Mucus Trails Research Articles

Mucus trail tracking in a predatory snail: olfactory processing retooled to serve a novel sensory modality

IntroductionThe rosy wolfsnail (Euglandina rosea), a predatory land snail, finds prey snails and potential mates by following their mucus trails. Euglandina have evolved unique, mobile lip extensions that detect mucus and aid in following trails. Currently, little is known of the neural substrates of the trail-following behavior.MethodsTo investigate the neural correlates of trail following we used tract-tracing experiments in which nerves were backfilled with either nickel-lysine or Lucifer yellow, extracellular recording of spiking neurons in snail procerebra using a multielectrode array, and behavioral assays of trail following and movement toward the source of a conditioned odor.ResultsThe tract-tracing experiments demonstrate that in Euglandina, the nerves carrying mucus signals innervate the same region of the central ganglia as the olfactory nerves, while the electrophysiology studies show that mucus stimulation of the sensory epithelium on the lip extensions alters the frequency and pattern of neural activity in the procerebrum in a manner similar to odor stimulation of the olfactory epithelium on the optic tentacles of another land snail species, Cantareus aspersa (previously known as Helix aspersa). While Euglandina learn to follow trails of novel chemicals that they contact with their lip extensions in one to three trials, these snails proved remarkably resistant to associative learning in the olfactory modality. Even after seven to nine pairings of odorant molecules with food, they showed no orientation toward the conditioned odor. This is in marked contrast to Cantareus snails, which reliably oriented toward conditioned odors after two to three trials.ConclusionsThe apparent inability of Euglandina to learn to associate food with odors and use odor cues to drive behavior suggests that the capability for sophisticated neural processing of nonvolatile mucus cues detected by the lip extensions has evolved at the expense of processing of odorant molecules detected by the olfactory system.

Snails and their trails: the multiple functions of trail‐following in gastropods

Snails are highly unusual among multicellular animals in that they move on a layer of costly mucus, leaving behind a trail that can be followed and utilized for various purposes by themselves or by other animals. Here we review more than 40 years of experimental and theoretical research to try to understand the ecological and evolutionary rationales for trail-following in gastropods. Data from over 30 genera are currently available, representing a broad taxonomic range living in both aquatic and terrestrial environments. The emerging picture is that the production of mucus trails, which initially was an adaptation to facilitate locomotion and/or habitat extension, has evolved to facilitate a multitude of additional functions. Trail-following supports homing behaviours, and provides simple mechanisms for self-organisation in groups of snails, promoting aggregation and thus relieving desiccation and predation pressures. In gastropods that copulate, trail-following is an important component in mate-searching, either as an alternative, or in addition to the release of water- or air-borne pheromones. In some species, this includes a capacity of males not only to identify trails of conspecifics but also to discriminate between trails laid by females and males. Notably, trail discrimination seems important as a pre-zygotic barrier to mating in some snail species. As production of a mucus trail is the most costly component of snail locomotion, it is also tempting to speculate that evolution has given rise to various ways to compensate for energy losses. Some snails, for example, increase energy intake by eating particles attached to the mucus of trails that they follow, whereas others save energy through reducing the production of their own mucus by moving over previously laid mucus trails. Trail-following to locate a prey item or a mate is also a way to save energy. While the rationale for trail-following in many cases appears clear, the basic mechanisms of trail discrimination, including the mechanisms by which many snails determine the polarity of the trail, are yet to be experimentally determined. Given the multiple functions of trail-following we propose that future studies should adopt an integrated approach, taking into account the possibility of the simultaneous occurrence of many selectively advantageous roles of trail-following behaviour in gastropods. We also believe that future opportunities to link phenotypic and genotypic traits will make possible a new generation of research projects in which gastropod trail-following, its multitude of functions and evolutionary trade-offs can be further elucidated.

