dominated the planktonic stages (>95%) while copepodids were absent from most samples. The highest observed copepodid density was 0.3 ind. m �3 , which is within the range found in open water. No diurnal vertical distribution pattern was observed for salmon lice nauplii in the net cages, which were most abundant in the top meter of the water column, and density decreased with depth. At 1 m depth, nauplii density was inversely proportional to the current speed at the same depth. From this relation, and the abundance of adult female sea lice on the farmed fish, the in situ nau- plii production was calculated to be within 26�68 nauplii female �1 d �1 . The lower end of this range is similar to production rates suggested by laboratory studies at similar temperatures (7.8°C).

Instability of spring environmental conditions as a driver of biotic interactions and crustacean structuring in meteorite crater ponds (Morasko, Poland)

Abstract There are 150 meteorite craters worldwide, however, their aggregations are rarely noted. The nature reserve ‘Meteoryt Morasko’ in Poland with fishless meteorite ponds was analyzed as a unique ecosystem for biological analysis of invertebrate interactions. The aim of the study was to recognize the main environmental drivers of cladoceran and copepod community structure from among biotic (competitors and predators) and abiotic factors (i.e. oxygen and pH level) in the spring season. The abundance of small cladocerans (Alonella excisa and Chydorus sphaericus) was the highest at the end of the spring season, i.e. in June, while large species (Daphnia pulex and Simocephalus exspinosus) were most abundant in May. Both size groups of Cladocera were negatively affected by invertebrate predators (Chaoborus crystallinus and carnivorous copepods), which are known to play an important role in structuring cladoceran communities due to the fishless character of the studied ponds. No negative effect of those predators was found for Copepoda, however, nauplii density was reduced by competitors (Aedes communis larvae and ostracods). The temporary character of the examined ponds, oxygen depletion and low pH of water in the shallowest pond resulted in the abundant occurrence of cladoceran males, whose high densities are usually observed in autumn.

Population Dynamics of Cyclopoid Copepods in Lake Kinneret (Israel)

Reports on the Kinneret zooplankton in general and particularly on copepods are dealing recently with numerical densities of feeding habit classes. Nevertheless, for the evaluation of the integrated role of copepod assemblages in the entire lake ecosystem, their life cycle stages fluctuations are essential. It was not done in previous reports. Therefore, long term analysis of the cyclopoid copepods life stages dynamics in Lake Kinneret was carried out. Due to information availability, two complementary methods of density concentrations were evaluated for two consecutive data sets: 1) 1969-1985 numerical (No/L) documentation of life cycle stages of nauplii (I - III and III - V), copepodites (I, II, III, IV, V) and adults; 2) 1969-2002 monthly averages of wet biomass density (g/m2) of zooplankton major groups combined with metabolic rates. nauplii densities represent June-August peaks and older stages spring decline and high levels during summer-early winter. Polynomial Regressions between Numerical annual averages of predator and Herbivore stages as well as young vs. older life stages indicate significant relations. During winter-spring season, temperatures are optimal for cyclopoid growth as a result of the high efficiency of metabolic activity and the low pressure of fish predation. The high rate of metabolism and intensive fish predation in summer enhance low densities of adult cyclopoids.

Augmenting the post-transplantation growth and survivorship of juvenile scleractinian corals via nutritional enhancement.

Size-dependant mortality influences the recolonization success of juvenile corals transplanted for reef restoration and assisting juvenile corals attain a refuge size would thus improve post-transplantation survivorship. To explore colony size augmentation strategies, recruits of the scleractinian coral Pocillopora damicornis were fed with live Artemia salina nauplii twice a week for 24 weeks in an ex situ coral nursery. Fed recruits grew significantly faster than unfed ones, with corals in the 3600, 1800, 600 and 0 (control) nauplii/L groups exhibiting volumetric growth rates of 10.65±1.46, 4.69±0.9, 3.64±0.55 and 1.18±0.37 mm3/week, respectively. Corals supplied with the highest density of nauplii increased their ecological volume by more than 74 times their initial size, achieving a mean final volume of 248.38±33.44 mm3. The benefits of feeding were apparent even after transplantation to the reef. The corals in the 3600, 1800, 600 and 0 nauplii/L groups grew to final sizes of 4875±260 mm3, 2036±627 mm3, 1066±70 mm3 and 512±116 mm3, respectively. The fed corals had significantly higher survival rates than the unfed ones after transplantation (63%, 59%, 56% and 38% for the 3600, 1800, 600 and 0 nauplii/L treatments respectively). Additionally, cost-effectiveness analysis revealed that the costs per unit volumetric growth were drastically reduced with increasing feed densities. Corals fed with the highest density of nauplii were the most cost-effective (US$0.02/mm3), and were more than 12 times cheaper than the controls. This study demonstrated that nutrition enhancement can augment coral growth and post-transplantation survival, and is a biologically and economically viable option that can be used to supplement existing coral mariculture procedures and enhance reef restoration outcomes.

