Antennae-whipping behavior in the American lobster, Homarus Americanus (Milne-Edwards)

Electrophysiological techniques were employed to demonstrate that an acrylic coating blocks the mechanosensory activity of the cuticular hair organs on the chelipeds of Homarus americanus (Milne-Edwards) without eliciting spurious activity in their innervation.Agonistic encounters between animals with acrylic on the dorsal surface of the claws (experimental), on the ventral surface of the claws (“plastic” control), and absent (“bare” control) were observed. Experimental animals responded to <3% of all antennae-whips, while “plastic” control animals responded to 73%, and “bare” control animals to 64%, of all antennae-whips. We conclude that antennae-whipping is a form of tactile communication, in which information probably is received through mechanosensory activity in the cuticular hair organs on the dorsal surface of the chelipeds.     

The successful induction of molting in the adult male lobster (Homarus Americanus) with a slow-release form of ecdysterone

In an initial, and then a confirmatory experiment, adult, male lobsters were injected with solvent, ecdysterone (E, 2.0 μg/g live weight) or ecdysterone acetate (EAc, 2.5 or 5.0 μg/g live weight) emulsions in Freund's incomplete adjuvant (FIA). Control lobsters underwent no molts and only one death in the two cases. The E treated animals all died (average: exp. 1, 19.2 ± 2.1 days; exp. 2, 25.3 ± 8 days). After the lobsters were treated twice with 2.5 μg EAc/g live weight, in the first experiment, four out of five molted and one died; in the second experiment six out of eight molted, one died and one remained refractory. The high EAc dose resulted in five deaths, one molt and two pseudomolts after one treatment. It is concluded that the use of the oil emulsion and EAc sufficiently slowed the release of free ecdysterone to allow complete premolt development in the lobster.     

An unusual cuticular tumor-like growth on the abdomen of a lobster, Homarus americanus

Tumors are rare in crustaceans, and whereas a few have been reported from the lobster Homarus americanus none have been adequately described. A lobster with an unusual, large, blue-colored tumor-like growth projecting laterally outward from the first abdominal somite was caught off Stonington, Maine, USA. The growth was rugose and covered by a relatively normal appearing cuticle with dispersed focal melanization. The underlying stroma consisted of an internal area of rescaffolded fibrous connective tissue, restructured muscle fibers, few arterioles, and an epidermal area comprised of columnar, highly vacuolated epithelial cells. No infectious pathogens or unusual inclusions were observed with microscopy and no eukaryotic pathogens were detected via molecular sequencing. Given the nature of the histology and the appearance of the growth, we identify the mass as a benign papilliform hamartoma that likely originated as a result of abnormal wound repair possibly initiated around ecdysis. This represents the first tumor-like hamartoma reported from a lobster, and the second hamartoma reported from a crustacean.     

Daily and circadian rhythms of locomotor activity in the American lobster, Homarus americanus

It is widely accepted that American lobsters, Homarus americanus (Milne-Edwards), are nocturnally active. However, the degree to which this rhythm is expressed by different individuals and the underlying causes of lobster activity rhythms, are poorly understood. In order to address these issues we recorded daily patterns of lobster locomotion using two novel techniques. In the first, reed switch assemblies were used to monitor the distance traveled by freely moving lobsters (n=43), each fitted with a small magnet, as they walked around a 1 m diameter racetrack. The advantages of this technique included: (1) lobsters were freely moving; (2) the system could be deployed in laboratory tanks or in the field and; (3) actual distances moved were measured, not just relative activity. The second technique involved placing individual lobsters (n=10) into custom-designed running wheels. This allowed for continuous monitoring of locomotor activity for extended durations (>45 days) under normal light/dark (L/D) cycles, as well as in constant darkness (D/D) and constant light (L/L).Under ambient light conditions lobsters in the racetracks moved an average of 60.1±6.5 m/day in flow-through seawater tanks. Overall, lobsters were significantly more active at night, moving 4.1±0.4 m/h in the dark vs. 1.0±0.2 m/h in the light. However, many of the lobsters moved as much during the day as during the night.Lobsters in the running wheels moved an average of 36.6±11.7 m/day and 80% expressed clear daily rhythms of activity, with a mean periodicity of 24.0±0.1 h under L/D conditions. Under D/D conditions 90% of the animals expressed free-running circadian rhythms with a mean periodicity of 24.2±0.3 h, indicating that this species possesses endogenous rhythmicity. While the running wheel results show that the nocturnal pattern of locomotor activity for this species is strongly influenced by an endogenous circadian clock, the results from the racetracks show that there is remarkable variability in the extent to which they express this pattern under natural conditions.     

