A DICHOTOMOUS KEY TO QUICKLY DIFFERENTIATE BETWEEN OSTRACODES TO ESTABLISH PRE-EUROPEAN ECOSYSTEM STATE FROM CONESUS LAKE

Conesus Lake experienced cultural eutrophication from the mid-late twentieth century, yet today ongoing remediation efforts have improved water quality. Yet, water quality monitoring efforts at Conesus Lake began well after elevated anthropogenic nutrient loading had begun. The geohistroical record is uniquely qualified to provide baseline data so that ongoing remediation efforts can be measured against a pre-European settlement baseline. Ostracodes, microscopic crustaceans, are widely used as indicators of past environments, including trophic state.

Six species of ostracodes were recovered from the sedimentary cores taken from Conesus Lake. Quickly differentiating between these six species is necessary for timely processing of sediment as both cores extend more than 1.5m below the lake bed, ostracodes will eventually be enumerated at 1-cm intervals down both cores, and each 1-cm stratigraphy interval may contain dozens of valves from adult ostracodes. Thus, a dichotomous key is necessary to facilitate quick differentiation between species.

To create this key, we standardized morphological terminology using Kesling (1951). We then generated a matrix of eighteen traits for all six species. Size proved to be a useful way to differentiate species as our fauna contained one large (>1mm in adult body size) species, Candona ohioensis. Carapace texture proved to be a useful way to differentiate three other species as only Limnocythre verrucosa has a reticulate carapace, only Cypridopsis vidua has a punctate texture, while only Darwinula stevensoni has a smooth texture. To differentiate between the two remaining Candona species, Ca. candida and Ca. elliptica, valve margin proved useful as Ca. elliptica has relatively straight dorsal and ventral margins compared to Ca. candida. Undergrad students have used this key to successfully and quickly identify ostracodes from Conesus Lake sediments. In addition, the standardized description of traits for all species enable the community-wide distribution of traits to be described for all stratigraphic intervals, thus creating a record not only of how species change as a result of trophic change, but also traits.

Kesling, R.V., 1951. Terminology of ostracod carapaces. Contributions from the Museum of Paleontology of the University of Michigan IX: 93-171.