Armin Eskandari, Estuarine System

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Information about Armin Eskandari, Estuarine System

Published on September 25, 2008

Author: eskandari2000



Estuarine Science : Estuarine Science All About Estuaries Classified by Geologic Features Classified by Water Circulation Estuaries of the World Water Properties Water Chemistry Circulation Daily/Seasonal Cycles Biological Communities Planktonic Pelagic Benthic Intertidal Global Changes Impacts Extreme Events Coping Strategies Winter Flounder Case Study Estuaries Classified by Water Circulation : Estuaries Classified by Water Circulation Estuaries may be classified based on the way that layers of water are formed within the estuary. Most estuaries have a range of salinity from salty sea water to nearly fresh water. The saltier ocean waters are more dense. Since the waters flowing into the estuary from land are less salty, they float on top of the sea water when they meet. Some mixing also occurs where the two water masses meet. Physical and environmental factors such as the shape of the basin, tides, river flow, and wind determine how much the water mixes. Estuary classifications based on water circulation include salt wedge estuaries, partially mixed estuaries, well-mixed estuaries, and fjord type estuaries. Partially Mixed Estuary : Partially Mixed Estuary Partially mixed estuaries have a tidal flow that provides a means of erasing the salt wedge. The salt water is mixed upward and fresh water is mixed downward. Deeper estuaries such as Puget Sound and San Francisco Bay are examples of partially mixed estuaries. Well Mixed Estuary : Well Mixed Estuary Well-mixed estuaries have strong tidal mixing and low river flow that mix the sea water throughout the shallow estuary. The mixing is so complete that the salinity is the same top to bottom and decreases from the ocean to the river. Shallow estuaries such as the Delaware Bay are well-mixed estuaries. Fjord-Type Estuary : Fjord-Type Estuary Fjord type estuaries are characterized by a deep elongated basin that is U-shaped and a ledge or barrier that separates the basin from the sea. They have moderately high river input and little tidal mixing. Fjord type estuaries are found along glaciated coasts such as British Columbia, Alaska, Chile, New Zealand, and the Scandinavian countries. Salt Wedge Estuary : Salt Wedge Estuary Salt wedge estuaries occur when the mouth of a river flows directly into salt water. The circulation is controlled by the river that pushes back the seawater. This creates a sharp boundary that separates an upper less salty layer from an intruding wedge-shaped salty bottom layer. The mouths of the Mississippi, Columbia and Hudson rivers are examples of salt wedge estuaries. Estuaries Classified by Geologic Features : Estuaries Classified by Geologic Features Estuaries can be described by how they were formed or by the characteristics of their circulation. This classification of estuaries is based on geologic features. Classifications include coastal plain estuaries, tectonic estuaries, bar-built estuaries, and fjords. Coastal Plain Estuary : Coastal Plain Estuary Narragansett Bay   Chesapeake Bay Coastal plain estuaries were formed at the end of the last ice age. As the ice melted and the waters warmed, sea level rose. The rising seas invaded low-lying coastal river valleys. These valleys are usually shallow with gentle sloping bottoms. Their depth increases toward the river's mouth. This type of estuary is common throughout the world. Examples include Narragansett Bay (RI), Chesapeake Bay (MD), Delaware Bay (DE), Thames River (England), Ems River (Germany), Seine River (France), Si-Kiang River (Hong Kong), and Murray River (Australia). Tectonic Estuary : Tectonic Estuary San Francisco Bay The earth's crust is constantly in motion. This motion causes large cracks or faults and folds to form in the crust. Often due to folding and faulting, the land sinks or subsides. Tectonic estuaries are created when the sea fills in the "hole" or basin that was formed by the sinking land. San Francisco Bay is a good example of this type of estuary. Bar-Built Estuary : Bar-Built Estuary Bar-built estuaries are formed when sandbars build up along the coastline. These sand bars partially cut off the waters behind them from the sea. Bar-built estuaries are usually shallow, with reduced tidal action. Wind is frequently the most important mixing tool for the fresh and salt water. This type of estuary is common along the Texas and Florida Gulf coasts (East Matagorda Bay), in The Netherlands, and in parts of North Carolina (Albemarle Sound and Pamlico Soun d). Fjord : Fjord Fjords are valleys that have been cut deeper by moving glaciers and then invaded by the sea. They have a shallow barrier at their mouth that limits water exchange between the deeper waters of the fjord and the sea. They are narrow with steep sides and usually straight and