Diel vertical migration in marine dinoflagellates

Increasing precipitation and surface water temperature due to global change may strengthen stratification in coastal regions, which could influence the behavior of dinoflagellate diel vertical migration (DVM). DVM is a behavioral mechanism by which dinoflagellates can access photosynthetically active radiation near the surface, and nutrients at depth. During this process, cells may need to cross both salinity and temperature gradients (haloclines and thermoclines, respectively). My results show that different dinoflagellate species display unique DVM behaviors in stratified waters and increasing halo- and thermocline strength may act as barriers between the surface- and bottom water. There is, however, large variation in how dinoflagellates cope with stratification and even closely related species have different strategies. Different DVM strategies may lead to a niche separation among species, which was also observed in my research. Moreover, during powerful mixing of the water column i.e. during strong winds in situ, the continuous DVM behavior was disrupted. In addition, as indicated by my experiments, dinoflagellates were influenced by the combination of salinity and temperature. An increase in temperature had no significant effect on growth rate if cells were grown in low salinity environments. The results indicate higher growth rates for two bloom-forming species when growing in salinities corresponding to bottom water conditions on the west coast of Sweden. Thus, there is a trade-off for dinoflagellates between low-salinity light-rich surface conditions and high-nutrient, low-light and high salinity bottom water conditions. If different species have different optimal growth conditions, a geographical separation among species is to be expected. Furthermore, the results indicate that the primary trigger for vertical migration is light in combination with an internal clock controlling the behavior. I show that there is a positive phototactic response to both white, blue and red light and demonstrate that the non-photosynthetic photoreceptor rhodopsin gene exists and is expressed in the cells. Harmful algal blooms (HABs) affect nearly every coastal region of the world and dinoflagellate blooms is a major problem for the shellfish industry. Efforts are made into designing accurate models that predict harmful algae blooms and these models need to be derived from reliable experimental and observational data. High resolution sampling and repeated measurements in time is needed to be able to detect DVM behavior in the field and species-specific data may need to be coordinated and integrated in the models. To predict harmful algal blooms of vertically migrating species, the migration patterns and the growth rates in the natural environment should be further clarified for each species. If increasing precipitation and temperature strengthen the gradient in coastal regions, the nutrient-rich bottom water will be inaccessible to cells unable to migrate through the gradient. Thus, stronger stratification will benefit migrating species able to cross the gradient during DVM and generate more variability in were we can expect to find specific species in situ

Species- and stratification-dependent diel vertical migration behaviour of three dinoflagellate species in a laboratory study

This study shows that different species of the same genus can behave differently in relation to a salinity gradient and suggests that a halocline can act as a barrier to the diel vertical migration (DVM) of dinoflagellate species. In a laboratory study, we found that the dinoflagellates Ceratium furca, C. tripos and Dinophysis acuta did not cross a salinity gradient of 5 psu, but instead exhibited DVM exclusively below and above the halocline. Furthermore, C. tripos aggregated in the halocline during the night and migrated to the surface at midday, whereas C. furca aggregated in the halocline at midday and migrated downwards to the bottom during the dark period. Dinophysis acuta was found exclusively above the halocline, with the highest density in the surface water at midday. The present results suggest that different dinoflagellate species display unique DVM behaviours in stratified waters. The species-specific DVM strategies revealed in this study are of central importance for understanding the ecology of these taxa and to further elucidate both the ecological significance and the mechanisms of DVM

UV protective compounds transferred from a marine dinoflagellate to its copepod predator

Planktonic organisms living in surface waters can be exposed to harmful levels of ultraviolet radiation (UVR), but few studies have examined accumulation of UV protective compounds in marine zooplankton. Zooplankters are suggested to lack the ability to synthesize these substances and hence must accumulate them from their algal food. Here, we show that both phytoplankton (dinoflagellates) and their zooplankton grazers (copepods) respond strongly to UVR exposure by, respectively, synthesizing and accumulating the natural sunscreens mycosporine-like amino acids (MAAs). In our experiment, the MAAs content increased approximately four times in dinoflagellates exposed to UVR and PAR, as compared to non-UVR controls only receiving PAR (PAR = photosynthetically active radiation). The elevated MAAs level in the dinoflagellates was mirrored in the copepods, which accumulated more MAAs when exposed to UVR as compared to a non-UVR treatment. Overall, copepods accumulated approximately 2-5% of the total MAAs pool. Other UV protective compounds, like carotenoids, were however not accumulated by the copepods. The ability of some species to produce or accumulate photoprotective compounds may lead to increased fitness, and thus these taxa may become more dominant in plankton communities. (C) 2010 Elsevier B.V. All rights reserved

