Lethal limits and the zoogeography of the faunal assemblages of Coastal Carolina waters

The offshore waters of Cape Hatteras, North Carolina, USA, is an area of dynamic encounter between the northerly flowing, warm waters of the Gulf Stream and the southerly flowing, colder water of the Virginia coastal current. The faunal assemblages north of the Cape and those associated with a reeflike formation southe of the Cape in the Gulf Stream are distinct, each having predominantly cold- or warm-water affinities. To assess the zoogeographical significance of temperature, high and low thermal limits of both adult and larvae of species from these 2 regions were determined. Lethal salinity limits of the first stage zoeae of a few Crustacea were determined. In general, southern affinity species survived higher temperatures than northerly displanced species. In some cases, species with overlapping distributional limits had different thermal tolerances, which could be correlated with differential microhabitat selection. Many of the southern affinity species could not survive low temperatures which were characteristic of either the water mass northe of Cape Hatteras (4 °C) or the waters between the Gulf Stream and the shore (10 °C). A few species were able to seasonally acclimate to temperature extremes. Zoeae of reef species are the least resistant to both low temperature and low salinity.Supported by Grant NSF GB 7435 from the National Science Foundation. The authors thank Duke University Marine Laboratory and the Cooperative Program of Biological Oceanography for the use of the R. V. Eastward. The Cooperative Program is supported through the National Science Foundation Grant GB-8189.     

Larval tolerance, gene flow, and the northern geographic range limit of fiddler crabs

Despite growing interest in species' range shifts, little is known about the ecological and evolutionary factors that control geographic range boundaries. We investigated the processes that maintain the northern range limit of the mud fiddler crab (Uca pugnax) at North Scituate, Massachusetts, USA (42 degrees 14' N), located approximately 60 km north of Cape Cod. Larvae from five populations in Massachusetts were reared under controlled temperatures to test whether cooler water near the edge of this species' range inhibits planktonic development. Few larvae completed development at temperatures < 18 degrees C, a threshold that larvae would regularly encounter north of Cape Cod. Extensive salt marshes are present north of the current range boundary, and a transplant experiment using field enclosures confirmed that benthic fiddler crabs can survive severe winter conditions in this northern habitat. Taken with oceanographic data, these results suggest that the range boundary of fiddler crabs is likely maintained by the influence of cooler water temperatures on the larval phase. Analyses of mitochondrial DNA sequences from a neutral marker (COI) indicate high gene flow among U. pugnax populations in Massachusetts with little differentiation across Cape Cod. Consistent with predictions regarding the homogenizing influence of gene flow, larvae from source populations north and south of Cape Cod shared a common lower threshold for development. However, larvae produced near the range edge had faster growth rates than those from the south side of Cape Cod (typically reaching the final megalopal stage 1.0-5.5 d faster at 18 degrees C). Additional studies are needed to determine the mechanism underlying this counter-gradient variation in development time. We hypothesize that dispersal into cooler water on the north side of Cape Cod may act as a selection filter that sieves out slow developers from the larval pool by increasing planktonic duration and exposure to associated sources of mortality. Thus while high gene flow may prevent the evolution of greater cold tolerance in northern populations, recurrent selection on existing variation may lead to an unexpected concentration of favorable adaptations at the edge of the range. Such a pattern could permit edge populations to play a dominant and unrecognized role in future range extensions.     

Satellite tracking reveals a dichotomy in migration strategies among juvenile loggerhead turtles in the Northwest Atlantic

