Fall 2019 APES chapter 16

Lecture Outlines

Chapter 16

Marine and Coastal Systems and Resources

Withgott/Laposata

This lecture will help you understand:



The marine environment



Ocean-climate relationships



Marine ecosystems



Marine pollution



The state of ocean fisheries

Central Case Study: Collapse of the Cod

Fisheries



No fish has had more impact on civilization than the

Atlantic cod



Cod have been fished for centuries

Central Case Study: Collapse of the Cod

Fisheries



Cod eat small fish and invertebrates



They inhabit cool waters on both sides of the Atlantic



Large ships and technology have overfished the cod



Cod populations shrank in the 1980s and crashed in

the early 1990s

Central Case Study: Collapse of the Cod

Fisheries



Fishing for cod was temporarily banned in numerous

fisheries



Cod fishing was a major source of employment and

income for many areas along the Atlantic coast

Central Case Study: Collapse of the Cod

Fisheries



Even with the fishing ban, stocks of cod were not

recovering

 Fish that had been cod prey were eating young cod



Bans were extended

The Oceans



Oceans are an important part of the Earth’s

interconnected aquatic systems

 Receive most inputs of water sediments, pollution



Oceans influence climate, teem with biodiversity,

provide resources, and help transportation and

commerce



Oceans cover 71% of Earth’s surface and contain

97.5% of its water

 They are a single vast body of water

Seafloor topography can be rugged

 The seafloor consists of underwater volcanoes, steep

canyons, mountain ranges, vast trenches, mounds of debris, and some flat areas

 We can look at the ocean’s bathymetry (depths) and topography (landforms)

 Continental shelves  areas of shallow, gently sloping sea floor next to the continents

 Sea floor angles down from there at the self-slope break

Seafloor topography can be rugged



Some island chains are formed by reefs on the

continental shelf (e.g., Florida Keys)



Others are volcanic in origin (e.g., Aleutian Islands)



Where underwater structures exist, life thrives

Ocean water contains high concentrations of

dissolved salt



Ocean water is 96.5% water by mass

 Remainder is mostly ions of dissolved salts

 Ocean water is over 33,000 parts per million salts, fresh water is 500 ppm



Salts enter oceans in runoff from the land

Ocean water contains high concentrations of

dissolved salt



Oceans contain low levels of nutrients (nitrogen and

phosphorus)



Oxygen is added by plants, bacteria, and

atmospheric diffusion

Solar energy structures ocean water from

surface to bottom



Water temperature declines with depth



Heavier (colder, saltier) water sinks; light (warmer,

less salty) water stays near the surface



Surface zone

 Warmed by sunlight and stirred by wind

 Consistent water density down to about 150m

 Contains about 2% of the oceans water



Pycnocline



zone below the surface

 Density increases rapidly with depth

Solar energy structures ocean water from

surface to bottom

 Deep zone  zone below the pycnocline; remaining 80%  Dense, sluggish water

 Unaffected by winds, storms, sunlight, temperature

 Temperatures are more stable than land temperatures

 Water has high heat capacity heat required to increase temperature by a given amount

 It takes more energy to warm water than air  Oceans regulate Earth’s climate

 They absorb and release heat

Surface water flows horizontally in currents



Currents



vast river like flows in the oceans

 Move horizontally in the upper 400 m of water

 Driven by density differences, heating and cooling, gravity, and wind



Some currents such as the Gulf Stream are rapid

and powerful

Surface water flows horizontally in currents



Currents have helped carry people across the globe

 Also transport heat, nutrients, pollution, and the larvae of many marine species

Vertical movement of water affects marine

ecosystems



Upwelling



the upward flow of cold, deep water

toward the surface

 Water is rich in nutrients

 Sites of high primary productivity and lucrative fisheries

 Also occurs where strong winds blow away from, or parallel to, coastlines



Downwelling

= process in which oxygen-rich water

sinks where surface currents come together

Ocean currents affect Earth’s climate

 Horizontal and vertical movement of oceans affects global and regional climates

 Thermohaline circulation  a worldwide current system  Warmer, fresher water moves along the surface

