Eelgrass in Tomales Bay

Kayaking on Tomales Bay, near shore and in shallow water, we see long green strands that look a lot like seaweed, but actually, it is eelgrass. Eelgrass moved into the marine environment from land around 65 million years ago. It's actually a flowering plant, one of only two in the oceans.

Embarking on an Eelgrass Adventure, Tomales Bay.
Photo by Joseph Kinyon 2009. All rights reserved.

As the days grow longer, and the water warms, millions of pieces of pollen are released and fertilization takes place. In August these plants will then release hundreds of tiny seeds that will sink to the muddy bottom or be carried away by the current. Eelgrass beds have been the subject of interest for awhile, and scientists have some very cool findings. This plant helps to stabilize the coastal zone. Because their leaves are close together and often interwoven by the tides, they actually reduce the motion of the water. As the water slows, suspended material carried around by the tide and current, sinks to the bottom. The important supply of detritus that the eelgrass beds provide for near shore and off shore systems creates areas 10-100 times richer in animal life      compared to adjacent habitats.

In September, the leaves break away from the roots. Some float away, carried by currents; others fall to the bottom where a large percentage of the leaves decompose. Microscopic organisms begin to break down the leaves into smaller particles, and these become surrounded by bacteria and fungi. Bacteria and fungi are consumed by filter feeders such as clams and scallops. Deposit feeders (such as sea urchins) and sediment feeders (worms and snails) also join in to feast. The adult and larval forms of these invertebrates become food for larger life forms such as fish. The closely packed leaves provide a safe haven for young fish to try to avoid predation, the dense jungle of leaves often deters larger fish from going in too far. Thus the continuous cycle that eelgrass plays such a vital role is illuminated.

Eelgrass is difficult to eat for many birds because it is extremely fibrous. However, Brandts Geese rely on eelgrass to survive their 3000 mile migration. They have a specialized crop to ease digestion. Surf Scoters and Scaups swim down and clip off pieces of eelgrass in order to eat the herring eggs that are developing on the blades.

Dendronotus Iris Nudibranch. Photo by Joseph Kinyon 2009.
All rights reserved.

Waterfowl are often easy to spot, but what they are looking for in the eelgrass often eludes us, unless we look carefully. Hiding within the jungle of blades one can find: herring eggs, nudibranch (sea slugs) and their eggs, copepods & isopods (small crustaceans), polychates (marine worms), clams, bryozoans, and varying forms of bacteria and fungus. At least 20 species of commercially valuable fish rely on eelgrass for food and habitat at some point in their lives. Searching for food in the rich, muddy areas surrounding the beds we often see leopard shark, bat rays, and other large predatory fish.

As we learn more and more about eelgrass, we also learn that eelgrass is helping to mitigate the impacts of humans on our waterways. Eelgrass is crucial to maintaining water quality. 1 acre of eelgrass absorbs 6.4 pounds of nutrients. This is equal to the effluent from 490 people for 1 year. Eelgrass plays a significant role in moderating the effects of increased carbon dioxide on our planet. 1 acre of eelgrass removes 7400 pounds of carbon. This is equal to the carbon dioxide emitted from a car traveling 3860 miles. Eelgrass beds are very difficult to restore once they have been destroyed (by pollutants, boat propellers and anchors, dredging and development). Less than 10% of restoration attempts are successful after 10 years.

Splendor in the Eelgrass, Taylor's Sea Hare. Photo by Joseph Kinyon 2009.
All rights reserved.

Next time you are out on the water, tread lightly in eelgrass zones and be sure to take a closer look at the eelgrass beneath your boat. For a special treat, check out the eelgrass beds after dark. Bring a headlight and be prepared to get wowed by all of the creatures.

Want more: Check out Joseph Kinyon’s article Splendor in the Grass, on Bay pipefish, an eelgrass resident with some extraordinary adaptations for its environment.
Photos provided by Joseph Kinyon. All rights reserved. To contact Joseph or to see more of his photos, Find his "palustrine" Flickr  page.