C^^.S - d8a/ -Sr. Coastal Awareness: A Resource Guide For Teachers in Senior High Science U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration Office of Coastal Zone Management s*VJ\ % 1 a o Coastal Awareness: A Resource Guide For Teachers in Senior High Science U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration Office of Coastal Zone Management September 1978 Washington, D.C. ^lw f "of^ Prepared By: Frederick A. Rasmussen Curriculum Consultant RDD Consultants Boulder, Co. 80303 For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 Stock Number 003-019-00043-8 FOREWARD This series of Resource Guides on Coastal Awareness in Science was developed for elementary, junior high and high school teachers who would like to instill in children and young adults an appreciation of the ecologic value of the coast. Each of the Guides contains concepts, and activities which could be used in a week long unit on Coastal Awareness. The purpose of this guide is not to present a definitive work on coastal ecology, but to entice teachers to explore ecological aspects of coastal awareness. A more complete under- standing of the coast requires study of the interactions of ecology with economics, humanities, and government. As state governments develop coastal management programs, citizens must make choices as to the most important uses of the coast. An understanding of coastal ecological processes will aid students as they participate in future decision making . The Coastal Awareness Series in Science includes : Coastal Awareness in Elementary Science Coastal Awareness in Junior High Science Coastal Awareness in Seniro High Science These are available from the Office of Coastal Zone Management, National Oceanic and Atmospheric Administration, 3300 Whitehaven Street, N.W., Washington, D. C. 20235. OUfl^juJjtr Robert W, Knecht Assistant Administrator Office of Coastal Zone Management Digitized by the Internet Archive in 2012 with funding from LYRASIS Members and Sloan Foundation http://www.archive.org/details/coastalawarenessOOrasm Acknowledgements Many people contributed their time and efforts to the development of these Guides. Special thanks are due to Dr. Robert Stegner, Director of Project COAST at the University of Delaware, and the project on Decision Making for the Coastal Zone at the New Jersey Council for Environmental Education for permission to use their materials. Teachers who evaluated the guides were: David Madfes, Lowell High School, San Francisco Karen E. Reynolds, Havenscourt Junior High School, Oakland Joan E. Steinberg, Lafeyette School, San Francisco Joan Froede of the University of Colorado, Institute for Equality in Education, contributed substantially to the Guides. John Evans from RRD and Bill Welsh of the National Oceanic and Atmospheric Administration illustrated the text. Joann Dennett of RDD contributed to the production of the Guides and Linda Sadler of the Office of Coastal Zone Management provided support and assistance. TABLE OF CONTENTS The Character of the Coast The Coasts The Shore Page Ocean in Motion: Wind, Waves, Currents and Tides 3 Waves 3 Tides 5 Currents 7 The Sandy Beach Sand Dunes Rocky Shores Splash Zone High Tide Zone Mid-Tide Zone Low Tide Zone 8 14 16 19 19 19 19 Estuaries Marshes Activities Further Resources 20 26 31 43 Reading Suggestions List of Suggested Films Games Where to Obtain Data Where to Get Information Sea Grant Institutions 45 56 56 57 59 61 Glossary 65 THE CHARACTER OF THE COAST NOT SHOWN Guam Virgin Islands Northern Marianas American Samoa Puerto Rico THE COASTS The shore lines of the United States — where the land meets the sea — measure more than 140,000 km (88,000 mi). If straightened, they would stretch more than three times around the equator of the earth. Our nation's coasts include the sea shores of the continental United States, Alaska, Hawaii, four Atlantic island groups, and nine Pacific island groups. The Great Lakes and all the sounds, bays, creeks, and rivers washed by tidal waters are also included . What are the special characteristics that define a coast, that make coasts valuable and vulnerable to human activities? Why and how should we protect this vital area of our nation? The coast is a place of untold natural resources. It is a place to which one can escape, a place to play, to be serene, to be inspired. In near- shore ocean waters fish can be caught for sport or for food, and the coast itself can be a significant agricultural area. Each coast has a different history, different pressures, and different problems. Yet, in a physical sense, many of their problems may be similar. Pollution is one such common problem. The Great Lakes are the largest fresh water resource in the world. Pollution of these lakes, which began in the 1800 's, has continued steadily: forests were cleared, disrupting the natural balance, and increases in population, industry, commerce, and recreation continue to encroach. -1- The development that has plagued the Great Lakes for a century is only just beginning in Alaska. But changes come quickly where the margin for life is narrow, and in the frigid waters of the Bering Sea there is little room for error. The Bering Sea is literally the "fish basket" of the northern hemisphere. It supports a surprising variety of life, including one of the largest marine mammal populations of the world, what may well be the world's largest clam population, one of the world's largest salmon runs, some of