As with other aquaculture systems, selection of a suitable site is critically important for a new seaweed farm. The success of Eucheuma farming does not only depend on farming technology, but also to a large extent on the proper selection of the site. Since an actual on-site investigation to determine site suitability for any type of aquaculture system is time-consuming and expensive, the investor tends to “cut corners” by only allowing a very shallow and short-term examination of site suitability in order to get the project moving. In many cases, a combination of luck, wisdom and subsequent design modification does result in commercial success. However, failure of a project is often later blamed on some unsuitable conditions of the site. This would not occur, if a more thorough examination were made at the beginning.
Plate 1. Commercially cultured Eucheuma species. A) E. cottonii and B) E. spinosum. (Source: Padilia and Lampe, 1989).
In order to reduce time-consuming activities and unnecessary expenditure for site selection, potential sites should be pre-selected through a first-stage screening to provide an inventory of the potential sites available for Eucheuma culture. The areas have to be physically inspected to locate the best site in terms of physical, geographic and pollution parameters, for which information and data are already available. This information is used in conjunction with maps, tide table, aerial photography, and nautical charts. Specific screening parameters, analytical activities, and conclusions to be drawn on the suitability of a given area based on single screening parameters are shown in Table 3.
The areas that are ranked as “acceptable” or “good” for Eucheuma culture will be further investigated at the field level. The main parameters that need to be verified during the second-stage screening are risk factors and socio-economic considerations which can be arranged in the form of a checklist as suggested in Table 4.
Table 3. Parameters, analytical activities and interpretation for the first-stage screening process in site selection for seaweed farming.
|Analytical activity and action
|Interpretation site/ area selection
|Physical and Geographic Parameters
|a) Characteristics of coastal lagoons, and estuarine
|Using nautical charts, and meteorological records determine the incidence of storms, major wind directions and velocities for the the areas.
|Indicates possible suitability of sites based on depth and weather/climate criteria.
|b) Areas of lagoons
|Using nautical charts, determine surface areas which might be suitable for culture.
|Showing sites and locations of lagoons that might be developed for seaweed culture
|c) Tidal characteristics
|Using tidal tables and coastal maps, plot sections of the coastline where tidal ranges are suitable for seaweed culture
|Demarcates coastal areas where tidal characteristics are favorable for seaweed culture.
|a) Industrial pollution
|Plot locations of industrial estates and mining areas in relation to rivers on the large-scale map.
|Delimits coastal and estuarine areas probably not suitable for seaweed culture because of polluted water supplies.
|Plot as above but for agro-primary industry (e.g. palm-oil processing plants).
|Further delimits coastal areas where the risk of pollution is probably great or at least where water quality may be suspected.
|c) Domestic pollution
|Plot locations of cities not known to have waste treatment plant.
|Shows coastal areas where domestic pollution may prejudice water quality for culture purposes.
Source: Modified from Gedney et al., 1982.
Table 4. Checklist and rating guide for second-stage field site selection activities.
|O M A G
|O M A G
|O M A G
|1. Risk factor
|1.1 Human problem
|1.2 Conflicting problem
|1.3 Convenience factor
|1.4 Water pollution risks
|- ship traffic
|2.1 Availability of seed
|2.3 Water movement
|2.4 Indicator species
|2.8 Light penetration
|2.9 Water temperature
|a) Service provided by government
|b) Private sector service
|a) Ex-farm price
|b) Seed availability
|c) Operation costs
|Rating: O = not suitable
|M = marginal, can be accepted if other parameter are good
|A = Acceptable, i.e., average
|G = good
Source: Modified from Gedney et al., 1982.
Problems classified under risk factor are human problems, conflict problems, and convenience factor.
Poaching and intentional sabotage are common in aquaculture with no exception in seaweed culture. Human problems are difficult to overcome, but with appropriate management, these problems can be minimized. It would appear that skills and sound experience in handling human problems are the pre-requisites in solving such problems.
These refer to problems arising from conflicting activities of the “common users” of the sea. Capture fisheries and ornamental fish collecting activities are harmful to seaweed culture by damaging the culture ground, culture facilities as well as the crop itself. The potential site should be free from such conflicting activities.
In this consideration, the area opposite or near the residence of the culturist is the most suitable area based on the priority need to keep constant watch on the crops and facilities. Ready accessibility to roads, and markets are also important and should be considered during the process of site selection. Thus, a particular site can be rated against the availability of the following kinds of goods and services, as well as the time or cost to obtain them.
Services provided by government and private sectors such as medical care, schools, post office/communications, electricity, aquaculture extension services, roads, water supply (domestic), access to shopping facilities for food clothing and other necessities (public/private transport) should also be taken into considerations for family welfare.
Ecological parameters are the most important factor that determine the success of the farming operation. Ecological parameters that should be assessed are availability of seed, shelter, water movement, indicator species, substratum, depth, salinity, light intensity temperature and pollution.
The availability of local stocks of the species to be cultured at the site is a good indicator that the ecological conditions of the site are favourable for the growth and development of the species. The presence of stocks at the site or in nearby areas eliminates the problem of seed acquisition. For areas where no wild Eucheuma is growing, test plants must be conducted to determine its growth rate for a period of 2–6 weeks.
A suitable culture site for seaweed culture is that which is well protected from tidal waves and strong winds that come from the open sea or monsoonal weather conditions. Wave-exposed areas are not good sites for Eucheuma farming because of the destructive effects of waves on the farm. Waves can have a severe impact on seaweed culture operation not only removing significant amount of seaweed from culture facilities, but also damaging the culture facilities. A good site should be a lagoon sited between an island or coral reefs that are bare during low tide covering the area to prevent destruction or disturbance of seaweeds planted.
