Youth Science Lesson – Marine Biology & Conservation Lesson 1 – Marine Environments

The term environment is defined as a location, or set of conditions, in which people and creatures exist.

The term marine pertains to saline aquatic conditions.

Within the saltwater world there are many environments. They differ in what we call abiotic factors, or abiotic parameters and are often labeled by the dominant plant form living there.


Within marine environments the abiotic factors usually consist of salinity, temperature, pressure, light, and energy (i.e. waves, currents, and tides). In this lesson we will also include the barrier islands as a marine environment even though it is not submerged. The reason… it is heavily impacted by the surrounding marine environment and has many “maritime” qualities. Let’s begin there… barrier islands.


Barrier Islands

Along the northern Gulf coast is a string of long-thin sand bar islands we call barrier islands. They are called this because they serve as a barrier to the mainland from open water storms. These long sandy islands are very dynamic and constantly shift and move with the tides, currents, and waves. They can shift as far as 300 feet after a strong hurricane.

The long, thin sand bar that is a barrier island.
Photo: Molly O’Connor

Life on these islands can be very tough. In addition to the constantly moving sand, there is salt spray in the wind, intense sunlight much of the year, high winds at times, and little rainfall to provide freshwater. Even though our area can receive as much as 60 inches of rain a year, much of this falls in the northern end of the counties, and not on the beaches. That said, there are freshwater ponds on some the islands and even larger dune lakes in Walton County – here life is not as hard.


As you cross a barrier island from the Gulf to the bay, you will cross distinct environmental zones. These zones are defined by the abiotic factors we have described, are named by their dominant plant forms, and have distinct animal life associated with them.

The beach is a high energy zone of the is land is devoid of plants.
Photo: Rick O’Connor

The beach is barren. This is the section of sand that extends from the water line of the Gulf to the first line of dunes. Few, if any plants can grow here. The high wave energy will not allow plants to grow along the shoreline, nor in the water itself. The wind and salt spray are high and the sand ever changing. All of the animal life her lives beneath the sand. They emerge when the wind and waves have slowed and scavenge on what they can find for food. Their primary production comes from the decomposition of the strands of seagrass and seaweed that line the shore – what we call wrack. Many will filter phytoplankton from the water as the waves wash in and seabirds are constant predators. When conditions get a little too much, they migrate a little offshore in deeper water to wait it out. But here fish and larger invertebrates become predators – so, they may not stay long.

Sea oats cast a dramatic profile on Gulf beaches, but their most important work is underground, where their root systems anchor the dunes. Photo credit: Carrie Stevenson, UF IFAS Extension

Inland of the beach is the first dune line – the primary dune. This dune field is dominated by grasses because woody plants cannot tolerate the high wind. Most of these herbaceous plants have fibrous root systems that trap blowing sand and form dunes. The dominant grasses found here would include panic grass, beach elder, and the sea oat. The seeds of these plants provide food for creatures like the beach mice and some birds. Ghost crab burrows are often found here seeking shelter from the high energy environment of the beach. And, as you would expect, predators visit. Snakes, coyotes, and fox seeking the small mice.

Small green shrubs found in the secondary dune field.
Photo: Rick O’Connor

This primary dune line blocks some of the wind and salt spray from the Gulf and allows small woody shrubs to grow. These shrubs will form a secondary dune system, which may grow slightly higher than the primary dunes. Shrubs like seaside rosemary, goldenrod, and false rosemary can be found here and give the dunes color when they are in bloom. The grasses found in the primary dune can also be found here. Beach mice and ghost crabs can work their way to this environment but because the wind is blocked by the primary dune other animals can be found here including: armadillos, opossum, a variety of snakes, and maybe even a gopher tortoise. Within the secondary dune field there are low areas that, at times, fill with rainwater. These are called swales and have their own unique wildlife. Grasses like broomsedge, needlerush, and bull rush can be found here. Along the edge you may find carnivorous plants such as the sundew. Freshwater attracts all wildlife, but the tenants could include a variety of amphibians, reptiles, and even some hardy species of fish.

