The harpacticoid copepod genus Tigriopus is characteristic of shallow upper shore rock pools in both hemispheres. Tigriopus are necessarily physiologically tolerant as the pools feature extreme physicochemical conditions; their lower limit on the shore is apparently set by competition/predation. There are several species, differentiated by relatively minor morphological distinctions; speciation appears to be favoured by restricted gene flow between populations, even over short distances. This paper briefly reviews the literature concerned with the taxonomy, physiology and ecology of the genus, and compares environmental conditions and salinity/thermal tolerance data for three species: T. brevicornis from Scotland, T. fulvus from Madeira, and a previously undescribed population of the Southern Ocean ‘T. angulatus’ group from subantarctic South Georgia. Particularly interesting was a low upper lethal temperature in ‘T. angulatus’ (21·9°C) that probably restricts the species to relatively large pools that buffer environmental thermal extremes. Unlike the other species, T. fulvus cannot withstand freezing conditions. Evidence is presented to show that the South Georgian Tigriopus differs slightly, but significantly, in its morphology from two sibling species that inhabit the subantarctic Kerguelen and Crozet Islands but which cannot interbreed. If the South Georgian copepods are indeed a separate species and do not occur elsewhere (e.g. the Falklands), this indicates rapid speciation within the genus; the coasts of South Georgia were covered by an icecap until 10,000–14,000 years ago and no rock pool habitats were then available. It is suggested that Tigriopus may have reached South Georgia by rafting within Enteromorpha tubes.

Behavioural patterns of crustaceans are known to vary within the 24 hour cycle and in relation to environmental signals. Light and chemical stimuli induce specific behavioural responses. Retinal and extra-retinal photoreceptors use different motor responses to illumination selectively. Light responsiveness is modulated at various levels, from the light admittance to the retina, up to the integration in higher order interneurones and motorneurones. An endogenous circadian rhythmicity contributes to the various elements of the system.

Using video and image analysis techniques we analysed the response of swarms of the mysid Paramesopodopsis rufa to food and predatory attack. After food was added to the tank, mysid aggregations initially (up to 45 s) increased in volume. Subsequently volume decreased significantly until it was smaller than the initial level. After a period of ~12 h during which no food was added, the swarm expanded to near its original volume. These changes are interpreted as resulting from a need by individuals to optimize food capture and protection. The pattern of volume changes in response to food was independent of aquarium size but the magnitude of the changes was reduced in a smaller tank.

Predatory attacks on mysid swarms were simulated using a model fish which ‘swam’ a single pass along the tank driven by an electric motor. Models (latex-covered real preserved fish), represented two different attack styles: ambush (seahorse Hippocampus abdominalis); and lunging (Australian salmon Arripis trutta). ‘Swimming’ speeds resembled those measured for real fish i.e. 0·5–2·0 cm s-1 for seahorse and 15 cm s-1 for salmon. Again changes in swarm volume were recorded. No obvious response by the swarm to the approaching seahorse was apparent; the aggregation simply parted to allow the fish through. No tailflips were seen among the mysids. The swarm resumed the original volume rapidly after the fish had passed. Approach of the salmon was evidently detected from further away, escape reactions were frequent and energetic, and tailflipping was common. After the fish had passed, it took longer for the original swarm volume to be restored. These results suggest that seahorse ambush techniques have evolved to minimize warning of the predator's approach. When the salmon ‘menaced’ the swarm at seahorse speeds, it appeared the mysids still reacted as though it was a ‘normal’ salmon attack so the fright response was not just a function of speed of attack.

Dynamic changes in swarm volume seem to be a useful simple index of motivational state of individuals.

Male fiddler crabs, Uca pugilator (Crustacea: Decapoda), respond to conspecifics by claw waving, and to predators by freezing or escape. In field experiments it was found that this distinction was not made on the basis of angular size and speed, nor was shape important. The remaining possibilities were either the absolute size of the stimulus, determined from angular size and distance, or the position of the stimulus relative to the horizon. To distinguish between these, a crab was placed in a glass dish, and moved black stimuli on a white background, at a distance of 22 cm. Stimuli below the crab's horizon hardly ever evoked escape. However, identical stimuli partially or wholly above the crab's horizon produced escape responses whose frequency varied with the angular size of the stimulus. Halving the distance of the stimulus showed that it was angular and not absolute size that determines escape frequency; and experiments with a tilted horizon showed that it is the position of the stimulus relative to the eye equator that is important, rather than the geographical horizon itself. It has been concluded that crabs categorize stimuli as dangerous or otherwise by their position relative to the crabs’ visual horizon.

