Zooid size parallels contemporaneous oxygen isotopes in a large colony of<Emphasis Type="Italic"> Pentapora foliacea</Emphasis> (Bryozoa)

The relationship between seasonal changes in temperature and the size of zooids within cheilostome bryozoans is explored by comparing zooid size and contemporaneous carbonate mineralogy within a single colony of a perennial species that grew in a highly seasonal environment. Previously published oxygen isotope profile data from two fronds of a large colony of Pentapora foliacea from the Irish Sea record the cyclical patterns related to seasonal changes in temperature experienced by the colony over 3 years of growth. Zooid size data gathered from the same points at which the oxygen isotope data were taken reveal that zooid size and contemporaneous ¹⁸O values covary. These and previously published data show that zooid size profiling can be confidently used to easily estimate rates of growth and longevity of bryozoan colonies, and further illustrate the negative relationship between zooid size and ambient temperature. Some inconsistencies in timing between zooid size and ¹⁸O data may provide insights into the mechanisms behind temperature mediated body size changes in poikilothermic animals.Communicated by P. W. Sammarco, Chauvin     

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.     

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.     

Rate of growth and longevity of a large colony of Pentapora foliacea (Bryozoa) recorded in their oxygen isotope profiles

We studied the growth patterns and the stable oxygen isotopic composition of an individual of Pentapora foliacea (Ellis and Solander 1786) collected on October 6, 1978 from the Bristol Channel, Pembrokeshire, UK, Irish Sea. The stable oxygen isotopes are in equilibrium with the ambient seawater and show a marked seasonal variation reflecting seasonal water temperature changes. The stable oxygen isotopes further suggest that regular growth patterns of less calcified growth bands, which are secreted in winter, are perennial. These winter growth check lines can easily be used to determine longevity of these bryozoa colonies and of annual growth rates. The colony analysed is at least 3-years-old with an annual growth rate of approximately 2 cm per year.     

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 trajectories of corallites and ages of polyps in massive colonies of reef-building corals of the genus Porites

Massive colonies of the reef-building coral genus Porites were collected at inshore, midshelf and shelf-edge reefs in the central section of the Great Barrier Reef in November 1987. These colonies were comprised of 4 species: P. lobata, P. lutea, P. solida and P. mayeri. X-radiographs made of skeletal slices cut from the skeletons displayed the annual density-banding pattern characteristic of massive corals, and appeared to show corallites within each slice. The average age of the 36 colonies was 41±12 yr (mean±SD). The images of corallites displayed by the X-radiographs were not images of actual corallites, but approximated the position and size of actual corallites. Consequently, X-radiographs provide information about the formation and growth trajectories of corallites, and about the history of the polyps which deposited the corallites. Individual corallites were always normal to the growth surface. The growth surface of the colonies became bumpy when they reached 50 to 80 mm in height and, as a result, corallites took on a fan-shaped arrangement within a bump. New corallites were initiated at the summit of each bump and grew upwards and outwards. Thus, growth of colonies resulted in corallites becoming increasingly displaced from the summit of a bump. The X-radiographs showed that corallite growth becomes occluded at the bottom of valleys between adjacent bumps. Corallite growth then stops and the associated polyps are probably resorbed. Annual density banding showed that the average age of polyps in these colonies was 2 to 3 yr, average life expectancy 5 yr, and that no polyp was likely to be older than 8 yr. Small but significant variations in polyp longevity between corals from different reefs were probably associated with significant differences in bumpiness of growth surfaces. Even in Porites colonies which have been growing for several centuries, polyp longevity is likely to be 5 yr.     

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.     

