Southwestern Gulf Of California Research Articles

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.

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.

Fecundity traits of young ovigerous females of yellow-line-arrow spider crab Stenorhynchus debilis (Brachyura: Inachoididae) in Bahía de La Paz Baja California Sur, México

The southwestern Gulf of California is an important source of ornamental marine species traded worldwide, wherein spider crabs Stenorhynchus debilis are popular items. However, little is known about species biology and ecology. This study involves young ovigerous females (28 in total) recollected at Bahía de La Paz, Mexico, into bivalve mariculture devices cleaned every 3-4 months. Total carapace length (TL) and carapace width (CW), weight without eggs (TW), and fecundity (F, number of eggs) were analyzed for multiple relationships. F varied into 162 and 2205 eggs (x̄ = 1171 ± 689 eggs), their diameter into 0.38 to 0.45 mm (x̄ = 0.396 ± 0.027 mm). Three persistent and interactive modes were detected: low/moderate/high F, small/medium/large size (TL and CW), and light/middle/heavy TW. Log-linearized allometric regressions were applied to determine the relative fecundity constants (RFC) by body complexion, finding high parallelism between TL and CW related to step-wise growth and size categorization upon the isosceles-shaped carapace. In contrast, TW denoted an increase in body complexion across intermolt phases. S. debilis likely completes three maturation/molt cycles within 3-4 months after the first crab instar. RFC values confirmed positive trends by body complexion where egg size and F are related to species size and shape, establishing the trade-off proportions in this study case.

Anomalous thermal and winds condition drove low surface chlorophyll-a in La Paz Bay during the 2015–2016 El Niño event

La Paz Bay (LPB) considered one of the most highly productive bays in the southwestern Gulf of California, Mexico, recently established as Priority Marine Region, supports many species of ecological importance. In this context, daily composites of surface chlorophyll a (Chl-aSAT), sea surface temperature (SST) satellite images derived from the MODIS-Aqua sensor, and a wind intensity index (WI) calculated with data recorded simultaneously at four points along the coast, were used to describe the strong 2015–2016 El Niño impact over the surface chlorophyll pigments in LPB, relative to its average for 2003–2013. Significant relationships between SST, WI (used as environmental factors) and Chl-aSAT (RSST = −0.74, RWI = −0.40, P < 0.01) were found using exponential models for the entire study period, with moderate correlation during El Niño winter condition (December 2015 to March 2016) between SST and Chl-aSAT (RSST = 0.45, P < 0.02). The Chl-aSAT showed unexpectedly low values (∼0.5–1.2 mg m−3) with one month-lag of the winter bloom period jointly with the presence of warmer-than-usual water (∼1.0 °C) and episodes of strong northwesterly winds (speed 8.0–10.0 m s−1) that began in autumn that drove a ∼2 month-lag in its winter peak. The Chl-aSAT and SST winter spatial patterns, showed low Chl-aSAT values (∼−0.5 to −1.0 mg m−3) along the bay and higher-than-usual SST by ∼ 0.5–1.0 °C relative to a year under the La Niña winter condition (2017–2018). This triggered the possible thermocline deepening and the lowest levels of nutrient supply to the photic layer during the El Niño winter episode. Hovmöller diagrams of Chl-aSAT and SST anomalies along the coast revealed a sharp drop to negative anomaly values (∼− 0.7 to −1.2 mg m−3), in-phase but negatively correlated with the SST coastal anomalies (R = − 0.88, P < 0.01). This biophysical coupling played a crucial role in the exceptional drop to the lowest winter Chl-aSAT levels seen in LPB since the MODIS satellite sensor began taking measurements in 2002 (Chl-aSAT values were lower than usual by ∼ 0.9–1.2 mg m −3). Besides the lowest winter levels observed, this research reflected the El Niño signal-driven changes over the basic seasonal average of the LPB climate system The non-significant negative trend observed in the winter average Chl-aSAT values, indicates that LPB may be less resilient to future environmental disturbances.

Seasonal and diel influences on bottlenose dolphin acoustic detection determined by whistles in a coastal lagoon in the southwestern Gulf of California.

