Rhein et al. (2013) has established that global mean temperature has increased since the late 19th century, and the increase in temperature is especially in the marine environment. Furthermore, heat wave events have become more frequent and of longer duration (Pedersen and Salo n.d. unpublished). Temperature is important because it affects all biological systems from molecule to ecosystem level, and sessile species inhabiting the oceans, e.g. multiple macro algae, are especially susceptible to superoptimal temperatures and risk extinction of local populations. Furthermore, or-ganisms inhabiting the intertidal zone already live close to their upper thermal tolerance limits (Somero 2010; Tomanek 2010) and consequently they have a low potential to cope with a further increase in temperature and heat waves of extended frequency and/or duration. I investigated how long-term superoptimal temperatures affect the physiology and fitness of Danish Fucus vesiculosus (Phaeophyceae) and if F. vesiculosus have any acclimation potential to increasing temperatures. I found that the physiology and fitness of F. vesiculosus was greatly affected by long-term exposure to thermal stress, and the tolerance limit during the 50 days exposure was 25 oC. The optimal tem-perature for photosynthesis (15 °C) was similar to that for growth (15–20 °C). Above these tempera-tures growth decreased rapidly and at temperatures above 27.5 oC growth ceased and became nega-tive. At temperatures above 25 oC F. vesiculosus was photoinhibited and both maximum electron transport (ETRmax), the initial rate of electron transport (αETR), and the overall efficiency of pho-tosynthesis (Fv/Fm) were significantly lower in algae cultivated above 25 oC. Photoinhibition leads to an overexcitation of the photosynthetic machinery and consequently the formation of reactive oxygen species (ROS). Fucus vesiculosus respond to thermal stress and photoinhibition, by decreas-ing light harvesting antenna pigments (fucuxanthin, chl a and chl c), increase xanthophyll cycling and pigments/enzymes with antioxidant properties (β-carotene and ascorbate peroxidase(APX), re-spectively), to reduce the risk of overexcitation and ROS formation. The stress response was accel-erated by temperature and clearly show that the overall stress response of F. vesiculosus is a combi-nation of the stress intensity and the duration of the exposure. Fucus vesiculosus did not show any acclimation potential to long-term exposure to temperatures above 25 oC, on the contrary the toler-ance limit was greatly affected by the exposure time. By the end of the cultivation period algae from the 25 oC treatment began to show signs of photoinhibition, indicating that temperatures mere-ly 5-10 oC above optimal temperatures, may have substantial consequences for F. vesiculosus if ex-posure time is long enough.
|Uddannelser||Miljøbiologi, (Bachelor/kandidatuddannelse) KandidatMolekylærbiologi, (Bachelor/kandidatuddannelse) Kandidat|
|Udgivelsesdato||7 jul. 2017|
|Vejledere||Morten Foldager Pedersen & Hans Ramløv|