Uncommon diversity in developmental mode and larval form in the genus <Emphasis Type="Italic">Macrophiothrix</Emphasis> (Echinodermata: Ophiuroidea)

Development mode in the ophiuroid genus Macrophiothrix includes an unusual diversity of planktonic larval forms and feeding types. The modes of development for seven congeners that coexist in coral reef habitats at Lizard Island, Australia were compared using larvae generated from crosses over several reproductive seasons from 1999 to 2003. Three species (Macrophiothrix koehleri Clark, Macrophiothrix longipeda Lamarck, Macrophiothrix lorioli Clark) develop from small eggs (<170 μm) into typical obligately feeding planktonic (planktotrophic) pluteus larvae with four larval arm pairs. The remaining four species develop from larger eggs (≥230 μm) into either facultatively-feeding or non-feeding (lecithotrophic) larval forms. The facultative planktotroph (Macrophiothrix rhabdota Clark) retains the ability to digest and benefit from food but does not require particulate food to complete metamorphosis. Among the lecithotrophic species, Macrophiothrix caenosa Hoggett retains the pluteus morphology with four pairs of larval arms, but is incapable of feeding, depending instead on maternal provisions for larval development. The remaining two lecithotrophs have simplified larval morphologies with only a single pair of full length (Macrophiothrix nereidina Lamarck) or highly reduced (Macrophiothrix belli Doderlein) larval arms and no functional mouth or gut. This genus includes the first example of facultative planktotrophy in ophiuroids, the first example in echinoderms of a complete pluteus morphology retained by a lecithotrophic larva, and three degrees of morphological simplification among lecithotrophic larval forms. Egg volume varies 20-fold among species and is related to variation in feeding mode, larval form, and development time, as predicted for the transition from planktotrophic to lecithotrophic development.     

Halogenated metabolites in two marine polychaetes and their planktotrophic and lecithotrophic larvae

This study investigated the occurrence and ontogenetic changes of halogenated secondary metabolites in planktotrophic and lecithotrophic larvae and adults of two common, infaunal polychaetes, Streblospio benedicti (Spionidae) and Capitella sp. I (Capitellidae), with different life-history traits. S. benedicti contains at least 11 chlorinated and brominated hydrocarbons (alkyl halides) while Capitella sp. I contains 3 brominated aromatic compounds. These halogenated metabolites are potential defense compounds benefiting both larvae and adults. We hypothesized that: (1) planktotrophic larvae contain halogenated metabolites because they are not protected by adult defenses, (2) quantitative and qualitative variation of planktotrophic larval halogenated metabolites parallels that of adults, and (3) brooded lecithotrophic larvae initiate the production of halogenated metabolites only after metamorphosis. To address these hypotheses, volatile halogenated compounds from polychaete extracts were separated using capillary gas chromatography and identified and quantified using mass spectrometry with selected ion monitoring. All four life stages (pre- and post-release larvae, new recruits, adults) of both S. benedicti and Capitella sp. I contained the halogenated metabolites previously identified from adults. This is the first report of halocompounds identified and quantified in polychaete larvae. Allocation of potential defense compounds to offspring varied as a function of species, feeding type and developmental stage. Pre-release larvae of S. benedicti with planktotrophic development contained the lowest concentration of total halogenated metabolites (1.75 ± 0.65 ng mm⁻³), post-release and new recruits contained intermediate concentrations (8.29 ± 1.72 and 4.73 ± 2.63 ng mm⁻³, respectively), and planktotrophic adults contained significantly greater amounts (28.9 ± 9.7 ng mm⁻³). This pattern of increasing concentrations with increasing stage of development suggests synthesis of metabolites during development. Lecithotrophic S. benedicti post-release larvae contained the greatest concentrations of halometabolites (71.1 ± 10.6 ng mm⁻³) of all S. benedicti life stages and developmental types examined, while the amount was significantly lower in new recruits (34.0 ± 15.4 ng mm⁻³). This pattern is consistent with a previously proposed hypothesis suggesting a strategy of reducing potential autotoxicity during developmental transitions. Pre-release lecithotrophic larvae of Capitella sp. I contained the highest concentration of total halogenated metabolites (1150 ± 681 ng mm⁻³), whereas the adults contained significantly lower total amounts (126 ± 68 ng mm⁻³). All concentrations of these haloaromatics are above those known to deter predation in previously conducted laboratory and field trials. As a means of conferring higher larval survivorship, lecithotrophic females of both species examined may be expending more energy on chemical defenses than their planktotrophic counterparts by supplying their lecithotrophic embryos with more of these compounds, their precursors, or with energy for their synthesis. This strategy appears common among marine lecithotrophic larval forms. Received: 14 July 1999 / Accepted: 20 January 2000     

