Copepod Calanoides Acutus Research Articles

Thysanoessa macrura in the southern Kerguelen region: Population dynamics and biomass

Thysanoessa macrura is well adapted to the strong seasonality of the Southern Ocean. A flexible diet, large lipid reserves and a winter reproductive period provide T. macrura with the ability to capitalise on the pulses of primary and secondary reproduction in spring and summer. The population dynamics of T. macrura were examined over the southern Kerguelen Plateau region as part of a large-scale ecosystem assessment. Larval stages were present in high abundances, exceeding 4000 Ind. 1000 m−3, with a peak in early furcilia (FI − FIV) and lower abundances of calyptopis stages (CI − CIII) indicating the end of a prolonged spawning period. High abundances of T. macrura were recorded throughout the entire study region, although they tended to be highest over the southern extent of the Banzare Bank and Princess Elizabeth Trough. This maximum appeared to be driven by the presence of the copepod Calanoides acutus, a dominant prey source. The first biomass estimates of T. macrura were determined for the region using length-frequency and abundance distributions. A mean biomass of 1.66 mg m−3 (wet weight) was calculated for the region, however localised biomass over the southern tip of the Banzare Bank exceeded 9 mg m−3 in the upper 200 m of the water column. The high biomass of T. macrura highlights their significance as an energy-rich resource for larger predators, inferring they play a currently underappreciated role in pelagic food-webs of the Southern Ocean.

Position-resolved determination of trace elements in mandibular gnathobases of the Antarctic copepod Calanoides acutus using a multimethod approach

Previous studies have revealed silica formation in the teeth of mandibular gnathobases of copepods while significant amounts of zinc and copper are present, which might improve mechanical stability of the teeth and represent an adaptation to compact food particles. The present study aimed at analysing the distribution and concentration of trace elements in the mandibular gnathobases of females of the Antarctic copepod species Calanoides acutus. Because of the low overall masses of few micrograms per specimen the application of a combination of position-resolved micro-beam techniques was necessary and micro-particle-induced X-ray emission spectrometry and laser ablation inductively coupled plasma mass spectrometry were used to determine Ba, Br, Ca, Cl, Cu, Fe, K, Mg, Na, Ni, P, S, Si and Zn in the samples with μm to sub-μm resolution. Calibration strategies were optimised to fit for the carbonate matrix. The analyses revealed a distinct enrichment of Br, Ca, Fe, K, S, Si and Zn in the teeth of the gnathobases.

Early is better: seasonal egg fitness and timing of reproduction in a zooplankton life‐history model

Timing of reproduction influences future prospects of offspring and therefore the reproductive value of parents. Early offspring are often more valuable than later ones when food availability and predation risk fluctuate seasonally. Marine zooplankton have evolved a diversity of life history strategies in response to seasonality. We present a state‐dependent life history model for the annual and herbivorous high‐latitude copepodCalanoides acutus. Individuals are characterised by four states; developmental stage, structural size, energy reserves and vertical location. There are two habitats, a surface habitat with seasonal predation risk and food availability, and a safer deep habitat with no food and low metabolism (diapause). Optimal life histories (diapause and energy allocation strategies) are found by dynamic programming. Seasonal egg fitness (reproductive value) emerges from the model and peak values are typically before the feeding season. Disentangling the fitness components, we conclude that seasonality in egg fitness is caused both by environmental seasonality in food and predation risk and by time‐constraints on development and diapause preparation. Realised egg production, as predicted from population simulations, does not match the seasonal peak in offspring fitness but is delayed relative to peak egg fitness. We term this an ‘internal life history mismatch’ as constraints and tradeoffs cause sub‐optimal birth dates for most eggs whereas mothers maximise their reproductive value by high number of eggs rather than few and optimally timed eggs. The earliest eggs have a disproportionately high contribution to population recruitment, emphasising the importance of early eggs and the need to understand seasonal patterns in offspring fitness.

