Monterey Bay Aquarium Research Institute
Marine Botany

Chondracanthus Aquaculture

Economically valuable algae?
    Who would have thought?  In fact, the economically important polysaccharide found in C. exasperatus, carageenan, was estimated in 1991 to have generated $100 million dollars and involved the consumption of 250,000 tonne of algae per year (Lobban and Harrison, 1997). Carageenan, is one of the two most economically valuable red algae products, the other being agar, and the demand for both substances has risen to the point where it justifies aquaculture endeavors.  Carageenan has a gelling ability and is often used in pharmaceutical applications, cosmetics and the food industry, both as a food substitute and a food stabilizer.  This last area may be the greatest source of demand for carageenan, as it has a lesser stiffening ability than agar and is thus more applicable for stabilizing food stuffs at a gel phase.  For example, carageenan is increasingly used to stabilize dairy products such as milk and ice cream, as well as instant puddings, creams, and sauces which need to gel without refrigeration (Lee, 1980).

The product: Carageenan
    Carageenan is a phycocoloid comprised of two components, kappa-carageenan and lambda-carageenan, both of which are negatively charged polymers.  Together the two principal components, kappa and lambda-carageenan, form a gel when heated or cooled in the presence of potassium ions.  Kappa carageenan has been found to be the sole gelling component, an important distinction as the relative concentrations of the two components vary between species and life history phases of the same species.   For example, in C. exasperatus, the relative kappa carageenan content of a gametophyte is much higher than the relative concentration in a tetrasporophyte, making the gametophyte the more valuable phase economically.  Because C. exasperatus is isomorphic, identifying the different life history phases requires microscopic analysis or chemical tests, such as the resorcinol test (Lee, 1980).

The development of field cultivation methods
    Scientists at the University of Washington, specifically J. Robert Waaland, have been especially active in exploring the possibilities for C. exasperatus aquaculture.  C. exasperatus has high aquaculture potential because it is large, abundant, and has a high carageenan content.   Attempts at developing C. exasperatus as a commercial crop have had to start at ground one, because there are no traditional aquaculture methods for this species.  The major limiting factor in C. exasperatus' s growth rates is the availability of appropriate rock substrate, and thus efforts have focused on growing this algae on artificial substrates.  Not only would this procedure allow algae to be cultivated more widely than the limitation of substrate availability allows, but using artificial substrates would also simplify harvesting procedures.
    Attempts have been made to grow C. exasperatus on a number of artificial substrates with general success.   The first trial was to grow thalli transplants on plastic lines.   These transplants were successful and also indicated the maximum growth depth and season for C. exasperatus, which were 3m below M.L.L.W. (mean low low water) and spring through summer  respectively.  Frame transplant trials were also found to be successful (Waaland, 1973).
    The next step to investigate was spore colonization.   This was accomplished simultaneously by studying spore colonization in the field on various artificial substrates (including nylon and polypropylene lines, nylon webbing, and concrete blocks) and spore colonization in the laboratory under controlled conditions with subsequent transplanting to the natural world.   Both techniques were successful at increasing understanding of small scale aquaculture techniques for C. exasperatus, and opened the door for larger scale cultivation studies.

Large Scale Cultivation
    Large scale cultivation techniques for C. exasperatus have since been designed.   Overall, this algae has been found to be an attractive species for aquaculture as it propagates readily vegetatively and can probably produce two harvests if harvested at the beginning and end of its growth season (early summer to late summer).  Below is an outline of proposed cultivation techniques in natural waters.

  • Stock Selection: This step has led to the isolation of a fast-growing strain of C. exasperatus, now commonly used.                            
  • Site Selection: Growth in small test frames to test site suitability.
  • Tank Growth: Laboratory germination and holding of germlings for early growth.
  • Outplant:  Transplant of germlings to nets, either surface of bottom in natural waters.
  • Harvest from Net: So far only accomplished successfully for surface nets.   Multiple harvests during one growing season (ie. at beginning and end of summer) found to extend and increase growth.

Alternative cultivation techniques have also been proposed in tanks or ponds, which would be filled with seawater and aerated.  Aquaculture efforts with C. exasperatus according to these techniques have also been successful, negating concerns that year-round cultivation might be unattractive because of difficulties in maintaining adequate winter species density (a problem run up against with many other similar red algae species) (Mumford and Waaland, 1980).

Extraction
    One of the benefits of cultivation is that the harvest can be guaranteed to be uniform in life history phase (ie. uniform in major carageenan type), which makes extraction and processing easier.  Once harvested, C. exasperatus is dried and then washed with freshwater.   This reduces the salt concentration before the alga is boiled.   Carageenan is readily soluble in hot, but not cold, water, and thus must be separated from the water and insoluble residue by a centrifuge.  Finally, the product is filtered and any remaining water is evaporated.  At this point, the carageenan goes to a baler, where it is shipped to the processor, or to a mill, where it is converted to powdered form (Mumford and Waaland, 1980).

Ecological Problems and Solutions:
Ecological:  Initial germination of C. exasperatus seedling was found to be disrupted by diatom fouling. The diatoms would shade out the new germlings, and efforts to dry the nets were ineffective as the diatoms were more resistant to desiccation than the germlings.  Small snails, such as Lacuna, Callistoma, and Lirularia, were first considered to be possible herbivores of the net cultures, however, they were actually found to serve a positive function in initial germling growth.  At this stage, growth is too rapid to allow the snails to settle on the germlings, however they are responsible for limiting diatom populations and thus reducing fouling.  The second major ecological problem facing cultivation efforts is the shading by drifting kelp, specifically Laminaria. This problem was dealt with by the replacement of submerge for floating frames, decreasing the amount of shading by floating kelp and thus maintaining adequate light for growth (Mumford and Waaland, 1980).

  [ C. exasperatus Home | Marine Botany Home ]
Last modified: 3/18/99
©1999 Devon Lake