Population genetic structure of escolar (<Emphasis Type="Italic">Lepidocybium flavobrunneum</Emphasis>)

Escolar (Lepidocybium flavobrunneum) is a large, mesopelagic fish that inhabits tropical and temperate seas throughout the world, and is a common bycatch in pelagic longline fisheries that target tuna and swordfish. Few studies have explored the biology and natural history of escolar, and little is known regarding its population structure. To evaluate the genetic basis of population structure of escolar throughout their range, we surveyed genetic variation over an 806 base pair fragment of the mitochondrial control region. In total, 225 individuals from six geographically distant locations throughout the Atlantic (Gulf of Mexico, Brazil, South Africa) and Pacific (Ecuador, Hawaii, Australia) were analyzed. A neighbor-joining tree of haplotypes based on maximum likelihood distances revealed two highly divergent clades (δ = 4.85%) that were predominantly restricted to the Atlantic and Indo-Pacific ocean basins. All Atlantic clade individuals occurred in the Atlantic Ocean and all but four Pacific clade individuals were found in the Pacific Ocean. The four Atlantic escolar with Pacific clade haplotypes were found in the South Africa collection. The nuclear ITS-1 gene region of these four individuals was subsequently analyzed and compared to the ITS-1 gene region of four individuals from the South Africa collection with Atlantic clade haplotypes as well as four representative individuals each from the Atlantic and Pacific collections. The four South Africa escolar with Pacific mitochondrial control region haplotypes all had ITS-1 gene region sequences that clustered with the Pacific escolar, suggesting that they were recent migrants from the Indo-Pacific. Due to the high divergence and geographic separation of the Atlantic and Pacific clades, as well as reported morphological differences between Atlantic and Indo-Pacific specimens, consideration of the Atlantic and Indo-Pacific populations as separate species or subspecies may be warranted, though further study is necessary.     

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 of euphausiid assemblages in the Mediterranean Sea

Eleven species of euphausiids from 24 Isaac-Kidd Midwater Trawl (IKMT) night collections taken at stations throughout the Mediterranean Sea were counted. The frequency of occurrence and dominance of individual species and percent similarity faunal analysis of the euphausiid community were used to describe changes in faunal composition between geographical areas and differences in vertical distribution. Although most species were widespread, three distinct patterns of abundance were apparent: Euphausia krohnii, Nematoscelis megalops, Meganyctiphanes norvegica, and Stylocheiron abbreviatum predominated in western basin areas west of the Tyrrhenian Sea; Euphausia hemigibba, Thysanopoda aequalis, and Stylocheiron longicorne predominated in the Tyrrhenian Sea and eastern Mediterranean Sea; Euphausia brevis and Stylocheiron suhmii predominated in the eastern Mediterranean Sea. Percent similarity analysis of data from the IKMT samples and data from Ruud (1936) indicates the Tyrrhenian Sea fauna at the time of the collections was more similar to eastern Mediterranean areas than to most other areas in the western basin, although the degree of similarity was dependent, to some extent, on the depth at which the samples were collected. The composition of euphausiids living above 150 m at night in this area was more similar to eastern basin areas, while the composition of deeper living forms was more similar to those of the rest of the western basin. Comparison of euphausiids collected at three points over a 60 year time-span in the Balearic Sea shows the similarity in composition to be greater within the area over time than between adjacent areas in the western Mediterranean Sea.Contribution No. 2732 from the Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, USA. This research was supported by the Atomic Energy Commission Contract AT (30-1)-3862, ref. NYO-3862-49, National Science Foundation Grant GA 29303 and Office of Naval Research Contract N00014-71-C-0284.     

