Prevalence of Panulirus argus Virus 1 (PaV1) and habitation patterns of healthy and diseased Caribbean spiny lobsters in shelter-limited habitats

Caribbean spiny lobsters Panulirus argus are socially gregarious, preferring shelters harboring conspecifics over empty shelters. In laboratory trials, however, healthy lobsters strongly avoided shelters harboring lobsters infected with the highly pathogenic Panulirus argus Virus 1 (PaV1). Because PaV1 is transmitted by contact, this behavior may thwart its spread in wild lobsters. In a field experiment conducted from 1998 to 2002 in a shelter-poor reef lagoon (Puerto Morelos, Mexico), densities of juvenile P. argus increased significantly on sites enhanced with artificial shelters (casitas) but not on control sites. Because PaV1 emerged in this location during 2000, we reexamined these data to assess whether casitas could potentially increase transmission of PaV1. In 2001, PaV1 prevalence was 2.5% and the cohabitation level (percentage of healthy lobsters cohabiting with diseased lobsters) was similar between natural shelters (3.5%) and casitas (2.4 %). The relative lobster densities in casita sites and control sites did not change significantly before (1998-1999) or after (2001-2002) the disease emergence. In late 2006, data from casita sites showed a significant increase in prevalence (10.9%) and cohabitation level (29.4%), but no significant changes in lobster density. In May 2006, casitas were deployed on shelter-poor sites within Chinchorro Bank, 260 km south of Puerto Morelos. In late 2006, prevalence and cohabitation level were 7.4 and 21.7%, respectively. Our results are inconclusive as to whether or not casitas increase PaV1 transmission, but suggest that across shelter-poor habitats, lobsters make a trade-off between avoiding diseased conspecifics and avoiding predation risk.     

Transmission of Panulirus argus virus 1 (PaV1) and its effect on the survival of juvenile Caribbean spiny lobster

The Caribbean spiny lobster Panulirus argus, an important fisheries species, is host to Panulirus argus virus 1 (PaV1), a lethal, unclassified virus--the first found in any species of lobster--prevalent in juvenile lobsters. We describe a series of laboratory experiments aimed at assessing the likely modes of disease transmission, determining the survival of lobsters relative to each transmission pathway and identifying potential alternate hosts. Given evidence for lower prevalence of PaV1 in large lobsters, the effect of lobster size on susceptibility was also examined. Results demonstrated that PaV1 can be transmitted to juvenile lobsters via inoculation, ingestion of diseased tissue, contact with diseased lobsters and--among the smallest juveniles--through water over distances of a few meters. Contact and waterborne transmission, the most likely modes of transmission in the wild, were less efficient than inoculation or ingestion. Nevertheless, about half of the smallest lobsters in contact and waterborne trials contracted the disease and died within 3 mo. Other decapods that co-occur with P. argus (e.g. spotted lobster P. guttatus, stone crab Menippe mercenaria, channel crab Mithrax spinosissimus) did not acquire the disease after inoculation with PaV1-infected hemolymph. Our results confirmed that PaV1 is highly infectious and lethal to juvenile P. argus, particularly early benthic juveniles in the wild, and, hence, is a threat to mariculture.     

First evidence of Panulirus argus Virus 1 (PaV1) in spiny lobster from Cuba and clinical estimation of its prevalence

The present study documents the first finding of Panulirus argus Virus 1 (PaV1) in spiny lobster Panulirus argus from Cuba. Samples originated from 2 nursery sites, Matias Keys and Bocas de Alonso Keys, and 2 fishing sites, La Grifa and El Ramajo. Lobsters from the nursery sites (artificial reefs) were collected by SCUBA diving, while those from the fishing sites were collected from artificial shelters known as 'casitas cubanas'. In these shelters it was observed that healthy lobsters tended to avoid infected lobsters. Prevalence of PaV1 in the sampling sites was assessed by using clinical signs such as lethargy, an opaque reddish shell coloration, and milky white hemolymph with loss of clotting activity. The presence of PaV1 was subsequently confirmed by histology and PCR of tissues and hemolymph samples from suspected individuals. Histological sections of the hepatopancreas, gills, gonads, and gut showed infected hemocytes with hypertrophied nuclei and eosinophilic intranuclear Cowdry type A inclusions. A 499 bp band was observed by PCR. The sequence of the amplified fragments was 96% similar to the PaV1 sequence in GenBank. The overall mean prevalence of PaV1 was 4.48% (range: 0 to 9.3%) after pooling the results of the 4 sampling sites.     

