Relationship between duration of cyprid attachment and drag forces associated with detachment ofBalanus amphitrite cyprids

Relationships between the duration of antennular attachment of cyprids ofBalanus amphitrite and forces associated with detachment were assessed in a small flume. For six of twelve sets of measurements obtained on separate dates between 27 January and 2 June 1989, drag forces associated with detachment were significantly and positively correlated with duration of attachment within the range 10⁰ to 10³ s. In general, the instantaneous drag force exerted on cyprids at detachment was more strongly correlated with duration of attachment than was either the maximum or mean force exerted prior to detachment. Our indirect method of estimating drag forces from shear velocities measured 0.5 cm from cyprids (i.e., 10 body lengths) probably underestimated the true association between detachment force and attachment time since the spatial coherence of shear velocities characterizing turbulent flows in the flume was not strong at these scales. The relationship between attachment time and drag force at detachment suggests that spatial and temporal variability in fluid forces in situ may contribute to stochastic variations in intensities of settlement ofB. amphitrite. Stresses sustained by the antennular adhesive of cyprids ofB. amphitrite were calculated to standardize forces to the area of antennular contact and permit comparisons with similar measurements made onSemibalanus balanoides by other investigators. Stresses sustained by the adhesive ofB. amphitrite were an order of magnitude lower than those reported for the adhesive of the larger cyprids ofS. balanoides. This difference may reflect differences in the stress sustainable by the adhesive secreted onto antennular pads when loaded purely in tension (measured previously) rather than in a combination of shear and tension (calculated here). Alternatively, there may be interspecific differences in the adhesive used for reversible attachment or in behavioral responses of exploring cyprids to strong flow.     

Importance of physical and biological settlement cues used at different spatial scales by the larvae of Semibalanus balanoides

The settling cues used by larvae of Semibalanus balanoides (L.) were examined at large (1 m), medium (1 mm), and small (<300 m) spatial scales, corresponding roughly to choices made during broad and close exploration and final inspection within the settling zone. The experiments were carried out at two locations in Canada in May and June 1984. Samples of substratum surfaces from above (n=87 sites unselected by cyprids) and below (n=84 sites selected by cyprids) the upper limit of the barnacle zone were characterized according to 13 quantitative and semi-quantitative variables (diatom cover, macroalgae, detritus) using scanning electron microscopy (SEM). The data were analysed using a stepwise logistic regression. At the large scale, the presence of an alga (Urospora wormskjoldii Mertens) in the upper uncolonized zone and a diatom (Achnantes parvula Kützing) within the settling zone are potential settlement cues. At the medium scale in the settling zone, larvae select clean sites, devoid of detritus and diatoms or on which detrital matter, when present, is of finer texture than on the unchosen sites within the settling zone. At the smallest scale (<300 m, equal to the average maximum width of the larvae), we tested the hypothesis that the larva seeks optimal microheterogeneity (presumably providing good adhesion). Microheterogeneity of the surface was measured immediately under the larva, around the settling organs, the antennules. Our results show that such surface microheterogeneity is significantly greater and the vertical center of gravity of the surface significantly lower on the sites selected by the cyprids than on the unselected contiguous sites. Fractal measurements carried out on selected and contiguous unselected surfaces indicate that larvae discriminate microheterogeneity levels below a step length of 35 m, a value approximately the size of the diameter of the antennular discs (40 m), which are used to explore the substratum and attach.Contribution to the programme of GIROQ (Groupe interuniversitaire de recherches océanographiques du Québec)     

The unusual floatation collar around nauplii of certain parasitic barnacles (Crustacea: Cirripedia: Rhizocephala)

Nauplii of the rhizocephalan families Peltogastridae and Lernaeodiscidae carry a torus-shaped collar around the body. It consists of an exceedingly thin cuticle connected to the general body cuticle along a continuous narrow ridge. In nauplii of some species, the collar is very large and its surface ornamented by a very conspicuous reticulated pattern of ridges. In other species the collar is smaller and with a smooth surface that impedes its detection when using a light microscope. The collar is absent from nauplii of all investigated species of the Sacculinidae. Transmission electron microscopy shows that the collar of the succeeding nauplius instar is formed in an unexpanded state beneath the old cuticle and it must therefore be inflated at or immediately after ecdysis. At ecdysis the collar of the old instar breaks along the attachment ridge, leaving the empty collar and the exuvium of the general body as separate objects. The collar must have a profound influence on the hydrodynamic properties of the nauplius, both when swimming and passively sinking. We therefore consider it as a floatation device, a view supported by the absence of the collar in the rapidly swimming cypris larvae. There is no obvious homology to the collar outside the Rhizocephala, and it therefore appears to have evolved only once.Communicated by L. Hagerman, Helsingør     

