2011 NORTHEASTERN NATURALIST 18(4):445–456 The Nymphal Odonate Fauna of Two Watersheds in the Lower Potomac River Basin, Maryland, with Emphasis on Rare Taxa Patrick H. Graves III1,* and Patrick J. Ciccotto2 Abstract - Sixty percent of Maryland’s odonate species are considered to be in need of conservation. To prioritize areas for the protection of biodiversity, the Maryland Department of Natural Resources (MD DNR) has identified 10 watersheds with the highest rates of occurrence of imperiled and rare stream species, including odonates. We examined the lotic-breeding odonate fauna of two of these high priority watersheds to determine the distribution and status of several imperiled odonate species in Maryland. Odonate nymphs from two Lower Potomac River basin watersheds, Zekiah Swamp Run and Breton Bay, were collected by volunteers and MD DNR’s Maryland Biological Stream Survey from 2000–2010 and were identified to species level when possible. Thirty-four species were collected during this survey, 10 of which are state-listed species. The data collected in this survey detail the distributions, habitats, and microhabitats of rare odonates in two priority watersheds in Maryland that can be used to aid in the conservation of these species and their habitats. Introduction Dragonflies and damselflies (Insecta: Odonata) comprise a widespread faunal group, with approximately 499 species in the United States (NatureServe 2010). Approximately 18% of the odonates in the US are globally ranked as “at risk” by The Nature Conservancy and NatureServe (Master et al. 2000, Natureserve 2010). While a number of state checklists and distributional records are available for the US (e.g., Cruden and Gode 2000, Evans 1988, Johnson and Valley 2005, Tennessen et al. 1995), few lists are published for purposes of conservation planning in areas where distributional data, like natal habitat use, are critical for the protection of biodiversity (Bried 2005, Bried and Ervin 2005, Hunt et al. 2010, Muise et al. 2007, Orr 2001). The Atlantic Coastal Plain physiographic province of the southeastern United States, within which lies over 60% of Maryland, is a center of odonate diversity and endemism (Kalkman et al. 2008). Well over half (109 species) of the approximately 180 dragonfly and damselfly species that have been documented in Maryland are considered rare, threatened, or endangered (RTE) in the state (Maryland Department of Natural Resources 2010). Pollution, sediment disturbance, and loss and degradation of critical habitats are among the threats to odonates and other aquatic fauna in Maryland (Kayzak et al. 2005; Southerland et al. 2005a, b). While the knowledge of adult odonate species distribution is abundant for Maryland 1Monitoring and Non-tidal Assessment Division, Maryland Department of Natural Resources, 580 Taylor Avenue, Tawes Building C-2, Annapolis, MD 21401. 2Department of Biological Sciences, University of Maryland Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250. *Corresponding author - pgraves@dnr.state.md.us. 446 Northeastern Naturalist Vol. 18, No. 4 (Czaplak 1995; Donnelly 1961; Fisher 1940, Moorefield 1941; Orr 1995, 1996a, 1996b, 1996c, 1998a, 1998b, 2000a, 2000b; Root 1923; Solem and Solem 1999), less is known about the distribution and habitats of odonate nymphs. Detailed distributional and ecological data for the nymphal stage are needed to better assess the conservation status of, and potential stressors to, Maryland’s odonate fauna. The Maryland Biological Stream Survey (MBSS) is a statewide assessment of the biodiversity of Maryland’s freshwater streams undertaken by the Maryland Department of Natural Resources (MD DNR). The MBSS has documented the distributions of, and threats to, a number of aquatic species, notably fishes and other vertebrates (Kazyak et al. 2005, Kilian et al. 2009, Kline and Morgan 2000, Stranko et al. 2008). These data have led to the designation of high priority watersheds, i.e., areas with high levels of aquatic biodiversity and high numbers of occurrences of state rare aquatic species. Recent efforts by the MBSS have begun to examine the distributions of invertebrate species, specifically freshwater mussels and crayfishes (Ashton 2009, Kilian et al. 2010), to assess their role in the designation of these conservation watersheds. Similar endeavors are needed for species of other invertebrate groups, of which little is known about their distributions. We report the results of a comprehensive survey of nymphal odonates in two high priority watersheds in the Lower Potomac River basin, Zekiah Swamp Run and Breton Bay. These two watersheds, along with eight others throughout the state, have been designated by MD DNR as areas that provide the best opportunities to maintain populations of aquatic RTE species. The