Agonistic interactions between the invasive green crab, Carcinus maenas (Linnaeus) and juvenile American lobster, Homarus americanus (Milne Edwards)

Invasive organisms have the potential for competition with native organisms. In the Southern Gulf of St. Lawrence, juvenile American lobsters have a potential spatial overlap with adult green crabs. Crustaceans use agonistic behaviour to settle disputes, with the larger organism often winning contests for limited resources such as food and shelter. Two experiments were carried out using adult green crabs (53-76 mm carapace width) and juvenile American lobsters (28-57 mm carapace length). The first experiment used a limited food resource. We found that green crabs were the first to the food in all trials, fed in significantly more trials than lobsters and spent a significantly greater proportion of time with the food. The lobsters were only able to displace the green crabs from the food in 2 of 65 attempts. The second experiment was designed to examine shelter competition; unexpectedly some predation by green crabs on lobsters occurred, which allowed us to test hypotheses about how relative size and shelter use affect predation. Green crabs captured and consumed juvenile lobsters in 6 of 11 trials. The lobsters that survived spent significantly more time in shelter. There was no clear relationship between shelter use and size of lobster. The lobsters that were larger in relation to the green crabs suffered a higher rate of predation, which we believe was due to more conspicuous activity and less use of shelter. It appears that green crabs have the potential to negatively impact native juvenile lobster.     

Effects of near-bed current speeds on the distribution and behaviour of the lobster, Homarus gammarus (L.)

The distribution of the lobster, Homarus gammarus (L.) appears to be limited to areas of the sea bed with rocky outcrops. It seems likely that this limitation operates because lobsters need to be able to avoid currents created by tidal and wave action and that it is size selective. A series of experiments was made with lobsters in a flume tank, to observe the effects of a range of current speeds and substratum types on lobster behaviour. In addition, depth profiles of flow rates were made by Pitot tube measurements to estimate flow rates within the boundary layer immediately above the sea bed. Predictions of the influence of natural water currents on lobster behaviour have been made using available data on near-bed current speeds. The implications of these predictions to fisheries management and reef construction plans are discussed.     

Subtidal-intertidal trophic links: American lobsters [Homarus americanus (Milne-Edwards)] forage in the intertidal zone on nocturnal high tides

Homarus americanus (Milne-Edwards), the American lobster, is a predator in New England subtidal communities, feeding on ecologically important grazers (sea urchins), mesopredators (crabs), and basal species (mussels). In this study, we provide the first report of adult American lobsters foraging in rocky intertidal habitats during nocturnal high tides. Censuses by SCUBA divers in the low intertidal (Chondrus crispus Stackhouse) zone showed mean densities of 2.2 lobsters/20 m² on nocturnal high tides, with contrasting low densities of 0.18/20 m² during diurnal high tides. Nocturnal high-tide intertidal densities were 62% of those reported in a previous study of lobsters in nearby subtidal rocky areas (Novak, 2004). The average carapace length of lobsters in the intertidal at night was > 50 mm. These lobsters were actively foraging in the intertidal with collected individuals having a mean stomach fullness of 67%. Prey found in the stomach contents primarily consisted of crabs, mussels and snails. Field experiments showed that lobsters rarely fed on medium to large size individuals of the common intertidal snail, Littorina littorea (L.). In contrast, experiments with local crab species demonstrated that lobsters actively and readily prey on Cancer irroratus (Say) and Carcinus maenas (L.), but were significantly less likely to consume Cancer borealis (Stimpson). The abundance of Carcinus maenas and blue mussels (Mytilus edulis L.) in the intertidal zone may explain the upshore movement of lobsters. Since nocturnal migration of Homarus americanus into the intertidal zone has not been documented before, our understanding of the dynamics of New England intertidal communities needs to be expanded to include this predator.     

