Bryozoans are commonly among the 

 first organisms to settle on newly exposed 

 substrata in kelp forests, and may remain 

 abundant in shaded habitats or those 

 protected from predation (Foster 1975a, 

 b). Selective predation by the bat star, 

 Patiria miniata , can alter succession in 

 the bryozoan assemblage (Day and Osman 

 1981). One species, Cryptoarachnidium 

 (= Victorella ) argil! a , is a common early 

 colonizer on nearshore artificial reefs in 

 southern California (Turner et al. 1969, 

 Grant et al . 1982). This animal forms 

 encrusting sheets composed, in part, of 

 consolidated sediments and can dominate 

 reef surfaces for long periods. Dominance 

 is probably maintained in the absence of 

 predators by inhibiting settlement of and 

 growing over other sessile species (LOSL 

 1983). Bryozoans, and sessile animals in 

 general, appear capable of inhibiting the 

 settlement and growth of benthic algae, 

 even in subtidal habitats with sufficient 

 light for algal growth. Predators 

 (particularly fish and sea stars) of these 

 sessile animals may mediate this 

 competitive dominance, allowing local 

 coexistence (Foster 1972, 1975b). 



4.4.2.4 



Brittle stars, sea stars, 



sea cucumbers and sea urchins (Echinoder - 

 mata ). Brittle stars are extremely abun- 

 dant in kelp forests. They are not. obvi- 

 ous because they are normally found out of 

 sight under cobbles, in holdfasts, dense 

 algal turfs, and other cryptic habitats. 

 These animals generally feed by extending 

 their arms and trapping food particles 

 using the sticky mucous on the spines and 

 podia. They are particularly active at 

 night, when one can see hundreds of arms 

 sticking out in the water among the 

 haptera of giant kelp holdfasts. 



The abundance of one of the more 

 common brittle stars, Ophiothrix spiculata 

 (Figure 19), ranged up to 21 

 individuals/100 cm 3 in giant kelp 

 holdfasts from southern California 

 (Ghelardi 1971). Andrews (1945) found 

 total brittle star densities of up to 

 300/m 2 of holdfast (projected surface 

 area), with 0. spiculata and Amphipholis 

 pugetana most abundant. Unfortunately, 

 other than occasional species lists and 

 abundance estimates, little is known of 

 the ecology of these ubiquitous animals. 



Most common sea stars in kelp forests 

 are predators, the exceptions being the 

 red-orange Henri ci a leviuscula that traps 

 small food particles in mucous on the 

 undersides of its arms (Morris et al. 

 1980), and the bat star Patiria miniata , 

 an omnivorous scavenger. The latter is 

 discussed in more detail under Grazers 

 below. 



Sea cucumbers use their tentacles to 

 extract food from sediments or water, and 

 only the tentacles of some species can 

 normally be seen protruding from crevices, 

 holes, or holdfasts. Common species 

 include the red Cucumaria miniata in 

 central California, the small (2-3 cm) 

 orange Pachythyone rubra from Monterey to 

 southern California, and the small, white 

 Eupentacta quinquesemita , and large, brown 

 Parastichopus spp. (Figure 19) throughout 

 the range of Macrocystis pyrifera . P. 

 rubra can occur at densities of up to 

 10,000/m 2 in some areas at San Nicolas 

 Island off southern California (Cowen 

 pers. comm. ) Sea cucumbers are eaten by 

 various sea stars (Morris et al . 1980). 



All species of sea urchins found in 

 kelp forests can capture and feed on drift 

 algae, and this may be their most common 

 mode of feeding. However, because they 

 can graze attached plants (and are most 

 notorious for it), they are discussed 

 under Grazers below. 



4.4.2.5 Molluscs (Mollusca) . Numer- 

 ous filter-feeding clams inhabit sandy 

 areas in kelp forests, but the most common 

 on hard substrata are the rock-boring pho- 

 lads (Family Pholadidae) seen as siphons 

 extending out of short calcareous tubes 

 above the substratum. The most abundant 

 of these is Parapholas californica , whose 

 densities can be over 50/m 2 in kelp 

 forests with relatively soft shale 

 bottoms. Bore depth can be 30 cm, and 

 these clams can cause considerable erosion 

 of soft rock bottoms (Morris et al. 1980). 

 The sea star Pisaster brevispinus is 

 capable of extruding its stomach into 

 pholad burrows and digesting the clams in 

 place (Van Veldhuizin and Phillips 1978). 



Mussels ( Mytilus spp.) are most 

 common in the intertidal zone, but are 

 occasionally found in deep water (Chan 

 1973, Paine 1976). The size record for M. 



58 