Interpreting seawater temperature range using oxygen isotopes and zooid size variation in Pentapora foliacea (Bryozoa)

This is the first investigation of how two independent proxies for seawater temperature inference (zooid size variation and oxygen isotope ratios of skeletal carbonate) relate to the actual measured ranges of temperature experienced by cheilostome bryozoan colonies. Nine specimens of the bimineralic marine cheilostome bryozoan Pentapora foliacea (Ellis and Solander, 1786) were analysed, collected from ~18-m depth at two localities in Wales, UK—four from Skomer Island (51°42′510″N, 5°13′42.60″W) and five from Porth Ysgaden, Lleyn Peninsula (52°54′6.75″N, 4°38′47.34″W). The annual range of temperature implied by zooid size variability provides a good approximation of the actual range of temperature recorded by a datalogger. However, annual ranges of temperature reconstructed from skeletal oxygen isotope ratios were narrower, typically not showing the lowest temperatures experienced by the colonies. This can be explained by progressive thickening of zooid skeletal walls during the life of the colony that homogenises the temperature signal by time-averaging over the lifetime of the colonies. Our study provides evidence that a combined morphological isotope approach has great potential in the reconstruction of annual ranges in seawater temperatures from historical and fossil bryozoans, particularly for species that lack ontogenetic skeletal wall thickening and bimineralic skeletal composition. As cheilostome bryozoans have been common in benthic communities since the Late Cretaceous, they represent a valuable and underutilised resource for the interpretation of environmental regimes.     

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     

Morphology and growth of the deep-water gorgonians <Emphasis Type="Italic">Primnoa resedaeformis</Emphasis> and <Emphasis Type="Italic">Paragorgia arborea</Emphasis>

The morphology of the gorgonian corals Paragorgia arborea and Primnoa resedaeformis was studied from video records and colonies collected from different locations in Atlantic Canada, at depths between 200 and 600 m. Growth was studied by relating colony height to age (number of growth rings) in P. resedaeformis, and from a photographic time-series of a P. arborea colony in a Norwegian fjord. The highest P. resedaeformis and P. arborea colonies were 86 and 180 cm, respectively. The height of P. arborea seemed to be restricted by the size of the boulder it was attached to. When the coral exceeds a critical height (approximately twice the stone size), the drag of strong currents can turn the coral and its substrate over. No limiting factors for the height of P. resedaeformis colonies were identified. P. arborea occurred in three colour varieties: red, salmon red, and white. The red and white contributed 41% to the population each, while 18% of the colonies were salmon red. On average the salmon red P. arborea were taller than the red and white. P. arborea colonies >50 cm were mainly concave fan shaped. The orientation of these indicated a near-bottom current pattern similar to what is known from previous current measurements in the area. P. resedaeformis occurred mainly on the up-current side of boulders, but its bushy morphology does not indicate influence by unidirectional current to the same degree as P. arborea. The different height, morphology, and position on boulders of the two species indicate that they utilize different food sources. P. resedaeformis seems to be adapted to a near-bottom environment with turbulent currents, whereas P. arborea utilize uni- or bidirectional currents higher above bottom by developing planar colonies perpendicular to the current. The oldest P. resedaeformis colony was 61 years. The relationship between height and age indicated an average growth of 1.7 cm year^–1 for P. resedaeformis. X-ray images of skeletal sections of P. arborea showed clear growth bands with a maximum band width of 1.3 cm. It is not clear what time scales these bands represent, and they could therefore not be used for indicating age. The limited previously reported data on age and growth of P. arborea indicate an average growth rate of 1 cm year^–1. This gives an age of about 180 years for the largest colony in this study. The time-series photographs, however, indicated a much higher growth rate (varying between 2 and 6 cm year^–1 within the colony), which may be more representative for colonies of an intermediate size.Communicated by R.J. Thompson, St. Johns     

A survey of translocation in laminariales (Phaeophyceae)

A survey of translocation of photoassimilates in 13 genera of Laminariales is presented. All showed long-distance transport of ¹⁴C-labeled products from mature source tissue to meristematic sinks (haptera and intercalary growing regions). In plants with several laminae forming one frond, older laminae may provide assimilates for the growth of younger ones, and in Macrocystis spp., where fronds of different ages and developmental stage arise from a common holdfast, mature fronds initiate and support new fronds. Translocation velocities vary from species to species but are in the range of 55 to 570 mm/h. The results strongly support the hypothesis that Laminariales in general have an effective translocation system, on which their thallus growth depends.     

