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Grazing in Macroalgae Communities of the Baltic Sea
University of Kalmar, School of Pure and Applied Natural Sciences.
2003 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Fucus vesiculosus and Fucus serratus are the only large, structuring perennial brown macroalgae in the low salinity waters of the Swedish coast of the Baltic Proper. Since the 1970s there are reports of declining Fucus vesiculosus stands from several locations around the Baltic Proper, but also indications of recoveries e.g. in Finland, in the Askö area of the northern Baltic proper and in the south east coast of Sweden. There are probably several causes for these changes. This thesis focuses on how, among biological and other factors, grazing may be the proximate factor to structure the rocky phytal zone of the Baltic Sea.

Destructive effects on F. vesiculosus may be connected to extreme densities of grazers. In a field survey large densities of the potential mesograzer Idotea baltica correlated positively with grazing injuries on and reduced depth penetration of Fucus vesiculosus. In a grazing experiment biomass of F. vesiculosus was halved within two weeks at a grazer density found in the field (80 I. baltica per 100 g of Fucus wet weight). In a second survey large numbers of the gastropods Theodoxus fluviatilis and Lymnaea peregra coincided with unsuccessful recruitment of F. vesiculosus. In an experiment these gastropods grazed germlings of F. vesiculosus up to sizes of 0.8 and 1.0 mm respectively. Abundances of gastropods were highest in autumn, indicating that autumn reproductive F. vesiculosus might be more influenced than spring reproductive F. vesiculosus as the latter would have surpassed the critical size in autumn.

Grazing may be modified by environmental factors. Comparatively small densities of Theodoxus fluviatilis correlated positively with abundances of Fucus vesiculosus and negatively with abundances of filamentous algae. Grazing effects advantageous to F. vesiculosus were tested in a field experiment with manipulation of grazers, nutrients and propagules of filamentous algae. At low nutrient loads grazers tended to clear the substrate from filamentous algae and strengthen the competitive ability of F. vesiculosus. At high nutrient loads the grazers could not prevent dominance of filamentous algae with detrimental effects to F. vesiculosus. Physical factors like wave-action may also modify grazing effects. In a wave-exposed coastline with mixed stands of perennial brown algae and frequent occurrences of grazing isopods, F. vesiculosus declined faster than F. serratus. In an experiment F. vesiculosus was more heavily grazed than F. serratus, but only at intense water motion. Thus F. serratus seem to have a competitive advantage to F. vesiculosus in wave exposed coasts where severe grazing occurs.

The fact that the grazer I. baltica often has been connected with F. vesiculosus, might indicate that this animal would be dependent on F. vesiculosus as habitat and/or food. In a wave-exposed habitat on the eastern coast of Öland, probably earlier dominated by F. vesiculosus but now holding discrete patches of either red algae {Polysiphonia fucoides) or saw-wrack (F. serratus) I. baltica used both species as habitat and food. In addition to the two macroalgae faecal pellets contained 30-40 % microalgae, indicating that mixed diets may be important for this species.

In monitoring programs of rocky bottom communities fixed sites may be revisited on a yearly bases to estimate the development of the community. There is an underlying assumption that the observations at a fixed site are representative to surrounding areas. This assumption was tested along a 350 km coastline in SE Sweden. 18 years of observations were evaluated and compared to complementary sites. Within areas of similar wave exposure there was good agreement between fixed sites and surrounding areas.

When all fixed sites within wave-protected areas were analysed together for long-term trends, there was an agreement in development between sites över the whole geographic area. The Fucus community increased its distribution during the 1980s, decreased during the early ]990s (probably from grazing as described above), to increase again in 2000-2001, that is an oscillating pattern is suggested. In wave-exposed sites, along a 100 km coastline, the F. vesiculosus stands were destroyed, seemingly by grazing as described above, around 1992-1994, with no signs of recovery as late as in 2002.

The results are discussed in the context of grazing, regulation of grazing by predation, eutrophication and physical factors. The importance of the lack of fish predators is suggested for further research.