Epizoic acoelomorph flatworms compete with their coral host for zooplankton

Satisfying nutrient requirement of corals is still a major constraint for maintaining corals in marine aquariums. Corals are polytrophic in nature. Heterotrophic feeding on zooplankton is one of the corals’ strategies to overcome nutrient deficiency. Artemia salina nauplii are commonly used as biocarriers for many fish larvae in aquaculture and can also serve as a biocarrier for coral in aquariums, provided coral acceptability, optimal feeding rate, and digestibility of the nauplii are well understood. Feeding rate and digestibility of coral fed on A. salina nauplii at 100, 2,000, 4,000, 6,000, and 10,000 ind. l-1 under light and dark conditions was assessed in this study. The maximum feeding rates of Galaxea fascicularis under light and dark conditions was 113.6 ind. polyp-1 h-1 and 76.9 ind. polyp-1 h-1, respectively. The daily feeding rates of G. fascicularis varies and depends on nauplii density. Light plays an important role in coral feeding. Nevertheless, the quantity of A. salina nauplii consumed by the coral under light and dark conditions was not significantly different (P > 0.05). A. salina nauplii are well accepted by G. fascicularis. Complete nauplii digestion was observed after 180 min. Digestibility of A. salina nauplii by G. fascicularis was positively correlated with digestion time.

Densities of planktonic Lepeophtheirus salmonis before and after an Atlantic salmon farm relocation

AEI Aquaculture Environment Interactions Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections AEI 1:225-232 (2011) - DOI: https://doi.org/10.3354/aei00022 Densities of planktonic Lepeophtheirus salmonis before and after an Atlantic salmon farm relocation Michael J. Penston*, Alastair J. A. McBeath, Colin P. Millar Marine Scotland Science, Marine Laboratory, PO Box 101, 375 Victoria Road, Aberdeen AB11 9DB, UK *Email: m.penston@marlab.ac.uk ABSTRACT: Relocating Atlantic salmon Salmo salar L. farms away from important salmonid rivers is possibly a means to reduce Lepeophtheirus salmonis (Krøyer, 1837) interactions between farmed Atlantic salmon and wild salmonids. However, to date, no data have been presented on the consequences of salmon farm relocation in terms of densities of planktonic L. salmonis. Near-surface plankton were sampled at 5 stations during 2 full farming production cycles; 1 before and 1 after a salmon farm relocation within a sea loch/fjord. The relocation comprised the removal of a salmon farm and the reallocation of its fish biomass to a different farm within the same management area. Over 85% of the larval sea lice we identified in sub-samples were L. salmonis; we therefore assumed that the majority of the larvae found were of that species. Densities of L. salmonis larvae increased significantly at all stations post relocation, except at the station near the vacated farm site where mean densities of nauplii were significantly lower and mean densities of copepodids were lower without statistical ­significance. The removal/relocation of the salmon farm significantly reduced the production of L. salmonis larvae, but did not significantly reduce the infection pressure, as represented by densities of the infectious copepodid stage, at the vacated farm site. This finding indicates that planktonic L. salmonis were transported to the vacated farm site from sources at a minimum of 5 to 8 km distant. KEY WORDS: Scotland · Sea lice · Relocation · Management · Salmon aquaculture · Sea trout Full text in pdf format PreviousNextCite this article as: Penston MJ, McBeath AJA, Millar CP (2011) Densities of planktonic Lepeophtheirus salmonis before and after an Atlantic salmon farm relocation. Aquacult Environ Interact 1:225-232. https://doi.org/10.3354/aei00022 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AEI Vol. 1, No. 3. Online publication date: April 15, 2011 Print ISSN: 1869-215X; Online ISSN: 1869-7534 Copyright © 2011 Inter-Research.

