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Larval supply determines year-class strength of fisheries and complex ecological interactions among adults of benthic marine species. In upwelling regions, a latitudinal cline in the intensity and persistence of upwelling is thought to affect larval advection and recruitment, thereby regulating the intensity of interactions in adult populations and communities. We tested this hypothesis by determining the monthly cross-shelf abundances of nearshore benthic crustacean larvae throughout development during the peak upwelling season for 7 years in a region of intermittent upwelling and high recruitment (45°N). We tested whether larvae were found farther offshore during upwelling conditions, and we compared their interspecific cross-shelf distributions to previous results from a region of strong, persistent upwelling (38°N). We also compared larval abundances across the 2 upwelling regions for 1 year. Most species were retained nearshore, regardless of intra- and inter-annual variations in the intensity of upwelling. In both upwelling regions, larvae of each species consistently occurred at different distances from the shore. Further, there were no differences in nearshore larval abundance across upwelling regions for all but 1 larval stage of 1 species. Thus, latitudinal variations in the intensity and persistence of upwelling do not appear to affect larval survival, providing further evidence that nearshore processes may be a primary determinant of larval delivery to the rocky intertidal across these regions. © Inter-Research 2014.

Identifying biophysical mechanisms of larval transport is essential to understanding the delivery of larvae to adult habitats. In addition, harmful algal blooms (HABs) can be transported onshore from populations that form offshore. In summer 2011, we measured sea surface and bottom temperatures and daily phytoplankton abundance and intertidal cyprid (barnacle post larvae) settlement at Carmel River State Beach, California, USA. Using time-series analysis, we compared the abundance of Pseudo-nitzschia spp. and daily cyprid settlement to physical forcing mechanisms (e.g. internal tides and upwelling-relaxation events) that could generate onshore delivery. Minimum bottom water temperature was significantly cross-correlated with the spring-neap tidal cycle; minimum temperatures occurred between neap and spring tides, and maximum temperatures were recorded around neap tides. When the temperature data were transformed to remove the relationship between tides and temperature, we found significantly higher maximum sea surface temperatures during upwelling-relaxation events. We observed 4 pulses in Pseudo-nitzschia spp. abundance. Pseudo-nitzschia spp. chains were longest at the start of pulses and then decreased, suggesting that they had been transported to shore from a more productive site offshore, likely the upwelling front. Pulses occurred during periods of maximum sea surface temperature associated with upwelling-relaxation events. In contrast, cyprid settlement was significantly cross-correlated with the spring-neap tidal cycle, with settlement peaks occurring during fortnightly periods of cold bottom temperatures; onshore transport of cyprids appears to have been due to the internal tides. © Inter-Research 2014.

ABSTRACT: Explorations of the dynamics of nearshore regions of the coastal zone are missing from many efforts to understand larval transport and delivery to suitable habitats. Larval distributions in the coastal ocean are variable and depend on physical processes and larval behaviors, leading to biophysical interactions that may increase larval retention nearshore and bolster their return to natal sites. While recent evidence suggests that many larvae are retained within a few kilometers from shore, few studies incorporate measurements sufficiently close to shore to plausibly assess supply to the shoreline benthos. We measured cross-shore distributions of larvae of benthic crustaceans between 250 and 1100 m from shore (i.e. just beyond the surf zone) within the coastal boundary layer (CBL)-a region of reduced alongshore flow-and simultaneously quantified a suite of physical factors that may influence larval distributions. We found high larval abundance within the CBL, with a peak at 850 m from shore, and a decrease in abundance along the shoreward edge of the sampled transect. We also found distinctly different larval assemblages at outer stations within the CBL, as compared to inner stations that are more influenced by shoreline dynamics. These patterns persisted across sample dates, suggesting that the spatial structure of nearshore larval assemblages is at least somewhat robust to temporal changes in physical conditions. Thus, while larval abundance appears to be high within the CBL, larvae appear to be sparse within the narrow band of water adjacent to the surf zone. Low larval supply adjacent to suitable habitats has important implications for the coupling of supply and recruitment, and resulting dynamics of shoreline populations.© Inter-Research 2013. www.int-res.com.