Nutritional indices of juvenile Caribbean spiny lobsters in a Mexican reef lagoon: Are changes over a 10-year span related to the emergence of Panulirus argus Virus 1 (PaV1)?

We compared two indices of nutritional condition, the relative weight of the digestive gland (RWDG) and the ratio of weight to carapace length (weight/CL ratio), of the first three benthic phases, algal juveniles (7–25 mm CL), postalgal juveniles (25–45 mm CL), and subadults (45–79 mm CL) of Caribbean spiny lobster (Panulirus argus) dwelling in a shelter-poor reef lagoon before (1995) and after (2005) deployment of large artificial shelters (“casitas”) in 1998. To provide an experimental baseline, in 2005 we also conducted a laboratory experiment to assess the effect of starvation on both nutritional indices. Through 25-day trials, starvation significantly decreased the mean RWDG of all three juvenile phases, but did not affect their weight/CL ratios. In the field, casitas significantly enhanced juvenile lobsters relative to control sites and to prior values, but between 1995 and 2005 there was a significant decrease in condition of algal juveniles (both indices) and postalgal juveniles (only the RWDG), but not of subadults. These results would appear to counter previous findings that, for P. argus, food is not limiting and nutritional condition is not density-dependent. However, in 2000, a new pathogenic virus that has a distinct predilection for small juveniles, Panulirus argus Virus 1 (PaV1), emerged in the reef lagoon. Among other effects, this lethal virus causes a marked atrophy of the digestive gland. Through the laboratory trials and in the field, prevalence of visibly diseased individuals was highest in algal juveniles and lowest in subadults. These individuals were excluded from statistical analyses, but the disease progression may affect the digestive gland progressively given that newly infected lobsters take several weeks to become visibly diseased. Up to 2006, PaV1 had not significantly impacted lobster density on casita sites, but because P. argus is highly gregarious and transmission of PaV1 appears to be mainly by contact, futher investigation is required. These issues are relevant to enhancement of spiny lobsters and assessment of ecological impacts of marine diseases.     

Detection of Panulirus argus Virus 1 (PaVI) in the Caribbean spiny lobster using fluorescence in situ hybridization (FISH)

Panulirus argus Virus 1 (PaV1) is the first virus known to be pathogenic to a wild lobster. It infects the Caribbean spiny lobster P. argus from the Florida Keys, and has a predilection for juveniles. The monitoring of the virus in wild populations and study of its behavior in the laboratory require the development of reliable diagnostic tools. A sensitive and specific fluorescence in situ hybridization (FISH) assay was developed for detection of PaV1. The lower detection limit using a 110 bp DNA probe in a dot-blot hygridization for PaV1 DNA was 10 pg of cloned template PaV1 DNA and 10 ng of genomic DNA extracted from the hemolymph of diseased spiny lobster. The fluorescein (FITC)-labeled probe specifically hybridized to PaVl-infected cells in the hepatopancreas, hindgut, gills, heart, foregut, and nerve tissues. FITC staining was observed around the inner periphery of the nuclear membrane, with lighter staining in a more dispersed pattern within the nucleus. The probe did not hybridize with host tissues of uninfected spiny lobsters, nor did it cross-react with 4 other virus samples tested. This assay will facilitate our understanding of the pathogenesis of the viral disease and help in monitoring efforts directed at determining the prevalence of PaV1 in juvenile nurseries for this lobster.     

Review of Panulirus argus virus 1--a decade after its discovery

In 2000, a pathogenic virus was discovered in juvenile Caribbean spiny lobsters Panulirus argus from the Florida Keys, U.S.A. Panulirus argus virus 1 (PaV1) is the first naturally occurring pathogenic virus reported from lobsters, and it profoundly affects their ecology and physiology. PaV1 is widespread in the Caribbean with infections reported in Florida (U.S.A.), St. Croix, St. Kitts, Yucatan (Mexico), Belize, and Cuba. It is most prevalent and nearly always lethal in the smallest juvenile lobsters, but this declines with increasing lobster size; adults harbor the virus, but do not present the characteristic signs of the disease. No other PaV1 hosts are known. The prevalence of PaV1 in juvenile lobsters from the Florida Keys has been stable since 1999, but has risen to nearly 11% in the eastern Yucatan since 2001. Heavily infected lobsters become sedentary, cease feeding, and die of metabolic exhaustion. Experimental routes of viral transmission include ingestion, contact, and for newly settled juveniles, free virus particles in seawater. Prior to infectiousness, healthy lobsters tend to avoid diseased lobsters and so infected juvenile lobsters mostly dwell alone, which appears to reduce disease transmission. However, avoidance of diseased individuals may result in increased shelter competition between healthy and diseased lobsters, and greater predation on infected lobsters. Little is known about PaV1 outside of Mexico and the USA, but it poses a potential threat to P. argus fisheries throughout the Caribbean.     

