November-December 2008

Municipal In-Stream Macroinvertebrate Sampling

Part 3: Aquatic dwellers’ habitat habits

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This is the third of three related articles on in-stream water monitoring and sampling. The first, in the September 2008 issue, dealt with comprehensive sampling methods. The second, in the October 2008 issue, dealt with chemical sampling and monitoring.

Striders on the Storm
As explained in the article in the September issue, a plethora of terrestrial adult insects spawn and mature in aquatic environments, and the relative numbers of one group compared with another indicate general trends in water quality for a site. Cobb County, GA, stream monitoring personnel sample five sub-habitats for aquatic macroinvertebrate indicators of water quality. As submerged organisms, they are subject to chemical, sediment, and physical flows of stormwater, qualifying them as truer striders on the storm than their water-strider co-survivors perched on the surface of deep, turbulent water-quality tempests.

Cobb County’s macroinvertebrate biotic evaluations are sanctioned in the state of Georgia’s Standard Operating Procedures protocol III. For this article, I discuss habitat and fish assessments, but emphasize macroinvertebrate assessments because they are somewhat of a practiced standard for long-term water-quality analysis. Macroinvertebrates are prized as indicators because they distribute so well on a scale of group-specific water-quality sensitivity ratings. They are also, well, easier to catch. I will focus on those specific groups that frequently contribute to Cobb County stream monitoring macroinvertebrate scores.

The related, relative presence of different fishes is evaluated at sites every five years. Water-quality-influencing physical stream features are “scored” on biannual habitat assessments of 10 metrics of the EPA rapid bioassessment: epifaunal substrate/cover, embeddedness, velocity/depth, sediment deposition, channel flow, channel alteration, frequency of riffles, bank stability, vegetative protection, and riparian zone width.

Water World
General discussion of aquatic dwellers and their habitats is served by supporting discussions on general principles of life in water. Although my discussion of the physical properties of water in the previous articles promotes an understanding of life in water, we need to discuss general aquatic living adaptation trends in order to describe aquatic macroinvertebrate life in any detail.

With regard to feeding behaviors among aquatic macroinvertebrates, there are several types: herbivorous macrovores and microvores, as well as carnivorous macrovores and microvores.

Aquatic macroinvertebrate herbivorous macrovores feed on vascular plants and filamentous algae by chewing into plant tissue, as do caddisfly larvae; boring into it, as do midges and flies; or sucking plant juices, as do semi-aquatic Homopterans.

Herbivorous microvores, such as the suspension-feeding netspinning caddisflies and midge larvae, feed on plant, animal, and detritus matter (diatoms are common in their diet) caught in nets, as brushlegged mayflies and blackfly larvae utilize brushes of foreleg hair to capture suspended matter.

Carnivorous macrovores like damselfly and dragonfly larvae wield “an elaborate labium that is quickly extended to capture and hold” whole, live prey (McCafferty 1983). Megalopteran dobsonfly larvae use their well-developed mandibles, or feeding pincers, and many Hemipteran water bugs have grasping, raptorial forelegs and mouthparts adapted for piercing and sucking. Strong, large, and quick carnivores like Megalopteran dobsonfly larvae prey on weak, small, slow detritivores like netspinning caddisflies in the laissez-faire-for-all market of the bustling stream substrate. At the close of business, there are two types of aquatic macroinvertebrates: the quick and the dead. Or to indulge a more contemporary film culture cliché, every day above substrate is a good day.

Predacious, burrowing dragonflies partially bury themselves using digging spurs on their legs.

Carnivorous microvores are really general omnivore-detritovores and filter-feed seston or suspended material that includes small zooplankton (e.g., caddisfly, Dipteran, and mayfly larvae); some midge and mosquito larvae actively prey on zooplankton.

Respiration features in aquatic invertebrates can be described as adaptive features and benefits of extended environmental opportunism.

Mosquitoes, aquatic soldier fly pupae, and others utilize long siphons or respiratory horns as snorkels to obtain atmospheric oxygen, while submerged just under the surface.

