44 



acre/year still exceeds that of almost any other plant on earth for which there is 

 well documented evidence, the only possible exceptions being the best yields of 

 sugar cane grown in the tropics, the freshwater weed, water hyacinth, and perhaps 

 a few tropical grasses. 



Gracilaria is grown commercially in southern Taiwan, in shallow ponds averaging 

 25 acres in size that were originally constructed for fish culture. The seaweed is 

 grown on the bottom of the ponds that range from one-quarter to one meter in 

 depth, depending on the season. Water in the ponds is exchanged sporadically with 

 the adjacent estuary, at intervals of days to weeks as needed to control temperature 

 and salinity, but the water is usually not enriched. The seaweed is harvested seven 

 or eight times a year by dip-netting a portion of the plant population from the pond 

 and spreading the remainder evenly over the pond bottom. 



This relatively passive, non-intensive culture technique results in a yield of about 

 five dry tons per acre per year, only 10 percent of that achieved in Florida. Thus it 

 would appear, as a rule to thumb, that the more intensive the culture system, the 

 higher the yield. Attempts are now being made to develop a culture system that is a 

 compromise between the low-cost, low-energy-input, passive Taiwanese technology 

 and the intensive Florida system and that may result in yields intermediate be- 

 tween the two that would be cost effective but could still be impressive relative to 

 plant biomass production elsewhere. 



Equally important, however, is the development of a culture method whereby the 

 plants can be grown offshore in the open ocean. Since seaweeds normally grow 

 attached to the bottom, they are restricted in their natural distribution to the 

 shallow fringes of the sea, in depths of water never exceeding 100 meters and 

 usually in less than 10 meters. The few culture operations are similarly restricted to 

 shallow coastal waters or to impoundments on land, as in the Taiwanese Gracilaria 

 industry. But coastal lands and waters are among the most costly and heavily used 

 parts of our country. If prime agricultural land is in heavy demand for food 

 production, the coastal zone is in even heavier demand for that and almost every 

 other form of human activity including industry, housing, recreation, transportation 

 and waste disposal, among others, many of which are already in confict with each 

 other. Large-scale energy farming could not possible compete with these other 

 multiple uses of coastal lands and waters. Rather it would have to be conducted 

 offshore in the relatively inaccessible and little used parts of the oceans. This 

 immediately imposes a host of new problems, both technical and economic. New 

 methods must be developed for growing seaweeds offshore, at or near the sea 

 surface, within the relatively shallow depths where there is sufficient light for 

 photosynthesis, in trays or baskets, or nets, or woven into ropes, in or on some type 

 of structure that is moored or suspended in such a way as to withstand normal 

 waves and currents and ocean storms. 



Preliminary experiments have been initiated in Florida to develop such tech- 

 niques for offshore culture of Gracilaria, but perhaps, in the long run, some other 

 species of seaweed will turn out to be better adapted to cultivation in the open sea. 

 The ubiquitous brown alga Sargassum is a logical candidate, since it occurs natural- 

 ly in the central gyres of the oceans, where it lives at the sea surface, buoyed by 

 small floats or bladders. Such a floating habit is an obvious advantage to open ocean 

 culture, eliminating the need for costly suspending structures or devices. One spe- 

 cies, S. natans, which gives the Sargasso Sea its name, grows only vegetatively, 

 never having been known to produce or bear fruiting, reproductive bodies. Unfortu- 

 nately, the evidence to date indicates that the drifting species of Sargassum grow 

 very slowly, but more work needs to be done with that otherwise promising genus. 



Another very attractive candidate for offshore marine biomass production is the 

 giant kelp Macrocystis pyrifera \ This large alga, which may reach 50 meters or 

 more in length, is one of the most important resources of the California coastline, 

 not only for its own commercial value, but also as the dominant species and habitat 

 of the local ecosystem. 



In the mid-1970's an ambitious Ocean Food and Energy Farm (OFEF) Program 

 funded jointly by ERDA, NSF, the American Gas Association (AGA), the U.S. Navy 

 and various organizations in public and private sectors was begun. The primary 

 objective of the farm was to cultivate kelp as a source of energy. An ocean farm 

 system was designed under the management of H. O. Wilcox of the Naval Undersea 

 Center, San Diego and production costs and performance of the system were esti- 

 mated. 



' The section on giant kelp is taken from a special topical report on sources and systems for 

 aquatic biomass as an energjf resource by E. H. Wilson, J. C. Goldman and J. H. Ryther, which 

 is part of the cost analysis of algal biomass systems by Dynatech R/D Company referred to later 

 in this article. It is based on material provided by Prof Wheeler J. North, California Institute of 

 Technology. 



