AMER. ZOOL., 33:588-598 (1993)
Conservation of Aquatic Insects: Worldwide Crisis or
Localized Threats?1
D A N A. POLHEMUS
Dept. of Entomology, Bishop Museum, P.O. Box 19000-A, Honolulu, Hawaii 96817
An overview is presented on the current worldwide status of
aquatic insect conservation. Despite extensive habitat destruction or modification, aquatic insects as a whole do not appear to have suffered as great
a proportional loss of species over the last century as members of other
groups. In North America, for example, only 204 species are considered
at risk out of a total fauna of over 10,000 species, and no species has been
documented as having gone extinct. Even so, aquatic insect diversity is
subject to a broad spectrum of threats, including chemical pollution of
waters from industry and agriculture, physical destruction of habitat from
impoundments or drainage, and introduction of alien aquatic biota, primarily sport or aquarium fishes. Adequate legislation exists in the United
States and Europe to provide protection to aquatic insect taxa atrisk,but
the implementation of this legislation is often hampered by a lack of
taxonomic and distributional knowledge, and by a concentration of recovery efforts on more highly visible vertebrate taxa. The case of the Ash
Meadows Naucorid, the only aquatic species currently protected under
the Endangered Species Act, is examined in detail. It is concluded that
the listing of this species has had no discernable effect in halting its
population decline, partly due to the fact that recovery efforts for endangered fishes have proven deleterious to the insect. It is recommended that
future listing efforts be conducted in the context of national biological
surveys, and that an ecosystem rather than single species approach be
applied to aquatic conservation efforts.
SYNOPSIS.
INTRODUCTION
The present paper provides a brief overview of issues concerned with the conservation of aquatic insect species. Unlike the
situation seen in fishes, where several recent
studies have concluded that on a worldwide
basis at least 20 percent of the world's freshwater fish species are either threatened or
extinct (Reinthal and Stiassny, 1991; Moyle
and Leidy, 1992), there does not seem to be
an imminent extinction crisis in regard to
aquatic insects, although this is not meant
to imply that certain species are not at
The sections below examine the current
major threats to aquatic insect diversity,
review existing protective legislation in
Western Europe and the United States, and
conclude with a case study of the Ash Meadows Naucorid, the only aquatic insect presentl
y receiving protection under the EndanSered Species Act. Given the limitations of
space the present review should not be considered comprehensive, and readers wishing further detail are directed to the references cited and the additional citations
contained therein,
n
ncxrr x
A
AT
^^l^Zlls^
risk.
ir^tci wvtKMi Y
Threats to aquatic insect diversity are
llkel t 0 v a r
y
y from country to country, and
also
between the temperate zone and the
tropics. The primary threats to British
aquatic insects listed by Foster (1991) in
order of decreasing importance were agri1
From the Symposium The Crisis in Invertebrate cultural development (primarily drainage of
Conservation presented at the Annual Meeting of the
American Society of Zoologists and the Canadian Society of Zoologists, 27-30 December 1992, at Vancouver, British Columbia.
wet]ands\
weuanas
urhaniyatinn industrial devel
A ur Damzation, industrial deveiopment and pollution, recreational pressures (golf course construction, etc.), and
588
AQUATIC INSECT CONSERVATION
natural environmental changes. Similarly,
the International Union for the Conservation of Nature (IUCN) listed wetland drainage, river impoundment, water pollution,
and introduction of alien species as the major
threats to aquatic insect diversity in its
worldwide review of invertebrate species at
risk (Wells et ai, 1983). These concerns were
reiterated once again in a survey of leading
American aquatic insect workers conducted
for this report, which found that physical
habitat destruction due to impoundments
was considered the greatest threat to rare
aquatic insects, followed by water pollution,
and siltation due to loss of vegetative cover.
By contrast the introduction of alien fish
species, although often ignored by workers
in continental settings (Pyle et ai, 1981), is
considered one of the primary threats to
aquatic insects on the isolated tropical
islands of Hawaii (Zimmerman, 1948;
Moore and Gagne, 1982).