Settlement of barnacle larvae: surface structure of the antennular attachment disc by scanning electron microscopy

The surface morphology of the antennular attachment disc of the cypris larva of Balanus balanoides has been investigated by scanning electron microscopy, and its function is considered in the context of settlent behaviour. It is concluded that the attachment organ acts as an adhesive pad for temporary attachment while the larva explores the substratum. The surface of the disc is covered with villi, which could retain an adhesive substance thought to be produced by the antennular glands. The open-ended hair of the axial sense organ on the disc is shown.     

Dimorphism and possible sex change in copepods of the family Calanidae

Adult females of 14 of 25 species of the family Calanidae were found to be dimorphic with respect to the number of aesthetases on the first antenna. The trithek morph, in which most antennal segments bear a complement of one aesthetasc and two setae, appears to be the typical female phenotype. The quadrithek morph is less common and, as in males, odd-numbered segments 2b, 3, 5, 7 and 9 carry quadritheks, i.e., two aesthetascs as well as two setae. Segment 21 in the quadrithek female bears an aesthetasc that is absent in the trithek female. Male antennal segments are distinguished from those of trithek and quadrithek females by pronounced morphological differences in aesthetasc shape and size as well as fusion of one or more pairs of antennal segments. The quadrithek morph usually comprised only a small proportion (<10%) of a local population. Quadrithek morphs were found in tropical and subtropical genera (Cosmocalanus and Nannocalanus), broadly ranging genera (Calanoides), as well as in cool-water lineages (Calanus s.s., Calanus s.l. cristatus, C. s.l. plumchrus, C. s.l. propinquus and C. s.l. tonsus). Maximum frequencies of quadrithek morphs (10 to 12%) in Calanus pacificus californicus occurred during the upwelling season from late winter into spring. No indication of sexual or antennal dimorphism was found in CV C. pacificus californicus sexed by examination of gonad and gonaduct. The quadrithek dimorph appears to be the product of sex change by the larger-sized late-juvenile potential male. The evolutionary and ecological significance of this presumptive hypothesis is that the larger-sized potential male reaching adulthood one or more weeks before maturation of genotypic females may increase its reproductive output by sex change in the course of the final molt to mature as a functional female. Given the sex-change hypothesis, morphogenesis of secondary sexual structures would appear to be controlled by androgenic-like secretions from the genital tract, as has been shown in malacostrocans.     

An energy budget for the free-swimming and metamorphosing larvae of Balanus balanoides (Crustacea: Cirripedia)

Analysis of biochemical components and measurements of oxygen consumption rates of cypris larvae of Balanus balanoides (L.) maintained in the laboratory at 10°C for up to 5 weeks after capture shows that lipid is the primary energy reserve, although later protein is utilised. Initially, the cyprids swim freely with an oxygen consumption rate of ca. 37×10^-3 l O₂ h^-1 cyprid^-1, but within a few days the rate falls to ca. 21×10^-3 l O₂ h^-1 cyprid^-1 when they cease swimming and explore the substratum. The cost of metamorphosis was calculated both from the loss of biochemical components and oxygen consumption rates during metamorphosis; the values were 2.8×10^-2 and 3.2×10^-2 cal cyprid^-1, respectively. A budget was collated from the data on respiration and biochemical composition, whereby the energy per cyprid was partitioned into that required for essential structural components (6.8×10^-2 cal), that needed for metamorphosis (3.0×10^-2 cal) and an excess available for swimming and exploring, which in the batches studied was about 5.0×10^-2 cal. This excess is mainly derived from the utilisation of lipid reserves and is used up usually 2 1/2 to 4 weeks after capture. During these measurements, samples of cyprids were taken at weekly intervals to test the rate of settlement and success of metamorphosis. The results showed that they lose their competence to metamorphose successfully approximately at the same time (3 to 4 weeks) that the energy supply for swimming and exploration is used up.     

