Southern Gulf Of California Research Articles

A new species of the genus Monstrilla (Copepoda: Monstrilloida: Monstrillidae) from the Gulf of California, Mexico

Based on deep-water (700-750 m) biological samples obtained from the southern Gulf of California, Pacific coast of Mexico, a new species of the monstrilloid copepod genus Monstrilla Dana, 1849 is described based on a single subadult female collected close to the bottom with an epibenthic sledge. Monstrilla hendrickxi sp. n. is distinguished by a unique combination of characters including: 1) no trace of eyes; 2) strong, thick antennules with segments 2-4 partly fused; 3) strongly developed apical elements on antennular segment 5 and spinous processes on segments 2-5; and 4) bilobed fifth legs with 2 apical setae on the exopodal lobe and a digitiform, unarmed endopodal lobe. The new species exhibits some affinity with surface-dwelling species of Monstrilla that have 2 setae on the exopodal lobes of the fifth legs. This is the fifth record of a species of the order Monstrilloida in the Gulf of California. The present discovery in deep oceanic waters significantly adds to our knowledge of the habitat range of this copepod order and likely anticipate further interesting findings of monstrilloids in deep waters worldwide.

Morphological, Toxicological, and Biochemical Characterization of Two Species of Gambierdiscus from Bahía de La Paz, Gulf of California.

We describe five new isolates of two Gambierdiscus species from Bahía de La Paz in the southern Gulf of California. Batch cultures of Gambierdiscus were established for morphological characterization using light microscopy (LM) and scanning electron microscopy (SEM). Pigment and amino acid profiles were also analyzed using high-performance liquid chromatography (HPLC-UV and HPLC-DAD). Finally, toxicity (CTX-like and MTX-like activity) was evaluated using the Artemia salina assay (ARTOX), mouse assay (MBA), marine fish assay (MFA), and fluorescent receptor binding assay (fRBA). These strains were identified as Gambierdiscus cf. caribaeus and Gambierdiscus cf. carpenteri. Toxicity for CTX-like and MTX-like activity was confirmed in all evaluated clones. Seven pigments were detected, with chlorophyll a, pyridine, Chl2, and diadinoxanthin being particularly noteworthy. For the first time, a screening of the amino acid profile of Gambierdiscus from the Pacific Ocean was conducted, which showed 14 amino acids for all strains except histidine, which was only present in G. cf. caribeaus. We report the presence of Gambierdiscus and Fukuyoa species in the Mexican Pacific, where ciguatera fish poisoning (CFP) cases have occurred.

Climate variability effects on autotrophic picophytoplankton in the southern Gulf of California

Climate variability effects on autotrophic picophytoplankton in the southern Gulf of California

Strain localization instabilities and the genesis of multiple axes of seafloor spreading in the Carmen basin, southern Gulf of California

We present new insight into the tectonic evolution of the Carmen basin (CB) in the southern Gulf of California (GC) from high-resolution bathymetry and two-dimensional seismic reflection data. Our goal is to document the seafloor morphology and sub-surface acoustic characteristics to understand the structure and crustal lithology across the CB. We identify three sub-basins with distinct geometries and evolutionary histories, with basement structures displaying a strong affinity with highly reflective, sigmoidal-shaped layers and the emplacement of high-amplitude tabular material underlying sediments with varying stratigraphic thicknesses. From the extent of new oceanic crust accreted along the CB, we estimate the age of the basin using a seafloor spreading rate of 52 mm/year, which is the average velocity of the relative plate motion between the Baja California microplate and the North American plate, as documented by previous authors. The southern and central sub-basins of the CB are mainly abandoned, while the northern one is currently the locus of seafloor spreading. This is evidenced by the juxtaposition of oceanic crust younger than ~ 1.9 Ma against older oceanic crust correlating in age with the adjacent Guaymas and Farallon basins to the northeast and southwest, respectively. We propose that mantle upwelling beneath the CB is a northward continuation of the East Pacific Rise, resulting in a fast-evolving system with sharp variations in strain localization within the seafloor spreading centers of the CB.Graphical

Cryptonome beatrizae n. sp., from drifting wood in Western Mexico, with remarks on Pareurythoe Gustafson, 1930 (Annelida, Amphinomidae)

