Ecological features of harmful algal blooms in coastal upwelling ecosystems

Upwelling regions are the most complex habitats in which dinoflagellates pr oduct red tides, but the flora is not unique. Many species also bloom in nu trient-enriched, non-upwelling systems, share the collective dinoflagellate trait of low-nutrient affinity, and can achieve relatively fast growth rat es. Blooms occur over the range of nutrient - mixing - advection combinatio ns found in upwelling habitats, rather than bring restricted to the high-nu trient high-irradiance low-turbulence conditions posited by Margalef's clas sical Mandala and its Bowman rr al. and Pingree versions. The bloom species are primarily ruderal strategists (R-species), which typify "mixing - drif t" life-forms adapted to the velocities associated with frontal zones, entr ainment within coastal currents, and vertical mixing during upwelling relax ations. Collectively, dinoflagellates appear capable of surviving fairly hi gh turbulence spectra formed at representative Kolmogorov length scale - wi nd speed conditions. This biophysical protection might be the result of cel l size-facilitated entrainment within the micro-eddies formed during turbul ent energy dissipation. The swimming speeds of 71 clones of dinoflagellates are compared and related to reported rates of vertical motion in coastal u pwelling systems. There are slow and fast swimmers: many exhibit motility r ates that can exceed representative in situ vertical and horizontal water m ass movements. At least four dinoflagellates from upwelling systems form ch ains leading to increased swimming speeds, and may be an adaptation for gro wth in coastal upwelling habitats. Red tides are frequent and fundamental f eatures of upwelling systems, particularly during intermittent upwelling re laxations, rather than dichotomous (sometimes catastrophic) interruptions o f the diatom blooms characteristically induced by upwelling. Successional s equences and the "red tide" zone may differ between upwelling and non-upwel ling systems. In the latter, red tides diverge from the main sequence and a re appropriately positioned in the Mandala's ecological space of high nutri ents and low turbulence. An amended Mandala based on Pingree's S-kh model a nd the Smayda and Reynolds life-form model is presented to accommodate the range of red tide development and their successional routing found in coast al upwelling systems. Ecophysiological data support the pitcher and Boyd se eding mechanism model, which can lead to red tides in upwelling systems. Nu trients, phyto-stimulation and grazing pressure as triggering factors in up welling-system red tides are considered. Some red tides may be stimulated b y nutrients and growth promoting factors excreted by migrating shoals and " boils" of clupeoid stocks, with selective zoo-plankton grazing contributory . Substantial collapses in grazing pressure may be essential in anoxic red tide events. The mass mortalities that accompany anoxia, common to the Beng uela and Peru upwelling systems, may be a trophic control mechanism to main tain biogeochemical balance and regional homeostasis, which are vital to up welling ecosystem dynamics. Some traditional concepts of phytoplankton ecol ogy may not completely apply to dinoflagellate bloom events in coastal upwe lling systems.