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Author(s): Morgan, SG; Dibble, CD; Susner, MG; Wolcott, TG; Wolcott, DL; Largier, JL | Abstract: Plankton are widely considered to be at the mercy of ocean currents, even after decades of research revealing that plankton regulate dispersal by positioning themselves in surface and bottom currents flowing in different directions. The degree of effectiveness of these behaviors remains controversial, because tiny plankters cannot be tracked at sea. Here, we experimentally tested the effectiveness of 3 vertical positioning behaviors in nature by developing a biomimetic robot that emulates them. We conducted a challenging test by deploying them in complex circulation during strong upwelling winds and wind relaxation and reversal events. Behavior alone dramatically affected transport. Transport trajectories of robots with 3 different behaviors diverged markedly while those sharing the same behavior were very similar. Moreover, all 3 behaviors produced trajectories that matched previously modeled projections during both upwelling and relaxation conditions at the study site: shallow plankton disperse far, deep plankton move little, and plankton migrating from depth during the day to the surface at night travel an intermediate distance. The ability of weakly swimming plankton to control their fate and replenish populations in a dynamic ocean is of central importance to the ecology and evolution of marine life and to the management of resources in a changing climate.

Populations of the toxic dinoflagellate Karenia brevis that remain near the benthos in deep shelf water in the Gulf of Mexico could be the source for toxic bloom occurrences near shore. A biophysical dynamic simulation model and migrating drifters were used to assess whether such 'seed populations' could persist in nature. The vertical migration responses of plankton to an exclusively benthic nutrient source and light limitation would result in near-benthic behavioral trapping of a slowly growing population in conditions found on the West Florida Shelf (WFS). The model in- dicated that for a 50 m deep bottom, a 2-m-thick layer of ≥2 µmol NO3 - /NO2 - fluxing from the benthos was the minimum needed to permit growth for dark- adapted K. brevis in an oligotrophic water column. Growth rates depended more on the duration of expo- sure to nutrients than on concentration; a 1-m-thick nutrient layer sustained minimum growth levels inde- pendently of the nutrient distri bution at depths ≤40 m. Field experiments using Autonomous Behaving La- grangian Explorer drifters (ABLEs) that exhibited bio- mimetic vertical migration responses to the external environment demonstrated a benthically-oriented movement pattern in response to natural light and cues correlated with elevated near-benthic nutrients. Aver- age measurements of nutrients and light from the bot- tom 2 m of the water column in a potential bloom- forming region of the WFS were higher than the model-generated requirements for growth, suggesting that coastal nutrient distributions could support a ben- thic population offshore. Under upwelling conditions, such populations could be advected inshore to frontal convergence zones and form toxic 'red tide' blooms.

Selective tidal-stream transport (STST) is used by many estuarine organisms. Spawning blue crabs use a form of STST, ebb-tide transport (ETT), to migrate to high-salinity areas of the lower estuary and coastal ocean for larval release. In tidal estuaries, ETT is driven by a circatidal rhythm in vertical swimming with episodic ascents into the water column during ebb tide. This study examined vertical swimming behavior of migrating female blue crabs tethered in habitats they could encounter during migration. A combined bio-physical field study in the summer of 2009 simultaneously measured physical parameters of the water column and vertical swimming behavior of tethered ovigerous crabs using pressure-recording dataloggers. Tethering sites were in the tidal Beaufort Inlet drainage and the non-tidal Albemarle-Pamlico Estuarine System, North Carolina, USA. Crabs tethered in tidal areas swam primarily during ebb tides, both day and night. Swimming frequency increased as embryonic development progressed and ebb-tide swimming continued after larval release. Swimming frequency varied among habitats with the highest swimming frequency in the known migratory corridor. Swimming did not occur in the non-tidal habitat. Differences in swimming frequency among sites are hypothesized to be responses to environmental cues, including flow regime. Some habitats serve as migratory corridors while others serve as foraging stopovers. These areas are likely defined by a combination of environmental cues including flow regime.

Little is known about the migration of female crabs (Callinectes sapidus) to spawning grounds, or how effectively they are protected by North Carolina's “spawning sanctuaries.” To investigate migration, we tagged and released a total of 2700 mature female crabs in the fall of 2001 and the summer and fall of 2002 in the three tributaries of Pamlico Sound. Tag returns indicate that females begin migration during September to November and that they probably do not complete it until the next spring. To assess site fidelity and protection of females by spawning sanctuaries, 398 tagged adult females were released in or near sanctuaries at Ocracoke and Hatteras inlets. Most recaptures occurred near the barrier islands (Outer Banks), suggesting that mobility declines once females reach euhaline waters, but recapture data also showed that crabs move over scales larger than sanctuaries and derive only temporary protection by entering sanctuaries. Ovigerous females fitted with ultrasonic pingers were tracked after release inside the boundary of Ocracoke spawning sanctuary. Crabs with orange (new) egg masses meandered over small areas, but those with eggs approaching hatching moved directly seaward. Apparently spawning sanctuaries must be large to be effective; where this is not practical (as in North Carolina), other strategies should be considered.

