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EFFECTS OF SEAWEED FARMING ON SEAGRASS
Jillian Ooi Lean Sim, Department of Geography, Faculty of Arts & Social Sciences, Universiti [email protected]
Workshop on Marine Environmental Pollution,Attorney General’s Chambers, 24-25 May 2012
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Presentation outline
1. What is seagrass
2. Seagrass distribution in Malaysia
3. Significance of seagrass ecosystems
4. Seaweed farming in seagrass meadows
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UNEP-WCMC 2005
Seagrasses: widely distributed but are most diverse in Southeast Asia
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ISI pub-lications (1986 – 2009)
Ooi et al (2001), Estuarine, Coastal and Shelf Science
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Halophila ovalis
Halodule uninervisCymodocea serrulata Thalassia hemprichiiSyringodium isoetifolium
Halophila spinulosa
Enhalus acoroides
14-15 species in Malaysia
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Source: Seagrass Atlas of the World (2003)
Seagrass site
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Professor Gary Kendrick, Merambong shoals
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Seahorse Dugong feeding trail
Source: Seagrass Atlas of the World (2003)
Seagrass site
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Affendi Yang Amri
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Jillian Ooi
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Source: Seagrass Atlas of the World (2003); Leela Rajamani (pers. comm.)
Seagrass site
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Source: National Report on Seagrass in the South China Sea - Malaysia
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More than just plants. Seagrasses are habitats
Siti Maryam YaakubBarang Lompo, Sulawesi
African fishermen: seagrass (73%); corals (23%); mangroves (0%)
(Torre-Castro & Ronnback 2004)
Which habitats best for fisheries?
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Base of the food web
Store carbon
Trap sediment & filter water
Nutrient cycling
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Economic value of seagrasses
According to Costanza et al (1997):
Seagrass (USD) = 1,900,400/km2/year
Corals (USD) = 607,500/km2/year
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SEAWEED FARMING EFFECTS ON SEAGRASS
Photo: Scubazoo
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Competitors in the natural world
Seaweeds – partial cause of global seagrass decline (Thomsen et al 2011, PloS ONE)
In the wild, sheet-forming and coarsely-branched algae have the most negative impacts on seagrass species (Thomsen et al 2011)
Kappaphycus alvarezii Eucheuma spinosum
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Do seaweed farms and seagrass habitats coincide?
Primary seaweed farming locations
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Raft method Long-line method
Off-bottom (stake) method
All methods, when farmed over seagrass meadows, involve direct impacts on seagrasses.
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Are there scientifically documented impacts?
Reduced shoot
density
Reduced biomass
Reduced growth
Source: de la Torre-Castro & Ronnback 2004; Eklof et al 2005; Eklof et al 2006.
Seagrass
loss
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SHALLOW WATER< 1 m – 2.5 m
Keith Ellenbogen, Conservation International (Giuseppe Carlo in Madagascar)
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Impacts
1. Manual removal of long seagrass (Enhalus acoroides)
2. Mechanical damage: Trampling, boat moorings, abrasion by seaweeds
Photo: ZanzibarImages: FAO 1988
Farming methods: Stake/Off-bottom & Long-line
<1 m – 2.5 m
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11 – 18% surface irradiance
Light reduces with depth
How much light is needed?
3. Shading Irradiance
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Seagrasses need more light than seaweeds
Minimum light needed = 11-18% surface irradiance (seagrass)
Minimum light needed = 1-3% surface irradiance (seaweeds)
Source: Duarte 1991; Lee 2007
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Shading effects
Small species will be more affected
Reference: Ooi et al (2011), Continental Shelf Research Thomsen et al (2011), PlosONE
Halophila ovalis
Haloduleuninervis
Syringodiumisoetifolium
Cymodocea serrulata
Thalassia hemprichii
Enhalus acoroides
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Seaweed Farming in Nusa Lembongan
Bali Lombok
Farming intensity and plot sizes determine shading effects
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Nusa Lembongan
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Intensive seaweed farming has impacts
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Ground view, Nusa Lembongan
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2.5 – 8 mMEDIUM DEPTH WATER
Affendi Yang Amri, Semporna
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Impacts
• Shading – more severe than in shallow water• Small species are most abundant at this depth
and may be the most affected
Farming methods: Long-line & Raft
2.5 – 8 m
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Ooi et al, PhD Thesis (2011)
Halophila ovalis
Haloduleuninervis
2.5 – 8 m
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>8 m
DEEP WATER
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Impacts
• Very little seagrass at this depth (only small species), except for certain clear-water areas.
• Therefore, potentially less severe impacts.
Farming methods: Raft
>8 m
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Halophila ovalis
Haloduleuninervis
>8 m
Ooi et al, PhD Thesis (2011)
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Potential impacts <1 – 2.5 m 2.5 – 8 m >8 m
RemovalTrampling, mooring, abrasionShading
Potential impacts of seaweed farming on seagrass meadows
Assumption: farms are located in/above seagrass meadows
Summary
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Suggestions
1. Farms should be located outside seagrass meadows2. If in seagrass meadows,
a. farm in water deep enough not to physically disturb seagrass (> 8 m) , i.e. long-line method or floating rafts
b. Smaller rather than larger plotsc. Low-density plots (adequate spacing between)d. Rotational location of plots within seagrass meadows
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AcknowledgmentsThe Department of Geography, Universiti MalayaDepartment of Marine Parks, MalaysiaSEABUDS