Ferenc A. de Szalay

Effects of Hydrology on Unionids (Unionidae) and Zebra Mussels (Dreissenidae) in a Lake Erie Coastal Wetland

Abstract Infestation by introduced zebra mussels has extirpated native unionids in many Great Lake habitats. Shallow areas in coastal wetlands are intermittently dewatered by seiches and seasonal water level changes, and we examined how water level fluctuations and sediment characteristics affected interactions among unionids and zebra mussels in a Lake Erie coastal marsh. In 2001 we sampled unionid distributions and measured zebra mussel colonization on PVC plates at 1 cm, 18 cm and >35 cm water depths. We found a diverse unionid community (15 species) with many juvenile unionids. Unionid densities (0.01 unionids/m2) were comparable to other coastal wetlands, but are lower than reported in offshore areas before zebra mussels were introduced. Zebra mussels colonized plates at >3000 individuals/m2 in some locations. Although >60% of unionids had byssal threads on their shells, >75% of unionids had no attached zebra mussels. Therefore, zebra mussels are colonizing unionids, but are not surviving. Unionid numbers and zebra mussel colonization were low in shallow (1–35 cm) water depths, indicating that water level fluctuations limited their distributions. Only two species of unionids were collected in 1–17 cm deep areas, and areas that became mudflats in September had almost no unionids. Numbers of zebra mussels and unionids were not correlated with organic content or silt/clay content of the sediments. Habitat characteristics shared by this wetland and other coastal wetlands that are important refuges of unionids include: a hydrological connection with the lake, areas deep enough for unionids to survive low water levels and soft sediments that allow unionid burrowing.

Effects of Muskrat (Ondatra zibethicus) Lodge Construction on Invertebrate Communities in a Great Lakes Coastal Wetland

Abstract Muskrat (Ondatra zibethicus) herbivory and lodge construction create open water areas in stands of emergent vegetation. This study examined how aquatic invertebrates are affected by changes in the physical structure of plant stands created by muskrats. We compared density, species composition and functional feeding groups of benthic macroinvertebrate communities and abiotic conditions in open water areas at muskrat lodges and in adjacent cattail stands. Although total numbers of macroinvertebrates were not affected by muskrat activities, communities at muskrat lodges were less diverse than in cattail stands. Gathering collectors such as chironomid midges that feed on fine particulate organic matter were the dominant trophic group; these were significantly more abundant at muskrat lodges than in cattail stands. Scrapers, such as gammarid scuds that feed on periphyton, were also abundant; these were significantly more abundant in cattail stands than at muskrat lodges. Water temperature, dissolved oxygen, pH, conductivity and sediment organic content were different in these habitats. These results indicate that muskrats alter abiotic conditions and invertebrate communities in wetlands, which will affect food resources for wildlife and fish that feed on aquatic invertebrates in these habitats.

FISH PREDATION OF ZEBRA MUSSELS ATTACHED TO QUADRULA QUADRULA (BIVALVIA: UNIONIDAE) AND BENTHIC MOLLUSCS IN A GREAT LAKES COASTAL WETLAND

Although the introduced zebra mussel, Dreissena polymorpha, has eliminated most native unionid populations within the lower Great Lakes, some recent surveys have found diverse unionid communities in several Lake Erie coastal wetlands. In 2004, we tested whether fish predators reduced zebra mussels on Quadrula quadrula (Unionidae) in a Lake Erie coastal wetland. In June, we placed unionids and colonization plates in small-mesh exclosures (2.5-cm × 2.5-cm mesh), large-mesh exclosures (5-cm × 10-cm mesh), and open exclosures (2.5-cm × 2.5-cm mesh with two 40-cm × 40-cm openings). Zebra mussels and other benthic molluscs were sampled in October, and zebra mussel numbers on Q. quadrula outside exclosures were significantly higher in October than in June. Densities of zebra mussels on Q. quadrula and colonization plates were much higher in small-mesh and large-mesh treatments that excluded large fish than open treatments. Mean (±1 SE) densities of zebra mussels/unionid were also higher inside (1041 ± 103) than outside (6.9 ± 1.5) exclosures in October. These results indicate that large-bodied molluscivores (e.g., common carp, freshwater drum, channel catfish) can limit zebra mussel numbers in coastal wetlands. Densities of other molluscs (Sphaeriidae, Corbiculidae, Gastropoda, and Unionidae) were not different in sediments of exclosures and uncaged areas, suggesting that fish can have a greater impact on numbers of attached zebra mussels than benthic molluscs.

