In lieu of an abstract, here is a brief excerpt of the content:

187  The marine macroalgae, or seaweeds, are a heterogenous group historically lumped together as “Protists,” an assemblage of taxa whose members typically lack true roots, shoots, leaves, seeds, or water-conducting tissues. They comprise the multicellular green algae (Chlorophyta), red algae (Rhodophyta), and brown algae (Phaeophyceae). Until very recently, the relationship among the Algae and other Protists remained inconclusive and often contradictory (Adl et al. 2005). Our understanding of algal phylogeny has dramatically increased with molecular evolutionary methods, and the latest research indicates that the Rhodophyta is a distinct eukaryotic lineage that shares a most common ancestry with the Chlorophyta in the Plant lineage (Oliveira and Bhattacharya 2000). A second cluster, the Chromalveolata , comprises the Stramenopiles, in which the brown algae belong, in addition to diatoms, many zoosporic fungi, and the opalinids, among others (Palmer 2000, Adl et al. 2005). Of the three seaweed groups, the red algae are unique in the Tree of Life in that they share a suite of characters that do not occur together in any other eukaryote , namely, a complete lack of flagellated stages including absence of centrioles, flagellar basal bodies, or other 9+2 structures (Adl et al. 2005). The seaweeds exhibit a broad variety of morphologies and life histories. Unlike green plants, animals, and even brown algae, red algae have attained this diversity without having evolved true tissue differentiation (Hommersand and Fredericq 1990). The molecular and biochemical mechanisms of their development remain largely unexplored. The classification within the Rhodophyta at the ordinal level is unstable and in a constant flux, more so than in the Chlorophyta and the Phaeophyceae, and it is currently undergoing much taxonomic revision that has led to proposals of new and recircumscribed orders (Adl et al. 2005). As misinterpretations of superficial similarities have resulted in erroneous systems of classification at a variety of taxonomic levels, molecular-based phylogenies in the red, brown, and green algae each provide an independent test of classification to the one based on morphological or ultrastructural evidence. Besides elucidating relationships, phylogenetic hypotheses inferred from gene sequence data provide the critical framework for studies of morphological character evolution and life history evolution. Hence, as is the case for other taxa previously referred to as “Protists,” we have here opted to follow a hierarchical system of listing the taxa from the Gulf of 187 9 Seaweeds of the Gulf of Mexico Suzanne Fredericq, Tae Oh Cho, Sylvia A. Earle, Carlos Frederico Gurgel, David M. Krayesky, Luz Elena Mateo-Cid, A. Catalina Mendoza-González, James N. Norris, and Ana María Suárez A green seaweed, Acetabularia. After Taylor 1954. 188 ~ Seaweeds (Rhodophyta, Chlorophyta, and Phaeophyceae) 1978). Green and brown algae lack phycoerythrin, and brown algae contain chlorophyll c in addition to chl a. In addition, the red, brown, and green seaweeds contain a suite of additional secondary pigments (Lobban and Harrison 1994). The cell walls of red algae consist of cellulosic fibers embedded in a matrix of nonfibrillar materials, the phycocolloids . The most abundant of these polysaccharides are referred to either as agars or carrageenans, and they are of economic importance (Abbott 1996). Agar finds its widest use as a solid microbiological culture substratum and in a range of laboratory applications. It is not used for nutritional value in food, but rather as an emulsifier as a pectin in preserves; as a clarifying agent in the production of beer, wine, and coffee; and in the cosmetic and medical industries (Zemke-White and Ohno 1999). Agarophytes that produce high-quality agar are found in the Gelidiaceae and Gracilariaceae (Craigie 1990). Carrageenans are used by the food industry as texture modifiers because of their high viscosity and gelling properties (Santos 1989, De Ruiter and Rudolph 1997). It is the gelling-strength, kappa-type carrageenans that are much sought after by the phycocolloid industry (Knutsen et al. 1994). Current markets for kappa carrageeenan are concentrated in the food, dentifrice, pharmaceutical , and cosmetics industries (Kapraun 1999). Economically important carageenophytes are members of the Gigartinaceae-complex and the Solieriaceae-complex (McCandless 1978, Doty and Norris 1985). More and more, chemists are discovering that cell wall composition is highly correlated with revised systematic concepts at every taxonomic level, and recent papers deal with the integration of polysaccharide chemistry, anatomical features , and DNA sequences (Usov 1992, Liao et al. 1993, Chiovitti et al. 1995, 2001, Fredericq, Hommersand, and Freshwater 1996, Fredericq, Freshwater, and Hommersand 1999, Chopin, Kerin, and Mazerolle 1999). Alginates are extracted from the cell walls of brown algae (Chapman and Chapman...

Share