Growth and reproduction in the Antarctic brooding bivalve Adacnarca nitens (Philobryidae) from the Ross Sea

We present information on the reproductive biology, population structure, and growth of the brooding Antarctic bivalve Adacnarca nitens Pelseneer 1903, from the Ross Sea, Antarctica. Individuals ranging from 0.85 to 6.00 mm were found attached to a hydrozoan colony. This species shows low fecundity and large egg size, common to other brooding species. The minimum size at which oogenesis was detected was 2.3 mm and the minimum size at which brooding was evident was 3.9 mm. Embryos of a full range of developmental stages were brooded simultaneously in females. The population showed a log–normal distribution and results suggest non-periodic reproduction with continuous embryonic development. The reproductive traits of A. nitens are discussed in the context of circum-Antarctic species distribution and limitations to dispersal in brooding benthic invertebrates.     

Comparison of the statolith structures of <Emphasis Type="Italic">Chironex fleckeri</Emphasis> (Cnidaria,Cubozoa) and <Emphasis Type="Italic">Periphylla periphylla</Emphasis> (Cnidaria,Scyphozoa): a phylogenetic approach

The rhopalia and statocysts of Periphylla periphylla (Péron and Lesueur in Ann Mus Hist Nat Marseille 14:316–366,1809) and Chironex fleckeri Southcott (Aust J Mar Freshw Res 7(2):254–280 1956) were examined histologically and showed several homologous characteristics. Differences in sensory area distribution could be connected to a slightly different functionality of equilibrium sensing. In P. periphylla, the statoliths (crystals) grow independently of each other; whereas in C. fleckeri, one large crystal covers the smaller ones. The structures of both statoliths were examined in detail with single-crystal diffraction, microtomography and diffraction contrast tomography. The single compact statolith of C. fleckeri consisted of bassanite as was previously known only for other rhopaliophoran medusae. An origin area with several small oligocrystals was located in the centre of the cubozoan statolith. The origin areas and the accretion of statoliths are similar in both species. Our results lead to the assumption that the single bassanite statolith of C. fleckeri (Cnidaria, Cubozoa) is a progression of the scyphozoan multiplex statolith. It is therefore suggested that the Cubozoa are derived from a scyphozoan ancestor and are a highly developed taxa within the Rhopaliophora.     

Riverine and marine ecotypes of <Emphasis Type="Italic">Sotalia</Emphasis> dolphins are different species

The current taxonomic status of Sotalia species is uncertain. The genus once comprised five species, but in the twentieth century they were grouped into two (riverine Sotalia fluviatilis and marine Sotalia guianensis) that later were further lumped into a single species (S. fluviatilis), with marine and riverine ecotypes. This uncertainty hampers the assessment of potential impacts on populations and the design of effective conservation measures. We used mitochondrial DNA control region and cytochrome b sequence data to investigate the specific status of S. fluviatilis ecotypes and their population structure along the Brazilian coast. Nested-clade (NCA), phylogenetic analyses and analysis of molecular variance of control region sequences showed that marine and riverine ecotypes form very divergent monophyletic groups (2.5% sequence divergence; 75% of total molecular variance found between them), which have been evolving independently since an old allopatric fragmentation event. This result is also corroborated by cytochrome b sequence data, for which marine and riverine specimens are fixed for haplotypes that differ by 28 (out of 1,140) nucleotides. According to various species definition methods, we conclude that marine and riverine Sotalia are different species. Based on priority criteria, we recommend the revalidation of Sotalia guianensis (Van Bénéden 1864) for the marine animals, while riverine dolphins should retain the species name Sotalia fluviatilis (Gervais 1853), thus becoming the first exclusively riverine delphinid. The populations of S. guianensis show a strong subdivision (Φ_ST=0.628) along the Brazilian coast, with at least three evolutionarily significant units: north, northeastern and south/southeastern.     

