September 1980 (Foster and Heine 1981). 

 When water containing this bloom moved 

 into the kelp forests, visibility was 

 reduced to zero on the bottom. Whether or 

 not they produce a bloom, some dino- 

 flagellate species are toxic to man. As 

 dinoflagel lates are usually most abundant 

 in summer and early autumn, harvesting of 

 filter feeding shellfish (particularly 

 mussels) that may concentrate 

 dinoflagel lates is banned during this 

 period. 



Phytoplankton reduce water clarity 

 and therefore contribute to the reduction 

 of light within kelp forests (see Chapter 

 2). Because phytoplankton growth is often 

 stimulated by increased nutrients, these 

 organisms may be particularly abundant 

 around sewer outfalls (Eppley et al . 1972, 

 Kleppel et al. 1982), and along with 

 increased turbidity from suspended solids, 

 can affect macroalgal populations by 

 reducing light. Reduced light associated 

 with the Los Angeles sewer discharge at 

 White Point may have contributed to the 

 loss of kelp forests at Palos Verdes 

 (Wilson 1982). 



4.2.2. Zooplankton 



Almost all nearshore zooplankton 

 species can also be found in kelp forests 

 at various times. Holoplanktonic species 

 can be an important source of food for 

 some kelp forest fishes (particularly the 

 blacksmith; Bray 1981; see Section 4.5 

 below), and are imported as energy and 

 nutrients into the kelp forest from 

 planktonic communities as fish feces (Bray 

 et al . 1981). Zooplankton may 

 occasionally have dramatic effects on kelp 

 forests. Duggins (1981a) described a 

 reduction in sea urchin grazing on 

 macroalgae in Alaska caused by an increase 

 in benthic diatoms and an influx of 

 pelagic salps. The sea urchins 

 temporarily fed on the diatoms and salps, 

 grazing on macroalgae decreased, and 

 macroalgal abundance increased. 



One group of zooplankton, the mysids 

 or opossum shrimp (Figure 14) are usually 

 associated with kelp forests, and can form 

 extremely dense, migrating swarms on the 

 bottom or under the Macrocystis surface 

 canopy (Clarke 1971). Individuals may be 

 up to 2 cm long, and swarms may be 



extensive (meters thick and wide) and so 

 dense as to obscure the bottom completely. 

 Mysids apparently feed on both small 

 plankton and macroalgal detritus, and are 

 fed upon by many kelp forest fishes 

 (Clarke 1971), and even gray whales (see 

 Section 4.6.2.3 below). 



In addition to the above zooplankton, 

 there is an assemblage of primarily small 

 crustaceans that migrate at night from the 

 bottom up into the water column (Hobson 

 and Chess 1976, Hammer and Zimmerman 1979, 

 Hammer 1981). These demersal zooplankton 

 often use bottom cover algae as habitat 

 during the day, and at Catalina Island at 

 least, are fed upon in the plankton at 

 night by a variety of fishes (Hobson and 

 Chess 1976). 



4.3 MACROSCOPIC PLANTS 



4.3.1 Introduction 



The west coast of North America is 

 unique in the number of subtidal algal 

 species that form canopies extending to 

 the surface of the sea, and perhaps with 

 the exception of Australia, in the number 

 of species which form an understory canopy 

 1-2 m high. Most of these are 

 Laminariales of the families Alariaceae, 

 Laminariaceae, and Lessoniaceae (Druehl 

 1970). The distribution of surface canopy 

 species is discussed in Chapter 3, along 

 with depth-distribution patterns. 



Within any kelp forest, the vertical 

 stratification of canopy levels in the 

 water column is an obvious feature to any 

 observer. The density of the vegetation 

 layers may have several effects in a kelp 

 forest. The biomass and vertical 

 structuring they form provide a nursery 

 and protective cover for many species of 

 fish (Quast 1971a). These layers may 

 sequentially reduce the light that reaches 

 primary substratum to < 1% of surface, a 

 reduction that may affect the recruitment 

 and growth of algal species (see Chapter 

 2). Water motion may also be altered 

 within dense stands by the kelp themselves 

 (see Section 2.6). The result of inter- 

 actions of environmental and biotic 

 factors is, therefore, quite complex. 

 While the presence of recruits of a 

 species and subsequent growth rates and 

 survival may be directly related to 



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