Littorina obtusata is an epiphytic gastropod which lives for three to four years on its host Ascophyllum nodosum, a long-lived brown alga. Most of the population consists of adults, present throughout the year in the size range 14 to 17 mm. Newly hatched individuals appear between April and October with a peak in July; the immature winkles grow to merge with the adult cohort in May.

In contrast Littorina mariae is an annual; newly hatched individuals grow to maturity by the winter of their first year. Those reaching maturity overwinter as adults but very few live beyond spring of their second year. The population dynamics of L. mariae are closely linked with changes in the biomass of the alga Fucus serratus on which it lives.

The pyloric caeca and posterior intestine of Howella brodiei are bioluminescent, and are associated with internal reflective tissues. The bioluminescence is not bacterial in origin. Unlike that of several shallow water apogonids, it does not depend upon Vargula luciferin. Florenciella lugubris has bioluminescent oesophageal diverticula and is able to eject a pulse of luminescent material from beneath the operculum.

The luminescence of the two species is compared with that of other perciform fishes.

Introduction

The perciform family Apogonidae (cardinal fishes) contains several bioluminescent coastal species in the Indopacific genera Siphamia, Rhabdamia, Archamia, and Apogon. Their oceanic relatives are less well known and their systematic position is still a matter of some conjecture. Howella has been assigned to the Apogonidae but has also been included in the Moronidae (Tortonese, 1986), and, more recently, in the Percichthyidae (Post & Quéro, 1991). Some authors have followed Mead & De Falla (1965) in assigning the oceanic apogonid-like fishes to the family Cheilodipteridae (e.g. Fedoryako, 1976), in recognition of the fact that they ‘are so different from their coastal relatives that comparison is pointless’ (Mead & De Falla, 1965).

Bioluminescence has not been described in detail in any of the oceanic species. Mayer (1974) reported that one of the pyloric caeca in Epigonus macrops was separated from the others and associated with reflective structures. This strongly suggested that it was bioluminescent, based on comparisons with known luminescent shallow water perciforms, such as species of Pempheris and Parapriacanthus. Mead & De Falla (1965) described a ventral reflective strip in Rosenblattia robusta which, by analogy with similar appearances in luminous neritic species, they considered a possible indication of bioluminescence.

Physical factors affecting the fate and functional capabilities of the pedal mucus of Patella vulgata L. deposited in the intertidal have been examined. Mucus dehydration, rehydration and degradation were assessed. Mucus dehydration is dependent on ambient wind speed, temperature and relative humidity. Of these, over naturally encountered ranges, wind speed produces the greatest water loss over a 6-h period and it is surmised that mucus deposited at mid-shore will lose >60% of its water when exposed by the tide on days when the air is not still. The more dehydrated pedal mucus is, the longer it subsequently takes when immersed to reach a fully hydrated state.

When observed from a submersible, the mesopelagic paralepidid Notolepis rissoi (Pisces: Paralepididae) will hover head up with the body at about 45°. The fish's swimming motion is restricted to the extreme caudal region with most of the body rigid. The trunk lateral-line canal ends at about the position that caudal motion becomes noticeable and there is a great decrease in neuromast size near the posterior end of the canal. The size of the neuromasts is also inversely related to the percentage of red muscle at the same body level. The eyes have an aphakic space oriented dorso-anteriorly at about 45° to the body axis so that during hovering the aphakic space is oriented vertically. Retinal anatomy indicates that photoreceptors opposite the aphakic space appear to enhance resolution at the cost of sensitivity, whilst lateral photoreceptors enhance sensitivity at the expense of resolution. We interpret the swimming attitude and mechanics as adaptations to minimize self-induced oscillations which would be deleterious to visual and lateral-line function.