Several of the major threats listed above
are discussed in greater detail below:
1. Extirpation due to water pollution. —
The role of water pollution in the loss of
aquatic biota has been well publicized over
the last several decades, and a vast body of
literature exists dealing with the subject, a
review of which is beyond the scope of this
paper (but see Heliovaara and Vaisanen,
1993, and references therein). In addition
to traditionally recognized industrial point
sources, chemical pollutants may also enter
aquatic systems in the form of pesticide residues from mosquito control programs
(Wells et ai, 1983), a particular problem in
the southeastern United States, or as fertilizer and herbicide runoff from nearby agricultural lands (Franz, 1982). Acid rain has
also had an impact on aquatic insect diversity, particularly in Canada and northern
Europe, but the results of acidic deposition
are not uniformly deleterious across all
aquatic insect groups. Certain orders, such
as Ephemeroptera and Plecoptera, decline
in diversity at pH values below 5.5, while
species in other orders, such as Heteroptera,
Coleoptera and Odonata, are more acid-tolerant and actually increase in abundance
(Legge and Crowther, 1987). The situation
is also difficult to assess in the tropics, since
many tropical blackwaters are naturally
589
acidic and have a correspondingly adapted
biota.
Chemical pollution appears to be responsible for the only documented case of an
apparent extinction in aquatic insects,
involving the caddisfly Hydropsyche tobiasi.
This species formerly inhabited the River
Rhine in western Germany, but no specimens have been taken since the 1920s, even
though the insect is easily captured in light
traps. The situation in regard to H. tobiasi
is somewhat unclear, since the species was
not described until 1977, having before that
time been confused with H. exocellata, a
species still abundant in Germany (Wells et
ah, 1983). As a result the decline ofH. tobiasi is poorly documented, and it is possible
that some populations still remain but are
being misidentified as the more common H.
exocellata.
A much better documented example of
an aquatic insect species driven to the brink
of extinction as a result of pollution is the
large burrowing mayfly Palingenia longicauda, which was once abundant throughout much of western and central Europe.
The species had disappeared from Germany
and the Netherlands by early in this century,
and displayed a progressive retreat down
the Danube system over the last 50 years.
By the late 1970s the species persisted only
in the lower Bulgarian course of the Danube
and in the basin of the Tissa, a left bank
tributary (Russev, 1987). Even these populations appear to be at risk, and the mass
emergenceflightsthat once carpeted the river
with newly hatched adults are now a thing
of the past.
Similar losses of burrowing mayflies
inhabiting large rivers are also seen in North
America. Pentagenia robusta McDunnough
was formerly abundant in the Ohio River
system, but appears to have disappeared
from that portion of its range (G. Edmunds,
personal communication). Similarly,
Ephemera compar Hagen was described in
1873 from specimens taken in the Platte
River drainage along the foothills of the
Rocky Mountains in Colorado, an area now
occupied by the city of Denver, but has never
been collected since (Edmunds and
McCafferty, 1984). The above examples
illustrate a general pattern, in which aquatic
590
DAN A. POLHEMUS
insect species inhabiting large rivers along observed in response to stream acidification
which settlements and industrial develop- (Halle/ ai, 1980).
ments congregate are more vulnerable than
Perhaps the best documented case of an
those found in small headwater streams.
aquatic insect species on the brink of extincIncreased public awareness and the tion due to habitat destruction is that of
implementation of strong anti-pollution Ambrysus amargosus, the Ash Meadows
legislation has mitigated the threat of chem- Naucorid (discussed in greater detail subical pollution to some extent in the United sequently), a creeping water bug confined to
States and western Europe, but it still a single set of thermal springs at Ash Meadremains a major problem in eastern Europe ows, Nevada. The hot spring habitat of this
and the developing countries of the tropics. species was extensively modified by irrigaStudies indicate that the effects of pollution tion schemes, and though now protected is
are reversible, however, and that locally still at risk due to a gradual depletion of the
extirpated species will return to habitats underlying aquifer by pumping to supply
where pollution abatement has been suc- municipal water for nearby Las Vegas. Specessful (Cochran, 1992).
cies confined to limited habitats like this are
2. Extirpation due to physical destruction vulnerable to natural as well as human perof habitat.—The most frequent causes of turbations; the June 1992 Yucca Valley
physical (as compared to chemical) habitat earthquake produced notable changes in the
destruction are stream impoundment, flow rates of many springs at Ash Meadows
drainage of wetlands, and depletion of aqui- (D. Threloff, personal communication),
fers by pumping (Moore, 1976; Wells et ai, causing concern for the future survival of
1983). In addition to these widespread certain endemic fish and insect taxa in the
problems, many other activities can con- area.
