Reproduction in Anthelia glauca (Octocorallia: Xeniidae). II. Transmission of algal symbionts during planular brooding

The soft coral Anthelia glauca Lamarck, 1816, of the family Xeniidae, is found on the reefs of KwaZulu-Natal, South Africa. Its gastrodermal cells contain numerous endosymbiotic unicellular algae (zooxanthellae). A. glauca is a gonochoric species that simultaneously broods its planulae within the pharyngeal cavity of the polyps. Symbiotic algae appear with zygote formation within the pharynx, embedded in amorphous material. The algal cells adhere to the ciliated ectodermal surface of immature planulae and are most probably endocytosed by them. Zooxanthellae are translocated towards the basal part of the ectoderm. Gaps are subsequently opened in the mesoglea into which symbionts surrounded by ectodermally derived material, including plasma membrane, pass. The basal membrane of endodermal cells disintegrates, and the algae bulge into spaces formed in the underlying endoderm. Throughout the process, each zooxanthella resides within a vacuolar membrane in the detached ectodermal cytoplasm. The acquisition process is essentially one in which zooxanthellae are translocated from the pharyngeal cavity into the ectoderm and then through the mesoglea into the endoderm, culminating in the final symbiotic state. The direct transmission of symbiotic algae to the eggs or larvae probably provides the most efficient means whereby zooxanthellae are acquired by the host progeny. Received: 15 July 1997 / Accepted: 25 February 1998     

Gametogenesis and larval development in Sabella spallanzanii (Polychaeta: Sabellidae) from the Mediterranean Sea

Sabella spallanzanii (Gmelin) is one of the best known and widely distributed Mediterranean polychaetes, but available data on its general biology has been inferred mostly from populations recently introduced to Australia. In the present paper, data on gametogenesis and larval development of a Mediterranean population from the Gulf of Taranto (Ionian Sea, Italy) are reported. Histological and electron microscopical analysis of gametogenesis showed that oogenesis, a long process beginning soon after spawning in February, is of extraovarian type. By contrast spermatogenesis is a very fast process lasting from September to December, when the coelomic cavity is completely packed with mature gametes and almost devoid of coelomocytes. During the period of spawning, some experiments of in vitro fertilisation were performed, always without success, while some of the collected females naturally spawned fertilised eggs (100%). Particularly interesting was the discovery of a small percentage of eggs which appeared fertilised but unspawned within the coelomic cavity of female. Investigation of the S. spallanzanii life cycle, from the naturally spawned fertilised eggs to embryonic and juvenile stages, was performed by daily microscopical observations and by SEM. Despite the presence of large eggs giving rise to a lecithotrophic larva, a long pelagic phase was observed, the longest found among Sabellidae. The larval development pattern is also described. Settlement began after about 2 weeks; metamorphosis occurred 10 d after settlement, when mucus was secreted abundantly and an external tube was formed. The long larval pelagic period and the development pattern, suggesting a high potential for dispersal, support both the introduction and invasive behaviour of the species in Australian waters. Received: 28 May 1999 / Accepted: 10 December 1999     

Reproduction of Dendronephthya hemprichi (Cnidaria: Octocorallia): year-round spawning in an azooxanthellate soft coral

Sexual reproduction in the azooxanthellate octocoral Dendronephthya hemprichi Klunzinger, 1877 was studied in Eilat (Red Sea) for 2 years beginning March 1989. D. hemprichi is a gonochoric broadcasting species. Gonads at all developmental stages were found throughout the year. Small-sized oocytes and sperm sacs, 51 to 100 μm in diameter, are highly abundant, accompanied by numerous smaller primordial gonads. These features result from continuous gametogenesis, and lead to year-round oocyte and sperm maturation and release. Gamete release was observed in the laboratory on all monitoring dates, and most of the female colonies spawned repeatedly for several successive nights. The reproductive features of D. hemprichi constitute an exception to the generalization that free-spawning reef-corals have brief and synchronized broadcast-spawning episodes. This species demonstrates early onset of first reproduction, which further increases its reproductive output. Received: 7 May 1997 / Accepted: 15 May 1997     