Behavioral response to hydrostatic pressure in larvae of two species of xanthid crabs

Responses of pelagic larvae of two species of xanthid crabs to manipulations of hydrostatic pressure were examined and compared. One species, Rhithropanopeus harrisii (Gould), is a temperate estuarine species, while the other, Leptodius floridanus (Gibbes), inhabits shallow water and reefs in tropical and subtropical regions. All zoeal stages of R. harrisii detected pressure stimuli presented in increments as small as 0.025 atm. Both Stage I and II zoeae of L. floridanus responded to pressure stimuli presented in increments of 0.1 atm. Stage I responded when pressure was changed by the smallest increment tested, 0.025 atm, but Stage II did not. L. floridanus zoeal Stages III and IV, however, did not change vertical position relative to control larvae when subjected to pressure stimuli. The capacity of R. harrisii zoeae to respond to changes in hydrostatic pressure may be related to their retention in the estuarine environment. In L. floridanus, a non-estuarine species, the pressure response is important only in the first zoeal stage and may function promarily in dispersal.     

Types of larval development in marine bottom invertebrates,their distribution and ecological significance: a re-evaluation

The distribution of various types of larval development among marine bottom invertebrates has been discussed on the basis of ecological evidence by Thorson (1936, 1946, 1950, 1952) and Mileikovsky (1961b, 1965). The information at hand is reviewed anew in this paper and is re-evaluated in the light of modern pertinent literature. The interrelationships between certain larval types and their distribution are not as rigid and direct as originally assumed. This can be proved even by the copy book example of the distribution of the various forms of development among species of the coastal gastropod genus Littorina. Especially among species with wide distributional areas, local populations may exhibit greater diversity in larval types than has previously been thought. Different types of larval development have now become known to exist in different populations of opisthobranch gastropods and lamellibranchs, i.e., in invertebrate groups in which such variability had been ruled out by Thorson. Variability in the type of larval development within given species — as a function of geographical, seasonal and other environmental parameters —is also more common in other marine bottom invertebrates than formerly considered. Marine bottom invertebrates are characterized not only by the 3 main different types of larval development proposed by Thorson (pelagic, direct, viviparous), but also by a fourth type: demersal (free non-pelagic) development. This fourth type occurs at all water depths and in all geographic zones of the oceans. The most important of the 4 types is pelagic (planktotrophic) development. Thorson's rule (decrease in numbers of species possessing pelagic development from the Equator towards the Poles, and from shallow-shelf waters to greater oceanic depths) is well substantiated by new data. However, one correction is necessary: pelagic development is not completely absent in the abyssal zone, as was proposed by Thorson (1950, and later), but is represented in it by at least several species belonging to various groups of invertebrates, and is also fairly common in the bathyal zone. A detailed analysis of the distributional pattern of the different types of development of marine bottom invertebrates must further take into consideration asexual reproduction with all its different modifications. Asexual reproduction in benthonic invertebrates is ecologically significant because of its common occurrence in nature; in numerous species it is also important as a biological supplement to sexual reproduction. The vast majority of species inhabiting the shallow-shelf zone and, partly, the higher levels of the slope zone of ocean areas located roughly between the polar circles, reveals development by means of planktotrophic larval stages. In the highest latitudes and on the slopes to abyssal depths—characterized by low water temperatures, scarcity of food, increasing hydrostatic pressure and other environmental peculiarities—other types of larval development prevail and, progressively, replace pelagic development with increasing latitude or depth. The distributional patterns of the various types of development among marine bottom invertebrates form one of the most important factors determining the basic distributional dynamics of the whole benthos in all oceans, both in the geological past and at the present time.Dedicated to the memory of Professor G. Thorson —founder of modern reproductive and larval ecology of marine bottom invertebrates.     

