Calanoid Species Research Articles

Effects of formalin preservation on stable carbon and nitrogen isotope signatures in Calanoid copepods: implications for the use of Continuous Plankton Recorder Survey samples in stable isotope analyses

Preserved and archived organic material offers huge potential for the conduct of retrospective and long-term historical ecosystem reconstructions using stable isotope analyses, but because of isotopic exchange with preservatives the obtained values require validation. The Continuous Plankton Recorder (CPR) Survey is the most extensive long-term monitoring program for plankton communities worldwide and has utilised ships of opportunity to collect samples since 1931. To keep the samples intact for subsequent analysis, they are collected and preserved in formalin; however, previous studies have found that this may alter stable carbon and nitrogen isotope ratios in zooplankton. A maximum ~0.9‰ increase of δ(15) N and a time dependent maximum ~1.0‰ decrease of δ(13) C were observed when the copepod, Calanus helgolandicus, was experimentally exposed to two formalin preservatives for 12 months. Applying specific correction factors to δ(15) N and δ(13) C values for similarly preserved Calanoid species collected by the CPR Survey within 12 months of analysis may be appropriate to enable their use in stable isotope studies. The isotope values of samples stored frozen did not differ significantly from those of controls. Although the impact of formalin preservation was relatively small in this and other studies of marine zooplankton, changes in isotope signatures are not consistent across taxa, especially for δ(15) N, indicating that species-specific studies may be required.

Calanoida (Crustacea Copepoda) from the inland waters of Apulia (south-eastern Italy)

The currently available knowledge on biodiversity and species distribution of Italian fauna still presents some gaps to be filled, in particular in the southern part of the country. This study represents the first survey aimed at assessing the presence and distribution of Calanoida in inland waters of Apulia (south-eastern Italy). The research lasted five years and led to the mapping of 121 inland water bodies, most of which are characterized by temporary hydroperiods. Fifty-five of the sampled sites hosted at least one calanoid species, and 48 sites (among the 55 sites hosting Calanoida) are temporary water bodies. Thirteen calanoid species were detected in total; several of these are first records for Apulia and three species are new records for mainland Italy. The efficiency of the sampling effort was tested for both the entire Apulian territory and its main subareas, namely Gargano (in northern Apulia), and Salento (southern Apulia). Central Apulia showed the lowest species richness among the three sampled subareas. This is probably due to the scarcity of inland water bodies. Species composition of Apulian calanoid fauna was compared to the ones of the geographically close areas for which data are available: the other Italian faunal provinces (Alpine, Apennine, Padanian, Sardinian and Sicilian provinces) and the Balkans (Albania, Corfu, Croatia, Greece and Turkish Trace, Macedonia, Slovenia). Gargano and Salento showed a different assemblage of vicariant species but both the areas showed a remarkable presence of Mediterranean elements that, in fact, characterize the whole Apulian faunal province. The highest similarities for inland water calanoid fauna, which were observed between Gargano and the Apennine province, and between Salento and Sicily, are discussed, along with the total assessment of the whole Apulian calanoid fauna.

Automatic measurement of Acartia tonsa nauplii density, and estimation of stage distribution

Copepods are increasingly seen as an important feed in the culture of marine fish. Calanoid species such as Acartia tonsa have been studied for mass culture purposes. In this work, a plankton counter developed for automatic measurement of density in rotifer ( Brachionus plicatilis) cultures has been tested for Acartia nauplii. The plankton counter, after adaptation, can estimate both the size and density of the nauplii within reasonable margins of error. Size estimates were validated against measurements made by microscope, and density estimates against manual counts. The plankton counter makes it possible to automatically monitor metrics like hatching success, mortality and development rate in Acartia cultures, as well as monitoring of densities in larval first feeding tanks. The latter opens the opportunity for appetite based feeding of larvae. The area measurement can be used to estimate the biomass and the development stage of the nauplii.