A tropical/subtropical biogeographic disjunction in southeastern Africa separates two Evolutionarily Significant Units of an estuarine prawn

Recent phylogeographic research has indicated that biodiversity in the sea may be considerably greater than previously thought. However, the majority of phylogeographic studies on marine invertebrates have exclusively used a single locus (mitochondrial DNA), and it is questionable whether the phylogroups identified can be considered distinct species. We tested whether the mtDNA phylogroups of the southern African sandprawn Callianassa kraussi Stebbing (Decapoda: Thalassinidea) are also recovered using nuclear sequence data. Four mtDNA phylogroups were recovered that were each associated with one of South Africa’s four major biogeographic provinces. Three of these were poorly differentiated, but the fourth (tropical) group was highly distinct. The nuclear phylogeny recovered two major clades, one present in the tropical region and the other in the remainder of South Africa. Congruence between mitochondrial and nuclear DNA indicates that the species comprises two Evolutionarily Significant Units sensu Moritz (1994). In conjunction with physiological data from C. kraussi and morphological, ecological and physiological data from other species, this result supports the notion that at least some of the mtDNA phylogroups of coastal invertebrates whose distributions are limited by biogeographic disjunctions can indeed be considered to be cryptic species.     

Hydrography and distribution dynamics of larval and juvenile fishes in the coastal waters of the Tanshui River estuary,Taiwan, with reference to estuarine larval transport

Distribution dynamics of fish larvae and juveniles in the coastal waters of the Tanshui River, Taiwan was studied fortnightly using surface horizontal tows with a larval net in daytime during the period from early April through early June 1991. Environmental factors, including water temperature, salinity, dissolved oxygen, pH, transparency and depth at sampling stations, were also monitored. A total of 10737 fish eggs and 1387 individuals, representing 43 families and 93 species, was collected during five cruises from 12 stations in the coastal waters. Most fish were estuarine-dependent marine species. Liza macrolepis, Ambassis gymnocephalus, Terapon jarbua, Mullidae and Gobiidae were the most dominant, making up 64.7% of the total catch. Early life stages, including egg, preflexion, flexion and postflexion larvae were abundant in surface samples. However, yolk-sac larvae were absent in the surface water, probably due to an ontogenetic behavioral shift as a consequence of a change in specific weight during early development. The species composition of fish larvae and juveniles was related to the microhabitats found in the coastal waters. The physico-chemical conditions, along with ontogenetic behavior, played an important role in larval fish distribution in the coastal waters.     

Community interactions and zoogeography of the Indian Ocean Candaciidae (Copepoda: Calanoida)

Eighteen species of Candaciidae have been identified from collections made at 339 stations in the Indian Ocean. Most species are zonally distributed; however, on the eastern and western sides of the Indian Ocean, species ranges are extended north or south by boundary currents. Factor analysis was used to cluster phenotypically similar species based on 130 characters taken from the maxilla (a feeding appendage), the first swimming foot, and the fifth foot (a secondary sexual structure). Four morphological clusters were extracted. Clusterings based on separate factor analyses limited to characters from feeding or from sexually adapted appendages are in substantial agreement with the clusters based on composite morphology. Two geographically recurrent groups of species were also identified, one from equatorial waters, one from the central gyre. Each recurrent group is composed of species exceptionally different in body size and belonging to different morphological clusters. Niches of the species are compared using Hutchinson's multidimensional hypervolume as a model. An attempt is made to describe the niche of each species in terms of environmental variables measured at stations where the species was abundant. Environmental variables (dimensions) included in this study are space, time, temperature, food, oxygen and salinity. Mean niche adaptations of most of the species are separable from congeners along at least one niche dimension. It is proposed that community relationships among the Candaciidae developed to prevent both gamete loss and to avoid trophic competition. It is postulated that newly evolving species underwent contemporaneous displacement of both secondary sexual and trophic characters as a condition for sympatry, or diverged in their physiological adaptations to escape sympatric interference.Contribution No. 3686 of the Woods Hole Oceanographic Institution. This research was supported by NSF Grants GB 27405 and GA 43126 and is based on a doctoral dissertation submitted to the Curriculum in Marine Sciences of the University of North Carolina at Chapel Hill.     

