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105
6
Diversity and Ecology
of Vernal Pool
Invertebrates
Elizabeth A. Colburn, Stephen C. Weeks, and
Sadie K. Reed
CONTENTS
Invertebrate Distributions, Life Histories, and Dispersal .....................................107
Factors Influencing Invertebrate Distributions and Life Cycles...............107
Life History Strategies of Vernal Pool Invertebrates................................108
Dispersal ....................................................................................................109
Basics of Invertebrate Community Ecology.........................................................110
Common Invertebrates of Vernal Pools ................................................................112
Large Crustaceans......................................................................................112
Fairy Shrimp
(
Order: Anostraca).....................................................112
Clam Shrimp (Orders: Laevicaudata, Brevicaudata, and
Spinicaudata)....................................................................................112
Tadpole Shrimp
(Order: Notostraca) ............................................... 114
Small Crustaceans......................................................................................114
Ostracodes (Order: Podocopida)......................................................114
Copepods (Class:Copepoda)............................................................114
Water Fleas (Order: Anomola) ........................................................114
Free-Living Flatworms (Class: Turbellaria) .................................... 115
Oligochaetes (Class: Oligochaeta)................................................... 115
Mollusks.....................................................................................................115
Snails (Class Gastropoda, Order Basomatophora)..........................115
Fingernail Clams (Class: Bivalvia)..................................................116
Aquatic Insects ..........................................................................................117
Caddisflies (Order: Trichoptera)......................................................117
Aquatic Beetles (Order: Coleoptera) ............................................... 117
True Bugs (Order: Hemiptera).........................................................118
Damselflies and Dragonflies (Order: Odonata)...............................118
True Flies, Exclusive of Mosquitoes (Order: Diptera)....................118
Mosquitoes (Order: Diptera)............................................................119
Water Mites................................................................................................ 120
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Science and Conservation of Vernal Pools in Northeastern North America
Summary................................................................................................................120
Conservation Implications and Recommendations...............................................121
Pool Protection Efforts .............................................................................. 122
Habitat Enhancement and Aesthetics........................................................ 122
Mosquito Control....................................................................................... 123
Pesticides and Other Chemicals................................................................123
Public Education........................................................................................123
Acknowledgments..................................................................................................124
References.............................................................................................................. 124
Hundreds of invertebrate species can be found in vernal pools across northeastern
North America — a dramatic contrast to the more than dozen or so amphibians,
handful of reptiles, and few opportunistic bird and mammal species that breed, feed,
or water in pools. Many invertebrates are temporary water specialists that occur in
no other habitats and thus represent important components of local and regional
biodiversity. Some are rare or endangered. Ecologically, invertebrates are key to
energy and nutrient cycling in vernal pools and play important roles throughout the
food web, both as prey and predators. Additionally, invertebrates provide innumer-
able examples of adaptation and beauty. Changes in hydrology, water quality, veg-
etation, and light, as well as the introduction of new species, all can profoundly alter
invertebrate communities in vernal pools.
The best known pool invertebrates are large crustaceans — fairy, clam, and
tadpole shrimp — and aquatic insects, especially larval caddisflies, damsel and
dragonfly nymphs, and mosquitoes. These represent only a fraction of the fauna.
Less well-recognized, but equally important ecologically, are rotifers, gastrotrichs,
worms (flatworms, roundworms, horsehair worms, aquatic earthworms, and leeches),
small crustaceans (water fleas, copepods, and ostracodes), molluscs (snails and
fingernail clams), arachnids (water mites and spiders), and a wide variety of aquatic
insects (including water beetles and bugs, and many kinds of two-winged flies)
(Williams 2006) (Color Figure XX*). We generally lack adequate information on
distribution and trends in abundance for even the best known of the invertebrates
found in vernal pools, such as fairy shrimp (Belk et al. 1998, Jass and Klausmeier
2000).
Vernal pools with different hydroperiods and patterns of flooding typically
contain different, though often closely related, species of invertebrates (Wiggins et
al. 1980, Williams 1997, Colburn 2004). Thus, a landscape containing a cluster of
pools with different hydrogeological characteristics (see Chapter 2, Rheinhardt and
Hollands, and Chapter 3, Leibowitz and Brooks) is likely to support a greater overall
richness of invertebrates and to contribute more to regional biodiversity than a single
pool or series of similar pools. Unfortunately, many studies of animal life in vernal
pools identify invertebrates only to the level of genus and often only to family or
order, so that the true diversity represented by vernal pool invertebrates goes unrec-
ognized (Figure 6.1).
* See color insert following page xxx.
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Diversity and Ecology of Vernal Pool Invertebrates
107
In this chapter, we look at general patterns and trends in the distributions and
ecology of invertebrates in vernal pools. First, we review invertebrate life-history
strategies and community ecology in the context of pool habitat characteristics,
especially hydrology. In many cases ecological patterns are suggested by studies
carried out elsewhere; there is a need for fundamental ecological work on vernal
pool invertebrates in the glaciated Northeast. Next, we briefly introduce some of the
most characteristic groups and species, especially those that are restricted to vernal
pools and have particularly interesting adaptations and life histories. Finally, we
discuss conservation issues and make recommendations based on what is known
about the ecology of vernal pool invertebrates. For more in-depth taxonomic and
life history details, readers are referred to the cited literature and Colburn (2004).
INVERTEBRATE DISTRIBUTIONS, LIFE HISTORIES,
AND DISPERSAL
F
ACTORS
I
NFLUENCING
I
NVERTEBRATE
D
ISTRIBUTIONS
AND
L
IFE
C
YCLES
A commonly cited benefit of life in vernal pools is the release from predation (and
competition) from fish and invertebrates that cannot withstand drying (Williams
1997). This relative freedom from predators allows pool inhabitants unprecedented
access to the abundant detrital and algal food (Bärlocher et al. 1978). Vernal pools
are not predator-free, however, and some pool invertebrates’ life histories and behav-
ior may be tailored to avoid predation (Soderstrom and Nilsson 1972, Schneider and
Frost 1996, Brendonck et al. 2002). For example, fairy shrimp (
Eubranchipus
spp.)
mature, drop their eggs on the pool bottom, and die by late spring before the water
warms, oxygen levels decline, and predaceous salamander and beetle larvae become
abundant. The dry eggs overwinter and hatch the following spring. Young
Stagnicola
FIGURE 6.1
Comparative data from 2 New England vernal pools sampled in 1997, illustrat-
ing how the taxonomic level to which animals are identified influences the measured biodi-
versity (richness). (From E.A. Colburn, unpublished data.)
Level of Identification Affects Recorded
Biodiversity
0
10
20
30
40
50
60
70
80
Pool 1 Pool 2
Number of Taxa Recorded
Order
Family
Genus
AU: Year
“1987” in ref.
list.
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Science and Conservation of Vernal Pools in Northeastern North America
elodes
(snails) adapt to pool drying by climbing shrubs and trees to aestivate; they
return to the pools in fall. This behavior may help the snails avoid parasitism by
sciomyzid fly larvae (Jokinen 1978). Similarly, predator life cycles may track prey
populations. The complexity of such interactions highlights how pool alterations can
have unexpected ecological effects (see below).
The distributions and trophic relationships of aquatic invertebrates vary with
physical substrate, vegetation, and food; changes in any of these may alter the
community (e.g., Merritt and Cummins 1996). For example, herbivores are more
likely to occur in vernal pools with open canopies, abundant vegetation, and algal
growth than in small, closed-canopy pools where the main food source is detritus
from annual leaf fall.
