Abstract Title

Session S-01D: Pelagic Ecology in the Salish Sea I

Keywords

Species and Food Webs

Start Date

30-4-2014 10:30 AM

End Date

30-4-2014 12:00 PM

Description

Recent analysis of community structure in the pelagic ecosystem of the greater Puget Sound has revealed a shift in species composition and abundance in some areas from those dominated by fish to those dominated gelatinous mesozooplankton (“jellyfish”). Unfortunately, the mechanisms behind these shifts are unclear due to a deficit of ecological understanding of this system. The analysis of foodweb structure, which reflects the flow of carbon and nutrients, is useful to complement composition and abundance information in order to understand the energetic processes underlying pelagic communities and why they may be changing. In this talk, we examine foodweb structure and trophic ecology of middle trophic level pelagic fish and jellyfish in six oceanographic sub-basins in Puget Sound from April to October 2011. Specifically, we assessed spatial and seasonal variation in 1) the isotopic composition of abundant species of salmonids, forage fish and jellyfish, 2) the trophic overlap between fish and jellyfish and 3) foodweb attributes of whole pelagic communities including niche width, trophic length and basal resource diversity. At the species level, there were strong spatial differences in isotopic composition among sub-basins. Seasonal patterns, possibly suggesting ontogenetic diet shifts or changes in basal carbon sources, were also evident but were more pronounced in fish than jellyfish. The degree of trophic overlap between fish and jellyfish varied among sub-basins and generally decreased seasonally. At the community level, overall community niche width was higher in Whidbey basin in spring and summer months then switched to a north-south gradient in fall months with the highest value in South Sound. Both the trophic length and basal resource diversity exhibited contrasting seasonal patterns among basins with values decreasing seasonally in northern basins (Whidbey and Rosario) and increasing in southern basins (Central and South Sound). Taken as a whole, our observations suggest that the trophic ecology and overall structure of pelagic fish and jellyfish are heavily influenced by local processes at the sub-basin scale as well as temporally dynamic biotic processes such as changes in body size. Our analysis provides an important groundwork to understand how Puget Sound’s pelagic ecosystem is structured and why it may be changing.

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Apr 30th, 10:30 AM Apr 30th, 12:00 PM

Trophic structure of pelagic fish and jellyfish across spatial and seasonal gradients in the greater Puget Sound

Room 611-612

Recent analysis of community structure in the pelagic ecosystem of the greater Puget Sound has revealed a shift in species composition and abundance in some areas from those dominated by fish to those dominated gelatinous mesozooplankton (“jellyfish”). Unfortunately, the mechanisms behind these shifts are unclear due to a deficit of ecological understanding of this system. The analysis of foodweb structure, which reflects the flow of carbon and nutrients, is useful to complement composition and abundance information in order to understand the energetic processes underlying pelagic communities and why they may be changing. In this talk, we examine foodweb structure and trophic ecology of middle trophic level pelagic fish and jellyfish in six oceanographic sub-basins in Puget Sound from April to October 2011. Specifically, we assessed spatial and seasonal variation in 1) the isotopic composition of abundant species of salmonids, forage fish and jellyfish, 2) the trophic overlap between fish and jellyfish and 3) foodweb attributes of whole pelagic communities including niche width, trophic length and basal resource diversity. At the species level, there were strong spatial differences in isotopic composition among sub-basins. Seasonal patterns, possibly suggesting ontogenetic diet shifts or changes in basal carbon sources, were also evident but were more pronounced in fish than jellyfish. The degree of trophic overlap between fish and jellyfish varied among sub-basins and generally decreased seasonally. At the community level, overall community niche width was higher in Whidbey basin in spring and summer months then switched to a north-south gradient in fall months with the highest value in South Sound. Both the trophic length and basal resource diversity exhibited contrasting seasonal patterns among basins with values decreasing seasonally in northern basins (Whidbey and Rosario) and increasing in southern basins (Central and South Sound). Taken as a whole, our observations suggest that the trophic ecology and overall structure of pelagic fish and jellyfish are heavily influenced by local processes at the sub-basin scale as well as temporally dynamic biotic processes such as changes in body size. Our analysis provides an important groundwork to understand how Puget Sound’s pelagic ecosystem is structured and why it may be changing.