Quantitative sampling for the genus Eurydice (Isopoda: Cirolanidae) was conducted on 25 sand beach sites along the Atlantic coast of the Iberian Peninsula. Five species were recorded intertidally: Eurydice affinis, E. pulchra, E. naylori sp. nov., E. lusitaniensis sp. nov. and E. spinigera. Physical data collected were used to construct an index of exposure to rank each site. The distribution of intertidal Eurydice sp. is described in relation to exposure to wave action and to tidal level. Peak abundance of E. affinis, E. pulchra and naylori occurred most frequently between mean high water neap (MHWN) and mean tide level (MTL). Whilst E. affinis occurred over a wide range of exposure, E. naylori exhibited a marked preference for exposed sites and E. pulchra was only recorded from sheltered and semi-exposed sites. Surf plankton collections revealed the presence of E. lusitaniensis, but as only two specimens were collected, its ecology remains unknown. The zoogeographical distribution of the genus on North Atlantic and Mediterranean coasts is briefly reviewed.

Marked genetic differentiation in the intertidal isopod, Jaera albifrons (Crustacea: Isopoda) has been shown to occur on a scale of just a few metres on British shores. Allozyme electrophoresis at 21 enzyme-coding loci has been employed to examine genetic structure in other UK members of the complex (Jaera forsmani, J. ischiosetosa, J. praehirsuta), and explore the relationship between genetic diversity and perceived niche-width. Comparisons were made with the nonsibling species J. nordmanni. Three subpopulations of each species taken from each of two shores on Anglesey, UK (subpopulations N=30) were assayed for electrophoretic variability. Data from 11 polymorphic loci (P0·95) demonstrated marked genetic differentiation in all populations of J. albifrons and J. praehirsuta, and on one shore for each of J. ischiosetosa and J. nordmanni, with J. praehirsuta (GST=0·207) and J. albifrons (GST=0·121) showing the highest genetic differentiation. In contrast, J. forsmani exhibited population homogeneity on both shores studied. Genetic diversity ranged markedly across species (H0=0·165—0·040), with the two most widely distributed species, J. albifrons (H0=0·135) and J. ischiosetosa (Ho=0·165) exhibiting the highest genetic variability, providing support for the niche-width variation hypothesis. Data indicate that although habitat fragmentation and direct development is associated with microgeographic differentiation in Jaera spp., localized factors such as habitat continuity and exposure to water movements determines the magnitude of such effects.

Tissue growth in Crustacea occurs at specific stages of the moult cycle and is influenced by a number of physical, hormonal and environmental factors. In order to understand the mechanisms responsible for controlling intermittent muscle growth in Crustacea, the effects of various factors on rates of protein synthesis and gene expression for the myofibrillar proteins, have been examined. These studies include the effects of mechanical stretch on muscle fibres; the influence of the moulting hormones, ecdysteroids; and the effect of temperature which is an important environmental variable. Sarcomeric proteins have been cloned and used to measure mRNA levels of actin, myosin HC and tropomyosin in various muscles over the moult cycle. Results from these studies demonstrate that both transcriptional and translational regulation occurs in response to hormonal and mechanical stimulation. Temperature has a direct effect on rates of protein synthesis and transcription in intermoult muscles but overall protein turnover may remain unchanged due to a concomitant increase in protein degradation rates.

The crustacean moult cycle is a convenient model system in which to study calcium (Ca) homeostasis as vectorial movement across Ca transporting epithelia (gills, gastric epithelium, cuticular hypodermis, antennal gland) which occurs in either direction at different stages of the moulting cycle. Intermoult crustaceans are in relative Ca balance. During premoult, at the same time as the cuticle decalcifies, epithelia involved in Ca storage (e.g. gastric) calcify and/or increase their intracellular Ca stores. Premoult Ca balance is typically negative as Ca is excreted. During postmoult the soft new cuticle is remineralized largely with external Ca taken up across the gills and gastric epithelium (positive Ca balance); conversely during this time internally stored Ca is remobilized. This review (1) compares the relative roles of Ca transporting epithelia in Ca balance for crustaceans from different habitats; (2) proposes up-to-date cellular models for both apical to basolateral and basolateral to apical Ca transport in both noncalcifying and calcifying epithelia; (3) compares kinetics of the Ca pump and exchanger during intermoult; (4) presents new data on specific activity of calcium adenosinetriphosphatase (Ca2+ATPase) during the moult cycle of crayfish and (5) characterizes a partial cDNA sequence for the crayfish sarcoplasmic reticular Ca2+ATPase and documents its expression in gill, kidney and muscle of intermoult crayfish. The physiological and molecular characterization of Ca transporters in crustaceans will provide insight into the function, regulation and molecular evolution of mechanisms common to all eukaryotic cells.

