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EFFECTS OF SEAWEED FARMING ON SEAGRASS Jillian Ooi Lean Sim, Department of Geography, Faculty of Arts & Social Sciences, Universiti Malaya

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Presentation on theme: "EFFECTS OF SEAWEED FARMING ON SEAGRASS Jillian Ooi Lean Sim, Department of Geography, Faculty of Arts & Social Sciences, Universiti Malaya"— Presentation transcript:

1 EFFECTS OF SEAWEED FARMING ON SEAGRASS Jillian Ooi Lean Sim, Department of Geography, Faculty of Arts & Social Sciences, Universiti Malaya Workshop on Marine Environmental Pollution, Attorney General’s Chambers, May 2012

2 Presentation outline 1. What is seagrass 2. Seagrass distribution in Malaysia 3. Significance of seagrass ecosystems 4. Seaweed farming in seagrass meadows

3 UNEP-WCMC 2005 Seagrasses: widely distributed but are most diverse in Southeast Asia

4 Ooi et al (2001), Estuarine, Coastal and Shelf Science

5 Halophila ovalis Halodule uninervis Cymodocea serrulata Thalassia hemprichii Syringodium isoetifolium Halophila spinulosa Enhalus acoroides species in Malaysia

6 Source: Seagrass Atlas of the World (2003) Seagrass site

7 Professor Gary Kendrick, Merambong shoals

8 SeahorseDugong feeding trail Source: Seagrass Atlas of the World (2003) Seagrass site

9 Affendi Yang Amri

10 Jillian Ooi

11 Source: Seagrass Atlas of the World (2003); Leela Rajamani (pers. comm.) Seagrass site

12 Source: National Report on Seagrass in the South China Sea - Malaysia

13 More than just plants. Seagrasses are habitats Siti Maryam Yaakub Barang Lompo, Sulawesi African fishermen: seagrass (73%); corals (23%); mangroves (0%) (Torre-Castro & Ronnback 2004)

14 Base of the food web Store carbon Trap sediment & filter water Nutrient cycling

15 Economic value of seagrasses According to Costanza et al (1997): Seagrass (USD) = 1,900,400/km 2 /year Corals (USD) = 607,500/km 2 /year

16 SEAWEED FARMING EFFECTS ON SEAGRASS Photo: Scubazoo

17 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 alvareziiEucheuma spinosum

18 Do seaweed farms and seagrass habitats coincide? Primary seaweed farming locations

19 Raft method Long-line method Off-bottom (stake) method All methods, when farmed over seagrass meadows, involve direct impacts on seagrasses.

20 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 Seagrass loss

21 SHALLOW WATER < 1 m – 2.5 m Keith Ellenbogen, Conservation International (Giuseppe Carlo in Madagascar)

22 Impacts 1.Manual removal of long seagrass (Enhalus acoroides) 2.Mechanical damage: Trampling, boat moorings, abrasion by seaweeds Photo: Zanzibar Images: FAO 1988 Farming methods: Stake/Off-bottom & Long-line <1 m – 2.5 m

23 11 – 18% surface irradiance Light reduces with depth How much light is needed? 3. Shading Irradiance

24 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

25 Shading effects Small species will be more affected Reference: Ooi et al (2011), Continental Shelf Research Thomsen et al (2011), PlosONE Halophila ovalis Halodule uninervis Syringodium isoetifolium Cymodocea serrulata Thalassia hemprichii Enhalus acoroides

26 Seaweed Farming in Nusa Lembongan Farming intensity and plot sizes determine shading effects

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29 Intensive seaweed farming has impacts

30 Ground view, Nusa Lembongan

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33 2.5 – 8 m MEDIUM DEPTH WATER Affendi Yang Amri, Semporna

34 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

35 Ooi et al, PhD Thesis (2011) Halophila ovalis Halodule uninervis 2.5 – 8 m

36 >8 m DEEP WATER

37 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

38 Halophila ovalis Halodule uninervis >8 m Ooi et al, PhD Thesis (2011)

39 Potential impacts<1 – 2.5 m2.5 – 8 m>8 m Removal Trampling, mooring, abrasion Shading Potential impacts of seaweed farming on seagrass meadows Assumption: farms are located in/above seagrass meadows Summary

40 Suggestions 1.Farms should be located outside seagrass meadows 2.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 plots c.Low-density plots (adequate spacing between) d.Rotational location of plots within seagrass meadows

41 Acknowledgments The Department of Geography, Universiti Malaya Department of Marine Parks, Malaysia SEABUDS


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