Kinematic and Dynamic Scaling of Copepod Swimming

Calanoid copepods have two swimming gaits, namely cruise swimming that is propelled by the beating of the cephalic feeding appendages and short-lasting jumps that are propelled by the power strokes of the four or five pairs of thoracal swimming legs. The latter may be 100 times faster than the former, and the required forces and power production are consequently much larger. Here, we estimated the magnitude and size scaling of swimming speed, leg beat frequency, forces, power requirements, and energetics of these two propulsion modes. We used data from the literature together with new data to estimate forces by two different approaches in 37 species of calanoid copepods: the direct measurement of forces produced by copepods attached to a tensiometer and the indirect estimation of forces from swimming speed or acceleration in combination with experimentally estimated drag coefficients. Depending on the approach, we found that the propulsive forces, both for cruise swimming and escape jumps, scaled with prosome length (L) to a power between 2 and 3. We further found that power requirements scales for both type of swimming as L3. Finally, we found that the cost of transportation (i.e., calories per unit body mass and distance transported) was higher for swimming-by-jumping than for cruise swimming by a factor of 7 for large copepods but only a factor of 3 for small ones. This may explain why only small cyclopoid copepods can afford this hydrodynamically stealthy transportation mode as their routine, while large copepods are cruise swimmers.

Genetics redraws pelagic biogeography of Calanus

Planktonic copepods of the genus Calanus play a central role in North Atlantic/Arctic marine food webs. Here, using molecular markers, we redrew the distributional ranges of Calanus species inhabiting the North Atlantic and Arctic Oceans and revealed much wider and more broadly overlapping distributions than previously described. The Arctic shelf species, C. glacialis , dominated the zooplankton assemblage of many Norwegian fjords, where only C. finmarchicus has been reported previously. In these fjords, high occurrences of the Arctic species C. hyperboreus were also found. Molecular markers revealed that the most common method of species identification, prosome length, cannot reliably discriminate the species in Norwegian fjords. Differences in degree of genetic differentiation among fjord populations of the two species suggested that C. glacialis is a more permanent resident of the fjords than C. finmarchicus . We found no evidence of hybridization between the species. Our results indicate a critical need for the wider use of molecular markers to reliably identify and discriminate these morphologically similar copepod species, which serve as important indicators of climate responses.

Size Variation of Neocalanus plumchrus and Neocalanus flemingeri in a 20-yr Sample Series from the Gulf of Alaska

Prosome length of the resting stages of Neocalanus plumchrus and Neocalanus flemingeri varied significantly, but modestly, among years at Station P in the Gulf of Alaska. The range of variation over 20 yr was small relative to the known geographic variation. Among-year length variations were significantly greater than within-year variations, implying similarity of year-to-year variation in growth conditions over an indeterminate, subregional scale. The two species tended to vary in the same fashion both among and within years, despite the offset of about 1 mo in their developmental schedules. Length of N. plumchrus was negatively correlated with Emerson's (1987. J. Geophys. Res. (Oceans) 92(C6): 6535–6544) estimates of May–August new production at Station P from 1969 to 1978.

Factors Governing Clutch Size in Two Species of Diaptomus (Copepoda: Calanoida)

We conducted a synoptic survey of 11 nonstratifying takes in eastern Quebec to investigate the relative importance of water temperature, food concentration ([Chl a]), female prosome length, copepod density (population and community densities), and mate availability (sex ratio and density of males) in determining the clutch size of two freshwater copepods, Diaptomus minutus and D. oregonensis. Multiple regression analyses indicated that 60% of the variation in clutch size of D. minutus could be accounted for by temperature and [Chl a] (n = 33; P = 0.0001), while 80% of the variation in the D. oregonensis data (n = 11; P = 0.0017) was explained by temperature and prosome length. Addition of other variables to either model did not significantly reduce the residual variation. We also investigated the effect of interspecific interaction on the egg-bearing potential of D. minutus and found some evidence that animals in sympatry may have lower clutch size than those in allopatry when temperature and food concentration were held constant. By using an independent measure of food and mate availability, we confirmed that clutch size decreased significantly in relation to food limitation for both species, but was unaffected by mate limitation for either.

An Empirical Model to Predict in situ Grazing Rates of Diaptomus minutus Lilljeborg on Small Algal Particles

Grazing rates of Diaptomus minutus were measured in situ in six lakes in south-central Ontario using the tracer species Chlorella vulgaris and Scenedesmus ovalis. An empirical model was constructed to predict grazing rate as a function of the relative proportion of small (<10 μm)to large (10–30 μm) algal particles in the nanoplankton. It accurately predicted diaptomid grazing rates for three lakes in an independent lake set; however, it produced overestimates for two other lakes. There was also a significant positive correlation between grazing rate and the biomass concentration of small algae in the lakes. Difference in ambient lake temperature did not contribute significantly towards explained variation in grazing rate; prosome length was also a poor predictor of grazing rate. In parallel experiments, diaptomid grazing rates were higher when Pediastrum was used than when Scenedesmus was used as the tracer; in a similar set of experiments, grazing rates were higher when Chlamydomonas was used than when Scenedesmus was used.

Patterns of Variation in The Prosome Length of Overwintering Stage V Copepodites of Calanus Finmarchicus in The Firth of Clyde

In attributing variations in growth and metabolism within a population to environmental fluctuations, and in interpreting the biological response to environmental fluctuations, it is important to recognize the variations that are intrinsic to the population or species. Consequently, it is common practice in studies on the growth and metabolism of calanoid copepods to separate instars and, in the case of adults, males and females when analysing measurements. Although studies on calanoids, in particular species of Calanus and Euchaeta, have demonstrated the existence of pronounced sexual differences in parameters such as dry weight, biochemical composition and respiration rate (e.g. Comita, Marshall & Orr, 1966; Marshall, 1973; Bamstedt, 1975, 1979; Gatten et al. 1979, 1980), the possibility that similar differences might occur in pre-adult instars has not been examined, this despite the fact that in many species in this group it is possible to distinguish the sex of copepodites IV and V, the two instars preceding the adult.

The copepod width–weight relation and its utility in food chain research

A review of several methods for estimating copepod wet weight from linear dimensions shows that, as expected, precision in estimation is gained at the expense of generality. Body width, however, is a better estimator of wet weight than either total length or prosome length and is less ambiguous in use.Body width is also the controlling parameter in prey selection by many important marine and freshwater predators including birds, fish, and some plankters. For estimating ingested prey biomass it thus seems the best single linear size parameter.