Southern Baja California Peninsula Research Articles

Geochemistry of coastal geothermal systems from southern Baja California peninsula (Mexico): Fluid origins, water-rock interaction and tectonics

The Baja California peninsula forms the western margin of the Gulf of California (GC) rift system, which is an active tectonic setting manifested by seismicity and numerous geothermal sites. The present study examines the geochemistry of thermal fluids (major ions and gas species, δ18O-δD, δ13C, 3He/4He) from the southern tip of the peninsula (Los Cabos Block, LCB). Sampling was mostly focused on the coastal thermal manifestations in the towns of Buenavista and El Sargento, but other sites further inland are also included for broadening the scope of the study. The main objectives include: (i) characterize water-rock interactions and other processes controlling the fluid composition, (ii) constrain solute geothermometry estimates through multi-step geochemical modeling, and (iii) discuss the fluid origins in terms of tectonics and regional shear-wave velocity anomalies in the upper lithosphere. The geothermal systems in the area have a tectonic origin and result from fluid circulation along regional faults that penetrate the upper crust through the granitic basement. Mixing between the thermal fluids and seawater at the coast is clearly illustrated through major ions and δ18O-δD relationships. Reconstruction of the pre-mixing chemical compositions indicates a low-salinity fluid at Buenavista (Cl = 104–109 mg L−1) and a saline fluid at El Sargento (Cl = 7169 mg L−1). The geochemical modeling allows us to validate these endmember compositions and to address a common issue when using solute geothermometry, which is the uncertainty on the state of equilibrium of the thermal fluid with respect to wall-rock minerals. The corresponding results reveal contrasting thermal regimes at depths (Buenavista: 101–122 °C, El Sargento: 212–220 °C), likely associated with differences in geothermal gradient and fluid circulation depth. Our gas samples have among the lowest He isotopic ratios (0.07–0.95 Ra) in the Baja California peninsula, indicating that the origin of helium is mainly crustal. Shear wave tomography demonstrates that the study area is associated with two low velocity regions, one in the crust and the other one in the upper mantle. Our results favor the hypothesis that the heating of fluids is produced by lower-crustal flow driven by strong topographic gradients along the rifted margin. This study provides new insights into the origin of the thermal anomalies in the LCB and the adjacent GC rift system.

Estimation of the desert dust balance and its relationship with environmental factors in the southern Baja California Peninsula

The emission, transport, and deposition of desert dust are influenced by environmental factors evaluated mainly as a function of precipitation, air temperature, and wind. The present study estimates the desert dust balance and its relationship with environmental factors for the period 1981–2020 in the Baja California Sur region, Mexico. Monthly data on wind, air temperature, precipitation, dust emission and deposition from in situ measurements, reanalysis, satellite estimates and a numerical parameterization scheme are used. First, the in-situ time series were reconstructed with a non-linear principal component analysis based on an autoassociative neural network. We then evaluated the performance of the satellite estimates and the reanalysis data using the matching technique, after which we quantified the dust emission in three source zones. To estimate the state of the climate, we obtained the annual cycle of monthly climatologies, and yearly averages. The effect of climate on the dust budget is estimated by means of non-parametric associations between the variables of interest. Finally, we estimate climate trends using Pettitt, Modified Man-Kendall and Theil-Sen tests. The results show that the data sets used represent the mean and variability of in situ measurements. There are three seasons with transitional periods for precipitation and air temperature. The wind shows a longitudinal west–east gradient. Its maximum intensity is from April to September. Northern zone was dominated by highest emissions. Dry deposition mechanism was the most representative. Emissions and dry deposition are controlled by wind intensity and precipitation, while precipitation controls wet deposition. The Pettitt test showed that abrupt changes in the time series coincide with periods where positive sunspot anomalies converge with negative PDO and SOI anomalies. Finally, trend analyses identified a temporal broadening of the dry season, warmer winters, and summers with increases of ~ 0.02 °C, predominantly increasing trends in dust emissions and wind intensity, and a progressive decrease in dust deposition mechanisms.

A new species of Encelia (Compositae, Heliantheae, Enceliinae) from the southern Baja California Peninsula.