Day/night vertical distribution of euphausiids in the eastern tropical Pacific

Between March 23 and April 4, 1981, samples were taken in the eastern tropical Pacific. The day/night vertical distribution of euphausiid species and biomass are described and contrasted in detail on two eastern tropical Pacific stations, the DOME station, in a region of continuous upwelling and the BIOSTAT station, in a nonupwelling area. The effects of various biological parameters, such as temperature, salinity and oxygen concentrations on the distributions of the species are examined. The numbers of euphausiids m^-2 on both stations were highest during the day, indicating that avoidance of the sampler was not a problem. During the day the largest concentration of adult euphausiids was between 300 and 350 m whereas the juveniles were concentrated between 170 and 80 m on both stations. Very few individuals were found within the oxygen minimum layer, but low concentrations of some species were found below the oxygen minimum down to 1 000 m. At night the euphausiid concentration migrated upward into the mixed layer (20 to 30 m) at BIOSTAT and to the base of the mixed layer at the DOME. Significant differences in the night depths of the species were found on both stations. The oxygen minimum layer appeared to act as a barrier to the vertical distribution of all species. Only two species were found in water with an oxygen concentration of <0.1 ml O₂ l^-1. Twentyone species of euphausiids were found on the two stations but the adult population was dominated by only two or three species on both stations. The reproductive state of the species suggested that some species reproduced earlier on the DOME than on BIOSTAT. Analysis of the depth distribution by cluster analysis showed that the most abundant species occupied different depths during the night and day at BIOSTAT but the two most abundant species were concentrated at the same depth at the DOME station although portions of each species population occupied different pelagic zones.     

Effect of the receding ice-edge on the condition of mid-water fishes in the northwestern Weddell Sea: results from biochemical assays with notes on diet

Electrona antarctica and Bathylagus antarcticus are dominant fishes in the Southern Ocean pelagic ecosystem with disparate life histories, making them excellent subjects for comparative studies. Twenty-one indices of nutritional condition were compared in both species by observing changes in each index as it varied spatially and temporally in association with the marginal ice-zone bloom in the northwestern Weddell Sea. E. antarctica and B. antarcticus exhibited very different patterns of response to the bloom. Nutritional condition increased in 11 of 21 measures in E. antarctica, suggesting that it was in poorer condition at ice-covered stations and in greatly improved condition in post-bloom, open-water stations. The data, combined with a few observations of larvae, indicate that E. antarctica increases feeding before the spring bloom, rapidly building stores of lipid, which are probably used for spawning. In contrast, only three measures of condition were variable in B. antarcticus, and lipid actually decreased from ice-covered to open water. RNA:DNA values increased in open water, coinciding with an increase in food volume present in their guts. These observations, coupled with observations of larvae in ice-covered stations, suggest that B. antarcticus possesses sufficient energetic stores to spawn prior to the bloom, so that larvae are able to fully utilize available resources associated with the spring bloom. Increased somatic growth, as indicated by RNA:DNA, may not begin until later, when the bloom was beginning to decline. Earlier work, which suggested that the deeper living, non-migrating species, like B. antarcticus, would not be affected by the bloom until after shallower, migratory species, like E. antarctica, is supported. Of the assays tested, RNA:DNA appeared to be the most sensitive. The combined assessment of many measures including biochemical, compositional, dietary, and age estimates from single specimens is possible if the samples are treated with sufficient care. The reliance upon a single measure to help interpret the ecology of a species, especially in nekton-sized species, is not as effective as techniques used in combination. Received: 12 January 2000 / Accepted: 16 August 2000     

A method for detecting and identifying the lethal environmental factor on a dominant macrobenthos and its application to Lake Shinji,Japan

