Using laser optics to illuminate high-resolution video-recordings, we revealed behavioural mechanisms through which males of the calanoid copepod speciesTemora longicornis locate females. Males of T. longicornis swam at signi¢cantly faster speeds than females along more sinuous routes, possibly re£ecting adaptations to increase encounter with females. Upon approaching within 2 mm (i.e. two body lengths) of a female's swimming path, males accelerated to signi¢cantly higher pursuit speeds. Pursuit trajectories closely traced the trajectories of females, suggesting that males were following detectable trails created by swimming females. Males of T. longicornis detected female trails up to at least 10-s old, and tracked trails for distances exceeding 13 cm, or 130 body lengths. Females were positioned up to 34.2 mm away from males (i.e. reactive distance) when males initiated`mate-tracking'. It was always the males of T. longicornis that detected and pursued mates. In rare events, males pursued other males. Behavioural £exibility was exhibited by males during mate-tracking. Males generally tracked the trails of`cruising' (i.e. fast-swimming) females with high accuracy, while the pursuits of`hovering' (i.e. slow-swimming) females often included`casting' behaviour, in which males performed sharp turns in zigzag patterns within localized volumes. This casting by males suggested that hovering females create more dispersed trails than cruising females. Casting behaviour also was initiated by males near locations where females had hopped, suggesting that rapid movements by females disrupt the continuity of their trails. Males were ine¤cient at choosing initial tracking directions, following trails in the incorrect direction in 27 of the 67 (40%) mating pursuits observed. Males usually attempted to correct misguided pursuits by`back-tracking' along trails in the correct direction. Males were observed to detect and track their own previous trajectories without females present, suggesting the possibility that males follow their own trails during back-tracking. Observations of males tracking their own trails and the trails of other males bring into question the speci¢city of trails as a mechanism promoting reproductive isolation among co-occurring planktonic copepods.

Within laboratory-induced swarms of the marine copepod Temora longicornis, the male exhibits chemically mediated trail-following behaviour, concluding with £uid mechanical provocation of the mate-capture response.The location and structure of the invisible trail were determined by examining the speci¢c behaviour of the female copepods creating the signal, the response of the male to her signal, and the £uid physics of signal persistence. Using the distance of the mate-tracking male from the ageing trail of the female, we estimated that the molecular di¡usion coe¤cient of the putative pheromonal stimulant was 2.7 Â10 À5 cm 2 s À1 , or 1000 times slower than the di¡usion of momentum. Estimates of signal strength levels, using calculations of di¡usive properties of odour trails and attenuation rates of £uid mechanical signals, were compared to the physiological and behavioural threshold detection levels. Males ¢nd trails because of strong across-plume chemical gradients; males sometimes go the wrong way because of weak along-plume gradients; males lose the trail when the female hops because of signal dilution; and mate-capture behaviour is elicited by suprathreshold £ow signals. The male is stimulated by the female odour to accelerate along the trail to catch up with her, and the boundary layer separating the signal from the chemosensitive receptors along the copepod antennule thins. Di¡usion times, and hence reaction times, shorten and behavioural orientation responses can proceed more quickly. While`perceptive' distance to the odour signal in the trail or the £uid mechanical signal from the female remains within 1^2 body lengths (55 mm), the`reactive' distance between males and females was an order of magnitude larger. Therefore, when nearest-neighbour distances are 5 cm or less, as in swarms of 10 4 copepods m À3 , mating events are facilitated. The strong similarity in the structure of mating trails and vortex tubes (isotropic, millimetre^centimetre scale, 10:1 aspect ratio, 10 s persistence), indicates that these trails are constrained by the same physical forces that in£uence water motion in a low Reynolds number £uid regime, where viscosity limits forces to the molecular scale. The exploratory reaches of mating trails appear inscribed within Kolmogorov eddies and may represent a measure of eddy size. Biologically formed mating trails, however, are distinct in their £ow velocity and chemical composition from common small-scale turbulent features; and mechanoreceptive and chemoreceptive copepods use their senses to discriminate these di¡erences. Zooplankton are not aimless wanderers in a featureless environment. Their ambit is replete with clues that guide them in their e¡orts for survival in the ocean.