long. Fjords are found in areas that have been covered by glaciers. Examples include regions along the coasts of Chile, New Zealand, Canada, Alaska, Greenland, Norway, Siberia, Scotland, and other countries. Estuaries of the World North America : Estuaries of the World North America Albemarle-PamlicoSound Chesapeake Bay Esteros Americanoand de San Antonio Le Conte Bay Morro Bay Narragansett Bay Puget Sound San Francisco Bay Estuaries of the World South America : Estuaries of the World South America Gulf of Nicoya Rio de la Plata Estuaries of the World Africa : Estuaries of the World Africa . Kosi Bay Heuningnes Estuary St. Lucia Estuary System Sundays RiverEstuary Estuaries of the World Europe : Estuaries of the World Europe Severn Estuary Solway Firth Wadden Sea Estuaries of the World Asia : Estuaries of the World Asia . Phang Nga Bay Bay of Bengal White Sea Estuaries of the World Australia & New Zealand : Estuaries of the World Australia & New Zealand . Gulf of Carpentaria Milford Sound. Water Properties in Estuaries : Water Properties in Estuaries . Water Chemistry Temperature Salinity Oxygen Chlorophyll a pH Circulation Tides Currents Density Fresh Water Input Flushing Rates Seasonal and Daily Cycles Yearly Cycles Daily Cycles Tidal Cycles Water Chemistry(temperature ) : Water Chemistry(temperature ) What is the temperature of Narragansett Bay? The average surface water temperature of Narragansett Bay ranges from 32°F (0°C) in the winter to 68°F (20°C) in the summer. In the past few years the peak temperature in the Bay has reached 72°F (22°C) and in the summer of 2001 the temperature reached 75°F (24°C). The bottom water is cooler than the surface in summer and warmer than the surface in winter. The temperature varies in different parts of the Bay. In shallow areas, the temperature can get much higher than the average summer temperature. Narragansett Bay's temperature will depend on a combination of many factors (see below . 15.5°C 31°C Water Chemistry(Salinity) : Water Chemistry(Salinity) How do we measure salinity? Salinity is often measured by measuring how well electricity travels through the water. This property of water is called conductivity. Water that has dissolved salt in it will conduct electricity better than water with no dissolved salt. The more salt that is dissolved in the water, the better the water conducts electricity. The salt content of the water can be measured very precisely using the conductivity method. Salinity can also be measured with a hand held refractometer. A refractometer measures the change of direction or bending of the light as it passes from air to water. Light moves slower in water than air. The more salt in the water, the slower the light moves.             You can see the effect of light bending (refracting) as it passes from the water into the air by placing a pencil in a glass of water. The pencil appears to bend where it enters the water. The pencil is not really bent. The light we see has bent as it moves from water to air.A refractometer is the best choice for measuring salinity when only approximate values are needed. Refractometers are easy to use in the field and relatively inexpensive.   Method of Salinity Measurement  Precision  Hand-held refractometer   1 part in 70  Laboratory titration   1 part in 350  Modern salinometer (conductivity)   1 part in 40,000 Water Chemistry(Oxigen) : Water Chemistry(Oxigen) What is dissolved oxygen? Dissolved oxygen (DO) is the amount of oxygen (O2) dissolved in the water. Dissolved oxygen is one of the best indicators of water quality. People need oxygen in the atmosphere to survive and animals that live in the ocean, like fish, need dissolved oxygen in the water to survive. The amount of dissolved oxygen that the water can hold depends on the temperature and salinity of the water. Cold water can hold more dissolved oxygen than warm water and fresh water can hold more dissolved oxygen than salt water. So the warmer and saltier the water, the less dissolved oxygen there can be. The maximum amount of dissolved oxygen that the water can hold is called the saturation value. Dissolved oxygen measurements are given as a percent of saturation (%) or in units of milligrams per liter (mg/l). Oxygen enters the water at the surface of the water where exchange between the atmosphere and the water can take place. Waves and wind help put oxygen into the water. Dissolved oxygen is also put into the water as a byproduct of phytoplankton photosynthesis. The oxygen found in the deeper water comes from mixing with surface water. Photosynthesis can cause the water to have more dissolved oxygen than the saturation amount. When that happens it is called supersaturation. Animals, such as fish, breathing in the water consume dissolved oxygen. It is also used in the break down of organic matter. As organic matter sinks to the sea floor it begins to decompose. Bacteria in the water use oxygen to break down this