Regional differences in duration of the planktonic larval stage of reef fishes in the eastern Pacific Ocean

Regional variation in the duration of the planktonic larval phase of three species of reef fishes, Thalassoma lucasanum (Labridae), Stegastes flavilatus, and Microspathodon dorsalis (Pomacentridae) was investigated between 1982 and 1991 at several sites in the tropical eastern Pacific over a distance of 3500 km, encompassing virtually their entire range of distribution. Durations of the larval phase, determined from counts of daily otolith increments, were significantly different (1.3 to 1.6 x) between sites. Populations of all three species had a consistently shorter larval life at the most northern site, Cabo San Lucas (Mexico) compared to Panamá and the offshore islands of Galápagos and Cocos. Analyses of otolith increment width over the precompetent period revealed that this disparity in larval duration primarily reflected differences in larval growth rates: faster growing fish spent less time in the plankton. In T. lucasanum, some of the variation in larval duration between Panamá and offshore sites (Galápagos Islands and Cocos Island) may be accounted for by a higher frequency of individuals delaying metamorphosis at the offshore sites. These data indicate that conditions in the planktonic environment are not homogeneous throughout the tropical eastern Pacific and may have a profound effect on aspects of the larval ecology of reef fishes in this region.     

Planktonic larval duration and settlement marks on the otoliths of Mediterranean littoral fishes

The planktonic larval duration (PLD) was estimated for 42 species of littoral fishes from the north-western Mediterranean Sea. Daily increments and settlement marks on the otoliths (sagittae or lapilli) of new settlers and post-settlers were used to determine the larval stage duration. We also used PLD in the new settlers of some species to confirm the accuracy of the settlement marks in post-settlers. The duration of the planktonic larval stage ranges from 9 days in Symphodus ocellatus to 55 days in Xyrichtis novacula and 71 days in Lipophrys trigloides. Species in the same family did not display any clear tendency toward having similar PLDs. On the other hand, larval duration tended to be similar within a genus, with the exception of Lipophrys. Among conspecifics, the time spent in the plankton usually varied only by 2-7 days, except in Aidablennius sphynx, Lipophrys trigloides, Coris julis and Thalassoma pavo. No clear patterns were discernible in genera, with some species that settled in winter and other species that settled in summer, although we observed a certain tendency of individuals of closely related species (e.g. family Sparidae) to have a shorter larval duration in the warmer part of the year than in the colder part of the year. Settlement marks have been observed on the otoliths of all the species studied, and the PLDs in new settlers are an appropriate means of validating settlement marks. A rapid decrease in increment width over settlement (type Ia) is the most common type of mark (66.7% of the total species studied).     

Duration of the planktonic larval stage of one hundred species of Pacific and Atlantic wrasses (family Labridae)

The planktonic larval durations of a preliminary sample of one hundred species of wrasses from both the Pacific and Atlantic Oceans were estimated with the use of the daily otolith-increment aging-technique. Larval durations were determined by counting the number of daily increments between the center of the otolith and the mark corresponding to settlement. The duration of the planktonic larval phase of wrasses appears to be extremely variable between species, ranging from 15 d in Diproctacanthus xanthurus to 121 d in a specimen of Thalassoma ballieui. Larval durations within species were also variable, especially in species with relatively long durations. Congeners tended to have similar larval durations and similar otolith-increment characteristics. Hawaiian and Eastern Pacific species had longer larval durations than their Caribbean or Western Pacific congeners. Similarly, Hawaiian populations had significantly longer larval durations than their Western Pacific conspecifics. The implications of these findings for biogeographical studies are discussed.     

Growth,dispersal, and identification of planktonic labrid and pomacentrid reef-fish larvae in the eastern Pacific Ocean

Planktonic larvae of six genera of labrid and pomacentrid reef fishes were captured in march 1985 in the eastern Pacific Ocean several hundred kilometers from the nearest reefs. The larvae were identified to genus by fin-ray counts as well as by comparison of their larval otolith morphology with that of known species. The larval otolith morphologies of known species were derived from measurements of the larval otolith embedded within the otoliths of settled juveniles (as delineated by the daily otolith-increment marks corresponding to the late larval period). The body morphology and melanophore patterns of the eastern Pacific labird and pomacentrid larvae closely matched those of congeneric larvae described from other oceans. Growth rates of larvae less than about 70 d old were similar between taxa (from 0.13 to 0.19 mm d^-1). After about 70 d in the plankton, labrid larvae grew much more slowly (0.06 mm d^-1 in Xyrichtys sp.). Labrid larvae had long larval durations (up to 131 d in Xyrichtys sp.), while the larval lives of the pomacentrids appeared to be shorter and much less variable. Larvae of many different ages occurred within the same water mass, and young cohorts of larvae appeared continuously over the sampling period. Some larvae were as young as 21 d, indicating that reef-fish larvae are capable of rapid long-distance dispersal (at least 18 km d^-1).     

