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Audra Kristofik
Tropical Marine Ecology
30th April 2009
Tropical Marine Algae of Florida and the Bahamas
Introduction
According to the Biology-Online Dictionary, the definition of Algae is, ÒA group of aquatic, photosynthetic, eukaryotic organisms ranging from unicellular to multicellular forms, and generally possess chlorophyll but lack true roots, stems and leaves characteristic of terrestrial plantsÓ. The number of algal species is estimated to be between one to ten million and most are microalgae (Baranti & Gualtieri, 2006). Most algal groups are considered photoautotrophs, meaning that they get their food and nutrients from the sun through photosynthesis. All algae contain chloroplasts, which pick up the energy from the sun to go through photosynthesis Algae are dependent on solar radiation into the water therefore algae can only grow near/on the surface of the water (Round, 1981). Algae are autotrophic therefore habitats that are not exposed to solar radiation are unlikely to support algal growth. However, some are heterotrophic but are very rarely seen. Depending on the algal type, the method of reproduction can be vegetative, asexual, or sexual by means of alternation of generations. Algae are a very important part of the ecosystem, serving as sources of life for many organisms including symbiotic relationships. Algae can also pose serious problems like coral bleaching and algal blooms that can be caused by human impacts on the environment (Duddington, 1966).
Blue-Green Algae:
The phyla, Cyanophyta, are more commonly known as blue-green algae, has gotten its name from the most prominent member of this phyla, Cyanobacteria. Cyanobacteria is a photosynthetic bacteria that can aid in nitrogen fixation of many plants, also a member of the kingdom bacteria. This sub-phylum of algae has been on the Earth for more than 500 million years ago and many species have remained the same to this day (Duddington, 1966). More recently, scientists have established a different view of the relationships between the cyanobacteria and blue-green algae. Blue-green algae and the bacteria can now be seen in the same group, prokaryotes (Lewin, 1976). They are the most widely distributed of any other group of algae, usually found in intertidal zones.
Characteristics of blue-green algae are those of the most primitive life forms on Earth, cyanobacteria (Humm & Wicks, 1980). Blue-green algae contain chlorophyll a and three biliprotein pigments: C-phycoerythrin, C-phycocyanin, and allophycocyanin, which give them their color (Humm & Wicks, 1980). Pigments are not contained in chloroplasts but dispersed throughout the cytoplasm of the cells (Duddington, 1966). They may also be other colors such as red, bright yellow, pale violet, purple, and black due to proportion of pigments (Boney, 1966). Their cell walls contain pectin and cellulose for strength (Boney, 1966). Blue-green algae are obligate autotrophs, meaning they depend on light for energy and carbon dioxide as a carbon source. They reproduce by asexual reproduction, where they experience alternation of generations. Alternation of generations is when a plant spends half of its life in a haploid stage (n) and half of its life in a diploid stage (2n) (Boney, 1966). Some species of these algae are found free-living but most grow on or in other algae (Duddington, 1966). The major threat blue-green algae pose to the environment is the formation of plankton blooms also called red tides (Dawes, 1974).
Green Algae:
Phylum Chlorophyta consists of green algae, the most diverse of all algae phyla. There are over 5000 species of green algae, only 20% living in marine environments (Dawes, 1974). They are found primarily in shallow water. Green algae are believed to be the ancestors of land plants, sharing common characteristics such as having a cell wall, similar pigmentation, and food storage. Green algae have cellulose as their cell walls which serve as a secondary barrier to the outside and gives extra strength. Green algae contain principle pigments chlorophyll A and B with trace carotenoids, that give algae their green color. They also store their food as starch like most land plants. This phylum is distinguished by its photosynthetic pigments, chloroplast structure, and flagella (Sze, 1998). The main structure used in photosynthesis is the chloroplast. The chlorplast has an envelope of two membranes indicating endosymbiosis of cyanobacteria (blue-green algae). Lastly, green algae usually have two or four flagella used for movement in reproduction and daily life. There are four subgroups of green algae, two that live in a marine habitat (Prasinophyceae and Ulvophyceae) and two that live in a freshwater habitat (Chlorophyceae and Charophyceae) (Sze, 1998).
Golden Brown/Brown Algae:
Golden Brown algae are contained in the Phylum Chromophyta and brown algae phylum is Phaeophyceae (Sze, 1998). The most familiar and largest algae phyla (Duddington, 1966), there are approximately 1500 species of brown algae. The majority being found in cold temperatures to arctic marine waters (Dawes, 1974). The chromophytes are divided into seven classes distinguished by sell coverings, pigments, and complex multicellular contruction in the phaeophyceae (Sze, 1998). Golden brown algae are the largest and most complex plant bodies observed in the algae- not unicellular or colonial (Boney, 1966). Chromophyta algae contain chlorophylls a and c, and heterokontous flagellated stages. The carotenoid fucoxanthin is an important photosynthetic pigment that gives cells their brown color. Colors range from dark or golden brown to olive green (Boney, 1966). Phaeophyceae also contain polyphenolics, compounds that protect brown algae from herbivores and parasites. The life cycle of brown algae is alternation of generations (sexual and asexual generations) (Smith, 1969). Brown algae are used in many commercial products and are cultivated for food in Asia (Sze, 1998).
