Abstract 



A survey of intertidal gammaridean Amphipoda of the southern 

 half of California is based on 360+ quantitative and non-quantitative 

 samples taken primarily in the Phyllospadix-pelvetiid zone below 

 mean low water. The samples were collected at 7 rocky intertidal 

 sites from Monterey Bay to La Jolla. The coastal region embraces 

 portions of both warm- and cold-temperate environments and as a 

 result the distributional limits of many northern and southern species 

 were expected to occur in the region. The logic of this supposition 

 is shown by the analysis of 139 species, 39 of which occur primarily 

 north and 30 primarily south of Pt. Conception. Of the remainder, 

 31 occur on both sides of the point in equal density and the distribu- 

 tions of 39 are poorly known. About 20 additional species occur in 

 the intertidal zone only as strays from deeper water. 



A checklist of 155+ species from the Calif ornian intertidal is pre- 

 sented. Nineteen species and 4 genera are described for the first time. 



About 20 species of Amphipoda are numerically dominant in the 

 intertidal zone, 2-4 of each occurring dominantly in each of several 

 habitats, such as the Phyllospadix-pelvetiid zone, kelp holdfasts, 

 articulated corallines, sponges and tunicates, and phragmatopomid 

 masses. Localities impoverished of flora owing to heavy surf or sand 

 scouring are dominated by different species of Amphipoda than those 

 localities having dense floral stands. Lysianassa macromerus is be- 

 lieved to be an indicator of sedimentary inundation while Oligochinus 

 lighti and Parallorchestes ochotensis are believed to be indicators of 

 heavy surf conditions. Most of the dominant Amphipoda belong to 

 diverse, rather than to monotypic genera. 



Domiciliary Amphipoda comprise more than a third of the species 

 of the Californian fauna but their tubes apparently are so fragile 

 that they never form the bulk of intertidal fouling organisms. In 

 contrast, amphipodan tubes often dominate pilings in protected 

 harbors. 



The Phyllospadix-pelvetiid zone is shown to support 72 species 

 throughout the coastal region but a maximum of 47 occurs at any one 

 locality (Cayucos). Intermixture of northern and southern species is 

 very strong at Cayucos, adjacent to Pt. Conception. 



Kelp stipes of the intertidal zone are poorly populated with Am- 

 phipoda, except those of Egregia having numerous individuals of 