Faunistical Overview of Calanoid Copepods (Crustacea) from Continental Waters of Ukraine

Faunistical Overview of Calanoid Copepods (Crustacea) from Continental Waters of Ukraine Faunistic overview together with updated checklist, comprising 38 species and 2 subspecies of calanoid copepods inhabiting fresh and brackish Ukrainian waters classified in three families and twelve genera is provided. The only freshwater calanoid species endemic to Ukraine is Speodiaptomus birsteini Borutzky, 1962, a stygobiont found once in an underground lake in the Skels'ka Cave (Crimean Peninsula). Two species, Hemidiaptomus (Hemidiaptomus) rylovi Charin, 1928 and S. birsteini are included as a threatened species in the Red Book of Ukraine. Dubious records and distribution patterns of some calanoid taxa are discussed. The calanoid fauna of Ukraine is compared with those of adjacent countries.

Spatial and temporal patterns in abundance and distribution of zooplankton in the Tanzanian waters of Lake Victoria

Zooplankton composition and abundance, and its spatial and temporal distribution patterns were investigated from September 2005 to October 2007 at 51 sampling stations at various depths in the near shore, intermediate, and offshore waters of Lake Victoria. Relative to near shore (54.86 ± 32.33 ind. l−1) and far offshore (38.63 ± 11.14 ind. l−1), the intermediate waters (109.56 ± 64.70 ind. l−1) had highest abundance of zooplankton. A total of 43 zooplankton species were encountered: of those 26 species were rotifers, with Brachionus angularis, Brachionus calyciflorus, and Asplanchna sp. as the most abundant species. There were 9 species of cladocerans, with Diaphanosoma excisum and Bosmina longirostris as the most abundant species. There were 7 cyclopoid species with Thermocyclops emini, Tropocyclops tenellus, and Thermocyclops neglectus as the most abundant species. Only one calanoid species, Thermodiaptomus galeboides was encountered. Cyclopoid copepods were the most abundant (76.5%) followed by calanoids (11.3%), rotifers (8%) and cladocerans (4.3%). The present findings contrast with earlier studies from the 1930s and 50s, but agree with many thereafter. There is change of zooplankton composition and abundance with a trend towards small sized species instead of the large. Increased eutrophications, pollution, and predation pressure from an increasing abundance of dagaa, juvenile perches, and reappearing haplochromines, among others, are responsible for the observed spatial and temporal variability in distribution and abundance patterns, and generally, change.

Mesozooplankton distribution in the Spermonde Archipelago (Indonesia, Sulawesi) with special reference to the Calanoida (Copepoda)

In September 2005 the mesozooplankton distribution, taxonomic composition and community structure were studied on four cross-shelf and one coastal transects in the Spermonde Archipelago off Makassar (SW Sulawesi). A total of 47 higher taxonomic groups and 89 calanoid copepod species were identified. Copepods outnumbered the other mesozooplankton taxa with 29 to 69%, increasing in importance towards the offshore stations. Appendicularians ranked second (16–24%) followed at the offshore stations by chaetognaths (4.5%) and, at shelf and coastal stations by echinoderm pluteus larvae (11–15%). Within the calanoids, species of the family Paracalanidae, especially Paracalanus cf. parvus, were dominant at all stations. Other abundant families were Temoridae (6.5–17%), Acartiidae (7.2%) and Pontellidae (6.2%) at shelf and coastal stations while Clausocalanidae (8.7%) and Calanidae (6.7) were more abundant at offshore stations. To investigate the mesozooplankton distribution the 25 stations were grouped into 3 geographical zones based on their topographical and hydrographical differences (coastal, shelf and offshore zone). Some higher zooplankton taxa and about half of the calanoid species occurred only in one or two categories. In general the abundant taxa were spread throughout the Archipelago. To investigate their distribution the abundance data were subjected to a multivariate discriminant function analysis (MDFA). The results revealed that the composition of the mesozooplankton community changed from the coastal zone with a high abundance of meroplankton and neritic copepod species to an offshore community with a higher abundance of holoplanktonic organisms and oceanic copepod species.