tribute to habitat loss on a local scale, such
3. Extirpation due to introduction of alien
as siltation from poorly maintained agri- species.—Introduction of and competition
cultural fields, which impacts the mayfly from alien species, particularly fishes introbiota of sand bottomed rivers in Florida duced for sport, aquaculture or biological
(Franz, 1982), and sand mining, which control, appears to be an increasingly serithreatens certain Odonata confined to dune ous problem for aquatic insects throughout
lakes in Australia (Key, 1978). Loss of hab- the world (Howarth, 1991). Few studies have
itat is particularly critical for species occu- addressed alien species directly, however,
pying extremely restricted ranges, such as and their impacts are thus largely unproven.
isolated thermal springs or oceanic islands, Many species of trout, for example, have
and accounts for most of the known aquatic been introduced into the rivers of the westinsect species that are currently considered ern United States, but their effect (if any)
in imminent danger of extinction.
on the composition and density of native
Dams are viewed by aquatic insect spe- stream insect faunas is poorly documented,
cialists as being the most widespread and due in large part to the absence of adequate
destructive of all habitat alterations, but their baseline surveys conducted prior to the
documented effects on aquatic insect biotas introductions. Tillyard (1926) stated that the
are quite variable, and few generalizations release of trout into the streams of New Zeacan be made (Petts, 1984, and references land in the early 1900s had drastically
therein). In some cases aquatic insect diver- diminished the abundance of native maysity increases downstream following dam flies in the family Oniscigastridae, noting,
construction, while in other cases there is a "The introduced trout have greatly reduced
loss of overall diversity, which may ironi- this once abundant fauna and some species
cally be accompanied by an increase in are now extinct or nearly so . . . . Unfortuoverall aquatic macroinvertebrate biomass nately, the mayfly fauna of Australia and
due to the proliferation of Chironomidae, New Zealand is not specialized to hold its
Simuliidae, and certain Trichoptera. This own against the introduced brown and rainlatter pattern is in many ways similar to that bow trout and is rapidly being reduced to a
AQUATIC INSECT CONSERVATION
minimum." Tillyard's observations were
anecdotal, however, and few subsequent
workers in these countries have echoed his
concerns (but see Greenslade and New,
1991).
In Hawaii, the occurrence of damselflies
in the native genus Megalaghon appears to
be inversely correlated with the presence of
introduced fishes. This seems to be particularly true for lowland species whose larvae
breed in lentic habitats. One of these species, M. xanthomelas, expanded its range
widely in the early 1900s at a time when the
construction of plantation reservoirs and
cattle ponds provided many new and suitable habitats (Williams, 1936), and at one
point it was probably the most abundant
damselfly in the islands. Populations
declined precipitously, however, following
the introduction of Gambusia mosquito fish
into these waters (Zimmerman, 1948), and
recent surveys indicate that M. xanthomelas is now the rarest and most endangered
of all Megalagrion species.
CONSIDERATIONS IN AQUATIC
INSECT CONSERVATION
Despite the threats discussed above,
available knowledge indicates that although
certain aquatic insect species have suffered
severe population declines, most do not
appear to be in imminent danger of extinction. This may be in large part due to the
ability of aquatic insects to tolerate changes
to the surrounding terrestrial environment,
and to disperse by flight during their adult
stages. That aquatic insects are able to persist in areas where the natural vegetation
has been greatly altered, and the native terrestrial biota correspondingly replaced or
extirpated, was illustrated by a study undertaken in Moloaa, on the Hawaiian island of
Kauai (Asquith and Messing, 1993). Of 283
insect species sampled from this lowland
agricultural area, only 24 species (less than
10 percent) were native taxa, yet of these 24
species 12 (50 percent) were aquatic insects
associated with a stream that passed through
the area. The authors of this study note that
in Hawaii "Abundant anecdotal evidence
suggests that the loss of native [insect] species in the lowlands has been accelerated in
591
historical times, due in large part to the land
use and pest control methods of agriculture,
both Polynesian and European," but also
conclude that "Stream and riparian systems, more than any other habitat appear
to still harbor the greatest number of
endemic species."
A similar pattern was observed by the
author on the Indian Ocean island of Mauritius, where a diverse assemblage of
endemic and indigenous aquatic insect species, many of them described over a century
ago, was collected from a stream flowing
through sugar cane fields in an area that had
historically been covered with rain forest.
