Seaweed uses: the outlook for mariculture

Seaweeduses:the outlook for mariculture K. W. Gellenbeck and D. J. Chapman The decade of the 1970s heralded a major research effort into mariculture of economically important red and brown seaweeds. Limited and declining natural populations, lack of synthetic substitutes for the phycocolloids, and their upwardly spiralling costs have emphasized the need for more research in this area. Algal mariculture is now technically and scientifically feasible, but the economic realities are still undetermined. This article examines what is known about seaweed mariculture and discusses where future research efforts must go. To most people the topic of seaweeds (macroscopic marine algae) is very unfamiliar. To those of us fortunate enough to have the opportunity to investigate intertidal areas along a coastline, appreciation for the variety and intricate beauty of many of these plant forms is easily gained. However, the most common question put to anyone who studies these organisms is ‘What are they good for?’ The perhaps surprising answer is that they have been utilized for thousands of years for a wide variety of uses [I]. The most obvious use of seaweed material is for food. This utilization has reached its peak in Japan and other parts of the Orient where many different species are harvested for this purpose. Western civilization, on the other hand. has generally cultivated an aversion to consumption of ‘slimy algae’, making its marketing for this purpose difficult. In Wales and Ireland, however. laver (Porphyru umbiliculis) is a traditional delicacy. Many areas of the world use seaweed biomass as animal fodder rather than for human consumption. Other uses for seaweed biomass are as a fertilizer or as an energy source. Seaweed extracts and composts are applied to crops as a nutrient source For energy and soil conditioner. K. W. Gellenbeck,

B.S.

Is a Ph.D. candidate majoring in Phycology, at the University of California, Los Angeles. After his graduation from Arizona State University he spent a year as a Research Associate in Aquatic Biology. David. J. Chapman,

B.Sc., Ph.D., D.Sc., F.L.S.

Is a Professor of Botany at the University of Callforma. Los Angeles. Since earning his doctorate at the Scripps Institution of Oceanography in 1965, he has maintained his major interest in experimental phycology and biochemical evolution. Endeavour.NewSeries.Volume7.No.1.1983 (Cc. Pergamon Press. PrintedinGreat 0160.9327/83/010031-07503.00.

Britain1

production the biomass can be decomposed in an anaerobic digestion process producing clean-burning methane gas. The algal uses or products that most touch our lives are the mucilages and chemical constituents of the algal cell walls that are used commercially. Phycocolloids is the term used to describe these polysacchaiide agar. which include polymers carrageenan and alginic acid as the most widely used. These colloids, found principally in certain orders of the red and brown seaweeds (Table l), have considerable and widely varied uses. Their use for gelling, as in microbiological media support and commercial gelatin, is the most obvious, but applications as emulsifiers, thickeners, and stabilizers in foodstuffs and pharmaceuticals, and as water-holding agents in paper and textile printing are equally important. Demand for these products increases yearly, but increased availability probably will not be able to keep up with demand. Ecological pressure from thermal and chemical pollution, herbivores, over-harvesting of crops, and mankind’s tendency to ignore the fragile balance of marine communities have contributed to this lack of balance. ln the absence of synthetic substitutes (and there appear to be none developing in the foreseeable future), three major approaches to the supply problem are possible. These are the discovery and development of new natural sources; improved management of existing crops; and the artificial culture (mariculture) of phycocolloidproducing algae. The first approach appears to have the least future. While there are a number of algae that may yet prove to give very high phycolloid yields, this in itself is not sufficient. Such algae must grow in beds or areas that are readily and economically

harvestable, but the possibilities are very few. Crop management is the current favourite. This may include controlled harvesting procedures, control or eradication of herbivores, or the restocking of depleted beds. These approaches have been applied with most success to Macrocystis on the North American Pacific Coast. This work, originating principally in the laboratories of Wheeler North, has been described in detail elsewhere. We will focus our attention on the mariculture of phycocolloid-producing algae. Mariculture:

a resume

The idea behind mariculture is certainly not new. In its simplest form it is just the very large-scale culture of commercially useful algae to produce economically harvestable crops. Many algae can be maintained or grown on a or small scale in laboratories environments where the factors that control or influence growth and yield can themselves be monitored and varied. Expansion to large-scale systems (for example large outdoor ponds) will usually mean that many of into controls incorporated the laboratory systems to maximize yield must be sacrificed for economic reasons. Such systems must be regarded as only semi-controlled. Two basic types of mariculture systems have been investigated [5]. The first uses structures placed in coastal waters to anchor the algae, and is referred to as an open ocean system. The second uses shore-based facilities (tanks or ponds) as the culture vessels and supplies them with seawater pumped from, and returned to, the ocean. This is known as a semi-closed system. The most successful open ocean systems (Table 2) are those operating in Japan and China for the growth of algae for human consumption. The

