WATER

Water Biomes

Depends on: • Water temperature

– Warmer waters are more rich

• Water Depth – Light can only go a

certain depth in water

• Salinity (saltiness)

Water Biomes – Freshwater – Marine (Coral reefs) – Estuaries

AQUATIC ENVIRONMENTS

• Saltwater and freshwater aquatic life zones cover almost three-fourths of the earth’s surface

Figure 6-2

AQUATIC BIODIVERSITY

• We know fairly little about the biodiversity of the world’s marine and freshwater systems. – The greatest marine biodiversity occurs in coral

reefs, estuaries and the deep ocean floor. – Biodiversity is generally higher near the coast and

surface because of habitat and food source variety.

• The world’s marine and freshwater systems provide important ecological and economic services.

FRESHWATER LIFE ZONES • Standing (lentic) water such as lakes, ponds,

and inland wetlands.

Freshwater Lifezones • Flowing (lotic) systems such as streams and

rivers.

Lakes: Water-Filled Depressions

• Lakes are large natural bodies of standing freshwater formed from precipitation, runoff, and groundwater seepage consisting of: – Littoral zone (near shore, shallow, with rooted

plants). – Limnetic zone (open, offshore area, sunlit). – Profundal zone (deep, open water, too dark for

photosynthesis). – Benthic zone (bottom of lake, nourished by dead

matter).

Lakes: Water-Filled Depressions

Figure 6-15

Lakes: Water-Filled Depressions

• During summer and winter in deep temperate zone lakes the become stratified into temperature layers and will overturn. – This equalizes the temperature at all depths. – Oxygen is brought from the surface to the lake

bottom and nutrients from the bottom are brought to the top.

Lake Turnover

• Water is densest at 39°F (4 °C) • Mixing occurs due to density changes

Thermocline

• The middle layer that acts as a barrier to the transfer of nutrients and dissolved oxygen.

Types of Lakes • Plant nutrients from a lake’s environment affect the types and numbers of organisms it can support.

• Oligotrophic

• Mesotrophic

• Eutrophic

Figure 6-16

Oligotrophic Lakes • "Oligo" means few/very

little • So it has low:

– nutrient content (Phosphorous and nitrogen)

– primary productivity

• High oxygen content • Usually found in colder

latitudes

Oligotrophic Lakes

• Deep clear water

• Rocky and sandy bottoms, and very little algae.

• The fish found in oligotrophic lakes like cold, high oxygenated water (e.g. lake trout and whitefish) – Cold water can hold more dissolved oxygen than warm

water. Since oligotrophic lakes are less fertile and have less algae and other organisms, there is less decomposition and the oxygen doesn't get used up.

Mesotrophic Lakes

• “Meso” means middle

• May have some algae on top

• O2 high on top and low at bottom

• Stratifies and turns over

• Great fishing lakes

• Fish include walleye, perch, smallmouth bass, and northern pike

Eutrophic Lakes

• They have high: – nutrient content

(Phosphorous and nitrogen)

– primary productivity

• Low oxygen content due to decomposition of biomass

Eutrophic Lakes

• Shallow • Murky and Mucky • Fish include:

– largemouth bass, perch, carp and catfish. As a lake becomes increasingly eutrophic, sport fish dwindle.

– Very eutrophic lakes may lack fish.

How does eutrophication happen?

• Higher nutrients (nitrates and phosphates) cause producers to boom. (Algal blooms)

• Dead algae and organic material decompose reducing the amount of dissolved oxygen.

• Fish and other animals suffocate. • If anaerobic conditions continue, bacteria

(sometimes toxic) can grow.

Cultural Eutrophication • Human inputs of nutrients from the atmosphere and

urban and agricultural areas can accelerate the eutrophication process.

Overfertilization of lakes with nutrients causing excessive plant/algae growth.

Ecological Effects of Eutrophication

• Decreases biodiversity • Changes in species composition and

dominance • Toxicity effects

Combating Eutrophication

• Attack the symptoms – Decrease nitrogen and phosphorous deposition – Chemical treatment – Aeration – Harvesting aquatic weeds – Drawing water down

Dead Zones • Dead zones are hypoxic (low-oxygen) areas in the world's

oceans and large lakes • Caused by excessive nutrient pollution from human activities

that deplete the oxygen required to support most marine life in bottom and near-bottom water

Dead Zone in the Gulf of

Mexico

• Much of the water deposited on the US drains into the Mississippi river.

