We describe the composition and distribution of bivalve molluscs from the sandy and rocky intertidal and the shallow subtidal environments of Bahía de Mazatlán, México. The bivalve fauna of the bay is represented by 89 living species in 28 families, including 37 new records and four range extensions: Lithophaga hastasia, Adula soleniformis, Mactrellona subalata, and Strigilla ervilia. The number of species increases from the upper (44) and lower intertidal (53) to the shallow subtidal (76), but only 11 (17%) have a wide distribution in the bay (i.e., found in all sampling sites and environments). The bivalve assemblages are composed of four main life forms: 27 epifaunal species, 26 infaunal, 16 semi-infaunal, and 20 endolithic. A taxonomic distinctness analysis identified the sampling sites and environments that contribute the most to the taxonomic diversity (species to suborder categories) of the bay. The present work increased significantly (31%) to 132 species previous inventories of bivalves of Bahía de Mazatlán. These species represent 34% of the bivalve diversity of the southern Golfo de California and approximately 15% of the Eastern Tropical Pacific region.

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For more than 10 years (2007-2018), the benthic macroinvertebrates of Bahía de Chamela (Mexican Pacific) were sampled at 31 sites (0-25 m depth). A total of 308 species of the five main classes of benthic molluscs were obtained (106 bivalves, 185 gastropods, 13 polyplacophorans, two scaphopods and two cephalopods). This is a significant increase in the number of species (246 new records) compared to the 62 species previously recorded more than 10 years ago. The distribution in the 31 localities of the bay is given for the first time for most of the species, together with information on its ecological rarity (incidence in the samples). Two families of bivalves (Veneridae and Mytilidae) and three families of gastropods (Calyptraeidae, Muricidae and Collumbellidae) comprised ~ 30% of all species. Ecological rarity was evident with 45 families (45.0%) with only one species and 178 species (57.8%) collected in one site and 67 (21.8%) in two sites. The molluscs of Bahía de Chamela represent 12.2% of all species recorded in the Mexican Pacific. Their biogeographic affinities are mostly related to the Tropical Eastern Pacific (TEP) including the oceanic islands and a few are restricted to the Tropical Mexican Pacific (TMP). Some have broader distributions to adjacent northern and southern temperate regions of the American Pacific, one to the western Atlantic, two pantropical (PAN) and two cosmopolitans (COS). The range distribution of each species was reviewed and updated, thus finding that seven species have extended their ranges of geographic distribution.

Many crustacean species are obligate associates of pocilloporid corals, where they feed, reproduce, and find shelter. However, these coral-associated crustaceans have been poorly studied in the eastern tropical Pacific. Determining the crustacean richness and taxonomic distinctness could help in comparing different coral reefs and the potential effects of degradation. This study evaluated the spatio–temporal variation of the taxonomic diversity and distinctness of coral-associated crustaceans in four ecosystems of the Central Mexican Pacific (CMP) with different conditions and coral cover. In all ecosystems, 48 quadrants were sampled during the summer and winter for two years. A total of 12,647 individuals belonging to 88 species, 43 genera, and 21 families were recorded. The sampling effort yielded 79.6% of the expected species richness in the study area. Species rarity had 19% singletons, 4% doubletons, 22% unique, and 9% duplicate species; two species represented new records for the Mexican Pacific, and six were new to the CMP. This study recorded most of the symbiotic crustacean species in pocilloporid corals previously reported in the CMP. The taxonomic diversity and distinctness differed significantly between coral ecosystems and seasons, which was also visualized by nMDS ordination, showing an evident spatio–temporal variation in the taxonomic beta diversity.

This work presents an inventory of the Polyplacophora species registered in December 2019 in the intertidal environment of 10 sampling sites of the Northern Gulf of California, México. Fifteen species were obtained from a total of 33 species previously reported throughout the Gulf. Acanthochitona avicula, Ischnochiton guatemalensis, Lepidozona serrata, and Dendrochiton lirulatus are rare with only 1 to 3 specimens recorded of each species. Stenoplax mariposa and Lepidozona subtilis were the most abundant with 162 and 284 specimens, respectively. Acanthochitona avicula, I. guatemalensis, Lepidozona serrata, and Lepidochitona beanii are rare and each was only recorded at one sampling site. For a better recognition of these species, we provide a dichotomous identification key, which is complemented with high-resolution photographs and images obtained by scanning electron microscopy. In addition, habitat data and taxonomic comments are included to facilitate a better understanding of the habitat preferences, relationships and current taxonomic position of these species.

Careyes en el centro, tuvieron una buena representación taxonómica. La contribución de la costa de Jalisco al inventario general de especies de macroalgas del Pacífico tropical mexicano es del 69 %, lo que resalta la importancia de esta región para la diversidad de macroalgas de México. Algas marinas mexicanas, lista de especies, distribución, Jalisco, distinción taxonómica.

There have been no published studies of the genus Donax in the eastern tropical Pacific. This work describes the morphometric relationships, growth and mortality of the bean clam Donax punctatostriatus Hanley, 1843 in the sandy beach of Isla de la Piedra, south of Mazatlán Bay, Mexico. Direct collections by hand were performed during 20 monthly sample periods (November 2008 to June 2010) in the intertidal zone of the beach. A total of 2,324 clams of different sizes were removed from the sand, then measured and weighed in the laboratory. The length range of the shells was 2.78-25.64 mm (mean = 12.61 ± 4.04 mm). The length-weight relationship of the total sample indicated isometric growth (a = 0.0002 g; b = 3.0 g mm-1 , R 2 = 0.97); there was positive allometric growth in the recruits (<6.99 mm) (b = 3.4) and in juveniles (b = 3.2); in adults there was negative allometric growth (b = 2.6). Negative allometry of the length/width (log Wd =-0.239 + 0.922 log L) and height/width (log Wd =-0.054 + 0.900 log H) ratio of adults is consistent with a more compressed form of their shell, which assists rapid burying behavior in the sand. The maximum-recorded size of an empty shell (39 mm) was used to set the value of L∞ and to estimate K with the Shepherd (SLCA) method. The average growth rate during the life cycle was 0.43 mm yr-1. Values of L∞ between 29.16 and 34.22 mm were estimated with the Powell-Wetherall method using different class intervals. The mortality coefficient estimated with various methods was variable (0.84-1.15 yr-1). The growth of the clam is rapid and the mortality high, probably because of the characteristics of the habitat, in a subtropical region with high hydrodynamics and sediment transport.