the largest bird populations per unit area, the world's largest eelgrass beds, and unusually high numbers of bottom-dwelling fish. Any coast consists of two primary elements: the water and the land. The area where these meet — the coast — has unique characteristics due to periodic inundation and continual changes in salinity. The biological com- position of the coasts is often in delicate balance. The science student concerned with the coastal zone will want to investi- gate both the water and the land as well as their interaction. Coastal waters are generally rich in nutrients that have been carried from the land by the rivers and streams. Near-shore coastal waters are particularly productive. These waters are a basic resource; they are affected by a variety of factors — the forces that cause tides, the winds that augment the waves, and the activities of human beings, including exploration and exploi- tation. THE SHORE There can be other definitions, but for our study, we define the shore as the narrow strip between the high-water and low-water marks of spring tides. Thus, there are regular, yet extremely variable local environments. First, the sea covers and uncovers the coastal area twice daily. Temperature ranges may be great within a single day. The salt concentration may vary greatly. The extent to which this intertidal zone is uncovered at low tide depends on the sharpness of its slope which in turn depends on a variety of factors including the nature of the land, its configuration, and the action of the tides, currents, and rivers. The three basic types of shore are rock, sand, and mud. They are often mixed together. The waves have the greatest influence on molding the shore as they break against the land, washing away loose materials, eating into hard rocky coasts, and sometimes forming an abrasion platform at the base of high cliffs. Powerful crosscurrents deposit banks of sand that have been formed by the disintegrating rocks. Mud flats occur at the mouths of rivers or in sheltered creeks and inlets where the sediment brought from the land is deposited. Ice, weather, and the elements all work to help form the shore. -2- Plants and animals are other factors in coast building. Plants may act to bind sand and mud together into dry land. Encrusting animals may serve to protect rocks or to destroy them. Light plays a significant role in this environment, affecting growth of vegetation which, in turn, affects animal growth and survival. Estuaries, too, affect the shore environment. Dilution by fresh water will occur at the mouths of rivers, while increased concentrations of salt will occur as a result of evaporation during the summer. OCEAN IN MOTION: WIND, WAVES, CURRENTS AND TIDES Wind generates waves. The wind, blowing irregularly, causes significant pressure differences that deform the water's surface, creating wave crests of many heights. The wind then pushes against these crests, supplying energy to the waves as they grow and become more regular in height and length. Wave growth depends on four factors: wind velocity, distance of open water over which the wind has blown (called the "fetch"), duration of the wind, and the state of the sea (waves that were present when the wind started blowing) . The wind also plays a part in coast formation. In addition to their indirect effect through action on the water, powerful winds can cut into rock, tearing away gravel that slides to the water's edge. They may also pick up grains of sand and pile them into dunes. WAVES Waves are the sculptors of the coasts. Forceful or gentle, loud or lulling, they combine two distinct types of motion. One is the circular motion of the water molecules within the wave, the up and down motion of the droplets. The other is the advancing movement. The actual water mole- cules have no horizontal motion as the wave advances through the ocean. -3- Waves are described by their height, length, velocity, and period. Period is the number of seconds it takes for two successive crests to pass a stationary point. Height is the vertical distance from the crest (high point) to the trough (low point) and length is the distance from one crest to the next. Period, length and wind velocity are interrelated. Wave height, however, is not related to these factors. The height of a wave in meters is usually about one-tenth the wind's speed in kilometers per hour. CREST As they move away from the winds that started them, waves tend to expand laterally and to become lower, more rounded, and more symmetrical. They then move in groups of similar size, called "wave trains"; the individual waves are called "swells." Once a wave train has formed, it will continue to travel over the sea until it either breaks on a shore oris flattened by opposing winds or wave systems. (In these materials, we will be concerned in particular with the breakers because of their effect on the coastal area.) As a swell approaches the beach, the topography of the ocean bottom takes effect. Depending on wave length and bottom contour, waves may break at depths from one-half to three times their height. The bottom slope is the key determinant not only of the depth at which a wave breaks but also of the manner in which it breaks. A steep bottom results in a wave that retains all its energy until the last possible moment, when the crest peaks up suddenly and plunges violently forward into the trough. As the crest folds over it becomes concave, creating a "tube" or