Aquatic Ecology Chapter 7

Types of aquatic life zones: Saltwater or marine Estuaries, coastlines, coral reefs, coastal marshes, mangrove swamps, and oceans Freshwater Lakes and ponds, streams and rivers, and inland wetlands

Major types of organisms Phytoplankton – plant plankton Free-floating microscopic cyanobacteria and algae The producers and the basis of the food chain Zooplankton – animal plankton Nonphotosynthetic herbivores that feed on phytoplankton Secondary consumers that feed on other zooplankton Range from single-celled protozoa to large invertebrates such as jellyfish.

Nekton Benthos Decomposers Fish, turtles, and whales Bottom-dwellers – barnacles & oysters that anchor to one spot Worms – burrow into sand or mud Lobsters and crabs – walk on the bottom Some are filter-feeders Decomposers Bacteria that break down organic compounds

Key Characteristics of aquatic organisms Less pronounced and fixed physical boundaries; therefore difficult to count and manage populations More complex and longer food chains More difficult to monitor and study because of their size and they are hidden from view.

Limiting Factors Aquatic life zones are divided into three layers – surface, middle, and bottom Factors are: Temperature Access to sunlight for photosynthesis Dissolved oxygen (DO) content Availability of nutrients such as carbon (CO2), nitrogen (NO3), and phosphorus (PO4) for producers

Photosynthesis can take place only as deep as light can penetrate (euphotic zone) Oxygen gets in from photosynthesis and diffusion for air and is removed by aerobic respiration (includes decomposition) O2 can vary greatly in aquatic ecosystems Most aquatic organisms cannot survive below 5 ppm of DO DO and CO2 concentrations vary with depth

Why are oceans important? Cover 71% of earth’s surface Contain about 250,000 known species Provide many ecological and economic services Less that 5% has been explored and mapped

Coastal zone Warm,nutrient-rich,shallow water that extends from the high tide mark to the margin of the continental shelf makes up less than 10% of ocean but contains 90% of all marine species and is especially important to commercial fisheries. Gets: Sunlight and nutrients

Coastal Wetlands – covered by water all or part of the year Estuaries – a partially enclosed area where seawater mixes with fresh water An ecotone Coastal Wetlands – covered by water all or part of the year river mouths, inlets, bays, sounds, mangrove swamps, and salt marshes Temperature and salinity vary widely Tides, seasonal variation in water flow, unpredictable flows after heavy rains and floods VERY PRODUCTIVE AREAS!

Intertidal zone – area of shoreline between high and low tides Very stressful zone for organisms: Wave stress Immersed during high tides and dry during low tides Changing levels of salinity Organisms usually cling to something, dig or hide in shells.

Barrier Islands Long, thin, low offshore islands of sedement that generally run parallel to shore Help protect mainland Constantly shift

Coral reefs Form in clear, warm, coastal waters in tropics and subtropics Have many types of organisms Attached – corals, algae, and sponges Fishes Small organisms that bore into or attach themselves to coral Easily damaged, grow slowly, can survive only in clear, shallow, warm water Have been harmed by global warming They face many threats from pollution and other human activities.

Open Sea Beyond the continental shelf Euphotic zone: lighted upper area Photosynthesis Low nutrient levels High DO Bathyl zone: dimly lit middle zone No photosynthesis Abyssal zone: dark lower zone Very cold Little DO Many nutrients

Some open sea organisms Deposit feeders Take mud into their bodies and extract nutrients from it Filter feeders Pass water through or over their bodies and extract nutrients from it Average primary productivity & NPP are low.

