Larval Dispersal Potential Research Articles

Abundance and dispersal potential of horseshoe crab (Limulus polyphemus) larvae in the Delaware estuary

The distribution, abundance, and dispersal patterns of horseshoe crab (Limulus polyphemus) trilobite larvae were determined from 671 plankton tows taken near a spawning beach in lower Delaware Bay, New Jersey, in 1998 and 1999. In both years, peaks in larval abundance occurred during periods of rough surf (>30 cm wave heights). Planktonic larvae were significantly more abundant nocturnally than during the day, but there was no evidence of a lunar component to larval abundance. Larvae were strongly concentrated inshore; trilobites were 10–100 times more abundant in the immediate vicinity of the shoreline than they were 100–200 m offshore. The strong tendency ofLimulus larvae to remain close to the beach suggests that their capability for long-range dispersal between estuaries is extremely limited. We suggest that limited larval dispersal potential may help explain previously observed patterns of genetic variation among the Mid-Atlantic horseshoe crab populations.

DISPERSAL POTENTIAL OF MARINE INVERTEBRATES IN DIVERSE HABITATS

Life-history parameters were used to estimate the dispersal potential of 1021 marine macroinvertebrates recorded in species lists from 91 sites comprising rocky intertidal, subtidal, kelp forest, sandy beach, and soft-bottom habitats in Washington, Oregon, and California. Mean species richness was significantly greater in the California rocky subtidal habitat. Data on development mode, planktonic larval duration, rafting potential, and adult mobility were compiled, and summaries of the dispersal potentials of taxa within each habitat type were generated and compared. In summary, development mode was known or estimated for 76% of species; larval planktonic duration for 49%; adult mobility for 76%; and rafting potential for 46%. In comparisons of species' life-history traits among habitats, sand-dominated habitats were distinct from rocky habitats. In rocky habitats, ∼42% of species had planktonic feeding larvae, 43% had planktonic nonfeeding larvae, and 15% had nonplanktonic larvae. Sandy intertidal habitats had higher proportions of taxa with nondispersing, nonplanktonic larvae and lower proportions of planktonic feeding and nonfeeding larvae than all other sites. Soft-bottom subtidal communities had the highest proportion of taxa with planktonic feeding development and larvae with planktonic lifespans >30 d. Species in soft-bottom subtidal sites, therefore, have the greatest potential for extensive larval dispersal, whereas species in soft-bottom intertidal sites have the least potential for larval dispersal. In these sites with limited larval dispersal potential, there is greater potential for adult dispersal through adult movement and rafting. These differences in the dispersal potential of larvae and adults suggest that the effect of environmental changes and the effectiveness of reserves may differ between habitats. Conservation methods, including the use of marine reserves, must therefore be tailored to the habitat of interest if effective protection of community resources is to be achieved.

Larval dispersal potential of the tubeworm Riftia pachyptila at deep-sea hydrothermal vents.

Hydrothermal vents are ephemeral because of frequent volcanic and tectonic activities associated with crust formation. Although the larvae of hydrothermal vent fauna can rapidly colonize new vent sites separated by tens to hundreds of kilometres, the mechanisms by which these larvae disperse and recruit are not understood. Here we integrate physiological, developmental and hydrodynamic data to estimate the dispersal potential of larvae of the giant tubeworm Riftia pachyptila. At in situ temperatures and pressures (2 degrees C and 250 atm), we estimate that the metabolic lifespan for a larva of R. pachyptila averages 38 days. In the measured flow regime at a fast-spreading ridge axis (9 degrees 50' N; East Pacific Rise), this lifespan results in potential along-ridge dispersal distances that rarely exceed 100 km. This limited dispersal results not from the physiological performance of the embryos and larvae, but instead from transport limitations imposed by periodic reversals in along-ridge flows and sustained episodes of across-ridge flow. The lifespan presented for these larvae can now be used to predict dispersal under current regimes at other hydrothermal vent sites.