organic material. When there is a lot of organic debris, the dissolved oxygen in the deeper water can be used up. If the water at the surface (which has plenty of dissolved oxygen) is not mixed with the deeper water layers form and the water becomes stratified. Then there is no new dissolved oxygen for the deep water. When this happens, the deep water can become unhealthy. Above 5 mg/l dissolved O2, most marine plants and animals have plenty of oxygen. When the dissolved oxygen is low, below 3 mg/l, the water is called hypoxic. If all the dissolved oxygen is used up, below 0.5 mg/l, the water is called anoxic. Under hypoxic conditions, many marine plants and animals may not survive. No marine plants and animals that require oxygen can survive in anoxic conditions. How do we measure dissolved oxygen? Dissolved oxygen is measured two different ways. The first method is the Winkler titration, a chemical measurement of dissolved oxygen. The Winkler titration has been used for a long time and can give very good results if done carefully. Field test kits are based on the Winkler titration. The second method is using an electronic oxygen meter. The oxygen meter is generally fairly expensive (several hundred dollars) and requires proper care and calibration. Oxygen meters give good results and are often the best option for looking through the water column and continuous measurements. Oxygen meters are commonly used on research buoys and oceanographic research vessels. Water Chemistry(chlorophyll ) : Water Chemistry(chlorophyll ) What is chlorophyll a? Chlorophyll is the green pigment in all plants. Chlorophyll a is the most common type of chlorophyll. Plants use chlorophyll to capture sunlight for photosynthesis. Plants may use pigments other than chlorophyll for photosynthesis but chlorophyll is the most common. Chlorophyll a is measured to estimate the abundance of phytoplankton in the water. More chlorophyll a indicates that there are more phytoplankton present. Most chlorophyll a is found near the surface of the water because there is less light at depth. Chlorophyll a concentrations are often highest just below the surface, not at the surface of the water. Phytoplankton need the sunlight during the day to grow. The graph below shows chlorophyll a and dissolved oxygen in the surface water for October 15, 2000 in upper Narragansett Bay (Bullock Reach). The dissolved oxygen and chlorophyll begin increasing at the same time. They both start increasing at sunrise as the phytoplankton begin photosynthesizing and producing oxygen. In mid-afternoon the chlorophyll a starts decreasing and continues decreasing after sunset.Chlorophyll a concentrations change with the factors that affect phytoplankton growth. Some of those factors are: Amount of sunlight Nutrient concentrations (nitrate and phosphate) Amount of mixing (stratification) Water temperature Water quality How do we measure chlorophyll a? Chlorophyll a can be measured in several ways. Individual samples of chlorophyll a are measured by filtering a known amount of sample water through a glass fiber filter. The filter paper itself is used for the analysis. The filter is ground up in an acetone solution and either a fluorometer or spectrophotometer is used to read the light transmission at a given wavelength, which in turn is used to calculate the concentration of chlorophyll a. Measurements are made with a fluorometer in the field. The water sample is exposed to light of a single wavelength. Some substances in the water sample, including chlorophyll a, will give off light, fluoresce, in response to the light. The amount of light emitted by the chlorophyll a is measured and used to calculate the chlorophyll a concentration. A field fluorometer needs to be calibrated with filtered samples. This is the method used on the buoys in Narragansett Bay Water Chemistry(pH ) : Water Chemistry(pH ) What is the of Narragansett Bay? Narragansett Bay surface water usually has a pH between 7.8 and 8.3. However, the pH can be higher during large phytoplankton blooms. Bottom water pH is usually between 7.4 and 8.1. During times of hypoxic or anoxic conditions, the pH can be much lower. When the pH is outside the normal range, many organisms in the Bay may have trouble surviving. The pH of Narragansett Bay can change rapidly when there are rain events or during large phytoplankton blooms. The input of human pollution into the Bay can also change the pH. Pollutants may have an effect in just one local place or affect a large part of the estua How do we measure pH? Measuring pH in salt water is more difficult than measuring pH in fresh water. The salt in seawater can interfere with the measurement. The pH paper tests are not suitable for measuring pH in salt water. There are two methods commonly used to measure pH in an estuary. Colorimetric means to measure color. In the colorimetric method, chemicals are added to the water sample and those chemicals