 Cooler, saltier, denser water moves deep beneath the surface

 North Atlantic Deep Water (NADW)  one part of the thermohaline conveyor belt

 Water in the Gulf Stream flows to Europe

Ocean currents affect Earth’s climate



Interrupting the thermohaline circulation of the

NADW could trigger rapid climate change

 Melting ice from Greenland will run into the North

Atlantic, making surface waters less salty, less dense

 Could stop NADW formation and shut down the northward flow of warm water

 Europe would rapidly cool



This circulation is already slowing

Ocean currents affect Earth’s climate



El Niño–Southern Oscillation (ENSO)



a

systematic shift in atmospheric pressure, sea

surface temperature, and ocean circulation in the

tropical Pacific Ocean



Normal winds blow east to west, from high to low

pressure

Ocean currents affect Earth’s climate



Winds push water west, causing it to “pile up”

 Nutrient-rich, cold water along Peru and Ecuador rises from the deep



Decreased pressure in the eastern Pacific triggers

El Niño

Ocean currents affect Earth’s climate

 Coastal industries (e.g., Peru’s anchovy fisheries) are devastated (no upwelling means low productivity)

 Worldwide, fishermen lost $8 billion in 1982–1983  Global weather patterns change

 Rainstorms, floods, drought, fires  La Niña  the opposite of El Niño

 Cold waters rise to the surface and extend westward

 ENSO cycles are periodic but irregular (every 2–8 years)

Climate change is altering ocean chemistry

 Global climate change will affect ocean chemistry and biology

 Burning fossil fuels and removing vegetation increase CO₂, which warms the planet

 Oceans absorb carbon dioxide (CO₂) from the air

 But oceans may not be able to absorb much more CO₂

 Increased CO₂ in the ocean makes it more acidic

 Ocean acidification makes chemicals less available for sea creatures (e.g., corals) to form shells

Marine and Coastal Ecosystems



Regions of ocean water differ greatly

 Some zones support more life than others



Photic zone



well-lighted top layer

 Absorbs 80% of solar energy

Marine and Coastal Ecosystems



Pelagic



habitats and ecosystems between the

ocean’s surface and floor



Benthic



habitats and ecosystems on the ocean

floor



Most ecosystems are powered by solar energy

 But even the darkest depths host life

Intertidal zones undergo constant change



Intertidal (littoral) ecosystems



ecosystems

where the ocean meets the land

 Between the uppermost reach of the high tide and the lowest limit of the low tide



Tides



periodic rising and falling of the ocean’s

height due to the gravitational pull of the sun and

moon

 High and low tides occur roughly 6 hours apart



Intertidal organisms spend part of their time

Intertidal zones undergo constant change



Intertidal zones are a tough place to live, but they

have amazing diversity

 Rocky shorelines, crevices, pools of water (tide pools)

 Anemones, mussels, barnacles, urchins, sea slugs, starfish, and crabs



Temperature, salinity, and moisture change

dramatically from high to low tide

 Environmental variation creates horizontal bands of habitat

Salt marshes line temperate shorelines

 Salt marshes  occur along coasts at temperate latitudes  Tides wash over gently sloping sandy, silty substrates

 Rising and falling tides flow into and out of channels called tidal creeks and overflow onto marsh flats

 Salt marshes have very high primary productivity  Thick with salt-tolerant grasses, sedges, shrubs

 Critical habitat for birds, commercial fish, and shellfish  They filter pollution

 They stabilize shorelines against storm surges

Mangrove forests line coasts in the tropics and

subtropics



In tropical and subtropical latitudes mangrove

forests replace salt marshes along sandy coasts



Mangroves



salt-tolerant trees that can live in

changing water levels

 Their unique roots curve up for oxygen and down for support



Provide nesting areas for birds, nurseries for fish

Mangrove forests line coasts in the tropics and

subtropics



Half the world’s mangrove forests are gone

 Developed for residential, commercial, and recreational uses

 Removed for shrimp farming



Once destroyed, coastal areas no longer:

 Slow runoff

 Filter pollutants

 Retain soil

Fresh meets salt water in estuaries



Estuaries



water bodies where rivers flow into the

ocean, mixing fresh and salt water



They are biologically productive

 Have fluctuations in salinity



Critical habitat for shorebirds and shellfish



Transitional zone for fish that spawn in streams and

mature in salt water

Kelp forests harbor many organisms



Kelp



large, dense, brown algae growing from the

floor of continental shelves

 Can reach 60 m (200 ft) long and grow 45 cm (18 in) per day



Dense strands form kelp forests along temperate

coasts

 They provide shelter and food for organisms

 They absorb wave energy and protect shorelines from erosion

Coral reefs are treasure troves of biodiversity



Coral reef



a mass of calcium carbonate

composed of the skeletons of tiny marine animals

(corals)

 May be an extension of a shoreline

 Or exist along a barrier island, parallel to the shore

 Or as an atoll (a ring around a submerged island)



