James E. McKenna

COMMUNITY METABOLISM DURING EARLY DEVELOPMENT OF A RESTORED WETLAND

Productivity is an important ecological function of any natural system and may be quite high in wetlands. Restoration of productive wetlands may play a key role in re-establishing ecological function to portions of the vast areas of wetlands (roughly 86%) drained and otherwise altered in the United States over the past two centuries. A restored wetland at the Montezuma National Wildlife Refuge (upstate New York, USA) was examined to determine if ecological function (i.e., productivity), as well as biotic structure, was restored. Physicochemical conditions and both aquatic and terrestrial productivity were measured at the restoration site and compared with rates and conditions in a reference wetland. Gross aquatic community production rates (based on diurnal oxygen curves) were similar at each site (1,679 and 2,311 g O2 · m−2 · yr−1) and within the range expected for the habitat. Terrestrial Net Aboveground Primary Production rates (measured by monthly biomass changes) (2,400 and 2,500 g dry wt. · m−2 · yr−1) were also similar between sites when tree and herb production were combined. Aquatic respiration rates (3,704 and 4,552 g O2 · m−2 · yr−1) were also similar but high, typically more than twice as large as gross aquatic production. As a result, net aquatic production rates at both sites were usually negative, indicating that these small wetlands are organic matter sinks that satisfy aquatic respiration by consumption of both autochthonous aquatic production and imported terrestrial production. They enhance diversity of the local landscape by producing populations of aquatic consumers that cannot be supported by aquatic production alone. Typical wetland conditions and processes developed quickly after restoration, but differences in biotic community structure indicate that observed rates of production and respiration at both sites were maintained by flow through different foodweb pathways. Despite the relatively high process rates, and successional progress of the restoration site is expected to be slow.

Feeding ecology of lake whitefish larvae in eastern Lake Ontario

ABSTRACT We examined the feeding ecology of larval lake whitefish (Coregonus clupeaformis) in Chaumont Bay, Lake Ontario, during April and May 2004–2006. Larvae were collected with towed ichthyoplankton nets offshore and with larval seines along the shoreline. Larval feeding periodicity was examined from collections made at 4-h intervals over one 24-h period in 2005. Inter-annual variation in diet composition (% dry weight) was low, as was spatial variation among collection sites within the bay. Copepods (81.4%), primarily cyclopoids (59.1%), were the primary prey of larvae over the 3-year period. Cladocerans (8.1%; mainly daphnids, 6.7%) and chironomids (7.3%) were the other major prey consumed. Larvae did not exhibit a preference for any specific prey taxa. Food consumption of lake whitefish larvae was significantly lower at night (i.e., 2400 and 0400 h). Substantial variation in diet composition occurred over the 24-h diel study. For the 24-h period, copepods were the major prey consumed (50.4%) and their contribution in the diet ranged from 29.3% (0400 h) to 85.9% (1200 h). Chironomids made up 33.4% of the diel diet, ranging from 8.0% (0800 h) to 69.9% (0400 h). Diel variation in the diet composition of lake whitefish larvae may require samples taken at several intervals over a 24-h period to gain adequate representation of their feeding ecology.

A heuristic simulation model of Lake Ontario circulation and mass balance transport

The redistribution of suspended organisms and materials by large-scale currents is part of natural ecological processes in large aquatic systems but can contribute to ecosystem disruption when exotic elements are introduced into the system. Toxic compounds and planktonic organisms spend various lengths of time in suspension before settling to the bottom or otherwise being removed. We constructed a simple physical simulation model, including the influence of major tributaries, to qualitatively examine circulation patterns in Lake Ontario. We used a simple mass balance approach to estimate the relative water input to and export from each of 10 depth regime-specific compartments (nearshore vs. offshore) comprising Lake Ontario. Despite its simplicity, our model produced circulation patterns similar to those reported by more complex studies in the literature. A three-gyre pattern, with the classic large counterclockwise central lake circulation, and a simpler two-gyre system were both observed. These qualitative simulations indicate little offshore transport along the south shore, except near the mouths of the Niagara River and Oswego River. Complex flow structure was evident, particularly near the Niagara River mouth and in offshore waters of the eastern basin. Average Lake Ontario residence time is 8 years, but the fastest model pathway indicated potential transport of plankton through the lake in as little as 60 days. This simulation illustrates potential invasion pathways and provides rough estimates of planktonic larval dispersal or chemical transport among nearshore and offshore areas of Lake Ontario.

Fall diel diet composition of American eel (Anguilla rostrata) in a tributary of the Hudson River, New York, USA

American eel (Anguilla rostrata), a once common species, is now in decline throughout much of its native range in North America. There is little information on the role of American eel in river food webs. A better understanding of the diet and ecological role of American eel will help in the conservation of this important species. During autumn 2009, eel and aquatic invertebrate samples were collected from Hannacroix Creek, a tributary of the Hudson River, in Albany and Greene counties, New York, USA. Eel diet was analyzed by the eel size and time period (day or night). A high proportion of eel stomachs were empty (73%). Eel diets varied among size classes and day and night feeding periods (p = 0.001). Diet overlap was significant between small and medium eels caught both during the day (α = 0.71) and at night (α = 0.84). Nocturnal diet and nocturnal invertebrate samples were similar (α = 0.65), indicating a preference for bottom feeding during the night. Mayfly nymphs were the major prey consumed in each period by all size classes. Among eels that fed, night-feeding eels had the greatest stomach weight (as a percent of total body weight). The swim-bladder parasite, Anguillicoloides crassus, was also observed in eels of all size classes with nearly 50% afflicted.