Reproduction of the intraovarian brooding apodid Leptosynapta clarki (Echinodermata: Holothuroidea) in British Columbia

Reproduction in the viviparous apodid sea cucumber Leptosynapta clarki was examined in Grappler Inlet, Bamfield, Vancouver Island, Canada from July 1989 through July 1991. The reproductive cycle of L. clarki is annual with gonad growth during the summer months. Male sea cucumbers spawn during November and December and internally fertilize, through as yet undetermined means, the oocytes within the ovary. Embryonic development is rapid, so that within 2 wk fertilized eggs reach the pentactula stage. Pentactulae have an open mouth and anus and actively move in the ovarian tubules feeding on droplets and fluid derived from the resorption of unfertilized eggs. Histological examination of gametogenesis shows similar development to that found in non-brooding holothurians. However, the protandric sex change observed in some male L. clarki after spawning and changes to the overian wall structure prior to fertilization are previously undescribed in sea cucumbers.     

Reproduction and larval development of Marenzelleria viridis (Polychaeta: Spionidae)

The pelagic larvae of the polychaete Marenzelleria viridis (Verrill, 1873) are newcomers among the meroplankton of the Baltic Sea, where they sometimes achieve an abundance of up to 21x10⁶ ind m^-3 near the coast, especially in late autumn and even in winter. Benthos samples were collected in the Darss-Zingst bodden chain from April 1992 to 1993 and used to ascertain the reproductive stages of individuals. Development from fertilized egg to benthic juvenile is described on the basis of field material. Details of the morphology of various pelagic stages and the young benthic worm are presented as drawings and scanning electron microscope photographs. In 1992, development of the gametes started in mid-May. The individuals reached maturity in late September after about 20 wk. The first planktonic stage was the fertilized egg. The larvae have initially one and later two pairs of black eyes and, in the 2nd segment, a ciliated pit. Gastrotrochs are present on the third and thereafter every alternate segment. Neuropodial setae develop once the 7-setiger stage is reached. Palps appear at the 10-setiger stage, and neuropodial bidentate hooks from the 10th to 11th setiger on. Metamorphosis into the juvenile benthic stage takes place at the earliest when the 15-setiger stage has been reached. The reproductive seasons of various populations of M. viridis and the developmental patterns of their larvae are discussed, and differences are compared with relevant findings for the spionids.     

Gametogenesis in Harmothoe imbricata (Polychaeta: Polynoidae)

The processes of gametogenesis in Harmothoe imbricata are described and illustrated. For most of their development the gametes are attached to the walls of segmental blood vessels. In males, only meiosis and sperm differentiation occur while the cells are free in the coelom. In females, oocytes are only released into the coelom briefly, after vitellogenesis has been completed. H. imbricata thus differs from most polychaete species so far described — where in males the spermatogonia divide mitotically to form rosettes after they have been released into the coelom, and in females the whole of vitellogenesis occurs after release of oocytes into the coelom. The oocytes of H. imbricata enter the first metaphase of meiosis before they are shed at spawning. The elongated head of the sperm in H. imbricata is atypical of polychaetes in general.     

Reproduction in the externally brooding sea anemone Epiactis georgiana in the Antarctic Peninsula and the Weddell Sea

External parental care is uncommon among actiniarians but common in Epiactis species. Here, several aspects of reproduction are analyzed for of one of them, Epiactis georgiana. Samples were collected in December, January, February, March, and April in the Antarctic Peninsula and the eastern Weddell Sea, during 1998, 2000, 2002, and 2003. Most sexually mature individuals of E. georgiana are male or female, but some are hermaphrodites. This is the first report of hermaphroditism in E. georgiana, which is the third species of the genus with this sexual pattern. The results suggest that oogenesis starts in December and that at least two generations of oocytes overlap; a third generation is often brooded externally. Putative fertilization is likely internal, and larvae and/or embryos are externally brooded on the distal part of the adult column until an advanced developmental stage. Apparently E. georgiana reproduces seasonally, probably releasing the embryos/larvae in the last months of the austral spring (December). Inter-individual variability was observed in gametogenesis. In addition, specimens from the Antarctic Peninsula were larger than those from the Weddell Sea. This study represents the first step in understanding the reproductive mode of E. georgiana.     