Daily otolith increments and recruitment in two coral-reef wrasses,Thalassoma bifasciatum and Halichoeres bivittatus

Increments on the otoliths of two common coral reef fishes, the bluehead wrasse Thalassoma bifasciatum and the slippery dick Halichoeres bivittatus, were demonstrated by mark-recapture experiments to be daily. Otoliths were marked in two ways; by depriving fish of light, food, and temperature cycles and also by supplemental feeding in the field. Both experiments were performed in late 1980 in the San Blas Islands of Panamá. A mark corresponding to settlement of the planktonic larva onto the reef was found on the otoliths of the bluehead wrasse. This settlement mark was used to calculate the dates of settlement of a collection of juveniles of this species taken from a patch reef in the San Blas Islands of Panamá in 1981. Settlement occurred in short and irregular bursts. The number of daily increments before the settlement mark indicates a planktonic larval life of 40 to 72 d.     

Comparison of larval duration and pre- and post-settlement growth in two species of damselfish,Chromis atripectoralis andPomacentrus coelestis (Pisces: Pomacentridae), from the Great Barrier Reef

Light traps were used to capture larval fishes, immediately before settlement, at two localities 500 km apart on the Great Barrier Reef (GBR) in December, 1987. Samples from Lizard Island, in the northern GBR, and Davies Reef, in the central GBR, were dominated by two species of damselfish:Chromis atripectralis andPomacentrus coelestis. Analysis of otoliths revealed significant differences in both size and age at settlement between the two localities forP. coelestis, but not forC. atripectoralis. Growth rates determined for pre- and post-settlementP. coelestis suggested a sigmoidal growth trajectory through the larval life, with growth slowing as fishes approached the time of settlement. Post-settlement growth rates were faster than growth prior to settlement in both species. Growth in both species was, however, similar between localities. The relationship between fish size and otolith size was complex, varying both between pre- and post-settlement fishes, and among localities. This emphasizes the need to validate the relationship between fish size and otolith size before otoliths may be used to back-calculate individual growth trajectories.Contribution No. 500 from the Australian Institute of Marine Science     

Gene flow at three spatial scales in a coral reef fish, the three-spot dascyllus, Dascyllus trimaculatus

Dispersal in coral reef fishes occurs predominantly during the larval planktonic stage of their life cycle. With relatively brief larval stages, damselfishes (Pomacentridae) are likely to exhibit limited dispersal. This study evaluates gene flow at three spatial scales in one species of coral reef damselfish, Dascyllus trimaculatus. Samples were collected at seven locations at Moorea, Society Islands, French Polynesia. Phylogenetic relationships and gene flow based on mitochondrial control region DNA sequences between these locations were evaluated (first spatial scale). Although spatial structure was not found, molecular markers showed clear temporal structure, which may be because pulses of settling larvae have distinct genetic composition. Moorea samples were then compared with individuals from a distant island (750 km), Rangiroa, Tuamotu Archipelago, French Polynesia (second spatial scale). Post-recruitment events (selection) and gene flow were probably responsible for the lack of structure observed between populations from Moorea and Rangiroa. Finally, samples from six Indo-West Pacific locations, Zanzibar, Indonesia, Japan, Christmas Island, Hawaii, and French Polynesia were compared (third spatial scale). Strong population structure was observed between Indo-West Pacific populations. Received: 26 May 2000 / Accepted: 10 October 2000     

Settlement patterns and post-settlement survival in two Mediterranean littoral fishes: influences of early-life traits and environmental variables

We examined the relationships between daily pattern of settlement and environmental parameters during two consecutive years in two littoral fishes, Lipophrys trigloides (Blenniidae) and Chromis chromis (Pomacentridae), in the NW Mediterranean Sea. We also used individual early-life traits (pelagic larval duration, size at hatching and size at settlement) calculated from otoliths, to study the proximate causes of settlement variability and size-selective mortality after settlement. Several early-life characteristics of L. trigloides (planktonic larval duration and size at hatching), and environmental variables averaged during the whole planktonic period (e.g. water temperature, wave height, solar radiation) were related with the magnitude of settlement. In contrast, C. chromis showed no significant relationships between early-life traits and the magnitude of settlement, and a weak relationship between settlement magnitude and environmental variables. Furthermore, juvenile survivors showed larger size at hatching than settlers, indicating that size at hatching affected the juvenile survival of the two species. These results suggest that survival was linked largely to conditions at hatching for both species.     