Habitat variables are strong drivers of invertebrate life histories in vernal pools
and may be especially important for rare species. Every species must deal with pool
drying and the between-year variability in timing of pool filling and total pool
duration. Some species, especially molluscs, are sensitive to calcium and pH and
do not occur in pools where these are low. Many pools freeze solid in winter,
precluding those species lacking freeze-tolerant life stages. Summer produces high
daily and seasonal temperature variations. Turbidity and seasonally high solute
concentrations, low dissolved oxygen, and variable pH can pose problems for some
aquatic species (Williams 1987).
L
IFE
H
ISTORY
S
TRATEGIES
OF
V
ERNAL
P
OOL
I
NVERTEBRATES
Understanding the wide range of ways that animals deal with complex environmental
conditions will contribute to an appreciation of year-to-year variations in community
composition in vernal pools. The variety of strategies also illustrates how changes
in habitat associated with development or other human activities can have a range
of effects, depending on the species involved and the habitat characteristics that are
altered.
Because hydrology is ephemeral, or least highly variable (see Chapter 3, Lei-
bowitz and Brooks), vernal pool invertebrates need to start their lives quickly and
complete the aquatic portions of their life cycles rapidly (Williams 1987). Such
conditions select for two general life history strategies: (1) “early colonization,” so
that animals can move into new sites wherever conditions are favorable, and (2)
“drying response,” i.e., an ability to avoid, resist, or tolerate pool drying (Wiggins
et al. 1980; Williams 1996, 1997).
Many animals are permanent residents that remain in the pool sediments and
become active as soon as water appears and when other conditions (e.g., temperature)
are suitable. Some, including mollusks such as the fingernail clam (
Sphaerium
occidentale
)
,
burrow into the mud and become dormant as juveniles or adults. Others
hatch from desiccation-resistant eggs that can lie in the sediment for months and,
in some cases, up to decades, serving as what is known as an “egg bank” (e.g., many
crustaceans, including the common fairy shrimps
Eubranchipus neglectus
in the
Midwest,
E. vernalis
in the East, and
E. bundyi
in the North).
Dormancy that begins only when pools start to dry allows some permanent
residents, such as the water flea (
Daphnia pulex
)
or the pond snail
Fossaria
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Diversity and Ecology of Vernal Pool Invertebrates
109
modicella
,
to grow and reproduce as long as water is present. Other species have an
obligatory dormant period. Rapid growth and early transformation to adults is seen
in many pool inhabitants. The lives of some pool insects include a mixture of short
aquatic phases, drought-resistant terrestrial adults, and eggs that resist drying for a
few months (e.g., the mosquito
Ochlerotatus
[formerly
Aedes
]
excrucians
and the
“log-cabin caddisfly,”
Limnephilus indivisus
) (see Chapter 6 and Chapter 9 in Col-
burn 2004).
Like amphibians, many mobile aquatic insects are migrants that use vernal pools
only seasonally. Mosquitoes in the genus
Culex
overwinter as terrestrial adults and
migrate to flooded pools in spring to lay their eggs. Water boatmen, backswimmers,
and some predaceous diving beetles migrate between permanent waters where they
overwinter and vernal pools where they feed and, in many cases, breed. The larvae
of some water mites are parasitic on some of these migrants; they avoid seasonal
drying and are dispersed to new pools as their hosts fly first to permanent waters
and then to vernal pools in spring and summer.
Life history strategies of animals in vernal pools respond to local habitat vari-
ability. For instance, some fairy shrimps’ eggs are deposited at a depth level that
maximizes the chance that when the eggs are flooded, enough water will be present
to let the life cycle be completed before the pool dries. Eggs of many species hatch
only when certain cues are present (e.g., average temperature, daylight, osmotic
shock, and fill level) (Brendonck 1996, Dodson and Frey 2001). Because such cues
are sometimes unreliable, most species with egg banks have a “bet-hedging” strategy:
only some eggs hatch at any filling in case the pool dries before the life cycle can
be completed (Fryer 1996, Simovich and Hathaway 1997, Ripley et al. 2004). As
with the long lives and multiple breeding opportunities of amphibians, these strat-
egies let invertebrates adapt to a range of conditions and contribute to the unique
and variable communities in vernal pools.
D
ISPERSAL
Vernal pools are isolated from permanent water bodies, yet, once flooded, they are
rapidly populated by a variety of aquatic invertebrates. How do these animals
colonize the pools? In existing pools, we have seen that many species survive
drawdown via eggs or drought-resistant larvae and hatch or become active upon
flooding. In contrast, species without stages that can withstand drying or freezing
in the sediment colonize vernal pools each year.
In new vernal pools, the sediment lacks an egg bank and other dormant stages.
Readily dispersed migratory species, such as flying insects, are the earliest coloniz-
ers, finding newly formed and freshly flooded pools in as little as 24 h (Grensted
1939, Williams 1987). Most of the species that, once established, can persist by
remaining dormant in the sediment during drawdown tend to be less mobile and are
dispersed by wind or water, or carried by larger animals (e.g., fingernail clams and
crustacean eggs carried by birds, fairy-shrimp eggs transported by crayfish, and
leeches dispersed by turtles) (see Chapter 9, Mitchell et al., and Chapter 6 in Colburn
2004). They arrive more slowly; the rate depending primarily on the distance to the
nearest source pool (Maguire 1963). Constructed vernal pools, detention basins, and
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Science and Conservation of Vernal Pools in Northeastern North America
other impoundments are often colonized in this way. These dispersal mechanisms
also regulate recolonization of pools after local populations have been eliminated
due to unfavorable hydrology, predation, or other causes (Chapter 3, Leibowitz and
Brooks). For these reasons and more, it is important to maintain a mosaic of pools
well distributed in the landscape.
BASICS OF INVERTEBRATE COMMUNITY ECOLOGY
Invertebrates represent most of the animal species, numbers, and biomass in land,
sea, and freshwater ecosystems, including vernal pools, and their ecological impor-
tance is proportional to their numbers (Strayer 2006). They play three major roles
in vernal pools: (1) helping to cycle algae and dead plant material into animal life,
(2) controlling the populations of other animals by competition and predation, and
(3) serving as prey for other animals (Figure 6.2).
The aquatic communities of vernal pools can be relatively complex, with many
kinds of animals that exhibit a broad range of ecological interactions and collectively
occupy a range of trophic levels within pool food webs (Williams 1987, 1997)
(Figure 6.2). Some species eat plants and algae. Most taxa — worms, ostracodes,
caddisflies, midges, and mollusks on the pool bottom, and filter-feeding crustaceans
and insects in the water — feed on detritus, making large amounts of nourishing
food available to the rest of the community (detritus, mainly in the form of leaves
from the surrounding forest, constitutes more than 50% of the energy input into
vernal pools) (Barlöcher et al. 1978). Others are predators and parasites (see Chapter
13 in Colburn 2004).
Competition and predation strongly structure pool communities. Competition
can occur between dramatically divergent taxa. Snails compete with American toad
(
Bufo americanus
) tadpoles for algae in streamside pools in Kentucky (Holomuzki
and Hemphill 1996). In Europe, cooccurring mosquito larvae and toad tadpoles
negatively affect one another (Blaustein and Margalit 1994). Unquestionably, hun-
dreds of interactions occur among members of the aquatic communities in north-
eastern vernal pools. Equally important are the effects of intraspecific competition
on invertebrate growth, reproduction and survival. For example, high intraspecific
densities reduce growth in parasitic water mite larvae and clam shrimp and decrease
survival in temporary-pool mosquitoes (Lanciani 1976, Gleiser et al. 2000, Weeks
and Bernhardt 2004).