Water movement is a key factor that controls or influences the growth of seaweed. It plays an important role in preventing an increase in pH, caused by consumption of carbon dioxide, and in supplying nutrient. It is also important in water aeration, and preventing the rise in water temperature. Water movement caused by currents is considered a better form of water motion than wave. It is more predictable and less destructive. In an ordinary site, a current of about 20 cm/sec is considered suitable for seaweed culture. However, if the site is rich in nutrients, the current can be as slow as 10 cm/sec. On the contrary, if the site is deficient in nutrients, a faster current is required but should not exceed 30 cm/sec. A strong current not only damages plants and washes away planted lines by pulling down the stakes, it also makes it difficult to work in the farm.
The presence of wild stocks of seaweed at the site or in nearby areas is not only a good indicator of ecological suitability of the site, but also eliminates the problem of seed acquisition. The presence of some species of benthic coelenterate is also an indicator to support the suitability of the site for Eucheuma in terms of good water movement, high level of phosphate, silicate, salinity, dissolved oxygen and high transparency. The abundance of soft corals for instance is an indicator of good water movement.
The substratum provides mechanical support or attachment of the seaweeds. Seaweeds have different types of attachment adapted to various types of substrata. Eucheuma prefers sand or sandy loam substratum with a limited amount of other seaweeds (Fig. 1). The Eucheuma will not grow well on bottoms covered with seagrasses. The unwanted seaweeds might compete for nutrients or cover the farm-raised Eucheuma resulting in quick deposition of silt on the stems and branches.
A sea bottom with hard coral formations and coral heads is also not a good site for a seaweed farm. It is difficult to secure the stakes and the area is a good habitat for seaweed predator such as rabbit fish, puffer fish and sea urchin.
Figure 1. Showing type of sea bed suitable for seaweed culture. (Source: Foscarini and Prakash, 1990).
A muddy sea bottom is not advisable because silt or mud covers the plants reducing growth. Extra work is also required to keep the seaweed clean. Murky waters will also limit the amount of sunlight that reaches the plants. Type of sea bed also reflects the oceanographic conditions of the site and determines the degree of ease in constructing the supporting culture facilities. Areas which are too rocky are generally wave-exposed while those characterized by fine sand and silt are generally protected. On the other hand, a site with coarse sandy bottom mixed with coral fragments is generally a current-washed area.
Water depth is an important factor to consider when selecting a site for the establishment of seaweed farms. Greater tidal ranges allow for less working hours at a farm. Area with too high tides reduces working hours since diving is not very efficient. Areas with low tides and which are consistently exposed should also be avoided. However tidal ranges can also be associated with water motion. Therefore, one needs to compromise between suitable tidal range and water motion. Areas where depth of the water is between 45–90 cm during extreme tides are preferred. At this depth the farmer can stand or walk on his knee to waist-deep water instead of swimming and diving such as the case in deeper areas (Fig. 2).
Areas that are near the mouth of rivers or where there is a heavy freshwater runoff should be avoided (Fig. 3). Freshwater from rivers might decrease the salinity of seawater to a level that is detrimental to the growth of the seaweed. The optimum salinity required for Eucheuma is about 28–34 parts per thousand (ppt).
Seaweeds require light as a source of energy for the synthesis of organic products necessary for their normal growth and development. The potential site should have water with good transparency. Clear seawater allows sunlight to penetrate more easily to the plants. This is why when seaweed is planted close to the sea surface, it grows faster and healthier compared to those planted close to the sea bottom or in deeper water (Fig. 4). Water with a high silt load is not good for seaweed growing. Silt hinders light penetration and accumulates on the algal thalli which adversely effects plant growth and development.
A water temperature ranging from 25–30 °C is best for growing Eucheuma. In shallow waters near the beach, the water temperature can become high especially during a sunny day. Such an area is not suitable for planting seaweeds. The ideal area is one between the spring low tide limit and the reef edge or the area which does not dry up during these extreme low tides occurring during full or new moon.
Figure 2. Water depth suitable for seaweed culture. (Source: Foscarini and Prakash, 1990).
Figure 3. Unsuitable location for seaweed culture. (Source: Foscarini and Prakash, 1990).
|Seaweed planted in water near the surface (30–50cm) receives plenty of sunlight for a good growth.
|Seaweed planted in waters deeper than 1 m from the surface will have inadequate sunlight for a good growth.
Figure 4. Seaweed culture in relation to water depth and light penetration. (Source: Foscarini and Prakash, 1990).
Eucheuma prefers clear clean seawater. Areas should be free from pollution caused by floods, rivers and such other sources of pollution. In site selection, though water quality may be acceptable or good, the risk of pollution accidents arising from activities of industries, agriculture, settlements, nearby shipping lanes, and tankers' terminals should be carefully considered. Although having the above-mentioned activities in the vicinity of an aquaculture site does not necessarily imply chronic pollution (though it is very likely), tanker accidents, pipeline, ruptures, leakage of chemical industries storages, or wastes of livestock are a possible major danger.
Socio-economic parameters need to be considered for a given site. A simple costs and returns exercise would indicate suitability from this economic stand point. The first stage screening of socio-economic parameters can be looked at the district level, whereas the second-stage screening may have to be at the community or village level. The main socio-economic parameters to be collected and evaluated are the following:
Supply and demand of seaweed at a given site.