The genetic structure of intertidal populations of two species of nudibranch molluscs with planktotrophic and pelagic lecithotrophic larval stages: are pelagic larvae “for” dispersal?

Planktonic larvae of benthic marine invertebrates may confer larval dispersal and colonization potential on the reproductive adult. Analyses of genetic heterogeneity of local populations provide an indirect means of assessing gene flow and the scale of realized dispersal of larval migrants. Here we compared populations of two species of nudibranchs with long term planktotrophic ( Goniodoris nodosa) and shorter term pelagic lecithotrophic ( Adalaria proxima) veliger stages. Both species have annual life cycles, population turnover is absolute and free-swimming larvae hatch from benthic spawn masses. G. nodosa larvae are pelagic for up to ∼3 months, whereas those of A. proxima can metamorphose within 1–2 d of release although, at least in the laboratory, they may delay metamorphosis for several weeks. The broad ranges of pelagic larval transport potential were estimated at 10 2–10 3 km for G. nodosa and 10 1–10 2 km for A. proxima: significant differentiation of populations of G. nodosa was predicted to occur on a scale of 10 3–10 4 km, whereas for A. proxima differentiation was expected on a scale of perhaps only 10 2–10 3 km. For both species, analyses were undertaken of allozyme variation among sites throughout the 1600 km British Isles range of A. proxima. F-statistic analyses showed no evidence of population differentiation for G. nodosa (11 populations). By contrast, comparable data for 19 populations of A. proxima showed very high levels of differentiation, but no obvious pattern of variation or significant isolation by distance. More detailed sampling of nine populations of A. proxima over a 26.18 km range in W Scotland – in a location characterised by highly dispersive tidal currents – revealed (1) similar levels of differentiation to the 1600 km range, (2) clear distance-related clinal patterns of variation, and (3) a significant inverse relationship between genetic differentiation and geographic distance. For Adalaria proxima there was evidence of significant differentiation of populations on a scale of ≤10 1 km. This was counter to our expectations of larval transport potential for A. proxima and implies that these larvae are behaviourally adapted to avoid dispersal in the water column and thereby recruit locally. Whilst the planktotrophic species, G. nodosa, conformed to our expectations, the clear implication of the data for A. proxima is that possession of a pelagic larval stage does not necessarily facilitate dispersal and colonisation potential for this sedentary invertebrate. Extrapolations and predictions of dispersal potential, and gene flow in natural populations, based on laboratory observations of the larval phase duration may be markedly error-prone.

Genetic relationships among subpopulations of the American lobster (Homarus americanus) as revealed by random amplified polymorphic DNA

Random amplified polymorphic DNA (RAPD) profiles were used in a preliminary investigation of the genetic relationships among American lobsters (Homarus americanus) from the ecologically disparate and geographically separate regions of the southern Gulf of St. Lawrence, a bay off southwestern Nova Scotia, and a deep-sea canyon off Georges Bank. Phenotypic analyses of the RAPD bands showed no significant difference between samples caught at these three geographic locations. Lobsters from the Gulf of Maine, collected inshore from Lobster Bay, Nova Scotia, and offshore from Georges Bank, were genetically the most similar (D = 0.002), whereas Gulf of St. Lawrence lobsters were about three times as genetically distant from these two subpopulations (D = 0.005-0.006). However, FSTvalues at each RAPD band ranged from <0.000 to 0.073, indicating that lobsters at these three locations are not genetically isolated. The number of migrants needed to account for this observed level of genetic differentiation could be as few as five animals in each generation. The present findings should not have been surprising given the enormous potential for larval dispersal, the wide ranging movements of adult lobsters within each region, and the level of anthropogenic interference through both displacement of larvae and adults over the past century in the name of conservation, particularly adults released into the Gulf of Maine.