Substrate Attributes Determine Gait in a Terrestrial Gastropod

Some terrestrial gastropods are able to move using two gaits: adhesive crawling, where the entire foot is separated from the substrate only by a thin layer of mucus and the snail leaves a continuous mucus trail; and loping, where regions of the foot arch above the substrate and the snail leaves a discontinuous mucus trail. Loping has been interpreted as a means of rapidly escaping predators. We found that the pulmonate Cornu aspersum moved using adhesive crawling on dry acrylic or glass substrates, but loped on dry concrete or wood. Loping snails did not move more rapidly than snails using adhesive crawling. Snails moving on concrete secreted a greater volume of pedal mucus per area of trail than those moving on acrylic; locomotion on concrete thus requires greater expenditure of mucus than does locomotion on acrylic. Because loping snails deposit a smaller area of mucus per distance traveled than do snails using adhesive crawling, loping may conserve mucus when moving on porous, absorbent substrates. Members of several other terrestrial pulmonate taxa can also lope on concrete, suggesting that this plasticity in gait is widespread among terrestrial snails.

Do Micro Snails Follow Conspecific Mucous Trails? Experiments withVallonia excentrica(Pulmonata: Valloniidae)

We examined whether the terrestrial micro snail Vallonia excentrica Sterki, 1893 detects and follows conspecific mucous trails. A trail-layer snail moved on a transparent 5×5 cm plastic sheet to establish a mucous trail then was removed. A trail-follower snail of the same species was allowed to move on the same plastic sheet. Of 30 trials, 24 trail-followers encountered the laid trail. We compared with null models the distance that the trail-follower trail was coincident with the laid trail, and the turning angle of the trail-follower trail upon meeting the laid trail, to determine that V. excentrica follows conspecific mucous trails more, and showed sharper turning angles upon meeting a trail, than expected by the null model.

Monotypic gland-cell regions on the body surface of two species of Arion: ultrastructure and lectin-binding properties

Distinct areas of the body surface of Arion (Arion) rufus (Linnaeus, 1758) and A. (A.) vulgaris Moquin-Tandon, 1855 contain only one type of glandular cell. The specific monotypic glandular cells that are characteristic for each of these areas differ with respect to staining properties, the structure of glycans (binding of different lectins) and in their ultrastructure, particularly in the appearance of the endoplasmic reticulum. Four such glandular areas can be defined. (1) The protein gland of the anterior margin of the foot probably produces the proteins responsible for changing the trail mucus produced from other glands to strong glue-mucus. Histochemical reactions point to the presence of neutral mucosubstances, probably mucoproteins. The strongest binding of applied lectins were those specific for N-acetyl-α-d-galactosaminyl residues, specific for β-linked terminal galactose, and specific for galactose β1-3N-acetylgalactosamine. A characteristic feature of the ultrastructure of the gland cells is tightly arranged membranes of the endoplasmic reticulum as typically found in protein secreting cells. (2) The suprapedal gland consists of a flat anterior part (located in the bottom of a funnel-shaped cavity between the ventral surface of the head and the opposite dorsal surface of the anterior foot) and a posterior tubular part on the dorsal side of the foot musculature (opening by an excretory duct into the funnel-shaped cavity). Histochemical reactions indicate the presence of acid glycosaminoglycans of high negative charge density. Binding of lectins with all secretion stages indicate the presence of the terminal sequence Galα-1-3Galβ1-R. As a special feature of the ultrastructure of the gland cells, their endoplasmic reticulum contains densely packed tubules protruding at right angle from its membrane into its lumen. (3) On the ventral surface of the head, a monotypic glandular region extends into the roof of the funnel-shaped recess. Histochemical reactions indicate the presence of neutral mucosubstances. The strongest bindings of the applied lectins with the secretion were specific for N-acetyl-α-d-galactosaminyl residues and for β-linked terminal galactose. (4) Another monotypic glandular region is situated in the ventral surface of the anterior part of the mantle. Histochemical reactions indicate acid mucosubstances with high negative charge density. None of the applied lectins reacted with cells of that region. Each of the first three glandular regions has an extension into the peripodial groove on either side of the foot sole; the ‘peripodial gland’ of authors is therefore a compound structure. The branches of the protein gland extend as far back as the level of the pneumostome, while the branches of the suprapedal gland and of the glandular region of the ventral surface of the head extend further, to the corners of the base of the triangular caudal gland. The trail mucus is produced mainly by the suprapedal gland that extends with its branches into the peripodial groove. Monotypic gland cell regions are possible candidates as sources of mucus of known cellular origin for biochemical analyses.