Male blue crabs, Callinectes sapidus Rathbun, transfer sperm and seminal fluid to their mates. The quantity of both of these components can vary, and may be particularly reduced in the ejaculate of males that have recently mated. While the potential consequences for fitness of receiving less sperm are obvious, the same is not true of seminal fluid; its role in the blue crab, other than as a sperm plug, is not known. We documented the changes in seminal fluid over time following controlled matings in the laboratory. By allowing males to mate repeatedly in quick succession, we were able to manipulate both the amount of sperm and of seminal fluid that females received. We measured the initial amount of seminal fluid and sperm transferred, and followed the number and viability of sperm, and condition of the spermathecal organs and ovaries, in cohorts of females held for various times post-mating. Females whose mates had mated recently received only about 33% as much ejaculate as those whose mates had full sperm stores. Sperm viability was unaffected, and regardless of male mating history, sperm number declined nearly 50% prior to brood production. We found that all seminal fluid is gone by 5 weeks post-mating, making it unlikely that it plays a role during long-term storage of sperm. The amount of ejaculate was independent of the size of the mate. The spermathecal organs themselves lose 86% of their mass prior to brood production, and this allowed us to develop a staging system for spermathecal condition that was useful for estimating reproductive timing in a field population in North Carolina. Essentially all field-caught females had mated, but sperm viability, sperm number, and ejaculate weight varied with season.

The movement of mature female blue crabs Callinectes sapidus Rathbun from lower salinity areas to spawn near the mouths of estuaries is well documented, but specific details of the post-copulatory phase of their migratory behavior are poorly understood in Chesapeake Bay. To test the hypotheses about the timing and route of this migration, we conducted a mark-recapture study of mature females released in a mesohaline portion of the upper Chesapeake Bay. From June 1999 to October 2002, 1440 mature female blue crabs were obtained from fishers, tagged, and released in the vicinity of the Rhode River, Maryland, approximately 200 km distant from the mouth of the Bay. As of the end of 2002, 167 crabs were recaptured (11.6%), with considerable variation in recapture rates among years. All recaptures except one (in Flagler Beach, Florida) were caught within the Chesapeake Bay proper. Recaptures of female crabs released at monthly intervals from June-November indicated that migration occurred during a short fall period rather than over the prolonged period of summer to fall mating. The distances traveled by crabs before recapture differed significantly among release months. On average, crabs released in September and October traveled greater distances than crabs released in earlier months (June-August). Depths of recapture sites differed significantly among months, with shallow depths in June-August increasing in September to a maximum in November. The locations and bathymetry of recapture sites showed that female crabs used areas near the deep channel, especially the eastern shoulder, of the Bay as a migration corridor to the spawning areas of the lower estuary. The distinct fall season and route of migration should provide valuable management information for protecting the declining spawning stock of Chesapeake blue crabs.

A male-focused size-selective fishery, like the one targeting the blue crab (Callinectes sapidus Rathbun) along the Atlantic and Gulf coasts of the U.S., has the potential to reduce the average size of the males in the population, reduce the density of males in the population, and/or raise the ratio of females to males. All of these may affect the mating dynamics of the population by reducing the amount of sperm that males provide to females and decreasing the number of males available for copulation. We investigated the effect of the fishery on a blue crab population in upper Chesapeake Bay by collecting crabs in areas of markedly different fishing pressure. Crabs were taken as individuals and as mating pairs, which permitted assessing the size of males currently mating in nature, and the seminal resources they possess and transfer to females. Average size of males in subpopulations that have been subjected to heavier fishing pressure is indeed smaller, and the smaller males pass less sperm and accessory fluid to females than would larger males if they were still present. Some males in pre-copulatory pairs are as sperm depleted as males that had just completed copulation, indicating that they are mating more frequently than they can replace their seminal resources. The most sperm-depleted males in the population are not even pairing or attempting to mate.

Remote measurement of the physiology, behaviour and energetic status of free-living animals is made possible by a variety of techniques that we refer to collectively as 'biotelemetry'. This set of tools ranges from transmitters that send their signals to receivers up to a few kilometers away to those that send data to orbiting satellites and, more frequently, to devices that log data. They enable researchers to document, for long uninterrupted periods, how undisturbed organisms interact with each other and their environment in real time. In spite of advances enabling the monitoring of many physiological and behavioural variables across a range of taxa of various sizes, these devices have yet to be embraced widely by the ecological community. Our review suggests that this technology has immense potential for research in basic and applied animal ecology. Efforts to incorporate biotelemetry into broader ecological research programs should yield novel information that has been challenging to collect historically from free-ranging animals in their natural environments. Examples of research that would benefit from biotelemetry include the assessment of animal responses to different anthropogenic perturbations and the development of life-time energy budgets.

After molting to maturity, female blue crabs must rebuild muscles atrophied to permit molting and grow larger ones commensurate with the larger exoskeleton. They also must acquire energy for oogenesis and for migration to high-salinity spawning habitat, a distance of >150 km for females mating in the Upper Chesapeake Bay. Using telemetry and mark–recapture techniques, post-copulatory females in the upper bay were shown to forage at high rates, alternating between meandering and directed movement in the area of mating for weeks to months, and to begin migrating in October. Consequently, females from the Upper Chesapeake Bay probably do not spawn until the season after mating. Their priority seems to be to acquire energy before migrating. After molting, energy was allocated first into somatic tissue and eventually into hepatopancreas and gonads. Telemetry of feeding and movement showed that habitat utilization, traveling velocities, foraging patterns, and movements were similar to those already determined for males. However, females appeared to invest proportionally more energy (calories per gram dry weight) into their somatic and reproductive tissues than did males. A newly designed transmitter that telemetered depth showed that females moved during both ebbs and floods and remained at or near the bottom of the water column.

