Biodiversity patterns of epibiotic invertebrates occupying an edible polyplacophoran across a latitudinal gradient of the Mexican Pacific

Abstract

The broad perspective regarding marine-organisms biodiversity indicates a latitudinal gradient. Understanding gradients in diversity at large scales has important applications for understanding future impacts on local and regional communities. We use and propose the edible mollusk Chiton articulatus as the basibiont proxy to analyze the spatio-temporal changes in biodiversity patterns of the epibiotic community occupying its scleritome surface. The analyses covered approximately 1817 km of the Mexican Pacific, using seven sites that included samples from Sinaloa “SIN” (23°38′N, 106°48′W); Nayarit “NAY” (20°45′N, 105°22′W); Jalisco “JAL” (19°13′N, 104°41′W); Colima “COL” (19°06′N, 104°20′W); Michoacan “MIC” (17°54′N, 102°11'"W); Guerrero “GRO” (16°48′N, 99°52′W) and Oaxaca “OAX” (15°39′N, 96°30′W). A temporal gradient (monthly sampling from October 2015 to October 2016) was also analyzed. Evaluation of the sampling effort demonstrated that 76–86% of the epibiotic fauna was recovered. The most representative epibionts were barnacles, a limpet and an acrothoracican. Abundances of the barnacles and the limpet tended to decrease southwards, while the acrothoracican tended to increase northwards. The epibiotic community did not exhibit the typical latitudinal gradient of diversity expected, but a fragmented pattern within three main areas, which coincide with three of the marine biogeographic ecoregions proposed for the shallow waters of the Warm Temperate Northern Pacific and Tropical Eastern Pacific provinces. These were a northern group within SIN, which belong to the southern border of the Magdalena Transition ecoregion (subtropical); a middle group within NAY, JAL, COL, MIC, and GRO, which belongs to the Mexican Tropical Pacific ecoregion (tropical); and a southern group within OAX exclusively, belonging to the northern border of the Chiapas-Nicaragua ecoregion (tropical). The southern localities showed larger dominances and the central localities exhibited more stable communities. Our evidence suggests that as we move across the different shore types of the Mexican Pacific, the coastline supports distinct biotic assemblages, and the community on the rocky shores is biologically heterogeneous and mainly influenced by conditions at the local level. In consequence, conservation and protection efforts should consider preserving the local heterogeneity of habitats in the study area. Furthermore, since C. articulatus is edible, its epibiota represents an incidental fishing bycatch, with the result that the extraction of the chiton and its epibiota can jeopardy the diversity in the intertidal rocky shore of the Mexican Pacific.