Lower Gulf Of California Research Articles

Four new species of Kinorhyncha from the Gulf of California, eastern Pacific Ocean

Several meiofaunal samples from the central and lower Gulf of California were studied. Four new species of kinorhynchs, Cristaphyes fortis sp. nov., Higginsium mazatlanensis sp. nov., Cephalorhyncha teresae sp. nov. and Echinoderes xalkutaat sp. nov., are described herein. C. fortis sp. nov. may be distinguished from its most similar congeners by its more strongly developed pachycycli and ball-and-socket joints and the presence of unpaired paradorsal setae on segments 2, 4 and 6, two pairs of ventrolateral setae on segment 5, one pair of ventrolateral setae on segments 2–4, 6–7 and 10, and one pair of ventromedial setae on segments 8–9. H. mazatlanensis sp. nov. is easily distinguished from its congeners by the combined presence of subdorsal setae only on segment 1 and lateroventral setae only on even segments. C. teresae sp. nov. is unique within the genus by the presence of acicular spines in middorsal position on segments 4, 6 and 8, in sublateral position on segment 7 and in lateroventral position on segments 8 and 9, as well as tubes in subdorsal position on segment 2, and in lateroventral position on segment 5. Moreover, this species has primary pectinate fringes of segments 2–7 bearing a tuft of elongated spinous projections in middorsal position, which is unique among its congeners. E. xalkutaat sp. nov. belongs to a group of Echinoderes characterized by possessing type 2 glandular cell outlets in subdorsal, laterodorsal, sublateral and ventrolateral positions on segment 2, together with middorsal spines on segments 4–8, lateroventral spines on segments 6–9 and lateroventral tubes on segment 5, but the arrangement of the remaining type 2 glandular cell outlets (in midlateral position on segment 5, in sublateral position on segment 8 and in laterodorsal position on segment 10) and the cuticular composition of segment 11 (one tergal and two sternal plates) allow its morphological differentiation.

Occurrence of a juvenile white shark (Carcharodon carcharias) in the southeastern Gulf of California, Mexico

Records of white sharks ( Carcharodon carcharias ) sightings or captures from the southern Gulf of California have been poorly documented and anecdotal evidence is limited. Even rarer is the event of a juvenile in subtropical waters. In the present paper, we report the capture of a juvenile female white shark taken in the lower Gulf of California, which represents an important contribution among the connectivity between individuals from California, United States and the Gulf of California, Mexico.

Bathymetric patterns of polychaete (Annelida) species richness in the continental shelf of the Gulf of California, Eastern Pacific

The mid-domain effect was tested to evaluate the bathymetric patterns of the polychaete species richness in the Upper and Lower Gulf of California as a possible hypothesis to explain the species richness gradient, exploring the overlapping of species depth ranges towards the middle continental shelf. The bathymetric gradient of the number of species was estimated with the depth ranges of 554 polychaete species, and the mid-domain effect was tested using a Monte Carlo simulation program at bands of 10m depth. The Upper (251 species) and Lower (491 species) Gulf regions showed clear differences in their faunal composition (Jaccard similarity index=0.34); the species richness pattern was characterized by a highly significant presence of polychaetes with short depth ranges (<10m). The richness distribution could be described as a cubic polynomial curve, but the maximum values in both Gulf regions (141 and 317 species, respectively for Upper and Lower Gulf regions) are strongly biased to shallow waters (40m). This is not consistent with the peak of diversity at 60–70m predicted by the model. The observed patterns cannot be reproduced by the mid-domain effect, suggesting the existence of non-random factors affecting the species richness gradients in the Gulf.

Changes in the taxonomic diversity of the reef fish community of San José Island, Gulf of California, Mexico

Although San Jose Island is considered one of the most important islands in the lower Gulf of California due to its commercial fishing activities, few studies have evaluated their fish taxonomic diversity. The aim of this study was to determine the variation in the taxonomic diversity of the conspicuous fish community in eight locations around San Jose Island from March 2001 to February 2002. We assessed the changes in the diversity of rocky reef fish based on the taxonomic distances between species, using Fisher’s alpha diversity index, average taxonomic distinctiveness (AvTD Δ+), and taxonomic distinctiveness (Δ*). Visual censuses were conducted in 48 transects consisting of 100 × 5 m quadrants (500 m2 sampling area) at an average depth of 5 m, from 09:00 to 16:00. A total of 26,608 fishes belonging to 112 species and 76 genera were found. The index of relative abundance was used to determine the most important species, which were in order of abundance: Abudefduf troschelii, Thalassoma lucasanum, Stegastes rectifraenum, Mulloidichthys dentatus, Chromis atrilobata, Lutjanus argentiventris, and Scarus ghobban. According to Fisher’s alpha diversity index, the highest diversity of species was found in July and the lowest in February. The indices of Δ+ and Δ* indicated significant temporal and spatial differences.