Production and Collection of Copepod Nauplii from Brackish Water Ponds

Copepod nauplii are a nutritious food item for first-feeding marine fish larvae. Unfortunately, mass culture techniques for producing copepod nauplii are not well established. Copepod nauplii can be collected from wild zooplankton populations or specially prepared ponds and transferred to larval fish tanks for feeding. This study evaluated the use of two trapping methods for harvesting zooplankton, particularly copepod nauplii, from fertilized ponds and the impact on the zooplankton population. Nine, 0.11 ha brackish-water (∼2-7 ppt salinity) ponds were filled and fertilized with organic and inorganic fertilizers. The change in zooplankton abundance, mainly rotifers, nauplii and adult copepods, was monitored in the ponds for 22 d following initial pond filling. Beginning on day 8, three ponds were trapped with a large plankton net (Trap I), three with a pump and bag trap method (Trap II), and three ponds were not trapped. The ponds were trapped with the corresponding method for 1 h per day, for 15 d. The two trapping methods were similar in their efficiency to harvest nauplii, averaging 8,383,400 ± 2,508,378/h and 6,695,822 ± 433,533/h for Traps I and II, respectively. The zooplankton harvested by Trap I was not correlated to the densities in the ponds. However, the number of rotifers and nauplii harvested by Trap II was correlated to the rotifer and nauplii densities in the ponds. Both trapping methods were similar in terms of labor requirements and ease of use. Both methods were effective in collecting zooplankton without negatively impacting pond abundance.

Feeding of scleractinian coral, Galaxea fascicularis, on Artemia salina nauplii in captivity

Satisfying nutrient requirement of corals is still a major constraint for maintaining corals in marine aquariums. Corals are polytrophic in nature. Heterotrophic feeding on zooplankton is one of the corals’ strategies to overcome nutrient deficiency. Artemia salina nauplii are commonly used as biocarriers for many fish larvae in aquaculture and can also serve as a biocarrier for coral in aquariums, provided coral acceptability, optimal feeding rate, and digestibility of the nauplii are well understood. Feeding rate and digestibility of coral fed on A. salina nauplii at 100, 2,000, 4,000, 6,000, and 10,000 ind. l−1 under light and dark conditions was assessed in this study. The maximum feeding rates of Galaxea fascicularis under light and dark conditions was 113.6 ind. polyp−1 h−1 and 76.9 ind. polyp−1 h−1, respectively. The daily feeding rates of G. fascicularis varies and depends on nauplii density. Light plays an important role in coral feeding. Nevertheless, the quantity of A. salina nauplii consumed by the coral under light and dark conditions was not significantly different (P > 0.05). A. salina nauplii are well accepted by G. fascicularis. Complete nauplii digestion was observed after 180 min. Digestibility of A. salina nauplii by G. fascicularis was positively correlated with digestion time.

Reduced Lepeophtheirus salmonis larval abundance in a sea loch on the west coast of Scotland between 2002 and 2006

A survey for planktonic sea louse larvae was carried out in Loch Shieldaig, Scotland, between 2002 and 2006, and spanned 2 successive production cycles (Cycles 1 and 2) at a local Atlantic salmon Salmo salar L. farm. The vast majority of the caligid copepodids recovered were Lepeophtheirus salmonis; however, the methodology was unable to determine the species of the caligid nauplii. Greatest densities of nauplii were found at the sampling station adjacent to the salmon farm, and larval densities were low during the fallow period of both cycles. Peaks in nauplius densities occurred around the same time in the 2 cycles, but the peaks were significantly lower during Cycle 2 than Cycle 1. Lepeophtheirus salmonis copepodid densities varied temporally, but not spatially. During most of Cycle 2, copepodid densities were significantly lower than those recovered during Cycle 1. Numbers of gravid L. salmonis at the local salmon farm correlated significantly with densities of louse nauplii and L. salmonis copepodids in the water at time lags of 0 and 1 wk, and 1 and 2 wk, respectively. This survey demonstrated a reduction in densities of L. salmonis larvae in the plankton (an indication of L. salmonis infectious pressure) between the 2 cycles and indicated that the farm was an important source of L. salmonis larvae. The application of anti-louse treatments using emamectin benzoate reduced the numbers of gravid L. salmonis at the farm, and this was the main factor influencing the apparent reduction in L. salmonis infectious pressure in the loch between cycles.

