1.16: Lab 16 - Coastal Geomorphology

This lab contains potentially inaccessible interactive resources. Please work with your instructor and local campus resources to identify accommodations for these resources.

Learning Objectives

• Explain how longshore currents and beach drift transport coastal sediment.
• Describe the stages of barrier island development.
• Identify features on emergent and submergent coastlines.
• Interpret sea level rise data.
• Explain the location and formation of coral reefs.
• Assess threats to coral reefs.

Introduction

Coasts are the dynamic junction of water, air, and land. Winds and waves, tides and currents, migrating sand dunes and mud flats, and a variety of plant and animal life all combine to form our ever-changing coasts. Their dynamic nature results in their great diversity. Most of us envision a coast as a broad stretch of sand with frothy surf breaking along the shore; in fact, many types of coasts are found within the United States, ranging from sandy beaches to rocky shores, from coral reefs to coastal wetlands.^[282]

We think of land as stable and treat it as a permanent asset. For most land, this premise is reasonable because land generally changes very slowly. Although tectonic and geologic processes, such as continental drift and erosion, are always at work, they usually result in very gradual changes that are barely noticeable during a human lifetime. Coasts, however, are not static; they are dynamic. They quickly change shape and location in response to natural forces and human activities. These forces and activities continually push and pull at coasts—sometimes in the same direction, but often in opposite directions. As a result, the shape of the coastline changes. Sand and other materials are moved onto and off of beaches by currents and waves. Seasonal movement of coastal materials creates broad summer beaches followed by narrow winter beaches in an annual cycle. During major storms, huge waves and storm surges can move large amounts of coastal sediments and can flood vast areas in a matter of hours.¹

In this lab, you will investigate the dynamic processes that shape coasts: the erosional and depositional forces, sea level fluctuations, and coral reef development (and threats).

Part A. Sediment Transport and Barrier Islands

Ocean waves are the primary cause of erosion along a coast, which eventually influences the shape of the coastline. When a wave moves toward the shore, the wave slows down in shallow areas but maintains its speed in deeper areas. This causes the wave to bend as you can see in Figure 16.1. This phenomenon is called wave refraction and is important in coastline formation. Because of wave refraction, coastlines are not straight; instead, they bend much like the shape of the waves themselves.

Figure 16.1: Wave Refraction. Figures by Jeremy Patrich are licensed under CC BY-NC-SA 4.0

As waves crash onto the shore, they cause weathering by breaking down rock into smaller and finer pieces called sand and sediment. Over time, coastal sediment transport occurs in which sand and sediment are transported along a shoreline in a process called erosion.

Sediment moves along a shoreline by two primary processes: the longshore current and beach drift. Longshore currents are ocean currents that move parallel to the shore yet approach the shoreline at a slight angle (Figure 16.2). Longshore currents drag water down the length of the beach in the same direction the wind is blowing. Beach drift also carries sand and sediment along the shoreline. As waves wash on and off the beach, they transport sediment and sand with them in a zigzag-like movement.

Figure 16.2: Longshore Current and Beach Drift.

Exercise \(\PageIndex{1}\)

1. Label Figure 16.3 (shown below) with the following terms: longshore current, beach drift, net movement of sand grains, upstream, and incoming wave direction.

Figure 16.3: Model of How Sediment Moves along a Coastline. Figure by Jeremy Patrich is licensed under CC BY-NC-SA 4.0

2. Describe the path of sand and sediment particles along a coastline.

3. Explain how longshore current and beach drift are similar.

4. Use Your Critical Thinking Skills: Think about the formation of beaches as we see them. Explain how a beach might form along a coastline.

Coastal sediment transport can form landscapes away from the shore as well. Barrier islands are long, narrow, offshore deposits of sand or sediments that run parallel to the shore. Barrier islands are separated from the mainland by a bay or lagoon.

Barrier islands can be fairly short or in some cases incredibly long. For example, Padre Island, Texas, shown in Figure 16.4, is less than 3.2 kilometers (2 miles) wide but is 182 kilometers (113 miles) long! Fun fact: the United States has more than 400 barrier islands, more than any other country.

