Life history characteristics of a coral reef sponge

Study of the life history characteristics of the common Red Sea sponge Mycale fistulifera (Poecilosclerida: Demospongiae) reveals several traits which may categorize it as an opportunistic species: (1) at least part of the population is reproductively active throughout the year, providing a continuous supply of larvae for settlement; (2) sponges may produce and release a large number (152±39 larvae d^-1) of brooded larvae; (3) released larvae are capable of fast settlement and metamorphosis (minutes to 30 hours post-release); (4) the turnover of the population is high and population size varies with time. From 48 initial sponges plus 94 recruits, only 25 remained alive after 14 months of observation; (5) most members of the population (>70%) have a small body size (<30 cm²); (6) sexual maturity may occur at an early age. These traits facilitate continuous establishment of M. fistulifera in new spaces on the reef; (7) M. fistulifera, preferred substrate is another opportunistic species, the coral Stylophora pistillata which it overgrows.     

Transmission,plasticity and the molecular identification of cyanobacterial symbionts in the Red Sea sponge <Emphasis Type="Italic">Diacarnus erythraenus</Emphasis>

Cyanobacterial symbionts in the sponge Diacarnus erythraenus from the Red Sea were identified in both adult sponges and their larvae by 16S rDNA sequencing. A single cyanobacterial type was found in all samples. This cyanobacterial type is closely related to other sponge cyanobacterial symbionts. The cyanobacterial rDNA, together with the morphological analysis by electron and fluorescence microscopy, provided evidence for vertical transmission of the symbionts in this sponge. In addition, we show phenotypic plasticity of the symbionts inside the sponge, probably as a result of variability in light availability inside the sponge tissue. Finally, the reproduction of Diacarnus erythraenus is also described.Matan Oren, Laura Steindler have contributed equally to the work.     

Influence of sponges on invertebrate recruitment: A field test of allelopathy

We manipulated live sponges in Belize, Central America, Big Pine Key, Florida (USA), and Indian River lagoon, Florida (USA) in summer/autumn, 1988. At each location, live sponges of three species were placed within 0.5 cm of ceramic tiles. Tiles with synthetic sponges positioned in the same manner and tiles with no sponges served as controls. Of 26 recruiting species analyzed, only one (Sponge sp. 6 — Indian River) was inhibited by living sponges. Four species (Perophora regina — Belize;Aiptasia pallida — Big Pine Key; andCrassostrea virginica andAscidia nigra — Indian River) recruited in greater numbers in the presence of sponges, suggesting that some larvae may be attracted rather than repelled by sponge allelochemicals. Allelopathic effects were less important than small-scale flow effects and patchy larval supply in determining recruitment patterns on surfaces adjacent to sponges.     

Photoadaptation of zooxanthellae in the sponge Cliona vastifica from the Red Sea, as measured in situ

In the Red Sea, the zooxanthellate sponge Cliona vastifica (Hancock) is mainly present at >15 m depth or in shaded areas. To test whether its scarcity in unshaded areas of shallower waters is linked to the functional inefficiency of its photosymbionts at high irradiances, sponges were transferred from 30 m to a six times higher light regime at 12 m depth, and then returned to their original location. During this time, photosynthetic responses to irradiance were measured as rapid light curves (RLCs) in situ by pulse amplitude modulated (PAM) fluorometry using a portable underwater device, and samples were taken for microscopic determinations of zooxanthellar abundance. The zooxanthellae harboured by this sponge adapted to the higher irradiance at 12 m by increasing both their light saturation points and relative photosynthetic electron transport rates (ETRs). The ETRs at light saturation increased almost fourfold within 15–20 days of transfer to the shallower water, and decreased back to almost their original values after the sponges were returned to 30 m depth. This, as well as the fact that the photosynthetic light responses within an individual sponge were in accordance with the irradiance incident to specific surfaces, shows that these photosymbionts are highly adaptable to various irradiances. There was no significant change in the number of zooxanthellae per sponge area throughout these experiments, and the different photosynthetic responses were likely due to adaptations of the photosynthetic apparatus within each zooxanthella. In conclusion, it seems that parameters other than the hypothesised inability of the photosymbionts to adapt adequately to high light conditions are the cause of C. vastifica's rareness in unshaded shallow areas of the Red Sea. Received: 25 April 2000 / Accepted: 13 October 2000     