Predators such as dragonfly nymphs, diving-beetle larvae, flatworms, and sala-
mander larvae can dramatically affect invertebrate species’ abundances and the
composition of the entire community (Blaustein et al. 1996, Brendonck et al. 2002,
Eitam et al. 2002). Interactions between amphibians and invertebrates, with inver-
tebrates serving as prey in some cases, and as predators in others, are a common
and necessary component of normal functioning in vernal pool ecosystems. For
instance, egg predation by leeches (Cory and Manion 1953) and giant tube, case-
making caddisfly larvae (
Ptilostomis
and
Banksiola
spp.) can influence the hatching
success of wood frogs (
Rana sylvatica
) and spotted salamanders (
Ambystoma mac-
ulatum
); predation by dragonfly nymphs affects the survival of toads, chorus frogs
(
Pseudacris
spp), and salamanders, whereas amphibian larvae consume a wide array
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Diversity and Ecology of Vernal Pool Invertebrates
111
FIGURE 6.2
A generalized vernal-pool food web. Herbivorous grazer/scrapers and filter-
feeders feed on algae and living plants; microbes decompose and detritivores consume dead
plant and animal materials; and predators and parasites feed on the living animals that are
sustained by the rich plant-derived diet of the pool bottom and water column. (From Colburn,
E.A. [2004].
Vernal Pools: Natural History and Conservation
. McDonald and Woodward
Publishing Company, Blacksburg, VA. With permission.)
3675_C006.fm Page 111 Monday, February 12, 2007 11:45 AM
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Science and Conservation of Vernal Pools in Northeastern North America
of invertebrate prey (Brockelman 1969, Smith 1983, Stout and Stout 1992, Rowe et
al. 1994). In other parts of the world, introduced fish or dragonfly nymphs have
disrupted food webs and threatened native species by altering predator–prey rela-
tionships in pools (Courtenay and Meffe 1989).
COMMON INVERTEBRATES OF VERNAL POOLS
L
ARGE
C
RUSTACEANS
Six major groups of large crustaceans occupy vernal pools in the northeastern United
States and Canada. Typical — and indicative — of temporary waters are fairy shrimp,
clam shrimp, and tadpole shrimp (Table 6.1). All are found in temporary waters
worldwide, all have similar life-history strategies that include production of resting
eggs that lie in the egg bank and hatch upon flooding at a later time, and all “hedge
their bets” through staggered hatching (see above). Isopods, amphipods (Color
Figure XX), and crayfish occur in a variety of aquatic habitats and are not discussed
here.
Fairy Shrimp
(
Order: Anostraca)
Among the general public interested in natural history, fairy shrimp are probably
the best known of the invertebrates unique to vernal pools. In our region, the common
species are in the genus
Eubranchipus
. The eggs typically require cold-conditioning
and drying before they will hatch. Once flooded, eggs typically hatch in 1–14 d,
depending on temperature. Animals are sexually mature in as few as 2–4 weeks,
although maturation can be delayed by colder water temperatures. Fairy shrimp can
be recognized by their large size — up to 2 cm (0.8 in.) — and orientation during
swimming: they swim “upside down,” with their numerous, feathery, plate-like
appendages aimed upwards (Color Figure XX). Males are recognized by the enlarged
second antennae (“claspers”) that are used to grasp females during mating. Females
have a clear “brood pouch” in which eggs are held for fertilization and often a bright
blue patch near this pouch. Both sexes are typically clear or white but can take on
various colors, including blue, red, and orange.
These interesting crustaceans are primarily filter feeders that consume algae,
zooplankton, and even bacteria (Dodson and Frey 2001). They tend to swim up in
the water column but will hide in the leaf litter when disturbed. Males actively search
for mates and thus are often more conspicuous than females. Because of their
inability to avoid fish predators, fairy shrimp are found exclusively in fishless ponds.
Also, because eggs require a period of drying, fairy shrimp are not common in
semipermanent pools with little fluctuation in water depths. Several species are rare
or endangered in our region.
Clam Shrimp (Orders: Laevicaudata, Brevicaudata, and Spinicaudata)
In vernal pools, different species of clam shrimp can be found primarily from
early May to mid- September. Many species have restricted distributions and are
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Diversity and Ecology of Vernal Pool Invertebrates
113
considered rare. The bivalved carapace of clam shrimp is either spherical or oval
and can be clear to dark brown. Because they look much like small (4–20 mm)
clams, they are often misidentified as freshwater bivalves. Some species are easy to
overlook, as they tend to be on pool bottoms, where they scavenge among the leaf
litter, or are actually slightly buried in the sediment.
Lynceus brachyurus,
a broadly
distributed species in vernal pools with an adult diameter of 5 mm, is a filter feeder
that swims in the water column. Clam shrimp usually develop faster and have shorter
lives than fairy shrimp. Populations either comprise males and females, all females,
or males and hermaphrodites (Sassaman 1995).
TABLE 6.1
Large Branchiopod Species of Vernal Pools, Including Seasonal
Information
Genus Species Season Location
a
A. Fairy shrimp
Branchinecta paludosa
Su AB, LB, NS, QB
Eubranchipus bundyi
W, Sp IL, IN, MA, MI, MN, NH, NY, OH, VT,
WI, AB, ON, QB
intricatus
W, Sp MA, ME, AB
ornatus
W, Sp MN, WI, AB
holmanii
W, Sp CT, IL, MN, NJ, NY, OH
neglectus
W, Sp IL, IN, MI, OH, ON
vernalis
W, Sp CT, MA, ME, NJ, NY, PA, RI
serratus
W, Sp IL, IN, OH, WI
Streptocephalus sealii
W, Sp, Su IL, MN, NJ, NY, AB
B. Clam shrimp
Lynceus brachyurus
Sp, Su MA, IL, IN, MI, NH, OH, RI, AB, ON
Cyzicus mexicanus
Su IL, OH, AB
Caenestheriella gynecia
Su MA, OH, PA
Limnadia lenticularis
Su MA
Eulimnadia diversa
1
Su IL, IN, MI, OH
agassizii
2
Su CT, MA
C. Tadpole shrimp
Lepidurus cousii W, Sp MN
Note:
W= winter form; Sp = spring form; Su = summer form) and geographic location (by
U.S. state/Canadian province within the glaciated Northeast.
a
Location codes for (1) U.S. states: CT = Connecticut, IL = Illinois, IN = Indiana, MA =
Massachusetts, MI = Michigan, MN = Minnesota, NH = New Hampshire, NJ = New Jersey,
NY = New York, OH = Ohio, PA = Pennsylvania, RI = Rhode Island, VT = Vermont, WI =
Wisconsin; (2) Canadian provinces: AB = Alberta, LB = Labrador, NS = Nova Scotia, ON =
Ontario, QB = Quebec.
1
Includes
E. thomsoni
and
E. inflecta
.
2
Includes
E. stoningtonensis.
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Science and Conservation of Vernal Pools in Northeastern North America
Tadpole Shrimp
(Order: Notostraca)
In our study area, tadpole shrimp have been described only from Minnesota, where
Lepidurus cousii
can be found rooting around pool bottoms (Rogers 2001, D. Batzer,
personal communication). They are omnivorous scavengers and opportunistic or
facultative predators (Weeks 1990). Superficially resembling amphibian tadpoles or
miniature horseshoe crabs, these “living fossils” are generally the largest branchio-
pods in vernal pools where they occur, reaching lengths of 4 cm.