The relationship between population genetic structure and pelagic larval duration in coral reef fishes on the Great Barrier Reef

Pelagic larval duration (PLD) is a commonly used proxy for dispersal potential in coral reef fishes. Here we examine the relationship between PLD, genetic structure and genetic variability in geographically widespread and ecological generalist species from one coral reef fish family (Pomacentridae) that differs in mean larval duration by more than a month. The genetic structure was estimated in eight species using a mitochondrial molecular marker (D-loop) and in a sub-set of five species using nuclear molecular markers (ISSRs). Estimates of genetic differentiation were similar among species with pelagic larvae, but differed between molecular markers. The mtDNA indicated no structure in all species except one, while the ISSR indicated some structure between the sampling locations in all species. We detected a relationship between PLD and genetic structure using both markers. These relationships, however, were caused by a single species, Acanthochromis polyacanthus, which differs from all the other species examined here in lacking a larval phase. With this species excluded, there was no relationship between PLD and genetic structure using either marker despite a range of PLDs of more than 20 days. Genetic diversities were generally high in all species and did not differ significantly among species and locations. Nucleotide diversity and total heterozygosity were negatively related to maximum PLD but again these relationships were caused by A. polyacanthus and disappeared when this species was excluded. These genetic patterns are consistent with moderate gene flow among well-connected locations and indicate that at this phylogenetic level (i.e., within family) the duration of the pelagic larval phase is unrelated to the patterns of genetic differentiation.     

Effects of selective settlement and of aggression by residents on distribution of young recruits of two tropical damselfishes

The reef fishes that settled on an array of experimental corals at Lizard Island, Queensland, Australia, were counted during a pulse of recruitment in December 1986. NeitherPomacentrus sp. norP. amboinensis showed any evidence that harassment by residentDascyllus aruanus caused a decrease in persistence during the first day after settlement. LarvalPomacentrus sp. settled selectively on corals without residentD. aruanus. The results forP. amboinensis were ambiguous. Settlers of both species positioned themselves closer to the sand on corals with residentD. aruanus than on unoccupied corals. This could reduce access to planktonic food and increase the risk of predation. Adult aggression may be less important and active selection of settlement sites by larvae may be more important to the distribution of recruits than is suggested by the literature. The presence or absence of particular species should be included among the cues that larval reef fishes use to choose settlement sites.     

Early life history of the American conger eel (<Emphasis Type="Italic">Conger oceanicus</Emphasis>) as revealed by otolith microstructure and microchemistry of metamorphosing leptocephali

The early life history of the American conger eel, Conger oceanicus, was studied using otolith microstructure and chemical composition in metamorphosing leptocephali collected from New Jersey estuarine waters. The age of leptocephali was estimated by counting daily growth increments. Age of early metamorphosing leptocephali at recruitment to the estuary ranged from 155 to 183 days, indicating that migration of conger eel leptocephali from their oceanic spawning ground to the estuary requires 5–6 months. Back-calculated hatching dates suggest that the spawning season lasted 3 months, from late October to mid-December. However, in the late metamorphic leptocephali, the presence of an unclear peripheral zone in the otolith prevents the accurate estimation of the larval stage duration. The calcium content was almost constant throughout the otoliths. Both strontium and Sr:Ca ratios increased with age, but dramatically decreased at age 70–120 days. The otolith increment width also showed a marked increase at the same ages, indicating the onset of metamorphosis. A negative correlation between age at metamorphosis and otolith growth rate indicates that faster growing leptocephali arrive at the estuary earlier than slower growing ones. A close relationship was also found between age at recruitment and age at metamorphosis, suggesting that individuals that metamorphosed earlier were recruited to the estuary at a younger age. This larval migration pattern appears to be similar among anguilliform fishes.Communicated by S.A. Poulet, Roscoff     

Implications of life history for genetic structure and migration rates of southern African coastal invertebrates: planktonic,abbreviated and direct development

