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Seagrasses are globally acknowledged as crucial habitats as they provide a variety of ecosystem services. Mexico's legislation protects most of these marine plants; however, the protection often fails in application. The Gulf of California, despite being a biodiversity hotspot, has scant data on seagrasses. Here, human activity and climate change increasingly threaten these coastal ecosystems, with conservation and research efforts lacking coordination at a regional level. Our manuscript aimed to review and standardize existing data on Gulf of California seagrass species, ensuring open access for data updates; pinpointing conservation deficiencies; and guiding future research. We have added new records to the official public data, but we were able to recapture only 25% of the seagrass locations meaning a potential reduction in their historical distribution of 45.8%. Even though Mexico's legislation protects some species of seagrasses, it protection often fails in the application. We identified that only 6.1% of the seagrass locations are within protected areas that recognize their presence in their management plans (e.g., the Balandra Flora and Fauna Protected Area and the Upper Gulf of California and Colorado River Delta Biosphere Reserve). At least 55.9% of seagrass records are associated with potentially damaging activities like pollution, coastal modification or biological resources use, while 23% are exposed to higher frequency of marine heatwaves. Given the importance of seagrass meadows under Mexican law and their internationally recognized ecological value, sharing current information and guiding research is essential. Our study seeks to galvanize renewed research initiatives and raise more awareness on the conservation of the Gulf of California's seagrasses. [ABSTRACT FROM AUTHOR]

We analysed the floristic turnover, or β-diversity patterns, of woody legumes in Baja California, the 1300 km long peninsula in NW Mexico. From the specimen labels of nine herbaria, we digitized 4205 records from 78 species and projected them onto a grid of 205 cartographic cells (20 longitude&tims; 15' latitude). We found that the E-W turnover from the Pacific coast to the Sea of Cortés was high (ca, 60% change from one cell to the next) and that it was significantly associated with topographic variation across the peninsula. An analysis of between-site similarities showed that floristic regions in the peninsula have well defined boundaries, and that floristic similarities tend to extend for long distances along the coastal corridor of the Sea of Cortés, Finally, a numerical classification of Baja California based on the floristic attributes of the cells separated the peninsula into five well defined regions that coincide very closely with regionalizations, previously proposed by various authors using descriptive methods, and with the areas of endemism described for the peninsula in a previous paper. We conclude that the ecological regions of woody legumes in the peninsula clearly reflect the two main environmental forces that act on it, namely, the 1300 km long temperate-tropical climatic gradient and the dramatic E-W gradient running from the Pacific Ocean ca, 100 km across the mountain range into the Sea of Cortés. [ABSTRACT FROM AUTHOR]

Coastal wetlands are rich and productive ecosystems historically used by small-scale fisheries due to their role as refuges and nursery habitats for commercial target species. We document the environmental history of coastal wetlands in the Northern Gulf of California, Mexico, through bibliographic sources, photographic records, and wetland resource users' Local Ecological Knowledge. We identify impacts that could have affected coastal fisheries by assessing historical patterns of commercial species abundance, areas of fishing importance, trophic levels, and species richness and composition. Areas of fishing importance within coastal wetlands decreased over time. We found a consistent downward trend in target species abundance that was perceived as more pronounced by fishers who began fishing in or prior to the 1950s, pointing to shifting baselines and the failure of resource users to recognize environmental changes and accept degraded states as normal. Perceived species richness and composition increased with wetland size. The trophic level of catch showed no distinct pattern across wetland sites or over time. Our analysis is relevant to food security and provides insight into how local populations adapt to depleted coastal food webs. [ABSTRACT FROM AUTHOR]