Timing of larval release by many shore crabs is cued by environmental cycles to occur during nocturnal spring ebb tides, when larvae are transported away from high densities of planktivorous fishes in the dark. However, a recent laboratory study indicated that larval release may be weakly synchronized relative to this safe period in upwelling regions, potentially increasing fish predation. We determined the timing of larval release and predation in marshes in an upwelling region by sampling plankton and fishes during flood and ebb tides on either side of high slack tide. Larval release was weakly synchronized, peaking during spring and intermediate ebb tides in twilight and darkness. Almost all larvae (99.8%) were eaten at twilight during peak release, when they likely were more visible than at night. However, larvae comprised only 4.1% of the diets of the 3 fish species that ate them. These fish species were often absent when conditions would make larvae most vulnerable to predation, and they preferred other prey to welldefended larvae. Larvae released outside the safe period were eaten more than those that were released during the safe period, providing selection for the timing of larval release. However, despite the large numbers of larvae present outside of the safe period, predation by fishes was much lower than expected. Thus, the selective effects of fish predation may be relaxed, raising the possibility that the strength of fish predation as a selective force varies among coasts and other selective forces that may affect the timing of larval release. © Inter-Research 2013.

The maintenance of marine populations depends on the completion of larval migrations between adult and larval habitats, but the ability of microscopic larvae to regulate their movements in such a dynamic environment has been debated. Using a comparative hypothesis testing approach and intensive hourly sampling throughout the water column, we determined the ability of larvae of 6 species with different swimming abilities (2 gastropods, 2 crabs, 2 fishes) to overcome strong tidal mixing during spring tides and regulate their vertical, and hence, horizontal position, in opposing depth-stratified currents in the upper Hudson River estuary, USA. The vertical distributions of nonmotile eggs and swimming larvae generally differed, suggesting that larvae regulated depth. Eggs were passively mixed by tidal currents, but larvae typically aggregated in stratified portions of the water column, which fostered retention in the upper estuary. However, the capacity to regulate depth depended on swimming ability and the degree of mixing. In a predominantly mixed tidal environment upstream, mixing overcame most larvae when current velocities were maximal during mid-ebb or mid-flood tides; tidal vertical migrations were not evident for any species, and diel vertical migrations were apparent for only 1 species. In a partially stratified water column downstream, diel vertical migrations were apparent for larvae of 3 of 4 invertebrate species, and tidal vertical migrations were apparent for the 2 fish species. The presence of all larval stages showed that all species regulated depth sufficiently well to remain in the upper estuary. Regardless of swimming ability, larvae were retained in the estuary by occurring near the level of no net motion, even without completing tidal vertical migrations. Continuous profiling of larvae and hydrodynamics is necessary to reveal the ability of larvae to regulate depth in tidal mixing and recruit to adult populations. © Inter-Research 2013.

Trace elemental signatures incorporated into calcified structures in fish and mollusk larvae have been used to reveal population connectivity and larval dispersal trajectories. To determine whether trace element analysis could be applied to larvae that do not permanently retain calcified structures, we raised larvae of the porcelain crab Petrolisthes cinctipes from multiple locations along the northern California, USA, coast in a common water source for up to 8 wk. We analyzed 20 elements in extractions of soft tissues from embryos and the 2 larval and 1 postlarval stages. Elemental signatures of individuals in each developmental stage were compared to an atlas of signatures from each collection site using discriminant analysis to determine whether larvae could be accurately assigned to their site of origin in 2 ways. First, postlarvae were classified using a natal site atlas constructed using embryonic signatures from each site, and this classification had poor success (average 39.7% correct). Second, larvae of each stage were classified using a natal site atlas constructed using signatures of larvae from that same stage. This yielded considerably better classification success (81.7% correct overall). Thus, the same trace element signatures were not consistently maintained from embryos to postlarvae, but differences in signatures among natal sites were maintained during the larval period. Trace element signatures in soft tissues could be useful in tracking dispersal between stages and determining how many sites, rather than which sites, contributed to a cohort of larvae or settlers. © Inter-Research 2013.

