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Natural Communities in Catch Basins in Southern Rhode Island
Mari Butler, Howard S. Ginsberg, Roger A. LeBrun, Alan D. Gettman, and Fred Pollnak

Northeastern Naturalist, Volume 14, Issue 2 (2007): 235–250

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2007 NORTHEASTERN NATURALIST 14(2):235–250 Natural Communities in Catch Basins in Southern Rhode Island Mari Butler1,2,*, Howard S. Ginsberg2, Roger A. LeBrun1, Alan D. Gettman3, and Fred Pollnak1 Abstract - Storm-water drainage catch basins are manmade structures that often contain water and organic matter, making them suitable environments for various organisms. We censused organisms inhabiting catch basins in southern Rhode Island in 2002 in an effort to begin to describe these communities. Catch-basin inhabitants were mostly detritivores, including annelids, arthropods, and mollusks that could withstand low oxygen levels and droughts. Our results suggest that catch-basin inhabitants were mostly washed in with rainwater, and populations increased over the summer season as biotic activity resulted in increased nutrient levels later in the summer. In contrast, mosquitoes and other Diptera larvae were abundant earlier in the summer because the adults actively sought catch basins for oviposition sites. Mosquito larvae were likely to be abundant in catch basins with shallow, stagnant water that had relatively low dissolved oxygen and pH, and relatively high total suspended solids, carbon, and nitrogen. Introduction Storm-water catch basins often contain stagnant, highly organic water providing suitable breeding conditions for several species of mosquitoes and a variety of other organisms (Ishii and Okubo 1989, Kikuchi 1992). Mosquito species commonly found in catch basins in temperate regions include Culex species such as C. pipiens Linnaeus and C. restuans Theobald (Covell and Resh 1971, Gerry and Holub 1989, Ishii and Okubo 1989, Kikuchi 1992, Knepper et al. 1992, McCarry 1996, Munstermann and Craig 1977, Siegal and Novak 1997) and Aedes species such as A. vexans Meigen (Covell and Resh 1971, Gerry Holub 1989) and A. albopictus Skuse (Ishii and Okubo 1989). Many of these species are known vectors of diseases including arboviruses such as West Nile Virus. Considering the close proximity of catch basins to humans, many municipalities target them for mosquito control. Presently, methoprene slow-release pellets and briquets are popular choices to use for mosquito control in these environments (Knepper et al. 1992, McCarry 1996, Schoeppner 1978). Other organisms inhabiting catchbasin environments are also exposed to methoprene and other pesticides, yet they have not been carefully examined. Information about biotic communities living in catch basins, including biological, physical, and chemical 1University of Rhode Island, Kingston, RI 02881. 2Current address - Endicott College, 376 Hale Street, Beverly, MA 01915. 3USGS Patuxent Wildlife Research Center, Kingston, RI 02881. 4Rhode Island Department of Environmental Management, Mosquito Abatement Office, Kingston, RI 02881. *Corresponding author - mbutler@endicott.edu. 236 Northeastern Naturalist Vol. 14, No. 2 parameters may also be useful in improving mosquito control tactics. For example, understanding environmental conditions most likely to harbor large numbers of mosquitoes and learning to take advantage of naturally occurring mosquito predators may help target mosquito control efforts. One objective of this study was to census organisms living in catch basins, and to describe seasonal patterns in abundances of taxonomic groups. The second objective was to model the abundance of mosquitoes, the major group that actively oviposited in catch basins, as a function of environmental factors (temperature, pH, dissolved oxygen, depth, conductivity, total suspended solids, and the amount of carbon and nitrogen in the water). Methods Catch basin census Thirty catch basins from two sites in Narragansett, RI, were sampled six times between May 10 and November 7, 2002. One site consisted of 16 catch basins all connected along a single street sharing an outflow pipe into Narragansett Bay. The second site consisted of 14 catch basins on three parallel roads that emptied into the Narrow River, Narragansett, RI. Each catch basin covered an area of approximately 1.5 m2 with varying depths. Biotic communities were sampled using a custom-made catch-basin sampler capable of sampling the water column and the neustonic and benthic interfaces. The sampler was constructed of a Plexiglas tube 15.24 cm in diameter and 85 cm tall, opened at the bottom and sealed at the top except for a small hole the size of a standard boat plug. Two poles were attached on opposite sides