The community of epiphytes on the giant kelp Macrocystis pyrifera, is simple, consisting primarily of the bryozoans Membranipora membranacea, Hippothoa hyalina, and Lichenopora buskiana; the serpulid polychaete Spirorbis spirillum; and the hydroids Obelia sp. and Campanulaia sp. Abundances of the organisms vary rapidly, by an order of magnitude or more in 2 wk. In spite of this short—term unpredictability, broad patterns of distribution are predictable. Membranipora, the competitive dominant, is abundant during winter and spring and absent during summer and fall when surface waters are warm and thermally stratified. When present, it occurs primarily in the canopy along the outer edge of the large (1 X 11 km) Point Loma, San Diego, kelp bed. The distribution of the subordinate epiphytes complements that of Membranipora. They occur in the interior portions of bed, and on the lower, older blades of Macrocystis plants. These patterns are maintained by a sophisticated suite of larval behaviors and settlement preferences. The subordinate epiphytes settle preferentially on the older blades of Macrocystis, and avoid blades from plants on the outer edge of the bed where competitive overgrowth by Membranipora is more likely. In addition the extremely short larval life—spans of the subordinate epiphytes (a few hours) mean that offspring will settle near where they were released, in the interior of the bed. Membranipora, in contrast, has a planktonic lifetime of 2 to 4 wk. Nearshore current measurements indicate that as a result its larvae are flushed from the bed, and that the source of larvae ready to metamorphose and settle must be external to the bed, from other kelp beds in the area. This helps restrict Membranipora to the outer edge of the bed, since larvae are removed from the water as it passes through the bed both by settlement on Macrocystis blades and by plankivorous fish that feed on them. The labrid fish Oxyjulis californica is an important predator in this system. It is a curious, actively searching generalist that excludes large, erect epiphytes such as the barnacle Lepas pacifica and the bivalve Leptopecten latiauritus from the nearshore kelp bed. Field and laboratory experiments imply that Oxyjulis forms short—term search images and switches among prey species. One of the species it regulates is the herbivorous isopod Pentidothea resecta, which, when released from regulation, multiples rapidly and destroys the kelp canopy. Oxyjulis, though it buffers the system from extinction due to Pentidothea, is also potentially destructive. Small kelp beds, too small for the filtering action to take effect, become heavily encrusted with Membranipora and can be destroyed by Oxyjulis predation on the encrusted blades. The set of relationships among species in this community can fruitfully be viewed as having coevolved to contribute to persistence in this unstable environment. Indeed, some factors that contribute to instability are the very ones necessary for persistence. Competition, predation, habitat selection, and life ...

This paper introduces a series of 6 additional papers in this issue that describe an in-depth analysis of options for decommissioning oil and gas platforms offshore southern California. Although current leases require lessees in both state and federal waters to completely remove all production facilities and restore the seafloor to its pre-platform condition, other options have emerged since these leases were signed. Laws and regulations in other jurisdictions (particularly in federal waters) have evolved to allow a number of other uses such as aquaculture, alternative energy production, and artificial reefing. In response, the California Natural Resources Agency initiated an effort to investigate the issues associated with these and other decommissioning alternatives. The papers in this series are the result of the second phase in this process, a broad investigation of the engineering, economic, and environmental costs and benefits of the most feasible and likely options. In addition to the project's final report, the authors produced an interactive mathematical decision model, PLATFORM, that enables users to explore the implications of different decommissioning projects and options, as well as the effects of different approaches to valuing the associated costs and benefits.

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We performed a multilevel factorial field experiment to identify the effects of five factors on sea urchins' (Strongylocentrotus droebachiensis) aggregating behavior. The factors were (1) source of urchins (kelpbed or barrens), (2) density of urchins (high or low), (3) location of treatment (kelpbed or barrens), (4) the presence and type of invertebrate predators (crabs or lobsters), and (5) season (summer or winter). These manipulative experiments were performed in flexible, resilient cages designed to withstand the severe wave surge in Nova Scotia's shallow subtidal environment. Interactions identified by ANOVA among the various factors showed that urchins aggregate more at high (20∙m−2) than at low (4∙m−2) density. The presence of lobsters in the kelpbed, and of crabs in the barrens, triggered the formation of even larger aggregations. These aggregations remain in the open even in the presence of predators. We argue that this behavioral mechanism (a defensive aggregation response to lobsters in the kelpbed) is the trigger that precipitates widespread destructive urchin grazing and the transformation of kelpbeds to barrens. Lobsters thus play two opposite roles. At low urchin density lobsters keep urchins in hiding and thereby contribute to kelpbed persistence. At higher urchin density, lobsters trigger the formation of large, exposed urchin aggregations that graze destructively on kelp. Urchin responses to predators are probably mediated by a combination of conditioning and sensitivity to biochemical cues. The large-scale change in community structure, from kelpbed to barrens, can thus be understood in terms of the adaptive behavioral responses of individual organisms. We review the roles of other predators in this system and show that they have varying effects on the intensity of urchin grazing, depending on urchin density, season, and habitat type.

Five 0.25‐m2 box cores (four open cores and one vegematic core subdivided in situ into 25 contiguous 10‐ × 10‐cm subcores) reveal that populations of benthic agglutinated Foraminifera in the central North Pacific are extremely abundant and diverse. As many as 120 species and 10,310 total fragments occur in a single open core, and the Foraminifera outnumber all metazoan taxa combined by at least an order of magnitude. Significant patchiness occurs on both the between‐core scale of kilometers and the within‐core scale of centimeters. Few species occurred in all cores and those that did were not abundant. Hierarchical classification and multiple discriminant analysis on the resultant subcore groups in the vegematic core suggest potential interactions between certain species of Foraminifera and such external variables as surface deposit feeders, subsurface deposit feeders, carnivores, filter feeders, biogenic surface structure, and manganese nodules. Multiple regressions of foraminiferan species against all the external variables substantiate the existence of patterns of association. Foraminifera are important components of the benthic fauna, acting, among other things, as predators and disturbance agents. It may well be that they have a more significant effect on the structure and dynamics of deep‐sea henthic communities than have any of the metazoan macrofaunal taxa that are the usual objects of deep‐sea studies.