Dispersal is fundamental to understanding the ecology and evolution of species and effectively managing resources, but information on dispersal is rare for the vast majority of marine life that develops as miniscule larvae in the plankton. Until recent evidence to the contrary, it was widely suspected that larvae developing in productive upwelling regimes along eastern ocean margins are susceptible to cross-shelf transport by strong, dynamic currents and often are unable to replenish populations. We now show that interspecific differences in depth preference likely play a role in regulating differences in offshore migration from adult populations. Two open-coast species (Petrolisthes cinctipes and Pachygrapsus crassipes) did not undertake endogenously timed tidal vertical migrations but an estuarine species (Hemigrapsus oregonensis) did, which would facilitate seaward dispersal. Surprisingly, none of the 3 species undertook diel vertical migrations in the laboratory, even though all do in the field. Diel vertical migrations in marine and freshwater species elsewhere in the world are cued by light and reduce fish predation, but they may be cued by turbulence in upwelling regimes, thereby reducing transport from adult populations. Thus, larvae of species that hatch in different locations and develop at different distances from the shore exhibit diverse larval swimming behaviors that regulate transport in dynamic upwelling regimes in previously undescribed ways, which has implications for population connectivity, local adaptation and resource management. Copyright © 2013 Inter-Research.

Natural trace element signatures have increasingly been used to track the dispersal of marine larvae, and these studies require an atlas of potential source populations with distinctive elemental signatures. To determine whether natal site atlases could be used repeatedly and to identify site characteristics that yield the best results, we built atlases in 5 consecutive years using embryos of the porcelain crab Petrolisthes cinctipes that were collected from 15 sites spanning 190 km of the open coast of northern California, USA. We analyzed the elemental composition of the embryos using a discriminant function optimization procedure to determine the suite of elements that resulted in the best reclassification success for individual sites and groups of sites each year. No single element or group of elements succeeded in discriminating the origins of embryos every year, and the reclassification success of the atlas varied at all spatial scales among years. Average reclassification success at the site level ranged annually from 39.5 to 54.3% correct, and combining sites into 2 or 3 areas improved the overall reclassification success to 72.5 to 97.7% correct. Sites with (1) distinctive elemental compositions of rocks, (2) unusual habitats, (3) consistent freshwater input, (4) consistent anthropogenic inputs, or (5) complex local oceano graphy had the highest reclassification success (up to 86.7% correct), but interannual variation in runoff reduced the temporal stability of the atlas. To improve population connectivity estimates, future trace element studies should consider these 5 key characteristics when selecting sites and anticipate temporal variation in natal site signatures. © Inter-Research 2013.

Many organisms live in spatially delimited habitat patches, where local extinctions are compensated by dispersal and recolonization of empty habitat patches. To predict the dynamics of such metapopulations in an era of large environmental changes, it is essential to understand the key abiotic factors affecting local occurrence and temporal variation in patch occupancy. Here, we investigated the metapopulation dynamics of the marine copepod Tigriopus californicus, which is restricted to high intertidal and supralittoral rock pools. We monitored populations of T. californicus in northern California for almost 2 yr and observed pronounced seasonal changes in patch occupancy with

