THE DISTRIBUTION OF THE POLYCHAETE NEANTHES LIGHTI IN THE SALINAS RIVER ESTUARY, CALIFORNIA, IN RELATION TO SALINITY, 1948-1952 RALPH I. SMITH Department: of Zoology, Unh'ersity of California, Berkeley 4, California The estuarine nereids, with representatives widely distributed, offer excellent material for studies in comparative physiology and ecology. The present study is part of an attempt to work out the nature of the adaptation to brackish waters as seen in one species occupying ecologically distinctive habitats within a limited geo-graphical area. Neanthes light! furnishes favorable material for studies of the invasion of fresh waters by marine annelids, since it equals or exceeds the much-studied Nereis diversicolor in its ability to live and reproduce in waters of low salinity. Its viviparous mode of reproduction, described in an earlier report (Smith, 1950), has perhaps been of adaptive significance in this respect. The fact that the species appears to consist of self-fertilizing hermaphroditic individuals, living in widely separated rivers, may have favored the appearance of local races, reproductively and spatially isolated from each other. In the Salinas River estuary, some twelve miles north of Monterey, California, the species occurs under a wide range of conditions, and so furnishes material for a study of ecological limi-tations and adaptations which can form a background for, and give meaning to, studies upon its physiology. As a preliminary to more detailed studies upon the mechanism of osmotic regulation, the present report describes the physical and biotic conditions under which N. Hghti occurs in the Salinas River. These find-ings in themselves depict extremely variable estuarine conditions, and may be use-ful in studies on other animals, and in amplifying our information on estuaries in general. An understanding of the history of salinity changes in an estuary is a pre-requisite for studies on the distribution and physiology of its inhabitants. Observations were begun in 1948, coincidentally with other work, and have been carried out as opportunity offered until the fall of 1952. During certain periods the river could be visited only infrequently, hence the data include numerous gaps. However, the total four and one half year record does reveal in a general way the pattern of salinity changes in an estuarine system, and covers the full range of climatic conditions characteristic of this area. It is believed that the results clarify the relationship of salinity to climatic conditions, and will make future studies of estuaries in this area more rewarding. PHYSICAL AND BIOTIC CONDITIONS IN THE SALINAS ESTUARY The estuary of the Salinas River (Fig. 1) presents an extremely varied set of conditions, especially in relation to salinity. This variation in salinity charac-terizes estuaries in general ; for an excellent discussion of estuarine conditions, the review by Day (1951) should be consulted. The Salinas falls into Day's category 335
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