tunnel of air on the shoreward face. These are known as "plunging waves." Hollow plunging waves are the most challenging for surfers because their steepness makes for a very fast ride and it is often possible to crouch under the falling crest — to be "locked in the tube." The plunging waves that curl over the dangerously shallow coral reefs of Hawaii's "Banzai Pipeline" are a famous example of this kind of wave. -4- A gradually shoaling bottom results in a wave that releases its energy more slowly. When a crest finally becomes unstable, it rolls down or spills into the trough and the wave face remains gently sloped. It is these "spilling waves" that display white water at the crest. Irregularities in the ocean bottom tend to make waves spill rather than plunge. Even long-period waves break as spillers on a flat sloped beach, but any suddenly shallow spots will cause most waves to "suck out" and plunge, regardless of their periods. Most surf zones are in a state of constant change . Wind is not the only generator of waves. Earthquakes on the land or under the sea may cause a drastically low tide that is followed by destructive giant waves (sometimes called tsunamis) hurling relentlessly against the shore. TIDES The tides are important in determining the character of the coast. Tides result from the effect on the waters of the gravitational attraction among the sun, moon, and earth. -5- The masses of the earth and the moon exert a gravitational pull on each other that affects every particle on earth, including water. The force is greatest on those particles nearest the moon, but it is much smaller than the earth's force. Although the force required to pull water vertically off the earth would be great, a much weaker force can pull the water horizontally, in effect sliding it across the face of the earth. Water is drawn toward the point directly "below" the moon, and high tides occur when water piles up in this way. Identical forces cause comparable effects on the side of the earth farthest from the moon. In both cases, the water moving into the high tide is being drawn away from another region of the earth. Thus, there are high tides on opposite sides of the earth on a line directly extended between the moon and the earth, and there are low tides midway between the two high tides, in the area from which water for the high tides was drawn. s FULL KAOON UMAjTiDe: N 3PRlNC$ TIDE3 NEW LAST QJfiJZTZR MEAP TIDES V^T^ FIRST QuARTEK. -6- Due to the changing position of the moon, a tidal pulse sweeps around the surface of the earth, causing secondary waves that move across the oceans. In mid-ocean the secondary waves may be only as high as 1 meter, but where the water is shallow these sea waves become much higher. The increased height is the result of a tremendous friction force which slows the wave down. When such tidal pulses move through narrow channels, the water is "bottled up." The highest tides occur in these narrow channels; a well known example of such tides is the Bay of Fundy between Nova Scotia and New Brunswick in Canada. Because the earth and the moon move orbitally (the earth around the sun and the moon around the earth) , both the timing of the tides and their range vary in response to these gravitational forces. The greatest difference between high-water and low-water is found at the "spring" tide, when sun and moon exert their force in the same direction during the new or full moon. The highest tide is during the new moon when the moon is in line with the sun, with the earth between them, and the gravitational pull is all in the same direction. The smallest , or "neap" tide occurs when the high-water mark is at its lowest, and the low-water mark is at its highest. CURRENTS The forces that keep the great mass of ocean water in motion are many and varied; important among them are the heat of the sun and the rotation of the earth. As the sun warms the surface water at the equator, the water expands and raises the surface just enough to cause a gentle slope. Water at the equator therefore runs downhill to the poles. The heavier polar cold water sinks and spreads slowly along the bottom of the ocean toward the equator. This interchange of warm equatorial waters with cold polar waters is compli- cated by a variety of additional forces. For example, the earth's motion toward the east affects the water on the surface of the earth both directly, by causing waves to pile up, and indirectly, by creating winds. The spin of the earth also results in the Coriolis effect — the tendency of water (or any moving object) to turn slightly to the right in the northern hemisphere and slightly to the left in the southern. Consider the Atlantic Ocean waters in the region just north of the equator, where the Gulf Stream originates. Heated by the tropical sun, the salt concentration of the water steadily increases as a result of constant evaporation. Meanwhile, the trade winds (a consequence of the earth's spin) continually blow over the warm, salty waters, pushing the surface waters in a westerly direction toward the north coast of the South American continent. The waters then move toward the Caribbean Sea and on, northwesterly, into the Gulf of Mexico where they pile up, raising the surface level. Following its natural tendency to seek equilibrium, the water drops into the Florida Straits, the only possible egress. From there the Gulf Stream runs northward along the coast. -7- As the Gulf Stream moves north