Further contributions to the Hydradephaga (Coleoptera, Haliplidae, Gyrinidae and Dytiscidae) fauna of Prince Edward Island, Canada: new records, distributions and faunal composition

Abstract The Haliplidae, Gyrinidae and Dytiscidae (Coleoptera) of Prince Edward Island, Canada were surveyed during the years 2004–2005. A total of 2450 individuals from 79 species were collected from 98 different localities, among which 30 species are newly recorded from that region. Among these, Acilius sylvanus Hilsenhoff, Rhantus consimilis Motschulsky and Neoporus sulcipennis (Fall) stand out as representing the easternmost reports of these species in Canada. Once removed, Gyrinus aquiris LeConte (Gyrinidae) is reinstated in the faunal list of Prince Edward Island. According to this study and literature 84 species of Hydradephaga are currently known from Prince Edward Island. The Nearctic component of the fauna is made up of 68 species (80.9%) and the Holarctic component of 16 species (19.1%). Most species are characteristic of the Boreal and Atlantic Maritime Ecozones and have a transcontinental distribution. In an examination of the Hydradephaga of insular portions of Atlantic Canada, we found that despite significantly different land areas and different distances to the neighbouring continental mainland the island faunas of Prince Edward Island and insular Newfoundland are very similar in the number of species (84 and 94 species respectively) despite differences in composition. With a land area significantly larger than that of Prince Edward Island, however, the fauna of Cape Breton Island was 39% smaller consisting of 53 species. This difference could be due to the comparative lack of collecting efforts on Cape Breton Island.


Introduction
The Maritime Provinces are a region of eastern Canada on the Atlantic coast consisting of New Brunswick, Nova Scotia, and Prince Edward Island. These provinces lie within the Atlantic Maritime Ecozone along with Québec's Gaspé Peninsula, Magdalen Archipelago and portions of the south shore of the St. Lawrence River. The climate of this ecozone is strongly influenced by the Atlantic Ocean, which produces cooler summers (average 14 °C) and warmer winters (average -5 °C), with coastal areas having slightly warmer winters and cooler summers than inland. The Atlantic Ocean also provides moisture to the region, producing mean precipitation of 900 mm a year inland and 1500 mm a year on the coast. Geologically, this region is a mix of sedimentary and igneous bedrock (Alarie 2009).
Prince Edward Island is located at 46 degrees latitude, 63 degrees longitude in the Gulf of St. Lawrence, off the Atlantic Coast of the Canadian mainland. This crescent shaped Island is only 224 km long and between 6 km and 64 km wide and is separated from the mainland by the Northumberland Strait. Its total land mass is 5,656 sq. km. The island has many wetlands and rivers, most of which are quite small. Often wide and relatively shallow many of these rivers experience a tidal influence over much of their length. Extensive salt and freshwater wetlands are, therefore, associated with several of the larger rivers.
Aquatic Adephaga have many morphological adaptations to their aquatic environment, making them excellent subjects for ecological and biogeographic studies (Moreno et al. 1997). Additionally, these beetles are important indicators of spatial and temporal changes in the environment. This is why some authors have used them as bio-indicators of habitat quality in terms of nutrient enrichment or the presence of potential pollutants (e.g., Arnott et al. 2006;Sánchez-Fernández et al. 2006). These ecosystems, however, are highly vulnerable to threats related to intensive human influences (Della Bella et al. 2005), thereof the importance of conducting faunistic surveys to help at documenting the diversity of these beetles.
Investigations of the Dytiscidae, Haliplidae, and Gyrinidae of the Maritime Provinces have been sporadic and regionally variable. Recent papers (Majka 2008;Majka and Kenner 2009;Alarie 2009;Webster 2008;Webster and DeMerchant 2012;Webster et al. 2016) resulted in a better understanding of the Hydradephaga fauna in some areas. Despite many additions made recently by Majka (2008) the faunal list of Hydradephaga of Prince Edward Island is deemed incomplete (Majka 2008). This study aims to fill this gap by presenting for the first time the results of an extensive field oriented research on the Hydradephaga biodiversity of Prince Edward Island. It is conceivable that this study, complementing the previous works, should help to get a clearer picture of the diversity of Hydradephaga on this region.