Locomotion,feeding, grooming and the behavioural responses to gravity,light and hydrostatic pressure in the stage I zoea larvae of Ebalia tuberosa (Crustacea: Decapoda: Leucosiidae)

The stage I zoeae of Ebalia tuberosa swam by sculling with the exopodites of the 1st and 2nd maxillipeds and flexed the abdomen to brake or change direction. The larvae gained depth by stopping all natatory movements and sinking passively at rates of 6 mm s^-1. The zoeae refused both living and dead nauplii of Artemia spp., as well as two species of diatoms, but fed readily on detritic material on the bottom which they scooped up using the endopodites of the maxillipeds and pressed against the mouthparts using the telson. The setae on the posterior border of the telson were used for grooming the maxillipeds and the anterior mouthparts. Day-old stage I zoeae were negatively geotactic, positively phototactic and responded to pressure increases by swimming upwards and by high barokinesis. By the third day some larvae had become positively geotactic but were photopositive, and the majority responded to pressure increases as in the day-old larvae. Five-day old larvae were still photopositive but the majority had become positively geotactic and fewer himbers responded to pressure. Seven-day old larvae failed to respond to any of the stimuli used and assumed a predominantly benthic lifestyle. It is suggested that this anomalous behaviour is related to the dispersal of the larvae and to the specialized habitat requirements of the adults while the rather unusual morphology of the larvae is related to their feeding behaviour and semi-benthic lifestyle.     

Antifouling adaptations of marine shrimp (Crustacea: Decapoda: Caridea): Functional morphology and adaptive significance of antennular preening by the third maxillipeds

Preening (cleaning, grooming) of the antennules and other cephalothoracic appendages by the third maxillipeds was observed in several species of shrimp. Distribution and ultrastructure of serrate grooming setae on the third maxillipeds, which scrape the antennules, was studied with light and scanning electron microscopy. The motor patterns of antennular cleaning were similar for all species. Antennular preening was the most frequent grooming behavior observed, but the duration of other grooming behaviors was greater. Tidepool shrimps (Heptacarpus pictus) experimentally prevented from grooming the antennules by ablation suffered fouling of the olfactory hairs of the antennules with their subsequent breakage and loss; antennules of controls remained clean and undamaged. Antennular preening, a frequent and widespread behavior of caridean shrimps and other decapod crustaceans, is suggested as having high adaptive value in keeping sensory sites free of epizoic and sedimentary fouling which might render them inoperative.     

Settlement behavior and antennulary biomechanics in cypris larvae of Balanus amphitrite (Crustacea: Thecostraca: Cirripedia)

The settlement behavior, antennulary biomechanics and morphology were investigated in the intertidal cypris larvae Balanus amphitrite. The very maneuverable antennule of the cyprid consists of four jointed segments, and it is the prime appendage for substratum exploration and final settlement. We recorded several previously undescribed settling behaviors, such as the "tight direction change", for this intertidal species and discovered that the antennulary morphology is modified to facilitate such behaviors. Segment 2 has a modified lateral cuticle, which gives the segment an additional higher degree of maneuverability compared to non-intertidal cirripede species of Rhizocephala. Additional supporting muscle groups were also found in the antennule of our species, which were not found in the investigated rhizocephalan larvae. The results could very well be associated with the higher needs of substratum recognition in intertidal species, due to more heterogeneous habitats such as intertidal rock flats.     