Sulphide occurs widely in marine sediments and is highly toxic to most organisms. Its principal poisoning effect occurs at extremely low concentrations and is the result of inhibition of mitochondrial cytochrome c oxidase. Mud-shrimps (Crustacea: Thalassinidea), construct burrows in sublittoral muddy sediments. The sediment in which they burrow is markedly reduced and conditions within the burrow are usually hypoxic and hypercapnic. Field measurements indicate that the shrimps may be exposed to potentially toxic levels of sulphide in the burrow water (range 0–206 μM, N=37). Laboratory experiments carried out on Calocaris macandreae, Callianassa subterranea and Jaxea nocturna have shown that these species have a high tolerance of sulphide. An oxygen dependent detoxification mechanism exists to defend cytochrome c oxidase from sulphide poisoning. The main detoxification product of this mechanism is thiosulphate which accumulates rapidly even during brief exposures to low concentrations of sulphide. Sulphite also appears as a secondary detoxification product. Aerobic metabolism can be maintained even under severe hypoxia and toxic sulphide conditions. The mud-shrimps switch to anaerobiosis when the detoxification mechanism is saturated. These data indicate that mud-shrimps are physiologically adapted to tolerate elevated levels of sulphide that they may encounter in their natural habitat.

The present study confirms the findings that in the two ocypodid crabs Ocypode saratan and O. ryderi haemocyanin oxygen affinity is increased in ‘replaced’ or dialysed blood compared to whole haemolymph and that this difference can be attributed to a plasma factor. After the replacement of the plasma, the haemocyanin of both species showed up to a 39% increase in oxygen affinity. The change in oxygen affinity was proportional to the logarithm of the amount of native plasma present. Further investigations have shown that this difference is not due to changes in plasma urate or bicarbonate concentrations. Using plasma exchange experiments it could be shown that the factor acts specifically on the haemocyanin of Ocypode spp. and not on Carcinus maenas haemocyanin. Fast protein liquid chromatography (FPLC) techniques indicate that the molecular weight of the factor is <5000 daltons and a specific peak could be isolated. This isolated peak is linearly correlated with changes in haemocyanin oxygen affinity. The results are discussed in the light of the overall modulation of haemocyanin oxygen affinity and the need for negative effectors.

Trypsin-like enzyme activity of the larvae of two planktonic predatory crustaceans, Homarus gammarus and Nephrops norvegicus (Decapoda: Nephropidae) and the omnivorous larvae of Carcinus maenas (Decapoda: Brachyura) were investigated at each larval stage until metamorphosis. Two copepods, herbivorous or omnivorous grazers, Centropages typicus and Temora longicornis (Copepoda: Calanoidae) were also investigated for this enzyme. A comparison of trypsin-like activity in these and other decapod larvae shows a pattern with high levels in herbivores, low levels in carnivores and intermediate levels in omnivores. Herbivorous planktonic crustaceans appear to rely on high digestive enzyme activities to extract nutrients from less digestible algae or particulates, whereas carnivorous larvae have limited enzymatic capacity as they feed at higher trophic levels upon large and easily digestible prey. Omnivorous Carcinus maenas larvae have intermediate levels of digestive enzymes and are able to transfer between herbivorous and omnivorous feeding.