Study areas
Geologically, Prince Edward Island is part of the 'Maritimes Basin', a geographically low area that was filled hundreds of millions of years ago by sandy sediments eroded from the newly formed Appalachian Mountains to the south and west. Prince Edward Island's landscape has been largely influenced by the shape of the bedrock and by the ease with which it has been eroded. Low cliffs predominate along much of the shoreline especially on the northern headlands. The southern coastline, however, is more protected and erosion is, therefore, less pronounced. The several glaciers, which once covered Prince Edward Island, resulted in a nearly level to gently rolling landscape over much of the province. Approximately three-quarters of the land area is less than 50 meters above sea level, but a few hills throughout the central section of the Island have elevations of 150 meters (MacAlpine and Smith 2010).
Geographically, Prince Edward Island is subdivided into three counties: Kings, Prince, and Queens. Kings County is the province's smallest, most rural and leastpopulated county. That region is also least dependent upon the agriculture industry compared with the other two counties, while being more heavily dependent on the fishery and forest industry. Prince County is located in western part of the island; its defining geographic feature is Malpeque Bay, a sub-basin of the Gulf of St. Lawrence, which creates the narrowest portion of Prince Edwards's landmass. Much of Prince Edward Island's industrial base is concentrated in the eastern part of that county. Lastly, Queens County, located in central Prince Edward Island. The county is geographically divided by the Hillsborough River's estuary, a tidal inlet, which almost splits the county and Prince Edward Island. It is the richest and most populous county in the province. Queens County's geography varies from picturesque shorelines of sandstone cliffs, sandy beaches and sheltered bays on the Gulf of St. Lawrence and Northumberland Straight, to extensive farming operations throughout interior regions. Topography ranges from relatively flat to rolling hills in the central hill lands known as the Bonshaw Hills.

Collecting methods
Collections were conducted over three periods, May 15-19, 2004, September 19-24, 2004and September 17-21, 2005, which essentially reflects a similar collecting effort in each county. Sampling was unstructured and qualitative with the goal of obtaining a strict inventory of Hydradephaga of Prince Edward Island. Beetles were collected using D-net sweeps in a variety of microhabitats including macrophyte beds, rocky shores, organic-rich sediments, and open water. Overall 98 samples were obtained, which are listed in Table 1, along with locality data and habitat information.

Depositories
Voucher specimens are deposited in the author's research collection (Department of Biology, Laurentian University, Sudbury, Ontario).

Results
A total of 2450 specimens representing 79 species of Hydradephaga (9 Gyrinidae; 6 Haliplidae; 64 Dytiscidae) were collected in this study (Table 2). Among these, 30 species are reported for the first time and an additional one is reinstated in the faunal list of Prince Edward Island.

Gyrinus aquiris LeConte
Note. Gyrinus aquiris was the most abundant (45.4%) and one of the most frequently collected gyrinid (6%) in this survey. The species was collected in every county of Prince Edward Island (Table 2).
Habitat. In Prince Edward Island, G. aquiris was collected both from lotic (50%) and lentic (50%) environments (Tables 1-2), which is similar to the observations made by Alarie (2009) in the Magdalen Islands. Oygur and Wolfe (1991), however, reported 80% of specimens from lentic habitats whereas Morrissette (1979) reported the species from ponds and lakes invaded by aquatic plants.
Distribution in the Maritime Ecozone. Gyrinus aquiris was reported from the Magdalen Islands (Alarie 2009), and the Maritime Provinces of New Brunswick (Oygur and Wolfe 1991;Roughley 1991a;Webster 2016) and Nova Scotia (Campbell et al. 1987). Although Roughley (1991a) reported it from Prince Edward Island, Majka (2008) removed it from the province's faunal list since there were no voucher specimens or published records.