react with the water to produce a color change. The color indicates the pH of the water. The color can be measured visually or electronically. The colorimetric method does not work when the water is already colored because it contains dissolved organic matter or large amounts of algae. Colorimetric test kits are inexpensive and can cover a wide range of pH values. pH electrode and meter (Click for larger image) The second method uses a pH meter and pH probe. The pH probe is placed in the water sample and connected to the pH meter. At the tip of the probe there is a thin glass bulb. Inside the bulb are two electrodes that measure voltage. One electrode is contained in a liquid with a fixed pH. The other electrode responds to the pH of the water sample. The difference in voltage between the two probes is used to determine the pH. There are many pH meters designed for use in the field. The pH probe is used by research scientists and is how the pH of Narragansett Bay is measured on the RI/MA EMPACT Buoys. The cost of a pH meter and probe can be very expensive. Sensors used on the RI/MA EMPACT Buoys. If you were looking straight at the end on the instrument, the probe in the 9 o'clock position is a pH probe. Circulation : Circulation . Tides Currents Density Fresh Water Input Flushing Rates What are tides? : What are tides? Tides are the rising and falling of the water level in the ocean. Tides are caused by the gravitational attraction of the moon and the sun. The moon has the single greatest influence on the tides. Tidal forces cause the water level to rise and fall in a cyclic manner. To make the water level rise and fall, a lot of water gets moved around and this can cause tidal currents. Tides in Narragansett Bay are semidiurnal, meaning that there are two high tides each day and two low tides each day. The tidal range changes depending on the relative positions of the moon and the sun. If the moon and the sun are acting together, we get a higher than normal tide called a spring tide. When the moon and sun are acting opposite to each other, we get a lower than normal tide called a neap tide. There are other astronomical factors that can change the tidal height.For an in-depth explanation of how the gravity of the moon and the sun cause tides, In addition, there are local influences on the tides. Some of those factors are: Shape of the land Shape of the ocean floor (bathymetery) Depth of water Restrictions to flow (narrow inlets to bays, etc.) Local winds How do we measure the tides? Tides have been measured many different ways. The National Oceanic and Atmospheric Administration, NOAA, is responsible for measuring tides at a series of stations all around the United States. There are 6 tide stations in Narragansett Bay: Providence, Conimicut Light, Fall River, Prudence Island, Quonset Point, and Newport. In the past, tides were measured with a floating ball in a pipe open to the water. As the water level moved up and down, the floating ball moved with the water level. The ball was connected to a recording device to record the tides. Currents : Currents Circulation is the movement of water. Circulation in Narragansett Bay is the result of a complex combination of forces produced by the tides, wind, and differences in water density. In an estuary, the basic circulation is a result of fresh water entering at the head of the estuary and flowing toward the ocean. Fresh water stays at the surface as it flows seaward because fresh water is less dense than seawater. However, the fresh water will be mixed with the seawater, producing a range of salinities through the estuary. Seawater will enter the estuary at depth and flow up the estuary. Estuaries are classified by their circulation pattern. Narragansett Bay is a well-mixed estuary in the lower two thirds while the Providence River is often stratified. Image courtesy of Dr. John Mustard, Brown University(Click for larger image) The thermal remote sensing image above shows Mt. Hope Bay in the middle of the afternoon. You can see a current of warmer water from Mt. Hope Bay moving into the relatively colder Narragansett Bay water in the lower left corner of the image. In Mt. Hope Bay, you can see several currents from the rivers draining into the Bay and from the tidal flow. The red streak in Mt. Hope Bay is a plume of warm water coming from the Brayton Point Power Plant. The most obvious currents in the Bay are tidal. These currents are caused by the movement of water as the tides ebb and flow. Tidal currents often reach their highest speed midway between high and low tide. In Narragansett Bay tidal currents of 1.5 knots (77 centimeters per second) are common. The size of the tidal current is related to the tidal range. During spring tides, higher tidal current speeds can be expected. The tidal current is slowed by friction near the bottom and the shore. The highest speeds will be found in the middle of the Bay. The shape of the Bay and