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Is the Salinity Good Enough for Scallops? The 2021 3rd Quarter Community Science Salinity Report

No question…

The amount of rainfall Pensacola is getting this year (2021) has been amazing.  At the time of this writing, we are at 84.86”.  But it has not been just this year.  Over the last decade total rainfall for a community that averages around 60-65”/year has been…

 

Year Rainfall (inches)
2010 62.96
2011 48.68
2012 66.63
2013 74.67
2014 83.17
2015 75.69
2016 64.62
2017 91.91
2018 90.01
2019 52.56
2020 76.49
MEAN 71.58

 

There has been talked for a few years now about restoring seagrasses and scallops.  The species of seagrass – shoal grass (Halodule wrightii) and turtle grass (Thalassia testudinum) – that historically grew in Santa Rosa Sound and Big Lagoon, and supported scallops, prefers salinities at 20 ppt and higher.  The same can be said for the scallop itself.

 

So, how is all of this rainfall impacting the salinities in the bay area?  Do these species of seagrasses, and the bay scallop, have a chance?

 

To help look at this Sea Grant in Escambia County has been working with volunteers to monitor salinity at 16 locations around the bay.  Several of them are not in areas where scallops and turtle grass were once found, and some volunteers have been inactive for a bit, but it still gives us an idea of how this rain may be impacting the bay.

 

It is understood that the best locations to monitor the salinity for this question would be in Santa Rosa Sound and Big Lagoon at the bottom where scallops and turtle grass exist.  But not having the equipment and funding to sample there, volunteers use a simple refractometer to take a reading at the end of their dock, or at a local beach.  We ask them to get a reading once a week and are targeting 100 readings from each location before we stop (2 years of monitoring if they can do this).

 

Below is the 2021 3rd Quarter Report

 

Body of Water   (n=) Surface    
Mean Median Mode
           
Bayou Grande   29 20 21 21
  Navy Point SE 7 13 11 11
  Navy Point SW 7 10 10 10
Bayou Texar   10 8 7 NA
Bayou Chico   7 10 5 5
Big Lagoon Grand Lagoon 15 23 23 20
  State Park 10 17 16 14
Big Sabine   47 21 21 22
Bruce Beach   1 18 18 NA
Galvez Landing   3 11 12 NA
Kees Bayou   89 20 20 14
Little Sabine   31 21 21 19
Lower Perdido Bay   100 16 15 20
Old River   36 23 23 25
Sanders Beach   29 16 16 16
Shoreline Park   1 18 18 NA

 

Results

 

Eight of the 16 sites (50%) are from locations that historically did not have turtle grass or scallops.

One of those – Bayou Grande – does have salinities at the 20 ppt mark (though only 29 readings have been logged at this point).  Suggesting that turtle grass could survive here.  But there are no records of that plant growing in Bayou Grande and no scallops as well.

 

Of the eight sites that did have historic records of both – currently three do not meet the 20 ppt threshold for success of these species.  Big Lagoon State Park, Galvez Landing, and Shoreline Park all are below 20 ppt.  But it must be noted that the number of readings at these sites are low.  Ten readings have been conducted at Big Lagoon SP, three at Galvez Landing, and only one at Shoreline Park.  The volunteers at Big Lagoon SP and Galvez Landing are new and have just begun their monitoring.  We also know that turtle grass does exist at all three locations, so the 20 ppt mark must be occurring here.  We also know that scallop have been found in Big Lagoon.

 

Five of the historic sites – Big Lagoon/Grande Lagoon, Big Sabine, Kees Bayou, Little Sabine, and Old River – despite the heavy rains, are holding above 20 ppt.  You would like to see values between 25-30 ppt but remember – these volunteers are sampling at the surface near the beach.  The salinities in the deeper water where we would expect turtle grass and scallops may be in that range.

 

Discussion

 

With the increase rainfall some monitoring is better than no monitoring.  There are several groups and organizations that conduct monitoring in the bay system that collect salinity as part of what they do, and these data could tell a different story.  We only have one site that has reached the 100-reading mark (Lower Perdido Bay), and only one other that has more than 50 readings (Kees Bayou n=89) – Big Sabine (n=47) is very close.  We will continue to monitor these sites and post quarterly reports.

 

October 2021.