The Hydradephaga (Coleoptera, Haliplidae, Gyrinidae, and Dytiscidae) fauna of Cape Breton Island, Nova Scotia, Canada: new records, distributions, and faunal composition

Abstract The Haliplidae, Gyrinidae, and Dytiscidae (Coleoptera) of Cape Breton Island, Nova Scotia, Canada were surveyed during the years 2006–2007. A total of 2027 individuals from 85 species was collected from 94 different localities, which brings to 87 the number of species recorded for this locality. Among these, Heterosternuta allegheniana (Matta & Wolfe), H. wickhami (Zaitzev), Hydroporus appalachius Sherman, H. gossei Larson & Roughley, H. nigellus Mannerheim, H. puberulus LeConte, Ilybius picipes (Kirby), and I. wasastjernae (C.R. Sahlberg) are reported for the first time in Nova Scotia. The Nearctic component of the fauna is made up of 71 species (81.6%), the Holarctic component of 16 species (18.4%). Most species are characteristic of both the Boreal and Atlantic Maritime Ecozones and have a transcontinental distribution but 19 species (21.8%), which are generally recognized as species with eastern affinities. In an examination of the Hydradephaga of insular portions of Atlantic Canada, it was shown that the island faunas of Cape Breton Island and Prince Edward Island are very similar (87 and 84 species, respectively) despite differences in composition suggesting that more Hydradephaga species have yet to be found on Cape Breton Island.


Introduction
Cape Breton Island is a large (10,311 km 2 ) rugged and irregularly shaped island, approximately 175 km long by 135 km at is widest, located at 46 degrees latitude, 60 degrees longitude in northern Nova Scotia, Canada at the eastern extremity of the Gulf of St. Lawrence. It lies within the Atlantic Maritime Ecozone along with Québec's Gaspé Peninsula, Magdalen Islands 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. Geologically, this region is a mix of sedimentary and igneous bedrock (Alarie 2016). Cape Breton land mass slopes upward from south to north, culminating in the massive highlands of its northern cape, the highest elevation in the Atlantic region. Water beetles make up a large part of aquatic invertebrates (Jäch and Balke 2008) and as such they play a vital role in terms of biodiversity and ecosystem functioning, and consequently in the stability of ecosystems (Wallace and Webster 1996). Investigating water beetle assemblages may be particularly illuminating considering the potential these groups are demonstrating as bioindicators of aquatic ecosystem viability (Foster et al. 1990;Fairchild et al. 2000;Lundkvist et al. 2001;Arnott et al. 2006). They also allow the diagnosis of alterations causes, the establishment of criteria for protection and restoration of interesting ecosystems and finally the integrated management of watersheds (Abellán et al. 2007). Thus, good knowledge of the species presence and distribution is necessary to protect biodiversity (Millán et al. 2014). Moreover, primary biodiversity data represent the fundamental elements of any study in systematics and evolutionary processes (May 1990;Funk and Richardson 2002;Hortal et al. 2015).
Investigations of the Hydradephaga (Dytiscidae, Haliplidae, Gyrinidae) of the Canadian Maritimes have been sporadic and regionally variable. Recent papers (Majka 2008;Majka and Kenner 2009;Alarie 2009Alarie , 2016Webster et al. 2016) resulted in a better understanding of the Hydradephaga fauna in some areas. Despite this rapid increase in knowledge of faunal composition, there are still many Hydradephaga species waiting for discovery in eastern Canada. This is amply evidenced by the fact that 30 species were recently added to the list of Prince Edward Island (Alarie 2016).
Little is known about the Hydradephaga fauna of Cape Breton Island. Prior to this study, 51 species were reported as valid records in the faunal list for Cape Breton Island (Alarie 2016), a small proportion of the 118 (43.2%) reported in Nova Scotia (Bousquet et al. 2013). This study was conducted as part of a comprehensive baseline field survey of Hydradephaga biodiversity of Canadian Maritimes Islands (Alarie 2009(Alarie , 2016. Its main objective is to improve knowledge of the Hydradephaga of Cape Breton Island. Of particular interest was the identification of new species additions to the known fauna of Nova Scotia.