Gyrinus latilimbus Fall
Note. This very small gyrinid was collected in relatively low number (five specimens) at four different localities of Kings and Prince Counties (Table 2).

Gyrinus pugionis Fall
Note. Eight specimens were collected from four different localities of Kings and Prince Counties (Table 2).

Haliplus connexus Matheson
Note. Whereas found in relatively low numbers (5 specimens) Haliplus connexus is reported for in each of the three Prince Edward Island counties (Table 2).
Habitat. In Atlantic Canada, there are records from small streams, eutrophic ponds, river margins, slow streams and temporary habitats ). In Prince Edward Island, all specimens of Haliplus connexus were collected along the edge of weedy lentic habitats (Tables 1-2).
Distribution in the Maritime Ecozone. The species is known also from the neighboring Maritime Provinces of New Brunswick and Nova Scotia (Matheson 1912;Wallis 1933;Roughley 1991b).

Acilius sylvanus Hilsenhoff
Note. This species is known from Prince Edward Island by a single specimen record from Prince County (Table 2).
Habitat. These beetles occur in the emergent zone of sun-warmed permanent or semi-permanent ponds in forested area (Larson et al. 2000). In Prince Edward Island, A. sylvanus was collected in a permanent pond on clay bottom located at the edge of a spruce and aspen forest (Tables 1).
Distribution in the Maritime Ecozone. This species is known only from the neighboring Province of New Brunswick (Webster 2008). The presence of A. sylvanus in Prince Edward Island represents the easternmost record of this species in Canada.
Habitat. Agabus bifarius occurs amongst emergent grasses and sedges at the margin of a variety of lentic habitats, but it is especially characteristic of the margins of shallow, exposed, vernal ponds (Larson et al. 2000), which is essentially the type of habitats where it was found in Prince Edward Island (Table 1).

Distribution in the Maritime Ecozone.
This species is also known from New Brunswick and Nova Scotia (Larson et al. 2000).

Agabus erytropterus (Say)
Note. Agabus erytropterus is reported from eight specimens collected at five localities of Kings County (Table 2).
Habitat. This species is usually associated with slowly flowing water but occurs in depositional areas with thick organic silt (Larson et al. 2000), which is exactly the type of habitats where it was found in Prince Edward Island (Table 1).
Distribution in the Maritime Ecozone. Agabus erytropterus is also known from the neighboring Provinces of New Brunswick and Nova Scotia (Larson et al. 2000).

Agabus punctulatus Aubé
Note. Agabus punctulatus is reported from nine specimens collected at one locality in Prince County (Table 2).
Habitat. The most typical habitat of this species is flooded grass along the margin of vernal ponds in open grassland areas (Larson et al. 2000), which is similar to the habitat where A. punctulatus was found in Prince Edward Island (Table 1).
Distribution in the Maritime Ecozone. This species is known also from the neighboring Maritime Provinces of New Brunswick and Nova Scotia (Larson et al. 2000).

Agabus semipunctatus (Kirby)
Note. Agabus semipunctatus is reported from nine specimens from six localities of Kings and Prince Counties (Table 2).
Habitat. Agabus semipunctatus most often occurs in Sphagnum bogs but can also be collected regularly from Carex-choked waters (Larson et al. 2000). In Prince Edward Island, this species was essentially found in similar type of habitats (Table 1).
Distribution in the Maritime Ecozone. This species is also known from the neighboring Maritime Provinces of New Brunswick and Nova Scotia (Larson et al. 2000) and the Magdalen Islands (Alarie 2009).

