The morphology and infraciliature of a population of Pseudokeronopsis flava, a yellow-coloured ciliate collected from the coastal water near Zhanjiang, South China are investigated and described. Based on previous and present studies, an improved diagnosis is supplied: yellow to yellow-brown coloured marine Pseudokeronopsis, in vivo 140–350×30–50 μm with flexible and slender body; bicorona comprising about five pairs of frontal cirri; one buccal, 2–3 frontoterminal and 2–4 transverse cirri; midventral rows consisting of ≈30 pairs of cirri, which terminate subcaudally above the inconspicuous transverse cirri; about 50 adoral membranelles; left and right marginal rows separated at posterior end; 3–4 dorsal kineties; colourless, blood-cell-shaped cortical granules ellipsoid in shape, distributed over whole cell while yellow to yellow-brownish pigments positioned in a P. rubra-pattern; contractile vacuole positioned in posterior 1/4–1/5 of body; numerous macronuclear segments.

The trophic interactions between primary consumers and the organic matter sources in a man-made intertidal ecosystem were investigated. The most representative invertebrates that occupied the different habitat types tend to use similar food sources, namely benthic diatoms and suspended particulate or sedimentary organic matter, although they do so in different proportions. Fucus vesiculosus was abundant on the rocky substrate but this macroalga nor its epiphytes contributed importantly to the diet of the primary consumers inhabiting these assemblages. In contrast, benthic diatoms from the nearby mudflat were directly used as a food source because of their re-suspension in the water and transport by the tide to the artificial rocky shore. The results suggested that the trophic pathways in this intertidal environment were relatively simple.

A new genus and species of sabellid polychaete from an organically enriched beach in São Sebastião, State of São Paulo, is described. Kirkia heterobranchiata is unique among sabellids for brooding the embryos on the dorsalmost pair of radioles, which exhibits several modifications for this purpose, rather than on ventral radioles. Morphologically, K. heterobranchiata is most closely related to Perkinsiana riwo, here referred to as the new genus, as suggested by phylogenetic analysis. The new genus is characterized by the shape of the lips (dorsal lips roughly triangular, broader than long; ventral lips lower, ventrally fused and distally rounded), by the absence of both radiolar and pinnular appendages, by having uncini with very short handles in both the thorax and abdomen, and by the ability to brood embryos in cocoons attached to the branchial crown.

The population dynamics in the coastal bacterioplankton community off Plymouth (UK) was studied in samples proportionally diluted (99%, 90%, 66% and 0%) with sterile seawater, incubated in the dark for 2–4 days and monitored by flow cytometry. Nucleic acid content of cells, stained with SYBR Green I DNA specific dye, was used as an index of a genome size. Using flow sorting and fluorescence in situ hybridization (FISH) with a set of ribosomal RNA targeted oligonucleotide probes, the phylogenetic composition of dominant cytometric groups of bacterioplankton was determined to be similar during growth in the dilution series. The proportion of the low nucleic acid (LNA) group decreased and correspondingly the high nucleic acid (HNA) groups increased with dilution. The assimilation rates of free amino acids, a highly labile nutrient pool, were determined by flow sorting the dominant groups after short incubations with 35S-methionine tracer. The relative cellular amino acid assimilation by the LNA cells increased with dilution, while the activity of the HNA cells either decreased or remained unchanged. However, highly metabolically active LNA bacteria were overgrown by the HNA bacteria, presumably because the small genome size—an adaptation to living in an oligotrophic environment—did not allow the LNA group to grow sufficiently fast to compete with the HNA group under experimentally reduced grazing pressure. To examine the experimental results a numerical model of bacterioplankton population dynamics was formulated based on the hypothesis that the LNA cells consume only a labile fraction of organic nutrients (amino acids etc.), while the HNA cells feed on both the labile and more refractory sources of nutrients, and that in the absence of phytoplankton the labile source of nutrients is produced entirely by the bacterivorous flagellates. The model simulations gave credence to the hypothesized primary dependence of the LNA group on labile organic nutrients recycled within the microbial loop.

The long term effects of macroalgal canopy removal on community composition were investigated over a 12 year period. Experimental removal of the dominant Ascophyllum nodosum canopy led to short term changes in community composition, the major features of which were still apparent 12 years later. Ascophyllum was slow to recover despite high recruitment, and experimental plots were dominated by Fucus species. After 12 years a mixed assemblage of Fucus serratus, Fucus vesiculosus and Ascophyllum had developed. Canopy removal resulted in a change in the balance between grazing limpets and the cover of red algal turf in the understorey community. The cover of turfing algae declined significantly allowing the area grazed by limpets to extend. This led to a 3–6 fold increase in the limpet population 12 years after canopy removal.

