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Aquatic Invasive Species and Recent Food Web Disruptions in the Great Lakes Thomas F. Nalepa Great Lakes Environmental Research Laboratory, National Oceanic and Atmospheric Administration Ann Arbor, MI Recent aquatic invaders into the Great Lakes fish hook waterflea “ Zebra Mussel Echinogammarus Ruffe Round Goby Quagga mussel “Invasion Meltdown” Established invaders alter habitat conditions and food webs that may favor other invaders, creating a positive feed-back system. Round goby Echinogammarus feeds on mussel biodeposits Zebra mussel feeds on mussels Food Web Interactions Echinogammarus Round goby Zebra mussel Diporeia Gammarus positive impact negative impact What are the general ecological consequences of invasive species ? Creates ecosystem instability Loss of predictability Uncertainty of management actions When (if ever) does an invasive species contribute to ecological stability? Populations stabilize and are integrated into the food web Zebra Mussel and Quagga Mussel Impacts Physical Impacts Water Clarity Bottom Structure Chemical Impacts Nutrient Cycling Contaminant Cycling Biological Impacts Direct and indirect impact on just about all organisms from bacteria to fish Diporeia spp. Cold,deepwater organism – native to the Great Lakes Comprised 70 % of benthic biomass in offshore waters High lipid content, rich in calories Fed upon by most fish species Areas Where Diporeia is Naturally Not Found Areas Where Diporeia is Now Rare or Gone Diporeia in Lake Michigan 94% Decrease in 10 Years 1994/95 2000 2005 Diporeia in Lake Huron 57% Decline in 3 Years 2000 2003 Zebra Mussel 1994/95 2000 2005 Quagga Mussel 1994/95 Zebra Mussels in Lake Michigan, 2002 10 m 30 m 15 m 40 m 20 m 60 m Quagga Mussels in Lake Michigan – 100 m Theories for the Disappearance of Diporeia 29 Decreased Food Availability Food Quantity Food Quality/Nutrient Deficiency 28 Toxic Excretions/Metabolic Wastes 25 Disease/Pathogen/Infection 9 Increased Contaminant Sensitivity 6 Low Oxygen in Upper Sediments 3 Fish Predation Inconsistencies in Decline Patterns Rates of decline are highly variable Decline occurs in areas far-removed from Dreissena Mortality cannot be induced in the laboratory Diporeia and Dreissena coexist in areas outside the Great Lakes Some fish species that feed on Diporeia lake whitefish lake trout yellow perch white perch slimy sculpin deepwater sculpin alewife rainbow smelt bloater spottail shiners sticklebacks trout-perch Adjusted weight (loge kg) Lake Whitefish Condition – Southeast Lake Michigan Diporeia Decline First Observed 0.6 0.5 Zebra Mussels Arrive 0.4 0.3 1984 1988 1992 1996 2000 Study to Assess Impact on Prey Fish X : Sampling Transect 20- 80 m X X X Prey Fish Alewife Sculpin Bloater Smelt Impact on Prey Fish Adult Alewife: moved, changed diet, reduced energy density Young Alewife: changed diet Adult Bloater: moved, changed diet Slimy sculpin: moved, changed diet, reduced weight Deepwater sculpin: reduced energy density and weight Smelt: no effect Prey Fish Biomass in Lake Huron M e a n b io m a s s p e r to w (k g ) 40 35 30 25 20 15 10 5 0 1975 1980 1985 1990 1995 2000 2005 YEAR Courtesy of Stephen Riley, USGS-GLSC Energy Content of Common Prey Joules per gram (wet) 5000 4000 3000 2000 1000 0 Live deep in sediments, difficult to get Not abundant Small, lower energy Low energy,shell Low energy,shell a a e n t a s e g a i i e o a e g d t s a i r d a k ii u m n r My och po o a i Q e l n a D p ig & o h l o ir O ra h Sp Zo b C Ze Ponto-Caspian species predicted to invade the Great Lakes (source: Ricciardi and Rasmussen 1998) Taxon Species Common Name Polychaeta Amphipoda Hypania invalida Corophium curvispinum Corophium sowinskyi Dikerogammarus haemobaphes Dikerogammarus villosus Pontogammarus robustoides Pontogammarus obesus Obesogammarus crassus polychaete worm corophiid amphipod corophiid amphipod gammarid amphipod gammarid amphipod gammarid amphipod gammarid amphipod gammarid amphipod Mysidea Limnomysis benedeni Paramysis intermedia Paramysis lacustris Paramysis ullskyi Hemimysis anomala Hypanys colorata mysid shrimp mysid shrimp mysid shrimp mysid shrimp mysid shrimp clam Clupeonella capia Benthophilus stellatus Neogobius fluviatilis Caspian kilka starry goby monkey goby Bivalves Fishes Great Lakes, British Isles Threatened By New Predator Ecologists are predicting an invasion of the North American Great Lakes and the British Isles by a killer shrimp from Russia, with disastrous results for the local aquatic species. Results indicate that the voracious shrimp, Dikerogammarus villosus, will have a severe impact on the areas it invades, causing local extinctions and reducing biodiversity. Feb 2001, Daily University Science News “Killer” Shrimp Blue: Native range Red: Range expansion between 1992 and 1995
