Larval Retention Research Articles

Distribution and retention of Sabellaria alveolata larvae (Polychaeta: Sabellariidae) in the Bay of Mont-Saint-Michel, France

The gregarious polychaete Sabellaria alveolata is an important foundation species whose reef structures add topographic complexity and high levels of biodiversity in sandflats. In the Bay of Mont-Saint-Michel, France, S. alveolata reefs are considered the largest reef formations in Europe and are increasingly endangered by anthropogenic pressure. In order to understand the role of larval transport on the resilience capacity of these biogenic reefs, multiple complementary approaches were carried out within the bay in 2002 to study horizontal and vertical distribution of S. alveolata larvae and assess larval dispersal processes. Plankton samples collected twice a month from March to October showed an extended period of larval occurrence, from the end of April to October, with 2 peaks of high abundance. The main spawning period occurred early in May, and a smaller peak occurred in September. Mean planktonic lifetime has been calculated to be between 4 and 10 wk. At large scale, larval distribution was patchy and the maximal abundance could reach about 28 000 larvae m -2 . Larval densities were strongly correlated with physico-chemical parameters so that larvae were more abundant in a warmer and less saline coastal water mass characterised by a higher concentration in chlorophyll a. The presence of a large anticyclonic gyre in the bay seemed to play a significant role in controlling larval dispersal by concentrating larvae within the bay. At 1 station in the bay, short-term variations of larval abundances in the water column appeared to be regulated by the tidal cycle, as larvae were more abundant at the end of ebb tide, confirming the very coastal distribution of larvae. Furthermore, S. alveolata larvae tended to migrate closer to the surface during flood and near the bottom during ebb, promoting a net landward transport of larvae. Despite a long larval lifespan, our results indicate that tidal residual currents, especially a coastal gyre, and tidal vertical migration may favour larval retention within the bay.

How far can marine species go? Influence of population biology and larval movement on future range limits

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 344:15-28 (2007) - DOI: https://doi.org/10.3354/meps06940 How far can marine species go? Influence of population biology and larval movement on future range limits Piers K. Dunstan*, Nicholas J. Bax CSIRO Marine and Atmospheric Research, GPO Box 1538, Hobart, Tasmania 7001, Australia *Email: piers.dunstan@csiro.au ABSTRACT: The range of a marine species varies with a wide range of factors including temperature, currents, interspecific interactions and available habitat. Invasive species offer insights into the processes that influence range expansion because they are in the initial stages of an expansive period. We modelled the range expansion of an invasive seastar with an extended larval period throughout southern Australia using a linked physical and biological model. We found that the establishment of new populations was dependent on larval supply and, critically, on the ability of new habitats to retain larval production within the local habitat to compensate for Allee effects at low population densities. Larval supply from existing populations determined the locations of invasions, whereas local retention of larvae determined how fast and how large a population could grow. Increased diffusion dispersed larvae to areas otherwise inaccessible to them in a purely advective model, and had the potential to increase establishment probabilities. Range extension progressed as new populations were established downstream of source populations in locations where the retention of locally produced larvae was sufficient to generate long-term positive growth rates. KEY WORDS: Dispersal · Allee · Larval retention · Population dynamics Full text in pdf format PreviousNextCite this article as: Dunstan PK, Bax NJ (2007) How far can marine species go? Influence of population biology and larval movement on future range limits. Mar Ecol Prog Ser 344:15-28. https://doi.org/10.3354/meps06940 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 344. Online publication date: August 23, 2007 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2007 Inter-Research.