Life histories and seasonal dynamics of common boreal pelagic copepods (Crustacea, Copepoda) inhabiting an oligotrophic Fennoscandian lake

The annual seasonal abundance and spatial distribution of four widespread pelagic copepods, the Palaeartic calanoid Eudiaptomus gracilis, the cyclopoids Mesocyclops leuckarti and Thermocyclops oithonoides, and the Holartic Cyclops scutifer were investigated in Lake Gjerstadvann, an oligotrophic boreal lake. Important ecological traits such as life cycles, pelagic microhabitats and wintering strategies varied strongly between the investigated copepods, and influenced seasonal succession in the plankton community. Fish predation did not seem to affect copepod abundances, except perhaps the two lage-sized, less abundant species, the Palaeartic calanoid Heterocope saliens and the Holartic cyclopoid Cyclops abyssorum. Life cycles varied from one (C. scutifer) to three (M. leuckarti and E. gracilis) complete generations per year, primarily related to habitat temperatures. Wintering took place as late instars (C. scutifer, C. abyssorum) or cop V and adults (E. gracilis) in the plankton, late instars in profundal (T. oithonoides) or littoral (M. leuckarti) sediment diapause, and embryonic diapause in sediment egg bank (H. saliens). C. scutifer and C. abyssorum exhibited delayed development in the profundal waters during winter, which could be characterised as so-called "active diapause". C. scutifer, T. oithonoides, and C. abyssorum in Lake Gjerstadvann were probably negatively affected by acidified waters. M. leuckarti seemed to be the most acid-tolerant of these species being able to endure pH slightly below 5.0, whereas T. oithonoides was usually absent at such pH levels. The calanoid species H. saliens and E. gracilis were extremely tolerant towards acidic environments. The yearly differences in population abundance as indicated by the fluctuations in the diapausing populations were probably due to environmental variations in water chemistry occurring during the most vulnerable ontogenetic stages, i.e., eggs and nauplii. Even if the pelagic ecosystem in boreal and oligotrophic lakes may appear homogeneous, a whole array of life histories and dormancy patterns has evolved among copepods.

Occurrence and Interannual Abundance Variation of Glacial Relict Calanoids Limnocalanus macrurus and Eurytemora lacustris in Lithuanian Lakes

In Lithuania, permanent populations of glacial relict calanoids Limnocalanus macrurus and Eurytemora lacustris inhabit lakes of 25–48 and 38–60 m maximal depth, correspondingly. There are 45 lakes, which due to their morphometric characteristics may be considered to be potentially suitable for these calanoid species. For these lakes, there are historical records of the presence of L. macrurus in 13 lakes and that of E. lacustris in seven lakes. In the current survey, the glacial relict calanoid L. macrurus was found in 12 lakes, including one new locality, while another calanoid E. lacustris was present in five lakes. The habitat-specific interannual abundance variation in populations of L. macrurus was higher than that in E. lacustris suggesting a greater sensitivity of the former species to oxygen conditions in the lake hypolimnion. Although L. macrurus is more widespread throughout Lithuanian lakes in comparison to E. lacustris, the probability of its local population’s extinction in lakes is higher.

Mesoscale structure of copepod assemblages in the coastal transition zone and oceanic waters off central-southern Chile