Figure 16.4: Map of Padre Island. Figure by National Park Service is in the public domain

Barrier islands have several important functions, including protecting shorelines from severe storm damage and allowing native plant and animal habitats to thrive in a somewhat protected area of the coastline. Barrier islands are quite common in the United States, particularly along the Gulf Coast and East Coast, where approximately 300 barrier islands have been mapped. Barrier islands form over thousands of years as a result of weathering and erosion from interglacial periods. As ice melts on land, it flows downstream toward the sea, forming creeks and rivers. River flow carries sediment and rock with it as it drains into the sea. This sediment and sand form pieces of land near and along the shore of large land masses (Figure 16.5). Eventually, the pieces of land separate from the large land mass completely, forming a barrier island.

Figure 16.5: Barrier Island Development. Figure by Jeremy Patrich is licensed under CC BY-NC-SA 4.0

Barrier islands have been instrumental in protecting coastline from storm damage; but unfortunately, development and construction over the last 100 years has caused serious deterioration of barrier islands in the United States. In addition, sea level rise poses a threat to barrier islands with communities and vulnerable habitats.

Exercise \(\PageIndex{2}\)

5. Refer to Figure 16.5.

1. During Stage 1, why would sea level be lowest compared to the other stages?

2. During Stage 2, what might explain the flooding from river valleys upstream?

3. During Stage 3, what would cause the land to be broken into spits? (Tip: refer to Figure 16.6, which shows a sand spit).

4. During Stage 4, how might the newly formed barrier islands serve as a resource to communities of people living along the coast?

Case Study: Louisiana Barrier Islands

Sea level rise and the increased erosion that results is a serious concern for barrier islands. NASA provides a quote from geoscience researcher Matthew Stutz that explains how every barrier island is unique:

"However, rising sea level is not just like pouring more water into a bathtub," Stutz emphasized. Islands react differently based on the geology in a region and how the waves and tides in an area are affected. People tend to assume sea level rise means fewer islands no matter what, but the rate of rise is critical."^[287]

Decreases in upstream sediment supplies from human activities such as dam construction also play a role in disappearing barrier islands, especially along the Mississippi Delta. The USGS explains that:

Louisiana's barrier islands are eroding so quickly that according to some estimates they will disappear by the end of this century. Although there is little human habitation on these islands, their erosion may have a severe impact on the environment landward of the barriers. As the islands disintegrate, the vast system of sheltered wetlands along Louisiana's delta plain are exposed to increasingly open Gulf conditions. Through the processes of increasing wave attack, salinity intrusion, storm surge, tidal range, and sediment transport, removal of the barrier islands may significantly accelerate deterioration of wetlands that have already experienced the greatest areal losses in the U.S. Because these wetlands are nurseries for many species of fish and shellfish, the loss of the barrier islands and the accelerated loss of the protected wetlands may have a profound impact in the billion dollar per year fishing industry supported by Louisiana's fragile coastal environment.^[288]

Exercise \(\PageIndex{3}\)

6. List the causes of barrier island destruction:

7. List the effects of barrier island destruction:

Let’s explore Louisiana’s barrier islands by comparing satellite imagery across multiple years.

Step 1

Go to Esri’s World Imagery Wayback website. Or, if you have Google Earth Pro you could look at the historical imagery in that program.

Step 2

In the search box, type Louisiana and click the magnifying glass.

Step 3

Zoom in on one of the barrier islands off the coast of Louisiana (pick any named island).

Exercise \(\PageIndex{4}\)

8. What is the name of the barrier island that you zoomed in on?

Step 4

Zoom in as far as you are able to.

Step 5

Click the “Only versions with local changes” box.

Exercise \(\PageIndex{5}\)

9. What is the date of the oldest imagery available?

10. What is the date of the most recent imagery available?

Step 6

Click on each date available to see how the barrier island landscape changed over time.

Exercise \(\PageIndex{6}\)

11. In two to three sentences, describe the changes that you observe.

12. Use Your Critical Thinking Skills: If the historical imagery at the barrier island that you selected went back 10, 50, or 100 years, what changes do you think you would have observed? Respond in one to two sentences.

