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