(For questions about mosses, liverworts, and animals living in mosses, please contact Kathy Merrifield at merrifik@science.oregonstate.edu.)
Mosses are small, attractive plants that thrive in urban environments as well as natural systems. In many temperate climates, they live truly right outside our doors, perhaps even on the doorstep. Magnification even at low power enables us to look deeply into the plants and to appreciate their beauty and intricacy. Most terrestrial mosses dry during warmer, drier days and seasons, and their beauty is hidden when they are dry. When dry mosses are moistened, they expand as their cells absorb water, they become translucent rather than opaque, and they release pleasant odors often reminiscent of the forest floor. Moss rehydration and expansion may be frustratingly slow or dramatically fast.
* Many kinds of mosses thrive in western Oregon because of the influence of the Pacific Ocean. Air carrying water vapor from the ocean flows east. Rain and snow fall from the clouds that form as the air rises to drift over the Coast Range and the Cascades. The western slopes of these mountains are especially moist, but much of Oregon west of the Cascade crest is moist enough to harbor abundant moss growth.
A surprising number of moss species may grow in a relatively small area. For example, 84 moss species (and 30 species of liverworts, another group of bryophytes) grow in 5,325-acre Finley National Wildlife Refuge in western Oregon (Merrifield 2001). In Corvallis, Oregon, a large urban lot hosting houses and other old structures and objects supports 31 moss species. In an acre of old growth forest, the number of species of bryophytes and larger lichens just on tree bark is typically 40 to 75, often exceeding the number of vascular plant species in the same acre of forest.
* Mosses, along with lichens (another small life form often growing on trees consisting of a sandwich of fungus and algae), are important components of ecosystems. For example, the dry weight of living mosses and lichens in old growth coniferous forests may exceed that of the foliage of all other plants, including trees.
In addition to their beauty, mosses play important roles in many ecosystems, from untouched wilderness to agricultural fields to deep inner cities. First, like all green plants, they capture energy in the chemical bonds of carbon compounds made from water and carbon dioxide and then make this energy available to other organisms in the food web. Mosses also act as hydrologic buffers: they absorb water quickly and release it slowly. Furthermore, bryophyte masses accumulate nutrients. Nutrient accumulation may be closely related to another bryophyte function, that of providing habitat for invertebrates. The cycling of nutrients by moss-dwelling invertebrates retains nutrients within the moss system while releasing them slowly to surrounding organisms.
Mosses provide good habitat for invertebrates because
Moss plants actually serve as temporary bodies of water that can support aquatic as well as terrestrial fauna. The terrestrial animals are more active when mosses are drier, and the aquatic animals are active in the film of water covering wet mosses. Many mosses can dry almost as fast as their environment and resume normal metabolic activity upon remoistening. Many of the aquatic invertebrates that live in mosses have adapted to the repeated drying and remoistening of their moss habitat through cryptobiosis.
Cryptobiosis is a latent metabolic state induced by removal of water from an animal by evaporation. The term is derived from the Greek words for "hidden" (crypto) and "life" (bios). Dehydrated animals may remain viable in this state from minutes to decades. When free water becomes available, they rapidly swell and resume active life. Since humidities over 80% are required for survival during the dehydration process, the environmental mitigation by moss enables moss-dwelling cryptobiotic invertebrates to successfully enter this latent state.
Nematodes, tardigrades, and bdelloid rotifers are the dominant aquatic moss-dwelling invertebrate groups. All three require free water for activity but are all capable of cryptobiosis to tolerate periodic drought. Although physiological adaptations to survive periods of drought are not characteristically present in typical freshwater nematodes and tardigrades, they are pronounced in typical moss-dwellers and so may be said to be a characteristic of the aquatic bryofauna. Coiling by nematodes and tun formation by tardigrades, both through active antero- posterior contraction, reduce the rate of evaporative water loss by removing areas of high permeability in the cuticle from direct contact with the air. Bdelloid rotifers also undergo considerable antero- posterior contractions, which dry and shrink their body contents and cuticle to the smallest possible volume.
