Long-term changes in the seasonality of selected diatoms related to grazers and environmental conditions

Abstract

The decoupling of trophic interactions could be one of the severe consequences of climate warming in aquatic systems. The timing of phytoplankton blooms, in particular, can affect competition within the plankton community as well as food-web interactions with zooplankton and fish. Using long-term data from Helgoland Roads in the southern North Sea, we examine diatom seasonality, using three representative diatom species combined with environmental and copepod time series over the last four decades. The long-term annual abundances of Guinardia delicatula, Thalassionema nitzschioides and Odontella aurita exhibited interannual variations and dissimilar cyclic patterns during the time period under study . Of the three diatoms, G. delicatula showed a significant trend towards earlier bloom timings for 1962-2008 and a later decline of its abundance over time was found. Grazing and water transparency explained most of the bloom timing fluctuations of the diatoms considered. The annual timing of occurrences of each diatom species was correlated with their preceding concentrations. Earlier bloom timings occurred when autumn/winter concentrations were higher than average and later bloom timings occurred when autumn/winter concentrations were lower than average. Different environmental and predation variables related to the diatom bloom timings were found suggesting that climate warming might not affect the onset of the blooms of the three diatom species in the same manner. The results of the multiple linear regression analyses showed that the timings of decline of the three diatoms were mainly correlated with decreasing nutrient concentrations. Sunshine duration could prolong the duration of the blooms of T. nitzschioides and O. aurita provided that enough nutrients were available. In the case of G. delicatula, however, sunshine duration was negatively correlated with its end of the growth period. G. delicatula and T. nitzschioides showed later decreases in abundances under warmer spring and summer temperatures. Such species specific differences in the sensitivity to the forcing variables could lead to shifts in community structure and could ultimately have wider implications to the overall ecosystem health of the North Sea.

Parasitic infection of the diatom Guinardia delicatula, a recurrent and ecologically important phenomenon on the New England Shelf

“…From an ecological perspective, major questions persist concerning the factors that promote diatom bloom events and determine how long a bloom lasts. Schlüter et al (2012) have recorded 45 yr of G. delicatula blooms showing a predominantly summer bloom with decadal scale changes in duration and timing of onset; in our shorter time series, we also see some variation, but with a predominantly winter bloom. The nanoflagellate parasite of G. delicatula is recognizable throughout our data set during 2 of its presumed 3 life stages due to the distinct morphology within G. delicatula frustules during infection.…”

“…While many species are present in the MVCO time series and blooms are typically multispecies events, G. delicatula represents one of the greatest contributors to phytoplankton biomass, which is also true in another temperate coastal time series (Schlüter et al 2012). From an ecological perspective, major questions persist concerning the factors that promote diatom bloom events and determine how long a bloom lasts.…”

Environmental Impacts—Marine Ecosystems

“…The diversity of dinoflagellates has increased in the Northeast Atlantic and in the North Sea as both temperature and seasonal stability in temperature have increased, whereas diatoms, which have higher diversity at intermediate and less seasonally stable temperatures, have shown less increase in diversity. Analysis of daily (work days) sampling of phytoplankton, nutrients and temperature at Helgoland Roads (54°11′ 3″N, 7°54′E) from 1962 to 2008 showed that the phenology of three diatom species Guinardia delicatula, Thalassionema nitzschioides and Odontella aurita did not respond to climate warming in the same way and that overwintering population size, grazing, nutrient levels and water clarity affected their bloom timing (Schlüter et al 2012). Such species-specific differences in sensitivity to forcing factors could lead to shifts in community structure with potentially far-reaching consequences for ecosystem dynamics.…”

“…trophic level) are sufficient to predict future outcomes or whether careful study of the individual species is required, however the differences in phenological responses between different diatom species indicates the latter (Schlüter et al 2012).…”

Analysis of phytoplankton distribution and community structure in the German Bight with respect to the different size classes

“…Information is available regarding seasonal succession patterns (Hagmeier and Bauerfeind, 1990;Reid et al, 1990), response to environmental factors (Freund et al, 2012;Gillbricht, 1988;Hickel, 1998;Schlüter et al, 2012), and biodiversity (Hoppenrath, 2004;Hoppenrath et al, 2007;Wiltshire and Dürselen, 2004). However, since most of this information is based on microscopic observation, it covers mainly the microphytoplankton (20-200 μm).…”