Larval salinity tolerance of the South American salt-marsh crab, Neohelice (Chasmagnathus) granulata: physiological constraints to estuarine retention, export and reimmigration

The semiterrestrial crab Neohelice (=Chasmagnathus) granulata (Dana 1851) is a predominant species in brackish salt marshes, mangroves and estuaries. Its larvae are exported towards coastal marine waters. In order to estimate the limits of salinity tolerance constraining larval retention in estuarine habitats, we exposed in laboratory experiments freshly hatched zoeae to six different salinities (5–32‰). At 5‰, the larvae survived for a maximum of 2 weeks, reaching only exceptionally the second zoeal stage, while 38% survived to the megalopa stage at 10‰. Shortest development and negligible mortality occurred at all higher salt concentrations. These observations show that the larvae of N. granulata can tolerate a retention in the mesohaline reaches of estuaries, with a lower limit of ca. 10–15‰. Maximum survival at 25‰ suggests that polyhaline conditions rather than an export to oceanic waters are optimal for successful larval development of this species. In another experiment, we tested the capability of the last zoeal stage (IV) for reimmigration from coastal marine into brackish waters. Stepwise reductions of salinity during this stage allowed for moulting to the megalopa at 4–10‰. Although survival was at these conditions reduced and development delayed, these results suggest that already the zoea-IV stage is able to initiate the reimmigration into estuaries. After further salinity reduction, megalopae survived in this experiment for up to >3 weeks in freshwater, without moulting to juvenile crabs. In a similar experiment starting from the megalopa stage, successful metamorphosis occurred at 4–10‰, and juvenile growth continued in freshwater. Although these juvenile crabs showed significantly enhanced mortality and smaller carapace width compared to a seawater control, our results show that the late larval and early juvenile stages of N. granulata are well adapted for successful recruitment in brackish and even limnetic habitats.

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.

Physical and biological processes controlling the distribution of fish larvae in the NW Mediterranean

The Mediterranean is globally considered an oligotrophic sea. However, there are some places or certain seasons in which mechanisms that enhance fertility may occur. These mechanisms and related processes are especially relevant when they take place during the period of larval development. This study analyzes how environmental conditions occurring in the NW Mediterranean, at local and seasonal scales, contribute to determine the temporal and spatial patterns of fish reproductive activity in the region. The structure of the bathymetry, types of bottoms, diversity of adult fish habitats, as well as mechanisms conditioning the primary production of the region determine the location of spawning, whereas physical processes (e.g., shelf-slope density front and associated current, continental water inflows, winter mixing, stratification of the water column) determine the final distribution patterns of fish eggs and larvae. High larval concentrations occur over the edge of the continental shelf in relation to the presence of the shelf-slope front and its associated convergence. However, this pattern is subject to considerable spatio-temporal variability, due to frontal mesoscale activity. High larval abundance can also be observed near the coast in zones with topographic irregularities that can greatly modify circulation favouring penetration of slope waters into the shelf. Finally, larvae of large pelagic migratory species are mainly distributed in areas under the influence of recent Atlantic Water (AW) and near the frontal system between these inflowing AW and the more saline waters of the northern basin. A pronounced seasonal variability regarding both the number of species and the number of fish larvae in the plankton can be observed throughout the year. The two dominant species, sardine and anchovy, have non-overlapping spawning periods, autumn–winter and spring–summer, respectively. The diversity of feeding patterns as well as the fact that different fish species have different spawning periods might reduce inter- and intra-specific competition for food resources in this area. Most NW Mediterranean fish reproduce during the spring–summer stratification period, when the phytoplankton biomass values at the upper layers of the water column are lower than in winter. The development of the Deep Chlorophyll Maximum in this period and the high zooplankton biomass associated to it offers an important food source for the larvae. Additionally, during this period the inputs of continental waters in certain areas are one of the fertilization mechanisms of surface waters and some species, as anchovy, takes advantage of this situation. Autumn–winter is the period with lower ichthyoplankton diversity, being dominated by sardine, which reproduces on the continental shelf. The mixing of the water column during winter is one of the mechanisms that enhances productivity on continental shelves. Moreover, there are no intense currents on the shelf and the circulation is usually anticyclonic, favouring larval retention in this zone. Fish species show reproductive strategies and larval fish behaviour that allow them to take advantage of the available resources throughout the seasonal cycle. These strategies, together with the high ecological efficiency of oligotrophic systems, contribute to the relatively high yield of Mediterranean fisheries.