Colymbetes paykulli Erichson
Note. Colymbetes paykulli is reported from two specimens each collected in Queens and Kings Counties (Table 2).
Habitat. These beetles are almost entirely restricted to the cold water of Sphagnum bogs. They occur most frequently in small pools with emergent Carex, or along the edges of bog-ring lakes in embayments and beaver runs, often or near the willow zone (Larson et al. 2000). The two specimens collected in Prince Edward Island were from a Sphagnum bog and a shallow pool covered with vegetation respectively (Table 1).
Distribution in the Maritime Ecozone. This species is known also from the neighboring Maritime Provinces of New Brunswick and Nova Scotia (Larson et al. 2000).
Habitat. These beetles generally occur in boggy (often brown water) ponds and lakes. They are usually found at the edge of the encircling bog in embayments or beaver runs (Larson et al. 2000). The two specimens collected in Prince Edward Island were from Sphagnum bog ponds (Table 1).
Distribution in the Maritime Ecozone. This species is known also from the neighboring Maritime Provinces of New Brunswick and Nova Scotia (Larson et al. 2000).

Hydrocolus paugus (Fall)
Note. This species is reported from several specimens collected at various localities in each county of the province (Table 2).
Habitat. These beetles occur among moss or dense emergent vegetation and debris along the margins of small pools, ponds and springs. They occur in peatland as well as in sites where the water surface is shaded and the water is cool (Larson et al. 2000). Specimens were collected in Prince Edward Island from a variety of lentic and lotic habitats (Table 1).
Distribution in the Maritime Ecozone. This species is known also from the neighboring Maritime Provinces of New Brunswick and Nova Scotia (Larson et al. 2000), and the Magdalen Islands (Alarie 2009).

Hydroporus fuscipennis Schaum
Note. This species is reported from several specimens collected at several localities of Prince and Kings Counties (Table 2).
Habitat. These beetles occur among dense emergent vegetation along the margins of small, often temporary pools, usually situated in grasslands, cleared areas or at the edges of forest, but not typically in forest pools. Hydroporus fuscipennis is usually found in more or less eutrophic pools and is not common in peatlands (Larson et al. 2000). Specimens were collected in Prince Edward Island essentially from cattail ponds and roadside ditches (Table 1).
Distribution in the Maritime Ecozone. This species is known also from the neighboring Maritime Provinces of New Brunswick (Larson et al. 2000).

Hydroporus gossei Larson & Roughley
Note. This species is reported from several specimens collected in Prince and Kings Counties (Table 2).
Habitat. In Newfoundland, this species has been collected from flooded grasses and emergent Carex along the margins of beaver ponds and roadside ponds. Specimens, which occurred on peaty substrates near boggy areas, were collected from areas exposed to the sun as well as from shorelines shaded by overhanging alder. In Prince Edward Island, H. goosei was collected in similar habitats, in addition to Sphagnum bogs and eutrophic creeks (Table 1).
Distribution in the Maritime Ecozone. This large, distinctive Hydroporus Clairville species has generally been confused with H. rectus Fall. In the Maritime ecozone, H. gossei is also reported from the neighboring Province of New Brunswick (Larson et al. 2000).

Hydroporus obscurus Sturm
Note. This species is reported from 16 specimens collected at two localities of Prince and Kings Counties (Table 2).
Habitat. This species occurs in very small peatland pools, as well as in the moss mat along the margins of larger peatland pools and ponds (Larson et al. 2000). Specimens collected in Prince Edward Island were from a Sphagnum bog and the grassy shoreline of a pond (Table 1).
Distribution in the Maritime Ecozone. This species is known also from the neighboring Maritime Provinces of New Brunswick and Nova Scotia (Larson et al. 2000).
Habitat. Hydroporus striola occurs in almost all types of small, standing water where emergent vegetation is dense. Specimens occur in peatland pools, being most common in fen habitat and rather infrequent in ombrotrophic bog pools (Larson et al. 2000). Specimens collected in Prince Edward Island were from an array of lentic habitats as described above (Table 1).
Distribution in the Maritime Ecozone. Hydroporus striola is the most ubiquitous species of Hydroporus in the boreal zone of the North Temperate Region (Larson et al. 2000). In the Maritime ecozone, this species is known also from the neighboring Provinces of New Brunswick and Nova Scotia (Larson et al. 2000), and the Magdalen Islands (Alarie 2009).