Marine mammals in subtropical coastal habitats are sentinels of the health of the ecosystem and offer important ecosystem services. They rely on prey that pursues feeding opportunities, while both avoid unfavorable conditions. In many cases, these predator-prey dynamics fluctuate seasonally and are regulated by lunar, tidal, and/or diel cycles (hour). However, these rhythmical patterns may vary under different seasonal conditions. Bottlenose dolphins (Tursiops truncatus) in the Ensenada de La Paz in Baja California Sur, Mexico, were detected acoustically over the course of an annual cycle on 21 separate occasions, covering 640 h from June 2017 to May 2019. The presence of bottlenose dolphins was examined using Generalized Additive Models (GAM) including variables that are related directly to their habitat (direct variables: hour, distance, depth) and to their prey (indirect variables: SST, moon phase and tides). Seasonal differences in the presence of bottlenose dolphins were influenced more by indirect variables (explained deviance: 34.8% vs. 37.7%). Hourly acoustic detections occurred less frequently when SST exceeded 27.4 °C (Aug–End of Nov.) and more frequently at moderate temperatures (22.7 °C to 26.3 °C) in May through July. Moreover, bottlenose dolphins were detected more frequently during waning and new moon phases, at the onset of flood and ebb tides, and during day (04:00 to 20:00). The seasonal differences in acoustic detections rates were highlighted by the global GAM and hierarchical clustering. The strong seasonal pattern indicated possible interactions with rhythmic pattern of bottlenose dolphins. Four candidate variables (SST, moon, tide, and hour) were tested for plausible interaction terms additional to their individual consideration, out of which only hour changed significantly between seasons. The patterns of presence likely increase feeding opportunities or may favor other behaviors such as socializing, resting, or nursing. These might prove responsible for the distinct occurrence and hourly patterns of bottlenose dolphins.

Cyclonic circulation and climatology of SST, CHL and wind stress curl in a semi-enclosed bay (Bahía de La Paz, Gulf of California)

The first direct current observations (with LADCP and surface drifters) in Bahía de La Paz, a bay in the southwestern Gulf of California (GC), concur with previous reports that the main dynamical feature during summer is a closed cyclonic circulation. However, we found that geostrophic calculations overestimate the speed of the orbital velocity: actual speeds (0.20-0.25 m s-1) were ~25-40% lower than those estimated from geostrophic balance (0.25-0.35 m s-1). The reason is that the centrifugal force cannot be neglected in this case. The mean rotation period during ship-borne observations in August 2004 was ~1.4 days, but it varied during the time that surface drifters were inside the bay, from ~1-2 days in June-July to ~2.5-3 days in September-October. The analysis of satellite data (wind velocity, sea surface temperature and chlorophyll) show that from May to September the wind stress curl is strong and cyclonic, and the surface of the bay is cooler and richer than the adjacent Gulf of California waters, which could be attributed to the positive wind stress curl. This positive wind stress curl on the bay is part of a larger-scale positive wind stress curl distribution that surrounds the southern part of the Baja California Peninsula during summer, probably enhanced in the bay by local topography features. Although there is an exchange of water between the bay and the GC, its effect on the dynamics is poorly known.

Reproductive Cycle and Size at First Maturity in Females of Brown Crab Callinectes Bellicosus (Stimpson 1859) in the Southwestern Gulf of California, Mexico

Abstract The reproductive cycle of the crustacean family Portunidae on the coast of the Pacific is not well known. Therefore, the reproductive cycle and the size at first maturity of brown crab Callinectes bellicosus and its relationship with environmental factors in the El Colorado Lagoon, Ahome, Sinaloa has been determined. A total of 360 females were collected from March 2012 to March 2013. The gonads were fixed in 10% formalin, histological cuts were made by the paraffin inclusion method and the hematoxylin and eosin staining technique. The diameter of oocytes was determined by stage. The size at first maturity was estimated by a logistic model. Females showed gametogenic activity during the entire study period. The maturity period was from March to November 2012, with two spawning peaks, in September 2012 and March 2013. Maturity was inversely influenced by temperature (r = -0.4454, P &lt; 0.05) and no influence by salinity was observed (P &gt; 0.05). The diameter of the oocytes showed significant differences between the development stages of the gonad (P = 0.001). The size at first maturity was 11.57 cm of carapace width for females of C. bellicosus.