Moss-dwelling algae and some bacteria as well as mosses themselves capture energy through photosynthesis and make it available in carbon compounds to other functional groups in the community. Most tardigrades and some nematodes consume mosses and algae: they pierce cells and suck out the contents. Some nematodes as well as the tardigrade genus Milnesium are predators: they eat nematodes, tardigrades, and rotifers. Fungi and other bacteria decompose dead organisms: they break them down into smaller pieces (detritus) and smaller chemical compounds. Several kinds of nematodes feed on bacteria, both those that capture energy and those that release energy through decomposition. Other nematodes pierce and suck out the contents of fungal cells. Omnivorous nematodes use several food sources, including moss cells, algae, fungi, and other small invertebrates. Rotifers are filter feeders which ingest a variety of plant and animal prey including algae and detritus. Nutrients released through decomposition of all these organisms by bacteria and fungi are used again by primary producers - mosses, algae, and some bacteria - to capture more energy through photosynthesis. Terrestrial animals duplicate these functions as well as adding additional ones. Thus, mosses and their accompanying organisms form a complete food web.
A tremendous number of many kinds of invertebrates lives in mosses. The three most abundant aquatic groups are nematodes, tardigrades, and rotifers. All are active in the film of water that covers wet mosses. Mites and springtails are among the best represented air-breathing groups.
The diverse moss community indicates a high degree of biological interaction and thus nutrient cycling. A complete community of green plants and algae (producers), non-green producers, plant consumers, predators, decomposers, bacteriovores, fungivores, detritovores, and omnivores lives in moss, which is itself part of its community. Nutrients are obtained from the bryophyte substrate (soil or rock) and from windblown and rainwashed particles that lodge in the moss plant. Nutrients are then cycled through the moss community. Subsequently, some nutrients may be released into the surrounding environment through wind or water flow, and some are recycled within the moss community.
EXTRACTING AQUATIC ANIMALS FROM MOSS. Put a clump of moss in 100-200 ml of water. After 24 to 48 hours, take the moss out, squeeze it over the water, and set it aside in case you want to identify it later. Filter the water through a tea strainer into another container. (A conical container, such as a centrifuge tube, works the best.) If desired, use coarser strainers over the tea strainer to remove larger debris. Let the water sit for about eight hours. During this time, the invertebrates will settle to the bottom. Carefully decant off most of the water after this settling period. Most invertebrates will remain in the container. Pour this remaining water into a shallow dish and examine the invertebrates under a dissecting microscope.
Baermann funnels, standard apparatus in nematology studies, are a variant of the above method. Mosses can also be squeezed several times in fresh water to remove invertebrates more quickly. Invertebrates thus obtained can be concentrated using different sizes of screens or through settling and decanting as described above.
EXTRACTING AIR-BREATHING ANIMALS FROM MOSS. One of the most widely used devices for extracting hidden insects is the Berlese (pronounced "ber-LAY-zee") funnel. Components are a 25 watt light, a plastic or metal funnel, a mesh screen, a stand, and a sample container. In addition to moss, other invertebrate habitats including leaf litter, other layers of forest floor debris, rotting wood, bark beetle gallery crumbs, beach drift, flood debris, and soil may be explored using Berlese funnels.
A low cost Berlese funnel may be constructed using a 2 or 3 liter pop bottle, a 6 to 8 inch square piece of window screen, a small collecting bottle, and a light source. Cut the bottle around its circumference 5 to 6 inches below the mouth and again 5 to 6 inches below the first cut. Discard the bottom of the bottle. Cut a circle of screen to fit into the neck of the bottle about 2 inches from the mouth. Invert the top part of the bottle (the part now shaped like a funnel) over the cylinder that was cut from the lower part of the bottle, which now forms a stand. The moss will be placed on the screen in the funnel, which will be supported above the collecting bottle and below the light.
From one to hundreds of Berlese funnels may be used at one time. The only limitations are space, number of funnels, and mechanisms to hold the components in place. Larger numbers of funnels may be set up in various racks or frames with rows of light bulbs affixed above them.
To extract invertebrates, place the funnel in a stand or support and the screen in the base of the funnel. Position the collecting bottle under the funnel. Carefully place the habitat sample on the wire screen. Moss should be loosely arranged rather than tightly stuffed to provide space for air to circulate and organisms to move.