Part B. Emergent and Submergent Coastlines

Emergent coasts occur where sea levels fall due to tectonic uplift or ice ages. Emergent coasts are also called erosional coasts. Some features associated with emergent coasts include high cliffs, headlands, exposed bedrock, steep slopes, rocky shores, arches, stacks, tombolos, wave platforms, and wave notches (Figure 16.6, top). In emergent coasts, wave energy, wind, and gravity erode the coastline. The erosional features are elevated relative to the wave zone. Sea cliffs are persistent features as waves cut away at their base and higher rocks calve off by mass wasting. Refracted waves that attack bedrock at the base of headlands may erode or carve out a sea arch, which can extend below sea level. When a sea arch collapses, it leaves a rock column called a stack.^[289]

When rock behind the stack erodes, sand can erode from the headland. Eroded sand that collects from the headland to the stack forms a tombolo: a sand strip that connects the stack to the shoreline. Where sand supply is low, wave energy may erode a wave-cut platform across the surf zone, exposed as bare rock with tidal pools at low tide. This bench-like terrace extends to the cliff’s base. When wave energy cuts into the base of a sea cliff, it creates a wave notch.⁸

Submergent coasts are also known as depositional coasts. Submergent coasts occur where sea levels rise due to tectonic subsidence—when the Earth’s crust sinks—or when sea levels rise due to glacier melt. Features associated with submergent coasts include river mouths, fjords, barrier islands, lagoons, estuaries, bays, tidal flats, and tidal currents (Figure 16.6, bottom). In submergent coastlines, river mouths are flooded by the rising water.⁹ As sediments travel along the longshore current and are deposited, long ridges called spits extend parallel to the coastline.

Figure 16.6: Coastal Features. Figure by Waverly Ray is licensed under CC BY-NC-SA 4.0

Exercise \(\PageIndex{7}\)

13. Refer to Figure 16.6.

1. In one to two sentences, explain how a sea stack forms.

2. Apply What You Learned: On the depositional coastline diagram at the bottom of Figure 16.6, draw and label an arrow that represents the longshore current.

3. In one to two sentences, explain how a bay mouth bar forms.

14. For each of the four photographs shown in Figure 16.7, indicate whether the coastline is erosional or depositional and identify the features(s) shown on the photographs.

Figure 16.7: Coastal Features Identification Activity. Figure with public domain photographs by NASA Earth Observatory and the National Park Service are in the public domain

Sea Level Rise

Both erosional and depositional coastlines will be impacted by sea level rise. There are several important ideas to understand about sea level rise, which were published by NOAA in 2019^[292]:

➢ Global sea level has been rising over the past century, and the rate has increased in recent decades. In 2014, global sea level was 2.6 inches above the 1993 average—the highest annual average in the satellite record (1993 to present). Sea level continues to rise at a rate of about one-eighth of an inch per year.

➢ The two major causes of global sea level rise are thermal expansion caused by warming of the ocean (since water expands as it warms) and increased melting of land-based ice, such as glaciers and ice sheets. The oceans are absorbing more than 90 percent of the increased atmospheric heat associated with emissions from human activity.

➢ With continued ocean and atmospheric warming, sea levels will likely rise for many centuries at rates higher than that of the current century. In the United States, almost 40 percent of the population lives in relatively high population density coastal areas, where sea level plays a role in flooding, shoreline erosion, and hazards from storms.

➢ Globally, 8 of the world's 10 largest cities are near a coast, according to the U.N. Atlas of the Oceans.

➢ Sea level is primarily measured using tide stations and satellite laser altimeters. Tide stations around the globe tell us what is happening at a local level—the height of the water as measured along the coast relative to a specific point on land. Satellite measurements provide us with the average height of the entire ocean. Taken together, these tools tell us how our ocean sea levels are changing over time.

To understand the projected impacts of sea level rise to the United States, NOAA developed a Sea Level Rise Map Viewer. This website provides mean higher high water (MHHW) data, which represents the average of the higher high water height of each tidal day. This average is based on the current National Tidal Datum Epoch of 19 years from 1983 to 2001. Figure 16.8 provides an example diagram of all of the data collected at a monitoring station at Apra Harbor, Guam. The data is shown in feet and is referenced on the mean sea level (MSL) based on the same time period (1983 to 2001). Notice that the MHHW is the highest value shown on Figure 16.8.

