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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.


Simulated retention in Lurefjorden (dimensionless) depending on the number of individuals used in the simulations. Confidence intervals (95%) for the mean optical retention (n = 7) are shown.
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FBQ015F2: Simulated retention in Lurefjorden (dimensionless) depending on the number of individuals used in the simulations. Confidence intervals (95%) for the mean optical retention (n = 7) are shown.

Mentions: In a sensitivity analysis, we investigated how variations in the topographical characteristics and in the light attenuation affected the optical retention of P. periphylla. The light attenuation coefficient (K500 for the wavelength 500 nm) was varied over the range 0.02–0.14 m−1. In order to simplify the interpretations of the analysis, we assumed four idealized fjords characterized by two discrete sill depths (10 and 100 m, which correspond to the thickness of the advective layers) and two discrete bottom depths (100 and 500 m), but later on we will consider continuous sill and bottom depths. In the sensitivity analysis, the exchange rate of the advective layer, Ffjord, was kept constant at 3.08 × 10−7 s−1 which corresponds to that approximated for Lurefjorden (Table III). We used 320 individuals in the simulations. This number ensured relatively low computation time and acceptable uncertainty (Fig. 2).Table III:


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

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

Simulated retention in Lurefjorden (dimensionless) depending on the number of individuals used in the simulations. Confidence intervals (95%) for the mean optical retention (n = 7) are shown.
© Copyright Policy - creative-commons
Related In: Results  -  Collection

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

FBQ015F2: Simulated retention in Lurefjorden (dimensionless) depending on the number of individuals used in the simulations. Confidence intervals (95%) for the mean optical retention (n = 7) are shown.
Mentions: In a sensitivity analysis, we investigated how variations in the topographical characteristics and in the light attenuation affected the optical retention of P. periphylla. The light attenuation coefficient (K500 for the wavelength 500 nm) was varied over the range 0.02–0.14 m−1. In order to simplify the interpretations of the analysis, we assumed four idealized fjords characterized by two discrete sill depths (10 and 100 m, which correspond to the thickness of the advective layers) and two discrete bottom depths (100 and 500 m), but later on we will consider continuous sill and bottom depths. In the sensitivity analysis, the exchange rate of the advective layer, Ffjord, was kept constant at 3.08 × 10−7 s−1 which corresponds to that approximated for Lurefjorden (Table III). We used 320 individuals in the simulations. This number ensured relatively low computation time and acceptable uncertainty (Fig. 2).Table III:

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.