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Fredericq, S., T. O. Cho, S. A. Earle, C. F. Gurgel, D. M. Krayesky, L. E. Mateo-Cid, A. C. Mendoza-González, J. N. Norris, and A. M. Suárez. 2009. Seaweeds of the Gulf of Mexico, Pp. 187–259 in Felder, D.L. and D.K. Camp (eds.), Gulf of Mexico–Origins, Waters, and Biota. Biodiversity. Texas A&M Press, College Station, Texas. •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 The marine macroalgae, or seaweeds, are a heterogenous group historically lumped together as “Protists,” an assem- blage 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 contradic- tory (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 A green seaweed, Acetabularia. After Taylor 1954. eukaryotic lineage that shares a most common ancestry with the Chlorophyta in the Plant lineage (Oliveira and The classification within the Rhodophyta at the ordi- Bhattacharya 2000). A second cluster, the Chromalveo- nal level is unstable and in a constant flux, more so than lata, comprises the Stramenopiles, in which the brown in the Chlorophyta and the Phaeophyceae, and it is cur- algae belong, in addition to diatoms, many zoosporic rently undergoing much taxonomic revision that has led fungi, and the opalinids, among others (Palmer 2000, Adl to proposals of new and recircumscribed orders (Adl et al. et al. 2005). Of the three seaweed groups, the red algae 2005). As misinterpretations of superficial similarities are unique in the Tree of Life in that they share a suite of have resulted in erroneous systems of classification at a characters that do not occur together in any other eukary- variety of taxonomic levels, molecular- based phylogenies ote, namely, a complete lack of flagellated stages including in the red, brown, and green algae each provide an inde- absence of centrioles, flagellar basal bodies, or other 9+2 pendent test of classification to the one based on mor- structures (Adl et al. 2005). The seaweeds exhibit a broad phological or ultrastructural evidence. Besides elucidat- variety of morphologies and life histories. Unlike green ing relationships, phylogenetic hypotheses inferred from plants, animals, and even brown algae, red algae have gene sequence data provide the critical framework for attained this diversity without having evolved true tissue studies of morphological character evolution and life his- differentiation (Hommersand and Fredericq 1990). The tory evolution. Hence, as is the case for other taxa previ- molecular and biochemical mechanisms of their develop- ously referred to as “Protists,” we have here opted to follow ment remain largely unexplored. a hierarchical system of listing the taxa from the Gulf of 187 188 ~ 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 Har- rison 1994). The cell walls of red algae consist of cellulosic fibers embedded in a matrix of nonfibrillar materials, the phy- cocolloids. 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 A green seaweed, Batophora. After Børgesen 1913. of beer, wine, and coffee; and in the cosmetic and medical industries (Zemke- White and Ohno 1999). Agarophytes Mexico without formal rank designations, such as “class,” that produce high- quality agar are found in the Gelidi- “subclass,” “super- order,” or “order”; this approach is cur- aceae and Gracilariaceae (Craigie 1990). rently the preferred decision primarily motivated by util- Carrageenans are used by the food industry as tex- ity, to avoid the common problem of a single change caus- ture modifiers because of their high viscosity and gell- ing a cascade of changes to the system (Adl et al. 2005). ing properties (Santos 1989, De Ruiter and Rudolph There are 10,000–20,000 accepted species names of 1997). It is the gelling- strength, kappa- type carrageenans seaweeds worldwide (Woelkerling 1990, Norton, Melko- that are much sought after by the phycocolloid industry nian, and Andersen 1996, Guiry and Guiry 2007). There (Knutsen et al. 1994). Current markets for kappa carra- are about 5900 validly accepted species of red algae; geeenan are concentrated in the food, dentifrice, pharma- of these, only 3 percent are freshwater. There are about ceutical, and cosmetics industries (Kapraun 1999). Eco- 1600 species of marine green algae and 1800 species of nomically important carageenophytes are members of brown algae listed in AlgaeBase (Guiry and Guiry 2007). the Gigartinaceae- complex and the Solieriaceae- complex Seaweeds are most common on hard- bottom habitats (McCandless 1978, Doty and Norris 1985). More and in marine environments, growing as epiphytes on other more, chemists are discovering that cell wall composi- algae, seagrasses, or mangrove roots, epizooic on animals, tion is highly correlated with revised systematic concepts epilithic on pebbles or rocky substrata, psammophilic in at every taxonomic level, and recent papers deal with the sand, or pelagic and drifting (Lüning 1990). They occur at integration of polysaccharide chemistry, anatomical fea- all latitudes from the Arctic to the Antarctic and occupy tures, and DNA sequences (Usov 1992, Liao et al. 1993, the entire range of depths inhabitable by photosynthetic Chiovitti et al. 1995, 2001, Fredericq, Hommersand, and organisms, from high intertidal regions to subtidal depths Freshwater 1996, Fredericq, Freshwater, and Hommer- as great as 268 m (San Salvador I., Bahamas, is the greatest sand 1999, Chopin, Kerin, and Mazerolle 1999). Alginates depth for known plant life) (Littler et al. 1985). are extracted from the cell walls of brown algae (Chapman Historically, the seaweeds were defined as taxonomic and Chapman 1980). groups based on their pigmentation. The red color in the Antiviral and anticoagulant properties of the insoluble red algae is due to the presence of phycoerythrin that re- polysaccharide fraction have been reported, which sug- flects red light, absorbs blue light, and masks the green gest promising antiherpetic activity (Caceres et al. 2000, chlorophyll a (Gantt 1990). The color varies according Lee et al. 2004). In Asia, seaweeds are important sources to the ratio of phycoerythrin to phycyocyanin and may of food with a high vitamin and protein content, such appear green or bluish from the chlorophyll and other as nori (Oohusa 1993). Many red algae metabolize poly- masking pigments. Because blue light penetrates water unsaturated fatty acids to oxidized products resembling to a greater depth than light of longer wavelengths, these the eicosanoid hormones from mammals (Wise et al. pigments allow red algae to photosynthesize and live at 1996). Because of their biological properties, seaweed- somewhat greater depths than most other algae (Ramus derived oxylipins have potential utility as pharmaceutical Fredericq et al. ~ 189 and research biochemicals (Gerwick et al. 1993, Fenical increases and other stresses, biotic reefs shift from coral 1997). to fleshy macroalgal- dominated communities with high Some seaweed species reproduce by vegetative frag- gross and net primary productivities (Miller and Hay mentation (Hernandez- Gonzalez et al. 2007) or spore 1996, Morand and Brian 1996). In this state, production formation, but most undergo a complex life cycle involv- of a calcified framework is low, and as a result of constant ing an alternation of generations. It was only after culture carbonate bioerosion, the reef begins to degenerate to a methods were introduced (von Stosch 1965) that it was more- or- less flat pavement. The transformation repre- finally verified that in most red algae there is a fundamen- sents serious environmental degradation, with the deli- tal linkage of the sexual system and a life history consist- cate balance between nutrients, grazing, and reef com- ing of three phases (Hawkes 1990). It has been argued that munity structure extensively studied in the past decades selection has favored the evolution of a triphasic life his- (Littler and Littler 2007). Whereas frondose macroalgae tory in red algae as a compensation for an inefficient fer- normally are rare on reefs because of intense grazing pres- tilization in the absence of motile gametes (Searles 1980, sure by herbivorous fishes, mollusks, crustaceans, and sea Maggs 1988). The comparative morphology of the great urchins, sparse mats of fast-growing, opportunistic fila- diversity of postfertilization fruiting body types, ranging mentous red and green algae and agal turfs usually are from simple to very complex, has traditionally formed the responsible for the