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Macroalgal photosynthetic responses to light in relation to thallus morphology and depth zonation
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolutionary Biology, Plant Ecology.
2002 (English)In: Marine Ecology Progress Series, ISSN 0171-8630, E-ISSN 1616-1599, Vol. 244, 63-72 p.Article in journal (Refereed) Published
Abstract [en]

We show how photosynthesis and UV sensitivity of algae are related to thallus morphology and depth distributions. This was studied for typical depth zonations of red and brown macroalgae in the Skagerrak (ca. 25 psu) and the Baltic Sea (6.5 psu). The algae were collected from the water surface down to 20.5 m of depth, whereby each species was sampled at its maximum abundance depth. Altogether, we measured photosynthetic and respiratory rates of 19 red and 13 brown algal species as O2 evolution at different light intensities. Photosynthesis versus irradiance curves (PI curves) showed that light-saturated net photosynthetic rates (Pmax), respiratory rates in darkness (Rd) and the initial slope (α) were strongly related to algal morphology with higher values for thinner species. The compensation irradiance (Ic) and saturating irradiance (Ik) were strongly related to water depth with lower values at greater depth. A novel approach to analyse PI data with principal component analysis (PCA) is presented. The method makes it possible to assign a quantitative morphological gradient to algal species based on photosynthetic properties. Such a gradient can be used in ecological studies as an alternative to more subjective discrete subdivisions into functional-form groups. Another type of PCA analysis, with the relative shapes of the PI curves as input data, summarises α and convexity but discards all interference of morphology. This results in a gradient of genuine physiological responses, which in our study was strongly correlated to maximum abundance depth. The UV sensitivity of the same 32 algal species was determined as the change in net O2 evolution after exposure to UV light and the recovery after this treatment. Deeper-growing algae were more sensitive to UV and species with thinner thalli recovered better after UV treatment in the Skagerrak. No such trends were observed for the algae in the northern Baltic Sea, which suggests that no real deep-water species occur here. This is further supported by the lack of a clear pattern in Ic and Ik values with depth for the algae in the Baltic Sea. Our results advocate that the reduced species diversity of the Baltic Sea is also coupled to a loss of functional groups in the sense of general photosynthetic performance and not only in the sense of pure morphology (loss of canopy-forming species).

Place, publisher, year, edition, pages
2002. Vol. 244, 63-72 p.
National Category
Natural Sciences
URN: urn:nbn:se:uu:diva-90028DOI: 10.3354/meps244063OAI: oai:DiVA.org:uu-90028DiVA: diva2:162055
Available from: 2002-10-16 Created: 2002-10-16 Last updated: 2013-06-19Bibliographically approved
In thesis
1. Factors Affecting the Distribution of Rocky-Shore Macroalgae on the Swedish Coast: Morphological, Physiological, Reproductive and Genetic Aspects
Open this publication in new window or tab >>Factors Affecting the Distribution of Rocky-Shore Macroalgae on the Swedish Coast: Morphological, Physiological, Reproductive and Genetic Aspects
2002 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The aim of this thesis was to examine factors affecting the distribution of macroalgal species both vertically (depth zonation) and geographically along the Baltic Sea salinity gradient. Interactions between the physical environment and basic biological traits of the algae are emphasised.

Previously well-described macroalgal vegetation profiles were re-investigated. Long-term changes of the vegetation that can be coupled to an increased large-scale eutrophication were recorded in both the Baltic Sea and in the Skagerrak.

Photosynthetic properties of macroalgae with different morphologies from typical depth zonations in the Skagerrak and the Baltic Sea were assessed. A novel method that makes it possible to classify macroalgal species along a morphological gradient based on photosynthetic properties is presented. Such a gradient can be used as an alternative to more discrete subdivisions into functional-form groups.

Small-scale variation in the natural sediment load was shown to affect the composition of sublittoral rocky-shore macroalgal communities in a long-term field experiment. Generally, species with an extended reproductive period were more tolerant to sedimentation than species depending on short periods of spore release. The effect of the sediment treatments increased with depth.

Field experiments in the Baltic Sea showed that fragments of Furcellarialumbricalis, Polysiphoniafucoides and Rhodomela confervoides are able to reattach to the substrate under field conditions. This enables persistence of populations since these species are practically sterile in the area. Field observations suggested that sessile animals can facilitate the fixation of algal fragments to the substrate.

Genetic variation of the chlorophyte Cladophorarupestris was assessed by allozyme electrophoresis. Two genetically differentiated groups of populations were found, one Baltic Sea group and one North Sea group, with a distinct border in the southern Kattegat near the entrance to the Baltic Sea.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2002. 34 p.
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 759
Ecology, Ekologi
National Category
Research subject
Ecological Botany
urn:nbn:se:uu:diva-2693 (URN)91-554-5430-5 (ISBN)
Public defence
2002-11-08, Department of Plant Ecology, Villavägen 14, Uppsala, 10:00
Available from: 2002-10-16 Created: 2002-10-16Bibliographically approved

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