Population dynamics of Sargassum lapazeanum (Fucales, Phaeophyta) from the Gulf of California, Mexico

Abstract

M. Rivera and R. Scrosati. 2006. Population dynamics of Sargassum lapazeanum (Fucales, Phaeophyta) from the Gulf of California, Mexico. Phycologia 45: 178–189. DOI: 10.2216/05-47.1

We studied the population dynamics of Sargassum lapazeanum from the southwestern Gulf of California, Mexico, between February 2000 and February 2001. We qua.gified the seasonal changes in frond density, stand biomass, frond size structure and inequality, presence of reproductive structures, and rates of recruitment, growth, and mortality. Fronds were present during the entire year, although with a marked seasonality: mean frond density, frond length, and stand biomass were highest in spring and lowest in winter. The strong increase in frond density between winter and spring resulted from the combination of high recruitment and low mortality rates. Growth rates were highest in spring; the highest absolute value (3.6 cm d⁻¹) is among the highest found for brown seaweeds. The frond size structure became best developed in late spring. Reproductive structures peaked in abundance in late spring and became mostly lost by late summer. Senescence started in late spring and increased dramatically during the summer. The strong decrease in frond density between summer and autumn resulted from the combination of low recruitment and high mortality rates. In early autumn, primarily only small fronds remained in the population, including new recruits and remnants of previously large fronds. The seasonal pattern in the temporal abundance changes for S. lapazeanum agrees with a general model proposed for subtropical species of this genus.

Key Words::

• biomass
• density
• Gini coefficient
• growth
• mortality
• recruitment
• Sargassum lapazeanum
• size inequality
• size structure

ACKNOWLEDGMENTS

This study represents part of the M.Sc. thesis of M. Rivera, directed by R. Scrosati. We are grateful to Gustavo Hernández-Carmona, Gustavo de la Cruz, Rafael Riosmena-Rodríguez, and two anonymous reviewers for their comments on earlier versions of the manuscript. M. Rivera was supported by a PIFI (Institutional Program for the Promotion of Researchers) graduate scholarship from the National Science and Technology Council of Mexico (CONACYT). This study was funded by a CIBNOR research grant (RM-7) to R. Scrosati. Support from the National System of Researchers (SNI) of CONACYT to R. Scrosati is also acknowledged.