Transcript EFFECTS OF SEAWEED FARMING ON SEAGRASS Jillian Ooi Lean Sim, Department of Geography, Faculty of Arts & Social Sciences, Universiti Malaya [email protected] Workshop on Marine Environmental.

EFFECTS OF SEAWEED FARMING ON SEAGRASS
Jillian Ooi Lean Sim,
Department of Geography,
Faculty of Arts & Social
Sciences, Universiti Malaya
[email protected]
Workshop on Marine Environmental Pollution,
Attorney General’s Chambers, 24-25 May 2012
Presentation outline
What is seagrass
2. Seagrass distribution in Malaysia
3. Significance of seagrass ecosystems
4. Seaweed farming in seagrass meadows
1.
Seagrasses: widely distributed but are most diverse in
Southeast Asia
UNEP-WCMC 2005
 ISI
publications
(1986 – 2009)
Ooi et al (2001), Estuarine, Coastal and Shelf Science
30
25
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0
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14-15 species in Malaysia
Halophila spinulosa
Halophila ovalis
Enhalus acoroides
Cymodocea isoetifolium
serrulata
Syringodium
Thalassia hemprichii
Halodule uninervis
Seagrass
site
Source: Seagrass Atlas of the World (2003)
Professor Gary Kendrick,
Merambong shoals
Seahorse
Dugong
feeding trail
Source: Seagrass Atlas of the World (2003)
Seagrass
site
Affendi Yang Amri
Jillian Ooi
Seagrass
site
Source: Seagrass Atlas of the World (2003); Leela Rajamani (pers. comm.)
Source: National Report on Seagrass in the South China Sea - Malaysia
More than just plants.
Seagrasses are habitats
African fishermen:
seagrass (73%); corals (23%); mangroves (0%)
(Torre-Castro & Ronnback 2004)
Siti Maryam Yaakub
Barang Lompo, Sulawesi
Base of the
food web
Nutrient
cycling
Store
carbon
Trap
sediment &
filter water
Economic value of seagrasses
According to Costanza et al (1997):
Corals (USD) = 607,500/km2/year
Seagrass (USD) = 1,900,400/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
All methods, when farmed
over seagrass meadows,
involve direct impacts on
seagrasses.
Off-bottom (stake) method
Are there scientifically documented impacts?
Reduced
growth
Seagrass
loss
Reduced
biomass
Reduced
shoot
density
Source: de la Torre-Castro &
Ronnback 2004; Eklof et al 2005;
Eklof et al 2006.
< 1 m – 2.5 m
SHALLOW WATER
Keith Ellenbogen, Conservation International
(Giuseppe Carlo in Madagascar)
<1 m – 2.5 m
Impacts
Farming methods: Stake/Off-bottom & Long-line
1. Manual removal of
long seagrass
(Enhalus acoroides)
2. Mechanical damage:
Trampling, boat
moorings, abrasion
by seaweeds
Photo: Zanzibar
Images: FAO 1988
3. Shading
Irradiance
How much light is needed?
11 – 18% surface
irradiance
Light
reduces with
depth
Seagrasses need more light than seaweeds
Minimum light needed = 1-3%
surface irradiance (seaweeds)
Minimum light needed = 11-18%
surface irradiance (seagrass)
Source: Duarte
1991; Lee 2007
Shading effects
Small species will be more affected
Halophila
ovalis
Halodule
uninervis
Cymodocea
serrulata
Syringodium
isoetifolium
Thalassia
hemprichii
Reference: Ooi et al (2011), Continental Shelf Research
Thomsen et al (2011), PlosONE
Enhalus
acoroides
Farming intensity and plot sizes determine shading effects
Seaweed Farming in Nusa Lembongan
Intensive seaweed farming has impacts
Ground view, Nusa Lembongan
Affendi Yang Amri, Semporna
MEDIUM DEPTH WATER
2.5 – 8 m
2.5 – 8 m
Impacts
Farming methods: Long-line & Raft
• Shading – more severe than in shallow water
• Small species are most abundant at this depth
and may be the most affected
2.5 – 8 m
Ooi et al, PhD Thesis (2011)
Halophila
ovalis
Halodule
uninervis
>8 m
DEEP WATER
>8 m
Impacts
Farming methods: Raft
• Very little seagrass at this depth (only small species),
except for certain clear-water areas.
• Therefore, potentially less severe impacts.
>8 m
Ooi et al, PhD Thesis (2011)
Halophila
ovalis
Halodule
uninervis
Summary
Potential impacts of seaweed farming on seagrass meadows
Assumption: farms are located in/above seagrass meadows
Potential impacts
Removal
Trampling, mooring,
abrasion
Shading
<1 – 2.5 m 2.5 – 8 m
>8 m
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
Acknowledgments
The Department of Geography, Universiti Malaya
Department of Marine Parks, Malaysia
SEABUDS