the seafloor also influence the tidal currents. Narrow passages will cause a faster current. Tides slosh water back and forth. Water from the upper Bay is not moved out into Rhode Island Sound by a single outgoing tide. A barrel floating in the Providence River would be carried a few miles down the Bay by the outgoing tide and then be carried back up the Bay by the incoming tide. The barrel would end up a short distance down the Bay after one tidal cycle (ignoring all other influences on the barrel). Tides and tidal currents can also cause some vertical mixing of the water column. Nontidal currents are caused by the flow of fresh water into the Bay and the density differences that result. Nontidal currents move slowly, at less than 0.5 knots (10 centimeters per second). Nontidal currents gradually flush water from the Bay into Rhode Island Sound. In Narragansett Bay the winds can be an important part of the circulation pattern in the Bay. Winds can dominate the flow, producing flows different than the normal current. The winds are quite variable and can only be predicted in general terms. Southerly winds will push water to the head of the Bay and northerly winds will push water out of the Bay. Winds will also contribute to vertical mixing of the water column. Density : Density The density of water depends on the temperature of the water and the amount of salt dissolved in the water. More salt makes the water denser and colder water is denser than warm water. Cold salty water is the densest and warm fresh water is the least dense. All bodies of water have the least dense water on top and the densest water on the bottom. Water will always arrange itself so that there is an increasing density toward the bottom. In an estuary, the fresh water flowing in is found at the surface because it has no dissolved salts and is much less dense than the salty water in the ocean. The fresh water will mix with the ocean water and there will be less difference in density. Sometimes there is a big difference in density between the surface layer and the bottom layer. The big difference in density will prevent mixing between the surface and bottom layers. This condition is called stratification. Stratification often occurs in Narragansett Bay during the summer months. The surface water warms and becomes much less dense than the bottom water. If there is not wind driven mixing, the stratification can persist for some time. The Providence River is often stratified because the surface water is fresh water from the rivers and the bottom water is salty, Bay water. Stratification can be a problem for the health of the Bay because when the surface and bottom layers don't mix, there is no source of dissolved oxygen for the bottom layer. The dissolved oxygen can be used up and hypoxic or anoxic conditions can occur, leading to the death of creatures living in the bottom water. Fresh Water Input to Narragansett Bay : Fresh Water Input to Narragansett Bay Fresh water enters Narragansett Bay from rivers and groundwater. The three main rivers bringing fresh water to Narragansett Bay are the Blackstone, Taunton, and Pawtuxet. The rivers draining into Narragansett Bay have a combined drainage area of 4,790 square kilometers (1,849 square miles) of land. Most of this drainage basin is in Massachusetts. The average fresh water from all rivers is about 2.1 billion gallons a day (8 million cubic meters). In contrast, the total volume of the Bay is about 706 billion gallons. Daily river fresh water input is less than 1% of the volume of Narragansett Bay. River flow is well known because the USGS measures stream heights with automated guages on a thousand rivers nationwide. The realtime and historical stream gauge data for Massachusetts and Rhode Island can be seen at A USGS stream gauge used to measure river flow. From the USGS educational web page Groundwater input is important but poorly known in Narragansett Bay. In some drainage basins, the river input to the Bay is 70% of the fresh water input and groundwater is 30% of the fresh water input. Sewer input to the Bay may be as much as 10% of the fresh water input at some times. Fresh water will also enter the Bay in small streams and creeks, by sheet runoff during storms, and by rainfall directly on the Bay. These sources are hard to measure. Freshwater input is not constant; there are seasonal variations and individual rain or snow storms. More fresh water from rivers enters the Bay in the winter and spring. Big rainstorms can bring a lot of fresh water to Narragansett Bay over a very short time. This big input of fresh water is a large influence on the conditions in the Bay (see the tidal cycles page). The links below will take you to a page about each of the major rivers draining into Narragansett Bay. Flushing Rates : Flushing Rates The flushing rate is how long it takes a parcel of water to travel through Narragansett Bay. It is somewhat difficult to measure or