Proteomic Profiling of the Planarian Schmidtea mediterranea and Its Mucous Reveals Similarities with Human Secretions and Those Predicted for Parasitic Flatworms

The freshwater planarian Schmidtea mediterranea has been used in research for over 100 years, and is an emerging stem cell model because of its capability of regenerating large portions of missing body parts. Exteriorly, planarians are covered in mucous secretions of unknown composition, implicated in locomotion, predation, innate immunity, and substrate adhesion. Although the planarian genome has been sequenced, it remains mostly unannotated, challenging both genomic and proteomic analyses. The goal of the current study was to annotate the proteome of the whole planarian and its mucous fraction. The S. mediterranea proteome was analyzed via mass spectrometry by using multidimensional protein identification technology with whole-worm tryptic digests. By using a proteogenomics approach, MS data were searched against an in silico translated planarian transcript database, and by using the Swiss-Prot BLAST algorithm to identify proteins similar to planarian queries. A total of 1604 proteins were identified. The mucous subproteome was defined through analysis of a mucous trail fraction and an extract obtained by treating whole worms with the mucolytic agent N-acetylcysteine. Gene Ontology analysis confirmed that the mucous fractions were enriched with secreted proteins. The S. mediterranea proteome is highly similar to that predicted for the trematode Schistosoma mansoni associated with intestinal schistosomiasis, with the mucous subproteome particularly highly conserved. Remarkably, orthologs of 119 planarian mucous proteins are present in human mucosal secretions and tear fluid. We suggest planarians have potential to be a model system for the characterization of mucous protein function and relevant to parasitic flatworm infections and diseases underlined by mucous aberrancies, such as cystic fibrosis, asthma, and other lung diseases.

Life Span of Cercariae of Postharmostomum helicis (Trematoda: Brachylaimidae) Under Different Temperatures and Relative Humidity

Survivorship of cercariae of Postharmostomum helicis (Trematoda: Brachylaimidae) was examined under different temperatures and relative humidities. Cercariae were isolated from naturally infected snails (Anguispira alternata) and maintained at combinations of 3 temperatures (16.6, 22.2, and 29.4°C) and 5 relative humidities (0%, 25%, 50%, 75%, and 100%). Cercariae maintained at low relative humidities (0–50%) died rapidly at all temperatures, surviving 30 min or less on average. At higher relative humidities, life span extended for 3 or more hr. Vapor pressure deficit was a good predictor of life span except for trials at 100% relative humidity, wherein cercariae often died prior to desiccation of the mucous trails in which they were shed. The results of the present investigation suggest that life span is highly limited except under the moistest conditions.

Finding paradise: cues directing the migration of the waterfall climbing Hawaiian gobioid Sicyopterus stimpsoni

A series of waterfall-climbing trials were conducted to identify cues that direct the climbing of juvenile Sicyopterus stimpsoni. In the first experiment, whether climbing juveniles preferentially ascend water sources with conspecifics or whether the presence of just stream water is sufficient to attract fish to ascend a climbing path were assessed. In the second experiment, whether climbing juveniles create a trail of mucus that facilitates the ability of conspecifics to follow their lead was determined. The results indicate that juvenile S. stimpsoni are less likely to climb in waters devoid of organic cues but are strongly attracted to stream water with or without the odour of conspecifics. Once climbing, performance did not differ for juveniles climbing in differing water choices, suggesting an all-or-nothing commitment once climbing commences. Climbing S. stimpsoni did produce a mucous trail while climbing that was associated with a mucous gland that dramatically increases in size just prior to juveniles gaining the ability to climb. The trail was not followed closely by subsequent juveniles traversing the same channel, however, suggesting only weak trail-following in waterfall climbing S. stimpsoni. Previous genetic studies suggest that juvenile S. stimpsoni do not home to natal streams in the face of strong near-shore oceanic currents. Instead, these fish appear primarily to rely on cues that suggest the presence of organic growth in streams, a factor that may indicate suitable habitat in an ever-changing stream environment but which may also be vulnerable to interference through human activity.