In the Humboldt Current System, the region off central-southern Chile has relatively high eddy kinetic energy, generating an extensive coastal transition zone (∼600 km offshore) in which coastally derived eddies are recurrent features. This energy might promote strong exchanges of water, biogeochemical properties, and plankton between the coastal upwelling band and the adjacent oceanic zone. In this study, the mesoscale structure of epipelagic copepod assemblages and its relationship to environmental variability and the eddy field in the coastal transition zone and oceanic areas off Concepción (34–39°S, 73–84°W) were investigated. Zooplankton samples were collected during cruises of opportunity carried out during the 2006 coastal upwelling season and the oceanographic conditions were derived from satellite data on sea surface height, temperature, and chlorophyll a. The use of cluster analyses and indicator species revealed two main copepod assemblages: (i) species with a mainly coastal distribution, the maximum in total abundance being found nearshore and (ii) species with a mainly oceanic distribution (beyond ∼500 km from the coast), where a secondary maximum was observed. Both types of assemblages, however, included species widely distributed in the coastal transition zone. An ordination analysis identified sea surface temperature and chlorophyll a as the main factors affecting the distribution of most species and the clustering of stations resembled the distribution of these variables. Some of the large calanoid species that are common in shelf waters were more abundant within nearshore eddies rich in chlorophyll a and other cyclonic eddies far offshore; however, the eddy field alone did not explain the copepod mesoscale distribution. Altogether, the wide distribution of shelf/slope copepod species in this region suggests that physical and biological mechanisms might be acting to extend the productive area of the coastal upwelling zone.

Modelling the effect of constant and fluctuating food supply on egg production rates of Acartia grani

A mathematical model of the individual budget of a spawning female of the copepod Acartia grani (Sars) has been used to simulate the time-scale of egg production over various external forcings (or inputs) of food fluctuation conditions. The budget matter in the body of the copepod females is distributed through four compartments: the whole digestive tract (globally named as gut), the hemolymph (which include the body fluid with available nutriments for the organs), the structural body weight, and the gonad. This small calanoid species does not carry lipid reserves but cumulate some labile reserves in its body, according to food availability. The model results show how the continuous spawning varies with food fluctuations, and suggest the mechanisms inducing the delay of response to starvation by using the metabolic reserves. Three different patterns in egg production response are observed: food fluctuations with frequencies below 12 h have no effect on egg production; food fluctuations of 12 h to 5 days induce synchronous egg production fluctuations; beyond 5 days the strong physiological changes induced by long starvation durations create delays in the responses to food replenishment. The available data of cultivated cohorts under laboratory conditions are used to validate the model. The properties underlined by the model, in particular its weak capacity to respond to starvation, allow explaining A. grani distribution in specific habitats. Different experimental protocols for complementary experiments are proposed to complete the model validation in other forcing conditions.

Spatial and Temporal Distribution of Zooplankton Communities of Coastal Marine Waters Receiving Different Human Activities (Fish and Pearl Oyster Farmings)

Seasonal changes of zooplankton communities were monitored at two coastal marine areas, Uchiumi and Fukuura Bays located at the Uwa Sea, east side of Bungo Channel. The two sites are close to each other (c.a. 20 km) with similar habitat environments, but receive different environmental stresses from aquaculture activities, pearl oyster farming for Uchiumi Bay and fish farming for Fukuura Bay. Since both bays have no inflowing river and small populations in the catchment, the impacts of different aquaculture activities on meso- and microzooplankton communities were compared. As results, Fukuura Bay showed higher ammonium and phosphate concentrations, suggesting that fish farming could accelerate eutrophication more seriously. The dominant species of mesozooplankton were similar at the two sampling sites with dominance of small coastal calanoid copepod, Paracalanus spp., but the abundances of larger calanoid species, Calanidae, Eucalanidae, Temoridae and Acartiidae, were markedly higher in Uchiumi Bay. Small cyclopoid copepods, Oithona spp. were abundant at both sites, but the densities varied seasonally, and often more abundant at Fukuura Bay. The abundances of microzooplankton including rotifers and small Oithona copepodids were higher at Fukuura Bay. Results suggest that fish farms accompanying discharge of nutrients from additional food supply for fish may seriously modify zooplankton community structure by decreasing the abundance of mesozooplankton through accelerating the eutrophication of coastal waters.

