Guam’s Seagrass Meadows

Seagrass Basics

Deep green seagrass blades up close

  • It is a type of plant that lives underwater!

    More specifically, Seagrasses are marine flowering plants that are different from algae or seaweed. They have roots, flowers, and vascular structures (tubes) that help move nutrients and water around. There are many different varieties of seagrass of all different shapes and sizes!

  • Seagrass and seaweed may look similar, but they are actually completely unrelated!

    If you see something with an odd irregular shape, brown or red colored, it is most likely seaweed, not seagrass.

    Here are some of their differences:

    • Seagrasses are plants, while seaweeds are protists (a protist is not an animal, a plant, or fungi; it is its own special category of living thing!)

    • Seagrasses tend to be green and have long, narrow blades, while seaweeds can be many different colors (green, brown, red, purple, etc.) and many different shapes (they can resemble ferns, lettuce, bubbles, ruffles, etc.)

    • Seagrasses can produce flowers, while seaweeds cannot

    • Seagrasses have roots but seaweeds have a holdfast instead (a holdfast is a root-like structure that helps anchor the seaweed to a rock but doesn’t suck up any nutrients like roots do)

  • Yes, it is!

    Seagrasses evolved from land plants and still have some characteristics in common. Seagrass generally looks similar to grass you find on land, and has narrow leaves (also called blades), or round leaves.

    • While seagrasses are indeed related to land grass, they are more closely related to giant taro (Alocasia macrorrhizos), fivefingers (Syngonium angustatum), and other land plants that are members of the order Alismatales.

    • Seagrasses fall into four main families: Zoseraceae, Hydrocharitaceae, Posidoniaceae, and Cymodoceaceae.

  • Mostly around the southern part of the island.

    Seagrasses are mainly found south of Tamuning and Pago Bay. The largest seagrass beds (large continuous patches) are in Hagåtña, Hågat, Malesso’, and Inalåhan.

    Check out this map for more details on where to find these cool habitats!

Why are seagrasses important to our community?

Green seagrass underwater with several small silvery fish swimming nearby

Fish and Seafood

  • Seagrass blades provide lots of places for fish to hide and provide food sources to marine life

  • Young fish use the seagrass as a nursery, including young mafute’ (emperorfish) and mañahak (juvenile rabbitfish)

Several small blue fish swimming above a tan-colored coral colony

Healthy Water and Clean Coral

  • Seagrasses absorb many types of pollution that washes into the ocean from land as run-off

  • Seagrasses store a lot of carbon in the sediment below them, which helps fight climate change, a major threat to coral

A seagrass bed underwater growing in the sand

Erosion Prevention

  • Seagrass blades help absorb the energy from incoming waves, protecting the coast from erosion

What can I do to protect seagrasses?

Unfortunately, Guam's seagrasses were estimated to have declined by approximately 22% between 2005 and 2015. (LaRoche et al. 2018) Here are some simple ways you can help support our seagrasses so they can continue to provide habitat for wildlife and benefits to our coral reefs and community:

  • Repeated trampling of seagrasses can damage them, which can happen in popular recreational areas such as Piti Bomb Holes. Walk around or swim through the seagrasses rather than walking through them. Cutting seagrass damages the environment and tape grass does not grow quickly and can take a decade or more to reestablish once removed.

  • Although seagrasses help protect coral reefs by absorbing pollution, they also have a limit to what they can absorb. You can help by reducing your disposing of waste properly, including items like old electronics and household chemicals. Keeping vegetation and trees on your property will also help absorb water and prevent sediment from running off into the ocean.

  • Healthy populations of fish, sea cucumbers, and other marine life help keep the seagrasses healthy. Follow marine preserve fishing guidelines and obtain the necessary permits to help prevent overharvesting.

What kinds of seagrasses do we have in Guam?

  • A hand holding thin, green blades of seagrass underwater

    Needle Grass

    This smaller seagrass, often about 10cm long, can be found mixed in with larger seagrasses or by itself. It helps stabilize sediments and can grow faster than tape grass.

    Scientific name: Halodule uninervis

  • Long strands of green seagrass waving underwater with the sun filtering in

    Tape Grass (Lo'u)

    This is the largest and most common type of seagrass in Guam. It forms large underwater meadows that can grow over a meter in length, which provides lots of habitat for fish.

    Scientific name: Enhalus acoroides

  • Small green round leaves growing out of the sand underwater

    Spoon Grass

    This is Guam’s only species of round seagrass and is small growing only a few centimeters tall. It also helps to stabilize sediments and can recover quickly after a disturbance like a storm.

    Scientific name: Halophila gaudichaudii

Which animals live in seagrass meadows?

  • Cymbal bubble snail

    Scientific name: Lamprohaminoea cymbalum

  • Humpback cardinalfish

    Also known as the coastal cardinalfish or pinstripe cardinalfish

    Scientific name: Fibramia lateralis

  • Anemones

    Anemones are related to corals and also use their tentacles to capture food in the water and have special algae inside their bodies to also help capture energy from the sun.