Here, we describe and illustrate Enceliabalandra sp. nov., a new species of Compositae from the Baja California Peninsula. It is rare and known only from the rocky hills around Puerto Balandra and Pichilingüe, inside the bay of La Paz, in the State of Baja California Sur, Mexico. We determine that this new species has affinities with Encelia, based on its suffruticose woody habit, neuter ray florets and compressed disc cypselae with a cleft apex. The taxonomic placement within Encelia is supported by nuclear ribosomal sequence data from two regions, ITS and ETS. We also present detailed photographs, a conservation assessment and a dichotomous key to the Encelia of the southern Baja California Peninsula. Finally, we discuss the uniqueness of Enceliabalandra amongst peninsular Encelia and its potential significance for understanding the enigmatic biogeography of this ecologically important genus.

High heat flow at the SW passive margin of the Gulf of California

AbstractNew high heat flow data confirm the presence of a heat source in the passive margin of the southern Baja California Peninsula that is not linked with volcanic activity. The high heat discharge is spatially associated with low seismic velocity, crustal thinning, intense seismic activity, documented local extension, shallow Curie Point Depth and silica geothermometer temperatures above 100°C. The highly oblique rifting regime in the centre of the Gulf of California generates a transtensional setting conducive to local extension in its southwest margin. Similar high heat flow in a rifted margin has been reported only in the Gulf of Aden that is also an obliquely spreading ridge. The intense heat discharge, with heat flow values as high as 613 mW/m2, indicates the presence of a heat source consistent with mantle upwelling. Heat transfer calculations indicate that the heat source emplacement would be at most 2 Ma old.

Trends of daily extreme and non‐extreme rainfall indices and intercomparison with different gridded data sets over Mexico and the southern United States

AbstractTrends of 15 extreme and non‐extreme daily rainfall indices for Mexico and the southern United States are analyzed for the extended boreal winter (November–March) and summer (June–October) during 1981–2010. The analysis includes gridded observations (CHIRPS and Livneh), reanalyses (ERA5, ERA‐Interim, MERRA2, and CFSR), the regional climate model RegCM4.7 (forced by ERA‐Interim), and four general circulation models (GCMs) from the CMIP5 (HadGEM2‐ES, CNRM‐CM5, MPI‐ESM‐MR, and GFDL‐ESM2M). The domain is divided into 13 regions with similar seasonal rainfall patterns according to the k‐means algorithm applied to CHIRPS monthly precipitation, as a reference. Gridded observations and reanalyses (O&R) show similar regional annual cycles and metrics of precipitation. The two observational data sets show the largest differences in the magnitude of some indices in the wettest region (southeastern Mexico) and in the monsoon. During summer, O&R show positive significant trends in extreme rainfall indices in regions commonly affected by tropical cyclones (southern Baja California Peninsula, northeastern Mexico, and the southeastern United States), while negative significant trends of seasonal accumulation of rainfall are seen in the Mediterranean Californias and the Sonoran Desert region. There is an agreement among most data sets that the frequency and intensity of extreme winter precipitation indices have declined in northwest Mexico and the southwestern United States, but trends are not statistically significant, while southeastern Mexico shows significant increases in 5‐days accumulation (rx5d). ERA5 followed by MERRA2 show the best performance. RegCM4.7 reproduces the annual cycle of precipitation in most of the regions and captures the main trend signals especially in winter, but it has difficulties in reproducing the summer interannual variability of few indices. The GCMs tend to overestimate (underestimate) the annual cycle of precipitation and the median values of extreme indices in the driest (wettest) regions. They are not able to capture the regional trends of the indices.

Functional traits of leaves and photosynthetic stems of species from a sarcocaulescent scrub in the southern Baja California Peninsula.

Photosynthetic stems represent a source of extra carbon in plants from hot and dry environments, but little is known about how leaves and photosynthetic stems differ in terms of photosynthetic capacity, trait coordination, and responses to seasonal drought in subtropical systems. We studied photosynthetic, hydraulic, morphometric (specific leaf area [SLA], wood density [WD]), and biochemical (C and N isotopes) traits in leaves and photosynthetic stems of 12 plant species from a sarcocaulescent scrub in the southern Baja California Peninsula, Mexico, in wet and dry seasons. Leaves and stems had similar mean photosynthetic capacity, as evaluated by chlorophyll fluorescence traits, indicating similar investment in leaf and stem photosynthesis. We did not find a relationship between stem hydraulic conductivity and leaf or stem photosynthetic traits. However, we found resource allocation trade-offs, between WD and both stem hydraulic conductivity and SLA. Leaf and stem photosynthetic traits did not change with season, but specific stem area was one of the few traits that changed the most between seasons-it increased during the dry season by as much as 154% indicating substantial water storage. Our results indicate the same proportional investment in photosynthetic capacity and dry matter in both leaves and photosynthetic stems across all 12 species. We identified multiple strategies at this seasonal site, with species ranging from high WD, low SLA, low hydraulic conductivity, and high specific bark area on one end of the spectrum and opposite traits on the other end.

