California Sea Grant College Program

Measurement of the spatial and temporal scales of nearshore chlorophyll-a (chl) is critical to our ability to understand or predict dense, and potentially harmful blooms of phytoplankton along the California Coast. Patchiness in chl may result from patchiness in nutrient availability, swimming or sinking, predation, or transport and mixing by breaking waves, currents, internal waves and tides. We performed a study during the Fall 2006 Huntington Beach (HB06) experiment to investigate the biological and physical factors that affect phytoplankton patchiness. Autotrophic phytoplankton require light and nutrients to survive. However, the nearshore euphotic zone (the critical depth for photosynthesis) is often nutrient-depleted due to uptake and planktonic growth. In order to sustain populations, phytoplankton rely on delivery of new nutrients from below the euphotic zone through upwellling or vertical mixing. or 2) terrestrial sources (from rain, ground water, tidal flushing or river outflow) that feed directly into the nearshore.