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Unit 10 Notes: Adaptations and Organisms in Freshwater Habitats 2013 I. Freshwater Macroinvertebrates A. General Characteristics Freshwater macroinvertebrates are animals without backbones that live in or near the bottom of freshwater ponds, lakes, streams, and rivers for all or part of their life cycle. They are very important indicators of the health of these bodies of water, reflecting the quality of the water and the conditions of the habitat. Freshwater insects are a large group within the macroinvertebrates found in bodies of freshwater. They make up 90% of the organisms living at the bottom of a stream. Organisms that live on the bottom are called benthic. Of the 2 million known insect species, there are over 80,000 species that fall into the macroinvertebrate category. Examples include mayflies, dragonflies, and beetles. Other benthic macroinvertebrates that do not fall into the insect group include crayfish, clams, snails, worms, and leeches. B. Aquatic Adaptations Freshwater macroinvertebrates are usually grouped by three characteristics: how they move, how they feed, and their tolerance to pollution (intolerant, moderately tolerant, or tolerant) How They Move: In order to adapt to the aquatic environment, macroinvertebrates have to be able to move or maintain their position in the water. Type Description Planktonic Divers Swimmers Clingers Skaters Sprawlers Climbers Burrowers Adapted for movement on the water’s surface Scavenge on organisms caught in the surface film May float and swim in open water or float at the surface to get oxygen or food; can dive when alarmed Inhabit open water (limnetic zone) of lakes, ponds, and bogs (lentic systems) Can swim by rowing with the hind legs in lentic habitats and lotic pools Adapted for fish-like swimming in lotic and lentic habitats Construct shelters, have long claws and flattened bodies for attaching to rock or other surfaces in lotic riffles and wave-swept rocky littoral zones Live on the surface of floating aquatic plants or fine sediments Adaptations include long legs Live on overhanging branches, logs, roots, or aquatic macrophytes Adapted for climbing plants or debris Inhabit fine sediments of streams (pools) and lakes Adapted for digging How They Feed: Feeding Group Food Preference Feeding Habits Shredders Collector-gatherers Collector-filterers Scrapers Piercers Live or dead aquatic plant material Small bits of decomposed organic matter Small bits of decomposed organic matter Algae, diatoms, bacteria, and fungi found attached to plants or rocks Live aquatic plants Predators Live animals Chew, bore, or gouge Gather deposits from the bottom Filter matter out of the water Scrape food from the surface it is found on Pierce into the plant and suck fluids out Engulf whole animals, or pierce into the animal and suck fluids out Pollution Tolerance Aquatic macroinvertebrates are also put into categories based on their tolerance to pollution. Tolerance values range from 0 to 10 with 0 being the least tolerant, and 10 the most tolerant. Tolerance values are assigned to those organisms used as pollution indicators. Freshwater macroinvertebrates are used as indicators of pollution for many reasons: Important part of all aquatic ecosystems Most live or stay over a small area Found in all types of aquatic habitats Life cycles of most groups are well documented Fairly easy to collect Have different levels of tolerance to an environmental disturbance II. Freshwater Fish A. General Characteristics Fish are cold-blooded animals, meaning their body temperature changes with the temperature of their surroundings. They have backbones and live their entire lives in water, breathing with gills and moving with fins. There are 247 species of freshwater fish in Texas alone. Some of these species are able to live in brackish (partly salty) water, such as in estuaries. All fish play an important role in the aquatic ecosystem. B. Fish Habitat Each species of fish has its own distribution and range of tolerance in which it can survive or thrive. The basic requirements for a fish’s survival include prey, cover, suitable water temperature, and dissolved oxygen levels. Habitat Types with Representative Fish Species Habitat Types Fish Species Streams Riffles (high dissolved oxygen) Pools (calm) Backwater areas (low dissolved oxygen) Darters, shiners Sunfish, bass, catfish, suckers Gar, bowfin, pirate perch Reservoirs Open water Shorelines with aquatic vegetation Quiet coves Shad, white bass, striped bass Sunfish, bass, shiners Gar, suckers C. Feeding Groups Fish feed at all levels of the food chain, from bottom scavengers to top-level predators. Fish can be categorized into groups based on food preferences. Fish in each of these groups have form and structure adaptations to allow more efficient feeding. Trophic Group Food Preferences of Fish Food Preferences Adaptations Piscivores (Predators) Fish that eat other fish Invertivores Omnivores Fish that eat invertebrates (insects, worms, crayfish, mollusks, etc.) Fish that eat any available food Herbivores Fish that eat plant material Large eyes for better sight, well-developed lateral line to detect vibrations of prey in the water Feed on bottom – fleshy lips (suckers) or taste buds on their barbels (catfish) to detect prey Use pharyngeal teeth (a modified gill arch in the throat) for crushing plant material Examples / Adaptations Large and small mouth bass,Flathead catfish, Gar, crappie Blue sucker, red shiner, bluegill, longear sunfish Shad, carp, channel catfish Grass carp, stoneroller D. Pollution Tolerance Fish can be used to evaluate the water quality and health of an aquatic ecosystem. Fish are categorized as either intolerant, tolerant, or intermediate. Freshwater fish are used for many reasons: Live in water for their entire life Have long life spans Easy to identify in the field because of established key characteristics of fish species Fairly easy to collect Wide range of tolerance levels