Massive seagrass die-off leads to widespread erosion in a California
estuary

Date:
July 28, 2020
Source:
California Polytechnic State University
Summary:
The large-scale loss of eelgrass in a major California estuary --
Morro Bay -- may be causing widespread erosion. Over the last
century, Morro Bay has been building up sediment quickly. After
the die-off, however, erosion took place in more than 90% of the
places where eelgrass previously grew.



FULL STORY ==========================================================================
The large-scale loss of eelgrass in a major California estuary -- Morro
Bay - - may be causing widespread erosion, according to a new study from California Polytechnic State University.


==========================================================================
In recent years, Morro Bay's iconic eelgrass beds, which provide the
estuary's primary living habitat, experienced a massive die-off, declining
more than 90 percent since 2007. Efforts to restore the eelgrass have
had mixed success in many parts of the bay, and this seagrass is now only
found close to the mouth of the bay and sporadically in other regions.

Seagrass systems are found throughout the world and provide many ecosystem services including fish nursery habitats, forage for migratory birds,
nutrient cycling, carbon storage and sediment stabilization.

"The loss of eelgrass in the Morro Bay estuary is analogous to the
loss of trees in a rainforest," says lead author and Cal Poly physics
Professor Ryan Walter. "Not only do you lose the plants, but you also
lose all of the services that they provide for the entire ecosystem."
By slowing down currents and decreasing wave forces, seagrasses help
stabilize sediment and prevent erosion. Over the last century, Morro
Bay has been building up sediment quickly and is dredged annually.

After the eelgrass died off, however, erosion took place in more than
90% of the places where eelgrass previously grew. In some places, the
erosion removed enough sediment to cause the water depth to increase by
as much as 50% compared to when eelgrass was present. At the mouth of
the estuary where eelgrass remains, sediment is still building up as it
did in the past.

"These erosional changes are sizable considering that Morro Bay,
a modified estuary, has historically suffered from accelerated
sedimentation," Walter said.

Globally, seagrasses in the nearshore coastal environment are among the
most threatened ecosystems on the planet. Generally, losses of seagrasses
can lead to increased shoreline and estuarine erosion.

On the other hand, it is possible that the erosion in Morro Bay may
create new opportunities for seagrass recovery by increasing the
depth and suitable habitat for eelgrass in certain locations. Recent restoration attempts by the Morro Bay National Estuary Program have been successful, and there is evidence of a partial recovery in portions of
the bay. Tracking changes in sediment in places like Morro Bay will
become increasingly important as climate change is expected to drive
sea level increases and shoreline change.

"Morro Bay is an estuary of national importance that is under transition
with system-wide eelgrass loss, subsequent sediment loss and now some
signs of eelgrass recovery. Understanding the dramatic changes in Morro
Bay can help identify important factors for management and conservation
of eelgrass- dominated systems globally," said coauthor Jennifer O'Leary, former California Sea Grant Extension Specialist.


========================================================================== Story Source: Materials provided by
California_Polytechnic_State_University. Note: Content may be edited
for style and length.


========================================================================== Journal Reference:
1. Ryan K. Walter, Jennifer K. O'Leary, Sean Vitousek, Mohsen
Taherkhani,
Carolyn Geraghty, Ann Kitajima. Large-scale erosion
driven by intertidal eelgrass loss in an estuarine
environment. Estuarine, Coastal and Shelf Science, 2020; 106910
DOI: 10.1016/j.ecss.2020.106910 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/07/200728113605.htm

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