Zekiah Swamp Run and Breton Bay watersheds are located in an area where large human population growth is projected over the next 30 years (Maryland Department of Planning 2008). The first step in rare species conservation is to identify those places where the species occurs. We examined the nymphal odonates of these two high priority watersheds to determine the distribution, habitats, and microhabitats of several rare and imperiled odonate species in the region. We anticipate this information to be useful in the conservation of Maryland’s odonate diversity and its odonate habitat and in determining the conservation status of lotic-breeding odonate species in Maryland. Methods Study sites The target watersheds for this study, Zekiah Swamp Run and Breton Bay, are located southeast of Washington, DC in the Lower Potomac River basin on the Atlantic Coastal Plain physiographic province (Figs. 1 and 2). Zekiah Swamp Run and Breton Bay drain approximately 28,300 and 15,600 ha, respectively. In both watersheds, soils transition from moderately to well-drained silt or loam in the north to predominately clay soils in the south. Pine-hardwood forests cover over half of the area in both of these watersheds, with agricultural, urban, wetland, and minimal proportions of other land-cover types comprising the remaining portions of the landscape (Boward et al. 1998). The topography is characterized by flat upland surfaces comprised of alluvial plains and fluvial-estuarine terraces with steep-sided valleys created by stream incision (Reger and Cleaves 2008). Stream habitats in Zekiah Swamp Run and Breton Bay range in pH from slightly acidic 2011 P.H. Graves and P.J. Ciccotto 447 to neutral and are influenced strongly by seasonal precipitation, with the larger tributaries expanding onto the floodplain after significant wet periods and drying during the summer months. Substrates vary from predominately silt, sand, and gravel in the smaller tributaries of the watersheds to sand and cobble in the larger tributaries. Several imperiled aquatic animal species are native to these two watersheds, including six fish species and two freshwater mussel species, having led to their designation as conservation priority watersheds. Figure 1. Rare, threatened, and endangered (RTE) odonate species richness at sites in the Zekiah Swamp Run watershed, MD. 448 Northeastern Naturalist Vol. 18, No. 4 Odonate data During March and April 2000–2010, benthic macroinvertebrates were collected from 327 stream sites using MBSS sampling protocols (Stranko et al. 2007). Thirty of these sites were sampled by the MBSS staff, and 297 were sampled by Stream Waders volunteers, a group organized to supplement MBSS data through volunteer sample collections. Criteria used for selection of MBSS and Stream Waders sites are outlined in Klauda et al. (2008) and Boward and Figure 2. Rare, threatened, and endangered (RTE) odonate species richness at sites in the Breton Bay watershed, MD. 2011 P.H. Graves and P.J. Ciccotto 449 Bruckler (2008). In brief, this sampling protocol consisted of sampling 1.86 m2 (20 ft2) of site-specific characteristic habitats (most productive macroinvertebrate habitats, as defined in Stranko et al. [2007]) using a 540-micron mesh D-net. Organisms were dislodged from substrates and organic debris, such as wood and leaf packs, by disturbing these habitats upstream of the D-net with kicking and rubbing by hand. Contents of the D-net samples were washed into a sieve bucket, and large debris was removed, inspected for organisms, and discarded. The sample was preserved in at least 70% ethyl alcohol. In the lab, odonate nymphs were sorted from the samples, and late-instar individuals were identified by DNR taxonomists to species level. Individuals in an early instar stage or missing a body part were identified to either family or genus level. Individuals identified to species level were compared to DNR voucher specimens when that species was present in the voucher collection. Twenty individuals (eight taxa) were sent to a Maryland odonate expert for verification. The primary sources used for identification of specimens were Needham et al. (2000) and Westfall and May (1996). Other sources of information used include Cashatt and Vogt (2001), Kennedy (1924), and Tennessen (2008). Specimens collected in this study are housed at MD DNR in Annapolis, MD. Stream-reach habitat information was recorded for MBSS sites in these watersheds from 2000–2010. Microhabitat information (e.g., dominant substrate [sand, cobble, silt, etc.], habitat components [depth, velocity, rootwad, woody debris, etc.], channel unit [pool, riffle, etc.]) was recorded, when possible, by the authors at MBSS Breton Bay watershed sites during 2009 and 2010. In 2009, 15 sites in the Breton Bay watershed were sampled similarly