Effects of duration of larval swimming period on early colony development in Bugula stolonifera (Bryozoa: Cheilostomata)

Laboratory experiments with larvae of the cheilostome bryozoan Bugula stolonifera Ryland, 1960 assessed the time to settlement in the presence of a constantly available polystryrene substrate, the development of competence for metamorphosis, and the effects of the duration of swimming period on early colony development. Sexually mature colonies of B. stolonifera were collected on 11 and 18 September 1987; 2 and 18 August, 1988; and 6, 12, 19, and 26 September 1988, from Eel Pond (Woods Hole, Massachusetts, USA) and were maintained at 20°C. In the presence of a constantly available substrate, cumulative percent settlement curves were sigmoid, with 75% of larvae settled in 3.2±0.5 h. Typically, 50% of the larvae settled in less than 3 h and 95% settled in 6.1±1.2 h. The number of settled individuals that developed feeding ancestrulae by 3 d and the number that developed first-feeding autozooids by 6 d was assessed as a function of duration of larval swimming. Individuals which were kept swimming for 8 and 10 h after hatching developed significantly more slowly to the ancestrula and autozooid stages in 13 out of 14 experiments than did larvae that swam 2 or 6 h. This is the first report for any bryozoan that prolongation of the larval free-swimming period affects the rate of colony development.     

Larval bloom of the oviparous sponge Cliona viridis: coupling of larval abundance and adult distribution

 We performed an intensive year-round sampling with the aim of studying the abundance of sponge larvae in four Mediterranean benthic communities: photophilic algae, sciaphilous algae, semi-obscure (i.e. low light-intensity) caves and sandy bottoms. We record here for the first time, a larval bloom of Cliona viridis (Schmidt 1862), the most common excavating sponge in the Mediterranean, which took place simultaneously in several rocky communities of the Blanes sub-littoral (NE Spain), and discuss the role of restricted larval dispersal in the distribution of adult sponges. In the communities studied, C. viridis larvae bloomed synchronously once, in June. Spawning and consequent embryo development presumably occurred in May, when water temperature was 16 °C. The free larva is a small, evenly ciliated, weakly swimming parenchymella with low dispersal capabilities. The number of larvae m⁻³ and sponge abundance (as percent cover and biomass) were significantly higher in the community of sciaphilous algae than in the other communities studied. Because of limited larval dispersal, larval and adult abundance in the communities were positively correlated. Larvae developed into juvenile sponges 10 to 15 d after settlement. Settlers displayed distinctive features: a peripheral cuticle, vacuolar etching-like cells at the sponge base, absence of oscular chimneys, and the presence of zooxanthellae, which were presumably transmitted during oocyte maturation. Received: 24 January 2000 / Accepted: 4 July 2000     

Variability in reproductive output across a water quality gradient for a tropical marine sponge

To establish a complete understanding of reproductive variability, larval supply and ultimately population demographics of a species it is important to determine reproduction across a broad spectrum of environmental conditions. This study quantified sexual reproduction of the brooding, gonochoristic sponge Rhopaloeides odorabile from populations across the shelf reefs of the central Great Barrier Reef (GBR). Histological sections of reproductive sponges collected at increasing distances from the coast were used to determine if numbers of reproductive sponges, reproductive output (using a reproductive output index), size at sexual maturity, and sex ratios varied according to their location (distance) from the coastline and therefore from influences of terrigenous/riverine discharge. Significantly higher proportions of reproductive sponges occurred with increasing distance from the coast. The proportion of all reproductive sponges (both male and female) on offshore reefs ranged from 77 to 90%, during November and December, the peak reproductive months of this sponge, compared to 47 to 50% for sponges occurring on coastal reefs. Levels of female reproduction increased with increasing distance from the coastline on two levels. First, oocytes from offshore sponges were significantly larger than oocytes from coastal sponges. Second, sponges from offshore reefs showed a reproductive index (proportions of oocytes, embryos and larvae mm⁻²) approximately 15 times higher than coastal reef sponges. Therefore, both numbers of oocytes, embryos and larvae in conjunction with larger oocytes contribute to a higher reproductive output index for offshore sponges. The production of spermatic cysts in males was consistent across the GBR. Sex ratios for coastal reef sponges showed a male bias while offshore sponges showed approximate equal sex ratios. The effect of terrigenous riverine input from coastal fluvial plains to the inner GBR is well established and is likely to contribute to the lower levels of reproduction associated with female sponges inhabiting coastal reefs of the central GBR.     