to extend the reach of the two people lowering the sampler. The catchbasin cover was removed, and the sampler was lowered vertically to the bottom with the hole on top of the sampler left open. Once the sampler was resting on the bottom, the boat plug was inserted into the hole using another custom-designed pole. The sampler, containing a known volume of water (area of sampler [m2] x depth of water [m]) that spanned from the air/ water interface to the water/sediment interface, was lifted until the bottom of the sampler was just below the surface of the water. At this point a 164-􀂗m sieve attached to another pole was held under the sampler and all were slowly lifted above the surface of the water. As water drained out of the sampler and through the sieve, particles greater than 164 􀂗m were captured and rinsed into a sampling jar. The efficacy of the sampler was tested by taking several samples with the sampler from test catch basins in the lab, and then comparing abundances estimated by the sampler to abundances estimated from the entire catch-basin contents. The proportions of different taxa collected by our sampler did not differ significantly from samples taken by subdividing the entire catch-basin contents (G < 7.1, P > 0.06). In 16 of 180 sampling attempts, catch basins were completely dry, and samples were not taken. In three of the 164 samples taken, water was present, but too shallow to use the catch-basin sampler. In these cases, a 250-ml standard mosquito dipper was used to collect organisms. Samples 2007 M. Butler, H.S. Ginsberg, R.A. LeBrun, A.D. Gettman, and F. Pollnak 237 were stored on ice while the rest of the sampling was completed (usually not more than 6 hours). Samples were brought back to the laboratory where they were placed in near-boiling water to fix soft-bodied organisms, and preserved in 70% ethanol. After 24 hours, the majority of the ethanol was replaced with fresh ethanol. Organisms were later sorted from debris, enumerated, and identified to the lowest possible taxonomic level. Because annelids were often broken, their abundance was estimated as biomass. Biomass of oligochaete worms was calculated from displacement volume, and for other annelids (Hirudinea), a conversion factor (assuming all leeches were of similar size) was calculated and applied to the numerical abundance data. Abundances for all other taxonomic groups were calculated as number per liter, and communities were characterized by plotting dominance-diversity curves. Modeling mosquito abundance The number of mosquito larvae-per-liter living in each of the 30 catch basins was monitored for six months as part of the catch-basin census. Environmental factors included temperature, pH, conductivity, dissolved oxygen, and water depth. Particulate carbon and nitrogen, and total suspended solids greater than 0.7 􀂗m per liter, were also measured in the same 30 catch basins at the time the biological samples were taken. A Quanta® environmental sensor probe was used to measure temperature, dissolved oxygen, pH, and conductivity. Water depth was measured using a tape measure. Total suspended solids and the amount of carbon and nitrogen per liter were measured by filtering a known amount of water collected from the catch basin thru a pre-weighed, pre-combusted glass fiber filter. The filters were dried in a drying oven at 60 °C, weighed again, and the weight of material collected on the filter calculated. Filters were then analyzed for carbon and nitrogen content using a Carlo Erba EA1108 CHN analyzer located at the Graduate School of Oceanography, University of Rhode Island. Carbon and nitrogen were not measured in May and June due to a problem with sampling methodology. Step-wise regression analysis was used to model the number of mosquitoes per liter based on independent variables consisting of the environmental factors mentioned above (Tabachnick and Fidell 1989). Independent variables were left in the model if P < 0.1 and removed from the model if P > 0.2 using Statistical Package for the Social Sciences (SPSS), and multicolinearity was monitored and addressed if it significantly affected the models (Pallant 2001). Results Catch-basin census All animals collected were from the phyla Annelida, Mollusca, and Arthropoda (Table 1), and total animal density (excluding Annelida) ranged from an average of 5.4 per liter in June to an average of 43.0 per liter in 238 Northeastern Naturalist Vol. 14, No. 2 August (Fig. 1). The average number of different taxonomic groups in individual catch basins ranged from 4.8 in October to 5.7 in August. Oribatei soil mites were the most abundant organisms in May (2.9 per liter), when overall average counts were low (9.5 organisms per liter), and they were present throughout the sampling