Seagrass under nutrient load and grazing

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Information about Seagrass under nutrient load and grazing

Published on October 26, 2007

Author: guestb538ca

Source: slideshare.net

Description

A brief presentation for master students in Biology

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

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.

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 ground 10-20% of population remained Threats: Turtle egg and meat intake Caught during fishing Diseases Habitat loss (seagrass beds, nesting beaches) (c) WWF Indonesia

Largest nesting + feeding ground

10-20% of population remained

Threats:

Turtle egg and meat intake

Caught during fishing

Diseases

Habitat loss (seagrass beds, nesting beaches)

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.

With increasing river influence:

Seagrass cover  ,

Number of seagrass species  ,

Species composition changed;

Nitrogen content of above ground seagrass tissues 

Hypothesis Shifts between different states

Shifts between different states

Hypothesis (2) Direct toxicity of nitrogen to seagrass occurs at environmentally relevant concentrations in tropical seagrass beds; a positive feedback increases vulnerability to nitrogen loads, Strong grazing may protect seagrass meadows from overgrowth by epiphytes, increasing critical loads, 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.

Direct toxicity of nitrogen to seagrass occurs at environmentally relevant concentrations in tropical seagrass beds; a positive feedback increases vulnerability to nitrogen loads,

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

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

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

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

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)

Seagrass species Thalassia hemprichii Halodule uninervis Cymodocea rotundata © Arie Vonk 2004

 

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