The paradox of Rockall: why is a brooding gastropod (Littorina saxatilis) more widespread than one having a planktonic larval dispersal stage (L. littorea)?

In benthic invertebrates dispersal of planktotrophic larvae is generally considered more effective than is, for example, the rafting of adults or egg masses. It is certainly true that over short distances, viz., in the range of tens of kilometres or less, a moderately long-lived planktotrophic larva represents an effective mechanism of dispersal. However, turbulent mixing and mortality will decrease the concentration of planktotrophic larvae, and at some distance from the ancestral population the density of settlers may be too low to enable future matings between adults of low mobility. On the other hand, adults, juveniles or benthic egg masses drifted over long distances may colonize new habitats. The crucial point is the type of larval development of the organism. If the founder group belongs to a species with direct development or which produces very short-lived planktonic larvae, the low mobility of all life-stages will maintain a population within a restricted area so that mates will be likely to encounter each other even in a small population. Even if transport of benthic stages happens very rarely, this may be more influential than larval dispersal over long distances. To show that this may be true the detailed geographical distribution of two intertidal gastropod species with contrasting modes of development is presented and further support from the literature for this hypothesis is discussed.     

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.     

Gametogenesis of Pollicipes cornucopia (Cirripedia: Scalpellomorpha) in north-west Spain

The gametogenesis and gonad microanatomy of the stalked barnacle Pollicipes cornucopia (Leach) is described. An histological classification of gametogenic development is proposed for the firt time for a species of the Cirripedia. This species has an annual gametogenic cycle on the north-west Spanish coast. Spawning takes place mainly from March to September. Ovaries release gametes at least twice during the gametogenic cycle.     

The ecophysiological complex of Bathyporeia pilosa and B. pelagica (Crustacea: Amphipoda). I. Respiration rates

The metabolic rates of high and low shore estuarine populations of Bathyporeia pilosa Lindström and an open coast population of B. pelagica (Bate) have been determined over a range of temperatures during January and February, and June and July, 1968. Changes in oxygen uptake have also been measured monthly at 15°C. During the winter, oxygen uptake was in the order: high shore B. pilosa>low shore B. pilosa>B. pelagica. During the summer, high shore B. pilosa and B. pelagica had similar metabolic rates, but both were significantly higher than low shore B. pilosa. Both populations of B. pilosa had lower metabolic rates in summer than in winter, whereas the metabolic rate of B. pelagica remained much the same. Seasonal changes in metabolic rate are closely correlated with reproductive cycles. The possible influences of environmental parameters are discussed.     

Studies on sharks. I. Reproduction in the female sumitsuki shark Carcharhinus dussumieri

During the last 5 years, the T.S. Nagasaki Maru, Nagasaki University, Japan, carried out trawling operations in the waters off Kuching, northwest Borneo, for 1 week in July of each year. During this period, 119 specimens of the sumitsuki shark Carcharhinus dussumieri Valenciennes (Müller et Henle, 1841) were caught and their reproductive system investigated. In these waters, C. dussumieri has no definite reproductive seasons; it was, therefore, possible to obtain sufficient suitable material to examine all stages of the sexual cycle. The left ovary is rudimentary throughout the life cycle, and only the right ovary is functional. The ova in the ovary are already developing for the succeeding ovulation while the embryo already present in the uterus is growing; the 2 mature eggs from the right ovary are ovulated in the peritoneal cavity soon after parturition. The developing ova which remain in the ovary after ovulation are reabsorbed. The 2 mature eggs ovulated enter a common ostium and each oviduct receives one egg. In the nidamental gland, the fertilized egg is enclosed by an embryonic membrane and descends into the uterus where it grows into an embryo (simple pregnancy: 1 embryo in each uterus). During earlier embryonic development, nourishment is obtained from the yolk stored in the yolk sac. The placenta is established when the embryo attains a total length of about 150 mm; the embryo is thenceforth nourished by the placenta through the umbilical stalk until birth.     

