The state of Oaxaca in southern Mexico harbors the highest faunistic and floristic biodiversity of the region; however, to date, research effort has focused on terrestrial flora and fauna. Despite this bias, there is a large amount of dispersed information regarding the coastal and marine biodiversity of Oaxaca. The present study aimed to: 1) update and synthesize existing information to improve understanding of coastal and marine biodiversity; and 2) provide a baseline for future biodiversity studies in Oaxaca. The review of 198 references about Oaxaca's flora and fauna produced 2, 157 species records, from 15 taxonomic groups (Division, Phyla or Class). Nevertheless, knowledge about the fauna and flora of Oaxaca remains scarce compared to other regions, such as the Gulf of California. Additionally, floristic and faunistic knowledge is heterogeneous among the taxonomic groups; for instance, 242 (11 .2 °/o) species represent macroalgae, three invertebrate groups (annelids, crustaceans and mollusks) represent about 44.0% (949 species) of all species recorded, while the vertebrates are represented by 762 species (35.3°/o). Similarly, many invertebrate groups recorded in adjacent regions have not yet been recorded on the Oaxaca coast, including some platyhelminthes, rotifers, nematodes, oligochaetes, sipunculids, echiurans, tardigrades, pycnogonids, some crustaceans, brachiopods, chaetognaths, ascidians and cephalochordates. The study of the marine flora and fauna is far from finished; additional effort is required to complete the marine biodiversity inventory of Oaxaca.

The starfishPharia pyramidatusis a tropical species of high ecological importance, mainly because of its role as generalist predator. Nevertheless, there are no studies about its reproduction. This study analysed the reproductive biology ofP. pyramidatusbased on monthly time-series samples from April 2008 to March 2009 at Isla Montosa in the Mexican tropical Pacific. The gonad index (GI), and pyloric caecum index (PCI) were determined and the results were corroborated by histological examination of the gonads.Pharia pyramidatusis a gonochoric asteroid and the ratio of males to females was not significantly different throughout the year. Gametogenesis showed high synchrony among males and females and five stages were recognized for both sexes. Spawning occurred from July to September. Maximum oocyte size was ~150μm and mean fecundity was 7.3 ± 1.2 millions of oocytes per female. GI and PCI showed seasonal variations and an inverse relationship from May to August. Sea-bottom temperature and photoperiod showed a direct relationship with GI, and apparently constitute the proximate causes of the seasonal reproductive pattern observed inP. pyramidatus, while the highly seasonal rainfall and strong upwelling probably act as ultimate causes.

Tropical coastal lagoons are important ecosystems that support high levels of biodiversity and provide several goods and services. Monitoring of benthic biodiversity and detection of harmful or invasive species is crucial, particularly in relation to seasonal and spatial variation of environmental conditions. In this study, eDNA metabarcoding was used in two tropical coastal lagoons, Chacahua (CH) and Corralero (C) (Southern Mexican Pacific), to describe the benthic biodiversity and its spatial–temporal dynamics. The distribution of benthic diversity within the lagoons showed a very particular pattern evidencing a transition from freshwater to seawater. Although the two lagoon systems are similar in terms of the species composition of metazoans and microeukaryotes, our findings indicate that they are different in taxa richness and structure, resulting in regional partitioning of the diversity with salinity as the driving factor of community composition in CH. Harmful, invasive, non-indigenous species, bioindicators and species of commercial importance were detected, demonstrating the reach of this technique for biodiversity monitoring along with the continued efforts of building species reference libraries.