it trends increasingly toward the right (to the east) because of the Coriolis effect. By the time it reaches 40°N latitude, it is flowing due east across the Atlantic, has lost considerable speed, and has widened; it has also cooled down. Currents similar to the Gulf Stream move the waters of the Pacific, Indian, and other oceans. Other factors affecting water currents include ice floes moving from polar seas on the cold currents. As the ice moves southward it cools the water. Since cool water is heavier than warm water, it sinks and is then replaced by warm water near the surface. The most economically important currents are upwellings of cold bottom water. This vertical motion brings to the surface an unusually heavy concen- tration of nutrients. When offshore winds drive surface waters out to sea, they are replaced by the upwelling nutrient -rich deep water. Mineral-rich waters from the land add to the nutrient supply. This upwelling supports a rich growth of phytoplankton, the start of a complex food chain, and makes possible intensive commercial fisheries such as those off the coast of Peru and the Grand Bank off the coast of Newfoundland, Canada. THE SANDY BEACH Of all the coastal elements, sandy beaches probably have the highest recreational value. These beaches vary considerably from one part of our -8- country^to another.. They have different sand, different waves and winds, and different dunes and other inland formations. They are composed of grains as diverse as the black lava sands of Hawaii, the golden sands of Lake Michigan, the white coral sands of Florida, and the seemingly endless sandy expanse from San Diego to Los Angeles. Florida's popularity as a vacation land almost certainly is in large part due to the fact that so much of its coastline is sandy ocean beach. NIGH TIDE L0N6SHORE BAR A TYPICAL SANDY BEACH Although sandy beaches differ in many ways, they also share certain characteristics. A cross section of almost any sandy beach in early summer would probably reveal a structure like that shown above. Waves moving on- shore break on the longshore bar and roll up onto the beach. Each wave moves sand from the longshore bar and slowly, almost imperceptibly, a longer more sloping beach is created. Then, as the season changes, blustering winter winds and heavy seas begin to attack the sloping summer beach. The winter waves are higher, steeper, and closer together than those of summer. Some- times sand is carried away from the berm and even from the dunes or other land areas behind the berm. This pounding winter wave action generally deposits some sand on the berm, but it carries away far more sand and deposits it in longshore bars, setting the scene for another yearly cycle. -9- The texture of the sand plays a role in the kind of beach that will be built, because the slope of the beach relates directly to the particle size of the deposited material. The coarser the particles, the more the waves sink into the beach, depositing their load of sand. Since coarse sand does not pack down and is easily moved around, steep beaches result. When the particles are finer the sand packs down more tightly; the waves do not sink in, and their action leaves a harder, smoother, and gentler slope. Waves and wind thus work endlessly building, shaping, and reshaping beaches. Large particles grind against each other, creating progressively smaller fragments. The largest of these are dropped on the beach and smaller less dense particles are carried out to be deposited in quieter, deeper regions of the ocean. Regardless of the season, the markings on sandy beaches are intriguing. The graceful swash marks left by an ebbing morning tide are composed mostly of detritus — fragments of once living things — that are not only a source of food for many beach inhabitants but are also a treasure trove for human beach explorers. Parallel ridges and troughs, called ripple marks, are often seen on sandy beaches: if the ripple marks are in dry sand they were caused by wind, but if they are lower down on the beach they were caused by moving water. Whether caused by wind or water, the process of ripple formation is essentially the same. When wind or water moving over the sandy surface meets an obstacle in the surface it turns downward, excavating a trough. The sand thus thrown up creates another obstacle and the wind or water then creates another trough. ERODIKK3 HEAP LAND -10- WAVES ^ OFF SHORE CANVON LITTORAL CELL LONGSHORE MOVEMENT Ocean beaches are moving, active places that gain and lose sand continuously. Beach sand is transported by waves, wind, and wave currents in three kinds of movements: offshore, on-shore, and longshore. When put into suspension by wave action, sand can move laterally along the shore in long- -11- shore currents at the same time that it is being moved offshore and returned onshore. Sand movement along the shore occurs within relatively distinct sections of the coast, sometimes called "littoral cells." The boundaries of a cell extend from the place where sand is introduced onto the shoreline (generally by a stream) to the place where it is swept out to the sea. Where beach indentations in the coast are isolated from the general sand movement of the "cell" within these areas, shore erosion and onshore currents can supply sand to smaller "pocket" beaches. Human activity often has had disastrous effects on the natural supply of sand to beaches. Reducing high water runoff from rivers