Spatial and temporal distribution of Lepeophtheirus salmonis (Krøyer) larvae in a sea loch containing Atlantic salmon, Salmo salar L., farms on the north‐west coast of Scotland

A plankton survey investigated spatial and temporal distributions of larval sea lice in a sea loch on the north-west coast of Scotland. Plankton tows were collected approximately weekly at two depths (0 and 5 m) at five sample stations over a 2-year period. The survey began in March 2002 when Atlantic salmon, Salmo salar L., farms in the study area stocked with fish and finished in March 2004, after farms completed harvesting. Over 90% of lice recovered were Lepeophtheirus salmonis (Krøyer); therefore, the results of this paper refer largely to that species. The data were analysed using generalized additive models with explanatory variables for time, depth and station. Greatest densities of nauplii were recovered at stations adjacent to farms indicating that the local salmon farms were a likely source of larvae at times during the production cycle. There were significant temporal trends in larval densities and the stocking and harvesting of farms can possibly account for these increases and decreases, particularly at the start and at the end of the production cycle. The distribution of copepodids was more widespread than that of nauplii, indicating that the larvae can be transported several kilometres from the point of release.

Variação espacial e temporal da densidade da assembléia de microcrustacécos em diferentes sistemas da planície de inundação do alto rio Paraná (PR/MS-Brasil)

The present study evaluated the influence of water level fluctuations and the system type on the structure of planktonic microcrustacean assemblage, in different lagoons on the Upper Parana River floodplain. Sampling was performed in pelagic region from 15 lagoons associated with three rivers, during flood (February 1999) and dry (October 1999) periods. Forty nine cladoceran species and sixteen copepods species were identified. Null model ANOVA results did not show significant differences in microcrustacean densities among systems. Only B. hagmanni, B. deitersi and Calanoid nauplii densities were significantly different between periods. Differences between periods in each system and among systems in each hydrological period were not significant either. Thus, spatial differences were not superior in microcrustacean structuring. However, some temporal differences were observed for bosminids and Calanoid nauplii

Efeito da salinidade e do esgoto orgânico sobre a comunidade zooplanctônica, com ênfase nos copépodes, do estuário do rio Itanhaém, Estado de São Paulo

The objective of this work is to analyze the effects of salinity and wastewater on the zooplankton community of the Itanhaem river estuary, Sao Paulo state. Samples of zooplankton as well as physical and chemical variables of water were collected in four sites, located between the coastal line and the superior part of the estuary, including a secondary channel where wastewater is thrown without previous treatment. The samples were collected in low and high tide in winter and summer. Results showed that the estuary presents a temporal and spatial variation of physical and chemical characteristics, especially salinity, in function of the tide and seasonal variation of rain. The high values of salinity occurred in winter and high tide. Zooplankton community was adapted to the dynamic of salinity, and marine and estuarine species occurred in the low part of the estuary in winter. Although the Itanhaem river estuary has the same temporal and spatial dynamic of other estuaries, the values of salinity are low when compared with others located in the southern coast of Sao Paulo . Consequently, mainly oligohaline and fresh water species constitute the zooplankton community. These characteristics are due to the great drainage area of the Itanhaem river basin. The waste water modified physical and chemical characteristics of water that now presents higher concentrations of nutrients, higher values of suspended matter and lower concentrations of oxygen. It was observed a positive relation between the density of nauplii of copepods and organic pollution in this estuary

Preliminary results on settlement of the barnacles Tetraclita stalactifera and Chthamalus bisinuatus on a Brazilian tropical rocky shore under upwelling conditions

Summary The abundance of the larvae (nauplii and cyprids) and larval settlement of the barnacles Tetraclita stalactifera and Chthamalus bisinuatus were quantified on a rocky shore in the Arraial do Cabo region of Brazil from January to June 2000. This sampling period included times of spring/summer upwelling when water temperatures can fall from 24°C to 15°C. In the summer, densities of cyprids and settlement rates of both species were low, whereas densities of nauplii were high densities. By contrast, in autumn/winter, high densities of cyprids and high settlement rates were found, while densities of nauplii were lower than cyprids. These results may be related to higher water temperatures, which may accelerate larval metamorphosis, and/or due to winter storms that may increase transport to the shore. These results contrast with those from other upwelling regions where settlement is highest during spring/summer.

Effect of Environmental Factors on Development of Rotifer and Copepod Nauplii Populations in Sunshine BassMorone chrysops×M. saxatilisNursery Ponds without Fish

Knowledge of the effect of environmental factors on timing and production of zooplankton populations would enable sunshine bass Morone chrysops×M. saxatilis farmers to stock fry when live food is most available and thereby increase fry survival. Relationships of morning water temperature, morning and average daily air temperature, day length, number of rain days and daily rain fall, and dissolved oxygen concentrations to time required for rotifer and copepod nauplii populations to peak in freshly filled freshwater nursery ponds was determined. Relationships of the same independent variables to concentrations of rotifers and copepod nauplii at the peak were also determined. For rotifers, day length, dissolved oxygen, and water and air temperatures were highly correlated with time to the peak density, but not concentration of rotifers. Time required for copepod nauplii densities to peak was associated with rain events; whereas, nauplii concentration was related to day length, dissolved oxygen levels and, to a lesser extent, water and air temperatures. Regression equations of the independent variables had very low predictive value for rotifer or nauplii densities or time to reach initial peak nauplii populations. Regressions of day length, morning water temperature, morning and average daily air temperature had moderate values (r2 > 0.7) for predicting time to initial peak rotifer densities.

