Preliminary rearing experiments on the larvae of Sergestes lucens (Penaedia,Natantia, Decapoda)

Sergestes lucens Hansen, a mesopelagic shrimp fished commercially in Suruga Bay, Japan, was successfully reared from egg to post-larval stage V under laboratory conditions. Chaetoceros ceratosporum and Artemia nauplii were found to be satisfactory food in the laboratory during rearing. Growth, mortality, food preference, and feeding and swimming activities during the various developmental stages were investigated. Temperature changes greatly affected the speed of development and the mortality of the larvae. The optimum temperature range for larval development was 18° to 25°C. The growth rate (length) of larval stages was as rapid as 0.16mm/ day at 20 °C and 0.21 mm/day at 23 °C. The larvae first started feeding on phytoplankton at elaphocaris stage I, and then gradually became predators in the post-larval stages. It is suggested that the critical period for the species occurs in the elaphocaris stages. Environmental data, vertical distribution of the species, and data obtained from laboratory experiments suggest that the fluctuation in the abundance of S. lucens is greatly influenced by the water temperature at around 50 m from June to August. Feeding mechanisms observed in the post-larval stages are described.     

Benthic invertebrate larval response to substrate characteristics at settlement: Shelter preferences of the American lobsterHomarus americanus

The factors controlling shelter selection by the first post-larval stage of the American lobsterHomarus americanus were studied in the laboratory in 1988 using an experimental approach. The relative importance of shelter size, light level within shelters, number of shelter entrances, and presence of algal-film cover in and around them were investigated. Post-larvae showed a strong preference for opaque versus transparent shelters. No difference in post-larval selectivity was observed either for shelters of different widths or heights or between shelters with different numbers of entrances. Post-larvae showed no preference for microhabitats colonized by microorganisms compared to others without colonization. The intensity of the response measured suggests a possible hierarchical organization of the different cues involved in shelter selection, the light level within the shelter apparently being the most important. Simple linear regression was used to assess the effect of shelter area on the number of post-larvae occupying a shelter. Up to four post-larvae were observed simultaneously in a shelter of 40 cm² basal area, indicating that they can cohabit at settlement. The minimum shelter area necessary to the first post-larval stage was estimated to be about 3.25 cm². The results are discussed with reference to recent hypotheses concerning the mechanisms controlling larval settlement in other benthic species with relatively weak mobility during the larval and the post-larval phases.Contribution to the programmes of GIROQ (Groupe interuniversitaire de recherches océanographiques du Québec) and of the Institut Maurice-Lamontagne     

Post-larval development of the common north-west European brittle stars Ophiura ophiura,O. albida and Acrocnida brachiata (Echinodermata: Ophiuroidea)

The post-larval skeletal plate ontogeny of the ophiuroids Ophiura ophiura (Linnaeus) and Acrocnida brachiata (Montagu) from the recently metamorphosed 0.3 mm disc diameter size to a juvenile size of 2.0 mm disc diameter has been examined using scanning electron microscopy. Post-larval development of O. albida Forbes is briefly described for sizes between 1.0 and 2.0 mm disc diameter. Early post-larval development in the 0.2 to 1.0 mm discsize range involves considerable morphogenetic change and necessitates the use of a developmental series in the identification of newly settled ophiuroids. Comparison of these ophiuroids with other closely related species reveals that the post-larvae are readily distinguishable at even the smallest sizes by their transient post-larval morphologies. Abbreviated larval development in A. brachiata is suggested from the egg size and post-larval form. The ophiuroid post-larvae were collected from the shallow sublittoral of Oxwich Bay, Bristol Channel, UK, during the years 1980 to 1982.     

