Seagrass Systems under Nutrient Loads and Grazing

Marjolijn Christianen, 1th October 2007, NIOO

Promoters: Prof. Dr. P. Herman, Prof. Dr. J.G.M. Roelofs

Supervisors: Dr. M.M. Van Katwijk, Dr. T.J. Bouma, Dr. L.P.M. Lamers

Counterparts: Dr. S. Wouthuyzen, Dr. M. Hutomo

Importance of Seagrass

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Increased Nutrient and Sediment loads

Berau delta: and

• 1.2 million hectare MPA (2005)• Zoning plan • Initiated by local people, bottom-up• Enhancing managing capacity of local government and

communities• Enforcing existing Indonesian laws• Raising awareness.

Turtle Conservation

Largest nesting + feeding ground10-20% of population remained

Threats:• Turtle egg and meat intake• Caught during fishing• Diseases• Habitat loss (seagrass beds,

nesting beaches)

(c) WWF Indonesia

Pilot Study 2003 EKP

With increasing river influence:• Seagrass cover , • Number of seagrass species , • Species composition changed; • Nitrogen content of above ground seagrass tissues

These variables are therefore potential indicators for river influence.

Hypothesis

Shifts between different states

Hypothesis (2)1. Direct toxicity of nitrogen to seagrass occurs at

environmentally relevant concentrations in tropical seagrass beds; a positive feedback increases vulnerability to nitrogen loads,

2. Strong grazing may protect seagrass meadows from overgrowth by epiphytes, increasing critical loads,

3. Under increased organic loading of the sediment, iron deficiency may push the system in a state of increased sulphate reduction, a positive feedback may arise through sulphide toxicity effects and decreased aeration of the rhizosphere.

Method

Test the validity of the general hypotheses in:• Field experiments: sites representing 4 states• Mesocosm experiments

Method (2)

Provoke shifts • Nutrients (N, P)• Shade

Compare grazed - non-grazed• Primary production seagrass• Biomass epiphytes and macro algae• Tissue contents (plant stress) • Morphology

Results

• Used to validate hypotheses• Provide thresholds for shifts, which can be used for:

– Modeling– Management– Assessment of restoration possibilities in disturbed areas

Vragen?

Questions?

Seagrass Condition Berau Delta (2000)

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Seagrass species

Thalassiahemprichii

Haloduleuninervis

Cymodocearotundata

© Arie Vonk 2004