seriously reduces the sand supply available since it reduces the erosion along river banks. Improper construction, of groins, jetties, and breakwaters can change the distribution of sand by longshore currents, causing excessive sand build-up in some places and sand loss in others. The biological production of shorelines is also affected when normal water circulation patterns are changed. Careful study is needed before any major beachfront modifications are under- taken. The long stretches of sun-baked sand and the breaking waves that delight vacationers are also what make sand beaches among the most barren of coastal environments. Because of its shifting nature, the sand offers a poor substrate for anchoring plants. Thus, beaches essentially lack the producers in the food chain and the few animal residents of the sand must depend on small wave- borne particles for food. Usually such residents are tiny crustaceans or mollusks which live in the moist upper surface of the beach close to the water line and filter the food from the retreating waves. Other crustaceans and sand hoppers inhabit the upper beach, feeding at night along the tide line. Each sunrise they dig new burrows often peppering the sand with their holes. Sand beaches are superb places for bird watching. Some birds are full-fledged swimmers and obtain their food from the ocean and the near-shore ocean bottom. Others parade incessantly up and down the beach at the water ' s edge in search of food. The specific kinds of bird inhabitants vary from one part of the country to another, but certain general kinds can be recognized. Medium-sized birds PELICAN CORMORANT -12- that are flying across the surface of the water or riding on it are likely to be gulls, terns, or cormorants. The cormorant is a dark bird that dives and dis- appears for a considerable time while swimming in search of food. Gulls and terns do not swim under water. Terns can be seen flying over the water and diving into it to catch small fish, but gulls are less likely to dive for their food. Gulls, either singly or in groups, can also be seen on the beach itself in search of food. A group of large birds flying grace- fully in formation just above the surface of the water is probably a flock of pelicans. Sand pipers and plovers are the smaller birds that run up and down the beaches, carefully avoid- ing the breaking waves. They are generally long-legged, small to medium in size, and inconspicuous in color. Their food consists of animal and plant fragments that have been cast onto the sand by waves and the tiny animals that live in the upper surfaces of the sand. GULL SHORE BIRDS -13- SAND DUNES Sand dunes form when large amounts of sand are blown inland from a constant source of supply such as a beach. Where the wind is slowed by a log or clump of grass, it drops its load of sand, and a mound slowly builds up, As the mound grows, more sand is deposited behind it; growing larger and higher, the mound becomes a small hill, a ridge, and finally a dune. Wind- blown sand blowing up the face and falling down the crest gives the dune its characteristic shape -- a long sloping windward side and a steeper slope on the lee side. If nothing interferes with the wind or anchors the sand, the dune creeps inland as the wind moves sand from the windward to the lee side. The rate at which a dune advances can vary from a few centimeters to many meters per year. A fast-moving dune can bury everything in its path. The movement of sand dunes may be slowed by the invasion of pioneer plants that can root and grow in the shifting sands; often it is grasses, such as Marran grass — or Poverty grass — which begin the stabilization process. After the clumps of grass have become established, shrubby plants can take root on the lee face of the dune. Protected from the wind QN SHORE WlMD SAND DEPOSITION DIRECTION CF MOVEMENT SAND DUNE FORMATION -14- and with their roots close to the water table, these shrubs often form dense thickets, providing shelter and food for small mammals and birds. Dune life tends to progress from that of bare sand to dense woodland, but this progression can be halted and hundreds of years of growth destroyed in a very short time. Hurricanes, fires, or construction (the building of homes, cottages, or roads) can disrupt the stability that took so long to establish. When a break in the vegetation mat occurs, the wind can quickly charge through it, tearing at the roots of nearby plants. As successive clumps of plants are exposed, more and more sand is released, and the dune begins to move again. HARDY HERBACCUS PLANTS TREES FORE DUNE STABILIZED DUNE -15- ROCKY SHORES Rocky shores are the coastal areas where the confrontation of land (continent or island) with the ocean is most evident. Here the rocky under- pinnings are ceaselessly attacked by moving water, sometimes on a spectacular scale. For example, on our Pacific shores, where wind-driven waves can build -16- up over almost 10,000 km (6,000 mi) of open ocean, the surf is as violent as anywhere in the world. Even normal winter storms generate 6m (20 ft) waves that break against the shore with a shock equivalent to an automobile striking a wall at about 145 km/h (90 mph) . Even though the glass beacon on Tillamook Rock light house on the coast of Oregon is some 42 m (140 ft) high, a grating had to be installed over the glass to protect it from rocks tossed up by the pounding seas. Of course, not all rocky coasts are as exposed