Volcanogenic massive sulfide (VMS) deposits are the most conspicuous type of deposits that formed during the Mesozoic in Mexico. Many Mexican VMS deposits display “classical” Kuroko-type mineral zonation and structure, and some of them, as Cuale and La Minita formed in shallow submarine environments. The most prospective time window for the formation of VMS deposits in Mexico comprises the Late Jurassic and the Early Cretaceous. VMS stopped forming during the progressive continentalization of Mexico, since its metallotectonic processes (dominated by extensive tectonics) changed giving way to compression during the late Early Cretaceous; new VMS deposits did not form until after the opening of the Gulf of California. Mesozoic VMS deposits in Mexico occur in submarine volcano-sedimentary sequences that deposited essentially in association with back-arc basins (now found roughly along the boundaries between tectonostratigraphic terranes) or within juvenile and slightly evolved arcs (at the internal parts of the terranes), while few others occur on the epicontinental seafloor and hinterlands of eastern Mexico. VMS deposits are especially abundant in the Guerrero composite terrane, and are also present in the Alisitos and Parral terranes. However, new evidence referred in this paper indicate the western continental edge of the cratonic block of Oaxaquia as a promising, new prospective region for VMS deposits. Interestingly, no VMS deposits are found in the northern part of the Guerrero composite terrane despite the occurrence of marine volcano-sedimentary sequences similar to those in the south; such absence can be related to differential extensional unroofing, much larger in the southern part of the Guerrero composite terrane than in the northern part. Many VMS deposits occur along or close to terrane boundaries, especially around the Guerrero composite terrane. This distribution reflects the association between VMS deposits and back-arc basins, which represented the frontal part of terranes or sub-terranes that were ultimately accreted to the Oaxaquia cratonic block. As a consequence, VMS deposits usually display strong deformation and thrusting, and their mineral and compositional zonation can be found overturned. Due to such common association between these deposits and terrane boundaries that reactivated during the Cenozoic, VMS deposits are especially susceptible to overprinting by later metallogenic processes, unrelated to VMS-producing environments. This susceptibility may be held accountable for the complex mineral associations found in the Francisco I. Madero deposit. The inclusion fluids in the Cuale, La Minita, El Rubí, Tizapa and Campo Morado deposits have salinities that range from 2.5 to 20.0 wt.% NaCl equiv. and temperatures of homogenization from 110° to 420 °C, although a particular fluid inclusion assemblage (with daughter halite and sylvite) from a stockwork at the Tizapa deposit ranged salinities from 39.7 to 64.7 wt.% NaCl and from 35.9 to 43.5 wt.% KCl, and temperatures of homogenization from 440° to 550 °C. The general characteristics listed above may account for mineralizing fluids from magmatic, marine, and modified marine sources. The entrainment of cool and oxidizing seawater within upwelling fluids increased as the paleohydrothermal systems waned. The waning stages are normally represented by barite-rich mineralizations and, in the case of the La Minita deposit, this notoriously outlasted by Mn oxide mineralization that reflects even more oxidizing conditions. A similar evolution is deduced in Cuale, which is the only known Mesozoic VMS deposit in Mexico that formed in a shallow-submarine environment together with La Minita. The shallower the formation of VMS deposits is, the more quickly mineralizing fluids evolve into highly oxidized end-members, once the paleohydrothermal systems cooled down. The extremely high-salinity and hot inclusion fluids in Tizapa, despite the unavailability of further geochemical data, are likely to represent magmatic brines that did not undergo significant mixing with seawater. As for the temporal evolution of the studied deposits, they generally exhibit (1) an increasing magmatic contribution from early to middle stages for both fluids (as mineralizing fluids grew hotter and more saline) and sulfur, and (2) the waning of hydrothermal activity towards the last stages on mineralization, which is characterized by the prevalence of seawater (as fluids grew cooler, and more diluted and oxidizing), thus reflecting quite a typical evolution for most VMS deposits elsewhere. New δ 34 S values for the same VMS deposits reflect multiple sources of sulfur in the mineralizing fluids: magmatic, sedimentary/metasedimentary, and marine. Different degrees of dominance of either source for sulfur in these deposits and in their stages of mineralization have been inferred, in a way that also responds to a schematic evolution from magmatic- to seawater-dominated paleohydrothermal systems. [ABSTRACT FROM AUTHOR]

This study used photogrammetry to analyze digital video taken before and after a new moon perigean spring tide that caused extensive damage to archaeological sites along the Upper Gulf of California coastline, south of San Felipe, Baja California, México. We created a 3D digital surface model (DSM) and orthophoto of the Conchero 4 site, a large multicomponent shell midden and sand dune. Results showed mass wasting (∼100 linear meters and ∼1500 m3) across the entire east-facing dune front and particularly heavy damage along the site's southern boundary, which faces the mouth of a large drainage. Our research adds a significant dimension to mounting global evidence that cultural heritage sites are eroding away in a wide variety of types of coastal environments, including low-energy tidally-dominated coastlines like the Upper Gulf of California. [ABSTRACT FROM AUTHOR]