Rapid biogeographical plankton shifts in the North Atlantic Ocean

AbstractLarge‐scale biogeographical changes in the biodiversity of a key zooplankton group (calanoid copepods) were detected in the north‐eastern part of the North Atlantic Ocean and its adjacent seas over the period 1960–1999. These findings provided key empirical evidence for climate change impacts on marine ecosystems at the regional to oceanic scale. Since 1999, global temperatures have continued to rise in the region. Here, we extend the analysis to the period 1958–2005 using all calanoid copepod species assemblages (nine species assemblages based on an analysis including a total of 108 calanoid species or taxa) and show that this phenomenon has been reinforced in all regions. Our study reveals that the biodiversity of calanoid copepods are responding quickly to sea surface temperature (SST) rise by moving geographically northward at a rapid rate up to about 23.16 km yr−1. Our analysis suggests that nearly half of the increase in sea temperature in the northeast Atlantic and adjacent seas is related to global temperature rises (46.35% of the total variance of temperature) while changes in both natural modes of atmospheric and oceanic circulation explain 26.45% of the total variance of temperature. Although some SST isotherms have moved northwards by an average rate of up to 21.75 km yr−1 (e.g. the North Sea), their movement cannot fully quantify all species assemblage shifts. Furthermore, the observed rates of biogeographical movements are far greater than those observed in the terrestrial realm. Here, we discuss the processes that may explain such a discrepancy and suggest that the differences are mainly explained by the fluid nature of the pelagic domain, the life cycle of the zooplankton and the lesser anthropogenic influence (e.g. exploitation, habitat fragmentation) on these organisms. We also hypothesize that despite changes in the path and intensity of the oceanic currents that may modify quickly and greatly pelagic zooplankton species, these organisms may reflect better the current impact of climate warming on ecosystems as terrestrial organisms are likely to significantly lag the current impact of climate change.

An all-conquering ecological journey: from the sea, calanoid copepods mastered brackish, fresh, and athalassic saline waters

Although it is commonly acknowledged that calanoid copepods inhabiting fresh water evolved from marine ancestors via the brackish water of estuaries, it is less well appreciated that a restricted number of species with freshwater affinities have conquered athalassic saline waters. The global importance of the latter habitat has been under-estimated and, with climate change and human population growth, it is expanding at the expense of fresh waters. Considering Australia, South America and the Holarctic, at least seven halobiontic calanoid species occur in athalassic saline waters (the situation in Africa is not visited). In Australian inland-water Centropagidae, there is a high degree of congruence between the ecological trend in habitat occupancy (marine through brackish and fresh to athalassic saline waters) and the assumed evolutionary trend towards reduction in the setation and segmentation of swimming legs. The validity of the inference by Adamowicz et al. (Biological Journal of the Linnean Society of London 90: 279–292, 2007a) that a hypothesis of oligomerization was not supported as the mode of evolution of South American non-marine Centropagidae is criticized for reasons of inadequate character sampling. The phylogeny, biogeography and osmo-regulatory physiology of Southern Hemisphere inland-water centropagids are reviewed in some detail. Calanoids have mastered a significant portion of the total salinity range for athalassic saline waters (3 to 300+ g l−1) but, unlike brine shrimps, they have not evolved a mechanism for hypo-osmotic regulation and do not tolerate saturated or near-saturated brines.

Temperature effects on fecundity, development and survival of the benthopelagic calanoid copepod, Pseudocyclops xiphophorus

