Morten Foldager Pedersen

Estuarine nutrient cycling: The influence of primary producers

Interactions Between Vegetation And Nutrient Dynamics In Coastal Marine Ecosystems: An Introduction by M.F. Pedersen, S.L. Nielsen and G.T. Banta Estuarine Primary Producers by K. Sand-Jensen and S.L. Nielsen Effects Of Nutrient Loading On Shallow Seagrass-Dominated Coastal Systems: Patterns And Processes by J. Hauxwell and I. Valiela Plant Bound Nutrient Transport. Mass Transport In Estuaries And Lagoons by M.R. Flindt, J. Neto, C.L. Amos, M.A. Pardal, A. Bergamasco, C.B. Pedersen and F.O. Andersen Grazing On Pelagic Primary Producers - The Role Of Benthic Suspension Feeders In Estuaries by J.K. Petersen Grazing On Benthic Primary Producers by J. Cebrian Decomposition Of Marine Primary Producers: Consequences For Nutrient Recycling And Retention In Coastal Ecosystems by G.T. Banta, M.F. Pedersen and S.L. Nielsen Burial Of Nutrient In Coastal Sediments: The Role Of Primary Producers by J.J. Middelburg, K. Soetaert, P.M.J. Herman, H.T.S. Boschker and C.R. Heip The Importance Of Primary Producers For Benthic Nitrogen And Phosphorus Cycling by K.J. McGlathery, K. Sundback and I.C. Anderson Denitrification by N. Risgaard-Petersen Attempting A Synthesis - Plant/Nutrient Interactions by S.L. Nielsen, M.F. Pedersen and G.T. Banta

Epibiota communities of the introduced and indigenous macroalgal relatives Sargassum muticum and Halidrys siliquosa in Limfjorden (Denmark)

Sargassum muticum (Phaeophyceae, Fucales) has recently been introduced to Limfjorden (Denmark) where its closest relative is the indigenous Halidrys siliquosa. Previous studies have demonstrated large quantitative (canopy biomass) and qualitative (canopy persistence) differences in the habitat available to epibiota within the canopies of these two macroalgae. We therefore hypothesised that these algae would support different epibiota communities and tested this by sampling the epibiota of S. muticum and H. siliquosa on seven occasions throughout 1997 by enclosing entire thalli in mesh bags. We found 53 epibiota taxa and, with only one exception, they were all recorded on both host species. Species richness and abundance of epibiota exhibited clear seasonal variation on both host species, although epibiota biomass was seasonally constant on H. siliquosa but not on S. muticum. These patterns were consistent with the different life histories of the host species. There was a weakly negative correlation between thallus size and epibiota biomass for both host species. When taking species-specific seasonal variation in thallus size into consideration, S. muticum and H. siliquosa were found to support significantly different epibiota biomasses. Multivariate analyses showed that epibiota community structure was different, although highly overlapping, between the two species, whereas there was an almost parallel temporal development in epibiota community structure. We conclude that it is unlikely that the introduction of S. muticum to Limfjorden has caused major changes in local epibiota community structure. However, the standing stock of epibiota is likely to have increased.

