William F. Herrnkind

The guide effect influence on the gregariousness of juvenile Caribbean spiny lobsters

Abstract Many animals are gregarious and potentially benefit from the presence of conspecifics. We examined both den finding and den sharing by vulnerable juvenile Caribbean spiny lobsters, Panulirus argus, and compared three functional explanations of why lobsters might benefit from being gregarious. Lobsters sharing dens did not have higher survival than those in dens by themselves, suggesting that cooperative group defence may not be important at this life history stage. Lobsters in areas of high conspecific density did not have higher survival than those in areas of low density, suggesting that the dilution effect may not be important either. Den sharing provided no additional benefit beyond that provided by the shelter. However, lobsters were able to find shelter significantly faster when conspecific residents were already present in a den. This ‘guide effect’ benefits the shelter-seeking individual by reducing the time of exposure and associated predation risk. Habitat or risk assessment based solely on the presence of conspecifics may be a critical first step in the evolution of more complex social behaviours.

Field studies of homing, mass emigration, and orientation in the spiny lobster, panulirus argus.

The western Atlantic spiny lobster, Panulirus argus, is known to be migratory7*9J2 and capable of homing.4~~ Yet, there is little quantitative or experimental information characterizing their orientation and indicating mechanisms of directional orientation. Creaser and Travis8 reported that 20 percent of tagged lobsters returned to the site of original capture after displacements up to several miles. Several lobsters remarkably reappeared at their capture site within a few days after release one mile offshore at a depth of 500 m. However, the trap-tag-recapture method used gave no indication of pathways, guideposts, or sensory systems involved. Recently, preliminary sonic tracking studies showed the typical nocturnal period of activity to consist of spontaneous movements from specific den sites off the reef and return, often to the same den, before dawn, with distances of hundreds of meters being covered.4 Although the latter report is briefly descriptive, it demonstrated the suitability of diver-operated sonic tracking techniques for such homing studies and suggested that homing plays a significant role in the normal behavior of spiny lobsters. Past migration studies based upon inferential evidence from trapping and tagrecapture techniques suggest seasonal trends of generalized inshore-off shore and random population movements, with occasional long distance movements by i n d i v i d u a l ~ . ~ , ~ ~ ~ J ~ J ~ For example, Dawson and Idylls reported that lobsters released at various places in the Florida Keys and southeast coast usually stayed within five miles of the release point, and that those moving farther traveled northward or southward up to 100 miles in three to four months. Again, this type of study provides no evidence of mode of migration (individual or group), pathway (direct or circuitous) or any indication of orientational components. A very distinctive mode of migration was described by Cummings and Herrnkind in which thousands of spiny lobsters emigrated en masse, by day, southward along the west coast of Bimini, Bahamas.12 During the mass movements lobsters joined in long, single-file columns or queues, all of which exhibiting an equivalent bearing.10 The group heading was maintained despite variable bottom slope, changing terrain and currents, poor visibility and overcast skies, making it difficult to postulate orientation by gravity gradient, chemorheotaxy or celestial cues. This paper presents information to characterize homing, mass emigration, and orientation by spiny lobsters more fully in the field and presents evidence for a nonvisual mechanism operating by hydrodynamic cues.

Molecular phylogeny of the spiny lobster genus Panulirus (Decapoda: Palinuridae)

Phylogenetic relationships among all described species and four subspecies (total of 21 taxa) of the spiny lobster genus Panulirus White, 1847, were examined with nucleotide sequence data from portions of two mitochondrial genes, large-subunit ribosomal RNA (16S) and cytochrome oxidase subunit I (COI). Multiple sequence alignments were subjected to maximum-parsimony, neighbour-joining, and maximum-likelihood analysis with Jasus edwardsii as the outgroup. Two major lineages within Panulirus were recovered by all three methods for both the 16S and COI alignments analysed separately and for the combined alignment. The first lineage included all species of Panulirus classified as Groups I and II by previous morphologically based definitions. The second included all species classified as Groups III and IV. Relationships within major lineages were not well resolved; the molecular phylogeny did not support separation of Group I from Group II or of Group III from Group IV. The degree of sequence divergence between different pairs of species was higher in pairwise comparisons between species in Group I/II (16S: 2.8–19.4%; COI: 12.4–31.8%) than in those between species in Group III/IV (16S: 5.3–13.2%; COI: 12.6–19.6%). This pattern suggests that the Group I/II lineage may represent an earlier radiation of species within Panulirus.