Sequences of the 16S ribosomal RNA gene of luminous bacterial symbionts from the escas of the deep sea anglerfishes Melanocetus johnsoni and Cryptopsaras couesi were determined by direct sequencing of polymerase chain reaction products. A sequence was also obtained from a strain of Photobacterium phosphoreum, the culturable light organ symbiont of Opisthoproctus grimaldii. Comparison of these and other published sequences showed that the anglerfish symbionts group with the marine luminous bacteria but are not closely related to P. phosphoreum. The two ceratioid symbionts differ from each other at least at the species level.

The upper bathyal sea-pen Kophobelemnon stelliferum extends to depths of about 1600 m in the Porcupine Seabight, to the south-west of Ireland, but is rare below about 1150 m. Photographic data suggest that the species attains numerical abundances of more than 2 m−2and a wet weight biomass of at least 4 g m−2. The highest densities, however, do not necessarily correspond to the highest biomass values since there is a clear depth-related change in population structure. The largest sea-pens are restricted to the deeper parts of the bathymetric range of the species. There is also a marked change in the growth form at a total colony length of about 250 mm, with larger colonies having relatively more polyps than smaller ones. The sexes are separate in Kophobelemnon stelliferum and the sex ratio of colonies is about 1:1. The maximum oocyte diameter is about 800 μm, but there is no evidence of seasonal reproduction by this pennatulid in the Porcupine Seabight.

The occurrence and intensity of infection of caligid species on the five species of wrasse commonly found in British waters are reported from twelve localities in the British Isles and from seven fish-farms in Scotland where wrasse are used to remove sea lice from salmon (Salmo salar L.). A low prevalence of infection was recorded for all wrasse species except ballan. Chalimus of Caligus centrodonti Baird were identified from fins of ballan, rock cook and goldsinny wrasse, this being the first host record for the latter two species. Single chalimus stages of Caligus elongatus Nordmann were identified from a ballan wrasse and a goldsinny wrasse and are similarly first records from these host species. No C. centrodonti were found on farmed salmon and conversely no Lepeophtheirus salmonis (Krøyer) were identified from wrasse kept in contact with infected salmon. This suggests that transfer of caligids between wrasse and salmon and vice versa does not pose problems for fish health on sea-farms.

Samples of branched and unbranched forms of the marine thecate hydroid Aglaophenia pluma (L.) (Hydrozoa, Plumulariidae) were collected from the western and eastern sides respectively of Carmarthen Bay (South Wales). Tissue from various colonies of each type was cleaned of epifauna and homogenized for horizontal starch gel electrophoresis. Useful results were obtained for 14 enzyme loci coding for a total of 11 different enzymes. Eleven of the 14 loci showed no common allele between the branched and unbranched forms. Nei's genetic identity was estimated as 0·18 and genetic distance as 1·7. Such a high level of genetic differentiation between morphotypes provides strong evidence that the populations are reproductively isolated and should be regarded as distinct species. It is suggested that the branched form may be Aglaophenia parvula Bale, a species until recently better known from the southern hemisphere. Morphological distinctions between the two species are discussed.

The distribution, morphology and sensory cell polarity of neuromasts were followed in developing larvae and recently settled juveniles of Dover sole (Solea soled) and plaice (Pleuronectes platessa) using scanning electron microscopy. In plaice the number of neuromasts increased at a similar rate on both sides of the fish throughout development, and most head neuromasts became incorporated into canals. On the trunk presumptive canal neuromasts were outnumbered by accessory superficial neuromasts in early juveniles. In sole the number of neuromasts increased at a similar rate on both sides until the start of metamorphosis. Subsequently a proliferation of superficial neuromasts on the abocular side of the head resulted in 80% of all the neuromasts on this side of the fish being located on the head in early juveniles. Both species had developed asymmetry of the head canals by the early juvenile stage, while canal formation on the trunk commenced later on the abocular side than on the ocular side. Mean numbers of sensory hair cells per neuromast showed little change until metamorphosis in both species, after which there was a two- to three-fold increase in hair cell number. The polarities of the sensory hair cells showed more variability on the head than on the trunk in both species. In general, hair cells were aligned for maximum sensitivity along the axes of the canals which would subsequently enclose them, but in the case of the superficial neuromasts on the abocular side of the head in sole the polarities followed surface features such as the nares, papillae and fin rays.