Changes in morphology and physiology of an East Mediterranean sponge in different habitats

The sponge Tetilla sp. (Tetractinomorpha: Tetillidae) is a common species in the eastern Mediterranean. This sponge inhabits four different habitat types differing in wave impact and irradiance levels. Two of these habitats (a shallow cave and deep water) are characterized by relatively calm water, whereas the other two (shallow exposed site and tide pools) are in turbulent water with high energy flow. The present study examined the influence of physical (depth, illumination and water motion) and biotic factors on morphology, skeletal plasticity and reproductive traits among the four spatially separated populations. Sponges from tidal pools had significantly larger body volume than sponges from deep water and from shallow caves (ANOVA: tidal-deep P<0.0001; tidal-shallow caves P<0.05). Sponges from exposed habitats were significantly larger than deep-water sponges (ANOVA: P=0.01). In addition, individuals from tide pools and from the exposed habitat had a significantly higher proportion of structural silica than sponges from the calmer deep water and from the cave sites. Oxea spicules in sponges from the calm habitats were significantly shorter than in those from the tidal pools and the exposed habitats. The percentage of spicules out of a sponges dry weight in individuals transplanted from deep (calm) to shallow (turbulent) water significantly increased by 21.9±12.9%. The new spicule percentage did not differ significantly from that of sponges originally from shallow water. Oocyte diameter differed significantly between habitats. The maximal size of mature eggs was found in deep-water sponges in June (97±5 m). In the shallow habitats, a smaller maximal oocyte diameter was found in the cave, in May (56.5±3 m). Furthermore, oocyte density in shallow-water sponges was highest in May and decreased in June (with 88.2±9 and 19.3±9 oocytes mm^–2, respectively). At the same time (June), oocyte density of deep-water sponges had just reached its maximum (155±33.7 oocytes mm^–2). The difference in oocyte size and density between deep- and shallow-water individuals indicates an earlier gamete release in the shallow sponge population. The results suggest that plasticity in skeletal design of this sponge indicates a trade off between spicule production and investment in reproduction.Communicated by O. Kinne, Oldendorf/Luhe     

Evidence for morphology-induced sediment settlement prevention on the tubular sponge<Emphasis Type="Italic"> Haliclona urceolus</Emphasis>

Several mechanisms are known to assist the survival of sponges in highly sedimented environments. This study considers the potential of sponge morphology and the positioning of exhalant water jets (through the osculum) in the adaptation of Haliclona urceolus to highly sedimented habitats. This sponge is cylindrical with an apical osculum, which is common in sedimented subtidal habitats at Lough Hyne Marine Nature Reserve, Cork, Ireland. Fifteen sponges were collected, preserved (killed with the structure and morphology maintained) and then replaced in a high sediment environment next to a living specimen (at 24 m). After 5 days, the sediment settled on both living and preserved sponges was collected and dried. No sediment was collected from living sponges, while preserved specimens had considerable amounts of settled sediment on their surfaces. The amount of sediment collected on these preserved specimens was significantly linearly correlated with sponge dry weight, maximum diameter and oscula width (R²>0.70, P<0.001, df=14). Observations of flow direction (using coloured dye) through H. urceolus showed that water is drawn into the sponge on its underside and exits via a large vertically pointing osculum. Sponge morphologies (shape) have often been considered as a means of passive adaptation to a number of different environmental parameters with oscula position enabling entrained flow through the sponge in high flow conditions. However, this study shows how the combination of sponge morphology (tubular shape) and positioning of the osculum may enable H. urceolus to survive in highly sedimented environments. Similar mechanisms may also aid the survival of some deep-water sponge species with similar morphologies.Communicated by J.P. Thorpe, Port Erin     

