Pelagic Development Research Articles

Пищевые отношения между пелагическими личинками рыб и планктонными организмами в прикамчатских водах

The nutritional relations between fish larvae and zooplankton organisms in marine waters off Kamchatka Peninsula based on the ichthyoplankton samples as well as changes in the diet of fish larvae in Kamchatka waters are considered. In spring, the most suitable food organisms for small fish larvae are polychaeta larvae, Cirripedia and Calanoida nauplii, small forms of copepods, mollusks, juveniles of amphipods. In early summer larvae of Polychaeta, nauplii of Cirripedia and Calanoida, small forms of Cladocera and Copepoda are also available. The main forage organisms for larger larvae are furcilia and calyptopis of euphausiids, small larvae of Decapoda. In the second half of summer, larger forms, mainly of the same organisms, are available for late larvae of many fishes. The relationship between the distribution of marine fish larvae and zooplankton organisms is shown. A list of available food organisms for fish larvae during pelagic development has been compiled. Three main trophic groups have been proposed.

The taxonomic position of brooding limpets of the genera Erginus and Rhodopetala (Patellogastropoda)

Limpets of the genera Erginus Jeffreys, 1877 (previously in Lottiidae) and Rhodopetala Dall, 1921 (previously in Acmaeidae), unlike other patellogastropods, brood larvae and juveniles in the modified pallial cavity. A phylogenetic analysis using three mitochondrial gene markers (cytochrome c oxidase subunit I, 16S rRNA, and 12S rRNA) has shown that Rhodopetala rosea (Dall 1872) and four Erginus species form a highly supported clade that cannot be assigned to Acmaeidae or Lottiidae. The transition from external fertilization and pelagic development to internal fertilization with brooded larvae and juveniles in the special pallial cavity occurred in the evolution of patellogastropods only once. The genera Erginus and Rhodopetala belong to Rhodopetalidae Lindberg, 1981 stat. nov. (= Erginidae Chernyshev 2018 syn. nov.) elevated from subfamily Rhodopetalinae to family status. Erginus puniceus Lindberg, 1988a is restored from synonym of Erginus sybariticus (Dall 1871) for both typical purple forms and the ‘sybariticus’ forms with small shell.

Changes in Panulirus cygnus Settlement Along Western Australia Using a Long Time Series

The pelagic development stages of many marine invertebrate species dictates their spatial and temporal distribution once reaching their benthic second phase of life. This life cycle is associated with the Western Rock Lobster (Panulirus cygnus) along the coast of Western Australia. Over the past 50 years, the number of puerulus reaching the nearshore reefs after their first 9 to 11 months of pelagic life in Western Australia has been monitored. These numbers, collected now at eight sites over the latitudes of the fishery, are indicative of the catchable stock 3–4 years into the future. In 2008, the fishery experienced a recruitment failure which lasted for several years before recovering to mean numbers pre-2008. This was associated with spatial and temporal shifts in the patterns of puerulus settlement. Previous research has hypothesized that physical and biological conditions in the south-east Indian Ocean no longer favored their survival. However, this decline has not been attributed to a single process. As the recovery is ongoing, contrasts in the settlement data before and after the decline are not completed. Here we characterize the data using ANOVA and pairwise comparisons to gain a better understanding of the typical patterns after the decline. Our results demonstrate that there has been a significant reduction in puerulus numbers over the first half of the season at all sites post decline. For the sites south of Lancelin there has been a significant reduction in puerulus numbers over the whole season. In addition, sites that show signs of recovery indicate that the majority of settlement occurred in the second half of the season. We anticipate these results to be the starting point for focused research into the environmental changes which may have occurred to generate these shifts in settlement numbers both from a timing and spatial perspective.

Behavioral Variability of Hatchlings Modifies Dispersal Potential in Crown Conch (Melongena corona): Why Do Larvae Crawl Away but Sometimes Swim?

