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- Eriksson, Britas Klemens, et al.
(författare)
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Declines in predatory fish promote bloom-forming macroalgae.
- 2009
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Ingår i: Ecological Applications. - 1051-0761 .- 1939-5582. ; 19:8, s. 1975-1988
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Tidskriftsartikel (refereegranskat)abstract
- In the Baltic Sea, increased dominance of ephemeral and bloom-forming algae is presently attributed to increased nutrient loads. Simultaneously, coastal predatory fish are in strong decline. Using field data from nine areas covering a 700-km coastline, we examined whether formation of macroalgal blooms could be linked to the composition of the fish community. We then tested whether predator or nutrient availability could explain the field patterns in two small-scale field experiments, by comparing joint effects on algal net production from nutrient enrichment with agricultural fertilizer and exclusion of larger predatory fish with cages. We also manipulated the presence of invertebrate grazers. The abundance of piscivorous fish had a strong negative correlation with the large-scale distribution of bloom-forming macroalgae. Areas with depleted top-predator communities displayed massive increases in their prey, small-bodied fish, and high covers of ephemeral algae. Combining the results from the two experiments showed that excluding larger piscivorous fish: (1) increased the abundance of small-bodied predatory fish; (2) changed the size distribution of the dominating grazers, decreasing the smaller gastropod scrapers; and (3) increased the net production of ephemeral macroalgae. Effects of removing top predators and nutrient enrichment were similar and additive, together increasing the abundance of ephemeral algae many times. Predator effects depended on invertebrate grazers; in the absence of invertebrates there were no significant effects of predator exclusion on algal production. Our results provide strong support for regional declines of larger predatory fish in the Baltic Sea promoting algal production by decreasing invertebrate grazer control. This highlights the importance of trophic interactions for ecosystem responses to eutrophication. The view emerges that to achieve management goals for water quality we need to consider the interplay between top-down and bottom-up processes in future ecosystem management of marine resources.
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| 2. |
- Nilsson, Martin, 1966, et al.
(författare)
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Competitive physical activity early in life is associated with bone mineral density in elderly Swedish men
- 2008
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Ingår i: Osteoporosis International. - : Springer Science and Business Media LLC. - 0937-941X .- 1433-2965. ; 19:11, s. 1557-1566
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Tidskriftsartikel (refereegranskat)abstract
- In this population-based study of 75-year-old men (n = 498), we investigated the association between physical activity (PA) early in life and present bone mineral density (BMD). We demonstrate that a high frequency of competitive sports early in life is associated with BMD at several bone sites, indicating that increases in BMD following PA are preserved longer than previously believed. Introduction Physical activity (PA) increases bone mineral density (BMD) during growth. It is unclear if the positive effects remain at old age. In this study, we aimed to determine if PA early in life was associated with BMD in elderly men. Methods In this population-based study, 498 men, 75.2 +/- .3 (mean +/- SD) years old, were included. BMD was assessed using DXA. Data concerning lifetime PA, including both competitive (CS) and recreational sports (RS), and occupational physical load (OPL), were collected at interview. Results Subjects in the highest frequency group of CS in the early period (10-35 years), had higher BMD at the total body (4.2%, p < 0.01), total hip (7.0%, p < 0.01), trochanter (8.7%, p < 0.01), and lumbar spine (7.9%, p < 0.01), than subjects not involved in CS. A stepwise linear regression model showed that frequency of CS in the early period independently positively predicted present BMD at the total body (beta=0.12, p < 0.01), total hip (beta=0.11, p < 0.01), trochanter (beta=0.12, p < 0.01), and lumbar spine (beta=0.11, p=0.01). Conclusions We demonstrate that PA in CS early in life is associated with BMD in 75-year-old Swedish men, indicating that increases in BMD following PA are preserved longer than previously believed.
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