Distribution of encrusting bryozoans and other epifauna on the subtidal bivalveChlamys opercularis

The shells of living queen scallops,Chlamys opercularis (L.), are often completely colonised with epifauna. In this study, the distribution of the major epifaunal groups across the surfaces of left (upper) and right (lower) valves is examined using samples from two commercial queen scallop beds off the Isle of Man. The composition of the epifauna differs across and between the valves and also varies with the age of the scallop. YoungerC. opercularis are commonly encrusted by sponges, but on older shells other epifauna colonise the surfaces. The encrusting bryozoan assemblage found on livingC. opercularis is not as abundant or speciose as on some other substrata such as stones and dead shell. This may be a result of intense competition from other phyla. The distribution of different bryozoan species between the surfaces is examined. Most species are more abundant on the lower valves.     

A pelagic bryozoan from Antarctica

Spherical or sub-spherical bryozoan colonies were collected from the surface waters of a coastal polynya in the southeastern Weddell Sea near Halley Station in February 1992. These are the first truly pelagic marine bryozoan colones yet recorded. The collection site is the edge of the Brunt ice shelf, which is between 150 and 250 m thick in this area, and the depth of water to the seabed is -400 m. The colonies were hollow, composed of a single layer of autozooids, and appeared complete and undamaged. They were between 5.0 and 23.0 mm in diameter, were brownish in colour in life, and pale yellowish brown after preservation. Light and scanning electron microscope investigations of the colonies indicated that they belonged to the genus Alcyonidium, and they are here compared with A. flabelliforme Kirkpatrick, a known antarctic benthic species. Both a pelagic existence and hollow spherical colony form are new attributes for the phylum Bryozoa. However, because of the plasticity of form of species belonging to the genus Alcyonidium, these is not enough evidence for the introduction of a new species at this time. The colonies found may represent a previously undescribed juvenile stage of a known Alcyonidium species. It is postulated that these colonies may obtain nutrition from the often abundant populations of ice algae present in the lower layers of permanent sea-ice.     

Spatial and temporal patterns of recuruitment of juvenile coral reef fishes to coral habitats within “One Tree Lagoon”, great barrier reef

Recruitment of juvenile fishes to coral grids, each comprising 4 colonies of 3 species of coral (Acropora formosa, Seriatopora hystrix and Pocillopora damicornis), was examined at 4 widely separated sites within the lagoon of One Tree Reef over two successive summers and intervening months (November 1976–January 1978). Recruitment was highly seasonal, with most recruitment occurring during summer. For many species, numbers settling differed greatly from year to year with total numbers (over all sites) differing as much as an order of magnitude between summers. Many fish species demonstrated marked preference among the three coral species as settling sites. The distribution of each of the 20 commonest species across the 4 lagoon sites differed significantly from a random pattern. Differences of an order of magnitude were common in the numbers of a given species recruited to different sites. Each site was preferred by at least one species. In each of 5 cases examined, the pattern of settlement of the species across the 4 sites changed significantly from one summer to the next. The distribution of recruits of a number of species corresponded to the distribution of adults, but for other species there was no correspondence. It is concluded that, at the spatial scale examined, patterns of recruitment of some taxa are consistently more variable than those of other taxa. The implications of spatial variability of recruitment for the distribution of adult fish is discussed and the importance of being able to discriminate such natural variability from other kinds of change is stressed.     

Response of a soft-bottom harpacticoid community to stingray (Dasyatis sabina) disturbance

The recolonization by harpacticoid copepods of patches disturbed by stingrays [Dasyatis sabina (LeSeur)] feeding in a subtidal (2–3 m depth) site off the Florida gulf coast (Lat. 29°54.55N, Long. 84°31.45W) was followed. Samples from disturbed patches could no longer be distinguished from control samples in terms of numbers of harpacticoids 29 h after disturbance. No species became significantly disproportionately abundant during the recovery suggesting that small-scale natural disturbances are not an important organizing force in this community.     