Water retention and limited larval dispersal: implications for short and long distance dispersers in marine reserves

Although the establishment of reserves is central to marine conservation, previous criteria for the selection of appropriate areas has often been based on historical, aesthetic or logistic factors, resulting in a network of marine reserves that may not effectively meet conservation objec- tives. Since the dispersal of larvae plays an integral role in determining whether reserves can sustain themselves, whether they can exchange larvae with other protected sites, or whether they can supplement surrounding exploited areas, effective reserve design requires consideration of the pro- cesses that may affect larval dispersal. Plankton tows were conducted monthly for 12 mo in a semi- enclosed marine reserve with long water retention time, in bays with low water retention, and along open coastline, to establish whether larval retention plays an important role in limiting dispersal and creating discrete communities. Significant spatial and temporal differences in larval assemblages were found, with the semi-enclosed reserve, bay, and coast areas showing consistent differences throughout the year. An ANOVA carried out on 11 species identified as differentiating between these areas supported the hypothesis that limited larval exchange was occurring between reserve and non- reserve areas, despite potentially large dispersal distances. Designating bays as reserve areas may provide a means of protecting various species with both long and short dispersal distances, but this must be balanced against the reduced likelihood of closed populations to recover from local catastro- phes and the possibility of limited genetic differentiation and inbreeding.

Vertical structure of very nearshore larval fish assemblages in a temperate rocky coast

Small-scale vertical patterns of larval distribution were studied at a very nearshore larval fish assemblage, during the spring–summer period of several years, at two depth strata (surface and bottom) using sub-surface and bottom trawls. A total of 4,589 larvae (2,016 from surface samples and 2,573 from bottom samples) belonging to 62 taxa included in 22 families were collected. Most larvae belonged to coastal species. Although inter-annual variations in larval density and diversity could be found, total larval abundance was always higher near the bottom whereas diversity was higher at the surface. A marked distinction between the structure of surface and bottom assemblages was found. Sixteen taxa explained 95% of the similarity among surface samples. Larvae which contributed most to this similarity included species like clupeiformes, sparids and serranids, and also blenniids, tripterygiids and some labrids. In the bottom samples, fewer species were present, with only six taxa, almost exclusively from species which lay demersal eggs, contributing to 95% of the similarity between samples. Larvae present at the surface were significantly smaller than at the bottom. For some of the most abundant species found at the bottom, only small larvae occurred at the surface while the whole range of sizes was present at the bottom, indicating that larvae may be completing the entire pelagic phase near the adults’ habitat. These results indicate that larval retention near the reefs probably occurs for these species, although for others dispersal seems to be the prevailing mechanism.

Population genetic structuring of the king weakfish, Macrodon ancylodon (Sciaenidae), in Atlantic coastal waters of South America: deep genetic divergence without morphological change

Phylogeographic patterns in Macrodon ancylodon sampled from 12 locations across all its range were investigated using mitochondrial DNA cytochrome b sequences, and analysed together with patterns of morphometric differentiation. Populations of the North Brazil and the Brazil currents, with warmer waters, form a clade (tropical clade) separated by 23 fixed mutations from the populations that inhabit regions of colder waters influenced by the Brazil and Malvinas currents (subtropical clade). No gene flow exists between the tropical and subtropical clades, and most likely also between the two groups of the tropical clade. Distribution of these clades and groups is correlated with flow of currents and their temperatures, and is facilitated by larval retention and low adult migration. Despite differentiation at the molecular level, fishes analysed from all these current-influenced regions are morphometrically homogeneous. Throughout its range M. ancylodon inhabits the same, or very similar niche; thus, stabilizing selection probably promotes the retention of highly conserved morphology despite deep genetic divergence at the mitochondrial DNA cytochrome b.