S
MALL
C
RUSTACEANS
Some of the most diverse vernal pool inhabitants are small crustaceans in the classes
Ostracoda (seed shrimp) and Copepoda (copepods), and the Order Anomola (cla-
docerans, or water fleas) (for details and species lists, see Colburn 2004) (Color
Figure XX). All 3 groups are found worldwide. Most are filter feeders and detriti-
vores, but they include a broad diversity of ecological types. All are important prey
for other animals in vernal pools, and all contribute desiccation-resistant eggs to the
egg bank. Many species are undescribed (King et al. 1996).
Ostracodes (Order: Podocopida)
Ostracodes are small, bivalved, benthic crustaceans with a spherical, ovoid, or
elongate-cylindrical shape. They look much like white, brown, green, or purple
sesame seeds, reaching ~2 mm in length in our region. Ostracodes are the oldest
microcrustaceans known (Delorme 2001) with at least 29 species associated with
vernal pools, where they are scavengers, herbivores, and detritivores in the sediment.
Copepods (Class:Copepoda)
Copepods constitute the most diverse group of the microcrustaceans, with over
10,000 described species (Williamson and Reid 2001). At least 16 species are found
in vernal pools. Copepods are cylindrical to tear-drop-shaped, with a long, bifurcated
tail with several setae, and with two antennae used in some species for rapid
swimming (Plate xx). They can be planktonic or benthic and include filter feeders,
omnivores, and carnivores. Some diaptomid copepods reach several millimeters in
length, are bright blue, and are readily visible as they swim upside-down in the
water column in early spring.
Water Fleas (Order: Anomola)
Water fleas, or cladocerans, are small (generally <5 mm), planktonic or benthic
microcrustaceans (Color Figure XX). At least 17 species have been reported from
vernal pools. Most are filter feeders, using their plate-like appendages to create
currents within their bivalved carapaces from which they filter out small food
particles. Ironically, when food becomes superabundant, water fleas can starve
because the energy required to clean their filtration apparatus is greater than their
food intake (Dodson and Frey 2001). Cladocerans are clear to a yellowish color and
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Diversity and Ecology of Vernal Pool Invertebrates
115
swim in jerky, small jumps. They either brood live young under their carapace or
produce desiccation-resistant eggs (ephippia) that will lie dormant in the egg bank
until conditions are favorable for hatching. Many of these crustaceans reproduce via
“cyclic parthenogenesis,” wherein all-female populations reproduce asexually for
most of their lives, and then produce males and reproduce sexually (producing the
ephippia) as the pond is finally drying up.
Daphnia pulex
, commonly studied in
biology courses, is widely distributed and abundant in vernal pools.
Flatworms and oligochaetes:
Vernal pools support a wide variety of worms from
several phyla, including Platyhelminthes (flatworms), Annelida (leeches and earth-
worm-like segmented worms), Nematoda (roundworms), and Nematomorpha (horse-
hair worms). Worms play key roles in vernal pools as predators, scavengers, and
detritovores (for more information on worms in vernal pools, see Colburn 2004).
Free-Living Flatworms (Class: Turbellaria)
Related to the
Planaria
that most people see in biology classes, but usually without
the distinctive triangular head, the dozen or so species of vernal-pool flatworms are
small (mostly < 5 mm long and 1–2 mm wide), flattened, drably colored (coming
in grays, light browns, pale pinks and, in one species, bright lime green), and slow-
moving; they tend to remain hidden under leaves on the pool bottom (Color Figure
XX). They are permanent residents that survive pool drying by fragmenting into a
series of small pieces that become hardened and resist drying until the pool refloods
and water temperatures are low. Flatworms are cold-water specialists. Best observed
in vernal pools in winter or early spring, they are important predators and scavengers
(Kenk 1949, Wiggins et al. 1980, Ball et al. 1981).
Oligochaetes (Class: Oligochaeta)
Oligochaetes in vernal pools look like small, freshwater earthworms. As on land,
they are key to energy cycling: they ingest sediment, absorb nutrients, and produce
castings that are then colonized by microbial decomposers and grazed by other
animals, including amphibian tadpoles. They are found in the decomposing leaves
on the pool bottom, and in late summer or fall they are among the most abundant
animals living in the wet pool substrate. To survive pool drying, these worms
fragment into cysts, encase themselves in a coat of protective mucus, or deposit eggs
in desiccation-resistant cocoons (Kenk 1949, Wiggins et al. 1980).
M
OLLUSKS
Air-breathing snails and fingernail clams (also known as pill clams) are common in
many vernal pools. Their shells on a dry pool bottom indicate the seasonal presence
of water there.
Snails (Class Gastropoda, Order Basomatophora)
Gilled snails with opercula that close off the shell do not occur in vernal pools; all
of the snails in pools are pulmonates, or air-breathers. Most of the 19 species reported
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116 Science and Conservation of Vernal Pools in Northeastern North America
from vernal pools occur widely in floodplains and other kinds of wetlands, but the
common stagnicola (Stagnicola elodes), the polished tadpole snail (Aplexa elongata),
and the toothed planorbid (Planorbula armigera) are especially characteristic of
vernal pools (see Chapter 7 in Colburn 2004).
Snails often hang upside-down from the water’s surface, taking air into the
mantle cavity, from which they absorb oxygen into their blood. Most are grazers,
feeding on algae, aquatic plants, dead plant and animal matter, and small organic
particles on the water’s surface and pool bottom. However, the common stagnicola
is a predator, feeding on mosquito larvae and other prey. Snails are preyed upon by
a variety of invertebrates and vertebrates and are hosts for parasitic flukes —
including species that parasitize amphibians — and sciomyzid fly larvae.
When vernal pools dry, most snails aestivate by secreting a mucus membrane
across their shell opening and burrowing into the sediment, where relative humidity
remains high. Some species only resist drying as juveniles, whereas others can do
so as adults. Most snails can grow for as long as water is available. High reproductive
output and continuous growth help compensate for naturally high juvenile mortality
in these seasonally drying habitats. When pools flood, animals emerge from the
mud, feed, grow, mature, mate (they are hermaphroditic and can mate with any other
individual), and lay eggs. They may produce several broods during a single season.
Young snails hatch directly and start at once to feed and grow. The cycle continues
until pool drying.
Fingernail Clams (Class: Bivalvia)
Fingernail clams are so-called because their adult size is about that of a human
fingernail. They are highly efficient filter-feeders (McMahon and Bogan 2001) and,
unlike freshwater mussels which have a mobile aquatic larva, they bear live young
that are released as miniature replicas of their parents. Four of the 5 common species
occur in a wide range of habitats, but Herrington’s fingernail clam (Sphaerium
occidentale) is a vernal-pool specialist.
Like snails, fingernail clams survive pool drying by remaining dormant in the
pool sediment. Broadly distributed, species of Musculium and Sphaerium can resist
drying only as newly hatched juveniles. They emerge in spring-filling pools as waters
start to warm, feeding and growing until ready to reproduce, and releasing young
that immediately enter summer diapause. Mature individuals continue to feed and
produce young until pool drying, when they die. In fall-filling pools, young may
emerge from diapause and grow until temperatures become cold, resuming growth
in spring. In contrast, the vernal pool-specialist Herrington’s fingernail clam tolerates
drying in all life stages and thus can feed and grow continuously from hatching until
pool drying. It produces more young than other fingernail clams found in vernal
pools and lives for 3 years, as opposed to a 1-year lifespan for most other species,
and thus can compensate for high juvenile mortality and a short growing season in
short-hydroperiod pools (Heard 1977; Mackie 1979; McKee and Mackie 1980,
1981).