Glycolytic activity of the claw and tail muscle homogenates of the lobster, Homarus vulgaris

The fate of D-glucose-6-phosphate and phosphoenolpyruvate in homogenates of tail and claw muscles of the lobster (H vulgaris) has been studied. With both substrates oxygen utilization is higher for the claw than for the tail muscle. Succinate is not an end product of anaerobic D-glucose-6-phosphate-U- ¹⁴C degradation in either muscle but L-lactate is the major product of such catabolism in tail muscle whereas both L-lactate and L-alanine are produced in claw muscle. Dihydroxyacetone phosphate production was observed both tissues: this can be related to the known high lipid content of these tissues.     

Changes in blood serum protein levels during the moulting cycle of the lobster, Homarus gammarus (L.)

The blood serum protein level of lobsters kept in a stable environment rose from a mean value of 36.5 μg protein/ml of blood shortly after moulting to about 70 μg/ml in the first 40 % of the moult cycle; in the next 30 % of the cycle there was little change but in the last 30 % the mean blood protein level rose to ≈ 85 μg/ml. It is concluded that the variation in blood protein level between lobsters is too great at any stage of the moulting cycle for the technique to give an indication of the onset of moulting.     

Observations on the feeding mechanism,structure of the gut,and digestive physiology of the european lobster Homarus gammarus (L.) (Decapoda: Nephropidae)

Investigations have been made on the feeding mechanism, structure of the gut, and digestive physiology of the European lobster Homarus gammarus (L.).Ciné-photography has shown that the mandibles do not possess a masticatory function, merely serving to grip food morsels during the tearing process effected by the pulling action of the third maxillipeds. The remaining maxillipeds, together with the maxillae, then direct food fragments to the mouth for ingestion.Ingestion is facilitated by mucoid secretions discharged from the oesophageal tegumental glands; the glands do not appear to produce any enzymes which directly contribute to the digestive processes.The hepatopancreas is the principal organ concerned with digestion. It possesses a complex tubular organization in which sequential cellular differentiation culminates in the discharge of enzymes from the B-cells for extracellular digestion in the cardiac stomach. The enzymes are synthesized within vacuoles contained in the B-cell precursors (F-cells) and are secreted in three bursts of activity at 0–15 min, 1–2 h, and 3.5–5 h after a meal. The initial secretory phase is holocrine. Extracellular digestion involves esterases, arylamidases, and lipases; endopeptidases have not been positively identified by histochemical means despite the fact that Homarus is a carnivore. There is an intracellular digestive phase, not previously described in decapod crustaceans, at the 7–9 h post-ingestive stage in the hepatopancreatic R-cells which is effected by arylamidases and lipases.Various phosphatase enzymes have been identified in the hepatopancreatic cells. Acid and alkaline phosphatases are apparently concerned with several stages in the digestive cycle, including enzyme synthesis and secretion, and the absorption of digestive products. Adenosine triphosphatase activity is primarily associated with granules located in the distal R-cell cytoplasm; the possible significance of these granules in the elimination of metabolic wastes is discussed. Acid phosphatases and esterases are present in the midgut epithelium. The possibility of a passive uptake of material from the midgut lumen is considered.Faecal material in the hindgut is bound by mucoid secretions derived from the tegumental glands of this alimentary region; the mucus may also assist in defaecation.A complete digestive cycle in Homarus occupies ≈ 12 h.Food reserves in the gut consist principally of fat deposits in the R-cells, but minute amounts of glycogen can also be detected.No evidence of calcium, copper or ferric iron deposition in any part of the alimentary tract was found.     

Agonistic interactions between invasive green crabs, Carcinus maenas (Linnaeus), and sub-adult American lobsters, Homarus americanus (Milne Edwards)

The invasive green crab, Carcinus maenas, has recently expanded its range into the Southern Gulf of St. Lawrence, where there is potential for substantial niche overlap with juvenile American lobsters, Homarus americanus. We used two experiments to elicit, record and analyze the agonistic interactions of adult green crabs (carapace width of 63-75 mm) and sub-adult (carapace length of 55-70 mm) lobsters. The first experiment gave each animal equal access to a limited food resource. The green crabs were first to the food in significantly more trials, spent a significantly greater proportion of time with the food, and were able to successfully defend the food from attacks by the heavier lobsters. In the second experiment, we allowed the lobsters to gain possession and initiate feeding on the food before releasing the green crabs. In these trials, the lobsters spent significantly more time with the food, and were able to defend the food from the green crabs. The results of both experiments are discussed in the context of game theory. The different behaviour of the crustaceans in the two experiments is consistent with the “bourgeois” strategy in a hawk and dove game simulation. With this strategy, an animal acts like a hawk if in possession of a resource, but acts like a dove if the other animal is in possession of the resource. The fact that the green crabs were able to physically compete with, and in many cases dominate the larger, heavier lobsters supports the potential for competitive impacts of green crabs on sub-adult lobsters.     

