STATUS OF THE SPECIES RANGEWIDE
Northeastern beach tiger beetle (Cicindela dorsalis dorsalis)(NBTB)
Species Description and Life History –NBTB has been listed as a threatened species under the ESA since August 7, 1990 (Service 1990). It is a beach-dwelling insect measuring approximately 0.5 inch in length, from the family Cicindelidae. It has white to light tan wing covers, often with several fine grayish-green lines, and a bronze-green head and thorax (Service 1994).
Adult NBTBs are active, diurnal surface predators. They forage along the water's edge on small amphipods, flies, and other beach arthropods, or scavenge on dead amphipods, crabs, and fish (Knisley et al. 1987, Service 1994). Most foraging occurs in the damp sand of the intertidal zone and scavenging has been observed to occur more often than predation (Knisley et al. 1987). Adult NBTBs are present on beaches from early June through early September, and spend most of the day along the water’s edge (Knisley et al. 1987). Adults are active on warm, sunny days when they can be seen feeding, mating, or basking (Service 1994). They are less active on rainy, cool, or cloudy days because they cannot maintain their body temperature (C.B. Knisley, pers. comm. 1994). They rely on a variety of behaviors, such as foraging and basking, to maintain their high body temperatures (Knisley et al. 1987).
Adult NBTBs mate and lay eggs on the beach during the summer (starting in June and ending by mid July). Eggs are deposited near the sand surface or in shallow pits excavated by adults, usually within 1 inch of the beach surface (Knisley 1997b). The eggs hatch in 10-14 days, depending on soil moisture. Adequate moisture may allow a shorter hatch period (C.B. Knisley, pers. comm. 2008). Larvae pass through three instar stages, pupate, and emerge as adults two years following hatching (Knisley et al. 1987, Service 1994). However, some larvae that hatch early and find sufficient food may develop more rapidly and emerge as adults after only one year (Service 1994). Development through three larval stages and pupation takes place within a larval burrow (Knisley et al. 1987). First instars generally occur from late August through September, second instars from September to late fall, and third instars from late fall to early spring and through the second year (Knisley et al. 1987).
Knisley et al. (1987) found that the distribution of first and second instars was similar and highest densities of third instars were on the beach in the mid- to upper-tidal zone. Therefore, most burrows were underwater during high tide. Larvae can survive flooding for 3-6 days (Service 1994). Larval burrow depths ranged from 3.5-9.5 inches and increased with distance from the water’s edge, suggesting that burrow depth may be related to subsurface moisture (Knisley et al. 1987). Knisley (1997b) found that larvae rarely occur on sites with less than 5 degrees slope. Larvae typically occur in an area of beach 26-39 feet (ft) wide, but have been documented at narrower widths, within and above the intertidal zone. Areas wider than 39 ft where washover has occurred or where the upper beach is flat and periodically inundated by high tides also are occasionally occupied by larvae (Service 1994).
Larval activity is highly variable and greatly influenced by temperature, substrate moisture, tide levels, and season (Service 1994). They overwinter in their burrows until mid-March, with low levels of activity when the sand is damp and cool (C.B. Knisley, pers. comm. 1994). The highest, most predictable periods of larval activity are from late August through early November. Active primarily at night, larvae plug their burrows during most of the daylight hours. They have been found crawling on the beach, apparently moving to dig a new burrow in a better location (Service 1994). This behavior is likely a response to variations in tide levels, soil moisture, or sand accretion and erosion patterns. Larvae lack a hard cuticle and are susceptible to desiccation, which may explain why they tend to become inactive during hot, dry conditions (Service 1994). Generally, larval burrows are plugged and not visible when the sand is dry and warm.
Larvae feed by ambushing passing prey. Little is known about the precise types of microarthropods eaten by NBTB larvae, but prey that have been identified include beach fleas, lice, flies, ants, and other small insects (Pearson et. al. 2006, Knisley 2008). While little information on the necessary prey abundance is known, lack of prey base may explain why NBTBs are not found in certain areas.
