that migrate between the benthos and the 

 water column above; and mysids that may be 

 in both of these categories as well as 

 being holoplanktonic. 



Even less is known about bacteria and 

 fungi that decompose organic matter within 

 kelp forests. These organisms and the 

 materials they produce and degrade are 

 probably important sources of food for the 

 largely detritus-based food web, but 

 perhaps less important than direct 

 consumption of drift algae by detritivores 

 (see Section 3.6.4). General character- 

 istics of surface bacteria and 

 decomposition by bacteria and fungi are 

 briefly discussed by Scotten (1971) and 

 ZoBell (1971). 



General composition and natural 

 history of the more abundant kelp forest 

 plankton are discussed below. 



4.2.1 Phytoplankton 



Probably all species of phytoplankton 

 found in nearshore waters could be found 

 in kelp forests at some time and there 

 appear to be no species endemic to kelp 

 forests. Clendenning (1971a) listed 58 

 species of diatoms and dinoflagellates 

 collected from the La Jolla kelp forest in 

 June 1958, with the diatom 

 Leptocyl indricus spp. and the 

 dinoflagel late Diplopel topsis minor most 

 abundant. Miller and Geibel (1973) did 

 not identify phytoplankton to the species 

 level in their study of the Point Cabrillo 

 kelp forest, but they stated that the 

 diatom genera Coscinodiscus and 

 Rhizosolenia were most commonly observed. 



Various species of benthic diatoms 

 are also found in the plankton, particu- 

 larly after storms when individuals or 

 "chains" have been dislodged by water 

 motion. The most common species are 

 Licmophora abbreviata , Meloseira 

 monil iformis , and the large, angular 

 Isthmia nervosa (Figure 14). The former 

 is particularly common on giant kelp 

 blades. When attached, these and other 

 benthic species often form soft, hair-like 

 coverings on senescent macroalgae, 

 attached understory plants, and unoccupied 

 hard substrata if light intensity is high. 

 If the water is calm and light is high for 

 long periods, other diatoms may form thin 



Figure 14. Common 

 mysid shrimp. 



benthic diatoms and a 



brown films or even thick mats on patches 

 of soft substrata within a kelp forest. 

 We commonly observe late spring "blooms" 

 of benthic diatoms on understory 

 articulated corallines in Carmel Bay, 

 California, when the overstory canopies of 

 Pterygophora cal ifornica and Macrocystis 

 pyrifera are still reduced from winter 

 storms. When connected in long chains or 

 in a common mucilagenous sheath, these 

 diatoms may be confused with small, 

 filamentous brown algae whose external 

 form can be similar. 



Planktonic and benthic diatoms are 

 consumed by filter feeders and grazers, 

 but little is known about consumption 

 rates or consumer feeding preferences in 

 kelp forests. Trotter and Webster (1984) 

 have shown that free-living nematodes 

 associated with Macrocystis integrifol ia 

 eat bacteria and diatoms, and that 

 particular species of nematodes may prefer 

 one food source or the other, and may also 

 prefer particular species of diatoms. 



Dinoflagellates may become extremely 

 abundant in kelp forests during red tides 

 (up to 20 x 10 6 cells/liter; Holmes et al. 

 1967). An extensive nearshore bloom of 

 Ceratium sp. occurred in the vicinity of 

 Monterey, California in August and 



44 