31

TABLE 1

PRINCIPAL COMMERCIAL

Agar producers (Red Algae) Order: Nemaliales Gelidiella Gelidiopsis Gelidium Pterocladia Order: Gigartinales Gracilaria Carregeenin producers Order: Gigartinales Chondrus Eucheuma Furcellaria Gigartina Gloiopeltis Gracilaria Hypnea lridaea Ph yllophora

1 species 1 species Approximately 4 species Approximately

32

6 species

2 species 5 species 1 species Approximately 1 species Approximately 2 species 3 species 1 species

7 species 6 species

Algae)

concerned are mainly a red alga, marketed as nori, and various species of brown algae, mostly laminarians, marketed as kombu, wakame, etc. These operations use large embayments of relatively calm water strung with various styles of rope netting for algal attachment. The ropes are impregnated with spores or juveniles of the desired species before being deployed in the ocean; at harvest time they are simply pulled up. A similar type of culturing (pioneered by Max Doty) is conducted by family units in the Philippines for the growth of the red alga Eucheuma [3]. Small pieces of the plants are tied to the ropes and harvested after a sufficient growing period. These labour-intensive systems operate well in their current areas but the high labour costs in the United States and Europe would limit their applicability there. An open ocean system that is being investigated in the United States by Wheeler North’s group involves the development of an offshore kelp farm for the growth of the giant kelp Mncrocystis for conversion to methane gas. Large structures with ropes for plant attachment are to be supplied with deep, nutrient-rich water pumped to the area of the growing plants. Prototype units are currently being tested. Semi-closed systems in artificial enclosures were first pioneered for ChondruJ crispus in Nova Scotia by A. C. Neish. These studies have since been continued by Neish and a group Porphyra,

16 species

(Red Algae)

Alginate pioducers (Brown Order: Laminariales Ecklonia Eisenia Laminaria Macrocystis Order: Fucales Ascophyllum Sargassum

species

SOURCES OF ALGAL PHYCOCOLLOIDS

2 species 1 species Approximately 1 species 1 species Approximately

8 species

4 species

led by F. J. Simpson [ll, 13-161. A group at Woods Hole, Massachusetts (now at Harbor Branch Foundation, Ft Pierce, Florida), led by J. H. Ryther have also extensively studied semiclosed and semi-controlled large-scale mariculture of algae [9, lo]. The Woods Hole efforts were concentrated primarily on planktonic forms used as food for commercially demanded shellfish such as oysters. Their system consisted of large ponds fed continuously by fresh seawater. No TABLE 2

attempt was made to control temperature and illumination, natural ambient conditions sufficing. Additional nutrients were supplied through the continous addition of secondarily treated sewage effluent, an excellent source of nitrogen and phosphorus supplements. Simple calculations demonstrate that artificial control of temperature and light, and the addition of commercial nitrates and phosphates, are economically out of the question. Since the start of these pioneering investigations, a number of other systems have been tested, particularly on the Pacific coast of North America in California (J. E. Hansen, M. Neushul) and Washington (T. R. Mumford and J. R Waaland). These systems have emphasized the three basic requirements for economical mariculture: 1. Continuous outdoor operation under natural conditions of light and temperature. 2. Nutrient supplements, if any, provided only by natural sources (for example, sewage effluent). 3. Low energy input (= low technology), requiring minimal incorporation of energy systems such as stirring, pumping, harvesting. Many different species of algae have been successfully grown and maintained in various types of mariculture systems. A number of examples are given in Table 3. We will assume, then, that the mariculture of macroscopic marine algae is technically feasible on a small scale. In designing and planning a full size mariculture system, however, what are the principal problems and factors

MARICULTURE SYSTEMS IN CURRENT COMMERCIAL EXAMPLES OF PRINCIPAL UTILIZED ALGAE Red Algae

Brown

Algae

Direct harvesting from managed natural populations

Chondrus Eucheuma Furcellaria Gelidium Gigartina Gracilaria Hypnea lridaea Palmaria Porphyra Pterocladia

Ascophyllum Ecklonia Eisenia Laminaria Macrocystis Sargassum Undaria

Direct harvesting of populations established by outplanting of sporelings, spores, juveniles

