Paralytic shellfish toxins in the chocolata clam, Megapitaria squalida (Bivalvia: Veneridae), in Bahía de La Paz, Gulf of California

Occurrence and toxic profiles of paralytic shellfish toxins (PST) in the chocolata clam Megapitaria squalida were investigated. From December 2001 to December 2002, 25 clams were obtained monthly from Bahia de La Paz, Gulf of California. Additionally, net (20 microm) and bottle phytoplankton samples were also collected to identify toxic species. Toxins were analyzed by HPLC with post-column oxidation and fluorescence detection. Toxicity in the clam was low and varied from 0.14 to 5.46 microg/STXeq/100 g. Toxicity was detected in December, March, April, June, and August. Toxin profile was composed mainly by STX, GTX2, GTX3, dcGTX2, dcGTX3, C2, dcSTX and B1. Gymnodinium catenatum was the only PST-producing dinoflagellate identified in the phytoplankton samples throughout the study period. G. catenatum was observed mainly in net samples from December 2001 to December 2002; however, in bottle samples, G. catenatum was only observed in five months. Highest abundance (2600 cells l(-1)) was observed in March and the lowest (160 cells l(-1)) in June. G. catenatum mainly formed two-cell chains and rarely four or eight. The presence of PST in net phytoplankton samples support the fact that G. catenatum is the main source of PST in the clams. This study represents the first report of PST toxins in the chocolata clam from Bahia de La Paz.

The use of pigment "fingerprints" in the study of harmful algal blooms

Along the Mexican coast, harmful algae blooms (HAB) have become more frequent, and therefore, there is an urgent need to establish monitoring programs to avoid the undesired consequences of HAB in human and natural ecosystems. In this work, we analyzed the pigment signatures and the species composition from phytoplankton samples to evaluate the utility of the specific pigment "fingerprints" in HAB monitoring programs. Vertical profiles from a coastal lagoon and temporal samples of a red tide occurring in a shrimp-culture pond and in a coastal zone were taken into consideration. Between 76% and 84% of dinoflagellate and diatom cell density was explained by their specific signature variation, in both vertical and temporal samples. Only the variation of zeaxanthin and the cyanobacteria Anabaena sp. showed a poor relationship, probably from difficulties in counting other cyanobacteria present in the samples examined with the microscopic method. These results suggest that inclusion of pigment analysis in the study and monitoring programs dealing with harmful algae would be very useful.

Blooms of Cochlodinium polykrikoides (Gymnodiniaceae) in the Gulf of California, Mexico

Cochlodinium polykrikoides was the species responsible for the discoloration that occurred between September 15th and 27th, 2000 in a shallow coastal lagoon located in the southern part of the Bahia de La Paz, on the west side of the Gulf of California. Blooms of C. polykrikoides were observed four days after two rainy days with a seawater temperature of 29 to 31 degrees C. Nutrient concentration ranges during the bloom were 0.165-0.897 microM NO2+NO3, 0.16-3.25 microM PO4, and 1.0-35.36 microM SiO4. Abundance of C. polykrikoides ranged from 360 x 10(3) to 7.05 x 10(6)/cells l(-1). Biomass expressed in terms of chlorophyll a was high, ranging from 2.7 to 56.8 mg/m3. A typical dinoflagellate pigment profile (chlorophyll a and c, peridinin, diadinoxantin, and beta-carotene) was recorded. In this study, the red tide occurred in front of several fish and shrimp-culture ponds. No PST toxins were found in the samples. However, 180 fish were found dead in the infected fish-pond; the gills were the most affected part. C. polykrikoides is a cyst-forming species that recurs in this area. New blooms were observed in November 2000 and September-November 2001 in the same area. Anthropogenic activities, such as eutrophication caused by water discharge in this shallow lagoon, and nutrient enrichment in the culture ponds, as well as effects from precipitation and wind stress, could have favored the outbreak of this dinoflagellate.

[Stomach content of Spondylus leucacanthus (Bivalvia: Spondylidae) and its relationship with reproduction and phytoplankton in Isla Danzante, Gulf of California]

During 1994 we collected specimens of Spondylus leucacanthus near Isla Danzante, Gulf of California. We measured seawater temperature, and sampled stomach contents and phytoplankton. The reproductive season was assessed through the gonadic index. There is a cool season from December to May and a warm season from June to November. The stomach content was composed of detritus (60%), phytoplankton (30%), and unidentified materials (10%). The highest abundance of phytoplankton cells in the bottom water and the stomach content were in March, April, and May, during the seasonal change of temperature. The gonadic index showed a single peak, confirming that the population has an annual pattern of reproduction. The start of gametogenic phase and maturity in the population coincide with the abundance of phytoplankton.