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This study will be designed to determine the response mechanisms of representative species of macrophytes along the tide flat to provide the physiological basis for answers for ecological questions, in particular how the community structure of various beds of macroalgae from the intertidal to the subtidal (eulittoral to sublittoral) region of the coastal ecosystem is affected by enhanced UV radiation. In situ measurement of photosynthetic efficiency, growth, community structure and succession will be conducted to investigate how do different species of macrophytes respond to changes in the light environment over a depth gradient and across seasons of the year. It is hypothesized that the differences in the ability to tolerate stress are the main factors controlling the distribution pattern of macrophytes. With the limited understanding in the control of tolerance, elucidating the mechanism of stress in the physiology and ecology of the organisms will allow us to quantify the impediments encountered by organisms inhabiting the tide flats. Objectives: 1. To measure the daily and seasonal variation in photosynthetically active and ultraviolet radiation. 2. To characterize the macrophyte community structure of the coastal habitat. 3. To perform UV exclusion and UV supplementation experiments in order to assess its effect on the growth of some macrophyte species in the field and in mesocosms. 4. To assess the prevention of UV damage in selected macroalgae by production of sunscreen pigments. 4. To determine the recruitment rate, recolonization pattern and succession under PAR and varying UVR condition.
Due to its high energy, UV radiation can induce severe damage at the molecular and cellular level. On the molecular level proteins and lipids, as well as nucleic acids are particularly affected. Conformation changes of certain proteins involved in photosynthesis, such as the reaction center protein (D1) of photosystem II or the CO2 fixing enzyme in the Calvin cycle (RuBisCo) lead to an inhibition of photosynthesis, and consequently to a decrease in biomass production. This might shift certain algal species into deeper waters, not reached by UV radiation. The aim of the studies is to demonstrate how strong an increase of UV radiation due to stratospheric ozone depletion will influence the depth distribution and biomass production of macroalgae, and which molecules and processes are most severely affected. Moreover, it will be studied, which stage in the life cycle of the individual species is most sensitive to UV radiation as it will be this particular stage, which in the end determines the upper distribution limit of a certain species on the shore.