Chapter 8Chapter 8

Aquatic EcologyAquatic Ecology

© Brooks/Cole Publishing Company / ITP

OUTLINEOUTLINE

1. Factors Affecting Life in Aquatic Ecosystems1. Factors Affecting Life in Aquatic Ecosystems

2. Saltwater Ecosystems2. Saltwater Ecosystems• the ocean & its zones

• estuaries & coastal wetlands

• barrier islands

• coral reefs

3. Freshwater Ecosystems3. Freshwater Ecosystems• lakes

• rivers & streams

• wetlands

© Brooks/Cole Publishing Company / ITP

1A. Factors Affecting Life in Aquatic Ecosystems1A. Factors Affecting Life in Aquatic Ecosystems

A. temperature• decreases with depth because of decreasing energy input

from sun;• high temperature lowers dissolved gases, • High temperature speeds rates of chemical reactions, • Affects where organisms can live; (trout fishing!)

B. light (solar radiation)• decreases with depth because of absorption by water,

(red & green algae!)• decreases with suspended materials, & phytoplankton; • essential for photosynthesis; in phytoplankton & coral

1A. Factors Affecting Life in Aquatic Ecosystems1A. Factors Affecting Life in Aquatic Ecosystems

C. dissolved oxygen• lowers as temperature rises, (Arctic krill!)• producers produce O2 by photosynthesis, • consumers consume O2 in respiration, (dead

zones!)D. nutrient availability • most limiting macronutrients are

phosphorus (P) & nitrogen (N); limiting micronutrients include iron (Fe); essential for growth of phytoplankton. (Fe spiking experiment!)

2. Saltwater Ecosystems2. Saltwater Ecosystems• Oceans

• cover 71% of the earth’s surface

• ocean currents distribute solar heat

• Act as reservoir for carbon dioxide (CO2)

• regulate temperature of the troposphere (weather)

• habitat for plants & animals, including critical food sources for humans

• communal dumping ground (tragedy of the commons)

Life zones of the OceanLife zones of the Ocean

• zones are defined by amount of solar radiation penetrating the water

• zones - euphotic zone, bathyl zone, abyssal zone

• (in order of declining solar radiation):

Coastal Zone of the OceanCoastal Zone of the Ocean

• extends from high–tide mark to edge of continental shelf

• entirely within the euphotic zone & includes estuaries, wetlands, barrier islands, & coral reefs

• nutrient–rich & the site of most commercial fisheries

• high primary productivity: sunlight + nutrients from land & ocean currents

Estuaries & Coastal WetlandsEstuaries & Coastal Wetlands

Estuary:

where seawater mixes with freshwater from land, generally at the mouth of a river

(see Fig. 8–5) (Demo Google Earth)

Coastal wetland:

areas of coastal land covered all or part of the year with salt water

Estuaries & Coastal WetlandsEstuaries & Coastal Wetlands

• Importance

• nutrient rich

• high primary productivity

• nurseries for fish & other aquatic animals (salmon & barracuda!)

• waterfowl & shorebird breeding areas

• filter water pollutants

Human ImpactsHuman Impacts on Estuaries & Coastal Wetlands on Estuaries & Coastal Wetlands

• world has lost over half of its estuaries & coastal wetlands (e.g. Netherlands)

• percentage lost in the U.S. even higher most lost to coastal development (e.g. Seattle & Boston)

• causes of degradation urban runoff, sewage treatment plant effluent, sediment & chemical runoff from agricultural lands

• (Cathy Laetz guest speaker next Tuesday)

Barrier IslandsBarrier Islands

• Barrier Islands: long, thin, low offshore islands of sand that run parallel to the shore.

• Importance• protect mainland from

offshore storms (Katrina!)• shelter inland bays,

estuaries, & wetlands• popular recreational &

residential areas (N.C.)

