Les zostères

Les estuaires logent une grande quantité de zostères (eelgrass). Quoique souvent confondue avec les algues, la zostère est bel et bien une plante.

Plusieurs espèces de poissons s’abritent sous ces plantes, dont l’anguille, le flet, l’épinoche et la morue. Les zostères peuvent mesurer plus de trois pieds. En observant la plante avec une loupe, on peut apercevoir de nombreuses algues, brunes, rouges et vertes, et d’autres formes de vie étranges. Sa biomasse est à peine plus grande que la biomasse des espèces qui s’y greffent.

En dépit du fait que ces plantes n’ont pas beaucoup été étudiées, les zostères jouent un rôle clé dans les cycles biologiques des estuaires.

The Eelgrass Beds of Our Estuaries:
A forest under water

Sabine Dietz
Piper Project
October 1998

e.gif (324 bytes)stuaries can be encountered wherever a river meets the sea. They are places where the freshwater of the river mingles with the saltwater of the ocean, creating unique conditions, and a very special place for a great number of living creatures. On the eastern coastline of New Brunswick estuaries are sheltered areas, particularly where barrier beaches protect them from the ravages of storms. This is where eelgrass is particularly abundant.

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(photo: NBEN-RENB)

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The author:
Sabine Dietz
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A little bit more peaceful?

The eastern coastline of New Brunswick is more peaceful in terms of obvious ocean activity than the Bay of Fundy. Scientists call it a low energy environment. In contrast, the Bay of Fundy is a high energy environment. Beaches on the Eastern shore are mainly gentle, sandy, and extensive. They are still very dynamic and this is clear to anybody who has visited a beach before and after a storm. Sometimes the beach is unrecognizable after the storm.

Hidden from view

When you spend some time along the coast, and start exploring some of its estuaries, you'll discover that these places are teeming with life. So much so that walking on a muddy, smelly, oozing estuary bed with the eelgrass snaking around your legs, you might wonder what sort of living beings are hidden from your view and what hidden creatures might grab you.

The amazing mud plant!

There is more than just eelgrass to tickle your toes. This plant makes life possible for many creatures that spend some time, or their whole lives, in our estuaries. It grows like an underwater forest, and is, in many places, so dense that the sandy or muddy bottom cannot be seen from a boat or canoe. It provides shelter for fish such as the American Eel, Tomcod, flounder, Atlantic Silverside, different species of Stickleback, Mummichogs, and many others. Among its blades, that can grow more than 3 feet long, salmon and trout might hide during their time spent in the estuary before going either upriver to spawn or moving out to the open ocean.

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(photo: Mary Ann Coleman)

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Eelgrass Tours
with Author
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A seaweed?

Eelgrass is not a seaweed, even though the dried black strands of this plant can be found washed ashore on our ocean beaches and are often confused with seaweed. The Eelgrass (Zostera marina) is a true submerged, aquatic, flowering plant that lives in our estuaries, especially in the large expanses of shallow water behind barrier beaches, called lagoons.

The Eelgrass itself is worth looking at more closely with a magnifying glass. Its shiny green blades are often covered with brown, red, or green seaweed, stalked jellyfish, bryozoans, and other very strange living beings. True, you will need a magnifying glass to really explore the surface of its leafs. Scientists actually consider the biomass that grows on the blades of Eelgrass almost as significant as the biomass of the plant itself.

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(photo: NBEN/RENB)

Eelgrass cannot grow everywhere. The plant prefers a certain level of salinity, and it needs the relatively calm waters of the estuary to grow in. It also needs a sandy or muddy bottom, as it has roots that need to pick up the nutrients. It is unlike most seaweed which attaches itself to some hard object, such as a rock, with a structure called a holdfast.

A critical link

Eelgrass is a very important plant. Although not studied very well, the importance of other seagrass beds further south in the United States has been shown in a number of studies. This plant is a keystone species in the estuaries.

Some unanswered questions.

Some fishermen have indicated that the number of eels caught is diminishing. Another fisherman has indicated that he has observed a dieback of Eelgrass in the estuary. In the 1930's, an epidemic reduced the extensive Eelgrass beds to little patches here and there. The resulting reduction of species in the estuaries that depended directly on Eelgrass was noted at that time.

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(photo: Mary Ann Coleman)

It's surprising that not more research has been done into this subject and we might want to consider stepping more lightly in our estuaries and our Eelgrass beds, as they play a major role in our coastal ecosystems.