Mercury, selenium, and stable carbon and nitrogen isotopes in the striped marlin Kajikia audax and blue marlin Makaira nigricans food web from the Gulf of California

Mercury (Hg) concentrations based on dietary sources have shown to predict differences in fish; however, they are usually applied at an individual scale and are rarely directed at a known trophic transfer. We combined gut content analysis and stable isotope analysis (δ15N and δ13C) to provide a quantitative estimate of Hg and selenium (Se) biomagnification in the striped marlin (Kajikia audax) and blue marlin (Makaira nigricans) food web from the southwestern Gulf of California. Hg and Se concentrations (mean ± SD; μg g−1, dw) were different among K. audax (Hg = 3.6 ± 2.1, Se = 5.5 ± 5.4) and M. nigricans (Hg = 19.0 ± 29.6, Se = 8.8 ± 10.5). Such variations of element concentrations could be linked to predation with different Hg and Se contents. Diet data presented as prey weight (%W) indicated a higher proportion of large prey fish for the blue marlin than the striped marlin. δ15N and δ13C indicated pelagic food sources with epipelagic preferences for the blue marlin and mesopelagic for the striped marlin. The relationship between Hg concentrations and δ15N was positive along the food web of both marlin species, indicating biomagnification of Hg. However, Se biomagnification was not clearly evidenced, and Se:Hg ratios decreased with δ15N, attributed to increasing Hg concentrations with increased trophic level.

Genetic and morphological evidence of the presence of Phyllorhiza punctata in the southwestern Gulf of California (NE Pacific Ocean)

Genetic and morphological evidence of the presence of Phyllorhiza punctata in the southwestern Gulf of California (NE Pacific Ocean)

Zooplankton abundance during summer in the Bay of La Paz (southwestern Gulf of California, Mexico)

Marine zooplankton play key roles in the transfer of energy to higher trophic levels and the removal of CO2 from the atmosphere through the sedimentation of inorganic and organic carbon compounds included in their fecal pellets. Therefore, differences in the zooplankton groups driven by climate variations could influence the biogeochemical cycles at large oceanic scales. As a contribution to this topic, we analyzed the zooplankton groups in the Bay of La Paz, Gulf of California, Mexico, a highly dynamic basin characterized by its high biological productivity. We used information gathered during multidisciplinary research cruises in the summers of 2008 and 2009. The results showed differences in the hydrographic parameters between both summers, with a higher temperature recorded in 2009. The zooplankton groups showed that the calanoid copepods were the most abundant; however, there were important differences in the relative abundance of the rest of the analyzed groups as an effect of the temperature distribution along the study area, which was confirmed by multivariate statistical methods. These temperature changes were associated with increased gelatinous zooplankton (Cnidaria, Chaetognatha, Appendicularia, and Ctenophora) in 2009 in a region where the temperature was higher, possibly as a result of changes in food (phytoplankton) availability.

Interannual variability of surface satellite-derived chlorophyll concentration in the bay of La Paz, Mexico, during 2003–2018 period: The ENSO signature