Rocks from subvolcanic silicic magmatism (SSM) are exposed intermittently over a wide area along the Sonora coast, NW Mexico. This region is characterized by syn-rift volcanism related to the development of the Pacific-North America transform plate boundary during the Late Miocene (~12.5-~6 Ma). The ca. 11 Ma U-Pb age obtained from the SSM in the study area makes this magmatism part of the first stages of this tectonic event. Variations in magnetic mineralogy and textural relationships of the SSM suggest that they are a hypabyssal suite emplaced at distinctive depths. The anisotropy of magnetic susceptibility used for the petrofabric analysis reveals that, generally, the magnetic lineation is subparallel to the magnetic foliation and both are subhorizontal, suggesting a lateral emplacement. Palaeomagnetic analysis of 31 sites on the intrusive bodies indicates clockwise vertical axis rotations up to 90° related to dextral strike-slip faults. The fieldwork observations, magnetic fabric orientation, and the distribution of the SSM suggest that the magmas were propagated in a transtensional setting ascending probably through tension gashes from a deep main magma body, and emplaced as sheet intrusions in the syn-rift volcanic sequence. We propose that the vertical axis rotations of the SSM bodies are part of a unique transtensional-type deformation system of the oblique-divergent plate boundary, which it gradually changed. The SSM rocks are distinguished from other plutonic rocks forming most of the basement of NW Mexico by their age, distribution, emplacement environment, and deformation style. Finally, this study provides compelling evidence of igneous plumbing system within rift zones and a valuable contribution to the history of magmatism and tectonic control related to the development of the oblique rifting in the Gulf of California plate boundary. [ABSTRACT FROM AUTHOR]

Dinoflagellate cysts from the LB-5 core in the San Gregorio Formation (SGF) from the La Purísima area, Baja California Sur, Mexico, limit the age of the studied succession to Oligocene–Miocene (28–20 Ma). Our results allow correlation of this core with the type locality and another well-dated sections of the SGF in the region, namely the nearby La Purísima section, with an unequivocal Oligocene–Miocene boundary (O/M – 23 Ma). Lithology and dinoflagellate cyst data indicate mainly marine sedimentary environments, with a transgression from continental at the base to upper bathyal (200–500 m) in the O/M level (∼243 m), and a regression towards the top of the unit. Dinoflagellate cysts are virtually absent in some intervals, probably due to oxidation during diagenesis. The abundance of heterotrophic taxa during intervals with high cyst concentrations indicates that palynological preservation was adequate for quantitative analyses in the rest of the samples. Samples with dinoflagellate cyst concentrations >2000 cysts/gram of sediment (c/g sed), the abundance of heterotrophic taxa, and the presence of phosphoritic layers and diatomites indicate high biogenic productivity during the deposition of the SGF. Intense upwelling conditions in the area are probably associated with the cold events Mi-1 (∼23 Ma) near the O/M and Mi-1a (∼21.7 Ma) at ca. 170 m depth. Quantitative dinoflagellate cyst data in the LB-5 core suggest lower productivity (mean = 203 c/g sed) in the Oligocene than during the Miocene (mean = 848 c/g sed) interval. The absolute abundances of the Miocene intervals indicate similar dinoflagellate cyst concentrations in the LB-5 core and modern samples from the Pescadero Basin in the southern Gulf of California. [ABSTRACT FROM AUTHOR]

We report the presence of striped marlin larvae in coastal waters of the mouth of the Gulf of California, collected during seven oceanographic cruises during 1990 to 1993. From 169 sampled stations, 30 produced a total of 68 larvae of 2.4–30.5 mm total length. Most of the larvae were about 3 mm, indicating a recent spawn. The sea surface temperature at the sampled stations ranged from 19.4°C to 32.0°C, but larvae were caught at stations with temperatures between 27.8°C and 31.5°C. These results clarify the existence of a spawning area of striped marlin in the eastern Pacific, located closer to the coast than previously believed, during several months of the year. [ABSTRACT FROM AUTHOR]

We estimated Moho depths from data recorded by permanent and temporary broadband seismic stations deployed in northern Baja California, Mexico, using the receiver function technique. This region is composed of two subregions of contrasting geological and topographical characteristics: the Peninsular Ranges of Baja California (PRBC), a batholith with high elevations (up to 2,600 m); and the Mexicali Valley (MV) region, a sedimentary environment close to sea level. Crustal thickness derived from the P‐to‐S converted phases at 29 seismic stations were analyzed in three profiles: Two that cross the two subregions, in ∼W‐E direction, and the third one that runs over the PRBC in a N‐S direction. For the PRBC, Moho depths vary from 35 to 45 km, from 33°N to 32°N; and from 30 to 46 km depth from 32°N to 30.5°N. From a profile that crosses the subregions in the W‐E direction; Moho depths vary from 45 to ∼34 km under western and eastern PRBC, respectively; with an abrupt change of depth under the Main Gulf Escarpment (30°), from ∼32 to 30 km; and depths of 17–20 km under the MV. Moho depths of the profile in an ∼ W‐E direction at ∼31.5°N are from ∼30 to 40 km, under topography that increases from 0 to 2,600 m; and became shallower (16 km depth) as the profile reaches the Gulf of California. These results show that deeper Moho is related to higher elevations with an abrupt change under the Main Gulf Escarpment, except for western PRBC where the Moho depth is not simply reflecting isostatic compensation. Key Points: Moho variations in Northern Baja CaliforniaReceiver functions of stations belonging to the Northwest Mexico seismic networkCrustal thickness of the Peninsular Ranges of Baja California and the Mexicali Valley [ABSTRACT FROM AUTHOR]