Figure 16.8: Tidal Data for Apra Harbor, Guam. Figure downloaded on September 20, 2020, by NOAA Datums is in the public domain

Table 16.1 provides the abbreviations (Abbrev.), names, and descriptions of each of the tidal datums shown on Figure 16.8. Arithmetic mean is the average that is calculated by adding all of the values together and then dividing that number by the total number of values. Some locations have diurnal tides—one high tide and one low tide per day. At most locations, there are semidiurnal tides—the tide cycles through a high and low twice each day, with one of the two high tides being higher than the other and one of the two low tides being lower than the other.^[294]

Exercise \(\PageIndex{8}\)

15. Label the abbreviations shown on Figure 16.8 with the names of the tidal datums. The MSL abbreviation has been labeled as an example.

Table 16.1: Tidal Datum Abbreviation and Descriptions

Abbrev.	Tidal Datum	Description
MSL	Mean Sea Level	The arithmetic mean of hourly heights observed over the National Tidal Datum Epoch.
MHW	Mean High Water	The average of all the high water heights observed over the National Tidal Datum Epoch.
MHHW	Mean Higher High Water	The average of the higher high water height of each tidal day observed over the National Tidal Datum Epoch.
DHQ	Mean Diurnal High Water Inequality	One-half the average difference between the two high waters of each tidal day observed over the National Tidal Datum Epoch. It is obtained by subtracting the mean of all the high waters from the mean of the higher high waters.
MTL	Mean Tide Level	The arithmetic mean of mean high water and mean low water.
MN	Mean Range of Tide	The difference in height between mean high water and mean low water.
DTL	Diurnal Tide Level	The arithmetic mean of mean higher high water and mean lower low water.
Ortho	Orthometric Height	Distance from a reference elevation, using a system called NAVD 88.
GT	Great Diurnal Range	The difference in height between mean higher high water and mean lower low water.
MLW	Mean Low Water	The average of all the low water heights observed over the National Tidal Datum Epoch.
DLQ	Mean Diurnal Low Water Inequality	One-half the average difference between the two low waters of each tidal day observed over the National Tidal Datum Epoch. It is obtained by subtracting the mean of the lower low waters from the mean of all the low waters.
MLLW	Mean Lower Low Water	The average of the lower low water height of each tidal day observed over the National Tidal Datum Epoch.

16. Use Your Critical Thinking Skills: Why do you think that a website designed to inform stakeholders about the potential of coastal flooding would use MHHW data rather than some of the other data shown in Figure 16.8?

Before you navigate the Sea Level Rise Map Viewer website, you will complete a tutorial that takes you through the website navigation. Complete Steps 1 through 5 below to answer questions 17 through 21 using the tutorial. Then, complete Steps 6 through 8 using the Sea Level Rise Map Viewer to answer questions 22 and 23.

Step 1

Go to the Sea Level Rise Viewer: Local Scenarios Quick Start Tutorial. (Note: the tutorial does not have audio).

Step 2

Click the blue next button on the bottom-right of the screen.

Step 3

Read each slide and continue to click the blue next button on the bottom-right of the screen to advance the slides.

Step 4

Follow any prompts provided. For example, you will need to search for Ship Bottom, New Jersey. You will be prompted to click on certain components in gray comment boxes. In the first example scenario, you will help to develop an adaptation plan for a highly populated area where stakeholders have a low tolerance for risk and the “high” sea level rise scenario should be used.

Exercise \(\PageIndex{9}\)

17. In what year can Ship Bottom be expected to experience 3 feet of inundation?

18. What color are low-lying areas?

19. When low-lying areas are flooded, what color do they change to?

Step 5

Begin the second scenario, in which you will help develop a forty-year adaptation plan.

Exercise \(\PageIndex{10}\)

20. In 2060, what is the water level where widespread inundation is visible with roads and property flooded?

21. Which of the following scenarios would you recommend for the forty-year adaptation plan for Ship Bottom: intermediate low, intermediate, intermediate high, high, or extreme?

Step 6

Now that you are acquainted with the website, go to the Sea Level Rise Viewer website and click Get Started.