Other air-breathers like the diving beetle Dytiscus capture an air bubble and draw oxygen from it as dissolved oxygen (DO) from the water replenishes oxygen used in order to re-establish the original oxygen-to-nitrogen equilibrium ratio. Nitrogen does not diffuse readily into water and maintains the bubble, but waste carbon dioxide in the bubble diffuses out into the water, maintaining equilibrium in the conversion of CO₂ to H₂CO₃. Plastron films of air on other aeropneustic divers in Hemiptera (true bugs) and Coleoptera (beetles) are held in place with special hairs over spiracle breathing holes in the same manner as the beetle’s “Self-Contained Underwater Bubble Breathing Apparatus.”

Hydropneustic or dissolved-oxygen breathers are widespread and do not rely on body wall spiracles, but take dissolved oxygen in through membranous areas of the body wall that include platelike or filamentous extension gills in many. Many stoneflies, dobsonflies, and caddisflies, as well as some beetles and aquatic flies, utilize gills.

Many oligochaete worms and other gill-less vermiform insect larvae like “micro” caddisflies are small enough for sufficient DO to diffuse across high-surface-to-volume-ratio body walls. Some siphon breathers, like soft-bodied aquatic flies, respirate hydropneustically as well in appreciably oxygenated waters.

Larger stoneflies, case-making caddisflies, and burrowing mayflies ventilate their gill-less or gill-poor bodies by “exercising”; stoneflies perform a kind of push-up, augmenting dissolved-oxygen flow over and under their bodies. Caddisflies undulate within their cases, and burrowing mayflies pulse their gills to create a current within their burrows.

Dragonfly and damselfly larvae ventilate by drawing water in and out of a rectal chamber; damselflies have finlike caudal lamellae extending from the abdomen that can function as gills as well stabilizing fins in significant flow.

Lastly, in hyperosmotic freshwater conditions, where ion concentration is much greater in the organism than in the aquatic medium, ion uptake due to dilution loss is undertaken by “chloride cells” distributed usually on the abdomen and gills, by chloride epithelia tissue patches, or by papillae outgrowths that extend, balloon-like, from the posterior abdomens of, say, aquatic flies.

Habitats of Subhumanity: Get Your Kicks
Riffles are one especially significant sub-habitat. As I explained in the September article, Cobb County stream personnel perform a riffle kick, a kind of soft stomping dance, in the rocky, high-flow area of a stream, upstream of a net held on the bottom. This motion jostles insect larvae and nymphs (incompletely metamorphosing aquatic insect young, distinguished in some texts from larvae, called larvae in others) into the net. Because high flows push sediment on and dissolved oxygen is generated by the aeration of water over the uneven rocks, diverse and demanding (and, thus, pollution-intolerant) orders of macroinvertebrates can be collected, including the orders Plecoptera (stoneflies), Trichoptera (case-making caddisflies), Ephemeroptera (mayflies), and Megaloptera (dobsonflies).

A mature Dobsonfly. Dobsonfly larvae occur in and are indicators of well-oxygenated flowing water.

In habitat assessments, lack of embeddedness (in silt) and frequency of riffles are key metrics scored on the habitat assessment field sheet. The shallow water and turbulence of rocky riffles sponsor critical oxygen uptake as well as release of toxic gases. Rocks stabilize the stream and provide macroinvertebrates shelter from velocity, especially for filter feeders relying on particulate food matter borne in swift currents. Purity and frequency of riffles score high in habitat assessment.

Stoneflies are particularly sensitive (and consequently their presence is an indicator of superior water quality), because many have no gills and are forced to rely on cutaneous or body-wall uptake of DO. McCafferty (1983) explains that they “are relatively restricted in habitat, and organic enrichment or other forms of pollution that will reduce available dissolved oxygen in the water can prohibit their occurrence.” Those in the family Perlidae have filamentous gills and some advantage in obtaining DO, but they are still limited to consistently superior sub-habitats like riffles and well-oxygenated leaf packs (as crawlers, they don’t swim well enough to escape habitats). As described earlier, they often have to resort to performing a kind of push-up when stressed in order to augment flow around their bodies.