Genetic variation in marine teleosts: High variability in habitat specialists and low variability in habitat generalists

Genetic variation was reviewed in 106 species of marine teleosts. Two heterozygosity estimates were used, one including all protein and enzyme loci and a second excluding the non-enzymatic protein loci. Mean heterozygosities are 0.055±0.036 based on all loci in 106 species and 0.060+0.038 based on enzymatic loci in 89 species. A significant negative correlation was noted between heterozygosity and the proportion of general protein loci included in the estimate. A comparison was made of heterozygosities among taxonomic orders and families, life zones, reproductive mode, geographical range and size. High levels of genetic variation are found in Clupeiformes, Atheriniformes, Pleuronectiformes, temperate pelagic, tropical, intertidal-sublittoral and wide-range species. Low levels of genetic variation are found in Gadiformes, Scorpaeniformes, temperate demersal, polar, and narrowrange species. The most striking differences in heterozygosities are between temperate demersal flatfishes and temperate demersal round fishes. It is suggested that much of the data can be explained by a habitat specialist-generalist model, with high heterozygosities in specialists and low heterozygosities in generalists, but that this is only one of a mosaic of factors which influence genetic variation.     

Mitochondrial DNA variation and population structure in the spiny lobster Panulirus argus

Adult spiny lobsters (Panulirus argus) were collected from nine locations throughout the tropical and subtropical northwest Atlantic Ocean and examined for mitochondrial DNA (mtDNA) variation. 187 different mtDNA haplotypes were observed among the 259 lobsters sampled. Haplotype diversity was calulated to be 0.986 and mean nucleotide sequence-diversity was estimated to be 1.44%; both of these values are among the highest reported values for a marine species. Analysis of molecular variance (AMOVA) and phenetic clustering both failed to reveal any evidence of genetic structure within and among populations of P. argus. The present data are consistent with high levels of gene flow among populations of P. argus resulting from an extended planktonic larval stage and strong prevailing ocean currents.     

Microsatellite analysis of plaice (Pleuronectes platessa L.) in the NE Atlantic: weak genetic structuring in a milieu of high gene flow

Many species of marine fish are typified by large population sizes, strong migratory behavior, high fecundity, and pelagic eggs and larvae that are passively transported by ocean currents, all features that tend to increase gene flow, and hence reduce genetic partitioning, among localized populations. The plaice, Pleuronectes platessa, is a commercially important demersal species that exhibits all of these characteristics. We analyzed genetic variation at eight microsatellite loci in samples of spawning adults (N = 348) from the coasts of Ireland, Iceland, and, for the first time, from the Baltic Sea. Significant differentiation was observed between Iceland and Irish and Baltic Sea samples. However, there were no genetic differences between Irish and Baltic Sea samples, which contrast with the significant differentiation reported between Baltic Sea and North Sea/Atlantic populations of other flatfish species. To increase the data set, we carried out a cross-calibration exercise, allowing us to perform a joint analysis of data with an earlier study on adult and juvenile plaice (N = 480) collected over a broad geographic range, using six microsatellite loci in common to the two studies. Significant differentiation was observed between fish collected at the northern (Iceland, Faeroes, Norway) and southern (Bay of Biscay) parts of the species range. In contrast, the results showed little evidence of genetic structuring over much of the continental shelf of Europe. We believe that bathymetric and hydrographic barriers are the major factors shaping genetic structure, while lack of structure over much of the European continental shelf may be explained by a combination of past historical events, population structure, and dynamics of the species.     

The swimming crab Charybdis smithii: distribution, biology and trophic role in the pelagic ecosystem of the western Indian Ocean

Surface “swarms” of the swimming crabs Charybdis smithii are still considered as an unusual phenomenon in the open Indian Ocean, although their dense pelagic aggregations were already reported in waters off the Indian coast and in the northern Arabian Sea. Based on an extensive large-scale data series taken over 45 years, we demonstrate that C. smithii is common in the pelagic provinces of the western Indian Ocean driven by the wind monsoon regime. Swimming crabs are dispersed by the monsoon currents throughout the equatorial Indian Ocean. They aggregate at night in the upper 150-m layer, where their estimated biomass derived from pelagic trawling data can exceed 130 kg km⁻². Abundance of C. smithii can reach >15,000 ind. km⁻² in July (i.e. the peak of the south-west monsoon), declines by 50-fold in March and is negligible in May. C. smithii is an important prey for more than 30 species of abundant epipelagic top predators. In turn, it feeds on mesopelagic species. This swimming crab is a major species of the intermediate trophic levels and represents a crucial seasonal trophic link in the open ocean ecosystem of the western Indian Ocean. Outbursts in pelagic waters of huge biomasses of ordinarily benthic crustaceans (C. smithii and Natosquilla investigatoris) are a remarkable feature of the Indian Ocean, although similar, but smaller, events are reported in the Pacific and Atlantic Oceans.