The Response of Experimental Rocky Shore Communities to Nutrient Additions

The aim of this study was to determine whether the experimental nutrient enrichment of littoral rocky shore communities would be followed by a predicted accumulation of fast-growing opportunistic algae and a subsequent loss of perennial benthic vegetation. Inorganic nitrogen (N) and potassium (P) was added to eight concrete mesocosms inhabited by established littoral communities dominated by fucoids. The response to nutrient enrichment was followed for almost 2 1/2 years. Fast-growing opportunistic algae (periphyton and ephemeral green algae) grew significantly faster in response to nutrient enrichment, but the growth of red filamentous algae and large perennial brown algae was unaffected. However, these changes were not followed by comparable changes in the biomass and composition of the macroalgae. The biomass of opportunistic algae was stimulated only marginally by the nutrient enrichment, and perennial brown algae (fucoids) remained dominant in the mesocosm regardless of nutrient treatment level. Established rocky shore communities thus seem able to resist the effects of heavy nutrient loading. We found that the combined effects of the heavy competition for space and light imposed by canopy-forming algae, preferential grazing on opportunistic algae by herbivores, and physical disturbance, succeeded by a marked export of detached opportunistic algae, prevented the fast-growing algae from becoming dominant. However, recruitment studies showed that the opportunistic algae would become dominant when free space was available under conditions of high nutrient loading and low grazing pressure. These results show that established communities of perennial algae and associated fauna in rocky shore environments can prevent or delay the accumulation of bloom-forming opportunistic algae and that the replacement of long-lived macroalgae by opportunistic species at high nutrient loading may be a slow process. Nutrient enrichment may not, in itself, be enough to stimulate structural changes in rocky shore communities.

Regulation of eelgrass (Zostera marina) cover along depth gradients in Danish coastal waters

A large data set, collected under the national Danish monitoring program, was used to evaluate the importance of photon flux density (PFD), relative wave exposure (REI), littoral slope, and salinity in regulating eelgrass cover at different depth intervals in Danish coastal waters. Average eelgrass cover exhibited a bell-shaped pattern with depth, reflecting that different factors regulate eelgrass cover at shallow- and deep-water sites. The multiple logistic regression analysis was used to identify regulating factors and determine their role in relation to eelgrass cover at different depth intervals. PFD, REI, and salinity were main factors affecting eelgrass cover while littoral slope had no significant effect. Eelgrass cover increased with increasing PFD at water depths of more than 2 m, while cover was in versely related to REI in shallow water. This pattern favored eelgrass cover at intermediate depths where levels of PFD and REI were moderate. Salinity had a minor, but significant, effect on eelgrass cover that is most likely related to the varying costs of osmoregulation with changing salinity. The analysis provided a useful conceptual framework for understanding the factors that regulate eelgrass abundance with depth. Although the regression model was statistically significant and included the factors generally considered most important in regulating eelgrass cover, its explanatory power was low, especially in shallow water. The largest discrepancies between predicted and observed values of cover appeared in cases where no eelgrass occurred despite sufficient light and moderate levels of exposure (almost 50% of all observations). These discrepancies suggest that population losses due to stochastic phenomena, such as extreme wind events, played an important regulating role that is not adequately described by average exposure levels. A more thorough knowledge of the importance of such loss processes and the time scales involved in recovery of seagrass populations after a severe disturbance are necessary if we are to understand the regulation of seagrass distribution in shallow coastal areas more fully.

THE EFFECT OF GROWTH IRRADIANCE ON THE COUPLING OF CARBON AND NITROGEN METABOLISM IN CHAETOMORPHA LINUM (CHLOROPHYTA)

The influence of growth irradiance on the non‐steady‐state relationship between photosynthesis and tissue carbon (C) and nitrogen (N) pools in Chaetomorpha linum (Muller) Kutzing in response to abrupt changes in external nitrogen (N) availability was determined in laboratory experiments. For a given thallus N content, algae acclimated to low irradiance consistently had a higher rate of light‐saturated photosynthesis (Pmax normalized to dry weight) than algae acclimated to saturating irradiance; for both treatments, Pmax was correlated to thallus N. Both Pmax and the photosynthetic efficiency (αdw) were correlated in C. linum grown at either saturating or limiting irradiance over the range of experimental conditions, indicating that variations in electron transport were coupled to variations in C‐fixation capacity despite the large range of tissue N content from 1.1% to 4.8%. Optimizing both α and Pmax and thereby acclimating to an intermediate light level may be a general characteristic of thin‐structured opportunistic algae that confers a competitive advantage in estuarine environments in which both light and nutrient conditions are highly variable. Nitrogen‐saturated algae had the same photosynthesis–irradiance relationship regardless of light level. When deprived of an external N supply, photosynthetic rates did not change in C. linum acclimated to low irradiance despite a two‐fold decrease in tissue N content, suggesting that the active pools of chlorophyll and Rubisco remained constant. Both α and Pmax decreased immediately and continuously in algae acclimated to high irradiance on removal of the N supply even though tissue N content was relatively high during most of the N‐starvation period, indicating a diversion of energy and reductant away from C fixation to support high growth rates. Carbon and nitrogen assimilation were equally balanced in algae in both light treatments throughout the N‐saturation and ‐depletion phases, except when protein synthesis was limited by the depletion of internal N reserves in severely N‐starved high‐light algae and excess C accumulated as starch stores. This suggests that the ability for short‐term adjustment of internal allocation to acquire N andC in almost constant proportions may be especially beneficial to macroalgae living in environments characterized by high variability in light levels and nutrient supply.