Hydroporus tenebrosus LeConte
Note. Several specimens of Hydroporus tenebrosus were collected in each of the three counties of Prince Edward Island (Table 2).
Habitat. This species occurs mainly in forested regions but is also common in the prairie parkland. Beetles occur in the emergent zone of small, usually temporary pools and ponds. They are usually found in eutrophic, sun-warmed sites (Larson et al. 2000). In Prince Edward Island, H. tenebrosus was almost essentially collected only in ponds, ephemeral pools, and roadside ditches (Table 1).
Distribution in the Maritime Ecozone. The species is known also from the neighboring Provinces of New Brunswick and Nova Scotia (Larson et al. 2000), and the Magdalen Islands (Alarie 2009).
Habitat. This species occurs in a variety of lentic habitats. Specimens are usually found among dense emergent vegetation at the margin of small, often more or less shaded pools. Hydroporus tristis is also common in small peatland pools (Larson et al. 2000). Whereas collected in few eutrophic creeks in Prince Edward Island, H. tristis was most generally found in ponds and shallow pools characterized by heavy accumulation of organic debris as well as in Sphagnum bogs (Table 1).
Distribution in the Maritime Ecozone. The species is known also from the neighboring Province of New Brunswick (Larson et al. 2000), and the Magdalen Islands (Alarie 2009).

Hygrotus compar Fall
Note. Hygrotus compar is reported from six specimens collected Prince County (Table 2).
Habitat. In the Prairies, H. compar has been recorded from the margin of temporary ponds, usually in fresh water but specimens have also been found in saline ponds (Larson et al. 2000). In Prince Edward Island, specimens were found in a roadside ditch and a clay bed pond at the edge of a spruce and aspen forest (Table 1).
Distribution in the Maritime Ecozone. The species is known also from the neighboring Province of New Brunswick (Larson et al. 2000).
Habitat. This species has been collected from a variety of small ponds. It appears to be most common among emergent grasses and sedges along the margin of permanent, or at least long lasting ponds. Specimens have been found most frequently in ponds in open country cleared of forest but they have also been collected in woodland ponds, especially beaver ponds (Larson et al. 2000). In Prince Edward Island, specimens were most frequently found in ponds and roadside ditches (Table 1).
Distribution in the Maritime Ecozone. The species is known also from the neighboring Provinces of New Brunswick and Nova Scotia (Larson et al. 2000).

Ilybius discedens Sharp
Note. Although found in relatively low numbers (seven specimens), this species is reported from each of the three Prince Edward Island counties (Table 2).
Habitat. Ilybius discedens is one of the most characteristic water beetle species of boreal peatland generally occurring in small, moss-ringed pools, often where the water is cold to the touch (Larson et al. 2000). In Prince Edward Island, the majority of specimens were collected from Sphagnum bogs, although a few specimens were associated with eutrophic lotic habitats (Table 1).
Distribution in the Maritime Ecozone. This species is also known from the neighboring Provinces of New Brunswick and Nova Scotia (Larson et al. 2000), and the Magdalen Islands (Alarie 2009).

Ilybius erichsoni (Gemminger & Harold)
Note. This species is reported from three localities of Prince County (Table 2).
Habitat. This is a species of forested regions where it occurs amongst dense vegetation, usually Carex, at the margins of both temporary and permanent ponds (Larson et al. 2000). Except for one specimen, which was collected in a shallow creek, all specimens of Ilybius erichsoni were collected in the type of habitats mentioned by Larson et al. (2000) (Table 1).
Habitat. This species occurs among emergent vegetation such as sedges, along the margins of slow, marshy streams, beaver ponds, and small lakes. Beetles are generally found where there is some water movement and are usually on mineral substrates (Larson et al. 2000). With few exceptions, most specimens collected in Prince Edward Island were from creeks and small rivers (Table 1).
Distribution in the Maritime Ecozone. Neoporus clypealis is known also from the neighboring Provinces of New Brunswick and Nova Scotia (Larson et al. 2000).