Molecular size of riverine dissolved organic matter influences coastal phytoplankton communities

Dissolved organic matter (DOM) concentrations in many northern European freshwater systems have been increasing during the past decades. DOM affects the marine plankton community where rivers discharge into the sea. Large DOM molecules have been suggested to be more available to aquatic plankton than smaller ones due to their more recent origin in the degradation process. In this study, we investigated the effect of riverine DOM molecular size on coastal plankton with the hypothesis that nitrogen associated with large molecules stimulates the plankton more than nitrogen in smaller molecules. Three size fractions of riverine DOM were isolated with tangential ultrafiltration and introduced at similar nitrogen concentrations to mesocosms with a natural coastal marine plankton community under nitrogen limiting conditions. The results show that growth of bacteria and dinoflagellates, but not diatoms, was stimulated by addition of large DOM molecules. Even though organic nitrogen concentrations tended to decrease more in large DOM treatments compared to smaller DOM treatments, no significant differences were detected. However, proteolytic enzyme activities were elevated in treatments with the largest DOM molecules, suggesting that more organic nitrogen was utilized in this treatment. We suggest that input of larger river DOM molecules to nitrogen limited coastal systems may influence the composition of the coastal phytoplankton community in favour of dinoflagellates

Dependency of dinoflagellate vertical migration on salinity stratification

Increasing precipitation and surface water temperature due to global change may strengthen the salinity gradient in coastal regions, which could influence the behaviour of dinoflagellate migration. We studied diel vertical migration (DVM) behaviour in the dinoflagellates Prorocentrum minimum and Heterocapsa triquetra using vertically stratified laboratory columns with 3 different salinity gradients (difference of 6, 11 and 16 psu). With nutrient-depleted conditions at the surface, and with nutrients added below the halocline, P. minimum remained mainly concentrated in the bottom water, while H. triquetra performed DVM under all 3 salinity treatments. H. triquetra migrated through a salinity difference of 6 and 11 psu, concentrated at the surface at noon, then migrated to the nutrient-rich bottom water during the night. A salinity gradient of 16, however, stopped H. triquetra cells from moving through the gradient and resulted in a concentration of cells in the cline during the night. At midday, cells were again found at the surface. P. minimum and H. triquetra grown in 4 different salinities (10, 15, 20, 26 psu) and at 3 different temperatures (10, 15, 20 degrees C) showed higher specific growth rates with increasing temperature only in the 2 highest salinity treatments. At 10 degrees C, specific growth rates were not affected by different salinities

Dominant impact of water exchange and disruption of stratification on dinoflagellate vertical distribution

The vertical positions of four dinoflagellate species in three 48 h periods in late summer in a Swedish fjord (the Gullmar Fjord) reflect changes to the depth of the halocline. During stable, stratified conditions, the chlorophyll a maximum exhibited a diurnal migration pattern, which was disrupted when the halocline was forced closer to the surface by the inflow of more saline water. While conditions were stable, all studied dinoflagellate species were most abundant below the halocline at 06:00 in contrast to the other times of the day when the highest cell concentrations were above the halocline, indicating diurnal vertical migration. However, when wind-induced inflow of more saline water forced the halocline closer to the surface, these patterns were disrupted and there was no sign of diurnal vertical migration. Despite this, there was a vertical heterogeneity in the distribution of dinoflagellates with Dinophysis spp. found mainly above the halocline, while Ceratium spp. also occurred in high cell numbers below the halocline. We acknowledge the importance of representative resolution when sampling in the field, both in time and concerning vertical resolution. (C) 2012 Elsevier Ltd. All rights reserved