AbstractThe diversity and consequences of development in marine invertebrates have, for a long time, provided the opportunity to understand different evolutionary solutions to living in variable environments. However, discrete classifications of development can impede a full understanding of adaptation to variable environments when behavioral, morphological, or physiological flexibility and variation exist within traditionally defined modes of development. We report here novel behavioral variability in hatchlings of a marine gastropod, the Florida crown conch (Melongena corona), that has broad significance for understanding the correlated evolution of development, dispersal, and reproductive strategies in variable environments. All hatchlings crawl away from egg capsules after emergence as larval pediveligers. Some subsequently swim for a brief period (seconds to minutes) before crawling again. From detailed observations of 120 individuals over 30 days, we observed 28 (23.3%) hatchlings swimming at least once (8%-50% per maternal brood). The propensity to swim was unrelated to time spent encapsulated or size at hatching and lasted for 22 days. We manipulated hypothesized environmental cues and found that the proportion of hatchlings that swam was highest in the absence of cues related to habitat or juvenile food and lowest when only habitat cues were present. The relative growth rate of hatchlings was highest when habitats contained a putative juvenile food source. About 44% of hatchlings were competent to metamorphose at emergence but did not metamorphose at this time in the lab or the field. The rate of metamorphosis increased with age and depended on the presence of unknown cues in the field. Crawl-away larvae with prolonged swimming ability may be an adaptation to balance the unpredictable risks of exclusively benthic or pelagic development and to allow the option to disperse to higher-quality habitat.

Developmental studies provide new insights into the evolution of sense organs in Sabellariidae (Annelida)

BackgroundSabellarids, also known as honeycomb or sandcastle worms, when building their tubes, produce chemical signals (free fatty acids) that are responsible for larval settlement and the formation of three-dimensional aggregations. The larval palps and the dorsal hump (becoming the median organ in adults) are presumed to participate in such a substrate selection during settlement. Notably, the sabellariid median organ is an apparently unique organ among annelids that has been attributed with a sensory function and perhaps with some affinities to the nuchal organs of other polychaetes. Nevertheless, detailed investigations of this prominent character complex including ultrastructural examinations are lacking so far.ResultsOur comprehensive investigations provide data about the anterior sensory organs in Sabellariidae and inform about their transformation during pelagic larval development. We used a comparative approach including immunostaining with subsequent confocal laser scanning microscopy (clsm), histological sections as well as electron microscopy in a range of larval and adult stages of two sabellariid species. We find that the neuronal innervation as well as the ultrastructure of the sabellariid ciliary structures along the median organ are highly comparable with that of nuchal organs known from other polychaetes. Furthermore, the myoinhibitory protein (MIP) – a protein known to be also involved into chemo-sensation - was detected in the region of the larval median organ. Moreover, we reveal the presence of an unusual type of photoreceptor as part of the median organ in Idanthyrsus australiensis with a corrugated sensory membrane ultrastructure unlike those observed in the segmental ocelli of other polychaetes.ConclusionsWe are describing for the first time the nuchal organ-like structures in different developmental stages of two species of Sabellariidae. The external morphology, neuronal innervation, developmental fate and ultrastructure of the newly-discovered median organ-based ciliary pits are comparable with the characteristics known for annelid nuchal organs and therefore indicate a homology of both sensory complexes. The presence of myoinhibitory peptide (MIP) in the respective region supports such a hypothesis and exhibits the possibility of an involvement of the entire sabellariid median organ complex, and in particular the prominent ciliated pits, in chemo-sensation.

Oceanographic barriers to gene flow promote genetic subdivision of the tunicate Ciona intestinalis in a North Sea archipelago

Pelagic larval development has the potential to connect populations over large geographic distances and prevent genetic structuring. The solitary tunicate Ciona intestinalis has pelagic eggs and a swimming larval stage lasting for maximum a few days, with the potential for a homogenizing gene flow over relatively large areas. In the eastern North Sea, it is found in a geomorphologically complex archipelago with a mix of fjords and open costal habitats. Here, the coastal waters are also stratified with a marked pycnocline driven by salinity and temperature differences between shallow and deep waters. We investigated the genetic structure of C. intestinalis in this area and compared it with oceanographic barriers to dispersal that would potentially reduce connectivity among local populations. Genetic data from 240 individuals, sampled in 2 shallow, and 4 deep-water sites, showed varying degrees of differentiation among samples (FST = 0.0–0.11). We found no evidence for genetic isolation by distance, but two distant deep-water sites from the open coast were genetically very similar indicating a potential for long-distance gene flow. However, samples from different depths from the same areas were clearly differentiated, and fjord samples were different from open-coast sites. A biophysical model estimating multi-generation, stepping-stone larval connectivity, and empirical data on fjord water mass retention time showed the presence of oceanographic barriers that explained the genetic structure observed. We conclude that the local pattern of oceanographic connectivity will impact on the genetic structure of C. intestinalis in this region.

