EFFECTS OF SEAWEED FARMING ON SEAGRASS

Jillian Ooi Lean Sim, Department of Geography, Faculty of Arts & Social Sciences, Universiti Malayajillian_03@um.edu.my

Workshop on Marine Environmental Pollution,Attorney General’s Chambers, 24-25 May 2012

Presentation outline

1. What is seagrass

2. Seagrass distribution in Malaysia

3. Significance of seagrass ecosystems

4. Seaweed farming in seagrass meadows

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

Halophila ovalis

Halodule uninervisCymodocea serrulata Thalassia hemprichiiSyringodium isoetifolium

Halophila spinulosa

Enhalus acoroides

14-15 species in Malaysia

Source: Seagrass Atlas of the World (2003)

Seagrass site

Professor Gary Kendrick, Merambong shoals

Seahorse Dugong feeding trail

Source: Seagrass Atlas of the World (2003)

Seagrass site

Affendi Yang Amri

Jillian Ooi

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

Seagrass site

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

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?

Base of the food web

Store carbon

Trap sediment & filter water

Nutrient cycling

Economic value of seagrasses

According to Costanza et al (1997):

Seagrass (USD) = 1,900,400/km2/year

Corals (USD) = 607,500/km2/year

SEAWEED FARMING EFFECTS ON SEAGRASS

Photo: Scubazoo

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

Do seaweed farms and seagrass habitats coincide?

Primary seaweed farming locations

Raft method Long-line method

Off-bottom (stake) method

All methods, when farmed over seagrass meadows, involve direct impacts on seagrasses.

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

SHALLOW WATER< 1 m – 2.5 m

Keith Ellenbogen, Conservation International (Giuseppe Carlo in Madagascar)

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

11 – 18% surface irradiance

Light reduces with depth

How much light is needed?

3. Shading Irradiance

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

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

Seaweed Farming in Nusa Lembongan

Bali Lombok

Farming intensity and plot sizes determine shading effects

Nusa Lembongan

Intensive seaweed farming has impacts

Ground view, Nusa Lembongan

2.5 – 8 mMEDIUM DEPTH WATER

Affendi Yang Amri, Semporna

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

Ooi et al, PhD Thesis (2011)

Halophila ovalis

Haloduleuninervis

2.5 – 8 m

>8 m

DEEP WATER

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

Halophila ovalis

Haloduleuninervis

>8 m

Ooi et al, PhD Thesis (2011)

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

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

AcknowledgmentsThe Department of Geography, Universiti MalayaDepartment of Marine Parks, MalaysiaSEABUDS