Ecological and physiological effects of PaV1 infection on the Caribbean spiny lobster (Panulirus argus Latreille)

Pathogens can profoundly impact the ecology of the organisms they infect through changes in host behavior that influence demographic processes. For example, juvenile Caribbean spiny lobsters (Panulirus argus Latreille) infected with the PaV1 virus (Panulirus argus Virus 1) are avoided by their normally social conspecifics, which alters local spatial distributions and presumably rates of disease transmission. PaV1 infections are nearly always lethal, but prior to succumbing to the disease, infection may impact other host dynamics (e.g., movement, growth, or survival) that effect transmission of the virus. We used mark-recapture surveys and laboratory studies to determine the impact of PaV1 infection on lobster movement and physiological condition, and in turn, the effect of condition on susceptibility to infection. Significantly more healthy lobsters were recaptured than heavily diseased lobsters in 5-d mark-recapture surveys, indicating either greater emigration or greater mortality of infected lobsters. Results of a laboratory bioassay suggest that lobsters with early-stage infections moved at an equivalent rate to healthy lobsters, however, as infection progressed, lobsters inoculated with PaV1 moved less than healthy lobsters ultimately remaining sedentary. Infected lobsters captured in nature also had significantly lower hemolymph (blood) serum protein values, indicating poor physiological condition. However, poor condition did not predispose lobsters to greater risk of infection because prevalence was not different between starved lobsters and healthy lobsters challenged with PaV1. Although lobsters infected with PaV1 eventually become sedentary and of poor nutritional condition, during the early stages of infection they remain active and are thus capable of dispersing the virus throughout the population.     

Short- and long-term movements of painted lobster (Panulirus versicolor) on a coral reef at Northwest Island, Australia

Understanding movements of palinurid (spiny) lobsters is important to fisheries management. However, movement data obtained with mark-capture techniques are often influenced by artefacts (e.g., displacement, tag-loss, tag-induced injury). To avoid these problems, a novel approach was employed to investigate the movements of an important coral reef palinurid, the painted lobster (Panulirus versicolor). Eighty adult individuals were captured by hand near Northwest Island, Australia. Each lobster was tagged internally (with elastomer) and externally (with plastic zip-ties) to enable both short- (1–10 days) and long-term (6–24 months) observations. Shortly thereafter, all lobsters were manually returned to their shelters (dens). After 6–24 months, 44 lobsters were recaptured, giving an overall recapture rate of 55%. All of these individuals were recaptured within 500 m of their original den, thus indicating a high level of site-fidelity for this species. Short-term observations revealed that individuals moved frequently to and from nearby dens, and that male lobsters typically moved further than female lobsters. It is hypothesized that male lobsters move about their home range more actively, perhaps to seek mating opportunities or to defend resources. The significance of these observations is discussed with respect to the management of this important fishery resource.     

Relative predation risk in two types of habitat for juvenile Australasian spiny lobsters,Jasus edwardsii

The decline in kelp habitat on coastal reefs resulting from changes in ocean climate and the distribution and abundance of herbivorous species is common in many temperate regions of the world. Kelp habitat is highly productive, biodiverse and provides a complex habitat into which many organisms recruit, including spiny lobsters, such as the Australasian red spiny lobster, Jasus edwardsii. The displacement of kelp habitat by less-complex barren reef habitat has the potential to influence the risk of predation for early juvenile lobsters. Therefore, relative predation risk on the juvenile spiny lobster, J. edwardsii, was compared for kelp and barren habitats on the northeast coast of New Zealand using juvenile lobsters held in transparent containers and recording predators with a video recorder. In total, 188 predation attempts were observed within 420?h of video recordings gathered over 3 weeks of sampling. There was an overall higher predation risk in barren habitats. Daytime predation attempts were higher in barren compared to kelp habitat; however, there was no difference between the habitats for night time, dawn or dusk observations, when juvenile lobsters are emergent from shelters and vulnerable to predation. Similar numbers of predatory species were identified in kelp (13) and barren habitat (12). Other factors, such as food availability and time spent away from shelter, especially during night and crepuscular periods, need consideration in future studies when investigating the cause of differences in juvenile lobster mortality among habitats.     

