Diversity of ichthyoplankton in the central Mexican Pacific: a seasonal survey

The seasonal variation in the diversity of ichthyoplankton was analyzed from samples collected monthly during a year cycle off the central Pacific coast of Mexico. Samples were collected using a Bongo net at 12 stations during 11 months, from December 1995 through December 1996. The most dominant species was Bregmaceros bathymaster, its relative density varied between 77 and 98%. Two main seasonal patterns were revealed after analyzing the dynamics of the coastal water mass and the ichthyoplankton assemblage ordination in relation to diversity. Diversity values ( jack-knifed H ¼ 0:24) were relatively low from January to May, and indicated a first seasonal pattern, related to a period dominated by the influence of the California Current, with surface temperatures ranging between 21 and 24 C. The second pattern was featured by diversity values five-fold higher than in the winter-spring ðH ¼ 0:92Þ. These were related to the influence of warm, tropical waters from the Equatorial Countercurrent, with associated temperatures ranging between 26 and 29.2 C. A transitional period was identified in June and December; it represented a mixed assemblage and yielded the highest richness. Diversity null models were useful as tools to confirm the major seasonal patterns of the surveyed ichthyoplankton community.