Effect of habitat conditions on reproduction of the European anchovy (Engraulis encrasicolus) in the Strait of Sicily

AbstractThe aims of this study were to describe the reproductive cycle of the European anchovy (Engraulis encrasicolus) off the south coast of Sicily and determine whether intra‐ and inter‐annual reproductive trait variations, if any, are adaptive responses which maximize reproductive success under environmental fluctuations. Biological data were collected from purse seine and mid‐water pelagic trawl commercial catches landed in Sciacca (Sicily) over 6 yr (1997–2002) at fortnightly intervals, analysing a total of 84 581 individuals. No inter‐annual changes in length at first reproduction were observed, with a mean pooled value of 11.26 cm for both sexes being found. Spawning intensity, indicated by gonadosomatic index, condition factor and length–weight relationships, seem to be governed by food availability prior to spawning. Anchovy reproductive investment was limited by the area's low primary production. There was a synchrony between reproductive cycle and temperature. Water warming marks the onset of a period of high water stability in the area, and its later cooling marks the onset of a period with low water stability. The relationship between reproductive cycle and temperature is therefore probably a reproductive strategy having evolved to ensure that spawning takes place during the period of the year when water column stability is higher, favouring food concentration and egg and larval retention in the spawning areas.

Contrasting population genetic structures of sympatric, mass-spawning Caribbean corals

Coral reef conservation management policy often focuses on larval retention and recruitment of marine fish with scant data available on important, less motile reef-building species such as corals. To evaluate the concept of population connectivity in corals, we tested whether broadcast spawning reproduction per se confers the same degree of dispersal to two sister species, Montastraea annularis (Anthozoa: Scleractinia; Ellis and Solander 1786) and M. faveolata (Ellis and Solander 1786), both dominant taxa in reefs of the northern Caribbean. Genetic analyses of ten nuclear DNA loci (seven microsatellite and three single-copy RFLP) reveal strikingly different patterns of population genetic subdivision for these closely related, sympatric species, in spite of likely identical dispersal abilities. Strong population genetic structure typified the architecture of M. annularis, whereas M.faveolata populations were principally genetically well mixed. A higher level of clonality was observed in M. annularis potentially because of a susceptibility to physical fragmentation. Clonality did not, however, significantly contribute to population genetic structure or low-level Hardy–Weinberg and linkage disequilibria observed in some populations. The lack of consistent association between reproductive mode and dispersal reinforces the perspective that population connectivity is not so much a function of predictable marine population source and sink relationships as is due to a more complex interface of oceanic currents interacting with and amplifying stochastic fluctuations in larval supply and settlement success. Our results support others promoting an overall ecosystem approach in marine protected area design.

Spawning pattern variability and its effect on retention, larval growth and recruitment in Georges Bank cod and haddock

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 310:193-212 (2006) - doi:10.3354/meps310193 Spawning pattern variability and its effect on retention, larval growth and recruitment in Georges Bank cod and haddock R. G. Lough1,*, C. G. Hannah3, P. Berrien2, D. Brickman3, J. W. Loder3, J. A. Quinlan4 1Northeast Fisheries Science Center, 166 Water St., Woods Hole, Massachusetts 02543, USA 2Northeast Fisheries Science Center, James J. Howard Marine Science Laboratory, Magruder Road, Highlands, New Jersey 07732, USA 3Ocean Sciences Division, Fisheries and Oceans Canada, Bedford Institute of Oceanography, PO Box 1006, Dartmouth, Nova Scotia B2Y 4A2, Canada 4Institute of Marine and Coastal Science, Rutgers University, New Brunswick, New Jersey 08901, USA *Email: glough@whsun1.wh.whoi.edu ABSTRACT: The MARMAP 11-yr time series (1977 to 1987) of cod and haddock egg/larval distributions was used as a basis for examining the consequences of spawning between eastern and western Georges Bank. For each year, from 1978 to 1987, weekly mean flow fields were based on linear interpolation of seasonal velocity fields with wind and upstream boundary-forcing anomalies. Particles were released from the Northeast Peak (NEP) and western Georges Bank (WGB) spawning areas to assess the relative number of larvae retained within the 70 m isobath after 8 wk. A scaled aggregate Georges Bank (AGB) retention index was also created by weighting the relative number of eggs spawned on the eastern and western halves. While there was considerable interannual variability, mean retention for particles released from NEP at the surface (0 to 10 m) was low (<20%) during winter but increased in the spring to about 50% by mid-April, declining through May. Mean retention at 30 m, however, was consistently between 30 and 40%. Mean retention of particles from WGB was higher for surface releases than at depth, and reached 50% during May. The NEP usually had higher retention than WGB, but the WGB releases could contribute significantly to retention, especially near the surface during the winter period, when there was a loss of particles from NEP due to wind. The 2 yr of high recruitment for cod, 1980 and 1985, occurred during periods of high retention over the spawning season, despite the fact that in 1980 spawning was primarily in the eastern area, while, in 1985, spawning was split between the areas. The large year class of haddock in 1978 had high larval retention and the latest seasonal growth optima in the time series, extending through May. KEY WORDS: Georges Bank · Cod · Haddock · Spawning pattern · Larval transport · Growth · Recruitment Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 310. Online publication date: April 03, 2006 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2006 Inter-Research.