Diseases of spiny lobsters: a review

Spiny lobsters have few reported pathogens, parasites and symbionts. However, they do have a diverse fauna comprised of a pathogenic virus, several bacteria, protozoans, helminths and even symbiotic crustaceans. A few idiopathic syndromes have also been reported, but these appear correlated with lobsters held in poor conditions. Fungal and bacterial pathogens present significant threats for rearing spiny lobsters in aquaculture settings, but only one pathogen, Panulirus argus virus 1, is thought to have damaged a fishery for a spiny lobster. No doubt others will emerge as lobsters are brought into aquaculture setting and as fishing pressure intensifies with stocks become more susceptible to anthropogenic stressors.     

Identification of steroid hormones and fatty acids during gonadal maturation of spiny lobster Panulirus homarus

Information on steroid hormones and fatty acids that play roles in lobster reproduction is still very limited although the data are indispensable to seed production in hatchery. The study was designed to identify steroid hormones and fatty acids during gonadal maturation of spiny lobster (Panulirus homarus). Male spiny lobsters were treated with and without thyroxine injection. Female spiny lobsters were treated with and without eyestalk ablations during mature and immature gonad developments. Androst-5-en-17-one,3β (androst) and estran-3-one,17β (estran), two steroid hormones were identified at different levels of gonadal maturity of spiny lobsters. High concentrations of androst and estran were detected in the male spiny lobsters treated with thyroxine injections. Estran showed high concentrations in female brood stock of spiny lobsters during oogenesis stages both without eyestalk ablation and with ablation of one or two eyestalks, except in the immature female gonads. It was found that stearic acid was the highest and dominant fatty acid in mature male spiny lobster. Stearic acid, oleic acid, palmitic acid and caprylic acid were fatty acids with high concentrations in immature and mature female spiny lobsters. After 30 days in captivity, only stearic acid and oleic acid were found dominantly in eyestalk ablated mature female spiny lobsters.     

Influence of conspecific and heterospecific aggregation cues and alarm odors on shelter choice by syntopic spiny lobsters

In spiny lobsters, conspecific scents ("aggregation cues") may mediate gregarious diurnal sheltering, but scents from injured conspecifics ("alarm odors") may elicit avoidance behavior. In laboratory experiments, individuals of two coexisting species, Panulirus guttatus (a reef-obligate) and P. argus (a temporary reef-dweller), significantly chose shelters emanating conspecific aggregation cues and responded randomly to shelters emanating heterospecific aggregation cues. However, despite evidence that the two species perceived each other's alarm odors to a similar extent, P. guttatus responded randomly to shelters emanating either conspecific or heterospecific alarm odors, whereas P. argus significantly avoided both. This differential influence of alarm odors likely reflects interspecific differences in life history, sociality, and behavior. The less social, reef-obligate P. guttatus lobsters forage close to their reef dens, into which they retract deeply upon perception of risk. This cryptic behavior may offset the need to avoid conspecific (and heterospecific) alarm odors. In contrast, avoidance of conspecific alarm odors by P. argus is consistent with its ontogenetic habitat shifts and greater sociality. Furthermore, because reef-dwelling P. argus lobsters forage across open areas away from the reef, an ability to avoid alarm odors from P. guttatus upon returning to their reef dens may increase their fitness.     

Temporal shift in the presence of a chemical cue contributes to a diel shift in sociality

Spatial and temporal variation in animal aggregations may be due to variation in the presence of cues for aggregation (or disaggregation) or to variation in the receptivity of the animal to a particular cue or suite of cues. Spiny lobsters, Panulirus argus, forage solitarily but are often found aggregated in their diurnal shelters. An important proximate cause of aggregation among spiny lobsters is a scent they produce that influences shelter choice by conspecifics. We examined how variability in the presence of, or response to, such a chemical cue may contribute to diel shifts in sociality among spiny lobsters. We conducted a series of Y-maze shelter choice experiments using lobsters that were either maintained under altered dark:light schedules in the experimental arena or under natural lighting in the head tanks. Lobsters that were maintained on a light schedule 8 h later than normal chose shelters at their dawn (corresponding to the middle of the night for lobsters in the head tanks); however, their choices of shelter were not influenced by scents of conspecifics. Lobsters that were maintained on a schedule 8 h earlier than normal chose shelters in the middle of their night (corresponding to dawn for the lobsters in the head tanks). Their choices of shelter were significantly influenced by conspecific scents. These results suggest that the chemical cues for aggregation, released by spiny lobsters, are present discontinuously, that spiny lobsters are influenced by conspecific odours continuously, and that aggregation is controlled by temporal variation in the presence of a chemical cue. Copyright 2000 The Association for the Study of Animal Behaviour.     