Five species of crabs were recorded in the Forth Estuary, of which Liocarcinus depurator and Cancer pagurus were confined to the lowest reaches where salinities are 24–35%‰. Carcinus maenas, Liocarcinus holsatus and Hyas araneus also occurred in the middle estuary where salinities are 22–31%‰ in summer but often fall to ~12%‰ in winter. A very few L. depurator and Cancer pagurus were confined to the lower estuary and mostly occurred in low tide trawls in summer. Carcinus maenas alone was recorded much further up the estuary where salinities rarely exceed 0–5·7%‰. Carcinus maenas predominated numerically throughout with an overall mean density of 0·0075 m−2 in the middle and lower estuary. Carcinus maenas in the estuary channel measured 16·6–82·9 mm carapace width (CW) with a modal size–class of 50–60 mm. Males were outnumbered by females (0·68:1 overall), and more markedly in summer than winter. Yet males were significantly bigger on average than females. Egg-masses were borne by 7·5% of all trawled females, but by 31·1% in April–May. On adjacent shores, by contrast, the much higher numbers of C. maenas were nearly all <20 mm CW. Low water trawls yielded significantly more C. maenas, but significantly lower proportions of males, than high water trawls. Liocarcinus holsatus was most abundant within the mid-lower estuary basin, with numbers decreasing both upstream and at the estuary mouth. Males outnumbered females by 2·26:1 overall, and most markedly at the extremities of the range. Males were significantly bigger than females, although sizes of both generally increased towards the mouth of the estuary. Only three of the 101 females bore eggs. Low water trawls yielded slightly more L. holsatus than high water trawls. Numbers of H. araneus increased markedly from mid-estuary to the estuary mouth where counts averaged 0·0021 m−2. Males outnumbered females by 2·17:1, and more so among those >40 mm CW. No female bore eggs. Records of the presence of C. maenas, Liocarcinus sp. and Hyas sp. all increased in the estuary from 1985 to 1995 reflecting increases in intertidal faunal diversity and changes in industrial practices since the early 1980s.

Columbus crabs, Planes minutus (Crustacea: Brachyura) live in the open ocean attached to floating substrata including Sargassum, flotsam, and sea turtles. Eighty-two percent of 128 loggerhead turtles (Caretta caretta) checked, harboured a total of 172 crabs. Crabs inhabiting flotsam occurred in mixed sex groups of adults and juveniles, with a mean group size of 8.2 ±;11.8 (N=17). In contrast, crabs living on sea turtles around Madeira occur in smaller groups 1.6 ±0.5 (N=105) which are typically adult heterosexual pairs (61 out of 105). Crabs on turtles were bigger than on flotsam and a higher proportion of female crabs were brooding eggs. Columbus crabs exhibit different life history strategies depending on the substratum they inhabit.

Trace metals are accumulated by marine invertebrates to body concentrations higher, in many cases orders of magnitude higher, than the concentrations in an equivalent weight of the surrounding sea-water (Eisler, 1981; Rainbow, 1990; Phillips & Rainbow, 1993). Specific details of trace metal accumulation processes vary within the same invertebrate species between metals, and for the same trace metal between invertebrates, often between closely related species (Rainbow, 1990, 1993). This short review attempts to highlight some of the comparative aspects of the processes involved that are expected and explicable in terms of the chemistry of the respective elements, and those where the physiology of the species involved intervenes to offset predictions from purely chemical principles. Although an appreciation of trace metal chemistry is crucial to an understanding of trace metal accumulation, idiosyncrasies in the biology of the invertebrate (at any taxon level) may intervene to bring about significant and unexpected comparative differences in metal accumulation patterns.

Observations on living estuarine nematodes show that previous feeding type classifications do not accurately represent the trophic structure of an intertidal mudflat in the Westerschelde Estuary (Netherlands). A new scheme with six major nematode feeding guilds is proposed: (1) microvores; (2) ciliate feeders; and (3) deposit feeders sensu stricto are all nematodes without a distinct buccal armature. In the first two groups bacteria and protozoa, respectively are the major particulate food sources, while other items are included in the diet of the third. The three other categories are recognized among the nematodes with a buccal armature: (4) epigrowth feeders; (5) facultative predators; and (6) predators. Diatoms and other microalgae are an important particulate food for many epigrowth feeders. The importance of bacteria as a food source for these nematodes remains poorly documented. A strictly or mainly predatory behaviour has been described for only few species from the study area. Several nematodes, however, are facultative predators. The predatory strategy of Calyptronema maxweberi, as described in this paper, suggests the use of a paralysing or lethal secretion in prey capture, which, to our knowledge, is the first report for aquatic nematodes. Furthermore, the importance of sources other than particulate food in free-living aquatic nematodes is stressed. Our observations show that many aquatic nematodes are in fact opportunistic feeders, which may change feeding strategies in response to available food.