Characteristics of mesoscale convection over northwestern Mexico, the Gulf of California, and Baja California Peninsula

AbstractMesoscale convective systems (MCSs) are frequent, but understudied, components of the warm season climatology in northwestern Mexico. This study provides an update of previous research on convective development and examines MCS life cycle, structure, and motion from July through September. It focuses on a region south of the North American monsoon core and, from 2009 to 2018 satellite observations, on patterns of cloud tops higher than 10 km above sea level. The diurnal cycle of convection shows cells initiating in the early afternoon over the Sierra Madre Occidental mountains and becoming better organized over the next few hours. These features typically move westward, grow upscale to reach maximum vertical extent near local sunset, and weaken during the night. However, there is a distinct region of deep convection over and off the coast of Nayarit (20–23°N), in the Pacific Ocean, that remains active through the night and into the early morning, producing heavy rainfall and frequent lightning. Occasionally, the inner structure of these MCSs can move across the Gulf of California and reach the southern Baja California Peninsula. One particular long‐lived, fast‐moving MCS from July 23 and 24, 2014 was selected for in‐depth analysis, because it was associated with weather conditions that included unusual precipitation and extreme winds. The MCS caused damage from sustained winds of tropical‐storm strength and an intense gust front in the Los Cabos area, in the southern tip of the peninsula. This extraordinary MCS developed in the most unstable and humid environment recorded during the 1976–2018 period, and was supported by a collocated upper‐level, inverted trough and a lower‐troposphere tropical wave. We also found that the 10 most unstable conditions have all occurred after 2011, possibly indicative of a trend toward more frequent and favourable environments to spawn MCSs over the Gulf of California entrance.

Quantifying rates of “rifting while drifting” in the southern Gulf of California: The role of the southern Baja California microplate and its eastern boundary zone

AbstractThe southern Baja California (Mexico) microplate has been rapidly moving away from the North America plate since ca. 12 Ma. This relative motion toward the northwest developed an oblique-divergent plate boundary that formed the Gulf of California. The rift-drift hypothesis postulates that when a continent ruptures and seafloor spreading commences, rifting on the plate margins ceases, and the margins start to drift, subside, and accumulate postrift sediments, eventually becoming a passive margin. In contrast to this hypothesis, the southern part of the Baja California microplate (BCM), and in particular its actively deforming eastern boundary zone, has continued significant rifting for millions of years after seafloor spreading initiated within the southern Gulf of California at 6–2.5 Ma. This is a process we call “rifting-while-drifting.” Global positioning system (GPS)–based data collected from 1998 to 2011 show relative motion across the eastern boundary zone up to ∼2–3.2 mm/yr with respect to a stable BCM. Furthermore, the velocity directions are compatible with normal faulting across the eastern boundary zone nearly perpendicular to the trend of the plate boundary at the latitude of La Paz and therefore a highly strain partitioned domain. North of 25°N latitude up to the Loreto area, there is a domain with no strain partitioning, and northwest-directed transtensional deformation dominates. From long-term geologic and paleoseismology studies, late Quaternary faulting rates are equal to or less than the GPS-derived rates, while geologic rates older than 1–2 Ma are commonly much higher. We suggest that the “rifting-while-drifting” process may be caused by the large topographic relief across the BCM margin, which created a significant gradient in gravitational potential energy that helps in driving continued relatively slow faulting. The relief was inherited from the much faster faulting of the BCM eastern boundary zone before plate motions largely localized along the modern transform–spreading centers in the axis of the Gulf of California. The low sediment flux from the small drainages and arid climate on the southern Baja California Peninsula result in the maintenance of underfilled to starved basins, and the relatively slow late Quaternary active faulting promotes continued topographic relief over millions of years.

