William M. Hamner

Topographically Controlled Fronts in the Ocean and Their Biological Influence

Headlands, islands, and reefs generate complex three-dimensional secondary flows that result in physical and biological fronts. Mixing and diffusion processes near these reefs and headlands are quite different from these processes in the open sea, and classical advection-diffusion models that were developed for the open sea are not valid near shore. Topographically generated fronts affect the distribution of sediments, and they aggregate waterborne eggs, larvae, and plankton. This aggregation influences the distribution and density of benthic assemblages and of pelagic secondary and tertiary predators.

Animal groups in three dimensions

1. Unifying principles, galactic framework, and the holy grails of aggregation Julia K. Parrish, William M. Hamner and Charles T. Prewitt Part I. Imaging and Measurement: 2. Methods for three-dimensional sensing of animals Jules S. Jaffe 3. Analytical and digital photogrammetry Jon Osborn 4. Acoustic visualization of three-dimensional animal aggregations in the ocean Charles H. Green and Peter H. Wiebe 5. Three-dimensional structure and dynamics of bird flocks Frank Heppner 6. Three-dimensional measurements of swarming mosquitos: a probabilistic model, measuring system, and example output Terumi Ikawa and Hidehiko Okabe Part II. Analysis: 7. Quantitative analysis of animal movements in congregations Peter Turchin 8. Movements of animals in congregations: an Eularian analysis of bark beetle swarming Peter Turchin and Gregory Simons 9. Individual decisions, traffic rules, and emergent pattern in schooling fish Julia K. Parrish and Peter Turchin 10. Aggregate behavior in zooplankton: phototactic swarming in four developmental stages of Coullana canadensis (Copepoda harpacticoida) Jeannette Yen and Elizabeth A. Bryant Part III. Behavioural Ecology and Evolution: 11. Is the sum of the parts equal to the whole?: the conflict between individuality and group membership William M. Hamner and Julia K. Parrish 12. Why are some members more likely to be on the outside of the group?: Testing the evolutionary predictions William L. Romey 13. Costs and benefits as a function of group size: experiments on a swarming mysid Paramesopodopsis rufa fenton David A. Ritz 14. Predicting the three-dimensional structure of animal aggregations from functional consideration: The role of information Lawrence M. Dill, C. S. Holling and L. H. Palmer 15. Perspectives on sensory integration systems: problems, opportunities, and predictions Carl R. Schilt and Kenneth S. Norris Part IV. Models: 16. Conceptual and methodological issues in the modeling of biological aggregations Simon A. Levin 17. Schooling as a strategy for chemotaxis in a noisy environment Daniel Grunbaum 18. Trail following as an adaptable mechanism for popular behavior Leah Edelstein-Keshett 19. Metabolic models of fish school behaviour: The need for quantitative observations William McFarland and Akira Okubo 20. Social forces in animal congregations: interactive, motivational and sensory aspects Kevin Warburton.

A physical context for gelatinous zooplankton aggregations: a review

The magnitude and extent of jellyfish blooms are influenced not only by the biology and behavior of the animal, but also by the geographic setting and physical environment. Hydrography alone is often thought to cause or favor gelatinous zooplankton aggregations, however, it is clear that interactions between biology of the animal and physics of the water are very important sources of population variations, especially at local scales. We summarize the role of physical processes and phenomena that promote aggregations of gelatinous zooplankton. We have identified and discussed a suite of physical gradients that can be perceived by gelatinous zooplankton. These include light, gravity, temperature, salinity, pressure and turbulence. A recurring theme is accumulation of jellyfish around physical discontinuities such as fronts (shelf-break, upwelling, tidal and estuarine) and pycnoclines (thermoclines and haloclines). Interestingly, there are few data to suggest that large-scale, quasi-stationary features, such as the largest oceanic fronts, serve to physically aggregate gelatinous animals at a similar scale. Rather, examples of local aggregations appear to dominate the literature. We also discuss various jellyfish behaviors that are theorized to promote aggregation, feeding and reproduction in relation to physical discontinuities.

Behavior of Antarctic Krill, Euphausia superba: Chemoreception, Feeding, Schooling, and Molting

Krill do not feed by passive, continuous filtration but use area-intensive searching and various rapid feeding behaviors to exploit local high food concentrations. Chemicals alone at low concentrations, not particles, trigger feeding. Krill form dense schools that move rapidly and migrate primarily horizontally. Abrupt disruption of a school can trigger mass molting, and molts may act as decoys.

