**5. Conclusion**

A significant portion of bioluminescence in all oceans is produced by dinoflagellates. The number of bioluminescent species and their relative abundance changes temporally and spatially. There is evidence that dinoflagellates exhibit changes in per cell bioluminescence magnitude which may be attributable to environmental conditions such as light, temperature, and nutrient history. In the present study, photosynthetic and heterotrophic dinoflagellates were collected and tested for bioluminescence on a quarterly basis from 1994-1996 at San Clemente Island, located 100 km off the Southern California coast. Per cell bioluminescence was measured for the phototrophs *Ceratium fusus, Pyrocystis noctiluca, Gonyaulax polyedra* as well as 3 other species of *Gonyaulax*, and in 6 species of the heterotroph *Protoperidinium*. Our data strongly suggests that dinoflagellates have a marked seasonality in the open ocean which may be attributable to regional environmental events such as upwelling and associated winter storm land runoff. We observed correlations between surface (0-50m) nitrates and Chl *a* with bioluminescence in *Pyrocystis noctiluca* and *Protoperidinium pellucidum*. Increased levels of Chl *a* measured in the winter and spring '95 correlated with increased *P. pellucidum* bioluminescence. Both nitrates and mean bioluminescence cell-1 in *P. noctiluca* showed similar trends temporally and in magnitude. Peak levels of nitrates were found in the Southern California Bight in the summer months followed by increases in bioluminescence during the fall months. Peak bioluminescence was observed to occur in the fall for both years in *P. noctiluca* whereas peak bioluminescence in *P. pellucidum* was measured in winter '95 and later in fall '95.