Episodic hypoxic events in estuaries can alter the trophic dynamics of important benthic predators. During hypoxic upwelling events mobile predators may reduce their feeding activity as they migrate to relatively shallower, oxygenated water, and may reinvade deep-water habitats dur- ing relaxation of hypoxia to exploit vulnerable infaunal prey (e.g. clams and polychaete worms) that have reduced their burial depth in response to hypoxia. We used biotelemetry techniques with con- current measurements of dissolved oxygen (DO) to monitor the feeding and movement responses of free-ranging blue crabs Callinectes sapidus to episodic hypoxic upwelling and subsequent relaxation events within the Neuse River Estuary (NRE), North Carolina, USA. Although telemetered crabs fed in hypoxic water with DO concentrations as low as 1.01 mg l -1 , percent feeding occurrence declined slightly when crabs were exposed to mild (DO = 2 - 4 mg l -1 ) and severe hypoxia (DO 4 mg l -1 ). Crabs reduced the proportion of time spent feed- ing during hypoxic upwelling conditions except for the most severe events when DO dropped rapidly from normoxia to severe hypoxia. The proportion of time crabs spent feeding did not increase and crabs did not reinvade deeper water habitats during relaxation events, as was hypothesized. These results are somewhat inconsistent with previous studies and we suggest that crabs may have fed on prey other than benthic infauna, or that upwelling events may not have lasted long enough to cause infauna to migrate close enough to the sediment surface to be vulnerable to predation by blue crabs. Our study highlights the importance of examining the complex interaction between the hydrody- namics of episodic events and various behaviors (e.g. feeding and movement) when trying to under- stand the impact of these events on estuarine trophic dynamics.

Laboratory experiments were used to determine the influence of male Callinectes sapidus (Rathburn) size (larger vs smaller than the size limit of the hard crab fishery in Chesapeake Bay, which is 127 mm carapace width) and mating history (recently mated males with depleted seminal stores vs those with fully recovered resources) on number of sperm transferred to females. Females mated by males with fully recovered seminal resources received significantly more sperm than those mated with males that had mated once previously, regardless of male size. No significant difference was found between the number of sperm delivered by small and large males with similar mating history. The sperm content of ejaculates from these laboratory experiments was compared to sperm received by females collected in the field. Only 11 % of field-collected females received an amount of sperm as large as that delivered by the fully recovered males in our laboratory experiments. Of the field collected females, 77 % received much less sperm, similar to or below the number delivered by depleted males in our laboratory experiments.

Biologists must remember that physiology is the product of natural selection on organisms interacting with heterogeneous environments. “Behaving” organisms may alter the osmotic conditions they experience and achieve results unexpected from laboratory studies. Their ability to exploit environmental heterogeneity depends on its temporal/spatial scale relative to that of the organism, and the correspondence between the osmotic differences and the organism's sensory and osmoregulatory physiology. “Behaviors” include evasion of stressful habitats, selection among differing microenvironments, changing body characteristics that affect salt/water uptake/loss, manipulating fluids differing in osmolytes, and modification of osmotic microenvironments (especially for vulnerable offspring). To draw “comparative and integrative” inferences, investigators must strive to understand an organism's actual challenges by “seeing” the world from its perspective, and then making observations and performing experiments in the context of the “real world” experienced by that organism.

We evaluated the depletion and recovery rates of sperm number and vas deferens weight following mating for male Callinectes sapidus both below (140 mm) the fishery size limit for hard crabs in Chesapeake Bay (127 mm). Large males had low sperm count and vas deferens weight immediately after mating and required approximately 9–20 days to fully recover. After mating, small males had significant reduction in sperm number despite no significant change in vas deferens weight. Furthermore, small males with completely recovered seminal stores had significantly lower vas deferens weight than fully recovered large males but did not differ significantly from large males in number of sperm. The changes in vas deferens weight and sperm count following experimental mating suggest that large males delivered 21 times as much seminal fluid and 2.25 times as much sperm as small males. Field collections in a subestuary of Chesapeake Bay revealed that the majority (50–90%) of males had extremely low vas deferens weight relative to males with fully recovered sperm volume. Since the fishery targets males primarily, reducing both the number and average size of males in the population, many females may be mated with small or recently mated males that transfer less seminal material.