Grain size, heavy minerals, mineralogical, and geochemical analyses were undertaken on the sand samples from Huatabampo (HB) and Altata (AA) beaches to infer palaeoweathering conditions and source rock characteristics. The mean grain size of HB and AA sands is fine‐grained and fine‐ to medium‐grained, respectively. Magnetite and hypersthene are the common heavy minerals identified in HB sands, whereas magnetite and ilmenite are the dominant heavy minerals in AA sands. HB sands have a high proportion of quartz and plagioclase followed by K‐feldspar and zeolite. Quartz is the dominant mineral in the AA sands, followed by plagioclase and K‐feldspar. Geochemically, the sand samples from HB are classified as wacke, whereas AA sands are classified as wacke and arkose. In chondrite‐normalised REE plot, HB and AA sands show LREE enriched and HREE depleted pattern with negative Eu anomaly. Chemical index of alteration (CIA), plagioclase index of alteration (PIA) values and Th/U ratios of HB and AA sands suggest a low intensity of chemical weathering in the source area. The tectonic discriminant function diagram suggestsan arc setting for HB sands, whereas a rift setting for AA sands. The chondrite‐normalised REE patterns, Eu anomaly, Al2O3/TiO2 ratio, trace elemental ratios, discriminant function, and ternary diagrams suggest that the HB and AA sands were dominantly derived from felsic source rocks. The comparison of REE patterns of HB and AA sands with the source rocks exposed near to the study area suggest that the central granites of Laramide plutonic rocks exposed in Sonora were contributing sediments to the HB beach, whereas AA sands received sediments mainly from the felsic Francisco gneiss in the western Sonobari Complex of Sinaloa. [ABSTRACT FROM AUTHOR]

For breath-holding marine animals, tradeoffs between 'active' and resting behaviours during periods of submergence can have consequences for acquisition and allocation of energy to vital life history requirements. In this study, we fitted 18 green turtles (Chelonia mydas) with detachable time-depth recorder (TDR) systems to obtain and analyse fine-scale dive behaviour and daily activity – with a focus on resting dive bouts – at Bahía de los Angeles (BLA), a warm-temperate foraging area in the Gulf of California, México. Our results showed that resting bout durations increased with water depths among all turtles, but patterns of resting bout durations and depths varied widely among individuals. To evaluate potential consequences to green turtles of tradeoffs between time spent 'active' versus resting, we also compared behavioural parameters (e.g. time spent resting, home range sizes) and life history traits (e.g. growth rates, body size at maturity) of green turtle populations from around the world, including BLA. We found that BLA green turtles spend less time resting, spend more time actively swimming and diving, occupy larger home ranges, and exhibit slower growth rates and smaller adult body sizes compared to their counterparts in other parts of the world. Unique characteristics of the BLA foraging habitat (e.g. patchy resources and temperature extremes) appear to require increased diel movements and foraging activity and decreased resting opportunities. These interactions between habitat and turtle behaviour not only influence expression of life history traits, but can also increase turtles' exposure to human activities (e.g. vessel traffic and fisheries bycatch) as they move throughout the area. [ABSTRACT FROM AUTHOR]

High diversity of marine macroalgae is reported for Mexican coasts, including numerous endemic species. Seaweed research in Mexico has focused on the northern regions of the Pacific coast (Temperate Pacific and Gulf of California) and on the Mexican Caribbean coast, leaving aside other regions (Tropical Pacific and Gulf of Mexico). Utilization of seaweed resources within the country has been based on artisanal collection of wild populations mainly for polysaccharide extraction, fertilizers, raw material for animal feed and cosmetic products. The main exploitation has occurred along the coasts of Baja California peninsula, based on few species (Gelidium robustum, Macrocystis pyrifera, Chondracanthus canaliculatus and Gracilariopsis lemaneiformis). Governmental regulations for management have allowed harvesting to reach approximately 11,500 wet tons per year (2013–2016). Nevertheless, in recent years (2014–2016) the total seaweed import volume has increased (5302 tons per year in average) over the export volume (2156 tons per year in average), suggesting a notably growing demand for seaweed resources in the country and representing an opportunity for investment projects. Several pilot studies on seaweed cultivation in Mexico propose that sustainable aquaculture techniques could complement the harvest in natural populations and ensure a homogeneous production with high quality in the long term. [ABSTRACT FROM AUTHOR]