  • Several small green patterned fish swimming by rocky substrate

    Scribbled rabbitifsh (mañahak)

    Juvenile scribbled rabbitfish can be found close to shore and eat algae and seagrass. Photo by Brent Tibbatts

    Scientific name: Siganus spinus

  • A large peach-colored snail shell rests on the white sand underwater in front of seagrass beds

    Snails

    Snails can be found on the sand, and many smaller ones will also live and graze on the seagrass itself

  • A small hermit crab in a white shell on a blade of seagrass

    Hermit crabs (duk duk)

    Hermit crabs can often be found clinging to the seagrass blades, and reusing the shells of snails that formerly lived in the seagrass.

  • A transparent fish with black stripes and dots with seagrass in the background

    Orbiculate cardinalfish (lånse)

    Scientific name: Sphaeramia orbicularis

  • Bright orange blob-shaped sponges resting on the sand underwater next to seagrass

    Sponges

    This particular sponge is not identified but various sponges of different shapes and colors can be found living among the seagrass

  • A few bright green small fish swimming in front of seagrass

    Three-line wrasse

    Juveniles of this species appear green and can sometimes be found swimming through seagrass beds in large schools.

    Scientific name: Stethojulis strigiventer

  • Small snails, algae and other growth on a piece of seagrass zoomed in

    Epibiota

    The term epibiota refers to the plants and animals that live on the surface of the seagrass, which can include different types of algae, snails, worms, single-celled organisms, anemones, and many other organisms.

  • Two small, thin cornetfish swimming above a seagrass bed underwater

    Cornetfish

    Cornetfish are long, skinny fish that belong to the same order as pipefish and seahorses. The two in this photo are juveniles.

  • A white pufferfish with yellow fins swimming in front of seagrass underwater

    Narrow-lined puffer

    Puffers eat small animals such as clams and shrimp.

    Scientific name: Arothron manilensis

  • A white clam shell partially buried in the sand next to some seagrass

    Clams

    Clams are a type of bivalve (animals with two shells). Different types of clams can be found in and around seagrass beds, often fully or partially buried under the sand.

  • Four small goatfish of varying colors hovering above rocky substrate with seagrass nearby

    Manybar goatfish

    Goatfish use their barbels (whiskers) to help them sense food

    Scientific name: Parupeneus multifasciatus

  • An orange lumpy sponge-like organism with many dots growing on a piece of seagrass

    Invertebrates

    This cool invertebrate (animal without a backbone) could be a type of sponge or a type of sea squirt; we aren’t sure! Seagrass beds are full of wacky and wonderful species like this one.

  • A small grey fish with a black spot swimming through dense seagrass

    Thumbprint emperor (Mafute')

    Scientific name: Lethrinus harak

    *the one shown in this photo is a juvenile

Where can I snorkel in seagrass meadows on Guam?

1. Piti Bomb Holes Marine Preserve: 

  • This location is one the easiest places to access to check out some seagrasses: snorkelers and divers often walk right by the seagrasses on the way to the coral reef. 

  • If you choose to explore these seagrasses remember to snorkel instead of walking through the seagrass and trampling it!

  • ***Note: the seagrass at Piti Bomb Holes has been declining and is currently very short and sparse. However, throughout Guam’s past, this has been a great area to check out seagrass.

2. Hagåtña:

  • A large seagrass meadow exists right along the shore in East Hagåtña.

  • Public parking allows easy access, and this area also has pavilions for shade. The seagrass meadows are the dark, rounded shapes running along the coast, as shown in the map below.

 

Tips for snorkeling in seagrass meadows

Despite seagrasses being important homes for many animals, they are often overlooked. Seagrasses can be uncomfortable to walk through and can get damaged by repeated trampling. Here are some helpful tips for snorkeling in seagrass:

The best way to experience and protect seagrasses is by snorkeling over them, not walking through them

Remember!

  • Seagrasses generally live in very shallow water, so going during high tide allows you to better swim over the seagrass.

  • There are many amazing animals hiding in our seagrasses, however, some of them are small, well-camouflaged, and shy! By going slowly and looking closely, you will be better able to spot some of these awesome creatures. Sea creatures can be found on all parts of the seagrass, so be sure to look all around you: on the sediment in between the seagrasses, on the seagrass blades themselves, and hovering just above the seagrass beds.

  • Some seagrasses might have small organisms that can cause mild skin irritation, and some people find the feeling of seagrass touching their skin to be uncomfortable. If you have sensitive skin or are sensitive to touch, consider wearing a full-length rashguard and leggings for full protection. Alternatively, you can snorkel along the edge of the seagrass instead of directly over it.

Want to learn more?

Click here to check out our seagrass resources!

Explore next: Guam’s mangrove forests

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