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 (φST=0.008, P=0.228) than H. ascensionis (φST=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.

Subsurface recirculation and larval retention in the lee of a small headland: A variation on the upwelling shadow theme

The interaction of alongshore coastal currents with large headlands has been shown to increase the retention of planktonic organisms through the formation of headland eddies or upwelling shadows in their lee. This study investigates the circulation within Bodega Bay (in the lee of a small headland), in an upwelling region, and the potential for retention of plankton. During the upwelling season of 2004, time series of temperature and velocity were recorded throughout Bodega Bay, conductivity‐temperature‐depth (CTD) surveys were conducted, and surface drifters were released during upwelling, downwelling, and relaxation conditions. Postlarval settlement was monitored daily over two periods coinciding with CTD surveys. Under strong upwelling favorable conditions, wind‐driven surface currents were equatorward both offshore and throughout the bay. However, there was significant current shear along the eastern shore of the bay where cold bottom waters move poleward, counter to the direction of the wind‐driven surface flow. During downwelling and relaxation conditions, flow was poleward throughout the water column along the eastern shore of the bay. Postlarvae settled during all wind conditions, but greatest settlement was observed at the onset of upwelling favorable conditions. While no “typical” upwelling shadow is evident in the lee of the Bodega headland, subsurface recirculation driven by the alongshore flow past Bodega Head may facilitate the retention of plankton in the bay. Previous studies have generally focused on large headlands; however, it is likely that other small embayments in the lee of small headlands may also provide retention opportunities for planktonic organisms in upwelling regions.

Temporal and Spatial Genetic Structure among Some Pacific Herring Populations in Puget Sound and the Southern Strait of Georgia

AbstractWe investigated temporal and spatial genetic variation in Pacific herring Clupea pallasii collections from six sites in Puget Sound (PS) and the southern Strait of Georgia (SOG), using 12 microsatellite loci. Loci were highly variable with up to 70 alleles per locus (mean = 30.67 alleles), and observed heterozygosity was high (mean = 0.823). Analysis of molecular variance (AMOVA) indicated significant structure, with over twice as much variance among sites as among collection years, although among‐site variance was mainly due to Cherry Point and Squaxin Pass collections. In an AMOVA excluding Cherry Point and Squaxin Pass, only temporal variance was significant. With the exception of the Cherry Point and Squaxin Pass collections, pairwise genotypic and FST tests show some differences among collection years within a site and some genetic overlap among most PS and SOG collections. The Cherry Point and Squaxin Pass collections had no differences in genotypic distributions among collection years, and in cluster analyses the Cherry Point and Squaxin Pass collections each formed groups separate from other PS and SOG collections. Cherry Point herring have a later spawning time than other PS and SOG herring, and Squaxin Pass is physically isolated in southern Puget Sound. We hypothesize that spawn timing differences and spatial isolation generated genetic structure among some Pacific herring in PS and SOG. We suspect that, as in the case of Atlantic herring C. harengus, population genetic structure in Pacific herring in PS and southern SOG is a combination of a larval retention model and a metapopulation model. Because Cherry Point and Squaxin Pass herring are genetically and behaviorally differentiated from other PS and SOG herring populations, this unique variation should be preserved through careful management.