We describe the seasonal changes in the horizontal and vertical distribution and abundance of euphausiid species associated with seven physical and 61 biological variables in the Gulf of California (24–31°N). Euphausiid community structure was explored in the epipelagic habitat (<200 m) in January, July, and October 2007 and in epipelagic to bathypelagic habitats (<1400 m depth) in May 2015. Twelve euphausiid species comprising two distinct regional assemblages were identified. Nyctiphanes simplex and Nematoscelis difficilis were the most abundant species (>90%) in all cruises carried out in the 26–31°N region and Euphausia distinguenda in the 24–26°N region (mostly in October >90%). We confirmed that Euphausia gibboides and Nematobrachion flexipes inhabit the mesopelagic habitat, adapted to <1 ml O 2 l –1 environmental condition. Although Euphausia lamelligera and N. simplex populations were concentrated in well-oxygenated water (>3 ml O 2 l –1 ) near the surface (<50 m), they were also detected in low densities in the hypoxic mesopelagic habitat (250–800 m), but only at oxygen levels less than 0.09 ml O 2 l –1 . Stylocheiron affine and Stylocheiron carinatum were numerous well below the seasonal thermocline (100–350 m). Nematoscelis difficilis and N. simplex extended into the hypoxic mesopelagic habitat, but at low densities. Multivariate analyses showed six seasonal and regional krill assemblages, which are characterized by different species (Similarity percentage analysis). Canonical Correspondence Analysis show that, of 68 variables, three abiotic factors (temperature, dissolved oxygen, and OMZ depth) and eight biotic factors (accessory pigments; zeaxanthin and 19'-hexanoyloxyfucoxanthin, and the abundance of six copepod species; Candacia pectinata , Canthocalanus pauper , Centropages furcatus , Rhincalanus nasutus , Scolecithrix danae , and Temora discaudata ), were the most influential variables associated with the vertical distribution and abundance of euphausiids. Krill‒copepod (predator–prey) relationships may be important determinants of daily and seasonal vertical distribution patterns. We conclude that the euphausiid vertical habitat reaches down to 900 m depth (with historical records of six species collected between 1000 and 2280 m) but with lower diversity and abundance in the mesopelagic and bathypelagic habitats than in the epipelagic habitat. [ABSTRACT FROM AUTHOR]

In this work, a suite of diagnostic biomarkers was applied to seven cetacean species to evaluate the role of the feeding habits and migratory behavior in the toxicological status of these species from the Gulf of California, Mexico. We investigate the interspecific differences in cytochrome P450 1A1 and 2B (CYP1A1 and CYP2B, respectively), aryl hydrocarbon receptor and E2F transcription factor 1 and the contaminants levels [organochlorine compounds, polybrominated diphenyl ethers (PBDEs) and polycyclic aromatic hydrocarbons (PAHs)] in four odontocete species (common bottlenose dolphin, long-beaked common dolphin, sperm whale and killer whale) and three mysticete species (blue whale, fin whale, and Bryde's whale) using skin biopsy. Differences in contaminant levels and molecular biomarker responses between the odontocete and mysticete species have been pointed out. The canonical discriminant analysis on principal component analysis factors, performed to reveal clustering variables, shows that odontocete are characterised by the highest levels of lipophilic contaminants compared to the mysticete, with the highest levels of polychlorinated biphenyls, dichlorodiphenyltrichloroethanes and PBDEs detected in killer whale and the lowest levels in Bryde's whale. The biomarker data show interspecific differences amongst the seven species, revealing highest CYP1A and CYP2B protein levels in the mysticete fish-eating species (Bryde's whale). In conclusion, three main factors seem to regulate the biomarker responses in these species: (a) the inductive ability of persistent organic pollutants and PAHs; (b) the different evolutionary process of the two CYPs related to the different feeding habits of the species; (c) the migratory/resident behaviour of the mysticete species in this area. [ABSTRACT FROM AUTHOR]

Wetlands worldwide, the fisheries they support, and the communities that depend on them are threatened by habitat modification. We describe strategies being used for wetland conservation in the Gulf of California, Mexico, their effectiveness, and challenges for implementation. We base our analysis on the authors' experience working for local environmental non-governmental organizations and available literature. The strategies discussed include public and private policy instruments such as Environmental Impact Evaluations, environmental land easements, concessions and transfer agreements, Natural Protected Areas, and international agreements such as the Ramsar convention and the North American Wetlands Conservation Act. We present examples from the Gulf of California that highlight some of the challenges to wetland conservation. These challenges range from governmental failure to enforce existing environmental legislation, lack of verification of requirements for development projects, to low economic penalties for wetland modification or destruction. We found that in the Gulf of California successful conservation of coastal wetlands required a combination of policy instruments and relied on integrating science, management, and public participation through partnerships between non-governmental institutions, academic institutions, community stakeholders, and government agencies. [ABSTRACT FROM AUTHOR]