The gametogenic and spat settlement patterns of two Mytihis edulis beds were studied in Dundrum Inner Bay, Northern Ireland. There was evidence of gonad development throughout the year with the main development period between November and March. Spawning was protracted, lasting from May to November. Slight inter-annual and inter-population differences in the riming of the phases were observed but the cycles at both beds were broadly similar to each other and to those of other British and Irish sites. Settlement occurred throughout the year and there was evidence of both primary and secondary spat settlement at both sites. Although the reproductive cycles were similar, distinct seasonal and inter-site differences in spatfall were apparent. At the Downshire Bridge bed, settlement peaked during summer and was dominated by spat in the 0·;5-1·0 mm size range. At Ballykinler, settlement levels were highest in the winter months and larger (>1 mm) spat dominated the samples. The orientation of spat collection pads also significantly affected numbers of the larger (>1 mm) spat. Collectors facing the flood tide attracted significantly more secondary settlers than ebb-facing collectors. This effect varied seasonally and was greater at the Ballykinler bed. It is suggested that hydrodynamic regimes may be an important factor in the differences in settlement patterns of M. edulis.

The known geographical distribution of the sea anemone Actinothoe sphyrodeta (Gosse) (Cnidaria, Actiniaria), hitherto generally believed to occur in the north-eastern Atlantic Ocean from the Shetland Islands to the Bay of Biscay, has been extended with new records from the Iberian Peninsula. These records comprise three from the west coast of Portugal and one from the Mediterranean coast of Spain.

The sea anemones (Actiniaria) of the north-eastern Atlantic Ocean have been closely studied for at least a century and a half, and along with those of the Mediterranean Sea, constitute perhaps the best known actiniarian fauna in the world. Furthermore, there has long been discussion of the endemicity of Mediterranean sea anemones, and of apparent overlaps between the distributions of some Atlantic and Mediterranean species. It is, therefore, of particular interest when a species thought to have a solely Atlantic or solely Mediterranean distribution is discovered on the ‘wrong’ side of the Strait of Gibraltar. The anemone Actinothoe sphyrodeta (Gosse) was hitherto generally believed to occur only in north-western Europe, with a range from the Shetland Islands to the Bay of Biscay (e.g. Fischer, 1890; Manuel, 1981). It is reported here for the first time from Portugal and from the Mediterranean coast of Spain.

The dry weights, carbon and nitrogen content of fresh dried Calanus spp. Pseudocalanus elongatus, Acartia clausi, Temora longicornis, Mesocalanus teniricornis, Metridia lucens and Candacia armata were determined from samples taken in the southern North Sea, the English Channel, the Irish Sea and the Celtic Sea in December 1984 and February 1987. Usually adult females were picked out but some data were obtained for adult males and copepodites of Calanus spp. and T. longicornis and male M. tenuicornis. Significant differences were found between stations on the same cruise in the results for adult females of the same species. The weights of Calanus spp. females in February 1987 were found to be inversely related to temperature.

Data are presented on the density of ten species of Amphipoda and two species of Isopoda from terrestrial to aquatic (freshwater through brackish water to marine) habitats, derived using a new modification of the displacement method involving batch testing of animals and subsequent Probit Analysis of data.

Surprisingly few data are available in the literature concerning the densities of marine organisms. Extensive work on this topic was published some half a century ago by A.G. Lowndes. He reported widely on crabs and lobsters (Lowndes, 1943a), echinoderms (Lowndes, 1953) and fishes (Lowndes, 1955). In his paper to the Linnean Society (Lowndes, 1938a) he included data on some of the smaller freshwater Crustacea. Gross & Raymont (1942) have published on the specific gravity of the marine copepod Calanus finmarchicus.

In espousing the displacement method for dealing with live individuals (Lowndes, 1938a,b, 1942, 1943b, 1955), he dismissed summarily earlier techniques that involved ascertaining whether killed or narcotized animals sank or floated in liquids of known density. While we recognize the limitations of the old methods, Lowndes’ displacement technique, although very accurate for individuals (he quoted figures to five decimal places), is very tedious to replicate [“elegant if somewhat exacting”, according to Hutchinson, 1967] and so reliance tends to be placed on figures obtained for very few individuals, typically only one or two. Even Lowndes himself was wary of attributing significance to the last two decimal places in his estimations, since individuals will vary in density according to sex, the contents of the gut etc. (Eyden, 1923; Lowndes, 1938b; but see Fox & Mitchell, 1953).