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Effects of delayed feeding and temperature on the age of irreversible starvation and on the rates of growth and mortality of Pacific herring larvae

The time periods from exhausion of the yolk to the age of irreversible starvation for Pacific herring Clupea harengus pallasi larvae were 8.5, 7.0 and 6.0 d at 6°, 8° and 10°C, respectively. These periods are within the range perviously measured for Atlantic herring larvae and other temperature zone fish species; they are long compared to the periods for tropical species. The variation in the length of this period is due almost entirely to temperature; the natural logarithm of the time period from fertilization to irreversible starvation is highly correlated (r=0.91) with the mean rearing temperature for 25 species of pelagic marine fish larvae. The rates of growth and mortality, measured for 26 experimental populations of Pacific herring larvae reared at 6°, 8° and 10°C and ten ages of delayed first feeding, decreased and increased, respectively with increasing age of first feeding and increasing temperature. These rates, adjusted for the effects of rearing conditions, were compared with the rates for natural populations of herring larvae. Growth is generally faster in the sea than in experimental enclosures. Two of the eleven estimates of natural mortality rate were high enough to indicate possible catastrophic mass starvation. This is consistent with Hjort's critical period concept of year class formation and it suggests that mass starvation occurs in 18 to 36% of the natural populations of first feeding herring larvae.     

Matter accumulation and energy expenditure in planktonic ecosystems at different trophic levels

Functional peculiarities of pelagic communities from temperate and tropical zones of the ocean have been investigated in terms of food-web interrelations and balance sheets of matter and energy of the major populations and ecological groupings. Ranging from temperate or epiplankton ecosystems to tropical oceanic or deepwater ones, as well as from upwelling zones to stable oceanic oligotrophic regions, the following regular changes in the communities' main functional indices have been established: (1) enlargement of the food spectrum, omnivorousness and predatory activity; (2) reduction of rations and rates of organic matter accumulation in the lower heterotrophic levels with simultaneous increase of energy expenditure; (3) increased trophic complexity and stability of communities. Epiplanktonic systems of low stability proved to be richer and commercially more profitable.     

Quelques données sur le déterminisme ecologique de la reproduction des annélides polychètes

The geographical distribution of marine invertebrate species — Annelida Polychaeta in the present case — is not random. It permits the definition of partially overlapping biogeographical groups. These groups are disposed in a line corresponding to a north-south axis. The seasonal cycles of occurrence of pelagic larvae are considered in southern Scandinavia (on the basis of literature sources), in the western Mediterranean Sea, and in the Indian Ocean (both on the basis of own data). The criterium of reproduction is the presence of meroplanktonic larvae of benthonic species. In this way, it has been possible to distinguish stocks of boreal, temperate and sub-tropical affinity. Within a given stock, the breeding season depends on the site of observation and on ecological factors. The breeding season is retarded for 6 months in southarn Scandinavia as compared to the western Mediterranean Sea, although these species belong to the same stock. This type of comparative study allows emphasis of the role of certain ecological factors related to reproduction (temperature, abundance of phytoplankton, etc.). Breeding may be triggered by different ecological factors, even in animals belonging to one and the same geographical stock: in the Mediterranean Sea, the breeding of the so-called subtropical species seems to be controlled by temperature (monthly variations); in the Indian Ocean, by high levels of phytoplankton abundance. A comparison of temperate species with those of southern Scandinavia and the Mediterranean Sea reveals differences in breeding seasons, which are correlated with thermal regime; breeding does not occur below or above a specific temperature, but is restricted to an optimum value, which appears to be a physiological species characteristic.     