Temporal patterns of settlement, recruitment and post-settlement losses in a rocky reef fish assemblage in the South-Western Mediterranean Sea

Post-settlement events can significantly alter the density distribution of settlers and subsequently the adult population structure. The temporal and inter-annual variability of settlement and the effects of mortality on recruitment were investigated across 2 years in the vicinities of Cabo de Palos–Islas Hormigas Marine Reserve by visual census and light trap sampling. Settlement was seasonal with greater species richness and abundance in summer. Although temporal synchronization was observed between larval supply and settlement, densities of settlers could not be predicted from post-larval abundances. Timing of settlement was consistent between years but with high inter-annual variation in abundance. High mortality (~80 %) and general decoupling between post-larval and settlement stages suggest that early mortality is driving such patterns. Nevertheless, indications of habitat-mediated mortality were found for benthic species such as Symphodus and Diplodus, highlighting the importance of habitat in shaping population demography.     

Population structure of the Spanish sardine Sardinella aurita: natural morphological variation in a genetically homogeneous population

The importance of larval dispersal in determining the distribution and abundance of benthic marine organisms is well recognized; however, the contribution of post-larval dispersal has not been measured. I compared the dispersal of swimming larvae with that of rafting colonies in a population of compound ascidians, Botrylloides sp., living attached to leaves of the eelgrass Zostera marina in Tomales Bay, California, USA in 1990–1992. Colonies rafting on broken eelgrass traveled over 200 times farther and had comparable recruitment success relative to swimming larvae. The recruitment of rafting colonies into new habitats was facilitated by the ability of thesecolonial animals to grow asexually onto surrounding substrata. Rafting colonies brooded larvae that were subsequently relased after the colony settled into a new habitat. These results suggest that colonization of new habitats can occur by post-larvae as well as larvae, and that long-range dispersal by species with short-lived larvae may occur by post-larval rafting.     

Larval period and its influence on post-larval life history: comparison of lecithotrophy and facultative planktotrophy in the aeolid nudibranch Phestilla sibogae

The variable duration of the pelagic phase of metamorphically competent larvae of benthic marine invertebrates is set by an interaction between environmental factors and larval traits that together influence the chance that a larva will encounter and respond to a suitable settlement site. In the Hawaiian aeolid nudibranch Phestilla sibogae Bergh, an extended competent larval phase resulted in a cascade of negative effects on larval and post-larval life-history traits. When raised as fed (i.e., facultatively planktotrophic) larvae, an extended larval period resulted in lower larval survival, slightly lower metamorphic success, and delayed reproduction. When raised as unfed (i.e., lecithotrophic) larvae, an extended larval period resulted in lower larval and post-larval weights, survival, metamorphic success, and reproductive output, and also resulted in a longer juvenile period and delayed reproduction. The chance nature of locating a settlement site generally spreads these negative effects over all larvae of a cohort, and so balances the relative fitness of the genetic lineages within a population.     

An unusual abbreviated larval life in the estuarine burrowing prawn Callianassa kraussi (Crustacea: Decapoda: Thalassinidea)

The larval stages of Callianassa kraussi Stebb. were previously unknown. Larvae were bred out in the laboratory and found to be incapable of swimming. There are two larval stages, lasting 3 to 5 days in sea water of 34 to 35 S at 20 °C. Observations under simulated field conditions in the laboratory, and in the field—where burrow casts were made using a polyester resin, indicated that the larvae metamorphose to the first post-larval stage in the parent burrow, and then burrow directly into the wall of the parent burrow.     

Biomineralization markers during early shell formation in the European abalone <Emphasis Type="Italic">Haliotis tuberculata</Emphasis>, Linnaeus

Larval shell formation was investigated in the European abalone Haliotis tuberculata. Stages of mineralization as well as enzymatic and endocrine biomarkers were monitored throughout larval development, from hatching to post-larval stages. Polarized light microscopy and infrared spectroscopy analyses revealed the presence of crystallized calcium carbonate arranged in aragonite polymorphs from the late trochophore stage. A correlation between the main steps of shell formation and enzymatic activities of alkaline phosphatase and carbonic anhydrase was seen. The variations of these biologic activities were related to the onset of mineralization, the rapid shell growth, and the switch from larval to juvenile shell following metamorphosis. Furthermore, a strong increase in the level of calcitonin gene-related molecules was measured in post-larvae, suggesting that endocrine control takes place after metamorphosis. The changes measured for the three biomineralization markers together with mineralogical analysis allowed us to correlate physiologic mechanisms with early steps of abalone shell formation.     