Changes in O2 concentration were measured during in situ incubation of whole, young Laminaria hyperborea and used to evaluate primary production and respiration over a 3-y period (1995–1998). The exudation of dissolved organic carbon (DOC) during incubation was also measured. Total carbohydrates and polyphenols in the exudates and the regional seawater were determined and fractionated into low molecular weight (LMW) and high molecular weight (HMW) species.  Net production rates varied significantly, being highest during the growth phase (March), while respiration rates did not vary significantly. The exudation rates correlated with the plant strategy of growth and production in which high requirements for growth led to a lower proportion of fixed carbon being exuded. More fixed carbon was exuded during the non-growth phase. The annual exudation of DOC is estimated to be ∼26% of fixed carbon and amounts to ∼1·29 kgC m−2 y−1. The annual amount of carbon retained by the kelp (the difference between fixed and exuded carbon), assumed to contribute to growth, corresponds to a biomass increase of 3·0 kgC m−2 y−1, a value similar to those reported using direct measurements of biomass increase in the region.  Carbohydrate concentrations in the exudates were lower during March than in other months, in accordance with the plant growth strategy. Phenols, on the other hand, which are assumed to function as predator deterrent, showed no significant variations in the exudate. The fraction is dominated by carbohydrates while phenols occurred mainly in the LMW fractions.

Male Chondracanthus lophii was studied using light and electron microscopy. Observations on external morphology and internal anatomy are presented. Males possess a full set of functional mouth parts, the digestive system is active and the dominant cell type in the midgut is identified as the vacuolar type B-cell, but the gut is a blind ending sac with no anus. The gut contents were a homogenous, amorphous mass. The combination of active feeding and digestion with a blind ending gut supports the inference that males feed on special secretions produced by glands in the nuptial organs of the female. It is speculated that dependence on such secretion reduces or eliminates the production of faecal matter. Observations on the reproductive system confirmed the typical chondracanthid pattern.

Two species of the genus Schizotricha new to science (Schizotricha crassa sp. nov. and S. southgeorgiae sp. nov.) have been studied. Both species are described and figured and their systematic position amongst the remaining species of the genus is discussed. The material was collected during the United States Antarctic Research Programme (USARP) with RV ‘Eltanin’ and RV ‘Islas Orcadas’. A comparative table listing the main features and distribution of the known species of Schizotricha, together with an identification key, are presented.

A new genus of marine, interstitial schizorhynch (Platyhelminthes: Kalyptorhynchia) is described from sediment collected in Mosquito Lagoon and Indian River Lagoon, Florida, USA. Smithsoniarhynches is characterized by the presence of proboscis hooks constructed of ten individual spine-like teeth that emerge separately from a basal plate. Histology and confocal laser scanning microscopy are used to reveal additional details of the proboscis musculature and reproductive anatomy. The type species, Smithsoniarhynches sherryreedae sp. nov., is characterized by well-developed proboscis pads, four pairs of proboscis retractor muscles, and a pharynx in the midbody region. The male reproductive system consists of an anterior testis, muscular seminal vesicle, copulatory bulb lined with spiral and circular muscles, and a sclerotic stylet. The female system consists of an unpaired vitellarium, ovary, uterus and bursa. The bursa tissue surrounds a muscular bursa seminalis with distinct sphincter muscles. The new genus is compared with the known 11 genera within the Gnathorhynchidae to establish a tentative hypothesis of relationships.

Crab-baited traps, with a 5-mm diameter opening, were deployed 90 mm off the seabed monthly at Lobster Bay, Hong Kong, for one year between 1998 and 1999. Visitors drawn to the traps were mainly species of Ceradocus (Gammaridea: Melitidae), Tisbe (Harpacticoida: Tisbidae) and Nebalia (Leptostraca: Nebaliacea). Apart from Ceradocus sp., all were scavengers with catches using baited traps significantly exceeding unbaited controls. Ceradocus sp. was apparently drawn to traps for refuge. The trapped scavenger community composition changed with deployment duration in the presence of bait. Nebalia sp., Neanthes cricognatha (Polychaeta: Nereidae) and Lepedepecreum sp. (Gammaridea: Lysianassoidea) were identified mostly two/three-days post-deployment, exhibiting a potential preference for rotten organic matter. Seasonal catches were also identified for all three visitors with maxima between October 1998 and April 1999. Such seasonal patterns might be related to either turbulence destabilizing the substratum during this period or life cycle patterns in the study area.