This paper describes the locomotor movements of the tadpole larvae of the ascidians Ciona and Dcndrodoa and the associated electrical activity of the caudal muscle cells. Although very different in size and trunk shape, both larvae show essentially the same two movement patterns; symmetrical swimming and asymmetrical tail flicks. Swimming movements at tailbeat frequencies up to 40 Hz and forward speeds up to 10 L s (in the Reynold's number range 5·25) involve large lateral movements of the tail, and large yaw of the trunk. Tail oscillations are produced by muscle cells arranged in three segmented rows along the tail, coupled by gap junctions. Swimming is driven by axons innervating anterior ventral muscle cells. The second type of movement, single or multiple tail flicks, is driven by axons innervating dorsal muscle cells, all of which are innervated along the length of the tail. The middle row of muscle cells is not innervated. This small scale oscillatory swimming system is compared with those of chordates and larvacean tunicates, and it is concluded that both of these are very different from that of the ascidian tadpole.

The status of the prayine siphonophore genus Prayoides, monotypic for the species Prayoides intermedia Leloup, 1934, is reviewed in the light of recent collections made by the submersibles ‘Johnson-Sea-Link’ I and II. It is concluded that the genus is not valid, and that the species name should be reduced to that of a junior synonym of a Praya species. The bracts of the two Praya species, P. dubia (Quoy & Gaimard (1833) 1834) and P. reticulata (Bigelow, 1911) are re-described, as in the past there has been much confusion as to their true identity.

The swimming and buoyancy of the gelatinous pteropod, Cymbulia peroni, was observed and recorded on videotape from a submersible in the western Mediterranean. When not swimming Cymbulia peroni hangs neutrally buoyant, with its parapodia outstretched and motionless. Two modes of swimming were observed, slow swimming and rapid or ‘escape’ swimming. Slow swimming predominated, at speeds between 2 and 11 cm s−1. Most slow swimming was directed vertically up or down. Slow swimming is probably used for vertical migration and the avoidance of turbulence. Turbulence frequently occurs both at epipelagic and mesopelagic depths in the Mediterranean. Escape swimming was more rapid, and speeds up to 40 cm s−1 were measured. Differences between slow and escape swimming appear to be quantitative rather than qualitative, in contrast to other cymbuliids. Cymbulia peroni is an active and vigorous swimmer, clearly capable of vertical migration, and probably attains speeds greater than the highest measured in this study. Its behaviour in the field differs dramatically from its behaviour in the laboratory.

Deep-sea holothurians of the genus Paroriza (Family Synallactidae) have often been observed or photographed in pairs or triplets. Observations of tracks on the sea floor suggest that pairs may remain together for some time. We explored the reasons for pairing in a study of reproductive condition and diet, using animals collected by trawl from the bathyal and abyssal north-east Atlantic and by manned submersible from the bathyal slope of the Bahamas. Both species of Paroriza studied were found to be simultaneous hermaphrodites producing yolky oocytes. Oocytes of Paroriza pollens were about 350μm in diameter, whereas those of P. prouhoi were up to 450μm. Examination of oocyte size-frequency distributions suggests that reproduction is continuous for both species. Neither mean oocyte size, nor shape of the oocyte size-frequency distribution differed significantly between paired and unpaired P. pallens collected during the same season. These deposit-feeding holothurians appear to take food from the nutrient-rich phytodetrital layers on the surface of the sediment. Because their food resources are probably not patchy on small scales, the observed pairs are not likely to be feeding aggregations. We hypothesize that pairing increases the likelihood of external fertilization and that spawning in these species may be induced at any time by the presence of a conspecific rather than by seasonal cues.