Study areas
All of Nova Scotia mainland and Cape Breton Island sit within the Acadian Forest region as described by Rowe (1972), which has a mixed-forest species composition consisting predominately of conifers, especially on sites where drainage is impeded. The major conifers include red, white, and black spruce; balsam fir; eastern white and red pine; and eastern hemlock. Common hardwoods include red and sugar maple; white and yellow birch; trembling and largetooth aspen; and beech (Neily et al. 2005).
Although physically separated from the Nova Scotia peninsula by the Strait of Canso, Cape Breton is artificially connected to mainland Nova Scotia by the Canso Causeway. The island is located east-northeast of the mainland with its northern and western coasts fronting on the Gulf of Saint Lawrence; its western coast also forming the eastern limits of the Northumberland Strait. The eastern and southern coasts front the Atlantic Ocean; its eastern coast also forming the western limits of the Cabot Strait. Cape Breton Island is composed mainly of rocky shores, rolling farmland, glacial valleys, barren headlands, mountains, woods and plateaus. The boreal highlands of Cape Breton reach elevations of 300-500 m and represent true boreal forest habitat, which is rare in Nova Scotia (Neily et al. 2005). Geological evidence suggests that at least part of Cape Breton was originally joined with present-day Scotland and Norway (www. newworldencyclopedia.org/entry/Cape_Breton_Island).
Cape Breton Island's hydrological features include the Bras d'Or Lake system, a salt-water fjord at the heart of the island, and freshwater features including Lake Ainslie, the Margaree River system, and the Mira River. Innumerable smaller rivers and streams drain into the Bras d'Or Lake estuary and onto the Gulf of St. Lawrence and Atlantic coasts (www.newworldencyclopedia.org/entry/Cape_Breton_Island).
Geographically, Cape Breton Island is subdivided into four counties: Cape Breton, Inverness, Richmond, and Victoria. More than 70% of the total Cape Breton population live in the industrialized Cape Breton County. The boreal highlands of Cape Breton are located in the northern parts of Victoria and Cape Breton Counties. The climate of this region is influenced by the higher elevations, strong ocean winds and heavy blankets of dense fog that occur during spring and summer. The headwater streams of the highland regions flow over a primarily ancient metamorphic and granitic dominated geologic landscape, originating from cool springs or draining acidic, sphagnum bogs (Ogden et al. 2018). Inverness and Richmond Counties are largely rural and boast Nova Scotia's most pristine areas. Located within Inverness County, the Margaree River is one of the world's most famous fishing rivers. There are almost no lakes in this region, but there are many steep-fast flowing rivers and streams. Inverness County includes some of the most interesting old forests and undisturbed areas in Nova Scotia. Richmond County is the least well-known county in all Nova Scotia in terms of its beetle fauna. There are many lakes, marshes, and bogs in this area, which have been very little investigated.

Collecting methods
Collections were conducted over three periods, 05- 10 May 2006, 17-22 August 2006, and 14-19 May 2007. Sampling was unstructured and qualitative with the goal of obtaining a strict inventory of Hydradephaga of Cape Breton 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 94 samples were obtained, which are listed in Table 1, along with locality data and habitat information.

Nomenclature
Nomenclature is based on the classification in Oygur and Wolfe (1991)

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

Results
In total, 2027 specimens representing 85 species of Hydradephaga were collected in this study (Table 2). Among these, eleven species are reported for the first time for Nova Scotia. Details of species added to the Nova Scotia's fauna follow.
Habitat. All specimens were collected on pebble substrate or in leaf litter along the margin of cold creek and streams in accordance with Matta and Wolfe (1981).
Distribution in the Maritime Ecozone. Prior to this study, Heterosternuta allegheniana had only been reported from New Brunswick and southern Québec (Bousquet et al. 2013). Its presence in Nova Scotia therefore represents its easternmost distribution in Canada.
Habitat. Like the previous species all specimens were collected in gravel along the margins of streams. Matta and Wolfe (1981) state this species is most common at the margin of medium to small streams.
Distribution in the Maritime Ecozone. This is the first record of H. wickhami in the Maritimes. Prior to this study it had only been reported from Ontario and Québec. Its presence on Cape Breton Island represents a significant extension of this species to eastern Canada (Bousquet et al. 2013).

Hydroporus appalachius Sherman
Notes. Several specimens of this distinctive species were collected at two different sites in Inverness County (samples I79, I86).
Habitat. Hydroporus appalachius is usually found in habitats where there are some water movements either along the margins of small lakes or in small streams and springs (Larson et al. 2000), which describe exactly the habitats where these beetles were found in Cape Breton Island.
Distribution in the Maritime Ecozone. This species has a wide range in North America east of the Rocky Mountains. It occurs from Labrador and New Hampshire west to the northern Great Plains and north into the boreal zone and southern limits of the low artic (Larson et al. 2000). Its presence in Cape Breton Island represents the first mention of the species in the Canadian Maritimes (Bousquet et al. 2013).

Hydroporus gossei Larson & Roughley
Notes. This species is reported for the first time in Nova Scotia from eleven specimens collected in Cape Breton County, Inverness County and Victoria County (samples V12, V26, V27, C53, C59, I88, I90).
Habitat. In Newfoundland and Prince Edward Island, this species has been collected from among flooded grasses and emergent Carex along the margins of beaver ponds and roadside ponds, which is similar to the habitats where these beetles were collected in Cape Breton Island which include also eutrophic creeks.
Distribution in the Maritime Ecozone. This large, distinctive Hydroporus species has generally been confused with Hydroporus rectus Fall. In the Maritime ecozone, H. gossei is also reported from the neighboring province New Brunswick and Prince Edward Island (Larson et al. 2000;Bousquet et al. 2013;Alarie 2016).