The different families of case-making caddisflies can undulate within their cases and augment DO, but, with limited or no gills, they are more sensitive than net-spinning Hydropsychidae with their ventral branched gills. Stone- and wood-case makers also build ballast stones and trailing twig rudders into their cases as adaptive behaviors in desired high-flow riffles. With these DO limitations and case-stabilizing adaptations, case-makers are generally more limited and adapted to riffle and high-flow areas and are thus indicators of such superior habitats. They are classified as sensitive in the Georgia Adopt-A-Stream field guide and score likewise in Cobb County’s adaptation of the Georgia Environmental Protection Division macroinvertebrate protocol.

Minnowlike mayflies especially take to riffles, with their “sleek streamlined bodies and almost finlike tails (e.g., many minnowlike mayflies)” (McCafferty 1983). Mayflies of the flathead variety, family Heptageniidae, have adapted abdominal discs of modified gills or brushes of hair that enable them to cling to rocks in heavy riffle flow.

Dobsonfly larvae in Megaloptera, family Corydalidae, occur in and are indicators of well-oxygenated flowing water (McCafferty 1983), because their sheer bulk and predator lifestyle requires a lot of oxygen and prey, abundant in riffles. They do have ventral gill tufts.

The Roots of Clinging Resilience
Undercut bank and “root” sampling involves agitating a net under bank roots, or agitating the roots when net movement is not possible. “Roots also provide habitat for many of the macroinvertebrates listed above for riffles and also are important for many species of Odanata (dragonflies), Elmidae (riffle beetles), and Chironomidae or midges” (Bourne 2003).

Odonata dragonfly larvae in the family Aeshnidae are slender-bodied and -legged, adapted for climbing and predating among roots. Somewhat sensitive nymphs, they are hydropneustic, respiring cutaneously along their bodies, but when conditions oblige, they can also pump water in and out of a selectively permeable rectal chamber where gas and ion exchange can take place. Curiously, certain Odonata damselfly larvae (or nymphs in some texts) can harbor a specialized euglenoid (chloroplast-containing) flagellate in the rectal chamber during winter, which provides some oxygen for the damselfly.

Riffle beetles, as the name implies, inhabit riffles but are also found often in roots and other habitats. “Riffle beetle larvae and adults scrape food from rocks, wood, and roots in streams and consume periphyton, detritus, wood, and some animal and mineral material, and are considered mineral scrapers, collector gatherers, or shredders” (Seagle 1982). The presence of adults is especially an indicator of superior conditions, because, as adults, their existence per se demonstrates consistent water quality, and also because they are able to stay submerged indefinitely using a plastron air blanket only in well-oxygenated water. Adult and larvae riffle beetles are adapted as crawlers and clingers with effective grasping tarsal claws.

Discovering and assessing stream macroinvertebrates

Chironomidae midges found in roots are sometimes adapted to cling with hooked abdominal prolegs; the Dipteran order, and its Chironomidae midges in particular, are found in almost all aquatic habitats, including the body surface of mayflies and other aquatic insects.

Habitat assessments score high on the bank stability, vegetative protection, and epifaunal substrate metrics when thick roots are associated with stable undercut banks where aquatic fish and macroinvertebrates can shelter from predators and high wet-weather flows. As stated in the September article, the importance of trees and shrubs to stream ecology is demonstrated in the fibrous mats of roots’ “resilient matrix for attachment and for shelter for … vertebrates and invertebrates” (Bourne 2003).

Coarse Particulate Organic Matter
CPOM and “leaf packs” of decaying matter snagged in areas of appreciable flow can be collected by hand and often include Tipulidae, or crane flies, as well as stoneflies. Stoneflies can live in leaf packs that break the surface, snagged on woody debris in high-flow areas—functional stonefly-friendly “deep water riffles.”

The Tipulidae family in the order Diptera is somewhat sensitive to pollution and contributes toward average-to-better scores. They are generally aeropneustic, using posterior spiracles (holes) to obtain atmospheric oxygen, but they can utilize dissolved oxygen directly through the body wall in well-oxygenated, negligibly polluted water. As fairly large, herbivorous organisms, they don’t move much, yet they don’t enjoy the oxygen diffusion success of greater surface-to-volume ratio in smaller vermiform larvae. As shredder feeders, they particularly take advantage of the abundant organic matter in leaf packs.

