Seasonal variations in dinoflagellate cyst fluxes and assemblage composition were investigated for the first time on the west coast of the United States of America. We analyzed the palynological content of an ~two year-long (May 1995 to March 1997) fortnightly sediment trap time series from the Santa Barbara Basin (SBB, off Southern California), a region characterized by seasonal upwelling and high levels of primary productivity. A total of 47 dinoflagellate cyst taxa were identified in the trap samples, with assemblages dominated by cysts produced by heterotrophic taxa. Multivariate analyses support that dinoflagellate cyst fluxes and assemblages are reliable indicators of primary productivity, and reflect sea surface temperature (SST) variations associated with upwelling in the SBB. In particular, Brigantedinium spp. are associated with active upwelling intervals (fluxes up to 127,430cystsm-2day-1 and up to 86.6% of the assemblage), when SST is lower, stratification is weaker and diatom production is maximal. Conversely, Lingulodinium machaerophorum indicates relaxed upwelling conditions (up to 9640cystsm-2day-1 and 29.9% of the assemblage) characterized by higher SST, stronger stratification and reduced primary productivity. Selenopemphix undulata is associated with colder SST in the region, whereas cyst type A abundances increase with higher SST. Thecae of potentially toxic dinoflagellates are also documented, such as Lingulodinium polyedrum and Prorocentrum micans, which are mainly recorded under conditions of higher SST and strong stratification, and Dinophysis spp. with higher fluxes between June and September of both 1995 and 1996.
Bibliographical noteFunding Information:
M. Bringué was supported by the Fonds Québécois de la Recherche sur la Nature et les Technologies (FQRNT) B2 fellowship. The research was funded by a Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery grant ( 224236 ) to Dr. V. Pospelova. The Santa Barbara Mooring Project was funded by the National Science Foundation grant OCE-952984 and the NOAA grant NA77RJ0453 to Drs. A. Alldredge and M. Brzezinski. We thank C. Gottschalk, S. Anderson and C. Wyatt-Evans for the technical support with the mooring. We are deeply grateful to Drs. A. Alldredge and U. Passow (University of California, Santa Barbara), and R. Shipe (University of California, Los Angeles) for sharing the environmental and geochemical data collected during the UCSB Santa Barbara Mooring Project. We also thank Dr. David Field (Monterey Bay Aquarium Research Institute) for providing a dated sediment sample from the SBB. Finally, the authors thank Dr. R. Jordan and two anonymous reviewers for their constructive and thoughtful comments.
- Harmful Algal Blooms
- Lingulodinium machaerophorum
- Northeastern Pacific
- Primary productivity
- Sea surface temperatures