Rhodolith Stranding Event on a Pliocene Rocky Shore from Isla Cerralvo in the Lower Gulf of California (Mexico)

JOHNSON, M.E.; PEREZ, D.M., and BAARLI, B.G., 2012. Rhodolith stranding event on a Pliocene rocky shore from Isla Cerralvo in the lower Gulf of California (Mexico).Controls on present-day sedimentation around Isla Cerralvo in the southern Gulf of California provide a model for restricted Pliocene limestone distribution. The 10.46-km2 island is elongate and roughly parallel to the direction of prevailing north winds. Debris washed from deeply dissected valleys build fan deltas of sand-to-boulder size igneous clasts. These are transported south by long-shore currents, but the fans also create leeward zones with less agitated water. Remnants of a large Pliocene fan are exposed during low tide at Los Carillos on the SE side of the island. Adjacent is an unconformity between granite and granite-derived conglomerate with Nerita scabricosta. This extant gastropod is typical of the high intertidal rocky shore. The conglomerate is capped by a sandstone ramp with Argopecten abietus as an offshore facies. Basalt dikes exhumed from the granite formed natural groins that captured sediments and shells in the sand ramp. Whole rhodoliths, mostly 3.5 cm in diameter and 15-cm deep, covered 150 m2 within the ramp, now partly exposed among boulders in the basal conglomerate. Many rhodoliths encrust pea-sized rock cores. Accretion occurred in shallow water protected from extreme agitation by the nearby fan delta. Stranding of rhodoliths on the rocky shore was a storm-induced event.

Distribution, Sediment Source, and Coastal Erosion of Fan-Delta Systems on Isla Cerralvo (Lower Gulf of California, Mexico)

BACKUS, D.H.; JOHNSON, M.E., and RIOSMENA-RODRÍGUEZ, R., 2012. Distribution, sediment source, and coastal erosion of fan-delta systems on Isla Cerralvo (lower Gulf of California, Mexico).Located near the tip of the Baja California peninsula, Isla Cerralvo is the sixth largest island in the Gulf of California. Although surrounded by some of the most productive waters in the world, field surveys show that Isla Cerralvo's shelf is largely devoid of biogenic carbonates, especially rhodolith beds, which are found in abundance elsewhere within the region. In counterpoint, a series of prominent fan deltas extend from the mouths of arroyos on Isla Cerralvo, despite the fact that the island has a granitic core, suggesting that the island's bedrock is severely weakened. Field observations suggest that the fracture pattern (submeter), hydrothermal alteration, as well as the orientations of metamorphic foliation, fracture sets, and fault planes all play a role in the accelerated rate of erosion on the island. The role of hydrothermal alteration is illustrated by a principal components analysis of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) Short Wave Infrared (SWIR) bands, which links heavily eroded areas at the south end of the island to areas with high concentrations of clays.A synthetic drainage system created using a 30-m-resolution digital elevation model (DEM) generated from an ASTER image was used to model the Isla Cerralvo drainage basins and stream channel networks. Analyses of basin and stream network information, including basin slope values and channel slope values, were used to identify islandwide differences in basin morphology and erosion characteristics. Stream channel profiles and slope-area data supported by limited uplift data indicate that Isla Cerralvo has not been uplifted as a single block, but it is broken into at least two major structural blocks with different uplift histories.Due to the arid climate and low annual precipitation, we find that sediment removal from the interior of Isla Cerralvo can only be accomplished by episodic, but very short (hours to days), catastrophic rainfall events caused by hurricanes or chubascos (winter storms). Subsequently, the sediment is eroded from fan deltas and transported southward by longshore currents and wind-generated waves, choking carbonate production along Isla Cerralvo's shore and shelf.

PATTERNS OF OCCURRENCE AND ABUNDANCE OF LAND BIRDS ON ESPÍRITU SANTO ISLAND, GULF OF CALIFORNIA, MÉXICO

Abstract Land-bird density on Espiritu Santo Island, lower Gulf of California, Mexico, was determined bimonthly from November 1998 to October 1999. Bird density was quantified in 4 habitats on the island using the line transect sampling method. Fiftyeight species were recorded, of which 44 were detected in the transects and the other 14 in adjacent sites. The highest bird densities were observed in March and June, coincident with the lowest rainfall months in the neighboring peninsular mainland. Average density (birds/ha) was highest in alluvial fans (18.14) and lowest in mesas (8.08). Migratory bird density on the island was relatively low and commonly less than 10% of the observed total density. The average land-bird density on the island (13.29/ha) was greater than that previously recorded.

Decadal surface ocean variability in the lower Gulf of California: Records for the past 300 years