Few data are available on the movements and behavior of immature Atlantic loggerhead sea turtles (Caretta caretta) from their seasonal neritic foraging grounds within the western north Atlantic. These waters provide developmental habitat for loggerheads originating from several western Atlantic nesting stocks. We examined the long-term movements of 23 immature loggerheads (16 wild-caught and seven headstart turtles) characterizing their seasonal distribution, habitat use, site fidelity, and the oceanographic conditions encountered during their migrations. We identified two movement strategies: (1) a seasonal shelf-constrained north–south migratory pattern; and (2) a year-round oceanic dispersal strategy where turtles travel in the Gulf Stream to the North Atlantic and their northern dispersal is limited by the 10–15°C isotherm. When sea surface temperatures dropped below 20°C, neritic turtles began a migration south of Cape Hatteras, North Carolina (USA) where they established fidelity to the waters between North Carolina’s Outer Banks and the western edge of the Gulf Stream along outer continental shelf. Two turtles traveled as far south as Florida. Several turtles returned to their seasonal foraging grounds during subsequent summers. Northern movements were associated with both increased sea surface temperature (>21°C) and increased primary productivity. Our results indicate strong seasonal and interannual philopatry to the waters of Virginia (summer foraging habitat) and North Carolina (winter habitat). We suggest that the waters of Virginia and North Carolina provide important seasonal habitat and serve as a seasonal migratory pathway for immature loggerhead sea turtles. North Carolina’s Cape Hatteras acts as a seasonal “migratory bottleneck” for this species; special management consideration should be given to this region. Six turtles spent time farther from the continental shelf. Three entered the Gulf Stream near Cape Hatteras, traveling in the current to the northwest Atlantic. Two of these turtles remained within an oceanic habitat from 1 to 3 years and were associated with mesoscale features and frontal systems. The ability of large benthic subadults to resume an oceanic lifestyle for extended periods indicates plasticity in habitat use and migratory strategies. Therefore, traditional life history models for loggerhead sea turtles should be reevaluated.     

Zoogeography of Northwest Atlantic opisthobranch molluscs

Currently available information on the distribution of species of the opisthobranch orders Cephalaspidea, Nudibranchia and Sacoglossa (Mollusca: Gastropoda) in the northwest Atlantic Ocean is presented. Except for Sacoglossa, the fauna is markedly amphiatlantic, but the temperate West Atlantic component increases southward and dominates south of New Jersey. Species' diversity of nudibranchs and cephalaspids on the continental shelf decreases between northern New England and Cape Hatteras in association with a southward decline in the proportion of amphiatlantic species. This is not evident for the cephalaspids of the continental slope, a higher percentage of which are amphiatlantic. The entire fauna is subdivided into 5 groups: arctic, boreo-subarctic, boreal, West Atlantic temperate, and West Atlantic tropical. The latter does not extend north of Cape Hatteras, but the remaining groups broadly overlap in the northwest Atlantic. The southward limits of amphiatlantic species are presented and related to sea surface temperatures. The thermal characteristics of a critical zone between Cape Cod and Connecticut are discussed, and a maximum temperature of 15 °C is suggested for successful reproduction of the boreo-subarctic component, and 25 °C for the boreal component. The distribution of boreal species on both sides of the North Atlantic is discussed, and a suggestion is made that the southward speread of these species in North America is limited by extreme summer warming south of New Jersey, despite favorable winter temperatures, which extend much farther south.Contribution No. 66 of the Marine Research Laboratory, University of Connecticut, USA.     

Genetic structure of summer flounder (Paralichthys dentatus) populations north and south of Cape Hatteras

Genetic divergence among samples of summer flounder (Paralichthys dentatus, Linnaeus) was estimated to evaluate the effect of Cape Hatteras, a well-known zoogeographic barrier in the western Atlantic Ocean, on intraspecific gene flow. Previous studies based on meristic and morphometric variation and tagging data suggested that gene flow might be limited among summer flounder populations north and south of Cape Hatteras, although the high vagility of both juveniles and adults suggests otherwise. We analyzed genetic diversity revealed in the mitochondrial DNA (mtDNA) control region in samples of juveniles and adults collected in 1992 to 1996 from coastal sites from Buzzard's Bay, Massachusetts to Charleston, South Carolina. In contrast to previous morphological studies, analyses of mtDNA variation reveal no significant population subdivision centered around Cape Hatteras. Received: 17 September 1997 / Accepted: 8 September 1998     

Ancient divergences and recent connections in two tropical Atlantic reef fishes<Emphasis Type="Italic"> Epinephelus adscensionis</Emphasis> and<Emphasis Type="Italic"> Rypticus saponaceous</Emphasis> (Percoidei: Serranidae)

