The Distribution of Nephtys californiensis and N. caecoides on the Californian Coast

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Abstract
Both polychaete spp.live in intertidal sands on the Californian coast. Deposition beaches examined can be divided into the following categories extremely exposed, with substrata too coarse for colonization by any burrowing animals; exposed beaches colonized by anomuran Emerita analoga, of these, coarsest and finest are sub-optimal for Nephtys californiensis and are rarely colonized by the worm, substrates of medium coarseness contain populations of 4-8/m2 of N. caliiorniensis; sheltered beaches with muddy substrata have a varied and abundant fauna and are colonized by Nephtys caecoides. There is no ecological overlap between two spp. of Nephtys N. californiensis is excluded from substrata with more than a trace of particles less than 0.15 mm diameter, N. caecoides only occurs in substrata with more than 0.8% particles less than 0.15 mm diameter and optimum substrata for this sp. contain about 2% particles smaller than 0.1 mm diameter. Detailed examination of beaches populated by two spp.shows no correlation between distribution and tidal level; distribution is determined rather by availability of a suitable stubstratum; accordingly, N. caecoides is common subtidally, but N. californiensis is rare.

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