to the protocol outlined in Stranko et al. (2007), with the exception that the more productive odonate habitat was sampled instead. This change was made in an effort to more accurately capture the odonate fauna at these sites by sampling habitats utilized by odonates (e.g., sand and silt, undercut banks, rootmats), which would typically be ignored otherwise. Results and Discussion During 2001 and 2008, 341 odonate nymphs were collected from 137 sites in the Zekiah Swamp Run watershed. This collection is represented by 24 species, 19 genera, and nine families (Table 1). From 2000–2010, 1044 odonate nymphs were collected from 190 sites in the Breton Bay watershed. The Breton Bay collection is represented by 25 species, 21 genera, and eight families (Table 1). The most-collected dragonfly family (Gomphidae), dragonfly species (Boyeria vinosa), damselfly family (Calopterygidae), damselfly genus (Calopteryx), and damselfly species (Calopteryx maculata) were similar between the two watersheds. Cordulegaster and Boyeria were the most collected dragonfly genera in the Zekiah Swamp Run and Breton Bay watersheds, respectively. Eleven species were present in both collections. The total number of individuals of each species (as well as the number of individuals identified to the genus or family level) and the percentage of sites each species was collected at within each watershed is shown in Table 1. 450 Northeastern Naturalist Vol. 18, No. 4 Table 1. Number of nymphal odonate individuals collected from streams in the Zekiah Swamp Run and Breton Bay watersheds. The percentage of sites at which a species was collected within the respective watershed is given in parentheses. An asterisk indicates a species listed as rare, threatened, or endangered in Maryland (Maryland Department of Natural Resources 2010). Individuals listed in this table at the family and genus level were not identifiable to species level due to immaturity or missing body parts. No. of individuals collected (% of sites collected at) Zekiah Scientific name Common name Swamp Run Breton Bay Anisoptera (dragonflies) Aeshnidae 1 - Aeshna umbrosa Walker Shadow Darner 3 (0.7) - Basiaeschna janata (Say) Springtime Darner 1 (0.7) 7 (2.1) Boyeria vinosa (Say) Fawn Darner 30 (16.1) 161 (36.8) Epiaeschna heros (Fabricius) Swamp Darner 2 (1.5) - Nasiaeschna pentacantha (Rambur)* Cyrano Darner - 1 (0.5) Cordulegastridae - - Cordulegaster bilineata (Carle)* Brown Spiketail 3 (2.2) - Cordulegaster erronea Hagen in Selys* Tiger Spiketail 17 (6.6) - Cordulegaster maculata Selys Twin-spotted Spiketail 10 (5.8) 8 (8.4) Cordulegaster obliqua (Say)* Arrowhead Spiketail 4 (2.2) 3 (1.6) Cordulegaster sp. A spiketail 45 131 Corduliidae 7 21 Epitheca cynosura (Say) Common Baskettail - 2 (0.5) Epitheca princeps Hagen Prince Baskettail - 1 (0.5) Epitheca sp. A baskettail 1 4 Helocordulia selysii (Hagen in Selys)* Selys' Sundragon 4 (2.2) 27 (7.9) Helocordulia sp. A sundragon 3 6 Neurocordulia sp. A shadowdragon 1 - Somatochlora linearis (Hagen)* Mocha Emerald 6 (2.9) - Somatochlora tenebrosa (Say) Clamp-tipped Emerald 1 (0.7) 13 (1.6) Somatochlora sp. An emerald 3 33 Gomphidae 67 90 Gomphus exilis Selys Lancet Clubtail - 2 (0.5) Gomphus lividus Selys Ashy Clubtail 1 (0.7) 13 (3.2) Gomphus rogersi Gloyd* Sable Clubtail 11 (5.8) - Hagenius brevistylus Selys Dragonhunter 3 (1.5) 9 (4.7) Progomphus obscurus (Rambur)* Common Sanddragon - 4 (2.1) Stylogomphus albistylus (Hagen in Selys) Eastern Least Clubtail 16 (8) 29 (11.1) Stylurus sp. A clubtail - 1 (0.5) Libellulidae 4 - Libellula cyanea Fabricius Spangled Skimmer 1 (0.7) - Libellula vibrans Fabricius Great White Skimmer - 1 (0.5) Libellula sp. A skimmer 2 4 Pachydiplax longipennis (Burmeister) Blue Dasher - 7 (2.1) Plathemis lydia (Drury) Common Whitetail - 2 (1.1) Macromiidae - 6 Didymops transversa (Say) Stream Cruiser - 1 (0.5) Macromia illinoiensis Walsh Swift River Cruiser - 4 (1.6) Macromia sp. A river cruiser 1 12 2011 P.H. Graves and P.J. Ciccotto 451 Overall, 38% of the individuals collected were identified to species level, and 47% and 17% were identified to genus and family level, respectively. Of the dragonflies collected, 48% were identified to species level. Due to immaturity or the loss of caudal gills, only 21% of damselflies were identified to species level. Six RTE dragonfly species were collected in Zekiah Swamp Run and four RTE dragonfly and two RTE damselfly species were found in Breton Bay (Table 1). Two of these species, Helocordulia selysii and Cordulegaster obliqua, were collected in both watersheds. The most collected RTE species was Cordulegaster erronea (17 individuals) in Zekiah Swamp Run and H. selysii (27 individuals) in Breton Bay. The least collected RTE species in each watershed was Cordulegaster bilineata in Zekiah Swamp Run