A response-surface approach to the combined effects of temperature and salinity on the larval development of Adula californiensis (Pelecypoda: Mytilidae). I. Survival and growth of three and fifteen-day old larvae

Laboratory experiments of a factorial design were used to examine the combined effects of temperature and salinity on the survival and growth of early and late-stage larvae of Adula californiensis (Phillippi, 1847). Response-surface curves were generated to predict optimal conditions for survival and growth in order to better understand the successful recruitment of this species within the Yaquina Bay estuary (Oregon, USA). Three-day old cultured larvae were more sensitive to reduced salinity than were 15-day old larvae. However, the 15-day old larvae showed a narrower temperature tolerance than the 3-day old larvae. A. californiensis larvae survived over a wider range of temperatures near optimum salinities than at salinities near their lower tolerance limit, and conversely. Temperature and salinity ranges for maximum survival (10° to 15°C, 31 to 33) were narrower than the ranges which occur within the estuary where the adult populations exist. Larval size did not increase markedly during the 15-day rearing period, and was not greatly affected by temperature or salinity. No statistically significant temperature-salinity interaction was found for either survival or growth.     

Molecular evidence for multiple lineages in the gorgonian family Plexauridae (Anthozoa: Octocorallia)

Octocorals are diverse and abundant on many marine hard substrates, and, within this group, members of the family Plexauridae are an important component of tropical reef assemblages, especially in the Caribbean. To understand historical relationships within this large and diverse assemblage, and to test the monophyly of the family and some of its genera, DNA sequences of two mitochondrial loci (msh1 and ND2, ~1,185 bp) were analyzed from 46 species in 21 genera from deep and shallow waters in the tropical western Atlantic and in the tropical western and eastern Pacific (plus 9 taxa in the closely related Gorgoniidae and 1 species of the more distantly related Alcyoniidae). Five strongly supported clades were recovered. Three large clades correspond roughly to the Plexauridae, Paramuriceidae, and Gorgoniidae, and two smaller clades were comprised of taxa previously assigned to several families. Astrogorgia sp. did not group with any of the clades. The mutual relationships among the five clades remain unclear. Several genera previously regarded as unrelated appear to be grouped among the three families; e.g. Hypnogorgia sp. (Paramuriceidae) falls within a clade consisting of both Pacific and Atlantic Muricea spp. (Plexauridae), while Swiftia sp., Scleracis sp., and an Atlantic Thesea sp. (all Paramuriceidae) group with the gorgoniids. In several instances, genera containing Atlantic and Pacific species were recovered as monophyletic (Muricea spp., Bebryce spp.). However, in at least three cases (Echinomuricea spp., Thesea spp., Villogorgia spp.), placement of Atlantic and Pacific species in the same genus may reflect convergence of sclerite morphology. The results indicate a strong need for reexamination of octocoral taxonomy using a combination of molecular, morphological, and chemical evidence.Electronic Supplementary Material Supplementary material is available in the online version of this article at http://dx.doi.org/10.1007/s00227-005-1592-y.Communicated by J.P. Grassle, New Brunswick     

Fouling organisms in the port of Mar del Plata (Argentina). I. Siphonaria lessoni: ecological and biometric aspects

The present paper deals with ecological aspects of the pulmonate gastropod Siphonaria lessoni (Blainville, 1824), a common member of fouling communities in Mar del Plata's port (38°0817 S, 57°3118 W). Populations on colonized panels of an experimental raft were studied during three annual cycles, to determine feeding habits, growth and various factors which restrict their distribution on floating substrata. Although S. lessoni is harmless as a fouling organism, its grazing on the algal belt clears a part of the substratum's surface, which is then quickly colonized by truly aggressive organisms such as Balanus amphitrite.     

