Acanthophora spicifera, a red alga considered an alien species, was discovered for the first time on the Pacific coast of Mexico in 2006 from a locality inside La Paz Bay, Gulf of California. Since then, more records have shown its presence, 17 localities having been added up to 2015. A two-year field study (2020-2022) visiting 31 sites along the coast of La Paz Bay, complemented with data from literature and citizen science, resulted in a database of 709 entries that spans the data from 2004 to 2023. These data showed a distribution that goes from Punta Coyote, close to Boca Grande, the northern entrance to the Bay to Playa Tecolote in the south, more than 100 km of coastline, including Espiritu Santo Archipelago, an area considered a natural reserve since 2007. Anthropogenic activity and environmental variables did not present statistical differences that explain A. spicifera spreading. It represents a naturalised alien species without evidence of a negative impact. Still, it soon could acquire the status of invasive species together with its epibionts Bryozoa and Hydrozoa detected in this study.

The Mexican Pacific has been the focus of several research expeditions, with 90 species of hydromedusae and more than 200 species of hydroids recorded for the region. However, only a few of these reports include taxonomic descriptions, hindering inferences of the phylogenetic relationships, species boundaries, and diversity of Hydrozoa in Mexican waters. In this study, we present detailed and illustrated descriptions of new records of hydromedusae and hydroids for La Paz Bay, Gulf of California. We found a total of 16 species comprising 15 genera, with three new records for the Gulf of California (polyps of Antennella secundaria, Bimeria vestita, and Ventromma halecioides), two new records for the Mexican Pacific (medusa of Clytia linearis, polyp of Halopteris violae), and we redescribe Obelia tenuis. We show that the diversity of Hydrozoa in the Mexican Pacific is likely underestimated, and we emphasize the importance of taxonomic and systematic studies of hydroids and hydromedusae in Mexico.

The cnidarians of the class Hydrozoa comprise 3720 species, are globally distributed, and can have complex life cycles. In the Espíritu Santo Archipelago (ESA), Mexico, hydrozoans are understudied, and, for this reason, the present work describes the taxocene of hydrozoans and their oceanographic preferences in the area. Hydrozoans were collected at 12 sampling stations in the archipelago during the temperate season; these organisms were morphologically identified and a systematic list including socioenvironmental attributes (SEA) was created. Species richness was used to assess the representativeness of the sampling and identify the distribution of species assemblages in relation to their SEA and environmental factors. In total, 31 species were described, representing 70% of the area’s potential diversity, and 97% of observations described species that had not yet been recorded in the area. Native, cryptogenic, and exotic species were found, including stinging and harvestable species. Groups with low, medium and high species richness were distributed heterogeneously, forming a spatial aggregation pattern. The results of this work suggest that the ESA has a highly diverse taxocene, with SEA and spatial aggregate structure relevant for integrative management and conservation of hydrozoans in natural protected areas.

Medusozoans are marine animals without backbones that live near the coasts, or in the depths of the oceans. Some of them are large, but others are even tinier than a seed. Medusozoans have been living on Earth for more than 600 million years. Their bodies are 95% water. Some medusozoans live attached to a surface, but others can swim freely. All medusozoans have tentacles, armed with stinging cells called nematocysts. When the nematocysts are triggered, the tiny stingers inside them can travel at speeds up to 67 km per hour. Around 3% of medusozoans are harmful to humans. Therefore, when visiting beaches where these harmful medusozoans live, it is necessary to take some precautions. Wearing protective clothing and not touching a medusozoan stranded on the beach will help you stay safe and healthy, so you can enjoy your beach day!