Allen, correct on that first part.

Here is one of several 'landmark' papers on this relationship, by one
of my college professors....

ArticlePDF Available
Ribbed Mussels and Spartina Alterniflora Production in a New England Salt Marsh
December 1984Ecology 65(6)
DOI:10.2307/1937776
Authors:
Mark D Bertness
Brown University
Download full-text PDF
Read full-text

Citations (220)
References (36)

Abstract
The ribbed mussel, Geukensia demissa, is commonly found associated
with the salt marsh cordgrass, Spartina alterniflora. Mussels attach
to the basal portion of S. alterniflora stems with strong
proteinaceous byssal threads and deposit fecal material on the
surrounding sediment as a byproduct of their filter-feeding activity.
Here I demonstrate by manipulating mussel densities in the field that
the presence of G. demissa stimulates S. alterniflora growth, and
examine experimentally a number of potential mechanisms of this
facilitation. In the natural habitat, mussel density is positively
correlated with increased grass height, biomass, and flowering, and
experimental removal and addition of mussels in these habitats
demonstrates that mussels stimulate both aboveground and belowground
S. alterniflora production. In tall-form S. alterniflora habitat, net
primary production is positively correlated with mussel density and
soil nitrogen levels. Experiments in this habitat show that mussels
increase soil nitrogen, and this increase in nutrients would appear to
be responsible for stimulating S. alterniflora growth. On the seaward
edge of the marsh, net primary production is strongly correlated with
mussel density, but not soil nutrients. On the marsh edge, mussels are
shown to bind sediments and prevent erosion and physical disturbance.
The relationship between S. alterniflora and G. demissa appears to
represent a facultative mu- tualism that leads to increased marsh net
primary production and stability. While previous research has shown
that S. alterniflora production increases G. demissa growth and
reproductive success, G. demissa also has strong stimulating effects
on S. alterniflora. Nonconsumer plant-animal interactions such as the
G. demissa-S. alterniflora association are potentially important
determinants of marsh growth, stability, and community structure that
have not been previously appreciated.

On 12/30/21, Allen Aigen
<[log in to unmask]> wrote:
>  The pseudofeces and feces ejected by the mussels probably also helps build
> up the sediment that is trapped between the Spartina stems, allowing the
> area to keep up with moderately rising sea levels.  The mussels often attach
> to the Spartina below the surface.Allen Aigen
>     On Thursday, December 30, 2021, 11:51:03 AM EST, Harry Lee
> <[log in to unmask]> wrote:
>
>   The role of Geukensia demissa in the structure SE US saltmarshes was
> mentioned in Lee (2009: 16, species 11): "An infaunal species typically
> attaching to hard objects buried in the muck of the estuarine Spartina
> community, of which it is an important member."
>
>  The Ribbed Mussel's special combination of epifaunal and infaunal habits
> provides a potent anchor for the root system of cordgrass and other flora in
> the habitat.
>
>  Harry
>
>
>  On 12/28/2021 7:09 PM, David Kirsh wrote:
>
>  Dear Listers,
>
> I was alerted to this information by a news item on public radio. Ribbed
> mussels play a leading role in the integrity of salt marshes and feral swine
> are the nemesis.
>
> But I hadn’t heard about the wider threat of feral swine described in the
> accompanying video.
>
> David Kirsh
> Durham, NC
>
> https://www.savannahnow.com/story/news/2021/12/07/wild-hogs-mussels-coasts-climate-change/8881734002/
>
> [log in to unmask]
> - a forum for informal discussions on molluscsTo leave this list, click on
> the following web
> link:http://listserv.uga.edu/scripts/wa-UGA.exe?SUBED1=conch-l-L&A=1Type
> your email address and name in the appropriate box andclick leave the
> list.----------------------------------------------------------------------
>
>
> ----------------------------------------------------------------------
> [log in to unmask] - a forum for informal discussions on molluscs
> To leave this list, click on the following web link:
> http://listserv.uga.edu/scripts/wa-UGA.exe?SUBED1=conch-l-L&A=1
> Type your email address and name in the appropriate box and
> click leave the list.
> ----------------------------------------------------------------------

----------------------------------------------------------------------
[log in to unmask] - a forum for informal discussions on molluscs
To leave this list, click on the following web link:
http://listserv.uga.edu/scripts/wa-UGA.exe?SUBED1=conch-l-L&A=1
Type your email address and name in the appropriate box and
click leave the list.
----------------------------------------------------------------------