Factors Affecting the Distribution of Tylos punctatus (Isopoda, Oniscoidea) on Beaches in Southern California and Northern Mexico

Abstract

Populations of the isopod Tylos punctatus were studied at five
\nwidely separated beaches between Los Angeles, California, and Punta Banda,
\nBaja California (Mexico). Population densities at these sites were 10 3-10 5
\nanimals per meter of beach frontage; smaller populations were not located,
\nalthough more than 30 intermediate sites were sampled.
\nCross-beach distribution appears to be related to sand moisture content
\nrather than sand coarseness. Longshore distribution on a given beach is patchy,
\nbut the causative factors for this were not determined.
\nStudies of the isopods' population dynamics on two beaches indicated that
\nthe populations were increasing, with doubling times of 2-12 years. If these
\nare minimum values, it is hypothesized that the discontinuous distribution of
\nthe animals on this coast can represent a balance between catastrophic beach
\nerosion and the natural ability of the populations to regenerate and disperse.