The amount of genetic structure in marine invertebrates is often thought to be negatively correlated with larval duration. However, larval retention may increase genetic structure in species with long-lived planktonic larvae, and rafting provides a means of dispersal for species that lack a larval dispersal phase. We compared genetic structure, demographic histories and levels of gene flow of regional lineages (in most cases defined by biogeographic region) of five southern African coastal invertebrates with three main types of larval development: (1) dispersal by long-lived planktonic larvae (mudprawn Upogebia africana and brown mussel Perna perna), (2) abbreviated larval development (crown crab Hymenosoma orbiculare) and (3) direct development (estuarine isopod Exosphaeroma hylecoetes and estuarine cumacean Iphinoe truncata). We hypothesized that H. orbiculare, having abbreviated larval development, would employ a strategy of larval retention, resulting in genetic structure comparable to that of the direct developers rather than the planktonic dispersers. However, regional population structure was significantly lower in all species with planktonic larvae, including H. orbiculare, than in the direct developers. Moreover, nested clade analysis identified demographic histories resulting from low levels of gene flow (isolation by distance and allopatric fragmentation) in the direct developers only, and migration rates were significantly higher in all three species having planktonic larvae than in the direct developers. We conclude that the amount of genetic structure within marine biogeographic regions strongly depends on the presence or absence of free-swimming larvae. Whether such larvae are primarily exported or retained, whether they have long or short larval duration, and whether or not they are capable of active dispersal seems to have little effect on connectivity among populations.     

Temporal genetic variation in subpopulations of bicolor damselfish (Stegastes partitus) inhabiting coral reefs in the Florida Keys

In 1986 we observed significant genetic heterogeneity among samples of bicolor damselfish (Stegastes partitus) from geographically proximate coral reefs in the Florida Keys. This result was in contrast to results of virtually all previous studies of coral reef fishes. To assess temporal stability of localized genetic differentiation, we resampled reefs in 1989. Within approximately two generations, allele frequencies at the most differentiated locus,ACO-1 ^*, had changed by as much as 0.65, resulting in almost complete homogeneity between previously differentiated subpopulations. Estimates of 10.78 migrants per generation suggested that high gene flow is the most likely factor responsible for the significant change in allele frequencies. We attribute the original genetic differentiation to a population bottleneck, possibly caused by environmental perturbations such as hurricanes and consequent genetic drift. For reef fishes with pelagic egg and/or larval stages, a growing body of data suggests that: (1) populations are geographically extensive gene pools, and (2) rates of dispersal appear to be high enough to allow for continual repopulation of isolated and/or perturbed coral reef communities.     

Influence of contrasting larval developmental types upon the population-genetic structure of cheilostome bryozoans

For many sedentary or sessile benthic marine invertebrates the planktonic duration of the larval stage is believed to be a key determinant of the magnitude of genetic differences between populations. An obvious dichotomy in dispersal potential exists within cheilostome bryozoans that develop from either (1) a cyphonautes larva that spends several weeks in the plankton or (2) a brooded coronate larva that settles soon after release from the adult colony. This study characterises the pattern of variation at allozyme loci among British populations of four species of bryozoan—two species with cyphonautes and two with coronate larvae. There is some variation in the estimates of genetic differentiation among similarly separated populations that may be a consequence of non-equilibrium genetic conditions arising from sporadic migration, possibly through dispersal by rafting on macroalgae by mature colonies. Despite this, however, both the level of genetic differentiation between populations and the pattern of migrant exchange correlate with the larval developmental mode. Bryozoan species that brood coronate larvae show higher levels of genetic heterogeneity between populations and significant isolation by distance genetic structure while, by contrast, distance has little or no effect upon the amount of genetic differentiation among populations of bryozoans with cyphonautes larvae. For cheilostome bryozoans, therefore, it appears that genetic differentiation between populations is directly associated with the type of larval development. These data are discussed also with respect to levels of gene diversity and the geological pattern of cheilostome bryozoan species diversity.     