Human Impacts• Development of barrier islands

– destroys dunes & dune vegetation

– causes beach erosion

– destroys or disturbs wildlife habitat (e.g., some endangered birds nest on barrier islands)

• Protecting barrier islands– jetties & seawalls

– beach replenishment

– replanting dune vegetation, controlling development

© Brooks/Cole Publishing Company / ITP

Barrier IslandsBarrier Islands

Coral ReefsCoral Reefs• What Are Coral Reefs?• reefs formed by mutualism between polyps &

algae• reefs built as colonies of polyps secrete limestone

hard deposits remain when the polyps die• reefs located in coastal zones of tropical oceans• reefs grow only in the photic zone where algae

inside coral can receive light for photosynthesis.

Coral ReefsCoral Reefs• Importance • high biodiversity like

“tropical rain forests of the ocean”

• protect coastlines from storms & high waves

• nurseries for many fish species

• Disappearing

Coral ReefsCoral Reefs• Vulnerability

• slow growing

• easily disturbed

• thrive only in clear water

• Bleaching???

• Human Impacts

• sediment runoff & effluent

• increased UV radiation

• fishing with cyanide & dynamite

Fig. 8–12© Brooks/Cole Publishing Company / ITP

Coral Reef Food WebCoral Reef Food Web

Coral Reef Bleaching

• http://www.reefrelief.org/

• http://www.marinebiology.org/coralbleaching.htm (technical)

• http://en.wikipedia.org/wiki/Coral_bleaching (good summary)

3. Freshwater Ecosystems - Lakes3. Freshwater Ecosystems - Lakes

Lake:

Littoral zone:

Limnetic zone:

Profundal zone:

Benthic zone:

• deep, open water where there is no light penetration.

• shallow area near the shore, to the depth at which rooted plants stop growing.

• the bottom of a lake; inhabited by insect larvae, decomposers, & clams.

• open, sunlit, surface layer away from the shore. Depth is the limit of light penetration.

• standing (lentic) body of freshwater formed when rain, runoff, or groundwater fills depressions in the landscape

LAKES – OligotrophicLAKES – Oligotrophic

– low nutrient supply

– low primary productivity

– clear water, few plants & fish

– Example: high alpine lake

LAKES - LAKES - Eutrophic• excess supply of

nutrients

• high primary productivity

• murky water,

• large phytoplankton population

• Eventual filling of lake with organic matter.

• e.g. Panther Lake

LAKES - LAKES - Thermal stratification• during summer

(temperate lakes)

• epilimnion: warm, upper layer of water

• thermocline: zone of lake where temperature changes rapidly with depth

• hypolimnion: colder, denser lower layer of water can be depleted of oxygen in eutrophic lakes

LAKES - LAKES - Overturn

• spring & fall (temperate zone lakes)

• upper layer of water sinks & winds mix layers

• redistributes oxygen & temperature evenly

• redistributes nutrients from the lower layers

Streams & RiversStreams & Rivers• watershed:

• source zone:

• transition zone:

• flood plain zone

• many streams join to form a broad, slow–moving, meandering river in lower watershed

• the land area that delivers water, sediment, & dissolved substances to a water body.

• cold, clear, fast–running streams in upper watershed

• middle part of watershed, where streams widens & join, flow slows, water temperature increases

Human Impacts on Streams & RiversHuman Impacts on Streams & Rivers

• pollution• sediments• Channelization (Green

River, Rhine)• dams• introduction of exotic

species, (Japanese Knotweed)

• removal of vegetation from banks

• change of flow (more floods, lower base flow)

WetlandsWetlandsWhat are Wetlands?• lands covered with fresh water all or part of the time

(not including lakes & streams)Wetland functions• wildlife habitat, especially for waterfowl & amphibians• filter sediments & pollutants from runoff , “nature’s

kidneys”• flood attenuation (absorbs like a sponge)Human impacts:• some states have lost over 90% of their wetlands• loss because of filling for development (Harbor Island)• loss because of draining for agriculture (Netherlands)