Ecological and genetic evidence for impaired sexual reproduction and induced clonality in the hydroid<Emphasis Type="Italic"> Sertularia cupressina</Emphasis> (Cnidaria: Hydrozoa) on commercial scallop grounds in Atlantic Canada

Colonial epifauna are vulnerable to the effects of bottom fishing, but impacts on the life histories of these non-target animals have not been examined extensively. Dredging potentially impairs sexual reproduction by invoking regeneration and induces clonality by severing colonies or through the abortion of damaged modules. This study investigated the potential for commercial-scale scallop dredging to alter sexual and asexual (clonal) reproduction in the hydroid Sertularia cupressina. In total, 1,071 colonies from 104 epizoic microhabitats (upper valves of live scallops relatively undisturbed by fishing) and 75 epilithic microhabitats (cobbles more severely disturbed by fishing) were collected from 53 to 94-m depths in the Bay of Fundy (Atlantic Canada). Colony abundance, injury frequency (proportion of colonies with sealed, snapped off stems), percentage of fertile colonies and sexual fecundity (number of gonophores and gonophore dimensions) were measured on all substrata. Ten randomly amplified polymorphic DNA (RAPD) primers were used to estimate clonal diversity. Field experiments found no significant effect of microhabitat differences between scallop and cobble substrata on fecundity and clonality in S. cupressina, while experimentally-induced injuries suppressed the percent of fertile colonies. On the fishing grounds, colonies on scallop valves were more abundant and sexually fertile than their counterparts on cobble, and all were sexually derived. In contrast, colonies on cobbles had a greater percentage of injury, were less fertile and were frequently clonally-derived. Impacts of fishing-related injuries on reproduction in colonial epifauna have been overlooked, yet the long-term consequences of such impacts could result in reduced adaptability, recruitment and recovery potential of these and dependent organisms.Communicated by R.J. Thompson, St. Johns     

Biochemical composition,energy content and chemical antifeedant and antifoulant defenses of the colonial Antarctic ascidian<Emphasis Type="Italic"> Distaplia cylindrica</Emphasis>

The colonial ascidian Distaplia cylindrica occurs both as scattered individual colonies or in gardens of colonies in fine-grained soft substrata below 20 m depths off Anvers Island along the Antarctic Peninsula. Individual colonies, shaped as tall rod-like cylinders and anchored in the sediments by a bulbous base, may measure up to 7 m in height. D. cylindrica represent a considerable source of materials and energy for prospective predators, as well as potential surface area for fouling organisms. Nonetheless, qualitative in situ observations provided no evidence of predation by sympatric predators such as abundant sea stars, nor obvious biofouling of colony surfaces. Mean energy content of whole-colony tissue of D. cylindrica was relatively high for an ascidian (14.7 kJ g^–1 dry wt), with most of this energy attributable to protein (12.7 kJ g^–1 dry wt). The sympatric omnivorous sea star Odontaster validus consistently rejected pieces of D. cylindrica colonies in laboratory feeding assays, while readily ingesting similarly sized alginate food pellets. Feeding deterrence was determined to be attributable to defensive chemistry, as colonies of D. cylindrica are nutritionally attractive and lack physical protection (conspicuous skeletal elements or a tough outer tunic), and O. validus display significant feeding-deterrent responses to alginate food pellets containing tissue-level concentrations of organic extracts. In addition, high acidity measured on outer colony surfaces (pH 1.5) as well as homogenized whole-colony tissues (pH 2.5) are indicative of surface sequestration of inorganic acids. Agar food pellets prepared at tissue levels of acidity resulted in significant feeding deterrence in sea stars. Thus, both inorganic acids and secondary metabolites contribute to chemical feeding defenses. D. cylindrica also possesses potent antifoulant secondary metabolites. Tissue-level concentrations of hydrophilic and lipophilic extracts caused significant mortality in a sympatric pennate diatom. Chemical feeding deterrents and antifoulants are likely to contribute to the abundance of D. cylindrica and, in turn, play a role in regulating energy transfer and community structure in benthic marine environments surrounding Antarctica.Communicated by P.W. Sammarco, Chauvin     

The enantiomeric composition of monoterpene hydrocarbons in the defensive secretions ofNasutitermes termites (Isoptera): Inter- and intraspecific variations

Summary Frontal gland secretions of termite soldiers of the speciesNasutitermes costalis, N. ephratae, N. nigriceps, N. rippertii, andN. hubbardii were analyzed. The chiral compositions of the monoterpene hydrocarbons were investigated by means of two-dimensional gas chromatography. Two of them, 3-carene and-pinene were present in the form of (–)-enantiomers of high purity in the majority of the samples. The other monoterpenes,-pinene, camphene, sabinene, limonene, and-phellandrene, exhibited a great variation in the enantiopurity between different species.-Pinene and limonene varied significantly even between different colonies within the species.N. costalis was the only species with an invariable composition of the secretion, independent of the locality or origin.     