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Diversity and Ecology of Vernal Pool Invertebrates 117
AQUATIC INSECTS
Hundreds of species of aquatic insects occur in vernal pools, including members of
the orders Trichoptera (caddisflies), Coleoptera (water beetles), Odonata (dragonflies
and damselflies), Hemiptera (water bugs), and Diptera (true flies, including midges,
crane flies, and horseflies). Each common order contains multiple genera and species.
Some may be widely distributed in vernal pools, whereas others are quite localized.
Ephemeroptera (mayflies) (Color Figure XX), Plecoptera (stoneflies), and Mega-
loptera (alderflies) are relatively uncommon in vernal pools and will not be addressed
here. Of all the insects found in vernal pools, mosquitoes (Order Diptera, Family
Culicidae) have the greatest potential influence on the conservation of vernal pools
due to their links to public health and strong public and governmental sentiment in
favor of destroying breeding habitats.
Caddisflies (Order: Trichoptera)
Caddisflies are aquatic as larvae and pupae. Many are easily recognized by the cases
or retreats they construct with silk and either pebbles, sticks, or leaves (). The cases
(Color Figure XX) represent an important adaptation for life in nonflowing waters
such as ponds and wetlands, allowing the larvae to create water currents that increase
oxygen flow (Wiggins 1996). The larvae have three pairs of legs; elongate, cylindrical
bodies; soft, thin-skinned abdomens; a thickened head; and a hardened plate on the
first thoracic segment. A pair of prolegs, each with a claw-like hook, is found at the
end of the abdomen. Like moths and butterflies, adults hold their wings together
above the body when at rest. Caddisfly larvae are highly diverse in their feeding
strategies and include shredder-detritivores, shredder-herbivores, collector-gatherers,
collector-filterers, scrapers, and engulfer-predators. The most common caddisflies
in vernal pools have adults that diapause during hot, dry periods, later emerging to
produce eggs that resist drying on the pool bottom until flooded. Larvae are found
in vernal pools around 1–3 d after flooding, and adults emerge in late spring/early
summer, depending on the species (Wiggins 1973). The empty cases on the dry
bottom provide evidence during drawdown of a pool’s existence.
Aquatic Beetles (Order: Coleoptera)
The water beetles are in the largest order of insects and can be found in just about
any vernal pool sampled. They include species of whirligig beetles that swim on the
surface, predaceous diving beetles (some with fierce larvae known as “water tigers”),
water scavenger beetles, crawling water beetles, minute moss beetles, snout beetles,
and others. They comprise shredder-herbivores, collector-gatherers, collector-filter-
ers, scrapers, and engulfer-predators. Water beetles are aquatic as larvae and adults
but pupate on land. The larvae have three pairs of legs; thick, hardened skin on their
head; and, often, large pincer-like mandibles. In adults, the front wings are modified
into hard plates or “elytra” that cover the hind wings and abdomen.
Some adults diapause in the substrate when pools dry. Others are migrants and
arrive in vernal pools anywhere from just a few days after pond filling to several
weeks later, and they may remain present until drawdown (Williams 1987). A few
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118 Science and Conservation of Vernal Pools in Northeastern North America
water beetles have diapausing eggs, but most species’ larvae appear after eggs are
laid in the water by resident adults or by adults dispersing into the vernal pool to
breed (Wiggins et al. 1980). Beetles show some of the greatest overall biodiversity
in vernal pools, and their distributions may vary with forest composition and other
local factors. Some species are restricted to vernal pool habitats, and some may be
rare.
True Bugs (Order: Hemiptera)
True bugs include backswimmers, water boatmen, giant water bugs, creeping water
bugs, water striders, water scorpions, and marsh treaders. Nymphs and adults occur
in the same habitat. Nymphs look like adults with undeveloped wings. The mouth-
parts are modified into a cone or beak, and each leg has two claws. All are piercer-
predators (except for the water boatmen, most of which are collector-gatherers) that
feed on other invertebrates and on larval amphibians. Hemipterans do not undergo
egg diapause; most are migratory. Eggs are laid when adults arrive at the pools and
hatch within 1–2 weeks; nymphs grow rapidly in order to be ready to fly from the
pool before it dries (Voshell 2002).
Damselflies and Dragonflies (Order: Odonata)
Damselflies and dragonflies are aquatic only as nymphs. They are recognized by the
long lower lip (labium) that folds back against the head and is used as a powerful
pincer to capture prey. plate-like gills extending from the end of the abdomen. The
colorful adults have very long abdomens and large heads and eyes. Dragonflies hold
their wings out to the sides of their body when at rest and damselflies hold them
together, or nearly so (i.e., Lestes spp.), above the body.
All odonates are engulfer-predators. Adults of some species, such as the common
green darner (Anax junius), migrate from the south to breed in vernal pools. In
others, the females lay diapausing eggs in aquatic plants or on the pool bottom, and
the eggs remain dormant until the next pond filling (Wiggins et al. 1980, Voshell
2002). Closely related species may occur in adjacent pools with different hydrologic
regimes.
True Flies, Exclusive of Mosquitoes (Order: Diptera)
The true or two-winged flies include the mosquitoes (see below), midges, phantom
midges (see Color Figure XX), craneflies, horseflies, marsh flies, and common flies.
In water-dependent groups, larvae and pupae are aquatic, and adults are terrestrial.
Unlike other insects found in vernal pools, the larvae of true flies lack segmented
legs. The thorax and abdomen are soft and thin-skinned, and the head is either
continuous with the thorax or thick skinned and separated from the thorax. The
diversity of this group also equates to diverse distributions and ecology. Most
dipterans are collector-gatherers, but some are scrapers, shredder-detritivores, and
engulfer-predators. They can undergo long egg diapause during the dry period, and
eggs hatch just a few days after the vernal pool is hydrated (Voshell 2002).
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Diversity and Ecology of Vernal Pool Invertebrates 119
Mosquitoes (Order: Diptera)
The best known (and least loved) dipterans are the mosquitoes (family Culicidae).
About 30 species have been identified from vernal pools (see Colburn 2004). The
eggs of many species overwinter in the sediment and hatch when flooded, but Culex
females overwinter as adults and lay their eggs in spring on the water’s surface. In
early spring, mosquito larvae are present in the thousands in some vernal pools.
They eat decaying material, microorganisms, pollen, and small particles on the
surface or in the water. They are fed upon by snails, bugs, copepods, beetle larvae,
caddisflies, phantom midges, odonate nymphs, newts, and salamander larvae; fewer
than one percent of larvae survive to adulthood (Collins and Washino 1985).
Like all dipterans, the aquatic larvae are legless. They have a round head, a
swollen thorax, bristly hairs all over their bodies, and typically a tubular siphon at
the end of the abdomen through which they obtain air at the water’s surface, where
the larvae tend to congregate. When disturbed, larvae (“wrigglers”) thrash about.
After going through several molts, larvae transform into pupae (“tumblers”), which
are somewhat comma shaped, with a large swollen upper end containing the head,
upper body, a pair of horn-like breathing tubes, legs, and developing wings; the
narrow abdomen extends below. Once the body has been reorganized, the pupal skin
splits and the adult emerges. Only females bite: the blood meal provides protein that
is used to produce eggs. Depending on the species, females lay their eggs on the
water’s surface or on the damp substrate of a drawn-down pool.
In our geographic region, mosquitoes are largely nuisances that annoy humans
with their buzzing and cause discomfort but no lasting harm with their bites. How-
ever, two mosquito-borne diseases, West Nile virus (WNV) and eastern equine
encephalitis (EEE), are of public health concern and have important implications
for vernal pools. These are primarily viral diseases of birds, but they can be trans-
mitted to horses, humans, and other mammals by mosquitoes that have bitten an
infected bird. From both EEE and WNV, birds suffer the most illness and mortality.