In tropical Asia, densities of certain aquatic
insects such as the creeping water bug Aphelocheirus are actually greater in areas where
the surrounding forest has been felled,
allowing increased sunlight to reach the
streams (Polhemus and Polhemus, 1988).
Such studies and observations indicate that
aquatic environments are not tightly linked
to vegetative communities, and that as long
as some type of vegetative cover remains to
provide sufficient riparian shading and prevent siltation aquatic insect communities
can persist long after the surrounding native
terrestrial biota has been reduced or extirpated.
In some cases environmental disturbances can apparently even be beneficial to
aquatic insect species considered to be at
risk. This is illustrated by the Hawaiian
damselfly Megalagrion amaurodytumpeles,
which occurs in the Puna District of Hawaii
island, breeding in the phytotelmata of
arboreal Astelia plants, and is currently held
as a Category 2 listing candidate on the Federal Register. Studies by personnel from
Hawaii Volcanos National Park have shown
that this species is in fact relatively abundant, but occurs in dense forest areas where
it is rarely collected. Even more ironically,
densities of this species were found to be
increased in areas of rain forest heavily disturbed by introduced pigs, which opened up
the understory and provided a habitat more
favorable for its host plant (D. Foote, personal communication).
Despite these examples, there are cases in
which aquatic insect species are facing
592
DAN A. POLHEMUS
extreme threats, and require action in order
to prevent their extinction. These cases are
best documented in the developed countries
of the northern temperate zone, since reliable information is almost nonexistent concerning the precise distributions of tropical
aquatic insects.
CURRENT LAWS PROTECTING
AQUATIC INSECTS
In western Europe, aquatic insects are
protected under the Ramsar Convention,
and the Convention on the Conservation of
Wildlife and Natural Habitats (the Bern
Convention of 1979). As of 1989 Appendix
2 of this latter agreement listed 17 aquatic
insects, one in the order Coleoptera and the
remainder in the Odonata. Most of these
are species endemic to the Iberian Peninsula
or certain Mediterranean islands. It has been
difficult to argue convincingly for international protection of aquatic insects in
Europe, since most species, although perhaps locally endangered in certain regions,
are widespread across the continent, and
even naturally disjunct populations are
reproductively compatible.
Britain is the most heavily developed
country in Europe, and thus an examination
of its aquatic insect biota considered to be
at risk is informative. Information on British aquatic insect species considered to be
rare, vulnerable, or endangered is contained
in the British Red Data Book (Shirt, 1987).
This document, which has no force of law
but is used for conservation planning purposes, lists 133 taxa of aquatic insects in the
above three categories, distributed across the
insect orders as follows: Odonata, 9;
Orthoptera, 1; Heteroptera, 1; Coleoptera,
51; Diptera, 37; Trichoptera, 31; Lepidoptera, 3 (Foster, 1989). Of these taxa, 56 were
considered endangered in Britain, but few
of these are endemic to the British Isles, and
most are not in imminent danger of extinction in Europe as a whole.
Aquatic insects at risk in the United States
are afforded protection under the Endangered Species Act, which is currently the
strongest conservation legislation available
in any country. As of late 1991, the Federal
Register listed 204 aquatic insect species.
Of these, none were listed as endangered,
one (the Ash Meadows Naucorid) was listed
as threatened, and the remaining 203 were
Category 1 and 2 candidates for listing.
These 203 proposed taxa were distributed
across the major aquatic insect orders as
follows: Ephemeroptera, 15; Odonata, 37;
Plecoptera, 9; Heteroptera, 4; Coleoptera,
56; Diptera, 1; Trichoptera, 81. Comparison of the American taxa at risk with those
from Britain demonstrates that the number
of species listed under the different orders
does not necessarily reflect the actual relative vulnerability of species within these
groups to extirpation, but rather the energy
with which specialists in particular groups
have petitioned species for listing.
