Diversity and seasonal variation of the molluscan community associated with the seagrass Halodule wrightii in a marine protected area in the southern Gulf of California

The structural complexity of Halodule wrightii enhances the abundance and diversity of mollusks in the marine protected area of Bahía Balandra, in the southern Gulf of California. Marine mollusks are considered ecosystem engineers because they create, modify, and maintain habitats. Taxonomical and functional analyses of the mollusk community were carried out from May 2016 to 2017. The total abundance in all sampled periods was 7284 individuals and comprised 52 families, 69 genera, and 89 species. The Gastropoda class showed the highest number of species (61 species, 68.53%), followed by Bivalvia (24 species, 26.96%) and Scaphopoda (4 species, 4.49%). The highest density of mollusks was in the summer of 2016 (ca. 6500 ind. m−2), while the highest richness was found in spring 2017 (60 species). Five trophic levels were identified. All trophic groups were present in all the seasons with carnivores showing the highest species richness and herbivores the highest abundance, followed by filter-feeders. A positive and moderate relationship between the total biomass of seagrass and gastropod richness was found, while the relationship between gastropod abundance and seagrass biomass was negative. Halodule wrightii in the Gulf of California represents a unique niche that supports a high mollusk biodiversity and offers great variability of resources for this group. Halodule wrightii represents a suitable habitat for reproduction, metamorphosis, nursery, refuge, and feeding for mollusks. Finally, the functional group concept was applied to evaluate the ecosystem seagrass health of Bahía Balandra resulting in a moderate score.