Massive Porites sp. corals as indicators of historical changes in river runoff:
A case study for Antongil Bay (Masoala National Park, NE Madagascar)
J. Zinke1, C. Grove2, G. J. Brummer2
1Vrije Universiteit Amsterdam, The Netherlands
2Royal NIOZ, The Netherlands
in cooperation with WCS Madagascar
Ecological Response of Reefs: global & local impacts
ALGAE
Algal Reef
GLOBALClimate Change
• Global Warming (coral bleaching)
• Increased pCO2 (ocean acidification)
• Sea Level Rise
HERBIVORESFish, Invertebrates
competition
CROWN OF THORNS
reproductionCORALS
AdultsJuveniles
for space
Healthy Reef
LOCAL IMPACTS• CORAL PREDATORS – Crown of Thorns (COTS)• FISHING/TRAWLING – Reef ecology• RIVER RUNOFF - Sediments, Nutrients, Freshwater input
Study area: NE Madagascar, Antongil Bay, St. Marie, Ifaty
• Main climatic variables in the region: Rainfall and SST
Rainfall (cyclonic) impacts on:1) Freshwater runoff and sedimentation of river systems2) Ocean chemistry and physical conditions3) Nutrient and pollutant export rates
Sea surface temperature patterns affect rainfall variability
• Climate change impacts on reefal ecosystem:1) Multiple stress factors: SST, salinity, sediments, pollutants, nutrients
• Impact on livelihoods:• large-scale flooding of villages• Erosion of agricultural land, loss of fertile soil• Sewage export impacts on fisheries
Objectives Madagascar
Recontruction of surface ocean chemistry, temperature andsalinity related to global and local factors:
To provide baseline of natural variability against which anthropogenic impacts can be assessed
Learn about spatial and temporal changes in climate
Study sedimentation, pollutant and nutrient export and howit relates to climate variability
Quantify the impacts of climatic and environmental changeson coastal ecosystems
Our monitoring tool:
Massive corals Porites sp.Life span: up to 400 years
Geochemical proxies in corals:
-Sr/Ca for SST-Oxygen isotopes for salinity-Combination Sr/Ca and d18O for hydrology
- Ba/Ca, Y, Mn for river runoff
-Cu, Zn etc. for biological activity
- Luminescence for runoff
- Density and Calcification for status of coral health
Zinke et al., 2004
Ifaty and Reunion corals record link to Pacific Decadal Oscillation (18-25 years)
Ba/Ca as a proxy for sediment river discharge
McCulloch et al., 2003, Nature 421
Ba is highly abundantin river sediment load
Ba is released when riverwater flows into seawater(salinity, pH gradient)
Freshwater plumes intothe coastal ocean are correlated with higherBa/Ca ratios in corals
Floods after drought yearscontain more Ba than innormal years
Increase in temperature and sedimentation over 20th century:Antongil Bay
Ba/Ca: late summer/winter max Mn: summer max
Seasonal timing of runoff
Luminescence bandingrelated to river runoff:
Quantification of runoffintensity in single years
XRF-scanning luminesecence (Royal NIOZ Netherlands): subweekly resolution
Calcification rate and density decrease over the 20th century:Ocean Acidification?
MAS1 coral, Masoala Park
Gaps in monitoring and research:
• monitoring natural variability of sedimentation, nutrient and pollutant export to provide natural levels
• combine environmental monitoring with ecosystem studies (reef monitoring)
• monitor SST and salinity to evaluate choice of MPA’s
• climatological monitoring land and ocean (isotopes in precipitation, isotopes in groundwater/seawater)
• combine terrestrial (tree rings, stalagmites, lakes) and marine studies (corals, bivalves) to investigate land-ocean interaction (gradients)
• hydrological modelling of climate and land-use impacts