Larval supply and early postsettlement mortality are crucial to the maintenance of most manne populat~ons Larval supply may be espec~ally important in regulating populat~ons of blue crabs Callinectes sapidus because many larvae could be lost during long migrations between estuanes and offshore waters We examined the relative contnbutions of different~al transport and habltat preferences of megalopae (postlarvae) to 5 potential nursery habitats In Mobile Bay and M~ssissippl Sound Alabama USA Settlement In each habitat was determined dally during summer and fall for 2 yr and was related to sea surface temperature wind stress, tides, current velocity and the lunar and tidal amplitude cycles In 1990, most megalopae settled when winds blew megalopae onshore and tidal amplitudes were m~n i m a l In 1991, onshore winds were light and Infrequent, and megalopae settled even more densely d u n n g minlmum amplitude tides Sem~dally collect~ons of megalopae at dusk and dawn revealed that most megalopae recruit to estuanes during nocturnal flood tldes, which only occur dunng summer and fall in this diurnal tidal regime Thus, onshore winds facilitated transport of megalopae into estuanes ep~sodically, but megalopae recruited regularly and abundantly d u n n g nocturnal mlnilnum a m p l~t u d e flood t~d e s even when onshore w~n d s were light or absent most megalopae were collected in the lower bay although some megalopae settled at the head of the estuary 50 km away from the baymouth Megalopae required about 2 d to travel this distance as they became increasingly conlpetent to settle from the plankton Physiological tolerances may e x p l a~n why most larvae settled in high salinity waters, but differences in current regunes may best explain differences in settlement among sites In the lower bay Several types of substrate were transplanted from nursery habitats to a sandy area at the baymouth to d e t e r m~n e whether megdlopae prefer to settle in seagrass beds, marshes or unvegetated substrate once they arnve at a site Megalopae strongly preferred to settle on vegetation, but ~t remains unclear whether or not they discriminate among plant types Thus, passlve dehvery and habitat preferences of megalopae both may d e t e r m~n e the initial distnbutions of l u v e n~l e blue crabs

The utility of the lined shore crab Pachygrapsus crassipes as an indicator of small-scale variation in the condition of salt marshes was determined by conducting detailed mark-recapture studies of the spatial and temporal patterns of movement in 2 marshes in northern and southern California, and by conducting a stable isotope study along a nutrient gradient at one of the marshes. Crabs (1158) were captured from creek bank and vegetated marsh habitats, tagged, and released. Most crabs were recaptured in the same trap where they were originally tagged, and on average, they traveled less than 5 m from the site of first capture. The mean distance traveled did not increase significantly with the time between captures. A high percentage of crabs (62.1%) tagged near the creek bank remained there; fewer tagged crabs moved between the creek bank and the marsh plain (18.2%) or remained on the marsh plain (12.6%). Crabs moved least along creek banks and farthest when crossing creeks, although few of them did the latter (6.2%). During spring tides, crabs moved from tidal creeks onto the marsh plain. The nitrogen isotope data mirrored the gradient in nutrient input, supporting the conclusion that P. crassipes remained and fed within a localized area. Thus, the lined shore crab can serve as an indicator of small-scale differences in contaminant exposure. Furthermore, semiterrestrial species that are readily sampled and move little are abundant around the world, making them ideal indicators of habitat condition.KEY WORDS: Movement · Indicator species · Mark-recapture · Nitrogen stable isotope · Crab · Pachygrapsus crassipes · Salt marsh Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 314: [271][272][273][274][275][276][277][278][279][280][281] 2006 understanding of crabs residing in salt marshes has developed in many parts of the world from studying ocypodid species, such as fiddler crabs (Uca spp.), which leave their burrows to forage during low tides (Crane 1975). However, our understanding of crabs occupying marshes along the west coast of North America is much more limited because the grapsid crabs Hemigrapsus oregonensis and Pachygrapsus crassipes primarily remain in burrows during daytime low tides (Hiatt 1942, Willason 1981, Ricketts et al. 1985, making them difficult to observe. The utility of crabs as an indicator of small-scale differences in habitat condition critically depends on the extent of their movements.Movement is a fundamental part of animals' lives, being essential for foraging, reproduction, and avoiding predators and competitors. However, movement receives more attention on land than in the marine environment, where sessile and sedentary lifestyles are more common due to (1) the delivery of food, (2) removal of waste, and (3) transfer of gametes by currents (Strathmann 1990). In the case of crabs, many juveniles and adults rely on heavy exoskeletons coupled with burrows, holes and crevices for protection from predators, seemingly moving little...

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.