Marine Environments

  • The total surroundings of a living thing are called the environment . All environments have living ( biological ) and nonliving ( physical and chemical ) components.
  • The living or biotic things in an environment are called the biota . For example, the bacteria, crustaceans, fish , sponges, and other organisms that live in and around a coral reef are all part of the coral reef’s biota . The nonliving or abiotic parts of a coral reef environment would include the water chemistry, light , salinity, temperature , and water pressure. Interactions between the biotic and abiotic factors characterize all environments.
  • The place or “home” in which an organism is typically found is called its habitat . A life zone is a region that contains organisms that interact with one another and with their environment.

Marine Life Zones

Marine life zones include: the intertidal zone, the supratidal zone, the subtidal zone, the pelagic zone, the neritic zone, the oceanic zone, and the benthic zone.

  • The intertidal zone is the area located between high and low tide. The highest point the high tide reaches on the beach is marked by a debris line called the strandline , which is a line of seaweed, sticks, and floating material deposited on the beach during each high tide. The intertidal zone contains a wide variety of marine invertebrates ( animals without backbones ), including crustaceans , worms , and mollusks . Organisms that live in the intertidal zone are well adapted to living in an environment that has alternating periods of wet and dry , and the tides come in and go out each day.
  • The supratidal zone is the area above the intertidal zone up to the sand dunes. This area is characterized by salt-tolerant grasses, shrubs, and then, in the upper supratidal zone , trees.

The diagram above shows the coastal marine life zones, and some common inhabitants.

  • The subtidal zone lies below the low tide line, which means this marine life zone remains underwater . The subtidal zone includes an area that is subject to heavy wave impact , and underwater turbulence. Because of this, some organisms in this zone have structures that help them cling to hard substrates to prevent their being swept away by waves and currents . Examples of organisms that live in the subtidal zone include: sea stars (incorrectly called starfish ), marine snails, sea anemones , mussels, barnacles , sand dollars, flounder , crabs, shrimp, clams, marine algae, and kelp .

Fill in the table below with some subtidal zone organisms and their adaptive clinging structures

Subtidal zone organism / Adaptation to the turbulent subtidal zone
Sea stars / Suction pads on their tube feet
Marine snails / Muscular foot designed for clinging and movement
Sea anemones / Muscular feet designed for clinging (sea anemones are sessile- they cannot move about)
Mussels / Secrete byssal threads- tough, fibrous threads that stick to hard substrates
Barnacles / Secrete an organic glue- allows them to cement themselves to rocks or other hard substrates
Flounder / Have flattened bodies and lie on, or bury themselves in, the sand
Sand dollars / Have flattened shells and bury themselves in the sand, move slowly using tube feet
Kelp / Anchor themselves to rocky surfaces using a fibrous pad of tissue called a holdfast
  • The pelagic zone is the largest life zone in the ocean. The pelagic zone covers the entire ocean of water above the sea bottom.
  • The neritic zone is part of the pelagic zone, and covers the region of water that lies above the continental shelf. This zone is generally less than 200 meters deep. This is an extremely productive zone of the ocean, and most of the world’s commercial

fishing takes place in the neritic zone. The neritic zone is so productive because rivers provide nutrients from the continents to the ocean in these zones.

  • The oceanic zone is the life zone that extends beyond the neritic zone , and includes most of the open ocean. The upper part of the ocean zone receives sunlight , whereas the lower part (the vast majority of the ocean) is in darkness. The part of the ocean that receives light is called the photic zone (also called the euphotic

zone). Sunlight does not penetrate more than 200 meters deep. Beyond this is the aphotic zone (meaning “no light”). There is more life in the photic zone because sunlight allows plants and algae to live and be an abundant source of food for marine animals.

  • The benthic zone includes the entire ocean floor, from the shallow intertidal zone , to the deep abyssal plain. Organisms that inhabit the benthic zone are called benthos .

A cross section of the ocean’s life zones; the pelagic zone includes the neritic and oceanic zones.

Questions:

1)Which life zone is more productive, the neritic or the oceanic?

2)How are some benthic organisms adapted to live in turbulent waters?

3)What are some adaptations of organisms that live in the aphotic zone?

1)Why were marine scientists surprised by the biodiversity among the benthos?

2)What kinds of organisms have been found in the samples that were collected?

3)How do scientists collect invertebrates that live more than 1km deep?

Estuaries and Coral Reefs:

Habitats of Abundance and Diversity

  • Where rivers enter into oceans, freshwater and salt water mix, forming an environment known as an estuary .
  • Along the shores of an estuary , there are many inland bays and creeks. The varied terrain of an estuary, along with its brackish water (water that is a mixture of fresh and salt water), provides diverse habitats for marine life. Because they are very nutrient-rich, and are shielded from turbulent wave action, estuaries are generally the most biologically productive and diverse environments found along coasts.

Cross section of an estuary and a barrier beach.

  • Sediment, carried to the ocean by rivers, is deposited in deltas at river mouths. This sediment is then moved by wave action forming long ridges of sand called barrier beaches . On one side of a barrier beach is the bay and on the other side is the open ocean . The estuary lies on the bay side of a barrier beach.