The adaptive significance of male polymorphism in the acarid mite Caloglyphus berlesei

Summary Two forms of males occur in the acarid mite, Caloglyphus berlesei. One of them uses its thickened third pair of legs to kill other males; the other, without modified legs, does not attack other males. Previous studies have shown that the form of the male is environmentally determined: fighter males develop only at low population densities and their development can be suppressed by substances emanating from dense colonies. In this study, the duration of development, longevity and virility of the two male morphs were measured. The only significant difference was that fighters had a shorter development time between the two last moults. In another experiment, two groups of colonies were maintained under the same conditions but had different numbers of individuals: small colonies contained 2 fighters and 2 non-fighters, whereas large colonies contained 30 males of each type. The relative reproductive success of both morphs was estimated from numbers of matings. In small colonies, the estimated reproductive success (ERS) was significantly higher for fighters than for non-fighters, mainly because in over 50% of these colonies a single fighter male managed to kill all the rival males and monopolize the females. The opposite was true in large colonies, in which non-fighters achieved significantly higher ERS, mainly because the fighters were killed in fights more often than the non-fighters. This implies that the ratio of costs to benefits obtained by adopting the fighter-male strategy increases with the number of rival males, which may explain conditional male development in C. berlesei.     

Predation on zooplankton by the benthic anthozoans Alcyonium siderium (Alcyonacea) and Metridium senile (Actiniaria) in the New England subtidal

The Alcyonacean octocoral Alcyonium siderium Verrill and the sea anemone Metridium senile (L.), the only common perennial zooplanktivores on shallow (16-m depth) subtidal rock walls in much of northern New England, USA, are of similar heights and overlap in their habitat and microhabit distributions. The coelenteron contents of both species were sampled at four-hour intervals over a diel cycle and were compared to zooplankton available in the water at 1 to 5 cm from the rock wall, the height at which the cnidarians held their feeding tentacles. Prey in coelenterons of A. siderium were significantly smaller (means of 256 to 345 m), and those in coelenterons of M. senile were equal to or slightly greater in length (means of 415 to 1006 m) than the available zooplankton. The diets of A. siderium and M. senile differed significantly from each other and from the available zooplankton. A. siderium showed strong positive electivites for ascidian larvae and for foraminiferans, and strongly negative electivities for most crustaceans. M. senile had strong positive electivities for barnacle cyprids, ascidian larvae, and gammarid amphipods, and strong negative electivities for invertebrate eggs, foraminiferans, calanoid and harpacticoid copepods, and ostracods. Electivities may reflect tentacle avoidance or escape by motile prey as well as predator preference. Substratum-associated organisms (e.g. demersal crustaceans, larvae of benthic invertebrates) were the most common items in the diets of both species, suggesting a tight benthic food web, similar to the situation for coral reef anthrozoans which rely on reef-generated zooplankton. A. siderium ate large numbers of ascidian larvae which, as benthic adults, compete for space with A. siderium and can overgrow small colonies. Predation on the larvae of a competing species may alleviate competition by decreasing the competitor's recruitment.     

A new method for detecting pollution effects on marine macrobenthic communities

A method is described by which the pollution status of a marine macrobenthic community may be assessed without reference to a temporal or spatial series of control samples. Theoretical considerations suggest that the distribution of numbers of individuals among species should behave differently from the distribution of biomass among species when influenced by pollution-induced disturbance. Combined k-dominance plots for species biomass and numbers take three possible forms representing unpolluted, moderately polluted and grossly polluted conditions, one curve acting as an internal control against which the other can be compared. Field data from unpolluted communities and from a well documented temporal pollution gradient support the model, but further empirical testing is required.     

Influence of phosphate depletion on the growth and colony formation of Phaeocystis pouchetii

The haptophycean alga Phaeocystis pouchetii (Hariot) Lagerheim, a bloom-forming species in the North Sea, formed massive colonies in batch cultures only when the phosphate concentration in the medium was below 1 mol l^-1. In general, colony cells and single cells showed a similar response to phosphate depletion: decreased cellular phosphate (up to a factor of 32), decreased chlorophyll-a concentration (up to a factor of 4.2) and high activities of alkaline phosphatase (APA). However, the growth rate of colony cells was reduced at low phosphate concentrations (<1 mol l^-1) in contrast to that of single cells. Colony cells tended to have a slightly higher phosphate concentration than single cells, while the increase in APA was delayed. The differences between single cells and colonies in phosphate utilization, cellular phosphate content, and growth rate cause, at low phosphate levels, a shift towards the formation of colonies. Similar changes seem to occur in nature during transition of nutrient-sufficient to nutrientlimited conditions.This investigation was supported by the Foundation for Fundamental Biological Research (BION), which is subsidized by the Dutch Organization for the Advancement of Pure Research (ZWO). Publication No. 8 of the project Ecological Research of the North Sea (EON)     

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.     