The population biology and habitat of Haliclystus auricula was studied from samples taken every two months in southern Chile between November 2001 and November 2002. A total of 3790 medusae were collected and examined. The abundance of H. auricula varied seasonally. Maximum densities occurred in summer (1405/m2) and minimum densities during the winter, when the population gradually disappeared. Gonads were observed in medusae starting from a size of 2·0 mm. Stauromedusae were found most often on the red filamentous alga Ceramium rubrum (69%), followed by Gymnogongrus furcellatus (12%) and Ulva sp. (10%). There were highly significant differences in mean abundance of medusae on these three algae (P<0·05). The remaining 9% of medusae were found on other seaweeds. The smallest medusae (0·08–0·9 mm umbrella height) were found exclusively on C. rubrum. The highest densities were recorded in the midlittoral zone.

The near-bottom mesozooplankton was caught by a four net suprabenthic sledge on six sites in the English Channel during both spring and autumn. Taxa richness showed no significant difference between seasons, nevertheless diversity (H′), evenness (J) and normalized rarefaction number of taxa E(S91) were higher in autumn than in spring at each site except at Site 2 offshore Plymouth, where Calanus helgolandicus dominated at both seasons. Copepods dominated in abundance at each site in spring while crustacean larvae were dominant in autumn except at Site 2 offshore Plymouth, where copepods remained dominant and, at Site 6 in the Dover Strait, where no significant difference occurred between copepod and crustacean larvae abundances. Four assemblages were distinguished depending on the season. Abundance was higher during the day than at night as a result of a mesozooplankton concentration in the near-bottom layer during the daytime. Moreover, three vertical patterns of suprabenthic mesozooplankton were identified according to their distribution above the near-bottom layer: taxa distributed homogeneously in the four nets; taxa concentrated in nets 2 and 4, and taxa concentrated in the three upper nets.

The occurrence of morpho-chronological variations was demonstrated in three Australian species of phanerogams, Posidonia australis, Posidonia coriacea and Posidonia sinuosa, which are found living around Rottnest Island (Western Australia). Three chronological parameters were identified: the thickness of dead sheaths, the internodal distance and the regular presence of floral stalk remains. The foliar primary production for these three species, as estimated using the lepidochronology method, is very high since values of 1374, 1811 and 678 mg dw shoot−1 y−1 were recorded, respectively. Rhizome production values range from 70·6 and 376·7 mg dw shoot−1 y−1 for Posidonia coriacea and Posidonia australis respectively. The results obtained are very encouraging and confirm that these morpho-chronological variations are particularly well developed for the genus Posidonia.

This paper describes a new species, genus, and subfamily within the Scyphomedusae. Stellamedusa ventana is a relatively large scyphomedusa that reaches up to 9·4 cm in diameter. The medusa is rare, with only seven observations in over a decade of extensive surveys of the Monterey Bay and Sea of Cortez using remotely operated vehicles. Stellamedusa ventana continues the trend found in several other deep-sea semaeostome medusae in lacking marginal tentacles. The exumbrella and oral arms are covered with large nematocyst laden projections which are able to capture food items of various sizes in the laboratory. A large cydippid ctenophore was found in the gut of one captured specimen.

Structural adaptations of the mouthparts and digestive tract of four talitrid amphipods were examined in relation to diet, habitat and phylogeny. The species differed in their habitat relative to the shoreline and also in their diet: a 5-dentate ‘sandrunner’, Talorchestia species II (a mid to low shore intertidal diatom feeder), a 5-dentate sandhopper, Talorchestia marmorata (a strandline kelp feeder); a 4-dentate sandhopper, Talorchestia species I (extreme high shore, feeding on spinifex grasses), and a 4-dentate landhopper, Keratroides vulgaris (forest leaf litter, litter feeding). Gross structural characteristics of the mouthparts were similar among all three Talorchestia species reflecting their phylogenetic relatedness. Increased setation and minor structural differences among the Talorchestia species could be attributed to dietary differences, reflecting the zones across the shoreline that they inhabit. Mouthparts of K. vulgaris were elongate, with markedly different setation to the Talorchestia species, reflecting its more distant phylogenetic position and its diet of decaying leaf litter. Digestive tract structure was more conserved among all species due to their phylogenetic relatedness. The gross digestive structure conformed to the general plan exhibited by most gammaridean amphipods. However, an additional pair of lateral pyloric caeca was evident in all species, the function of which is uncertain.

A study was initiated to identify trematode patterns in Cyathura from two key sites in the Mondego Estuary: a Zostera-bed and a sand flat. The two subpopulations of Cyathura differ, as the annual recruitment success is much higher and more regular on the sandflat than on the Zostera-bed.

