Aída Martínez-López

First Record of Vegetative Cells of Pyrodinium bahamense (Gonyalucales: Goniodomataceae) in the Gulf of California

ABSTRACT As part of an ongoing monitoring study of phytoplankton in coastal lagoons on the east side of the Gulf of California, Pyrodinium bahamense Plate, 1906 var. bahamense was collected in the Topolobampo–Santa Maria–Ohuira coastal lagoon system in the Gulf of California in May 2005. Average concentrations of P. bahamense were 100 cells liter−1. This finding is the first observation of vegetative cells of this tropical species in the Gulf of California and represents its northernmost occurrence to date.

Phytoplankton photosynthetic parameters from the Gulf of California southern region

Se determino la respuesta fisiologica del fitoplancton en la zona eufotica por medio de experimentos fotosintesis-irradiancia realizada de junio del 2000 a junio del 2001 en la Bahia de La Paz, Golfo de California, Mexico. Durante el periodo estratificado que comprende de junio a septiembre (indice de estratificacion > 200 J m-3) el numero de asimilacion (Pm) estuvo representado por un valor promedio de 3,7 mg C m-3 h-1, mientras que de noviembre a febrero, cuando la columna de agua fue homogenea (indice de estratificacion = 0 J m-3) fue de 9,2 mg C m-3 h-1. La eficiencia fotosintetica maxima a baja irradiancia (α) tuvo un valor promedio de 0,017 mg C m-3 h-1 (µmol cuanta m-2 s-1)-1 representativo del periodo estratificado, mientras que durante el periodo homogeneo fue de 0,063 mg C m-3 h-1 (µmol cuanta m-2 s-1)-1. Los parametros fotosinteticos (Pm y a) durante la mayor dinamica de la zona epipelagica evidencian la fotoaclimatacion del fitoplancton a la irradiancia promedio en la zona eufotica. Valores altos de Pm se relacionaron con la abundancia de diatomeas (Pseudo-nitzschia delicatissima, Chaetoceros compressus y Coscinodiscus perforatus), mientras que los valores menores de este parametro se asociaron con el grupo de los dinoflagelados. Los valores promedio estimados para el parametro de saturacion de luz (Ek) fueron 334, 173 y 91 µmol cuanta m-2 s-1 para superficie, 10 y 1% de la zona eufotica, respectivamente. De manera general, la comunidad fitoplanctonica estuvo dominada por nanofitoplancton (2-20 µm) durante todo el periodo considerado.

Producción primaria y eficiencia fotosintética en Cuenca Alfonso, Bahía de La Paz, Golfo de California, México

Quantification of photosynthetic efficiency and productive capacity of the phytoplankton community was the objective of the surveys that were conducted in December 2005, May and August 2006; and February, May and November 2007 in Bahia de La Paz (Cuenca Alfonso). Samples of water were collected from 7 levels of surface irradiance (100, 55, 33, 10, 3, 1 and 0.1%), of the euphotic zone (Zeu). In situ primary production estimations were performed by 14C assimilation methodology. There were 2 basic assimilation ratios patterns; one with subsurface maxima during February and May 2007 and other with a tendency of increasing values as the lower limit of the Zeu was approached (December 2005; May and August

Assessment of eutrophication in a subtropical lagoon in the Gulf of California

Understanding the susceptibility of coastal ecosystems to nutrient loads from anthropogenic sources and the extent of eutrophication in subtropical and tropical estuaries is still a challenge. This study assessed eutrophication in Guaymas Bay, a subtropical lagoon that receives nutrient-rich urban wastewater discharges. Eutrophication was evaluated by means of the Assessment of Estuarine Trophic Status model. Our results showed that the trophic status of Guaymas Bay was “good.” It is important to consider that: (1) the dissolved oxygen and chlorophyll a levels observed are indicative of a healthy ecosystem, and (2) the key factors explaining this finding are the high susceptibility to eutrophication of the lagoon and the dominance of macroalgae species that respond to nutrient enrichment. This implies that the Overall Eutrophic Condition Index of the Assessment of Estuarine Trophic Status model is a valuable tool for use as an eutrophication indicator based on the abundance of primary producers (macroalgae and phytoplankton). One source of uncertainty in the application of the model to this semi-arid coastal lagoon deals with estimating its susceptibility to eutrophication. The model showed that the lagoon is a highly sensitive ecosystem; however, significant factors are in place, such as an adequate water exchange, that reduce its susceptibility to eutrophication. In conclusion, the trophic status observed at Guaymas Bay is acceptable; however, an environmental management plan is necessary to prevent any adverse effects of eutrophication.

Detecting Eutrophication Symptoms in a Subtropical Semi-Arid Coastal Lagoon by Means of Three Different Methods

Excess supply of nutrients of anthropogenic origin is one of the main drivers of global change that is affecting the ecological function and provision of ecosystem services by coastal wetlands. This study examines the response of a subtropical semi-arid coastal lagoon to anthropogenic nutrient input, through the use and comparison of eutrophication indices and models, and compares the usefulness of such methods to identify eutrophication symptoms. The Lobos Lagoon is located on the eastern coast of the Gulf of California and receives agricultural and urban wastewater discharges. To identify potential eutrophication symptoms, the Trophic IndeX (TRIX), the Arid Zone Coastal Water Quality Index (AZCI) along with the Assessment of Estuarine Trophic Status (ASSETS) model were used. Lobos Lagoon was found to have good environmental condition; however eutrophication symptoms were identified in the zone where untreated urban and agricultural wastewaters are discharged. Results obtained using the three methods were consistent and, thus, their performance can be considered as good and complementary, and can be used to evaluate the extent of eutrophication in subtropical semi-arid coastal lagoons.

Primera estimación de la tasa de fijación biológica de nitrógeno en Cuenca Alfonso, región sur del Golfo de California

Nitrogen-fixation (FBN) rates were determined for the first time in the euphotic zone (0-43 m) and at 150 m depth using the high-sensitive 15N2 tracer method...