Only five species of fireworms (Annelida: Amphinomidae) belonging to the genera Cryptonome Borda, Kudenov, Bienhold & Rouse, 2012, Linopherus de Quatrefages, 1866 and Pareurythoe Gustafson, 1930 have been reported as xylophilic. In this study, a new species of Cryptonome is described from driftwood found in the southern Gulf of California, including a short comment on other associated stowaways. Cryptonome is amended based on the presence of dorsal cirri being cirriform, smooth or pseudarticulate; Pareurythoe is restricted to specify the presence of caruncle sigmoid without lateral lobes and parapodial cirri smooth; and a key for identifying the species in Cryptonome is also included. The holotype of Hipponoe elongata Treadwell, 1931 is redescribed and newly combined in Cryptonome, whereas the holotype of Eurythoe spirocirrata Essenberg, 1917 previously regarded as Pareurythoe is returned to its original genus, Eurythoe Kinberg, 1857, and some of its morphological features are clarified.

Local diver knowledge reveals decline in scalloped hammerhead sharks (Sphyrna lewini) at seamounts in the southwestern Gulf of California

The Gulf of California is a marginal sea that has seen widespread species declines due to fishing. The scalloped hammerhead shark (Sphyrna lewini) is a semi-pelagic species that form large schools at seamounts where they refuge during the day. El Bajo seamount off Espíritu Santo Island and Las Animas seamount off San José Island in the southern Gulf of California are long-established scuba-dive destinations for observing S. lewini. In this study local scuba-diver knowledge was used to determine changes in S. lewini school abundance over a 50 year period between 1970 and 2020. The abundance of S. lewini encountered per dive at El Bajo was reported to have significantly declined, falling by 97%, from an average of 150 sharks in the 1970 s to 5 sharks in the 2010 s and at Las Animas by 100%, from an average of 100 sharks in the 1970 s to 0 sharks in the 2010 s. A shifting baseline was evident and there was a significant relationship between the year participants had first dived the seamounts and the number they considered to be a ‘very abundant’ school of S. lewini (GAM p < 0.001). This study demonstrates the importance of collecting local ecological knowledge to document declines in species populations, especially for S. lewini which is currently listed as ‘Critically Endangered’ on the IUCN Red List.

Reproductive behavior, seasonality, and distribution of three devil ray species (Mobula mobular, M. thurstoni, and M. munkiana) in the Southern Gulf of California, Mexico

We examined the reproductive behavior (courtship and mating), seasonality and its distribution in three Mobula species, spinetail, bentfin, and Munk’s devil rays (M. mobular, M. thurstoni, and M. munkiana) in the southwestern Gulf of California, Mexico, using boat surveys (with drone and in-water observations) (n = 69 survey days), spotter planes (n = 428 flights), and citizen science observations (n = 31). We examined whether (1) reproductive grounds existed within the area for any of these species, (2) whether reproductive behavior followed seasonal patterns, and (3) if this behavior was similar among all mobula rays. We observed reproductive behavior in 221 events in 2017 and 2021–2022, for M. mobular (n = 10), M. thurstoni (n = 3), and M. munkiana (n = 208) dispersed along 312 km of the eastern Baja California Peninsula between 4 m and 6.3 km away from the coast. Most events (n = 209) occurred in the La Ventana and Ensenada de Muertos areas. Courtship was observed for M. mobular and M. thurstoni and a copulation attempt for M. munkiana, with reproductive behavior following a seasonal pattern occurring from March to August, with a peak during May (81.9% of the events). Mobula munkiana displayed previously undescribed behaviors, such as the “piggyback leaps” as a pre-copulatory position and the “courtship vortex”, where 122 individuals were observed circling in a clockwise direction for 5 h with courtship groups joining and leaving the main vortex formation. This study highlights the areas of La Ventana and Ensenada de Muertos as critical habitats for reproductive behavior of two endangered and one vulnerable devil ray species.

Mercury and selenium concentrations in lanugo of free-ranging California sea lions in the southern Gulf of California, Mexico

Total mercury ([THg]) and selenium ([TSe]) concentrations were determined in California sea lion (Zalophus californianus) lanugo from the Gulf of California in 2021 and 2022. Relationships with sex, morphometrics, and year were evaluated. Following toxicological thresholds of concern for piscivorous mammals, most pups had a [THg] < 10 ppm, one pup (2021) had a [THg] > 20 ppm, no pups had a [THg] > 30 ppm. Females had significantly higher [TSe] than males; sex did not influence [THg]. [THg] and [TSe] in 2022 were significantly higher in the general population and male cohorts compared to 2021. Significant negative correlations were observed between [THg], [TSe], and morphometrics (2021). These results indicate that, compared to other pinniped species, regional California sea lions may have a decreased likelihood of experiencing Hg-related adverse health effects. Year-related changes in element concentrations suggest continued monitoring of this population to assess pinniped, environmental, and potentially, human health.