Orientation in Shore-Living Arthropods, Especially the Sand Fiddler Crab

The motile macrofauna of coastal and estuarine sand beaches is represented nearly exclusively by arthropods, particularly semiterrestiral marine crustaceans. The permanent residents include amphipods (Talitridae; Hurley, 1968), isopods (Tylidae; Edney, 1968), and decapod crustaceans (Ocypodidae, Grapsiade, Mictyridae, Coenobitidae; Bliss, 1968). More occasional residents are wolf spiders (Lycosidae; Papi and Tongiorgi, 1963), beetles (Carabidae, Staphylinidae, Tenebrionidae; Papi, 1955a; Pardi, 1956), and mole crickets (Gryllotalpidae; Pardi, 1956). The groups successfully populating this environment do so in spite of the deleterious effects of variable and extreme physical conditions (Pearse et al., 1928; Moore et al., 1968). These include physical stresses posed by abrasion and removal of habitable substrate, or deposition of sediment, during storms. Physiological stresses, including insolation, osmotic imbalance, drying, anoxia, drowning, and poisoning by high concentrations of hydrogen sulfide, occur more regularly as a result of heavy rain, periodic tidal inundation, and aerial exposure. Biological pressure is also considerable, since the beach inhabitants are subject to predation from the land by mammals (rodents and raccoons) and toads (Bufo), from the air by shorebirds, and from the water by fishes (sciaenids) and portunid crabs, especially Callinectes spp. (Herrnkind, 1968a,b, and unpublished observations). The environmental conditions are such that Pearse et al. (1928) commented, “A marine sandy beach seems like an inhospitable place for ... animals to become established.”

Drag Reduction by Formation Movement in Spiny Lobsters

Movements of spiny lobsters (Panulirus argus) in formation reduce drag during locomotion; such movement is of particular significance during mass migration. Queues (single-file lines) of spiny lobsters sustain less drag per individual than do individual lobsters moving at the same speed. It is proposed that queuing behavior conserves energy and is a consequence of the evolutionary role of migration in this particular species.

Queuing Behavior of Spiny Lobsters

Autumnal mass migrations of spiny lobsters, Panulirus argus, involve diurnal movements of thousands of individuals in single-file queues. Initiation, posture, and alignment of a queue can be effected entirely by tactile cues received through antennular inner rami, pereiopods, and antennae. Since spiny lobsters queue when deprived of shelter, this behavior may serve a defensive function. Specimens captured while migrating maintain the queue indoors for up to several weeks, whereas at other times the queue lasts only a few hours. Hence, the migratory behavior probably depends in part upon environmentally induced neurohormonal changes.

A quantitative analysis of social interaction of the guppy, Poecilia reticulata (pisces: Poeciliidae) as a function of population density

Abstract Various controlled densities of guppies, Poecilia reticulata, wer observed in order to determine the effects of population density on frequency of courtship and agonistic interactions. Populations with single male exhibit a low level of courtship activity; the presence of a second male increases this level of activity markedly. Populations with a 1:1 sex ratio in densities greater than one pair exhibit a constant mean number of courtship interactions but, with increased crowding, an increasing variance in level of courtship activity. This results in a frequency profile of courtship interaction characteristic of each observed density. Each population density exhibits a density-dependent pattern of social interaction defined quantitatively by frequencies of courtship aggressive interactions at the population level. The contribution of the behaviour of individual males and to this patterning of social interaction in each population was partially determined.

Cooperative defence and other benefits among exposed spiny lobsters: inferences from group size and behaviour

Caribbean spiny lobsters show strikingly coordinated queuing behaviour and resting, outward-facing radial formations, especially during mass migrations when large numbers cross shelter-poor substrate in daylight. The close association of individual lobsters during these behaviours could be due to chance or some benefit of association such as dilution (and associated selfish-herd effects), group vigilance, cooperative defence, and/or drag reduction during migration. To infer probable beneficial functions, we examined the frequency distributions of individuals and groups using a seven-year set of field data and additional behavioural observations in large seawater enclosures. Group size distributions were not significantly aggregated in dens during the non-migratory period but became highly aggregated during migration. The group size distributions of lobsters initially leaving dens and those observed moving in the open were statistically different from one another, indicating that group sizes at each of these steps in the migration are not simply the result of previous group sizes. The distribution of group sizes suggests that, during movement in the open, dilution, vigilance, cooperative defence, and/or drag reduction may all favour the formation of queues. During resting in the open, dilution, vigilance, and cooperative defence may continue to favour individuals that remain in formation within the group.