Behavioral ecology of the neotropical termite-hunting ant Pachycondyla (= Termitopone) marginata: colony founding,group-raiding and migratory patterns

This study provides the first detailed field account of colony founding, group-raiding and migratory habits in the neotropical termite-hunting ant rPachycondyla marginata, in a semi-deciduous forest in south-east Brazil. New colonies can originate by haplometrosis, pleometrosis, or colony fission. Incipient colonies with multiple foundresses persisted longer in the field, and most excavated nests contained more than one dealated female. A total of 202 group raids by P. marginata were registered, and in all cases the raided termite species was Neocapritermes opacus. Nearly 20% of the workers within a colony engage with raiding activity. Colonies of P. marginata hunt for termites approximately every 2–3 weeks, and group-raids may last for more than 24 h. Target termite nests are up to 38 m from the ant colony, and occasionally two nests are simultaneously raided by one ant colony. Raiding ants carry 1 or 2 paralysed prey, and nearly 1600 termites can be captured during a 9-h raid. Migration by P. marginata colonies lasted over 2 days and covered distances of 2-97 m (n = 48). Average residence time at a given location was 150 days. Three basic migratory patterns were noted: colony fission (only part of the colony moves), long-distance migrations, and short-distance migrations. Both raiding and migratory activities appeared to be strongly affected by seasonal factors. The group raiding and migratory patterns of P. marginata are compared with other ant taxa with similar habits. It is concluded that P. marginata presents a rudimentary form of the so-called army ant behavior, which is highly developed in the subfamilies Dorylinae and Ecitoninae. The extremely specialized diet of P. marginata and the associated high costs of migration are features likely to prevent it from evolving a full army ant life pattern.     

Genetic variation and biochemical systematics in the marine bryozoan Alcyonidium mytili

For many years the taxonomic position of the marine ctenostome bryozoan Alcyonidium mytili Dalyell (1848) has been in doubt, with some authorities regarding it as being conspecific with A. polyoum (Hassall). We have set out to resolve this problem using enzyme electrophoresis to examine the genetics of the population structure in the two species. The results show beyond reasonable doubt that sympatric populations of the two species are indeed from quite separate and non-interbreeding gene pools. An examination of various allopatric populations shows a new species of A. mytili to exist sympatrically with the other at Langstone Harbour, Hampshire, England. This species can be readily distinguished on morphological as well as genetic ground. Samples of A. mytili from Guernsey also show substantial genetic differences from other populations examined. It is tentatively concluded that this population also represents a separate gene pool and consequently should be recognised as a third species of A. mytili.     

Temporal and spatial components of variability in benthic recruitment,a 5-year temperate example

Deployment of artificial substrata is a common method of investigating early community development and recruitment, but rarely are such experiments of long enough duration to include even year time scales. We placed replicate, machined-slate panels (15×15 cm) in the intertidal and at depths of 6 and 12 m at two sites of differing flow rate at Lough Hyne, SW Ireland. These were serially replaced every 30–60 days for a period of 5 years (1997–2002), except in the intertidal (2000–2002). The number and identity of all recruits were recorded. Recruitment varied over several orders of magnitude both on temporal and spatial scales. The greatest source of variability was between the intertidal (with few species or recruit numbers) and the subtidal zones (many species, some with thousands of recruits per panel per 30 days). Highest levels of recruitment occurred at the low-flow site (Labhra Cliff). Here, recruitment was dominated by the serpulid polychaete, Pomatoceros sp., reaching ~4000 individuals per panel per 30 days. Highest species richness occurred, however, at the high flow site (Whirlpool Cliff). At this site more colonial forms (e.g. bryozoans) settled. Season was found to be the dominant pattern explaining subtidal recruit and species number variability. Year, however, was the dominant temporal pattern explaining change in diversity (Shannon–Wiener H). In space, depth explained most variability of recruit numbers, whereas site explained more variation in species richness. Both these spatial factors contributed similarly to variability of diversity (H). Recruitment has long been known to vary considerably over large spatial scales, such as with latitude and isolation, but we that show changes of a similar magnitude in recruitment can occur across small spatial scales. Individual taxa showed varied temporal patterns of recruitment including continuous, regular seasonal fluctuations and irregular pulses in particular years.     