Coral Gardens: Paternity and Drug Testing on the Reef

An international team has used molecular genetics and chemical tagging to trace how baby clownfish travel from their mother's nest through the ocean to the anemone they will live on. More than one out of five juveniles came from nests that were only meters away, despite spending over a week drifting in ocean currents. Such surprising fidelity to a small area of the coral reef bodes well for efforts to preserve coral reef diversity with reserves.

POPULATION PERSISTENCE OF CALIFORNIA CURRENT FISHES AND BENTHIC CRUSTACEANS: A MARINE DRIFT PARADOX

Because flow in the California Current is unidirectional for months, larvae of coastal species may drift and settle downstream of their parents, potentially causing the parental population to go extinct from upstream to downstream; this is a marine equivalent of the drift paradox in streams. Unidirectional larval drift might, however, be minimized by when, where, and how organisms reproduce. We compiled data on California Current fishes (89 nearshore, 65 shelf/slope) and benthic crustaceans (35 nearshore, 15 shelf/slope) and found three unique sets of life history traits displayed by (1) shelf/slope species, (2) nearshore pelagic‐spawning fishes (all from the Southern California Bight [SCB] and Baja California), and (3) all other nearshore species. Pelagic larval durations (PD) of shelf/slope species are long (∼136 d); offspring are pelagic winter through summer and are found at depth below the mixed layer offshore. Offspring experience northward flow in winter and southward flow in spring/summer, perhaps minimizing net alongshore drift. Adults are both long‐lived and highly fecund. Nearshore species have short PDs (∼45 d), and offspring are pelagic during spring/summer upwelling and are found nearshore and near the bottom. Nearshore larvae may experience southward flow during upwelling and northward flow during relaxation events, minimizing net alongshore transport. Nearshore species have shorter lives and are less fecund than shelf/slope species. Nearshore pelagic‐spawning fishes (all from the SCB and Baja) have short PDs (∼48 d), but in contrast to other nearshore species, their larvae are pelagic from spring into fall and are found far from shore. Adults are long‐lived, highly fecund, and have numerous broods per year. These life history traits may have evolved to exploit eddies and countercurrents present in the SCB and off Baja for larval retention. Each set of life history traits appears to improve chances of offspring recruiting to parental populations. The pelagic phase, rather than being dispersive, may be selected to achieve a migration between larval pelagic and adult benthic habitats.

Ecosystem indicators derived from satellite remotely sensed oceanographic data for the North Pacific

Abstract Satellite remotely sensed oceanographic data provide reliable global ocean coverage of sea surface temperature, sea surface height, surface winds, and ocean colour, with relatively high spatial and temporal resolution. We illustrate approaches to use these data to construct indicators that describe aspects of ecosystem dynamics in the North Pacific. Specifically, altimetry data are used to construct regional indicators of the ocean vertical structure, ocean colour data to describe the temporal chlorophyll dynamics of the coastal zone, ocean colour, sea surface temperature, and altimetry data to develop indices of biologically important ocean features, and finally altimetry data to drive a larval transport model and develop an index of larval retention. Recent changes in the North Pacific based on these indices are discussed.