We examined the relat~ve Importance of phytoplankton and ciliates as prey for metazoan zooplankton and the role of predation in regulating ciliate populat~ons In 2 Long Island (USA) bays Depth-integrated primary production (mg C m h-') was dominated by nannoplankton < 5 pm In d~a meter throughout the year, ranging from > 9 5 " of total production in mid-summer to an average of about 60%, in winter and early spnng Predator exclusion and addition experiments conducted in microcosms showed that the mortality coeff~cient of cil~ates (d.') from zooplankton predation was higher when larger phytoplankton ( > l 0 pm) contributed less to total primary productivity For adult copepods an Increase In the percentage ciliate contribution compdred to phytoplankton contnbution to total carbon Intake also coinc~ded with the higher prrcrntages of small microdlgal production Egg production rates of Acartia spp were positively correlated to the net growth coefficient of cili~ites In contrast, mlcrometazoa routinely obtalned > 7 0 % of t h~~r total carbon ratlon from phytoplankton, and at times d u n n g spnng and summer, removed 23 to 52' 0 of the total depth-~ntegrated prlmary production In a d d i t~o n to protozoa, w e suggest that microinetazoa part~cularly copepod nauplii, may serve as a trophlc llnk between phytoplankton and mesozooplankton In Long Island bays

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BackgroundOysters play important roles in estuarine ecosystems but have suffered recently due to overfishing, pollution, and habitat loss. A tradeoff between growth rate and disease prevalence as a function of salinity makes the estuarine salinity transition of special concern for oyster survival and restoration. Estuarine salinity varies with discharge, so increases or decreases in precipitation with climate change may shift regions of low salinity and disease refuge away from optimal oyster bottom habitat, negatively impacting reproduction and survival. Temperature is an additional factor for oyster survival, and recent temperature increases have increased vulnerability to disease in higher salinity regions.Methodology/Principal FindingsWe examined growth, reproduction, and survival of oysters in the New York Harbor-Hudson River region, focusing on a low-salinity refuge in the estuary. Observations were during two years when rainfall was above average and comparable to projected future increases in precipitation in the region and a past period of about 15 years with high precipitation. We found a clear tradeoff between oyster growth and vulnerability to disease. Oysters survived well when exposed to intermediate salinities during two summers (2008, 2010) with moderate discharge conditions. However, increased precipitation and discharge in 2009 reduced salinities in the region with suitable benthic habitat, greatly increasing oyster mortality. To evaluate the estuarine conditions over longer periods, we applied a numerical model of the Hudson to simulate salinities over the past century. Model results suggest that much of the region with suitable benthic habitat that historically had been a low salinity refuge region may be vulnerable to higher mortality under projected increases in precipitation and discharge.Conclusions/SignificancePredicted increases in precipitation in the northeastern United States due to climate change may lower salinities past important thresholds for oyster survival in estuarine regions with appropriate substrate, potentially disrupting metapopulation dynamics and impeding oyster restoration efforts, especially in the Hudson estuary where a large basin constitutes an excellent refuge from disease.

We have analysed the fine-scale kinematics of movement of male and female copepods, Temora longicornis, to resolve how these small animals find their mates. Location of the trail initially involves rapid random turning and high rates of directional change. Males subsequently increase their rate of movement as they follow the trail, and execute a regular pattern of counter turns in both x,z and y,z planes to stay near or within the central axis of the odour field. Pursuit behaviour of males is strongly associated with female swimming behaviour, suggesting that quantifiable variations in the structure of the odour signal released by females affects male tracking. The behavioural components of mate tracking in Temora are very similar to those of other animals that employ chemically mediated orientation in their search for mates and food, and we conclude that male Temora find their mates using chemoperception. The kinematic analysis indicates both sequential and simultaneous taxis mechanisms are used by Temora to follow the odour signal. This, in turn, indicates that rather than responding to a diffuse plume, males are following a signal more accurately characterized as a chemical trail, and copepods appear to use mechanisms that are similar to those employed by trail-following terrestrial insects such as ants. While Temora expresses similar behaviours to those of a variety of chemosensory organisms, the ability to track a three-dimensional odour trail appears unique, and possibly depends on the persistence of fluid-borne odour signals created in low Reynolds number hydrodynamic regimes.

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