Abstract
11 páginas, 5 figuras.
Meadows of the endemic seagrass Posidonia oceanica are threatened in the Mediterranean
due to a general deterioration of the light environment that becomes critical when light
irradiance is insufficient to meet the carbon requirements of the system. Here, we conduct a 3 wk,
in situ shading experiment (8 levels plus controls) to determine the threshold of irradiance for balanced
metabolism in a shallow P. oceanica meadow and further assess the recovery of the system
1 wk later. Reduced light irradiance decreased the net community production of the meadow,
which may turn negative (i.e. respiration exceeded gross community primary production) under
338 μE m−2 s−1. Shading throughout the experiment did not appear to cause sustained physiological
damage to the system since values of net community production after the cessation of shading
were similar to pre-experimental, ambient levels. Sediment acid volatile sulfide pools ranged
between 0.002 and 0.058 mol m−2 across shading treatments, and the highest pools were observed
in the most shaded sediments. At high light impairment, meristematic cell divisions were low, and
carbohydrate content in young rhizomes decreased throughout the experiment. Eight days after
the cessation of shading, reduced rhizome carbohydrate stores and elevated sediment sulfide levels
still persisted in the previously intensively shaded areas. The present study provides evidence
of resistance and resilience of the seagrass Posidonia oceanica to light impairment for short (3 wk)
periods of time. Although the compensation irradiance of the system varied by ~2-fold, it provides
a quantitative estimate of the irradiance threshold at which seagrass meadows may shift from
being coastal carbon sinks to CO2 sources.
This research is a contribution to the
project ‘Praderas’ funded by the Fundación BBVA.
Peer reviewed