Several states, including Florida, Virginia, California and Michigan have legislation providing protection to threatened
taxa, including aquatic insects, found within
their borders, with the first two states having
published inventories of taxa at risk (Franz,
1982; Terwilliger, 1991). Florida currently
considers 43 aquatic insects threatened or
rare, distributed across the major orders as
follows: Ephemeroptera, 3; Odonata, 22;
Trichoptera, 18. No aquatic insect in the
state is listed as endangered. A similar
inventory in Virginia lists 41 aquatic insect
species as endangered, threatened, or of special concern, taxonomically distributed as
follows: Ephemeroptera, 11; Plecoptera, 17;
Odonata, 14; Hemiptera, 4. Of these, 12 are
considered endangered. State inventories of
this type have inherent limitations, since
they consider only taxa within state borders
and use definitions of threatened and
endangered that are more liberal than those
specified in the Endangered Species Act. In
many cases the state inventories confuse taxa
that are merely potentially vulnerable due
to naturally limited ranges with those that
are truly endangered due to imminent
threats. In addition the state inventories
make no allowance for species that may be
rare within the boundaries of a certain state
such as Florida, which might lie on the
periphery of their natural range, but widespread elsewhere in the country.
THE PROS AND CONS OF LISTING UNDER
THE CURRENT ENDANGERED SPECIES ACT
The difficulties involved with aquatic
insect conservation strategies may perhaps
be most profitably analyzed in the context
AQUATIC INSECT CONSERVATION
of the Endangered Species Act. This legislation provides several criteria for judging
the threats facing a species, meeting any one
of which is sufficient to justify protection.
The first is habitat destruction or modification, which is relatively easy to demonstrate in most instances and constitutes the
most prevalent perceived threat to aquatic
insects. The second is overutilization, which
is not generally a problem, except perhaps
in the case of rare Odonata which are sought
by collectors. The third is disease or predation, the latter of which may be significant
in relation to introduced species but is difficult to demonstrate. The fourth is inadequacy of existing regulations, an area that
has not been widely considered in relation
to aquatic insects. There is also a catch-all
clause that allows consideration of "other
natural or manmade factors affecting the
species' continued existence."
Given the broad range of threats that may
be considered, nearly any aquatic insect that
is truly in jeopardy or perceived as such may
be accommodated within the scope of the
existing legislation. Listing of an aquatic
insect species as threatened or endangered
serves an immediate beneficial purpose by
providing it with legal protection, restricting its collection and curtailing the destruction of its habitat. Against this clear benefit,
however, must be weighed certain disadvantages that are inherent in the listing and
recovery process as it currently operates.
These were reviewed in a broad context by
Rohlf (1991), and are discussed briefly below
in relation to aquatic insects.
The first of these involves the reliability
of the distributional studies on which listing
petitions are based. Species have been proposed for listing on the basis of inadequate
survey data which made their distributions
appear more restricted than was actually the
case. This was well illustrated by the Wilbur
Springs Shore Bug, an littoral hemipteran
which was proposed for listing because it
was believed to occur only at a single thermal spring in the Coastal Ranges of California that was under consideration for geothermal development. A detailed survey of
the surrounding region, however, proved
that the species was actually far more widespread than had been realized, occurring in
four adjoining counties as localized popu-
593
lations along the margins of nearly every
thermal spring that exhibited suitable water
chemistry (Resh and Sorg, 1983). As a result
of these discoveries the proposed listing was
denied. Such cases of listing petitions based
on inadequate knowledge of distributions
are the rule more than the exception, since
biological survey data, even in well studied
countries like the United States, are generally inadequate to determine the true
extent of species ranges. The problem is
compounded in the tropics, where any speculation on the conservation status of aquatic
insect species is futile except in the case of
small islands where all potential habitats
may be identified and investigated.
A second problem concerns inadequate
taxonomic knowledge, which has lead to the
proposed listing of named taxa that are in
fact synonyms of more widely distributed
species. An example of this may be seen in
the Hawaiian Megalagrion damselflies,
where M. amaurodytum fallax is held as a
Category 2 candidate on the Federal Register even though the name was synonymized under M. amaurodytum peles (also a
Category 2 candidate) by Schmidt in 1938.
Taxonomic errors in listing petitions are
common (Standley, 1992), and as in the case
above can create the impression that more
taxa are at risk than is actually the fact. The
current shortage of adequately trained taxonomists capable of detecting such errors
only serves to compound problems of this
type.