Estuary communities- Three common types of communities that arise in estuary environments are: salt marshes , mudflats ,

and mangroves. The type of environment that is formed depends upon several factors including climate, geology, and topography.

  • Salt marshes (aka wetlands) are typified by marsh grasses such as cordgrass , a course, tough grass that has special glands that allow it to secrete salt crystals through its leaves.

Characteristic organisms of a salt marsh community in an estuary.

Question: Create a food chain in this salt marsh community using as many of the organisms pictured above as you can.

  • The calm and nutrient-rich waters of the salt marsh provide an ideal environment for marine animals to produce offspring . In fact, these wetlands are often described as the “nurseries” for many species of ocean fish. One example is the flounder , which feeds on killifish, which, in turn, feed on insect larvae.

Question: Why would estuaries be ideal environments for eggs and newly-hatched fish?

  • Mud flats are characterized by dark muddy sand and no marsh grasses. Just as the salt marshes are the nurseries in an estuary, the mudflats are the graveyards , where bacteria decompose wastes and turn sand into a dark mud. If you were to dig a hole in the sand of a mud flat, you would see that under the surface the sand is black and gives off a foul odor, like rotting eggs.

Characteristic organisms of a mud flat community in an estuary.

  • This smell is caused by the presence of hydrogen sulfide, a compound that is the product of decomposition and that accumulates in sediments that are deficient ( very low ) in oxygen .
  • In regions with tropical climates, mangrove communities, or mangrove swamps often form along the coastal shores of bays and inlets. These areas are named for their abundance of red mangrove trees . At low tide, the arching roots, which anchor the mangrove trees in the muddy sand, are visible. At high tide , the water covers the roots, but the tree trunks and leaves remain

above the water.

  • Like salt marshes, mangrove swamps are extremely rich in marine life. Also like salt marshes, mangrove swamps help protect the shore from erosion. The roots of the mangrove tree hold the sand and prevent it from being carried away by waves and currents .
  • During storms, mangrove swamps act like giant sponges, absorbing the water and the impact of storm surges. Federal and local governments spend hundreds of millions or even billions of dollars building dikes, levees, and barrier walls to protect against flood damage from hurricanes along coasts. However, mangrove swamps are extremely effective natural barriers that protect areas farther inland. If these areas were left in a natural state, rather than removed for development , our coastal areas would be much better protected from hurricanes.

Organism commonly found in mangrove swamp communities.

Question: What are three benefits mangrove swamps provide for organisms and the environment?

“Coral reefs are the rainforests of the sea.”

Coral Reef Environments: Coral reefs are tremendously diverse habitats made up of very hard formations of calcium carbonate ( CaCO3) built up from the seafloor by living organisms called coral polyps .

  • coral reef formation begins when microscopic coral larvae settle on a hard substrate in the sand and develop into coral polyps.
  • Coral polyps live in colonies, with each new coral polyp living in its own limestone home, which it builds. Each new generation of polyps lay down a new layer of limestone, causing the reef to expand upward at a rate of about 2-3 cm per year.
  • Some massive reefs, such as Australia’s Great Barrier Reef, are more than 40 meters high and more than 2000 km long. Corals can grow right up to the ocean surface, but cannot grow out of the water .
  • Tropical coral reefs are only found in tropical and subtropical regions of the world, between about 30 degrees north and 30 degrees south latitude. Between theses latitudes, the ocean water is warm , clear , and there is plenty of sunlight . These are the conditions necessary to promote the growth of symbiotic algae within the coral polyps that build the reefs.

Characteristic organisms commonly found in coral reef communities.

  • The many types and shapes of corals in a coral reef create an irregular pattern of crevices, depressions, and caves in which organisms can live and hide . These solid, stable features provide habitat for a great abundance and biodiversity of organisms in coral reefs.

Types of Corals

  • Corals are classified into two types, hard corals and soft corals . Hard corals include elk horn, staghorn, and brain coral, all of which are rigid. Soft corals include sea fan and sea rod , which are flexible and sway in the currents.

Threats to Corals

  • Coral reefs are very productive environments, but they are also very fragile . Pieces of coral can be broken off easily; even touching coral can damage the thin membrane that protects its surface. In addition, overfishing , unrestricted or unregulated

diving , and development along coasts (which contributes large amounts of sediment to coastal waters) all lead to the degradation of coral reefs.

  • Coral reef bleaching is the whitening of coral reefs which results from the death of symbiotic zooxantheallae (yellow-green algae that live within the cells of coral). When these symbiotic organisms inside the coral die, the coral itself dies.
  • Coral reef bleaching is caused by human actions and natural variations in the reef environment including changes in sea temperature, and the amount of solar radiation, sedimentation, pesticides, and fertilizers.
  • Question: Describe some sources of the impacts listed above, and explain how they directly effect coral reefs. Changes in sea temperature due to man-made global warming, leading to death of coral from coral bleaching. Sedimentation due to poor farming and logging practices, leading to death of coral from siltation/burying. Pesticides and fertilizers due to poor farming practices, leading to death of coral from toxic compounds (pesticides) and algae bloom related low oxygen dead zones (fertilizers).
  • Coral bleaching events have increased significantly worldwide in the past 20 years. Global climate change may play a role in the increase in coral bleaching events, and could cause the destruction of major reef tracts and the extinction of many coral species.