Structure, litter fall, decomposition, and detritus dynamics of mangroves in a Mexican coastal lagoon with an ephemeral inlet

Abstract

Dynamics of litter fall, de composition, littertransport, and forest structure of white mangroves Laguncularia racemosa Gaertn were studied in a small coastal lagoon on the Pacific coast of Mexico from June 1979 until October 1981. The lagoon is characterized by an ephemeral inlet which is open to the ocean for 3 to 4 mo per year during the wet season. Total litter fall was 1100 g dw m- 2 yr-1. Leaf decomposition was much more rapid in litter bags placed in the water (0.26 mo -1 ) than in bags placed on the dry forest floor (0.05 mo -1 ). Experimental 20 g (dw) samples of leaves placed on the forest floor were flushed out after the opening of the lagoon inlet. We estimate that almost 90 % of total litter fall was exported from the mangroves to the lagoon waters and that most of this was flushed to the ocean. This is due to a number of factors. Litter decomposition on the dry forest floor is very slow, peak litter fall occurs just before the onset of the rainy season, and the rapid outflow of accumulated water when the inlet opens flushes almost all accumulated detritus from the forest floor and lagoon sediments. Structural, productivity, and litter transport patterns of this system suggest that mangrove forests in lagoons with ephemeral inlets do not fit well into existing classification schemes.