period (0.7 per liter in June to 3.8 per liter in September). Copepods were the most abundant organisms in June (1.6 per liter) and in September (11.3 per liter). They were consistently present throughout the sampling period, sometimes in high numbers (86.4 per liter from a single catch basin in August and 193.0 per liter from a single catch Table 1. Taxa present in catch basins in southern Rhode Island. Phyla, class, order Family, genus, and species Phylum Arthropoda Class Insecta Order Diptera Family Culicidae Culex restuans Theobald Culex pipiens Linnaeus Aedes japonicus Theobald Unknown Culicid larvae Famly Psychodidae Family Chironomidae Family Ceratopogonidae Unknown Diptera larvae Order Coleoptera Family Ptelalidae Unknown Coleopteran larvae Order Collembola Family Entomobryidae Family Isotomidae Family Onchyuridae Family Poduridae Family Sminthuridae Unknown Collembola Class Crustacea Order Podocpoia (Ostracods) Order Amphipoda Family Talitridae Order Isopoda Family Assellidae (Caecidotea) Order Copepoda Family Cyclopoida Macrocyclops albidus Jurine Paracyclops poppei Rehberg Family Harpacticoid Unidentified nauplii Class Arachnida Order Acarina Suborder Hydracarina Suborder Oribatidae Phylum Mollusca Class Gastropoda Order Basommatophora Family Planorbidae Family Physidae Class Pelecypoda Family Bivalvia Sphaerium occidentale Lewis Phylum Annelida Class Oligochaeta Class Hirudinea 2007 M. Butler, H.S. Ginsberg, R.A. LeBrun, A.D. Gettman, and F. Pollnak 239 basin in September). They were also present in every catch basin in our study at least once during the six-month study period. Mosquitoes dominated the communities during July and August, but were present in all months sampled. It is clear from the dominance-diversity curves (Fig. 1) that when mosquitoes were abundant (July and August), they comprised a large portion of the community. Hydracarina (water mites) were the most abundant as fall approached. Because volume rather than number was measured for Annelida (primarily Oligochaeta with a few Hirudinea), biovolume data are shown separately (Fig. 2). Oligochaete worms were the only other organisms that were present in all 30 catch basins at least once during the sampling period. Figure 1. Dominance-diversity plots of organisms caught each month. The Y-axes are the number of organisms per liter, and the X-axes list the organisms from the most abundant to least abundant. Numbers per liter shown above each graph are the average numbers of organisms captured each month. The "n" is the number of catch basins sampled. 240 Northeastern Naturalist Vol. 14, No. 2 Mosquitoes included both larval and pupal stages of C. pipiens, C. restuans, and Aedes japonicus Theobald. The vast majority of the mosquito larvae were Culex spp. Only 1 A. japonicus out of 1890 total mosquitoes was positively identified for the month of July, and 8 out of 1390 total mosquitoes from the month of August. Diptera included larval Diptera other than mosquitoes such as Psychodidae, Chironomidae, Ceratopagonidae, and other unidentified larvae. Coleopterans included larval Ptelalidae and other unidentified larvae. Collembola included representatives from the following families: Entomobryidae, Isotomidae, Poduridae, Sminthuridae, and Onychiuridae. Gastropods included Physidae and Planorbidae. Ostracods included a small number of specimens likely from the order Podocopida. Bivalves were identified as Sphaerium occidentale Lewis (Harrington’s fingernail clam), which is a new Rhode Island record (Jay Cordeiro, NatureServe and the American Museum of Natural History, Boston, MA, pers. comm.). Copepods included predominantly cyclopoids with a small number of harpacticoids. Harpacticoids were likely Harpacticus spp. and the two dominant cyclopoids were identified as Macrocyclops albidus Jurine and Paracyclops poppei Rehberg (Janet Reid, Virginia Museum of Natural History, Martinsville, VA, pers. comm.). Hydracarina (water mites) included a variety of different stages and species of water mites. All darkcolored, thick-skinned mites were classified as Oribatei (soil mites). Isopods were identified as the family Asellidae and the genus Caecidotea. Amphipods included mostly immature specimens, thought to be from the family Talitridae and species Hyalella azteca Saussure (Maria Aliberti, University of Rhode Island, Kingston, RI, pers. comm.). In addition to the aquatic organisms addressed in this paper, a variety of terrestrial arthropods were found in many of the catch basins, but not included in these analyses since they were not truly members of the aquatic community. Orders represented included: Protura, Diplura, Figure 2. Mean volume of Annelida (± one standard error) caught each month. The number of samples taken per month ranged from 25 to 30. 