Date of Award

May 2013

Degree Type

Thesis

Degree Name

Master of Science

Department

Freshwater Sciences and Technology

First Advisor

Harvey Bootsma

Committee Members

Val Klump, Qian Liao, Brenda M. Lafrancois

Keywords

Benthic, Dreissenids, Lake Michigan, Oxygen

Abstract

The intense colonization of the Laurentian Great Lakes by dreissenid mussels has profoundly changed ecosystem processes, particularly benthic oxygen dynamics. Dissolved oxygen concentrations in mussel beds, sloughed Cladophora mats, and sediment indicate that hypoxia forms and disappears in some substrata (ephemeral Cladophora mats), while occurring consistently in others (depositional areas of sloughed Cladophora). Dissolved organic carbon concentrations are high (mean: 143 ± ± 28 ppm) in depositional Cladophora mats but lower (˂ 10 ppm) in most other environments. Field sampling and laboratory experiments suggest that under conditions of low water velocity and thick Cladophora cover, hypoxia may develop atop and within mussel beds. Sloughed Cladophora areal respiration was ~ ∼80% of mussel assemblage areal respiration and shallow anoxia developed within 3-6 hours of algal incubation. Vertical mixing rates in mussel beds with attached Cladophora were inferred from measurements of oxygen flux and vertical gradients. The diffusion coefficient into mussel beds ranged from 6.9 x 10-4 to 2.4 x 10-3 cm2 s-1.

Respiration rates of the quagga mussel (Dreissena rostriformis bugensis) were determined for the shallow and profunda morph phenotypes from in situ and laboratory experiments under a range of temperature (4-20°C °), shell size, and food availability conditions. Temperature-normalized oxygen consumption was significantly lower for the hypolimnetic profunda phenotype. Mass-normalized respiration rates were inversely related to mussel size, and the slope of this relationship increased with temperature. Mussels adjusted their oxygen consumption in response to food enhancement and deprivation, lowering their respiration to a basal metabolic rate 18 hours after food deprivation. In response to decreasing ambient oxygen, quagga mussels exhibited first-order reaction kinetics, with mass-normalized respiration rate at a dissolved oxygen concentration of 0.10 mg L-1 being 1% of that at saturation. Using published data on quagga mussel energy budgets and respiratory quotients, oxygen consumption rates were converted to organic carbon consumption rates. Using these values, along with data on mussel biomass and size frequency distribution in Lake Michigan, it is estimated that quagga mussels consume 15% of annual phytoplankton production. Dreissenids appear to exert significant direct and indirect influences on benthic oxygen dynamics with implications extending up the food web.

 

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