Eucheuma Gloiopeltis Gracilaria Porphyra

Laminaria Undaria

Culture in enclosed systems

Chondrus Gracilaria

USE WITH

Green

Algae

Enteromorpha Monostroma Ulva

TABLE 3 ALGAL GENERA THAT HAVE BEEN GROWN IN SEMI-CLOSED MARICULTURE SYSTEMS Red Algae

Brown

Algae

Chondrus Eucheuma Gelidium Gigartina Gracilaria Gracilariopsis Hypnea lridaea Neoagardhiella Pa/maria Rhodoglossum

Sargassum

that must be considered? They fall into four major categories, namely capital cost of a production size facility; mechanical design and operation; considerations for maximum growth and yield; and the choice of alga. Obstacles production

to the development of size mariculture systems

Outside the success achieved by the Japanese and Chinese open ocean cultures systems described earlier, seaweed mariculture operations have not progressed much beyond smallscale experimental facilities. This is mainly due to our lack of understanding of the various operating parameters involved in a productionsize system that will determine its costeffectiveness and consistency of yield. These are the main items of concern for investors and engineers involved in the construction of such systems. The design of the physical plant of a culture facility is probably the most obvious factor affecting its cost and efficiency [2,7.X]. The most inexpensive design would be one using naturally occurring embayments and areas of relatively calm water that are easily accessible to workers and machinery. This approach, used extensively in the Orient, is impractical on many coasts (such as that of California) due firstly to a general lack of this type of coastal area and secondly to competition where they do occur, with other uses such as shipping, recreation, and residential land use by reclamation. Efforts to transform open ocean areas into suitable culture areas by providing substrate for attachment and adding a nutrient supply in some form have come up against considerable engineering problems. The currents and storm conditions of open-ocean waters require quite sturdy and consequently expensive equipment. Additionally, with rising energy, and costs the therefore transportation movement of men and machinery between onshore stations and offshore farms can be a substantial financial

consideration. An offshore location also does not eliminate the problems of conflict with shipping activity: large areas of ocean located suitably close to onshore facilities will probably coincide with existing shipping lanes. These problems have turned the bulk of investigations towards suitable designs for onshore facilities that use water pumped from the ocean. This type provides additional advantage in allowing a much greater degree of control over relevant factors such as water quality, flow rates, water depth, and nutrient levels. Work done in square or rectangular tanks has shown that the tank’s surface area rather than its volume is the factor most important to the plants’ growth, due to absorption of incident radiation by both the plants and the water column. Additionally, some source of agitation seems to be required to obtain optimal growth of the plants. This mixing probably provides adequate gas exchange, nutrient supply. and waste removal horn the mdivtdual plants by .eliminating localized depletions and allowing utilization of the entire water column. Commonly this agitation is effected by the use of compressed air distributed within the tank to cause circulation of the water. If this circulation is strong enough the plants themselves will move around the tank, a technique referred to as ‘tumble culture’. In addition to the agitation, this bubbling provides carbon dioxide to the plants for photosynthesis. Based on these requirements, two major designs for culture raceways have usually been used 18. 101. Successful results have been obtained with both types, but much further work is required to determine the optimal design. Perhaps the design will have to be varied in accordance with factors such as the species that is cultured, the location of the facility, and the TABLE 4 TYPICAL STOCKING DENSITIES” OF ALGAE GROWN IN ENCLOSED MARICULTUREb kg.m* Red algae

-

Chondrus crispus * Gelidium coulteri* Gigartina exasperata Gracilaria foliifera Hypnea musciformis lridaea cordata Neoagardhiella baileyi Palmaria palmata* Rhodoglossum affine

4-6 2.5-3.2 2.4-4.8 2-4 1.5-3.2 1 A-3.5 2.8-4.5 2.2-3.5 3.5

Brown algae Sargassum

3.3-4.5

m&cum*

a As wet weight b Dataabstractedfrom referenced literature * See figure 1.