Histopathology of Aerococcus viridans var. homari infection (Gaffkemia) in the lobster, Homarus americanus, and a comparison with histological reactions to a gram-negative species, Pseudomonas perolens

Histological response of lobsters to injection of Aerococcus viridans var. homari, cause of gaffkemia, was followed over a 14-day period. Salient features in infected lobsters, Homarus americanus, were: aggregations of hemocytes occurring in hemal spaces throughout the tissues and increasing in number and size with time; the early phagocytosis of bacteria by the system of fixed phagocytes (FPs) present in hemal spaces of the hepatopancreas; and premature release of differentiating hemocytes from the hemopoietic tissue, so that by 14 days that tissue consisted mainly of large stem cells. Mass release of differentiating hemocytes presumably occurred to replace hemocytes lost from the circulation by their incorporation into aggregations or by lysis of individual cells ruptured through the pressure of phagocytized bacteria that were multiplying in them. Bacteria and their remains were present in FPs at 2 days but not visible in single or aggregated hemocytes until 6 days, when free bacteria were also present in the hemolymph. By 6 days, all bacteria, whether phagocytized or free, appeared normal and were surrounded by nonstaining halos that extended well beyond the stainable capsular material. As predicted earlier in physiological studies, gaffkemia is a nontoxic, noninvasive bacteremia. There was hemal stasis and consequent injury in the antennal gland due to free and aggregated hemocytes that occluded hemal spaces of that organ, but other tissues and organs appeared normal except for depletion of glycogen. Aggregations of hemocytes were present in lobsters 2 and 12 days after injection of a nonpathogenic, Gram-negative bacterium, Pseudomonas perolens. Unlike the case with gaffkemia, necrotic hemocytes were common in the aggregations, presumably in response to damage by endotoxin. A further difference was that aggregations were common in the heart of P. perolens-injected lobsters but rare in the heart of gaffkemic lobsters. Bacteria were not seen in hemolymph, hemocytes, or other cells of P. perolens-injected lobsters.     

Osmotic regulation in late embryos and prelarvae of the American lobster Homarus americanus H. Milne-Edwards, 1837 (Crustacea,Decapoda)

Osmotic regulation of embryos, hatching prelarvae, and free prelarvae was studied in Homarus americanus H. Milne-Edwards, 1837. Adaptation time in dilute media was much longer in embryos than in hatchlings and prelarvae. Regulation in dilute media was hyperosmotic in embryos and hyperosmoconforming in hatchlings and prelarvae. The change in type of osmoregulation that occurred during the hatch is due to the rupture of the relatively impermeable outer egg membrane.     

Spatial overlap and interaction between sub-adult American lobsters, Homarus americanus, and the invasive European green crab Carcinus maenas

Invasive species are considered one of the major threats to biological diversity, and they can negatively impact species of particular ecological and/or economic importance. In this study, we investigate the potential threat that the European green crab, Carcinus maenas, represents to sub-adult lobsters, Homarus americanus, in Passamaquoddy Bay, Canada, northwest Atlantic. We conducted transect surveys using SCUBA diving to evaluate spatial overlap between these species inside, and immediately adjacent to, a lobster nursery area, and ran two laboratory experiments to investigate interactions between them in conditions of limited food and shelter availability. We found marked spatial overlap between these species in nature, particularly between adult green crabs and sub-adult lobsters in the shallower parts of the nursery area. It was not uncommon to see green crabs and sub-adult lobsters less than 1-2 m from one another, and we estimated mean nearest-neighbor values as low as 0.5-1 m on certain transects and months, with a grand mean of 5.17 ± 1.62 m (SE). Monte Carlo randomization of positional data revealed that green crabs and lobsters were randomly distributed relative to one another; individuals of one species did not seem to aggregate or segregate relative to individuals of the other species. In the lab, green crabs did not negatively affect survival (one exception), growth, activity, feeding, or shelter use of sub-adult lobsters. In fact, sub-adult lobsters regularly preyed upon green crabs in the first lab experiment, where heterospecific individuals were matched for body mass. Our results suggest that green crabs do not pose a significant threat to sub-adult lobsters in Passamaquoddy Bay, and may in fact represent a food subsidy for them.     