To define general principles of predator-prey dynamics in an estuarine subtidal environment, we manipulated predator density (the blue crab, Callinectes sapidus) and prey (the clam, Macoma balthica) patch distribution in large field enclosures in the Rhode River subestuary of the central Chesapeake Bay. The primary objectives were to determine whether predators forage in a way that maximizes prey consumption and to assess how their foraging success is affected by density of conspecifics. We developed a novel ultrasonic telemetry system to observe behavior of individual predators with unprecedented detail. Behavior of predators was more indicative of optimal than of opportunistic foraging. Predators appeared responsive to the overall quality of prey in their habitat. Rather than remaining on a prey patch until depletion, predators appeared to vary their patch use with quality of the surrounding environment. When multiple (two) prey patches were available, residence time of predators on a prey patch was shorter than when only a single prey patch was available. Predators seemed to move among the prey patches fairly regularly, dividing their foraging time between the patches and consuming prey from each of them at a similar rate. That predators more than doubled their consumption of prey when we doubled the number of prey (by adding the second patch) is consistent with optimizing behaviors - rather than with an opportunistic increase in prey consumption brought about simply by the addition of more prey. Predators at high density, however, appeared to interfere with each other's foraging success, reflected by their lower rates of prey consumption. Blue crabs appear to forage more successfully (and their prey to experience higher mortality) in prey patches located within 15-20 meters of neighboring patch, than in isolated patches. Our results are likely to apply, at least qualitatively, to other crustacean-bivalve interactions, including those of commercial interest; their quantitative applicability will depend on the mobility of other predators and the scale of patchiness they perceive.

Male Callinectes sapidus allowed complete recovery of sperm resources and then mated a single time had significantly lower vas deferens weight than males allowed complete recovery of sperm resources but prevented from mating. In laboratory experiments, when a recently mated male (having low sperm volume) competed with a male that had not recently mated (having high sperm volume) for a single pubertal female, the female was just as likely to initiate pairing with the recently mated male as with a male that had not recently mated, despite possible reduction in her fertilization potential. At the end of trials in which stable pair formation occurred, recently mated males were paired significantly more often than males that had not recently mated. The combined effects of the lack of mate choice by females and high mating frequency of some males may result in many females in the population receiving low quantities of sperm.

To define the temporal and spatial patterns of agonism and foraging activity in blue crabs ( Callinectes sapidus ), we monitored five free-ranging animals in the Rhode River subestuary of the central Chesapeake Bay by ultrasonic telemetry during the summers of 1991–93. The interdependence between the two activities was of special interest. High crab densities have been associated with more frequent aggressive interactions and decreased foraging success in previous laboratory studies. High crab population density is correlated with increased frequency of aggression-related injury (autotomy) and cannibalism in the field. Consequently, we predicted that as crabs aggregate to clam patches during feeding periods in the field, the level of aggressive interactions would increase. In early trials, we collected data on location and agonistic activity (the stereotypical spreading of the chelae in the `meral spread' threat display) of crabs moving freely in the estuary by using single-channel telemetry transmitters. With subsequent technological advancements, we received simultaneous data on agonism and feeding. Crabs exhibited a diel pattern of agonism with peaks in threat display occurring in mornings and sometimes in evenings. Crabs fitted with single-channel telemetry transmitters were observed interacting aggressively most often at times previously identified as feeding periods, although the highest levels of agonism came slightly later than periods associated with the highest levels of feeding. Simultaneous telemetry of the two behaviors indicated that periods of increased agonism and feeding overlapped. Feeding activity tended to wane as threat activity increased, consistent with the hypothesis that aggressive interference impairs foraging.

The interactive effects of predator density and prey distribution on the foraging behavior of an important estuarine predator were studied, at a fine temporal scale, using ultrasonic telemetry. The movement and agonistic activity of individual blue crabs Callinectes sapidus were monitored in large field enclosures, in which the density of crabs and the distribution of patches of bivalve prey Macoma balthica were varied. Agonism-related injury in blue crabs is common and may be quite costly. On a scale of days, blue crabs have been shown in previous studies to disperse, sometimes into prey-impoverished areas, in response to conspecific interference. On the scale of minutes to hours addressed in the present study, the density of predators and the distribution of their prey interacted to affect the foraging behavior and success of blue crabs. When only a single clam patch was available, blue crabs at high density interfered with each other's foraging by direct agonistic encounters, shown by an inverse correlation between agonistic activity and foraging success. Conversely, when prey were partitioned into 2 patches, blue crabs at high density apparently dispersed among the patches, thus minimizing direct agonistic clashes. Although crabs reduced the occurrence of agonistic encounters further than the 50 % attributable to their effectively halving their densities on each patch, they did not take refuge in the prey-impoverished areas between experimental patches for significant periods. Instead, they seemed to respond instantaneously to changing degree of risk by moving off the clam patch when another conspecific approached.

A new acoustic transmitter for monitoring the tailbeat frequency of free-swimming fishes and sharks is described. The transmitter is externally mounted on the fish's caudal peduncle and produces an acoustic pulse with every lateral movement of the tail. Field tests on obligate-swimming juvenile scalloped hammerhead sharks (Sphyrna lewini) show these transmitters accurately telemeter tailbeat deflections from free-swimming sharks. Tests in a flume show sharks with transmitters work harder and swim slower than sharks without transmitters, but these laboratory data can be used to correct for instrument artifacts on free-swimming sharks. A shark tracked with a tailbeat-sensing transmitter exhibited similar movement and activity patterns to shark pups tracked with smaller, orally inserted internal transmitters. The similarity of tracks indicate that the shark equipped with the tailbeat transmitter behaved normally. Thus, this new transmitter design offers a cost-effective, minimally intrusive method for accurately measuring activity rate and energy consumption of active fishes and sharks in the field.

