Marine Cyanobacteria: the undiscovered treasures of rocky shores
by Sanjay NagarkarCyanobacteria, also known as blue-green algae, comprise a unique group of micro-organisms whose distribution around the world is rivaled only by bacteria. These organisms were considered as algae due to their microscopic morphology, pigmentation and oxygen-evolving photosynthesis. This group with several other microalgae was treated with contempt as 'scum', since it was believed that these organisms had only nuisance value - fouling water bodies, causing disease and toxemia and causing unwary ecologists to slip over on wet rocks. Ecologists, however, started giving them respect as primary producers, in aquatic and marine systems and realized that without them no animal populations such as fish, molluscs etc. could exist.
With the development of sophisticated instruments such as the electron microscope it was realized that so- called blue-green algae are actually 'gram-negative bacteria' in their cell structure and chemistry and form a connecting link with algae by their pigment composition (chlorophyll a) and photosynthetic mechanism. These, along with bacteria and actinomycetes, constitute a group called 'prokaryotes' whereas the rest of the living organisms, irrespective of their plant or animal status, belong to another major group termed 'eukaryotes'. The discovery of the prokaryote nature of cyanobacteria coupled with the discovery that a number of these organisms are unique in not only having trophic independence for carbon but also for nitrogen, has evoked considerable interest in these organisms around the world.
In the marine environment, intertidal rocky shores are a rich potential habitat for cyanobacteria. Hong Kong rocky shores are no exception and are covered with various species of cyanobacteria throughout the year. In fact, in terms of primary producers, rocky shores in the tropics are dominated by cyanobacterial species. Due to their oxygen-evolving and nitrogen-fixing activities, cyanobacteria form the energy base of the rocky intertidal benthic food web. Cyanobacteria also provide the primary substrate with which all benthic organisms are in contact on rocky shores. Some of these cyanobacterial species contain toxins or secondary metabolites although they are generally of high nutritional quality and can, therefore, influence grazer distribution and abundance - and as a result, secondary production and community structure -on rocky shores.
Though having great ecological significance, biodiversity studies of cyanobacteria in general, and intertidal epilithic cyanobacteria in particular, were overlooked for many years in Hong Kong. Only two epilithic cyanobacteria were recorded from Hong Kong previously. When I arrived in Hong Kong in 1992 with my previous experience in microbiology, I took the challenge to explore the world of epilithic cyanobacteria in Hong Kong. With the help of excellent instrumental facilities (i.e. confocal laser and scanning electron microscopes), I recorded 44 cyanobacterial species from various rocky shores of Hong Kong (see references). My estimate is there will be more than 200 cyanobacterial species in my sample collection awaiting identification, many of which are new to science and all of them new records for Hong Kong. I was amazed to see such a vast biodiversity of epilithic cyanobacteria. The most interesting part of cyanobacteria diversity is the wide range of genera from unicellular to filamentous, nitrogen fixing to non-nitrogen fixing, all of which are present on Hong Kong shores. These are Aphanocapsa, Aphanothece, Brachytrichia, Calothrix, Chroococcus, Dermocarpa, Entophysalis, G/oeocapsa, Hormothamnion, Hyella, Kyrtuthrix, Lyngbya, Microcystis, Nodularia, Oscillatoria, Phormidium, Plectonema, Spirulina, Stichosiphon, Symploca and Synechocystis (see the attached check list).
Beside their ecological significance, cyanobacteria offer a great potential as organisms for biotechnology purposes. Cyanobacteria, until recently in oblivion, uncared for and unrecognized, have shot into fame and popularity owing to a host of their innate properties that make them ideal organisms for use in a variety of ways to meet our needs and to promise us a bright future. Among these potential biotechnological tools, it is the freshwater forms which have been most studied. Now, people have started realizing the scope available to harness the marine forms and to make them perform exacting tasks in varied areas such as chemical and dye, food, feed and fuel, fertilizer and medicine etc. Cyanobacteria have proved especially useful for the pharmaceutical industry. For example, debromoaplysiatoxin extracted from Lyngbya sp. shows antileukemia activity, sulfolipids extracted from Oscillatoria sp. show antiviral activity on the AIDS virus and an extract from Phormidium sp. shows antihepatitis B activity. Cyanobacteria are also used in wastewater treatment, pollution treatment, and ammonia and hydrogen gas production. Some species which have proved useful are present m Hong Kong, e.g. Lyngbya, Oscillatoria and Phormidium species.
