Puget Sound eelgrass beds create a 'halo' with fewer harmful algae, new
method shows

Date:
June 24, 2020
Source:
University of Washington
Summary:
DNA clues show that eelgrass growing underwater along Washington
state shorelines is associated with fewer of the single-celled
algae that produce harmful toxins in shellfish. Observations show
this effect extends 45 feet beyond the edge of the eelgrass bed.



FULL STORY ========================================================================== Eelgrass, a species of seagrass named for its long slippery texture, is
one of nature's superheroes. It offers shade and camouflage for young
fish, helps anchor shorelines, and provides food and habitat for many
marine species.


==========================================================================
A University of Washington study adds one more superpower to the list of eelgrass abilities: warding off the toxin-producing algae that regularly
close beaches to shellfish harvests. Researchers found evidence that there
are significantly fewer of the single-celled algae that produce harmful
toxins in an area more than 45 feet, or 15 meters, around an eelgrass bed.

"We're not in the laboratory. The effect we're seeing is happening in
nature, and it's an effect that's really widespread within this group
of harmful algae.

What we see is this halo of reduced abundance around the eelgrass beds,"
said Emily Jacobs-Palmer, a research scientist at the UW. She is the
lead author of the study published this spring in the open-access
journal PeerJ.

Researchers sampled five coastal sites three times in the spring and
summer of 2017. Four sites were within Puget Sound and one was in Willapa
Bay, on Washington's outer coast.

In addition to a traditional visual ecological survey at each site,
the researchers used a type of genetic forensics to detect species that
might not be easily seen or present at the time of the survey.

Scientists put on waders and walked parallel to shore in water less than
knee deep while scooping up seawater samples to analyze the environmental
DNA, or eDNA, present. This method collects fragments of genetic material
to identify organisms living in the seawater.



==========================================================================
The researchers sampled water from each site at the same point in the
tidal cycle both inside the eelgrass bed and at regular intervals up to
45 feet away from the edge. For comparison they also surveyed a location farther away over bare seabed.

"In the DNA fragments we saw everything from shellfish to marine worms,
osprey, bugs that fell in the water," Jacobs-Palmer said. "It's quite fascinating to just get this potpourri of organisms and then look for
patterns, rather than deciding on a pattern that we think should be there
and then looking for that." The researchers analyzed the eDNA results
to find trends among 13 major groups of organisms. They discovered that dinoflagellates, a broad class of single- celled organism, were scarcer in
and around the eelgrass beds than in surrounding waters with bare seabed.

"We were asking how the biological community changes inside eelgrass beds,
and this result was so strong that it jumped out at us, even though we
weren't looking for it specifically," said senior author Ryan Kelly,
a UW associate professor of marine and environmental affairs.

The result has practical applications, since certain species of
dinoflagellate populations can spike and produce toxins that accumulate
in shellfish, making the shellfish dangerous or even deadly to eat.



==========================================================================
The phrase "harmful algal bloom" has a formal definition that was not
measured for this study. But authors say the trend appeared when the
overall dinoflagellate populations were high.

"I have heard people talk about a trade-off between shellfish and
eelgrass, in terms of land use in Puget Sound. Now, from our perspective, there's not a clean trade-off between those things -- these systems
might be able to complement one another," Kelly said.

To explore the reasons for the result, the authors looked at differences
in water chemistry or current motion around the bed. But neither could
explain why dinoflagellate populations were lower around the eelgrass.

Instead, the authors hypothesize that the same biological reasons why dinoflagellates don't flourish inside eelgrass beds -- likely bacteria
that occur with eelgrass and are harmful to dinoflagellates -- may extend
past the bed's edge.

"It was known that there is some antagonistic relationship between
eelgrass and algae, but it's really important that this effect seems to
span beyond the bounds of the bed itself," Jacobs-Palmer said.

The discovery of a "halo effect" by which eelgrass discourages the
growth of potentially harmful algae could have applications in shellfish harvesting, ecological restoration or shoreline planning.

"These beds are often really large, and that means that their perimeter
is also really large," Jacobs-Palmer said. "That's a lot of land
where eelgrass is potentially having an effect." In follow-up work, researchers chose two of the sites, in Port Gamble on the Kitsap Peninsula
and Skokomish on Hood Canal, to conduct weekly sampling from late June
through October 2019. They hope to verify the pattern they discovered
and learn more about the environmental conditions that might allow the
halo to exist.


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


========================================================================== Journal Reference:
1. Emily Jacobs-Palmer, Ramo'n Gallego, Ana Ramo'n-Laca, Emily
Kunselman,
Kelly Cribari, Micah Horwith, Ryan P. Kelly. A halo of reduced
dinoflagellate abundances in and around eelgrass beds. PeerJ,
2020; 8: e8869 DOI: 10.7717/peerj.8869 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/06/200624172049.htm

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