Jan E. Vermaat

Seasonal variation in the intertidal seagrass Zostera noltii Hornem.: coupling demographic and physiological patterns

The considerable seasonal variation in biomass (2–130 g ash-free dry weight (AFDW) m−2) and cover of intertidal Zostera noltii Hornem. in the Zandkreek estuary (SW Netherlands) was mainly caused by changes in shoot density (1000–23000 m−2) and not in shoot size (shoot weight 1–3.6 mg AFDW, shoot leaf area 0.3–1.5 cm2). The spring increase in shoot density was realised through continuous monopodial branching of the rhizome, which commenced when light available during low tide increased above 15 E m−2 day−1, in mid April. Branching stopped by the end of July, about 6 weeks before the onset of the annual biomass decline, due to a combination of: (a) self-shading during low tide; (b) high respiratory demand by the expanded rhizome network; (c) the seasonal decline in light availability during late summer. Nutrients were probably not limiting since concentrations in shoots remained high: 3.6% N and 0.6% P of dry weight are seasonal means. During the period of maximal biomass the primary rhizome axes decayed, leaving single shoots on short pieces of rhizome, the former secondary axes. The rapid decline in biomass from mid September onwards could be attributed to grazing by herbivorous migratory waterfowl. It was estimated that brent geese, Branta bernicla (L.), and wigeon, Anas penelope L. (about 200 and 300 birds, respectively, on the bed of 30 ha) together removed 45 g AFDW m−2 month−1, whilst autumn storms were insignificant. As established experimentally, winter survival was by single shoots enclosing an active meristem, and not by rhizome fragments without leaves. Sucrose was the main storage carbohydrate. The rhizome was the main storage organ, with maximal carbohydrate content observed in mid July (190 mg g−1 dry weight, sucrose + starch in glucose weight equivalents), and a gradual decline during autumn and winter. We estimated that the storage carbohydrates could cover 28% of the respiratory needs during winter, which would necessitate a substantial photosynthesis to meet the remaining 72%. From iteratively fitted photosynthesis-light curves we conclude that this intertidal Z. noltii population is high-light adapted compared with permanently submerged seagrasses and freshwater angiosperms: estimates for the light compensation point (LCP) and half-saturation constant (Km) were comparatively high (July LCP and Km: 98 μE m−2 s−1 and 236 μE m−2 s−1, respectively), maximum photosynthetic rate was high (Pmax: 236 μg O2 g−1 AFDW min−1) and the initial slope of the curve was low (α: 0.63 μg O2 g−1 AFDW min−1/μE m−2 s−1). Estimated daily oxygen balances confirmed that positive net photosynthesis was largely limited to low tide daylight in this turbid estuary (mean high tide light attenuation coefficient: 2.1 m−1).

Seed-bank development, germination and early seedling survival of two seagrass species from The Netherlands: Zostera marina L. and Zostera noltii hornem

Abstract Flowering and seed-bank development of annual Zostera marina L. and perennial Z. noltii hornem. were studied in the Zandkreek (S.W. Netherlands). Flowering of Z. noltii started at the end of June and continued until the end of September. A maximum of ca. 1000 flowering shoots (11% of the total amount of shoots per square metre) occurred in early August. Flowering of Z. marina started at the end of July and continued throughout October. Seed banks of both species appeared to be annual. Actual seed densities of Z. noltii were much lower than predicted on the basis of the amount of inflorescences. Germination was studied in the laboratory in relation to temperature (10, 20 and 30°C), salinity (1.0, 10.0, 20.0, 30.0 and 40.0‰) and stratification (at 4°C). Both species showed a maximal germination at 30°C and 1.0‰ salinity, decreasing with higher salinities and lower temperatures. Stratification stimulated germination only at salinities ⩾20.0‰ . Desiccation and anaerobia were lethal to Z. marina seeds. Seedlings of Z. marina survived best at 10°C and 10.0–20.0‰ salinity and those of Z. noltii survived best at 10°C and 1.0‰ salinity. Overall, seedlings of Z. marina survived better than those of Z. noltii.