Check list of intertidal epilithic cyanobacteria of Hong Kong
Aphanocapsa banaresensis Bharadw.
Aphanocapsa biformis A. Br.
Aphanocapsa elachista var. conferta West et G. S. West
Aphanocapsa littoralis Hansgirg
Aphanocapsa muscicola (Menegh.) Wille
Aphanocapsa senciacensis Frémy
Calothrix contarenii (Zanardini) Bornet et FlahaultCalothrix crustacea Thuret
Calothrix javanica de Wilde
Calothrix scopulorum (Weber et Mohr.) C. Ag. ex Born. et Flah.
Chroococcus minor (Kützing) Nägeli
Chroococcus turgidus (Kützing) Nägeli
Dermocarpa leibleiniae (Reinch) Bornet et Thur.Dermocarpa olivacea (Reinsch) Tilden
Entophysalis granulosa Kütz.
Gloeocapsa aeruginosa (Carm.) Kützing
Gloeocapsa crepidinum Thuret
Gloeocapsa pleurocapsoides Novacek
Gloeocapsa stegophila (Itzigs.) Rabenh
Hormothamnion enteromorphoides Grunow ex Born. et Flah.
Hyella caespitosa Bornet et Flahault
Kyrtuthrix maculans (Gomont) Umezaki
Lyngbya confervoides C. Agardh ex GomontLyngbya martensiana Meneghini ex Gomont
Lyngbya semiplena (C. Agardh) J. Agardh ex Gomont
Microcystis elabens (Bréb.) Kütz.
Microcystis fios-aquae (Wittr.) Kirchner
Microcystis robusta (Clark) Nygaard
Microcystis viridis (A. Br.) Lemm
Nodularia spumigena Mertens ex Bornet et FlahaultOscillatoria cf. earlei Gardner
Oscillatoria subbrevis Schmidle
Oscillatoria vizagapatensis C.B. Rao
Phormidium corium (C. Agardh) Gomont
Phormidium foveolarum (Montagne) Gomont
Phormidium fragile (Meneghini) Gomont
Phormidium tenue (Meneghini) Gomont
Plectonema terebrans Bornet ex Gomont
Scytonema cf. crustaceum C. Agardh ex Bornet et FlahaultSpirulina labyrinthiformis (Meneghini) Gomont
Spirulina subsalsa Oersted ex Gomont
Stichosiphon sansibaricus (Hieron.) Drouet et DailySymploca laete-viridis Gomont
Synechocystis pevalekii ErcegovicThere is an urgent need to describe the biodiversity of marine cyanobacteria in the light of their ecological significance and biotechnology potential. This urgency is only exacerbated by the vulnerability of cyanobacteria to environmental impacts and their possible depletion or extinction, as with other microalgae. Currently, together with Dr. Gray A. Williams I am documenting these species on an RGC funded project. Our research investigates their distribution patterns and possible causes of these patterns. We are also collaborating with Prof. G. Subramanian of the National Facility of Marine Cyanobacteria, Bharathidasan University, India to culture these species, and then Dr. Geoff Brown in the Chemistry Department (HKU), will isolate any novel compounds. Previous work on novel compounds from Hong Kong cyanobactefla by Geoff Brown and Charles Lee has revealed new chemical families which Charles and Benny Chan have shown to kill barnacle larvae. Such biocidal properties could be important in the antifouling industry and have applied uses. So, the next time you slip on a blue-green slick on the shore - don't swear -collect it! You may be sliding on a potentially very important species.
References
Nagarkar, S. 1998a. New Records of Marine Cyanobacteria from Rocky Shores of Hong Kong. Botanica Marina 41: 527-542.
Nagarkar, S. 1998b. New Records of Coccoid Cyanobacteria from Hong Kong Rocky Shores. Asian Marine Biology 15:121-127.
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