Growth and metamorphosis of Aplysia oculifera larvae in laboratory culture

Eggs of Aplysia oculifera (Adams and Reeve, 1850) were incubated in the laboratory. They hatched 8 to 9 d after spawning. Shell length (SL) of the hatched larvae was 102±2 m. Larvae were fed on the unicellular algae Isochrysis galbana in a concentration of 10⁴ cell ml^-1, and after 45 to 60 d grew to a maximum SL of 385±11 m. Larvae survived up to 330 d. A total of 12 species of algae from the natural habitat of A. oculifera were examined as metamorphosis inducers. Red algae Dasia sp., Jania sp., Hypnea sp. and Liagora sp. induced metamorphosis in 66.7±21.2, 28.3±17.7, 26.0±18.5 and 4.0±8.0% of the larvae, respectively. Green algae Enteromorpha intestinalis and Ulva sp. induced metamorphosis in 37.0±11.0 and 9.0±10.4% of the larvae, respectively. Cladophora sp. and Codium dichotomum, and the brown algae Padina pavonia, Colpomenia sinuosa, Hydroclathrus clathratus and Cystoseira sp. did not induce metamorphosis. There was no significant difference in the rate of metamorphosis between young (2 to 4 mo) and old (6 to 8 mo) larvae. Postmetamorphic juveniles grew and developed only when fed with E. intestinalis. They grew to a body length of>8 mm in 50 d. Postmetamorphic juveniles did not survive on other algae. The longevity of the planktonic A. oculifera larvae supports the hypothesis that the larvae can exist in the plankton and survive for several months until the next recruitment. The advantage of non-specificity in metamorphosis induction is discussed.     

Reproduction and development of the blue coralHeliopora coerulea (Alcyonaria: Coenothecalia)

Up to the present time, the reproductive cycle and larval development ofHeliopora coerulea, living fossil and sole member of the alcyonarian order Coenothecalia, have been undescribed. Populations ofH. coerulea studied on the Great Barrier Reef between 1984 and 1989 were found to have separate sexes and an annual gametogenic cycle. Mature eggs were large (>800µm diam), and their development was initiated internally. There appeared to be a lunar or semi-lunar periodicity in reproductive behaviour, with brooding of larvae commencing around either full or new moon. Development proceeded via superficial cleavage and a solid stereoblastula. Subsequent development took place on the surface of the colony, within a temporary brood-space created by protracted distension of the polyps. Larvae lacked zooxanthellae and were brooded for between 6 and 14 d prior to leaving the colony. Reproduction and development reflected the taxonomic affinities ofH. coerulea, but brooding and embryological development also appeared to be constrained by its morphology. Reproductive and larval characteristics ofH. coerulea may offer a partial explanation of the current biogeographic range ofH. coerulea.     

Spatial and temporal patterns of reproduction,larval settlement,and recruitment of the compound ascidian Aplidium stellatum

Spatial and temporal variation in recruitment of the compound ascidian Aplidium stellatum was examined on a shallow-water limestone outcropping in the Northeastern Gulf of Mexico from 1983 to 1985. Fifty-two percent of the recruits appeared on vertical surfaces, which were rare at this site. In the laboratory, tadpole larvae of A. stellatum consistently settled on vertical vs horizontal surfaces in a 2 to 1 ratio, regardless of the area of vertical surface offered. This settlement response was insufficient to account entirely for the field recruitment pattern, suggesting greater mortality of newly-settled individuals or larvae on horizontal vs vertical surfaces. Fifty-six percent of the variation in recruitment over 21 months could be explained by variation in the percentage of zooids brooding larvae in adult colonies. Over 28 consecutive months, the percentage of zooids brooding larvae was positively correlated with egg counts of the previous month (r ²=0.75), which in turn were weakly correlated with monthly average water temperature (r ²=0.36). These results suggest that larval production contributed substantially to temporal variation in recruitment of A. stellatum. The short larval life of tadpoles of A. stellatum and the relative isolation of the population were probably responsible for the correlation between recruitment and larval production.     

