Incorporating Traditional Management Techniques to Combat Effects of Ocean
Denver, Colo., USA: Ocean acidification is a major concern related
to climate change, with the oceans currently absorbing around a quarter of
the carbon dioxide that is released into the atmosphere. The increased CO 2 that is absorbed by the ocean in turn decreases its pH, making
the waters more acidic. These more acidic conditions put marine organisms
that create calcium carbonate shells and skeletons at risk.
New research that will be presented Monday at the Geological Society of
America’s GSA Connects 2022 meeting evaluated a strategy based on
Indigenous techniques that may help to mitigate the effects of ocean
acidification on calcifying organisms.
Hannah Hensel, a Ph.D. candidate at the University of California, Davis,
led a study that tested whether adding shell hash—pulverized clam shells—to
sediments could help raise the pH of pore waters and aid in calcification
for infaunal marine organisms.
“One of the things that marine invertebrates have to deal with regarding
climate change is ocean acidification,” said Hensel. “When researching
marine invertebrates that build shells and skeletons out of calcium
carbonate, I came upon some research by a diverse group of people up in
British Columbia working in clam gardens, an Indigenous shellfish
Clam gardens are a longstanding form of Indigenous coastal management in
Alaska, British Columbia, and Washington State that typically involve
building a rock wall in the intertidal zone that creates a level beach
terrace. Clam gardens expand the habitat where clams thrive and increase
productivity. Shell hash is also sometimes added to these environments to
help promote clam growth.
“I reached out to people from the Clam Garden Network and also started
looking into Indigenous management techniques in California to see if there
were connections that could be made between the two geographic areas,” said
Adding additional pieces of shelly material to sediments may help buffer
the water against acidification as they dissolve and release ions into the
water. Hensel ran laboratory experiments using juvenile Pacific littleneck
clams (Leukoma staminea), which are infaunal organisms that burrow
within the sediment, to test how adding shell hash to the sediments may
impact the pH and alkalinity of the water and calcifying conditions for the
Hensel gathered dead clam shells from a local California bay to pulverize
for the shell hash and then added the shell hash to juvenile Pacific
littleneck clams that were grown for 90 days in acidified seawater and
control seawater. Clams were also grown without the shell hash in acidified
and control seawater.
By analyzing the pH and alkalinity of the pore water in the sediments and
the overlying water, Hensel found that adding shell hash increased the pH
and alkalinity of the pore fluids both in the acidic and control seawater
conditions. The added shell hash thus worked to alter the chemistry of the
pore fluids, helping to buffer against acidic conditions, which can help
promote biologic calcification.
While these tests using shell hash were conducted in a laboratory, a next
important step will be seeing how the technique fares in a natural
“Next summer we’re going to mimic this experiment in the field to see if we
get a similar trend,” Hensel said.
Given the longstanding Indigenous knowledge regarding the many benefits of
adding shell hash and now experimental data showing its ability to help
buffer against acidic conditions, shell hash may be a useful tool for
combatting the local effects of ocean acidification.
“With more research and collaboration between local resource managers,
Indigenous scholars and citizens, and the aquaculture industry, I do think
it could be used in commercial aquaculture as a pointed and direct method
to protect specific organisms that are known to do poorly in acidic
conditions. The influence of shell hash on the pore fluids is very local,”
Pacific littleneck clam (Leukoma staminea) growth under
acidified conditions: Can adding shell hash to coastal sediments
mitigate the effects of ocean acidification?
Hannah (Kempf) Hensel (firstname.lastname@example.org)
Monday, 10 October 2022, 1:50–2:05 PM
Colorado Convention Center Room 407
Session 122: T145. Advances and New Voices in Marine and Coastal Geoscience
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