Salinity favorable for early development and gamete compatibility in two sympatric estuarine species of the genus Hediste (Polychaeta: Nereididae) in the Ariake Sea, Japan

Early development was examined, under various salinities, for two sympatric nereidid polychaetes, Hediste japonica and H. diadroma, which participated in a simultaneous reproductive swarming in an estuary of the Omuta-gawa River in Ariake Sea, Japan. The eggs of both species were isotonic to the medium of 27.5–30 psu salinity. The egg diameter in the isotonic salinity was 180–205 μm in H. japonica, and 130–160 μm in H. diadroma. Successful development of most embryos was observed in a salinity range of 22.5–30 psu in both species, while successful fertilization occurred in wider ranges of salinity, i.e., 10–34 psu in H. japonica and 10 to 30 psu in H. diadroma. In both species, free-swimming larval life started from the indistinct hatching of trochophores out of a jelly layer capsule. The lecithotrophic development appeared to run to the 4-setiger nectochaetes in H. japonica, while to 3-setiger nectochaetes in H. diadroma, resulting in a shorter pelagic larval life in H. japonica. In a comparison of larval morphology among Hediste species, we found a definite negative correlation between the prostomium width, which represents the larval size and depends on egg size, and relative length of chaetae to the prostomium width: the relative length of chaetae was the longest in H. diadroma (with the smallest egg size and long pelagic life), intermediate in H. japonica (intermediate egg size, short pelagic life), and the shortest in H. atoka (largest egg size, no true pelagic life). We also examined the possibility of hybridization between H. japonica and H. diadroma through cross-insemination experiments. The gametes of the two species were reciprocally compatible, and viable hybrid offspring were produced by the laboratory crosses. The hybrid larvae expressed intermediate phenotypes, but with a greater maternal influence in characteristics such as the relative length of chaetae and the lecithotrophic larval duration.     

Poecilogony in an estuarine opisthobranch: planktotrophy, lecithotrophy, and mixed clutches in a population of the ascoglossan Alderia modesta

A San Diego population of the opisthobranch mollusc Alderia modesta (Lovén, 1844) exhibits poecilogony, the presence of two development modes within a single species. In spring, half of the adults spawned masses containing ∼300 eggs with a mean diameter of 68 μm. After 3 d, these egg masses hatched planktotrophic veligers with a maximum shell dimension of 116 μm. The remaining adults spawned masses containing ∼30 eggs with a mean diameter of 105 μm. These egg masses hatched after 5 to 6 d, releasing lecithotrophic larvae with a maximum shell dimension of 186 μm. About 1% of field-collected adults produced mixed clutches containing a continuum of larval sizes, spanning the size extremes of planktotrophy and lecithotrophy and hatching larvae with a mean maximum shell dimension of 152 μm. Adults producing planktotrophic and lecithotrophic larvae were interfertile, and no hybrid breakdown was observed through the F3 generation. When starved, adults which previously produced only lecithotrophic larvae switched to producing planktotrophic larvae or mixed clutches with both planktotrophic and lecithotrophic larvae. Sequence-polymorphisms from a portion of the mitochondrial cytochrome c oxidase I gene support the conclusion that the two reproductive morphs represent a single species. Most of the lecithotrophic larvae and a small percentage of the larvae from mixed clutches were metamorphically competent within 3 d of hatching. A. modesta is the only molluscan species as yet known to have both planktotrophic and pelagic lecithotrophic development within a single natural population. Received: 14 August 1997 / Accepted: 11 April 1998     

Where are larvae of the vermetid gastropod <Emphasis Type="Italic">Dendropoma maximum</Emphasis> on the continuum of larval nutritional strategies?