2007 M. Butler, H.S. Ginsberg, R.A. LeBrun, A.D. Gettman, and F. Pollnak 241 Diptera adults, Hymenoptera (predominantly Formicidae), Hemiptera, Psocoptera, Coleoptera (including Carabidae, Scarabidae, Curculionidae, and others), Arachnida, Lepidoptera larvae, Thysanaptera, Homoptera (mostly aphids), Diplopoda (Millipedes), and Orthoptera. As the summer went on and the water temperature increased, abundances increased with peaks in most populations (Copepoda, Isopoda, Amphipoda, and Mollusca) occurring in August or September. The Diptera, including the mosquitoes, peaked earlier (July). Annelida populations were high in August continuing into October, and the mites were always present in relatively low numbers, increasing as the season progressed (Fig. 3). Figure 3. Average numbers from each taxonomic group (± one standard error) caught each month. The number of samples taken per month ranged from 25 to 30. 242 Northeastern Naturalist Vol. 14, No. 2 Environmental conditions and mosquito abundance Catch basins experienced a range of environmental conditions over the course of the season (Fig. 4). Water temperature spanned about 10 °C in 6 months. Conductivity varied little with the exception of one catch basin that emptied directly into the Narrow River, where a relatively high conductivity was recorded repeatedly. pH was approximately neutral, except for a single low reading of 3.97 taken in June and a single high measurement of 11.61 taken in August from two different catch basins. Dissolved oxygen (DO), total suspended solids per liter (TSS), the amount of carbon per liter (C), and the amount of nitrogen per liter (N) were variable, with a decline in DO and increase in particles per liter through the summer months (Figs. 4 and 5). The ability of environmental variables to predict mosquito abundance was assessed using stepwise regression on the samples taken each month (Table 2). Mosquito numbers were negatively related to DO in 3 of the 6 months and to pH levels in 2 months, and positively related to C in 2 months and to N and TSS in one month each. In October, only 4 mosquito larvae were caught. Correlations between environmental variables are shown in Table 3. Figure 4. Environmental factors measured each month. Symbols represent mean ± standard error. 2007 M. Butler, H.S. Ginsberg, R.A. LeBrun, A.D. Gettman, and F. Pollnak 243 Figure 5. Indices of available food by month (mean amount ± one standard error). No carbon or nitrogen samples were analyzed for May and June. Discussion Catch-basins census Very few researchers have examined organisms other than mosquitoes living in catch basins. However, Kikuchi’s (1992) work evaluating nontarget effects of methoprene in an urban drain in Tokushima, Japan provided some information about other organisms living in this sort of environment. He examined effects of methoprene on Syrphidae (hover flies), Assellus hilgendorforii Bovallius (isopods), Cleon dipterum Linnaeus (mayfly), Chironomidae (midges), and Hermetia illucens Linnaeus (black soldier 244 Northeastern Naturalist Vol. 14, No. 2 flies) living in catch basins. He also studied Physa fontalis Linnaeus (a mollusk) and Assellus hilgendorforii in the laboratory, suggesting that they too are found in catch basins (Kikuchi 1992). Ishii and Okubo (1989) evaluated one hundred and fifty-six catch basins in Tokushima City in the summer of 1988; of the 65% that were found flooded, 22% harbored Culicidae (mosquitoes), 17% harbored Chironomidae (midges) and 8% harbored Psychodidae (moth flies). Many of the organisms that we found were from the same families as were found in the studies mentioned above. Nearly all of the organisms captured in our study can be classified as scavengers or detritivores, feeding chiefly on dead plant or animal material as well as on fungi, algae, protozoans, periphyton, and other organic detritus. Over the course of our sampling, we observed increases in most organisms as the season progressed thru the summer months and a decline in October (Fig. 3). Annelids (Fig. 2), however, continued to increase into October. A similar trend was noted in organic matter, the probable source of food for most of these organisms, which we estimated by measuring TSS, C, and N (Fig. 4). Unfortunately, C and N data for May and June were not available. We speculate that organisms and other detritus were rinsed or blown into catch basins as the summer progressed, causing peaks in late summer or early fall. The only groups that did not follow this pattern were the mosquito larvae and other Diptera larvae. Their populations peaked in July and then declined. They were perhaps the only abundant organisms present due to the adults actively flying into the catch basin to lay their eggs, in contrast to