Effect of the mud snail Ilyanassa obsoleta on vital rates of the intertidal amphipod Corophium volutator

Negatively correlated densities between two species can be attributed to effects on vital rates and/or movement. On intertidal mudflats in the upper Bay of Fundy, Canada, mechanisms underlying the negative correlation between the densities of two dominant macro-invertebrates, the mud snail Ilyanassa obsoleta and the burrow-dwelling amphipod Corophium volutator, are unclear. We investigated the effect of mud snail density on survival, growth and fecundity of C. volutator in 2-wk experiments in the laboratory and field, and observed behavioral interactions between the two species. Snails negatively affected juvenile and adult survival of amphipods, juvenile growth, and proportion of females that were ovigerous. Behavioral observations revealed that snails are active predators of C. volutator, both juveniles and adults. We documented several attack methods by snails. As well, we observed that C. volutator could become entangled in laid mucus trails of snails, leaving them vulnerable to attack from snail trail-followers or other predators. Snail predation, in combination with increased C. volutator migration in the presence of snails, appears to be a primary short-term mechanism for the observed negative correlation between these invertebrate species. Competition (likely through interference), resulting in lowered growth and fecundity, may be a longer-term mechanism for this negative correlation.

Changing environments and structure–property relationships in marine biomaterials

Most marine organisms make functional biomolecular materials that extend to varying degrees 'beyond their skins'. These materials are very diverse and include shells, spines, frustules, tubes, mucus trails, egg capsules and byssal threads, to mention a few. Because they are devoid of cells, these materials lack the dynamic maintenance afforded intra-organismic tissues and thus are usually assumed to be inherently more durable than their internalized counterparts. Recent advances in nanomechanics and submicron spectroscopic imaging have enabled the characterization of structure-property relationships in a variety of extra-organismic materials and provided important new insights about their adaptive functions and stability. Some structure-property relationships in byssal threads are described to show how available analytical methods can reveal hitherto unappreciated interdependences between these materials and their prevailing chemical, physical and ecological environments.

Characterization of mucus‐associated proteins from abalone (Haliotis) – candidates for chemical signaling

Living in groups is a widespread phenomenon in the animal kingdom. For free-spawning aquatic animals, such as the abalone (Haliotis), being in the close proximity to potential mating partners enhances reproductive success. In this study, we investigated whether chemical cues could be present in abalone mucus that enable species-specific aggregation. A comparative MS analysis of mucus obtained from trailing or fixed stationary Haliotis asinina, and from seawater surrounding aggregations, indicated that water-soluble biomolecules are present and that these can stimulate sensory activity in conspecifics. Purified extracts of trail mucus contain at least three small proteins [termed H. asinina mucus-associated proteins (Has-MAPs)-1-3], which readily diffuse into the surrounding seawater and evoke a robust cephalic tentacle response in conspecifics. Mature Has-MAP-1 is approximately 9.9 kDa in size, and has a glycine-rich N-terminal region. Has-MAP-2 is approximately 6.2 kDa in size, and has similarities to schistosomin, a protein that is known to play a role in mollusc reproduction. The mature Has-MAP-3 is approximately 12.5 kDa in size, and could only be identified within trail mucus of animals outside of the reproductive season. All three Has-MAP genes are expressed at high levels within secretory cells of the juvenile abalone posterior pedal gland, consistent with a role in scent marking. We infer from these results that abalone mucus-associated proteins are candidate chemical cues that could provide informational cues to conspecifics living in close proximity and, given their apparent stability and hydrophilicity, animals further afield.