calculate the flushing rate of water in Narragansett Bay. There are many factors involved and they will change with time. There have been several estimates of the flushing rate of Narragansett Bay using several different techniques. The best estimate of the flushing time is 8 days to 26 days under normal river flow. Factors affecting the flushing rate of Narragansett Bay: Tidal range (i.e., spring or neap) Fresh water input Wind strength and direction Seasonal and Daily Cycles : Seasonal and Daily Cycles Seasonal and Daily Cycles The water properties of Narragansett Bay are constantly changing. One of the reasons to monitor the Bay is to measure these constant changes and look for patterns. Many of the changes in Narragansett Bay follow a pattern and change on a certain time scale. Some of the cyclic changes are illustrated below. Yearly Cycles The image above shows the water temperature in Narragansett Bay over a two year period, January, 1998 to December, 1999. The water is warmest during August and coldest in January or February. The water cools rapidly in September, October and November and warms rapidly in April and May. Contrast the water temperature with the air temperature in the graph below of monthly average air and water temperature. The highest air temperature is in July and the lowest air temperature is in January. The highest water temperature is in August and the lowest water temperature is in February (slightly colder than January). Seasonal and Daily Cycles : Seasonal and Daily Cycles Daily Cycles Many water properties change on a daily basis. One cause of daily changes is the day-night change in phytoplankton growth. Phytoplankton need the sunlight during the day to grow. The graph below shows chlorophyll a and dissolved oxygen in the surface water for October 15, 2000 in upper Narragansett Bay (Bullock Reach). The dissolved oxygen and chlorophyll begin increasing at the same time. They both start increasing at sunrise as the phytoplankton begin photosynthesizing and producing oxygen. In mid-afternoon the chlorophyll a starts decreasing and continues decreasing after sunset. Oxygen also decreases after the chlorophyll begins decreasing. Other factors such as wind may also play a role in the oxygen levels. Seasonal and Daily Cycles : Seasonal and Daily Cycles Tidal Cycles The tides slosh water back and forth in Narragansett Bay. The water properties will change over a tidal cycle as the surface water gets moved up and down the Bay. The graph below shows the temperature (red) and salinity (blue) at Pomham Rocks in March of 2000. The Blackstone River was above flood stage for several days. The black line represents the tidal cycle. The temperature and salinity are changing dramatically with the tidal cycle. As the tide ebbed (flowed out), it brought colder, fresher water from the river to Pomham Rocks. When the tide rises, it brings warmer, saltier water from the Bay to Pomham Rocks. This is an extreme example of tidal changes. The graph below shows the temperature (red) and salinity (blue) in November 2000 in the Providence River. The black line is the tide cycle. The salinity and temperature change a little with the tidal cycle. This graph shows the typical changes that occur over a tidal cycle. Note the difference in scale between this graph and the graph above. Biological Communities : Biological Communities Estuarine Science Biological Communities Plants and animals live together and interact with one another in groups known as communities. Communities can be very small, such as a tide pool or very large, encompassing the entire bay. Just as people may live in one town and vacation in another or even own homes in two different cities, some species may belong to more than one community. Some organisms use different habitats throughout their life cycles. Communities change in structure and composition with seasons and over long periods of time. They are affected by geography and the chemistry of the environment. They also change in response to a wide variety of pollutants. Planktonic Pelagic Benthic Intertidal Planktonic Community : Planktonic Community Why are plankton important to the biological community of estuaries? Phytoplankton are sometimes called the grasses of the sea. Like land plants, they produce lots of oxygen through photosynthesis. During photosynthesis they use the sun's energy to combine carbon dioxide and water into simple foods. This process removes carbon dioxide from seawater and allows the water to absorb a lot of carbon dioxide produced in the atmosphere. This "global carbon cycle" helps regulate the temperature of our planet. Plankton are an important source of food for larger animals. Phytoplankton are the first link in the food chain. They are known as primary producers because they produce the first forms of food. Zooplankton and other small animals that graze on the phytoplankton are known as primary consumers. These, in turn, become