The Larval Development of the Chiton Deshayesiella curvata (Carpenter in Dall, 1879) (Mollusca: Polyplacophora)

Chronological study of the larval development of the chiton Deshayesiella curvata with sketching of the first stages of egg division and embryos up to the seven-valved shell stage is presented for the first time. D. curvata exhibits pelagic development with lecithotrophic larvae. Larval eyes form at the age of 3 days; at the age of 6 days, a Schwabe organ appears near the eyes in the form of two pigmented spots. Chitons at the stage of seven-valved shell have larval eyes, as well as the Schwabe organ.

Larval traits show temporally consistent constraints, but are decoupled from postsettlement juvenile growth, in an intertidal fish

Complex life cycles may evolve to dissociate distinct developmental phases in an organism's lifetime. However, genetic or environmental factors may restrict trait independence across life stages, constraining ontogenetic trajectories. Quantifying covariance across life stages and their temporal variability is fundamental in understanding life-history phenotypes and potential distributions and consequences for selection. We studied developmental constraints in an intertidal fish (Bathygobius cocosensis: Gobiidae) with a discrete pelagic larval phase and benthic juvenile phase. We tested whether traits occurring earlier in life affected those expressed later, and whether larval traits were decoupled from postsettlement juvenile traits. Sampling distinct cohorts from three annual breeding seasons afforded tests of temporally variability in trait covariance. From otoliths (fish ear stones), we measured hatch size, larval duration, pelagic growth (larval traits) and early postsettlement growth (juvenile trait) in 124 juvenile B.cocoensis. We used path analyses to model trait relationships with respect to their chronological expression, comparing models among seasons. We also modelled the effect of season and hatch date on each individual trait to quantify their inherent variability. Our path analyses demonstrated a decoupling of larval traits on juvenile growth. Within the larval phase, longer larval durations resulted in greater pelagic growth, and larger size-at-settlement. There was also evidence that larger hatch size might reduce larval durations, but this effect was only marginally significant. Although pelagic and postsettlement growth were decoupled, pelagic growth had postsettlement consequences: individuals with high pelagic growth were among the largest fish at settlement, and remained among the largest early postsettlement. We observed no evidence that trait relationships varied among breeding seasons, but larval duration differed among breeding seasons, and was shorter for larvae hatching later within each season. Overall, we demonstrate mixed support for the expectation that traits in different life stages are independent. While postsettlement growth was decoupled from larval traits, pelagic development had consequences for the size of newly settled juveniles. Temporal consistency in trait covariances implies that genetic and/or environmental factors influencing them were stable over our three-year study. Our work highlights the importance of individual developmental experiences and temporal variability in understanding population distributions of life-history traits.

Parasitic copepods affect morphospace and diet of larvae of a temperate reef fish.

The effects of ectoparasites on larvae of the clingfish Gobiesox marmoratus were evaluated at the dietary and morphometric levels. The larvae and ectoparasites were collected by nearshore plankton samplings during October, November and December 2013 off El Quisco Bay, central Chile. The standardized abundance of total larvae and those ectoparasitized larvae (PL) was positively related and high parasite prevalence was found throughout the sampling period (up to 38%). Geometric morphometrics analyses indicate main changes in the shape through early ontogeny and subtle but significant variations between PL and non-parasitized larvae (NPL). Prey composition varied between PL and NPL; small size (<6 mm standard length, LS ) parasitized larval G. marmoratus ate mostly gastropod larvae, whereas small non-parasitized specimens ate mainly cirripede nauplii. All larger (>8 mm LS ), pre-settlement stages parasitized by Trifur and, or Caligus copepods had content in their gut, suggesting that ectoparasites did not diminish prey capture in host with larger size. Morphometric and dietary changes occurring during larval development were decoupled, both for PL and NPL. The maintenance of a slender, more hydrodynamic body through pelagic development and the ingestion of less-mobile prey in PL suggests non-lethal effects of ectoparasitism on rocky-reef fish larvae.