Temperature acclimation and heat tolerance of photosynthesis in Norwegian Saccharina latissima (Laminariales, Phaeophyceae)

Kelps, seaweeds and seagrasses provide important ecosystem services in coastal areas, and loss of these macrophytes is a global concern. Recent surveys have documented severe declines in populations of the dominant kelp species, Saccharina latissima, along the south coast of Norway. S. latissima is a cold‐temperate species, and increasing seawater temperature has been suggested as one of the major causes of the decline. Several studies have shown that S. latissima can acclimate to a wide range of temperatures. However, local adaptations may render the extrapolation of existing results inappropriate. We investigated the potential for thermal acclimation and heat tolerance in S. latissima collected from three locations along the south coast of Norway. Plants were kept in laboratory cultures at three different growth temperatures (10, 15, and 20°C) for 4–6 weeks, after which their photosynthetic performance, fluorescence parameters, and pigment concentrations were measured. S. latissima obtained almost identical photosynthetic characteristics when grown at 10 and 15°C, indicating thermal acclimation at these temperatures. In contrast, plants grown at 20°C suffered substantial tissue deterioration, and showed reduced net photosynthetic capacity caused by a combination of elevated respiration and reduced gross photosynthesis due to lowered pigment concentrations, altered pigment composition, and reduced functionality of Photo‐system II. Our results support the hypothesis that extraordinarily high temperatures, as observed in 1997, 2002, and 2006, may have initiated the declines in S. latissima populations along the south coast of Norway. However, observations of high mortality in years with low summer temperatures suggest that reduced population resilience or other factors may have contributed to the losses.

High Organic Carbon Export Precludes Eutrophication Responses in Experimental Rocky Shore Communities

AbstractWe studied the effect of nutrient inputs on the carbon (C) budget of rocky shore communities using a set of eight large experimental mesocosms. The mesocosms received a range of inorganic nitrogen (N) and phosphorus (P) additions, at an N:P ratio of 16. These additions were designed to elevate the background concentration, relative to that in eutrophic Oslofjord (Norway) waters, by 1, 2, 4, 8, 16, 32 μmol dissolved inorganic nitrogen (DIN)l−1 (and the corresponding P increase). Two unamended mesocosms were used as controls. The nutrients were added continuously for 27 months before gross primary production (GPP), respiration (R), net community production (NCP), and dissolved organic carbon (DOC) production were assessed for the dominant algal species (Fucus serratus) and for the whole experimental ecosystem. Inputs and outputs of DOC and particulate organic carbon (POC) from the mesocosms were also quantified. The F. serratus communities were generally autotrophic (average P/R ratio = 1.33 ± 0.12), with the GPP independent of the nutrient inputs to the mesocosms, and maintained a high net DOC production during both day (0.026 ± 0.008 g C m−2 h−1) and night (0.015 ± 0.004 g C m−2 h−1). All the experimental rocky shore ecosystems were autotrophic (P/R ratio = 2.04 ± 0.28), and neither macroalgal biomass nor production varied significantly with increasing nutrient inputs. Most of the excess production from these autotrophic ecosystems was exported from the systems as DOC, which accounted for 69% and 58% of the NCP of the dominant community and the experimental ecosystem, respectively, the rest being lost as POC. High DOC release and subsequent export from the highly energetic environments occupied by rocky shore communities may prevent the development of eutrophication symptoms and render these communities resistant to eutrophication.