On a small collection of mysids (Crustacea, Peracarida, Mysida) from the southern Gulf of California, western Mexico, with the description of new species of Mysidium and Cubanomysis.

Four species of Mysida were collected in the southwestern Gulf of California, Mexico, including a new species of Mysidium (Mysidium), Metamysidopsis frankfiersi, Siriella gracilis, and a new species of Cubanomysis. The new species of Mysidium is the eleventh species in this genus, with species represented along both coasts of the Americas. It is the third species occurring in the eastern Pacific. The new species of Cubanomysis is the third species in this genus; the other two occur in California and in the western Atlantic.

Trophic assessment of three sympatric batoid species in the Southern Gulf of California.

The competitive exclusion principle establishes that the coexistence of closely related species requires a certain degree of resource partitioning. However, populations have individuals with different morphological or behavioral traits (e.g., maturity stages, sexes, temporal or spatial segregation). This interaction often results in a multi-level differentiation in food preferences and habits. We explored such resource partitioning between and within three batoid species: Hypanus dipterurus, Narcine entemedor, and Rhinoptera steindachneri in the southern Gulf of California, Mexico, using a combination of stomach content (excluding R. steindachneri) and stable isotope analyses. We found a clear differentiation between H. dipterurus and N. entemedor, where the latter exhibited more benthic habitats, supported by a greater association to infaunal prey and higher δ13C values. Though the degree and patterns of intra-specific segregation varied among species, there was a notable differentiation in both sex and stage of maturity, corresponding to changes in specialization (i.e., isotopic niche breadth) or trophic spectrum (varying prey importance and isotopic values per group). This work is a promising step towards understanding the dietary niche dynamics of these species in a potentially important feeding area within the southern Gulf of California, as well as the biological and ecological mechanisms that facilitate their coexistence.

Multi-model selection in growth parameters estimation of blue thread herring Opisthonema bulleri in the southern Gulf of California

La sardina crinuda azul (Opisthonema bulleri) es parte de los desembarques comerciales de peces pelágicos menores del sur del Golfo de California; la pesquería está certificada como sostenible por Marine Stewardship Council. Los parámetros de crecimiento de esta especie son de gran interés en la evaluación y manejo de la pesquería del complejo Opisthonema. En este estudio, se generó un conjunto de datos de edad a la talla de 367 lecturas de otolitos de los años 2005 y 2015 para completar los meses del año calendario con información continua e inferir la periodicidad de formación de la marca de crecimiento. Se utilizó un enfoque de selección multimodelo en cinco submodelos especiales del modelo de Schnute generalizado, incluido uno equivalente al modelo de von Bertalanffy. El tipo de borde mensual de los otolitos sugiere una marca de crecimiento anual. Se identificaron seis grupos de edad (0-5 años), con una APE y CV de 4,5 y 2,9 % respectivamente. El análisis de edad a la talla del conjunto de datos con la selección multimodelo es una garantía de que el caso uno de Schnute es el mejor para describir y estimar los parámetros de crecimiento de O. bulleri del sur del Golfo de California.

Changes in carbon metabolism and dissolved organic carbon fluxes on seagrass patches (Halodule wrightii) with different ages in Southern Gulf of California

Seagrass meadows are highly dynamic, particularly in sites where extreme climatological events may produce a mosaic of patches with different ages. This study evaluates the community carbon metabolism, dissolved organic carbon (DOC) fluxes and associated fauna in patches of Halodule wrightii with different ages since establishment. Net community production declined as patch age increased, probably due to the increase in non-photosynthetic tissues, higher respiration rates of the community assemblage and a likely increase in self-shading of the canopy. The export of DOC was significantly higher in the youngest patches, mainly as a consequence of the lower seagrass net production recorded in older meadows. We concluded that ‘colonizers’ seagrass species may show higher production rates and DOC release during the first stages of colonization, which suggest that, the production, organic carbon exportation and their role as relevant blue carbon communities may be higher than expected.