Presence of Panulirus argus virus 1 (PaV1) in juvenile spiny lobsters Panulirus argus from the Caribbean coast of Mexico

Macroscopic evidence, histological sections, transmission electron microscopy (TEM) evaluation, and PCR analyses of 25 apparently diseased juvenile spiny lobsters Panulirus argus from the reef lagoon of Puerto Morelos, Mexico, showed the presence of Panulirus argus Virus 1 (PaV1). Cowdry Type A intranuclear viral inclusions were observed in histological analyses, icosahedral viral particles were observed by TEM, and PCR using specific primers for PaV1 amplified a fragment of 499 bp. This is the first report of PaV1 infecting P. argus outside the Florida Keys, USA.     

Primary culture of hemocytes from the Caribbean spiny lobster, Panulirus argus, and their susceptibility to Panulirus argus Virus 1 (PaV1)

Primary cultures of hemocytes from the Caribbean spiny lobster Panulirus argus were developed for studies on the in vitro propagation of Panulirus argus Virus 1 (PaV1). A modified Leibovitz L-15 medium supported the best survival of hemocytes in in vitro primary cultures. However, degradation of the cultures occurred rapidly in the presence of granulocytes. A Percoll step gradient was used to separate hemocytes into three subpopulations enriched in hyalinocytes, semigranulocytes, and granulocytes, respectively. When cultured separately, hyalinocytes and semigranulocytes maintained higher viability ( approximately 80%) after 18 days incubation compared with granulocytes, which degraded over 2-3 days. Susceptibility of the cell types was investigated in challenge studies with PaV1. Hyalinocytes and semigranulocytes were susceptible to PaV1. Cytopathic effects (CPE) were observed as early as 12h post-inoculation, and as the infection progressed, CPE became more apparent, with cell debris and cellular exudates present in inoculated cultures. Cell lysis was noticeable within 24h of infection. The presence of virus within cells was further confirmed by in situ hybridization using a specific DNA probe. The probe gave a unique staining pattern to cells infected with PaV1 24-h post-inoculation. Cells in the control treatment were intact and negative to hybridization. This assay was further applied to the quantification of infectious virus in hemolymph using a 50% tissue culture infectious dose assay (TCID(50)) based on CPE. These tools will now allow the quantification of PaV1 using established culture-based methods.     

A Holistic View of Dietary Carbohydrate Utilization in Lobster: Digestion,Postprandial Nutrient Flux,and Metabolism

Crustaceans exhibit a remarkable variation in their feeding habits and food type, but most knowledge on carbohydrate digestion and utilization in this group has come from research on few species. The aim of this study was to make an integrative analysis of dietary carbohydrate utilization in the spiny lobster Panulirus argus. We used complementary methodologies such as different assessments of digestibility, activity measurements of digestive and metabolic enzymes, and post-feeding flux of nutrients and metabolites. Several carbohydrates were well digested by the lobster, but maize starch was less digestible than all other starches studied, and its inclusion in diet affected protein digestibility. Most intense hydrolysis of carbohydrates in the gastric chamber of lobster occurred between 2–6 h after ingestion and afterwards free glucose increased in hemolymph. The inclusion of wheat in diet produced a slow clearance of glucose from the gastric fluid and a gradual increase in hemolymph glucose. More intense hydrolysis of protein in the gastric chamber occurred 6–12 h after ingestion and then amino acids tended to increase in hemolymph. Triglyceride concentration in hemolymph rose earlier in wheat-fed lobsters than in lobsters fed other carbohydrates, but it decreased the most 24 h later. Analyses of metabolite levels and activities of different metabolic enzymes revealed that intermolt lobsters had a low capacity to store and use glycogen, although it was slightly higher in wheat-fed lobsters. Lobsters fed maize and rice diets increased amino acid catabolism, while wheat-fed lobsters exhibited higher utilization of fatty acids. Multivariate analysis confirmed that the type of carbohydrate ingested had a profound effect on overall metabolism. Although we found no evidence of a protein-sparing effect of dietary carbohydrate, differences in the kinetics of their digestion and absorption impacted lobster metabolism determining the fate of other nutrients.     

