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kinds invading the areas is gradually enlarged and 

 approaches peak productivity. 



Ecologically these species vary according to the 

 sediments they occupy; whether mud, silt, sand, gravel, 

 rock, algae, or mixed bottoms. In the sediments they 

 maintain over (pelagic), on (epifaunal), or in (infaunal) 

 positions. The positions may differ according to stages 

 of life history, for some have pelagic eggs and larvae, 

 and at a certain age they sink to the bottom and creep 

 about, seeking suitable sediments for settling. Once 

 a suitable habitat is found, they metamorphose and grow 

 to maturity in the sediments. Other animals may be errant 

 or foraging as adults (crabs, Chloeia „ many snails), 

 or they may be attached to a substratum, as hydroids, 

 barnacles, bryozoans. Many are tubicolous and construct 

 characteristic tubes which require building materials of 

 exact kind and size, according to kind or species. Others 

 are nestling and occupy the burrows or tubes made by 

 other kinds, or they may be somewhat buried (seawhip, 

 Glottidia ) , or burrowing (many mollusks, worms, some 

 urchins). Each kind has specific requirements which 

 differ from those of others, and each species is uniquely 

 modified to occupy its niche at maximum efficiency. 



In Santa Monica Bay only a few boring species have 

 been identified. Such are some sipunculids, in dead 

 tests of Dendraster , Zone II, and others in shaley rocks 

 in outer parts of Zone I, A small clam ( Saxicava ) occurs 