food for larger organisms such as bivalves, crustaceans and fish. The fish and other animals then become food for animals near the top of the food chain, such as harbor seals and man. Estuarine fish and shellfish depend upon phytoplankton for survival. Zooplankton are the intermediate link that transfers energy captured by phytoplankton to these animals. Since the phytoplankton are the primary link, they must be produced in great quantities to support the estuarine food web. If the plankton disappear, the chain is broken and the animals will suffer. On the other hand, some phytoplankton produce chemicals that are harmful to humans and marine life. These species are not abundant but in some cases are cause for concern in coastal regions. What types of plankton live in Estuaries? The phytoplankton species mainly diatoms and flagellates. The most common phytoplankton in Narragansett Bay is Skeletonema costatum. Other genera of diatoms that are found in the bay include Asterionella, Chaetoceros, Ditylum, Eucampia, Leptocylindrus, Psuedonitzchia, Thalasionema, and Thalassiosira. The zooplankton types are:copepods, gelatinous organisms, and larval forms of many animals. The most common species are the copepods Acartia tonsa (most common in summer) and Acartia hudsonica (most common in winter). Other genera of copepods include Centropages, Eurytemora, Oithona, Paracalanus, Psuedocalanus, and Temora. Slide 36: . pelagic community : pelagic community The pelagic community lives in the water column above the seafloor and below the surface. It consists of free swimming creatures known as nekton. Unlike plankton that are at the mercy of the winds, tides and currents, nekton are capable of moving through the water at will. They are predominately vertebrates, including fishes, reptiles, birds and mammals. Some free-swimming invertebrates such as squid are also nektonic. Most estuaries, including Narragansett Bay are highly productive. These relatively shallow waters are rich in nutrients that support photosynthetic phytoplankton. Plankton are abundant in estuaries and serve as a food source for larger organisms. Small fish, bivalves and crustaceans feed on the plankton and they in turn become food for larger pelagic animals including larger fish, birds, and seals. Why are nekton important to the biological community of estuaries? Why are nekton important to the biological communities of estuaries? Estuaries are commonly nicknamed the "nurseries of the sea." The pelagic community is a large contributor to this nickname. Many species of fish and shellfish rely on the sheltered waters of estuaries as protected places to spawn. Other species use the estuary as a feeding ground. Nekton are abundant and provide food for other organisms. Hundreds of organisms depend on estuaries at some point during their development. Aerial photograph of Portsmouth and Tiverton , Rhode Island. Photo by Rob Arra, Everlasting Images and Stadium Views(Click for larger image) The pelagic community also serves as a source of energy and food for the benthic community. The benthic community relies on the bodies of animals that have died and particles of food that flow downward. Fish are the most abundant nekton in estuaries. This fish population is very important to humans, both as a source of food and income. Estuaries provide essential habitat for most of America's commercial and recreational fish catch. Trawler at sunset(Click for larger image) Fishing, tourism, and recreational boating depend on healthy and productive estuaries and provide millions of jobs for our nation. Commercial and sport fishing alone contribute billions yearly to the nation's economy. These industries are very important to many coastal communities, especially those close to fishing ports. Benthic Community : Benthic Community What is a benthic community? The Benthic Community is made up of organisms that live in and on the bottom of the ocean floor. These organisms are known as benthos. Benthos include worms, clams, crabs, lobsters, sponges, and other tiny organisms that live in the bottom sediments. Benthos are divided into two groups, the filter feeders and the deposit feeders. Filter feeders such as clams and quahogs filter their food by siphoning particles out of the water. Deposit feeders, such as snails and shrimp, ingest or sift through the sediment and consume organic matter within it. Lady crab Lobster Winter flounder (Click for larger images) Before the age of deep-sea exploration scientists believed that there could be no life in the absence of energy from the sun. Since sunlight only penetrates the first 30m in coastal areas and 100m in the open ocean, they believed there was no life to be found on the ocean floor. What they did not realize was that there is a steady production of energy in the oceans in other forms than direct sunlight. One source of energy or food is the bodies of organisms that have died in the upper sunlit