Spatiotemporal patterns of macrophyte subsidies to sandy beaches of Yucatán, Mexico

The spatial and temporal patterns of macrophyte wrack in six sandy beach localities of the northern Yucatán Peninsula were described to answer three main questions: (1) Is the composition and biomass of stranded macrophyte homogeneous along the coast and independent of climatic events?; (2) Which environmental features of beaches are the main predictors of macrophyte biomass deposition and retention?; and (3) Is there a significant relationship between deposited, retained, and buried wrack and the content of organic matter in sediments? To this end, the macrophyte wrack was collected in five random replicated quadrats along the recent drift line (representing the deposited wrack). The same operation was repeated along the aging strandline (representing the retained wrack). All material was washed and weighed. Macrophytes of each sample were separated into nine categories to determine variations in their composition. Macrophyte wrack patterns of species composition were primarily explained by large spatial scales (localities), separating the west side (Celestún and Sisal) from the rest of the Yucatán coast. The composition of macrophytes was consistent, although their temporal dynamics varied between sites and localities. Biomass patterns showed a more complex spatial and temporal pattern with a significant relation of the arrived and retained wrack biomass. The main environmental predictors of wrack biomass deposition and retention were longitude coordinates, shoreline orientation, grain size, and swash climate. However, the beach state did not correlate with the deposited and retained wrack biomass. The amount of buried wrack was significantly related to the amount of retained wrack, and the former significantly contributed to explaining the amount of organic carbon in sediments. In general, we hypothesized that the nearshore and heterogeneous habitats could be responsible for the complex spatiotemporal patterns of wrack variation found in the sandy beaches of Yucatán.