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.     

Growth and production of the red alga Gelidium sesquipedale off the Basque coast (northern Spain)

Several aspects of the growth of the agarophyte Gelidium sesquipedale Clemente (Thuret) were studied in sublittoral populations of the Basque coast (northern Spain) from 1981 to 1986. The standing stock of the populations varied greatly with season. During two consecutive years, 60 to 70% of summer biomass had been lost by the end of the unfavourable period of year to growth (autumn and winter). The decline in biomass was mainly due to partial losses of branches, with more branches being lost from larger fronds. Yearly variations in the standing stock were also recorded. Production estimates obtained by a destructive sampling method were not satisfactory because of the spatial heterogeneity of the populations at the three locations studied. Indirect estimation of production by measuring the growth of marked fronds in a control quadrat gave more reliable estimates. Production values of 622±124, 735±147 and 615±123 g dry wt m^-2 yr^-1 were obtained at the three locations, respectively. Frond elongation rates of 7.5, 6.1, 7.5 and 7.9 cm yr^-1, respectively, were recorded during four consecutive years. In winter elongation rates of fronds were rather low. Elongation did not seem to be affected by frond length, the self-shading effect of the canopy, or changes in depth. Cuts resulting from grazing were frequent on fronds through the year, decreasing significantly with increasing depth. Sheared fronds regenerated promptly, independent of season or height at which the cut was made. For commercial purposes the best season for harvesting is summer, which is the period of maximum standing stock, infertility, and calm warm waters that provide easier working conditions for divers.     

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.     

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.     

Metabolic responses of Azolla pinnata to cadmium stress: photosynthesis,antioxidative system and phytoremediation

This present study deals with the growth, photosynthesis, oxidative stress and phytoremediation character of Azolla pinnata L. exposed to different levels (0.05, 0.1, 0.5, 1.0, 1.5 and 2.0 mg·L^?1) of cadmium (Cd). Significant accumulation of Cd in Azolla fronds was noticed after 24 and 96 h of exposure and the accumulation rate was dose and time dependent. Growth of A. pinnata increased significantly after both exposure times with and without metal. At lower Cd doses (0.05 and 0.1 mg·L^?1), growth and photosynthesis of A. pinnata showed a marginal increase over the respective control, however, at higher Cd doses (0.5, 1.0, 1.5 and 2.0 mg·L^?1), a decreasing trend was noticed. At lower doses, Azolla fronds could counterbalance the negative effect of enhanced levels of superoxide radicals (SOR) and hydrogen peroxide (H₂O₂) through the greater activity of antioxidative enzymes. The decaresing trends in catalase and peroxidase activity at higher Cd doses suggest that Azolla fronds were not able to mitigate the negative effects of H₂O₂, hence an increase in malondialdehyde content was noticed. The study concludes that up to 0.1 ,mg·L^?1 Cd, A. pinnata can flourish and be used as biofertiliser and for phytoremedial purposes in Cd-contaminated fields; beyond this concentration poor growth may restrict its application.     

Dauerknospen (“Hibernacula”) bei den Bryozoa Ctenostomata in mesohalinen und vollmarinen Gewässern

Resting buds have been found in colonies of the ctenostomatous bryozoans Arachnidium cf. hippothooides, Valkeria uva, and Bowerbankia imbricata in mesohaline and marine waters. The development of zooids from the resting buds has been observed in different species. In each species examined, the colour of the resting buds is the same as that of eggs and embryos, probably because of similar reserves. The colour of the reserves may change with the food consumed. Resting bud formation is mainly induced by nutritional insufficiencies. The facts at hand suggest that salinity or temperature variations (within biologically adequate ranges) exert no direct influence on the formation of resting buds. Problems concerning food selection and immigration of bryozoans from the sea into the brackish-limic regions are brieffly discussed.     