Step 7

In the left-hand side of the screen, click on Local Scenarios.

Step 8

Exercise \(\PageIndex{11}\)

22. With the Intermediate High Scenario selected, complete Table 16.2 with two examples from each of the regions shown in the left-hand column. (You can select any two locations that you would like).

• Zoom in to each location marked with the green pin that shows buildings.
• For each location, be sure to use the Water Level slider bar to see the progression of flooding through 2100.
• Remember to use the Intermediate High Scenario.
• Keep the option to “View By Scenario”.

Table 16.2: Mean Higher High Water (MHHW) in feet

Region	Location Name	2020	2040	2060	2080	2100
Hawai’i
Hawai’i
West Coast
West Coast
Gulf of Mexico
Gulf of Mexico
East Coast
East Coast
Puerto Rico
Puerto Rico

23. Refer to your data in Table 16.2.

1. Which location has the highest MHHW in 2020?

2. Which location has the highest MHHW in 2040?

3. Which location has the highest MHHW in 2060?

4. Which location has the highest MHHW in 2080?

5. Which location has the highest MHHW in 2100?

6. Use Your Critical Thinking Skills: Which locations are examples of submergent coastlines? Explain your response in one to two sentences.

7. Which location seems to have the most flooding of buildings and infrastructure by 2060? Tip: estimate this by using the Water Level slider bar.

8. What are three conclusions that you can make based on the Sea Level Rise Viewer?

Part C. Coral Reef Coasts

Coral reef coasts are some of the most diverse and dynamic coastal systems on Earth! They are home to approximately 4,000 species of fish and 800 species of corals! Coral reefs provide essential habitat for tropical marine species to feed, breed, spawn, and nurse. Human societies greatly depend on marine ecosystems, including coral reefs. Approximately 500 million people worldwide depend on coral reefs for food, income, and shelter. Because coral reef structures are able to absorb much of the energy produced by ocean waves, a healthy coral reef has the ability to protect shorelines from coastal erosion, habitat loss, and property damage.

Coral reefs form in shallow warm waters of the ocean off the coasts of large land masses or around volcanic islands (Figure 16.9). The structure of the reef itself forms in shallow waters generally less than 27 meters (90 feet) deep, although reef-building corals have been found as deep as 70 meters (230 feet). Reef building corals are made of tiny animals, called coral polyps. Coral polyps attach themselves to the rock layer by secreting layers of calcium carbonate onto the rock. These polyps form colonies that can become quite large and weigh up to several tons. Coral colonies are unique in that they form a symbiotic and dependent relationship with microscopic algae called zooxanthellae. Because algae are plants and plants are producers, zooxanthellae must make their own “food” like other plants to obtain energy and survive through the process of photosynthesis. Shallow waters allow sunlight to reach the reef, which is required for photosynthesis to occur. Coral reefs are incredibly sensitive and tend to thrive in areas of ocean where surface temperatures (SST) range from 73° and 84° Fahrenheit (23° to 29° Celsius). Temperatures outside of that range cause serious harm to the health of the reef.

Fig 16.9: Spatial Distribution of Coral Reefs. Figure from NOAA’s National Ocean Service is in the public domain

Exercise \(\PageIndex{12}\)

24. Refer to Figure 16.9.

1. Explain the spatial distribution of coral reefs.

2. Where are coral reefs most concentrated? Why are they located there?

3. Which of the seven special lines of latitude (poles, circles, tropics, and equator) do coral reefs tend to grow near?

4. In what regions of the world do coral reefs tend to be absent? Why do you think this is?

5. What is your home state? Do coral reefs exist near your home state? Why or why not?

Coral reef coasts that form around volcanic islands can become some of the most beautiful and diverse places in the world (Figure 16.10). These reef structures begin around active volcanoes and continue to evolve over millions of years as a volcano becomes extinct. There are three key formations in the evolution of volcanic island coral reefs: fringing reefs, barrier reefs, and atoll reefs. Coral polyps secrete layers of calcium carbonate onto flanked pieces of land attached to the volcano; this is known as a fringing reef. Zooxanthellae quickly move in and begin a symbiotic relationship with coral polyps and soon a colony evolves. Over thousands of years, the volcano becomes extinct and weathering leads to erosion of the volcano, which causes the volcano to appear to “sink” into the ocean. Erosion causes sediment and rock to build up around the volcano, creating small bays and lagoons. This newer formation is now called a barrier reef. Over several million years, as weathering and erosion continue, the volcano appears to “sink” altogether and soon a large lagoon forms surrounded by coral colonies. This last formation is known as an atoll and can take up to 30 million years to form. Atolls are home to pristine habitats and can make a snorkeler feel as though they are swimming in an aquarium!