The shorter trees of the tertiary dune field – the maritime forest.
Photo: Rick O’Connor

On the back side of the island are some of the largest dunes. These are held in place by salt tolerant trees such as live oak, pine, and even magnolia. However, these trees look different than the ones that grow in our yards. They are the same species, but their growth seems stunted and often they look like the wind has blown their growth northward. This is known as wind sculpting and all of it is caused by the salt spray coming from the Gulf. These trees form a maritime forest where a variety of wildlife species do well. Deer, armadillo, opossum, skunks, coyote, fox, raccoon, hawks, owls, eagles, all sorts of snakes and woodland birds can be found here. In these xeric conditions, it is not uncommon to find a lot of cactus. Most of these creatures are hiding during the day, but at sunset they begin to move.

Salt marshes are composed of endless thickets of salt and water-adapted grasses, rushes, and sedges. Photo credit: Carrie Stevenson, UF IFAS Extension


Beyond the maritime forest (tertiary dune field) lies the salt marsh. This environment is found along the shoreline of the bay side of these islands. As the name implies – they are inundated with salt water during high tides and are dominated by grasses, hence the name marsh not swamp (which are dominated by trees). The high marsh is dominated by a grass known as black needle rush. The low marsh is in water more and is dominated by smooth cordgrass. This is a transition zone between land and water. Here you can find fiddler crabs, blue crabs, ribbed mussels, marsh periwinkle snails, oysters, mud crabs, mullet, killifish, wading birds, diamondback terrapins, salt marsh snake, hermit crabs, flounder, and sometimes cottonmouths. It has been stated that at least 90% of the commercially valuable marine species use either the salt marsh, or seagrass beds, as nurseries. They are teeming with life – including mosquitos!

The seagrass commonly known as Shoal Grass.
Photo: Leroy Creswell

In the open waters of the lagoon you will find submerged grasses known as seagrasses. This environment cannot tolerate the high energy of the Gulf side, so do not exist there. But in the shallow, low-energy lagoons of the estuary they do quite well. In the lower estuary there are two dominant grasses that form sub environments within the seagrass meadow. Shoal grass is a flat bladed grass but VERY thin (<5mm) and feels like human hair. This small blade grass can tolerate higher energy than the others and will grow in the shallowest waters, and closer to shore. Turtle grass has a wider blade (>5mm) and must grow in deeper water where the waves cannot rip it up. Often you will find algae growing on the grass as you find Spanish moss growing on trees. This environment is full of life. Pinfish, pipefish, blennies, gobies, flounder, toadfish, pigfish, speckled trout, puffers, mullet, hermit crabs, blue crabs, sea stars, urchins, scallops, clams, octopus, sponge, jellyfish, stone crabs, horseshoe crabs, barracuda, needlefish, silversides, anchovies, ladyfish, redfish, sea turtles, dolphin, and even manatees have been found here. These are very important nurseries for many marine species.

Freshwater sources, such as this river, impact the northern portions of the estuary.
Photo: Molly O’Connor

As you move inland within the lagoons you come closer to the freshwater discharge sources of the estuaries – the bayous and rivers. Here salinity begins to play a role in the environment. Many of the species mentioned cannot tolerate these lower salinities and thus are not found here. Others prefer the lower salinities and are quite common. Oyster reefs and eelgrass beds become more common. The salt marsh grasses still do well here and line the shorelines. Oyster reefs are also teeming with life. Not only water filtering oysters, an important member for keeping good water quality, but all sorts of sponges, worms, snails, bivalves, crustaceans, and fish can be found here. Terrapins still do well here, as do the salt marsh snakes, and you can still occasionally find dolphin. Manatees are fine with freshwater, but sea turtles are not.