Larval supply and juvenile recruitment of coral reef fishes to marine reserves and non-reserves of the upper Florida Keys,USA

For marine organisms, decoupling between the planktonic larval stage and the benthic-associated juvenile stage can lead to variable patterns of population replenishment, which have the potential to influence the effectiveness of marine reserves. We measured spatial and temporal variability in larval supply and recruitment of fishes to coral reefs of different protection levels and tested whether protection level influenced the relationship between supply and recruitment. We sampled pre-settlement larvae and newly settled recruits from four reefs (two reserves and two non-reserves) in the Florida Keys National Marine Sanctuary, USA. Replicate point measures of larval supply over 14 months and 17 monthly measurements of recruitment varied significantly among months and sites. Sites with the same protection level had significantly different patterns of larval supply as well as larval and recruit diversity, but recruitment magnitude differed only by protection level, where densities were greater at reserves. Differences in larval supply among sites included two particularly large peaks in larval abundance at one site, possibly associated with the observed passage of small-scale oceanographic features. To examine whether relationships between larval supply and recruitment varied by protection level, we selected one species that was present in both the light trap samples and the monthly recruitment surveys. Recruitment of the bicolor damselfish Stegastes partitus was significantly and positively related to larval supply at three of the four sites thus, protection level did not influence this linkage. Since local variability among sites can lead to spatial differences in population replenishment, characterization of larval supply and recruitment to potential marine reserve sites may help to identify optimal locations in a region and contribute to more effective reserve design.     

Giant larvae: Prolonged planktonic larval phase in the asteroidLuidia sarsi

The bipinnaria larva of the shelf-dwelling asteroidLuidia sarsi Duben and Koren, 1845, can attain (exceptionally) a length of 35 mm; metamorphosis to the adult benthic phase usually occurs well before this size is reached. A seastar rudiment develops at the oral end of the bipinnaria and, under normal circumstances, it detaches itself from its larval body before reaching a diameter of 5 mm. Midwater trawl samples taken from the surface to 1650 m in the Porcupine Seabight during 1978 and 1979, however, includedL. sarsi larvae with post-larval rudiments of 15 mm diameter and greater. It is shown that the bipinnariae and attached post-larvae both continued to grow until a point was reached when it appeared that the young sea-star could no longer be sustained by the bipinnaria. There is evidence that the largest post-larvae had absorbed the bipinnaria tissue and this, it is concluded, is the final stage before enforced settlement. From the estimated growth rate it is likely that many specimens had been in the plankton for >1 yr, giving this species a capability for long-distance dispersal.     

Effects on larval crabs of exposure to algal toxin via ingestion of heterotrophic prey

We tested whether ingesting toxic algae by heterotrophic prey affected their nutritional value to crab larval predators, using toxic algal strains that are either ingested directly by larval crabs or rejected by them. Ingestion of toxic strains of the dinoflagellates Alexandrium andersoni and A. fundyense by the rotifer Brachionus plicatilis was confirmed. Rotifers having ingested either algal type for five days were fed to freshly hatched larvae of three crab species, with larval survival and stage durations determined. For both algal/rotifer treatments in all three crab species, larvae fed algae directly died during the first zoeal stage, while those fed rotifers that had been fed either algal strain survived to the experiment’s end (zoeal stage 3). Survival was lower, and stage duration longer, for larvae fed rotifers cultured on toxic algae when compared to those fed non-toxic algae. The role of toxic algae in the planktonic food web may be influenced by its direct or indirect ingestion by larval crabs.     