The shallow-living, benthopelagic copepod species Pseudocyclops xiphophorus Wells (R Soc Edimburg 67:1967), collected over a yearly cycle from the fouling material in the brackish water Lake Faro (North-eastern Sicily), showed marked seasonal fluctuations in population abundances, with maximum numbers recorded in autumn. Highest in situ egg production rates coincided with periods of low adult and juvenile densities and vice versa, except in autumn when peaks in egg production and adult population densities were coincident. In this period, mean daily egg production rates reached a maximum of 4–5 eggs per female, when surface water temperature was 17–18°C. Egg production rates declined drastically in winter and were completely arrested when surface temperatures dropped to 10–12°C. In March, daily egg production rates began to increase again with an increase in ambient temperatures, reaching a maximum at the end of August. In the laboratory, as in the field, mean daily egg production rates were positively correlated with temperature, with values ranging from 2.2 ± 0.3 (16°C) to 8.9 ± 2.6 (30°C) (mean ± S.D.) eggs per female per day. At 32°C, P. xiphophorus females survived but did not reproduce. At 34°C, all specimens died after a few days. In terms of total egg production for the entire female lifespan, maximum values occurred at 16°C and minimum at 24°C. Temperature also dramatically affected female life span, which was shorter at higher temperatures. Development time of eggs decreased with increasing temperature, as also development time from egg to adulthood. Remating was necessary for the continued production of fertile eggs at 16°C because female life span was longer. The unique egg-laying behaviour in this species may ensure higher survival rates of egg stages compared to free-spawning and egg-carrying calanoid species. After releasing the egg pair, the female swims over the eggs with a rotatory motion, secreting a substance which facilitates the adhesion of the eggs to the bottom; she then continues to swim over the eggs until they are attached. Although egg production rates in this species are low compared to other pelagic copepods, they are within the range of values reported for egg-carrying species. The greater fecundity at higher temperatures compared to other subtemperate species indicates that the species is well adapted to the higher temperatures of coastal lagoons and brackish water lakes where it contributes to the biofouling community.

The plankton community of Lake Matano: factors regulating plankton composition and relative abundance in an ancient, tropical lake of Indonesia

Recent evidence reveals that food webs within the Malili Lakes, Sulawesi, Indonesia, support community assemblages that are made up primarily of endemic species. It has been suggested that many of the species radiations, as well as the paucity of cosmopolitan species in the lakes, are related to resource limitation. In order to substantiate the possibility that resource limitation is playing such an important role, a study of the phytoplankton and zooplankton communities of Lake Matano was implemented between 2000 and 2004. We determined species diversity, relative abundances, size ranges, and total biomass for the phytoplankton and zooplankton, including the distribution of ovigerous individuals throughout the epilimnion of Lake Matano in three field seasons. The phytoplankton community exhibited very low biomass (<15 μg l−1) and species richness was depressed. The zooplankton assemblage was also limited in biomass (2.5 mg l−1) and consisted only of three taxa including the endemic calanoid Eodiaptomus wolterecki var. matanensis, the endemic cyclopoid, Tropocyclops matanensis and the rotifer Horaella brehmi. Zooplankton were very small (<600 lm body length), and spatial habitat partitioning was observed, with Tropocylops being confined to below 80 m, while rotifer and calanoid species were consistently observed above 80 m. Less than 0.1% of the calanoid copepods in each year were egg-bearing, suggesting very low population turnover rates. It was concluded that chemical factors as opposed to physical or biological processes were regulating the observed very low standing crops of phytoplankton which in turn supports a very minimal zooplankton community restricted in both species composition and abundance. As chemical factors are a function of the catchment basin of Lake Matano, it is predicted that resource limitation has long played an important role in shaping the unique endemic assemblages currently observed in the food web of the lake.

Grazing impact of the copepod community in the Oyashio region of the western subarctic Pacific Ocean

