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The seaweed floras from the Goleta Slough and adjacent coastal sites near Santa Barbara, California are compared with several coastal and estuarine habitats within the southern Gulf of Maine. One hundred fifty-two taxa are described from the Goleta-Santa Barbara area, consisting of 104 Rhodophyta, 22 Phaeophyta and 26 Chlorophyta. Four of these taxa represent modest range extensions within the state (i.e., Farlowia conferta, Giffordia hincksiae var. californica, Lomentaria caseae and Prionitis australis, while two others found within the Slough (Capsosiphon fulvescens and Microspora pachyderma) are significant additions to the marine flora of the Pacific Coast. The patterns of species richness and composition at four contiguous southern California sites showed strong contrasts due to local environmental variability, with the highest numbers of taxa (117 taxa or similar to 77%) occurring at the sand-abraded nearshore Goleta Point site and the lowest within the shallow Slough (26 taxa or similar to 17%). The depauperate flora of this small arid salt marsh habitat is dominated by ephemeral green algae (16 species) and Salicornia virginica, with ten other seaweeds (i.e., 7 reds and 3 browns) only occurring just upstream from its mouth. By contrast, estuarine seaweed floras within New England usually have much higher numbers of red algal taxa, their ’’open coastal’’ floras often extend much farther inland (similar to 2.0-8.5 miles) and seaweed standing stocks are usually dominated by fucoid brown algae. The similarity of the Slough’s green algal Bora to New England’s estuarine vegetation is striking, with most of the latter sites exhibiting floristic affinities of 50% or more. The analogous distributional and abundance patterns of ephemeral green algae (Cladophora sericea and Enteromorpha compressa) and the California horn snail (Cerithidea californica) suggest several important interactions between seaweeds and snails, plus several other invertebrates and birds.