period of cooling which results in a surface 

 mass of water of uniform density to a depth of 

 100-200 m. Since vertical stability is minimal, 

 the surface waters become thoroughly mixed. 

 Upwelling occurs in late winter and early 

 spring as deep water from below the euphotic 

 zone rises to replace surface waters that are 

 displaced horizontally by westerly winds of 

 45-55 knots which blow for periods of about 

 40 hours. Upwelling provides nutrients to the 

 euphotic zone (Of these nutrients, it is the 

 abundance of nitrates which probably limits 

 primary production in the inshore area of 

 southern California). Spring passes into sum- 

 mer, and as solar radiation increases to 

 maximal annual intensity, vertical stability 

 develops in the water column; a shallow 

 thermocline forms at about the 10-m. isobath. 

 During the afternoon, onshore summer breezes 

 push the surface layers of water toward the 

 beaches and into the lee of sheltered locations. 

 Near the end of summer, the direction of the 

 flow of the inshore current systenn changes, 

 as slightly less saline water arrives indirectly 

 from the north Pacific(2). This introduction of 

 "northern water"(-^' continues until the cooling 

 cycle begins in late fall, when vertical mixing 

 again appears to become more important than 

 horizontal trainsport in determining the course 

 of biological events m the inshore area. 



Biological cycles parallel the sequence and 

 intensity of the physical processes. Concen- 

 trations of phytoplankton are low during the 

 winter, minimal during the upwelling period, 

 and maximal in the late spring and summer. 

 Usually an inferior secondary peak of plankton 

 production appears in the early fall''*'. Diatoms 

 are the first major group of phytoplankton 

 observed after the enrichment that results f ronn 

 upwelling. During the late spring and early 

 summer, available nutrients have declined to 

 approximately 10 percent or less of the con- 

 centrations present at the peak of upwelling; 

 the water column is approaching maximum 

 (i.e., vertical mixing is at a minimum). It is 

 then that the dinoflagellates become the donni- 

 nant phytoplankton. The dinoflagellates are 

 restricted to water above the thermocline. 

 During daylight in late spring and summer, 

 these phototactic, motile organisms concen- 

 trate at the surface. The surface layers of 

 water, crowded smd streaked with red dino- 

 flagellates, are blown inshore by the afternoon 

 winds, into the lee of headlands or artificial 

 structures such as breakwaters and harbors, 

 where the organisms accumulate. Cell densi- 

 ties of 10-40 million cells per liter are formed 

 as a result of this concentrationt^). These 

 massive standing crops of Gonyaulax polyedra 

 block light penetration, and therefore photo- 

 synthesis, at depths below 1 m. The dino- 

 flagellate respiration continues until all avail- 

 able oxygen is consumed. Massive numbers of 

 benthic plants and animals suffocate in this 

 anaerobic environment. Anaerobic digestion 



of the dead organisms begins to produce hydro- 

 gen sulfide from the reduction of sulphate 

 produced by the decomposition. 



During the climax of the bloom, the red tide 

 amounts to an extraordinary excess of primary 

 production unlimited by a proportionate in- 

 crease in zooplankton. The red-tide orgamisms 

 annihilate the zooplankton, the benthic filter 

 feeders, and themselves when oxygen becomes 

 depleted in the opaque reddish-brown water. 

 Local blooms appear to subside only when the 

 inshore water mass is replaced by "northern 

 water." 



Economic results of this calamity include 

 severe damage to the inshore fisheries, the 

 bait industry, shoreside rec reational facilities, 

 and the resort and restaurant business (an 

 intense red tide may be detected by its odor 

 6 to 8 miles inlauid); paint peels from boat 

 hulls, and shoreside and marine structures as 

 a result of H2S in the air and water. More- 

 over, cinnual recurrences of red tide destroy 

 the normal well-developed, highly diversified 

 climax community of perennial benthic or- 

 ganisms (°) of the intertidal and sublittoral 

 zones. 



To what extent the following three factors 

 are involved with the problem of the red tides 

 remains to be established: (a) Fish kills occur 

 primarily in artificial harbors and embay- 

 nnents, as already discussed by John Carlisle 

 earlier in this Symposium. If this relationship 

 is obligate, then the construction of additional 

 harbors can only result in increased red 

 tides. It would appear that the same physical 

 situation that causes these natural harbors to 

 act as sediment traps(') also favors the accu- 

 mulation of dinoflagellates. Changes in harbor 

 design may help solve problems of excessive 

 accumulation of sediment and plankton, 

 (b) Another possible factor is the disposal of 

 increasing quantities of domestic and indus- 

 trial wastes into the inshore area. This cur- 

 rently amounts to about 750 million gallons 

 per day, and prospects are for this volume to 

 double within the next 25 years. In theory, this 

 sewage would supply a nutrient enrichment 

 useful to the phytoplankton, but its significance 

 for the inshore area needs to be thoroughly 

 established, (c) A third factor of possibly 

 critical importance is the elimination of mas- 

 sive standing crops of benthic algae along the 

 shores of southern California(^). Benthic algae 

 compete with phytoplankton for nutrients and, 

 presumably, the standing crops of kelps are 

 also limited by nutrient abundance. In the 

 permanent sections of the kelp beds, stauiding 

 crops of phytoplankton could be expected to be 

 larger, as indeed they appear to be. 



Thus the major questions to be answered 

 are: What cam be measured that will permit 

 the prediction of the occurrence of a bloom of 

 red tide in advamce of its actual appearance? 

 Has the balance of primary production between 

 benthic and planktonic algae been upset or 



10 



