Effect of explosive shallow hydrothermal vents on δ¹³C and growth performance in the seagrass Posidonia oceanica

Abstract

Summary1. Explosive volcanic submarine activity is expected to affect seagrass communities due to sudden and dramatic changes in the physical and chemical features of sea water and sediments, with possibly large ecosystem effects. However, seagrass response to the harsh environmental conditions that arise due to explosive volcanism is as yet unexplored as it is not easy to predict when and where an eruption will occur. Here, we investigate the uptake of hydrothermal carbon within the seagrass Posidonia oceanica by the analysis of d 13 C and growth rates in tissue laid down before and after an exceptional and massive hydrothermal gas release in the Aeolian Islands (Italy, Mediterranean Sea). 2. Hydrothermal submarine activity was recorded by P. oceanica, which showed a large and persistent 13 C-depletion in both scales and rhizomes in the site close to the eruption. Both increased CO 2 availability and reduced carbon demand, as a consequence of stressful environmental conditions (e.g. light limitation due to turbidity, high temperature), combined to give much lower d 13 C signatures. Our results suggest that the explosive volcanism caused physiological stress in the seagrass, leading to a reduction in productivity, whereas slower, more diffuse release of hydrothermal CO 2 is known to enhance seagrass productivity. 3. Synthesis. We analysed the effect of a sudden and large hydrothermal event on d 13 C interannual variations and growth of the seagrass P. oceanica. Our results confirm that shallow submarine hydrothermal vents can be used as natural laboratories for exploring biological responses to acute and often extreme environmental conditions. P. oceanica can record geological events by capturing CO 2 derived from vent systems, with implications for habitat management to mitigate against raising CO 2 levels and ocean acidification. This leads the way to further studies to evaluate the effects of hydrothermal carbon on shallow ecosystems.

The Effects of Carbon Dioxide Fertilization on the Ecology of Tropical Seagrass Communities

“…Increases in the external supply of DIC impact plant δ 13 C values by allowing for increased discrimination against the heavier carbon isotope ( 13 C) during photosynthetic carbon fixation (Smith and Walker 1980). Thus, our shifts in δ 13 C with carbon enrichment are consistent with these statements, and are in agreement with previous studies which demonstrate that an elevated CO 2(aq) supply results in increasingly negative δ 13 C values within both seagrass tissues and marine macroalgae (Durako and Sackett 1993;Vizzini et al 2010). …”

“…If our carbon enriched treatments were effective in increasing the diffusive flux of CO 2 to the benthic seagrass community, we hypothesized significant reductions in the δ 13 C signature of the seagrass tissue growing within the enriched chambers, in accordance with previous correlative and experimental studies (Durako and Sackett 1993;Vizzini et al 2010). Every month, aboveground leaf material from 3-5 shoots of T. testudinum was collected within each chamber and control plot, scraped free of adhered epiphytes, separated according to leaf age, dried in the lab for 48 hrs at 60 o C, and ground to a fine power.…”

Ocean Acidification and Related Indicators

“…These are natural pH gradients, caused by the volcanic vents of CO 2 -rich gases or by low-pH, low carbonate saturation groundwater springs, which have been exploited to investigate how species, communities, and ecosystems react to acidified conditions in a natural environment. Most studied are the ones in Italy (Hall-Spencer et al 2008), Greece (Vizzini et al 2010), Papua New Guinea (Fabricius et al 2011;Uthicke et al 2013), and Mexico (Crook et al 2011(Crook et al , 2013.…”

The response of seagrass (<i>Posidonia oceanica</i>) meadow metabolism to CO<sub>2</sub> levels and hydrodynamic exchange determined with aquatic eddy covariance

“…Seagrass at CO2 vents have higher densities, biomass, and greater electron transport rates (Hall-Spencer et al, 2008;60 Fabricius et al, 2011;Takahashi et al, 2015). They may also be adversely affected by CO2 vent eruption (Vizzini et al, 2010).…”