Finally, in the absence of adequately
funded recovery programs the listing of
insect species can actually make it more difficult to perform research on them, since
most sampling methods for insects involve
killing a certain number of individuals,
which is restricted under the Endangered
Species Act. It is possible to secure permits
for taking, but these are not generally in the
possession of collectors operating in remote
areas, who might encounter a threatened or
endangered species but be left with the
unenviable choice of collecting a specimen
and thus breaking the law, or returning with
an anecdotal account of a sighting that cannot be confirmed in the absence of a voucher
specimen. Similarly, a flight intercept trap
set up for baseline faunal surveys might easily capture and kill endangered insect spe-
594
DAN A. POLHEMUS
cies that were not known to be present in
the area under study, leaving researchers in
inadvertent violation of the law. Any
research program involving a listed species
is unavoidably burdened with special
restrictions; as a result insect researchers may
tend to stay clear of listed species and study
those which they can collect and experimentally manipulate more freely, unless
there is a compelling financial incentive for
doing otherwise. Funds for recovery programs must therefore keep pace with listings, rather than lagging years behind as is
presently the case, otherwise listings may
end up as merely symbolic actions that actually serve to inhibit our understanding of
the rare species we are trying to protect.
The final problem with listing lies in the
designation of critical habitat for aquatic
insect species. In some cases, such as species
inhabiting single springs, caves, or lakes, this
matter is straightforward. In the case of
stream dwelling insects, however, which
may inhabit several watercourses or certain
particular reaches, the definition is more
problematic. Federal law allows critical
habitat to be designated when it is "prudent
and determinable," but even in light of
recent trends toward catchment reservation, setting entire stream systems off limits
is often politically difficult in the context of
local water rights, while ascertaining which
precise stream reaches are critical to a particular aquatic insect species is frequently
not determinable within typical time and
budgetary constraints. This leads to the issue
of whether species are best conserved by
protecting all populations, or by preserving
examples of the representative ecosystems
of which they are a part, a topic too lengthy
and complex to discuss in detail herein. Suffice it to say although a population based
approach is fundamental to initial listings
under the Endangered Species Act, the ecosystem approach appears to offer the most
stable long term solution in regard to recovery efforts for aquatic insects (Foster, 1991).
A CASE STUDY: THE ASH
MEADOWS NAUCORID
As noted previously the Ash Meadows
Naucorid {Ambrysus amargosus La Rivers),
which is listed as threatened, is the only
aquatic insect species in the United States
receiving any degree of formal protection
under the Endangered Species Act, and its
case is worth examination in the context of
the issues discussed above.
Ambrysus amargosus was described by La
Rivers (1953), based on a long series collected at the thermal Point of Rocks Springs,
in southern Nevada. In his paper, La Rivers
described the habitat as ". . . several water
sources emerging from the point of a low,
long limestone ridge in the east-central area
of Ash Meadows . . . . Water from isolated
springs collects in a pool some 30 feet long
and 15 feet wide from which it is discharged
by two outlet streams. Most of the discharge
was being carried by a stream which seemed
to be the natural outlet (the other apparently
a side ditch constructed for irrigation diversion). Both the natural outlet stream and
the pond itself were surfaced with hard
scrabble and loose rock. Extensive search in
the pool produced only a few specimens of
Ambrysus, the majority of them coming
from the stream. Here they were easily collected by fastening a net at a point against
the strong current, then working up and
down stream above the net and agitating
the loose rock bottom. The displaced insects
were carried downstream into the net in large
quantities. While the current in the stream
was swift, the latter was only a few inches
deep . . . . The stream flow in both places is
strong enough to keep the bottom sand free,
but too weak to move the gravel, and it is
under and about this gravel that the Ambrysi
seem most at home."
The next known collectors to visit Point
of Rocks were Arnold S. Menke and L. A.
Stange of the University of California, who
made collections at the site in April of 1958.
They made no report on the condition of
the habitat or the status of the naucorid population, but based on the large series of specimens that they collected one must assume
that the species was abundant at this time.
Six years later another specialist, Dr. John
T. Polhemus of the University of Colorado
Museum, visited the Point of Rocks Springs
in February of 1964 and made collections
of Ambrysus amargosus. Dr. Polhemus
(personal communication) reports that at the
AQUATIC INSECT CONSERVATION
time of his visit the habitat was much as La
Rivers had described it, with the spring outflow from what is now known as King's Pool
forming a broad, shallow stream with a
cemented pebble bottom running for a considerable distance out across the desert from
the base of the mountain. He recalls that
several trees, possibly mesquite, shaded the
upper section of the outflow stream where
it issued from the spring pool. He found the
naucorids to be abundant in the outflow,
and like previous workers was able to collect
a long series without any fear that he was
endangering the population.
