Plankton gross production and respiration in the shallow water hydrothermal systems of Milos, Aegean Sea

Plankton gross production, net community production and dark community respiration were measured at coastal sites around the island of Milos, Aegean Sea, during June and September 1996 and June 1997. Sampling sites were chosen to include those with and without visible signs of hydrothermal activity. Plankton gross production ranged from undetectable (<0.3 mmol O2 m−3 day−1) to 3 mmol O2 m−3 day−1; respiration rates ranged from 1 to 6 mmol O2 m−3 day−1. No significant difference was found between gross production or respiration rates measured at hydrothermally active areas and gross production or respiration rates measured at non-venting areas. The dissolved inorganic carbon concentration varied by ~200 mmol C m−3 between venting and non-venting sites. Temperature had a pronounced stimulatory effect on the rate of plankton dark community respiration. The Topt for plankton dark community respiration always lay above the highest incubation temperature of 30°C (i.e. >6°C above in situ temperature). Temperature had less of a stimulatory effect on the rate of gross production.