Figure 16.10: Evolution of a Volcanic Island Coral Reef. Figure by Jeremy Patrich is licensed under CC BY-NC-SA 4.0

Exercise \(\PageIndex{13}\)

25. Based on the descriptions provided in the above paragraph, label atoll, fringing reef, and barrier reef on Figure 16.10.

Threats to Coral Reefs

Today, there are two great threats to coral reefs around the world: rising sea levels and increasing sea surface temperatures (SST). Both of these have caused coral bleaching, a symptom of an unhealthy or dying reef. As sea levels rise, corals submerse in deeper waters, preventing sunlight from reaching the reef. As SST increases, the water in and around the reef becomes too warm. A lack of sunlight and heat stress create poor conditions for zooxanthellae, and they expel themselves from the reef altogether. Once the zooxanthellae leave a reef, the corals lose a source of food and their source of color. While reefs can survive bleaching events, continued increase in SST and warming waters over the last 50 years have prevented reefs from recovering from bleaching events, resulting in mass die offs around the world. Bleaching events begin when SST reaches 1 to 2°C (1.8°F) above average temperatures for a particular reef. More importantly, photosynthesis pathways in zooxanthellae become impaired when SST are greater than 30°C (86°F). Figure 16.11 is a map showing average sea surface temperatures from 1981 to 2020.

Figure 16.11: Sea Surface Temperatures Map. Figure by NOAA’s National Centers for Environmental Information is in the public domain

Exercise \(\PageIndex{14}\)

26. Refer to Figure 16.11.

1. Explain the global distribution of sea surface temperatures (SST).

2. What is the SST at 20°S, 150°W?

3. Between which latitudes do most of the warmer temperatures occur?

4. Which coast of the United States experiences warmer SST year-round? Explain why in one to two sentences.

5. Apply What You Learned: Do you think coral reefs would be more concentrated on the west coast of the United States or the east coast of the United States? Explain your response in one to two sentences.

Figure 16.12 shows the changes in SST between 1901 and 2015.

Figure 16.12: Map of Change in Sea Surface Temperature. Figure by the Environmental Protection Agency is in the public domain

Exercise \(\PageIndex{15}\)

27. Refer to Figure 16.12.

1. In one to two sentences, describe the overall trend in sea surface temperature change from 1901 to 2015.

2. Which areas of the oceans experienced the greatest increase in SST? Tip: refer to a world map to identify the locations.

3. Use Your Critical Thinking Skills: Why would there be insufficient data available for certain ocean locations? Explain your response in one to two sentences.

4. Use Your Critical Thinking Skills: Why might the ocean area southeast of Greenland in the North Atlantic Ocean be the only location to have cooled between 1901 and 2015? Explain your response in one to two sentences.

A third threat to coral reefs is low-oxygen (hypoxia) stress. When there are low or depleted dissolved oxygen levels in the oceans, life is unable to be sustained and dead zones are created. There may be die-offs of corals, aquatic plants, fish, and shellfish in dead zones. NOAA’s Ocean Service explains that “the amount of oxygen in any water body varies naturally, both seasonally and over time. This occurs due to a balance between oxygen input from the atmosphere and certain biological and chemical processes, some of which produce oxygen while others consume it”.^[299] NOAA’s National Centers for Coastal Ocean Science (NCCOS) further explains that:

Hypoxia (low oxygen) poses a serious and escalating threat to marine ecosystems globally. While the impacts of hypoxia have been well characterized in temperate marine systems, they remain poorly understood for tropical coral reef ecosystems. Preliminary studies indicate that hypoxia has negative consequences for coral health and reef diversity. With many of the world’s coral reefs in decline, it is important to understand the additional threat represented by hypoxia. Human-assisted coral restoration efforts are increasing to reverse the trends of coral reef loss. It is important to understand how hypoxia can impact the survival of corals to develop the best strategies for choosing restoration sites and coral species to maximize the likelihood of success.^[300]

Figure 16.13 shows documented dead zones in red dots, density of coral reefs in blue to purple shading, and hypoxia-related coral reef deaths (mortality) in yellow dots. Coral reef density is the coral reef area per local bioregion (x 1,000 km²).

