We report on a latitudinal pattern in the structure and species composition of epibenthic macroinvertebrate communities on rocky reefs along a gradient of eight degrees of latitude in the Gulf of California. We provide quantitative evidence of a prominent shift in the taxa dominating these communities, particularly the sessile taxa (Cnidaria, Bivalvia, Annelida, Ascidiacea and Porifera). This pattern was not found in non-sessile taxa (Echinodermata, Decapoda, Cephalopoda, Gastropoda and Polycladida). Based on Bray–Curtis similarity and indicator species analysis we found that the macroinvertebrates of rocky reefs in the Gulf of California are distributed in three broad regions, indicating that sessile taxa are creating such a structure and are related to environmental changes tied to latitude. The northern region (>28° N) was a temperate zone with the coolest water in winter and highest chlorophyll a concentrations, where Octocorallia of the genus Muricea were the dominant taxa. The central region (∼24–28° N) had a mix of oceanographic features of the northern and southern regions and was dominated by Echinodermata in terms of species richness and density. The southern region (<24° N) is a subtropical zone with typically warm and clear water, and dominated by Hexacorallia (stony corals). The southern area was less diverse and had lower densities than the central and northern areas. These three communities correspond to known oceanographic discontinuities in the Gulf of California. This implies that future coastal management plans and conservation efforts in the Gulf of California must be regionalized to support their distinct ecological communities.

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.

Determining age is an important step when assessing growth, mortality, and yield of cultivated and wild populations, but studies linking shell growth marks in the pearl oyster Pteria sterna with the age of individuals are lacking. Thirty juveniles (20.0 ± 1.2 mm shell height), collected from a winter spatfall, were marked with the fluorochrome calcein and kept in the field in culture containers. After day 16, the juveniles were cleaned and their shells cut along the sagittal axis to determine periodicity of micro growth bands formed in the inner shell layers and to estimate age. During this trial, fluorescent calcein marking succeeded in individuals larger than 20 mm shell height; these formed an average of 15 micro growth bands over the 16 days, representing 1 band per day. The marker created a wide fluorescent band containing three micro growth marks, suggesting that calcein was incorporated into the shell over the first three days. The use of calcein was found to be an accurate method for validating the micro growth band frequency of formation in P. sterna juveniles, which in turn can help to estimate age.