A survey was conducted from 1986 to 1987 to determine the spatial and seasonal distribution patterns of Ichthyophonus hoferi Plehn & Mulsow, 1911 in marine fishes, especially yellowtail flounder, Limanda ferruginea, from the Nova Scotia shelf, Canada. Ichthyophonus hoferi was found in 56 of 6759 (0·83%) yellowtail flounder, in one of 613 (0·16%) haddock, Melanogrammus aelgefinus, but in none of the other 1485 fishes representing seven species sampled from this area. Within the yellowtail flounder population, the fungus was distributed in patchy manner with infection prevalence ranging from 0·4% at Banquereau Bank to about 13% at Brown's Bank. Infection prevalence was the same in both the male and female flounder. There was no apparent seasonal cycle in infection, although pathogen recruitment into L. ferruginea was from early summer through to early fall months.

In this paper we present data on the organization of the territories in males of Lipophrys pholis during the breeding season. Data were collected during high tides by skin- and scubadiving and during low tides by direct inspection of nests. Our study area was located at Arrébida, Portugal. The main results are: (i) The territories of the breeding males of this species are temporary, being established each breeding season, (ii) The guarding males stay in the nest holes with the egg masses while the tide is low and are subjected to several hours of emersion in each tidal cycle, (iii) Even when the nests are submerged the fishes stay inside the nest for an average of 92% of the time. All the activities performed outside the nest correspond to an average of 27 minutes per day. (iv) There was a low frequency of territorial intrusions. Conspecific intruders released a significantly higher frequency of agonistic responses than did Coryphoblennius galerita. (v) Removal experiments showed that vacated territories are not occupied by other males during the same breeding season, (vi) Without the presence of the guarding male the eggs are slowly destroyed by predation and infection, but some eggs can still survive and hatch up to five days after the removal of the parental male. The results are discussed in terms of the probable costs and benefits of breeding intertidally.

A new species, Oikopleura villafrancae, from the family Oikopleuridae (Lohmann 1915), subfamily Oikopleurinae (Lohmann 1896), genus Oikopleura (Mertens 1830), is described from numerous specimens collected at mesopelagic depth (360–880 m) during two different cruises: Migragel II (May 1988) and Medapp (May 1990) in the Ligurian Sea (northwest Mediterranean) between Villefranche-sur-Mer (French Riviera) and Corsica, respectively by the ‘Cyana’ and ‘Johnson-Sea-Link’ manned submersibles.

A general description of the trophic inter-relationships and the food web within Bridgwater Bay, Somerset, England, is presented. This Bay is a lower estuarine site within the Bristol Channel. Particular attention is given to the use of the area by fish and larger crustaceans which are the dominant animal groups. Using data collected over a ten-year period of monthly sampling, the relative average biomass of all fish and larger crustaceans found within the Bay is calculated for each month of the year. These averages are used to produce food webs which also show species relative abundance for each calendar month.

It is shown that the trophic structure follows a seasonal cycle due to migration. The application of the concept of stability within such a dynamic system is discussed. The role of compartmentalization of the ecosystem into a number of loosely connected groups as an aid to overall stability is discussed. While there is no evidence that contemporaneous compartments exist, it is argued that inter-specific interactions are temporally limited because of the different periods of annual residence of the species. It is suggested that the stability and resilience to interference shown by these estuarine systems is enhanced by temporal partitions.

Relationships between size, wet weight, dry weight, carbon and nitrogen content were determined in Ophiothrix fragilis (Echinodermata: Ophiuroidea). Such relationships appeared very useful when studying dynamic processes such as nutrition, growth, excretion or reproduction, considered as fluxes of carbon and nitrogen in the ecosystem.

Relationships between size, wet weight, dry weight, ash free dry weight, carbon and nitrogen content of organisms are of fundamental interest in ecological studies of ecosystems. They allow us to understand and quantify the role of a species as it stores, consumes or produces organic matter during its life cycle. Determination of conversion factors are time-consuming but very useful for estimating flows in the ecosystem (Brey et al., 1988). Some compilations of conversion factors have been published (Båmstedt, 1981; Rumohr et al., 1987).

