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.     

Periods of non-feeding in Polysyncraton lacazei (Ascidiacea: Didemnidae): a rejuvenative process?

Polysyncraton lacazei (Giard) (Ascidiacea: Didemnidae) displays short periods of non-feeding during the warm season in the northwestern Mediterranean Sea (NE of Spain). These periods were analyzed from 1988 to 1990 by monitoring naturally occurring colonies and by morphological and histological observation of non-feeding colonies. During this phase the surface of the colonies is covered by a glassy pellicle and the siphonal apertures are sealed. The phenomenon consists of a reabsorption of the branchial portion of the zooids and a budding of new thoraces. This process does not fit into either the propagative or survival categories of budding proposed for ascidians, and is interpreted as a rejuvenative phenomenon which extends the life span of the zooids.     

Growth of Flustra foliacea (Bryozoa)

The perennial bryozoan Flustra foliacea L. has annual growth-checks which leave lines across the fronds. These growth-checks have been used to determine the age and the pattern of growth of the colonies in terms of height and numbers of zooids. Monthly samples have been used to find the annual growth cycle. Heavy encrustations of epizoites on the F. foliacea colonies reduce growth rate. As the fronds increase in height, frontal budding of zooids thickens, and thereby strengthens, the holdfast.     

The influence of seawater temperature on zooid size and growth rate in Pentapora fascialis (Bryozoa: Cheilostomata)

Zooid size variation and growth banding in the bryozoan Pentapora fascialis, collected from the South of Great Britain to the South of Italy, were investigated in order to test their relationship with the variation of seawater temperature. Zooid length appeared to be more sensitive than zooid area and width to temperature variation. The longest zooids were budded in localities that typically experience low seasonal variation in temperature (3.2–7.5°C) and low mean annual temperature (about 11°C). Zooid length demonstrated the strongest relationship with the range of seasonal variation in temperature rather than the mean annual temperature. Growth bands produced during colder months were less high than those produced during warmer months. Measurements of these alternating bands were used to calculate growth rate of the laminae, ranging from 20.7 at Plymouth to 29.3 mm year⁻¹ at Tino Island. Significant differences in zooid length were found between the two bands, with longer zooids within the band developed in colder months and shorter zooids in bands produced in the warmer period. We conclude that zooid size can be used as an environmental proxy of the seasonal temperature regimes experienced by the species.     

Seasonality of polypide recycling and sexual reproduction in some erect Antarctic bryozoans

The seasonality of polypide cycling has been investigated for three species of erect bryozoans from Antarctica: Isoseculiflustra rubefacta (Kluge, 1914), Nematoflustra flagellata (Waters, 1904) and Himantozoum antarcticum (Calvet, 1905). Approximately ten colonies of each species were collected monthly by SCUBA divers over a 14 mo period during 1992/1993, and the status of each individual zooid was classified as differentiating/regenerating, active (feeding autozooids), degenerate (brown body) or sexually reproductive (ovicells present, or zooid containing a larva). Polypide cycling in all three species was distinctly seasonal. New zooids formed at the growth margin and typically contained actively feeding polypides for ≃9 mo before these polypides degenerated into brown bodies in the austral winter (June). Very few polypides were active in the period from June to August, when water-column food levels were at their lowest; after this period new polypides differentiated. Individual zooids typically underwent a total of five (I. rubefacta and N. flagellata), or at least four (H. antarcticum) complete polypide cycles before becoming senescent. Polypide lifetimes generally became shorter as the age of the zooid increased. Sexual reproduction was also distinctly seasonal in these species, with bands of ovicells or sexually reproductive zooids being formed each year in late summer once a given colony had grown to a threshold size (or age). Larvae were then brooded for ≃10 mo before being released in January/February (N. flagellata) or February/March (H. antarcticum). The seasonal patterns of polypide cycling are related clearly to the variations in food availability, and these species appear to have the longest zooid lifetime (≃5 yr) and the slowest polypide cycling (once per year with polypide lifetimes up to 10 mo) reported for any bryozoan so far. Received: 7 May 1995 / Accepted: 19 November 1997     

The morphology,anatomy and life history of a complanate form of Scytosiphon lomentaria (Scytosiphonales,Phaeophyta) from southern Australia

Complanate Scytosiphon lomentaria (Lyngbye) J. Agardh is characterised and distinguished from the typical cylindrical form by a flattened thallus, plurilocular sporangia having a mucilaginous covering layer, and an autumn-spring seasonal growth pattern. Cultural studies show that zooids from the plurilocular sporangia give rise to an independent ralfsioid stage, to ralfsioid plethysmothalli bearing complanate fronds, and to a cylindrical form of S. lomentaria. In culture, the complanate thalli are initiated only in short-day conditions, cylindrical thalli are initiated in both short- and long-day conditions. Ralfsioid thalli are of two kinds: one developing independently of day length, the other developing only during long days; the alternative short-day thallus form is complanate.     