as Tillamook Rock. Offshore islands, reefs, and headlands provide protection from the pounding surf when they are in the direction of the prevailing winds. The composition of the rocky shores of the United States varies sig- nificantly from one place to another. In the northeastern United States, shorelines are made up largely of metamorphic and intrusive igneous rocks, but those on the southern Atlantic coast might be sandstone, coarse shell gravel, or coral. Continental Pacific coasts are largely sedimentary rock, and the Hawaiian coasts are igneous rock. The shores of the Great Lakes have rocky coasts, some of which are formed by older sedimentary rock and others by ancient metamorphic rock. Since the nature of the rocky substrate, the rate at which it erodes, the forms produced by erosion, and the mineral content released are so variable, it is not possible to deal with these factors in a publication of this nature. Teachers who want to explore the rocky coast should research their coastal zones in one of the publications cited in the bibliography. The kind of biological communities that will live on any particular rocky coast is determined largely by the degree of exposure to open surf, and by the extent of tidal exposure. Life forms can vary significantly from one side of an island or a headland to the other because conditions which regulate life are so different. Regardless of their exposure to violent surf, rocky shores are much more active biologically than sandy ones, for they offer a solid, unmoving (albeit hazardous) place where both plants and animals can attach and survive. Thus, rocky shores are better than sandy ones for providing opportunities to observe a wide assemblage of marine organisms. Significant differences in the appearance of the marine shoreline are evident at high and low tides. A careful observer can see the orderly pro- gression of plants and animals. These species lie in horizontal "belts" across the shore, one strip above another. In many places, these strips (or zones) are brightly colored by the resident organisms and therefore sharply delineated; a view of them from the shore is often startling. On other coasts such zones may be less obvious and more difficult to distinguish, but they are rarely absent. -17- Local zonation may vary considerably. Zones of a rocky face directed seaward will differ from zones facing the land or from those at right angles to the shore. Zones on a smooth, sloping rock surface may be immediately apparent whereas a shore of broken rock lying at random angles may seem not to have a pattern of zones at all. Similarly, the zones found on sunlit slopes are noticeably different from those in areas shaded by overhanging rock. TIDE Z.OMES OF A ROCKY SHORE: Adapted from Marine Advisory Publications -18- Turbulence governs the life of organisms living between tidemarks on rocky coasts. Even when the ocean surface appears to be calm, there is usually a swell which explodes when it strikes the coast. Animals that live there seem to prefer this turbulence, and the highly aerated water it produces is crucial to their existence. Organisms living near the upper tide mark must be able to resist desiccation during low tides. Many intertidal organisms have developed anchoring methods that keep them in place even during storms which batter them for hours on end. By and large, it is the adaptation of such organisms to life under very special conditions that governs intertidal zonation. The extreme variations found in coastal areas in the United States make it difficult to recognize the zones between tidemarks. The following definitions of the intertidal subdivisions may therefore be helpful. SPLASH ZONE The splash zone is the area of transition between water and land. Although it is affected by spray, it is covered by water only at the highest tides or during storms. Animals that might inhabit this area are the peri- winkle snail and the pill bug. HIGH TIDE ZONE Where the high tide zone is most fully developed, barnacles form a dense, almost continuous sheet on the rocks. Often this sheet has a sharp upper limit which is a very conspicuous part of the shore line. On some shores limpets are present with the barnacles. Rock weed can be found in the lower edges of this zone. MID-TIDE ZONE Each day the mid-tide zone is usually uncovered twice (at low tide) and covered twice (at high tide) . Animals found here are seldom found in the deeper waters that are not as affected by tidal fluctuation. Sea anemones, star fish, mussels, and hermit crabs are frequently found in this zone. LOW TIDE ZONE Only during the very lowest tides, once or twice a month, is the low tide zone exposed to view, and then only briefly. Animals found in -19- this zone can also be found in deeper water. The animal and plant pop- ulations of this zone are large and varied. In cold temperate regions, these populations consist of forests of the brown algae with animals and an under- growth of small plants on their holdfasts. Coral reefs commonly include or encompass the upper edge of the rich growth that extends down the reef face below low-water level. In warm temperate regions the low- tide zone may support dense colonies of tunicates and other ascidians, as well as dense growths of red algae. Before visiting your coast consult a local publication which describes in some detail the organisms present and their distribution. Living organisms should be observed where they are found, not