J. Stanley Cobb

Behavior and the Crustacean Molt Cycle: Changes in Aggression of Homarus americanus

The phase of the molt cycle affects dominance status and the performance of agonistic acts in individual juvenile lobsters (Homarus americanus). Lobsters in the midphase of proecdysis are more aggressive than those in intermolt; the latter are more aggressive than lobsters in early or late proecdysis and those in postecdysis.

EARLY LIFE HISTORY AND RECRUITMENT PROCESSES OF CLAWED LOBSTERS

This review focuses on the larval, postlarval, and early benthic life of Homarus and Nephrops, the two best studied, and commercially most important, genera of the Nephropidae. Processes acting during this time of the life cycle may be critical of the fate of a cohort. In the past decade, significant advances have been made in understanding events before and after settlement. Nephrops and Homarus are very similar with respect to the processes affecting the distribution of the pelagic larvae and postlarvae: wind, currents and larval behavior play a significant role. Duration of the pelagic phase is determined by temperature, timing of settlement, and perhaps nutrition. Both genera probably arc quite selective of substratum during settlement, but this has been investigated only in Homarus, where substratum type, odor, and predator presence affect choice of habitat. The two genera contrast, however, with respect to some of the processes occurring during and after postlarval settlement. Although both are cryptic, newly settled Homarus are found in shallow, rocky habitats, while settled Nephrops arc found in deep water, in burrows they construct in cohesivc mud. Homarus undergoes a developmental change in behavior within the first few years of benthic life that causes an increasingly wide range of movement; sexually mature H. americanus can move hundreds of kilometers in a year. Nephrops emerges more as it grows, but appears to be far more sedentary than Homarus. Thus in contrast to Homarus, a number of distinct populations of Nephrops exist within the species range that are clearly defined by habitat boundaries. New techniques now permit routine census and tagging of early benthic phase Homcarus, making it possible to follow year classes from the time of settlement. It is the years immediately after settlement that a cohort may be subject to density-dependent controls, a key issue facing workers on both groups.

Behavioral mechanisms influencing molt frequency in the American lobster, Homarus americanus Milne Edwards

The dominance relationship established among communally held juvenile lobsters (Homarusamericanus Milne Edwards) results in an increased time between molts of subordinates, slowing their growth. The experiments reported here elucidated some of the mechanisms of this behaviorally mediated change in growth rate. Rearing the lobsters in pairs on either side of a partition allowing chemical or visual communication showed that neither were sufficient to cause the decrease in molt rate. Removal of the claws reduced the extent of the molt delay and altered, but did not prevent, the development of the dominance relationship. The lobsters must be paired before proecdysis begins for the molt delay to occur. Most of the delay can be attributed to a lengthening of the Do phase of proecdysis. Observations on the feeding behavior of pairs separated and together at feeding time showed the subordinates did not feed as readily or as rapidly as dominants. The slower growth rate of the subordinate may be due to a lower food intake.

Timing of settlement by postlarval lobsters (Homarus americanus): field and laboratory evidence

ABSTRACT Observations of postlarvae of the American lobster Homarus americanus in large tanks indicate that the postlarvae start to exhibit bottom-seeking behaviors, such as diving, between 2 and 6 days after molting into the postlarval (fourth) stage. This correlates well with earlier suggestions that lobster postlarvae are pelagic until about midway through the postlarval period. However, field observations of the molt stages of postlarvae caught in Block Island Sound and in Buzzards Bay in the summers of 1985-1987 indicate that they may be pelagic until quite late in the postlarval period. In addition, differences in the frequency distributions of the molt stages of field-caught animals between Buzzards Bay and Block Island Sound and among years suggest considerable flexibility in the timing of settling.

Dominance status and molt order in lobsters (Hornarus americanus)

When juvenile lobsters (Homarus americanus) were held in pairs from one molt to the next, the dominant animal always molted first. Activity levels, size, and the availability of shelter and food are related to dominance rank. Immediately after molting the dominance status reversed; the previously dominant lobster usually regained its status several days later.