Deep convection, lightning activity and population impact over northwest Mexico: Coastal hotspots from 2009 to 2018

AbstractNorthwest Mexico (NWM) is an extensive region with a humid and unstable environment leading to atmospheric convection during the North American monsoon. Occasionally, extreme events are associated with severe weather, including deep convection, heavy rainfall and frequent lightning. Based on the period from July through September 2009–2018, the present study investigates general characteristics of convection. Geostationary satellites were used to document three‐dimensional cloud cover structures over the mainland, Gulf of California (GOC) and Baja California Peninsula (BCP). The convection developed over the Sierra Madre Occidental (SMO) mountains with a distinct cloud top structure over the southern GOC. In contrast, reduced cloud cover was observed over the peninsula and eastern Pacific Ocean. An active (2014) and inactive (2010) season are examined in more detail; the former had a more favourable environmental setting to support above‐normal convection and rainfall with respect to the 10‐year average. A regional‐scale analysis of lightning was computed with data from a ground‐based sensor network, including date, time and location of more than 16 million records. Major findings include: (1) lightning enhancement occurred in conjunction with deep convection, west of the SMO from the afternoon through the evening, while the gulf entrance became a well‐defined hotspot close to the mainland coastal plains overnight; (2) most lightning‐related deaths were in specific areas near the coastal plains or within isolated regions of the SMO foothills; (3) high exposure is expected in areas with considerable lightning and population located within 100 km from the gulf coastline. These findings are valuable for monitoring monsoon thunderstorms and for improving the ability to provide timely warnings of severe weather.

Strain localization instability in seafloor spreading centers of the Carmen Basin, southern Gulf of California

This study provides new insights into the geological evolution of the Carmen Basin (CB) in the southern Gulf of California (GC). Using high-resolution bathymetry and seismic reflection profiles, we establish a plate-kinematic framework for this oblique-divergent rift system. By analyzing the crustal composition, we investigate the growth of the bounding transform faults and their role in accommodating transtensional shearing. We propose that the mantle upwelling beneath the CB is a northward extension of the East Pacific Rise. The CB consists of three sub-basins with distinct geometries, morphologies, and evolutionary histories. While the southern and central sub-basins are mostly abandoned, the northern sub-basin is currently experiencing seafloor spreading. This is supported by the presence of younger oceanic crust, approximately less than 1.5 Ma, juxtaposed with older oceanic crust that aligns in age with the nearby Guaymas and Farallon basins to the north and south, respectively. Our findings also indicate favorable geological conditions in the CB for the development of hydrothermal systems similar to those observed in the neighboring Guaymas and Pescadero basins in the southern GC.

Distribution of water masses in the tropical-subtropical convergence off Mexico, using an autonomous profiler (2017–2021).

Data from an autonomous ARGO float launched on December 26, 2016, south of the entrance of the Gulf of California, reveal variations in the distribution of water masses in the tropical-subtropical convergence off Mexico. The float trajectory drifted through three areas of distinct characteristics: i) the southern Gulf of California in January 2017, ii) south of Cabo San Lucas from February 2017 to January 2018, when the float crossed an eddy, and iii) off Cabo Corrientes from February 2018 to April 2021. During the sampling, the vertical distribution of the water masses showed for the first time with “in situ” data a semiannual variability mainly in the salinity as response to poleward propagating semiannual Kelvin wave. The surface water masses had potential densities <26 kg m−3. A shallow salinity minimum (<34.6 g kg−1) observed at ∼ 70 m depth south of Cabo San Lucas provided a proxy for the California Current Water distribution, which had its maximum southern extension during winter. The Tropical Surface Water was observed off Cabo Corrientes mainly above 50 m depth and had maximum northern extension during summer. The Gulf of California Water was scarcely evident in the float trajectory in the southern Gulf. The Transitional Water was located above ∼ 50 m depth and was dominant southwest of Cabo San Lucas during winter and spring, when the California Current Water extended furthest south. The Subtropical Subsurface Water, in spite of its high density (>25 kg m−3) at times extended up to only 20 m below surface in the three areas around the summer as part of a semiannual cycle. The intermittent presence of this oxygen-deficient water close to the surface (∼ 20 m depth) is consistent with the on-going expansion of the shallow oxygen minimum zone. Wavelet analysis highlighted a bimonthly spectral frequency in the StSsW lower limit when the float crossed the eddy in the south of Cabo San Lucas, showing the influence of the mesoscale features of the area, and therefore a possible interchange of properties between deep waters.

The genus Metamysidopsis W. M. Tattersall, 1951 (Peracarida, Mysida, Mysidae) in the eastern Pacific with the description of a new species from western Mexico and notes on some diagnostic characters used in the genus

Abstract The genus Metamysidopsis W. M. Tattersall is currently represented by two species in the eastern Pacific: M. elongata (Holmes, 1910) in California, U.S.A., and M. pacifica (Zimmer, 1918) in Peru and Panama. The distribution and some morphological details of both species are presented and discussed and a new species is described from the southern Gulf of California, western Mexico. Commonly used diagnostic characters for the species of Metamysidopsis are analysed based on data available in the literature. A diagnosis is provided for the three species occurring in the eastern Pacific and a key to the 10 currently known species of the genus is provided.