Temporal patterns of larval settlement and survivorship of two broadcast-spawning acroporid corals

Acroporid corals are the main reef-building corals that provide three-dimensional habitats for other reef organisms, but are decreasing on many reefs worldwide due to natural and anthropogenic disturbances. In this study, temporal patterns of larval settlement and survivorship of two broadcast-spawning acroporid coral species, Acropora muricata and A. valida, were examined through laboratory rearing experiments to better understand the potential for larval dispersal of this important coral group. Many larvae were attached (but not metamorphosed) to settlement tiles on the first examination 3–4 days after spawning (AS). The first permanent larval settlement (i.e. metamorphosed and permanently settled juvenile polyps) occurred at 5–6 days AS, and most larval settlement (85–97% of total) occurred within 9–10 days AS. Larval survivorship decreased substantially to around 50% by the first week of the experiment and to approximately 10% by the second to third week. The rates of larval attachment, settlement, and the initial drop in survivorship of larvae suggest that effective dispersal of some acroporid species may largely be completed within the first few weeks AS.     

Variation in larval life-history traits among reef fishes across the Isthmus of Panama

We tested the hypothesis that regional differences in oceanic productivity have led to the evolution of predictable patterns of regional variation in life-history traits of pelagic larvae of tropical reef fishes. To do so we compared larval traits (egg and hatchling size, larval growth rate and duration, and size at settlement) among closely related reef fishes from the Atlantic and Pacific coasts of the Isthmus of Panama. This comparison provides a control for phylogenetic effects because those regions shared a common fauna prior to the rise of the Isthmus ˜3.5 million years ago, subsequent to which each fauna evolved independently under a very different productivity regime. We measured larval traits of 12 benthic-spawning damselfishes (Pomacentridae: Abudefduf, Chromis and Stegastes) and 13 pelagic-spawning wrasses (Labridae: Bodianus, Halichoeres and Thalassoma). These included members of each genus on each side of the Isthmus and four sets of transisthmian sister species of pomacentrids. Among the pomacentrids we found consistent transisthmian differences in hatchling size, but not in other larval traits. Essentially the reverse pattern occurred among the labrids – larval growth and duration differed consistently among congeners in the two regions, but without consistent differences in hatchling size or size at settlement. Neither relationship is predicted by the regional-productivity hypothesis. Most of the differences were quite small. Stronger phylogenetic effects on larval traits (inter- and intrageneric variation within regions) occur in both families and evidently overwhelm any effect of regional variation in productivity. Reassessment of data that takes into account such phylogenetic effects questions previous conclusions about the existence of regional differences in larval traits among damselfishes in the West Pacific and the Caribbean. Received: 19 January 2000 / Accepted: 26 September 2000     

Critical swimming speeds of late-stage coral reef fish larvae: variation within species,among species and between locations

The swimming abilities of larval fishes are important for their survival, potentially affecting their ability to avoid predators, obtain food and control dispersal patterns. Near settlement swimming abilities may also influence spatial and temporal patterns of recruitment. We examined Critical speed (U-crit) swimming ability in late stage larvae of 89 species of coral reef fishes from the Great Barrier Reef and the Caribbean. Coefficients of variation in U-crit calculated at the individual level were high (28.4%), and this was not explained by differences in size or condition factor of these same larvae. Among species U-crit ranged from 5.5 cm s⁻¹ to 100.8 cm s⁻¹ (mean=37.3 cm s⁻¹), with 95% of species able to swim faster than the average current speed around Lizard Island, suggesting that most species should be capable of influencing their spatial and temporal patterns of settlement. Inter-specific differences in swimming ability (at both the family and species levels) were significantly correlated with size and larval morphology. Correlations were found between swimming performance and propulsive area, fineness ratio and aspect ratio, and these morphological parameters may prove useful for predicting swimming ability in other taxa. Overall, the swimming speeds of larvae from the same families at the two locations were relatively similar, although the Lutjanidae and Acanthuridae from the Caribbean were significantly slower than those from the great barrier reef. Differences in swimming speed and body form among late stage larvae suggests that they will respond differently to factors influencing survival and transport during their pelagic phase, as well as habitat use following settlement.     

Development of the nasal olfactory organs in the larvae, settlement-stages and some adults of 14 species of Caribbean reef fishes (Labridae, Scaridae, Pomacentridae)