Hansen eta/. 15land

machinery that needs to be used within the raceway. In either case, the raceways are usually laid out in elongated rectangles, allowing easy bank accessand also providing a linear flow through the system by means of inlets and outlets at opposite ends. This flow pattern is efficient in removing nutrients from the water as it flows by the plants. This becomes especially important when flow from a sewage treatment plant is used as the nutrient source (see below). A number of researchers have investigated stocking densities within semi-closed systems (see Table 4). There is an optimal stocking density, generally in the range of 2-5 Kg m-‘. Lower densities result in higher growth rates because the plants are not in severe competition with their neighbours for sunlight, nutrients, etc. However, the yield from any given tank area per unit time is lower than it would be if there were more plants in Conversely, the tank. excessive interfere plant densities with circulation, cause self shading, and encourage, through the restriction of water movement, epiphytism by other algae and invertebrates. In addition to a lowered growth rate, one may also observe disintegration of the plants, as in the case of Sargassum. An optimum density must be experimentally determined for each culture \pccics extremes in order to avoid these and

maximize

the

harvestable

viclcl

(Table 5). Harvest rates and inoculum density are interwoven. If the algal crop is harvested totally, then a fresh inoculum must be supplied. requiring in turn the utilization of an enclosure for the growth and maintenance of inocula. The alternative is a partial harvest, leaving behind part of the stock as the new inoculum. Most mariculture systems follow, or have followed, the former practice. In this way, the starting algae would be healthy, actively growing juveniles, instead of older, slower-growing mature plants. As a practical matter algae that can be grown from small vegetative fragments have a distinct advantage over those that must be started as sporelings from zygotes (result of fusion of male and female reproductive cells) or asexual spores. If a system that operates all the year round using the alternative partial harvest method can be developed it would be the most useful from a water treatment and biomass production viewpoint. The nutrient source is another of the factors in seaweed culture that bears heavily on the operating cost. Nitrogen, and to some extent phosphorus, seem to be the most 33

Figure 1 (a) Chondrus (f)Sargassum muticum.

crispus;

(b) Euchema

important elements, since in most oceanic surface waters they occur at levels too low (0.5 mg/l nitrate and 0.1 mgil phosphate) to meet the optimal growth requirements of the plants in an intensive culturing system. Temporal and seasonal fluctuations in the concentrations of these nutrients also occur. The addition of these and other nutrients has been effected in a number of ways. Deep ocean water from below the photic zone, which is much higher in nutrients, is one source that has been utilized in various projects. Though this source works TABLE 5

PRODUCTION,

gelidium;

(c) Gelidium

coulteri;

(d) Pa/maria

well in the cultures, the cost associated with pumping the water to the surface is becoming more and more restrictive as energy costs increase. Chemicals added in either a liquid or solid form have also been very effective for increasing plant growth but again, as with terrestrial agriculture, the cost of fertilizers is consistently rising. An ingenious alternative to these methods has been found in the use of effluent from secondary sewage treatment plants as a nutrient source. This work was pioneered by W. J. Oswald in the 19.50sin the culturing of

AS DRY WEIGHT, FOR ALGAE IN MARICULTURE

SYSTEMS

g.m *.day. ’ Red algae Chondrus crispust (T) Eucheuma striatum (F) Gelidium coulterit (T) Gigartina exasperata (I Gracilaria foliifera (Woods (T) Gracilaria sp (Florida)* (T) Hypnea musciformis* (T) lridaea cordata (F) (T) Neoagardhiella baileyi’ IT) U) (F) U)

Pa/maria palmatat Porphyra spt Rhodoglossum affine

Hole)

26-30 27 17 1 l-20 7-18 Late summer 7-l 6 12-17 4-14 23-26 6 Winter 26-40 Spring-Summer 24 3.6 12-30

(T) = lank or semi-closed culture (F) = Field or natural population * = Populations with nutrient enrichment. Values taken from the literature are averages, and are given as indication of a production potential. Values may be higher or lower depending upon season. t See figure 3.

34

palmata;

(e) Porphyra

nereocystis;

freshwater phytoplankton. A typical effluent, derived from residential sources, may consist of the following. Nitrate 1523 mg/l Nitrite 0.3kO.2 mg/l Ammonia O.SrtO.5 mg/l Phosphate 3041 mg/l In mariculture applications the effluent water is added to seawater in dilutions ranging from about 1:4 to 1:lO ratios of effluent to seawater. For many seaweed species the consequent salinity reduction causes little or no reduction in growth or viability of the plants. ‘There are a number of advantages in this technique. First, the nutrients are free, since treatment facilities normally discharge their effluent directly to some receiving body of water. Second, the discharge of these effluents falls under a number of environmental regulations that becoming are increasingly difficult for the local government agencies involved to meet. Utilization of the effluent in a culture system (a type of tertiary treatment) would greatly reduce this discharge problem, and result in an indirect cost benefit by reducing waste-water treatment costs. Capital investment costs could be shared by all the parties involved. Third, the nutrients introduced into the water before it enters the sewage system are recycled into a useable product rather than being sent as waste to areas where overloading of the natural aquatic systems can occur. As is usually the case, however, there are also disadvantages. Depending on their

