Lourdes Morquecho

Raphidophyceans on the coasts of Mexico

The presence of ichthyotoxic phytoflagellates Chattonella marina, Fibrocapsa japonica, and Heterosigma akashiwo of the algal class Raphidophyceae are reported for first time in the Gulf of Mexico and the Pacific coast of Mexico. Phytoplankton were sampled to isolate and identify species, and to develop growth experiments in different media. We observed living material of the three species, but were unable to recognize specimens in preserved samples. Cultures were established by isolating single cells and diluting phytoplankton samples in modified f/2 and Erd–Schreiber media. Features, including morphological variations and pigment composition, of living cells under various nutrient conditions are described. These ichthyotoxic species produce harmful blooms in several parts of the world, although no documented cases have been reported in Mexico.

Seasonal occurrence of planktonic dinoflagellates and cyst production in relationship to environmental variables in subtropical Bahı´a Concepción, Gulf of California

Abstract We studied seasonal prevalence of dinoflagellates and of cyst production in relation to hydrological factors in Bahía Concepción, Mexico. In situ production of dinoflagellate cysts was recorded for the first time in Mexico. The resting stage of toxic Gymnodinium catenatum, potentially toxic Alexandrium pseudogonyaulax, and other red tideforming dinoflagellates were collected in traps. Cyst associations were linked with the composition of vegetative stages in the water column, and production yields (128 to 1.465×106 cysts m-2 d-1) were comparable with other reports in areas around the world. Seasonal abundance of major meroplankton dinoflagellates and relationships with yields of newly-formed cysts coincides with hydrographic transitional periods in the water column in spring and early fall. From factor analysis, the physico-chemical variables that correlate with the presence of the major meroplanktonic species are, in descending order of importance: temperature, phosphates, dissolved oxygen, silicate, nitrite, and nitrate. In Bahía Concepción, Gonyaulacales and Scrippsiella trochoidea cysts are present during declines in algal blooms as a mechanism to counteract adverse conditions, and to secure an inoculum for blooming when favorable conditions return. In contrast, G. catenatum cysts maintain the motile stage over prolonged periods with recurrent germination.

Dinoflagellate Cysts in Recent Sediments from Bahía Concepción, Gulf of California

Abstract The composition, abundance, and distribution of dinoflagellate resting cysts in recent sediments were analyzed at 12 sites in Bahía Concepción in the subtropical Gulf of California. Calcareous and organic Peridiniales, Gonyaulacales, and Gymnodiniales were identified at species level (25 cyst types). Empty cysts constituted 75–90% of cysts in the samples. Cyst assemblages were dominated by calcareous Peridiniales (30–70%) and Gonyaulacales (13–44%), represented mainly by Scrippsiella trochoidea and Lingulodinium polyedrum. In the first centimeter of sediment, cyst counts varied from 173 to 9, 933 cysts g−1 wet weight, and increased in abundance in the inner area of the bay. Cysts of the toxic species Gymnodinium catenatum were also detected, and successful cyst germination of Alexandrium margalefii is described. Cyst abundance and distribution patterns suggest that the bay acts as a cyst trap, and that the cyst assemblages reflect the local community of meroplanktonic dinoflagellates.

Variations of PSP toxin profiles during different growth phases in Gymnodinium catenatum (Dinophyceae) strains isolated from three locations in the Gulf of California, Mexico

In vitro experiments were performed with Gymnodinium catenatum Graham strains isolated from three locations in the Gulf of California to determine the variability in toxicity and toxin profiles. Strains were cultivated in GSe at 20°C±1°C, 150 μmol photons·m−2·s−1 (12:12 light:dark cycle), and harvested during different growth phases. Growth rates were higher than in previous studies, varying between 0.70 and 0.82 day−1. The highest cell yields were reached at 16 and 19 days, with maximum densities between 1090 and 3393 cells·mL−1. Bahía de La Paz (BAPAZ) and Bahía de Mazatlán (BAMAZ) were the most toxic (101 pg STXeq·cell−1), whereas strains from Bahía Concepción (BACO) were the least toxic (13 pg STXeq·cell−1). A strain isolated from cyst germination was one of the least toxic strains. No significant changes in toxin content with culture age were observed (0.2 and 0.6 pmol paralytic shellfish poisoning·cell−1). All strains contained neosaxitoxin (NEOSTX), decarbamoyl‐saxitoxin (dcSTX), decarbamoyl‐gonyautoxin‐2,‐3, (dcGTX2‐3), N‐sulfo‐carbamoylsaxitoxin (B1), N‐sulfo‐carbamoylneosaxitoxin (B2), and N‐sulfo‐carbamoylgonyautoxin‐2,‐3 (C1‐2). Bahía Concepción strains had the highest content of C1; BAPAZ and BAMAZ strains had a higher percentage of NEOSTX. Differences in toxin composition with culture age were observed only in BAMAZ and BAPAZ strains. Cultures with a higher percentage of long chains had more NEOSTX, while those with a higher proportion of short chains had a lower content of NEOSTX. Gulf of California strains are characterized by a high proportion of NEOSTX, and seem to have evolved particular physiological responses to their environment that are reflected in the toxin profile, suggesting different populations.