Symbiosis between bacteria and oceanic clonal sea star larvae in the western North Atlantic Ocean

Bacteria were present in the majority of clonal sea star bipinnariae (Luidia sp.) collected between June 1987 and August 1990 from oceanic populations in the subtropical western North Atlantic Ocean. Light and electron microscopy revealed dense aggregations of bacteria within lobes of the epidermal cuticle in the gastric region of larvae. Gram-negative rods and less-common elongate spiral bacteria were observed, always in close association with branching epidermal microvilli. Intact and partially digested bacteria occurred in vesicles and phagosomes within epidermal cells, a probable indication of phagocytotic activity by the host. The association of larvae of Luidia sp. and bacteria ranged widely on both geographical and temporal scales. During July and August 1988, larvae were abundant (1.6 to 11.1 m³) in the mixed surface layer (<10 to 100 m) of stations in the Gulf Stream, the Sargasso Sea and the North Equatorial Drift, and 96% (mean of 5 stations, n=8 to 10 larvae in each station) of the individuals surveyed harbored bacteria beneath their cuticle. In a single station on the Florida Current sampled during winter, spring, and summer months between 1989 and 1991, 79 to 90% of the larvae harbored bacteria. The incidence of symbiosis was higher in actively cloning larvae than in non-cloning larvae. This is the first documentation of a symbiosis in field populations of echinoderm larvae.     

Morphology of grooming limbs in species of Petrolisthes and Pachycheles (Crustacea: Decapoda: Anomura: Porcellanidae): a scanning electron microscopy study

The morphology of the grooming limbs, the 5th pair of pereiopods, was studied by scanning electron microscopy in six species of porcellanid crabs, Petrolisthes cabrilloi, P. cinctipes, P. armatus, P. galathinus, Pachycheles monilifer, and Pachycheles rudis, and their function was inferred by comparison with findings from previous studies. Grooming limb morphology was almost identical among the four Petrolisthes species and differed little compared to that of the two Pachycheles species. The 5th pereiopods bore a basal tuft of mechanoreceptive setae, three different types of grooming setae armed with setules or denticles, two types of smooth sensilla for location and identification of fouling objects, and a terminal, toothed chela for picking firmly attached objects off the gills and body. The grooming limb was extremely flexible and could reach most parts of the body, including the gill chamber on the opposite side. The grooming limb morphology in Petrolisthes cabrilloi is consistent with its wellknown effectiveness in preventing parasitism by the rhizocephalan Lernaeodiscus porcellanae. Grooming setae remove recently attached cyprids, while the chela can grip and remove the much smaller, firmly attached kentrogons. Porcellanid crabs not known to host rhizocephalans, however, had grooming limbs almost identical to those of Petrolisthes cabrilloi despite their previously demonstrated failure to prevent settlement and infestation by L. porcellanae larvae. The effectiveness of P. cabrilloi in removing kentrogons, therefore, seems also to depend on behavioral adaptations whereby this species recognizes the parasite larvae as high-threat objects.     

Invasive vermigon stage in the parasitic barnacles Loxothylacus texanus and L. panopaei (Sacculinidae): closing of the rhizocephalan life-cycle

 The parasitic barnacles, Rhizocephala, are unique in Crustacea by having an entirely endo-parasitic phase inserted into their lifecycle. A cypris larva, remarkably similar to the cypris of conventional acorn and goose barnacles (Thoracica), settles on the crustacean host and develops an infective stage, the kentrogon, underneath the exuviae of the cypris. The kentrogon penetrates the integument of the host by a hollow cuticle structure, the stylet, and injects the parasitic material into the hemocoelic fluid of the host. Although advanced stages of the internal development have been found and described several times, the nature of the originally injected parasitic material has remained obscure for decades. Recently, however, it was shown that the parasitic material was injected by the kentrogon in the form of a motile, multi-cellular and vermiform body. The present study demonstrates that the vermiform stage is an instar which forms the only and direct link between the kentrogon and the maturing internal parasite. The vermiform instar, or vermigon, is at all times clothed in a cuticle, contains several types of cells, including epidermis and the anlage of the later ovary, and stays intact while growing into the internal parasites with rootlets. Received: 12 August 1999 / Accepted: 3 November 1999     

Effects of nano carbon black and single-layer graphene oxide on settlement,survival and swimming behaviour of Amphibalanus amphitrite larvae