collected. Dis- turbing the shore line in any significant way is to be avoided at all costs. Remember that rocky coasts can be dangerous places to observe, es- pecially at low tide when the tendency is to walk out as far as possible. Even on relatively calm days unpredictable large swells may develop, so careful watch should be maintained. ESTUARIES An estuary is a partially enclosed body of water connected to the open sea; thus, the seawater is diluted by fresh water draining from the land. An estuary is the site of forceful interaction between sea, land, and air. Along the coasts of the United States there are almost 900 estuaries of many different types. Along the Atlantic coast there are drowned - valley estuaries, exemplified by Chesapeake and Delaware Bays. Estuaries that developed behind barrier beaches are found at Ocean City, Maryland, and at Biscayne Bay, Florida. In contrast, the estuaries along our north- west Pacific coastline are majestic glacier-gouged fjords, where the rivers are contained by steep rocky slopes. Earthquakes, land shifts, and other violent actions have created estuaries such as San Francisco Bay. S^LiNif^-^toALT WATER SO PART5/TH0USAI GENERALIZED CIRCULATION IN AM EiSTLlARY -20- Despite some very apparent differences, some characteristics appear to be common to estuaries: fresh water at the river end, salt water at the ocean end, and a mixing syste between them. In most estuaries the salinity gradient ranges from 30 to 35 parts of salt per thousand parts of water at the ocean end and to zero salinity at the river end. Water samples from estuaries usually show that deep waters are more saline than shallow waters — that is, a vertical gradient of salinity exists. This gradient not only moves up and down the estuary with the ebb and flow of the tide but also responds to high and low flows of river water. The net transport of the less salty water at the top is seaward, while the saltier water moves inland along the bottom. Thus, a stratified system, with a distinctive pattern of circulation evolves, resulting in the movement of surface organisms toward the sea and of bottom organisms toward the river. Although the circulation patterns in estuaries have many characteristics in common, different estuaries may have significantly different flow patterns. For example, in the delta of the Mississippi River, the volume of fresh water is so great that the fresh water overruns the salt water of the Gulf of Mexico and a tongue of less saline water extends far out into the salty Gulf of Mexico. In Chesapeake Bay, where the outflow of fresh water and the saline tidal inflow are nearly equal, a distinct salinity gradient is formed and the water stratifies within the estuary. A variety of other factors (such as the nature and slope of the bottom, and the force of prevailing winds, the amount and timing of rainfall) also affect the circulation and salinity of estuary waters. Rivers flowing into estuaries carry with them erosion products and detritus which tend to settle out as the current slows in the estuary. As they near the bottom, these sediments tend to be carried inland with nutrients carried in from the ocean; this creates a kind of nutrient trap that makes estuaries highly productive eco-systems. At the same time, the constant input of solid material from the river outflow contributes to the filling of the basin or to the creation of a delta extending into the sea. Unfortunately this deposition of solids also serves to trap contaminants such as heavy metals, pesticides, pathogenic bacteria,- and toxins. Increasing densities of industry and population along coasts -21- could thus produce unforeseen but far-reaching and permanent detrimental effects on the biological production of estuaries. MARSH PHVTOPLANKTOM V6UUG p5t4 ApUt-T o w^f»SM o Jjyy \\mi lf\ o ^. o EN&Eg V " POOC «^og6 -N AH -22- The food chains in estuaries include two distinct populations of primary producers — phytoplankton and rooted aquatic plants at the edges of the estuary. The abundant zooplankton present include larvae of most of the organisms that live in the estuary. The behavioral patterns of many species of zooplankton keep them within the circulation pattern of the estuary and prevent them from being washed out to sea. Benthos (bottom-dwelling species) are usually more abundant in estuaries than in either fresh or salt water environments. These species are quite diverse, ranging from annelid worms through a variety of crustaceans and mollusks. Many feed by various filtering processes, an effective way of trapping the nutrients flowing through the estuary. Oysters and clams are the most commercially valuable of these filter feeders harvested by man. -23- The benthic populations range from fresh to marine environments, but the most dense beds are often near the center of the estuarine system. The distribution of the oyster, for example, seems to be controlled primarily by three factors: the upstream limit is set by the maximum flow of fresh water from the river; the downstream limit is set by predators and parasites which are found only in high salinities; and the lateral limit depends on the presence of a relatively firm channel shoulder. Among our coastal fishes the most commercially valuable species are either partly or entirely dependent on estuarine environments. Fish use estuaries in many different ways. Some populations of striped bass spawn near the interface of fresh and low-salinity