Embryonic,larval, and post-metamorphic development of the sea urchin <Emphasis Type="Italic">Cassidulus mitis</Emphasis> (Echinoidea; Cassiduloida): an endemic brooding species from Rio de Janeiro,Brazil

Cassiduloids are currently rare irregular echinoids with a highly conserved adult morphology. Aristotle’s lantern is present only during the post-metamorphic stage, and little is known about the early development of species in this group. Cassidulus mitis produces eggs of about 375 μm in diameter, lecithotrophic larvae with four reduced arms with skeletal fenestrated rods, cilia along the body surface, and a ciliated band on arms and lobes. Offspring is brooded among the female spines from embryo to settler’s stage. The echinopluteus larval stage is reached 6 days after fertilization, and the settler’s stage is formed at the age of 17 days. Aristotle’s lantern appears around the thirteenth day of development. The lantern is well developed and functional in settlers. It remains until at least 62 days after fertilization and can be used to acquire food from the environment. The early development of C. mitis is unusual concerning features of typical lecithotrophic larvae (such as reduced arms), but retains some features of planktotrophic larvae (such as skeletal rods and a ciliated band). Regarding egg size, early development in C. mitis seems to be transitioning from facultative lecithotrophic to typical obligate lecithotrophic pattern in echinoid larval evolution.     

Cementation vs mobility: development of a cemented byssus and flexible mobility in Anomia chinensis

The mobility of Anomia chinensis Philippi was studied in relation to its byssal development stage. This species shows high mobility even after it begins cementation in its post-larval stage. Juveniles develop a calcified byssus in the post-larval stage and cement to substrata. However, juveniles up to about 10 mm in shell length can relocate by repeating a sequence of formation of the calcified byssus, abandonment of it, locomotion by crawling, reattachment, and recementation. Juvenile anomiids up to 25 mm in shell length also can move, without breaking their byssal attachments, by shifting the center of byssal calcification dorsally. Even an adult can change its orientation by forming a twisted byssus. These possible methods of movement are closely related to five stages of byssal development. Anomiids can use this mobility to seek a preferable position for attachment after initial cementation, or to adjust their orientation, and thus promote higher survivorship. Received: 18 August 1997 / Accepted: 19 July 1998     

Spawning and development of three coral-associated Lithophaga species in the Red Sea

Lithophaga date mussels from three species (L. lessepsiana, L. simplex and L. purpurea) were removed from their stony coral hosts in the Red sea at Eilat, Israel. Spawning, observed in the laboratory on several occasions during 1987–1988, appeared to be closely tied to lunar periods, occurring primarily during the last quarter and the new moon. Embryonic and larval development was typical of that described for other mytilids and, except for pigmentation differences, which could be discerned during embryogenesis, the developmental stages of the three species were indistinguishable. Development to the pediveliger stage took 3 to 4 wk in standard culture conditions, but raising the temperature to 27.5 °C increased the growth rate of larvae of L. lessepsiana by as much as three-fold, so that the pediveliger stage was attained in 16 d. Larvae resulting from spawning by L. simplex adults removed from the coral Astreopora myriophthalma grew significantly faster in culture than larvac from adults removed from the coral Goniastrea pectinata (comparison of slopes, p<0.05). The latter individuals showed a 6-d growth plateau at the early umbone stage. Metamorphically competent larvae were capable of delaying metamorphosis for up to 4mo, which would allow an extended period for dispersion and would increase the chance of finding a suitable substratum in the natural environment.     