Where habitat assessments are concerned, leaf packs relate to metrics of epifaunal substrate/available cover and degree of vegetative protection; discussed in the September article, leaf packs shelter and provide food for Tipulidae and other shredders whose discharged waste supports filter feeders downstream like Dipteran black fly larvae in the family Simuliidae as well as Hydropsychidae. In fact, “Stream ecology is fundamentally different from lakes and rivers in that CPOM, coarse particulate organic matter, not algae, is the most important food source” (Bourne 2003).

Woody Debris and Rocks
Woody debris is another important habitat source. Woody debris that has become anchored in the streambed or bank provides both a stable food source and an important substrate for attachment. This is especially true in streams where riffles are infrequent. Woody debris also impedes flow velocity and can thus reduce erosion within a stream. Large woody debris and large rocks are scraped with sensitive brushes, and often Trichoptera, or caddisflies, and Ephemeroptera, or mayflies, are swept into a collection bucket.

Demonstrating the size of a caddisfly found in a Cobb County stream

Among caddisflies, classified as either sensitive or somewhat sensitive by Georgia Adopt-A-Stream, the family Hydropsychidae (a net spinner) has a relatively high pollution-tolerance rating and can be found on debris as well as in riffles and in moderate water-quality conditions. This is probably because it has extensive ventral gills and therefore greater dissolved-oxygen-exchange surface area, as opposed to exercising simple cutaneous respiration through the body wall. Also, as a filter feeder, it can utilize degraded conditions, as more suspended algae and particulate organic matter are generally available. Case-making caddisflies, discussed in the riffle section, are also more tolerant than their gill-less, free-living cousins in the family Rhyacophilidae, because they undulate vigorously within their stone or wood-debris cases, augmenting flow and subsequent DO absorption. McCafferty (1983) states for many of the case-makers, “gills are usually either simple, branched, or absent.” As stated earlier, in more “cases” than not, there are limited or no gills.

Ephemeroptera (mayflies) found among woody debris and on rocks also include Heptageniidae (see the riffle discussion). As sprawlers and clingers, they are found grazing on algae and detritus of a particular (woody) substrate as well as attached to riffle rocks. Mayflies are classified sensitive by Georgia Adopt-A-Stream, as they demonstrate particular sensitivity to low-dissolved oxygen as well as to chloride ions, ammonia, metals, pesticides, and acidity. This can result from high metabolic DO demands (they are fairly mobile), or to their being relatively adapted to specific (and only) certain habitats, or to especially pollution-sensitive complex developmental stages, and to limitations of gill structures vis-à-vis oxygen demands.

Habitat assessments rank epifaunal substrate/available cover and vegetative protection for the potential to contribute to desired habitat features of trapped woody debris that co-form a sub-habitat with adjacent large rock surfaces. Indeed, aquatic macroinvertebrates and fish require rocks, logs, and snags where they can avoid predators and high flows. Cover also establishes territory and navigational markers for aquatic life.

Sand Dragons
Stable sand and sediment beds are home to many aquatic invertebrates, including burrowing dragonflies, chironomids, mayflies, oligochaetes, and mollusks. Sand samples are collected in a similar manner to riffle kicks, with the shuffling upstream of a bottom net, care being taken not to dredge too much sand. The family Gomphidae, or burrowing dragonflies, and/or burrowing mayflies, are often collected in this way.

The family Chironomidae, or midge flies, in the order Diptera, which are found in sand, and particularly red chironomids, are classified as especially tolerant, because their hemoglobin captures more precious dissolved oxygen in degraded conditions than that of their white chironomid cousins. To qualify somewhat what was said in the September article, clams and mussels in the class Bivalvia are somewhat sensitive according to the Aquatic Macroinvertebrate Field Guide for Georgia’s Streams (Georgia Adopt- A-Stream 2006), and yet invasive bivalves in Corbiculidae recovered here are tolerant of silting conditions. When they are present in large numbers with chironomids and oligochaete worms, as compared with low numbers for other macros, we can infer deteriorated water quality, because sensitive and somewhat-sensitive groups are not well represented.