It would be twenty years before another
specialist, in this case the author, returned
to Ash Meadows in search of Ambrysus
amargosus. During a visit to Point of Rocks
Springs in late November of 1984 it was
found that the entire area surrounding the
springs had been drastically altered from the
conditions described by La Rivers and J. T.
Polhemus. The desert flats below the spring
had been graded and levelled to create agricultural fields, and the outflow from King's
Pool had been diverted into a series of irrigation ditches. The smaller outflows issuing
from the base of the mountain to the east
now flowed only a short distance before
being captured in a large, deep, cold water
pond. A diligent search for the naucorids in
the channelized outflow from King's Pool
proved fruitless, but it was possible to locate
a moderate number of individuals in the
smaller outflows that supplied the pond.
Even these small outflow channels were
becoming clogged with tumbleweeds and
overgrown by various types of riparian vegetation, and it thus appeared that the Ash
Meadows Naucorid was in danger of being
extirpated completely from even these
remaining fragments of its original habitat.
In 1985 the Fish and Wildlife Service
requested a status evaluation for the Ash
Meadows Naucorid, which had at this point
been proposed for listing as a threatened or
endangered species at the suggestion of
Arnold S. Menke. This evaluation, completed by the author, concluded that the species was indeed in danger of extinction, and
cited concerns over continued loss of habitat. Ambrysus amargosus was subsequently
declared threatened, a status it currently
595
maintains. During this same period the species' habitat at Point of Rocks Springs
received protection within a newly created
Ash Meadows National Wildlife Refuge,
which was established in 1984 after the area
was purchased by The Nature Conservancy
and then transferred to the Fish and Wildlife Service (for further historical review of
the efforts to save the Ash Meadows ecosystem see Deacon and Williams, 1991).
During a recent visit to Ash Meadows in
July 1992, it was discovered that the largest
of the remaining spring outflows that had
harbored the species in 1984 had been seriously disturbed in the process of constructing a refugium for the endangered Devils
Hole Pupfish (Cyprinodon diabolis). In particular, large rocks had been placed in the
outflow channel to secure a plastic irrigation
pipe that carried water from the spring head
down to a small basin in which the pupfish
were maintained. The addition of these large
rocks, although done with good intentions
in regard to the fish, had proved disastrous
for the naucorids, effectively extirpating
them from one of their principal remaining
habitats. A few individuals were still found
below the rocked-in area, and in two other
small outflow channels nearby where the
insects had also been encountered in 1984,
but it was clear that the number of individuals had declined radically even from the
reduced population levels encountered at
that time. In addition, it was obvious that
various types of exotic vegetation had spread
uphill along the spring channels from the
pond below, overtopping much of the water
and rendering the channels much less suitable as naucorid habitat. Finally, wild horses
were using the spring head as a watering
hole, trampling the banks and causing siltation and degradation of the water quality.
At this time, it therefore appears that the
Ash Meadows Naucorid is continuing to
experience a progressive decline in numbers, due to a variety of physical and biological disturbances to its thermal spring
habitat. This example is illustrative because
it highlights many of the problems involved
in the conservation of aquatic insects under
the current United States law. Several conclusions can be drawn from this history:
596
DAN A. POLHEMUS
1. That the Ash Meadows Naucorid was an
inherently vulnerable species due to the
fact that it occupied a restricted habitat
that was prone to human disturbance.
2. That threatened and endangered species
often occur as communities rather than
individual taxa, and that conservation
plans that concentrate on saving only
single species (in this case the pupfish)
rather than entire endangered communities are at best inadequate, and at worst
actually deleterious to other sympatric
endangered taxa whose ecologies are not
considered.
3. That threats to endangered taxa are broad
spectrum and do not fall into single, easily remedied categories. The initial
threats to the Ash Meadows Naucorid
stemmed from human mediated habitat
destruction, which has been to a large
degree halted, while the current threats
arise primarily from introduced species,
in the form of wild horses and overtopping alien vegetation.