The emerald green waters of the Gulf of Mexico as seen from Pensacola Beach.
Photo: Molly O’Connor

Heading offshore in the Gulf direction of the local barrier islands you will find miles and miles of sand. Some sections of the bottom will have depressions called runnels where shell hash (crushed shells) can be found. In these sandy shell bottoms, most of the creatures live beneath the sand – where they can hide from fast moving fish predators. The open water is home to large schooling predatory fish – such as sharks. It is also the realm of the sea turtles that live here. Near shore you will find dolphin and occasionally manatees, but the larger whales are much further out.

An artificial reef of the coast of the Big Bend area of Florida. Photo: Dr. Bill Lindberg UF IFAS Florida Sea Grant

Offshore in deeper water there are areas of exposed hardbottom – usually limestone rock – where the sand has not settled. Here there are nooks and crannies where lobster, snapper, and grouper survive. There are numerous “reef fish” that call this area home, many are beautiful in color. It is also the haunt of octopus, sea cucumbers, and sand dollars. In recent years, humans have tried to increase biological productivity of the reef communities by sinking artificial reefs. These are structures designed to act as hard bottom environments. There are MANY sunk off our shores and though the science does not show they PRODUCE more life (they might), they certainly attract it.


Deeper still light becomes an abiotic factor. No light means no plants and no primary production. The creatures that live in the deep sea depend on the surface environments to provide primary production. As the surface creatures die, they sink to the deep – in what is called sea snow. Many of the deep-sea creatures scavenge on this sea snow as a source of food while others prey on those feeding on the “snow”. Obviously, animals who live here must deal with intense pressure from the surrounding environment. Many are gelatinous to the feel, so they can compress with the great pressure. Many produce light so that can attract food, mates, and possibly communicate with each other. This is the realm of the giant squid, gelatinous octopus, crustaceans, and some of the weirdest looking fish you will ever see.


At the surface of the open Gulf is another environment. Here there is no land and no bottom. These animals must hide amongst themselves, or swim very fast to survive. Marlin, sharks, jacks, and tuna are common here. Larger whales, drifting sunfish, and flying fish can be found here as well.


If you went far enough south in the Gulf you would reach the tropics. Here the sea temperatures are warm enough to support corals and the massive reefs they build. The biodiversity of these reefs is one of the highest found on the planet.


There are other marine environments found on coasts where the ocean currents are colder, the waves are larger, and the air temperatures cooler. The rocky shores of the American west coast support their own environment of creatures, as do the kelp forest found there. The polar regions are dominated by ice and support another world of marine life.



It will be hard, for many reasons, to visit this beach this time of year (2020-COVID and damaged bridge), but if you can will be worth it. If you cannot maybe you can find a virtual trip online.

Take a walk along one of these local marine environments and catalog the creatures you find there.

  1. The beach of one of our islands. Sift through the beach wrack while there.
  2. The primary dune. Notice the tracks of the animals that scurried around the night before.
  3. The secondary dune. Wear shoes here, there are cactus.
  4. The swale. This area can be wet, so shoes that can get wet. Look for frogs and tadpoles, maybe a sundew.
  5. The maritime forest. Lots of tracks, lots of cactus, lots of green briar. Be ready.
  6. The salt marsh. You will definitely get wet here and probably muddy. Some of these can be accessed by kayak or paddle boards.
  7. This is a snorkel trip. Remember to bring your dive flag, required by Florida law. You can also access this by kayak or paddle board.
  8. Oyster reefs. STAY OFF THE REEFS. Oysters are notorious for cutting badly – even with shoes on! You can pick up small sections of the reef (oyster clumps) and place in a tub of water to see who swims out. We recommend a white tub so you can see them easier.



Posted: November 30, 2020

Category: Coasts & Marine, Natural Resources
Tags: Barrier Islands, Florida Sea Grant, Marine Biology & Conservation Lessons, Marine Environment Lessons, Youth Science Lessons

Subscribe For More Great Content

IFAS Blogs Categories