Lab experiments will be designed to measure resistance and resilience of target species to possible GCC scenarios (WP5). These experiments will be addressed to the most ecologically relevant species, especially in terms of bioconstruction (e.g. Lithophyllum cfr. stictaeforme, see WP2 for species collection and WP3 for identification). Specimens of the coralline alga Lithophyllum cfr. stictaeforme, collected for experiments, will be transferred quickly and carefully to the laboratory, in order to minimize physiological stress. After spore release and settlement, the early-life stages will be cultured combining different conditions of pH and temperature. Values of temperature, pH and salinity will be set up according to model conditions for the Adriatic (WP5).

A synergistic effect of stressors has been observed in adult thalli of coralline algae (Martin et al. 2013) but it has  been rarely studied in early-life stages (Bradassi et al. 2013). Our approach will investigate the recruitment and ecophysiological responses to multiple stressors in germinative discs of target species. Algal recruitment success under different conditions will be analysed by count of sporelings, mortality rate and surface growth. Since a reduced calcification at these early phases could have severe consequences for survival, the skeletal composition, in particular the Mg/Ca ratio and the structural strength of the calcified coralline tissue (intra- and inter-filament cell wall thickness) will be analysed with SEM and Energy Dispersive Spectroscopy. Fractional calcite density (McCoy and Ragazzola 2014) will be measured using Image J analysis software. The lab experiments will also address the recovery capacity of young thalli after short term (hours) or long term (days/weeks) stress conditions exposure.

Field experiments will be designed to quantify the recruitment rates and the bioconstruction/erosion balance at different sites. Recruitment patterns together with data on genetic connectivity (WP3) allow to estimate the recovery potential of the assemblages and their resilience toward disturbances. Bioconstruction/erosion processes are a key element of MBH resistance and may provide further insight into possible responses towards human and GCC threats, to be used in predictive models (WP5). Experiments will be carried out using artificial recruitment panels and calcareous tiles. Panels will be placed both on biogenic structures and suspended in the water column to discriminate pelagic and benthic recruitment processes. Recruited and natural epibenthic assemblages will be periodically photo-sampled. This study will also benefit from an ongoing experiment started in 2005 on bioconstruction/erosion dynamics.

Computed Tomography Image Analisys to measure biocontruction and erosion volumes

Eva Turicchia is working at the Friday Harbor Laboratories, University of Washington, together with Adam Summers, closely analysing CT images.

Bioconstruction and bioerosion are key processes in mesophotic temperate reefs, and act at different spatial and temporal scales. The study of the microscale processes, driving the dynamic balance leading to the formation of coralligenous banks, requires sophisticated investigation techniques. High resolution Computed Tomography (CT), offers new opportunities to visualise the internal and external morphology of the bioconstructions. This technology is widely used in medical, archaeological, geological and industrial applications. CT combines the use of X-rays and computerised analysis of the images allowing the generation of 3D volume reconstruction of the object. This imaging technique allows investigating the inner structure of biogenic substrates at a very fine scale, without destroying the sample.

CTs are used to analyse short and long-term (i.e., 3 and 12 years) bioconstruction and bioerosion processes occurring in travertine tiles deployed on different typologies of mesophotic biogenic reefs in the northern Adriatic Sea. Builders were mainly represented by coralline algae, bivalves and polychaetes, while the most important borers were sponges and bivalves. Boring species leave recognisable traces inside the substrates allowing measuring the eroded volume and estimating the net balance between construction and destruction. Understanding of these processes is a major step towards the conservation of biogenic habitats in the Mediterranean Sea.

Bradassi, F., Cumani, F., Bressan, G., Dupont, S., 2013. Early reproductive stages in the crustose coralline alga Phymatolithon lenormandii are strongly affected by mild ocean acidification. Mar. Biol. 160, 2261-2269. http://dx.doi.org/10.1007/s00227-013-2260-2

Martin, S., Cohu, S., Vignot, C., Zimmerman, G., Gattuso, J.-P., 2013. One-year experiment on the physiological response of the Mediterranean crustose coralline alga, Lithophyllum cabiochae , to elevated p CO₂ and temperature. Ecol. Evol. 3, 676-693. http://dx.doi.org/10.1002/ece3.475

McCoy, S.J., Ragazzola, F., 2014. Skeletal trade-offs in coralline algae in response to ocean acidification. Nature Clim. Change 4, 719-723. http://dx.doi.org/10.1038/nclimate2273