Place, publisher, year, edition, pages
2003.
Series
Dissertation series / University of Kalmar, Faculty of Natural Science, ISSN 1650-2779 ; 7
National Category
Natural Sciences
Research subject
Natural Science, Aquatic Ecology
Identifiers
URN: urn:nbn:se:hik:diva-43ISBN: 91-89584-16-3 (print)OAI: oai:DiVA.org:hik-43DiVA, id: diva2:1899
Public defence
(English)
Supervisors
Available from: 2007-11-29 Created: 2007-11-29 Last updated: 2010-03-09
List of papers
1. Density dependent grazing effects by the Isopod Idotea baltica Pallas on Fucus vesiculosus L in the Baltic Sea
Open this publication in new window or tab >>Density dependent grazing effects by the Isopod Idotea baltica Pallas on Fucus vesiculosus L in the Baltic Sea
2000 (English)In: Aquatic Ecology, ISSN 1386-2588, Vol. 34, no 3, p. 253-260Article in journal (Refereed) Published
Keywords
Baltic Sea, Experimental study, Field study, Fucus vesiculosus, Grazing, Idotea baltica
National Category
Ecology
Research subject
Natural Science, Aquatic Ecology
Identifiers
urn:nbn:se:hik:diva-638 (URN)
Available from: 2007-11-29 Created: 2008-11-05 Last updated: 2010-03-09Bibliographically approved
2. Grazing effects of two freshwater snails on juvenile Fucus vesiculosus in the Baltic Sea
Open this publication in new window or tab >>Grazing effects of two freshwater snails on juvenile Fucus vesiculosus in the Baltic Sea
1999 (English)In: Marine Ecology Progress Series, ISSN 0171-8630, Vol. 188, p. 63-71Article in journal (Refereed) Published
Abstract [en]

The low salinity in the non-tidal Baltic Sea excludes many species, including marine littorinoids. The only large gastropods that occur in substantial quantities in the central Baltic proper are the freshwater snails Lymnaea peregra (O.F. Müller) and Theodoxus fluviatilis (L.); both are known to consume filamentous green and brown algae. The main objective of the present study was to test the hypothesis that freshwater snails can exert substantial grazing pressure on juvenile and regenerating Fucus vesiculosus populations in the Baltic Sea. In laboratory experiments, both snail species were able to graze on F. vesiculosus germlings up to a size of approximately 0.8 to 1.0 mm. During the study period (autumn 1996 and spring and summer 1997), the largest F. vesiculosus germlings of the cohorts settled in September and May reached approximately 1.0 mm at the same time (July). Thus, to reach the 'safe' size and escape grazing requires about 8 mo for germlings settling in autumn but only 1 mo for germlings settling in spring. The survival and growth rate of new fronds from regenerating F. vesiculosus holdfasts in outdoor tank experiments were higher than for sexually recruited juveniles. After 1 yr, 95% of the holdfasts had survived, and the mean length (±SE) of the largest frond on each holdfast was 12 ± 2 mm. Grazing by L. peregra or T. fluviatilis did not affect regeneration or frond growth. During a long-term field study (1991 to 1994), an average of 8.5 ± 0.7 T. fluviatilis ind. dm-2 were found, with a maximum density of 40 ind. dm-2 in September. During a 1 yr study (1996), the average density of L. peregra was comparatively low and varied from 0.5 ind. dm-2 in April to 20 ind. dm-2 in August. The higher density found in August (L. peregra) and in September (T. fluviatilis) suggests that both species may have a grazing impact during this time. We conclude that both T. fluviatilis and L. peregra have the capacity to graze on zygotes and germlings of F. vesiculosus until they reach a safe size of approximately 0.8 to 1.0 mm. Both snail species can occasionally reach abundances high enough to affect the recruitment of F. vesiculosus. Freshwater snails do not affect the regeneration from holdfasts. However, because the time for germlings settled in autumn to reach a safe size is much longer than for germlings settled in spring, it is possible that even a low snail density has an impact on recruitment in the field. This will, however, require verification because levels of grazing activity during different times of the year are unknown.

Keywords
Growth rate, Herbivory, Lymnaea peregra, Theodoxus fluviatilis
National Category
Ecology
Research subject
Natural Science, Aquatic Ecology
Identifiers
urn:nbn:se:hik:diva-639 (URN)10.3354/meps188063 (DOI)
Available from: 2007-11-29 Created: 2009-09-17 Last updated: 2010-03-09Bibliographically approved
3. Marine diversity shift linked to interactions among grazers, nutrients and propagule banks
Open this publication in new window or tab >>Marine diversity shift linked to interactions among grazers, nutrients and propagule banks
Show others...
1999 (English)In: Marine Ecology Progress Series, ISSN 0171-8630, Vol. 185, p. 309-314Article in journal (Refereed) Published
Abstract [en]

Diverse coastal seaweed communities dominated by perennial fucoids become replaced by species-poor turfs of annual algae throughout the Baltic Sea. A large scale field survey and factorial field experiments indicated that grazers maintain the fucoid cornmunity through selective consumption of annual algae. Interactive effects between grazers and dormant propagules of annual algae. stored in a 'marine seed bank', determine the response of this system to anthropogenic nutrient loading. Nutrients override grazer control and accelerate the loss of algal diversity in the presence but not in the absence of a propagule bank. This irnplies a novel role of propagule banks for community regulation and ecosystem response to manne eutrophication.

