Fishes in a California coastal lagoon: effects of major storms on distribution and abundance

Monthly beach seine samples were collected at 4 sites in the eastern arm of Mugu Lagoon, USA.from February 1977 to February 1982.The seasonal pattern of maximum abundance in spring or early summer and highest diversity in autumn is similar to reports for other regions.Declines in abundance and number of species, increases in Shannon-Weaver diversity and evenness, and alterations in the distribution of the total monthly catches among stations were evident over the 5-yr study.Most of the annual changes in the populations of fishes could be explained by major storms at the beginning of the second and fourth years of the study.Thick blankets of new, fine sediments differentially affected the sampling sites of the previously mostly sandy lagoon.Topsmelt Atherinops affinis and shiner surfperch Cymatogaster aggregatus, the 2 dominant species of Year 1 (accounting for 42 % and 3 4 % of total catch, respectively), suffered heavier reductions in number than the other common species.Species that spend the majority of their time in the water column were adversely affected to a greater extent than bottom-dwelling species.The disproportionate effects on watercolumn compared to bottom-dwelling species appear to result from the substantial reduction of the low tide volume of the lagoon, especially in the deepest parts, and the destruction of the eelgrass bed that originally covered most of the lagoon.The role of rare, very large natural disturbances may be important in most shallow water marine systems.The role of sedimentation in causing irreversible change as well as disturbance will apply to the small embayments along steep coastlines in regions with Mediterranean climates.