The effects of two carbon-based nanomaterials, nano-sized carbon black (nCB), and single-layer graphene oxide (GO) on settlement of Amphibalanus amphitrite (Cirripedia, Crustacea) cypris larvae (cyprids) were assessed after 24, 48, and 72 h of exposure. Additionally, the effects of these nanomaterials on the mortality and swimming behaviour of the nauplius larvae (nauplii) of the same organism were determined after 24 and 48 h. The data indicate that nCB is more effective as a potential antisettlement agent than single-layer GO; moreover, nCB did not show any adverse effects on the larvae. The swimming behaviour of II stage nauplii of A. amphitrite exposed to a suspension of nCB was inhibited only at very high nCB concentrations (≥0.5 mg/mL). Single-layer GO, on the contrary, showed lower antisettlement effects and was more active in altering the survival and inhibiting the swimming behaviour of the nauplii. An indication of the toxic or non-toxic mechanisms of the antisettlement properties of both of these nanomaterials is provided by the reversibility of the antisettlement activity. In conclusion, we propose nCB as an innovative antifouling nanomaterial that shows low toxicity towards the model organism (crustaceans) used in this study.     

Deep distributions of oceanic cirripede larvae in the Sargasso Sea and surrounding North Atlantic Ocean

From deep ( 1000 m), multi-depth zooplankton samples taken in the Azores frontal region from November 1980 to June 1981, high numbers of the two larval forms ofLepas pectinata, the commonest lepadid cirripede in this area, were sampled. The nauplii and cyprid larvae are large and long-lived. Nauplii were sampled where they feed, in the upper 150 m, closely associated with the fluorescence maximum. The cyprids were mainly sampled between 300 and 400 m, with a sharp cut-off in numbers just below the distribution peak. This deep distribution is intriguing, as the cyprids, which were not migrating diurnally, are non-feeding. To complete their life cycle they must settle on floating debris at the surface, where very few were sampled. They are negatively buoyant and there is no apparent physical reason for this deep distribution. There was no obvious pattern of changes in individual length or length/dry weight distribution with depth, the population appeared homogeneous. There was also no accumulation of other zooplankton at the same depth, or evidence from gut contents of large carnivores that the distribution pattern was caused by selective predation. A close association exists betweenL. pectinata andSargassum spp. weed, the cyprids preferentially settling on small fragments of weathered weed, the supply of which may be enhanced after winter. During winter, the harsh environment at the surface of the northern Sargasso Sea may discourage cyprid settlement. The deep distribution may be an ontogenetic migration conferring some survival advantage and saving energy due to the lower temperature and oxygen levels at depth. If it is a behavioural mechanism, duration of the cyprid stage will be extended until a more clement time of year, allowing them to settle over a longer period. The cyprids of other species were also sampled at depth, so the phenomenon appears to be widespread. If subsequent research confirms these observations as an ontogenetic migration, our current understanding of the fouling behaviour of oceanic lepadid cirripedes would be considerably modified.     

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.     

Experimental assessment of sensory modalities of coral-reef fish larvae in the recognition of their settlement habitat

One of the great mysteries of coral-reef fish ecology is how larvae locate the relatively rare patches of coral-reef habitat on which they settle. The present study aimed to estimate, by experiments in aquaria, the sensory modalities of coral-reef fish larvae for senses used in searching for their species settlement habitat. Larval recognition of settlement habitat can be based on the detection of conspecifics and/or of characteristics of coral habitat using visual, chemical and mechanical cues. For this study, larvae were captured with crest nets and were then introduced into experimental tanks that allowed testing of each type of cue separately (visual, chemical or mechanical cues). Among the 18 species studied, 13 chose their settlement habitat due to the presence of conspecifics and not based on the characteristics of coral habitat, and 5 species did not move toward their settlement habitat (e.g. Scorpaenodes parvipinnis, Apogon novemfasciatus). Among the different sensory cues tested, two species used the three types of cues (Parupeneus barberinus and Ctenochaetus striatus: visual, chemical and mechanical cues), six used two types (e.g. Myripristis pralinia: visual and chemical cues; Naso unicornis: visual and mechanical cues), and five used one type (e.g. Chrysiptera leucopoma: visual cues; Pomacentrus pavo: chemical cues). These results demonstrate that many coral-reef fish larvae could in practice use sensory cues for effective habitat selection at settlement, and have the ability to discriminate species-specific sensory cues.Communicated by J. Krause     

Energy content at metamorphosis and growth rate of the early juvenile barnacle<Emphasis Type="Italic"> Balanus amphitrite</Emphasis>