The Bay of La Paz (BLPZ), located in the southwestern Gulf of California, is a region of significant biological productivity and strong environmental variability that remains to be understood. In particular, the spatial signature of different El Niño-Southern Oscillation (ENSO) conditions and their impact on the ecology of the bay remains puzzling because of contrasting field observations. In this context, the available satellite-derived data on surface chlorophyll (ChlSAT), sea surface temperature (SST) derived from the MODIS-Aqua sensor, together with surface wind intensity (WI) derived from reanalysis datasets from the period 2003–2018 were analyzed to identify the influence of local and remote forcing over the interannual variability of chlorophyll pigment concentration in BLPZ using WI, SST, and the Oceanic El Niño Index (ONI) as environmental factors. Significant relationships between environmental factors and ChlSAT were found using exponential models, with the higher slopes and correlations during La Niña events. Empirical orthogonal function (EOF) analysis was used to extract the principal mode of the ChlSAT and SST interannual variability. The first mode (EOF1) accounted for 64% and 89% of the ChlSAT and the SST interannual variance, respectively, showing a strong gradient along the coast of the bay. The corresponding amplitude of the ChlSAT mode was significantly correlated with the independent variables PC1SST, ONI, and WI anomalies (RSST = − 0.60, RONI = − 0.57, and RWI = 0.44, P < 0.001). Monthly time series of ChlSAT anomalies along the coast where examined as a function of each independent variable using a multiple linear regression analysis (LRA), which revealed that during the 2005 to 2013 period, high peaks of positive ChlSAT anomalies in the central and southern coast were related to cold ENSO events and favorable wind forcing, which smoothed the effect of weak and moderate El Niño episodes. This period of high biological productivity was only interrupted by the strong and long 2015–2016 El Niño event. Since late 2013, the ChlSAT and the WI anomalies showed a sharp drop to negative anomaly values, which may be the result of complex interactions of physical and biological processes observed during strong warm ENSO events, showing one peak of persistent warm SST anomalies via a weakening of the wind intensity (i.e., from atmospheric teleconnection) and a second one due to the oceanic connection. It is confirmed that BLPZ maintains high pigment concentration levels, comparable to those reported on the mainland coast of GC, where only strong warm ENSO episodes cause changes in chlorophyll concentration.

Vertical variability of benthic foraminifera and trace elements in a tropical coastal lagoon in the Gulf of California

Population growth around water bodies is deteriorating environmental quality. The benthic foraminiferal and trace element concentration in a pair of short sediment cores were used to establish the quality of the sedimentary environment in a tropical coastal lagoon in the southwestern Gulf of California. From 25 cm depth towards the surface of the sediment core, Ammonia beccarii was dominant over nontolerant species and the concentrations of V, Ni, Co, Zn, Cu, Hg and Pb in the sediments increased compared with the lower depth intervals. This finding suggests a deterioration in the environmental quality of the lagoon since 1980, associated with an increase in the sizes of the population and vehicle fleet in the city of La Paz, Baja California Sur, and with the operation of three fossil fuel-based thermoelectric plants since 1985.

Fin whale movements in the Gulf of California, Mexico, from satellite telemetry.

Fin whales (Balaenoptera physalus) have a global distribution, but the population inhabiting the Gulf of California (GoC) is thought to be geographically and genetically isolated. However, their distribution and movements are poorly known. The goal of this study was to describe fin whale movements for the first time from 11 Argos satellite tags deployed in the southwest GoC in March 2001. A Bayesian Switching State-Space Model was applied to obtain improved locations and to characterize movement behavior as either “area-restricted searching” (indicative of patch residence, ARS) or “transiting” (indicative of moving between patches). Model performance was assessed with convergence diagnostics and by examining the distribution of the deviance and the behavioral parameters from Markov Chain Monte Carlo models. ARS was the predominant mode behavior 83% of the time during both the cool (December-May) and warm seasons (June-November), with slower travel speeds (mean = 0.84 km/h) than during transiting mode (mean = 3.38 km/h). We suggest ARS mode indicates either foraging activities (year around) or reproductive activities during the winter (cool season). We tagged during the cool season, when the whales were located in the Loreto-La Paz Corridor in the southwestern GoC, close to the shoreline. As the season progressed, individuals moved northward to the Midriff Islands and the upper gulf for the warm season, much farther from shore. One tag lasted long enough to document a whale’s return to Loreto the following cool season. One whale that was originally of undetermined sex, was tagged in the Bay of La Paz and was photographed 10 years later with a calf in the nearby San Jose Channel, suggesting seasonal site fidelity. The tagged whales moved along the western GoC to the upper gulf seasonally and did not transit to the eastern GoC south of the Midriff Islands. No tagged whales left the GoC, providing supporting evidence that these fin whales are a resident population.