This study evaluated whether larvae of the Indo-Pacific vermetid gastropod Dendropoma maximum are obligate planktotrophs, or whether they exhibit an intermediate feeding strategy. Experiments were conducted in Moorea, French Polynesia (149°50′W, 17°30′S), Sep–Oct 2009, to examine D. maximum larval growth and metamorphic responses to different diets and amounts of food. Dendropoma maximum larvae required particulate food to undergo metamorphosis, but were able to survive and grow in the absence of food for up to 20 days. Larvae in Low and Unfed food treatments exhibited phenotypic plasticity by growing a larger velum (the larval feeding structure) compared with those in high food. Unfed D. maximum larvae had a slower initial growth rate; however, by 11-day post-hatch fed and unfed larvae had converged on the same mean shell height (553 μm), which was only 10% larger than the initial size at hatching. Therefore, although the nutritional strategy of D. maximum larvae is best described as obligate planktotrophy, it appears to approach an intermediate feeding strategy.     

Reproductive ecology of <Emphasis Type="Italic">Fungiacyathus marenzelleri</Emphasis> from 4100 m depth in the northeast Pacific Ocean

Fungiacyathus marenzelleri (Vaughan, 1906) is a deep-water solitary coral, cosmopolitan in distribution that is found at depths of 300–6,328 m. This study examined gametogenesis, inter-annual variability and reproductive periodicity of F. marenzelleri collected from Station M (34°50′N, 123°00′W) in the northeast Pacific at a depth of 4,100 m. Samples were collected (May, June, October 1996; August 1998; February, June 2001; and June 2002) and histologically processed with spermatogenic stage, oocyte size and fecundity measured. Four stages of spermatogenesis were identified and all males contained multiple stages of sperm development in each seasonal sample. Three stages of oocyte development were identified; previtellogenic (<28–150 μm), vitellogenic (150–300 μm) and late vitellogenic (300–400 μm). Comparison of mean oocyte diameters among sampling dates showed there were no inter-annual variations or seasonal differences. Overall, fecundity was 1,290 (±407) oocytes polyp⁻¹, and with no significant differences between sample months. Fecundity was not polyp-size dependent. This study shows a similar quasi-continuous mode of reproduction to this species examined from the Northeast Atlantic Ocean, but the fecundity is reduced by 50%. The reproductive output may fluctuate in relation to the input of organic material at this site, as shown by non-significant trends in the oocyte size-frequency and fecundity data. A quasi-continuous output of gametes would promote successful fertilisation and wide dispersal of the lecithotrophic larvae.     

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.     

Dissolved histamine: a potential habitat marker promoting settlement and metamorphosis in sea urchin larvae

Many species of marine invertebrate larvae settle and metamorphose in response to chemicals produced by organisms associated with the adult habitat, and histamine is a cue for larvae of the sea urchin Holopneustes purpurascens. This study investigated the effect of histamine on larval metamorphosis of six sea urchin species. Histamine induced metamorphosis in larvae of three lecithotrophic species (H. purpurascens, Holopneustes inflatus and Heliocidaris erythrogramma) and in one planktotrophic species (Centrostephanus rodgersii). Direct comparisons of metamorphic rates of lecithotrophic and planktotrophic larvae in assays cannot be made due to different proportions of larvae being competent. Histamine (10 μM) induced metamorphosis in 95% of larvae of H. purpurascens and H. inflatus after 1 h, while the coralline alga Amphiroa anceps induced metamorphosis in 40–50% of these larvae. Histamine (10 μM) and A. anceps induced 40 and 80% metamorphosis, respectively, in the larvae of H. erythrogramma after 24 h. Histamine (10 μM) and the coralline alga Corallina sp. induced 30 and 70% metamorphosis, respectively, in the larvae of C. rodgersii after 24 h. No metamorphosis of any larval species occurred in seawater controls. Larvae of two planktotrophic species (Tripneustes gratilla and Heliocidaris tuberculata) did not metamorphose in response to histamine. Seagrasses, the host plants of H. inflatus, induced rapid metamorphosis in larvae of the two Holopneustes species, and several algae induced metamorphosis in C. rodgersii larvae. Histamine leaching from algae and seagrasses may act as a habitat marker and metamorphic cue for larvae of several ecologically important sea urchin species.     

