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Levels of ultraviolet-B radiation (UV-B: 280-315 nm) reaching the earth's surface have increased over the past few decades due to ozone depletion. It is well documented that exposure to UV-B radiation increases mortality in marine fish larvae. However, few studies have examined sub-lethal effects of UV-B radiation such as, for example, the possibility that it affects prey consumption by fish larvae. Atlantic cod larvae were exposed to a sub-lethal level of ultraviolet-B radiation (UV-B: 280-315 nm) for 15 h. After the exposure, rotifers (4/mL) were fed to cod larvae at three different post-exposure intervals (20 min, 3 and 6 h). Trials were replicated three times for each post-exposure interval. The number of rotifers in the gut and the percent of empty guts (number of fish with empty gut/ number of fish examined x 100) were analyzed. Results were compared to those of unexposed fish (the control treatment). UV-B exposed cod larvae had consumed significantly fewer rotifers than control fish at all post-exposure intervals. There was no significant difference in the frequency of empty guts between fish in the UV-B treatment versus fish in the control treatment at any of the post exposure time points (although the difference at 20 min post-exposure was borderline significant). These observations suggest that cod larvae exposed to sub-lethal levels of UV-B have lower net energy gain which may lead to reduced growth rate and possibly poorer survival., Introduction Biologically deleterious UV-B radiation (280-315 nm) is one of the major environmental stressors in epipelagic marine ecosystems (Hader et al. 2011). The depth to which UV-B penetrates into oceanic [...]

Paraeuchaeta norvegica (8.5 mm total length) and yolk-sac stage Atlantic cod larvae (4 mm total length) (Gadus morhua) larvae were observed in aquaria (3 l of water) using silhouette video photography. This allowed direct observations (and quantitative measurement) of predator-prey interactions between these two species in 3-dimensions. Tail beats, used by cod larvae to propel themselves through the viscous fluid environment, also generate signals detectable by mechanoreceptive copepod predators. When the prey is close enough for detection and successful capture (approximately half a body-length), the copepod launches an extremely rapid high Reynolds number attack, grabbing the larva around its midsection. While capture itself takes place in milliseconds, minutes are required to subdue and completely ingest a cod larva. The behavioural observations are used to estimate the hydrodynamic signal strength of the cod larva's tail beats and the copepod's perceptive field for larval fish prey. Cod larvae are more sensitive to fluid velocity than P. norvegica and also appear capable of distinguishing between the signal generated by a swimming and an attacking copepod. However, the copepod can lunge at much faster velocities than a yolk-sac cod larva can escape, leading to the larva's capture. These observations can serve as input to the predator-prey component of ecosystem models intended to assess the impact of P. norvegica on cod larvae., Author(s): Howard I. Browman [sup.1] [sup.4] [sup.5] , Jeannette Yen [sup.2] , David M. Fields [sup.3] [sup.4] , Jean-François St-Pierre [sup.1] , Anne Berit Skiftesvik [sup.4] Author Affiliations: (1) grid.23618.3e, [...]

In the north Atlantic, Meganyctiphanes norvegica feeds predominantly on copepods, including Calanus spp. To quantify its perceptual field for prey, and the sensory systems underlying prey detection, the responses of tethered krill to free-swimming Calanus spp. were observed in 3D using silhouette video imaging. An attack-which occurred despite the krill's being tethered-was characterized by a pronounced movement of the krill's antennae towards the target, followed by a propulsion and opening of the feeding basket. Frequency distributions of prey detection distances were significantly different in the light vs. the dark, with median values of 26.5 mm and 19.5 mm, respectively. There were no significant differences in the angles at which prey were detected by krill (relative to the predator's longitudinal body axis) in the light vs. the dark. Prey detections were symmetrically distributed on either side of the predator, in both light and dark. However, significant asymmetry was found in the dorsal-ventral direction with 80% of the prey detections located below the midline of the krill's body axis and, given the placement and orientation of the compound eyes, presumably outside its visual field of view. This indicates that, at least under these conditions, vision was not the main sensory modality involved in the detection of active prey by M. norvegica. However, under some circumstances, vision may provide supplemental information. Avoidance responses of copepod prey were nearly twice the velocity of their nominal background swimming speed (153 ± 48 and 85 ± 75 mm s.sup.-1, respectively), on average taking them 43 ± 16 mm away from the predator. This is far beyond the krill's perceptual range, suggesting that the escape reaction provides an effective deterrent to predation (although perhaps less so for free-swimming krill). This information can be used to parameterize models that assess the role of krill as predators in marine ecosystems., Author(s): Mari B. Abrahamsen [sup.1] , Howard I. Browman [sup.2] , David M. Fields [sup.2] [sup.3] , Anne Berit Skiftesvik [sup.2] Author Affiliations: (1) grid.10917.3e, 0000000404273161, Institute of Marine Research, [...]

Nearly all organisms show directional bias in sensitivity to environmental signals. In this study, the behavioral sensitivity of a common estuarine copepod, Acartia tonsa, varies significantly with respect to their orientation to a well-characterized fluid mechanical signal. Maximum sensitivity occurs at an angle of 25°-30° and lowest sensitivity occurs at angles of 60°-90° relative to the source. These results support the hypothesis that copepods are not uniformly sensitive to fluid signals and show directional bias in mechanosensitivity. The data also show that large copepods initiate their escape reaction further from the source than small copepods. There is, however, an uncharacteristically large increase in sensitivity at the transition between the nauplii and C1 stage despite being similar in size. This suggests that the mechanosensory system of the naupliar stages is less sensitive to fluid signals and helps to explain the higher predation rates experienced by nauplii., Author(s): David M. Fields [sup.1] Author Affiliations: (1) grid.296275.d, 0000000095164913, Bigelow Laboratory for Ocean Sciences, , 04575, West Boothbay Harbor, ME, USA Introduction > The spatial orientation of the prey [...]