Sea surface temperature, ocean color and wind forcing patterns in the Bay of La Paz, Gulf of California: Seasonal variability

Monthly climatologies are used to estimate the mean seasonal cycle of MODIS-Aqua satellite-derived sea surface temperature (SST), surface chlorophyll (Chl- a ) and their relationship with surface wind stress curl (from the Cross-Calibrate Multi-Platform, CCMP) in the Bay of La Paz located in the southwestern Gulf of California, a region identified as having high biological productivity and significant seasonal variability. Harmonic fit applied to the monthly climatologies of these variables indicate a best fit with annual and semi-annual constituents. The annual amplitude was the dominant signal in both SST and Chl- a , corresponding to the bay-wide seasonal cycle of warming and cooling associated with the influx of upwelled nutrient-rich coastal waters jointly with the water exchange between the bay and the Gulf of California. Empirical orthogonal function (EOF) decomposition yielded the annual and semi-annual patterns of the seasonal cycle that respond to wind forcing. The EOF 1 explained 93% of the SST variance and 48% of the Chl- a variance, showing a homogeneous variability of both variables across the bay and a strong thermal and biological gradient in the vicinity of the Gulf of California with their corresponding amplitude time series representing out-of-phase annual cycles, which corresponded to the regional dynamics of wind forcing pattern. The EOF 2 accounted for 6% of the SST variance and 31% of the Chl- a variance, which reached its peak during winter associated with the high Chl- a anomaly values (>1.5 mg m –3 ) observed along the coast. The intense biological productivity covaried strongly with the wind stress curl annual cycle ( R = 0.5, P < 0.05 ), suggesting that these Chl- a blooms could be associated with coastal currents and upwelling events regulated by the seasonal wind forcing pattern playing an essential role in the modulation of this quasi-permanent biophysical coupling observed in the Bay of La Paz during an annual cycle.

Structural Complexity and Biomass of Arid Zone Mangroves in the Southwestern Gulf of California: Key Factors That Influence Fish Assemblages

ABSTRACT Ochoa-Gomez, J.G.; Serviere-Zaragoza, E.; Lluch-Cota, D.B.; Rivera-Monroy, V.H.; Oechel, W.; Troyo-Dieguez, E., and Lluch-Cota, S.E., 2018. Structural complexity and biomass of arid zone mangroves in the southwestern Gulf of California: Key factors that influence fish assemblages. Arid zone mangroves of the southwestern Gulf of California provide ecosystem services because of their habitat heterogeneity, structure, and functions, which are important for the formation of fish assemblages. Structure, litterfall production, and leaf decomposition in three mangrove communities located at La Paz Bay, Mexico, were analyzed. Litterfall production was found to be within the range reported for the region. Leaf decomposition rate was similar between communities and species. The structural complexity and biomass of mangroves were inversely correlated with fish size, suggesting that they are key features, providing shelter and nursery for fish assemblages. Laguncularia racemosa appears to play an important r...

Ulva blooms in the southwestern Gulf of California: Reproduction and biomass

Ulvacean blooms are generally characterized by one or more Ulva species, some of which are common to blooms across a broad geographic range. In tropical environments the identified stimuli that induce reproductive development of Ulva are restricted to temperature, salinity, dehydration and fragmentation. Culture studies have been prolific in describing the reproduction of Ulva species, but its reproductive changes in natural environment have not been described yet. Hence, seasonal changes were described in reproductive stages and their relationship with biomass and environmental factors of Ulva species at four macroalgal blooms in a subtropical bay. Eight Ulva species were found: U. acanthophora, U. clathrata, U. flexuosa, U. intestinalis, U. lactuca, U. lobata, U. nematoidea and U. rigida. Reproductive stage and biomass varied according to site and season. Five species showed four reproductive stages (vegetative, thallus with fully differentiated zooids in formation and empty cells after zooids release); for the remaining species only vegetative thalli were found. Ulva rigida showed the highest biomass values, followed by U. acanthophora, following a seasonal pattern.

Gobiesox lanceolatus, a new species of clingfish (Teleostei: Gobiesocidae) from Los Frailes submarine canyon, Gulf of California, Mexico.