Effects of the 1983-El Niño on growth and carbon and nitrogen metabolism ofPleurophycus gardneri (Phaeopyceae: Laminariales) in the northeastern Pacific

Growth and compounds of carbon and nitrogen of the northeast Pacific kelpPleurophycus gardneri (Laminariales, Laminariaceae) were assessed before, during and after the 1983-El Niño Souther Oscillation event. This 2-yr study provides evidence that reduced ambient levels of nitrate and phosphate from March until August/September, 1983, in combination with elevated seawater temperature, caused a significant impairment of growth. Blade surface area, blade length, total fresh weight, and dry weight on an areal basis were significantly reduced in 1983 compared to 1982 (P<0.01). They were also significantly smaller in 1984 than in 1983 (P<0.05). The C:N values obtained both in May and July 1983 were considerably higher than in 1982, while those in May 1984 were strikingly smaller than in both 1982 and 1983. Mannitol content of the mibrid in May 1983, exhibited the highest levels recorded during the 2-yr study period, with ca. 19% dry weight and significantly exceeded mannitol content measured in May 1982 (average: 13%) and in May 1984 (average: 8%). The concentration factor for internal vs external nitrate in the midrib was 700 x ambient in May 1982 and 1984 compared with 20 x in May 1983. Ninhydrin positive substances (NPS) averaged 117 mol g dry wt^-1 in May 1984 compared with ca. 50 mol in May 1982 and 1983. The pigment ratios chlorophyllc: chlorophylla and fucoxanthin: chlorophylla in May 1983 were similar to those obtained in 1982, but were significantly different in May 1984. It is suggested that the interactive effects of temperature stress and nutrient limitation in 1983 caused a disruptive influence on C- and N-metabolism ofPleurophycus gardneri, which still affected growth performance in 1984.     

Aspects of the reproduction and life cycle of Rhabdopleura compacta (Hemichordata)

Rhabdopleura compacta Hincks is shown to be monoecious. It is suggested that the ovum is ovulated and extruded into the lumen of the coenecium via a temporary opening at the base of the metasome, and that the oviduct itself may serve only as a way for sperm to fertilise the ova internally. The zooids degenerate when reproducing sexually and when conditions are unfavourable. The larva and initial stages of astogeny are described. Some observations on seasonal variation in the colonies indicate that the dormant buds serve for storage of nutrients. Reproduction seems to occur throughout the year, but most actively in spring. Relationships with Cephalodiscus and the Bryozoa are briefly discussed.     

Reproduction, larval development and functional relationships of the burrowing, spionid polychaete Dipolydora armata with the calcareous hydrozoan Millepora complanata

Dipolydora armata (Langerhans, 1880) is a small (4 to 5 mm) spionid polychaete found burrowing in the calcareous hydrozoan Millepora complanata Lamarck, 1816, on coral reefs at Barbados, West Indies. It excavates complex networks of interconnecting burrows and forms aggregations of worms in cavities within branches of the coral. Adult worms have a mixed feeding mode (suspension feeding and deposit feeding). Size–frequency distributions of worms in branch samples suggest that they mature in a single year and that reproduction occurs throughout the year. Burrow openings on the surface of the coral develop distinctive, erect spines caused by combined growth of worm tubes and host tissue. Millepore zooids were absent in the vicinity of tube openings and on spines, and thus the potential feeding surface of the coral will be reduced in heavily colonized branches. Burrows and openings were densest at the bases of millepore branches where weakening of the skeleton would be expected to occur. The absence of openings near the branch tips suggests difficulty in larval settlement there, amongst stinging zooids. Reproduction␣and larval development of the worms were examined, and a sequence of larval stages from one to 20 segments and a juvenile stage of 22 segments are described. Eggs are deposited in brood sacs attached to the burrow wall, and the larvae feed upon nurse eggs (adelphophagy). The presence of larvae and juveniles occurring free in the burrows suggests that larval development may be completed within the host coral as an alternative or in addition to a planktonic larval phase. Lack of provisional larval setae, early development of adult capillary setae, production of special spermatophores and a protracted breeding cycle in D. armata are all traits which would favour complete development within the host skeleton. Received: 6 March 1997 / Accepted: 25 October 1997     