The Gulf of California hosts astounding biodiversity that supports numerous economic activities in the region. These activities, and emerging threats, are placing pressure on the region's ecosystems. Government and civil society are working to address threats through several conservation and management mechanisms. Nevertheless, the use and incorporation of scientific information—a key component for creating effective and durable management—is still deficient. This article presents the concept of science integration and discusses the findings of a study that assesses the regional landscape, existing institutional arrangements, and capacity for using science to inform policy and management decisions. It also explores the current use of science within fisheries policy and management and the capacity of the National Network of Information and Research of Fisheries and Aquaculture (RENIIPA) and the State Fisheries and Aquaculture Councils, two mechanisms in the region. Finally, it shares lessons learned and offers recommendations on how the region can strengthen science-based decision-making. Results indicate that while there are some actors in the Gulf of California producing relevant science, there is varying capacity of intermediary groups connecting producers with users of science, or mechanisms in place to ensure that science is being utilized in decision-making processes. Moreover, despite having a well-developed landscape of producers and intermediaries and mechanisms in place for fisheries management in the region, effective science integration is not occurring. [ABSTRACT FROM AUTHOR]

Addressing global fisheries overexploitation requires better understanding of how small-scale fishing communities in developing countries limit access to fishing grounds. We analyze the performance of a system based on individual licenses and a common property-rights regime in their ability to generate incentives for self-governance and conservation of fishery resources. Using a qualitative before-after-control-impact approach, we compare two neighbouring fishing communities in the Gulf of California, Mexico. Both were initially governed by the same permit system, are situated in the same ecosystem, use similar harvesting technology, and have overharvested similar species. One community changed to a common property-right regime, enabling the emergence of access controls and avoiding overexploitation of benthic resources, while the other community, still relies on the permit system. We discuss the roles played by power, institutions, socio-historic, and biophysical factors to develop access controls. [ABSTRACT FROM AUTHOR]

EMHOFF, K.F.; JOHNSON, M.E.; BACKUS, D.H., and LEDESMA-VÁZQUEZ, J., 2012. Pliocene stratigraphy at Paredones Blancos: Significance of a massive crushed-rhodolith deposit on Isla Cerralvo, Baja California Sur (Mexico). A white blaze across coastal cliffs is the hallmark of Paredones Blancos on Isla Cerralvo, Mexico. Cliff-forming strata include three roughly 10-m-thick units with a lateral coherence of only 0.75 km. The middle unit is a massive deposit of crushed rhodoliths. The other two units consist of matrix-supported conglomerate with cobbles and boulders of granodiorite, basaltic andesite, and hornblende diorite. By volume, the matrix accounts for >80%% of those units, mostly composed of grus from weathered granite. Thin sections were studied from samples collected at five levels through the middle rhodolith unit to determine carbonate purity as a ratio between organic CaCO3 and inorganic minerals. The bottom and top margins of the deposit show higher levels of mixed clastics, with 37%% inorganic mineral content, as compared with 11%% toward the middle. Original depositional environments are interpreted as a rhodolith bank adjacent to a large fan delta built seaward from a wide canyon mouth. The stratigraphic sequence records a rise in sea level that brought rhodolith debris to the flooded canyon mouth above the basal conglomerate, and a drop that emplaced another conglomerate above the rhodolith deposit. A Middle Pliocene age is based on co-occurrence of Clypeaster bowersi and Argopecten revellei within the carbonates. [ABSTRACT FROM AUTHOR]

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The relative motion of the Pacific plate with respect to the North America plate is partitioned between transcurrent faults located along the western margin of Baja California and transform faults and spreading ridges in the Gulf of California. However, the amount of right lateral offset along the Baja California western margin is still debated. We revisited multibeam swath bathymetry data along the southern end of the Tosco-Abreojos fault system. In this area the depths are less than 1,000 m and allow a finer gridding at 60 m cell spacing. This improved resolution unveils several transcurrent right lateral faults offsetting the seafloor and canyons, which can be used as markers to quantify local offsets. The seafloor of the southern end of the Tosco-Abreojos fault system (south of 24°N) displays NW-SE elongated bathymetric highs and lows, suggesting a transtensional tectonic regime associated with the formation of pull-apart basins. In such an active tectonic context, submarine canyon networks are unstable. Using the deformation rate inferred from kinematic predictions and pull-apart geometry, we suggest a minimum age for the reorganization of the canyon network. [ABSTRACT FROM AUTHOR]