Red Algae:
Red Algae are found in the phylum Rhodophyta. This phylum mostly consists of seaweeds but also included free-living unicellular microalgae. Rhodophyta are most abundant in tropic and subtropical regions of the ocean (Dawes, 1974). They pertain to coastal marine ecosystems but can also be found in freshwater and terrestrial environments (Baranti & Gualtieri, 2006). Red algae are the most exclusively marine with less than 2% living in freshwater (Dawes, 1974). Red algae are unique because they do not have a flagellated stage of development and their main storage component is Floridian starch unlike all other algal phyla (Baranti & Gualtieri, 2006). Floridean strarch is the way red algae store their carbohydrates (Dawes, 1974). Most Rhodophytes are photoautotrophic and have an asexual reproduction system meaning they divide and multiply. Red algae are divided into two subclasses: Bangiophycidae and Florideophycidae. Pigments in red algae are localized in one or more plastids (Smith, 1969). The only chlorophyll found in this phylum is chlorophyll A and phycobiliproteins: R. phycoerythrin and R. phycocyanin that mask other pigments and give algae their red color (Boney, 1966). Under field conditions red algae appear to be brown or even green (Boney, 1966). Rhodophyta are deep-water seaweeds, growing at the greatest depth possible for plant life because they donÕt need the same amount of light as other algal species (Duddington, 1966). Red algae experience triphasic alternation of generations, having two sporophyte (sexual) generations (Boney, 1966). Scientists have noted that Rhodophyta fossils show a lack of affinity with any other algal species meaning they have evolved along their own specialized line of phyla (Boney, 1966). Over the past few decadeÕs red algae has been grown for food purposes or harvested as phycocolloids which are used in a variety of commercial products (Sze, 1998). They are also harvested for extracts (Dawes, 1974).
Algae and Florida/Bahamas:
Around Florida and the Bahamas, species from all phyla described can be found. In Florida, the brown algae flora is best developed in the winter months in shallower, cooler waters (Dawes, 1974). Red algae are also recorded to grow at record depths, 300 ft., in this area due to the high light intensity and clear waters (Duddington, 1966). The highest concentration of algae especially the free-living algal flora is found on the coral reefs (Round, 1981).
Coral reefs can be considered as an ecosystem of their own, with the array of plants and animals that live within and among them. When corals were first discovered they were considered a branch between plant and animal because they ate but also used photosynthesis to acquire their food. When taking a closer look at an individual coral, scientists discovered that each coral had millions of microalgae living inside called Zooxs. Corals were found to only obtain about 20% of their food on their own by filter feeding while the rest of their food and nutrients came from the photosynthetic algae living inside them. This is a very important mutualistic relationship that the Corals and Algae share. The algae supply food for the corals and the corals supply protection to the algae. However, this relationship can cause serious problems for corals. When corals can no longer keep up their part of the relationship, the algae will essentially pack up and leave their homes in the corals. When the algae leave, corals starve to death because their food supply is diminished. This is called coral bleaching. Coral bleaching can be caused from natural events but more likely is an effect of human contact and destruction of the marine ecosystems (Davidson, 1998).
Literature Cited
Baranti, L., & Gualtieri, P. (2006). Algae: Anatomy, Biochemistry, and Biotechnology. Boca Raton: Tylor and Francis Group, CRC Press.
Boney, A. (1966). A Biology of Marine Algae. London: Hutchinson Educational LTD.
Davidson, O. G. (1998). The Enchanted Braid. New York: John Wiley and Sons Inc.
Dawes, C. J. (1974). Marine Algae of the West Coast of Florida. Miami : University of Miami Press.
Duddington, C. (1966). Flora of the Sea. New York: Thomas Y. Cromwell Company.
Humm, H. J., & Wicks, S. R. (1980). Introduction and Guide to the Marine Bluegreen Algae. New York: John Wiley and Sons, Inc.
Lewin, R. A. (1976). The Genetics of Algae. Oxford: Blackwell Scientific Publications.
Round, E. (1981). The Ecology of Algae. New York: Cambridge University Press.
Smith, G. M. (1969). Marine Algae of the Monterey Peninsula. Stanford: Stanford University Press.
Sze, P. (1998). A Biology of the Algae. The McGraw Hill Companies Inc.
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