Electrophysiological identification of the stimulatory and interactive components of a complex odorant

We are studying the olfactory system of the spiny lobster, Panulirusargus, to understand how chemical mixtures are coded. By monitoringthe activity of high-order interneurons which carry olfactoryinformation out of the brain, we have identified the componentsof a natural food of lobsters which contribute to the activityof the mixture by being either stimulatory by themselves orinteractive (suppressive or synergistic) with other componentsin the mixture. The results demonstrate that virtually all ofthe activity of this complex odorant resides in 15 stimulatoryand suppressive components, and that mixture suppression isa prevalent feature of chemosensory processing in the olfactorypathway of the spiny lobster.     

Enhancement of juvenile Caribbean spiny lobsters: an evaluation of changes in multiple response variables with the addition of large artificial shelters

Shortage of natural crevice shelters may produce population bottlenecks in juvenile Caribbean spiny lobsters (Panulirus argus), a socially gregarious species. We conducted a field experiment to test enhancement of a local population of juvenile P. argus with the addition of artificial shelters (“casitas”) that mimic large crevices (1.1 m² in surface area and 3.8 cm in height). Changes in density and biomass of juvenile lobsters 15–50 mm carapace length (CL) were assessed with a multiple before-after control-impact (MBACI) analysis. Separate analyses were also conducted on small (15–35 mm CL) and large (35.1–50 mm CL) juveniles to assess size-related effects. First, we carried out 13 lobster surveys on nine fixed 1-ha sites over a shallow reef lagoon (“before” period). Then, we deployed ten casitas in each of five sites and left four sites as controls, and conducted 22 further surveys (“after” period). Deployment of casitas resulted in a sixfold increase in juvenile density (76% contributed by small and 24% by large juveniles) and a sevenfold increase in biomass (40 and 60%, respectively). Capture–recapture results revealed that enhancement was achieved not by promoting individual growth but by increasing survival, persistence, and foraging ranges of small and large juveniles. Casitas both mitigated shortage of natural shelter and increased sociality, allowing for cohabitation of smaller, more vulnerable juveniles with larger conspecifics that have greater defensive abilities. Casitas may help enhance local populations of juvenile P. argus in Caribbean seagrass habitats, typically poor in natural crevice shelters. The use of MBACI and the simultaneous assessment of multiple interrelated response variables may be a powerful analytical approach to test shelter limitation in other species and to examine the function of structural habitat in other systems.     

Source and specificity of chemical cues mediating shelter preference of Caribbean spiny lobsters (Panulirus argus)

Caribbean spiny lobsters display a diversity of social behaviors, one of the most prevalent of which is gregarious diurnal sheltering. Previous research has demonstrated that shelter selection is chemically mediated, but the source of release and the identity of the aggregation signal are unknown. In this study, we investigated the source and specificity of the aggregation signal in Caribbean spiny lobsters, Panulirus argus. We developed a relatively rapid test of shelter choice in a 5000-l laboratory flume that simulated flow conditions in the spiny lobster's natural environment, and used it to examine the shelter preference of the animals in response to a variety of odorants. We found that both males and females associated preferentially with shelters emanating conspecific urine of either sex, but not with shelters emanating seawater, food odors, or the scent of a predatory octopus. These results demonstrate specificity in the cues mediating sheltering behavior and show that urine is at least one source of the aggregation signal.     

Locomotory activity and exploration behaviour of juvenile European lobsters (Homarus gammarus) in the laboratory

The behaviour of juvenile European lobsters (Homarus gammarus) in the wild is little understood. A laboratory system was designed with a maze-like environment as an alternative to the large technological expenditure of a field study. It provided an apparently endless runway with uniform thigmotactical cues. Juvenile lobsters having a total length of 68 to 115 mm were studied. The lobsters showed an extensive nocturnal locomotory activity. They established home shelters in which they spent the day and covered distances of 1200 to 1600 m during the night. On average, the lobsters performed 136 excursions from their shelters, of which 10% led only to the immediate surroundings of the shelters. Of all the excursions 90% were shorter than 16 m. In some exceptional cases distances of several hundred meters were covered in the maze between shelter visits. Excursions of less than 16 m lasted on average less than 5 min. The frequencies of shelter visits during the dark phase were highest in small lobsters (300 visits) and lowest in larger lobsters (50 visits). The time spent within shelters decreased from 10% to less than 2% with lobster size. A distinct change in behaviour was obvious at a body length of 75 to 80 mm. Smaller lobsters behaved defensively and relied on shelter protection. Larger lobsters were less dependent on shelter protection and thus were able to explore and utilize their environment more intensively.