Burrowing mayflies in families Ephemeridae have “broadened forelegs, shovel-like processes of the head, and tusks” adapted for digging, and they actually pulse rows of abdominal gills to “create a current through a burrow by pulsating movements … thereby maintaining the burrow and providing a flow of food particles and oxygenated water over the body” (McCafferty 1983).

Predacious, burrowing dragonflies in the family Gomphidae partially bury themselves using digging spurs on their legs and extend their long abdomens back out of the sand to extract dissolved oxygen through abdominal apertures; they lack, however, the gill-functioning, tail-like caudal lamellae of damselflies.

When present in large numbers with chironomids and oligochaete worms, these Corbicula can indicate poor water quality.

Although promoting expanded biodiversity when riffles and other habitat are adjacent in a stream run, sand generally scores low in habitat assessments. The sediment deposition metric considers less than 5% of the stream bottom affected by sedimentation as an optimal score, with ranges between 5 and 30% into scoring as suboptimal. However, slow pools where sand is deposited are important refuges and nesting grounds for fish, as well as habitats for macroinvertebrates adapted for lower dissolved oxygen associated with rich organic oozes of deposition and decay.

Riffle Real Estate Customers
Fish are not assessed in macroinvertebrate sub-habitats per se, but are shocked, recorded, and released in designated reaches of major Cobb County streams. Of particular interest for our discussion are some selected fish whose presence indicates something of interest to biologists, whether it involves fish relating to habitat, macroinvertebrate populations, or even land use trends. These will be covered in a future article.

In moderate to alleged “superior” water quality, we would expect to find the topminnow the southern studfish fundulus stellifer in quantity, as it is historically very common to local watersheds.

The mosquito fish gambusia affinis, however, is tolerant of more degraded, slow eutrophic (nutrient-choked) waters, as its upturned mouth and flattened head allow it to skim the oxygen-rich surface films of poorly oxygenated waters.

Two fish less commonly found than studfish that are indicative of superior water-quality habitat in Cobb County are darters in the family Percidae, such as the Endangered Species-listed Cherokee darter in the Etowah basin, and Cottidae, or sculpins, which seeks out high-quality riffle habitat. Riffle-habitat fish often are somewhat torpedo-shaped in order to accommodate high-flow potential for turbulence. The loss of superior habitat due to sedimentation from construction-site erosion and high impervious surface flows is of working concern to environmentalists in the area.

Shiners and chubs in the family Cyprinidae are often specialized, like the stoneroller campostoma, which scrapes algae off rocks with its curved, cartilaginous lower jaw; such specialization is accommodated by comprehensive and diverse habitat.

Best Minimal Practices
We are developing somewhat into a nation of better buyers than stewards, more empowered consumers than schooled citizens. Empowering institutions increasingly reward nominal obligation met rather than optimal purpose fulfilled in gratification stratification; do only what you have to do to get what you want. Many young professionals and, sadly, some in the municipal and private environmental ranks have only acquired a higher-RAM “busy box” than they enjoyed in the crib, and where they need only to manipulate the right series of levers and laptop dials in order to immediately delight in, say, completed asset management inventories, or perhaps researched, approved, downloaded, cost-effective, newly available best management practices.

We scoff at such environmental mercenary notions, and yet, many of us could use a paradigm re-shift. That is, as water-quality professionals, we sometimes rationalize efforts and resource expenditures for monitoring by citing permit-required sampling or project “best minimal practices,” when the stream ecosystem per se—the profoundly green, glistening world of gymnastic fish and Jurassic dragonflies itself—should be our focus and purpose, as it cradles the resource we most stand to lose in losing control. Watersheds should be preserved for their own sake, across political permit requirement boundaries, and with every available resource at our disposal.

Author's Bio: Lanse Norris is an environmental compliance technician in the Water Quality Section of the Cobb County, GA, Stormwater Management program.