A Veliconcha Unveiled: Observations on the Larva and Radula ofConus spurius, with Implications for the Origin of Molluscivory inConus

The veliconcha larva of the predatory gastropod Conus spurius Gmelin, 1791 is described and for the first time illustrated based on material from Sanibel Island, Florida. Hatchling veliconchas were 1470–1570 μm (mean = 1530) long, with first protoconch whorl maximum diameter 670–740 μm (mean = 710), and estimated egg diameter 570 μm. Veliconchas can swim for a few minutes to a few hours before settling. They have well-developed paired velar lobes each 600–700 μm in length, an extensible foot with a distinct metapodium separated from the remainder of the foot by a transverse fold, and operculum. Several early life history traits of C. spurius, particularly hatching as large veliconcha larvae with predominantly lecithotrophic, nearly non-planktonic development, closely resemble those of a well-defined clade of Conus Linnaeus, 1758 species that prey on other gastropods. They contrast with the majority of species in this hyperdiverse genus, which hatch as much smaller planktonic, obligatory planktotrophic veliger larvae. As adults they comprise a vermivorous feeding guild, preying exclusively or nearly so on polychaete annelids. Limited data suggest that C. spurius may share this trait with them but it may also prey on molluscs. Recent molecular phylogenetic trees suggest that the characters “pelagic development” and “non-pelagic development” (or nearly so: <1 day) are distributed independently of phylogeny in the larger clade that includes C. spurius and the molluscivorous species. Similarities in veliconcha morphology and developmental mode, adult radular tooth morphometry, phylogenetic position, and earliest fossil records suggest the speculative hypothesis that the monophyletic clade of extant molluscivorous Conus species may have evolved in the Miocene from a vermivore or mixed vermivorous-molluscivorous ancestor with these attributes, such as C. spurius.

The complete description of larval stages of the lobster shrimpLeonardsaxius amurensis(Kobjakova, 1937) (Decapoda: Axiidea: Axiidae) identified by DNA barcoding

The complete larval development of the lobster shrimpLeonardsaxius amurensis(Kobjakova, 1937) (Decapoda: Axiidea: Axiidae) is described and illustrated for the first time. The first zoeae of this species were collected from the plankton samples and reared in the laboratory before moulting to the megalopa. A molecular genetic analysis based on comparison of partial mitochondrial COI, 12S rDNA and 16S rDNA sequence data confirmed the identity of axiid larvae found in the plankton andL. amurensisadults collected in the same area. The larval development ofL. amurensisincludes five zoeal stages and a single megalopa. Zoeae I ofL. amurensisare characterized by the presence of one short posterodorsal spine on the fifth pleonite in contrast to the larvae of related sympatric speciesBoasaxius princepshaving four posterodorsal spines on the pleonites 2–5.Leonardsaxius amurensisoccupies an intermediate position between lobster shrimps with abbreviated pelagic development (2–3 zoeal stages) and species with long development (up to eight zoeal stages). Thus, the number of zoeal stages in the family Axiidae varies widely, similarly to that in the families Callianassidae and Upogebiidae.

Ontogenetic shifts in swimming capacity of echinoderm propagules: a comparison of species with planktotrophic and lecithotrophic larvae