Plankton community structure and variability in the Scotia Sea: austral summer 2003

Plankton community structure in the Scotia Sea was investigated during January/early February 2003 based on phytoplankton cell counts from 20 m depth and mesozooplankton counts from 0 to 400 m net hauls. Cluster analysis and multi-dimensional scaling revealed 4 major groups of stations within each ordination that broadly corresponded geographically. A grouping of stations to the east of the Antarctic Peninsula was characterised by low phytoplankton cell counts. The corresponding grouping of stations in the mesozooplankton data were characterised by low abundance, overwintered state of many species, low egg production rates, and low carbon mass of copepod instars. In contrast, groupings of stations in the northern part of the Scotia Sea were characterised as chlorophyll and mesozooplankton rich, and the summer generation was well advanced. Latitude was most strongly correlated with mesozooplankton community pattern (rank correlation ρ = 0.608), whereas surface chlorophyll a was a weaker correlate (ρ = 0.344) but along with measures of sizefractioned chlorophyll contributed towards explaining variation in species stages carbon mass and egg production rates. Additional hauls to 1000 m with an LHPR indicated copepod populations were broadly in an overwintered state in the south of the region, whereas to the north of South Georgia recruitment had been completed and some species were undergoing a seasonal descent. A comparison with January/February 2000 revealed higher abundances of krill larvae throughout the Scotia Sea in 2000 as well as a more advanced generation of the copepod Calanoides acutus. Ice cover during the 2 years differed considerably; in 2000 the position of the summer ice edge broadly accorded with the 25 yr average, whereas in 2003 the ice edge lay much further north than usual. We suggest that the timing of ice retreat influenced the timing of reproduction with the late retreat in 2003 causing delayed reproduction and reduced population sizes.

Relative production of Calanoides acutus (Copepoda: Calanoida) and Euphausia superba (Antarctic krill) at South Georgia, and its implications at wider scales

Antarctic krill are often described as the major species in Southern Ocean food webs, but there have been no direct site-specific comparisons between their production and that of copepods that dominate mesozooplankton biomass. Here, we compare biomass, growth and production of Euphausia superba (Antarctic krill) and the copepod Calanoides acutus at South Georgia, in the Atlantic sector of the Southern Ocean. Average acoustically derived krill biomass across the 5 study years was 2.6 g C m–2, 4 to 5 times that of Stages CIV and CV of C. acutus. Mean length of krill was 41 ± 4 mm, and the average growth rate was 0.10 mm d–1, giving an average mass-specific growth rate of 0.0084 d–1. This equated to a daily gross production of krill of 0.022 g C m–2 d–1. Gross production of Stages CIV and CV of C. acutus was similar, around 0.026 g C m–2 d–1. These stages of C. acutus represent about 25% of the total copepod biomass around South Georgia, so total copepod production here may exceed that of krill by a factor of 4 during the productive summer months. Biomass of copepods and krill in other parts of the Southern Ocean differ by similar orders of magnitude, whilst growth rates are likely to remain within the range measured in this study. Therefore, our finding has relevance outside the local South Georgia system. All of the krill production is likely to be rapidly consumed by higher predators within the surface layers, whilst it is estimated that around 17% of copepod production may be sequestered at depth during winter diapause.

Bioaccumulation of trace metals in the copepod Calanoides acutus from the Weddell Sea (Antarctica): comparison of two-compartment and hyperbolic toxicokinetic models

Bioaccumulation of Cd, Co, Cu, Ni, Pb and Zn in the Antarctic calanoid copepod Calanoides acutus (Giesbrecht, 1902) was investigated during a cruise of RV ‘Polarstern’ to the Weddell Sea. Main goals were to provide information on accumulation strategies of the organisms tested and to verify toxicokinetic models as a predictive tool. Except for Cd, the organisms accumulated metals upon exposure. It was possible to estimate significant model parameters of two-compartment and hyperbolic models. These models were successfully verified in a second toxicokinetic uptake study. The model verification was extended in a third uptake study with increasing external metal dosing. We found a linear increase of net uptake with external waterborne metal exposures up to 80 μg Pb l −1, with excellent predictions of the two-compartment model. For Co both models give reasonable predictions up to 20 μg Co l −1. Regarding Cu, Ni and Zn only hyperbolic model predictions were in good agreement with measured values up to 150 μg Cu l −1, 80 μg Ni l −1 and 290 μg Zn l −1. Due to a decrease of Cd body burden in the experiments, only the hyperbolic model was applicable, leading to reliable predictions up to 20 μg Cd l −1. These concentrations largely determine the range for which these models may serve as a predictive tool.