Larvae are considered to be highly susceptible to offshore transport, thereby limiting recruitment in productive upwelling regions, except in the recirculation features that form in the lee of headlands. We show that 19 of 20 taxa of nearshore crustaceans were at least as common on the open coast as they were in the lee of a headland in a recruitment-limited region characterized by strong upwelling. Nine of these taxa occurred in high concentrations throughout development, indicating that larvae completed development nearshore in a coastal boundary layer of reduced Ekman transport. Larvae of 9 more taxa were prevalent as early stage larvae, and later stages were uncommon, indicating that larvae migrated offshore. The relative abundance of larval stages largely matched the vertical distributions of larvae in this study and a previous cross-shelf survey at this site, indicating that larval behavior plays a substantial role in determining whether larvae complete development nearshore or migrate offshore later in development. Larvae of taxa that occurred nearshore in high concentrations throughout development resided below a shallow Ekman layer of seaward-flowing surface waters, whereas most larvae of the other taxa occurred closer to the surface. Whether larvae undertook ontogenetic and diel vertical migrations also appeared to determine whether they were retained nearshore. Thus larval retention may be more widespread in upwelling regions than is widely believed, and the cause of recruitment limitation along upwelling coasts needs to be determined to further advance our understanding of the connectivity, dynamics and structure of coastal populations. © Inter-Research 2010.

Larvae are thought to be highly vulnerable to offshore transport of upwelling regions, limiting recruitment to infrequent wind relaxation and downwelling events. However, larvae could also be transported onshore by upwelled bottom waters, onshore wind-forcing or internal tides throughout the water column. We determined the relative importance of these hypothetical mechanisms for the timing of recruitment of 8 invertebrate taxa during the peak upwelling season in a region of strong, persistent upwelling. Recruitment was determined for 5 yr at an open embayment near the surface and bottom of the water column to examine the interaction of behavioral and physical processes regulating larval recruitment. Postlarvae consistently recruited near the surface or near the bottom depending on the species. Onshore delivery of larvae during wind relaxations and reversals did not best explain recruitment patterns in our area for most taxa. Only mussels consistently recruited more during these events, and they recruited in bottom rather than surface waters. Six crab taxa recruited primarily during upwelling. Recruitment of 7 taxa was intermittently correlated with the maximum tidal range, suggesting that internal waves also may deliver larvae onshore. Thus larvae may recruit by multiple processes in upwelling regions rather than being limited to infrequent relaxation events, leaving the mechanisms responsible for observed spatial patterns in larval recruitment and adult densities unexplained. Comprehensive studies of the behavioral and physical processes underlying larval recruitment and post-settlement mortality are needed to explain observed temporal and spatial variation in population dynamics and community structure in upwelling regions. © Inter-Research 2009.

Larvae are thought to be highly vulnerable to offshore transport in productive upwelling regions, which increases cross-shelf and alongshore dispersal, limits recruitment, and reduces the strength of community interactions. We investigated whether the last planktonic stages of shallowwater crabs (1) occur far offshore during the peak upwelling season in a region of strong upwelling that is recruitment limited, (2) occur farther offshore during upwelling than relaxation conditions, (3) occur farthest from shore at a major headland where currents are deflected offshore, and (4) recruit less during years of stronger upwelling. Crab postlarvae were collected from between 1 and 70 km from shore at 3 locations across an upwelling cell during upwelling and relaxation conditions in northern California, USA, for 3 yr, and recruitment was measured at 2 sites during 2 of these years. Postlarvae of all species collected were most abundant on the inner continental shelf (84%) and were scarce in the open ocean. Postlarvae of 3 taxa only occurred on the inner shelf, whereas postlarvae of the other 3 taxa collected occurred in low abundances on the outer shelf even during prolonged upwelling. They were abundant close to shore at the Point Reyes headland where flow is deflected offshore. Postlarvae did not occur farther from shore during a year of very strong upwelling, and 4 of 7 taxa recruited more then. Thus, crab postlarvae do not appear to be advected far offshore or recruit less during strong upwelling conditions, and the cause and extent of recruitment limitation warrants further investigation. © Inter-Research 2009.