source, effluents can contain various heavy metals, toxic organic residues, and perhaps viral contaminants that are not removed in the secondary treatment process. These may or may not be incorporated into the plants as they grow. If they are absorbed, adequate water treatment is achieved with a concomitant build-up of these This materials in the plants. problem generally contamination restricts use to residentially derived the where effluent, sewage concentration of these undesirable materials is usually much lower. Many agencies have strict government regulations about the use for human consumption or use of plant materials subjected to sewage effluent. This is a major handicap if the algae, or any other products from the system, are to be used for human consumption, but less so in the case of algal biomass used for industrial purposes (for example, phycocolloids or methane production). Procedures for the safe removal of these materials can be integrated into utilize the processes that the contaminated biomass. A further difficulty arises in locating the culturing facilities sufficiently close to both seawater and effluent sources such that the transportation of either does not become an economic liability. Trace element deficiency (for example iron) is a possibility that has received very little attention in mariculture systems to date. This can be attributed in most circumstances to our lack of understanding of the physiological requirements of the plants involved. Harger and Neushul [6] emphasize that it is important to study a potential mariculture species in its natural environment in order to understand its physiology and growth requirements before it is moved to a culture system. In the case of identifiable trace element deficiencies, there is probably no alternative to industrial supplementation with chemicals. A recurring problem for most culturing projects has been the problem of epiphytism, or the growth of undesirable algal and animal species on the crop plants. A foreign algal species will compete with the crop plants for light and available nutrients and can become a separation problem at harvest time and during later processing. The most common plant epiphytes are diatoms, microscopic unicellular algae with silica walls. These tend to form golden brown films across almost any surface in the system that is constantly moist, but their small size usually keeps them from becoming a major problem. Blue-green algae, usually filamentous forms, are also

common contaminants along the walls of culture chambers. The most troublesome epiphytes however, seem to be species of the genus a flattened tubular Enteromorpha, form of green alga, and other filamentous forms such as the brown alga Ectocarpus. These relatively quickly growing forms have a very wide range of salinity tolerance and compete well with most species under the appropriate conditions. They can cover the surface of cultured plants (shading them from incident sunlight) in a relatively short period of time. Using hand labour to clean off these epiphytes is burdensome and though some operations in the Orient are able to elnploy this technique, labour costs in much of the rest of the world make this approach impossible. The most direct alternative approach to control of the invaders would be the addition of algicides specific to unwanted species. This procedure has been found to be fairly effective, but the chemical content of the waste water is not acceptable. A much simpler method of control is a by-product of the agitation required for optimum nutrient usage. The motion of the plants and water seems adversely to affect the establishment of the juvenile invaders of the epiphytic species: consequently, they are moved through the system with the flow of the water rather than becoming established. Another relatively simple approach utilizes control of the nutrient supply to the system. A periodic pulsing of the nutrients, rather than providing a constant supply, seems to favour the growth of the desired crop, which can take up and store the nutrients when they are available much more effectively than the smaller epiphytes can. Periods of low or zero nutrient availability will stress the epiphyte population much more than the crop plants, and perhaps eliminate it completely. In the same way, simple shading of the system can at times be an effective deterrent by giving the crop plant a competitive advantage for light over smaller epiphytes. A final technique, one that has received relatively little attention so far, is the use of specific animal grazers in the system to feed selectively on the epiphyte population. Amphipods and snails have been used in cultures of red algal species with encouraging success, Further efforts in this area of biological control would probably lead to effective control methods in the same way as they have in the control of terrestrial agriculture pests (for example, the release of sterile individuals of a pest species in order to lower reproduction rates). The methods for control of animal