Reef habitats of the tropical Atlantic are separated by river outflows and oceanic expanses that may preclude larval dispersal or other population connections in shorefishes. To examine the impact of these habitat discontinuities on the intraspecific phylogeography of reef-associated species we conducted range-wide surveys of two amphi-Atlantic reef fishes that have dispersive pelagic larval stages. Based on 593 bp of mtDNA cytochrome b from the rock hind Epinephelus adscensionis and 682 bp from the greater soapfish Rypticus saponaceous (n=109 and 86, respectively), we found evidence of relatively ancient separations as well as recent surmounting of biogeographic barriers by dispersal or colonization. Rock hind showed slight but significant population genetic differentiation across much of the tropical Atlantic Ocean (_ST=0.056), but deep divergence between the southeastern United States and seven other localities from the Bahamas to the south, central and east Atlantic (mean pairwise d=0.040, overall _ST=0.867). The geographic distribution of the two rock hind lineages is highly unusual in genetic studies of Caribbean Sea reef fishes, because those lineages are separated by less than 250 km of open water within a major biogeographic region. In contrast, highly significant population genetic structure was observed among greater soapfish from the SW Caribbean, Brazil, and mid-Atlantic ridge (_ST=0.372), with a deep evolutionary separation distinguishing putative R. saponaceous from West Africa (mean pairwise d=0.044, overall _ST=0.929). Both species show evidence for a potential connection between the Caribbean and Brazilian provinces. While widespread haplotype sharing in rock hind indicates that larvae of this species cross oceanic expanses of as much as 2000 km, such a situation is difficult to reconcile with the isolation of populations in Florida and the Bahamas separated by only 250 km. These findings indicate that populations of some species in disjunct biogeographic zones may be isolated for long periods, perhaps sufficient for allopatric speciation, but rare gene flow between zones may preclude such evolutionary divergence in other species.Communicated by P.W. Sammarco, Chauvin     

Larval development of the euphausiid Euphausia pacifica in the Yellow Sea

The complete larval development of Euphausia pacifica in the Yellow Sea is described and the stages are compared with larvae of E. nana. Euphausiid larvae examined in the present study were collected at 30 stations in the Yellow Sea in 1989. During the stages of Calyptopis III to Furcilia II, E. pacifica larvae are smaller than E. nana larvae but they are larger from Furcilia III onward. There are geographical variations in body size of Calyptopis III among the southern California waters, the eastern Japan waters, the Japan Sea, and the Yellow Sea; body size is smallest in the Yellow Sea and Japan Sea, while it is largest in southern California waters and intermediate in eastern Japan waters. Segmentation of antennal endopods was observed in the 56 to 51 furcilia forms in the Yellow Sea population, suggesting that this characteristic is not as reliable for identification of furcilia stages as the pleopods and terminal telson spines. Thus, we propose here that there are six furcilia stages of E. pacifica, instead of the seven previously reported by Boden (1950).     

Spread and potential impact of the recently introduced European green crab,Carcinus maenas,in central California

Our study examines the potential impact of the European green crab Carcinus maenas on communities of coastal embayments of western North America. We document the current distribution and range expansion of this species beyond San Francisco Bay, where C. maenas first became established along this coast in 1989–1990, and we test the effect of C. maenas predation on different species and sizes of infaunal invertebrates in field and laboratory experiments. In our samples from eight coastal locations in central California collected between June 1993 and May 1994, we found no green crabs at the two closest embayments south of San Francisco Bay and found the crabs in all four embayments sampled within 120 km north of San Francisco Bay, up to and including Bodega Harbor. C. maenas was not present in samples from sites farther north. This northward range expansion is apparently the result of larval recruitment by a single cohort, corresponding to the predominant northern transport of surface waters and the approximate distance water moves during larval green crab development. At Bodega Harbor, the current northern range limit, the C. maenas population is now well established and reproducing. Females and males became sexually mature within their first year at 40 mm carapace width, molting approximately monthly from summer through fall, and females were ovigerous in late fall of their first year at 50 mm. We expect larvae from this population to recruit locally and to the north, promoting episodic range extensions as new populations are established and reproduce. Enclosure experiments conducted during the summer of 1993 at the intertidal sandflats of Bodega Harbor showed that C. maenas significantly reduced densities of the most abundant taxa, including the bivalves Transennella confusa and T. tantilla, the cumacean Cumella vulgaris, and the amphipod Corophium sp. Furthermore, Carcinus maenas selectively removed larger (>3 mm) rather than smaller (<1 mm) Transennella spp. in both field and laboratory experiments. Based on the available data from this and other studies of green crabs, and our 10 yr study of community dynamics at Bodega Harbor, we predict C. maenas will significantly alter community structure, ecological interactions, and evolutionary processes in embayments of western North America.     