Prey, feeding rates, and asexual reproduction rates of the introduced oligohaline hydrozoan Moerisia lyonsi

Moerisia lyonsi Boulenger (Hydrozoa) medusae and benthic polyps were found at 0 to 5‰ salinity in the Choptank River subestuary of Chesapeake Bay, USA. This species was introduced to the bay at least 30 years before 1996. Medusae and polyps of M. lyonsi are very small and inconspicuous, and may occur widely, but unnoticed, in oligohaline waters of the Chesapeake Bay system and in other estuaries. Medusae consumed copepod nauplii and adults, but not barnacle nauplii, polychaete and ctenophore larvae or tintinnids, in laboratory experiments. Predation rates on copepods by medusae increased with increasing medusa diameter and prey densities. Feeding rates on copepod nauplii were higher than on adults and showed no saturation over the range of prey densities tested (1 to 64 prey l−1). By contrast, predation on copepod adults was maximum (1 copepod medusa−1 h−1) at 32 and 64 copepods l−1. Unexpectedly, M. lyonsi colonized mesocosms at the Horn Point Laboratory during the spring and summer in 4 years (1994 to 1997), and reached extremely high densities (up to 13.6 medusae l−1). Densities of copepod adults and nauplii were low when medusa densities were high, and estimated predation effects suggested that M. lyonsi predation limited copepod populations in the mesocosms. Polyps of M. lyonsi asexually produced both polyp buds and medusae. Rates of asexual reproduction increased with increasing prey availability, from an average total during a 38 d experiment of 9.5 buds polyp−1 when each polyp was fed 1 copepod d−1, to an average total of 146.7 buds polyp−1 when fed 8 copepods d−1. The maximum daily production measured was 8 polyp buds and 22 medusae polyp−1. The colonizing potential of this hydrozoan is great, given the high rates of asexual reproduction, fairly wide salinity tolerance, and existence of a cyst stage.

Distribution and Lipid Composition of Pandalus Shrimp Larvae in Relation to Hydrography in West Greenland Waters

The abundance and distribution of shrimp larvae were studied along four transects off West Greenland in June–July 1996. Zooplankton samples and vertical profiles of temperature, salinity, and fluorescence were obtained along the transects in order to relate larval distribution to hydrographical and biological characteristics. Eight species of shrimp larvae occurred in the samples; Pandalus montagui and Pandalus borealis were the most numerous constituting 61 and 29% of the larvae, respectively. Other species of shrimp larvae were, in declining order of abundance, Sabinea septemcarinata , Lebbeus groenlandicus, Spirontocaris spinus, Eualus galmardi, Pontophilus (norvegicus?), and Argis dentata. Pandalus shrimp larval density showed a significant positive association with mean fluorescence (5–80 m), but no association with mean temperature, or densities of copepod eggs and nauplii. However, most larvae were caught in water columns with temperatures and salinities of ~2°C. and ~33 psu, respectively. Abundance of P. montagui was negatively correlated with mean salinity and the proportion of P. montagui was higher in stations closest to the coast. Catches of P. montagui and P. borealis larvae were positively correlated (r = 0.729). Analysis for lipid class composition in P. montagui and P. borealis zoea stage 3 and 4 revealed that phospholipids were the most abundant lipid class (~80% of total lipid weight) followed by triacylglycerols (TAG) (10–15%), and wax esters (3–6%). TAG wet-weight ratios of P. montagui and P. borealis larvae were used as indices of feeding condition, and showed differences between larval species, zoeal stage, sampling station, and transect. In the same zoeal stage P. montagui larvae had higher TAG condition indices than P. borealis larvae suggesting that P. montagui may have a greater growth and survival potential. The TAG condition indices showed a significant negative association with fluorescence and indices of copepod productivity for stage 4 P. montagui larvae and no associations for P. borealis stage 3 and 4 larvae. Future studies should investigate lipid condition of the earliest stages of P. borealis and P. montagui larvae and establish trophic relationships (lipid nutrition) using food web tracer lipids. Such studies could be important to achieve better recruitment predictions for both species.