• Most of this land is agriculturally productive meaning that the runoff often contains excess fertilizer causing algal blooms leading to the Dead zone at the mouth of the river.

Freshwater Streams and Rivers

Headwater Stream Characteristics

• A narrow zone of cold, clear water that rushes over waterfalls and rapids. Large amounts of oxygen are present. Fish are also present. Ex. trout.

Downstream Characteristics

• Slower-moving water, less oxygen, warmer temperatures, and lots of algae and cyanobacteria.

Flooding

• Flood plain – area around river – Wetlands (natural flood/erosion control) – Recharge ground water – Fertile soil

• Human controls – Channels (straight) – Levees/walls – Dams

Wetlands • Hydric soil (soils that are

sufficiently wet in the upper part to develop anaerobic conditions during the growing season)

• Generally, the water table is at or near the land surface.

• Plants adapted to flooding • Includes marshes, swamps,

bogs, mangroves, estuaries

Ecosystem Services

• Flood control • Groundwater

replenishment • Shoreline stabilization

/ Reduces erosion • Storm protection • Water purification • Recharge aquifers

• Reservoirs of biodiversity

• Wetland products • Cultural values • Recreation and

tourism • Climate change

mitigation and adaptation

Estuaries and Coastal Wetlands: Centers of Productivity

• Estuaries and coastal marshes provide ecological and economic services. – Filter toxic pollutants, excess plant nutrients,

sediments, and other pollutants. – Reduce storm damage by absorbing waves and

storing excess water produced by storms and tsunamis.

– Provide food, habitats and nursery sites for many aquatic species.

Estuaries

• A partially enclosed area of coastal water where sea water mixes with freshwater.

Estuaries – Salinity

• Varies greatly. Depends on: – location in the estuary – the daily tides – the volume of fresh water flowing into the estuary – Seasons

• Salinity affect how much dissolved oxygen the water can hold. (higher salinity = lower dissolved oxygen)

Importance of Estuaries

• Just one acre of estuary provides $75,000 worth of free waste treatment, and has a value of about $83,000 when recreation and fish for food are included.

• Prime Kansas farmland has a top value of $1,200 and an annual production value of $600.

The Everglades - Problems • As Miami develops, it encroaches on everglades.

Plus, it prompts people vs. wildlife. It is freshwater and local areas are draining it.

Intertidal Zone • Intertidal Zone: area of

shoreline between low and high tides.

• Organisms develop specialized niches to deal with daily changes.

• Variable: – Temperature – Salinity – Wave action

• Inhabitants include: starfish, barnacles, mussels, sea urchins, crabs,

Barrier Islands

• Low, narrow, sandy islands that form offshore from a coastline.

• Primary and secondary dunes on gently sloping sandy barrier beaches protect land from erosion by the sea.

Figure 6-10

Coral Reefs

• Worlds most productive ecosystem

• Colonies of coral animals

• Warm, shallow environments

• High Biodiversity • Very vulnerable to

human activities

Atoll - an island of coral that encircles a lagoon partially or completely.

An atoll forms on top of the cone of a submerged volcanic island.

• Built from layers of calcium carbonate, coral reefs are found in warm, shallow sea water. The living portions must grow in shallow waters where light hits. They are the most diverse of all marine ecosystems.

Coral Reefs

Barrier Reef

• A lagoon of open water separates the land from the barrier reef.

• The largest barrier reef is the Great Barrier Reef off the coast of Australia.

• The second largest is off the coast of Belize.

Why Should We Care About Coral Reefs?

• Help moderate atmospheric temperature by removing CO2 from the atmosphere.

• Act as natural barriers that help protect coastlines from erosion by waves and storms.

• Provide habitats for a variety of marine organisms.

• Provides humans with seafood, pharmaceuticals, and recreational/tourism dollars

Coral Reef Risks

• Silt washing from downstream has smothered the reefs

• High salinity from fresh water diversion, over-fishing, boat groundings, fishing with dynamite or cyanide, hurricane damage, disease, coral bleaching, land reclamation, tourism, and the mining of coral for building materials.

Protection of

• 300 coral reefs in 65 countries are protected as reserves or parks, and another 600 have been recommended for protection.

• The good news is coral reefs can often recover from damage.

Biological Zones in the Pelagic Zone (open sea)

• Euphotic zone: brightly lit surface layer. – Nutrient levels low, dissolved O2 high, photosynthetic

activity.

• Bathyal zone: dimly lit middle layer. – No photosynthetic activity, zooplankton and fish live

there and migrate to euphotic zone to feed at night.