Knisley et al. (1987) found that first
emergence of adults ranged from June 5-13 in
Survey data from 1998-2002 (Knisley and Hill 1998, 1999; Knisley 2001; Knisley 2002) indicate that beaches with a length of at least 325 ft, a width of at least 6.5 ft, and an adult population of at least 30, serve as breeding sites and larvae should be considered present. Optimal NBTB habitat is a beach greater than 16-26 ft wide (C.B. Knisley, pers. comm. 1994). Preference for beaches with a width of 8-20 ft was found to be statistically significant, and NBTBs are rarely found on beaches less than 6.5 ft in width (Drummond 2002). Adult and larval NBTBs are typically found on highly dynamic beaches with back beach vegetation, and they prefer long, wide beaches that have low human and vehicular activity, fine sand particle size, and a high degree of exposure (Knisley et al. 1987). Although narrow beach width is frequently the reason for lack of larvae, there are instances where larvae have variable densities or are absent on wide beaches.
Preliminary work indicates a correlation between the extent of shallow water fronting the beach and the number of NBTBs present (the more sand bars, the more NBTBs) (Drummond 2002). A beetle with sedentary larvae is susceptible to wave impacts, and work by Rosen (1980) has shown that the greater the shallow zone fronting a beach, the lower the wave energy. There appears to be no beach aspect preference for NBTB (Drummond 2002).
Limited studies have been conducted to define the sand characteristics at sites where NBTBs currently occur, and further studies are needed to accurately identify the sand characteristics that NBTBs need to support all life stages. Knisley (1997b) found that larval densities were highly variable relative to sand particle size, and that larvae are rare at sites with greater than 60% coarse sand (defined as the percentage of sand particles too large to sieve through the 100-size mesh sieve) (Knisley 1997b). Drummond (2002) found that adult NBTBs occupied beaches with 40-80% coarse sand. If the sand size is too coarse, too fine, or contains a high organic content, it appears unsuitable for the larvae to burrow and maintain a larval tube. Preliminary data indicate that NBTB is found on beaches with a narrow range of bulk density ranging from 1.30-1.59 ounces/inch3 (Drummond 2002). Bulk density may impact NBTB distribution in two ways: (1) stability of larval burrows, and (2) prey base availability (Drummond 2002). Bulk density affects microarthropod abundance and type (Blair et al. 1994). During a study of two beach nourishment projects, Fenster et al. (2006) found that NBTB prefers beaches with sands having a mean grain size of 0.0196 to 0.236 inches, and with relatively compacted sediment. Mean grain size and sediment compaction are biologically important factors during oviposition and burrow building. Females oviposit in particular sediment types based on the shape of their ovipositor (Fenster et al. 2006). Larvae require sediments that they can build burrows in that do not collapse (Fenster et al. 2006).
– Populations of NBTBs are highly variable from year to year because they are
subject to local extirpations from storm events impacting the larval stage and
are affected by dispersal and recolonization movements (Service 1994). Two- to three-fold year-to-year variation in
numbers at a given site is common (Knisley and Hill 1989, 1990). The Service funded a PVA for the
in the Chesapeake Bay and
– Historically, NBTB was a common inhabitant of coastal beaches from
There are two naturally
occurring NBTB metapopulations in
A third population was
In 1990 when NBTB was listed (55 FR 32088), it was considered extirpated from (GRA 2 and 3) Rhode Island (RI), Connecticut (CT), and New York (Long Island), and is still considered extirpated in these states.
In 1994, larvae collected
from multiple sites in
NBTB populations in
From 1993-2009 annual
NBTB surveys were conducted at the four largest sites in
The two NBTB sites in
In 1999, 2002, 2005, and
2009, comprehensive NBTB adult surveys were conducted along the eastern
shoreline of the Chesapeake Bay in
In 1998, 2001, 2004, and
2008, NBTB surveys were conducted along the western shoreline of the
In 2009, the Service finalized a 5-year status review of NBTB (Service 2009). As a result of the continued loss of NBTB populations and habitat and the overall declining population trend described above, the Service recommended reclassifying NBTB from threatened to endangered. To date, no action has been taken to formally propose reclassification.