 

Keywords
Coastal ecosystems, Eutrophication, Baltic Sea, Macroalgae, Diversity, Community structure, Darmancy, Herbivory, Fucus vesiculosus
National Category
Ecology
Research subject
Natural Science, Aquatic Ecology
Identifiers
urn:nbn:se:hik:diva-640 (URN)
Available from: 2007-11-29 Created: 2009-09-17 Last updated: 2010-03-09Bibliographically approved
4. Possible modification of grazing effects by wave action, changing the relative dominance between Fucus serratus and Fucus vesiculosus in the southern Baltic Sea
Open this publication in new window or tab >>Possible modification of grazing effects by wave action, changing the relative dominance between Fucus serratus and Fucus vesiculosus in the southern Baltic Sea
(English)Manuscript (preprint) (Other academic)
National Category
Ecology
Research subject
Natural Science, Aquatic Ecology
Identifiers
urn:nbn:se:hik:diva-641 (URN)
Available from: 2007-11-29 Created: 2008-11-05 Last updated: 2016-02-26Bibliographically approved
5. Distribution and host plant preference of Idotea baltica (Pallas) (Crustacea: Isopoda) on shallow rocky shores in the central Baltic Sea
Open this publication in new window or tab >>Distribution and host plant preference of Idotea baltica (Pallas) (Crustacea: Isopoda) on shallow rocky shores in the central Baltic Sea
2004 (English)In: Sarsia, ISSN 0036-4827, E-ISSN 1503-1128, Vol. 89, no 1, p. 1-7Article in journal (Refereed) Published
Abstract [en]

Partially due to the mass occurrence of the isopod Idotea baltica, the perennial fucoid vegetation in the Baltic Sea has been destroyed over large areas and replaced by filamentous algae. With a combination of field investigations and laboratory experiments, we tested whether I. baltica preferred Fucus serratus to the dominant red alga Polysiphonia fucoides. In the field, the I. baltica density was higher inside F. serratus than P. fucoides patches when measured per unit area, but the situation was reversed if measured per biomass algae. Diet in the field was well correlated with the distribution of the isopods. A large proportion of the isopod faecal pellets collected in the field contained remnants of microalgae, planktonic animals, and bacteria, but the dominating material was always cells from the actual host plant. In a host plant preference experiment, I. baltica distributed evenly between the two host plant types, but the isopods grazed more heavily on F. serratus. We conclude that although F. serratus is the preferred food item in a choice situation, P. fucoides appears to have the potential to support the I. baltica population with food and shelter. A possible relationship between the weak host plant preference and the low stocks of predatory fish is discussed.

Keywords
Fucus, Polysiphonia, Filamentous algae, Structuring factors, Grazing, Herbivory
National Category
Ecology
Research subject
Natural Science, Aquatic Ecology
Identifiers
urn:nbn:se:hik:diva-642 (URN)10.1080/00364820310003217 (DOI)
Available from: 2007-11-29 Created: 2009-09-17 Last updated: 2017-12-13Bibliographically approved
6. Long-term decline and recent recovery of Fucus populations along the rocky shores of southeast Sweden, Baltic Sea
Open this publication in new window or tab >>Long-term decline and recent recovery of Fucus populations along the rocky shores of southeast Sweden, Baltic Sea
2004 (English)In: Aquatic Ecology, ISSN 1386-2588, E-ISSN 1573-5125, Vol. 38, no 4, p. 587-598Article in journal (Refereed) Published
Abstract [en]

The Fucus populations on rocky shores along 300 km of the coastal waters of southeast Sweden in the Baltic proper have been studied since 1984 at a number of fixed sites as part of monitoring programmes. This paper describes changes in distribution and abundance of F. vesiculosus and F. serratus during the period 1984–2001. Sheltered sites showed a consistent temporal and spatial pattern of Fucus spp. distribution over a coastline of 300 kilometres. The depth penetration and abundance of Fucus spp. increased during the 1980s. Around 1990 the development reversed as a consequence of grazing and in 1997 many sites were almost devoid of Fucus spp. Since 1998 both abundance and depth penetration have increased again, possibly as a result of local measures against eutrophication. Exposed sites, on the other hand, lost their Fucus populations at the beginning of the 1990s, and they have not recovered. Extended field studies lead us to deduce that the fixed sites referred to above were representative of the Fucus populations in the area investigated. Major declines, both at sheltered and exposed sites, are attributed to grazing by the isopod Idotea baltica. The populations of I. baltica may have been favoured by the continuing eutrophication of the Baltic, a series of mild winters in the 1990s, and a contemporary decline in some potential predators.

Keywords
Environmental monitoring, Eutrophication, Fucus serratus, Fucus vesiculosus
National Category
Ecology
Research subject
Natural Science, Aquatic Ecology
Identifiers
urn:nbn:se:hik:diva-643 (URN)10.1007/s10452-004-5665-7 (DOI)
Available from: 2007-11-29 Created: 2009-09-17 Last updated: 2017-12-13Bibliographically approved

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Citation style
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  • harvard1
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  • nn-NB
  • sv-SE
  • Other locale
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Output format
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  • asciidoc
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