Effects of Hydrology, Herbivory and Sediment Disturbance on Plant Recruitment in a Lake Erie Coastal Wetland

Abstract Coastal wetlands of the Laurentian Great Lakes provide many valuable ecological functions and, currently, there are extensive efforts to preserve and manage remaining habitats. We examined plant recruitment in a Lake Erie coastal marsh on bare mudflats exposed during 2 y of below average water levels. In 2000 mudflat vegetation was sampled in shallow, medium and deep water transects and compared to germinable seeds found in sediments from 0–15 cm below the surface. Effects of sediment disturbance and herbivory on plant recruitment were tested in 1 m2 quadrats in 2000 and vegetation was sampled in 2001 to assess how well the disturbance/herbivory experiment predicted plant communities that became established on the mudflats. In 2000, 18 species were found on mudflats and 19 species were reared from the seedbanks. Seed densities (∼3000 seedlings/m2) were comparable to other freshwater wetlands and did not differ by sediment depth. Taxa richness was highest in sediments 0–5 cm below the surface. Most plants on the mudflats were found in the shallow transect, but seed abundance and richness were highest in deep transects. Sediment disturbance decreased taxa richness and herbivory decreased both plant cover and richness; however, responses varied among plant taxa. Our results indicate that abundant seedbanks exist in this wetland, but plant recruitment will be restricted to shallow areas due to turbidity. Communities in 2001 were more diverse (40 species) than predicted from vegetation in 2000 probably because propagules were introduced from nearby habitats. Communities in 2001 were most similar to ungrazed and undisturbed quadrats in 2000 because these had the most species.

Effects of Water Level Fluctuations on Zebra Mussel Distribution in a Lake Erie Coastal Wetland

ABSTRACT In May–August 2002, we examined how seasonal water level changes and frequent wind-driven seiches limited the amount of habitat for zebra mussels (Dreissena polymorpha) in a Lake Erie coastal wetland. We counted numbers of veligers that colonized artificial substrates at different depths (1–17 cm, 18–34 cm and >34 cm below the water surface). Water levels decreased during the summer, and by August colonization plates set at 1–17 cm were exposed 85% of the time, plates set at 18–34 cm were exposed 15% of the time, but plates set at >34 cm were rarely exposed. The highest densities (numbers/m2) of colonization occurred in June (7176.1) and August (3119.5), and this bimodal pattern has been observed in other Great Lake habitats. Densities were highest at >34 cm depths (5552.7), intermediate at 18–34 cm (2802.1) and lowest at 1–17 cm (410.8). Veliger numbers on some plates in deep water levels were as high as 10,000/m2, which are similar to densities in the Great Lakes. We also measured survivorship of adult mussels in wire mesh cages from 28 July to 25 August. Most (~90%) adult zebra mussels survived in both 18–34 cm and >34 cm water levels, but only ~2% survived in 1–17 cm water levels. We determined the percent of Crane Creek Marsh in each of the three water depth zones and estimated that water level changes prevent zebra mussels from inhabiting 62% of this coastal wetland. The low survival of zebra mussels may be a reason why abundant unionids have recently been found in this and some other Great Lake coastal wetlands.

TEMPORAL OVERLAP OF NESTING DUCK AND AQUATIC INVERTEBRATE ABUNDANCES IN THE GRASSLANDS ECOLOGICAL AREA, CALIFORNIA, USA

Aquatic invertebrates are essential components of duckling diets, but little is known about temporal changes of invertebrate populations in different types of brood habitats. In spring and summer 1996 and 1997, we conducted searches for duck nests in upland fields in the Grasslands Ecological Area in Californias Central Valley to determine timing of nest initiation and hatching. We also sampled aquatic invertebrate populations in adjacent permanent wetlands, semi-permanent borrow areas within seasonal wetlands that were drawn down in spring, and reverse-cycle wetlands (i.e., wetlands flooded from spring to summer) to estimate invertebrate food resources available to ducklings. Abundances of many invertebrates important in duckling diets (Gastropoda, Cladocera, Ostracoda, Amphipoda, Corixidae, Dytiscidae, Hydrophilidae) were greater in borrow areas and reverse-cycle wetlands than in permanent wetlands. Peak macroinvertebrate densities in borrow areas occurred immediately after adjacent wetlands are drawn down in March–April. Peak densities in reverse-cycle wetlands and permanent wetlands occur in May. Although total numbers of microinvertebrates (<1 mm size) and macroinvertebrates (≥1 mm size) in all wetlands decreased after May, most mallard (Anas platyrhynchos) and cinnamon teal (A. cyanoptera) eggs hatched in May. Therefore, these ducklings hatch when abundant invertebrate food resources were most available in reverse-cycle wetlands. In contrast, most gadwall (A. strepera) eggs hatched in June after invertebrate numbers started to decrease. In areas where hydrology is controlled, managing for reverse-cycle wetlands may be a useful strategy to provide abundant invertebrate food resources during the waterfowl breeding season.