epiphytes are somewhat more limited. If the species involved do not feed directly on the crop plant there may be no need to control them if they do not affect growth or the processing techniques in any way. However, direct grazing on the plants must be controlled. The first point of control is in the seawater supply to the system. A filter system, such as sand, could be effective in keeping a population from ever becoming established. If this is not sufficient, another possibility would be ‘a biological control technique. If a predator species of some food value could be supported on the epiphyte enough profit could population, perhaps be derived from this alternate crop at least partially to offset the loss from the main crop. Even if a profit obtained, the could not be development of a fauna associated with the crop that was in some sort of ecological balance may serve to stabilize the system and control the epiphyte populations at a cost (represented by loss of some amount of the crop) that is lower than other methods. For either plant or animal epiphytization the selection of resistant crop plants would be desirable. The epiphyte problem can also be somewhat reduced by growing species that are relatively resistant to attack by plant or animal epiphytes. The best candidates for culture would therefore be species that support few epiphytes in nature or that remain clean in smallscale test systems. For animal epiphytes a number of anti-herbivore compounds are found in algae. These include phenolics and tannins in brown algae, and to some extent halogenated compounds in red algae. The benefit of these anti-herbivore compounds may be offset by interference with the use of the product-unpalatability for consumption or interferences to chemical extractions. Temperature affects the growth rates of the crop plants, but is one parameter that is very expensive to control. The water entering from a near surface level inlet in the ocean will take in water that varies in temperature according to the season of the year; changes in current and tide patterns; and periods of upwelling of deep, cold water. In addition, depending on the turnover rates of the seawater through the cultures (the lowest rates possible would minimize the cost of pumping the water), incident solar radiation would tend to raise the temperature of water that remained stationary in the system during daylight hours. This effect could be quite deleterious during summer periods in areas where the incoming water would already be relatively warm. On the other hand, in winter 35

conditions, especially in higher latitudes, this could combat potential freezing conditions. Operating routines that take these ideas into account could change the pumping rates in accordance with the conditions. Overheating problems could be combatted by either increased flow rates or shading of the water, but either of these could be prohibitively expensive. Proper designs of culture raceways may lessen this problem by providing sufficient depth to absorb the energy input without raising the water temperatures to unacceptable levels. Most research done so far has been in relatively mild climates. However, work with Chondrus in Canada was successful in maintaining seed stocks through the winter periods in tanks (both covered and uncovered) with circulating water as cold as -1°C. Pumping rates were kept relatively high to prevent freezing of the pipes. As alluded to earlier, selection of the species to be cultured may be the most important feature to be considered in culture systems since the attributes and requirements of the plants determine all the other parameters previously discussed. Members of the algal division Rhodophyta (the red algae) have been the most frequently investigated species. Gracilaria, Eucheuma, Chondrus, Iridaea, and Porphyra are some of the most prominent examples. The brown algae such as Macrocystis (the giant kelp), Laminaria, and Undaria have also been used, but mainly in open ocean systems. The product value of the plant biomass has the most direct bearing on the selection. Red algae are valuable for their food content in the case of the Japanese Nori industry (Porphyra), or for their carrageenan or agar content with most of the other investigated species. Similarly, the brown algal species are used for food (mainly in the Orient) or for their alginic acid content (almost exclusively from Macrocystis in the United States). With any of the phycocolloid extracts the quality, quantity, and ease of extraction are all important characteristics considered in the selection process. The vast majority of algae produce phycocolloids in the range of 15-35 per cent of dry weight. Values will of course fluctuate according to season, age of plant, and from one section of the alga to are noticeable another. There differences, for example, in alginate content between stipes, blades, and pneumatocysts (air bladders) in the brown algae. Tetrasporophyte plants of Chondrus and Gigartina have a very low k. A carrageenan ratio (less than one), whereas the gametophytes (male and female) typically have ratios of

36

1-4. Macrocystis has been the main organism investigated for methane production in the United States through the offshore kelp project, though other species of red and brown algae, whether before or after extraction of their phycocolloids, could be acceptable for bacterial digestion. In a very ingenious extension of this biomass-to-methane process, Ryther’s group [4] has utilized the residual supernatant effluent from the anaerobic digestion as a source of nutrient supplementation for further growth. Though the product value is of prime importance in species selection, it must be balanced against the ability of the species to be grown effectively and efficiently in an intensive culture system. With the design criteria discussed earlier, the ability of the plant to grow as a ‘free floater’ is required, because providing substrate for attachment is expensive in both construction costs and labour costs. Though relatively few species occur in this condition naturally (Sargassum spp. in the SargassoSea being the most prominent .examples) many species, especially within the red algae, seem to be capable of this type of growth. It should be pointed out, however, that phycologists know little about free floating algae. Inability to grow as a free floating form may be more imaginary than real. Related to this habit of growth is size, which is a restrictive factor for large kelps such as Macrocystis, Nereocystis, and Durvillea. However desirable they may be for their biomass and phycocolloid content, they simply do not lend themselves to semi-closed mariculture. Algae with long linear dimensions (long stipes with or without long blades) are ill-suited for tank growth as mature plants. Algae best suited for mariculture are those with a small busy life form, of which Chondrus crispus is a typical example. Such algae will circulate freely in tanks and will not interfere with water-flow patterns. Other algae such as Gigartina, Gracilaria, Iridaea, Hypnea, Eucheuma, l’terocladia, Gelidium, and Neoagardhiclla have a similar bushy