Fuels for development: evolution of maternal provisioning in asterinid sea stars

For marine invertebrates, larval developmental mode is inseparably linked to the nutritional content of the egg. Within the asterinid family of sea stars there have been multiple, independent, evolutionary transitions to lecithotrophic development from the ancestral, planktotrophic state. To investigate the evolution of maternal investment and development within the Asterinidae, we quantified individual lipid classes and total protein for eggs and larval stages of closely related species representing three developmental modes (planktotrophy, planktonic lecithotrophy and benthic lecithotrophy). Within species, maternal provisioning differed between females indicating that egg quality varied with parentage. Maternal investment was related to egg size but, after correcting for egg volume, we identified two major oogenic modifications associated with the evolution of lecithotrophic development: (1) a reduction in protein deposition that probably reflects the reduced structural requirements of nonfeeding larvae, (2) an increase in deposition of a single class of energetic lipid, triglyceride (TG). The exception was Parvulastra exigua, which has benthic, lecithotrophic development and lays eggs with a lipid to protein ratio close to that of planktotrophs. This oogenic strategy may provide P. exigua larvae with a protein “weight-belt” that assists in maintaining a benthic existence. Asterinids with planktotrophic development used a significant portion of egg TG to build a feeding bipinnaria larva. For Meridiastra mortenseni, female-specific differences in egg TG were still evident at the bipinnaria stage indicating that egg quality has flow-on effects for larval fitness. In lecithotrophic asterinids, TG reserves were not depleted in development to the larval stage whereas protein stores may help fuel early larval development. Available data indicate that there may be two evolutionarily stable egg lipid profiles for free-spawning, temperate echinoderms.     

Effect of temperature and food availability on reproductive responses of Streblospio benedicti (Polychaeta: Spionidae) with planktotrophic or lecithotrophic development

Streblospio benedicti (Webster) from Tar Landing North Carolina (NC), USA with either planktotrophic or lecithotrophic development were reared under two food levels and three temperature regimes (two mimicking seasonal cycles in NC and one at constant 20°C). During the eight-month experiment no females switched reproductive mode and no significant differences in survivorship or reproductive activity were observed between reproductive types. However, reproductive activity and fecundity-related parameters were subject to influence by food and temperature. Survivorship, body size, and larval production was greater in winter-spring than summer-fall regimes. Higher food levels produced increased survivorship, reproductive activity and egg production in adults with lecithotrophic development but no change in those with planktotrophic development. Body size, egg size, egg number, numbers of larvae per brood pouch, and brood size were strongly correlated in female S. benedicti and most correlation coefficients were similar (or identical) in individuals having planktotrophic and lecithotrophic development. A comparison of egg size and brood size in females from Tar Landing suggests that individuals with the two forms of development package offspring differently but expend approximately equivalent reproductive effort. Larval trophic mode is best viewed as a genetic polymorphism in S. benedicti. Individuals with planktotrophic and lecithotrophic development exhibit similar reproductive responses to environmental variation and there is no evidence for speciation.     

Spawning and development in <Emphasis Type="Italic">Osedax</Emphasis> boneworms (Siboglinidae,Annelida)

We report observations on spawning and early development in bone-eating worms of the genus Osedax. Individual females of Osedax rubiplumus were observed at 1820 m depth freely spawning hundreds of oocytes, and females of an undescribed species, Osedax “orange collar”, were observed spawning in laboratory aquaria. Cytological and molecular analysis of the spawned oocytes of two Osedax species revealed no evidence for the bacterial endosymbionts that the female worms require for their nutrition, suggesting that the bacteria must be acquired later from the environment, as they are in other siboglinids. Individual O. “orange collar” females released an average of 335 (±130) eggs per day, but the number of oocytes spawned per day varied greatly, suggesting that not all the females spawned daily. Fertilization rates of the spawned oocytes varied from 0 to 100%, though most females showed nearly 100% fertilization rates. Oocytes spawned in the laboratory at 4–6°C were negatively buoyant. If fertilized, these oocytes extruded polar bodies and then after at least four hours cleaved unequally. Subsequent cleavages occurred in a spiral pattern at roughly 2-h intervals, resulting in free-swimming trochophore larvae after 24 h. These lecithotrophic trochophores swam for 9–16 days before settling with several hooked chaetae, similar to those of dwarf Osedax males. The larval life span of the Osedax species studied in the laboratory appears to be shorter than in closely related Vestimentifera. Osedax rubiplumus, on the other hand, has much larger oocytes and so may have greater dispersal potential than these other Osedax species. The high fecundity and apparently continuous reproduction of Osedax boneworms permits the opportunistic exploitation of sunken vertebrate bones. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Sexual reproduction in solitary corals: Synchronous gametogenesis and broadcast spawning in Paracyathus stearnsii

