Effects of ultraviolet radiation on the pelagic Antarctic ecosystem, in: D-P. Hader (Ed.), The effects of Ozone

Ultraviolet radiation (UVR) affects biotic and abiot ic factors in marine ecosystems. Effects on organisms are mostly deleterious due co dam-age to DNA and cellular proteins that are involved in biochemical pro-cesses and which ultimately affect growth and reproduction. Differential sensitivity among microalgal species to UVR has been shown to shift community composition. As a result of this shift. the total primary pro-duction for the com munity may be maintained at pre-UVR levels. Simi-lar impacts and mechanisms are expected in Antarctic waters. The over-all effect of UVR on the ecosystem needs ro include relevant feedback mechanisms which can diminish, and sometimes reverse, deleterious ef-feers on population growth. For example. it has been speculated that UVR can increase iron-limited phytoplankton populations by photoin-duced reduction of Fe l- to Fe '-. a more soluble form of iron and readily avai lable for algal and bacterial uptake. An equally positive feedback can be attributed to diminished g razi ng by zooplankton. Thus. energy flow among [he troph ic levels can decrease as a result of damage to a certain trophic level. but overall biomass and ecosystem production might remain relatively unchanged. Similar positive and negative feedbacks associated wit h UVR are re-lated to the dissolved organic matter (DOM) pool, known to be recycled by baererial activity. Although it cou ld be expected t hat bacterial pro-duction in Antarctic surface waters would decrease when exposed to UVR, this effect can be counteracted by increased substrate nutrient availabi l-ity. Photolysis of high-molecular weight molecules by UVR produce