Storage of exogenous sperm by the compound ascidianDiplosoma listerianum

Experimental evidence is presented for the storage of exogenous sperm by zooids of the simultaneously hermaphroditic didemnid ascidianDiplosoma listerianum. Cross-fertilized zygotes can be produced up to 1 mo after a ramet is placed in reproductive isolation. Previously published observations, considered in the light of the present data, suggest that the lumen of the ovary is the site of sperm storage. This is believed to be the first report of post-transmission storage of sperm by an ascidian. Existing records of storage of exogenous sperm in other taxa rarely involve aquatic animals in which spermatozoa are transmitted between mates singly through the surrounding water, as inD. listerianum. The potential significance of sperm storage in the mating systems of sessile aquatic invertebrates is discussed.     

Competitive interactions between related clades: evolutionary implications of overgrowth interactions between encrustin cyclostome and cheilostome bryozoans

Overgrowth interactions between encrusting cyclostome (eight species) and cheilostome (over 50 species) colonies were examined in subtidal communities in the northern Adriatic Sea off Rovinj, Croatia, in May–June 1988 and September–October 1990. Cheilostome colonies occupied ca. 80% of the available substrate space, whereas the cyclostome colonies occupied <5%. Out of 210 recorded interactions, cheilostomes overlapped cyclostomes in 164, while cyclostomes overlapped cheilostomes in only 16; 30 encounters resulted in mutual overlap or at least temporary growth termination along the line of contact. Most of the recorded interactions were for the cyclostomes Diplosolen obelia (Johnston) and Plagioecia patina (Lamarck). Both species elevated their colony margins on contact with a cheilostome in some instances, but D. obelia only overgrew competing cheilostomes in 12/120 encounters, and P. patina never prevailed. I propose that the cheilostomes have a key evolutionary innovation, lacking in cyclostomes, consisting of more rapid ontogenetic development of zooids along colony margins so that encrusting cheilostomes have substantially higher colony margins. This results in an outflow of filtered water along the edge of encrusting cheilostome colonies, while cyclostomes take water in at colony margins. These contrasting feeding currents apparently give a competitive advantage to the cheilostomes where colony margins approach and make contact with those of cyclostomes.     

Distribution and abundance of eggs of Labidocera aestiva (Copepoda: Calanoida) in the bottom sediments of Buzzards Bay,Massachusetts, USA

Grain-size composition of the sea-bed and density of eggs of Labidocera aestiva in bottom sediments in Buzzards Bay were determined at approximately monthly intervals from March 1983 through April 1984. The results of this study, together with those of Marcus (1984), show that during the fall and winter periods of 1982–1984 the proportion of eggs of L. aestiva occurring in the surficial sea-bottom sediments declined and the proportion of eggs in the deeper sediment layers increased. High positive correlations (r ²=0.72 and 0.92) were observed during the early fall 1983 between egg abundance and the proportion of the total sediments represented by the mud fraction. During late fall, winter, and early spring 1983–1984, the coefficients of determination were much lower. Physical criteria (e.g. sedimentation and transport characteristics) can be used to accurately predict the distribution and abundance of recently spawned eggs on the sea-bottom.     

Demography and reproductive biology ofMelinna palmata (Ampharetidae: Polychaeta) in Inner Galway Bay on the west coast of Ireland

A high-density population of the polychaeteMelinna palmata Grube was the focus of a two-year study at a shallow-water location in Inner Galway Bay on the west coast of Ireland. Mean densities were highest in the second year of the study following successful recruitment. Size-frequency analysis of population structure (April 1983 to March 1985) revealed the presence of four cohorts, with the 1983 settlement becoming the dominant modal class. Size comparison of this cohort with the 1982 settlement showed that growth rates were lower and mortality higher in the 1983 settlement, which may be related to density dependent intra-specific competition.M. palmata at this location live for 2 to 2.5 yr with a small number surviving to 3 yr of age.M. palmata in Galway Bay is dioecious and has an even sex ratio. Reproductively mature worms were approximately 2 yr old when they first spawned. Spawning took place between May and July, when mature oocytes had a modal size of ca. 290µm. Proliferation of previtellogenic oocytes (ca. 10µm) from the gonads occurred following spawning. Growth over the winter was slow and was followed by a period of rapid growth between March and May, coincident with rising water temperatures. The presence of mature unspawned oocytes, which were resorbed after commencement of new proliferation, was taken as evidence of the species propensity for polytely. However, post-spawning mortality appeared to be high, so that only a small number of individuals survived to spawn the following year. The highest abundance of mature males was encountered between May and August, but lower levels of mature stages were present throughout the year.     

