A study of the fine-scale patchiness of selected copepod species in the California Current

Abstract

Seventeen Multiple Opening/Closing Net and Environmental Sensing System hauls were taken in the California Current at a depth of 90m and with a sample interval of 50m over a period of three days and three nights. Thirteen species were observed from the samples with average abundances greater than 5 individuals per 50m('3). Average daytime abundances ranged from 19.1 to 120.5 individuals per 50m('3). Average nighttime abundances ranged from 6.9 to 163.7 individuals per 50m('3). Fisher's index of dispersion ranged from 356 to 4590 during the day and 3,560 to 13,680 during the night. Patch parameters were determined using the Skellam Model for both day and night abundances. Patch diameters ranged from 160 to 360m at night and 180 to 480m during the day. Patch densities correlated significantly with Fischer's index of dispersion, implying a strong correlation with earlier measures of the intensity of patchiness. The spacing between patches appeared to be variable, suggesting a random distribution of the patches. Based on the correlations, patches were found to be multispecific, both by day and by night. Though some species failed to group consistantly, these did exhibit weak correlations with individual species. However, the groupings were not static for either day or night communities. The lack of zero abundances were not predicted by the model. The numbers of individuals observed between patches suggest that there are zones of exchange between patches. These observations suggest the temporary nature of the integrity of the patch structure. These data point out the dynamic nature of patches. Patch structure changes drastically from day to night. The coactive forces between species are obviously changing constantly as is the species makeup of the groups.