Osmotic and ionic regulation in the western rock lobster Panulirus longipes (Milne-Edwards)

The western rock lobster, Panulirus longipes (Milne-Edwards) is poikilosmotic over its tolerated salinity range, 25–45 ‰. Blood sodium is accumulated while chloride concentration is reduced. Sodium and chloride vary directly with the external salinity, although maintaining their differences in the same proportions as at normal salinity (36.0 ‰). Calcium is accumulated, ranging from over 150% at salinity 20 ‰ to about 117% at salinity 45 ‰. Potassium concentration is equivalent to the external at normal salinity, but is increased with lowered and decreased with raised salinity. Magnesium is reduced to about one-third that of the external concentration over the salinity range 20–40 ‰, but regulation begins to break down at 45 ‰. Individual ions exhibit, therefore, a range of regulation types, from poikilosmotic to homoiosmotic.Equilibrium for sodium, chloride, and calcium is attained in 10 h at salinities of 25, 30, 40 and 45 ‰ respectively. Rate constants for this exchange are linearly related to salinity differential, and rapid osmotic adjustment is by high permeability, equal in both directions, probably mainly via the gills. Muscle appears to act as a salt pool for sodium, chloride, and potassium but not for magnesium and calcium. Salt-loading causes a slight salt diuresis, the salts being excreted, probably via the gills. Except for calcium, there is no excretion of salt into the gut, but there is evidence of an exchange of chloride with another anion. Magnesium excretion is slow, and in the absence of osmotic stress possibly occurs via the antennal glands. All the ions examined appear to be regulated independently.     

The effect of flow and morphology on boundary layers in the scleractinians Dichocoenia stokesii (Milne-Edwards and Haime) and Stephanocoenia michilini (Milne-Edwards and Haime)

Mass transfer characteristics of scleractinian corals are affected by their skeletal morphology and the concentration gradients that develop as a consequence of the interactions of their morphology and biomass with the overlying seawater. These interactions can have a profound effect on coral metabolism. In this study, boundary layer characteristics were compared between different size colonies of the corals Dichocoenia stokesii and Stephanocoenia michilini to determine the relative roles of colony size and corallite structures (i.e. surface roughness) in mass transfer. Colonies of both species were rounded in shape, but differed in small-scale roughness as measured by the elevation of corallites. Additionally, D. stokesii had a greater aspect ratio than S. michilini, and their colonies were slightly taller for a given diameter. Boundary layers were characterized by placing dead coral skeletons in a flow tank and estimating shear velocities (u(*)) at different flow speeds. The effects of flow speed, size, and roughness on shear velocities were estimated for two juvenile size classes (10-20 and 30-40 mm diameter) of each species that were exposed to unidirectional flow regimes (4 and 17 cm s(-1)). Shear velocities were significantly greater in high, compared to low flow, and there was a significant interaction between colony size and surface roughness; the interaction was caused by a difference in magnitude, rather than direction, of the effect of roughness and size on u(*). Thus, there was a greater degree of turbulence at high flow compared to low flow, regardless of roughness or size, and the greatest turbulence occurred over large colonies of D. stokesii at high flow. Together, these results suggest that boundary layers around small corals are heavily influenced by upstream roughness elements, and more strongly affected by flow regimes than skeletal features. The relationship between colony morphology (i.e. aspect ratio and, possibly, surface roughness) and boundary layer characteristics may be non-linear in small corals.     

Short-term low-salinity response in lead-exposed lobsters, Homarus americanus (Milne Edwards)

The only effect attributable solely to lead exposure (50μg·l^?1, 30 days) in lobsters, Homarusamericanus (Milne Edwards), was decreased pentose shunt activity (G6PDH) in the antennal gland, which contained the greatest concentration of lead taken up by the tissues analyzed. Similarly-exposed lobsters were subsequently held for 2 days in clean, aerated sea water at either ambient or low salinity (27 or 17%., respectively), after which time the lead concentration in the antennal gland had dropped by one-third and G6PDH had returned to control values. Low-salinity effects far outnumbered lead-induced effects and were found primarily in the tail muscle, corroborating findings in an earlier study with cadmium. In that earlier study, cadmium produced more metabolic disturbance than did the lead exposure reported here. Lead exposure at low salinity abolished several normal hyposaline reactions seen in control animals.