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Simulation of optically conditioned retention and mass occurrences of Periphylla periphylla.

Dupont N, Aksnes DL - J. Plankton Res. (2010)

Bottom Line: Our results suggest that light attenuation, in combination with advection, has a two-sided effect on retention and that three fjord categories can be defined.In category 3, further increase in light attenuation, however, shoals the habitat so that individuals are increasingly exposed to advection and this results in loss of individuals and decreased retention.This classification requires accurate determinations of the organism's light preference, the water column light attenuation and topographical characteristics affecting advection.

View Article: PubMed Central - PubMed

Affiliation: Department of biology , University of Bergen , PO Box 7803, N-5020 Bergen , Norway.

ABSTRACT
Jellyfish blooms are of increasing concern in many parts of the world, and in Norwegian fjords an apparent increase in mass occurrences of the deep water jellyfish Periphylla periphylla has attracted attention. Here we investigate the hypothesis that changes in the water column light attenuation might cause local retention and thereby facilitate mass occurrences. We use a previously tested individual-based model of light-mediated vertical migration in P. periphylla to simulate how retention is affected by changes in light attenuation. Our results suggest that light attenuation, in combination with advection, has a two-sided effect on retention and that three fjord categories can be defined. In category 1, increased light attenuation turns fjords into dark "deep-sea" environments which increase the habitat and retention of P. periphylla. In category 2, an optimal light attenuation facilitates the maximum retention and likelihood for mass occurrences. In category 3, further increase in light attenuation, however, shoals the habitat so that individuals are increasingly exposed to advection and this results in loss of individuals and decreased retention. This classification requires accurate determinations of the organism's light preference, the water column light attenuation and topographical characteristics affecting advection.

No MeSH data available.


Sensitivity of the simulated retention [R dimensionless as defined in equation (10)] to the values of the light preference parameters ( and ) of P. periphylla. Only the value of  are indicated on the x-axis, but the value of  was also varied so that it was about four orders of magnitude lower than . The box indicates the light preference value assumed in Table I. The topography and light regime of Masfjorden was assumed in the sensitivity analysis.
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FBQ015F7: Sensitivity of the simulated retention [R dimensionless as defined in equation (10)] to the values of the light preference parameters ( and ) of P. periphylla. Only the value of are indicated on the x-axis, but the value of was also varied so that it was about four orders of magnitude lower than . The box indicates the light preference value assumed in Table I. The topography and light regime of Masfjorden was assumed in the sensitivity analysis.

Mentions: Sandsfjorden and Jøsenfjorden have the lowest simulated retention with values below 0.23 and 0.40 for large and small individuals, respectively. Thereafter follow Masfjorden, Sognefjorden and Lurefjorden, while Lysefjorden has the highest optical retention with values of 0.71 and 0.92 for large and small individuals, respectively. For all fjords, the large individuals have a lower optical retention than the small individuals because we have assumed higher light preferences for the large individuals. When the values of the light attenuation, K500, are increased by 25% (i.e. darker water than the values indicated in Table II), the optical retention decreases for both size groups for all fjords. This simulation result clearly opposes the suggestion that increased light attenuation increases the likelihood for mass occurrences (Sørnes et al., 2007), but the validity of this result critically depend on the assumed light preference values of P. periphylla (Table I). When these values are changed, so does the simulated optical retention. In Table I, it was assumed that 7.38 × 10−6 for the large individuals. This gives a simulated retention of 0.32 for e.g. Masfjorden (Fig. 7). If is altered as well as (Fig. 7), however, a maximal retention of 0.97 is obtained for close to 10−10. This demonstrates that accurate simulations require accurate estimates of the light preference parameters, but also of the water column light attenuation. As emphasized in Method and further discussed below this has implications for the interpretation of the simulation results for the six fjords (Table IV).Table IV:


Simulation of optically conditioned retention and mass occurrences of Periphylla periphylla.

Dupont N, Aksnes DL - J. Plankton Res. (2010)

Sensitivity of the simulated retention [R dimensionless as defined in equation (10)] to the values of the light preference parameters ( and ) of P. periphylla. Only the value of  are indicated on the x-axis, but the value of  was also varied so that it was about four orders of magnitude lower than . The box indicates the light preference value assumed in Table I. The topography and light regime of Masfjorden was assumed in the sensitivity analysis.
© Copyright Policy - creative-commons
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC2864668&req=5

FBQ015F7: Sensitivity of the simulated retention [R dimensionless as defined in equation (10)] to the values of the light preference parameters ( and ) of P. periphylla. Only the value of are indicated on the x-axis, but the value of was also varied so that it was about four orders of magnitude lower than . The box indicates the light preference value assumed in Table I. The topography and light regime of Masfjorden was assumed in the sensitivity analysis.
Mentions: Sandsfjorden and Jøsenfjorden have the lowest simulated retention with values below 0.23 and 0.40 for large and small individuals, respectively. Thereafter follow Masfjorden, Sognefjorden and Lurefjorden, while Lysefjorden has the highest optical retention with values of 0.71 and 0.92 for large and small individuals, respectively. For all fjords, the large individuals have a lower optical retention than the small individuals because we have assumed higher light preferences for the large individuals. When the values of the light attenuation, K500, are increased by 25% (i.e. darker water than the values indicated in Table II), the optical retention decreases for both size groups for all fjords. This simulation result clearly opposes the suggestion that increased light attenuation increases the likelihood for mass occurrences (Sørnes et al., 2007), but the validity of this result critically depend on the assumed light preference values of P. periphylla (Table I). When these values are changed, so does the simulated optical retention. In Table I, it was assumed that 7.38 × 10−6 for the large individuals. This gives a simulated retention of 0.32 for e.g. Masfjorden (Fig. 7). If is altered as well as (Fig. 7), however, a maximal retention of 0.97 is obtained for close to 10−10. This demonstrates that accurate simulations require accurate estimates of the light preference parameters, but also of the water column light attenuation. As emphasized in Method and further discussed below this has implications for the interpretation of the simulation results for the six fjords (Table IV).Table IV:

Bottom Line: Our results suggest that light attenuation, in combination with advection, has a two-sided effect on retention and that three fjord categories can be defined.In category 3, further increase in light attenuation, however, shoals the habitat so that individuals are increasingly exposed to advection and this results in loss of individuals and decreased retention.This classification requires accurate determinations of the organism's light preference, the water column light attenuation and topographical characteristics affecting advection.

View Article: PubMed Central - PubMed

Affiliation: Department of biology , University of Bergen , PO Box 7803, N-5020 Bergen , Norway.

ABSTRACT
Jellyfish blooms are of increasing concern in many parts of the world, and in Norwegian fjords an apparent increase in mass occurrences of the deep water jellyfish Periphylla periphylla has attracted attention. Here we investigate the hypothesis that changes in the water column light attenuation might cause local retention and thereby facilitate mass occurrences. We use a previously tested individual-based model of light-mediated vertical migration in P. periphylla to simulate how retention is affected by changes in light attenuation. Our results suggest that light attenuation, in combination with advection, has a two-sided effect on retention and that three fjord categories can be defined. In category 1, increased light attenuation turns fjords into dark "deep-sea" environments which increase the habitat and retention of P. periphylla. In category 2, an optimal light attenuation facilitates the maximum retention and likelihood for mass occurrences. In category 3, further increase in light attenuation, however, shoals the habitat so that individuals are increasingly exposed to advection and this results in loss of individuals and decreased retention. This classification requires accurate determinations of the organism's light preference, the water column light attenuation and topographical characteristics affecting advection.

No MeSH data available.