A new method to single out the environmental factor limiting the life of any macrobenthic animal under stressed condition is proposed. The method is based on the assumption that the influence of each environmental factor on the life of a species can be expressed by an S-shaped function having lethal, limiting and non-limiting ranges, and the combined effect of several environmental factors is expressed by a multiple of these functions. To single out a lethal factor, we used the cumulative curve of abundance arranged in the order of each environmental factor. Comparison of these curves enables us to identify the most effective environmental factor limiting the life of a particular species and determine its effective range. Determination can be made from a single field observation without recourse to specially prepared experimental data if a sufficiently extensive survey was made in a field observation. The method was applied to the field data obtained from 248 stations at Lake Shinji, Japan, in the summer of 1982.     

Sedimentary Pigments and Organic Matter in Relation to Benthic Fauna in the Tan-Shui Estuary,Taiwan

The benthic ecological structure of the Tan-Shui estuary, Taiwan is changed due to long term effects of dumping of urban wastewater and of engineering actions. to monitor these changes, we sampled and analyzed benthos and sediment from 12 stations on the estuary.

The composition of the dominant species of benthos varied seasonally, with molluscan and crustacean species having greater numbers and higher frequencies of occurrence than other species. the dominant taxa during winter were Nassarius sp. and Maldanidae at two stations. Analysis using Simpson's index and Shannon's index showed the benthic community varied more in coastal areas than in offshore areas.

Physicochemical analysis showed that most of the Tan-Shui estuary consisted of sandy sediment. the variations in concentrations of organic carbon and total nitrogen at each station were small. Although the concentrations of chlorophyll-a and carotenoid at all stations were generally low, the two stations had the highest concentrations, and we concluded that the concentration of pigments in these sediments was related to the abundance of benthos. the community structure of the benthos reflected the characteristics of the sediments, and benthic species exhibited selection of and adaptation to specific sedimentary environments.     

Scarred limpets at hydrothermal vents: evidence of predation by deep-sea whelks

The chaotic physical and chemical environment at deep-sea hydrothermal vents has been associated with an ecosystem with few predators, arguably allowing the habitat to provide refuge for vulnerable species. The dominance of endemic limpets with thin, open-coiled shells at north Pacific vents may support this view. To test their vulnerability to predation, the incidence of healed repair scars, which are argued to reflect non-lethal encounters with predators, were examined on the shells of over 5,800 vent limpets of Lepetodrilus fucensis McLean (1988) that were collected from 13 to 18 August 1996. Three vent fields on the Juan de Fuca Ridge at ca. 2,200 m depth were sampled, two within 70 m of 47°56.87′N 129°05.91′W, and one at 47°57.85′N 129°05.15′W with the conspicuous potential limpet predators, the zoarcid fish Pachycara gymninium Anderson and Peden (1988), the galatheid crab Munidopsis alvisca Williams (1988), and the buccinid snail Buccinum thermophilum Harasewych and Kantor (2002). Limpets from the predator-rich vent were most often scarred, a significant difference created by the high incidence of scars on small (<4 mm long) limpets in this sample. Collected with the limpets were small (median shell diameter 4.4 mm) buccinids. They, rather than the larger, more conspicuous mobile fishes and crabs are argued to be the shell-damaging predator. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Deep-sea bottom-living fishes at two repeat stations at 2 200 and 2 900 m in the Rockall Trough,northeastern Atlantic Ocean

Repeated sampling of deep-sea bottom-living fishes was conducted at two stations in the Rockall Trough at depths of 2 200 and 2 900 m. The 2 200 m station (M) was sampled 16 times by an Agassiz trawl between April 1978 and April 1985 and yielded 473 fish belonging to 17 species. The 2 900 m permanent station (PS) yielded 781 fish belonging to 11 species from 9 Agassiz trawls, 2 small box otter trawls, 4 semi-balloon otter trawls and 7 epibenthic sledges between March 1975 and April 1985. Macrourid fishes were numerically dominant at both stations with Coryphaenoides guentheri and Coryphaenoides (Nematonurus) armatus being the most abundant species at M and PS, respectively. In terms of biomass the morid, Antimora rostrata, was dominant at M but C. (N.) armatus was dominant at PS. The only species that showed clear evidence of a seasonal reproductive cycle was C. guentheri. Many species showed no indication of reproducing in the Rockall Trough. The diets of almost all the species are described and considered in relation to the food resources exploited. Investigations on the pelagic and benthic invertebrate faunas at these stations should reveal the extent to which the bottom-living fishes exploit the available resources.     