Isolation by distance in the scleractinian coral <Emphasis Type="Italic">Seriatopora hystrix</Emphasis> from the Red Sea

Pelagic dispersal of larvae in sessile marine invertebrates could in principle lead to a homogeneous gene pool over vast distances, yet there is increasing evidence of surprisingly high levels of genetic differentiation on small spatial scale. To evaluate whether larval dispersal is spatially limited and correlated with distance, we conducted a study on the widely distributed, viviparous reef coral Seriatopora hystrix from the Red Sea where we investigated ten populations separated between ~0.150 km and ~610 km. We addressed these questions with newly developed, highly variable microsatellite markers. We detected moderate genetic differentiation among populations based on both F _ST and R _ST (0.089 vs. 0.136, respectively) as well as considerable heterozygote deficits. Mantel tests revealed isolation by distance effects on a small geographic scale (≤20 km), indicating limited dispersal of larvae. Our data did not reveal any evidence against strictly sexual reproduction among the studied populations.     

Oxygen dynamics and transport in the Mediterranean sponge Aplysina aerophoba

The Mediterranean sponge Aplysina aerophoba kept in aquaria or cultivation tanks can stop pumping for several hours or even days. To investigate changes in the chemical microenvironments, we measured oxygen profiles over the surface and into the tissue of pumping and non-pumping A. aerophoba specimens with Clark-type oxygen microelectrodes (tip diameters 18–30 μm). Total oxygen consumption rates of whole sponges were measured in closed chambers. These rates were used to back-calculate the oxygen distribution in a finite-element model. Combining direct measurements with calculations of diffusive flux and modeling revealed that the tissue of non-pumping sponges turns anoxic within 15 min, with the exception of a 1 mm surface layer where oxygen intrudes due to molecular diffusion over the sponge surface. Molecular diffusion is the only transport mechanism for oxygen into non-pumping sponges, which allows total oxygen consumption rates of 6–12 μmol cm⁻³ sponge day⁻¹. Sponges of different sizes had similar diffusional uptake rates, which is explained by their similar surface/volume ratios. In pumping sponges, oxygen consumption rates were between 22 and 37 μmol cm⁻³ sponge day⁻¹, and the entire tissue was oxygenated. Combining different approaches of direct oxygen measurement in living sponges with a dynamic model, we can show that tissue anoxia is a direct function of the pumping behavior. The sponge-microbe system of A. aerophoba thus has the possibility to switch actively between aerobic and anaerobic metabolism by stopping the water flow for more than 15 min. These periods of anoxia will greatly influence physiological variety and activity of the sponge microbes. Detailed knowledge about the varying chemical microenvironments in sponges will help to develop protocols to cultivate sponge-associated microbial lineages and improve our understanding of the sponge-microbe-system.     

Sponge-inhabiting barnacles on Red Sea coral reefs

In this study eight different species of barnacles were found within nine species of sponges from the Red Sea. This brings to 11 the number of sponge-symbiotic barnacles reported from the Red Sea, two of these are new Acasta species (not described herein) and one (A. tzetlini Kolbasov) is a new record for this sea. This number is much higher than that of symbiotic barnacles found within sponges from either the N. Atlantic (2) or the Mediterranean (4). Two possible explanations for this are the presence of numerous predators in coral reefs and scarcity of available substrate for settlement. These factors can lead to high incidence of symbiotic relationships. Of the nine sponge species, only one (Suberites cf. clavatus) had previously been known to contain barnacles. Even at the family level, this is the first record of symbiotic barnacles in two out of the seven sponge families (Latrunculiidae, Theonellidae). Our present findings strengthen the apparent rule that the wider the openings in a barnacle shell, the fewer the host taxa with which it will associate, usually from one or two closely related families, and the more frequent it will associate with elastic sponges. Most Neoacasta laevigata found on Carteriospongia foliascens were located on the same side as the sponge's ostia, i.e. facing the incoming water. This adaptation allows the barnacles to catch more suspended particles from the water, provides them with more oxygen and prevents their exposure to discharged sponge waste. The highest density of barnacles observed on one face of a “leaf ” (with ostia) was 0.389 barnacles cm⁻² (one barnacle per 2.57 cm²) and on average 0.181 ± 0.68, while the average on the other side was only 0.068 ± 0.52 barnacles cm⁻². As indicated by the Morisita index, these barnacles most frequently (58%, n = 12) had a clumped spatial distribution (while the rest were randomly distributed), as is to be expected from such sessile organisms with internal fertilization via copulation. The presence of N. laevigata induced the growth of secondary perpendicular projections of its host C. foliascens. Of the N. laevigata examined, 17% brooded 324 ± 41 embryos each, of 286 ± 17 μm total length; only 5.7% (n = 123) were found to be dead. Size distribution analysis of skeletal elements from dead barnacles showed them to be significantly larger than the skeletal elements of the population of live barnacles ( p < 0.05). Received: 26 June 1998 / Accepted: 1 December 1998     

