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Baden, S. ., University of Gothenburg, Fiskebackskil, Sweden, susanne.baden@marecol.gu.se
Emanuelsson, A. ., University of Gothenburg/ SIK, Fiskebackskil, Sweden, andreas@mp.se
Pihl, L. ., University of Gothenburg, Fiskebackskil, Sweden, leif.pihl@marecol.gu.se
Svensson, C. J., University of Gothenburg, Gothenburg, Sweden, carl-johan.svensson@marecol.gu.se
Åberg, P. ., University of Gothenburg, Gothenburg, Sweden, per.aberg@marecol.gu.se

SHIFT IN SEAGRASS FOOD WEB STRUCTURE OVER DECADES LINKED TO OVERFISHING

Empirical field studies in seagrass show that overgrowth by filamentous algae, reducing seagrass growth, can be explained by a top-down cascade (due to overfishing) enforced by bottom-up interactions (due to eutrophication). On the Swedish west coast 60% of the seagrass has disappeared since the 1980’s. We hypothesize that the 4-8 times increase in nutrient load since the 1930’s, and overfishing causing a >90% decline in the cod stock have altered the seagrass structure and function during the last decades. In this study, quantitative samplings from 1980’s and 2000’s of four feeding guilds; top predatory fish, intermediate predatory fish, omnivorous crustaceans and mesoherbivores are compared. Since 1980’s the biomass of top predators (gadoids and trout) has decreased 4 times, intermediate fish predators (gobids and sticklebacks) has increased 6 times whereas mesoherbivores (idoteids and gammarids) has disappeared from the seagrass beds. Thus, we found clear evidence that a shift in seagrass food web structure has occurred over three decades. In concert with eutrophication the lack of grazers resulting from this shift most likely contribute to overgrowth by filamentous algae and vanishing seagrass.

Session #:GS05B
Date: 02-17-2011
Time: 08:00

Presentation is given by student: No