Cross-shelf distribution of copepods and fish larvae across the central Great Barrier Reef

The distribution of total dry weight of zooplankton, copepod numbers and ichthyoplankton across the outer continental shelf in the central Great Barrier Reef was examined at bi-weekly intervals for three months over summer of 1983. Copepods were sampled (236 m net) within 10 m of the surface and within 10 m of the bottom. Mean densities in surface waters decreased markedly from the mid-shelf to outer shelf and the Coral Sea, but no cross-shelf gradient occurred in the bottom-water. Densities of copepods on the mid-shelf (surface and bottom waters) and in bottom-waters of the outer shelf were typically ca. 400 m^–3. Significantly lower densities (ca. 100 m^–3) occurred in surface waters of the outer shelf, except during outbursts of Acartia australis, when densities in these waters differed little from those elsewhere on the shelf. In oceanic waters, 10 km from the outer shelf station, copepod densities in surface waters were ca. 40 m^–3. Four of the five most abundant copepod taxa in surface waters, Paracalanus spp., Eucalanus crassus, Acrocalanus gracilis and Canthocalanus pauper, tended to be most abundant at the mid-shelf end of the transect. Acartia australis was sporadically very abundant in surface waters of the outer shelf, as was Paracalanus spp. in bottom-water of the outer shelf. An assemblage of Coral Sea species of copepod occurred in bottom-water of the outer shelf during two major intrusions, but not at other times. Densities of all common species varied considerably between cruises. Maximum densities of all common species except A. australis tended to be associated with diatom blooms linked to intrusions but a bloom did not necessarily mean all common species were abundant. Fish larvae included both reef and non-reef taxa, with reef taxa predominating on the outer shelf (approx 2:1 in density of individuals) and non-reef taxa dominating in nearshore samples (approx 2:1). Nine of the ten most abundant taxa analysed showed highly significant variation in numbers among stations and all but one of these also exhibited significant station x cruise interactions. Interactions generally reflected changes in the rank importance of adjacent stations from one cruise to the next or lack of any significant cross-shelf variation on some cruises where overall abundance of the taxa was low.     

Breeding and larval distribution of the pteropod Clione limacina in the North Atlantic,Subarctic and North Pacific Oceans

The pteropod Clione limacina (Phipps, 1774) is an arcticboreal, circumpolar species, which is widely distributed in the North Atlantic and Subarctic Oceans; it also occurs in the North Pacific Ocean (in the Oyashio and neighbouring waters) and along the Atlantic coast of North America in the waters of the cold Labrador current to the Cape Hatteras region (35° N). The distribution of C. limacina larvae in the plankton of the Norwegian, Barents and White Seas, the Bear Island-Spitsbergen region of the Greenland Sea, the Newfoundland Grand Bank and the Flemish-Cap Bank region of the North-western Atlantic Ocean, and the Kurile-Kamchatka region of the North-western Pacific Ocean has been studied, and information from literature concerning the reproduction and larval occurrence of the species is summarized. Throughout its distributional are, spawning of C. limacina is characterized by the same general ecological pattern. This species breeds and spawns in all types of water masses occurring within the vertical range which it commonly inhabits — from surface layers to 500 m water depth. In all local populations of the species, the most intensive spawning is correlated with the spring/summer period of annual heating of the local waters, and the highest abundance parallels maximum growth of phytoplankton which serves as food for veligers and early polytrochous larvae. After the end of this period, spawning intensity in all local C. limacina populations declines sharply, but spawning continues at low intensity during the autumn/winter season, being practically continuous throughout the year. Distribution patterns of C. limacina larvae are determined by those of their parental forms (the parental forms spawn in the zones permanently inhabited). The earliest larval stages of C. limacina (veligers) are present predominantly in the upper 100 or 200 m water layer, i.e. in the zone of high phytoplankton abundance. Polytrochous larvae, after becoming predaceous feeders, are distributed throughout the whole water column from the surface to 500 m depth, similar to adult C. limacina. As with the adults, larvae are present (within the species' distribution area) in all types of water masses. Since the beginning of the twentieth century, in the course of the warming of the Arctic Ocean, the southern race of C. limacina (formerly a summer/autumn seasonal invader in the Norwegian Sea) has become a permanent component of the plankton fauna of the Norwegian and Barents Seas in regions influenced by the Norwegian-Northcape Current System.     