Growth, photosynthesis and nutrient content of seedlings and mature plants of Cymodocea nodosa — the importance of clonal integration

Abstract This paper presents data on nutrient (N and P) content, chlorophyll content, dark respiration, photosynthetic rate and relative growth rate of four types of shoots of Cymodocea nodosa in Alfacs Bay, NE Spain: (1) seedlings, i.e. young shoots still attached to the seed coat, (2) shoots in runners, i.e. shoots growing in fast-growing horizontal rhizomes extending centrifugally from the patch edge, (3) mature shoots with well-developed rhizomes growing in the patch proper, and (4) isolated mature shoots not attached to a seed coat and with rhizomes, but growing singly or with only a few (

The effect of temporal variability in salinity on the invasive red alga Gracilaria vermiculophylla

Non-native, invasive species are often characterized by being tolerant to environmental stressors, leaving them more fit relative to native species. The red alga Gracilaria vermiculophylla originates from the NW Pacific but has recently spread along the coastlines of Western Europe, where it has become abundant in many shallow, soft-bottom estuaries. Salinity is important for the local and regional distribution of algae. The distribution of G. vermiculophylla in Europe suggests that it thrives well in hyposaline environments and that it may be more fit than some native algae under such conditions. Little, however, is known about the ecophysiology of G. vermiculophylla and it is therefore difficult to predict its spread and future distribution. Laboratory experiments with G. vermiculophylla showed that steady-state salinity above 15 psu was optimal for growth and that the growth rate was reduced at salinities below 15 psu. Variable salinity reduced the growth rate and larger oscillations were more stressful than small ones. Exposure to very low salinity (0–5 psu) was stressful for the alga and algae exposed to these low levels for 2–4 days were unable to recover fully. Gracilaria vermiculophylla did not seem to perform better in hyposaline conditions than many native, estuarine species. The present distribution of G. vermiculophylla in Scandinavia can be explained well by its response to salinity, but this may not explain its present success relative to many naturally occurring algal species.

The effect of light and nutrient availability on growth, nitrogen, and pigment contents of Saccharina latissima (Phaeophyceae) grown in outdoor tanks, under natural variation of sunlight and temperature, during autumn and early winter in Denmark

Late summer harvest of cultivated Saccharina latissima, prior to seasonally determined negative length growth, is considered advantageous in North Atlantic waters to optimize biomass yields. We hypothesized that seasonal increase in tissue protein and pigments over autumn and early winter would counterbalance the loss of biomass, and increase the absolute harvestable amount of protein and pigments. The hypothesis was tested in a land-based, factorial-designed, pilot-scale experiment using whole algae individuals exposed to naturally relevant high or low availability of nutrients and light. The experiment was conducted during fall/early winter in Grenaa, Denmark, in outdoor tanks, exposed to ambient light and temperature variations. With high nutrient availability, the absolute harvestable amounts of nitrogen, fucoxanthin, and chlorophyll a increased by 50.1–60.1, 21.7–53.7, and 47.0–73.5 %, respectively, despite a loss of biomass of 16.2–18.7 %. Under low nutrient availability, there was a net loss of biomass (8.1–9.5 %), tissue nitrogen (10.7–44.1 %), and fucoxanthin (7.1–17.2 %), and a minor increase in chlorophyll a (2.5–22.8 %). Nutrient availability had a significant negative impact on the biomass growth, but a positive control on the tissue concentration of nitrogen, chlorophyll a, and fucoxanthin. Our results, from a land-based experiment, indicate that early winter harvest of S. latissima biomass grown under high nutrient availability in Denmark, fulfills a higher degree of nutrient bioremediation, and has an improved biomass quality in regards of increased concentrations of pigments and nitrogen rich compounds.