Concurrent temporal patterns in light absorbance and fish abundance

Abstract

The abundance of midwater fishes in fjord basins, as well as the abundance and size of mesozooplankton, have previously been related to optical properties of the basin water. Herein, we report on concurrent temporal changes in light absorbance and fish abundance for Masfjorden and modest changes in both variables for Lurefjorden and Sognefjorden, western Norway. The inverse relationship between fish abundance and absorbance in the temporal data, spanning 9 yr, is consistent with the relationship previously described for spatial data representing different fjords. The combination of salinity and oxygen accounted for 94% of the observed variance in absorbance of the 3 fjords, and we suggest that these variables serve as proxies for regional and local determinants of absorbance in fjord basins, respectively. While salinity indicates basin water origin and its optical properties, oxygen is a measure of turnover time and local degradation of organic matter, presumably affecting absorbance.

Mesozooplankton distribution in northern Svalbard waters in relation to hydrography

“…Thus to optimise their fitness zooplankton have to choose the optimal vertical position in the water column by balancing feeding conditions against predation risk. Several recent studies suggest that optical properties are important in shaping abundances and vertical distributions in plankton and fish populations (Aksnes et al 2004, Sørnes and Aksnes 2006, Sørnes et al 2007, Aksnes 2007. I observed a positive linear relationship between the vertical range of the depth distribution and the mean depth for the copepodite stages of C. finmarchicus and M. longa (paper III).…”

Plankton and Particle Size and Packaging: From Determining Optical Properties to Driving the Biological Pump

“…The size effect on light attenuation is secondary to concentration, but size is important in determining the flux of nutrient and light into phytoplankton cells and, hence, provides a physical constraint on their growth rate (Finkel & Irwin 2000, Karp-Boss et al 1996. Available light for visual predators may affect trophic interactions in the sea, as it has been proposed as an explanation for the shift between zooplanktonivorous fishes and jellyfish in the northern European seas (Aksnes et al 2004, Sornes & Aksnes 2006, Sornes et al 2008. Therefore, measuring PSD and knowing the particle properties (see Figure 5) to infer light attenuation in the water column of different particle size classes may be helpful in understanding changes in the pelagic ecosystem.…”

First assessment of flux rates of jellyfish carcasses (jelly-falls) to the benthos reveals the importance of gelatinous material for biological C-cycling in jellyfish-dominated ecosystems

“…Jellyfish are highly opportunistic because they are less sensitive to hypoxia compared to fishes and crustaceans (Vaquer-Sunyer and Duarte, 2008), warmer temperatures enhance jellyfish reproduction (Purcell et al, 2007;Purcell, 2012), and overfishing enhances prey availability and reduces competition pressure for jellyfish (Lynam et al, 2006). Eutrophication also benefits tactile predators like jellyfish by increasing water-column turbidity, whereas visual predators (e.g., fish) are at a competitive disadvantage compared to jellyfish in this situation (Sørnes and Aksnes, 2006;Sørnes et al, 2007;Aksnes et al, 2009). While recent meta-analyses have shown that global jellyfish populations have only increased slightly since the 1970s (Condon et al, 2012), numerous areas throughout the world have experienced large jellyfish population expansions (Lynam et al, 2006;Purcell, 2012).…”