Lake Veluwe, a macrophyte-dominated system under eutrophication stress

Preface W. van Vierssen, M.J.M. Hootsmans, J.E. Vermaat. 1. Introduction, the Scope of the Research Project W. van Vierssen, M.J.M. Hootsmans, J.E. Vermaat. 2. The Zuiderzee: Transformation of a Brackish Water Ecosystem W. van Vierssen, A.W. Breukelaar. 3. Twenty Years of Dynamics and Distribution of Potamogeton pectinatus L. in Lake Veluwe M. Scheffer, H. Drost, M.R. de Redelijkheid, F. Noppert. 4. Intraspecific Variation in Potamogeton pectinatus L., a Controlled Laboratory Experiment J.E. Vermaat, M.J.M. Hootsmans. 5. Growth of Potamogeton pectinatus L. in a Temperature-Light Gradient J.E. Vermaat, M.J.M. Hootsmans. 6. Light-Response Curves of Potamogeton pectinatus L. as a Function of Plant Age and Irradiance Level during Growth M.J.M. Hootsmans, J.E. Vermaat. 7. Photoperiodic Effects on Photosynthesis and Tuber Production in Potamogeton pectinatus L. W. van Vierssen, M.J.M. Hootsmans. 8. Early Growth Characteristics of Potamogeton pectinatus L.: the Significance of the Tuber W. van Vierssen, A. Mathies, J.E. Vermaat. 9. Seasonal Dynamics of a Field Population of Potamogeton pectinatus L. under Various Experimental Light Conditions W. van Vierssen, M.J.M. Hootsmans, A.W. Bruekelaar, R. Gijlstra. 10. Factors contributing to Light Attenuation in Lake Veluwe G. Blom, E.H.S. van Duin, J.E. Vermaat. 11. Allelopathic Limitation of Algal Growth by Macrophytes M.J.M. Hootsmans, I. Blindow. 12. Periphyton Dynamics in a Temperature-Light Gradient J.E. Vermaat, M.J.M. Hootsmans. 13. Periphyton Removal by Freshwater Micrograzers J.E. Vermaat. 14. A Growth Analysis Model for Potamogeton pectinatus L. M.J.M. Hootsmans. 15. Interactions between Aquatic Macrophytes and Fish in Lake Veluwe, Direct and Indirect Effects H.W. de Nie, J.J.G.M. Backx. 16. General Conclusions and Implications for Lake Management W. van Vierssen, M.J.M. Hootsmans, J.E. Vermaat. Appendices. Index.

Epiphyte Accrual on Posidonia oceanica (L.) Delile Leaves: Implications for Light Absorption

Abstract We examined the pattern of epiphyte accrual along the life-span of Posidonia oceanica leaves, both for the total epiphyte community and the main epiphyte groups (i. e. red encrusting algae and brown erect algae). Moreover, we document the importance of this epiphyte accrual pattern for evaluating P. oceanica-epiphyte interactions by assessing the dependence of the quantity and quality of light absorbed by epiphytes on their accrual pattern. Epiphyte biomass increased with leaf age following a sigmoidal curve (r2 = 0.90, P < 0.001), both for the epiphyte community and for the two main groups. Total epiphyte biomass increased with leaf age at a rate of about 0.03 day−1 to reach a constant maximum value of 2.60 mg DW cm−2 on leaves older than 200 days. Brown erect algae grew about an order of magnitude faster (0.120 day−1) than red encrusting ones (0.017 day−1). However, the former group of algae reached their maximum biomass (1 mg DW cm−2) on 150 days-old leaves, whereas red encrusting algae continued to grow along the whole leaf life-span to reach a maximum biomass of 1.70 mg DW cm−2. The non-linear increase in epiphyte biomass with leaf age involved a non-linear increase in epiphyte light absorption with leaf age, which reached a maximum constant value of 30% of incident light on 250 days-old leaves. Moreover, because red encrusting algae contribute a higher fraction to total epiphyte biomass on older leaves, we observed a shift in absorbed light quality with increasing leaf-age. Our results indicate the importance of accounting for the pattern of epiphyte accrual with leaf age when assessing seagrass-epiphytes interactions, especially for long-lived seagrass species where epiphytes may differ much in growth and biomass between young and old leaves.

Nutrient budgets for European seas: A measure of the effectiveness of nutrient reduction policies

Socio-economic development in Europe has exerted increasing pressure on the marine environment. Eutrophication, caused by nutrient enrichment, is evident in regions of all European seas. Its severity varies but has, in places, adversely impacted socio-economic activities. This paper aims to evaluate the effectiveness of recently adopted policies to reduce anthropogenic nutrient inputs to European seas. Nitrogen and phosphorus budgets were constructed for three different periods (prior to severe eutrophication, during severe eutrophication and contemporary) to capture changes in the relative importance of different nutrient sources in four European seas suffering from eutrophication (Baltic Proper, coastal North Sea, Northern Adriatic and North-Western Black Sea Shelf). Policy success is evident for point sources, notably for P in the Baltic and North Seas, but reduction of diffuse sources has been more problematic.

Major dimensions in food-web structure properties.

The covariance among a range of 20 network structural properties of food webs plus net primary productivity was assessed for 14 published food webs using principal components analysis. Three primary components explained 84% of the variability in the data sets, suggesting substantial covariance among the properties employed in the literature. The first dimension explained 48% of the variance and could be ascribed to connectance, covarying significantly with the proportion of intermediate species and characteristic path length. The second dimension explained 19% and was related to trophic species richness. The third axis explained 17% and was related to ecosystem net primary productivity. A distinct opposite clustering of connectance, the proportion of intermediate species, and mean trophic level vs. the proportion of top and basal species and path length suggests a dichotomy in food-web structure. Food webs appear either clustered and highly interconnected or elongated with fewer links.