Gobiesox lanceolatus is described from a single specimen collected from 300 meters depth in the Los Frailes submarine canyon in the southwestern Gulf of California. The "Canyon Clingfish" is unique within Gobiesox in having a lanceolate caudal fin, with the central rays longer than those above and below them. It is also distinguished by 14 dorsal-fin rays (first tiny and unsegmented), 11 anal-fin rays, 28 pectoral-fin rays, anus slightly closer to anal-fin origin than to posterior margin of pelvic disc, and dorsal-fin origin in front of vertical from anus. It is most similar to Gobiesox eugrammus, known from Isla Guadelupe, the coast of outer Baja California and southern California. This is the deepest record for a species of Gobiesox and only four other species of clingfishes are known from greater depths.

Seasonal shift in the taxonomic diversity of rocky reef fishes in the southwestern Gulf of California

el suroeste del Golfo de California se presentan capturas de peces de importancia comercial; sin embargo hay pocos estudios relacionados con la diversidad taxonomica de los peces en el area. Se determinaron los cambios en la diversidad taxonomica de la comunidad de peces en 8 localidades cercanas a Bahia de La Paz durante el periodo marzo 2002-abril 2003. Se analizaron los cambios estacionales en la diversidad de peces de arrecife rocoso considerando la distancia taxonomica entre especies de peces utilizando la diversidad alfa, promedio alfa, beta y gama, asi como la distintividad taxonomica (TD D*), y el indice promedio de distintividad taxonomica (AvTD D+). Se realizaron censos visuales submarinos en 48 transectos, de 100 × 5 m (500 m2) a 5 m de profundidad, en el horario diurno de 09:00 to 16:00 h. Se observaron 2 temporadas climaticas; una estacion fria con una temperatura de 22,57°C, y una temporada calida con temperatura promedio de 27,09°C. Se contabilizaron 24.633 peces de 92 especies y 67 generos. De acuerdo con los resultados del promedio de los indices de diversidad de alfa, beta y gama, agosto fue el mes con mayor diversidad (19,5, 40,5 y 60 especies, respectivamente), mientras que diciembre tuvo la menor diversidad (20,6, 27,4 y 48 especies, respectivamente). En los analisis espaciales del TD y AvTD no se presentaron diferencias significativas, mientras que en el analisis estacional de los indices, se presentaron diferencias significativas. Estas diferencias en ambos indices podrian ser debido a que la localidad El Guano tiene mayor impacto de actividades humanas.

Composition of metals in suspended particulate matter of Alfonso basin, southern Gulf of California

Suspended particulate matter residues collected by 0.4μm pore size filters were analyzed for 9 trace metals (Mp) and phosphorus (Pp) from seawater samples taken from depths ranging from 0–300 m. The samples were obtained from a marginal basin located in southwestern Gulf of California. Four different sampling trips occurred during the year to coincide with periods of known contrasting hydrographic conditions. The depth-integrated concentration values followed the sequence Fe>Pp>Zn>Cu>Ni>Mo>Cd>Pb>V>Co. Temporal and vertical distribution of the largest concentrations of Mp and Mp/Pp trace metals with their concentrations normalized to phosphorus were consistent with enrichment processes in March and May. These were respectively associated with intense mixing and a submesoscale cyclonic eddy. The highest abundances of autotrophic picoplankton and nanoplankton, diatoms and dinoflagellates and chlorophyll a concentrations were also noted at this time. Wind speed was the only environmental variable that correlated positively (Spearman, p<0.05) with the temporal distribution of most of the Mp trace metals (except Cd, Co and V) in the euphotic zone, which was attributed to increases in the eolic contribution, sediment resuspension and horizontal transport towards the basin. The biological significance of Fe, Cu, Ni, Mo and V is discussed within the document based on the detected significant correlations with phytoplankton-assessed components. Our observations suggest a link between environmental forcing, the entrainment of metals and phytoplankton response as a reservoir of these metals in the euphotic zone, and as a possible source of replenishment for remineralization in the deeper layer. Future research should corroborate the assumptions about the origin and dynamics of dissolved and particulate fractions of metals and influence the biological activity and biogeochemistry of these elements in the basin.