Figure 16.13: Change in Sea Surface Temperature Map. Figure by Jeremy Patrich is licensed under CC BY-NC-SA 4.0 adapted from Cmglee and Strebe

Exercise \(\PageIndex{16}\)

28. Refer to Figure 16.13.
    1. Analyze the map data to complete Table 16.3 below.

Table 16.3: Analysis of Hypoxia-Implicated Coral Reef Mortality

Region	Gulf of Mexico and Caribbean	Indian Ocean	North Pacific Ocean	South Pacific Ocean
Total Number of Gold Dots in this Region
Number of Gold Dots in Most Dense Coral Reef Areas (dark blue and dark purple shading)
Number of Gold Dots in Least Dense Coral Reef Areas (light blue and light purple shading)

2. Which region has the highest concentration of hypoxia-related coral reef deaths?

3. Is there a spatial correlation between hypoxia-related coral reef deaths and whether or not the coral is located in one of the most dense or least dense coral reef areas? Use the data in Table 16.2 in your response.

4. Use Your Critical Thinking Skills: What might explain the spatial distribution of hypoxia-related coral reef deaths? Explain your response in one to two sentences.

Case Study: The Great Barrier Reef

The Great Barrier Reef (Figure 16.14) is the largest coral reef system in the world. It is located in Australia in the Coral Sea, off the east coast of Queensland (one of six states of Australia). The Great Barrier Reef stretches approximately 2,300 kilometers (1,400 miles) over an area of approximately 344,400 square kilometers (133,000 square miles) and is home to nearly 3,000 individual reefs and 900 islands. By comparison, the coastline of California is approximately 1,350 kilometers (840 miles) long and the area of the Great Barrier Reef is approximately the same size as the countries of Japan and Germany.

Figure 16.14: Great Barrier Reef Locator Map. Figure by NeoGeneric is licensed under CC BY-SA 4.0

Figure 16.15 shows SST data collected by satellites for the Great Barrier Reef between January 7 and March 25, 2017. Temperatures were collected weekly and the data was plotted on a graph that indicates when coral reach their bleaching limit (29.7°C). Recall that coral bleaching is a stress response that results when corals expel zooxanthellae living in their tissues, which causes the coral to turn white.

Figure 16.15: Great Barrier Reef Weekly Sea Surface Temperature. Figure by Waverly Ray with data from NOAA is licensed under CC BY-NC-SA 4.0

Exercise \(\PageIndex{17}\)

29. Refer to Figure 16.15.

1. On the Great Barrier Reef, what temperature do sea surfaces need to reach to cause coral bleaching? Answer in both °C and °F. (See formula below).

Use this formula to convert °C to °F:

(Temperature in Degrees Celsius x 1.8) + 32 = Temperature in Degrees Fahrenheit

2. Coral bleaching events begin when SST reaches 1 to 2°C (1.8°F) above average temperatures for a particular reef. What is the average SST range for the Great Barrier Reef? Answer in both °C and °F.

3. Use Your Critical Thinking Skills: Do you think the difference in temperature between average SST and the bleaching limit is small or large? Explain your response in one to two sentences.

4. How many weeks did the temperatures exceed the ‘bleaching limit’?

5. How many degrees above the bleaching limit did the sea surface temperature rise during the week of January 28, 2017?

6. Were there any weeks between January 7 and March 25 when SST did not reach the bleaching limit?

7. Do you believe the corals on the Great Barrier Reef to be at high risk, moderate risk, or low risk of bleaching due to heat stress? Use the temperature data to explain your answer in one to two sentences.