Adaptive sub-images BSR pattern recognition system for seismic reflection images

Commonly, the Bottom-Simulating Reflector (BSR) location is done by hand-operation by a trained interpreter. Recently, a pattern recognition system named the 2D multiresolution automated system for detecting BSRs on post-stack seismic reflection images has been presented. That system focuses on locating BSRs parallel and non-parallel to the Sea-Bottom Reflector (SBR). However, in that system, the seismic reflection sub-images (containing a BSR) are of the same size. Also, the time contribution of the SBR is eliminated by semi hand-operation. The present work proposes a methodology that uses adaptive sub-images to get a more efficient BSR pattern recognition system. The lateral continuity, intensity, and the inclination angle of the BSR determine the number of traces in each adaptive sub-image. Also, this technique removes the SBR influence automatically. The system was tested using seismic reflection images from offshore the southern Baja California Peninsula. The adaptive sub-image BSR pattern recognition system locates the BSRs accurately in all the cases, even when the BSR cuts lithologic reflectors. Low time was employed to obtain the BSR position, which allows us to implement this methodology in desktop or laptop machines.

New biogeographical makeup for colonisation of the Baja California Peninsula, with the description of a new Onthophagus (Coleoptera: Scarabaeidae: Scarabaeinae)

ABSTRACTThe dung beetles of the Onthophagus chevrolati species group are preponderantly associated to montane habitats and high plains in the Mexican Transition Zone. Herein, we describe O. bajacalifornianus new species, the first of this species group from the southern Baja California Peninsula, which inhabits xeric shrublands near the sea level from the sandy foothills of the Sierra de la Laguna. The new species corresponds to a new monotypic phyletic lineage among the American Onthophagus. The multiple biogeographical origins of the Baja Californian endemic biota are briefly discussed. The need for recognising two new biogeographical elements is highlighted: the Baja Californian Paleoamerican sub-pattern (Miocenic Holarctic affinities) and the Neotropical Baja Californian pattern (Miocenic Neotropical affinities).http://www.zoobank.org/urn:lsid:zoobank.org:pub:7840ECCA-4CCC-4DB1-A30D-560FEE84AABF

Growth Variations in the Geoduck Panopea globosa in Different Climatological Regions of Northwestern Mexico

Growth curves of the geoduck Panopea globosa were compared from four zones in northwestern Mexico, with three zones in the Gulf of California (Guaymas, Puerto Penasco, and San Felipe) and one zone on the Pacific Coast of the southern Baja California Peninsula (Bahia Magdalena). The curves were shaped using the von Bertalanffy growth model. The lengths-at-age data for each location were obtained from fishery-independent data at each location. The average asymptotic lengths of P. globosa were 114.4, 156.6, 161.5, and 168.4 mm in Guaymas, Puerto Penasco, San Felipe, and Bahia Magdalena, respectively. The Kimura's likelihood ratio test was used as the goodness-of-fit trial. In comparison with geoducks from the other locations, geoducks from Guaymas, located on the central Gulf of California, were the shortest, with a significant difference in length from those at the other three sites. Geoducks from the upper Gulf of California (Puerto Penasco and San Felipe) and Pacific Coast had no significant differences among them. Because the fishing management strategy for this species uses the minimum legal size (MLS), the MLS should vary regionally to promote sustainable use.

Automation methodology to determine the inclination angle of non-parallel BSR on seismic reflection images

Based on the Radon transform, this work presents an automation methodology to determine the inclination angle of the non-parallel BSRs. The non-parallel BSR pattern recognition system was tested with synthetic and real seismic reflection images (from offshore the southern Baja California Peninsula) localizing the BSRs properly in all the cases. The pattern recognition system shows that low time is used to process the seismic images, the methodology is easy to implement in desktop or laptop machines. Therefore, it would be a useful tool to work in situ.

Impact of freezing and ethanol preservation techniques on the stable isotope analysis of humpback whale (Megaptera novaeangliae) skin.

RationaleDistinct techniques employed to preserve different types of tissues may affect stable isotope analyses conducted on samples, and this is critical when field work takes place in remote areas. To investigate this, the stable isotope ratios (δ13C and δ15N values) obtained using two methods commonly used to preserve humpback whale (and other cetaceans) skin samples were compared.MethodsA total of 54 pairs of skin samples of humpback whales from the southern Baja California Peninsula, Mexico, were preserved in ethanol (90%) and by freezing, between 2007 and 2009. The δ13C and δ15N values were determined using a PDZ Europa ANCA‐GSL elemental analyzer interfaced to a PDZ Europe 20‐20 isotope ratio mass spectrometer. Parametric and nonparametric tests were used to compare the isotopic results.ResultsA significant (t = 4.93; p = 0.000003) variation of −0.92‰ was found between the mean δ13C values in ethanol (from −19.38‰ to −16.07‰; mean = −17.86‰) and freezing (from −20.67‰ to −16.44‰; mean = −18.78‰) techniques. No significant (U = 1314, p = 0.38) differences were observed in the δ15N values. The δ13C values were compared between preservation methods for each of the three years under analysis. Significant differences were observed in 2007 (t = 3.45; p = 0.0012) and 2008 (t = 3.13; p = 0.0030), but not for 2009 (t = 1.66; p = 0.12).ConclusionsBased on the results of this study, the use of ethanol to preserve humpback whale skin samples collected for stable isotope analysis is not recommended, particularly regarding the analysis of δ13C values. This study serves as a point of reference for future research on humpback whales or other whales involving skin samples preserved by freezing or in ethanol.