Larval fishes likely use a variety of settlement cues to locate and navigate toward the habitats they will inhabit as juveniles. Information about the morphology and state of development of the sensory organs of larval stages of fishes provides insight into their capabilities at the time of settlement. The peripheral olfactory organ of wild-caught late-stage larvae and early juveniles and some adults of 14 species of the Caribbean reef fishes wrasses (Labridae), parrot fishes (Scaridae) and damselfish (Pomacentridae) were examined using scanning electron microscopy and compared in terms of settlement specificity. Ages in days after hatching and days post-settlement were determined from the otoliths. Morphology of the nares and the olfactory epithelium are described for these species by stage. The separation of the anterior and posterior nares occurred before settlement in the labrids but in some specimens of scarids this separation was not complete by the time of settlement. Densities of ciliated and microvillous receptor cells and non-sensory ciliated epithelial cells were calculated. Densities of ciliated receptor cells ranged from 0.389 μm⁻² in a specimen of Thallasoma bifasciatum to 0.0057 μm⁻² in Bodianus rufus and of microvillous receptor cells from 0.038 μm⁻² in a Clepticus parrae juvenile to 0.266 μm⁻² in a juvenile Doratonotus megalepis. Densities of non-sensory cilia, also associated with high olfactory ability, were also high. The olfactory organ in wrasses is well developed prior to settlement and is comparable to that of adult fishes. The possible role of olfaction in larval schooling, reef cue detection and orientation toward habitat at settlement is discussed.

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Phylogeography of two Atlantic squirrelfishes (Family Holocentridae): exploring links between pelagic larval duration and population connectivity

Genetic surveys of reef fishes have revealed high population connectivity within ocean basins, consistent with the assumption that pelagic larvae disperse long distances by oceanic currents. However, several recent studies have demonstrated that larval retention and self-recruitment may be higher than previously expected. To assess connectivity in tropical reef fishes, we contribute range-wide mtDNA surveys of two Atlantic squirrelfishes (family Holocentridae). The blackbar soldierfish, Myripristis jacobus, has a pelagic juvenile phase of about 58 days, compared to about 71 days (~22% longer) in the longjaw squirrelfish, Holocentrus ascensionis. If the pelagic duration is guiding dispersal ability, M. jacobus should have greater population genetic structure than H. ascensionis. In comparisons of mtDNA cytochrome b sequences from 69 M. jacobus (744 bp) and 101 H. ascensionis (769 bp), both species exhibited a large number of closely related haplotypes (h=0.781 and 0.974, π=0.003 and 0.006, respectively), indicating late Pleistocene coalescence of mtDNA lineages. Contrary to the prediction based on pelagic duration, M. jacobus has much less population structure (φ_ST=0.008, P=0.228) than H. ascensionis (φ_ST=0.091, P<0.001). Significant population partitions in H. ascensionis were observed between eastern, central and western Atlantic, and between Brazil and the Caribbean in the western Atlantic. These results, in combination with the findings from 13 codistributed species, indicate that pelagic larval duration is a poor predictor of population genetic structure in Atlantic reef fishes. A key to understanding this disparity may be the evolutionary depth among corresponding taxonomic groups of “reef fishes”, which extends back to the mid-Cretaceous and encompasses enormous diversity in ecology and life history. We should not expect a simple relationship between pelagic larval duration and genetic connectivity, among lineages that diverged 50–100 million years ago.     

Distribution and seasonal abundance of Polygordius spp. (Class: Polychaeta; Family: Polygordiidae) exo- and endolarvae in the southern Mid-Atlantic Bight,USA

The importance life history plays in understanding population dynamics and the functional roles of species for predicting climate change scenarios are well established. Yet, in the marine environment, the complete life history is unknown for many species, especially the link between morphologically and ecologically distinct planktonic larvae, and their corresponding benthic adult forms. Integration of meroplankton abundance, benthic adult species, larval morphology, and molecular data was employed to unravel the complete life history of Polygordius, a dominant polychaete in sandy shelf sediments of the Mid-Atlantic Bight. Polygordius species are unusual, having two distinct planktonic larval forms: an exolarva and an endolarva. Extensive sampling in the southern Mid-Atlantic Bight with careful preservation of meroplankton (2006–2007) revealed the identity of multiple stages of exo- and endolarvae, and their spatial, seasonal, and vertical distribution. Molecular and morphological evidence indicated exolarvae are Polygordius jouinae and endolarva are an undescribed species. Structure and development of these larvae differed greatly. P. jouinae exolarvae were found off Delaware Bay to North Carolina. At some stations, they were abundant, with densities up to 4,013 m^?3, comprising >90 % of the total meroplankton. Exolarvae spent up to a month in the plankton starting in March/May depending on year, settlement began in July when larvae were at least 2 mm in length, and by October were no longer observed in the plankton. These findings are consistent with the distribution patterns and life cycle known for adults. This is the first report of endolarvae north of Cape Hatteras.