Interspecific aggression in colonies of the slave-making ant Harpagoxenus sublaevis

Colonies of the slave-making ant, Harpagoxenus sublaevis, may simultaneously contain workers of several Leptothorax slave species. We observed aggressive interactions among slave-makers, between slavemakers and slaves, and among slaves in 11 mixed colonies. The first two types of aggression appear to be correlated with reproductive competition for the production of males. Aggressive interactions among slaves, however, occurred mainly between slaves belonging to different species. In two colonies, in which one slave species clearly outnumbered the other, the majority attacked and finally expelled all nestmates belonging to the minority species. Our observations thus suggest that in Harpagoxenus colonies a homogeneous colony odor is not always achieved and that heterospecific slaves may occasionally be mistaken for alien ants. Gas chromatographic analyses of ants from mixed colonies similarly show that cuticular hydrocarbon profiles may differ strongly between heterospecific nestmate slaves.     

In-situ studies on the life cycle of Diastylis rathkei (Cumacea: Crustacea)

Aspects of the life cycle of the cumacean Diastylis rathkei Kröyer, the most important food item of demersal fishes in the Western Baltic Sea, were investigated from the Underwater Laboratory (UWL) Helgoland in Lübeck Bay. In August the population density was 10.1±3.6 individuals 100 cm^-2 in fine-medium sand (Md=292 m), and 3.6±2.4 individuals in coarser medium sand (Md=470 m). In both substrata, abundance values decreased until October, at each station to a different extent. Particular attention was paid to vertical migrations of D. rathkei. Plankton catches and numerous direct observations provided evidence that the pelagic phase, observed at night, is always combined with ecdysis. During short periods of high swarming and moulting activities, the population structure changed considerably: juveniles of the 3rd stage dominated in early August; thereafter they were replaced by prematures, the last juvenile stage. The first mature individuals were observed in October. Some data are given on growth rate.     

Effects of temperature,size, and food on the growth of <Emphasis Type="Italic">Membranipora membranacea</Emphasis> in laboratory and field studies

In the rocky subtidal ecosystem of the western North Atlantic outbreaks of the introduced epiphytic bryozoan Membranipora membranacea cause defoliation of kelp beds and facilitate the introduction of other non-native benthic species. We quantified size- and temperature-dependent growth rates of M. membranacea colonies in the field and the laboratory for durations of 8–23 days. Also, we examined the interaction between food abundance and temperature on growth rates of newly settled colonies in the laboratory. Growth rates were positively related to temperature and increased exponentially with size of colonies over the ranges examined (5.7–16.2°C and 0.5–192 mm, respectively), and were significantly higher in the field than in the laboratory. There was an interactive effect between food and temperature on the size and growth rates of colonies, with the most pronounced effects of food limitation on colonies grown at the warmest temperatures, and no effect of food on colonies grown at the coldest temperatures. Quantifying the growth rates of introduced species is essential to understanding their population dynamics, particularly when outbreaks can have severe impacts on the native community.     

Spirorbinae (Serpulidae: Polychaeta) from South Africa,including three new species

Five Antarctic or south-temperate species of Spirorbiaae are centred in south-west Africa, whilst 6 tropical species extend round the south-east and another 4 are recorded from Mozambique. Of the three new species, Pileolaria (Pileolaria) annectans sp. n. has a rudimentary opercular plate surmounting a sort-walled sac of embryos, which somewhat resembles a thoracic brood pouch. Pileolaria (Pileolaria) dayi sp. n. has a helmet-like brood chamber, but this opens distally, like the brood cups found in the subgenus Duplicaria. Janua Pil-natalensis sp. n. has the dorsal collar folds usually separate, but partially fused in some juveniles.     

Effects of water-body characteristics other than temperature and salinity on respiration in Euphausia pacifica

Ample evidence exists that many planktonic species are limited in their distribution to a given water mass. It has been suggested that the temperature-salinity values which define a given water mass are in themselves limiting these species' distribution. Other workers have suggested that other unique properties of a water mass may be involved. Euphausia pacifica is distributed throughout the Pacific subarctic water mass; its distribution also extends into British Columbia coastal waters. Experiments have shown that E. pacifica can withstand temperature changes of up to 15 C°; it can also withstand salinity changes of up to 10. Coastal E. pacifica appear to be able to better withstand stress from changes in temperature and salinity in water from some sources than in water from others. These differences are thought to result from differences in the past history of the water in question.Contribution No. 75008 from the Bigelow Laboratory for Ocean Sciences.