Counting and sizing of trematode cysts inside the body of preserved Cyathura specimens enabled a description of trematode patterns in space and time. Further identification of trematodes was based on DNA studies of unpreserved cysts as well as on identification of parasites in co-occurring mud snails. Two trematode species dominated in Cyathura: Maritrema subdolum (cysts around 190 μm) and a hitherto unknown Levinseniella species (cysts around 340 μm), the latter being the most frequent one. Generally, the prevalence of both species peaked during winter months, when migratory water birds occur in the estuary. Cyathura from the Zostera bed harboured more infections per specimen than those from the sand flat. A much higher density of mud snails ≥52 mm (which can be host to microphallids) and a low abundance of Cyathura are thought to be the main reasons for this pattern. Field data did indicate a host size-dependent maximum number of cysts in Cyathura that could be a result of enhanced mortality at high cyst intensities. Furthermore, parasites were underrepresented among ovigerous Cyathura specimens, suggesting a negative impact on gametogenesis. As a consequence, microphallid trematodes may be a critical factor controlling recruitment strength in Cyathura, especially at the Zostera-site.

The diet of Haliclystus auricula was studied from the gut contents of Stauromedusae collected every two months in southern Chile between November 2001 and November 2002. A total of 3790 medusae were collected and examined. Stauromedusae prey consisted primarily of harpacticoid copepods (68·4%), followed by gammarid amphipods (15·4%), chironomid fly larvae (9·2%) and podocopid ostracods (5·9%). The remaining 1·1% of the diet was made up of empidid fly larvae, polychaete worms, isopods, juvenile decapod crustaceans and gastropods. Gut content was observed in 31% of the stauromedusae collected and only in medusae with an umbrella height greater than 0·4 mm. Frequency of medusae with prey items in their gut content increased with stauromedusae size. The type of prey most frequently found in the smallest medusae were copepods, whilst larger individuals contained mainly amphipods. A strong tendency for the length of prey consumed to increase with medusae size was found.

Meiobenthic community structure was investigated at different spatial scales (from 100 metres to centimetres) on and adjacent to a group of coral-topped sandy mounds in the bathyal north-east Atlantic (Darwin Mounds, Rockall Trough) and related to the environmental conditions in the area, mainly differences in sediment organic carbon content and presence of biogenic structures. Meiobenthos abundances were similar to those observed in other deep-sea sites, with nematodes representing at least 94% of the total community. The dominant nematode genera were Microlaimus, followed by Sabatieria, Richtersia, Rhynchonema and Trefusia, together with typical deep-sea genera (e.g. Halalaimus and Acantholaimus). Multivariate analysis of nematode generic relative abundances at the different stations indicated that there was no significant influence on distribution resulting from large scale topographic and biogeochemical conditions around the mounds. The same genera were associated with dead tests of the xenophyophore Syringammina fragilissima and in the surrounding sediments. The vertical distribution of nematodes on and adjacent to the mound showed some unusual features, as the deeper layers of the sediments were inhabited by stilbonematids. These genera harbour ectosymbiotic, chemoautotrophic bacteria and have not previously been recorded from the deep sea. The occurrence of stilbonematids in notable numbers in the subsurface layers of the sediments in the vicinity of the Darwin Mounds provides evidence for the occurrence of anoxic microenvironments.

We evaluated experimentally whether distance between patches of the brown alga Sargassum stenophyllum relative to the source of colonizers influenced colonization patterns by (1) mobile epifauna and (2) gammarid amphipods with distinct life habits. Amphipods were the dominant group, commonly dispersing to patches up to 8 m distant from the algal bed, with low densities of other faunal groups. Assemblage structure of both faunal groups and gammarid amphipods on defaunated algae generally converged to that of controls during the experiments in less than eight days. Gammarid amphipods were dominated by tube-dwellers, but free-living nestlers also colonized the available substrate, and both reached control densities during the study. The same pattern was observed for representative species within each group. Colonization rates were related to faunal densities on the algal bed for most groups, suggesting that mobile organisms disperse more to new habitat patches in high density conditions. Thus, species with direct development can rapidly establish new aggregations at favourable sites, and contribute to small-scale heterogeneity in faunal distribution.

Aricidea (Allia) pisanoi sp. nov. (Annelida: Polychaeta), is described from southern Chile. The new species was recorded from the Strait of Magellan (52°S) south to the continental slope of the Drake Passage (56°S). This new species is distinguishable from other species of the subgenus by only having capillary setae on postbranchial segments.