Corals are tiny colonial invertebrate animals related

to sea anemones and jellyfish

 Attach to a rock or reef and capture passing food with stinging tentacles

Coral reefs are treasure troves of biodiversity



Reefs consist of millions of densely packed animals

 Colors come from zooxanthellae



Reefs are located in shallow subtropical and tropical

waters

 Protect shorelines by absorbing waves



Reefs provide complex physical structure

 High primary productivity

Coral reefs are treasure troves of biodiversity



Coral bleaching occurs when zooxanthellae leave

the coral or die

 Corals lose their color and die, leaving white patches

 Results from climate change, pollution, or unknown natural causes



Nutrient pollution causes algal growth, which

smothers coral



Divers damage reefs by using cyanide to capture

fish

Coral reefs are treasure troves of biodiversity



A few coral species thrive in waters outside the

tropics

 On the ocean floor at depths of 200–500 meters (650–1650 ft)

 Occur in cold-water areas off the coasts of Spain, the British Isles, and elsewhere



Little is known about these reefs

 Already, many have been badly damaged by trawling

Open-ocean ecosystems vary in their

biodiversity



Microscopic phytoplankton are the base of the

marine food chain

 Productivity is concentrated in areas of nutrient-rich upwelling

 Algae, protists, cyanobacteria feed zooplankton, which then feed fish, jellyfish, whales, etc.



Predators at higher trophic levels

Open-ocean ecosystems vary in their

biodiversity



Animals of the deep ocean have adapted to extreme

water pressure and the dark

 Some scavenge carcasses or organic detritus

 Others are predators

 Others have mutualistic relationships with bacteria



Hydrothermal vents support tubeworms, shrimp, and

chemosynthetic bacterial species

Marine Pollution

 People use oceans as a sink for waste and pollutants

 Even into the mid-20th century, coastal U.S. cities

dumped trash and untreated sewage along their shores

 Non-point-source pollution comes from all over  Oil, plastic, chemicals, excess nutrients

 Also sewage and trash from cruise ships and abandoned fishing gear

Plastic debris endangers marine life



Plastic items dumped into the sea harm or kill

wildlife

 Organisms can become entangled in debris and drown

Plastic debris endangers marine life



Areas where circulating currents converge called

gyres

bring and trap plastic trash

 The North Pacific Gyre contains the Great Pacific Garbage Patch  an area larger than Texas where floating plastic bits outnumber organisms by a 6 to 1 margin



Plastic is designed not to break down so may drift

for decades

Plastic debris endangers marine life

 Trillions of tiny plastic pellets float in the oceans

 Some of the pellets sink, accumulating on the ocean floor where they do not degrade

 Organisms mistake the floating plastic for food

 The average fish in the great Pacific Garbage Patch had over two pieces of plastic in its digestive tract

 Over 40% of Albatross chick premature deaths have been attributed to pieces of plastic in their food

 Over 260 species are affected by marine plastic debris

Plastic debris endangers marine life

 Ingested plastics can also have toxic effects

 Plastics themselves contain harmful substances such as bisphenol A and pthalates

 May concentrate persistent organic pollutants

 Floating debris can transport organisms great distances  Some of these become invasive species

 Plastics are not easily removed, so prevention is key  The 2006 Marine Debris Research, Prevention, and

Reduction Act aids these efforts

Oil pollution comes from spills of all sizes



About 30% of oil and 50% of natural gas come from

seafloor deposits

 North Sea, Gulf of Mexico



Drilling in other places is banned

 Spills could harm valuable fisheries



The

Deepwater Horizon

exploded off Louisiana’s

coast

in April 2010

 Spilled 1800 gallons/min for 3 months

Oil pollution comes from spills of all sizes



Major spills make headlines

 Foul beaches, coat and kill animals, devastate fisheries



Countless non-point sources produce most oil

pollution

 Half of all oil comes from natural oil seeps

Oil pollution comes from spills of all sizes



Stricter regulations for oil tankers have been

enacted by many governments



The U.S. Oil Pollution Act (1990) created a $1 billion

prevention and cleanup fund

 Requires that all ships have double hulls by 2015

Toxic pollutants can contaminate seafood

 Toxic pollutants can make food unsafe to eat

 Mercury contamination from coal combustion and other sources bioaccumulates and biomagnifies

 Dangerous to children and pregnant or nursing women  Highest mercury levels will be in fish at the top of the

food chain

 Avoid eating swordfish, shark, and albacore tuna

 Eat seafood low in mercury (catfish, salmon, canned light tuna)