Patchy distribution of zooplankton: Behavior, population assessment and sampling problems

Zooplankton and micronekton are often highly aggregated. Density in aggregations can reach 100 to more than 1000 times the average density of the population as estimated by net sampling. In order to assess true abundance of the animals and understand the significance of the aggregations, more information is needed on the behavior and population ecology of individual species and the species-specific attributes of discrete assemblages. We present information on patterns of intense aggregations of protozoans, platyhelminthes, scyphomedusae, copepods, mysids, and sergestids from our own observations. Characteristics behaviors of different species include feeding swarms of Noctiluca miliaris, behaviorally maintained swarms of planktonic flatworms, diel horizontal migration of Mastigias sp. swarms, three patterns of copepod swarms, bathymetric zonation of mysid schools, and seasonal migration and near bottom swarming of Sergia lucens. After the principles were demonstrated, we consider how to relate sampling, behavior, and population dynamics. We stress that the methodology is the result of the question, not the other way round. To tackle the problems associated with “behavior” in the open ocean, which we did not observe from the surface, it is necessary to sample in more than one way to extract data on differences in population-specific biology that alternative methods supply.

Direct sampling and in situ observation of a persistent copepod aggregation in the mesopelagic zone of the Santa Barbara Basin

Observations from a one-person submersible (“Wasp”) in fall, 1982, revealed a persistent aggregation of non-migrating, Stage V copepodites of Calanus pacificus californicus Brodsky in a band 20±3 m thick at a depth of 450 m, about 100 m above the bottom of the Santa Barbara Basin, California. Copepod abundances, calculated from nearest-neighbor distances measured directly from the submersible, yielded maximum densities of 26×106 copepodites m-3. Quiescent behavior, low laminarinase activity, low protein content, high lipid content and evidence of low excretion rate all suggest that these copepodites were in a state of diapause. Diapausing C. pacificus californicus at other locations along the eastern Pacific coast were also captured in discrete depth plankton tows. Both the submersible observations and the net collections suggest that the dense aggregation of diapausing copepods we observed in the Santa Barbara Basin was a phenomenon associated with seasonal upwelling cycles, and that such aggregations occur during non-upwelling periods when food is scarce in surface waters. Numerous predators, especially the deep sea smelt Leuroglossus stilbius, were observed feeding upon the aggregated copepods; thus, in contrast to the conventional picture of surface-dominated food distribution, deep-water aggregations of C. pacificus californicus may support the mesopelagic community during periods of low food availability in surface waters.

ASPECTS OF SCHOOLING IN EUPHAUSIA SUPERBA

ABSTRACT Divers observed schools of Euphausia superba off the South Shetland Islands and in Gerlache Strait near the Antarctic Peninsula. Euphausiids almost always occurred within the confines of dense schools swimming in one direction. Schools formed an infinite variety of shapes but usually were narrow in at least one dimension, so that individuals within a school were never far from its edge. Schools moved at about 20 cm/s, primarily horizontally, and vertical displacement was always accompanied by much larger horizontal excursions. Opaque, presumably necrotic, euphausiids occurred within schools, indicating that schooling may have epidemiologic disadvantages. Schools exhibited a variety of behavioral responses to potential and actual predators (sea birds and whales). A hypothesis of ontogenetic differences in schooling behavior proposes that juveniles migrate long distances horizontally in search of food over both shallow and deep waters, but that schools of adults spawn in or near deep water so that rapidly sinking eggs are not deposited on the sea bed.

Sun-compass migration by Aurelia aurita (Scyphozoa): population retention and reproduction in Saanich Inlet, British Columbia

The scyphomedusa Aurelia aurita in Saanich Inlet, a north-south oriented fjord in British Columbia, uses a sun compass to migrate in a southeasterly direction during the day. When the sky is overcast and at night, A. aurita orients randomly and is dispersed passively by gentle tidal currents. The net result is daily reaggregation of medusae into enormous swarms along the southeastern shore of the fjord. Observations of spawning A. aurita in these swarms suggest that sun-compass migration and aggregative behavior may have evolved to facilitate reproduction and to maintain the population within this fjord throughout the year.

Collection and Culture Techniques for Gelatinous Zooplankton

Gelatinous zooplankton are the least understood of all planktonic animal groups. This is partly due to their fragility, which typically precludes the capture of intact specimens with nets or trawls. Specialized tools and techniques have been developed that allow researchers and aquarists to collect intact gelatinous animals at sea and to maintain many of these alive in the laboratory. This paper summarizes the scientific literature on the capture, collection, and culture of gelatinous zooplankton and incorporates many unpublished methods developed at the Monterey Bay Aquarium in the past 15 years.

Schooling behavior of Antarctic krill (Euphausia superba) in laboratory aquaria: Reactions to chemical and visual stimuli

Antarctic krill,Euphausia superba, often exhibit abnormal behavior in laboratory aquaria, usually hovering in a stationary position, unresponsive to most external stimuli. In the austral summer of 1985–1986 at Palmer Station on Anvers Island, Antarctica, we provided laboratory conditions which inducedE. superba to school in large aquaria. Captive krill swam horizontally and exhibited the full spectrum of behaviors normally displayed while schooling at sea. Schooling krill avoided visually contrasting stimuli, with avoidance distances correlated with stimulus size. Schools responded in qualitatively different ways to presentations of food, chemical compounds, and abrupt increases in light intensity. We describe the conditions necessary for aquarium schooling and discuss the importance of an appropriate social environment for displays of escape, avoidance, and feeding behaviors and of positional preference within the school.