GHOST SHRIMPS OF THE GENUS LEPIDOPHTHALMUS FROM THE CARIBBEAN REGION, WITH DESCRIPTION OF L. RICHARDI, NEW SPECIES, FROM BELIZE (DECAPODA: THALASSINIDEA: CALLIANASSIDAE)

ABSTRACT Lepidophthalmus jamaicense, originally described in limited detail on the basis of two male type specimens from Montego Bay, Jamaica, is redescribed and fully illustrated in the course of our examination of the original types, a large series of recently collected male and female topotypes, and recent collections from the southeastern Caribbean Sea. Comparative morphological studies of all the known western Atlantic species serve to distinguish materials from Belize, which are herein recognized as L. richardi, new species. Included in these comparisons and descriptions are detailed studies of ventral cuticular armor in the anterior abdominal somites, an apparent apomorphic character of particular value in segregating tropical western Atlantic populations. The occurrence of L. jamaicense in southeastern Cuba is confirmed from reexamination of museum material, and the range of the species is extended to Tobago and coastal Venezuela in the extreme southeastern Caribbean. While there appears to be strong potential for regional endemism in western Atlantic species of the genus Lepidophthalmus, the widely separated insular populations of L. jamaicense in the Antillean region appear to be undifferentiated. Reproductive history and potential for larval dispersal in this species remains unknown and may not conform to the abbreviated life histories reported for its western Atlantic congeners.

Drift Tube Studies of Bay-Ocean Water Exchange and Implications for Larval Dispersal

Surface water transport and larval dispersal potential within Mission Bay, San Diego, California and along the southern California coast were studied with drift test tubes. Drift tubes, released once during each season at six sites inside Mission Bay, traveled up to 173 km north and 205 km south of Mission Bay at maximum rates of 36 cm per s (north) and 50 cm per s (south). These findings were used to estimate probability of larval transport out of Mission Bay for the intertidal spionid polychaete Pseudopolydora paucibranchiata (Okuda) which occurred in the back of the bay. Outer coast drift tube returns were used to determine potential for gene flow, via larval exchange, between populations in isolated bays along the California coast. Drift tube recoveries and larval abundances in the plankton indicate that few Pseudopolydora larvae leave Mission Bay, but that longshore currents can carry those which do to other suitable bay habitats.

Genic Variability, Dispersal, and Differentiation in Two Species of Ophiuroids from Southern California

Genic Variability, Dispersal, and Differentiation in Two Species of Ophiuroids from Southern California

The Behavior of Stomatopod Crustacea, and Its Relationship to Rates of Evolution

The objective of this paper is to document patterns of complexity in the aggressive and reproductive behavior of mantis shrimps, and to test the hypothesis that lineages with more complex behavior evolve more rapidly than those with relatively simple behavior. Stomatopod taxa that occupy preformed holes in coral or rock habitats show more specialized social behavior, more elaborate morphological adaptations for aggression (color patterns, ornamentation, and armor), complex courtship and copulation, and more extensive parental care than taxa that excavate their own burrows in mud or sand substrates. Similarly, taxa of large body size in both coarse and level bottom habitats show more complex agonistic interactions and associated morphological adaptations than smaller relatives. We use a biogeographical and morphological method to examine degree of taxonomic divergence, degree of local species radiation, and incidence of apparent extinction in the East Pacific, West Atlantic, and East Pacific zoogeographic subregions for lineages of stomatopods with relatively complex or simple social behavior. We hypothesize that lineages with complex behavior have more endemic species, fewer cognates, and fewer conspecifics among these subregions than lineages with relatively simple social behavior; that lineages with complex behavior undergo more local species multiplication than lineages with relatively simple behavior; and that extinctions are more frequent in species with more complex than simple behavior. However, species that occupy coarse substrates and have associated complex behavior and morphology do not diverge, multiply, or become extinct significantly faster than expected. Similarly, larger taxa do not evolve more rapidly than relatives of smaller body size. Instead, rates of divergence and speciation are significantly inversely related to body size and larval dispersal potential. Although stomatopods show some of the most complex behavior known in invertebrates (with the possible exception of the cephalopods), this behavioral sophistication does not appear to be a predominant force molding the pace of evolutionary change in these marine crustaceans.