We relocated the hypocentral coordinates of small to moderate-sized earthquakes reported by the National Earthquake Information Center (NEIC) between April 2002 and August 2006 in the Gulf of California region and recorded by the broadband stations of the network of autonomously recording seismographs (NARS-Baja array). The NARS-Baja array consists of 19 stations installed in the Baja California peninsula, Sonora and Sinaloa, Mexico. The events reported by the preliminary determinations of epicenters (PDE) catalog within the period of interest have moment magnitudes ( M) ranging between 1.1 and 6.7. We estimated the hypocentral location of these events using P and S wave arrivals recorded by the regional broadband stations of the NARS-Baja and the RESBAN ( Red Sismológica de Banda Ancha) arrays and using a standard location procedure with the HYPOCENTER code ( Lienert and Havskov in Seism Res Lett 66:26-36, ) as a preliminary step. To refine the location of the initial hypocenters, we used the shrinking box source-specific station term method of Lin and Shearer (J Geophys Res 110, B04304, ). We found that most of the seismicity is distributed in the NW-SE direction along the axis of the Gulf of California, following a linear trend that, from north to south, steps southward near the main basins (Wagner, Delfin, Guaymas, Carmen, Farallon, Pescadero and Alarcon) and spreading centers. We compared the epicentral locations reported in the PDE with the locations obtained using regional arrival times, and we found that earthquakes with magnitudes in the range 3.2-5.0 mb differ on the average by as much as 43 km. For the M magnitude range between 5 and 6.7 the discrepancy is less, differing on the average by about 25 km. We found that the relocated epicenters correlate well with the main bathymetric features of the Gulf. [ABSTRACT FROM AUTHOR]

The study of the geochemical compositions and K-Ar or Ar-Ar ages of ca. 350 Neogene and Quaternary lavas from Baja California, the Gulf of California and Sonora allows us to discuss the nature of their mantle or crustal sources, the conditions of their melting and the tectonic regime prevailing during their genesis and emplacement. Nine petrographic/geochemical groups are distinguished: 'regular' calc-alkaline lavas; adakites; magnesian andesites and related basalts and basaltic andesites; niobium-enriched basalts; alkali basalts and trachybasalts; oceanic (MORB-type) basalts; tholeiitic/transitional basalts and basaltic andesites; peralkaline rhyolites (comendites); and icelandites. We show that the spatial and temporal distribution of these lava types provides constraints on their sources and the geodynamic setting controlling their partial melting. Three successive stages are distinguished. Between 23 and 13 Ma, calc-alkaline lavas linked to the subduction of the Pacific-Farallon plate formed the Comondú and central coast of the Sonora volcanic arc. In the extensional domain of western Sonora, lithospheric mantle-derived tholeiitic to transitional basalts and basaltic andesites were emplaced within the southern extension of the Basin and Range province. The end of the Farallon subduction was marked by the emplacement of much more complex Middle to Late Miocene volcanic associations, between 13 and 7 Ma. Calc-alkaline activity became sporadic and was replaced by unusual post-subduction magma types including adakites, niobium-enriched basalts, magnesian andesites, comendites and icelandites. The spatial and temporal distribution of these lavas is consistent with the development of a slab tear, evolving into a 200-km-wide slab window sub-parallel to the trench, and extending from the Pacific coast of Baja California to coastal Sonora. Tholeiitic, transitional and alkali basalts of subslab origin ascended through this window, and adakites derived from the partial melting of its upper lip, relatively close to the trench. Calc-alkaline lavas, magnesian andesites and niobium-enriched basalts formed from hydrous melting of the supraslab mantle triggered by the uprise of hot Pacific asthenosphere through the window. During the Plio-Quaternary, the 'no-slab' regime following the sinking of the old part of the Farallon plate within the deep mantle allowed the emplacement of alkali and tholeiitic/transitional basalts of deep asthenospheric origin in Baja California and Sonora. The lithospheric rupture connected with the opening of the Gulf of California generated a high thermal regime associated to asthenospheric uprise and emplaced Quaternary depleted MORB-type tholeiites. This thermal regime also induced partial melting of the thinned lithospheric mantle of the Gulf area, generating calc-alkaline lavas as well as adakites derived from slivers of oceanic crust incorporated within this mantle. [ABSTRACT FROM AUTHOR]

A case of bicephaly in embryos of the blue shark Prionace glauca in the Mexican Pacific Ocean is described. Malformed female shark embryos were found in pregnant females caught in the Gulf of California (Punta Arenas) and off the western coast of Baja California Sur, Mexico (San Lázaro). Abnormal sharks showed a symmetric bicephaly that could be caused by the high number of embryos found in the uterus of the blue shark, which is the most fecund species of shark in the world. The abnormality probably began during the embryonic development. [ABSTRACT FROM AUTHOR]