The energetic cost of metamorphosis in cyprids of the barnacle Balanus amphitrite Darwin was estimated by quantification of lipid, carbohydrate and protein contents. About 38–58% (4–5 mJ individual^–1) of cypris energy reserves were used during metamorphosis. Lipids accounted for 55–65%, proteins for 34–44% and carbohydrates for <2% of the energy used. Juveniles obtained from larvae fed 10⁶ cells ml^–1 of Chaetoceros gracilis were bigger (carapace length: 560–616 µm) and contained more energy (5.56±0.10 mJ juvenile^–1) than their counterparts (carapace length: 420–462 µm; energy content: 2.49±0.20 mJ juvenile^–1) obtained from larvae fed 10⁴ cells ml^–1. At water temperatures of 30°C and 24°C and food concentrations of 10⁴ and 10² cells ml^–1 (3:1 mixture of C. gracilis and Isochrysis galbana) as well as under field conditions (26.9±3.1°C and 2.2±0.8 µg chlorophyll a l^–1), juveniles obtained from larvae fed the high food concentration grew faster than juveniles obtained from larvae fed low food concentration until 5 days post-metamorphosis. Laboratory experiments revealed a combined effect of early juvenile energy content, temperature and food concentration on growth until 5 days post-metamorphosis. After 10 days post-metamorphosis, the influence of the early juvenile energy content on growth became negligible. Overall, our results indicate that the energy content at metamorphosis is of critical importance for initial growth of juvenile barnacles and emphasize the dependency of the physiological performance of early juvenile barnacles on the larval exposure to food.Communicated by O. Kinne, Oldendorf/LuheAn erratum to this article can be found at     

Being young in a changing world: how temperature and salinity changes interactively modify the performance of larval stages of the barnacle <Emphasis Type="Italic">Amphibalanus improvisus</Emphasis>

The fate of key species, such as the barnacle Amphibalanus improvisus, in the course of global change is of particular interest since any change in their abundance and/or performance may entail community-wide effects. In the fluctuating Western Baltic, species typically experience a broad range of environmental conditions, which may preselect them to better cope with climate change. In this study, we examined the sensitivity of two crucial ontogenetic phases (naupliar, cypris) of the barnacle toward a range of temperature (12, 20, and 28°C) and salinity (5, 15, and 30 psu) combinations. Under all salinity treatments, nauplii developed faster at intermediate and high temperatures. Cyprid metamorphosis success, in contrast, was interactively impacted by temperature and salinity. Survival of nauplii decreased with increasing salinity under all temperature treatments. Highest settlement rates occurred at the intermediate temperature and salinity combination, i.e., 20°C and 15 psu. Settlement success of “naive” cyprids, i.e., when nauplii were raised in the absence of stress (20°C/15 psu), was less impacted by stressful temperature/salinity combinations than that of cyprids with a stress history. Here, settlement success was highest at 30 psu particularly at low and high temperatures. Surprisingly, larval survival was not highest under the conditions typical for the Kiel Fjord at the season of peak settlement (20°C/15 psu). The proportion of nauplii that ultimately transformed to attached juveniles was, however, highest under these “home” conditions. Overall, only particularly stressful combinations of temperature and salinity substantially reduced larval performance and development. Given more time for adaptation, the relatively smooth climate shifts predicted will probably not dramatically affect this species.     

Suspected mechano- and chemosensory structures of Temora longicornis (Copepoda: Calanoida)

The antennulary (A1) setae of Temora longicornis Müller are suspected of being mechanosensory. In the present study, the fine structure of the antennule, setae and pegs was examined by scanning and transmission electron microscopy. Two setae arise proximal to each antennule segment junction. The supraaxial (Type 1) seta of each pair is innervated by a pair of ciliary dendrites and has the morphological characteristics of a mechanoreceptor. The sub-axial (Type 2) seta may be chemosensory, and is innervated by a varying number of dendrites, but always more than two. The antennulary pegs do not appear to be innervated. T. longicornis is directionally sensitive to water disturbances, and this is consistent with the physical structure of the setae. Integumental structures on the body and other non-feeding appendages are described. These observations support previous behavioural experiments which suggested the antennule to be the major site for mechanoreception in copepods; however, mechanoreceptors must also occur on other parts of the body.