Neoporus sulcipennis (Fall)
Note. Several specimens of Neoporus sulcipennis were collected at two localities of Prince County (Table 2).
Habitat. This species occurs in small to medium sized warm, clear streams, often in depositional areas along the stream margins (Larson et al. 2000). In Prince Edward Island, all specimens were collected along the margins of rivers (Table 1).
Distribution in the Maritime Ecozone. Neoporus sulcipennis is known also from the neighboring Province of New Brunswick (Larson et al. 2000). The presence of this species in Prince Edward Island represents the easternmost record in Canada.

Rhantus consimilis Motschulsky
Note. Rhantus consimillis is reported from five specimens collected at the same locality of Prince County (Table 2).
Habitat. This species occurs in warm, weedy ponds, generally in open grassland areas. It has been collected from both permanent and temporary habitats (Larson et al. 2000). The specimens collected in Prince Edward Island were from a permanent pond located at the edge of a spruce and willow forest (Table 1).
Distribution in the Maritime Ecozone. Prior to this study, R. consimilis had only been reported in New Brunswick (Webster 2008). The presence of this species in Prince Edward Island is its easternmost report in Canada.

Rhantus sinuatus (LeConte)
Note. Five specimens of R. sinuatus were collected at two localities of Kings County (Table 2).
Habitat. This species occurs in lentic habitats densely overgrown with emergent vegetation. The species is common in bogs, but it also occurs in habitats with dense sedges, rushes or Typha (Larson et al. 2000). In Prince Edward Island, specimens were collected from a permanent pond with Nymphaea and a Sphagnum bog (Table 1).
Distribution in the Maritime Ecozone. Rhantus sinuatus is known also from the neighboring Provinces of New Brunswick and Nova Scotia (Larson et al. 2000).
Habitat. These beetles occur in cold, densely shaded water in forested areas, frequently found in bogs and fens (Larson et al. 2000). In Prince Edward Island, the specimen collected was found in a Carex pool with black sediments in a spruce forest (Table 1).
Distribution in the Maritime Ecozone. Rhantus suturellus is known also from the neighboring Provinces of New Brunswick (Webster 2008) and Nova Scotia (Larson et al. 2000) and the Magdalen Islands (Alarie 2009).
Habitat. The species is very common in cold stenothermal springs where it can be taken either in the limnocrene pools or among the mosses along the spring margin (Larson et al. 2000). In Prince Edward Island, the only specimen collected was found in a narrow and shallow creek flowing on a sandy bed (Table 1).
Distribution in the Maritime Ecozone. This species is also known from the neighboring Province of New Brunswick (Webster 2008) and the Magdalen Islands (Alarie 2009).

Discussion
A total of 79 Hydradephaga species was recovered from 98 samples during a survey conducted on Prince Edward Island, Canada, between 2004Canada, between -2005. Included among these were 30 new provincial records consisting of one haliplid, 2 gyrinids and 27 dytiscids (Table 2). Acilius sylvanus, Rhantus consimilis and Neoporus sulcipennis stand out as representing the easternmost reports of these species in Canada. In addition to these new records, one species, Gyrinus aquiris (Gyrinidae), which had been removed by Majka (2008), is reinstated in the faunal list of Prince Edward Island. According to this study and literature, 84 species of Hydradephaga are currently known from Prince Edward Island (Table 3) Table 3. Checklist of species of Hydradephaga recorded from Prince Edward Island, Canada, and their provincial and territorial distribution within northeastern North America (NA). *, Holarctic species; †, species not collected in this survey but recorded in Majka (2008); K, Kings County; P, Prince County; Q, Queens County. providing detailed distribution of the Hydradephaga species in this province as well as detailed habitat information. Whereas additional species could potentially be found, this paper is deemed to represent an accurate account of the faunistic diversity of Hydradephaga on Prince Edward Island.