water, others move farther into the rivers, and some populations are even adapted to fresh water. In an estuary, eggs and larvae drift downstream. The developing fish feed throughout the system until they are adults and the cycle begins again. Anadromous fish, such as the shad or salmon, spend their adult lives in the open ocean but return to fresh water to breed. Shad also use the estuary as a nursery for the first summer before the young fish move to the ocean. In contrast, the croaker, which also depends on the waters of estuaries for reproduction, spawns at the entrance to the estuary and the young are transported upstream to the plankton-rich, less saline part of the estuary, where they develop before returning to the ocean. Open ocean fish, such as the bluefish, whose early life histories are totally marine, migrate into estuaries as adults to feed on the abundant food available there. These varied patterns of estuarine use are concurrent as each species follows its own seasonal and reproductive sequence. Thus an estuary may include the regular or occasional presence of several hundred species of fish. The low-salinity portion of the estuary is of exceptional importance since it receives the eggs, larvae, and young of fish with different kinds of spawning patterns. Although this aspect of the estuary is highly valuable, its value is not obvious because these stages in the life cycle -24- of fish, are not immediately recognizable. Since many large cities are located near estuaries close to the head of navigable waters, this potential impact merits special attention. -25- MARSHES Marshes are broad wet areas where grasses grow in abundance. When they are located along the margins of ponds, streams, or rivers, they are freshwater marshes. When they are found on ocean coasts or along the banks or margins of estuaries, they are salt water marshes. Salt water marshes are the nurseries of the sea. They are the most productive land on earth, producing three times more than the best wheat lands. Biologically, marshes are transitional between wet and dry areas, and they are usually very productive in terms of the biomass they can support. If undisturbed by nature or man, most marshes gradually fill with detritus and are eventually invaded by dry land plants. In freshwater ecosystems, marshes contain such water-tolerant species as cattails, bullrushes, horsetails, arrowgrass, flowering rushes, buttercups, crowfoot, and many types of grasses. These marshes are also homes for many aquatic insects, amphibia, crayfish, isopods, birds, and aquatic mammals; when they are associated with permanent bodies of water, they may serve as nurseries for young fish. Lake St. Clair (a very wide area in the isthmus connecting Lake Huron with Lake Erie) , which has extensive marshy areas built on the silt deposited from Lake Huron, is one of the most productive freshwater fisheries in the world. Salt water marshes can best be classified by their relation to the land or the ocean. Of all salt marshes, the most maritime (bearing the closest relation to the ocean) are those that develop on relatively open coasts. They are bathed in sea water at almost full strength since the freshwater drainage from land is usually minimal. These marshes are usually rich in algae, including free-living species and tiny forms of the brown algae derived from normal forms that are attached to rocky shores near the marshes. Marshes at the mouths of estuaries, usually found in the lee of coastal spits, are the next most maritime of the salt marshes. The coarse- grained soils of these marshes are subject to stronger saline influence than those of marshes further up the estuary. As their distance from the ocean increases toward the middle and upper reaches of the estuaries, the marshes tend to become progressively more terrestrial since the water becomes progressively fresher. Despite the wide range of conditions in the United States under which salt marshes exist, some general statements about their formation and the distribution of organisms within them can be made. Salt-marsh formation usually starts in an area that is subject to twice-daily salt water (tidal) inundation. Salt-marshes are replaced by freshwater marshes at -26- the upper level of tidal influence, where tidal inundations occur only a few times a year. Between these two extremes, plants and animals thrive according to the range of conditions they can tolerate - conditions that are dominated by the tides at the lower levels — and almost independent of them at the upper levels. Some factors of crucial importance to the survival, growth, and re- production of organisms in the intertidal zone are the intensity and frequency of mechanical disturbance due to tidal movement; the vertical range over which the tide operates, which determines flooding depths and the vertical extent of the marsh; the form of the tidal cycle, which determines both the frequency and the length of submergence and emergence; and the water quality, which determines, among other things, the amount of light reaching submerged growths and the salinity to which they are subjected. Grasses are the most prominent plants in salt marshes. Cord grass in a long and a short form, is the grass most likely to live in marsh areas covered by water at high tides. Other salt-tolerant plants and plants tolerant to salt spray make up the upper edges of the marsh and vary with the locality. Bull ROSW UiGU TfOET Salt grass" Black