Morro Bay seagrass loss causes change in fish populations
Date:
October 29, 2021
Source:
California Polytechnic State University
Summary:
The loss of seagrass habitat caused a dramatic shift in
fish species in Morro Bay. Areas once covered with lush
seagrass meadows and unique fish species are now home to
muddy-seafloor-loving flatfish. The research team saw decreasing
numbers of seagrass-specialist fish species, and an increase in
flatfishes like the speckled sanddab and staghorn sculpin.
The loss of eelgrass habitat along the California coast presents
a problem for species that depend on seagrass.
FULL STORY ==========================================================================
The loss of seagrass habitat caused a dramatic shift in fish species
in Morro Bay. Areas once covered with lush seagrass meadows and unique
fish species are now home to muddy-seafloor-loving flatfish, according
to a paper by Cal Poly researchers published in the October 2021 print
edition of Estuaries and Coasts.
========================================================================== Seagrass meadows were previously common throughout the Morro Bay estuary
but nearly disappeared over the last decade.
"Seagrass, like the eelgrass in Morro Bay, is important because it
supports a range of marine life," said Jennifer O'Leary, who led
the research as a California Sea Grant extension specialist based at
Cal Poly. O'Leary is now the Western Indian Ocean coordinator for the
Wildlife Conservation Society. "It's like the trees in a forest -- these underwater plants provide food, structure, and shelter to many of the
marine animals that live in the bay." Underwater seagrass meadows are
one of the main habitats in coastal estuaries, and represent one of the
most biologically productive biomes on our planet. Yet seagrass habitats
are being lost at an alarming rate, and their decline now rivals those
reported for tropical rainforests, coral reefs, and mangroves.
Loss is usually the symptom of a larger problem, and seagrasses are
therefore considered "coastal canaries." Their decline signals important
losses to biodiversity and often impacts the communities that depend
on them.
Morro Bay, one of 28 estuaries that the U.S. Environmental Protection
Agency designated as critical to the economic and environmental health
of the nation, has seen a dramatic loss in its seagrass habitat. Once
dominated by a common California eelgrass (Zostera marina), seagrass at
this site has declined by more than 95 percent, from covering 344 acres
in 2007 to less than 15 acres in 2017.
Seagrass meadows are a multifaceted habitat that secure sediments with
their root systems, and provide food, shelter and nurseries for many
types of fish and invertebrates. When seagrass meadows are lost, they
are often replaced with a less dynamic, muddy seafloor habitat.
========================================================================== O'Leary and colleagues found that seagrass loss did not result in fewer
fish but rather led to changes in the types of fish that live in the
bay. The research team saw decreasing numbers of some seagrass-specialist
fish species, such as the bay pipefish (Syngnathus leptorhynchus). With
long thin bodies and olive green coloration, bay pipefish are adapted
to hide among the seagrass blades.
In contrast, researchers observed an increase in flatfishes like
the speckled sanddab (Citharichthys stigmaeus) and staghorn sculpin (Leptocottus armatus).
These fish have flat bodies that are ideal for life along the muddy
seafloor and are common residents in California bays and estuaries. These species have moved into the former eelgrass habitats and now make up
the majority of the fish species present in Morro Bay.
The loss of eelgrass habitat along the California coast presents a larger problem for species that depend on seagrass, like the bay pipefish. If
seagrass doesn't recover, then the surviving meadows will be further apart
and have a more fragmented, or patchy, distribution. This distance and patchiness of habitat may impact specialists, like pipefish, by impairing
their ability to move to a new habitat to find food or mates. This
community isolation may alter the genetic structure and diversity of
the overall pipefish population over time.
"The relatively sudden and near complete collapse of eelgrass in Morro
Bay has not only changed fish populations, but it has also resulted in substantial changes to estuary physics and geomorphology," said study
coauthor Ryan Walter, a Cal Poly physics professor who has been studying eelgrass loss through a California Sea Grant-funded research project
that was launched in 2018.
Walter, O'Leary and other Cal Poly researchers, in conjunction with
the Morro Bay National Estuary Program, continue to study the cause and consequences of the eelgrass decline. In another study, the team recently
found that the loss of eelgrass in Morro Bay led to widespread erosion,
or loss of sediment, throughout the estuary.
The new research sheds additional light on changes within Morro Bay that
may inform how scientists learn about seagrass communities throughout California.
There has not been an eelgrass decline on the United States Pacific
Coast of this magnitude, making Morro Bay a novel event that may help
predict future estuarine change.
A multifaceted approach to protect and enhance the remaining seagrass
will be essential, according to the researchers. There is hope for the
future as the remaining eelgrass is slowly expanding with protection
and local planting initiatives, including successful transplant efforts
led by the Morro Bay National Estuary Program. Walter and O'Leary have
used drone-based surveys to document natural expansion and recovery of
eelgrass in areas where it was lost.
The mere 9.4 acres of seagrass left in Morro Bay in 2017 expanded to
36.7 acres by 2019. The researchers are still analyzing data from 2020
but are optimistic that the seagrass acreage continues to slowly increase.
========================================================================== Story Source: Materials provided by
California_Polytechnic_State_University. Note: Content may be edited
for style and length.
========================================================================== Journal Reference:
1. Jennifer K. O'Leary, Maurice C. Goodman, Ryan K. Walter, Karissa
Willits,
Daniel J. Pondella, John Stephens. Effects of Estuary-Wide Seagrass
Loss on Fish Populations. Estuaries and Coasts, 2021; 44 (8):
2250 DOI: 10.1007/s12237-021-00917-2 ==========================================================================
Link to news story:
https://www.sciencedaily.com/releases/2021/10/211029134032.htm
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