Resource translocation in a marine bryozoan: quantification and visualization of 14C and 35S

Colonial marine invertebrates are characterized by their ability to share resources among the modules of a colony. In most colonial groups, but particularly the Bryozoa, the dynamics of resource transport among modules is unknown. We developed radioisotope techniques to visualize and quantify the movement of carbon and sulfur-based compounds within colonies of the marine bryozoan Membranipora membranacea. The research was conducted in 1991 and 1992 in Friday Harbor, Washington, USA. Autoradiography, using X-ray film, was used to visualize the transport of both ¹⁴C and ³⁵S, and a liquid scintillation counter was used to quantify transport of metabolites. We were able to localize feeding by introducing 10 l aliquots of labelled algal cells with a microinjection syringe into a containment ring on the surface of the colony. The labelled cells were consumed by zooids feeding within the ring, but not by those outside. In time-course within the ring, but not by those outside. In time-course experiments, 15% of the ingested carbon radioisotope was transported from a source in the center of the colonies to the growing edges over a period of 48 h. Approximately 10% of the sulfur was transported from central to edge regions of colonies over 72 h. Transport of carbon isotope was unidirectional in all experiments, irrespective of whether colonies were fed near the edge or the center. Pulse-chase experiments revealed that up to 46% of the initial ¹⁴C radioisotope was lost from the colony to respiration and egestion in the 24 h following ingestion.     

Growth and utilization of internal nitrogen reserves by the giant kelp Macrocystis pyrifera in a low-nitrogen environment

An adult giant kelp plant (Macrocystis pyrifera), moved from an inshore kelp forest to an offshore, low-nitrogen environment near Santa Catalina Island, California (USA), maintained growth for 2 wk on internal nitrogen reserves. Frond elongation rates decreased significantly during the third week, and plant growth rate (wet wt) dropped from an initial inshore rate of 3.6 to 0.9% d^-1. During this 3 wk period, nitrogen contents and free amino acid concentrations decreased, while mannitol and dry contents increased in frond tissues. After depletion of internal nitrogen reserves, the nitrogen content of lamina and stipe tissues averaged 1.1 and 0.7% dry wt, respectively. The experimental plant was exposed to higher ambient nitrogen concentrations during the last 2 wk. Rates of frond elongation and plant growth increased, but nitrogen content and amino acids in frond tissues remained low. Of the total nitrogen contained in frond tissue of the plant before transplantation, 58% was used to support growth in the absence of significant external nitrogen supply. Amino acids constituted a small proportion of these internal nitrogen reserves. Net movement of nitrogen occurred within large fronds, but not between different frond size classes. The nitrogen content of holdfast tissue remained relatively constant at 2.4% dry wt and accounted for 18 to 29% of the total nitrogen. Holdfast nitrogen was not used to support growth of nitrogen-depleted fronds. In comparison to Laminaria longicruris, which is adapted to long seasonal periods of low nitrogen availability, M. pyrifera has small nitrogen-storage capacity. However, internal reserves of M. pyrifera appear adequate to make nitrogen starvation uncommon in southern California kelp forests.     

Cephalodiscus sp. (Hemichordata: Pterobranchia): observations of functional morphology,behavior and occurrence in shallow water around Bermuda

A pterobranch hemichordate, Cephalodiscus sp., was collected from Bermuda just below the low-tide mark in July 1983 and again in October through December 1983. This is the third report of this genus in shallow water and the second for the Western Hemisphere. Specimens were observed alive in the laboratory. Colonies consist of zooids at various stages of development arranged in clusters inside a translucent, collagenous coenecium. Cilia-driven currents of the zooids are used in a method of filter-feeding similar to phylactolaemate bryozoans.