Secondary production of bivalve populations in the Mangroves Swamps

Mangrove ecosystems are a critical habitat for many species. The productivity of mangroves is important due its contribution of organic detritus and secondary production. The objective was to identify indicators of secondary productivity of mangrove systems to establish a baseline for measuring changes in the mangrove system due potential natural or anthropogenic disturbances. The bivalve mollusks, the black ark Anadara tuberculosa and the palmate oyster Saccostrea palmula were chosen as indicators of secondary productivity. Samples were collected in three mangroves of the sand barrier El Mogote in the Ensenada de La Paz, from August 2007 to July 2009. Abundance and secondary production were estimated based on biomass increase. The estimated weight increase was performed by determining individual growth rates through an analysis of length frequency distributions. The average abundance was 1.27 and 510 ind. m-2 of black ark and palmate oyster respectively. Growth rates of 4.91 mm·month -1 (3.67 g month -1) for black ark and 3.80 mm month -1 (0.18 g month -1) for the palmate oyster were estimated. Average secondary production of black ark was 4.51 g m-2 month and was higher during the spring, while for the mangrove oyster was 97.9 g m-2 month-1, and the maximum production was recorded during the summer. We found 78 macroinvertebrate species within the mangrove swamps surveyed in this study. There are just a few species of bivalves associated with mangroves that represent an economic interest for their productivity. The black arks and oysters are among the most important mangrove-associated species because of their commercial value and continual exploitation. The obtained results, such as a quality index of benthos, are suitable for measuring changes to the mangrove system in the Ensenada of La Paz, Baja California Sur, Mexico.