Because EEE and WNV are transmitted by mosquitoes, there is a major focus
on controlling mosquito populations, and because mosquitoes are a substantial part
of the fauna of vernal pools, these habitats are vulnerable to mosquito control
activities. However, both EEE and WNV are transmitted to humans only if a mos-
quito first bites an infected bird. Most mosquito species found in vernal pools do
not feed on birds (and most do not feed on humans, either, although some important
pest species do breed in vernal pools). The most common mosquito transmitting
EEE is Culiseta melanura, which breeds preferentially in hardwood swamps and is
not commonly found in vernal pools. The most common vectors of WNV are Culex
spp., which similarly are not common in vernal pools. However, more than 60 species
of mosquito are known to carry WNV, and some of the common species from vernal
pools have tested positive for WNV (Center for Disease Control and Prevention
2006a, 2006b). Note that mosquito control activities usually involve altering hydrol-
ogy, introducing predators, and/or applying pesticides to breeding areas. Therefore,
diverse food webs, sensitive faunas, and long-term community viability (including
the viability of natural mosquito predators) are at risk if mosquito-control efforts
focus on vernal pools.
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120 Science and Conservation of Vernal Pools in Northeastern North America
WATER MITES
Around 50 species of water mites (Acari) are known from vernal pools, and there
are probably more. These tiny (usually < 5 mm), round, seemingly headless, 8-
legged animals; they come in reds, yellows, greens, blues, and browns, and can be
observed crawling on the substrate and swimming in the water. As larvae, they
parasitize adult aquatic insects (Figure 6.3). Some are attached to their hosts as the
latter fly around the pools seeking food or mates. These parasites can be so dense
that they affect the hosts’ ability to fly and reproduce. Once fed, the larvae drop off
of the hosts and back into the pool, where they transform into nymphs that prey on
the eggs of crustaceans or insects, or on insect larvae (especially midges and mos-
quitoes). The nymphs transform into predatory adults. Unless they migrate as par-
asitic larvae attached to hosts, water mites withstand pool drying as dormant adults
or nymphs. We recommend interested readers to additional information in Smith et
al. (2001).
SUMMARY
Aquatic macroinvertebrates make up most of the animal species and biomass in
vernal pools. Because the species that occur in short-duration pools are different
from those in pools with longer hydroperiods, and because vernal pool species differ
FIGURE 6.3 Generalized life history of water mites in vernal pools. (From Smith et al. 1997.
With permission.)
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Diversity and Ecology of Vernal Pool Invertebrates 121
from those in permanent waters, pool invertebrates contribute significantly to local
and regional biodiversity. They play key roles in the transfer of energy from leaves
and other detritus into animal biomass, serve as food for vertebrate predators (includ-
ing turtles and salamander larvae), and structure the populations of other species
(including amphibians) by predation and competition. Their life cycles are complex
and closely related to hydroperiod and other habitat variables. Some species can
grow and develop whenever conditions are favorable. For others, highly specific
cues of temperature, water level, and chemistry stimulate hatching, growth, and
maturation. The wide variety of strategies for dealing with seasonal pool drying
ranges from egg banks, in which dormant cysts remain viable for decades, to
facultative dispersal from permanent waters into flooded pools for feeding and
breeding. The protection and maintenance of a diverse habitat mosaic of vernal pools
with a range of hydroperiods and other physical conditions is key to the long-term
conservation of vernal pool invertebrate communities.
CONSERVATION IMPLICATIONS AND
RECOMMENDATIONS
Because invertebrate distributions and life cycles are closely tied to habitat variables
(such as hydrology, water quality, and both in-pool and surrounding vegetation),
activities that alter any of these variables have the potential to alter invertebrate
communities. Inadequate knowledge of the species in vernal pools and of their
interrelationships means that there is a risk of losing rare species and altering
community dynamics as pools and their watersheds are altered by human activities.
Natural year-to-year variability in weather and pool characteristics, and the high
plasticity of invertebrate life cycles, make it difficult to evaluate the effects of human
alterations, especially subtle changes over time.
Various factors threaten invertebrates in vernal pools. Direct threats include:
ditching and pesticide use for mosquito control; filling; excavation for detention
basins, fish ponds, mosquito control, and wildlife habitat enhancement; sedimenta-
tion; and chemical contamination from runoff. Less direct but potentially serious
threats include altered hydrology, water quality, and food associated with changes
in watershed land use or cover, atmospheric deposition, and climate change. Many
of these, such as pool destruction and watershed activities that alter hydrology or
water quality, affect both vertebrates and invertebrates. Alterations of forest compo-
sition, whether through forestry, clearing for development, or natural succession can
change inputs of light and leaf litter, affecting the base energy sources for pools and
the invertebrate communities therein.
Below, we comment briefly on several threats that we believe specifically affect
invertebrates in vernal pools. Additionally, best management practices for forestry
(Chapter 13, deMaynadier and Houlahan) and development (Chapter 12, Windmiller
and Calhoun), to the extent they maintain water quality, hydrology, and natural
vegetation adjacent to pools, will also benefit invertebrate conservation.
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122 Science and Conservation of Vernal Pools in Northeastern North America
POOL PROTECTION EFFORTS
A wide range of hydroperiods in temporary waters contributes to aquatic biodiversity.
In particular, although small, short-duration pools tend to support fewer species,
they also tend to support taxa that do not occur or reproduce successfully in longer-
hydroperiod pools. Conservation efforts often explicitly exclude small, short-dura-
tion pools because relatively fewer amphibian species breed in such pools compared
to longer-hydroperiod, annual and semipermanent pools, and because there has been
speculation (with little empirical evidence) that short-hydroperiod pools are sinks
in which amphibian breeding effort is wasted. This is problematic from the perspec-
tive of invertebrate biodiversity. We suggest that the full range of pool sizes and
hydroperiods needs to be protected to ensure the maintenance of regional biodiversity
and the persistence of invertebrate metapopulations.
HABITAT ENHANCEMENT AND AESTHETICS
Some efforts to enhance the value of vernal pools for amphibian populations, espe-
cially mole salamanders (Ambystoma spp), have involved dredging annual pools to
increase their hydroperiods, even to the extent of changing them to permanent or
semipermanent pools (Colburn, personal observation). Additionally, many vernal
pools are excavated by individual property owners to create “water features” in
gardens, to eliminate the unsightly appearance that many pools take on in the
summer, and/or to allow the stocking of ornamental fishes such as koi (Cyprinus
carpio) or of frogs such as bullfrogs (Rana catesbiana), which are readily available
from some garden centers. Such activities are of concern from several perspectives.
First, excavation of the substrate removes the egg bank to which many genera-
tions of permanent-resident crustaceans and other invertebrates have contributed. It
also removes insect eggs, dormant cysts of flatworms and oligochaetes, aestivating
mollusks, and a host of other species. Even if some individuals should persist, the
process would likely significantly reduce the genetic diversity of local populations,
very possibly dooming many of them to local extirpation. Some of the lost taxa may
be important food sources for the very amphibians that are the target of conservation.
Second, by increasing the hydroperiod, and especially by eliminating regular
drying, the pool is made potentially hospitable to long-lived, drought-intolerant
predators commonly excluded from seasonally drying pools, including several spe-
cies of dragonfly nymphs, backswimmers, giant water bugs, and predaceous diving
beetles. These predators are more widely distributed than many of the taxa typical
of short-duration pools and are less likely to be restricted to vernal-pool habitats.