While developmental strategies can modulate the dispersal and recruitment of marine benthic species, the significance and drivers of propagule motility throughout ontogeny remain incompletely understood. Species with lecithotrophic (non-feeding) development are rarely studied, despite their predominance in some taxa, including echinoderms. Quantification of the swimming capacity (i.e. speed and trajectory) of early life history stages and its variability with environmental factors is required to improve the ability to predict population connectivity and assess trade-offs associated with complex life histories. In general, lecithotrophic larvae of echinoderms are ascribed weak swimming abilities relative to planktotrophic larvae, although explicit measures are scarce. Here, we explored selected metrics of swimming capacity in four co-occurring species of North Atlantic echinoderms displaying different types of pelagic development: planktotrophs represented by the sea star Asterias rubens and the sea urchin Strongylocentrotus droebachiensis, and lecithotrophs represented by the sea star Crossaster papposus and the sea cucumber Cucumaria frondosa. Swimming was characterized in still water based on the horizontal speed and path straightness of early life-history stages, from late blastula (hatched embryo) to late-stage larva. We tested the hypotheses that swimming capacity of propagules increases with progression through developmental stages and with increasing seawater temperature. Swimming speed increased with ontogeny in two of the four species (A. rubens and C. papposus) and with temperature in all species, although the effects of temperature were not uniform across life stages. The fastest swimming speeds across all species and temperatures were recorded in lecithotrophic propagules (i.e. max speed 1.2 mm s− 1 in the brachiolaria of C. papposus), whereas propagules of species with planktotrophic development displayed faster relative speeds (body lengths s− 1). Relative speeds increased with temperature in all tested species except C. papposus. Swimming paths typically increased in straightness from early to later developmental stages, and also became straighter with increased temperature in most species, except in C. papposus where they became more circular and complex. In general, planktotrophic and lecithotrophic propagules had similar swimming capacities when tested at the same level of increased temperature, though several stage-specific differences were detected; propagules of species with planktotrophic development had greater relative speeds at the gastrula stage and greater path-corrected speeds at the larval stage. Swimming paths and swimming speeds were similar between propagules of species with planktotrophic development and lecithotrophic development, suggesting that phylogenetically conserved, ontogenetic patterns of swimming capacity (seen here between two sea stars) may supersede the contribution of larval nutritional mode.

Early metamorphosis is costly and avoided by young, but physiologically competent, marine larvae

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 559:117-129 (2016) - DOI: https://doi.org/10.3354/meps11914 Early metamorphosis is costly and avoided by young, but physiologically competent, marine larvae Benjamin Mos*, Symon A. Dworjanyn National Marine Science Centre, Southern Cross University, PO Box 4321, Coffs Harbour, NSW 2450, Australia *Corresponding author: benjamin.mos@scu.edu.au ABSTRACT: Dispersing organisms often cannot assess habitat quality directly, so they employ proxies (cues) to choose habitats that maximise fitness. Theory suggests organisms should settle as soon as they find appropriate cues in order to reduce physiological costs and mortality risk incurred whilst searching. We propose that for planktotrophic marine larvae, when resources are plentiful, development of adult structures during an extended larval phase provide post-metamorphosis benefits that offset the costs of remaining in the plankton. To test this, we measured fitness consequences of metamorphosis in response to habitat cues at a range of developmental maturities in 2 sea urchin larvae, Tripneustes gratilla and Centrostephanus rodgersii. We found larvae that were capable of responding to cues and settling accrued significant benefits if they extended their pelagic development. Compared to more developed larvae, larvae without adult structures took longer to metamorphose, and after metamorphosis were 11 to 25% smaller, 0.1 to 6 times more likely to lack defensive structures and 3 to 13 times more likely to have abnormal morphology. Most early settlers died within 1 wk compared to >40% survival for more developed larvae. We found larvae avoid the costs of early metamorphosis by only responding to low concentrations of cues in the water column once they have adult structures. Our results contrast with models of habitat selection that suggest organisms should settle in habitat quickly to minimise search costs. Incorporating the trade-off between the benefits of larval development and search costs into current models of habitat selection may provide new insights into how fitness consequences affect habitat selection. KEY WORDS: Delayed metamorphosis · Development · Fitness · Habitat selection · Search costs Full text in pdf format Supplementary material PreviousNextCite this article as: Mos B, Dworjanyn SA (2016) Early metamorphosis is costly and avoided by young, but physiologically competent, marine larvae. Mar Ecol Prog Ser 559:117-129. https://doi.org/10.3354/meps11914 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 559. Online publication date: November 09, 2016 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2016 Inter-Research.

Present-day connectivity of historical stocks of the ecosystem engineer Perumytilus purpuratus along 4500 km of the Chilean Coast