Distribution and abundance of fish larvae off the coast of West Pakistan

The material was collected during 4 different cruises on the shelf off the coast of W. Pakistan in November–December, 1964 and in March, 1967 and 1968. The hydrography as well as the zooplankton-biomass distribution are briefly described. A total of 5777 larval fish were taken in 33 positive vertical hauls by an Indian Ocean Standard Net. The number of larvae in positive hauls ranged from 2 to 1262 larvae haul^-1. The most productive area of the ichthyoplankton was the waters south of Karachi, covered during the Machera Cruise, where 828 to 1262 larvae haul^-1 were obtained. The larvae were identified to species, genera or family. Sardinella sindensis (specific identification uncertain) larvae dominated in abundance. The other abundant larvae belonged to Benthosema spp., Amentum commersonii, Vinciguerria spp. and Diaphus spp. Larval distributions and abundances are described. Aggregation and spawning of adult Sardinella (sindensis) in the waters off the coast of W. Pakistan in November/December, 1964, are discussed. Presumably, the waters south of Karachi represent good feeding grounds for s. (sindensis) larvae. Displacement volume, length and weight relationships of various larval size groups have been studied and a high rate of larval mortality (at a length of 5.0 to 8.5 mm) observed.     

Plankton inhabiting the surface layer of the southern and southwestern lagoon of New Caledonia

In the southern and southwestern coral reef lagoon of New Caledonia and the adjacent oceanic waters, 42 neuston samples were collected from the upper surface layer (0 to 10 cm) along nine transects from the coast to the coral barrier reef and the open ocean immediately beyond the reef, in March and April 1979. There was a progressive numerical decrease in zooplankton densities from the coast to the reef and from the reef to the open sea. Generally, 80 to 95% of the surface plankton consisted of holoplankton and 5 to 20% of meroplankton. Zooplankton was very abundant in littoral bays with a marked eutrophication. In a few samples collected in very shallow waters close to coral patches, cladocerans were numerous and constituted up to 75% of the total plankton, whilst in other samples collected above greater depths, copepods made up 60 to 85% of the total plankton. In the coral reef lagoon of south and southwest New Caledonia, typically hyponeustonic copepods (pontellids) often comprised 5% of the total copepod populations.     

Genetic structure of<Emphasis Type="Italic"> Linckia laevigata</Emphasis> and<Emphasis Type="Italic"> Tridacna crocea</Emphasis> populations in the Palawan shelf and shoal reefs

Allozyme variation of 10 populations of Linckia laevigata at 8 polymorphic loci and 13 populations of Tridacna crocea at 6 polymorphic loci were analyzed to compare genetic variability and genetic affinities among reefs in Palawan, Philippines. Two to five populations were sampled from each of four regions: the shelf reefs in (1) northern Palawan and (2) southern Palawan and the offshore reefs in (3) the Kalayaan island group (KIG) in the South China Sea and (4) the Tubbataha shoals in the Sulu Sea. Heterozygosity was highest in populations of L. laevigata from the south shelf of Palawan and populations of T. crocea from the Tubbataha shoals of the Sulu Sea. The lowest heterozygosity estimates were from the reefs of the KIG in the South China Sea, for both species. Overall F _ST values for both species were significant, with an estimated average number of effective migrants per generation (N _EM) of 4.85 (~5 individuals) for L. laevigata and 3.54 (~4 individuals) for T. crocea. Within-region comparisons showed N_EM ranging from 6.29 to 92.34 for L. laevigata and from 3.40 to 6.30 for T. crocea. The higher gene flow among L. laevigata populations relative to T. crocea is consistent with the greater dispersal potential of the former species. Finer scale genetic structuring was evident in T. crocea populations. For both species, the Tubbataha reefs in the Sulu Sea have higher genetic affinity with the populations from the southern shelf of Palawan, while the reefs in the KIG had higher affinity with the northern Palawan shelf reefs. The north and south shelf populations have the least genetic affinity. Genetic patchiness among reefs within regions suggests the importance of small-scale physical factors that affect recruitment success in structuring populations in small island and shoal reef systems in Palawan.     