Excess nutrients cause algal blooms



Nutrient runoff can allow explosive growth of marine

algae populations



Harmful algal blooms



blooms where nutrients

increase algae that produce powerful toxins

 Dinoflagellate algae toxins attack the nervous system

 Red tide  algae that produce red pigments that discolor water

 Cause illness and death among wildlife and humans

 Economic loss to fishing industries and beach tourism

Emptying the Oceans



Overharvesting is the worst marine problem



We are putting unprecedented pressure on marine

resources

 Half the world’s marine fish populations are fully exploited and can’t be fished more intensively

 28% of fish population are overexploited and heading to extinction



Total fisheries catch leveled off after 1988 despite

increased fishing effort

Emptying the Oceans

 If current trends continue, it is predicted that populations of all ocean species we fish for today will collapse by

2048

 If fisheries collapse as predicted, we will lose their ecosystem services

 Productivity will decline, and they will become more sensitive to disturbance

 Filtering of water will decline, causing more harmful algal blooms and beach closures

We have long overfished

 People began depleting sea life centuries ago

 Species have been hunted to extinction: Caribbean monk seal, Steller’s sea cow, Atlantic gray whale

 Decreased sea turtle populations cause overgrowth of sea grass and can cause sea grass wasting disease

 Overharvesting nearly exterminated many whale species

 People never thought groundfish could be depleted

 Local populations dwindled as far back as the 19th century

Fishing has industrialized



Factory fishing



huge vessels use powerful

technologies to capture fish in huge volumes



Driftnets



transparent nylon mesh nets that drift

with the current

 Used for herring, sardines, mackerel, sharks, shrimp



Longline fishing



extremely long (up to 80 km or

50 mi) lines with several thousand baited hooks

Fishing has industrialized



Trawling



using cone shaped nets with weights at

the bottom and floats at the top to catch pellagic fish

Fishing practices kill nontarget animals and

damage ecosystems



Bycatch



the accidental capture of animals

 A 2011 report found that 17% of all commercially harvested fish were captured unintentionally



Driftnetting drowns dolphins, turtles, and seals

 Fish die on deck

 Banned in international waters

 But is still used in national waters



Longline fishing kills turtles, sharks, and over

300,000 seabirds/year

Fishing practices kill nontarget animals and

damage ecosystems

 Dolphins are trapped in nets used to catch tuna  Hundreds of thousands of dolphins were killed

 The 1972 Marine Mammal Protection Act forced fleets to try to free dolphins

 Bycatch dropped dramatically

 Other nations fished for tuna, and bycatch increased

 The U.S. government required that nations exporting tuna to the United States minimize dolphin bycatch

 “Dolphin-safe” tuna uses methods to avoid bycatch  Other species (sharks) are still being caught

Fishing practices kill nontarget animals and

damage ecosystems

 Bottom trawling causes bycatch and harms entire ecosystems

 Heavy nets crush organisms and damage sea bottoms  Especially destructive to complex areas (e.g., reefs)

 It equals clear-cutting and strip mining

 The average spot of the sea floor in the Georges Bank has been trawled three times, destroying young cod as bycatch

Modern fishing fleets deplete marine life rapidly



Grand Banks cod have been fished for centuries

 Catches more than doubled with industrial trawlers

 Record-high catches lasted only 10 years

Modern fishing fleets deplete marine life rapidly



Worldwide, industrialized fishing is depleting marine

populations with astonishing speed

 90% of large-bodied fish and sharks are eliminated within 10 years after fishing begins

 Populations stabilize at 10% of their former levels



Communities were very different before modern

fishing

Several factors mask declines

 Industrialized fishing has depleted stocks

 But global catch has remained stable for the past 20 years  How can stability mask population declines?

 Fishing fleets travel farther to reach less-fished areas

 Fleets fish in deeper waters (now at 250 m)

 Fleets spend more time fishing and set more nets

 Improved technologies: faster ships, sonar mapping, satellite navigation, thermal sensing, aerial spotting

We are “fishing down the food chain”