Long-term variability in the structure of subtidal benthic communities in Puget Sound,Washington, USA

Data on benthic infauna from 4 permanent stations in Puget Sound off Seattle, USA, collected during 1963–1964, 1967, and 1969, revealed considerable stability in numbers of species and specimens and in diversity within stations among sampling dates. The species composition of the faunal assemblages also remained rather constant during the period of investigation, but the relative dominance among the numerically important species varied somewhat. Biomass data did not differ significantly in 1964 and 1969, but the 1967 data were considerably lower at all stations.     

Tisbe (Copepoda: Harpacticoida) species from the Lagoon of Venice. I. Seasonal fluctuations and ecology

Distribution and abundance of Tisbe species were studied throughout a period of 3 years at 3 stations in the Lagoon of Venice (Italy). At 2 other stations samples were taken occasionally, as also at the Lido station (open sea). Twelve species may be considered as common inhabitants of the lagoon, and 3 species appear to be occasional transients, compared to the 9 species found at the Lido. A comparison of the physical data shows that the stations were similar in temperature and salinity, but differed primarily in pH values, sediment characteristics, algal substratum and faunal benthic community. The fact that remarkable differences in species composition and distribution of Tisbe could be observed between the various parts of the lagoon and the lagoon and the open sea, indicates that temperature and salinity are not so important for species diversity as are biotic factors. A particularly strong difference existed between samples taken at the bottom and from pilings, which constitute a very special biotope for the benthic communities in the lagoon and seem to be a preferred habitat for T. lagunaris and T. cucumariae. The data suggest that there is a certain interaction between T. holothuriae and the other species. Whenever T. holothuriae was abundant, the other species were rare, but T. clodiensis, T. dobzhanskii (Stations 1 and 2) and Tisbe sp. (Station 3) attained high relative abundance whenever T. holothuriae decreased considerably in number. T. holothuriae represents certainly the hardiest species of the lagoon, displaying a great ability to cope with stress conditions, even those present in the interior lagoon where strong fluctuations in salinity, temperature, pH and oxygen prevail.     

Inf luence of Season and a Sympatric Congener on Habitat Use by Stephens' Kangaroo Rat

We examined habitat use by the endangered Stephens' kangaroo rat ( Dipodomys stephensi) in different seasons and assessed whether this may be influenced by a sympatric congener, the Pacific kangaroo rat (Dipodomys agilis). Trapping on three plots over 2 years revealed these species were rarely captured at the same trap stations. Spatial segregation was highly significant when both species were at high density. The spatial distribution of these species was temporally stable where both species were relatively abundant, but where D. agilis was relatively uncommon the distribution of D. stephensi varied from one census to another. The abundance of three microhabitats (grass, debris, and bare ground) followed a regular seasonal pattern of variation that was consistent across 2 years of substantially different rainfall. A canonical discriminant analysis showed that the five quantified microhabitats (those above and bush and rock cover) provided highly significant discrimination between the trap stations occupied by the two species. Dipodomys stephensi was associated with trap stations where grass cover and bare ground were abundant but where bush and rock were uncommon. Dipodomys agilis was associated with stations that had large amounts of bare ground and average abundances of bush and rock cover. The spatial segregation of these species appears to be mediated by habitat preferences; D. stephensi prefers grassland and D. agilis prefers sage scrub. This suggests that habitat management for D. stephensi should include (1) controlling the spread of shrubs into grassland and (2) creating dispersal corridors of open habitat to link areas of suitable habitat where none presently exist. Each of these options may be needed to maintain viable populations in all reserves designated for the conservation of D. stephensi.     

