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Global relationship between seaweed production and fish catch

James Hehre, Jessica Meeuwig | Feb 19, 2016

James Hehre, Jessica Meeuwig

Feb 19, 2016

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Farmed seaweed production is expanding rapidly in shallow marine habitats, and provides vital income to millions of artisanal farmers.

Photo: Claudio Contreras Koob/iLCP.

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CITATION

HIGHLIGHTS

  • Seaweed is farmed globally to produce carrageenan, a thickening agent used in everything from beer to day-to-day products such as toothpaste and lubricants. Seaweed production also provides a livelihood to millions of farmers many of whom fall well below global poverty standards.
  • There is concern that seaweed farms may damage coral reefs by shading them and through trampling associated with tending the plants.
  • Our study demonstrates that seaweed farms increase the food available to rabbitfish, a commercially valuable species. The additional food may allow rabbitfishes to grow faster, leading to higher catch rates.
  • As rabbitfish play a vital role in keeping reefs clear of algae, which can smother coral and prevent growth, our research suggests that seaweed farms may ultimately play a role in protecting degraded coral reefs.

ABSTRACT

Globally, farmed seaweed production is expanding rapidly in shallow marine habitats. While seaweed farming provides vital income to millions of artisanal farmers, it can negatively impact shallow coral reef and seagrass habitats. However, seaweed farming may also potentially provide food subsidies for herbivorous reef fish such as the Siganidae, a valuable target family, resulting in increased catch. Comparisons of reef fish landings across the central Philippines revealed that the catch of siganids was positively correlated to farmed seaweed production whilst negatively correlated to total reef fish catch over the same period of time. We tested the generality of this pattern by analysing seaweed production, siganid catch, and reef fish catch for six major seaweed-producing countries in the tropics. We hypothesized that increased seaweed production would correspond with increased catch of siganids but not other reef fish species. Analysis of the global data showed a positive correlation between farmed seaweeds and siganids in Southeast Asia (Indonesia, Malaysia, and the Philippines) but not Africa (Tanzania and Zanzibar), or the Western Pacific (Fiji). In Southeast Asia, siganid catch increased disproportionately faster with seaweed production than did reef fish catch. Low continuity, sporadic production and smaller volumes of seaweed farming may explain the differences.

 

FUNDING & ACKNOWLEDGEMENTS

We wish to thank Daniel Pauly and the Project Seahorse Foundation for Marine Conservation for supporting this project.