Grow Out

The time it takes for seaweed to grow from deployment to harvest varies significantly between tropical and temperate species. Seaweeds are low trophic species and generally do not need to be fed during the grow out process. Yet once the lines are in the water, some species require more attention than others. Risks during the grow out phase include epiphytes, diseases, pests, aquatic animal grazing and even strong weather events. Technology usage for production planning, communication or monitoring indicates how widespread digital solutions are.

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Eucheumatoids in the tropical regions can grow all year-round due to the relatively stable environmental conditions close to the equator. Moving further away from the equator, there is wider variation between the good and bad seasons.

Almost all regions are affected by seasonality to a certain extent, meaning they have specific times of the year where the seaweeds grow better than others. For most species, during the rainy season the drop in salinity and temperature affects them negatively. The temperature range is 27-31ºC, with an optimum temperature of 30ºC.  Most farmers we met had no means to track the temperature or other water quality parameters.

Farmers base their decisions on – for instance – when the next line will be harvested, on intuition. Some would work with a calendar, yet what mainly matters to them are the tide cycles. Especially in regions where farms are accessible by foot at low tide (mainly fixed off-bottom systems), all farming activities are timed according to tide.

Tasks during grow out

Eucheumatoids are farmed in cycles between 30 and 45 days and most farmers visit their lines on a daily basis. Besides bringing out new lines and harvesting activities, they check on their growing lines, mainly to keep them clean from epiphytes or sediments.

For instance, in some regions a lot of sediments tend to accumulate on the seaweed especially after heavy rains and fresh-water run-offs. This can inhibit good growth of the seaweed. To prevent this, some farmers reported that simply shaking the cultivation lines once in a while helps to remove these sediments.

Another example, which requires more work for the farmer is the filamentous algae, which is usually a seasonal issue. Farmers need to clean the lines in this case or can sometimes sink the entire lines for a little while. However, cottonii (Kapphaphycus spp.) is much more fragile than spinosum (Eucheuma denticulatum) to this practice. 

Consequently, when the season is not ideal for growing cottonii, with a possibility of being infected with ice-ice syndrome, or if epiphytes are very strong, farmers will grow spinosum instead.

Overall, spinosum needs less attention and is a more robust crop to farm than cottonii. Nevertheless, farmers prefer to grow cottonii whenever possible, since they get a much higher price for it.

Although the biological reasons for the ice-ice syndrome occurrence are not fully understood, it is characterised by bleaching of the seaweed followed by softening and degradation of affected parts of the plant. Infected parts of the seaweed should be removed from the lines.  Best practices suggest that removed parts and all filamentous algae collected must be brought to shore and should not be left behind at the farm site, to avoid further spread or problems on the rest of the crop.

In some regions, theft (poaching) of seaweed has also been mentioned as a risk to the farmers during the grow out period – especially when farm sites are several kilometres away from their base.

Seaweed farms affected by ice-ice suffer from loss of biomass and reduced carrageenan yield and quality. 

Explore another seaweed species:
Eucheumatoids  |  SaccharinaUndaria  |  PyropiaGracilaria

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