Complete trophic segregation between South Georgian and common diving petrels during breeding at Iles Kerguelen

The food and feeding ecology of the 2 closely related and sympatric species of diving petrels Pelecanoides georgicus and P. urinatrix was investigated over 3 consecutive summers at Iles Kerguelen, southern Indian Ocean, where they breed in large numbers. The 2 species fed consistently on different crustacean prey during the 3 yr, the diet of P. georgicus being dominated by the euphausiid Thysanoessa sp. (50% of the number of prey and 81% of the reconstituted mass) and the copepod Calanoides acutus (45 and 10%, respectively), and that of P. urinatrix by the hyperiid Themisto gaudichaudii (61 and 91%, respectively) and the copepod Paraeuchaeta antarctica (21 and 9%, respectively). Chicks of P. georgicus were fed less frequently (on 81 vs 97% of nights, respec- tively) with more digested prey items than chicks of P. urinatrix. This, together with visual observa- tions at sea and the known biogeography of their prey, shows a complete horizontal spatial segrega- tion between the 2 species of diving petrels, with P. urinatrix foraging in coastal waters in the close vicinity of their colonies and P. georgicus in more offshore waters. Maximum depth gauges indicate an incomplete vertical segregation in the water, P. georgicus reaching on average depths closer to the surface than P. urinatrix (26 vs 33 m, respectively). The stable-carbon and -nitrogen isotopic composi- tion of chick food and chick feathers differed between the 2 species, thus emphasising the segregation at sea during the breeding period when adult birds are central-place foragers. The stable isotopic com- position (δ 13 C and δ 15 N) of adult feathers were, however, identical in both species, indicating no trophic segregation during the moulting (inter-breeding) period when birds feed in offshore waters.

Chemical composition of antarctic zooplankton during austral fall and winter

Water level, ash content, proximate (protein, lipid, carbohydrate and chitin) and elemental (carbon and nitrogen) composition were analyzed in twentythree species of Antarctic Zooplankton collected during the austral fall (1986) and winter (1988) from the Scotia/Weddell Sea region. Extremes in water level, ash content and organic components were typified by copepods and gelatinous forms. Ostracods and polychaetes were generally similar in composition to copepods, being only slightly higher in water level and ash content. Chaetognaths exhibited a composition intermediate in character with some components similar in value to that shown by crustaceans (i.e. protein) while other components were more in the range of values seen in gelatinous forms (i.e. water level and ash content). Protein was the major proximate component and measured values (as % Afdw) were fairly uniform among non-gelatinous species (x=33.9±6.9). Lipid levels were variable, with high values (>30% AFDW) only found for the copepods Calanoides acutus, Calanus propinquus and Euchaeta antarctica. Carbohydrate values were low in all species examined. Chitin was measured in crustacean species only. With the exception of C. acutus (x=2.5% AFDW chitin), values were similar among species with mean values being slightly higher in fall (x=11.8±2.5) than in winter (x=6.7±1.8). Among non-gelatinous species, the ratio of carbon to nitrogen was positively correlated with the lipid to protein ratio, underscoring the compositional association between elemental and proximate components in these groups. In gelatinous species, the relationship between carbon:nitrogen and lipid:protein was inconsistent and less pronounced. Caloric content was estimated from recovered organic matter for nongelatinous species. As a function of wet weight and dry weight, values reflected differences in water level and ash content among individual species. As a function of ashfree dry weight, values were similar among all species (x=3.6±0.9 kcal/g).

Physiological characteristics of the antarctic copepod Calanoides acutus during late summer in the Weddell Sea

Physiological characteristics of the antarctic copepod Calanoides acutus during late summer in the Weddell Sea

Mesoscale distribution of zooplankton around South Georgia

A net sampling survey was conducted around the island of South Georgia in the austral summer 1981/1982 and again in winter 1983. This paper uses Principal Components Analysis to elucidate the mesoscale features of zooplankton distribution within the two survey grids. During both surveys the major contrast was between the plankton of the shelf and the surrounding ocean. However, within the oceanic part of each grid, localized areas of warmer water were inhabited by a fauna characteristics of warmer latitudes to the north. The biological and oceanographic evidence suggests that areas represents core rings or similar intrusions from north of the Polar Front. Not all of the characteristic warm- and cold-water species showed a clear correlation with water origin. For example, the swarming behaviour of Euphausia superba limited its usefulness as a mesoscale tracer. Likewise, the distribution of the Antarctic copepod Calanoides acutus was poorly related to water temperature during the summer survey because the timing of sampling coincided with its annual spawning cycle. Large-scale movement of oceanic fronts has already been identified as being important in dictating overall species composition around the island, but at a smaller scale these intrusions of warmer water may be an important intermediary mechanism of community advection into the area.