The sea-skater Halobates micans: an open ocean bioindicator for cadmium distribution in Atlantic surface waters

Our knowledge of the horizontal distribution of heavy metals in the open ocean with time and space is still very incomplete. Complementary to chemical water analyses suitable biological indicator species may be used to fill this gap. The pleuston organism Halobates micans was collected from 1966 to 1987 at 151 sampling stations of the tropical and subtropical Atlantic Ocean. The cadmium data from more than 1000 individuals analysed display a chemicaloceanographic meaningful distribution in surface waters and compare favourably to primary production values. Chemical analysis of individual plankton species offer a new tool for a better understanding of geochemical cycling of heavy metals in the ocean.     

Biological investigations of the deep sea. No. 48. Phyllosoma larvae of a scyllarid lobster,Arctides guineensis,from the western Atlantic

A series of scyllarid phyllosoma larvae obtained from plankton in the western Atlantic is described and illustrated. The earliest stages are not represented; the larvae reported range in length from 6 to 59 mm. They are characterized by a narrow, elongated cephalic shield, a broad thorax, a great proportional length of the eyestalk, and by a short dactyl of the fourth pereiopod. There is no direct evidence to establish the parentage of these phyllosomas. By their geographic distribution and the elimination of other species to which larvae have been previously assigned, they are provisionally referred to the scyllarid lobster Arctides guineensis (Spengler).     

Respiration and excretion by oceanic salps

Rates of oxygen consumption and ammonium nitrogen excretion were measured on the solitary and/or aggregate generations of ten species of oceanic salps collected by SCUBA divers during cruises in the Atlantic Ocean (1982–1985). Species that were visibly more active had higher metabolic rates than did less active species. Rates were 1.5 to 2 times lower and O:N ratios were lower when salps were held before incubation than when incubation began at the time of collection. Respiration rate showed a better relationship to length than to weight, suggesting that metabolic activity may be connected mainly with swimming. O:N ratios were between 13 and 28 for most species and generations, but higher and more variable in Pegea spp. Exretion of urea was low or undetectable. Rates of metabolic demand (turnover) ranged from 9.7 to 99% body carbon d^-1 and 6.4 to 55.6% body nitrogen d^-1.Contribution No. 5988 from the Woods Hole Oceanographic Institution and No. 412 from the Allan Hancock Foundation     

Inter-oceanic genetic differentiation among albacore (<Emphasis Type="Italic">Thunnus alalunga</Emphasis>) populations

Albacore (Thunnus alalunga) is a highly migratory pelagic species distributed in all tropical and temperate oceans. Recent analyses using both mitochondrial DNA (mtDNA) and nuclear DNA markers have demonstrated genetic subdivision within and between Atlantic and Pacific populations. However, although numerous biological differences have been reported for Atlantic and Mediterranean albacore, the genetic differentiation for these basins has not been demonstrated. We characterized 373 base pairs of nucleotide sequence from the mitochondrial DNA control region of 134 individuals collected in the Pacific (n=30), the northeast (NE) Atlantic (n=54) and the Mediterranean (n=50). Analysis of molecular variance (AMOVA) revealed a small, but highly significant, proportion of genetic variation separating these three regions (_st =0.041; P=0.009), a pattern also supported by pairwise comparisons. These results demonstrate for the first time the genetic distinctiveness of the Mediterranean albacore from the NE Atlantic population giving support to the current management practices based on separate units. This outcome is concordant with reported migratory movements related to reproductive behavior between the NE Atlantic and the Mediterranean Sea. Additionally, the phylogenetic analyses of DNA sequences revealed the presence of a shallow genetic discontinuity with no geographic association. These two phylogroups are more likely the result of the demographic history of this species (i.e. long demographic stable history) as opposed to historical vicariance as has been proposed for other highly migratory fishes.Communicated by P.W. Sammarco, Chauvin     

Hatching mode and latitude in marine gastropods: revisiting Thorson's paradigm in the southern hemisphere

