Presence of Conchoderma auritum and C. virgatum (Maxillopoda, Lepadidae) and Gloiopotes huttoni (Copepoda, Caligidae) on the black marlin, from the Gulf of Tehuantepec, Mexico

This is the first report of coexistence of pedunculate barnacles, Conchoderma auritum and C. virgatum in the mouth, and with the copepod Gloiopotes huttoni in the precaudal zone, on the black marlin, Istiompax indica, a as host. This is also the first note of a new non-mammalian host for C. auritum. The host specimen was caught in sport fishing in the Gulf of Tehuantepec, eastern Pacific. A review of registered occurrences of the genus Conchoderma in species of the fish family Istiophoridae is provided.

Local and regional patterns of fish assemblages in coastal lagoons surrounded by mangroves, Gulf of Tehuantepec in the south Pacific of Mexico

We analyzed the local variation of fish assemblages in four coastal lagoon systems surrounded by mangroves, draining into the Gulf of Tehuantepec (Pacific versant of Mexico), and determined the spatial patterns of alpha, beta, and gamma diversity. Fish were sampled between 2004 and 2016 at 63 sites using cast nets. The collected data were supplemented with information obtained from published works for three other coastal lagoons for the regional analysis. Local richness was high (89 species in a total of 19,017 specimens in four systems). Locally, dissolved oxygen, depth, and distance to mangrove were variables that significantly affected richness and abundance of fish in one or more systems. The Chantuto-Panzacola system showed the highest richness, significantly different from the other systems, although the trophic groups were similar. Regionally, two, Istmo and Soconusco complexes were identified, whose turnover rate (0.36) and gamma diversity (176) increased from north to south. Fish species richness and abundance increased with growing mangrove area, both locally and regionally, making this a highly explanatory variable. The Gulf of Tehuantepec is an environmentally heterogeneous region, with ecological patterns defined according to the spatiotemporal scale, which should be considered in the delineation of ecoregions and coastal management planning.

Paleoceanographic evolution of the Gulf of Tehuantepec (Mexican Pacific) during the last ~6 millennia

Oceanographic dynamics in the Gulf of Tehuantepec (GT) are the direct consequence of climate variability, mainly influenced by the strong wind regime locally called “Tehuanos” and the interactions between the Intertropical Convergence Zone (ITCZ) and El Niño Southern Oscillation (ENSO). The area is characterized by intense upwelling driven by the Tehuanos within one of the largest Oxygen Minimum Zones (OMZ) in the world. Upwelling carries nutrient-rich subsurface waters to the surface and provides marine resources to the coasts conforming one of the main economic sectors in the region. In this study, sediment core MD02-2521 is used to perform the first high-resolution paleoceanographic reconstruction of the last 6 millennia in the GT. The main focus is put on the analysis of the benthic foraminifera (BF) assemblages inhabiting within the OMZ, which appear to respond to bottom oxygenation and climate variations of the last ~6000 years. The microfossil assemblages throughout the sediment core revealed, first, intervals where the lack of foraminifera provide evidence of episodes of strong deoxygenation that triggered the dissolution of calcareous foraminiferal tests, second, a long-term decline of bottom-water oxygenation in the last ~2500 years likely responding to the southward migration of the ITCZ. Last, variations in response to the transitions between cold and warm periods occurred during the last 2–2.5 millennia and cyclicities of 1470 years resembling Bond Cycles suggest a climatic connection between the Pacific and Atlantic Oceans during the late-Holocene.

Energetic Rupture and Tsunamigenesis during the 2020 Mw 7.4 La Crucecita, Mexico Earthquake

The La Crucecita earthquake ruptured on the megathrust, generating strong shaking and a modest but long-lived tsunami. This is a significant earthquake that illuminates important aspects of the behavior of the megathrust as well as the potential related hazards. The rupture is contained within 15–30 km depth, ground motions are elevated, and the energy to moment ratio is high. We argue that it represents a deep megathrust earthquake, the 30 km depth is the down-dip edge of slip. The inversion is well constrained, ruling out any shallow slip. It is the narrow seismogenic width and the configuration of the coastline that allow for deformation to occur offshore. The minor tsunamigenesis can be accounted for by the deep slip patch. There is a significant uplift at the coast above it, which leads to negative maximum tsunami amplitudes. Finally, tide-gauge recordings show that edge-wave modes were excited and produce larger amplitudes and durations in the Gulf of Tehuantepec.

Five new species of cotylean flatworms (Platyhelminthes: Polycladida: Cotylea) from Oaxaca, southern Mexican Pacific

The flatworms of the suborder Cotylea live in diverse marine substrates such as rocks, seaweed and sand or in association with corals. In the Mexican Pacific, particularly on the coast of Oaxaca, knowledge about cotyleans is scarce, with only one record of the genus Pseudoceros. The aim of this work was to describe the cotylean species present in the area. A total of 48 specimens were collected, fixed, mounted in whole mounts or histological sagittal and frontal histological sections of the reproductive systems. These were examined for taxonomic identification, determining five new species of four genera: Boninia oaxaquensis sp. nov., Pericelis sigmeri sp. nov., Pericelis nazahui sp. nov., Pseudoceros bicuti sp. nov. and Thysanozoon estacahuitensis sp. nov. The present study establishes the first record of the genus Boninia and the family Boniniidae for the Tropical Eastern Pacific. It also confirms the presence of the genus Pseudoceros on the coast of Oaxaca, and break the disjunct distribution of this genus (from Gulf of California to Gulf of Tehuantepec), as well as the genus Pericelis (from Canada to Galapagos Islands) and Thysanozoon (from Chile to Gulf of California).

Reproductive ecology of the witch guitarfish Zapteryx xyster Jordan & Evermann, 1896 (Chondrichtyes: Trygonorrhinidae) in the Gulf of Tehuantepec, Mexican Pacific

From January 2008 to December 2009, 451 specimens of witch guitarfish Zapteryx xyster were caught in the Gulf of Tehuantepec. Total weight, total length (TL), sex, maturity stage and catch depth were recorded for each specimen. Maturity stage distribution exhibited significant differences with respect to depth. The data indicated that adults migrated towards shallow waters (25–37m) to reproduce, starting in February. Males reached maturity at 44cmTL, whereas females reached maturity at 48cmTL. Witch guitarfish females are synchronous; therefore, ovulation and mating begin in March and parturition begins in April. Females showed a 2-year cycle with consecutive vitellogenesis and gestation. Fecundity was five to eight embryos (mean six embryos) and the sex ratio of embryos was 1:1. Birth occurred in April and May, with an average size at parturition of 17.3cmTL. There was sexual dichromatism between males and females during the breeding period, and sexual polymorphism in adult females. The incidental catch of the witch guitarfish during courtship and mating threatens the survival of this species.