Seasonal distribution of modern coccolithophores in the western North Atlantic Ocean

The seasonal successions of standing crop and floral assemblage were studied for oceanic coccolithophores at 5 weather stations in the western North Atlantic Ocean. The coccolithophores were less populous during winter at the northern stations, whereas they became scarce during summer at the southern stations. The average standing crop in the surface water was quite consistent throughout all climatic regions, being a few tens of thousand cells per liter. The average standing crop at the 100 m level showed a clear trend of increasing southwards. The population at this depth was only one-tenth as large as that of the surface level at the northernmost station, whereas it was almost two-thirds as large as the surface levels at the southernmost station. Many of the major species exhibited seasonally biased occurrences. The trend was mostly repeated in consecutive years, although the magnitude of their abundances fluctuated from year to year in some case. The average species composition was obtained for the 5 weather stations at the surfacewater (surface and 20 m levels combined) and 100 m levels; Emiliania huxleyi dominated the flora at all stations. The relationship between occurrences of major species and ambient water temperature was also studied. Although some species were stenothermal, the majority exhibited eurythermal characteristics; this accounts for the high specific diversity of the coccolithophore community throughout the wide range of waters studied.Contribution No. 2899 of the Lamont-Doherty Geological Observatory of Columbia University.     

Offshore–inshore and vertical distributional patterns of heteropod mollusks off leeward Oahu, Hawaii

Replicated zooplankton tows were taken during day and night periods at neritic (1 nmi offshore) and oceanic (5 and 15 nmi offshore) stations off the leeward side of Oahu, Hawaii during fall (September) and spring (April). Plankton samples were obtained with a 1-m² MOCNESS net system towed obliquely through seven depth strata to 80 m (neritic station) and eight depth strata to 200 m (oceanic stations). Five more species were collected in April (17) than in September (12). During both months the number of species decreased from the 15 to the 1 nmi stations; from 11 to 9 in September and 15 to 11 in April. Species diversity, as measured by species accumulation (rarefaction) curves, was higher at the 15 than the 1 nmi stations during both months. Total nighttime water column density in April was about double that in September. In September, the density decreased sevenfold from the 15 to 1 nmi stations, but in April densities were comparable among the three stations; mainly as a result of the shoreward increase in density of Atlanta plana. The most abundant species in both months were A. plana, A. lesueuri, A. inflata, A. peroni, and Protatlanta souleyeti, which in combination accounted for 93% (September) and 91% (April) of the total nighttime water column densities. The vertical ranges of six species were limited to the upper 100 m, and nocturnal migration was suggested for two (A. helicinoides during both months and A. turriculata in April). The ranges of the remaining 11 species extended to 160 or 200 m, and among them nocturnal migration was suggested for five (A. plana, A. meteori and Pterotrachea hippocampus during both months, and A. peroni and Protatlanta soueleyti in April).     

Distribution and structure of benthic assemblages in Puget Sound,Washington, USA

Benthic infauna was collected with a 0.2 m² van Veen grab at 48 stations in Puget Sound, Washington, USA during February–March 1969. All the crustaceans, lamellibranchs, and echinoderms were identified and counted. Particle size distributions and nitrogen contents of the sediments, depths, and temperature and salinity of the bottom water were determined at all stations. The first three factors of a factor analysis applied to between-stations measures of affinity, explained 41.26% of the total variance. The first factor had representative stations on shallow-water mud bottoms, the second factor on bottoms dominated by coarse sediments, and the third factor had representative stations on deep-water mud bottoms. The multiple correlation coefficients for each of the three factors with depth and mean particle size of the sediments were 0.752, 0.897, and 0.706, respectively. The factor analysis did not result in clusters of stations that could be interpreted as discrete benthic communities. The number of species per 0.6 m² ranged from 8 to 55 species, with a mean of 26.4 species. The frequency distribution of specimens among the species was in good agreement with a log-normal distribution. The number of specimens per 0.6 m² ranged from 57 to 1733 specimens, with a mean of 584.0 specimens. The species diversity ranged from 0.34 bits/individual to 4.35 bits/individual, and there was a weak trend of increasing diversity towards coarser sediments. The first three factors applied to the matrix of between-species correlation coefficients explained 43.72% of the total variance. With each factor there was one group of species with high positive loadings and one group with high negative loadings. Each group of species could be identified with particular environments. The standing crop, measured as ash-free dry weight, ranged from 0.490 to 54.093 g/m², with a mean of 13.752 g/m². Only about 24% of the variability in standing crop could be attributed to variability in sediment types, nitrogen content in the sediments, salinity of the bottom water, and depth.     