To complete their life history, planktonic larvae of many marine species must be retained in or return to estuarine nursery grounds despite net downstream flows. Interactions between tidal currents and behaviour (vertical migration) of larvae are assumed to play an important role in upstream transport or station-holding, but the effects of tidal currents alone have not received close examination. To elucidate their effects, passive particles were followed numerically in a model of idealized flow. The model basin was patterned after the Newport River Narrows, part of a small coastal-plain estuary with simple bathymetry and a well-studied example of larval retention (mud crabs, Rhithropanopeus harrisii ). The flow field, governed by an analytical solution of the linearized equation of motion, was forced by oscillating tidal currents at the seaward end of the estuarine channel, and its energy was dissipated by bottom friction and eddy diffusion. Particles released at various locations showed a net upstream drift, produced by the combined effects of: (1) shear in the vertical profile of horizontal velocity; and (2) tidally-induced vertical motion. Velocity of upstream drift could partially offset net downstream transport by river flow. This velocity increased with distance downstream, providing a mechanism tending to stabilize positions of larvae in the basin. Tidal vertical migration of mud crab larvae in nature is in phase with, and presumably reinforced by, the predicted tide-induced vertical motions of the water. The passive, tidally-induced upstream drift could provide an important mechanism, in addition to larval behaviour, for the retention of larvae in estuaries.

The role of submerged aquatic vegetation in supporting enhanced growth of Callinectes sapidus was investigated through field and laboratory experiments. In predator-free enclosures (1 m 2 ) in the lower York River, Virginia, juvenile blue crabs within Zostera marina (L.) beds grew faster than crabs in enclosures deployed outside the beds. First stage crabs were introduced into vegetated or un vegetated enclosures at either 10 or 50 crabs m −2 . After the 6 wk experimental period, both survival and growth were significantly higher in vegetated treatments (growth was estimated by change in “volume,” the product of carapace width, length and depth). In fiberglass mesocosms (2.67 m × 1.33 m × 0.67 m) divided into vegetated and unvegetated halves, juvenile blue crabs grew faster in the vegetation, consistent with field findings. Where differences existed between density treatments in field enclosures, juvenile crabs grew faster in high density than in low density treatments. Aggregate crab growth (summed “volumes” of all recaptured individuals) for vegetated enclosures was greater than for unvegetated enclosures. Potential contribution of cannibalism was sufficient to explain some within-habitat density effects, but was not sufficient to account for the entire aggregate differences, suggesting that food may not be limiting within the seagrass beds even at 50 crabs m −2 . These results show that early stage blue crabs receive a substantial growth advantage, in addition to the refuge function shown in other studies, from their association with seagrass beds. This trophic advantage may be experienced by juveniles of other species that utilize vegetated nursery areas and may help explain the ontogenetic habitat shifts that characterize many life histories.

This paper is intended to acquaint physiological and behavioural ecologists with the options offered by modern telemetry technology, and encourage collaboration between biologists and engineers. When direct observation is impossible, telemetry can be used to acquire a wide spectrum of environmental, physiological and behavioural data. This spectrum is expanding rapidly due to dramatic increases in the availability of miniaturized, micropower transducers and electronic components. The “pros and cons” of telemetry are presented, particularly with reference to crustaceans in marine systems. The kinds of phenomena that now can be telemetered are listed, alongside representative devices that transduce them into electrical signals. Transduced data may be stored for subsequent uploading, or transmitted over radio or ultrasound carrier waves. Radio is most useful in air, ultrasound in saline (conductive) water. Data can be encoded on pulsed or continuous carriers, depending on the data rate needed; common schemes are summarized. A sequence of questions about crab ecology is used to illustrate how both simple and complex telemetry systems can provide unique data sets and provide significant insights into the biological system. Simple tracking transmitters provided time budgets for ghost crabs [ Ocypode quadrata (Fabr.)], revealing that they are predators rather than scavengers. Single-channel behavioural transmitters have provided detailed spatial and temporal data on how blue crabs ( Callinectes sapidus Rathbun) move about while seeking moulting sites or food, and where they feed or moult. A multichannel system incorporating microcontroller-based “smart” transmitters and multiple receivers integrated with a data-reduction unit is providing automated logging of feeding and threat behaviours, as well as location within a field enclosure, for multiple blue crabs. A rationale is presented for incorporating telemetry technology into a research programme. An incremental approach that involves experienced collaborators is most likely to yield results quickly and minimise expenditure of resources.