Feeding by larvae of two different developmental modes in Streblospio benedicti (Polychaeta: Spionidae)

Females of the spionid polychaete Streblospio benedicti (Webster) produce either small eggs (60–70 μm diameter) and planktotrophic larvae, or large eggs (100–200 μm) and lecithotrophic larvae that reportedly do not feed. This intraspecific polymorphism, a form of poecilogony, is potentially useful in studies of larval ecology and evolution, but necessary data on larval form and function are lacking. This study describes the morphology and nutritional biology of larvae obtained from Atlantic (South Carolina) and Pacific (California and Washington) populations from 2003 to 2005. The two types of larvae produced by Atlantic S. benedicti differed greatly in length (229±22 μm SD for planktotrophs vs. 638±40 μm for lecithotrophs) and chaetiger number (2–5 vs. 10–11) at release from the female’s brood pouch. Planktotrophic larvae bore long provisional chaetae on their first chaetiger; provisional chaetae were absent in lecithotrophic larvae. Larvae from Pacific populations were all of the lecithotrophic form, and were similar to their Atlantic counterparts in all respects. High-speed video microscopy revealed that both types of larvae used opposed bands of cilia to capture suspended particles and transport them to the mouth, where they were often ingested. Lecithotrophic larvae reared with suspended phytoplankton (Rhodomonas sp., 10⁴ cells ml⁻¹) for 2 days grew significantly faster than sibling larvae reared without added food, indicating that these larvae can digest and assimilate ingested food. Larvae of S. benedicti that develop from large eggs are thus facultative planktotrophs instead of obligately non-feeding lecithotrophs, a result that affects the interpretation of comparative studies of the ecology and evolution of larvae in S. benedicti and certain other marine invertebrates.     

Contrasting feeding patterns among species of fish larvae from the tropical Andaman Sea

Feeding habits of tropical fish larvae were analysed in a comparative study of four species (Scorpaenodes sp., Carangoides sp., Acanthocepola sp. and Cynoglossus sp.) from the Andaman Sea. We investigated morphological characteristics and their potential influence on larval feeding, and looked for common patterns in larval prey preference. Gut contents of a total of 300 larvae were examined and compared with local zooplankton composition. The feeding habits of the investigated larvae shared a number of characteristics. During ontogeny both the preferred prey size and the number of prey in the gut increased, and across all larval size classes the relative prey size spectrum stayed constant, of approximately the same magnitude for all four species. On the other hand, larval feeding also differed in a number of aspects, especially differences in the taxonomic composition of preferred prey were apparent. Scorpaenodes sp. preferred abundant and large prey taxa, Acanthocepola sp. and Carangoides sp. preferred large, but less common prey taxa, while Cynoglossus sp., which had the relatively smallest mouth size, preferred smaller sized prey groups. Hence, the findings indicate that from an offset of common characteristics, especially related to prey size preference, larvae have their individual feeding patterns related to specific morphology and patterns of distribution.Communicated by M. Kühl, Helsingør     

Host specificity in sponge-encrusting zoanthidea (Anthozoa: Zoantharia) of Barbados,West Indies