Subduction control on the curie isotherm around the Pacific-North America plate boundary in northwestern Mexico (Gulf of California). Preliminary results

Spectral analysis of NAMAG magnetic data enabled us to estimate depths to the Curie isotherm along the Pacific-North America plate boundary. The estimated depths for the Gulf of California, and southern Baja California peninsula, correlate quite well with the depths to the Moho available from previous studies based on receiver function, and seismic refraction. In northernmost Baja California, and southwestern USA no correlation is observed between depths to the Curie isotherm and depths to the mantle obtained from receiver function analysis. Depths to the Curie isotherm are shallower. Along the coastal plains of Sonora and Sinaloa, differences between receiver function based Mantle depths and Curie depths are equally large. However, there is more consistency with depths established by seismic refraction studies. Four zones with shallow Curie isotherm are identified in southern Gulf of California (GS1, GS2, GS3, and GS4). GS1 is located at the Gulf of California mouth. The Alarcón rise is located between GS1 and GS2. Pescaderos Basin is located northwest of GS2. GS3 stretches from the Carmen Basin to the Farallón Basin. GS4 extends from Tiburón Island up to northern Guaymas Basin. Northernmost shallow Curie depth zone (GN1) comprises Upper and Lower Delfín Basins, as well as the Consag and Wagner Basins. A northern prolongation also covers Pinacate Volcanic center. The southern shallow Curie isotherm zones are associated with lithospheric-asthenospheric material upwelling zones. GN1 also includes a convective component related to the younger magmatism of the Pinacate Volcanic Field.Deeper Curie depths are found at southern Baja California peninsula, interpreted as associated with thicker continental or stretched crust. It is possible that the crust is underlain or underplated by magnetic oceanic crust as suggested by satellite magnetic anomalies centered at the Magdalena shelf. A contrasting pattern features northern Baja California: deep Curie zones to the west contrasting with relative shallower Curie isotherm areas to the east. The prolongation towards the peninsula of the extinct Shirley transform fracture zone roughly separates the two domains observed along the peninsula, and suggests that the Curie isotherm along the peninsula is controlled by differences subduction of the Guadalupe and Magdalena microplates. Major differences pointed out between northern and southern Gulf of California might indicate that subduction also played a key role at the beginning of the opening of the Gulf of California, however, currently, the Curie pattern is controlled by the rifting processes (shallow Curie zones correlating quite well with the rift basins and the lithosphere-asthenosphere upwelling material).

Comparison of biological and biochemical characteristics of venom from rattlesnakes in the southern Baja California Peninsula

In Mexico more than 40% of reported snakebites are due to rattlesnake species. In general, the venoms of these snakes are characterized by the presence of highly enzymatic components that could provoke coagulopathies, local and systemic tissue damage and some cases neurotoxicity. In northwestern Mexico (Baja California Peninsula, Gulf of California and Pacific islands), 15 species of Crotalus are distributed. Such a biodiversity implies a high variability in venom compositions that in turns would results in high variability in clinical manifestations. In this work, venoms of Crotalus catalinensis, C. enyo enyo, C. mitchellii mitchellii and C. ruber lucasensis were studied. Lethal doses from 0.35 to 9.21 mg/kg were obtained being venom of C. m. mitchellii the most potent of all. Venoms of C. catalinensis, C. e. enyo and C. r. lucasensis show high hemorrhagic potency (1.34, 1.48 and 1.68 μg respectively). Coagulant activity was found in venoms of C. catalinensis (4.6 μg), C. e. enyo (101.9 μg) and C. m. mitchellii (13.6 μg). Our results point out hemorrhage as one of the most expected signs by three of the four most abundant species in the area. Also, neurotoxicity must be expected by C. m. mitchellii.