Changes in nucleic acids over the molt cycle in relation to food availability and temperature in Homarus americanus postlarvae

Postlarval lobsters Homarus americanus Milne Edwards hatched from three females collected in 1989 from Block Island Sound, Rhode Island were reared individually in the laboratory under nine treatment combinations of temperature (15, 18 and 21°C) and feeding (starved, low ration and full ration). Total RNA, DNA (mgind.-1), RNA:DNA ratios and molt stage were determined for individuals sampled at daily intervals. Postlarval lobsters had high resistance to starvation. A majority of the lobsters survive 12 d of food deprivation, with some surviving up to 24–29 d. During starvation, cell biomass (estimated from protein:DNA) decreased to a minumum size, whereas cell number (based on total DNA) was generally conserved. The molt cycle was arrested at molt stage C in the starved postalrvae. Instar duration was inversely related to temperature. However, the duration of the postlarval instar did not differ between the low and full ration treatments. Uncoupling of cell growth and the molt cycle was evident in the full and low ration treatments. In the full ration treatments, the postmolt through early premolt was characterized by a rapid increase in total RNA and DNA. Maximum cell biomass was attained by molt stage C or D0. In the low ration treatments, total RNA and DNA were less than those in the full ration treatments and the maximum cell biomass was attained only at molt stage D2-3. Notably, different feeding regimes resulted in different patterns in RNA:DNA ratios over the molt cycle during the postlarval instar. RNA:DNA ratio was a sensitive indicator of recent (2 to 3 d) food deprivation. However, this ratio was positively related to the level of feeding only at molt stages C to D1 and was inversely related to temperature regime. These results indicate that the use of RNA:DNA ratios to estimate the relative nutritional state of postlarval tobsters must be qualified with respect to the period of the molt cycle and the temperature regime.

The external morphology and distribution of cuticular hair organs on the claws of the American lobster, Homarus Americanus (Milne-Edwards)

Four classes of microscopic cuticular hair organs were found on the chelae of Homarus americanus (Milne-Edwards). Type I and Type II organs possess long single sensillae, 30–60 μm and 70–130 μm, respectively. Type III organs are toroid bumps 20–30 μm in diameter, with a small tuft of fibers projecting from the center. Type IV organs are small conical hairs ≈ 1 μm in length. Type IV organs were uniformly distributed over the claws. The distributions of Types I, II, and III organs were analysed through multivariate analysis of variance (MANOVA) with respect to claw, side, and area. Type I organs showed significance of the three-way interaction only. Type II organs showed significance of side, area, and the claw by area interaction. Type III organs showed significance of area, and all interactions. Changes in number and density of Types I, II and III organs, and in number of Type IV organs, were found with growth.

Building capacity for integrated coastal management in developing countries

The need for building human and institutional capacity has been identified in Agenda 21 of the UNCED conference as well as by a number of international environmental institutions as essential for integrated coastal management (ICM) and sustainable development in developing coastal states. There is a growing need for coastal management practitioners and organizations with expertise in planning and implementation for ICM. The application of strategies for institutional development and building human capacity in coastal management and other fields shows that short-term intensive training efforts and long-term institutional strengthening programs are appropriate to address the issues and needs of ICM. An overview of the experience of the URI/USAID International Coastal Resources Management Program in Sri Lanka, Thailand and Ecuador presents lessons learned for strengthening ICM efforts in developing countries.

Synaptic plasticity and humoral modulation of neuromuscular transmission in the lobster claw opener during the molt cycle

Abstract 1. Neuromuscular properties of the lobster dactyl opener were studied at different stages of the molt cycle. 2. Excitatory junctional potentials (EJPs) were found to be significantly larger in hard-shelled premolt lobsters than in soft-shelled postmolt animals. 3. Inhibitory junctional potentials (IJPs) were larger in postmolt claw preparations than in premolt ones. 4. Excitatory transmission was also monitored during superfusion with plasma samples obtained from lobsters in vartious stages of the molt cycle (postmolt = AB; intennolt = C; premolt = D 2 ). 5. D 2 plasma increased EJP amplitude by an average of 28% relative to baseline levels (in saline), while AB plasma reduced EJP size by an average of 6%. 6. Premolt and postmolt plasma produced opposite effects on quantal content ( m ); D 2 ; plasma increased m by a mean of 39%, whereas AB plasma caused a mean reduction by 10%, which suggests that humoral factors may act presynaptically to alter transmitter release. 7. These results provide evidence of neuromuscular plasticity in the opener muscle during the molt cycle, and are consistent with changes in claw-opening behavior seen during this cycle.

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.