and Nasiaeschna pentacantha in Breton Bay (one individual each). At least one RTE species was collected at 17% of the Zekiah Swamp Run sites and 14% of the Breton Bay sites. In general, RTE odonate species in Breton Bay and Zekiah Swamp Run were distributed in lotic habitats throughout the watersheds (Figs. 1, 2). Multiple RTE species were collected at sites in both watersheds. In the Zekiah Swamp Run watershed, 46% of the sites at which multiple RTE species were collected lie in the southern region of the watershed, including the most RTE-species-rich site (3 species) in either watershed. All four multiple RTE species sites in the Breton Bay watershed lie in the eastern half of the watershed. All but one of the 17 C. erronea individuals were collected at sites in the southern region of the Zekiah Swamp Run watershed. These eight sites were small, shaded tributaries to Zekiah Swamp Run with average depths ranging from 5–30 cm. Combined, seven other odonate species were collected along with C. erronea: H. selysii, G. rogersi, Stylogomphus albistylus, Calopteryx maculata, B. vinosa, Cordulegaster maculata, and Cordulegaster obliqua. Two RTE species, H. selysii and G. rogersi, were collected along with C. erronea at one site in the southwestern part of this watershed. In addition, C. erronea was found at three of the eight sites Table 1, continued. No. of individuals collected (% of sites collected at) Zekiah Scientific name Common name Swamp Run Breton Bay Zygoptera (damselflies) - - Calopterygidae - - Calopteryx maculata (Beauvois) Ebony Jewelwing 17 (11) 63 (18.4) Calopteryx sp. A jewelwing 44 248 Coenagrionidae 11 29 Argia fumipennis violacea (Hagen) Violet Dancer 1 (0.7) 26 (5.8) Argia sp. A dancer 3 43 Enallagma divagans Selys* Turquoise Bluet - 1 (0.5) Enallagma durum (Hagen)* Big Bluet - 5 (1.6) Enallagma sp. A bluet 1 11 Ischnura posita posita (Hagen) Fragile Forktail - 2 (1.1) Ischnura sp. A forktail 14 13 Lestidae - - Lestes sp. A spreadwing 2 452 Northeastern Naturalist Vol. 18, No. 4 at which G. rogersi was collected in the Zekiah Swamp Run watershed. Cordulegaster erronea was not collected in the Breton Bay watershed. Other than average wetted width and depth, detailed habitat information was not recorded at these sites, as they were all sampled by volunteers. Further investigation of these sites would reveal if the habitat requirements of C. erronea in this watershed are similar to those reported in New Jersey (Barlow 1995) and Ohio (Glotzhober 2006): shaded, small, permanent cool- to cold-water seeps/springs with sandy substrate and relatively free of fish, other odonate species, and organic matter. During the 2009–2010 Breton Bay watershed sampling, the microhabitats in which RTE species were collected were noted when possible. While the sample size of some of these species is small, we feel the description of the microhabitat in which these species were found adds to what little is known about the nymphs of these species and their microhabitat preferences in these watersheds as well as others throughout Maryland. Cordulegaster obliqua individuals were collected in both watersheds from small (less than 3 m average wetted width), shallow streams with sand-dominated substrate. The majority of these streams were temporary, and we found them dry upon a revisit in the summer. All Progomphus obscurus nymphs, a burrowing gomphid species, were collected in stable sand substrate with little to no silt in very shallow waters near the shoreline in three small streams and one large (6 m average wetted width) stream. Pool/glide habitat dominated the reaches in which P. obscurus were found. Twenty-four individuals of H. selysii, a species at or near the northeasternmost extent of its global range in Maryland, were collected in small, permanent streams with average depths of 20–30 cm, while two were collected in streams with average depths of 80 cm. Helocordulia selysii collected in 2008–2009 were primarily taken from sand and silt substrates beneath undercut banks. Nearly all individuals of H. selysii were collected at sites located 3 km or less from Breton Bay. The majority of individuals of the six species reported from Breton Bay that typically inhabit lentic systems or slow-moving areas of streams and rivers were collected from stream sites with dammed pool habitat and reduced flow resulting from Castor canadensis Kuhl (Beaver) activity or natural blockages (i.e., fallen tree). The RTE species Nasiaeschna pentacantha and Enallagma durum were among those collected at these sites. While the RTE status of Somatochlora tenebrosa was removed with the 2010 state rarity rank update (MD DNR 2010), the microhabitat of this species was observed and recorded at two different streams in the Breton Bay watershed in 2009 and 2010 and is included