We quantified and compared the photophysiological characteristics of Emiliania huxleyi with two marine diatoms Thalassiosira pseudonana and Coscinodiscus sp. under nitrogen-and phosphorus-replete and -depleted conditions. Under nitrogen-depleted conditions, E. huxleyi maintained significant photosystem II (PSII) function over at least 38 d, whereas for both diatoms, PSII function declined to marginal levels within 8-10 d of nitrogen depletion. In contrast, under phosphorus-depleted conditions, PSII function in E. huxleyi declined sharply within 7 d and in T. pseudonana within 3 d. Under nutrient-replete conditions, E. huxleyi had one of the highest PSII repair rate constants among phytoplankton examined to date. Under nitrogen depletion, E. huxleyi exhibited a decrease in susceptibility to photoinactivation of PSII, while the diatoms showed no significant change in susceptibility. The superior ability of E. huxleyi relative to the diatoms to limit PSII photoinactivation as well as to maintain PSII repair for many days of nitrogen depletion could help to explain why E. huxleyi is able to form blooms under the low-nitrate, high-light conditions that frequently occur in stratified surface waters.

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The introduced cordgrass Spartina anglica, a fertile hybrid of S. maritima and S. alterniflora, grows as a pioneer plant in the upper intertidal zone and has invaded most sheltered shorelines of the Wadden Sea. After its introduction in 1927 S. anglica has spread vigorously along the mainland shore and on some of the more southern islands. In contrast, it has later established on Sylt and spread at a lower pace. On the island of Sylt it occurs near at its northern limit in Europe. Due to rising sea level and storm frequency a decrease or steady state of S. anglica was expected because its niche is narrowing rather than widening and plants are more frequently eroded. Contrary to that, many new sites were colonized and dense monotypic swards have formed after 1985. This new spread coincided with a shift in the local temperature regime around 1987. The monthly mean temperature from January to April has increased significantly after 1987. Furthermore, the important physiological thresholds of 4°C for germination and 7°C for photosynthesis were more often exceeded during spring after 1987 than before. We suggest that warmer spring seasons since 1988 could have promoted germination, growth and the recent accelerated spread of this neophyte.

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