Download Effects of ocean acidification on calcifying organisms

Effects of ocean acidification on calcifying organisms
J.U. Hammel1,2, L. Möckel1, H. Jahn1, R. Dries2, J. Herzen3, F. Wilde3, F. Beckmann3,
Chia-Miin Chua4, F. Jansson2, P. Konglerd2, M. Nickel1 and J.A. Kaandorp2
1 Institut
für Spezielle Zoologie und Evolutionsbiologie mit Phyletischem Museum, Friedrich-Schiller-Universität Jena,
Ebertstr. 1, D-07743 Jena, Germany.
2 Section Computational Science, Faculty of Science, University of Amsterdam, PO Box 94248, 1090 GE Amsterdam,
The Netherlands.
3 Helmholtz-Zentrum Geesthacht, Institute of Materials Research, Max-Planck-Str. 1, 21502 Gesthacht, Germany.
4 James Cook University, ARC CoE for Coral Reef Studies, Townsville QLD 4811, Australia
Background
CO2 partial pressure (pCO2) has increased by 32% between 1880 and 2000 (280 vs. 379 μatm; IPCC 2007)
due to human activities, leading to global climate warming. About half the CO2 derived from fossil fuel
released between 1800 and 1994 has been absorbed by the oceans (Sabine et al. 2004). Observations since
1961 show that the average temperature of the global ocean has increased to depths of at least 3000 m and
that the ocean has been absorbing more than 80% of the heat added to the system (IPCC 2007). This makes
the world ocean the largest sink of anthropogenic CO2 and heat. CO2 uptake by the ocean is primarily a
physico-chemical process. As CO2 diffuses in seawater, it behaves like a weak acid leading to a decrease in
pH. This process is referred to as ‘Ocean Acidification’ (Orr et al. 2005), and results in acidification of
marine waters on a global scale. The impacts of increased CO2 on scleractinian corals may include not only
reduced calcification, but may ultimately include dissolution of calcified skeletons (Orr et al. 2005; Kleypas
et al. 2006). In this project we addressed aspects of biomineralization in the context of CO2 driven ocean
acidification (OA) and climate change. By studying the skeletal development in calcifying organisms like
corals we investigated the influence of ocean acidification on these ecologically highly important organisms.
Therefore developmental series of coral larvae hatched under laboratory controlled standard conditions and
manipulated CO2 concentrations have been studied for their ability to produce calcified skeletal structures
and the influence of pH alterations on these biominceralization processes.
Methodology
We imaged mineral skeleton samples of A. milepora coral larvae specimens hatched under different CO2
concentrations. Microtomography was operated by HZG using the beamlines P05 of the storage ring PETRA
III at DESY. Imaging was done at 15 keV or 20 keV and 2.52 µm voxel size in the 2 times binned datasets.
Resulting volume data sets of skeletal elements were segmented by thresholding and manual masking using
ImageJ/Fiji. For visual inspection rendering was performed by VG StudioMax (Volume Graphics).
Quantitative analysis including volume measurements, 3D convex hull determination and density analysis
was done with the 3D Shape (Sheets, K.G. et al., 2013) ImageJ plugin and custom written macros.
Results and discussion
Based on tomography datasets we compiled a table of developmental stages in biomineralization
(Fig 1) of A. milepora skeleton elements from larvae hatched under ambient and raised CO2
concentrations (385 ppm, 750 ppm and 1000 ppm). In order to quantitatively assess the
biomineralization we measured the total volume of calcified matrix and calculated the covering 3D
convex hull to compute porosity as measurement for the calcification process (Fig 2A). Our results
show no difference in terms of the performance of mineralization and skeleton growth form from
larvae hatched under raised CO2 concentrations in comparison to ambient conditions. However, on
the basis of density measurements of the mineralized skeleton elements we found a modification of
the calcified skeleton in the first week of development (Fig 2B). Within this period the density
increases and reaches the level observed in the larval stages up to one month age. This might
indicate a change in the composition of the skeletal matrix or might point to a condensation leading
to an increased density in later developmental stages. A detailed analysis of the density distribution
histogram of seven and 28 day old larvae from the three developmental series display almost no
variation between the different sample sets for selected time points (Fig 2C) or show an
inconsistent variation which seems not to be correlated to the environmental conditions they have
been hatched from (Fig 2D). We will complement our analysis of the density distribution on the
organismic scale with measurements on the local scale.
Fig. 1. Volume renderings of coral larvae developmental stages. Larvae were hatched under different CO2
concentrations ranging from ambient to 1000 ppm. Bottom row shows specimens from the control group
(385 ppm). Rows one and tow show larvae grown under 1000 ppm CO2 and 750 ppm CO2.
A
B
C
D
Fig. 2. Quantitative analysis of the biomineral skeleton of A. milepora larvae hatched under various CO2
conditions. A. Porosity of the developing skeleton in entire larvae B. Highes material density of the mineral
skeleton in developing larvae C. Skeleton density distribution based on the x-ray attenuation in 7 day old
larvae D. Skeleton density distribution based on the x-ray attenuation in 28 day old larvae.
References
Kleypas, J.A. et al. (2006) Impacts of ocean acidification on coral reefs and other marine calcifiers: a guide for future
research. NSF, NOAA, U.S. Geological Survey, St. Petersburg
IPCC (2007) Climate change 2007: the physical science basis. Cambridge University Press, Cambridge
Orr, J.C. et al. (2005) Nature 437:681-686
Sabine, C.L.et al. (2004) Science 305:367-371
Sheets, K.G. et al. (2013) Mol Vis 19:1747-1759