Reproduction,larval development and post-larval growth ofNaineris laevigata (Polychaeta,Orbiniidae) in the Mediterranean Sea

To investigate the life-history adaptations of a brackish-water population ofNaineris laevigata Grube, a population from Acquatina lagoon near Lecce (Italy) was studied. Benthos and plankton samples were collected monthly over a period of ca. 2 yr (1989–1990). Observations of gametogenesis indicate that oogenesis is intraovaric, probably with autosynthetic yolk formation. Oogenesis takes about 7 mo, from November to April–May, for both proliferative and vitellogenetic phases. Reproduction is synchronized within the population. Spawning has also been obtained under laboratory conditions where larval development and post-larval growth were studied. Eggs measured 240 µm in diameter and were spawned within a gelatinous mass. The lecithotrophic pelagic stage was very short. Reproductive effort was high, probably because of high food availability and low level of competition. One of the most interesting findings was the probable presence of a resting stage in the life-cycle. The adaptive significance of enclosing the eggs in gelatiuous masses and of reducing the duration of the pelagic stage is discussed.     

Mode of zooxanthella transmission does not affect zooxanthella diversity in acroporid corals

Two distinct modes of algal endosymbiont acquisition exist in corals, a direct transmission from the parental colony to the eggs and a larval or post-larval uptake from the environment. The former, maternal-transmission mode is expected to be a more closed system, while the latter is believed to be an open system. Here we test the hypothesis that the diversity of symbionts in closed systems is lower than that in open systems. We examine the identity and diversity of the algal endosymbionts (zooxanthellae) in 25 Montipora species sampled from Irian Jaya (Indonesia) and Magnetic Island (central Great Barrier Reef) and compare the results with those previously obtained from Acropora species, which belong to the same family. All Montipora colonies examined harbour clade C zooxanthellae, with two colonies harbouring both clade C and D zooxanthellae simultaneously. Two algal strains (named C· and D· in this study) present in Montipora have not been observed in Acropora, and may have co-evolved with Montipora. Symbiodinium C· shows approximately 5% sequence divergence from C strains observed in Acropora spp. and occurs in 76% of the colonies examined. Nevertheless, several other C strains commonly found in other corals occur in some of the Montipora colonies. Montipora species transmit their algal endosymbionts directly to the eggs, while Acropora species have to acquire zooxanthellae from the environment every generation. Contrary to our expectations, the diversity of zooxanthellae is similar for the two genera, indicating that the mode of symbiont transmission (i.e. maternal versus horizontal) does not affect symbiont diversity in acroporid corals.Communicated by M.S. Johnson, Crawley     

Spatiotemporal coupling/decoupling of planktonic larvae and benthic settlement in decapods in the Scottish east coast

Settlement patterns and the relationship between meroplanktonic larvae and settlement in decapods were studied on the Scottish east coast. Artificial settlement substrates (ASS), deployed at two locations (sandy vs. rocky sea substrates), were employed to collect megalopae and newly settled juveniles. Abundance of meroplanktonic larvae was used as an indicator of larval supply. The results showed a clear seasonality in settlement rates, and in some cases, significant differences between sites were detected. Nevertheless, the interference of the ASS with the surrounding habitat limits the study of spatial variability in settlement rates. Significant cross-correlation was found between the abundance of megalopae and juveniles in the collectors and planktonic larval abundance a month earlier. For individual species, this relationship was observed only in Pisidia longicornis. Complexities caused by the great variety of pre- and post-settlement processes, alongside effects of secondary dispersals of early juveniles may have obscured the relationship between meroplanktonic larvae and juveniles in other species.     

Growth and elemental composition (C,N, H) in Inachus dorsettensis (Decapoda: Majidae) larvae reared in the laboratory