4. That the listing process, though a first
step, does not insure recovery, since it is
basically a reactive rather than a proactive policy. There is now enough knowledge concerning the Ash Meadows Naucorid and its history of decline to
formulate a recovery plan for the species,
but this is still a distant goal due to budgetary constraints and a tendency at
higher administrative levels for emphasis to be given to vertebrate taxa. In order
to insure the survival of the species it
will be necessary to modify the outflow
ditch below King's Pool from its current
condition as a deep, swift, steep sided
irrigation channel back to a broad, shallow, unshaded stream more reminiscent
of the original habitat. Once such a channel has been created, travertine shingle
rock from the hillside above will have to
be added as a final substrate to provide
the correct habitat for the naucorids. Such
a process will involve significant time,
money, and labor, all of which are in
short supply for projects relating to
arthropod conservation.
CONCLUSIONS
The discussion above illustrates the fact
the current laws in the United States and
western Europe appear to be adequate in
principle to protect those aquatic insect species that are in danger of extinction. The
implementation of these laws, however,
requires precise and accurate information
on species ecologies and distributions, data
that is frequently not available and should
be addressed in the context of national biological surveys. Based on the taxa currently
listed or proposed for listing in the developed countries of the temperate zone it
appears that the total number of species at
risk is not excessive in relation to the total
size of the aquatic insect biotas found in
these areas; in the United States, for instance,
there are 204 aquatic insect species on the
Federal Register out of an estimated total
fauna of 10,000 species (Merritt and Cummins, 1978). The problem should thus be
considered one of localized threats rather
than worldwide crisis.
The situation in the tropics is more difficult to assess, due to higher taxonomic
diversity, the presence of numerous undescribed species, and the absence of comprehensive surveys. A poll of leading aquatic
insect specialists at ten major research institutions conducted during the course of this
research indicated their belief that tropical
aquatic insects are in greater danger than
those in temperate regions, but this perception was based uniformly on subjective personal assessment rather than published
studies. While it is clear that large areas of
tropical rain forest habitat are being lost at
a rapid rate, it is unclear whether the massive disruption of the terrestrial biota in
these regions is having a similarly catastrophic effect on their aquatic insect communities. The specialists consulted also uniformly agreed that the ability to answer such
questions was hampered by a lack of both
trained specialists and funding to support
adequate field surveys.
That mankind has been able to drive certain aquatic insect species to the brink of
extinction should surprise no one. But the
fact that in few cases can we actually document the final demise of such species
should be seen as a matter of both concern
and hope. It is worth remembering that
many aquatic insects have lineages that go
back over 200 million years; dragonflies
from the Carboniferous, except for their large
AQUATIC INSECT CONSERVATION
size, would not appear out of place above
contemporary ponds. They have survived
episodes of mass extinction that swept away
the dinosaurs and trilobites, and they seem
just as likely to weather the current environmental crises. This paper does not argue
for complacency in regard to aquatic insect
conservation, but neither does it counsel
undue panic. Rather, it seems justified to
retain a cautious optimism in regard to these
creatures, and a belief that we will still have
a world populated by mayflies and water
striders long after whales, tigers, and even
man are counted among the species that
were.
ACKNOWLEDGMENTS
I wish to thank Dr. Michael G. Hadfield
of the University of Hawaii for organizing
the symposium for which this paper was
prepared. Special thanks are also due to
Douglas L. Threloff and Suzanne D. Coltman of the U.S. Fish and Wildlife Service,
Ash Meadows National Wildlife Refuge, and
Dr. John T. Polhemus, University of Colorado Museum, for sharing their biological
and historical knowledge of the Ash Meadows Naucorid. The following persons kindly
returned a questionnaire circulated in the
course of this study and provided valuable
comments and opinions based on their many
years of research in the field: Dr. Boris C.
kondratieff, Colorado State University, Fort
Collins; Dr. Chad Murvosh, University of
Nevada, Las Vegas; Dr. Wayne N. Mathis,
Dr. Paul Spangler, and Dr. Oliver Flint,
Smithsonian Institution, Washington; Dr.
John T. Polhemus, University of Colorado
Museum, Englewood; Dr. George F.
Edmunds, Jr., University of Utah, Salt Lake
City; Dr. Willis W. Wirth, Gainesville; Dr.
Harley P. Brown, Norman; Dr. Jon Gelhaus, Academy of Natural Sciences, Philadelphia. Dr. Scott E. Miller and Dr. Francis
G. Howarth of the Bishop Museum, Dr.
Timothy R. New of La Trobe University,
and Dr. Adam Asquith of the University of
Hawaii read prepublication drafts of this
manuscript and provided many useful comments that greatly improved the final version.
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