Responses of plants and invertebrate assemblages to water-level fluctuation in headwater wetlands

Abstract Flood-pulsing is a key environmental factor that structures biotic communities in large-order river systems, but we focused our study on the effects of flood-pulsing in headwater systems. We used 10 mesocosm wetlands (10 m × 20 m) to test 2 treatments: a flood-pulse regimen in which natural flood events caused water levels to fluctuate and a static regimen in which water levels remained artificially stable. Abiotic characteristics, plants, and aquatic invertebrate communities were monitored from 2002 through 2005 in permanent pools, nonflooded banks in static wetlands, and intermittently flooded banks in flood-pulse wetlands. The flood-pulse treatment had minimal effects on environmental conditions of permanent pools, and submersed plant and aquatic invertebrate communities in permanent pools were similar in both treatments. This result suggested that resource subsidies from the floodplain to the pools were minimal. However, flood-pulsing caused observable changes to plant communities in the intermittently flooded zone (IFZ) above the permanently flooded pool. Overall plant diversity was higher in static wetlands, and % bare ground was higher in flood-pulse wetlands, results suggesting that the short, stochastic floods were a strong environmental stressor. In flood-pulse wetlands, the fluctuating water levels may have reduced the proportion of introduced, weedy, and upland plant taxa. Flood-pulse and static wetlands had distinctly different plant assemblage compositions, indicating that the abiotic stressors caused pronounced changes in the floodplain community. An indicator species analysis showed that taxa classified as obligate wetland plants were indicators in flood-pulse wetlands (e.g., Juncus canadensis, Ludwigia palustris, Dulichium arundinaceum, Eleocharis obtusa, Carex crinita, Carex lupulina, Carex vulpinoidea), but taxa classified as facultative wetland or upland plants were indicators of static wetlands (Cirsium arvense, Eupatoriadelphus maculatus, Plantago lanceolata, Bidens frondosus, Melilotus officinalis, Mentha arvensis, Daucus carota, Poa palustris). Many functional categories of plant species that were common in flood-pulse wetlands (e.g., obligate wetland plants, perennial, native and nonweedy species) are considered beneficial from a management perspective.

Seasonal and Diel Patterns of Biting Midges (Ceratopogonidae) and Mosquitoes (Culicidae) on the Parris Island Marine Corps Recruit Depot

ABSTRACT: The Marine Corps Recruit Depot on Parris Island, SC, is surrounded by tidal salt marshes, which are breeding habitats for many pestiferous biting flies. Knowledge of biting fly behavior patterns is needed to develop effective pest management strategies in urban areas adjacent to salt marshes. We measured biting midge (Ceratopogonidae) and mosquito (Culicidae) seasonal abundance and diel activity patterns on Parris Island using CO2-baited suction traps from November 2001 – November 2004. Of the three biting midge species collected, Culicoides furens was most abundant (86.2% of total) and was present in high numbers from late March to November. Culicoides hollensis (12.0% of total) was present during spring and fall but absent in summer and winter; and Culicoides melleus (1.7% of total) was present in spring through fall but absent in winter. Abundance of C. furens had a positive linear correlation with air temperature and rainfall. There were nonlinear correlations between air temperature and C. hollensis and C. melleus numbers, which were most abundant at moderate temperatures. Of 18 mosquito species collected, the most abundant were Aedes taeniorhynchus (42.7% of total), Aedes sollicitans (26.3% of total), Culex salinarius (15.6% of total), Culex quinquefasciatus (7.3% of total), and Aedes vexans (5.7% of total); other species comprised <5% of collections. Aedes taeniorhynchus numbers were positively correlated with temperature and rainfall, and Cx. salinarius was correlated with soil moisture. Activity of most biting midges and mosquitoes were highest the first two hours following sunset. Species of biting flies were present in all months, suggesting that yearround control measures are necessary to reduce exposure to potential disease vectors and nuisance biting.

Efficacy of aerial spray applications using fuselage booms on Air Force C-130H aircraft against mosquitoes and biting midges.

Abstract The effectiveness of a novel fuselage boom configuration was tested with flat-fan nozzles on US Air Force C-130H aircraft to create ultra-low volume sprays to control mosquitoes (Culicidae) and biting midges (Ceratopogonidae). The mortality of mosquitoes and biting midges in bioassay cages and natural populations, using the organophosphate adulticide, naled, was measured. Mosquitoes in bioassay cages had 100% mortality at 639 m downwind in all single-pass spray trials, and most trials had >90% mortality up to 1,491 m downwind. Mosquito mortality was negatively correlated with distance from the spray release point (r2  =  0.38, P < 0.001). The volume median diam of droplets collected was 44 µm at 213 m and decreased to 11 µm at 2,130 m downwind of the release point. Droplet density decreased from an average of 18.4 drops/cm2 at 213 m to 2 drops/cm2 at 2,130 m. Droplet densities of 10-18 droplets/cm2 were recorded at sampling stations with high mosquito mortality rates (>90%). In wide-area operational applications, numbers of mosquitoes from natural populations 1 wk postspray were 83% (range 55%–95%), lower than prespray numbers (P < 0.05). Biting midge numbers were reduced by 86% (range 53%–97%) on average (P  =  0.051) after 7 days. The results of these field trials indicate that the fuselage boom configuration on C-130H aircraft are an effective method to conduct large-scale aerial sprays during military operations and public health emergencies.