The predatory snail Euglandina rosea successfully follows mucous trails of both native and non‐native prey snails

AbstractMucous trail following is a primary means by which many predatory snails locate prey. I compared the ability of individuals of Euglandina rosea to follow mucous trails of two groups of gastropods: those found within its native habitat (southeastern USA), and those found outside its native range (Kansas). Members of E. rosea followed trails for both species found inside and outside its native range equally well. In contrast to previous studies, I found that the predatory snails consistently followed trails in the direction in which they were laid. I quantified the kinematics of trail‐following behavior using inter‐tentacle angle as the primary metric. In both prey groups, there were significant differences in the predator's inter‐tentacle angle when tracking a trail versus not, and when successfully following (in the direction the trail was laid) versus unsuccessfully following (opposite the direction that the trail was laid) trails. In addition, in both prey groups, there were significant differences in the predator's velocity when tracking a trail versus not, and when successfully versus unsuccessfully following trails. This study confirmed that members of E. rosea are robust generalist predators, capable of successfully tracking native and non‐native snails, and should not be introduced as biologic control agents. These results may be useful to managers, as they provide insight into how trail following could be used to trap members of this invasive species.

Mucus trail following as a mate-searching strategy in mangrove littorinid snails

Mate searching often involves chemical cues and is a key process in determining fitness in most sexually reproducing animals. Effective mate-searching strategies are, therefore, essential for individuals to avoid wasting resources as a result of misrecognition of mating partners. Marine snails in the genus Littoraria are among the most successful molluscan groups that live closely associated with mangroves. Their population densities are often low, and finding a mate within the complex three-dimensional habitat of tree leaves, branches and trunks requires an effective searching strategy. We tested whether males of L. ardouiniana and L. melanostoma located females by following their mucus trails. In the laboratory, male tracker snails followed mucus trails laid by conspecific female marker snails at a higher intensity compared with other markeretracker sex combinations in the mating season, but not in the nonmating season, and this was more pronounced in L. ardouiniana. Male trackers did not move faster when following the trails of conspecific female markers compared with other sex combinations; however, tracker snails moved faster in the mating than in the nonmating season, although this might be related to temperature. In both species, males tracked females regardless of trail complexity, and the majority of male trackers were able to detect the direction (polarity) of the trails of conspecific females. Together with previous studies on rocky shore Littorina species, these findings suggest that sex pheromones are incorporated into mucus trails to facilitate the reproductive success of these snails. Mucus trail following is, therefore, an adaptive mate-searching strategy in intertidal gastropod molluscs, and potentially in other gastropod groups in which trail-following behaviour is prevalent.

The chemosensory ability of the predatory leech Whitmania laevis (Arhynchobdellida: Haemopidae) for prey searching

Although prey-detecting and searching abilities of predatory leeches of rhynchobdellid or the Erpobdelliformes of arhynchobdellid species have been studied in the past, hirudiniformes leeches are rarely mentioned. In this study, we investigated the chemosensory ability for prey-detecting and searching in Whitmania laevis, a hirudiniformes species that mainly preys on freshwater snails, and examined if such ability aided in their prey selection. Five sympatric snail species, i.e., apple snail Pomacea canaliculata, thiarid snail Thiara tuberculata, viviparid snail Sinotaia quadrata, ear pond snail Radix auricularia swinhoei and tadpole snail Physa acuta were used as prey. Our results showed that W. laevis has the chemosensory ability to detect the waterborne odors of snails. However, they follow the snails by their mucus trails, and not by the odor that the snails leave in the water. Of these five snail species, W. laevis only followed the trails of the thiarid snails, ear pond snails and tadpole snails, and did not show a different response to the trails produced by snails of different sizes. Our results suggest that W. laevis can use waterborne odors to detect the existence of prey. They rely on mucus trails to follow their preferred prey, but do not distinguish between snails of a preferred size by their mucus trails. In addition, when following the trail of a preferred snail, W. laevis exhibits a newly described searching behavior, i.e., head tapping, and may use it to locate a snail trail and increase its probability of finding the trail-laying snail nearby.