Understanding interactions between invasive species and recipient communities is essential to determining whether invasive species will become established and spread. In this study, we explored the role of competition and the specific mechanisms of interaction in limiting the spread of the Mediterranean bay mussel Mytilus galloprovincialis within a Pacific Northwest invasion front. We examined the role of direct (interference) and indirect (exploitation) mechanisms of competition among M. galloprovincialis and 2 native mussels (M. trossulus and M. californianus). As the fastestgrowing organisms are often competitively dominant in space-limited systems, such as rocky intertidal communities, we used changes in relative performance (growth and survival) in monocultures and polycultures to assess interactions among mussels. Performance of M. galloprovincialis was always greater than that of the 2 native species of mussels in both field and laboratory manipulations of species composition and density, indicating that interspecific competition did not strongly limit the growth or survival of the invader. Moreover, the presence of M. galloprovincialis consistently led to both reduced growth and survival of M. trossulus. Laboratory studies of mussel feeding and behavior revealed M. galloprovincialis to be a robust interference competitor. The invader restricted movement, smothered and interfered with filter feeding of the 2 native species of mussels. Rather than limiting invasion, interference competition gave M. galloprovincialis a competitive advantage over the native mussels. Our results suggest M. galloprovincialis may have contributed to the displacement of M. trossulus along much of its historic southern range. ©Inter-Research 2009.

Trophic relationships among native and exotic species produce novel direct and indirect interactions that can have wide-ranging community level effects and perhaps confer invasion resistance. We investigated whether native predators have the potential to directly limit the spread of the exotic mussel Mytilus galloprovincialis or mediate interactions among native and invasive mussels at a rocky intertidal invasion front in northern California. Lower survival of M. galloprovincialis in transplanted cultures exposed to predators indicated that the invader was more vulnerable to predators than the numerically dominant native M. californianus. Survival and per capita mortality rate in monocultures and polycultures did not vary for either M. galloprovincialis or M. californianus, suggesting that predator-mediated apparent competition and associational defense did not occur. Complementary laboratory feeding trials determined which among 3 intertidal predators preferred the exotic to 2 native species of mussel. The whelk Nucella ostrina was most selective, consuming the thinner shelled mussels (M. galloprovincialis and the native M. trossulus) rather than the thickershelled native species M. californianus. The crab Cancer antennaiius and the sea star Pisaster ochraceus showed no preferences among mussel species. N. ostrina were commonly observed among field-transplanted mussels; thus whelk prédation may be especially important in limiting the establishment of the invasive mussel. However, 15% of M. galloprovincialis remained intact in the field after 1 yr, suggesting that prédation alone may not inhibit establishment of the invader. A tenuous balance between larval settlement and early post-settlement prédation likely characterizes the invasion front. © Inter-Research 2009.

Delivery mechanisms for crab postlarvae along upwelling coasts have been inferred from weekly sampling, but more frequent sampling is needed to better relate highly variable oceanographic conditions to postlarval supply. Settlement of 8 crab taxa was measured in Bodega Bay, California every 2 d from 12 May through 3 July, 2002. Abundance of postlarval and juvenile settlers was cross-correlated with physical variables. Four upwelling and 4 relaxation events were recorded as fluctuations in wind stress and sea temperature during this period. Transitions to and from upwelling conditions in Bodega Bay were brief and temperature changes occurred rapidly. The strongest correlations between crab abundance and physical variables indicative of upwelling and relaxation conditions were observed for Cancer magister, which settled primarily during relaxation-favorable conditions, and for Cancer antennarius/productus, which settled primarily during upwelling-favorable conditions, suggesting interspecific differences in delivery of postlarvae to adult habitat. Weak correlations with upwelling-favorable conditions were observed for Pugettia producta/richii and Pagurus spp. Settlement of Hemigrapsus nudus, Petrolisthes cinctipes, and P. eriomerus exhibited significant correlations with changes in tidal height. These results highlight the existence of multiple taxon-specific delivery mechanisms of closely related taxa in one small geographic region. © Inter-Research 2006.

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. © Inter-Research 2006.