Table 4. Summary of the status of NBTB throughout its range.
Site Specific Comments
Coastal Massachusetts and Islands
· Westport - population extirpated
· Martha’s Vineyard - overall numbers appear stable; Squibnocket site from 2010 to 2011 had significant drop of adult NBTBs from 1,500 to 93
· Monomoy National Wildlife Refuge translocation - numbers increasing
Block Island, RI
Long Island Sound, CT
· extirpated at time of listing, and to date still considered extirpated
Long Island, New York
· extirpated at time of listing, and to date still considered extirpated
Sandy Hook to Little Egg Inlet, New Jersey
· Sandy Hook translocation - 7 adults observed in 2008, multiple surveys since have located no NBTBs
Calvert County, Maryland
· 8 sites - extirpated, habitat lost or in poor condition
· Calvert Cliffs - status uncertain
· Western Shores/Calvert Beach - declined from high count of 4,198 in 1991 and is holding at 400-600, a 90% decline.
Tangier Sound, Maryland
· Janes Island - ≥ 1,100 adults (protected)
· Cedar Island - ≥ 1,100 adults (protected)
· Only GRA that meets delisting criteria (Service 1994)
Eastern Shore, Virginia
Stable to declining
· 2009 survey found the highest total count (46,082) of adults since start of comprehensive surveys
· Increase primarily result of increases at 7 sites (Church Neck North, Occahannock Neck, Silver-Downings Beach, Tankards Beach, Scarborough Neck, Church Neck, Hyslop Marsh)
· 7 sites with no NBTBs compared to 2 in 2005.
· Significant declines from 2005 occurred at 4 sites (Picketts Harbor, Cape Charles, Elliots Creek South, Kiptopeke), coincidental with increased shoreline modifications or other human impacts
· Largest decline was at Parkers Marsh (down from 12,554 in 2005, to 1,629 in 2009)
8 & 9
Western Shore, Virginia
· Since 2001 a 20% loss in occupied sites (12 of 58 occupied sites) and total numbers declined 70%
· Habitat loss due to Hurricanes Isabel and Ernesto
· Since 2001, the 8 largest sites that supported approximately 50% of the total NBTBs declined 78%
· GRA 8 - 4 occupied sites that support large populations (not protected); 1 “other” sized population Hughlett Point (protected)
· GRA 9 - 2 occupied sites that support large populations; 1 “other” sized population Bethel Beach
Factors Affecting the Species – In 1990, the Service listed NBTB as threatened because of its greatly reduced range and susceptibility to natural and human threats (55 FR 32088). Natural limiting factors include winter storms, beach erosion, flood tides, hurricanes (Stamatov 1972), and predators. Anthropogenic threats mentioned in earlier papers included pollution, pesticides, high levels of recreational activity, off-road vehicular traffic, and shoreline alteration (Knisley et al. 1987; Knisley and Hill 1989, 1990; Service 1994). Past extirpation of NBTB from most of its range has been attributed primarily to destruction and disturbance of natural beach habitat from shoreline development, beach stabilization, and high levels of recreational use (Service 1994). These threats continue to affect the long-term survivability of NBTB, but with the addition of sea level rise these factors are exacerbated. Sea levels will change the dynamics that maintain beach habitats, including increased shoreline erosion rates in some areas, and changes in sand deposition (USGS 1998). The accelerated changes in shoreline structure and composition, and the location of suitable sandy beaches will influence the ability of NBTB to adapt to climate change.