here. One of the streams is located in the southeastern part of the watershed, while the other lies in the northeastern part. In both streams, S. tenebrosa were found in a cluster of 4–5 late-instar individuals in a small area beneath undercut banks in stable sand substrate with a thin layer of silt on top. These individuals accounted for all but two of the S. tenebrosa collected during a 3–4 hour concentrated Somatochlora search at return visits to both stream sites. The individuals collected during this concentrated search were reared in a lab and identified as adults to species level. Stream site characteristics and the microhabitat in which the clusters of S. tenebrosa were found were similar among the two sites. The streams had a wetted 2011 P.H. Graves and P.J. Ciccotto 453 width of approximately 1.5 m and were shallow (5–10 cm). The individuals were underneath undercut banks cut less than 20 cm into the bank at bends in the stream. Immediately upstream of the undercut banks, woody debris created small pool habitat with reduced flow velocity in the segment containing the undercut bank. The two S. tenebrosa individuals that were not part of a cluster were collected separately in run habitat, against a bank containing numerous burrows of Cambarus diogenes Girard (Devil Crayfish). No observation was made of S. tenebrosa utilizing the burrows as refugia, but given the large number of burrows in the stream banks and seepage areas, and the observation by Soluk et al. (1996) of Somatochlora hineana utilizing C. diogenes burrows, it is worthwhile to investigate whether Somatochlora species, or any other odonate taxa, are using crayfish burrows in Breton Bay watershed streams and elsewhere. A sampling design that targets the most productive odonate habitats and not the most productive overall benthic macroinvertebrate habitats is encouraged for future nymphal odonate surveys. Even though only 8% of the sites in the Breton Bay watershed from 2002–2009 were sampled using the most productive odonate habitat sampling method, 32% of odonates analyzed in this study were collected from this watershed using this method. This includes 71% of libellulids, 44% of gomphids, 50% of coenagrionids, 29% of corduliids, and 52% and 53% of the RTE-rich genera Cordulegaster and Somatochlora, respectively. By focusing on odonate-preferred habitats, relatively odonate-poor habitats like riffles would not be sampled as rigorously as they would when using MBSS (Stranko et al. 2007) or other benthic macroinvertebrate protocols. This focus on odonate-preferred habitats allows for more sampling of habitats such as sand, silt, and undercut banks, for example, that otherwise would not receive the amount of attention they deserve. Conclusions The results of these studies highlight the RTE nymphal odonate fauna in two high priority watersheds of the Potomac River drainage in Maryland. These studies provide much needed data on the distribution and microhabitats of several RTE species and reveal odonate richness hotspots in these two watersheds. These data can also indicate sites for further quantitative sampling, which can be used to establish a baseline for tracking odonate species and community changes over time as well as further identify the core range of an RTE species in these watersheds or a subwatershed therein. This information will help facilitate future studies to better determine microhabitat requirements and environmental stressors that may impact these species. Such studies may be particularly important and timely as Charles County, which contains the majority of the Zekiah Swamp Run watershed, is one of the fastest growing counties in Maryland (Maryland Department of Planning 2008). Documenting changes in the distribution and status of odonates and other rare fauna and flora in this area may provide important information for planning future development projects in Maryland and in the conservation of Maryland odonate habitat and diversity. Our results also contributed to a recently completed status reassessment of Maryland’s odonate fauna (MD DNR 2010). The resulting status changes 454 Northeastern Naturalist Vol. 18, No. 4 included the downlisting of Gomphus rogersi from state endangered to in need of conservation and the listing of H. selysii as state threatened. Breton Bay odonate data, and that from watersheds yet to be sampled, can be used in future status updates of Maryland odonate species as well as aid in the conservation, management, and protection of the streams they inhabit. Acknowledgments This study was funded in part by State Wildlife Grant funds provided to the State Wildlife agencies by US Congress, and administered through the Maryland Department of Natural Resources’ Natural Heritage Program. 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