layers of the sea. They settle downward through the water column where they can be consumed. There is a constant vertical downflow of food or energy from the upper layers of the water to the benthic community. Benthic animals are much more abundant in the shallower waters off the coast. In the shallow water the dead food material is more abundant because there is a higher population of organisms near the surface in this area. In these waters food also arrives from river sediments. Once food has reached the sea floor, currents carry this food and organisms filter it without having to use their own energy to go and get food. Another way organisms use energy is by coming out at night and rising to feed on upper-level organisms. Many large organisms are formed as they feed on microscopic food. Why are benthos important to the biological community of estuaries? Benthos play a critical role in the functioning of estuaries. Benthic species are a diverse group that are a major link in the food chain. Filter feeders in the benthic community pump large amount of water through their bodies. As they filter this water for food, they remove sediments and organic matter, cleaning the water. Organic matter that is not used within the water-column is deposited on the bottom of the ocean floor. It is then remineralized by benthic organisms into nutrients which are given back into the water column. This remineralization of organic matter is an important source of nutrients to the ocean and is critical in maintaining the high primary production rates of estuaries Intertidal Community : Intertidal Community Where is the Intertidal Zone? The Intertidal Zone is where the land meets the sea. It is the area between high tide and low tide. Intertidal communities can be found on sandy beaches, in bays and estuaries, and along rocky shorelines. The rocky shores are the most diverse and highly populated. In this area where rocks are covered and uncovered daily by the ocean, unique and diverse tide pool communities are formed. The marine animals living in this zone are unique because of their ability to withstand exposure to air and the force of the pounding waves. The lowest levels of the Intertidal Zone are the most crowded with life and the higher, dryer levels are less populated. The organism's adaptations depend on where in the Intertidal Zone it will be found. What are the different regions of the Intertidal Zone? The Intertidal Community is composed of several different regions that differ depending on tidal and wave exposure and life within the zone. The different conditions in each region allow for a great diversity of marine life. This can also lead to a competition among organisms for limited space on the rocky shore. Black Point Rocky Intertidal Zonation(Click for larger image) The Intertidal Zone is divided into six specific regions: The Black Zone (or Splash Zone) The Periwinkle Zone (or Splash Zone) The Barnacle Zone (or Upper Zone) The Rockweed Zone (or Middle Zone) The Irish Moss Zone (or Lower Zone) The Kelp Zone (or Subtidal Zone) How do animals adapt to living in this community? The Intertidal Zone is a very harsh living environment for organisms because its ever changing conditions. Animals in this zone are constantly facing challenges such as varying salinity, drying out by wind and sunlight, predators, strong currents that carry them back to sea, and varying weather conditions. To help with these difficulties many organisms have special adaptation features.     How do organisms protect themselves from drying out?Some animals, such as sea urchins, carve holes in the rocks and hide in these holes that provide moisture during low tide. Mussels and other shell organisms will tightly close their shell to keep in moisture. Snails secrete a slime that gives them moisture during the long hours of low tide and anemones will fold in their tentacles to hold in moisture. Each of these techniques help the creatures from drying out. Anemone(Click for larger image)    How do organisms protect themselves from crashing waves and strong currents?Many organisms use rocks to help with this problem. Sea Stars and anemones have suction cups, which allow them to latch onto rocks so they are not carried out to sea. Mussels use a thread-like substance called byssal threads that stick to the rocks. Anemones have a unique jelly-like body, which can withstand the crashing waves. For the same reason, sea stars have a strong leathery coating, and many shell organisms such as barnacles have hard shell covering. Safe on the Rock(Click for larger image)     How do organisms protect themselves from predators?As stated previously sea urchins carve holes in rocks and can hide in these holes. Snails can also carve places for protection in rocks. Many other organisms, such as periwinkles and crabs, can hide in cracks and crevices of the rocks for shelter. Hermit Crab

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