Islands in the seas of northwestern Mexico have the largest number of insular endemic species in North America. The islands have the greatest number of extinct mammalian taxa in Mexico, and many of the remaining taxa are rare, threatened, or endangered. Thus the Mexican government's plan to build 24 modern ports--the "Escalera Nautica" project--will place enormous pressure on island species, which are exceptionally vulnerable to human activities, including the introduction of alien species. The intensified port activities would most likely lead to an ecological disaster. Several mammal species inhabiting the islands are already close to the limit of their capacity to survive. For many endangered species, a small change in habitat can be the final push into extinction. In this article, we make some recommendations to try to prevent the extinction of species at risk. [ABSTRACT FROM AUTHOR]

1. The vaquita Phocoena sinus is a small porpoise that is endemic to the northern Gulf of California, Mexico. It is the most critically endangered marine small cetacean in the world. The most precise estimate of global abundance based on a 1997 survey is 567 (95% CI 177–1073). 2. Vaquitas mainly live north of 30°45′N and west of 114°20′W. Their ‘core area’ consists of about 2235 km2 centred around Rocas Consag, 40 km east of San Felipe, Baja California. Genetic analyses and population simulations suggest that the vaquita has always been rare, and that its extreme loss of genomic variability occurred over evolutionary time rather than being caused by human activities. 3. Gill nets for fish and shrimp cause very high rates of by-catch (entanglement) of vaquitas. Estimates of bycatch rates are from 1993–94 and refer to one of three main fishing ports: 84 per year (95% CI 14–155) using only data collected by observers and 39 per year (95% CI 14–93) using combined data from observers and interviews with fishermen. Boats from other ports may experience similar rates, and the total is probably well above what would be sustainable. 4. Other less well-characterized and longer-term risk factors include the potential for disturbance by trawling to affect vaquita behaviour, and the uncertain effects of dam construction on the Colorado River and the resultant loss of freshwater input to the upper Gulf. However, entanglement is the clearest and most immediate concern. 5. Progress towards reducing entanglement has been slow in spite of efforts to phase out gill nets in the vaquita’s core range, and the development of schemes involving compensation for fishermen. The Biosphere Reserve in the northern Gulf has fallen far short of its potential for vaquita conservation. On 29 December 2005, the Mexican Ministry of Environment declared a Vaquita Refuge that contains within its borders the positions of approximately 80% of verified vaquita sightings. In the same decree, the state governments of Sonora and Baja California were offered $1 million to compensate affected fishermen. The effectiveness of this major initiative remains to be seen. 6. The vaquita’s survival does not depend on more or better science but on improved management. As a funding priority, implementation of conservation measures and evaluation of their effectiveness should come ahead of more surveys or improved estimation of by-catch. [ABSTRACT FROM AUTHOR]

The influence of corallivores on coral community structure of eastern Pacific reefs has been considered less important then that of abiotic oceanographic factors. The data that support this assumption, however, are only available for Central American reefs. To assess the role of predation on hermatypic corals in a different regional reef environment, the abundance, spatial distribution and consumption rate of three corallivores: the echinoid Eucidaris thouarsii (Valenciennes), the asteroid Acanthaster planci (Linnaeus) and the teleostean fish Arothron meleagris (Bloch & Schneider), were estimated at Cabo Pulmo reef, Gulf of California, México (23°25′ N, 109°25′ W). Statistically, the abundances of the species did not change in any sections of the reef (mean values: E. thouarsii, 0.17 indiv. · m-2; A. planci, 1.9 indiv. · m-2; A. meleagris, 39 indiv. · ha-1). The average daily individual consumption rates of coral were calculated at 1.83 g CaCO3 · m-2 for E. thouarsii, 118.4 cm2 for A. planci, and 16.38 g CaCO3 · m-2 for A. meleagris, and were lower than those reported for Central American reefs. Considering the mean estimated carbonate production (7.9 kg CaCO3 · m-2 · a-1), corallivores eliminate less than 4% of the coral standing stock of Cabo Pulmo reef. The low corallivore population density and consumption rates, together with high local coral cover, indicate that corallivores are not key factors determining scleractinian abundance in this marginal reef. [ABSTRACT FROM AUTHOR]

This study documents direct evidence of nematode predation in the free living marine nematode Synonchiella spiculora recorded in the intertidal of Santa Clara beach in the Upper Gulf of California, Mexico. The heavily armoured buccal cavity that allows S. spiculora to break larger particles and ingest other organisms is characteristic of nematodes categorized as predators and omnivores. The inferred feeding behaviour of S. spiculora and other Selachinematidae suggests that engulfing whole and relatively large prey items may be common in this group. Synonchiella spiculora could be classified in the guild of ‘predators’ sensu Jensen (1987) and Moens & Vincx (1997). Nevertheless, more direct observations are required to ‘ground truth’ inferences based on their morphological variation and to better understand their feeding ecology. [ABSTRACT FROM PUBLISHER]