Phytoplankton in the Weddell Sea,Antarctica: composition,abundance and distribution in water-column assemblages of the marginal ice-edge zone during austral autumn

At the compacted, north-south line of the ice edge, phytoplankton were sampled during early austral autumn of 1986 in the northwestern Weddell Sea. Cells from discrete water bottle samples from 12 stations on two east-west transects were counted to gain quantitative information on the composition, abundance, distribution, and condition of the phytoplankton in water-column assemblages. Over 70 species were found. The highest numbers of total cells (integrated through the top 150 m) were found in open water, well-separated from and to the east of the ice edge on the southern transect, with 6.01×10¹⁰ cells m^-2. The relative abundance of diatoms was low at ice-convered stations (< 35% of the total phytoplankton in preserved samples) and high at open-water stations (> 80%); however, the relative abundance of the prymnesiophyte Phaeocystis sp. was high at ice-covered stations (> 60%) and low at open-water stations (< 16%), with lower absolute abundances than during a previous austral-spring phytoplankton increase. In the open ocean, the dominants were the pennate diatoms Fragilariopsis cylindrus, Pseudonitzschia prolongatoides, F. curta, and a small form of the centric diatom Chaetoceros dichaeta in chains. Although the three pennate diatoms were frequently dominant in number, they represented less biomass than C. dichaeta in open waters. Mean phytoplankton abundance was low (0.2×10⁶ cells l^-1) but, overall, the diatom cell density (0.14×10⁶ cells l^-1) was similar to that found previously during a northward transect from ice-covered to ice-free water at the Weddell-Scotia Sea ice edge (spring 1983). The phytoplankton spatial patterns in the two autumn transects differed, with the more southerly transect exhibiting a higher abundance of diatoms and dinoflagellates. The ratio of full to empty diatoms was higher on the southern transect, indicating a healthy population, while lower ratios of full/empty frustules on the northern transect suggested a generally declining population. However, Phaeocystis sp. was more abundant on the northern transect.     

Fine-scale distribution of larval fishes: patterns and processes adjacent to coral reefs in Kaneohe Bay,Hawaii

Plankton samples were taken from January to June 1987 in Kaneohe Bay, Oahu, Hawaiian Islands, with a free-fall plankton net, to investigate the fine-scale distribution of larval fishes around coral reefs. Daytime samples indicated that the postflexion larvae of two gobiids (Psilogobius mainlandi and an unidentified species) were significantly more abundant at stations immediately adjacent to reefs (near-reef) than at stations in open water off the reef (off-reef). These postflexion gobiid larvae appeared to be capable of resisting advection and dispersal while remaining in the water column near suitable adult habitats. The larvae of Foa brachygramma (Apogonidae) and Encrasicholina purpurea (Engraulidae) were significantly more abundant at off-reef stations than at near-reef stations. Nighttime samples indicated that the gobiid larvae depend on visual cues to remain near the reef. The horizontal distributions of F. brachygramma and E. purpurea larvae appeared to be related to their vertical positioning. These data suggest that typical ichthyoplankton surveys which do not sample close to adult fish habitats would greatly underestimate the abundances of larvae such as the gobiids.