The Amazon River is the largest river on Earth. It rushes from the Andes Mountains in the west and snakes its way to the Atlantic Ocean on the east coast of South America—a distance of more than 6500 km. For six months of every year, water overflows the banks and floods the forest. Over 1 meter of rain falls per year in some parts of the Amazon basin! During the flood time, fishes hunt among the treetops, and rays and river dolphins swim through the branches.
The Amazon basin covers 640 million hA, and during the rainy season there are millions of hectares of flooded forests. The floodwaters rise between 1.5 and 15 m over the forest floor. From December to May, it rains every day, with storms lasting from a few minutes to a few hours. During the rainy season, nearly 200 million liters per second of water empties into the Atlantic Ocean!
Researchers have found that several species of fishes are helpful in forest regeneration. The fishes eat the fruit, then defecate or spit out seeds. This helps to disperse the seeds throughout the flooded forest. One of these fishes found in the Amazon is the Tambaqui (Colossoma macropomum). They have evolved huge teeth and powerful jaws that crush fruits and hard seeds. Their keen sense of smell helps them locate the fruit. The fish feast during the fruiting season and store fat for survival during the dry season.
The mangrove community is made up principally of flowering plants the size of small trees that inhabit the tropical coastline in areas of muddy estuaries, sheltered lagoons, bays and tidal inlets between latitudes 25° north and 25° south of the equator.
The soil is often high in salt, low in oxygen and very acidic. The 30 species of mangrove trees have adapted several different ways of dealing with the harsh soil and salt-water conditions. Red Mangrove, Rhizophora mangle is the most widespread species. The roots of this tree are called stilt roots or prop roots. Some of these roots go deep into the mud to anchor the large tree in the soggy soil. Others are very shallow and are able to take advantage of the surface oxygen. Pores in the stem bark called lenticels also permit gas exchange and increase breathing in waterlogged and poorly oxygenated soils. Specialized root cell membranes regulate the entry of salt. Excess salt is lost through the leaves. Other species of mangroves have large trunks with anchor roots and “pneumatophores”, “knee roots” or “buttress roots”—all of which are adaptations for gas exchange above the soil and help to stabilize the plant during storms.
Mangrove forests support about 60 other plant species, provide homes for hundreds of animals, are breeding grounds and nurseries to many species of invertebrates, fishes and birds and are resting spots for migratory birds. They protect the coast from wave and wind damage, reducing erosion. They protect coral reefs by absorbing excess fresh water runoff from the land. They also act as a natural filter by trapping and absorbing much of the debris, sediment, excess nutrients, and toxic substances before they are washed into the sea. Over time, this process of trapping sediments can produce new areas of dry land.
This tank represents a coral reef found near an island in the Indo–Pacific region, such as Tahiti. Coral reefs are found worldwide where water surface temperatures are 291 K (18° C) or higher, and the water is usually very clear and lacking in nutrients. Coral reefs are the most diverse communities on the planet and second to rainforests in species richness. More species are found in the coral reef habitat than anywhere else in the sea, and it is believed that there are many species here that have yet to be discovered.
Coral reefs are the largest biologically produced structures on earth, and hermatypic corals are the organisms that build the reef by secreting hard calcium carbonate skeletons. The polyp is the living part of the coral that feeds on zooplankton and secretes the calcium carbonate. Polyps can be solitary or colonial. Inside the polyp live specialized, single-celled algae called zooxanthellae, which produce energy via photosynthesis that they share with the polyp. The polyps feed by extending tentacles from their calcareous skeletons to catch drifting prey. The tentacles contain nematocysts (stinging cells) to disable and entrap the food as it drifts by. A thick layer of mucus, along with ciliary movement, transports the food to the polyps’ mouths.
Other algae are also very important to coral reef growth. Coralline algae also produce calcium carbonate, reinforcing the reef structure and protecting it from strong waves and currents. These algae form ridges along the seaward edge of the reef, sheltering it from storms. In addition to the encrusting coralline algae, sponges and bryozoans surround sediment and cement it in place, adding to the stability of the reef.
Like a tropical rain forest, kelp forests have a high diversity of species—an estimated 800 species of animals and about 130 species of plants and other photosynthetic organisms. Kelp forests are home to different layers of complex communities of plants and animals. Plants provide the structure, from tall canopies to understory. The multiple layers in a kelp forest offer many different kinds of habitats for all the animals and plants.
Kelp forests are located along ocean coasts in cool, nutrient-rich water with a rocky bottom. These conditions are provided off the coast of California by the cold California Current coming from the Gulf of Alaska. The dominant organism in a kelp forest is Giant Kelp (Macrocystis pyrifera), a brown alga. Kelps have an extraordinarily fast growth rate—as much as 30 centimeters per day! Giant kelp may grow to be 46 meters tall – half the length of a football field! More than 80 other species of algae also live in kelp forest.
Kelp forests grow on rocky substrates, which lack nutrients. The kelp plant is anchored to the rocky bottom by its holdfast, but the holdfast does not absorb nutrients like roots of land plants do. Instead, the whole kelp plant absorbs dissolved nutrients directly from the seawater.
Kelp forests experience drastic seasonal changes. Winter storms often break up a kelp forest. The holdfast breaks away and the kelp is sent adrift. You may have noticed huge amounts of brown seaweed washed up on the beach—a smelly haven for beach flies. The hole where a large kelp once stood provides an opportunity for younger kelp to grow. The sunlight can penetrate to the deeper water and thus give a boost to lower-growing algae.
The interactions of all the inhabitants make up the kelp forest community. There are other species of kelp that do not need as much sunlight as the giant kelp. Some grow like shrubs and fan out with many branches; while others, which are even more shade tolerant, live on the bottom and sprawl out like a carpet of grass. These plants provide food and shelter for many organisms, from nurseries for larval invertebrates and fish fry to shelter for marine mammals. Coralline algae, sponges, and other tiny invertebrates live in the holdfast and help anchor it to the rocky substrate.
Many animals feed on the different species of kelp. Surfperch eat the smaller kelps, while sea urchins and snails usually feed on drifting pieces of the larger kelp. Tiny invertebrates such as copepods, shrimp, and bryozoans live on the blades and stipes of the kelp. Small fishes called señoritas skim the kelp feeding on these organisms. Larger fishes such as sharks and sea bass eat the smaller fishes that feed on kelp. Marine mammals such as sea otters eat snails, urchins and other invertebrates that eat kelp and kelp holdfasts. Whales, dolphins, sea lions, harbor seals, and sea otters, as well as red phalaropes and other seabirds, come to a kelp forest for shelter as well as food.
Southern California freshwater streams
Most of the rivers and streams in Southern California arise from mountain runoff of snowmelt and ground water. While they are rushing down to the Pacific Ocean, these waters are home to seven species of fishes native to Southern California: Santa Ana sucker, threespine stickleback, arroyo chub, speckled dace, steelhead trout, lamprey and tidewater goby. Because most of the rivers are a result of mountain runoff, most of these fishes are adapted to cool, flowing water, although human modifications have changed conditions on the lower flood plains of the rivers.