Drivers of Wetland Conversion: a Global Meta-Analysis

Meta-analysis of case studies has become an important tool for synthesizing case study findings in land change. Meta-analyses of deforestation, urbanization, desertification and change in shifting cultivation systems have been published. This present study adds to this literature, with an analysis of the proximate causes and underlying forces of wetland conversion at a global scale using two complementary approaches of systematic review. Firstly, a meta-analysis of 105 case-study papers describing wetland conversion was performed, showing that different combinations of multiple-factor proximate causes, and underlying forces, drive wetland conversion. Agricultural development has been the main proximate cause of wetland conversion, and economic growth and population density are the most frequently identified underlying forces. Secondly, to add a more quantitative component to the study, a logistic meta-regression analysis was performed to estimate the likelihood of wetland conversion worldwide, using globally-consistent biophysical and socioeconomic location factor maps. Significant factors explaining wetland conversion, in order of importance, are market influence, total wetland area (lower conversion probability), mean annual temperature and cropland or built-up area. The regression analyses results support the outcomes of the meta-analysis of the processes of conversion mentioned in the individual case studies. In other meta-analyses of land change, similar factors (e.g., agricultural development, population growth, market/economic factors) are also identified as important causes of various types of land change (e.g., deforestation, desertification). Meta-analysis helps to identify commonalities across the various local case studies and identify which variables may lead to individual cases to behave differently. The meta-regression provides maps indicating the likelihood of wetland conversion worldwide based on the location factors that have determined historic conversions.

Human deforestation outweighs future climate change impacts of sedimentation on coral reefs.

Near-shore coral reef systems are experiencing increased sediment supply due to conversion of forests to other land uses. Counteracting increased sediment loads requires an understanding of the relationship between forest cover and sediment supply, and how this relationship might change in the future. Here we study this relationship by simulating river flow and sediment supply in four watersheds that are adjacent to Madagascar’s major coral reef ecosystems for a range of future climate change projections and land-use change scenarios. We show that by 2090, all four watersheds are predicted to experience temperature increases and/or precipitation declines that, when combined, result in decreases in river flow and sediment load. However, these climate change-driven declines are outweighed by the impact of deforestation. Consequently, our analyses suggest that regional land-use management is more important than mediating climate change for influencing sedimentation of Malagasy coral reefs.

The effect of atmospheric carbon dioxide elevation on plant growth in freshwater ecosystems

We developed a dynamic model to investigate the effect of atmospheric carbon dioxide (CO2) increase on plant growth in freshwater ecosystems. Steady-state simulations were performed to analyze the response of phytoplankton and submerged macrophytes to atmospheric CO2 elevation from 350 to 700 ppm. We studied various conditions that may affect this response, such as alkalinity, the air–water exchange rate of CO2, the community respiration rate, and the phosphorus (P) supply rate. The increase in atmospheric CO2 could affect submerged plant growth only under relatively eutrophic conditions and at a low community respiration rate. Alkalinity had little effect on the response of the different species. When the air–water exchange was low, the proportional effect of the CO2 increase on plant growth was higher. Under eutrophic conditions, algae and macrophytes using CO2 and HCO3− may double their growth rate due to atmospheric CO2 elevation, while the growth of macrophytes restricted to CO2 assimilation may be threefold. The differences in response of the species under various conditions indicate that the elevation of atmospheric CO2 may induce drastic changes in the productivity and species dominance in freshwater systems.

Temporal changes in the abundance, leaf growth and photosynthesis of three co-occurring Philippine seagrasses

The analysis of the temporal changes in shoot density, areal leaf biomass, leaf growth and parameters of the photosynthesis-irradiance relationship of three tropical seagrass species (Enhalus acoroides, Thalassia hemprichii and Cymodocea rotundata), co-existing in a shallow subtidal meadow in Cape Bolinao, Philippines, shows that species-specific traits are significant sources of temporal variability, and indicates that these seagrass species respond differently to a common environmental forcing. Species-specific differences are much less important as source of variability of the temporal change in chlorophyll concentration of seagrass leaves. The results indicate that the temporal changes in photosynthetic performance of these seagrasses were driven by environmental forcing and their specific responses to it mostly, but the temporal change in their abundance and leaf growth was also controlled by other factors. The significant contribution of species-specific factors in the temporal changes of biomass, growth and photosynthetic performance of co-occurring seagrass species in Cape Bolinao should contribute to the maintenance of the multispecific, highly productive meadows characteristic of pristine coastal ecosystems in Southeast (SE) Asia.