Six species of common Caribbean Zoanthidea, Parazoanthus swiftii, P. parasiticus, P. catenularis, P. puertoricense, Epizoanthus cutressi, and Epizoanthus sp., are virtually restricted to living on surfaces of reef-dwelling sponges. Quantitative surveys on Barbados reefs indicate that substrate specificity is relatively high among these zoanthids with three restricted to a single primary host sponge species and three restricted to three closely related sponges. One species, P. swiftii, exhibits a broad range of acceptable secondary substrates, due to its unique ability to execute migrational spread in the adult polyp stage. Variations in substrate specificity have been noted between island populations within the extensive Caribbean range and appear to be due to different species compositions of local sponge communities and slight differences in zoanthid larval settling specificities.     

Energy content at metamorphosis and growth rate of the early juvenile barnacle<Emphasis Type="Italic"> Balanus amphitrite</Emphasis>

The energetic cost of metamorphosis in cyprids of the barnacle Balanus amphitrite Darwin was estimated by quantification of lipid, carbohydrate and protein contents. About 38–58% (4–5 mJ individual^–1) of cypris energy reserves were used during metamorphosis. Lipids accounted for 55–65%, proteins for 34–44% and carbohydrates for <2% of the energy used. Juveniles obtained from larvae fed 10⁶ cells ml^–1 of Chaetoceros gracilis were bigger (carapace length: 560–616 µm) and contained more energy (5.56±0.10 mJ juvenile^–1) than their counterparts (carapace length: 420–462 µm; energy content: 2.49±0.20 mJ juvenile^–1) obtained from larvae fed 10⁴ cells ml^–1. At water temperatures of 30°C and 24°C and food concentrations of 10⁴ and 10² cells ml^–1 (3:1 mixture of C. gracilis and Isochrysis galbana) as well as under field conditions (26.9±3.1°C and 2.2±0.8 µg chlorophyll a l^–1), juveniles obtained from larvae fed the high food concentration grew faster than juveniles obtained from larvae fed low food concentration until 5 days post-metamorphosis. Laboratory experiments revealed a combined effect of early juvenile energy content, temperature and food concentration on growth until 5 days post-metamorphosis. After 10 days post-metamorphosis, the influence of the early juvenile energy content on growth became negligible. Overall, our results indicate that the energy content at metamorphosis is of critical importance for initial growth of juvenile barnacles and emphasize the dependency of the physiological performance of early juvenile barnacles on the larval exposure to food.Communicated by O. Kinne, Oldendorf/LuheAn erratum to this article can be found at     

Palatability of invertebrate larvae to corals and sea anemones

Risk of larval mortality is an underlying theme in debates and models concerning the ecology and evolution of the differing reproductive characteristics among marine benthic invertebrates. In these discussions, predation is often assumed to be a major source of larval mortality. Previous studies, focused primarily on planktotrophic larvae, suggested that marine larvae generally were susceptible to, and poorly defended against, planktivorous fishes and invertebrates. Larval-planktivore interactions involving larger and more conspicuous lecithotrophic larvae that are typical of many brooding sessile invertebrates have not been well studied. This lack of data for diverse larval types has hindered testing broad generalities about marine larvae and planktivore prey-preferences. This study demonstrates that lecithotrophic larvae of many Caribbean and temperate western Atlantic invertebrates are distasteful to co-occurring corals and anemones. These larval predators frequently rejected larvae of sponges (6 of 9 species), gorgonians (7 of 9 species), corals (3 of 3 species), hydroids (2 of 2 species) and a bryozoan. Larvae of three temperate colonial ascidians were readily consumed. Frequencies of survivorship for larvae captured but rejected by corals and anemones were generally high and, in 20 of 24 assays, were not statistically different from those of unattacked control larvae. Levels of metamorphosis (when it occurred) of rejected larvae also rarely differed significantly from those of unattacked controls. These results provide further evidence that larval palatability to predators may not be as high as once thought, particularly for brooded larvae of sessile colonial invertebrates. The means by which larvae may avoid or deter predators, and the demographic consequences for marine invertebrates and for the evolution of invertebrate life-history patterns, need to be assessed.