Place this assembly under a 25 watt light source so that the moss sample is 3 to 5 inches away from the light bulb. Avoid halogen bulbs due to fire danger. Turn on the light. The radiation will heat and dry the sample. The animals will respond by moving deeper into the moss until they fall through the screen, down the funnel, and into the bottle. If organisms are to be collected alive, put a piece of crumpled paper towel in the collecting bottle to provide hiding places for prey species to escape from predators. If organisms are to be collected in preservative, put a small amount of isopropyl (rubbing) alcohol in the bottle.
A Berlese extraction usually produces the first results within 30 minutes, but it takes at least a few hours to get most specimens out. Because the heat is gentle, there is no harm in continuing the extraction for several hours. The amount of time required to extract all the organisms varies with sample size and with consistency or particle size. KM uses a 24-hour extraction time for moss specimens.
If quantification of the organisms is desired, such as animals per gram dry moss, the moss can be weighed immediately after the Berlese extraction. The moss will be well-dried because of long exposure to heat, and its weight will be comparable to that of a sample left in a drying oven for a standard period of time.
NOTE: The same moss sample may be extracted successively using aquatic extraction and a Berlese funnel. KM has used the Berlese extraction first, but a case could be made for reversing the order. We are aware of no extraction efficiency studies on successive extraction methods.
1. NEMATODES: THE THREAD-FORMS. Nematodes are nearly microscopic unsegmented roundworms. A digestive tube within a body wall tube separated by a body cavity form nematodes' simple structure. They lack appendages. The term "nematode" comes from the Greek words for thread (nema) and form (toid). These long, slender animals are formed in the shape of a thread.
Nematodes are propelled by their characteristic longitudinal slow bending or fast twitching, a result of longitudinal but not circular muscles. The structure of a nematode's esophagus often indicates the kind of food it consumes.
2. TARDIGRADES: THE SLOW WALKERS. Tardigrades are nearly microscopic multicellular animals with four pairs of legs terminating in claws. They resemble little bears or pigs, and they are often called "water bears" or "water piglets." The term "tardigrade" comes from the Latin words for slow (tardi) and walk (grade). Tardigrades proceed slowly through the film of water, grasping mosses, lichens, or debris with their claws.
There are two main groups of tardigrades.
HETEROTARDIGRADES, the "armored tardigrades," include most marine and some terrestrial (soil and moss-dwelling) species. They have several sensory structures projecting from their heads and fewer from their bodies. The thickened cuticle of these armored species is divided into individual plates. Each foot bears four separate claws.
EUTARDIGRADES, the "naked tardigrades," include most freshwater and many terrestrial species. All but a few lack sensory structures on their heads. The cuticle of eutardigrades is thin and may be sculpted with pits or spines, but it never forms thickened plates. Each leg bears two double claws.
3. ROTIFERS: THE WHEEL BEARERS. Rotifers are nearly microscopic multicellular animals shaped like a sack or a cylinder. The esophagus of a rotifer contains a mastax, a set of hard jaws. The apical end ("head") of a rotifer bears two circles of cilia, which are used in both locomotion and food gathering. Synchronized beating of the cilia creates the impression of moving wheels and provides rotifers with their name. Rota is Latin for "wheel," and ferre is Latin for "bearer." Rotifers are the "wheel bearers."
Rotifers are widely distributed among all freshwater habitats, a few species are marine, and others live in mosses and soils. Most recovered from mosses are members of Class Belloidea. These bdelloids, like nematodes and tardigrades, are active in the film of water on moist mosses.
Bdelloid rotifers use their telescoping bodies to creep in a leech-like way. In fact, their name comes from the Greek word "bdella", which means "leech." Cement from toe glands enables them to stick to a surface or particle. They can also hold on with their heads if they retract their cilia.
Mosses and the communities of animals, plants, and fungi that live in them are valuable parts of many ecosystems. Mosses and moss communities are growing and active literally outside our doors. Recovery of animals from moss is simple, and the animals are easily visible under low magnification.
Moss communities are good projects to study in school or anyplace else where microscopes are available.
Moss communities help us to appreciate the many kinds of organisms in various ecosystems, to understand how those ecosystems work, and to realize that all organisms have an important function.
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