life form that is suitable for mariculture. Other requirements for an algal culture species concern the ability of the plants to tolerate the conditions economically attainable in a culture system (physiological adaptability). Most algae, especially those potentially suitable for mariculture, have definite physiological-environmental tolerances that restrict mariculture operations to the geographic limits of their natural distribution. There are, in fact, very few phycocolloid-containing genera or species that can be considered

cosmopolitan. Sargassum, and perhaps to a much lesser extent Gigartina, are the only genera that fall into this category. One well documented example that does have a full range of environmental versatility and geographical distribution is Sargassum muticum. In many respects this species is an ideal mariculture candidate and is currently being investigated in the author’s laboratory. If a single species was not found to meet all of the necessary criteria, perhaps a croprotation scheme could be utilized, species with different seasonal growth maxima being alternated with the major biomass producers as the seasons change. The biggest advances in terrestrial agriculture have come from breeding programmes that result in forms better adapted in crucial qualities, resulting in higher yield. In algal mariculture this type of work has not proceeded very rapidly. Most investigations have screened wild populations for individuals superior in desirable qualities, and then reproduced those individuals to create entire populations. The main technique used to obtain these identical copies of the individual plants (or clones) is vegetative reproduction of the plant body; that is, initiating growth from ‘cuttings.’ Unfortunately, not all species (for example, the large kelps) will readily undergo this process. If not, they need to complete their entire sexual mode of reproduction, a process which is much more difficult to control experimentally and is more time consuming. A notable result from this type of work was the discovery of a strain of Chondrus crispus (T4) by workers in Nova Scotia which grew more rapidly, stayed relatively free of epiphytes, and produced a higher percentage of carrageenan than harvested wild populations. This clone was successfully maintained and grown in a semi-closed mariculture system for a number of years, Successful strain selection has been achieved also with Gigartina exasperata (strain M-11) and Eucheuma. Genetic crosses to develop new forms have also been carried out on a limited basis. Most of this work has been done with brown algae, due partially to the relative complexity of the life cycle of members of the red algae. Encouraging results have been obtained so far with this type of genetic manipulation using Macrocystis and other related species. Much more work remains to be done in screening wild seaweed populations for new species and strains that are well adapted to mariculture applications. Caution is necessary in the use of valuable species in geographical areas where they did not previously occur, for the effect of a

newly introduced species on a naturally balanced community is not well understood. Recent examples include the explosive expansion of the Japanese endemic species Sargassum muticum to the west coast of North America and to England, and a proposal to introduce the giant kelp Macrocystis to the waters of Japan and China. Arguments both for and against this proposal have been strongly presented in publications. With our present knowledge we cannot predict the results of algal introductions and until this can be achieved, it may be advisable to avoid using foreign species in new areas and rely instead on endemic species. Another poorly understood aspect of seaweed mariculture is diseases. Any system growing a single crop (a monoculture) is extremely susceptible to a disease that can spread rapidly between the plants. An entire operation conceivably be could destroyed in a short period of time. The two most currently utilized seaweed species, Porphyra and Macrocystis, are both susceptible to serious disease. In Japan two fungal diseases, red wasting disease and chytrid disease, occur in epidemic proportions that destroy wide areas of Porphyra plantations. As with most fungal diseases, little can be done to destroy the pathogen once the infection is established. In Macrocystis beds, outbreaks of black rot and stipe rot (caused probably by either bacterial or fungal pathogens) can cause parts of the plants to slough away or break the holdfast, allowing the plant to float away. Current harvesting schemes of wild populations, by constantly trimming off the older more susceptible portions of Macrocystis plants, keep outbreaks to a minimum, but large scale artificial stands in the open ocean may present more difficult problems, especially from diseases attacking the attachments to artificial substrates. As mariculture systems expand and more species are put into culture the disease problem is going to become much more critical. One method of prevention would again be in species or strain selection. In most instances, however, some disease organism will sooner or later appear in any species and require treatment. The best prevention then may be to avoid a monoculture mode of operation and maintain heterogenous stocks of .several seaweed crops. This would help avoid epidemics that could be biologically and economically disastrous. Much more work is required in the area of diseases such as