Tidal variation may cause reproductive timing by fiddler crabs Uca pugilator (Bosc) to vary geographically and seasonally. Fiddler crabs in a semidiurnal tidal regime along the Atlantic coast of the USA were previously shown to release larvae synchronously during maximum amplitude evening high tides near new and full moons throughout the reproductive season. In the present study, fiddler crabs in a diurnal tidal regime on the Gulf coast of the USA released larvae during intermediate amplitude flood tides near dawn regardless of lunar phase throughout most of the reproductive season. Late in the summer, peak larval release occurred near maximum amplitude high tides as on the Atlantic coast. In a mixed semidiurnal tidal regime on the Gulf coast, peak larval release by fiddler crabs occurred during intermediate amplitude high tides near dawn, but biweekly periodicity was weak late in the reproductive season. Intraspecific variation in reproductive timing arose because nocturnal maximum high tides did not occur along the Gulf coast during most of the summer, but these tides returned during late summer in the diurnal tidal regime. Reproductive timing changed concomitantly with changing phase relationships of tides with light-dark and lunar cycles. Variation in reproductive timing is phenotypic because crabs that were translocated reciprocally between diurnal and mixed semidiurnal tidal regimes entrained to the timing patterns of local crabs. A hierarchy of rhythms regulating reproductive timing was revealed by the degree to which larval release kept phase with lunar, tidal amplitude, tidal and light-dark cycles. These hierarchies enabled crabs to track phase shifts of cycles in variable tidal environments and may enhance mean reproductive success throughout the range of the species.

Larval supply and early postsettlement mortality are crucial to the maintenance of most marine populations. Larval supply may be especially important in regulating populations of blue crabs Callinectes sapidus because many larvae could be lost during long migrations between estuaries and offshore waters. We examined the relative contributions of differential transport and habitat preferences of megalopae (postlarvae) to 5 potential nursery habitats in Mobile Bay and Mississippi Sound, Alabama, USA. Settlement in each habitat was determined daily 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 minimal. In 1991, onshore winds were light and infrequent, and megalopae settled even more densely during minimum amplitude tides. Semidaily collections of megalopae at dusk and dawn revealed that most megalopae recruit to estuaries during nocturnal flood tides, which only occur during summer and fall in this diurnal tidal regime. Thus, onshore winds facilitated transport of megalopae into estuaries episodically, but megalopae recruited regularly and abundantly during nocturnal minimum amplitude flood tides even when onshore winds 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 competent to settle from the plankton. Physiological tolerances may explain why most larvae settled in high salinity waters, but differences in current regimes 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 determine whether megalopae prefer to settle in seagrass beds, marshes or unvegetated substrate once they arrive at a site. Megalopae strongly preferred to settle on vegetation, but it remains unclear whether or not they discriminate among plant types. Thus, passive delivery and habitat preferences of megalopae both may determine the initial distributions of juvenile blue crabs.

Larval supply and early postsettlement mortality are crucial to the maintenance of most marine populations. Larval supply may be especially important in regulating populations of blue crabs Callinectes sapidus because many larvae could be lost during long migrations between estuaries and offshore waters. We examined the relative contributions of differential transport and habitat preferences of megalopae (postlarvae) to 5 potential nursery habitats in Mobile Bay and Mississippi Sound, Alabama, USA. Settlement in each habitat was determined daily 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 minimal. In 1991, onshore winds were light and infrequent, and megalopae settled even more densely during minimum amplitude tides. Semidaily collections of megalopae at dusk and dawn revealed that most megalopae recruit to estuaries during nocturnal flood tides, which only occur during summer and fall in this diurnal tidal regime. Thus, onshore winds facilitated transport of megalopae into estuaries episodically, but megalopae recruited regularly and abundantly during nocturnal minimum amplitude flood tides even when onshore winds 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 competent to settle from the plankton. Physiological tolerances may explain why most larvae settled in high salinity waters, but differences in current regimes 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 determine whether megalopae prefer to settle in seagrass beds, marshes or unvegetated substrate once they arrive at a site. Megalopae strongly preferred to settle on vegetation, but it remains unclear whether or not they discriminate among plant types. Thus, passive delivery and habitat preferences of megalopae both may determine the initial distributions of juvenile blue crabs.