Effects of increased CO2 and nutrients on seagrass (Cymodocea nodosa) metabolism

Continuous global change leads to acidify ocean through increasing of atmospheric CO2 level which is major issue for our ecosysem now-a-days. Addressing this ocean acidification and ongoing anthropogenic problems of eutrophication with ocean temperature increase and teir cumulative impacts or interactive effects are still demanding a lot in research arena of oceanic environment. In this connection, this experiment conducted to investigate the effect of both nutrient and CO2 enrichment on the net community production (NCP) of Cymodocea nodosa beds collected from the western sector of the highly dynamic coastal lagoon Ria Formosa (south Portugal: 37° 01´ N, 7° 50´ W) in a mesocosm set up situated in Ramalhete Marine Station of University of Algarve where the open circulation of seawater exiss. To address the interaction with seagrass metabolism; two types of CO2 concentration (enriched: 700 ppm with pH 7.84 and control: existing 370 ppm with pH 8.12) and two types of nutrient concentration (enriched and control) were used with seawater. However, four types of different combinations from CO2 and nutrient concentration can explain effects of net community production for to complementary methods performed: light incubation and dark incubation. To estimate seagrass community metabolism, I measured change in calculated concentration of dissolved inorganic carbon (DIC) throughout photosynthesis and respiration from conducted twelve light incubations and nine dark incubations respectively in diferent days and times in order to catch possible wider range of underwater irradiances in case of light incubations. There were mild different trends suggesting increased production (± 38000 µmol C h-1 m-2) at underwater irradiance of ± 900 PAR µmol m-2 s-1 in the treatment of enriched nutrients and control CO2 concentration while decreased production (± 30000 µmol C h-1 m-2) found in the treatment with control CO2 and control nutrient at same irradiance. However, in consider to daytime, the net community production in afternoon found to differ a little bit after photoinhibition (observed at 13.30 h with ±1100 PAR µmol m-2 s-1) where maximum increased of NCP (± 35000 µmol C h-1 m-2) found at 17.00 h in the enriched (both in CO2 and nutrient) treatment. In all cases, average positive NCP values (from light) are found lower than the average negative NCP values (from dark) suggesting more community respiration in the equal day-night dates though the treatment with control CO2 and enriched nitrogen showed maximum net community production (around 60000 µmol C h-1 m-2) in the study place of south Portugal in the month of April-May when the daylight existed around 14 hours in a day. However, both CO2 and Nitrogen contents of seawater were not significantly affected yet in Cymodocea nodosa beds in generally even thouh there was significant difference (p = 0.002) among the daily average net community production of the four treatments. Further study should be carried out in order to better understand the underlying metabolic activities of C. nodosa leading to net community production in elevated CO2 and nutrients concentration to meet the upcoming global change.

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

1. 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 δ13C 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 13C-depletion in both scales and rhizomes in the site close to the eruption. Both increased CO2 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 δ13C 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 CO2 is known to enhance seagrass productivity.
3. Synthesis. We analysed the effect of a sudden and large hydrothermal event on δ13C 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 CO2 derived from vent systems, with implications for habitat management to mitigate against raising CO2 levels and ocean acidification. This leads the way to further studies to evaluate the effects of hydrothermal carbon on shallow ecosystems.