Human Impact Losing coastal areas to development Housing, marinas, golf courses Filling in for agriculture Much beach erosion due to development and rising sea levels Dredging and heavy nets used in trawling is destroying bottom habitats Coral reefs are being severely damaged

Freshwater life zones Found where water with a dissolved salt concentration of less than 1% by volume either accumulates or flows through the surfaces of terrestrial biomes. Standing water – lakes, ponds, inland wetlands Flowing water – streams and rivers Covers less than 1% of the earth’s surface but ecologically and economically important Are very closely connected to terrestrial biomes due to nutrient run-off

Life zones Ponds – shallow – light often penetrates to the bottom – usually have only one zone Lakes – deeper – generally consist of four zones – defined by depth and distance from shore Littoral zone – shallow water near shore where rooted plants grow Limnetic zone – open sunlit water away from shore – as deep as sunlight penetrates Profundal zone – deep open water that receives no sunlight – cool so although oxygen is low, some fish live here. Benthic zone – bottom of lake – cool temperatures and low oxygen

© 2004 Brooks/Cole – Thomson Learning Freshwater Systems Ecological Services Economic Services • Climate moderation • Nutrient cycling • Waste treatment and dilution • Flood control • Groundwater recharge • Habitats for aquatic and terrestrial species • Genetic resources and biodiversity • Scientific information • Food • Drinking water • Irrigation water • Hydroelectricity • Transportation corridors • Recreation • Employment

Eutrophication – the natural ageing of a lake Classify lakes according to nutrient content and primary productivity OLIGOTROPHIC LAKE – low nutrients Geographically young Deep Blue in color Colder Low populations of phytoplankton More desirable fish – bass and trout Low NPP

EUTROPHIC LAKE – many nutrients Old lake Shallow Green or brown in color (algae) Warmer Algal blooms are common Less desirable types of fish – catfish, carp High NPP

Figure 7-21 Page 158 Sunlight Oligotrophic lake Sunlight Narrow littoral zone Little shore vegetation Low concentration of nutrients and plankton Limnetic zone Sparse fish population Sleepily sloping shorelines Profundal zone Sand, gravel, rock bottom Oligotrophic lake Sunlight Much shore vegetation Wide littoral zone High concentration of nutrients and plankton Dense fish population Limnetic zone Gently sloping shorelines Figure 7-21 Page 158 Profundal zone Silt, sand, clay bottom Eutrophic lake

Cultural Eutrophication Humans add nutrients from the atmosphere, urban, and agricultural areas accelerate eutrophication.

SEASONAL CHANGES IN LAKES Occurs in temperate lake Makes use of the property of water that it is less dense as a solid (0oC) then it is at a liquid (4oC);therefore ice floats on water. This causes THERMAL STRATIFICATION of deep lakes

Summer Lakes have three distinct layers: EPILIMNION – upper layer of warm water high levels of DO THERMOCLINE – layer where the temperature changes with depth – usually 1oC/meter increase in depth – moderate oxygen – during summer acts as a barrier between epilimnion and hypolimnion HYPOLIMNION – bottom layer of cold, dense water – low DO To keep cool fish would be at the bottom but low DO there

Fall Overturn Water begans to cool, becomes more dense and sinks to the bottom The thermocline disappears Water mixes – nutrients are carried to the top and oxygen to the bottom. Fish can be found at all depths

Winter Lake separates into layers again due to difference in density. Warmest (4oC)water is at the bottom Thermocline is reversed Coldest water is at the top and freezes forming ice which insulates and protects the lake.

Spring overturn Water begins to warm up Wind blows causing vertical currents Lake overturns again bring nutrients to the top and oxygen to the bottom

Characteristics of Freshwater Surface water forms when precipitation that does not sink into the ground or evaporate becomes run-off Watershed – the land area that delivers run-off, sediment, and dissolved substances to a stream. Streams join together to form rivers Rivers flow downhill to the ocean

Inland wetlands – land covered with water all or part of the year located away from the ocean Marshes – have a few trees Swamps –dominated by trees and shrubs Prairie potholes – depressions formed by glaciers Floodplains – receive water during heavy rains or floods Bogs and fens – waterlogged peaty areas

Human impact 60% of the world’s largest rivers are fragmented by dams – destroys wildlife and reduces water flow Flood control levees and dikes – destroy habitats, disconnect rivers from floodplains,and eliminate wetlands In U.S. 53% of the wetlands have been drained or filled to grow crops – this has increased flooding