Historical processes leading to the emergence of marine stocks, the mechanisms maintaining stock structure, and present-day connectivity patterns are elementary pieces of information to design wiser and more sustainable management of marine resources, and to understand speciation processes in the sea. Over geographical scales, biological and genetic continuity in the Southern Pacific coast is determined by historical geological-climate events (e.g., LGM), as well as by present oceanographic processes (Humboldt Current, ENSO and others) that can affect both, local adaptation and dispersal. The relative influence of such processes on the current distribution of species can be comprehensibly inferred from a detailed population sampling comprising the whole species range. In this work, we aimed to provide insights into historical and modern patterns of genetic connectivity between stocks of the intertidal mussel Perumytilus purpuratus, a species reported to have moderate pelagic development times of about 14–18 days. To this end, we analyzed the geographical pattern of variation of microsatellite polymorphisms across 17 localities scattered along ca. 4500km off the Chilean Coast and encompassing four biogeographic regions, previously defined based on compositional changes in marine flora and fauna, and which coincide with large changes in topography, the historical influence of glaciation, circulation patterns and upwelling variability around 26°S, 30°S and 40°S. Genetic structural data suggest that historical geological and climatic events have shaped the actual range of this species in the south-eastern Pacific, creating biogeographical limits, i.e., the north-central stock and the southern stock, that moderate to restricted dispersers cannot cross given present day coastal oceanographic processes. Conversely, the pattern of IBD observed within those two major biogeographical regions suggests that present-day coastal processes modulate the effective dispersal of this species.

The Capture Fishery Based Small Pelagic Business Development Opportunities Analysis with Purse Seine Fishing Gear in Maluku (Case Study on Financial Aspect in West Seram Regency)

&lt;p class="zhengwen"&gt;&lt;span lang="EN-GB"&gt;The study aims to find out and analyze the influence of running cost, shore cost, fishing duration and seasonal climate on profitability of purse seining small pelagic fishery business group in West Seram Regency in purpose to find out capture fishery development prospect by using such equipment in West Seram Regency. The data used in this study is primary data, i.e. a data collected from respondents through interview. Respondents are selected purposively from population of purse seining capture fishery business group. Multiple linear regression analysis method is applied to estimate the influence of running cost, shore cost, fishing duration and seasonal climate on the profitability variables (ROA). The findings reveal that running cost affects positively profitability, shore cost affects negatively and significantly profitability, fishing duration affects negatively and significantly profitability. On the contrary, seasonal climate does not affect profitability of purse seining capture fishery. Further, it is said that there is still a chance to develop purse seining small pelagic fishery business group under the condition that the activity has to be accompanied with control over running cost, shore cost, and fishing duration. &lt;s&gt;&lt;/s&gt;&lt;/span&gt;&lt;/p&gt;

Correlated evolution between mode of larval development and habitat in muricid gastropods.

Larval modes of development affect evolutionary processes and influence the distribution of marine invertebrates in the ocean. The decrease in pelagic development toward higher latitudes is one of the patterns of distribution most frequently discussed in marine organisms (Thorson's rule), which has been related to increased larval mortality associated with long pelagic durations in colder waters. However, the type of substrate occupied by adults has been suggested to influence the generality of the latitudinal patterns in larval development. To help understand how the environment affects the evolution of larval types we evaluated the association between larval development and habitat using gastropods of the Muricidae family as a model group. To achieve this goal, we collected information on latitudinal distribution, sea water temperature, larval development and type of substrate occupied by adults. We constructed a molecular phylogeny for 45 species of muricids to estimate the ancestral character states and to assess the relationship between traits using comparative methods in a Bayesian framework. Our results showed high probability for a common ancestor of the muricids with nonpelagic (and nonfeeding) development, that lived in hard bottoms and cold temperatures. From this ancestor, a pelagic feeding larva evolved three times, and some species shifted to warmer temperatures or sand bottoms. The evolution of larval development was not independent of habitat; the most probable evolutionary route reconstructed in the analysis of correlated evolution showed that type of larval development may change in soft bottoms but in hard bottoms this change is highly unlikely. Lower sea water temperatures were associated with nonpelagic modes of development, supporting Thorson's rule. We show how environmental pressures can favor a particular mode of larval development or transitions between larval modes and discuss the reacquisition of feeding larva in muricids gastropods.