For much of the last century the developmental mode of marine invertebrates, particularly of prosobranch gastropods, has been thought to reflect a latitudinal pattern known as Thorson's rule; the proportion of species with pelagic larvae decreases with increase in latitude. Although the predictions of this rule have been criticized recently, its validity along latitudinal transects in the world ocean still remains poorly tested. In the present work, we compare the frequency of occurrence of contrasting prosobranch hatching modes (pelagic versus benthic development) along two latitudinal gradients of the subequatorial coastline of South America: the southeast Pacific and the southwest Atlantic. The results are clearly contrasting. While the pattern observed along the Pacific (Chilean) coast fits the predictions of Thorson's rule very well, benthic development predominates all along the Atlantic coast, even at subtropical latitudes. This difference in observed patterns is attributable to the different compositions of the gastropod assemblages on each side of the South American continent, which are determined, in turn, by differences in the ecological conditions on the two sides of the continent. The scarcity of pelagic development among the Atlantic prosobranch gastropods reflects the near-continuous soft-bottom habitat there, and the consequent prevalence of predaceous, soft-bottom taxa that had acquired in their evolution more evolved, non-pelagic patterns of development. In contrast, the Pacific coast is much more heterogeneous, with a diverse mixture of benthic habitats, including rocky substrates that, in part, support grazing taxa. Our results indicate that two factors are important for Thorson's rule to be valid. First, the habitat needs to include rocky substrates, as soft-bottom habitats appear to favour non-pelagic development. Second, a diverse assemblage of taxa need to be compared to avoid the problem of phyletic constraints, which could limit the evolution of different developmental modes. Received: 23 May 2000 / Accepted: 13 October 2000     

The “pelagic larvaton” and its role in the biology of the World Ocean,with special reference to pelagic larvae of marine bottom invertebrates

Ecological subdivision of marine organisms is often based on two characteristics: presence in a defined environment, and types of locomotion (degree of free active movement) in such an environment. The use of these characteristics results in a simple scheme: (1) Inhabitants of the boundary surface “ocean-atmosphere” (a zone including not only the surface film but also the thin subsurface water layer below it and the air layer just above it, i.e., pleuston and neuston). (2) Inhabitants of the deeper water layers of the ocean i.e., excluding the zone mentioned under (1): (a) passively drifting forms with very limited locomotory capacity, moving practically in the vertical plane only (plankton); (b) actively moving forms which migrate both vertically and horizontally (nekton). (3) Inhabitants of the “bottom”-benthos (level-bottom of oceans and coastal waters, tidal zones up to the upper supralittoral, different types of drifting and floating substrata, e.g. ship bottoms, harbour structures, buoys, driftwood, sargassum, whales, etc.). This simple scheme is essentially based on characteristics of adults. If developmental stages are considered, pelagic larvae of bottom invertebrates, eggs and larvae of fishes and other forms, usually present only temporarily in the plankton, neuston, and pleuston, can be distinguished as “mero-plankton”, “mero-neuston” and “mero-pleuston”, from the permanent “holo”-components of these groups. Division into “mero”-subgroups opposes all these larvae to those of planktonic, neustonic and pleustonic forms developing within the “parental” groups and their environments. However, the last category of larvae in the light of world-wide distribution of the seasonal reproductive pattern of marine invertebrates and some other organisms — especially in temperate and high latitudes — can also be rated to some degree as “mero”-(not “holo”-) components. The present paper proposes to unite all larvae of marine invertebrates (and of other organisms) undergoing pelagic development into one biological group, the “pelagic larvaton”. The main characteristic for all forms of this group is the presence of one and the same life-cycle stage in one and the same environment. All forms of the “pelagic larvaton” are, to various degrees, biologically different from their respective adult forms. Even the pelagic larvae of the holoplanktonic species exhibit some differences. Within the “pelagic larvaton”, 3 subgroups can be distinguished on the basis of their ecological peculiarities;

1. Larvae undergoing their whole development in an environment different from that inhabited by their parents and belonging to a group different from that of their parental forms; e.g. the pelagic larvae of bottom invertebrates which develop in the plankton, neuston or pleuston.
2. Larvae undergoing development in the same general pelagic environment, but in “non-parental” ecological groups; e.g. larvae of nektonic species developing in the plankton, neuston or pleuston; larvae of planktonic species in the neuston or pleuston; larvae of neustonic and pleustonic species in the plankton.
3. Larvae undergoing development in the “parental” groups; e.g. larvae of planktonic species in the plankton, of neustonic species in the neuston, or of pleustonic species in the pleuston.