Time-lapse cinematography of feather stars (Echinodermata: Crinoidea) on the Great Barrier Reef,Australia: demonstrations of posture changes,locomotion, spawning and possible predation by fish

Aspects of feather star behavior and ecology were recorded by time-lapse cinematography approximately 1 frame min^-1 on the Great Barrier Reef, Australia over a 1 mo period in 1983. The current regime influenced body postures of most species studied, whether nocturnal or not. Moreover, feather stars of several species crawled on the substratum with their arms; each crawling episode lasted roughly 10 min, and the maximum speed attained was about 1 arm length min^-1. Nocturnal feather stars crawled to their nighttime feeding perches around dusk and crawled back to their daytime hiding places around dawn. Surprisingly, some species of feather stars living on the reef surface both day and night also crawled around at dawn and dusk for reasons that are not known. In the time-lapse films, and individual of Comanthus bennetti (sex undetermined) spawned for about 2 min just after dark on 5 July 1983. Another film showed possible predation on a feather star (Himerometra robustipinna) by a saddled coralfish (Chaetodon ephippium).     

Sexual reproduction in Acropora (Isopora) (Coelenterata: Scleractinia)

In contrast to the seasonal gamete and planula production of Acropora (Isopora) palifera on Heron Island reef (Lat. 23° S), populations on Lizard Island reef (Lat. 14° S), sampled in 1979, 1981 and 1983, and Salamaua and Busama reefs (Lat. 7° S), sampled from 1980 to 1983, planulated year-round. Intensive sampling of colonies at Salamaua and Busama showed that gametes ripened at two-month intervals and that up to six cycles of gametes and larvae could be produced by an individual colony. Gametes of only a portion of the population — usually close to 50% — ripened each month. The Salamaua population, on average, produced fewer and smaller planulae than the Heron Island population during each two-monthly reproductive cycle. Hypotheses correlating the annual periodicity of breeding in marine animals with latitudinal variation of temperature were tested. In general, the time of breeding in A. palifera at Heron Island reef is much more restricted than theories based on latitudinal variations of water temperature would predict. It is hypothesized that, in the near subtropical environment of Heron Island reef, this species has evolved a life-history strategy that limits the amount of energy allocated to reproduction and allocates more energy to growth.     

Paralytic shellfish poisoning due to Pyrodinium bahamense var. compressa in Mati,Davao Oriental,Philippines

On 26 August 1983, a single case of paralytic shellfish-poisoning (PSP) was reported in Davao City, Philippines. The poisoning was traced to ingestion of the green mussel Perna viridis Linnaeus, gathered from Balete Bay, Mati, Davao Oriental. Phytoplankton and zooplankton analyses on 12 October 1983 (47 d later), revealed the presence of the dinoflagellate Pyrodinium bahamense var. compressa, a cause of a series of red tides in the early and middle 1970's in Papua New Guinea, Sabah, and Brunei, and more recently, in Palau, and Western Samar and Leyte, Philippines. The dinoflagellate was not dominant; in fact the enumeration showed greater numbers of Ceratium sp., another dinoflagellate. Quantification of the neurotoxin by the standard mouse assay revealed a very high potency. Mussels collected from a new raft (transplanted in May 1983) had a toxicity of 7 960 mouse units (MU) per 100 g^-1 meat. Those from an old raft (transplanted in May 1982) had a toxicity of 9 620 MU per 100 g^-1 meat.SEAFDEC Contribution No. 145     

Le caryotype d'Aulacomya ater regia (Mollusca: Bivalvia: Mytilidae) des Iles Kerguelen

In 1983, specimens of the antarctic mussel Aulacomya ater regia Powell, 1957 were collected from the Kerguelen Islands and transported alive to the Zoological Station in Villefranche-sur-Mer, France. The chromosome complement of the mussel, as determined from branchial tissue, was found to consist of 13 pairs of chromosomes with terminal or subterminal centromeres. This species differs from the other species of Mytilidae studied up to the present in the number and the morphology of the chromosomes. A. ater regia is also unique among the known bivalves in displaying only terminal or subterminal centromeres.     