Oviposition site influences dispersal potential in a marine bubble snail

For benthic marine invertebrates that deposit offspring inside protective capsules or gelatinous egg masses, small-scale variation in environmental parameters can affect offspring mortality, performance, timing of hatching and dispersal potential. Plasticity in hatching and dispersal potential have received less attention than egg mass mortality and juvenile performance, but there may be adaptive responses that balance the costs and benefits of benthic and pelagic development in specific contexts, such as escaping poor environments. Some species, such as the bubble snail Haminoea japonica, produce two offspring phenotypes at hatching that differ in dispersal potential. Here, I investigated whether the substrata that egg masses develop on can influence whether offspring tended to hatch as either phenotype. In the field, egg masses were more commonly deposited in association with filamentous algae and in laboratory experiments, free-swimming larvae settled and metamorphosed more readily on algae. When egg masses developed on the algae that induced settlement, there were more crawl-away juveniles than free-swimming larvae. Such a response has important consequences for dispersal potential, hence the deposition substratum may have an adaptive value because crawl-away juveniles can avoid a potentially risky planktonic period when settlement substratum is present, but larvae can disperse when a suitable settlement substratum is absent.

C-Type Protoconchs and Planktotrophy in Small Eastern North AmericanFargoa(Pyramidellidae)

C-type protoconchs have been thought always to reflect a “direct” or short pelagic development, an idea deriving from Thorson's (1946) study of the early development (besides planktonic veligers) of only one pyramidellid species. The small-shelled genus Fargoa Bartsch (1955), some ectoparasitic on serpulid polychaetes such as Hydroides, apparently uniformly has C-type protoconchs. The eggs and early larval development of Fargoa dianthophila (Wells and Wells, 1961) (shells < 1.8 mm) and F. bartschi (Winkley, 1909) (< 4.0 mm) were studied in the laboratory at Woods Hole, Massachusetts. The eggs were only 53 to 57 µm and 55 to 60 µm in diameter, respectively, and as would be expected from eggs this size both species are definitely planktotrophic. Few other pyramidellids or other “opisthobranchs” lay eggs this small, and the single Brachystomia (Monterosato, 1884) species studied by Thorson (1946) was also planktotrophic. The protoconch diameters of F. dianthophila and F. bartschi are, respectively, about 260 to 315 µm and about 210 to 230 µm, i.e., surprisingly large. This variation parallels neither the nearly uniform egg size nor the disparate adult shell sizes. No attempt was made to rear the larvae in the laboratory because there were only a few newly hatched veligers and these protoconchs indicated much growth in the plankton. These Fargoa veligers may remain planktonic for longer times than planktotrophic Boonea Robertson (1978). One protoconch, an egg capsule containing a late blastula, and a newly hatched swimming veliger are illustrated. Small pyramidellids appear to lay the smallest eggs, but this seems not to be true of other “opisthobranchs.”

Comparison of benthic recruitment with pelagic growth of bloom-forming cyanobacteria

In eutrophic lakes, overwintering bloom-forming cyanobacteria such as Microcystis re-inoculate the water column in the spring, contributing to pelagic development as a cell source for initial pelagic growth and a direct inoculum for continued pelagic development as well. In the present study, recruitment and pelagic growth of cyanobacteria were monitored by using migration traps and phytoplankton chambers at a study site near Meiliang Bay (1.5 m deep) in Taihu Lake from March to June, 2008. Cell abundance from both sources was compared synchronously; in the meantime water temperature was recorded using an automatic sonde. Results showed that recruitment and pelagic growth of cyanobacteria already started at 11°C, and showed changing patterns over the time of the study. Benthic recruitment only accounted for a small portion of pelagic growth, which is similar to that found in deep lakes. Taken together, these findings suggest that studies on cyanobacteria blooms development should be mainly focused on the pelagic population development. Key words: Colony, cyanobacteria, Microcystis, pelagic growth, recruitment

Effects of heat-shock selection during pelagic stages on thermal sensitivity of juvenile sea cucumber, Apostichopus japonicus Selenka

The effects of heat-shock during pelagic stages on growth and survival of juvenile sea cucumber Apostichopus japonicus were investigated to test the possibility to acquire high thermal tolerance individuals after the heat-shock selection. Larvae at the stages of blastula, gastrula, and auricularia were heat-shocked at selected temperatures (21.5, control; 26, 28, and 30°C) for 45 min and returned to 21.5°C for continuous rearing. There was a significant difference in thermal sensitivity among different developmental stages, and thermal tolerance of the larvae was correlated with the expression of heat shock protein 70 (Hsp70). Juveniles after the heat-shock selection at pelagic stages showed higher induced thermotolerance than those without heat-shock. Therefore, heat-shock application at early pelagic development stages is potentially a useful way to select high-thermotolerance variety of the sea cucumbers.