Msc Thesis
Assessing edge-effects in Posidonia oceanica seagrass meadows: A multidisciplinary approach
Authors:
Jon Lapeyra Martin, Arnaud Abadie, Pierre Lejeune, Nicolas Sturaro, Loic Michel, Gilles Lepoint, Jonathan Richir, Sylvie Gobert
M E R M E R E EuurrooppeeaannMMSScciinn M MaarriinneeEEnnvviirroonnmmeenntt a annddRReessoouurrcceess U UPPVV//EEHHUU––SSOOTTOONN––UUBB--UULLgg RREEFF::22001133--00223377 E Euurrooppeeaann MMSScciinn M MaarriinneeEEnnvviirroonnmmeenntt a anndd RReessoouurrcceess U UPPVV//EEHHUU––SSOOTTOONN––UUBB--UULLgg RREEFF:: 22001133--00223377 Contact-mail:jon_lapeyra@hotmail.com
POSIDONIA OCEANICA MEADOWS
Endemic Posidonia oceanica (Magnoliophyta, kingdom Archaeplastida) dominant seagrass in the Mediterranean.
Most prominent aspect, its ecological role:
• Autogenic ecosystem engineer species
• Nursery areas
• Source of food for many organisms
• Stabilization of seabed à sediment trapping
INTRODUCTION _______________
WHAT ABOUT EDGES
?
INTRODUCTION _______________3
Structural boundaries play an important ecological role:
• “edge” is the boundary or interface between two
biological communities or different landscape elements.
(1m)
• “effect” refer to the changes in population or
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…to SEA SAND
CORRIDOR
INTRODUCTION _______________
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Specific Objectives
1. Determine whether there are differences/patterns between the EDGE and the CONTINUOUS meadow in measurements carried out.
2. Investigate if anthropogenic pressures (anchoring) could cause disturbances in the measured parameters.
Do the edges in
P. oceanica
differ ecologically from
continuous meadow?
STUDY AREA
POINTE DE LA REVELLATA
MATERIALS & METHODS _______________________
Site 1 Site 2 Calvi bay St a tio ns
EDGE EDGE EDGE EDGE
MEADOW MEADOW
9 Amphipods Mysids Gastropods …
Michell (2011)
Fish Assemblages
MEASURED PARAMETERS (Vagile-fauna)
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RESULTS: VAGIL-FAUNA COMMUNITY COMPOSITION 11
55 % AMPHIPODS
1546 RESULTS _______ OUT OF2653
ORGANISMS APHERUSA 35% CAPRELLIDAE 15% OTHERS 50%… 512
30 % MYSIDS
830
<8 % DECAPODS
192MYSIDACEANS
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<4 % OTHERS
85 POLYCHAETA FISH LARVAE ECHINODERMS PYCNOGIDS GASTROPODS14 DEC APO DS AMPH IPO DS MYSI DS GAST ROPO DS ECHI NODER MS POLYC HAET A PLAT IHEL MINT ES PICN OGYD A FISH LAR VAE OTH ERS 0 50 100 150 TAXON INDIVIDUALS EDGE 1 MEADOW EDGE 2 Community STARESO DEC APO DS AMPH IPO DS MYSI DS GAST ROPO DS ECHI NODER MS POLYC HAET A PLAT IHEL MINT ES PICN OGYD A FISH LAR VAE OTH ERS 0 50 100 150 Community ALGA TAXON INDIVIDUALS EDGE 1 MEADOW EDGE 2 DEC APO DS AMPH IPO DS MYSI DS GAST ROPO DS ECHI NODER MS POLYC HAET A PLAT IHEL MINT ES PICN OG YDA FISH LAR VAE OTH ERS 0 50 100 150 TAXON INDIVIDUALS EDGE 1 MEADOW EDGE 2 Community STARESO
NO SIGNIFICANT DIFFERENCES
HOW IS COMMUNITY DISTRIBUTED?
SEAGRASS STRUCTURE
Edge 1 Mead ow Edge 2 0 100 200 300 400 500Shoot Density STARESO
shoot.m -2 Edge 1 Mead ow Edge 2 0 100 200 300 400 500 shoot.m -2
Shoot Density L’ALGA
RESULTS _______
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SIGNIFICANT DIFFERENCES
Edge 1 Mead ow Edge 2 0.0 0.2 0.4 0.6
Epiphyte/leaf RATIO STARESO
Stations E/L Ratio Edge 1 Mead ow Edge 2 0.0 0.2 0.4 0.6 Stations E/L Ratio
Epiphyte/leaf RATIO L’ALGA
RESULTS _______ 16 EPIPHYTES ABUNDANCE SIGNIFICANT DIFFERENCES Site 1 Site 2
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Changes in seagrass structure and epiphyte biomass.
ECOLOGICAL RESPONSE TO HABITAT EDGES
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Epiphytes biomass Vagile-fauna
Ries et al. (2004)
CONCLUSIONS
CONCLUSIONS ______________19
ü Edges differ from continuous meadow ü Epiphytes increase?
ü Exposed areas, light penetration due to low shoot density
ü Deeper vagile-fauna taxonomic studies needed. ü No differences between sites were detected.
ü The ecological distinctions of natural and anthropogenic fragmented meadow is far from being well understood.
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