Samples of the temperate solitary coral Paracyathus stearnsii Verrill, 1869 were collected monthly or bimonthly from January 1977 to September 1978 off the California coast. This species is gonochoric and reproduces only sexually. Females produce a large number of small eggs (ca. 10⁵ per polyp) in gametogenic synchrony and both sexes spawn between February and May. A small planktonic planula (ca. 160 m long) develops following external fertilization. Broadcast spawning with planktonic development may be more common than previously assumed in scleractinians, and includes both lecithotrophic and planktotrophic larvae.     

Fecundity,brood loss and egg development through embryogenesis of <Emphasis Type="Italic">Armases cinereum</Emphasis> (Decapoda: Grapsidae)

The present work is a comprehensive study of reproduction and embryonic development of Armases cinereum. Ovigerous A. cinereum (Bosc, 1802) females from Sebastian Inlet, Florida (9.88–19.4 mm CW) lay 2,000–12,000 eggs per brood, depending on their CW (mm): fecundity = 24.662 CW^1.9432. A. cinereum displayed significant brood loss through development (ca. 500 eggs per brood) independently from their CW (no senescence). However, since smaller females lay fewer eggs than larger ones, the percentage of eggs lost during embryonic development is greater in smaller females. The number of eggs carried on a later stage of development (potential fertility = 5.5593 CW^2.4417) is a more accurate estimate of the reproductive output and subsequent recruitment. Egg volume increased during development (64%, 0.025–0.041 mm³ or 0.36–0.43 mm of diameter, N = 270) and was strongly correlated with egg water content increase (19.21%, r = 0.89). Lipids, particularly fatty acids, seem to be the major energy source for embryonic development, decreasing 56.31 and 37.08% (respectively) during embryonic development; both are negatively correlated with egg volume (r = −0.90). The utilization of fatty acids through the different developmental stages of A. cinereum is presented. The most consumed fatty acids are the monounsatured (43.33 μg mg⁻¹ dw), followed by the saturated (29.91 μg mg⁻¹ dw) and polyunsaturated (24.03 μg mg⁻¹). Palmitic (16:0) and linoleic (18:2n-6) acids are preferentially consumed (19.5 and 17.9 μg mg⁻¹ dw, respectively). The high proportion of essential polyunsaturated fatty acids of C₁₈ and C₂₀ reflects the consumption of primary producers such as mangrove leaves. EPA/DHA ratio (2.85–3.84) and low DHA content indicated that this species appears in a medium-low level of the trophic chain. The low ratio of 18:1n-7/18:1n-9 and high percentage of 18:1n-9 (marker of carnivory) may be a sign of the consumption of juvenile invertebrates. The high percentage of odd-numbered FA indicated the occurrence of detritivores/scavenger behaviours. The fatty acid composition of the eggs reflects adult feeding ecology (omnivorous) and habitat.     

Behaviour that influences dispersal and connectivity in the small,young larvae of a reef fish

Determining the scale of larval dispersal and population connectivity in demersal fishes is a major challenge in marine ecology. Historically, considerations of larval dispersal have ignored the possible contributions of larval behaviour, but we show here that even young, small larvae have swimming, orientation and vertical positioning capabilities that can strongly influence dispersal outcomes. Using young (11–15 days), relatively poorly developed (8–10 mm), larvae of the pomacentrid damselfish, Amblyglyphidodon curacao (identified using mitochondrial DNA), we studied behaviour relevant to dispersal in the laboratory and sea on windward and leeward sides of Lizard Island, Great Barrier Reef. Behaviour varied little with size over the narrow size range examined. Critical speed was 27.5 ± 1.0 cm s⁻¹ (30.9 BL s⁻¹), and in situ speed was 13.6 ± 0.6 cm s⁻¹. Fastest individuals were 44.6 and 25.0 cm s⁻¹, for critical and in situ speeds, respectively. In situ speed was about 50% of critical speed and equalled mean current speed. Unfed larvae swam 172 ± 29 h at 8–10 cm s⁻¹ (52.0 ± 8.6 km), and lost 25% wet weight over that time. Vertical distribution differed between locations: modal depth was 2.5–5.0 and 10.0–12.5 m at leeward and windward sites, respectively. Over 80% of 71 larvae observed in situ had directional swimming trajectories. Larvae avoided NW bearings, with an overall mean SE swimming direction, regardless of the direction to nearest settlement habitat. Larvae made smaller changes between sequential bearings of swimming direction when swimming SE than in other directions, making it more likely they would continue to swim SE. When swimming NW, 62% of turns were left (more than in other directions), which would quickly result in swimming direction changing away from NW. This demonstrates the larvae knew the direction in which they were swimming and provides insight into how they achieved SE swimming direction. Although the cues used for orientation are unclear, some possibilities seemingly can be eliminated. Thus, A. curacao larvae near Lizard Island, on average swam into the average current at a speed equivalent to it, could do this for many hours, and chose different depths in different locations. These behaviours will strongly influence dispersal, and are similar to behaviour of other settlement-stage pomacentrid larvae that are older and larger.     