Larvae of the spider crab Inachus dorsettensis were reared in the laboratory at constant 12 °C. Development lasted 8 to 10 d in the Zoea I, 10 to 12 d in the Zoea II and 14 to 20 d in the megalopa stage. During this time, larval growth was measured in samples taken every 2 to 4 d as dry wt (W), carbon (C), nitrogen (N), and hydrogen (H); energy content (E) was calculated from C. Biomass and energy (per individual) increased in each larval stage as a parabola-shaped function of age, which could be fitted by a power equation. C, H, and E show a higher percentage gain (relative to the initial values at hatching) than W or N, suggesting that proportionally more lipid than protein is accumulated during larval development. There are cyclical changes in the relative (per unit of W) biomass and energy figures, corresponding to the larval moult cycles: immediately after each ecdysis all these values decrease, presumably due to rapid uptake of water and minerals, then they increase again due to tissue growth and remain high until the next moulting occurs. Cyclical changes in the C/N ratio suggest that proportionally more lipid than protein is accumulated during the initial (postmoult) phase of the moult cycle, followed by a period of balanced or protein-dominated gain during the intermoult and premoult phases. These patterns of growth and elemental composition observed during the complete larval development and in single moult cycles of I. dorsettensis are compared with those described in the literature for other decapod species. This comparison suggests a high degree of similarity in biochemical composition and growth characteristics of larval decapod crustaceans.     

Laboratory study of predation by Aurelia aurita on larvae of cod,flounder, plaice and herring: development and vulnerability to capture

Capture success of the medusa Aurelia aurita preying on various developmental stages of fish larvae was measured together with larval reactivity and escape speed after being stung. These experiments were conducted in the spring of 1983 with A. aurita medusae collected from Loch Etive, Scotland and laboratory-reared larvae of Gadus morhua L., Platichthys flesus L., Pleuronectes platessa L. and Clupea harengus L. Capture success of the medusae increased with medusa size, but decreased with advancing larval development. Smaller species of larvae were more vulnerable to capture. Larval reactivity to encounters with medusae increased with advancing development, and larger species of larvae were more reactive to encounters. Larval escape swimming speeds also increased with advancing larval development and size. These results indicate that earlier stages of larvae within a species and smaller species of larvae at a given stage are more vulnerable to predation by medusae since they are less reactive to encounters. Apparently they are more susceptible to the effects of neurotoxins. Predation rates on different developmental stages of herring larvae are documented and compared with rates predicted by a predation model. Predictions fell within the range of observed predation rates, but tended to overestimate rates by larger medusae feeding on larger herring larvae. This indicates the possibility of predator satiation and/or behavioural avoidance.     

Larval settlement and metamorphosis of the mussel <Emphasis Type="Italic">Mytilus galloprovincialis</Emphasis> in response to biofilms

Biofilms were allowed to develop on glass slips immersed 1.0–1.5 m below the sea surface in Tachibana Bay, Nagasaki, Japan, for different periods of time from November 2003 to January 2005. The effects of age, immersion month, dry weight, bacterial and diatom densities of these biofilms on the settlement and metamorphosis of pediveliger larvae of the mussel Mytilus galloprovincialis were investigated in the laboratory. Furthermore, biofilms were subjected to various treatments to investigate the nature of the settlement and metamorphosis cue in the biofilm. Pediveliger larvae of the mussel settled and metamorphosed in response to biofilms. Settlement and metamorphosis to the post-larval stage significantly increased with the biofilm age. In addition, the biofilm activity varied depending on the immersion month (season), e.g., for biofilms with the same age, those immersed between June and August had higher activities than those immersed between November and March. The activity of the biofilm also positively correlated with the dry weight, bacterial and diatom densities. These three quantitative parameters of the biofilm were significantly affected by the film age but were not affected by the immersion month, suggesting that other parameters (e.g., community structures, extracellular products) also affected the inductive activity of the biofilm. The fixative agents (formalin and glutaraldehyde), heat, ethanol, ultraviolet irradiation and antibiotics treatments of the biofilm resulted in significant reduction or loss of its inductive activity. The survival of bacterial cells in the treated films where activities were either reduced or lost also decreased significantly. No settlement and metamorphosis were obtained when larvae were exposed to the conditioned water of the biofilm. Thus, larvae of M. galloprovincialis settled and metamorphosed in response to a cue produced by living bacteria in the biofilm. The cue may be a bacterial extracellular product which was susceptible to the above treatments.