A comparative analysis of alien plant species along the Romanian Black Sea coastal area. The role of harbours

Previous studies have found a higher proportion of alien plant species along the coastal area of the Black Sea. The goals of the present study were to assess the role of two harbours as gateways and reservoirs for alien plant species, to compare the structure and invasion pattern of the alien plants recorded there, and test methods useful for effective monitoring programs. We inventoried 12 sites along the western Black Sea coast from the harbour of Sulina in the north to Cape Kaliakra in the south. Each site was visited at least three times each. A more intensive survey was done in the two harbours targeted by our study: Constanţa and Sulina. The proportion of neophytes was higher in the harbours (representing about one third of the total plant species) and lower in coastal protected areas (with an average proportion of 6.7%). Species accumulation curves and estimators of species richness indicated that while the plant inventory was not complete, invasive alien species (IAS) were adequately inventoried. Harbours act not only as gateways for IAS but also as reservoirs, facilitating their acclimatization and naturalization. The use of species accumulation curves and estimators of species richness are useful tools in designing and evaluating simple monitoring programs based on repeated inventories. Our study has stressed the importance of monitoring not only coastal waters but also green areas in harbours for the early detection of IAS.     

Influence of UV radiation on the survival of larvae from broadcast-spawning reef corals

Effects of ambient ultraviolet light on the survivorship of eggs and planulae larvae was investigated for three species of broadcast-spawning reef corals, Acropora palmata, Montastraea annularis, and M. franksi. Eggs and larvae from these corals contain high concentrations of lipids (60–70% by weight) and float in surface waters for 3–4 days following spawning. Larvae originating from colonies living at deeper sites on the reef exhibited significantly lower survivorship than conspecifics originating from parents in shallow water when experimentally exposed for up to 4 days to ambient surface levels of ultraviolet radiation (UVR). Concentrations of the UVR-protective compounds correlated positively with survival and matched concentrations found in parent colonies, implying that higher concentrations of ultraviolet B protective compounds are responsible for greater survival of eggs and larvae from shallow compared to deeper-dwelling parents. Ultraviolet B appears to be responsible for most of the observed differences in larval survivorship with ultraviolet A playing a minor or insignificant role. Data presented here indicate that coral recruits on Caribbean reefs and elsewhere may originate primarily from adult colonies dwelling in shallow water.Communicated by P.W. Sammarco, Chauvin     

Possible effects of water pollution on the community structure of Red Sea corals

The community structure and species diversity of hermatypic corals was studied during 1969–1973, in two reef flats in the northern Gulf of Eilat, Red Sea: the reef flat of the nature reserve at Eilat, which is chronically polluted by oil and minerals, and a control reef, located 5 km further south, which is free from oil pollution. In 1969, the nature reserve and the control reef had similar coral community structure. In September, 1970, both reefs suffered approximately 90% mortality of corals, as a result of an unexpected and extremely low tide. In 1973 the control reef was “blooming” with a highly diverse coral community, while almost no signs of coral recolonization have been observed at the nature reserve, and it is significantly lower in diversity. It is suggested that phosphate eutrophication and chronic oil pollution are the major man-made disturbances that interfere with coral colonization of the reef flat at the nature reserve. Although no direct evidence is provided that oil damages hermatypic corals, the data strongly suggest that chronic oil spills prevent normal settlement and/or development of coral larvae. It is possible that chronic oil, pollution results in either one or a combination of the following: (1) damage to the reproductive system of corals; (2) decreased viability of coral larvae; (3) changes in some physical properties of the reef flat which interfere with normal settlement of coral larvae.     

Ecological investigations of the late-stage phyllosoma and puerulus larvae of the western rock lobster Panulirus longipes cygnus