They may exclude invertebrate taxa that originally inhabited the pool, and they may
prey on larvae of vernal pool amphibians, potentially contributing to decreased
reproductive success over time — an effect opposite to that intended.
Third, stocking of koi, bullfrogs, and other predators can devastate the native
invertebrate community. Before more pools are dredged, we believe there is a need
for: (1) long-term studies to determine the overall reproductive success of important
amphibian populations in pools of different hydroperiods, factoring in the normal
variability in flooding durations and the large natural variation in numbers of trans-
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Diversity and Ecology of Vernal Pool Invertebrates 123
forming juveniles across years; (2) comparative long-term studies of invertebrate
populations (especially predators) and amphibian reproductive success in pools in
which hydroperiods have been altered vs. those that are allowed to dry naturally;
and (3) a reassessment of management aims for wildlife reserves to determine
whether alteration of pool hydroperiods makes good conservation sense from the
perspective of both amphibian and invertebrate biodiversity.
MOSQUITO CONTROL
Ditching, draining, filling, excavation, and the application of pesticides all dramat-
ically alter vernal pool habitats and can adversely affect the entire pool community.
Individuals interested in and concerned about vernal pools and their wildlife need
to (1) educate their neighbors and public health officials about the larger ecosystem
values of vernal pools, (2) engage in public discussions of the relative risks of
infection from serious diseases, and of the nuisance aspects of mosquitoes vs. risks
to wildlife of mosquito control at individual pools, (3) help to minimize breeding
habitats (such as tires, gutters, and open containers) in which Culex spp. breed
preferentially, and (4) encourage people to use insect repellents, wear long sleeves
and pants, and avoid areas where mosquitoes congregate at dawn and dusk.
If mosquito control is absolutely critical for a specific vernal pool, the use of
the microbial larvicide Baccillus thuringiensis var. israeliensis (Bti), which kills
mosquito larvae and related flies such as midge larvae, is preferable to ditching,
excavation, introduction of fish, or the use of broader spectrum pesticides. However,
all of the affected insects are important components of the food web, and removing
them can have potentially wide-ranging, unintended ecosystem effects.
PESTICIDES AND OTHER CHEMICALS
Invertebrates are often highly sensitive to water chemistry and are good water quality
indicators (Rosenberg and Resh 1993). Very little is known about how pollutants
affect invertebrates in vernal pools (Chapter 11, Boone and Pauli). For instance, of
the hundreds of vernal pool invertebrates, only Daphnia pulex is routinely used in
bioassays of pesticide effects on “non-target” species. Thus, we cannot predict the
overall impacts of common pesticide formulations on pool fauna. Similarly, effects
of contaminants in runoff and precipitation are generally unknown.
PUBLIC EDUCATION
Aquatic invertebrates are fascinating, beautiful, and critically important components
of vernal-pool ecosystems. Their diminishment decreases overall biodiversity and
weakens the web of life connecting forests, waters, and humans. The loss of upland
woods, associated vernal pools, and aquatic biodiversity, is ongoing. To counter it,
public awareness and appreciation of vernal pools and their biota must be greatly
enhanced, and substantial areas of intact landscape must be acquired and conserved.
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124 Science and Conservation of Vernal Pools in Northeastern North America
ACKNOWLEDGMENTS
We thank M. Simovich, D. Batzer, A. Calhoun, B. Swartz, P. deMaynadier, and an
anonymous reviewer for helpful feedback on earlier drafts of this chapter, and I. M.
Smith, J. Semroc, and J. McDonald for permission to use illustrations, and J. Cossey
for assistance in production of Color Figure XX.
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in text.
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COLOR FIGURE 1
A comparison of commonly available aerial photographs for one locality
in Massachusetts. (a) Color infra-red (CIR) film; (b) true-color digital orthophoto; and (c)
black and white film emulsions. Scale is approximately 1:12,000.
a
b
c
3675_Color Insert.fm Page 9 Tuesday, February 13, 2007 11:52 AM
COLOR FIGURE 2
Color infrared digital ortho quarter quadrangle (DOQQ) with National
Wetland Inventory polygons (a) and USGS topographic map (b) for a selected southern New
Jersey coastal plain vernal pool complex. Blue arrow indicates a vernal pool that is part of a
palustrine forested wetland (PFO1); orange arrow indicates a vernal pool in an upland setting.
a
b
3675_Color Insert.fm Page 10 Tuesday, February 13, 2007 11:52 AM
COLOR FIGURE 3
True-color aerial photograph showing a site in Massachusetts where
intensive ground-truthing using calling and transect surveys identified significant errors of
omission. Photo-interpreted potential vernal pool data are in red (N = 11), field-verified pools
in yellow (N = 34). Omission errors were created by low topographic relief that limited cues
to basin presence, conifer stands that created shadow and obstructed views of the ground and
water surfaces, small pool size, and pools in atypical basins (e.g., stream backwater areas and
diffuse marsh habitat).
COLOR FIGURE 4
Computer screen shot of New Jersey’s interactive map server showing
CIR digital orthophotography and mapped potential vernal pools (in yellow), verified vernal
pools (in blue), and certified vernal pools (in green) for a selected kettlehole vernal pool
complex in northern New Jersey. (http://www.dbcrssa.rutgers.edu/ims/vernal/viewer.htm)
3675_Color Insert.fm Page 11 Tuesday, February 13, 2007 11:52 AM
COLOR FIGURE 5
A “classic” vernal pool in an upland depression. This vernal pool setting
is easily recognized by lay people in the spring but can be difficult for the untrained eye to
discern in late summer when it may be dry. This northern New England pool is surrounded
by softwood forest; pools in similar geomorphic settings in southern New England often occur
in hardwood forests (top). (Photo: Aram Calhoun.)
COLOR FIGURE 6
Vernal pools often are embedded in forested wetlands. This pool is part
of an extensive red maple (
Acer rubrum
) forested wetland. It is not uncommon for pools in
northern New England and Atlantic Canada to occur in forested wetlands including spruce-
fir flats (bottom). (Photo: Robert Bryan.)
3675_Color Insert.fm Page 12 Tuesday, February 13, 2007 11:52 AM
COLOR FIGURE 7
Vernal pools located in floodplain forests may provide foraging and
resting habitat for reptiles of conservation concern in the Northeast including ribbon snakes
(
Thamnophis sauritus
) and wood turtles (
Glyptemys insculpta
). Intermittent spring flooding
may introduce fish, but this is a temporary phenomenon. (Photo: Phillip deMaynadier.)
COLOR FIGURE 8
Vernal pools may occur in all freshwater wetland classes. This shrub-
dominated pool carpeted with sphagnum (
Sphagnum
spp.) provides ideal breeding habitat for
the rare ringed boghaunter dragonfly (
Williamsonia lintneri
). Winterberry (
Ilex verticillata
),
speckled alder (
Alnus incana
), highbush blueberry (
Vaccinium corymbosum
), and buttonbush
(
Cephalanthus occidentalis
) are common vernal pool shrubs in these systems. (Photo: Phillip
deMaynadier.)
3675_Color Insert.fm Page 13 Tuesday, February 13, 2007 11:52 AM
COLOR FIGURE 9
Emergent vegetation including sedges, rushes, and grasses may domi-
nate larger pools with open canopies such as this pool in coastal New England. The persistent
vegetation in these pools provides egg-attachment sites for wood frogs (
Rana sylvatica
) and
ambystomatid (
Ambystoma
spp.) salamanders in the spring. (Photo: Megan Gahl.)