Settlement of Spiny Lobster, Panulirus Argus (Latreille, 1804), in Florida: Pattern Without Predictability?

We used plankton nets, floating postlarval collectors, and arrays of benthic settling devices, along with diver surveys of juvenile lobster abundance and nursery habitat structure, to estimate the spatial pattern of settlement, abundance of settlers, and characteristics of postsettlement juvenile Panulirus argus populations in Florida Bay, the primary nursery for spiny lobsters in Florida. Within a 200 km 2 region of Florida Bay, settlement was patchy and locally unpredictable, although settlement occurred at most sites each lunar phase. However, the number of postlarvac entering inlets to the bay was significantly correlated with regional settlement, and areas with abundant red macroalgae (settlement substrate) and numerous sponges (benthic juvenile shelter) were the most productive sites, even though settlement within them varied widely during lunar influxes. Floating collector catches accurately estimated the number of postlarvae in the water column at inlets, but results from collectors deployed in the bay did not correlate with the number of postlarvae settling on benthic collectors nearby. Estimates of postsettlement mortality in the field yield a natural mortality of about 97% in the year following settlement.

FACTORS REGULATING MICROHABITAT USE BY YOUNG JUVENILE SPINY LOBSTERS, PANULIRUS ARGUS: FOOD AND SHELTER

Habitation patterns ofalgal-dwellingjuvenile spiny lobsters, Panulirus argus, are apparently regulated by a) the availability of epifaunal prey, and/or b) limited sheltering qualities provided by algal branching. Predictions derived from each hypothesis were tested by monitoring emigration from normal (prey abundant), rinsed (prey reduced), and rinsed but structurally enhanced clumps of red algae, Laurencia spp. Density dependent emigration from untreated clumps containing natural prey, and markedly increased emigration from clumps nearly void of potential prey, suggest that trophic pressures play an important role in regulating algal habitation. Solitary dwelling induced by agonistic behavior may function to reduce required foraging area, thus minimizing both exposure to predators and energetic expenditures. The young benthic stages of the spiny lobster Panulirus argus inhabit intricately branched clumps of red algae, Laurencia spp., in shallow habitats of Florida Bay and the Florida Keys (Marx and Herrnkind, in press). Small size, cryptic behavior, camouflaged pigmentation, and disruptive markings (light-dark banding of appendages and dorsal stripe), seemingly adapt the early stages to residency within algal clumps. Moreover, algae provide abundant prey in the form of diverse epifaunal invertebrates including small gastropod mollusks, isopods, amphipods, and ostracods, all of which are commonly found in the gut contents of young lobsters (Marx and Herrnkind, in press). Young benthic stages are typically solitary in small algal clumps, or occupy widely spaced portions of large clumps, and exhibit aggressively maintained isolation in aquaria. Solitary dwelling behaviorally distinguishes postsettlement stages from older juveniles which are gregarious (Kanciruk, 1980). These collective observations suggest that macroalgal habitation functions to protect the otherwise susceptible young stages from predators and physical stresses while simultaneously providing access to food, thus enhancing the value of algae as a refugium. We examined this relationship by experimentally testing the effects of food and physical sheltering factors on residency patterns of young benthic stages within algal clumps. Assuming trophic regulation, we reasoned that a young lobster should remain within a clump so long as sufficient food is available, but emigrate when prey abundance is low. Increased food searching when prey is scarce conceivably exacerbates agonism by causing frequent contact between residents, or food scarcity might induce increased individual aggressiveness. One predicts increased emigration as a result in either case. Assuming that refuge quality is a regulating factor, we propose that macroalgal clumps are selected as habitat because of physical features independent of prey availability. Alternatively, early benthic stages may occupy algae only in the absence of rock crevices, which constitute the typical shelter for slightly older juveniles in other habitats (Andree, 1981). Below, we report on experimental tests of each prediction and discuss the implications with respect to the behavioral ecology and population dynamics of young juvenile lobsters. Specifying the nature of the biological relationship between spiny lobsters and their settlement habitat is essential to management of the multimillion dollar spiny lobster fishery and will contribute to our understanding of life history tactics.