Interannual variability of the diversity and structure of ichthyoplankton assemblages in the central Mexican Pacific

Abstract

[Abstract] We examined larval fish diversity and assemblage structure on the central Mexican Pacific (coast of Jalisco and Colima) using data from samplings carried out with a Bongo net at 12 stations during 27 months, from December 1995 through December 1998. A total of 132 taxa were recorded, and the dominant species were Bregmaceros bathymaster (90% of the total abundance), Dormitator latifrons (1.9%) and Harengula thrissina (0.8%). Only B. bathymaster, D. latifrons and Gobionellus sp. attained the 100 % of occurrence. The effects of the 1997-98 El Niño event in ichthyoplankton diversity were significant, however the prevalence of the normal seasonality could be observed. Diversity null models were used to determine structural changes in the assemblage due to El Niño effects; both species richness and evenness were highest during El Niño. The most parsimonious models of assemblage organization include the El Niño and seasonality as most significant environmental variability sources. The small-scale spatial variability expressed as the cross-shore gradient was not relevant. The dominant species group formed by B. bathymaster, D. latifrons, and Vinciguerria lucetia typify for similarity both the previous and El Niño period and the only change was the abundance difference among periods. The El Niño period was typified by the dominant species Bentosema panamense and H. thrissina, and by the rare species Euthynus lineatus, and species of the genus Lujtanus. The assemblage shows a similar organization in the different seasons, sharing the same dominant species group. Seasonality produces only changes in the abundances and relative frequencies of dominant species and different rare species are characteristic of the different seasons. The average taxonomical distinctness, that could be considered as a measure of functional diversity, was highly sensitive to the seasonal change of the assemblages independently of the El Niño; this index showed lowest values during tropical and transition periods characterized by warm and oligotrophic waters