Settlement ofHaliotis australisLarvae: Role of Cues and Orientation of the Substratum

Haliotis australis is a medium-size New Zealand abalone with aquaculture potential. H. australis can be readily ripened and spawned, but larval settlement has proved difficult. The current study addressed aspects of larval settlement (i.e., attachment and metamorphosis) in laboratory experiments and small-scale hatchery trials. Competence to metamorphose was first seen weakly in larvae at 8 days old at 14.5°C, but larval metamorphosis rates increased progressively up to at least 12 days of age. In laboratory experiments, larvae showed a dose-dependent response to dissolved γ-aminobutyric acid (GABA), with settlement peaking at 1 µM (57% metamorphosis 4 days after settlement induction) and declining at higher and lower doses. Across a range of cues, metamorphosis was highest on crustose coralline algae (97 ± 4% metamorphosis after 4 days), intermediate on 1 µM GABA (55 ± 14%), and low on diatom films (<20%). GABA combined additively with diatom film to give strong metamorphosis (81 ± 6%). Metamorphosis induction by a diatom film was doubled if the film was pregrazed by juvenile H. australis (76% vs. 35%, P < 0.0001), but the grazing effect appeared to be species specific, because pregrazing by Haliotis iris had no effect (41% vs. 35%, P = 0.720). The species-specific response to trail mucus appears to preclude GABA as being the main inducer of metamorphosis in this case. On hatchery plates, settlement on pregrazed biofilms was approximately 4-fold higher when the plates were horizontal rather than vertical (41 % vs. 10% metamorphosis, P = 0.003). Settlement on ungrazed horizontal plates remained low even if those plates had been held in water with adult conspecifics, but without contacting the abalone. We conclude that tanks offering sloped or horizontal surfaces will be more effective than vertical plates for settlement of H. australis, and that pregrazed biofilms and/or GABA are promising settlement cues.

Prey-tracking behavior in the invasive terrestrial planarian Platydemus manokwari (Platyhelminthes, Tricladida)

Platydemus manokwari is a broadly distributed invasive terrestrial flatworm that preys heavily on land snails and has been credited with the demise of numerous threatened island faunas. We examined whether P. manokwari tracks the mucus trails of land snail prey, investigated its ability to determine trail direction, and evaluated prey preference among various land snail species. A plastic treatment plate with the mucus trail of a single species and a control plate without the trail were placed side by side at the exit of cages housing P. manokwari. All trials were then videotaped overnight. The flatworms moved along plates with mucus trails, but did not respond to plates without trails, blank control (distilled water), or with conspecific flatworm trails. When presented at the midpoint of a snail mucus trail, the flatworms followed the trail in a random direction. The flatworms showed a preference when choosing between two plates, each with a mucus trail of different land snail species. Our results suggest that P. manokwari follows snail mucus trails based on chemical cues to increase the chance of encountering prey; however, trail-tracking behavior showed no directionality.

Indiscriminate Males: Mating Behaviour of a Marine Snail Compromised by a Sexual Conflict?

BackgroundIn promiscuous species, male fitness is expected to increase with repeated matings in an open-ended fashion (thereby increasing number of partners or probability of paternity) whereas female fitness should level out at some optimal number of copulations when direct and indirect benefits still outweigh the costs of courtship and copulation. After this fitness peak, additional copulations would incur female fitness costs and be under opposing selection. Hence, a sexual conflict over mating frequency may evolve in species where females are forced to engage in costly matings. Under such circumstance, if females could avoid male detection, significant fitness benefits from such avoidance strategies would be predicted.Methodology/Principal FindingsAmong four Littorina species, one lives at very much higher densities and has a longer mating season than the other three species. Using video records of snail behaviour in a laboratory arena we show that males of the low-density species discriminate among male and female mucous trails, trailing females for copulations. In the high-density species, however, males fail to discriminate between male and female trails, not because males are unable to identify female trails (which we show using heterospecific females), but because females do not, as the other species, add a gender-specific cue to their trail.Conclusions/SignificanceWe conclude that there is likely a sexual conflict over mating frequency in the high-density species (L. saxatilis) owing to females most likely being less sperm-limited in this species. This has favoured the evolution of females that permanently or optionally do not release a cue in the mucus to decrease excessive and costly matings resulting in unusually high frequencies of male-male copulating attempts in the wild. This is one of few examples of masking gender identity to obtain fewer matings.