The role of copepod grazing on the ecosystem dynamics in the Oyashio region, western subarctic Pacific was investigated during six cruises from June 2001 to June 2002. In situ grazing rates of the copepod community (CGR) were measured by the gut fluorescence method in respect to developmental stages of dominant species. In terms of biomass, more than 80% of the copepod community was dominated by six large calanoid species ( Neocalanus cristatus, Neocalanus flemingeri, Neocalanus plumchrus, Eucalanus bungii, Metridia pacifica and Metridia okhotensis) throughout the year. Resulting from the observed pattern of the interzonal migrating copepods, the CGR in the Oyashio region was divided into three phases, i.e. spring (bloom), summer (post-bloom) and autumn–winter phase. During the spring bloom, late copepodites of the interzonal migrating species, N. cristatus, N. flemingeri and E. bungii appeared in the surface layer (0–50 m) to consume the production of the bloom, resulting in a high grazing rate of the copepod community (7.9 mg Chl m −2 d −1), though its impact on phytoplankton community was low due to the high primary productivity. During the post-bloom period, although the copepod community which was dominated by N. cristatus, N. plumchrus, M. pacifica and newly recruited E. bungii still maintained a high biomass, the CGR was generally lower (1.8–2.6 mg Chl m −2 d −1 for June and August 2001), probably due to the lower availability of phytoplankton. Nevertheless, the highest CGR was also observed during this period (10.5 mg Chl m −2 d −1 in June 2002). The high CGR on autotrophic carbon accounted for 69% of the primary production, suggesting that the copepod community in the Oyashio region potentially terminates the phytoplankton bloom. Abundant occurrence of young E. bungii, which is a characteristic phenomenon in the Oyashio region, was largely responsible for the high grazing pressure in June 2002 suggesting that success of reproduction, growth, and survival in E. bungii during the spring bloom is an important factor in controlling phytoplankton abundance during the post-bloom season. During autumn and winter, CGR was the lowest in the year (0.29–0.38 mg Chl. m −2 d −1) due to the disappearance of the interzonal migrating copepods from the surface layer. Diel migrant M. pacifica was the most important grazer during this period. The annual ingestion of the copepod community is estimated as 37.7 gC m −2 on autotrophic carbon (converted using C:Chl ratio of 30) or 137.9 gC m −2 on suspended particles (using C:Chl ratio of in situ value, 58–191), accounting for 13% and 46% of annual primary production, respectively. This study confirms that copepod grazing is an important pathway in carbon flow in the Oyashio region and in particular their role in the phytoplankton dynamics is significant for the termination of the spring bloom.

Escape reaction performance of myelinated and non-myelinated calanoid copepods

Calanoid copepods from seven families in three superfamilies were exposed to a controlled near-field hydrodynamic stimulus and their escape reactions were recorded using high-speed videographic techniques. Copepod species have two distinct mechanisms for increasing conduction speed of neural signals: larger diameter nerve axons and insulated axons, i.e., myelination. Myelinated axons have been found in certain species of the more recently-evolved calanoid superfamilies. Copepod representatives from these superfamilies were expected to have shorter response latencies than species from more ancestral superfamilies due to the increased conduction speed of nerve impulses in myelinated neurons. Using frame-by-frame playback and computerized motion analysis techniques, response latency, jump speed, and acceleration were measured. Kinetic performance of copepods was highly variable, with mean escape speeds ranging between 100–250 mm s − 1 and accelerations of 9–230 m s − 2 . Minimum behavioral response latencies of 2 ms were recorded for both myelinated and non-myelinated calanoids. There was no significant difference between the response latencies of copepods from the myelinated and non-myelinated superfamilies. Furthermore, no relationships were found between copepod latency and size for either myelinated or non-myelinated species. Previous research may suggest that myelin may shorten the response latencies of certain calanoid species. However, our results show that non-myelinated copepods are also capable of responding rapidly, within as few as 2 ms, to hydrodynamic stimuli and produce similar kinetic performance to myelinated species. The main advantage of myelination over giant nerve axons is their more efficient transfer of nerve impulses resulting in a metabolic energy savings. Although this energetic reward would be important for copepods in food-limited environments, for coastal copepods, in food-rich habitats, either mechanism is a viable solution.