The Importance of Pinnacles and Seamounts to Pelagic Fishes and Fisheries off the Southern Baja California Peninsula

The Importance of Pinnacles and Seamounts to Pelagic Fishes and Fisheries off the Southern Baja California Peninsula

Characterization of the northernmost spawning habitat of Dosidicus gigas with implications for its northwards range extension

The jumbo squid Dosidicus gigas is an ecologically and commercially important species whose northernmost geographic limit is the Gulf of California. However, over the last decades this species has extended its geographic distribution polewards, with associated impacts on the ecosystem. The origin of range-shifting individuals is poorly understood; therefore, we aimed to identify and characterize the northernmost spawning habitat of this species. Implications of the location and oceanographic conditions of the spawning habitats, migration capacity and life history characteristics of D. gigas are also discussed to elucidate its migration pattern. The northernmost spawning area was located between the biological activity centres (BACs) around the Gulf of Ulloa at the west coast of southern Baja California Peninsula during winter, summer and autumn 2005. Generalized linear models indicated that the interaction of sea surface salinity and thermocline depth, and the effect of latitude and sea surface temperature explained most of the variability in paralarval presence, whereas chlorophyll a and latitude explained paralarval abundance. Simulations indicated that paralarvae were dispersed towards the southwest or temporarily remained between BACs. The northwards incursion of D. gigas may be favoured by BACs and upwelling events along the coast of the northeastern Pacific. In warm years, D. gigas is likely to spawn off the Baja California Peninsula, it may actively migrate as far north as Alaska (USA) tracking BACs and upwelling conditions in search of feeding grounds, and it may return from different areas along the northeastern Pacific to spawn off the Baja California Peninsula.

Deep-water bivalve mollusks collected during the TALUD XV cruise off the west coast of the southern Baja California Peninsula, Mexico.

BackgroundDuring the TALUD XV research cruise off the southern part of the Baja California Peninsula, Mexico, samples of macro-invertebrates obtained in the deep-sea (296–2136 m) revealed a rich fauna of bivalves (17 species belonging to 10 families). The number of species per station varied from one to five. The richest families were Nuculidae, Nuculanidae, Neilonellidae, Limidae, and Cuspidariidae. Solemyidae, Lucinidae, Poromyidae, Verticordiidae, and Pectinidae were each represented by a single species. Some species groups need a thorough revision and were tentatively identified (Nuculana cf. hamata, Limatula cf. saturna).New informationSignificant new distribution information is provided for two species, both recorded for the first time from off western Mexico: Ennucula panamina with an extension of its known distribution over 20° of latitude north and Jupiteria callimene with an extension of 16° 42' of latitude to the north. One species (Ennucula taeniolata) is reported in shallower depth and one in deeper water (Acesta sphoni). New records are provided for an additional nine species. Environmental and habitat conditions are given for the first time for many of the bivalve species.

Caracara cheriway predation on migratory waterbirds, Egretta thula and Podiceps nigricollis, in southern Baja California Peninsula

Reportamos la depredación de aves acuáticas migratorias por Caracara cheriway. El 4 de enero del 2015 se observó a un caracara juvenil alimentándose de Egretta thula (juvenil) y a un caracara adulto de Podiceps nigricolis (adulto) en una playa al sur de la península de Baja California. Este es el primer reporte de Caracara cheriway depredando presas vivas de aves acuáticas migratorias.

Effects of the Arid Environment on the Reproductive Phenology of three Mangrove Tree Species in the Southern Baja California Peninsula, México

The flower and hypocotyl development of three mangrove tree species of the southern Baja California Peninsula were analyzed comparing four microtopographic flooding conditions and in relation to five environmental factors (relative humidity, rainfall ambient temperature, solar radiation and speed). The main objective was to evaluate the effects of an arid environment on the reproductive effort of the mangrove species present. Between 1 June to 5 November 2006 weekly measurements were made at three sites in La Paz Bay. During each visit we recorded the development of buds to flowers (anthesis) and eventually, if there was successful pollination, to propagule (viviparous embryo or hypocotyl) until they detached from the mother tree some time later. This was done for three selected stems of one tree per species for the four microtopographic conditions. Our results indicate that nearly 25 % of all flowering plants passed to hypocotyls and relative humidity and rainfall were the variables most associated with flower development. We found that humidity triggers the reproductive effort of mangroves species in this arid region and that the microhabitat coast (BO) is the best condition for the development of flowers to hypocotyls for all three species on the eastern Baja California Peninsula. Because of exposure to the sea the trees are not water stressed at these sites.