Trophic interactions in Zostera marina beds along the Swedish coast

We compared eelgrass Zostera marina communities in 3 regions in Sweden believed to be affected by eutrophication and overfishing, to determine whether bottom-up or top-down processes control the biomass of epiphytic macroalgae and grazers. Nitrogen and carbon isotope signatures were analyzed to explore the food webs and to identify the grazing species feeding on filamentous algae and/or eelgrass. Mixing model (IsoSource version 1.3.1) analysis of the isotope signatures indicated that the amphipods Gammarus locusta and Microdeutopus gryllotalpa fed primarily on filamentous algae and that only 2 small gastropod species consumed eelgrass. Moreover, the grass shrimp Palaemon elegans and F adspersus were ca. 1 trophic level above amphipods and algae, but according to the mixing model played different trophic roles in the different areas. The highest biomass of filamentous algae was found in the west coast beds housing grazers with the lowest biomass and mean size (predominantly G. locusta and M. gryllotalpa, 0.5 to 3 mm). In contrast, the Baltic Sea beds had low algal biomass, but the grazers (mostly G. locusta and Idotea baltica) had higher biomass and were significantly larger (mean size ca. 10 mm). An overall negative correlation was found between grazer biomass and biomass of filamentous algae. The significantly smaller grazers and absence of isopod grazers on the west coast may be due to substantial consumption by small predatory fish. This supports the suggestions that, in Swedish eelgrass beds, grazers are top-down controlled, and overexploitation. of large predators and eutrophication play an important role in the recent increases in algal biomass

Species-specific dinoflagellate vertical distribution in temperature-stratified waters

Thermal stratification is increasing in strength as a result of higher surface water temperature. This could influence the vertical distribution of vertically migrating dinoflagellates. We studied the diel vertical distribution of the dinoflagellates Heterocapsa triquetra and Prorocentrum minimum using stratified laboratory columns with two thermoclines of different strength (Delta TA degrees A = 10 or 17 A degrees C), with below cline temperature of 8 A degrees C. Above the thermocline, nutrient depletion simulated the natural summer conditions in the Baltic Sea. Our study shows that H. triquetra and P. minimum can behave differently in terms of their vertical occurrence, both in space and in time when subjected to thermoclines of different strength. Also, both dinoflagellate species showed species-specific distribution patterns. In the Delta TA degrees A = 10 A degrees C treatment, H. triquetra cells performed a diel vertical migration (DVM) behavior just above the thermocline, but not in the Delta TA degrees A = 17 A degrees C. In the Delta TA degrees A = 17 A degrees C, the cells did not migrate and cell densities in the water column decreased over time. Opposing results were observed for P. minimum, where a DVM pattern was found exclusively below the thermocline of Delta TA degrees A = 17 A degrees C, while in the Delta TA degrees A = 10 A degrees C treatment, no clear DVM pattern was observed, and the highest number of cells were found in the cold bottom water. These results indicate that an increase in thermal stratification can influence species-specific dinoflagellate distribution, behavior, and survival

Glacial clay affects foraging performance in a Patagonian fish and cladoceran

Climate change is altering temperatures and precipitation patterns all over the world. In Patagonia, Argentina, predicted increase in precipitation together with rapidly melting glaciers increase the surface runoff, and thereby the transport of suspended solids to recipient lakes. Suspended solids affect the visual conditions in the water which in turn restricts visual foraging. The native fish Aplochiton zebra Jenyns, and its filter-feeding cladoceran prey, Daphnia commutata Ekman, were subjected to foraging experiments at three turbidity levels. A. zebra foraging rate was substantially reduced at naturally occurring turbidity levels and the filtering rate of D. commutata was reduced at the highest turbidity level. This indicates that Daphnia may be partly released from predation from A. zebra at the same time as it can maintain relatively high feeding rates as turbidity increases. Lower foraging rates at the same time as the metabolic demand increases, through increased temperatures, may result in larger effects on A. zebra than could be expected from increases in turbidity or temperature alone. Turbidity may, as an indirect effect of climate change, decrease planktivore foraging rates and thereby alter the interaction strength between trophic levels

Environmental compensation as a policy tool in Swedish municipal planning

In the struggle to reach the national environmental policy objectives, environmental compensation has emerged as a possible policy tool that may contribute to achieving the objectives. In Sweden, environmental compensation is legally mandated mainly in cases of exploitation within Natura 2000 areas and nature reserves, which is handled through the Swedish Environmental Code. In contrast, regulatory support is weak when it comes to compensation for impacts arising from municipal development (e.g., housing, schools, hospitals, local roads, etc), even though detailed development planning is required through the Planning and Building Act. Despite this, some municipalities have voluntarily mainstreamed environmental compensation into their planning processes. In the research project ”MuniComp” (2018-2020) we investigate the more progressive use of environmental compensation in planning in two Southern Swedish municipalities, Lomma and Helsingborg (in the province of Skåne). We analyze the models and processes of compensation used, and planning cases where compensation have been applied, in terms of general aspects and criteria for environmental compensation and in light of the constraints of the Swedish legislative context. In the presentation, the compensation models and some of the results from the compensation cases will be presented