Movement in soft corals: An interaction between Nephthea brassica (Coelenterata: Octocorallia) and Acropora hyacinthus (Coelenterata: Scleractinia)

An interaction between the alcyonarian octocoral Nephthea brassica Kukenthal, 1904 and the scleractinian Acropora hyacinthus Dana was photographed and the assemblage collected at Rib Reef (18°15S; 146°45E), Central Region of the Great Barrier Reef, in September 1980. The interaction, which did not involve allelopathy, was characterised by extensive deposition of undifferentiated aragonite by the scleractinian in the vicinity of the soft coral, which moved across the surface of the acroporid. The basal attachment region of the nephtheid showed structural features which permitted movement. The net effect of this interaction was a series of divided trails across the surface of the acroporid plate evidencing the movement through growth and asexual division of the parent colony. These trails were susceptible to secondary colonisation by epifauna and algae which may reduce the fitness of the acroporid. This movement appears to afford N. brassica a distinct advantage in competing for space with acroporid corals.     

Isolation and cloning of DNA from somatic tissue of soft corals (Cnidaria: Octocorallia)

A method is described for isolating high molecular weight DNA from somatic tissue of soft corals. The method avoids problems associated with the presence of nucleases, pigments and other secondary metabolites in soft corals. Tissue is frozen in liquid nitrogen, pulverized with a pestle and mortar, and the powder extracted with buffered sodium dodecyl sulphate at 4°C in the presence of phenol/chloroform. This technique has been applied toAlcyonium, Sinularia, Sarcophyton andLobophytum species. Repeated sequences have been cloned fromAlcyonium sp., and used to probe slot-blots of genomic DNA and Southern blots of restriction digests. Homologous repeated sequences were detected in threeAlcyonium sp., but not in threeSinularia sp., despite these genera being closely related.     

Growth rate of the bathypelagic crustacean Gnathophausia ingens (Mysidacea: Lophogastridae). I. Dimensional growth and population structure

Gnathophausia ingens has 13 instars, each with a distinct range of sizes which does not overlap the sizes of adjacent instars. The intermolt interval, measured in the laboratory at 5.5°, 6.5° and 7.5°C, increases with increasing size and decreases with increasing temperature. At 5.5°C it varies from 166 days for the smallest individuals to 253 days for the oldest. The period of larval development in the marsupium of a female is estimated to be 530 days. The life span of females is estimated to be 2,950 days with the onset of reproduction at 2,400 days. It is sugquested that this species is semelparous. The population structure data suggest that there is low mortality through the first 7 instars, progressively higher mortality from Instar 8 through Instar 11, and slightly lower mortality in the remaining 2 instars. These life-history characteristics appear to be directed toward maximizing absolute fecundity (as opposed to time-specific fecundity) in a stable environment. These characteristics may have been selected for by low available food energy and made possible by the stability of the deep sea.     

Embryogenesis and acquisition of algal symbionts by planulae of Xenia umbellata (Octocorallia: Alcyonacea)

Early embryogenesis of the internally brooding soft coral Xenia umbellata and acquisition of algal symbionts in the course of its planular ontogenesis have been examined by scanning and transmission electron microscopy and by light microscopy. The endoderm of adult X. umbellata harbours symbionts mainly in the tentacles and in the peripheral solenia system. The colonies are gonochoric brooders. Algal symbionts were never found in the sperm sacs, and were only rarely found in the follicular tissue enclosing the oocytes. Fertilized eggs pass into endodermal brood pouches where embryogenesis occurs. Cleavage is holoblastic and leads to formation of a solid blastula. Algal symbionts are conspicuously embedded in the parental mesoglea that coats the young embryo, most probably transmitted by surface adherence. At a further stage, this integument disappears and the algae reside extracellularly among the cells of the newly-formed blastula. After subsequent cell proliferation developing planulae possess an inner mass of yolk-laden cells that contain numerous symbiotic algae. Gradually the yolk disintegrates, leaving a cavity enclosed by ectoderm, a thin mesoglea and an inner endoderm with intracellular symbionts. The mature planulae have already been provided with numerous intracellular symbionts by the time they are expelled from the brood pouches. The markedly early symbiont acquisition by the embryos of X. umbellata may help support their developmental requirements in the course of planular ontogenesis.