Biology and Ecological Niches in the Gulf of the Farallones 



Phytoplankton 



Gregg W. Langlois and Patricia Smith 



Phytoplankton play a key role in the marine 

 ecology of the Gulf of the Farallones. 

 These microscopic, single-celled plants are 

 found in greatest abundance in nearshore 

 coastal areas, typically within the upper 

 160 feet of the water column. The name 

 "phytoplankton" consists of two Greek 

 words meaning "plant" (phyto) and "wan- 

 derer" (plankton). There are two major 

 groups of phytoplankton (1) fast-growing 

 diatoms, which have no means to propel 

 themselves through the water, and (2) 

 flagellates and dinoflagellates, which can 

 migrate vertically in the water column in 

 response to light. Each group exhibits a 

 tremendous variety of cell shapes, many 

 with intricate designs and ornamentations. 



All species of phytoplankton are at the 

 mercy of oceanic currents for transport to 

 areas that are suitable for their survival and 

 growth. Thus, physical processes can play a 

 significant role in determining the distribu- 

 tion of phytoplankton species. Rapid cell 

 division and population growth in phyto- 

 plankton can produce millions of cells per 

 liter of seawater, resulting in visible blooms 

 or "red tides." 



With the potential for such high produc- 

 tivity, it is not surprising that phytoplankton 

 are the first link in nearly all marine food 

 chains. Without phytoplankton, the diver- 



sity and abundance of marine life in the 

 Gulf of the Farallones would be impos- 

 sible. Phytoplankton provide food for a tre- 

 mendous variety of organisms, including 

 zooplankton (microscopic animals), bivalve 

 molluscan shellfish (mussels, oysters, scal- 

 lops, and clams), and small fish (such as 

 anchovies and sardines). These animals, 

 in turn, provide food for other animals, 

 including crabs, starfish, fish, marine birds, 

 marine mammals, and humans. 



The coastal area of the Gulf of the Far- 

 allones undergoes periods of strong upwell- 

 ing during the spring and summer months 

 (see chapter on Current Patterns over the 

 Continental Shelf and Slope). In addition to 

 delivering colder, nutrient-rich waters from 

 depth, coastal upwelling concentrates phy- 

 toplankton near the surface. This concen- 

 tration of cells in sunlit surface waters, 

 together with increased nutrients, may pro- 

 vide a competitive edge for the faster grow- 

 ing diatoms during upwelling events. Con- 

 versely, a stratified water mass consisting 

 of a layer of warmer surface water and a 

 deeper layer of colder, nutrient-rich water 

 can form following upwelling. These con- 

 ditions favor the development of dinofla- 

 gellate blooms, such as toxic "red tides," 

 because these types of phytoplankton can 

 actively swim to the surface to photo- 



synthesize during the day and migrate to 

 deeper areas at night to absorb nutrients. 

 Such conditions can also be associated 

 with downwelling, in which warmer off- 

 shore waters move shoreward, pushing 

 coastal surface waters down and along the 

 sea floor to deeper areas. Research in other 

 parts of the world has shown that dino- 

 flagellates are commonly associated with 

 such nearshore downwelling. 



Of the more than 5,000 known species 

 of marine phytoplankton, approximately 40 

 species worldwide have been linked with 

 production of toxins. These marine biotox- 

 ins can have subtle to lethal effects on 

 various forms of marine life. Human con- 

 sumers of certain seafood items (especially 

 clams, oysters, and mussels) are also at 

 risk. It remains difficult to avoid the harm- 

 ful effects associated with blooms of these 

 toxic species because phytoplankton ecol- 

 ogy is not fully understood. 



Within the Gulf of the Farallones, red 

 tides are a common natural phenomenon, 

 usually occurring from August through 

 October, when a relaxation of coastal 

 upwelling results in a warmer, more stable 

 water mass nearshore that appears to favor 

 dinoflagellate populations. The commonly 

 used term "red tide" is misleading, because 

 phytoplankton blooms frequently are other 



colors, such as brown, green, and yellow, 

 and are in any case not a tidal phenomenon. 



Nearly all phytoplankton blooms along 

 the California coast and within the Gulf 

 of the Farallones involve nontoxigenic spe- 

 cies. Conversely, most incidents of paralytic 

 shellfish poisoning (PSP) in humans caused 

 by eating shellfish caught in California 

 waters have occurred in the absence of vis- 

 ible blooms of toxin-producing phytoplank- 

 ton. Because the coastal area encompassed 

 by the marine sanctuary has been the focal 

 point for PSP toxicity in California, and 

 because of the continued increase in com- 

 mercial bivalve shellfish aquaculture within 

 this area, the California Department of 

 Health Services has intensified its biotoxin- 

 monitoring efforts in the area. 



The key to understanding the combina- 

 tion of physical, chemical, and biological 

 factors that result in blooms of the phyto- 

 plankton species that produce PSP toxins 

 may lie within the Gulf of the Farallones. 

 Such understanding would greatly assist in 

 the protection of public health. 



32 Biology and Ecological Niches in the Gulf of the Farallones 