the other common organisms that arrived predominantly through passive dispersal. This might account for their lack of Table 2. Summary of environmental factors—dissolved oxygen (DO), the amount of carbon per liter (C), the amount of nitrogen per liter (N), and total suspended solids per liter (TSS)—as predictors of number of mosquito abundance. “n” is the number of catch basins sampled, and the “(-)” or “(+)” next to the variables contributing to the model denote correlation with mosquito abundance. Independent % catch variables basins with included in the Month n mosquitoes regression equationA R2 P May 30 10% DO (mg/L)(-) 0.1 0.038 44 June 29 38% pH (-) 0.5 < 0.001 74 July 25 56% DO (mg/L) (-) 0.2 0.015 Depth (cm)(-) 54 August 26 54% C (mg/L) (+) 0.6 < 0.001 N (mg/L) (+) 25 September 27 33% C (mg/L) (+) 0.7 < 0.001 TSS (mg/L) (+) 87 pH (-) DO (mg/L) (-) October 27 7% ns ns ns AStepwise analyses were added if P 􀂔 0.1 and removed if P > 0.2. 2007 M. Butler, H.S. Ginsberg, R.A. LeBrun, A.D. Gettman, and F. Pollnak 245 synchronicity with the rest of the catch-basin inhabitants. Mosquitoes might be responsible for transporting other organisms such as parasitic mites among catch basins. This transport might contribute to the slight increase in species richness that was seen in August and also the overall increasing numbers displayed by the other organisms. The structure of catch-basin communities is unique, but is similar in some ways to those of temporary woodland pools. Early colonizers of temporary pools are often detritivores that overwinter in resting stages and are capable only of passive dispersal. They include Copepoda, Ostracoda, Oligochaeta, Hirudinea, and Mollusca, as well as others not found in catch basins (Wiggins et al. 1980). This group accounts for the majority of organisms identified in Table 3. Correlation between independent variables used to predict mosquito abundances in catch basins in 2002. Month Related variables Pearson correlation May pH and Temp r = 0.987, P < 0.0001 Depth and TSS r = -0.478, P = 0.004 June TSS and Depth r = -0.442, P = 0.007 July N and C r = 0.864, P < 0.0001 TSS and C r = 0.840, P < 0.0001 DO and Temp r = -0.644, P < 0.0001 TSS and N r = 0.578, P = 0.001 DO and N r = -0.567, P = 0.002 Depth and C r = -0.464, P = 0.010 Temp and N r = 0.425, P = 0.017 Depth and N r = -0.425, P = 0.017 DO and C r = -0.382, P = 0.030 Aug. N and C r = 0.996, P < 0.0001 Temp and DO r = -0.629, P < 0.0001 Temp and TSS r = -0.493, P = 0.005 DO and TSS r = 0.399, P = 0.022 September N and C r = 0.982, P < 0.0001 TSS and N r = 0.958, P < 0.0001 TSS and C r = 0.945, P < 0.0001 C and pH r = -0.502, P = 0.009 N and pH r = -0.489, P = 0.010 C and Depth r = -0.450, P = 0.018 TSS and pH r = -0.398, P = 0.033 TSS and Depth r = -0.382, P = 0.040 N and Depth r = -0.378, P = 0.041 TSS and Temp r = -0.372, P = 0.044 C and Temp r = -0.362, P = 0.049 October N and C r = 0.969, P < 0.0001 TSS and N r = 0.946, P < 0.0001 TSS and C r = 0.896, P < 0.0001 pH and DO r = 0.565, P = 0.001 N and Depth r = -0.463, P = 0.008 Depth and C r = -0.450, P = 0.009 TSS and Depth r = -0.393, P = 0.021 N and pH r = -0.363, P = 0.031 Conductivity and pH r = 0.362, P = 0.032 TSS and pH r = -0.328, P = 0.047 246 Northeastern Naturalist Vol. 14, No. 2 this study and was present early in the season increasing as the summer progressed. The second group described by Wiggins (1980) consisted of organisms capable of some dispersal such as Diptera, including mosquitoes. Wiggins’ (1980) descriptions support our hypothesis that most of the organisms found in catch basins arrived there passively with the exception of the mosquitoes and other Diptera larvae. Another similarity between communities of catch basins and temporary pools is the taxa richness. Taxa richness in temporary pools was found to be related to habitat size and permanence. Larger temporary pools that were more permanent contained more species (Spencer et al. 1999). Catch basins have a small surface area (􀂧 1.5 m2), and the permanence of the water is extremely variable. A temporary pool of about 1 m2 has slightly fewer than 5 species (Spencer et al. 1999). This is in close agreement with the average taxa richness found in each catch basin, which ranged from 4.8 to 5.7 taxa. Furthermore, Spencer et al. (1999) found that smaller and less permanent pools had low proportions of predators. Perhaps the size or lack of permanence of catch basins limits the number of predators that can live there. Oribatei mites, Hydracarina, mosquito larvae, Copepoda, Collembola, and Isopoda repeatedly were the most abundant organisms during our sampling season. The dominance-diversity curves (Fig. 1) showed a community evenly spread between several different taxonomic groups for most