Late stage juveniles and adults of Callinectes sapidus in Chesapeake Bay, USA, and Maja squinado off the Ria de Arousa, Spain, were compared for ontogenetic changes in movement patterns (speed, distance, orientation) and habitat selection (depth, substrate) using ultra-sonic telemetry and published information. After settling in submerged grass beds in the lower Bay, 20-mm juvenile C. sapidus disperse long distances into low salinity sub-estuaries to feed and grow to maturity in two years. Within the Rhode River sub-estuary, juvenile C. sapidus moved with a mean speed of 12 m h1 in nearshore shallows (1·1 m); whereas adults averaged 24 m h·1 in the deeper (2·9 m) channel areas and moved freely in and out of the main estuary. Individuals of both life stages exhibited a pattern of slow meandering (juveniles, 2 m h1, adults 10 m h·1) within a limited area, alternating with faster, directionally-oriented movement (both stages >50 m h·1) between meandering sites. Juvenile and adult males over winter in deeper water nearby, while inseminated females migrate long distances into high salinity areas to incubate the eggs. Callinectes sapidus completes the migration cycle only once per 2·5-y generation. Maja squinado settles on rocks in shallow kelp forests in the coastal zone, where they grow to maturity in 2 y. Juveniles moved slowly (0·5 m h·1) while meandering without directional orientation on shallow (4 m) small patch reefs during summer. After the pubertal moult in summer, adults also meandered slowly (1 m h·1) mostly on rocks at slightly greater depth (7 m). In late summer and autumn, newly mature and older adults moved with directional orientation into deeper (10·40 m) water for the winter, until migrating back to the shallows for the summer; whereas juveniles remained inshore on rocks for the winter. Adult M. squinado live several years after puberty and complete the seasonal migratory cycle several times during their lives.

Terrestrial crabs are physiologically rather similar to their aquatic relatives, despite their markedly different access to water and ions. They have high evaporation rates and void vital salts in isosmotic urine. Some of them manage to have fairly miserly water and ion budgets, but others succeed despite profligacy. There is no single solution to the challenges of terrestrial life; each pairing of animal and environment must be seen as a system in which a unique suite of behaviors compensates for limited physiological prowess. By exploiting temporal and spatial variability of available microhabitats, each species assembles a “composite habitat” in which it can balance the “debit” sides of its water and ion budgets with the requisite “credits.”

The purpose of this study was to identify the physicochemical characteristics of microhabitats selected by molting blue crabs and to obtain further information concerning the behavior of premolt crabs prior to ecdysis. Premolt blue crabs (both mature males and pubertal females) were tracked until ecdysis using ultrasonic telemetry. Premolt movement patterns and certain characteristics of the ecdysial habitats were measured. There was no detectable difference between males and females in movement patterns or habitat depth, pH, dissolved oxygen, turbidity, salinity, sediment type, or shoreline preference. However, female crabs were found in habitats containing higher bivalve densities than the habitats occupied by male crabs. In addition, habitats used during premolt by male and female crabs had higher bivalve densities than did ecdysial habitats. Premolt crabs became more selective of habitat salinity and oxygen as they approached ecdysis. A decrease in the variability of habitat salinity was observed thre...

Herbivorous land crabs (Gecarcinus lateralis) in upland habitats have limited access to salts. They conserve ions extremely well and maintain high hemolymph concentrations in strongly hypoosmotic environments, despite producing urine isosmotic with their hemolymph. Location of the nephropores is favorable for transfer of urine to membranes with active transport pumps (gills, gut). We hypothesized that crabs minimize urinary ion losses by reprocessing (diluting) the isosmotic urine before discarding it, as previously shown for beach-dwelling ghost crabs (Ocypode quadrata). We infused crabs with deionized water (DW) or saline to produce volume loads with and without stimulus to conserve ions and analyzed 'final excretory product, " or p, discarded after urine was reprocessed. In saline-infused crabs, p concentrations converged to hemolymph values. In DW-infused crabs, decreases in osmotic, Cl⁻, and Na⁺ concentrations of p (often to less than 10 % of urine values) drastically reduced losses of ions that init...

In the Rhode River subestuary, higher proportions of molting male blue crabs occupy a tidal creek, while molting and mating pubertal females are more common in the adjacent river basin. Predation pressure, mate availability, and physiological costs or benefits (competency to molt, survive ecdysis, and postmolt size increment) were estimated for these two habitats using a combination of caging and tethering techniques. Predation on molting crabs was less in the tidal creek, however, cannibalism may not explain these site-specific predation differences. There were no site-specific differences in survival, postmolt size increment, or competency for premolt crabs to molt when protected from predators. The results suggest that by molting in the creek males avoid higher predation in the river. Habitat selection by pubertal females may depend more on mate availability. Females may actively select the river or simply molt in the habitat in which they encounter a mate. Further experiments are needed to resolve the selection pressures eliciting the observed distribution of pubertal females.

Most animals rely upon rigid skeletal structures to withstand the negative pressures required for inhalation. Some soft-bodied invertebrates (innkeeper worms, sea cucumbers) have pumping cloacae that are able to "inhale" without any hard supporting structures. Geometric analyses suggest that inhalation cannot be produced by relaxation of coelomic pressure and contraction of radial muscles connecting the body wall. Coelomic pressure must be maintained for body wall support and radial muscle antagonism. Mathematical models predict that maximum attainble suction in a hydrostatically supported sac-within-a-sac like the cloaca-body wall system will be proportional to coelomic pressure and exponentially related to the ratio of body wall diameter to cloacal diameter. A mechanical model gives results consistent with these predictions. "Cloacal" suctions are proportional to "coelomic" pressure, and maximum suction (20 x coelomic pressure) is produced when the cloaca is small relative to the body wall. In vivo reco...

