TheCladophoraresurgence in Lake Ontario: characterization and implications for management

Abstract

Nuisance growth of the alga Cladophora, reported from Lake Ontario since the 1930s, abated in the decades following implementation of phosphorus control measures in the 1970s. Our examination of beach fouling records and historical observations of algal biomass has confirmed literature reports that a resurgence in nuisance growth of Cladophora has occurred since invasion of Great Lakes waters by dreissenids. Our findings indicate that the growth rate of Cladophora (specific rate of net photosynthesis) has decreased by 44% since 1972 in response to phosphorus controls. However, improved transparency, a response to mussel activity, has increased the maximum depth colonizable by Cladophora by a factor of 5 over that same interval. The net result is a sixfold increase in production potential since the late 1980s (the Post-P Management II Period) and a threefold increase since the 1970s (the Pre-P Management Period). Although the Cladophora resurgence has been driven by dreissenid modification of the light environment, phosphorus management remains the only alternative for reversing and ameliorating nuisance conditions. Elucidation of the nature of the Cladophora resurgence will aid decision-makers in maintaining a focus on phosphorus management as the appropriate means of remediating nuisance growth of the alga.Résumé : La nuisible prolifération de Cladophora repérée sur le Lac Ontario au moins depuis les années 1930 a visiblement diminué après la mise en place de mesures de contrôle du phosphore à la fin des années 1970. Notre analyse des données historiques sur les plages souillées et sur la biomasse historique des algues a confirmé qu'il y a eu une résurgence de la nuisible prolifération de Cladophora sur la période qui a suivi l'invasion des Grands Lacs par les dreissenidés. Notre découverte indique que le taux net de photosynthèse en Cladophora a diminué de 44 % depuis 1972, en réponse aux réductions de concentration de phosphore. Pourtant, la meilleure transparence, une réponse aux activités des dreissenidés, a augmenté la profondeur maximum disponible pour la colonisation par Cladophora par un facteur de 5 durant le même intervalle. En résulte quasiment une augmentation de six fois du potentiel de croissance pendant les années 1980s (l'ère Post-P Management II) et une augmentation de trois fois depuis les années 1970s (l'ère Pre-P Management). Bien que cette augmentation ait été poussée par la modification de l'environnement de lumière par les dreissenidés, la gestion du phosphore demeure la seule alternative pour inverser et améliorer ces conditions nuisibles. L'élucidation de la nature de la résurgence de Cladophora aidera les décideurs en maintenant l'accent sur la gestion du phosphore comme le moyen approprié pour corriger la nuisible prolifération de cette algue.

Influences on Water Quality and Abundance of Cladophora, a Shore-Fouling Green Algae, over Urban Shoreline in Lake Ontario

“…External loading of TIN should be more evident compared to SRP because of the proportionally lower biological utilization of the total supply. Unlike phosphorus, TIN concentrations are thought to remain above growth-limiting levels for phytoplankton (e.g., [45]) and Cladophora [9,18]. Linear regressions predicting SRP and TP from TIN were significant for three and two of seven sampling events, respectively ( Table 7), suggesting that lakebed TIN may be a predicator of external loading of phosphorus, such as in August 2012, but that this is not consistently the case.…”

“…A key factor in the resurgence in Cladophora, previously a problem in the 1960-1980s when the lake was more nutrient enriched, is the improved light climate of the lake following the invasion of dreissenid mussels [16] in about 1990 [17]. Kuczynski et al [18] have convincingly demonstrated that there has indeed been a resurgence in Cladophora which can be directly attributed to the changing light climate. These studies have concluded that the growth potential for Cladophora has increased markedly compared with the period prior to the deepening photic zone.…”

“…The only tool available for abatement of Cladophora in Lake Ontario is the control of phosphorus inputs [18]. Based on the most recent published estimate, the single largest phosphorus input to the lake is upstream from Lake Erie, accounting for 27% of the annual loading [19].…”

Great Lakes Cladophora harbors phylogenetically diverse nitrogen‐fixing microorganisms

“…It has been suggested that the invasion of zebra mussels ( Dreissena polymorpha ) and quagga mussels ( Dreissena bugensis ) in the late 1980s amplified the expansion of Cladophora through a cascade of interrelated ecological processes. These influences include increased water clarity, which expanded algal growth conditions to deeper waters; availability of additional substrates (e.g., mussel beds) for attachment and growth; and nutrient capture and regeneration (e.g., phosphorus) (Auer et al, ; Davies & Hecky, ; Higgins, Pennuto, Howell, Lewis, & Makarewicz, ; Kuczynski, Auer, Brooks, & Grimm, ) (see Figure , left panel). Phosphorus is recognized as the limiting nutrient for Cladophora growth in the Great Lakes (Auer & Canale, ; Higgins et al, ), and phosphorus cycling by dreissenid mussels in benthic areas (e.g., via pseudofeces, inorganic excretion) (Nalepa, Gardner, & Malczyk, ) is believed to have played an important role in Cladophora expansion post‐mussel invasion.…”

“…It has been suggested that the invasion of zebra mussels (Dreissena polymorpha) and quagga mussels (Dreissena bugensis) in the late 1980s amplified the expansion of Cladophora through a cascade of interrelated ecological processes. These influences include increased water clarity, which expanded algal growth conditions to deeper waters; availability of additional substrates (e.g., mussel beds) for attachment and growth; and nutrient capture and regeneration (e.g., phosphorus) (Auer et al, 2010;Davies & Hecky, 2005;Higgins, Pennuto, Howell, Lewis, & Makarewicz, 2012;Kuczynski, Auer, Brooks, & Grimm, 2016) (see Figure 1, left panel).…”