Although phenotypic plasticity can be advantageous in fluctuating environments, it may come too late if the environment changes fast. Complementary chromatic adaptation is a colorful form of phenotypic plasticity, where cyanobacteria tune their pigmentation to the prevailing light spectrum. Here, we study the timescale of chromatic adaptation and its impact on competition among phytoplankton species exposed to fluctuating light colors. We parameterized a resource competition model using monoculture experiments with green and red picocyanobacteria and the cyanobacterium Pseudanabaena, which can change its color within ∼7 days by chromatic adaptation. The model predictions were tested in competition experiments, where the incident light color switched between red and green at different frequencies (slow, intermediate, and fast). Pseudanabaena (the flexible phenotype) competitively excluded the green and red picocyanobacteria in all competition experiments. Strikingly, the rate of competitive exclusion was much faster when the flexible phenotype had sufficient time to fully adjust its pigmentation. Thus, the flexible phenotype benefited from its phenotypic plasticity if fluctuations in light color were relatively slow, corresponding to slow mixing processes or infrequent storms in their natural habitat. This shows that the timescale of phenotypic plasticity plays a key role during species interactions in fluctuating environments.Keywords: adaptive dynamics, cyanobacteria, phycocyanin, phycoerythrin, resource competition theory, Synechococcus.Fluctuations in environmental conditions pose serious challenges to organisms. Many organisms respond to environmental changes by physiological and morphological adaptations. This flexible strategy, known as phenotypic plasticity, may improve their fitness in the new environments (Agrawal 2001). For example, plants increase their leaf area during periods of reduced light (Sultan and Bazzaz 1993), cladocerans develop armored helmets in the presence of predators (Woltereck 1909;Laforsch and Tollrian 2004), and some green algae aggregate into colonies to reduce their edibility for grazers (Hessen and Van Donk 1993;Lampert et al. 1994).Intuitively, phenotypic plasticity seems a suitable strategy to cope with environmental fluctuations. However, adaptation takes time. If adaptation is too slow, organisms will not be able to keep up with changes in their environment, resulting in a permanent mismatch between the physiology of the organisms and their environmental conditions. Indeed, theory shows that adaptation can even be disadvantageous when it has a strong time delay (Padilla and Adolph 1996;Gabriel 2005). Yet, although many studies have investigated phenotypic plasticity in fluctuating environments (e.g., Chesson et al. 2004;Egas et al. 2004;Abrams 2006aAbrams , 2006bGélinas et al. 2007; Van der Stap et al. 2007), the timescale of phenotypic adaptation has received surprisingly little attention (Miner et al. 2005).The colorful process of complementary chromatic ad-E170 ...

Recent discoveries show that small unicellular nitrogen-fixing cyanobacteria are more widespread than previously thought and can make major contributions to the nitrogen budget of the oceans. We combined theory and experiments to investigate competition for nitrogen and light between these small unicellular diazotrophs and other phytoplankton species. We developed a competition model that incorporates several physiological processes, including the light dependence of nitrogen fixation, the switch between nitrate assimilation and nitrogen fixation, and the release of fixed nitrogen. Model predictions were tested in nitrogen-limited and lightlimited chemostat experiments using the unicellular nitrogen-fixing cyanobacterium Cyanothece sp. Miami BG 043511, the picocyanobacterium Synechococcus bacillaris CCMP 1333, and the small green alga Chlorella_cf sp. CCMP 1227. Parameter values of the species were estimated by calibration of the model in monoculture experiments. The model predictions were subsequently tested in a series of competition experiments at different nitrate levels. The model predictions were generally in good agreement with observed population dynamics. As predicted, in experiments with high nitrate input concentrations, the species with lowest critical light intensity (S. bacillaris) competitively excluded the other species. At low nitrate input concentration, nitrogen release by Cyanothece enabled stable coexistence of Cyanothece and S. bacillaris. More specifically, model simulations predicted that fixed nitrogen release by Cyanothece enabled S. bacillaris to become four times more abundant in the species mixture than it would have been in monoculture. This intricate interplay between competition and facilitation is likely to be a major determinant of the relative abundances of unicellular nitrogen-fixing cyanobacteria and non-nitrogen-fixing phytoplankton species in the oligotrophic ocean.

High-grading is the decision by fishers to discard fish of low value that allows them to land more valuable fish. A literature review showed high-grading is reported in commercial and non-commercial fisheries around the world, although the number of observations is small. High-grading occurs in fisheries that are restricted to land their total catch due to management, market or physical constraints. Using the mixed flatfish fishery as a model system, a dynamic state variable model simulation showed that high-grading of certain grades occurs throughout the year when their ex-vessel price is low. High-grading increases with the degree of quota restriction, while the level of over-quota discarding is unrelated to the quota level. The size composition of the high-graded catch differs from the landed catch. Due to the differences in the seasonal variation in size specific ex-vessel price, the effect of quota restrictions on the size composition of the discarded catch is nonlinear. High-grading is difficult to detect for the fishery inspection as it occurs on-board during the short period when the catch is processed. We conclude that highgrading is under-reported in fish stocks managed by restrictive quota, undermining the quality of stock assessments and sustainable management of exploited fish stocks.

As a contribution to the ecosystem approach to fisheries management, we estimated the effects of spawning closures on stock status, ecosystem impacts and economic performance. We focused on the flatfish fishery in the North Sea and explored how spawning closures for plaice and sole contribute to sustainable management of 4 target species (sole, plaice, turbot and brill). Seasonal patterns in fishing effort and catchability by age group and area were estimated to quantify the effect of different spawning closure scenarios on the selection pattern. The scenario performance was evaluated using indicators of stock status (spawning stock biomass), economic performance of the fishery (yield, revenue) and ecosystem impact (discards, bycatch of cod and rays, seabed integrity, fisheries-induced evolution). In a single-species context, spawning closures may be beneficial for the target species, while in a mixed fisheries and ecosystem context, negative effects may occur. A spawning closure for plaice combines positive effects on the plaice stock and the revenue with reductions of the negative impact for several ecosystem indicators and only a small negative effect on sea bed integrity. The effects did not differ when evaluated at current levels of effort or at maximum sustainable yield (MSY) effort. Tailor-made solutions are required that need to be developed in stakeholder consultation to trade-off the ecological and economic objectives. Mixed-species MSY was lower than the sum of the single-species MSYs.

No abstract