Investment in testes, sperm‐duct glands and lipid reserves differs between male morphs but not between early and late breeding season in Pomatoschistus minutus

This study of the sand goby Pomatoschistus minutus, a nest-holding fish with paternal care, focused on gonadal investment among males of different sizes collected early and late in the breeding season. All males caught at the nest had breeding colour, whereas trawl-caught fish consisted of males both with and without colour. The absence or presence of breeding colour was a good predictor of testes investment. Compared to males with breeding colour, males without colour were smaller in body size but had extraordinarily large testes. In absolute terms, testes mass of males without breeding colour was on average 3.4 times greater than those of males with breeding colour. Since small colourless males are known to reproduce as sneaker males, this heavy investment in testes probably reflects that they are forced to spawn under sperm competition. Contrary to testes size, sperm-duct glands were largest among males with breeding colour. These glands produce mucins used for making sperm-containing mucous trails that males place in the nest before and during spawning. Since both sneakers and nest-holders potentially could benefit from having large glands, this result is intriguing. Yet, high mucus production may be more important for nest-holders, because it also protects developing embryos from infections. There was no significant effect of season on body size, testes or sperm-duct glands size, but colourless males tended to be less common late in the season. Possibly this may indicate that individual small colourless males develop into their more colourful counterparts within the breeding season.

Sediment recognition by post-larval stages of Eupolymnia nebulosa (Polychaeta, Terebellidae)

The displacements and activity by post-larval stages and early juveniles of Eupolymnia nebulosa sampled from two sites on the French (Bay of Banyuls) and Spanish (Bay of Blanes) Catalan coast were analysed and compared. Actographic track analysis indicated recognition of sediments that had been previously reworked by adults. Exploration time and track width were significantly different when more than one individual had explored the same area, which suggested that juveniles can recognise the biologically modified sediment and change their behaviour accordingly. This reaction may be related to the mucus trail left behind on the sand grains during displacements. Possible olfactory recognition either alone, or in combination with detection of the mucus film remaining on the sediment grains is hypothesised. Individuals from the Blanes population, living 150 km south of the Banyuls population, had a different type of behaviour in the presence of sediment reworked by adults from Banyuls. In the presence of sediment marked by adults from Banyuls they showed no positive response.

Inhibitory Effect of 2,4-Dibromophenol and 2,4,6-Tribromophenol on Settlement and Survival of Larvae of the Japanese AbaloneHaliotis Discus HannaiIno

We examined the inhibitory effects of 2,4-dibromophenol (DBP) and 2,4,6-tribromophenol (TBP), which are released by the large perennial brown algae Eisenia bicyclis and Ecklonia kurome, on settlement and survival of veliger larvae of the Japanese abalone Haliotis discus hannai. The proportion of larvae attached to a polycarbonate chip coated with pregrazed diatom films and abalone trail mucus reached 70% by 2 h, and the proportion of larvae that underwent metamorphosis rose gradually to 65% at 8 h and 85% at 24 h. DBP and TBP at 1 ppm had no effect on larval health or settlement. However, in the presence of 10 ppm DBP, the proportions of larvae attached and metamorphosed were reduced to less than 15% and less than 2%, respectively, and those of overturned and dead larvae were increased to 50% and 41% at 24 h, respectively. In the presence of 10 ppm TBP, the proportion of metamorphosed larvae was reduced to 53% and that of overturned larvae increased to 30% at 24 h. All larvae exposed to 50 ppm DBP or TBP died after 2 h or 8 h, respectively. These findings suggest that DBP and TBP strongly inhibit attachment, metamorphosis, or both at 10 ppm, and that DBP is more toxic than TBP. DBP and TBP may explain low recruitment levels of abalone in kelp forests.