Fish can indicate the following about water pollution: Long-term and short-term water quality trends Impacts of various pollutants Distribution, life histories, and pollution tolerances for most fish species are well documented Fish communities are persistent and can recover from natural disturbances Impact of changes to the physical habitat Improvements or declines in water quality III. Common Freshwater Reptiles A. Characteristics Reptiles are air-breathing vertebrates that are cold-blooded, meaning their body temperature is determined by their surroundings. Reptiles control their body temperature by moving to warmer or cooler areas as necessary. There are many groups of reptiles found in freshwater ecosystems: a. Crocodiles and Alligators There are 21 know species of alligators, crocodiles, and caimans in the world, but only two are native to the United States—the American alligator, and the American crocodile. The American alligator (Alligator mississippiensis) is native to Texas, but the crocodile is not. The American crocodile is native to the southern-most tip of Florida. The American alligator is the largest reptile in North America. It can grow to more than 19 feet long. They inhabit the eastern part of Texas, and most of the Gulf of Mexico coast. They are found in rivers, swamps, lakes, and bayous, and can tolerate the brackish water of coastal marshes. During the coldest months and in dry seasons, they dig deep holes in muddy banks, where they hibernate. They are carnivorous predators that feed mostly on fish, snakes, turtles, small mammals, and waterfowl. The alligator can chew underwater, but must surface to swallow. When breeding, the female builds a large mound of mud and leaves, and drops up to 60 hard-shelled eggs into the center. The female stays to protect the nest for the 9 weeks it takes for them to hatch. b. Turtles Turtles are the oldest living reptiles. Freshwater turtles have a toothless, horny beak and a shell of bony dermal plates, usually covered with horny shields, enclosing a soft body. The head, limbs, and tail may be drawn into the shell when necessary. Turtles have scaly skin and are often seed basking on rocks and logs. They lay eggs in cavities dug out by the female. Texas is home to 35 species, with about 240 found worldwide. There are 4 families of Turtles found in Texas: Snapping turtles, soft-shelled turtles, box and water turtles, and musk and mud turtles. c. Snakes Snakes are a limbless, scaled reptile with a long tapering body. Over 2300 species of snakes are known worldwide. They live all over the world, but are absent from many islands, such as Ireland, New Zealand, and Hawaii. There are two families of snakes in Texas: vipers (poisonous) and Colubrids (nonpoisonous) IV. Freshwater Amphibians A. General Characteristics Amphibians have many characteristics that are in between fish and reptiles. The work “amphibian” means “living a double life”. Larvae of amphibians have gills and live in water, while adults breathe air through either their skin or lungs. Amphibians, like reptiles, are vertebrates that are cold-blooded. They have moist, glandular skin and their toes lack claws. They lay gelatinous-covered eggs in moist areas. Groups include frogs, toads, salamanders, and newts. Frogs have smooth skin, webbed feet, no tail, and have long legs for leaping, while toads have warty skin and short legs for hopping. They both feed on insects, crayfish, minnows, and on almost anything smaller than themselves. V. Freshwater Aquatic Plants A. General Characteristics Aquatic plants have adapted to living in a variety of water conditions ranging from swift-flowing to stagnant. They are an important part of an aquatic ecosystem. Plants affect water quality by adding oxygen to the water column and by stabilizing bottom sediments and shorelines to reduce turbidity. They also provide protection, feeding areas, and spawning areas for fish, invertebrates, and waterfowl. B. Groups – Aquatic plants are grouped in three categories, according to their growth habits a. Floating plants – plants that float freely on the surface and plants that are rooted on the bottom with their leaves floating on the surface b. Emergent plants – plants that are rooted to the bottom and grow above the water along shorelines and in shallow water areas. c. Submerged plants – plants that are generally rooted at the bottom and are completely underwater, except for seed heads or flowers. Nearly all aquatic plants live in the littoral zone (near-shore area.) The extent to which they move away from shore depends on the depth that light penetrates into the water column. In large lakes, plants may inhabit only shallow nearshore areas. In shallow lakes, ponds, and slower-moving streams and rivers, aquatic plants may inhabit the entire water body. Free-floating plants cause problems by covering a water body and reducing the amount of light available to other aquatic organisms. VI. Nonnative and Invasive Species Most Texas streams or reservoirs are home to at least one nonnative species (those species that enter an ecosystem beyond their historic ranges). In Texas, at least 35 nonnative species have become established in aquatic habitats. How Did They Get Here? Increasing local food supplies Authorized enhancement of sport and commercial fisheries Manipulationg aquatic ecosystems to control pests or nuisance plants Improving the appearance of an area Unauthorized stocking of ponds or waterways by fishermen, etc. Negative Impacts of Non-native species Prey on native fish Altering established aquatic food webs Introducing new parasites or diseases Altering habitats Damaging the genetic integrity of native species by hybridization Hitchhiking on boats (snails, plants) Releases from personal aquariums (plectosimus) Escape from aquaculture facilities Canal systems Angler bait buckets Out-competing native species for resources Clogging irrigation canals Endangering commercial and recreational fishing due to lower numbers of native species