Harmful Algal Blooms (HABs) are becoming an increasing problem to human health and environment (including effects on natural and cultured resources, tourism and ecosystems) all over the world. In Mexico a number of human fatalities and important economic losses have occurred in the last 30 years because of these events. There are about 70 species of planktonic and non-planktonic microalgae considered harmful in Mexican coasts. The most important toxin-producing species are the dinoflagellates Gymnodinium catenatum and Pyrodinium bahamense var. compressum, in the Mexican Pacific, and Karenia brevis in the Gulf of Mexico, and consequently the poisonings documented in Mexico are Paralytic Shellfish Poisoning (PSP) and Neurotoxic Shellfish Poisoning (NSP). Although there is evidence that Amnesic Shellfish Poisoning (ASP), Diarrhetic Shellfish Poisoning (DSP) and Ciguatera Fish Poisoning (CFP) also occur in Mexico, these problems are reported less frequently. The type of phytoplankton and epiphytic microalgae, their toxins and harmful effects as well as current methodology used to study these phenomena are presented in this paper. As an experienced group of workers, we include descriptions of monitoring and mitigation programs, our proposals for collaborative projects and perspectives on future research.

The loculate ("chambered") valve structure of centric diatoms like Triceratium favus Ehrenberg has been mentioned time and again in the nanostructure literature. Here we draw attention to the fundamentally different alternative sandwich model nature developed in the genus Pleurosigma, where it is nonloculate. This has so far been overlooked in nanostructural studies. We suggest some mechanical aspects that would offer interesting avenues for experimental testing. The first description of the natural fabrication process ("morphogenesis") is presented. This begins with the development of the raphe sternum, which then acts as a rigid backbone. The inner layer of the sandwich-structured valve develops next, with relatively large +/- round single internal foramina not yet closed by a sieve membrane, in offset arrangement. This serves as a substrate for rows of stubby hollow pillars, also in offset arrangement. Then the outer layer of the sandwich develops and two different patterns ("coarse-mesh" and "stellate bridges") have been observed. At first, the external areolar foramina are relatively large and +/- oval, gradually filling up until the tiny slits characteristic of the genus remain. In Pleurosigma species with double internal areolar foramina, small bridges grow from the opposite margins of the single foramina until they fuse. The sieve-membranes then close the internal areolar foramina. The finished valve is a lightweight structure expected to offer excellent strength with parsimonious expenditure of the raw material-silica.

No abstract

Phytoplankton collected bimonthly by net during 1991-2 from the Sontecomapan lagoon (12 km long and 1"5 km wide), in the Gulf of Mexico, included four species and several forms of the diatom genus Ske]etonema. The spatial and temporal distribution of Skeletonema subsalsum, S. pseudocostatum and S. costatum in the lagoon varied with the salinity. S. subsa]sum was dominant in the rainy season (JulyFebruary), when salinity was 0-6 ppt. S. costatum was abundant in the adjacent marine zone, occasionally with S. tropicum, and occurred in the lagoon during the dry season (March) at salinities of 3"2-37"0 ppt. S. pseudocostatum was present the whole year showing a preference for brackish conditions (4-25 ppt). Morphological variation in three species was observed by light microscopy and studied in detail by electron microscopy. The shape of the external tubes of the fultoportulae, considered as an important taxonomic character, varied in S. subsalsum and S. pseudocostalum. We observed long threads in S. subsalsum and S. pseudocostatum, associated with unicellular or shortchained forms, probably to confer buoyancy. S. subsalsum, previously found only north of 40 ° N, is here reported for tropical waters. This is the first record of S. subsalsum and S. pseudocostatum in Mexico.

No abstract

No abstract

No abstract

Examination of net plankton samples from the Gulf of Tehuantepec (Mexican Pacific) yielded a rare tropical species of the genus Chaetoceros, C. buceros Karsten. This species is conspicuous because of its relatively large size, type of chain formation, and shape of the terminal setae. Electron microscopic study revealed other interesting characteristics: the intercalary values are more lightly silicified than the terminal valves and show a pattern of costae radiating form the center with various annuli (“central hyaline fields”) in the center of the valve face; both kind of valves are perforated by small poroids. Terminal valves possess several (21–30) slitlike and randomly oriented rimoportulae. Important morphological differences exist between the intercalary and the terminal setae. Morphological characters, comparision with related species, and the systematic position are discussed. A new section of the subgenus Hyalochaete, Conspicua, is proposed to include C. buceros.