Macroinvertebrates vary widely in the amount of time and the times of year in which they need to spend in the flooded pools to complete their development.  In her book Vernal Pools, Dr. Elizabeth Colburn outlines a system of categorizing aquatic macroinvertebrates based on their life histories.  The macroinvertebrates in a vernal pool may be categorized into two major life history groups which relates to when they occur in the pools--migrants and permanent residents.  (Colburn, 2004)

Migrant Macroinvertebrates:  Migrant macroinvertebrates may either be breeders or nonbreeders that leave when the pool dries up. 

Migratory breeders include limnephilid caddisflies, predaceous diving beetles, backswimmers, and water boatmen.  Among the migratory breeders, there are three types, early spring migrants, spring-summer migrants, and fall migrants. 

Non-breeding migrants include a variety of predaceous diving beetles.  Feeding in the vernal pools may represent an important phase of the life cycle and contribute to egg development and growth in non-breeding migrants. 

Permanent Residents: Permanent residents consist of either aestivators or drying-resistant eggs. 

Aestivators are species that spend hot or dry periods in a state of dormancy.  They have a higher tolerance to drying and a reduced metabolic rate during aestivation.  These species resume feeding and other activities upon flooding in the spring or fall.  Some types of macroinvertebrate aestivators include Hyroporus beetles, fingernail clams, pulmonate snails, rotifers, tardigrades, and nematodes. 

Drying-resistant eggs and cysts may hatch immediately upon flooding or show delayed development.  This group includes flatworms, fairy shrimp, some mosquitoes, and some beetles.  Many of these species are thermally cued hatchers, which rely on warmer temperatures or other cues, such as a photoperiod, to stimulate egg development and hatching.    

Non-Insect Macroinvertebrates

In Les’ vernal pool, there may be a number of macroinvertebrates which may be present.  The non-insect macroinvertebrates that may make up a vernal pool consist of hydras, sponges, flatworms, annelids, mollusks, nematodes, and  other arthropods.

Fingernail Clams are bivalves in Class Gastropoda.  Sphaerium, Musculium, and Pisidium are three generas.  Fingernail clams have gills that exchange oxygen, and they have filters for straining food, dissolved, and suspended organic material from the water.  Fingernail clams survive pool drying by burrowing into the damp sediment and aestivating.      

Fingernail Clam

Snails are in Class Gastropoda.  It has members from the families Lymnaeidae, Physidae, and Planorbidae.  Snails have a muscular foot that secretes mucus that it glides on, and its mantle functions in oxygen diffusion in its blood.  Snails are grazers, and they use radula to scrape algae, bacteria films, and fungi from substrates.

Aquatic Insects

Aquatic insects in vernal pools consist of caddisflies, water beetles, water bugs, damselflies, dragonflies, mosquitoes, phantom midges, crane flies, midges, horseflies, fishflies, mayflies, water mites, spiders, springtails, and other kinds of aquatic insects.  Some insects convert detritus into food for other pool animals, and some others are prey or predators on other invertebrates.

      Dragonflies are members of Order Odonata.  Nymphs, the immature stage of the dragonfly, is aquatic and may be found in vernal pools.  Nymphs eat other insects, including mosquitos and midges.  Gills are located in the rectum.  Nymphs have a swollen abdomen with gills in their rectum, which they breathe through by taking in water from the anus.  The insect moves by propelling itself. 

Dragonfly Larvae

 Phantom Midges are in Family Chaoboridae in Order Diptera and Suborder Nematocera.  The phantom midge is found in pools in the larvae stage.  They are transparent in color.  The larvae are predaceous and feed on zooplankton.

Phantom Midge Larvae

Aquatic Sowbugs are in Phylum Arthropoda, Class Crustacea, and in Family Isopoda.  They have 7 appendages that resemble legs.

Aquatic Sowbug

 

  Caddisflies are in three families, Limnephilidae, Phyrganeidae, and Polycentropodidae.  Many caddisfly species shred decaying leaves and other detritus.  Other caddisflies are predators that may eat mosquito larvae or amphibian eggs.  Caddisflies can either be migratory breeders that move to pools in the fall or permanent residents with desiccation-resistant life stages.  In family Limnephilinae, the eggs are deposited on moist wood and other debris on the dry pool bottom in the fall.  In family Phyrangeidae, the females lay their eggs on vegetation on the outside of water bodies or from the bottom of the pool.   Females in family Polycentropididae deposit their eggs in the water.