Potential and actual impacts of off-road vehicle (ORV) use on beach macroinvertebrates were examined on the Cape Lookout National Seashore (North Carolina). Mole crabs Emerita talpoida and coquinas Donax variabilis were not damaged. Ghost crabs Ocypode quadrata were completely protected by burrows as shallow as 5 cm, and therefore were not subject to injury during the day, but they could be killed in large numbers by vehicles while feeding on the foreshore at night. Ghost crab populations on the Seashore were large (10 000 km−1 of beach) and a small proportion of the population would be killed by a single vehicle pass. Nevertheless, predicted population mortalities calculated from observed kills of ghost crabs per vehicle-km ranged from 14–98% for 100 vehicle passes. Currently vehicle use on this beach is light and essentially none occurs on the foreshore after dark. Little impact on beach macroinvertebrates would be expected from this usage pattern. Actual impact on ghost crab populations, assessed by burrow censuses, was negligible. No differences were detected between heavy-use and light-use sites in total population size, average crab size or population change through the heaviest traffic season. However, increases in traffic to levels seen on other beaches, especially night driving, would probably have devastating effects on ghost crab populations. In heavily used areas, banning of ORVs from the foreshore between dusk and dawn may be required to protect this species.

Nitrogen (N) is a scarce and perhaps limiting nutrient for many herbivores. Herbivore populations that are able to adjust density rapidly in response to changes in ambient N levels would be able to optimize growth, survival, and reproduction during periods when N is more available and to avoid habitat depletion and mass starvation should N availability decline. We report here that the natural plant diet is growth limiting for the red land crab Gecarcinus lateralis (Freminville) on Bermuda, and that supplementation of the diet with high-nutrient food (soybeans) results in markedly reduced cannibalism of adults on conspecific juveniles. This predicts that populations in habitats where food quality is high will have greater survival of recruits than those in nutrient-deficient habitats. Nutritionally modulated cannibalism would allow population size to expand and contract with nutrient availability while minimizing mortality in reproductively active age classes.

The design and utilization ofa small (16 g in air, 6 g in water) ultrasonic transmitter for animal track ing and bio-telemetry of muscle activity are described. To our knowledge this is the first use of such devices to telemetera specific behavior(ingestion) from a free-rang ing marine predator. The transmitter produces regularly recurring short tracking pulses, and bongpulses triggered by the action potentials ofa muscle. Pulses are transmit ted through conductive estuarine water by a piezoelectric ring transducer at a frequency of about 75 KHz. The preparation of a subject animal, insertion of electrodes, and attachment of the transmitter are described for the telemetry of mandibular muscle contraction in the blue crab. The transmitter provides a signal that corresponds unequivocally with feeding activity and allows enumera tion of bites required to consume a food item. Number of bites, and feeding time, are both positively correlated with the size of the prey specimen. As a test of the tech nique's feasibility, a blue crab was equipped with one of the transmitters and released in a subestuary of Chesa peake Bay. The crab was tracked continuously for 96 hours while every contraction ofthe mandibular muscle was recorded. The crab traveled 4000 m along the subes tuary at an average speed of 12 rn/h, but showed periods of rapid movement of up to 325 m/h. The crab fed 2â€"7 times per day, with a feeding bout comprising 15â€"2750 bites. The limited data did not indicate that either move ment or feeding exhibit a die! or tidal cycle.

When placed under ecologically relevant hypo-osmotic conditions, ghost crabs lose salts at very low rates and osmoregulate well. How can they do this when they, like other brachyuran crabs, produce urine isosmotic with hemolymph? We tested two hypotheses to account for low rates of ion loss: that crabs reduce urine flow (abandon volume regulation); and that they osmoregulate without compromising volume regulation by producing a dilute excretory product through extrarenal modification of urine. Experimental crabs were volume-loaded and hemodiluted by infusion with deionized water; controls were volume-loaded without hemodilution by infusion with isosmotic saline. Crabs were held in containers which allowed the crabs to move fairly freely and to handle wastes normally, and allowed final excretory product to be collected without disturbing the crabs. Crabs infused with deionized water did not reduce urine flow acutely. They produced a dilute excretory fluid containing as little as 10% of the total osmolytes, Na, and Cl of hemolymph and urine. The net effect on osmoregulation was as though they, like other terrestrial animals when water-loaded, produced dilute urine.

Food habits and ecological role of the ghost crab. Ocypode quadrata ( Fabricius) on a North Carolina barrier beach have been investigated in field and laboratory studies. Despite previous reports that they are scavengers, the crabs spent little time in ureas where drifted material accumulated. Dead material accounted for less than 10% of the food in the field. The crabs did. however, give evidence of being facultative scavengers, readily consuming virtually any form of organic matter. Live prey, consisting almost exclusively of mole crabs, Emerita talpoida (Say), and coquina clams, Donax variabilis Say, made up more than 90% of the diet. Handling times indicate that about equal weights of E. talpoida and D. variabilis are consumed. Because of its higher caloric content E. talpoida provides ≈60% of the energy and D. variabilis ≈25%. The effect of O. quadrata on the prey species was assessed by comparing the estimated rates of its feeding (based on resting metabolism) with estimated production of E. talpoida and D. variabilis . Calculations indicate that ghost crabs consume most of the production of both species. Ghost crabs have essentially no terrestrial competitors or predators on the beaches concerned and the stability of this simple food web in such a physically unstable environment may be attributed to the flexible feeding behavior of the predators and their ability to endure long periods of starvation, and to the prey having high biotic potential and dispersal rates. Ghost crabs are the top carnivores in a simple, filter-feeding based food chain.