Check It Out! What You Can Do to Help Protect Coral Reefs

Visit the EPA’s website to learn what you can do every day to help protect coral reefs.

Australia has a population of 25 million people and nearly 65,000 are employed by industries that rely on the Great Barrier Reef. Table 16.4 shows the number of people employed and the value added by the economic activities associated with the Great Barrier Reef (GBR). This research conducted between 2015 and 2016 by the multinational accounting firm Deloitte shows the total economic value of the Great Barrier Reef to Australia to be $4.5 billion US dollars.

Table 16.4: Economic Contribution of the Great Barrier Reef (2015-2016). Data shown in US dollars based on report from Deloitte

Industry	Number Employed in GBR Regions	Number Employed in Australia	Value Added in GBR Regions	Valued Added in Australia
Tourism	19,855	58,980	1.7 billion	4 billion
Fishing	680	814	98 million	162 million
Recreation	2,889	3,218	199 million	170 million
Scientific Research	895	970	109 million	128 million
Total	24,139	64,044	2 billion	4.5 billion

Exercise \(\PageIndex{18}\)

30. Refer to Table 16.4.

1. Which industry operating in Great Barrier Reef (GBR) Regions brought the most economic value to Australia between 2015 and 2016?

2. Tourism in GBR Regions accounts for what percent of the total value added to the entire Australian economy? Show your calculation.

3. How many people did the Great Barrier Reef employ in all of Australia between 2015 and 2016? Show your calculation.

4. What could explain the higher numbers of employment in Australia versus the Great Barrier Reef Regions for tourism?

5. How might coral bleaching and the dying of coral reefs impact communities near GBR Regions?

6. How might coral bleaching and the dying of coral reefs eventually affect the general population of Australia?

Part D. Wrap-Up

Consult with your geography lab instructor to find out which of the following wrap-up questions you should complete. Attach additional pages to answer the questions as needed.

Exercise \(\PageIndex{19}\)

31. What is the most important idea that you learned in this lab? In two to three sentences, explain the concept and why it is important to know.

31. What was the most challenging part of this lab? In two to three sentences, explain why it was challenging. If nothing challenged you in the lab, write about what you think challenged your classmates.

31. What is one question that you have about what you learned in this lab? Write your question along with one to two sentences explaining why you think your question is important to ask.

31. Review the learning objectives on page 1 of this lab. How would you rate your understanding or ability for each learning objective? Write one sentence that addresses each learning objective.

31. Sketch a concept map that includes the key ideas from this lab. Include at least five of the terms shown in bold-faced type.

31. Create an advertisement to educate your peers on the important information that you learned in this lab. Include at least three key terms in your advertisement. The advertisement should be about half a page in size (about 4 inches by 6 inches).

31. One way to think of physical geography is that it is the study of the relationships among variables that impact the Earth's surface. Select two variables discussed in this lab and describe how they are related.

31. How does what you learned in this lab relate to your everyday life? In two to three sentences, explain a concept that you learned in this lab and how it relates to your day-to-day actions.

31. How does what you learned in this lab relate to current events?
    1. Write the title, source, and date of a news item that relates to this lab.
    2. In two to three sentences, discuss how the news item relates to what you have learned in this lab.
    3. In one to two sentences, discuss whether or not the news item accurately represents the science that you learned. Tip: consider whether or not the news item includes the complexity of the topic.

31. Search O*NET OnLine to find an occupation that is relevant to the topics presented in today's lab. Your lab instructor may provide you with possible keywords to type in the Occupation Quick Search field on the O*NET website.
    1. What is the name of occupation that you found?
    2. Write two to three sentences that summarize the most important information that you learned about this occupation.
    3. What is one question that you would want to ask a person with this occupation?

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^[282] Text by USGS is in the public domain

^[287] Text by NASA is in the public domain

^[288] Text by the USGS is in the public domain

^[289] Text by Chris Johnson, Matthew D. Affolter, Paul Inkenbrandt, Cam Mosher is licensed under CC BY-NC-SA 4.0

^[292] Text by NOAA is in the public domain

^[294] Text by NOAA is in the public domain

^[299] Text by NOAA’s National Ocean Service is in the public domain

^[300] Text and figure by NOAA’s NCCOS are in the public domain