• Abyssal zone: dark bottom layer. – Very cold, little dissolved O2.

Life in the Pelagic Zone

• Pelagic life decreases with increasing depth. • It is affected by light intensity, pressure,

temperature, salinity, the supply of dissolved oxygen and nutrients, and the submarine topography

• Phytoplankton is the basis of this food web

Benthic Characteristics (ocean floor)

• The ocean floor consists of sediments (mostly sand and mud)

• Many marine animals, like worms and clams, burrow

• Bacteria are common & can go down 500 meters below ocean floor. The Benthic environment extends from the shore to the deep.

Fig. 6-5, p. 130

Dar

knes

s Ph

otos

ynth

esis

Sun

Continental shelf

Estuarine Zone

High tide

Low tide

Coastal Zone

Bathyal Zone

Euphotic Zone

Abyssal Zone

Sea level

Open Sea

The Coastal Zone: Where Most of the Action Is

• Warm, nutrient-rich, shallow water that extends from the high-tide mark on land to the gently sloping, shallow edge of the continental shelf.

• The coastal zone makes up 7% of the world’s ocean area but contains 90% of all marine species. – Provides numerous ecological and economic

services.

Coastal Zone • Wide variety of plant and animal life • From surface to ~200m in depth • Sometimes called the epipelagic zone • Diverse basis of food web • Most influenced by human activity

– ~40% of the world’s population live within 100 km (62 mi) of a coastline

Kelp Forests

• The largest of the brown algae, many reach lengths of 60 meters (200 feet). Common in cooler water & are found along rocky coasts. Provide habitat for many animals like tubeworms, sponges, clams, fish, & mammals. Some animals eat the kelp.

What Kinds of Organisms Live in Aquatic Life Zones?

• Plankton • Nekton • Benthos • Decomposers

Phytoplankton

• Description – small drifting plants • Niche – they are producers that support most

aquatic food chains • Example – cyanobacteria & many types of

algae

Zooplankton • Description – herbivores that feed on phytoplankton

or other zooplankton • Niche – food stock for larger consumers • Example – krill; small crustaceans

Nekton • Description – swimming aquatic

organisms able to move independently of water currents

• Niche – top consumers in the aquatic ecosystem

• Example – fish, turtles, and whales

Benthos

• Description – bottom-dwelling creatures • Niche – primary consumers, decomposers • Example – barnacles, oysters, and lobsters

Fishing Problems & Techniques • The major decline in the worldwide catch of

fish since 1990 is because of over-fishing. • By-catch – fish or animals that were not

meant to be caught.

Overfishing and Extinction: Gone Fishing, Fish Gone

• About 75% of the world’s commercially valuable marine fish species are over fished or fished near their sustainable limits. – Big fish are becoming scarce. – Smaller fish are next. – We throw away 30% of the fish we catch. – We needlessly kill sea mammals and birds.

Purse Seines • A large purse-like net is put into the ocean and

is then closed like a drawstring purse to trap the fish.

• Tuna is a fish typically caught in purse seines • Dolphins are a by-catch of purse seines

Purse Seines

Long-line fishing • Lines are put out that can be up to 80 miles

long w/ thousands of baited hooks on them. These are left out free-floating for days and then the boat comes back and picks them up.

• Pilot whales, dolphins, sea turtles, and birds are by-catch of this technique.

Long-line Fishing

Drift-net fishing

• Each net hangs as much as 50 feet below the surface and up to 34 miles long.

• Anything that comes into contact w/ these nearly invisible nets are entangled.

• This leads to overfishing • Many unwanted fish and marine mammals, turtles

and seabirds are caught.

Drift Nets

Trawling

• Used to catch organisms that live on or near the ocean bottom like shrimp, cod, flounder, and scallops

• Drag a funnel shaped net along the bottom • Scrapes the floor and destroys habitats

Trawling

TEDs • Turtle Excluder Devices • a specialized device that allows a captured sea

turtle to escape when caught in a fisherman's net.

• 1987 – US law required boats to have TEDs

• 1989 – (Shrimp-turtle law) all importers of shrimp to US had to use TEDs

Fish Farms

• Also called aquaculture • Raising fish commercially in tanks or

enclosures, usually for food • Can reduce pressure on wild fisheries • Problem: Carnivorous fish (like salmon) are fed

fish meal consuming more weight than they produce

• Tilapia are filter feed on phytoplankton and are better suited to aquaculture