months. The curves were relatively flat in May and June, while curves from August, September, and October each showed one notably abundant taxonomic group (mosquitoes, Copepoda, and Hydracarina respectively), with the remaining groups still represented at numbers similar to other months. In July, mosquitoes clearly dominated the community (Fig. 1). The majority of catch-basin organisms can be classified at the trophic level of detritivore (Pennak 1978). However, there is evidence that some of the specific organisms identified might be involved in biological interactions of interest with regard to mosquito control. For example, although amphipods are usually considered benthic detritivores, Crangonyx shoemakeri Hubricht and Mackin was found to capture and ingest mosquito larvae, suggesting that amphipods may be facultative predators under some conditions (Schwartz 1992). In a laboratory study, amphipods left the benthos and consumed on average 3.5 ± 1.0 mosquito larvae in 24 hours and 6.0 ± 0.1 after 72 hours (Schwartz 1992). Under circumstances where other predators are lacking, such as may be the case in catch-basin environments, species traditionally thought to be benthic feeders may be at least facultative predators. Because amphipods eat fungi, they have enzymes needed to digest chitin, a major constituent of fungal cell walls and arthropod cuticle (Schwartz 1992). This would make them capable of digesting mosquito larvae, but whether this happens in catch basins has not yet been determined. We were unable to positively identify to species the majority of the immature amphipods we collected, which were present in 6 of the 30 catch basins sampled. One catch basin in particular had amphipods present every time it was sampled, and in 2007 M. Butler, H.S. Ginsberg, R.A. LeBrun, A.D. Gettman, and F. Pollnak 247 six months, only one mosquito larva was caught in that particular catch basin. This circumstantial evidence should be tested with laboratory feeding experiments to determine if the amphipods cohabitating with mosquito larvae in catch basins might be employed as biological control agents. Copepods can also be involved in biological relationships that might be of interest in mosquito control. Macrocyclops albidus and Paracyclops poppei were the two species of copepods commonly found in catch basins. M. albidus is a voracious predator of early instar mosquitoes (Calliari et al. 2003; Marten et al. 1994, 2000; Rey et al. 2004). M. albidus and P. poppei can also act as carriers of mosquito pathogens, potentially reducing populations of Culex spp., important vectors of West Nile Virus, thereby reducing the need for larvicide application without introducing chemicals into these environments. Certain species of copepods are intermediate hosts for species of microsporidia, a protist pathogen. Microsporidians can have complex life cycles, spending part in a copepod host and part in a mosquito host, usually leading to the demise of both hosts. Transmission of these pathogens can be both vertical to offspring and horizontal by mouth or via integument, increasing the potential for infection once the pathogens are introduced. Amblyospora salinaria Becnel and Andreadis n. sp. (Microsporidia: Amblyosporidae) is a known pathogen of C. salinarius with M. albidus as the intermediate host (Becnel and Andreadis 1998). Although C. salinarius was not the species of Culex we found in catch basins, perhaps this pathogen or a related one might also infect C. pipiens or C. restuans. Paracyclops poppei, a species previously thought to be a subspecies of P. fimbriatus (Fischer), was also found ubiquitously in catch basins. Presently, P. poppei is accepted as a distinct species, and P. fimbriatus is not thought to exist in North or South America since its redescription (Karaytug and Boxshall 1998) (Janet Reid, pers. comm). A species of microsporidia, Amblyospora camposi, has been described infecting the mosquito C. renatoi (Lane & Ramalho) and the copepod Paracyclops fimbriatus fimbriatus living in leaf axils in Argentina (Micieli et al. 2000). The species described as P. fimbriatus fimbriatus may or may not be what is now described as P. fimbriatus (Karaytug and Boxshall 1998), but regardless of the precise taxonomy, P. poppei should be tested for susceptibility to A. camposi, as should the pathogenicity of A. camposi to C. pipiens and C. restuans. Copepods were found in every catch basin at least once during the sampling period suggesting that these common mosquito habitats are quite suitable for copepods. Biological control of catch-basin breeding mosquitoes using endemic copepod species is worthy of further research. Modeling mosquito abundance Mosquitoes were the major group that actively entered catch-basin environments, so