Resilience of North Sea phytoplankton spring bloom dynamics: An analysis of long‐term data at Helgoland Roads

Abstract

Analyzing one of the most extensive long-term data series in the North Sea, the Helgoland Roads time series, we investigated the changes in the factors that potentially drive phytoplankton bloom dynamics in the German Bight. We compared the changes in these factors with the changes in the spring bloom phenology. We combined zooplankton, nutrient, weather, and phytoplankton data to analyze whether there has been a shift in trophic interactions in the North Sea affecting the spring bloom timing. The potential influence of temperature, with a mean increase of 1.5uC, was investigated. We showed that the German Bight around Helgoland is a highly dynamic system and has undergone considerable change in the last 30 yr. Nutrient levels, temperature, underwater light climate and wind speed have all changed. However, the spring bloom dynamics have hardly changed at all. We showed that the spring bloom tends to come later in warmer years but that this is not directly correlated with the overall warming trend. The known regime shift of the late 1980s is clearly visible in our data in terms of average phytoplankton winter densities and average cell size, but even so the start of the spring bloom has not changed.

Study on the effects of near-future ocean acidification on marine yeasts: a microcosm approach

“…This could be related to seasonality, as especially D. hansenii was reported to occur with algal blooms and is closely related to high nutrient situations (Meyers et al 1967;Ahearn and Crow 1980). In contrast, our study was carried out in mid-April, at the beginning of the spring bloom (chlorophyll a on April 14, 2011: 4.5 lg l -1 , maximum on April 26, 2011: 15.4 lg l -1 ; data obtained from the Helgoland Roads time series (Wiltshire et al 2008)). Furthermore, although year-round sampling campaigns were previously conducted, no reports about cold-adapted yeast species exist.…”

Temporal and Spatial Distribution Patterns of Potentially Pathogenic Vibrio spp. at Recreational Beaches of the German North Sea

“…Due to its semi-enclosed character, the North Sea is one of the seas most vulnerable towards such ocean warming trends [28]. Mean sea surface temperatures in the North Sea have increased two to four times faster than average, more than 1.3°C in the last decades [28][29][30]. The probability of extreme summers and years has more than doubled simultaneously [29], both of which could support the spreading of potentially pathogenic vibrios in this region.…”

Changes in the phytoplankton community at Helgoland, North Sea: lessons from single spot time series analyses

“…These species-comprehensive changes suggest that changes affected the whole habitat, an interpretation that is supported by Wiltshire et al (2008Wiltshire et al ( , 2010, who estimated trends for the habitat from the Helgoland Roads data. The fact that statistically significant shifts of the niche were detected mainly for the second break point indicates that driving mechanisms for these shifts have to be searched within the set of factors causing the later regime shift, that is, water temperature and weather conditions (Weijerman et al 2005).…”

“…A t-test (with 10 degrees of freedom (Zülicke and Peters 2010)) confirmed that the difference in salinity levels is highly significant (p = 0.001). Although no statistically significant trend of annual salinity averages (Wiltshire et al 2008), there was an increase in annual salinity means between the two considered periods (1968-1988 and 1989-2008) of 0.42 psu (difference between the medians 0.32 psu). However, this can only partly explain the increase of 0.8 psu we observed with the BTA segments (lengths 100 days) underlining the importance of a BTA.…”