1. This study tests the hypothesis that physical factors limit the ranges of five species of limpets (Acmaea) inhabiting the splash zone (Zone I) and upper midtidal (Zone II) of the Central California rocky shore. Two criteria are considered necessary to establish the hypothesis. First, interspecific differences in adaptation to physical factors must permit exploitation of different portions of the intertidal gradient. Secondly, physical conditions, by occasionally causing mortality, must set the limits of ranges at different levels depending upon the interspecific differences in physiological tolerances.2. Dilution by winter rainwater runoff probably presents no osmotic threat to Acmaea. No pronounced differences are evident in either resistance to or tolerance of dilution. All five species tolerate immersion in fresh water for periods in excess of the maximum exposure expected in nature. Under exceptional circumstances some Zone I limpets may experience entrapment and lethal dilution in fresh water seep...

Marine animals invading the intertidal zone face a number of potentially stressful or lethal physical factors (e.g. extreme temperatures, desiccation). As physiological ecologists, we have set out to investigate the various sorts of mechanisms by which animals cope with intertidal and supratidal existence, and our research has a larger physiological emphasis than most other programs represented in this symposium. However, many of the adaptations for coping with the challenges of the physical environment are behavioral, instead of (or in addition to) physiological. In this paper we discuss how the concept of physical “limiting factors” has been used to elucidate the coping mechanisms of a series of intertidal and terrestrial crabs. Two types of behavioral adaptation are included in the discussion: 1) behaviors which contribute to homeostasis during stress and might be considered part of physiological mechanisms (e.g., behaviors for taking up water); and 2) behaviors which remove the animal from stressful microenvironments (e.g., selection of specific microhabitats, locomotion, behavioral range limitation).

SEVERAL semiterrestrial crabs, including some ghost crabs (genus Ocypode) can extract interstitial water from damp sand1–3. This enables them to offset their high evaporative losses even in habitats lacking surface water. The mechanism involved has remained unknown, although there have been a few observations of how Gecarcinus lateralis takes up droplets of water applied to its venter4. I have found that uptake of soil water by Ocypode quadrata, the common ghost crab of Caribbean and temperate Atlantic North American beaches, is accomplished by a mechanism involving capillary attraction and the production of a substantial vacuum.

Obtaining access to the end of a burrow is often required to collect the inhabitant, sample food caches, observe nests, or open inspection windows. Because animal burrows often wind around roots, rocks, and other underground obstructions, excavation of an entire burrow system is labrious, particularly if large obstructions are encountered. It is necessarily damaging to the environment. Furthermore, excavation can only give information about a burrow that no longer exists, and is therefore not an appropriate technique for behavioral or other ongoing studies. These problems hampered my study of burrowing land crabs (Gecarcinus lateralis) on Bermuda, and stimulated the development of a radio probe that could be used to determine the location of the terminal chambers of burrows and their orientation in the ground. Thus, crabs and soil samples could be collected by digging straight down from the surface rather than by digging along the entire length of burrows that threaded through stony soil.

A miniaturized optical telemetry transmitter for small animals was designed, constructed, and field-tested on free-ranging nocturnal crabs. The device produces accurately timed flashes that can be used for individual tagging, tracking, and telemetry. When observed with a night vision scope, the flashes are visible for several hundred meters. Transmitters are inexpensive, relative simple, and rugged. Weight is less than 1 g, and working life is about 4 weeks with 4 g of hearing aid batteries. J. WILDL. MANAGE. 41(2):309-312 Little information exists concerning the behavior and ecology of nocturnal animals, due to the difficulty of observing unrestrained subjects in the dark. The optical device described here was developed to overcome some of the limitations of radiotelemetry for a study of ghost crabs (Ocypode quadrata). Radiotelemetry has been used successfully for long-range tracking (Cochran and Lord 1963), activity monitoring (Knowlton et al. 1968, Osgood and Weigl 1972) and tracing movements of mice (Rawson and Hartline 1964) and voles (Chute et al. 1974). However, the fixes provided by radio, even of animals held in an enclosure under an antenna grid (Chute et al. 1974) are approximate due to the 2-6 m wavelengths used. It is virtually impossible to localize precisely free-ranging animals by radiotriangulation without disturbing them, due to the necessity of taking bearings from several positions at close range. Exact localization and direct observation of nocturnal behavior require seeing in the dark. The image intensifiers ("starlight scopes") developed recently make this possible even in faint moonlight. Unfortunately most nocturnal animals are cryptically colored. Starlight scopes cannot create image contras where there is no target contrast; in fact, starlight scopes lose existing chromatic contrast by producing a monochromatic image. I found that ghost crabs, which are hard to see on their natural background by daylight, were impossible to see at night unless moving, even with a good-quality s arlig t cope ("Noctron IV", Varo, Inc.). The circuit described here overcomes this difficulty by producing a timed flashing light, visible to the unaided eye at close ranges, and capable of extending the useful range of a starlight scope to distances at which the subject animal would be total y undetectable. In actual use it survived exposure to surf and sand, and permit ed individual recognition and tracking of crabs from distances of up to 300 m in the field, for periods of several weeks. The circuit is quite flexible, and may be modified to telemeter I channel of data.