Storms impact the coast
throughout the year with nor’easters occurring in the winter and hurricanes in
the summer/autumn. Nor’easters affect
beach habitats from
Erosion within the Chesapeake Bay has occurred for thousands of years from natural sea level rise and wave action. However, this process has been exacerbated by beach development activities that interfere with natural beach dynamics and longshore sand transport. Beach stabilization structures such as groins, jetties, rip-rap revetments, and bulkheads, which are designed to reduce erosion, may interrupt and capture sand from longshore transport and build up the beach around the structure but prevent sand from moving to the down-drift shoreline. Bulkheads and rip-rap typically result in reflection of wave energy onto the forebeach, which ultimately narrows the beach and steepens the profile. Such changes in the beach profile can occur over periods of 1-30 years. These structures also prevent the back beach from supplying sand to the forebeach, and concentrate wave energy at the ends of the bulkhead or revetment, resulting in erosion at these points (Knisley 1997a). “Along a given length of shoreline, the first structure installed often has an adverse impact on the neighbor’s shoreline (usually downstream of a longshore current), thus forcing a sequence of other shoreline modifications. Eventually, as shoreline modifications increase in number and amount of shoreline modified, the sand ‘bank’ is further depleted as erosion is halted and sand moves offshore into deeper channels. The long-term (50+ years) impacts of this scenario are unknown, but may eventually lead to a collapse of the natural beach habitat. . .” (Hill and Knisley 1995).
conducted three years (1994-96) of research on the effects of shoreline
stabilization structures on the distribution and abundance of NBTB. A total of 24 sites (51 site sections) were
surveyed for adult and larval NBTBs in
Monitoring of shoreline stabilization projects since the Knisley (1997a) study continue to show that shoreline hardening generally is detrimental to NBTBs, though there is variability in the responses of habitat and NBTBs depending on other factors, including adjacent beach conditions, project design, and site-specific characteristics.
Beach nourishment may be
destructive to larvae and may render habitat unsuitable for subsequent larval
recruitment and development (Knisley 1991).
However, deposition of dredged material may also create habitat in some
cases (Knisley 1997a). Dredged sand was
placed south of Cape Charles in Northampton County, Virginia, in 1987, and the
number of adult NBTBs at this site increased from 700-800 to 2,000 in 1993
(Knisley 2002). Although the addition of
sand may maintain the habitat in the long term, it is likely that its immediate
effects result in some larval mortality through crushing, smothering, or
entombing (Service 1994). Sand
deposition could also have negative effects on food (amphipod) availability
(Service 1994). Fenster et al. (2006)
determined that two beach nourishment projects on the western shoreline of the
Non-jeopardy biological opinions anticipating take of NBTBs completed since 1994 have included 12,943 ft of shoreline hardening; 169 groins permanently covering 14,495 ft2 of habitat; 12 piers; and several projects involving breakwaters, beach nourishment, concentrated human use, and unusually large piers and groins. In addition to permanent loss of habitat, most of the projects have involved additional impacts, including mortality of NBTBs (primarily larvae), during construction. Fragmentation of NBTB habitat has also resulted from the installation of these structures.
In addition, many shoreline hardening projects (particularly revetments and bulkheads) have been completed that do not require Corps permits and the associated section 7 consultation and biological opinion. Furthermore, unpermitted activities (i.e., structures built without the required Corps permit) may be contributing to the reduction of NBTB habitat in Virginia as there appears to be more groins and other structures within NBTB habitat than have been permitted (C.B. Knisley, pers. comm. 2004).
Adult foraging, mating,
and ovipositing can be disrupted by human activity (Knisley et al. 1987). However, larvae are
probably more affected because they spend most of their time at the tops of
their burrows waiting for prey, and may be disturbed by even relatively minor
activities such as vibrations, movement, and shadows (Knisley et al. 1987). Knisley and Hill (1990) examined the effects
of visitor use of Flag Ponds, a park in
Primary predators of
adult NBTBs are wolf spiders (Arctosa littoralis), asilid flies (C.B.
Knisley, pers. comm. 1994), and birds (Service 1994). The primary larval predator is a small,
parasitoid wasp (Methocha sp.)
that enters the larval burrow, paralyzes the larva with a sting, and lays an
egg on the larvae. The egg hatches, and
as it develops the larval wasp consumes the larval NBTB. Mites have also been found on larvae at
NBTB larvae are probably
more vulnerable to habitat disruption than adults (Knisley et al. 1987), and similar to
other tiger beetle species, larval survivorship is low due to predators and
other limiting factors. “For example,
only about 5% of the first instar larvae of several
Oil slicks and use of
pesticides for mosquito control may have contributed to the decline of this
species (Stamatov 1972). Most of the
large NBTB populations in
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