. Bulletin. Science. Outside LA. harbor breakwater Off Santa Catalina Island -n Dinophysis B Prorocentrum H Protoperidinium ^D Ceratium tD naked dinoflagellates H Lingulodinium Fig. 3. Dinoflagellate community composition. dinoflagellate blooms, which coincided with other significant changes in the eco- logical system of the Bight, such as increased temperature, decreased small plank- ton volume, and a shift in larval abundance from anchovy to sardines. Beyond its coincidence with these other ecological changes, the ultimate reason for the change in the seasonal pattern of red tide development
. Bulletin. Science. Outside LA. harbor breakwater Off Santa Catalina Island -n Dinophysis B Prorocentrum H Protoperidinium ^D Ceratium tD naked dinoflagellates H Lingulodinium Fig. 3. Dinoflagellate community composition. dinoflagellate blooms, which coincided with other significant changes in the eco- logical system of the Bight, such as increased temperature, decreased small plank- ton volume, and a shift in larval abundance from anchovy to sardines. Beyond its coincidence with these other ecological changes, the ultimate reason for the change in the seasonal pattern of red tide development is not obvious. Even the causes of these bightwide red tides in general are still elusive. Potential causes may be related to wind and/or coastal runoff. The largest red tides during the years 1995 to 1997 followed windy periods. Wind blowing over the ocean can cause an increase in the mixed layer and/or coastal upwelling, thereby en- riching the euphotic zone with nutrients. There is also some indication that river and storm drain output, providing abundant nitrogen (including the forms of am- monia or urea), may be an important stimulus for bloom formation. Available nitrogen is often the limiting macronutrient in marine systems, with ammonia and urea being the preferred forms for algal uptake. The present study shows that both L. polyedra and P. micans are tolerant of depressed salinities associated with river runoff. Coastal southern California experiences appreciable rain and asso- ciated runoff only during the winter season, and during the present study period large scale red tides only occurred during the winter and early spring periods. The higher nutrient availability in the runoff may be exploited by dinoflagellates because of the coincidental availability of organic complexing agents (, humic acids) found in river and terrestrial runoff. These organic complexing agents bind with manganese and copper. Under offshore conditions (, upwelling rather than runoff)
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