Laboratory rearing of the clupeid fish Harengula pensacolae from fertilized eggs

Pelagic eggs of the scaled sardine Harengula pensacolae (Goode and Bean), have been hatched and reared in the laboratory for the first time. Larvae were reared in two 75 l aquaria under constant illumination, at an average temperature of 26.2°C. Zooplankton collected in a 35 mesh net was fed to the newly hatched larvae, and the diet was supplemented later with Artemia salina nauplii and a pelleted food. Larvae hatched at 4 mm TL (total length), and metamorphosed about 25 days later at 25 to 30 mm TL. Survivors averaged 76 mm TL 100 days after hatching. Of the 500 incubated eggs, 2.8% survived until 20 days, after which no significant natural mortality occurred. Sources of natural mortality included starvation, a copepod parasite (Caligus sp.), and injuries from contact with the sides of the tank. Larvae began feeding at 4.5 mm TL on copepod nauplii averaging 62 in body width. Scaled sardines were photopositive throughout the larval stage.Contribution No. 149, Bureau of Commercial Fisheries Tropical Atlantic Biological Laboratory, Miami, Florida 33149, USA.     

Production, hatching success and surface ornamentation of eggs of calanoid copepods during a winter at 57°N

Close to 50 species of marine Calanoid copepods have been reported to produce diapause eggs (Engel and Hirche in J Plankton Res 26:1083–1093, 2004); eggs that are viable but require a refractory phase before they hatch, sometimes after months. Diapause eggs are often described as morphologically different with respect to egg membrane ultrastructure and having a thicker egg shell with surface ornamentation as opposed to the smooth shell found in subitaneous eggs that hatch within days (Belmonte in J Mar Syst 15:35–39, 1998; Chen and Marcus in Mar Biol 127:587–597, 1997; Castro-Longoria in Crustaceana 74:225–236, 2001). Egg production rates, egg surface ornamentation, and hatching success were monitored in large aquaculture fish enclosures during winter with close to zero water temperatures (N57°). Surprisingly, all female copepods (Acartia spp.—presumably A. tonsa, and Centropages hamatus) produced eggs all through the winter with no obvious pattern with respect to light, temperature and food availability, and no diapause eggs were observed. However, individual females produced several categories of eggs with or without surface spines even within the same egg batch as evidenced by scanning electron microscopy (SEM). Four egg categories were distinguishable: ‘no spines’, smooth eggs; ‘short spines’, 5–15 μm long; ‘truncated spines’, with the spine tips cut-off <10 μm long; and ‘long spines’, up to 30 μm long. All egg categories remained unchanged with respect to surface structures from when we took them out of the incubation bottles until they hatched. In general, the frequency of ‘no spines’ was 10–40%, and most eggs were ornamented with ‘short-’ or ‘long spines’. Further, a given egg can be ornamented with all types of surface spines simultaneously, which might even be a fifth egg category. The different egg categories were all able to hatch within days when exposed to normoxic conditions suggesting that they were subitaneous.     