COLOR FIGURE 10
Following a brief appearance in breeding pools in the spring, spotted
salamanders (
Ambystoma maculatum
) spend most of their adult life in the surrounding upland
forest where they find refuge under logs, leaf litter, and inside small mammal burrows. (Photo:
Damon Oscarson.)
3675_Color Insert.fm Page 14 Tuesday, February 13, 2007 11:52 AM
COLOR FIGURE 11
Quacking choruses of wood frogs (
Rana sylvatica
) signal the beginning
of the vernal pool breeding season in the Northeast. This amplexed couple will deposit a
fertilized egg mass (often containing up to 1000 eggs) close to other wood frog egg masses
thereby providing potential protection from predation. (Photo: Tracy Rittenhause.)
COLOR FIGURE 12
Throughout much of the Northeast, polyploid hybrids (animals with
more than two sets of chromosomes) of Jefferson salamander (
Ambystoma jeffersonianum
)
and blue-spotted salamanders (
A. laterale
) are more common than either parental species.
Intermediate in morphology between the two parent species, distinguishing hybrids can be
challenging without the aid of genetic analysis. Generally, blue-spotted salamanders, or
animals with a predominance of blue-spotted chromosomes (L), are smaller and have more
distinct blue flecking than Jefferson salamanders, or animals with a predominance of Jefferson
chromosomes (J). (James P. Bogart/Michael W. Klemens, WCS).
AU: Cred-
ited for
what?
Photo?
3675_Color Insert.fm Page 15 Tuesday, February 13, 2007 11:52 AM
COLOR FIGURE 13
Among the rarest and most mysterious members of our pool-breeding
fauna is the eastern spadefoot Toad (
Scaphiopus holbrooki
). Their namesake is a hard,
crescent-shaped tubercle on the hind foot that permits them to dig vertically, disappearing
beneath sandy soils in a matter of seconds. Spadefoots can remain underground for weeks or
months at a time, only emerging to breed after heavy spring and summer downpours. (Color
figure: Brandon Ruhe.)
COLOR FIGURE 14
The last amphibian to breed in our region’s vernal pools is the marbled
salamander (
Ambystoma opacum
). Following late summer or fall courtship in the upland area
surrounding a vernal pool, females lay up to 200 eggs in a small depression at the bottom of
a dry basin. The adult female often stays with her eggs, offering protection from predation
and desiccation, until fall rains inundate the pool basin and nest chamber. (Photo: Patrick
Zephyr.)
3675_Color Insert.fm Page 16 Tuesday, February 13, 2007 11:52 AM
COLOR FIGURE 15
Wood frogs (
Rana sylvatica
) are among a small number of northern
amphibians capable of producing high levels of glucose in the liver, which functions as an
antifreeze compound. Freeze resistance is an important adaptation for a species that overwin-
ters above ground (under leaf litter or in shallow burrows), in proximity to their spring breeding
pools, and whose distribution extends as far north as the Arctic Circle. (Photo: Megan Gahl.)
COLOR FIGURE 16
Colorful and charismatic, spotted turtles (
Clemmys guttata
) are closely
associated with vernal pools in the Northeast where they spend considerable amounts of time
foraging, searching for mates and, in deeper, persistent pools, overwintering. (Photo: Phillip
deMaynadier.)
3675_Color Insert.fm Page 17 Tuesday, February 13, 2007 11:52 AM
COLOR FIGURE 17
Fond of tadpoles and frogs and adept at swimming, ribbon snakes
(
Thamnophis s. sauritus
) are one of the most commonly encountered snakes at vernal pools
in our region. Care is needed to distinguish this species from the easily confused eastern
garter snake (
Thamnophis s. sirtalis
), which is also commonly found foraging and basking
along the edges of vernal pools. (Photo: Will Brown/Blue Ridge Biological.)
COLOR FIGURE 18
Blanding’s turtles (
Emydoidea blandingii
) are recognizable by their
highly domed shell and bright yellow throat. Among the factors challenging conservation of
this species in the Northeast is the large number of small wetlands and vernal pools individual
turtles often weave together in an activity area. Long-distance upland movements place
Blanding’s, and other vernal pool turtles, at elevated risk of road kill, predation, and illegal
collection. Photo: Phillip deMaynadier.
3675_Color Insert.fm Page 18 Tuesday, February 13, 2007 11:52 AM
COLOR FIGURE 19
Eastern garter snakes (
Thamnophis s. sirtalis
) are just one of the many
common forest predators attracted to vernal pools because of the tremendous biomass of
frogs, salamanders, and other prey species produced annually from these ecosystems. (Photo:
Chris Franklin/CELT.)
COLOR FIGURE 20
Some examples of the great variety of invertebrates commonly found
in vernal pools. From top to bottom: Left: Phantom midge larva (Uniramia, Insecta, Diptera,
Chaoboridae, Chaoborus sp.)— the shiny round air chambers allow the larvae to control their
buoyancy. Small (recently hatched) swimming mayfly nymph (Uniramia, Insecta,
Ephemeroptera, Baetidae) — although diverse in streams and ponds, only a few mayfly species
occur in vernal pools. Water flea carrying eggs (Crustacea, Branchiopoda, Anomola, Daph-
niidae) — many pool inhabitants prey on these filter feeders. Cyclopoid copepods (Crustacea,
Copepoda, Cyclopoida, Cyclopidae) — tiny but fierce predators, some species control mos-
quito populations. Right: Amphipod ("scud") (Crustacea, Malacostraca, Amphipoda, Crang-
onyctidae) on caddisfly case (Uniramia, Insecta, Trichoptera, Limnephillidae) — the tan,
round balls are fairy-shrimp eggs incorporated into the case by the caddisfly larva. Flatworm
(Platyhelminthes, Turbellaria, Tricladida) — these cryptic animals are important cold-water
predators. Female fairy shrimp (Crustacea, Branchiopoda, Anostraca, Chirocephalidae,
Eubranchipus sp.) — species identification requires examination of male antennae. All are at
approximately the same scale. (Photos (c) Judy M. Semroc. Used by permission.)
1 mm
AU: Please
read this
caption care-
fully as it was
embedded in
the original
file and thus
had to be
input.
3675_Color Insert.fm Page 19 Tuesday, February 13, 2007 11:52 AM
COLOR FIGURE 21
Amphibian schematic. Following a brief period of breeding in vernal pools,
adult salamanders and frogs migrate significant distances into the surrounding forest where they
remain largely unseen and unheard for most of the year. Emerging metamorphs disperse into the
same forest habitat later in the season, generally in mid- to late summer and fall. The values
reported below each species contour line are mean and maximum distances (in meters) reported
from the literature for relatively better-studied pool-breeding taxa of northeastern North America.
The number of contributing studies for each estimate is given in parentheses. Readers are referred
to Chapter 7, Table 7.2 (Semlitsch and Skelly), for a comprehensive summary of migration distances
for pool-breeding amphibian specialists of the Northeast. (Drawing by Matt Burne and Phillip
deMaynadier.)
COLOR FIGURE 22
Forestry management schematic. An example of ecologically sensitive
forest management around a vernal pool located in a mature mixed forest. Implementation of the
vernal pool Habitat Management Guidelines (HMGs; Chapter 13, deMaynadier and Houlahan)
requires decreasing timber harvest intensity with increasing proximity to high value pools with
breeding indicator species. HMG zones are drawn to scale. (Drawing by Mark McCollough. From
Calhoun and deMaynadier 2004 . With permission from the Metropolitan Conservation Alliance.)
3675_Color Insert.fm Page 20 Tuesday, February 13, 2007 11:52 AM