The distribution and abundance of the late-stage phyllosoma larvae of Panulirus longipes cygnus George and the distribution and densities of the final larval stage, the puerulus, both in the plankton and at settlement along the coast, were investigated. A total of 3,617 late-stage phyllosoma (Stages VI to IX) and 301 puerulus larvae were caught at 187 plankton stations during the July to November periods 1974, 1975 and 1976 off the west coast of Australia between 29°00 to 32°30S and 113°30 to 115°00E. The depth range sampled was 0 to 35 m on the continental shelf and 0 to 90 m off the shelf. During onshore/offshore cruises with similar sampling effort on and off the shelf, 1,169 late-stage phyllosoma larvae were taken, of which only 9 were caught on the shelf, and these near the outer edge. A series of cruises sampling two areas beyond the shelf near 29°30 and 32°00S yielded 2448 late-stage phyllosoma, with greater densities of larvae in the northern location. The settlement of puerulus-stage larvae along the coast in the same geographical range was also greater in the north than in the south. The data from the onshore/offshore cruises showed a definite effect of moon phase on numbers of puerulus larvae caught on the shelf, with higher catches near new moon. The low numbers of puerulus larvae (usually 0, 1 or 2 individuals) caught at all stations showed that the puerulus stage is sparsely distributed in the plankton. Fewer puerulus larvae were present at the surface than at lower depths, but it was not possible to determine a depth preference for the puerulus between 10 m and the lowest depths sampled because of the low catch numbers. No relationships were found between puerulus larvae density and surface-water temperature, salinity, or plankton biomass at each station. Data on the larval distributions indicate that, near the end of their planktonic existence, the majority of the late-stage phyllosoma larvae of P. longipes cygnus are not carried onto the shelf, where mixing of oceanic and continental shelf waters occurs only on the outer third, but are transported southward by oceanic circulation beyond the shelf. The puerulus moults from the last phyllosoma stage beyond the shelf and completes the larval cycle by swimming across the shelf and settling in the shallow reef areas.     

Reef recovery 20 years after the 1982–1983 El Niño massive mortality

For over 20 years the El Niño-Southern Oscillation (ENSO) has caused damage to the coral reefs of the eastern Pacific and other regions. In the mid-1980s scientists estimated that coral cover was reduced by 50–100% in several countries across the region. Almost 20 years (2002) after the 1982–1983 event, we assessed the recovery of the virtually destroyed reefs at Cocos Island (Costa Rica), previously evaluated in 1987 and reported to have less than 4% live coral cover. We observed up to fivefold increase in live coral cover which varied among reefs surveyed in 1987 and 2002. Most new recruits and adults belonged to the main reef building species from pre-1982 ENSO, Porites lobata, suggesting that a disturbance as outstanding as El Niño was not sufficient to change the role or composition of the dominant species, contrary to phase shifts reported for the Caribbean. During the 1990s, new species were observed growing on the reefs. Notably, Leptoseris scabra, considered to be rare in the entire Pacific, was commonly found in the area. Recovery may have begun with the sexual and asexual recruits of the few surviving colonies of P. lobata and Pavona spp. and with long distance transport of larvae from remote reefs. We found an overall 23% live coral cover by 2002 and with one reef above 58% indicating that Cocos Island coral reefs are recovering.     

Species-specific grazing rates of heterotrophic dinoflagellates in oceanic waters,measured with a dual-label radioisotope technique

A dual-isotope method was developed to measure grazing rates and food preferences of individual species of heterotrophic dinoflagellates from natural populations, collected from the Slope, Gulf Stream, and Sargasso Sea and from a transect from Iceland to New England, in 1983. The isotope method measures the grazing rates of microzooplankton which cannot be separated in natural populations on the basis of size. Tritiated-thymidine and ¹⁴C-bicarbonate were used to label natural heterotrophic and autotrophic food, respectively. Nine oceanic dinoflagellate species in the genera Protoperidinium, Podolampas, and Diplopsalis fed on both heterotrophic and autotrophic food particles with clearance rates of 0.4 to 8.0 l cell^-1 h^-1, based on ³H incorporation, and 0.0 to 28.3 l cell^-1 h^-1, based on ¹⁴C incorporation. Two dinoflagellate species, Protoperidinium ovatum and Podolampas palmipes, fed only on ³H-labelled food particles. Several species of dinoflagellates fed on bacteria (<1 m) which had been prelabelled with ³H-thymidine. The clearance rates of heterotrophic dinoflagellates and ciliates were similar and within the range of tintinnid ciliate clearance rates reported in the literature. As heterotrophic dinoflagellates and ciliates can have comparable abundances in oceanic waters, we conclude that heterotrophic dinoflagellates may have an equally important impact as microheterotrophic grazers of phytoplankton and bacteria in oceanic waters.Partially supported by a grant from the National Science Foundation, OCE-81-17744     

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.