Reproductive Ecology of the Chilean Round Ray (Urotrygon chilensis, Günther, 1872) in the Southern Gulf of California

The Chilean round ray (Urotrygon chilensis, Günther, 1872) is commonly caught as bycatch in the Mexican Pacific, but changes in its reproductive ecology as a consequence of fishery effects have never been investigated. In this work, the reproductive ecology of this species was determined in the Southern Gulf of California (SGC). Total length (TL) ranged from 11.4 to 51.6 cm, and females were larger than males. Size at maturity (TL50) was estimated at 27.5 cm for females and 25.3 cm for males. The seasonal variation of mature individuals, the presence of pregnant females, the mean oocyte size, the size of embryos and the smallest free-living specimens along the year suggest the existence of two reproductive periods during the year in the SGC, and the size of birth was estimated to be 11.2 to 15.6 cm TL. The average fecundity was 2.14 embryos. Spatial variations detected in size at maturity, fecundity, and reproductive cycle along the Mexican Pacific coast suggest the presence of separated populations. Some of these differences could be related to differences in maximum size attained in each region, though fishing pressure and environmental factors could have an important role, too.

Diversity and seasonal variation of the molluscan community associated with the seagrass Halodule wrightii in a marine protected area in the southern Gulf of California

Diversity and seasonal variation of the molluscan community associated with the seagrass Halodule wrightii in a marine protected area in the southern Gulf of California

Comparative cranio-mandibular myology of three species of Batoidea from the Southern Gulf of California, Mexico.

The mandibular apparatus of batoids (skates, electric rays, guitarfishes, stingrays, and sawfishes) is composed of a few skeletal elements to which the muscular bundles, responsible for all movements involved in the feeding mechanism, are inserted. The description of the different mandibular morphologies can help to understand the different feeding guilds in this group. In this study, we examined the cranio-mandibular myology of adult Rostroraja velezi, Narcine entemedor, and Zapteryx exasperata, three species of rays that coexist in the Southern Gulf of California, Mexico. This study described the muscles on the ventral and the dorsal surfaces for each species, identified the origins and insertions of these muscles, as well as the general characteristics of muscle morphology. There were 17 and 18 muscle bundles attached to the feeding apparatus, including five on the dorsal surface. Only the levator rostri, which elevates the rostrum during feeding, showed considerable differences in shape and size among species. The muscles of the adductor complex showed the greatest differences in size among the three species. N. entemedor presented the exclusive muscle X in the lower mandibular area and the extreme reduction of the coracohyoideus in the pharyngeal area derived from the absence of the basihyal cartilage. The information generated in our study supports the morphological specialization of electric rays (N. entemedor) for an almost exclusive suction feeding strategy.

New records of invasive tubeworms (Ficopomatus, Serpulidae) in Mexico

AbstractFicopomatus Southern, 1921 is a serpulid genus currently composed of six species, two of which (F. enigmaticus and F. miamiensis) are reef-builders. The former has invaded subtropical and warm-temperate estuaries worldwide, causing environmental and economic harm. In this study, Ficopomatus miamiensis and F. uschakovi are reported from brackish-water coastal localities in both Atlantic and Pacific sides of Mexico, including a Biosphere Reserve, estuaries, as well as shrimp and oyster farms. Ficopomatus miamiensis is reported from Veracruz (southern Gulf of Mexico, Mexico territory) and Sinaloa (southern Gulf of California). Ficopomatus uschakovi is reported for the first time in the southern Gulf of Mexico (Mexico territory) and repeatedly recorded in Chiapas (southern Mexican Pacific). There are no phenotypic differences between specimens of F. miamiensis from both coasts of Mexico. Comparison of mitochondrial cytochrome b (Cytb) DNA sequences further support the notion that F. miamiensis from the type locality (Florida) and Atlantic coasts of Mexico is also found along the Pacific coast of Mexico. Morphological variability within specimens of F. uschakovi from a single locality (either Laguna del Ostión or La Encrucijada) in Mexico suggest potential presence of multiple cryptic species. Molecular genetics studies are needed to confirm the taxonomic and invasive status of F. uschakovi.