In contrast to the 5 ecological groups: benthos, plankton, nekton, neuston and pleuston, the “pelagic larvaton” represents rather a biological than an ecological group. The “pelagic larvaton” comprises the 5 ecological groups and maintains the permanent turnover of organic substances between water and bottom. This group short-circuits the interrelations between the 5 ecological groups in all possible combinations. The existence of the “pelagic larvaton” presents another illustration of the unity of the biological nature of the oceans. The present paper also discusses the specific distributional patterns of the pelagic larvae of bottom invertebrates and their biological role in the seas.     

Offshore distributional patterns of Hawaiian fish larvae

An analysis of ichthyoplankton samples based on relative abundance reveals pronounced inshore/offshore distributional gradients for most Hawaiian fish larvae. Larvae of pelagic bay species are found almost exclusively in semi-enclosed bays and estuaries. Larvae of pelagic neritic species are more or less uniformly distributed with distance from shore. The larvae of reef species with non-pelagic eggs are most abundant close to shore, while those of reef species with pelagic eggs are most abundant offshore. Finally, the larvae of offshore (primarily mesopelagic) species show no clear pattern but frequently occur in high numbers nearshore. Within any group, variation in pattern was often evident; for example, although Hawaiian fishes of both the families Labridae and Mullidae spawn pelagic eggs, larvae of the former had not peaked in abundance 12 km from shore while larvae of the latter had peaked between 0.5 and 2 km. Some larvae which occur offshore are highly specialized morphologically for a pelagic existence (e.g. Chaetodontidae, which is illustrated) while others are little modified (e.g. Labridae). These findings indicate ichthyoplankton surveys in tropical areas must sample offshore areas in addition to the inshore adult habitat to obtain a complete picture.Hawaii Institute of Marine Biology Contribution No. 484.     

Growth dynamics of the seagrass <Emphasis Type="Italic">Halophila nipponica</Emphasis>, recently discovered in temperate coastal waters of the Korean peninsula

Seagrass species in the genus Halophila are usually distributed in tropical or subtropical areas, but a Halophila species identified as H. nipponica was first observed in temperate coastal regions of Korea in 2007. Since this species mainly occurs in warm temperate regions influenced by warm currents, we hypothesized that H. nipponica may exhibit different growth patterns from those of other temperate seagrass species in Korea, instead showing similar growth dynamics to tropical/subtropical species. The growth and morphology of H. nipponica in relation to coincident measurements of environmental factors were investigated from July 2008 to September 2009 to examine the growth dynamics of this species. Water temperature at the study site ranged from 9.7°C in January to 25.1°C in August. Shoot density, biomass, and productivity exhibited significant seasonal variation, increasing during summer and decreasing during winter. Productivity was severely restricted to nearly ceasing at water temperatures less than 15°C, and winter minimum growth lasted until May. The optimal temperature for H. nipponica growth was approximately 25°C, which was the maximum water temperature at the study site, and no growth reduction in high summer water temperature was observed. Thus, H. nipponica on the temperate coast of Korea exhibited a distinctly different growth pattern from those of temperate seagrass species in Korea, which have shown great reductions in growth at water temperatures higher than 20°C. Higher below- to above-ground ratio and leaf burial into sediments with shorter leaf petioles during winter might be overwintering strategies in this species. The growth patterns of H. nipponica at the study site imply that this species still possess the tropical characteristics of the genus Halophila.