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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Gracilaria species are fairly easy to grow compared to other seaweeds, because they can adapt well to different environmental conditions other than their natural habitat and are quite robust.

Although farming in ponds is fairly simple compared to at-sea cultivation, farmers struggle during the wet season to maintain adequate salinity levels in culture ponds, because heavy rains easily cause flooding. In turn, when salinity drops below 10 ppt Gracilaria doesn’t grow well. Under normal circumstances salinity in the pond systems should be maintained at 20-30 ppt. In traditional pond systems, farmers regulate this by freshwater in- and outflows.

Temperature fluctuations can be modified by pond depth. Deeper ponds help maintain the temperature range during warmer seasons. When water temperatures rise above 32ºC, Gracilaria stops growing. Therefore prolonged high temperatures may significantly diminish harvest yield.

As for all seaweeds, the growth of Gracilaria varieties is influenced by the availability of major nutritional sources, namely nitrogen and phosphorus.
Some farmers therefore add additional mineral nutrients that enhance the growth of Gracilaria in the brackish water pond. In Indonesia, this is usually done when the pond is dry and minerals are applied directly on to the bottom of the pond. The farmers we visited applied Urea, which is a nitrogen-based fertiliser.

Gracilaria farmed in land-based ponds, is commonly done in co-cultivation with other species. Different examples of IMTA systems in Indonesia: 

  • Milkfish and Gracilaria
  • Milkfish, Black tiger shrimp and Gracilaria
  • Red tilapia, Tiger shrimp and Gracilaria

The polyculture systems or integrated multi-trophic aquaculture (IMTA) mentioned above have successfully produced seaweed and allow farmers to produce other valuable products during the farm cycle. Polyculture systems can also provide improved ecosystem services. (Yang et al., 2015, Wu et al., 2020, Diatin et al., 2020 and Pantjara et al., 2020). Gracilaria species are particularly interesting for use in IMTA systems since they have high bioremediation efficiency when they remove inorganic nutrients and have an added value due to their agar content (Torres et al., 2019). When using an IMTA system, the organisms co-cultured mutually benefit each other and since the animal wastes are high in nitrogen and phosphorus, it can increase the yield of Gracilaria (Yang et al., 2015, Wu et al., 2020, Diatin et al., 2020, Torres et al., 2019 and Pantjara et al., 2020).

Explore another seaweed species:
Eucheumatoids  |  SaccharinaUndaria  |  Pyropia |  Gracilaria

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