the method of infection; host-pathogen interactions; host protection reactions; geographical distributions of pathogens; and life cycles of both hosts and pathogens. Conclusions

discussed here All the points concerning the problems facing the developments of production size mariculture facilities concern the economics of the system. The growing feasibility of seaweeds successfully in open ocean or semiclosed culture systems has been shown, but the reality of business economics is the one aspect that has, regrettably, received the least attention. The biggest obstacle seems to be obtaining reliable data on the parameters that determine the cost-effectiveness of a system. These include biomass and product yields; nutrient, water flow, temperature and duration requirements; crop values and market demands; construction and land costs; and utilities, maintenance and personnel expenses. These parameters must all be geared to maximize the yield and guarantee the consistent operation of the system. It is one thing to examine scientific feasibility devoid of economic reality, but mariculture is an economic matter, as is indicated by the following 1982 costs of algal phycocolloid derivatives in the United States. Agar powder Alginic acid Carrageenan (commercial) K-carragee,nan A-carrageenan i-carrageenan

$30 $30

per Kg per Kg

$40

per Kg

$88

per 1OOg

The economic information required will not be forthcoming until investigations pass from the small scale to pilot-scale production systems. These systems could contain a number of raceways with varying designs and facilities making it possible to vary most of other the necessary parameters. Once optimal conditions are worked out, long-term operation would simulate complete mariculture farms. Information on the feasibility of construction would then be concrete enough for investment decisions to be made and for full scale facilities to be constructed. While considerable information is being obtained on costs of capital equipment, materials and labour for maintenance and operation, and crop control and management techniques, we are woefully short of hard data on the monitoring of crop

and culture conditions, harvesting and processing of yield, marketing and sales, and cost/benefit aspects of the system. One final conclusion then is that is mariculture while seaweed technically and scientifically a reality with tremendous potential, economic viability is still doubtful. Now. however. is the time to lay a solid foundation and develop the procedures and parameters to make the jump to production systems. Bibliography

The literature on algal mariculture is quite extensive. Three symposium publications which provide very good summaries of the current state of the art are listed. Abbott, I. A., Foster, M. S. and Eklund, L. F. (Eds.). Pacific SeaweedAquaculture. Inst. Mar. Resources. University of California, La Jolla, CA, USA. 1981. Jensen, A. and Stein, J. R. (Eds.) Proc. IXth International SeaweedSymposium. SciencePress.Princeton, USA. 1979. Krauss, R. W. (Ed.) The marine Plant Biomassof the Pacific Northwest Coast. Oregon StateUniversity Press,1977. References

[l] Chapman,V. J. and Chapman, D. J. Seaweedsand their uses. 3rd Ed. Chapmanand Hall, London. 1980. [2] Charters, A. C. and Neushul, M. Aquatic Bat. 6, 67. 1979. [3] Doty, M. MicIonesia, 9, 59. 1973. [4] Hanisak, M.’ D. Bot. Mar. 24, 57. 1981. [5] Hansen, J. E., Packard, J. E. and Doyle, W. T. Mariculture of red seaweeds.University of California Sea Grant Report T-CSGCP-002. 1981. (61 Harger, B. W. W. and Neushul, M. Biosaline Research(A. San Pietro, Ed.). p. 393. Plenum. New York. 1982. 9, 313. [S] Huegenin, J. E. Aquacuhre, 1976. [9] La Pointe, B. E. and Ryther, J. H. Aquaculture, 15, 185. 1978. [IO] La Pointe, B. E., Williams, L. D. er al., Aquaculture, 8, 9. 1976 [ll] Neish. A. C., Shacklock,P. F. et al., Canad.

J. Bot..

55, 2263.

1977.

1121Neish, I. C. J. Fish Res. Bd. Canada.. 33, 1007.1976. [13] Shacklock,P. F., D. R. Robsonet al., Tech. Rept. No. 18. Atl. Reg. Lab. Halifax, NRC Canada. 1972. [14] Shacklock.P. F., D. R. Robson er al., Tech. Rept. No. 20 Atl. Reg. Lab. Halifax, NRC Canada.1974. [15] Shacklock,P. F., D. R. Robson et al., Tech. Rept. No. 21. Atl. Reg. Lab. Halifax, NRC Canada. 1975. [16] Shacklock,P. F., D. R. Robsonet al., Tech. Rept. No. 22 Atl. Reg. Lab. Halifax. NRC Canada.1976. [17] Waaland, J. R. J. hp. Mar. BioL f%d.. 23. 45. lY7h.

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