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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.


Isolines of retention [R as defined in equation (10)] as a function of the optical bottom depth and the ratio between the sill and the bottom depth. Both axes are dimensionless (dim.). (A) Small and (B) large individuals. The light grey, grey and dark areas represent categories 1, 2, and 3 (see text), respectively.
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FBQ015F8: Isolines of retention [R as defined in equation (10)] as a function of the optical bottom depth and the ratio between the sill and the bottom depth. Both axes are dimensionless (dim.). (A) Small and (B) large individuals. The light grey, grey and dark areas represent categories 1, 2, and 3 (see text), respectively.

Mentions: As discussed in Aksnes et al. (Aksnes et al., 2004), it is convenient to summarize the light environment of a fjord (or more generally for a water column) by the optical bottom depth (OD):(11)where Z (m) is the bottom depth of the fjord and K500 (m−1) is the light attenuation of the water column. The optical bottom depth can be interpreted as an index of the darkness of a fjord, i.e. increasing OD means a darker fjord regardless of the cause (i.e. increased light attenuation and/or bottom depth). Our model predicts that the optical retention of P. periphylla is affected by the bottom depth as well as the light attenuation. These two variables, however, are combined in the dimensionless optical bottom depth. If we also represent the sill depth (i.e. the thickness of the advective layer) as a fraction of the bottom depth, our simulation results can be presented more generally. In contrast to the discrete sill chosen in the sensitivity analysis (Figs 5 and 6), it is now continuous. Figure 8 illustrates the variations in retention when the sill depth is a continuous variable. We see that the highest retention is obtained with a shallow relative sill depth and a high optical bottom depth for both small and large individuals (Fig. 8). The three fjord categories discussed earlier are indicated as shaded areas in Fig. 8. It can be seen that if the two dimensionless characteristics of a fjord fit into category 1 (light grey area in Fig. 8), an increase in the light attenuation (or in the bottom depth) of that fjord will increase the optical bottom depth and move the fjord closer to category 2 (grey area) which provides a higher optical retention of P. periphylla. On the other hand, if a fjord is of category 3 a decrease in the light attenuation (or in the bottom depth) is required to promote higher optical retention.


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

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

Isolines of retention [R as defined in equation (10)] as a function of the optical bottom depth and the ratio between the sill and the bottom depth. Both axes are dimensionless (dim.). (A) Small and (B) large individuals. The light grey, grey and dark areas represent categories 1, 2, and 3 (see text), respectively.
© Copyright Policy - creative-commons
Related In: Results  -  Collection

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

FBQ015F8: Isolines of retention [R as defined in equation (10)] as a function of the optical bottom depth and the ratio between the sill and the bottom depth. Both axes are dimensionless (dim.). (A) Small and (B) large individuals. The light grey, grey and dark areas represent categories 1, 2, and 3 (see text), respectively.
Mentions: As discussed in Aksnes et al. (Aksnes et al., 2004), it is convenient to summarize the light environment of a fjord (or more generally for a water column) by the optical bottom depth (OD):(11)where Z (m) is the bottom depth of the fjord and K500 (m−1) is the light attenuation of the water column. The optical bottom depth can be interpreted as an index of the darkness of a fjord, i.e. increasing OD means a darker fjord regardless of the cause (i.e. increased light attenuation and/or bottom depth). Our model predicts that the optical retention of P. periphylla is affected by the bottom depth as well as the light attenuation. These two variables, however, are combined in the dimensionless optical bottom depth. If we also represent the sill depth (i.e. the thickness of the advective layer) as a fraction of the bottom depth, our simulation results can be presented more generally. In contrast to the discrete sill chosen in the sensitivity analysis (Figs 5 and 6), it is now continuous. Figure 8 illustrates the variations in retention when the sill depth is a continuous variable. We see that the highest retention is obtained with a shallow relative sill depth and a high optical bottom depth for both small and large individuals (Fig. 8). The three fjord categories discussed earlier are indicated as shaded areas in Fig. 8. It can be seen that if the two dimensionless characteristics of a fjord fit into category 1 (light grey area in Fig. 8), an increase in the light attenuation (or in the bottom depth) of that fjord will increase the optical bottom depth and move the fjord closer to category 2 (grey area) which provides a higher optical retention of P. periphylla. On the other hand, if a fjord is of category 3 a decrease in the light attenuation (or in the bottom depth) is required to promote higher optical retention.

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.