Nuevos resultados de estudios observacionales y teóricos sobre la oceanografía del Golfo de California han aportado nuevas ideas y modelos para entender sus estructuras de circulación y controles en escalas interanuales a decadales, reconociendo la importancia del forzamiento de origen tropical y ecuatorial para explicar su variabilidad. El registro instrumental de este mar epicontinental es de corta duración, abarcando sólo desde la década de los 80 a la actualidad, mientras que para años anteriores su pobre resolución limita seriamente la validación de cualquier modelo sobre la variabilidad decadal de esta región. Para superar este problema recurrimos a una reconstrucción de las temperaturas de la superficie del mar (TSM) en el Bajo Golfo de California para los últimos dos siglos a partir de la composición isotópica del oxígeno en los caparazones de un foraminífero plánctico, Globigerina bulloides (d’Orbigny), preservados en los sedimentos laminados de alta resolución temporal que se acumulan en el fondo de la Cuenca de la Bahía de La Paz, frente al margen suroriental de la Península de Baja California. El análisis del registro instrumental muestra una variabilidad interanual mayor para las TSM de invierno que en las de verano para las últimas dos décadas. Los registros instrumentales más largos e incompletos muestran un cambio en las temperaturas de las estaciones frías hacia temperaturas relativamente más cálidas a comienzos del siglo pasado, mientras que las TSM de verano no muestran ninguna tendencia. Estas observaciones demuestran la sensibilidad de los meses fríos a la variabilidad interanual en las TSM. Presentamos un registro extendido a los últimos 300 años basado sobre la reconstrucción isotópica del oxígeno en el foraminífero plánctico Globigerina bulloides (d’Orbigny) del que sabemos su producción máxima durante los meses invernales en las aguas del Golfo. Este paleotermómetro muestra temperaturas medias de invierno similares a las registradas instrumentalmente para los últimos 170 años, mientras que para el período anterior comprendido entre 1700 a 1830 las TSM derivadas isotópicamente muestran inviernos más fríos alternándose con otros relativamente más cálidos. La variabilidad observada en las TSM de invierno a escalas interanuales a decadales parece ser modulado por las fluctuaciones de baja frecuencia asociadas al fenómeno de El Niño y Oscilación Austral (ENOA), posiblemente por una mayor frecuencia y/o intensidad de los eventos de El Niño y La Niña, que bloquean las TSM del Golfo en períodos cálidos/fríos a escalas decadales, posiblemente como respuesta no sólo al forzamiento ecuatorial introducido por el ENOA como a otros efectos de retroalimentación de origen oceánico.doi: sin doi

Oceanographic and climatic variability in the lower gulf of california: links with the tropics and north pacific

The links between climate and oceanography in the lower Gulf of California (LGC) and the observed physical variability in the open Pacific were studied on interannual to decadal timescales. Two indices reflect the North Pacific´ s oceanic and climatic variability: the El Niño Southern Oscillation index (ENSO) and the North Pacific Decadal Oscillation index (PDO). The sea surface temperatures, wind speed, precipitation and sea level records of La Paz region, Baja California Sur (Mexico) in the LGC were used to compare them with the PDO and ENSO indices. The most important forcing processes were observed coming from the tropical and the equatorial Pacific, represented by the ENSO index, significantly associated with precipitation, sea surface temperature (SST) and sea level. The Northern Pacific influence, represented by the PDO index, is associated with the winds and to a lesser extent with SSTs and precipitation. These results show that SST variability in the region is controlled by both indices. A model is proposed to explain the control that each of them exerts on the LGC SST variability. In this model the excess heat brought by surface tropical waters, especially after the intensification of ENSO events since the 1980s, in addition to the long term warming observed over the past century, is partially dissipated by stronger winter winds in the gulf. These stronger and cooler winds, derived from changes in the atmospheric circulation patterns of the North Pacific and captured by the PDO positive anomalies, act as negative feedback to the warming dissipating part of the accumulated heat and dampening the raise in SSTs. This process is proposed to operate, especially after the 1970s sign shift of the PDO, when no change in the SSTs´ trend occurs showing an opposite behavior in respect to wind variability, which was not observed for previous decades.

Status of the Pulmo Coral Reefs in the Lower Gulf of California

Status of the Pulmo Coral Reefs in the Lower Gulf of California

Eastern Pacific Crown-Of-Thorns Starfish Populations In The Lower Gulf Of California

Eastern Pacific Crown-Of-Thorns Starfish Populations In The Lower Gulf Of California

Clay-Mineral Distribution in Recent Sediments from Northern Pacific Coast of Mexico: ABSTRACT

The clay-mineral composition of 86 samples from the Northern Pacific coast of Mexico was identified and the relative abundance of each clay mineral was obtained. The known minus 2µ fraction was analyzed in oriented aggregates using X-ray diffraction. Prior to X-ray, the samples were freed of carbonates, organic End_Page 637------------------------------ matter, iron oxides, and colloidal silica and alumina. Montmorillonite, illite, and chlorite were found to be the most abundant clay minerals. Kaolinite and vermiculite were present in some samples, usually in minor amounts. The distribution patterns of clay minerals in the lower Gulf of California are determined by the source areas and strong diagenetic effects ensuing on contact with sea water. The clay-mineral distribution shows a sharp contrast in clay-mineral assemblages between the marine and non-marine sediments. The montmorillonite, illite, and chlorite content of the normal marine samples is very uniform. In the warmer hypersaline environment of the swamps, formed in the depressions between cheniers, the clay-mineral assemblages have greater proportions of chlorite, indicating that intense chemical conditions behind cheniers are particularly effective in modifying the composition and structure of the clays entering the sea from rivers. The clay mineralogy of the terrestrial samples is controlled by the source material and the weathering conditions of the area. In both terrestrial and marine environments, anomalous clay-mineral assemblages reflect small-scale or local geographic conditions (provenance). End_of_Article - Last_Page 638------------