Ophiothrix fragilis (Abildgaard) is the dominant species of the ‘pebbles with sessile epifaunal community’ (Davoult, 1990), located in the Dover Strait (eastern Channel), where tidal currents are very strong. It is considered as an efficient suspension feeder (Roushdy & Hansen, 1960; Warner, 1971) and lives in dense populations (1000–2000 individuals m-2; Davoult, 1989) which are assumed to have a significant effect on the fluxes of organic matter from the pelagic to the benthic system and on the fluxes of ammonium to the water column (Davoult et al., 1991).

Individuals were sampled in May and June 1991 off the Cape Gris-Nez (50°55′N 1°35′E). Two-hundred individuals were measured (diameter ±01 mm, after Guille, 1964), dried at 60°C for 48 h, weighed (±0·1 mg), burnt at 520°C for 6 h (Anonymous, 1986), and the ash weighed (±0·1 mg). Total organic carbon and nitrogen content were determined with a CHN element analyser (Carlo Erba 1106): after a flash combustion in a helium stream temporarily enriched with pure oxygen, quantitative combustion was achieved by passing gases over Cr2O3 after a transfer through a reduction reactor to eliminate the excess of oxygen; components were separated in a chromato-graphic column, eluted, then measured by a thermal conductivity detector. Thirty-eight dried ophiuroids were ground with a micro-grinder, then two sub-samples (except for individuals <2 mm) were weighed at ±1 μg (76 measurements).

The distribution of bass, Dicentrarchus labrax (L.), eggs taken in ichthyoplankton surveys of the Bristol channel and eastern Celtic Sea from April 1989 to May 1990 indicates that bass spawned predominantly offshore during March and April. Seventy-two bass larvae were captured by ring net and 16 by high-speed tow net during 19–27 May 1989, and 11 were captured by ring net during April and May 1990. Larvae were most abundant inshore where the water column was unstratified and less than 50 m deep.

Back-calculated egg fertilization dates were determined for 58 larvae captured in May 1989 by ring net, using estimates of temperature-dependent egg and larval development rates and counts of daily growth increments on sagittal otoliths. These dates ranged from 5 April to 10 May 1989, later than those for most young-of-the-year bass which first appeared in Welsh estuaries during June 1989. This implies that bass larvae would have been more abundant before the May sampling period, even though these catches are the largest reported from UK waters.

Bass larvae of 5–11 mm live notochord length were captured close to estuarine nursery areas, and their mean growth rate was approximately 0·2 mm per day. However, the smallest bass first arriving in the nursery areas during June, July and August were always larger than these larvae, and predominantly 15–20 mm total length. It is suggested that bass larvae hatching offshore either perish or are transported to unstratified coastal waters where they feed and remain for at least 30 days prior to their recruitment to the nurseries.

Enypniastes eximia (Echinodermata: Holothuroidea) is a prominent member of the benthic boundary layer community in deep Caribbean waters. Like most holothurians it feeds on benthic sediments. Feeding is episodic and after collecting food on the bottom it returns to the water column at altitudes within about 50 m of the sea floor. Direct observations from submersibles and laboratory studies of living specimens have shown how bioluminescence is produced. Light production in E. eximia is triggered mechanically, and is produced by hundreds of granular bodies within the gelatinous integument of the animal. Local stimulation yields a localized response which gradually spreads to the entire surface of the animal. Broad impact yields a whole-body luminescent response. The integument of E. eximia is quite fragile, and strong physical contact readily causes the skin to be sloughed off in a glowing cloud. The degree of luminous response is a function of the severity of contact. In the laboratory the skin of E. eximia, along with its luminescent capability, regenerated rapidly. The anti-predatory role of bioluminescence in this species is apparently a ‘burglar alarm’ strategy. In the dark, near-bottom habitat, physical contact by a predator elicits light production which reveals the presence of the attacker to its own visually-cued predators.