Growth and development of Pseudocalanus spp. in the northern Gulf of Alaska

Pseudocalanus are the numerically dominant calanoid species in coastal subarctic Pacific waters. We examined their juvenile growth rates, and explored their relationships to temperature, chlorophyll a and body size for Pseudocalanus spp. from 2002 to 2004 in the northern Gulf of Alaska. Generally, the monthly mean growth rates increased from 0.049 ± 0.007(SE) day −1 in March to 0.095 ± 0.016 day −1 in August, declining slightly to 0.074 ± 0.009 day −1 in October. Typically, growth rates at most stations were around 0.05 day −1 , with no consistent or significant pattern between stations. After standardization to 5 and 10°C, the mean growth rates were 0.045 ± 0.002 day −1 and 0.075 ± 0.004 day −1 respectively, with growth rate decreasing with increasing development stage. Unlike other local calanoid copepod species, Pseudocalanus species tend to be more temperature-dependent than food-dependent, with composite statistical models describing at most 30% of the observed variability in growth rate. Interestingly, development time was comparable to other co-occurring calanoid copepods; however, growth rates of Pseudocalanus spp. were considerably lower. We demonstrate this with a new multi-species model that describes the growth rates of other egg-scattering copepods in this ecosystem, but to which Pseudocalanus does not fit. Thus, the egg-carrying Pseudocalanus species appear to employ a life history strategy optimized for slow growth at low chlorophyll that keeps individuals relatively small, and may therefore reduce visual predation upon them.

Composition and community structure of zooplankton in the sea ice-covered western Weddell Sea in spring 2004—with emphasis on calanoid copepods

The mesozooplankton community, with special emphasis on calanoid copepods, was studied with respect to its species composition, abundance, vertical distribution and developmental structure during the “Ice Station POLarstern” (ISPOL) expedition to the ice-covered western Weddell Sea. Stratified zooplankton tows were carried out nine times between 1 December 2004 and 2 January 2005 with a multiple opening–closing net between 0 and 1000 m depth. Copepods were by far the most abundant taxon, contributing more than 94% of the total mesozooplankton. Numerical dominants were cyclopoid copepods, mostly Oncaea spp. A total of 66 calanoid copepod species were identified, but the calanoid copepod community was characterised by the dominance of only a few species. The most numerous species was Microcalanus pygmaeus, which comprised on average 70% of all calanoids. Calanoides acutus and Metridia gerlachei represented other abundant calanoid species contributing an average of 8% and 7%, respectively. All other species comprised less than 3%. The temporal changes in the abundance and population structure of M. pygmaeus and M. gerlachei were small while a shift in the stage frequency distribution of C. acutus was observed during the study: copepodite stage IV (C IV) dominated the C. acutus population with 48–50% during the first week of December, while C V comprised 48% in late December. C I and C II of C. acutus were absent in the samples, and males occurred only in very low numbers in greater depths. In M. gerlachei, C I was not found, whereas all developmental stages of M. pygmaeus occurred throughout the study. All three species showed migratory behaviour, and they occurred in upper water layers towards the end of the investigation. This vertical ascent was most pronounced in C. acutus and relatively weak in the other two species. In M. pygmaeus and M. gerlachei, copepodids were responsible for the upward migration in late December, while the vertical distribution of adults did not change. In C. acutus, all abundant developmental stages (C IV, C V and females) ascended to upper water layers. Almost exclusively (93%) medium- and semi-ripe females of C. acutus and M. gerlachei were found, and only 3–4% of the ovaries were ripe. The absence of C I and the low number of ripe females indicate that the main reproductive period had not started in C. acutus and M. gerlachei until the end of our study in early January. In contrast, the high portion of C I and C II of M. pygmaeus suggests that reproduction of this species had started in October–November and hence before the onset of the phytoplankton bloom in the water. The community structure did not differ between stations with one exception on 26 December, when the station was strongly influenced by the continental shelf.

A Faunistic Study on the Brackish-water Calanoid Copepods from South Korea

Eight calanoid species of 4 genera in 4 families are reported from the various brackish waters such as estuaries, brackish-water lakes, and coastal marshes in South Korea. Among them, Eurytemora affinis (Poppe) and Acartia (Acanthacartia) tsuensis Ito are newly added to Korean copepod fauna. Collection data, brief descriptions, illustrations and distribution maps for the eight species are prepared. A key to the genera and species of the brackish-water calanoids from Korea is also presented.