we studied the conditions that fostered mosquito abundance in catch basins in further detail. Mosquito species and abundances in catch basins have been closely evaluated because of their importance in human disease transmission (Kronenwetter-Koepel et al. 2005). Forty catch basins in Illinois sampled 248 Northeastern Naturalist Vol. 14, No. 2 twice per month during the summer months, yielded a total of 2147 mosquito larvae, captured using standard mosquito dippers. Sixty-three percent were C. pipiens and 37% were C. restuans (Gerry et al. 1989). Culex restuans were more common earlier in the sampling (June) and C. pipiens were more common later (July and Aug) both in Illinois and Kentucky (Covell and Resh 1971, Gerry and Holub 1989). Of the Culicidae observed in catch basins in Tokushima City, 77% were C. pipiens, 32% were A. albopictus, and 9% were C. halifaxii (Theobald) (Ishii and Okubo 1989). Other investigators examining pesticide efficacy in catch basins have noted the presence of Culex spp., C. restuans, and C. pipiens (Knepper et al. 1992, McCarry 1996, Munstermann and Craig 1977, Schoeppner 1978, and Siegal and Novak 1997) The mosquitoes we found were predominantly C. pipiens and C. restuans, both of which are known to prefer water with high organic content (Crans 2004). Low dissolved oxygen and indices of food availability (C, N, and TSS) repeatedly contributed to regression models predicting high mosquito numbers. Low oxygen was useful in predicting mosquito numbers in May, July, and September, and low pH was the best predictor in June. DO and pH are intimately related through the processes of respiration and decomposition, so it was not surprising that they were correlated. Decomposition of organic material uses up oxygen, makes water more acidic, and puts more organic particles into the water. In addition, oak leaves, rich in humic acid, are common in catch basins, no doubt contributing to the decreased pH, especially as they decompose. We did not monitor human factors such as the use of cleaning products, lawn chemicals, or automobile products, all of which could significantly affect pH and other environmental factors. Particles in the water were measured as indices of food availability, and predictors of mosquito abundance. Unfortunately, samples filtered for carbon and nitrogen analyses in May and June were not usable. Nonetheless, in August, either C or N successfully predicted where mosquito numbers were high, and in September, all three indices of food availability predicted mosquito numbers. In addition to the amount of food in the water, the depth of the water can influence availability of food particles to mosquito larvae. In July, depth was left in the model along with DO. In laboratory experiments, water depth affected the development and accumulation of caloric reserves in mosquito larvae (Timmermann and Briegel 1993). Since food particles often sink to the bottom, larval feeding may be hindered when the water is deeper than a few centimeters (Timmermann and Briegel 1993). It is generally accepted that C. pipiens and C. restuans prefer water that has a high organic content (Crans 2004). Gerry and Holub (1989) also observed that the amount of accumulated debris increased the incidence of mosquito larvae in catch basins. The analytical tools employed in this study clearly support these observations. The conditions known to harbor Culex mosquitoes were the same conditions, i.e., characterized by low DO, low pH, high TSS, high C, and high N. 2007 M. Butler, H.S. Ginsberg, R.A. LeBrun, A.D. Gettman, and F. Pollnak 249 In conclusion, we speculate that catch-basin communities are populated by organisms that are washed or rinsed passively into the system. These organisms tended to increase in abundance from May through September (Figs. 2 and 3). During this same time period, total suspended solids in the water as well as carbon and nitrogen gradually increased (Fig. 4). Mosquitoes and other Diptera, on the other hand, were an exception to this rule since they actively search out sites in which to lay their eggs. They peaked in abundance earlier in July (Fig. 3), a month before the other organisms. Our data showed the greatest numbers of Culex spp. larvae in shallow, putrid water characterized by high amounts of organic material (C, N, and TSS) and decomposition (low DO and low pH). Acknowledgments We are grateful to the following faculty, staff, and students at the University of Rhode Island: Maria Aliberti, Katie Allen, Dr. Steven Alm, Dr. David Bengtson, Adam Butler, Dr. Richard Casagrande, Charles Dawson, Caryn Debatt, Linda Green, Mary McDougle, Dr. Neeta Pardanani, Carl Sawyer, Jesse Siligato, Cannsotha Suom, and Jane Viera. 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