Hydroporus nigellus Mannerheim
Notes. This species is reported from only two specimens collected in Cape Breton County and Victoria County (samples C21, V28).
Habitat. These beetles are common in small pools with dense emergent vegetation. The two specimens collected in Cape Breton Island were from a sphagnum bog and a eutrophic pool besides a river.
Distribution in the Maritime Ecozone. Prior to this study, this species had only been reported from the neighboring province New Brunswick (Larson et al. 2000;Bousquet et al. 2013). The North American range of this Holarctic species includes most of the boreal zone and extends north to the southern arctic (Larson et al. 2000).

Hydroporus puberulus LeConte
Notes. Hydroporus puberulus is reported from nine specimens form two localities in Cape Breton County and Inverness County (samples C53, I71).
Habitat. These beetles were generally collected from small pools where the water is cool, such as small pools in bogs or habitats where the water is densely shaded by Carex (Larson et al. 2000), which is similar to the habitats where these beetles were collected in Cape Breton Island.
Distribution in the Maritime Ecozone. In North America this Holarctic species occurs in the boreal zone from western Newfoundland to Alaska (Larson et al. 2000). Prior to this study, this species had only been reported from the neighboring province New Brunswick in the Maritime Ecozone (Larson et al. 2000;Bousquet et al. 2013).

Ilybius picipes (Kirby)
Notes. Ilybius picipes is closely similar to I. angustior (Gyllehal) from which it can be differentiated by the relative expansion of the protarsal claw (Larson et al. 2000). In Cape Breton Island this species is reported from six specimens from two localities in Victoria County and Inverness County (samples V26, I76).
Habitat. These beetles are generally collected from peatland pools (Larson et al. 2000), which is similar to the habitats where these beetles were collected in Cape Breton Island.
Distribution in the Maritime Ecozone. This species has a Holarctic distribution. In North America it is transcontinental in the boreal region (Larson et al. 2000). Its presence in Cape Breton Island represents the first mention in the Canadian Maritimes (Bousquet et al. 2013).

Ilybius wasastjernae (C.R. Sahlberg)
Notes. Ilybius wasastjernae is reported in Cape Breton Island from only one specimen collected in Victoria County (sample V27).
Habitat. These beetles are generally collected from sphagnum pools, usually in, or adjacent to forest (Larson et al. 2000). In Cape Breton Island it was collected in an ephemeral woodland pool covered with Scirpus.
Distribution in the Maritime Ecozone. This species has a Holarctic distribution more or less throughout the boreal zone. In North America it is transcontinental in the boreal region (Larson et al. 2000). Prior to this study, this species had only been reported from the neighboring province New Brunswick in the Maritime Ecozone (Larson et al. 2000;Bousquet et al. 2013).

Discussion
A total of 85 Hydradephaga species was recovered from 94 samples during a survey conducted on Cape Breton Island, Canada, between 2006 According to this study and literature (Majka and Kenner 2009) (Larson et al. 2000;Bousquet et al. 2013) (Table 3).
The 87 Hydradephaga species known from Cape Breton Island represent approximately 74% of the fauna known for all Nova Scotia (Bousquet et al. 2013). As is typical of Hydradephaga, the Dytiscidae accounts for the largest share (78.2%) of the fauna, while Gyrinidae (13.8%) and Haliplidae (8.1%) are represented in lesser proportions. Forty-five species were observed at more than 5% of the sites (  (Fall), and Oreodytes s. scitulus (LeConte)) are worth emphasizing in that they illustrate the high abundance of lotic habitats in this portion of Cape Breton Island. In general, coexisting species may be more closely related than expected by chance if environmental features of a given habitat select for certain traits that are shared Notes: Regional Distribution information derived from Downie and Arnett (1996), Larson et al. (2000), Majka (2008), Alarie (2009Alarie ( , 2016, Majka et al. (2011), Elder andAbraham (2012), Bousquet et al. (2013), and Webster ( by closely related species (Vamosi and Vamosi 2007), which may explain particularly the highest diversity of Neoporus Guignot and Heterosternuta Strand in that region. The 87 species of Hydradephaga reported in this study represent an important richness, proportionally comparable to the number of species found in Prince Edward Island with similar environmental conditions (Alarie 2016 (Fall)) is worth mentioning as it suggests that the number of Hydradephaga species on Cape Breton island may be even greater than suggested by this study.

Conclusions
Our study adds considerably to the previous knowledge about Hydradephaga in the Canadian Maritimes, with eight new records for the province of Nova Scotia. The composition of the Cape Breton fauna reflects that of the Maritime Provinces as a whole. Whereas all the species found on Cape Breton Island have also been recorded in New Brunswick (Webster 2016) (except Gyrinus cavatus Atton, Heterosternuta wickhami, Hydroporus appalachius, and Ilybius picipes) the presence on Prince Edward Island (Alarie 2016) of 12 species not reported on Cape Breton Island suggests that additional species could potentially still be found.