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Marine Angiosperms: Types, Location & Examples

Instructor: Yuanxin (Amy) Yang Alcocer

Amy has a master's degree in secondary education and has taught math at a public charter high school.

Marine angiosperms are an important part of the underwater ecosystem as they provide shelter and food for many types of marine animals, as well as help to secure the sediment underwater.

Marine Angiosperms

Did you know that just like there are fields of grass on land, there are likewise fields of grass underwater?

Marine angiosperms are also called seagrass.
marine angiosperm

These fields of grass are made up of marine angiosperms, or underwater flowering plants that live in marine environments, which are commonly called seagrass. Just like grasses you see growing on a nice green lawn, seagrasses also have chloroplasts. But, one thing seagrasses lack that land grasses have are stomata, or small pores that let water in and out and control the exchange of gases. One thing that seagrasses have that land grasses don't have, however, are pockets of air called lacunae that are located in the veins of leaves which help to keep the leaves upright underwater.

Just like land grasses, seagrasses also take in carbon dioxide and release oxygen. Because they are oxygen producers, they are also called the ''lungs of the sea.'' Just one square meter (almost 11 square feet) can produce 10 liters (about 2.6 gallons) of oxygen each and every day. They grow either by cloning themselves as rhizomes grow and produce new plants or by releasing seeds into the water. Seeds allow the plants to start growing in a different area, while spreading rhizomes allow the plants to form meadows. The grasses are used by humans to make roofs, insulation, fertilizer, bandages, and filler for car seats and mattresses. Seagrasses are actually quite valuable, being worth an estimated $19,000 per year for one hectare (about two football fields).

Types

There are between 72 and 78 seagrass species organized into four major family groups or types. Here's a table listing each type, along with a description of each:

Type Description
Cymodoceaceae These seagrasses have rhizomes from which thin leaves grow out of sheaths.
Hydrocharitaceae Leaves of these seagrasses grow in clusters or circular whorls at nodes on a stem or rhizome.
Posidoniaceae These seagrasses have flat, medium-size leaves with flat sheathing that grow from a rhizome.
Zosteraceae Also referred to as the eelgrass family, these seagrasses have long, alternating leaves growing from rhizomes that end up spreading to form meadows.

Location

Marine seagrasses can be found practically anywhere (except around Antarctica), from tropical areas all the way to really cold areas, such as at the Arctic Circle. The majority live in coastal waters at depths between three to nine feet. It's in the tropical areas where more seagrass species are found living together. For example, up to 14 different seagrass species have been found living together along the tropical coasts of Asia and Australia. In addition, along the coast of Florida, seven species have been observed growing together. At these coastal locations, seagrass beds provide homes for a lot of marine wildlife, such as tiny crustaceans and marine slugs and snails. Many other marine wildlife species also come to the seagrass beds to forage for food.

Examples

An example of a seagrass from the Cymodoceaceae family is manatee grass (Syringodium filiforme), which is commonly found in coastal waters off of Florida, Bermuda, the Bahamas, and around the Caribbean. Manatee grass can grow as tall as 20 inches with cylindrical leaves coming out two to four at a time from each rhizome node. Manatees love to eat this type of grass.

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