Predation on Green Frog Eggs (Rana clamitans) by Ostracoda Evan P. Gray 1 , Schyler Nunziata 2 , Joel W. Snodgrass 2 , David R. Ownby 3 , and John E. Havel 4 Predation has long been known as a structuring force of larval amphibian assemblages with aquatic vertebrates and insect larvae being noted as important predators. However, no studies report predation by micro-predators (i.e., organisms less than one half the size of amphibian eggs) on eggs or larvae. Here we report the consumption of Green Frog (Rana clamitans) eggs by at least four species of the crustacean class Ostracoda (Dolerocypris sinensis, Cypridopsis vidua, Eucypris fuscatus, Physocypria sp.). We initially observed Green Frog egg consumption in microcosms containing sediment from stormwater management ponds. We subsequently conducted feeding studies in which we manipulated densities of three of the species and recorded time to complete consumption of a single egg. Ostracods often consumed eggs in three days (before eggs hatched), but did not appear to attack tadpoles in the microcosms. Overall density of ostracods was correlated with egg mortality in the microcosms and Eucypris fuscatus consumed eggs most efficiently during feeding trials. Because one of the ostracods we observed feeding on amphibian eggs (C. vidua) is common among temporary wetlands, and one (D. sinensis) represents the first reported occurrence of the species in North America, there is a need for further investigations of ostracod predation on amphibian eggs under field conditions. P REDATION is a strong force in structuring commu- nities of aquatic organisms (Wellborn et al., 1996) and can limit populations of amphibians (Reiger et al., 2004; Rubbo et al., 2006). Vulnerability of amphibian eggs to predation is highly variable among species, and some consider the egg stage to be the most vulnerable to predation because of its immobility and relative lack of defense mechanisms in comparison to other life stages (Romano et al., 2008). The most studied predators of amphibian eggs include adult and larval salamanders, snakes, tadpoles, larval insects, and various species of fish (Gunzburger and Travis, 2005). These studies focus on predators that are larger than the amphibian eggs on which they prey. No studies, to our knowledge, have considered micro-predators. Here we describe feeding of four species of the crustacean class Ostracoda from Maryland on eggs of the Green Frog (Rana clamitans), and report results from feeding trials designed to confirm direct consumption and docu- ment the effects of ostracod density on consumption rates. Ostracods are widespread in the environment (Meisch, 2000) and can be found in the benthic layers of both river and lake environments (Delorme, 2001) where their density is highly variable (Pennak, 1989). The eggs of ostracods are capable of withstanding both desiccation and freezing, which allows them to inhabit many ephemeral environ- ments (Delorme, 2001). Ostracods typically eat algae and detritus (Meisch, 2000; Delorme, 2001), although some species consume zooplankton (De Deckker and Geddes, 1980; Campbell, 1995) and others the soft parts of living and dead snails and other animals (Sohn and Kornicker, 1975; Wilkinson et al., 2007). Ostracod grazing and predation can be severe enough to limit the distribution of algae (Wickstrom and Castenholz, 1985) or change zooplankton community structure (Campbell, 1995). Ostracods have been shown to adhere to the backs of amphibians (Seidel, 1989), but consumption of amphibian eggs or tissues has not been reported. Therefore, our observations and exper- iments represent the first report and investigation of ostracod feeding on the eggs of any amphibian species. MATERIALS AND METHODS We first observed ostracods consuming amphibian eggs in laboratory microcosm set up with stormwater management pond sediments. Sediments were originally collected from six stormwater management ponds in the Red Run water- shed (Owings Mills, MD). Microcosms consisted of 2 L shoeboxes, 1 cm of pond sediment, and 1.5 L of aged tap water. Twelve microcosms were set up with each of the pond sediments. Sediments were collected and wetted initially five months prior to the addition of Green Frog eggs. After initial set up, microcosms were allowed to sit at ambient temperature (approximately 12–24uC) in a greenhouse until Green Frog eggs were added. During the time between initial set up and Green Frog egg addition, water completely evaporated from most boxes, with minimal water remaining in a few. This process allowed the development of ostracod populations. Before adding Green Frog eggs to microcosms we stirred sediments and added water to bring the microcosms back up to volume. We then allowed microcosms three days to equilibrate before adding 16 fertilized Green Frog eggs to each microcosm. We obtained Green Frog eggs from an uncontaminated wetland in Baltimore County, Maryland, within 24 hours of ovoposition. We monitored the devel- opment of embryos and resulting larvae for two weeks, at the end of which all surviving tadpoles had reached Gosner stage 25 (Gosner, 1960). To estimate the density of ostracods at the end of the two-week exposure period, we stirred all microcosms and collected 155 mL of water using a length of PVC pipe. After inserting the PVC pipe into the sediment, we used a syringe to remove all water and the top layer of sediment from the pipe. Each sample was filtered using a larval fish net (mesh size 65 m) and preserved in 70% 1 Huxley College of the Environment, Western Washington University, Bellingham, Washington 98225-9181; E-mail: graye7@cc.wwu.edu. 2 Department of Biological Sciences, Towson University, 8000 York Road, Towson, Maryland 21252; E-mail: (SN) snuni1@students.towson. edu; and (JWS) jsnodgrass@towson.edu. Send reprint requests to JWS. 3 Department of Chemistry, Towson University, 8000 York Road, Towson, Maryland 21252; E-mail: downby@towson.edu. 4 Department of Biology, Missouri State University, 901 S. National Avenue, Springfield, Missouri 65897; E-mail: (JEH) johnhavel@missouristate. edu. F 2010 by the American Society of Ichthyologists and Herpetologists DOI: 10.1643/CH-09-074 Submitted: 20 April 2009. Accepted: 16 February 2010. Associate Editor: S. A. Schaefer. Copeia 2010, No. 3, 452–456