 Figures on total global catch do not tell the whole story

 As fishing increases, the size and age of fish caught decline

 10-year-old cod, once common, are now rare

 As species become too rare to fish, fleets target more abundant species

 Shift from large, desirable species to smaller, less desirable ones

 This entails catching species at lower trophic levels

Marine biodiversity loss erodes ecosystem

services



Factors that deplete biodiversity threaten ecosystem

services we get from the oceans



Systems with reduced species or genetic diversity

show less primary and secondary production

 They are less able to withstand disturbance



Biodiversity loss reduces habitat for nurseries for

fish and shellfish



Less diversity leads to reduced filtering and

Fisheries management has been based on

maximum sustainable yield

 Maximizes harvest while maintaining fish for the future  Managers may limit the harvest or restrict gear used

 Despite management, stocks have plummeted  Requires accurate measurement of fish numbers

 Overestimates have resulted in overharvesting

 Ecosystem-based management shifts away from species and toward the larger ecosystem

 Considers the impacts of fishing on habitat quality, species interactions, and long-term effects

We can protect areas in the ocean



Marine protected areas (MPAs)



most are along

the coastlines of developed countries

 They still allow fishing or other extractive activities



Marine reserves



areas where fishing is prohibited

 Leave ecosystems intact, without human interference

 Improve fisheries, because young fish will disperse into surrounding areas



Many commercial and recreational fishers and

businesses do not support reserves

Reserves can work for both fish and fishers



A 2001 review showed that after just one to two

years of establishment, marine reserves:

 Increased densities of organisms by 91%

 Increased biomass by 192%

 Increased organism size by 31%

 Increased species diversity by 23%



Benefits inside reserve boundaries include:

 Rapid and long-term increases in abundance, diversity, and productivity of marine organisms

Reserves can work for both fish and fishers



Areas outside reserves also benefit



A “spillover effect” occurs when individuals of

protected species spread outside reserves

 Larvae of species protected within reserves “seed the seas” outside reserves

Reserves can work for both fish and fishers



Local residents who were opposed changed to

supporting reserves once they saw their benefits



Once commercial trawling was stopped on Georges

Bank:

 Populations of organisms began to recover

How should reserves be designed?



Reserves should be able to

 Protect ecosystems

 Sustain fisheries

 Include people



Most studies suggest that 20–50% of the ocean

should be protected in no-take reserves

 How large should the reserves be?

 How many should we have?

 Where should they be located?

Conclusion



Oceans cover most of our planet and contain

diverse topography and ecosystems



As we learn about oceans and coastal

environments, we are intensifying our use of their

resources and causing severe impacts



We need to address acidification, loss of coral reefs,

pollution, and fisheries depletion



Setting aside protected areas can maintain and

restore natural systems and enhance fisheries

QUESTION: Review

A “downwelling” is

a) the vertical flow of cold, deep water toward the surface.

b) the vertical flow of warm, deep water toward the surface.

c) when oxygen-rich water sinks.

QUESTION: Review

The area of an ocean that contains habitats on the

ocean floor is called the _______ zone.

a) littoral

b) photic

c) pelagic

QUESTION: Review

An area that occurs along coasts at temperate

latitudes is called a(n)

a) estuary.

b) mangrove swamp.

c) salt marsh.

QUESTION: Review

_____ is defined as “a mass of calcium carbonate

composed of the skeletons of tiny animals.”

a) A coral reef

b) Red tide

c) Bottomfish

QUESTION: Review

Which statement about coral bleaching is correct?

a) Corals reproduce most efficiently in colder waters.

b) Fish move into coral reefs and kill them.

c) Zooxanthellae leave the coral due to climate change or pollution.

QUESTION: Review

Which of the following does NOT mask the decline of

fisheries?

a) Fishing fleets travel longer distances to reach less-fished areas.

b) Fishing fleets spend more time fishing.

c) Fishing fleets use sophisticated methods of fishing.

QUESTION: Review

Marine reserves have all the following benefits

EXCEPT

a) fishing increases in areas surrounding the reserve.

b) the size of fish decreases.

c) larvae can “seed” areas outside the reserve.

QUESTION: Viewpoints

What would you think about letting another country fish

10 miles off the U.S. coast?

a) That’s fine, as long as the fleet paid the United States.

b) Let them fish, but make them follow the same rules as U.S. fishermen.

c) Let only U.S. fishermen fish in these waters.

QUESTION: Interpreting Graphs and Data

What does this graph show about the future of global

fisheries catch?

a) World fish catch has plummeted.

b) It is unlikely that world fish catch will increase.

c) The world will decrease its fishing pressure.

QUESTION: Interpreting Graphs and Data

Which conclusion can you draw from this graph about commercial catches of Atlantic cod?

a) Intensified fishing increased and the fishery crashed.

b) It is easier to find fish today.

c) There is little correlation between fishing and

fish stocks.