Hemolytic activity and fatty acids composition in the ichthyotoxic dinoflagellate Cochlodinium polykrikoides isolated from Bahía de La Paz, Gulf of California.

The hemolytic activity of the dinoflagellate Cochlodinium polykrikoides from Bahía de La Paz, Gulf of California was investigated as part of the ichthyotoxic mechanism of this microalga. Two different kinds of erythrocytes, fish and human, were tested for the hemolytic assay. Since fatty acids have been associated with hemolytic activity in C. polykrikoides, the composition of fatty acids of this dinoflagellate was also analyzed. The concentration of C. polykrikoides causing 50% hemolysis (HE(50)) was 4.88 and 5.27x10(6) cellsL(-1), for fish and human erythrocytes, respectively. According to the standard curve of saponin, an equivalence between the hemolytic activity of saponin and the dinoflagellate concentration was found with 1mug saponinmL(-1) equivalent to 1x10(6) cellsL(-1) of C. polykrikoides. The polyunsaturated fatty acids: hexadecaenoic (16:0), docosahexaenoic (22:6 n3) and octadecapentaenoic (18:5 n3) were found in an abundance of approximately 62% of total fatty acids.

Toxic effect of the harmful dinoflagellate Cochlodinium polykrikoides on the spotted rose snapper Lutjanus guttatus

The dinoflagellate Cochlodinium polykrikoides isolated from Bahía de La Paz, Gulf of California, showed an important short‐term toxic effect on the spotted rose snapper Lutjanus guttatus. This microalga was able to decrease fish liver catalase activity and lipid peroxidation. Fish exposed to live dinoflagellates developed an abnormal mucus secretion on the gills that was directly related to algal cell concentration. Hepatic catalase inhibition and an increase in mucus secretion on the gills occurred when fish were exposed to 2 × 106 cells L–1 of C. polykrikoides. Lipid peroxidation was significantly different at 4 × 106 cells L–1 and the hepatosomatic index decreased at 3 × 106 cells L–1. Our results suggest that oxidative stress contributes, at least in part, to the ichthyotoxic effect of C. polykrikoides from the Gulf of California.

Factors associated with moderate blooms of Pyrodinium bahamense in shallow and restricted subtropical lagoons in the Gulf of California

Abstract We examined the environmental and biological factors related to blooms of the toxic dinoflagellate Pyrodinium bahamense in three shallow, restricted subtropical lagoons in the Gulf of California during the rainy summer. In the San José, Yavaros, and El Colorado lagoons, the vegetative stage peaked at 63, 108, and 151 (×103 cells l-1), respectively. At San José, production of cysts peaked at 9.7×103 g-1 of dry sediment mass as the bloom declined. Large diatoms predominated, with P. bahamense the most common dinoflagellate during the blooms. Abundance of P. bahamense at San José was positively correlated with salinity (r=0.50, p=0.0003), seawater temperature (r=0.44, p=0.005), silicates (r=0.45, p=0.003), and ammonium (r=0.32, p=0.005), and negatively correlated with dissolved oxygen (r=-0.34, p<0.0001). No such correlations were found at El Colorado and Yavaros. The environmental window that favors development of blooms is restricted to the summer and is influenced by seawater temperature, salinity, and relative concentrations of ammonium and phosphates that, in turn, depend on rainfall and runoff, which is greater on the eastern side of the Gulf where seawater quality is degraded.

Cyst morphology, germination characteristics, and potential toxicity of Pyrodinium bahamense in the Gulf of California

Abstract Pyrodinium bahamense is a meroplanktonic dinoflagellate that produces paralytic shellfish toxins that cause human poisoning along tropical and subtropical coasts. Cyst morphology, germination characteristics, and toxicity were investigated using samples from Isla San José in the Gulf of California. Morphology was observed through light and scanning electron microscopy. Germination was tested at different temperature (15°C–35°C) and salinity (15–35) conditions in different culture media (natural seawater, GSe, and f/2). To elucidate toxicity of vegetative cells grown from cyst germination, nine strains were subject to toxin analyses through fluorescence high-performance liquid chromatography. Morphological features and size of cysts generally agree with previous descriptions, particularly morphotypes found in the subtropical North Atlantic, where P. bahamense var. bahamense occurs. Cysts exhibit thermophilic and euryhaline characteristics. Highest germination occurred from 20°C to 35°C with the peak between 25°C and 30°C. Excystment occurred at salinities from 20 to 35. Germination occurred in the three culture media, but was highest in the optimal temperature range in the culture medium that included terrestrial soil extract and selenium. Only one strain exhibited toxicity with high saxitoxin concentration (95 pg STX eq cell-1).

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.