Functional response and potential predatory impact of Tortanus dextrilobatus, a carnivorous copepod recently introduced to the San Francisco Estuary

Abstract

Despite a dramatic increase in the introduction of non-indigenous estuarine zooplankton in recent decades, the trophic implications of such introductions have rarely been quantified. Here we investigate predation rates of Tortanus dextrilobatus, a carnivorous copepod recently introduced to the San Francisco Estuary that achieves peak abundances in excess of 1000 ind. m . The functional response of T. dextrilobatus feeding upon 2 copepod prey types -the non-indigenous cyclopoid Oithona davisae, and the 'native' calanoid Acartia (Acartiura) sp. -was described by a type II functional response (Ivlev function) at 2 experimental temperatures. In 3 of these 4 treatments, 90% I max was achieved within a naturally occurring range of prey densities. Taxon-specific seasonal size variation was identified, and carbon-based consumption values were used to determine temperature-dependent rates of predation on both prey types. These empirically derived consumption rates and temperature dependence values were then applied to broadscale surveys (1997 to 1999) of zooplankton community composition in order to estimate the predatory impact of T. dextrilobatus upon prey populations in the San Francisco Estuary. Predatory impact estimates (% population consumed d -1 ) greater than 1% occurred on a regular basis when T. dextrilobatus was abundant, with maxima exceeding 20, 65, and 25% for O. davisae, Acartia (Acartiiura) sp. and all Copepoda, respectively. These observations support the hypothesis that non-indigenous invertebrate zooplanktivores can play a significant role, at least seasonally or episodically, in the secondary production dynamics of aquatic ecosystems.KEY WORDS: Zooplankton ecology · Feeding · Predation · Copepods · Tortanus dextrilobatus · Non-indigenous · Invasion · San Francisco Estuary Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 277: [167][168][169][170][171][172][173][174][175][176][177][178][179] 2004 A rapid increase in biological invasions of estuarine habitats in recent decades has increased the prospect of potential deleterious effects on community and ecosystem level dynamics (Carlton & Geller 1991, Ruiz et al. 1997, Parker et al. 1999). Yet, a recent literature review by Bollens et al. (2002) revealed a scarcity of studies exploring such impacts in zooplankton communities, despite widespread documentation of invasion occurrence and mechanisms. Determining the impacts of human mediated introductions has been a challenge for natural resource managers and ecologists alike, and while they may represent unfortunate cases of often inadvertent biomanipulation, they provide a unique opportunity for investigating fundamental questions in plankton community ecology and invasion biology. One such question is the degree to which predation pressures may be important in regulating population dynamics of secondary producers.The San Francisco Estuary has been identified as one of the most highly invaded aquatic ecosystems (Cohen & Carlton 1998), and the zoop...

Variability in copepod trophic levels and in feeding selectivity based on stable isotope analysis in Gwangyang Bay off the southern coast of Korea

“…These estimated results are consistent with the former experimental tests and field investigations (Ambler and Frost, 1974;Landry, 1978;Conley and Turner, 1985;Hooff and Bollens, 2004). Cyclopoids (primarily Corycaeus affinis) dominated copepod 20 assemblages in spring and autumn at the middle part and deep-bay channel of the bay (Table 1).…”

Biology of the introduced copepod Pseudodiaptomus inopinus in a northeast Pacific estuary

“…For example, several species of Asian mysids and the predatory copepod Tortanus dextrilobatus have recently been introduced to the San Francisco estuary (Modlin & Orsi 1997, Orsi & Ohstuka 1999. Tortanus dextrilobatus has become very abundant and appears capable of significantly affecting its copepod prey (Bollens et al 2002, Hooff & Bollens 2004. Therefore, it appears that planktonic invasions in northeast Pacific estuaries are ongoing, and in some estuaries are evolving.…”

“…The copepod fauna there is now primarily East Asian in some parts of the bay (Orsi & Ohtsuka 1999, S. M. Bollens & J. R. Cordell unpubl.). One species, T. dextrilobatus, appears to have the capacity to severely impact the remaining native copepods in San Francisco Bay through predation (Hooff & Bollens 2004). At least 3 of the introduced copepod species established in San Francisco Bay have also recently been introduced to the Columbia River estuary, L. tetraspina, P. forbesi and S. doerrii, and the latter 2 have become abundant there.…”

Zooplankton of tidal marsh channels in relation to environmental variables in the upper San Francisco Estuary

“…The zooplankton of the open waters of the SFE have been reasonably well studied to date, both at the community level (Ambler et al 1985, Kimmerer & Orsi 1996, Purkerson et al 2003, Gewant & Bollens 2005, Rollwagen-Bollens et al 2006) and at the individual species level (Orsi & Walter 1991, Rollwagen-Bollens & Penry 2003, Hooff & Bollens 2004, Bouley & Kimmerer 2006, Ger et al 2010, Gould & Kimmerer 2010. However, the zooplankton communities of tidal marshes of the SFE have never been reported.…”