Caddisfly

Water Beetles consist of predaceous diving beetles, water scavenger beetles, crawling water beetles, and whirligig beetles.  Crawling water beetles crawl around in submerged vegetation and are usually not very good at swimming.  Water scavenger beetles are in Family Hydrophilidae.  The legs have hairs on them and their larvae are predaceous.  These beetles may be colored black, brown, or yellow.  Other beetles that may be found are burrowing water beetles, long-toed water beetles, marsh beetles, minute bog beetles, snout beetles, rove beetles, straight-snouted beetles, ground beetles, and leaf beetles.  Beetles have a hardened outer pair of wings, elytra, that cover the membranous inner pair for flight.  Water beetles prey upon amphibian larvae, crustaceans, and other invertebrates.  Water beetles may be permanent residents, migratory breeders, and migratory non-breeders.  Permanent residents aestivate as adults in the damp or dry sediment.  Migratory beetle species move to the pools in the spring from overwintering sites in permanent waters.  These beetles mate and lay their eggs in the pools and complete their life cycle before the pool dries.  Some migrant beetle species have a complex life history, in which there are two overwintering periods as newly emerged adults and in spring-deposited eggs, and it takes two years for their life cycle to be completed.  Non-breeding migrants do not breed in pools, but use the temporary waters as feeding areas.  (Colburn, 2004)

Crawling Water Beetle

 

Water Scavenger Beetle

Water Bugs are mostly predators that feed on crustaceans and aquatic insects.  Other species of water bugs are omnivores that eat animals and scrape algae, detritus, protozoans, and other small organisms from the surface of the water.  Water boatmen backswimmers, water striders, giant water bugs, and water scorpions may be found in vernal pools. All water bugs are migrants that overwinter in permanent waters and fly into vernal pools in the spring or early summer to feed and breed.

Water Scorpion, Water Boatman, Mayfly larva

Illustrations of the water scorpion, water boatman, mayfly larvae, and fingernail clam were done by Jamie Buckwalter.  Illustrations of caddisfly, phantom midge larvae, aquatic sowbug, dragonfly larvae, crawling water beetle, water scavenger beetle were done by Annie Davis.   

Sampling Methods

Globe Protocol,  http://www.globe.gov/tctg/sectionpdf.jsp?sectionId=687

• Sorting, Identifying and Counting Freshwater Macroinvertebrate Protocol

• Freshwater Macroinvertebrate Sampling Technique for Gravel and Sand

• Freshwater Macroinvertebrate Sampling Technique for Vegetated Banks or Around Snags, Logs, and Roots

• Freshwater Macroinvertebrate Sampling Technique for Muddy Bottom

Department of Environmental Protection State Florida protocol and US Environmental protection Agency Field and Laboratory macroinvertebrate assessment (King, 2002)

Materials—

• D-net (.5mm mesh)

• Squirt bottles

• Trowel or shovel

• Large forceps

• Small forceps

• Magnifying glasses

• Several eyedroppers (3ml with end approximately 2 mm diameter)

• Many clear plastic jars (.5 to 3L)

• 1-4 spray bottles

• 2 white trays

• .5mm or smaller sieve

• 2- 5mm sieve

• 2-6 buckets

• Small specimen bottles

• Permanent markers

• Pencils

• Latex gloves

• Macorinvertebrate id keys

• Small plastic vials

• 20mL blasting syringes (end approximately 5mm diameter)

• Sub-sampling tray

• 1m x 1m quadrat

Literature Cited

Brooks, R.T.  "Annual and Seasonal Variation and the Effects of Hydroperiod on Benthic Macroinvertebrates of season Forest ("Vernal") Ponds in Central Massachusetts, USA."  Wetlands, the journal of the society of the Wetlands Scientists, 2000, vol 20 (4), pg 707-715.

Colburn, E.A. Vernal Pools: Natural History and Conservation.  McDonald and Woodward Publishing Company, 2004. 

Fairchild, G.W., "Microhbaitat and landscape influences on aquatic beetle assemblages in a cluster of temporary and permanent ponds." Journal of the North American Benthological Society, 2006, vol 22 (2), pg 224-240.

King, R.S., and C.J. Richardson.,  "Evaluating Subsampling approaches and macroinvertebrate resolution for wetland bioassessment."  Journal of the North American Benthological Society, 2002, vol 21, pg 150-171.

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