The present study investigated the effect of temperature on male and female swimming activity of the calanoid copepod Temora longicornis, sampled during winter (February) and summer (August) in the English Channel coastal ecosystem. Video recordings were conducted at 3 temperatures representative of those to which these organisms are normally exposed (13, 16 and 20°C) and one extreme-event temperature (24°C). Examinations of instantaneous velocity and symbolic analysis (i.e. dynamics of swimming states discretized from time series of instantaneous velocity) showed that T. longicornis changed its behaviour when confronted with environmental temperature variations. Swimming speed increased as temperature increased. In warmer water, this copepod displayed higher swimming activity, break periods were less frequent, and the frequency of jumps increased. This phenomenon was amplified when the environmental temperature was increased to 24°C. These observations revealed a considerable tolerance to high temperatures and an ability to adjust to environmental temperature changes. The 'summer population' was less active in the low temperature range, but the swimming speed reached a higher value at higher temperatures than that shown by the 'winter population'. The results of the present study highlighted changes in the individual behaviour of this copepod in response to changing seasonal conditions in the form of swimming activity, and thus its ability to maintain biological processes throughout the year, even in a restrictive environment. KEY WORDS: Copepod · Swimming behaviour · Temperature effect · Seasonal variation · Temora longicornis · Symbolic dynamicsResale or republication not permitted without written consent of the publisher Aquat Biol 16: 149-162, 2012 ronment, copepods have developed a range of strategies, including a wide spectrum of swimming behaviour to search for food (Tiselius 1992, van Duren & Videler 1995 and sexual partners (van Duren & Videler 1996 and to avoid predators (van Duren & Videler 1996, Tiselius et al. 1997. The patterns of zooplankton swimming behaviour may be affected by changing temperature con ditions, i.e. either no change (Metridia longa, Hirche 1987; Calanus finmarchicus, Lenz et al. 2005), or a decrease (Acartia tonsa, and C. glacialis, Hirche 1987, Larsen et al. 2008 or a rise in swimming activity during warmer conditions (Lenz et al. 2005).The effect of seasonal temperature variation on the swimming velocity of copepods, especially Temora longicornis, is not well known, although this variation may be important in the aquatic environment. With rising temperatures in the northern hemisphere (Levitus et al. 2000(Levitus et al. , 2005, there is a need to study behavioural observations in relation to variations in environmental temperature. This, in turn, will give us a better understanding of natural selection processes and their implications on larger-scale mechanisms such as spatial distribution (Beaugrand et al. 2002), demography and dynamic of the populations and co...

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We have studied experimentally in the laboratory the behavioural responses of females and males of the calanoid copepod Temora longicornis and their encounter probability with the alga Rhodomonas. Both sexes of this calanoid copepod adapted their motion velocity and style of swimming in reaction to the presence of prey. Their mean velocity, as well as the probability of high velocity values, increased in the presence of the algae. Moreover, the time spent in swimming activity increased, reflecting a possible adaptation in order to facilitate encounter with prey. Females were more sensitive to the presence of food: mean velocities showed a 40 % increase for males, from control to food conditions, whereas for females the increase was 240 %. This result was confirmed using several indicators: net‐to‐gross displacement ratio, probability density functions, and symbolic dynamics. This may indicate that female T. longicornis are more attracted by food than males.

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Harpacticoid copepods are being considered as alternative candidates for live feed in aquaculture, but their benthic affinity may pose problems for pelagic fish larvae. We compared the swimming behaviour and feeding incidence of herring larvae (Clupea harengus) in the presence of harpacticoid copepods (Tachidius discipes) and rotifers (Brachionus plicatilis). Additionally, we provided T. discipes via a floating sieve to improve the prey availability. The comparison was performed at 5 and 10 days post hatch (dph) via 2D-video observations. Quantitative analyses of larval trajectories allowed the estimation of feeding behaviour through a series of indicators: swimming speed, straightness of trajectories, turning angles and swimming activities (break, sink, slow, normal, fast). The outcomes highlighted that the prey type had no significant effect on swimming speed or straightness of the swimming path. However, at 10 dph directly copepod-fed larvae spent less time in slow but more time in the normal swimmingstate than rotifer-fed larvae and larvae fed with Tachidius via sieve. This suggests higher energy expenditure of directly copepod-fed larvae. Moreover, the feeding incidence was higher in larvae fed with Tachidius via sieve than directly Tachidiusfed larvae. Thus, providing harpacticoid copepods via a floating sieve can improve the rearing of marine fish larvae.