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Striebel M.,University of Oslo | Singer G.,WasserCluster Lunz | Singer G.,University of Vienna | Stibor H.,Ludwig Maximilians University of Munich | And 2 more authors.
Ecology | Year: 2012

Diversity-productivity relationships at the primary producer level have been extensively studied, especially for terrestrial systems. Here, we explore whether the diversity of aquatic primary producers (phytoplankton) has effects on higher trophic levels (zooplankton). We investigated the effect of phytoplankton diversity on an artificial zooplankton community in a laboratory experiment where phytoplankton biomass and elemental composition (carbon-to-phosphorus ratio) were kept constant. Phytoplankton diversity increased the means of both zooplankton growth rate and abundance while suppressing their variability, and sustained higher zooplankton diversity. Likely explanations include resource complementarity effects among phytoplankton species as food entities, as well as niche complementarity effects among Daphnia species as competitors. By affecting the productivity as well as the variability of the next trophic level, biodiversity of primary producers may have far-reaching consequences in aquatic food webs. © 2012 by the Ecological Society of America.

Behl S.,Ludwig Maximilians University of Munich | Donval A.,European Institute for Marine Studies | Stiborb H.,European Institute for Marine Studies
Limnology and Oceanography | Year: 2011

We conducted laboratory experiments with 85 assembled phytoplankton communities composed of species from four predefined functional groups (chlorophytes, diatoms, cyanobacteria, chrysophytes) to distinguish the relative importance of species diversity from functional group diversity on carbon uptake. We separated the observed diversity effects on carbon uptake into those caused by species with particularly important traits (selection effect) and those caused by positive interactions among species (e.g., complementary resource use or facilitation [complementarity effect]). Additionally, we measured the composition of photosynthetically active pigments and light absorbance in communities and monocultures, and related them to species and functional diversity effects on carbon accrual. Biodiversity effects were weak or even absent in pure cyanobacterial and diatom communities compared to strong effects in chlorophytes. Complementarity effects and light absorbance increased as functional (i.e., phylogenetic) diversity increased. There was a positive correlation between complementarity effects on carbon accrual and light absorbance. These findings support hypotheses regarding biodiversity- productivity relationships in phytoplankton communities based on niche separation along spectral light gradients.

Stockenreiter M.,Ludwig Maximilians University of Munich | Graber A.-K.,Ludwig Maximilians University of Munich | Haupt F.,Ludwig Maximilians University of Munich | Stibor H.,European Institute for Marine Studies
Journal of Applied Phycology | Year: 2012

Current research investigating the importance of diversity for biofuel lipid production remains limited. In contrast, the relationship between diversity and productivity within terrestrial and algal primary producers has been well documented in ecology. Hence, we set out to investigate, experimentally, whether diversity may also affect lipid production in micro-algae. We investigated the growth and lipid production of micro-algae using species from all major algal groups. Algae were grown in a large number of treatments differing in their diversity level. Additionally, we compared the growth and lipid production of laboratory communities to natural lake and pond phytoplankton communities of different diversity. Our results show that lipid production increased with increasing diversity in both natural and laboratory micro-algal communities. The underlying reason for the observed 'diversity-productivity' relationship seems to be resource use complementarity. We observed higher lipid production of highly diverse algal communities under the same growth and resource supply conditions compared to monocultures. Hence, the incorporation of the ecological advantages of diversity-related resource-use dynamics into algal biomass production may provide a powerful and cost effective way to improve biofuel production. © 2011 Springer Science+Business Media B.V.

Diehl S.,Ludwig Maximilians University of Munich | Diehl S.,Umea University | Berger S.A.,Ludwig Maximilians University of Munich | Berger S.A.,Leibniz Institute of Freshwater Ecology and Inland Fisheries | And 4 more authors.
ICES Journal of Marine Science | Year: 2015

Sverdrup's critical depth hypothesis, which has had an almost canonical status in biological oceanography, has recently been challenged as a universal explanation for the formation of oceanic spring blooms, and several alternative hypotheses have been proposed. Arguments pro and contra alternative explanations have so far relied on theoretical considerations and purely observational data. In this paper, we propose that mesocosm experiments with natural plankton communities could make important contributions to the resolution of the issue. We first briefly review the foundations of the critical depth concept and derive an approximate relationship that relates optically scaled critical depth (="critical optical depth", i.e. the product of the light attenuation coefficient and the critical depth) to light-dependent phytoplankton production in the mixed surface layer. We describe how this relationship can be used to scale experimental mesocosms such that they reproduce ambient light conditions of natural water columns from the surface down to the critical depth and beyond. We illustrate the power of the approach with a mesocosm study in which we experimentally controlled the onset of the spring bloom of a lake plankton community through the manipulation of optically scaled mixed-layer depth. This experiment may be the first experimental demonstration of the critical depth principle acting on a natural plankton community. Compensation light intensity (=minimum average mixed-layer light intensity required to trigger a bloom of the ambient plankton community) could be constrained to be somewhat above 3.2 moles PAR m-2 d-1, corresponding to a critical optical depth of 10.5. We compare these numbers to estimates from marine systems and end with a discussion of how experiments could be designed to (i) more accurately determine the critical depth in a given system and (ii) resolve among competing hypotheses for vernal bloom onset. © 2015 International Council for the Exploration of the Sea. All rights reserved.

Trommer G.,University of Tubingen | Trommer G.,European Institute for Marine Studies | Siccha M.,University of Tubingen | Siccha M.,Hebrew University of Jerusalem | And 6 more authors.
Climate of the Past | Year: 2011

This study investigates the response of Red Sea circulation to sea level and insolation changes during termination II and across the last interglacial, in comparison with termination I and the Holocene. Sediment cores from the central and northern part of the Red Sea were investigated by micropaleontological and geochemical proxies. The recovery of the planktic foraminiferal fauna following high salinities during marine isotopic stage (MIS) 6 took place at similar sea-level stand (∼50 m below present day), and with a similar species succession, as during termination I. This indicates a consistent sensitivity of the basin oceanography and the plankton ecology to sea-level forcing. Based on planktic foraminifera, we find that increased water exchange with the Gulf of Aden especially occurred during the sea-level highstand of interglacial MIS 5e. From MIS 6 to the peak of MIS 5e, northern Red Sea sea surface temperature (SST) increased from 21 °C to 25 °C, with about 3 °C of this increase taking place during termination II. Changes in planktic foraminiferal assemblages indicate that the development of the Red Sea oceanography during MIS 5 was strongly determined by insolation and monsoon strength. The SW Monsoon summer circulation mode was enhanced during the termination, causing low productivity in northern central Red Sea core KL9, marked by high abundance of G. sacculifer, which ĝ€" as in the Holocene ĝ€" followed summer insolation. Core KL11 records the northern tip of the intruding intermediate water layer from the Gulf of Aden and its planktic foraminifera fauna shows evidence for elevated productivity during the sea-level highstand in the southern central Red Sea. By the time of MIS 5 sea-level regression, elevated organic biomarker BIT values suggest denudation of soil organic matter into the Red Sea and high abundances of G. glutinata, and high reconstructed chlorophyll-a values, indicate an intensified NE Monsoon winter circulation mode. Our results imply that the amplitude of insolation fluctuations, and the resulting monsoon strength, strongly influence the Red Sea oceanography during sea-level highstands by regulating the intensity of water exchange with the Gulf of Aden. These processes are responsible for the observation that MIS 5e/d is characterized by higher primary productivity than the Holocene. © Author(s) 2011.

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