Some observations on gametogenesis,larval development and substratum selection of the sea pen Ptilosarcus guerneyi

Ptilosarcus (Leioptilus) guerneyi (Gray) maintained in the laboratory, were observed to spawn in late March, 1972. Gametes, developed in the leaf proper, discharged through the mouths of feeding polyps and were fertilized externally in the sea water. The sea pen's eggs are 500 to 600 in diameter; a large female is capable of producing over 200,000 eggs in one season. A pear-shaped and free-swimming planula larva developed 4 days after fertilization, at a temperature of 12 °C. The larvae were ready to settle and metamorphose when 7 days old if favorable substratum was available, but would remain as planulae for at least 30 days if kept in glass dishes only. The 30-day-old larvae would metamorphose if a suitable substratum (coarse sand, for example) was presented. The larvae do not feed and, hence, development is lecithotrophic. Studies of histogenesis showed that metamorphosis greatly enhanced the rate of cellular differentiation. The high fecundity, lecithotrophic development, and the ability of substratum selection by the larvae explain the success of this species in maintaining a high-density population in many areas of sandy substratum in the shallow waters of Puget Sound (USA), despite the fact that it is preyed upon by 7 species of predators.     

Feeding of Clausocalanids (Calanoida,Copepoda) on naturally occurring particles in the northern Gulf of Aqaba (Red Sea)

A total of 12 feeding experiments were conducted in the northern Gulf of Aqaba during spring (March/April) and autumn (September/October) 2002 at the Marine Science Station (MSS) in Aqaba. Females of three species of clausocalanids were selected: Clausocalanus farrani, C. furcatus and Ctenocalanus vanus. Natural occurring particle (NOP) larger than 5 μm were investigated as food source. The ambient chlorophyll a concentration at sampling depth (∼70 m) ranged between 0.15 and 1.00 μg chl a l⁻¹ and NOP concentrations ranged between 1.78 and 14.0 × 10³ cells l⁻¹ during the sampling periods. The division of particles into five size classes (5–10, 10–20, 20–50, 50–100 and >100 μm) revealed that most of the particles were found in the size classes below 50 μm (81–98%), while most of the natural occurring carbon (NOC) was concentrated in the size classes larger than 20 μm (70–95%). Ingestion rates were food density dependent rather than size dependent ranging between 0.02 and 1.65 × 10³ NOP ind⁻¹ day⁻¹ and 0.01 and 0.41 μg NOC ind⁻¹ day⁻¹, respectively, equivalent to a body carbon (BC) uptake between 0.4 and 51.8% BC day⁻¹. The share of the size classes to the total ingestion resembled in most cases the size class composition of the natural particle community.     

Fitting fertilisation kinetics models for free-spawning marine invertebrates

 To determine how fertilisation varied with sperm concentration for two species of scallop, Chlamys (Equichlamys) bifrons (Lamarck) and C. asperrima (Lamarck), we performed a simple series of sperm dilution experiments, and measured egg size and sperm swimming speeds. C. bifrons eggs were much larger (average diam=116.5 μm), and sperm swimming speeds faster (209.8 μm s⁻¹), than C. asperrima (71.2 μm, 166.0 μm s⁻¹). In both species, maximum fertilisation occurred at an ambient sperm concentration of around 100 sperm μl⁻¹; the maximum proportion of eggs fertilised was less than 0.70 in the C. bifrons experiments, but nearer 1.0 with C. asperrima. At high sperm concentrations (>100 sperm μl⁻¹), fertilisation decreased (presumably due to polyspermy) with increasing sperm concentration, but decreased more rapidly in C. bifrons than C. asperrima. A polyspermy-adjusted fertilisation kinetics model could be fitted to the experimental data, but unique parameter estimates could not be determined. Received: 7 October 1999 / Accepted: 8 July 2000     

Functional responses of copepod nauplii using a high efficiency gut fluorescence technique

To investigate copepod nauplii ingestion rates on phytoplankton, we have adapted the traditional gut fluorescence technique as it can be used with lower gut pigment concentrations. With the improved technique, laboratory experiments were performed to estimate functional responses for nauplii of Calanus helgolandicus and Centropages typicus. Nauplii were raised from eggs to copepodites and the experiments were performed with stages NIV-NV. Gut evacuation rates and ingestion rates were measured on Isochrysis galbana at different concentrations. Specific ingestion rates ranged between 0.038–0.244 μg C μg⁻¹ nauplii C d⁻¹ for C. typicus and 0.041–1.412 μg C μg⁻¹ nauplii C d⁻¹ for C. helgolandicus. Both species showed a type III functional response, reaching a saturation concentration at around 600 μgC l⁻¹ for C. typicus and 800 μgC l⁻¹ for C. helgolandicus. An erratum to this article can be found at