SC.912.L17. 2 Aquatic Ecosystems

Aquatic Ecosystems

SC.912.L17.2 You need to know that different types of organisms exist within aquatic ecosystems due to chemistry, geography, light, depth, salinity, and/or temperature.

The main aquatic ecosystems are lakes, rivers, wetlands, estuaries and the ocean.

TUTORIAL
Diving the Depths of Underwater Life

Conditions Underwater Aquatic ecosystems are determined mainly by the depth, flow, temperature, and amount of dissolved nutrients of the water.

The photic zone is the sunlit upper layer of water where photosynthesis can occur.
The aphotic zone is the dark lower layer where photosynthesis cannot occur.
The benthic zone is found on the bottoms of lakes, streams, and oceans. The organisms that live on the floor of a body of water are called benthos

Two key factors that determine which organisms can live in an aquatic ecosystem are:

1. Dissolved oxygen level
2. Water temperature.

Cold water can hold more dissolved oxygen than warmer water, so dissolved oxygen levels are related to water temperature.

In many aquatic ecosystems, tiny free-floating swimming organisms can be found. These organisms are called plankton.

Phytoplankton are single-celled algae that use nutrients in the water to make food (carry out photosynthesis)

Zooplankton are animals that feed on phytoplankton.

Salinity is a measure of the amount of salt in water.

There are three main groups of aquatic ecosystems:

1. Freshwater ecosystems can be divided into several types.

Flowing water ecosystems include rivers and streams. Organisms in these ecosystems are adapted to seasonal changes in water level and rate of flow. Many river animals have adaptations that help them avoid being washed downstream by the rapid currents. Fish, for example, have streamlined bodies that help swim against the currents. The larvae of insects may have suckers that allow them to attach to surfaces.
Standing water ecosystems include lakes and ponds. Water generally flows into and out of these ecosystems and circulates within them. The standing water provides a habitat for many different aquatic organisms. Ponds are generally shallower and have a smaller surface area.Sunlight reaches the bottom. This enables plants and algae, which need sunlight for photosynthesis, to grow throughout the pond. Lakes vary in surface area and water depth. In deep lakes, sunlight cannot reach the bottom in some areas. Also, water pressure increases with water depth and temperature decreases.
Freshwater Wetlands include bogs, marshes, and swamps. In wetlands, water covers the soil or is present at or near the surface for at least part of the year.

2. Estuaries are wetlands formed where rivers meet the sea. They contain a mixture of fresh and salt water.

3. Marine Ecosystems.The ocean is divided into three zones based on depth and distance from the shore:

The intertidal zone is the shallowest and closest to land. It is exposed to the rise and fall of tides each day.
The coastal ocean is the relatively shallow border of water that surrounds the continents. Coral reefs grow in tropical coastal oceans.
The open ocean begins at the continental shelf and extends outward. The open ocean can be divided into the photic zone and the aphotic zone.

The intertidal Zone is the part of the shore between the high tide mark and low tide mark. It is a very harsh environment. The organisms that live here have adaptations that allow them to live both submerged with water and out water exposed to air and direct sunlight. Some organisms like seastars , live in tide pools, low areas that remain filled with water at low tide.

Many organisms of the intertidal zone have adaptations to prevent them from being washed into the ocean by waves.

Crabs and clams, for example, burrow into sand.
Seaweeds have structures called holdfast that help them stay rooted.
Barnacles attach to surfaces like boats, other animals such as whales etc.

The neritic zone is the relatively shallow part of the ocean above the drop-off of the continental shelf, approximately 200 metres (660 ft) in depth. These shallow waters of the neritic zone allow light to penetrate almost to the ocean floor. Temperatures and salinity do not vary much. These conditions, along with abundant nutrients resulting from upwelling, make the neritic zone a good habitat for more kinds of organisms than either of the other life zones. Upwelling is the movement of cool, nutrient-rich waters from the deep ocean into shallower ocean areas.

Coral reefs are a major ecosystem in the neritic zone. Coral s are tiny animals that live attached to each other in large groups called colonies. Coral reefs have the greatest biodiversity of any aquatic ecosystem. They are called the rainforest of the sea.

The deep areas of the ocean form the oceanic zone. This zone extends from the surface to the ocean floor. Sunlight can penetrate only the top 200 meters of water in the oceanic zone (Photic zone). Almost all producers, such as phytoplankton, and most consumers live in these surface waters. Whales, squid, and jellyfish live in the oceanic zone.

The Aphotic zone underlies the photic zone, where light does not reach. Temperatures are nearly freezing and decreases with depth. In the aphotic zone, there virtually no light from the sun (1% or less of sunlight reached this zone), so photosynthesis
can not take place.

The floor scientists have discovered hydrothermal vents. A hydrothermal vent is a crack in the ocean floor that emits hot water. Many hydrothermal vents communities are inhabited by bacteria, these bacteria use chemicals ejected from the vent to make food by chemosynthesis. These bacteria are the producers. Tubeworms, clams and other animals feed on the bacteria of the deep ocean is called the abyss. High pressure, cold and darkness characterize this area. In some parts of the abyss,mineral-rich.

These dark, deep-ocean environments are characterized by an unusual combination of high temperatures, high pressure, and a unique chemistry that provides both an energy source and the chemicals required for life.

Ocean Life

Ocean organisms are classified according to how they move and where they live.

Benthos live on or near the ocean bottom Examples: kelp, sponges, algae, clams, snails, sea stars and sea urchins.

Plankton are tiny organisms that are carried by ocean currents. Phytoplankton, plantlike plankton that makes food via photosynthesis. Zooplankton includes animal-like plankton such as tiny shrimplike krill, protozoan, jellyfish and the eggs or larvae of many larger ocean fish that feed on phytoplankton.

Nekton are free swimmers. Example: Fish, whales, seals, shrimp, and squid.

WETLANDS

Water covers the soil or is present at or near the surface for at least part of the year.

Wetlands are often nutrient-rich and highly productive and serve as breeding grounds for many species of birds, fish, amphibians, insects and other animals. In addition to being a habitat for many species, wetlands help cleanse and purify water that moves through them and prevent flooding.

ESTUARIES

Where the river meets the sea

Estuaries contain a mixture of fresh and salt water and are affected by the rise and fall of ocean tides.
Characteristics

Changing water levels that are affected by tides
Salinity changes constantly depending on tides, rain, and coastal storms.
Protected from strong waves by barrier islands, reefs, or sand spits.
The calm waters contain abundant dissolved oxygen, nutrients and minerals. Many of the nutrients come from the river water.
Sea grasses provide ample food and shelter for a variety of animals.
Estuaries serve as spawning and nursery grounds for many ecologically and commercially important fish and shellfish species including bluefish, striped bass, shrimp, and crabs. These organisms thrive here.

Salt marshes and Mangroves swamps are two types of estuaries.