Sulfide assimilation by ectosymbionts of the sessile ciliate, <Emphasis Type="Italic">Zoothamnium niveum</Emphasis>

We investigated the constraints on sulfide uptake by bacterial ectosymbionts on the marine peritrich ciliate Zoothamnium niveum by a combination of experimental and numerical methods. Protists with symbionts were collected on large blocks of mangrove-peat. The blocks were placed in a flow cell with flow adjusted to in situ velocity. The water motion around the colonies was then characterized by particle tracking velocimetry. This shows that the feather-shaped colony of Z. niveum generates a unidirectional flow of seawater through the colony with no recirculation. The source of the feeding current was the free-flowing water although the size of the colonies suggests that they live partly submerged in the diffusive boundary layer. We showed that the filtered volume allows Z. niveum to assimilate sufficient sulfide to sustain the symbiosis at a few micromoles per liter in ambient concentration. Numerical modeling shows that sulfide oxidizing bacteria on the surfaces of Z. niveum can sustain 100-times higher sulfide uptake than bacteria on flat surfaces, such as microbial mats. The study demonstrates that the filter feeding zooids of Z. niveum are preadapted to be prime habitats for sulfide oxidizing bacteria due to Z. niveum’s habitat preference and due to the feeding current. Z. niveum is capable of exploiting low concentrations of sulfide in near norm-oxic seawater. This links its otherwise dissimilar habitats and makes it functionally similar to invertebrates with thiotrophic symbionts in filtering organs. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Inbreeding and hermaphroditism in the sessile-brooding bryozoan Celleporella hyalina

This study examined the occurrence and effects of inbreeding in the sessile, colonial hermaphrodite Celleporella hyalina. The results are discussed with regard to theoretical explanations for the prevalence of hermaphroditism in sessile clonal organisms. C. hyalina exhibited inbreeding depression at all stages, including the pre-zygotic. Outcrossing, sib and half-sib matings produced offspring but selfing did not. There was inbreeding depression in embryo production and survival. Inbred colonies showed slower growth and later maturation, with fewer reproductive zooids. The relative numbers of male and female zooids were affected by inbreeding; increased production of males is a sign of stress in C. hyalina. When mated with an outbred non-relative, inbred colonies had lower success both as males and as females in embryo production and offspring survivorship. The low survivorship of embryos fathered by inbred colonies is a clear effect of inbreeding on the F2 generation. These results indicate that C. hyalina is unlikely to inbreed in the wild, supporting the "space-limited" model of hermaphroditism for this species. This study indicates that hermaphroditism, by avoiding much of the cost of sex, can confer optimal reproductive fitness for sessile brooding animals in a space-limited habitat even in the absence of inbreeding.     

Spread ofCyclope neritea (Mollusca: Gastropoda) along the north-eastern Atlantic coasts in relation to oyster culture and to climatic fluctuations

The geographic distribution ofCyclope neritea (Linné) (Mollusca: Gastropoda) along the Atlantic coasts of Portugal, Spain and France is reported. Analysis of information published over the last 90 yr indicates that, since 1983,C. neritea has extended its range northwards from Arcachon Bay along the coast of the Bay of Biscay. The spread of this small gastropod is directly related to the commercial transport of the Pacific cup oyster (Crassostrea gigas Thunberg) to the Atlantic from Mediterranean oyster-culture sites, and to its encountering climatic conditions suitable for its settlement and reproduction in its new habitat. Its transport by human intervention explains the rapid spread ofCyclope neritea during 1983 and 1984, despite its lack of a planktonic stage or of effective natural migration by adults. Climatic conditions in the southern parts of the Bay of Biscay are similar to those of the French Mediterranean lagoons, explaining the easy acclimatization of this eurythermic gastropod. Also, coastal air and sea-surface temperature records over the last two decades (1971–1988) have revealed a slight warming of the southern parts of the Bay of Biscay. This has resulted in a more strongly marked latitudinal thermal gradient along the Bay of Biscay and has furthered survival and reproduction ofCyclope neritea emigrants. A detailed analysis of commercial supplies of cup oysters to the Bay of Biscay from the Mediterranean coast indicates that theC. neritea emigrants undoubtedly originated from the salt-water lagoons of Salse-Leucate and Thau (French Mediterranean coast).