Direct evidence of a biophysical retention mechanism for coral reef fish larvae

We examine the hypothesis that reef fish larvae have some direct influence on their own dispersal and ability to recruit to their natal reef by tracking cohorts of bicolor damselfish (Stegastes partitus) from hatching to settlement onto the reef, about 30 d later. We conducted high‐resolution sampling during two consecutive years in a small area (15 km × 20 km) off the west coast of Barbados, extending from depths of 0 to 100 m. Observations of discrete stage‐specific larval patches of mean size of 29.4 and 13.2 km2 for preflexion (1–5‐d old) and flexion/postflexion (.5‐d old) stages extending ca. 30 m in the vertical indicated that larvae initially dispersing as patches tend to stay in coherent patches throughout their pelagic duration. Highest concentrations of preflexion larvae within a patch were in the upper 20 m, while those of older larvae were always deeper. Downward migration of about 60 m throughout ontogeny within stratified currents represented a retention mechanism for locally spawned larvae. Most of the variability in estimated retention rates between daily cohorts occurred during the earliest stages as a result of the dynamic nature of surface currents experienced by larvae prior to the onset of vertical migration. Differences in residence time between experiments were consistent with observed intermonthly variability in recruitment strength, implying that pelagic processes can explain recruitment rates. These results provide empirical evidence for larval retention of coral reef fishes and stress the role of active behavior in larval transport.

Spatial and temporal patterns in larval supply at hydrothermal vents in the northeast Pacific Ocean

Larval supply in marine benthic invertebrates influences patterns of settlement and recruitment to adult populations. To successfully colonize newly formed or distant hydrothermal vents, which are discontinuous and ephemeral habitats, larvae of vent invertebrates must possess long‐range dispersal abilities. However, a significant proportion of locally produced larvae must remain within the adult habitat to maintain the observed dense assemblages of invertebrates. I compared spatial and temporal patterns in larval availability (flux and abundance) at hydrothermal vents within and between ridge segments in the northeast Pacific ocean at Axial Seamount and Endeavour Segment on the Juan de Fuca Ridge and at Magic Mountain on Explorer Ridge. Near‐bottom (within 50 cm) larval supply (individuals m−2 d−1) at five vents on Axial Seamount, measured with passively collecting traps in 2000 and 2001, varied temporally by an order of magnitude, but not spatially at scales of tens of meters to kilometers. The most abundant larval taxa were gastropods (particularly the limpet Lepetodrilus fucensis) and polychaetes. Larval abundance in the water column within the axial valley was measured with net tows by the remotely operated vehicle ROPOS at the three ridge segments: Axial Seamount (2000, 2001); Endeavour Segment (2001, 2002); Magic Mountain (2002). Abundance was greater by an order of magnitude at the Endeavour Segment than at Axial Seamount and Magic Mountain, and it did not differ between on‐vent (within tens of meters) and off‐vent (up to 5 km from the venting source) locations within the axial valley. The uniformly high abundance of larvae within axial valleys suggests that larval supply within a ridge segment is most likely localized, implying significant larval retention on the scale of vent fields and possibly ridge segments.

Influence of mesoscale physical forcing on trophic pathways and fish larvae retention in the central Cantabrian Sea

AbstractThis study was carried out over the central Cantabrian shelf during a post‐bloom phase in May. Late phases of the spring phytoplankton bloom, which are characterized by high crustacean mesozooplankton biomass, have been proposed to be a particular case for high‐energy flow towards large metazoans. The overall objective of the study is to analyse the influence of mesoscale physical forcing on primary production patterns, its implications on food web pathways, and on larval fish distribution during a period of intense spawning of Sardina pilchardus and Scomber scombrus. Physical and biological variables of different trophic levels show coupled cross‐shelf and along‐shelf heterogeneity. Quasi‐geostrophic analysis and other indirect approaches, such as the depth of the slope salinity maximum, reveal predictable patterns of vertical instabilities associated with mesoscale physical forcing that enhance production of large‐size phytoplankton. The latter is expected to enhance the energy flow towards higher trophic levels at a time of high mesozooplankton biomass. Distributions of S. pilchardus and S. scombrus eggs and larvae indicate retention related to the coastal salinity front and the overall eastward circulation pattern. The observed mesoscale physical processes may favour survival of early stages of fish by their influence on the energy flow of primary production towards higher trophic levels and larval retention at the coast.