Background

Historically the Pensacola Bay System supported large salt marsh and oyster reef habitats in the northern portions, and lush meadows of seagrasses near the southern end, particularly in Big Lagoon and Santa Rosa Sound.  These seagrass beds supported a variety of fisheries including the bay scallop (Argopecten irradians).

 

With the onset of industrialization, environmental stressors began to impact the bay as early as 1900, but became more intense, and noticeable, in the mid-20^th century.  By the 1970s seagrass acreage had declined and bay scallops were basically non-existent.  The bay area usually receives about 60 inches of rain annually, making it one of the wetter locations in the southeast, but over the last decade the annual rainfall has surpassed 70 inches, going over 90 inches in 2017 and 2018.  Growth and development have also increased in recent years which, along with the increased rainfall, has led to increased stormwater reaching the bay.

 

Purpose

The purpose of this salinity project is to determine whether the increased stormwater is lowering the salinity below the 20 ppt threshold needed for healthy turtle and shoal seagrass, as well as bay scallops.

 

Method

Community volunteers are trained how to use a handheld refractometer to measure salinity.  Each volunteer does so once a week at an assigned location around the bay area.  These readings are taken from a dock or at the beach.  The target is to record 100 readings at each location and calculate the mean, median, and mode of these data to determine whether the central tendency at that location is at, or above, 20 ppt.

 

Results

 

BIG LAGOON AREA

Body of Water	Location	Number of readings	MEAN	MEDIAN	MODE
Big Lagoon	Seaglades	15	23	23	20
	State Park	85	18	19	27
Ft. McRee		4	22	22	19
Galvez Landing		98	22	22	22
Kees Bayou		100	20	21	14
Lower Perdido Bay		100	16	15	20
Old River		36	23	23	25
Perdido Key State Park		61	23	24	29
Siguenza Cove		11	22	21	21
TOTAL SAMPLES		510	21	21	22

 

 

SANTA ROSA SOUND AREA

Body of Water	Location	Number of readings	MEAN	MEDIAN	MODE
Big Sabine		82	23	22	22
Little Sabine		100	23	23	25
Oriole Beach		81	26	26	30
Shoreline Park		36	24	25	25
TOTAL SAMPLES		299	24	24	26

 

 

PENSACOLA AREA

Body of Water	Location	Number of readings	MEAN	MEDIAN	MODE
Bayou Grande		29	20	21	21
	Navy Point SE	37	18	20	20
	Navy Point SW	38	17	18	20
Bayou Texar		60	12	12	15
Bayou Chico		7	10	5	5
Bruce Beach		1	18	18	–
Hawkshaw	Memorial	51	13	12	15
	9th Ave	26	16	17	15
Sanders Beach		82	18	18	18
TOTAL SAMPLES		331	16	16	16

 

 

As of the end of the 2^nd quarter in 2023, 1,140 readings have been logged.

 

510 (45%) have been logged from the Big Lagoon area.  Two locations (Kees Bayou, Lower Perdido Bay) have reached the 100 reading mark.  Galvez Landing has 98.  Central tendencies for the Big Lagoon area are Mean (21), Median (21), Mode (22).

 

299 (26%) have been logged from the Santa Rosa Sound area.  One location (Little Sabine) has reached the 100 reading mark.  Central tendencies for Santa Rosa Sound are Mean (24), Median (24), Mode (26).

 

331 (29%) have been logged from the downtown Pensacola area.  No locations have reached the 100 reading mark yet.  Central tendencies for upper Pensacola Bay area are Mean (16), Median (16), Mode (16).

 

Discussion

 

BIG LAGOON

Though there are several locations that have not reached the 100 reading mark at this point, the early data suggest that the salinities in the Intracoastal Waterway, Old River, and Big Lagoon proper remain high enough to support turtle and shoal grass as well as bay scallops.  Anecdotal reports suggest that the seagrasses in Big Lagoon proper are doing well and there is plenty of turtle grass (needed for scallops) even in some shallow water areas.  Lower Perdido Bay has reached the 100 reading mark and the salinities show that it would not support these grasses nor bay scallops.  However, it is believed that historically this system was probably more freshwater than it is now, supporting meadows of eel/tape grass (Vallisneria).  The higher salinities found in the lower portion of Perdido Bay may be due to the permanent opening of the pass at the west end of Perdido Key allowing tidal Gulf water to enter.  Results from the Great Scallop Search in Big Lagoon have found live scallops, though very few.

 

SANTA ROSA SOUND

Only Little Sabine has reached the 100 reading mark but all of the data suggests that Santa Rosa Sound could support both turtle and shoal grass as well as bay scallops.  Salinities here are slightly higher than those found in Big Lagoon.  As with Big Lagoon, anecdotal reports suggest that the seagrasses are doing well and that turtle grass is likewise growing near shore in many locations.  The results of the Great Scallop Search have also found live bay scallops in Santa Rosa Sound, again very few.

 

DOWNTOWN PENSACOLA

Though none of the nine monitoring locations have reached the 100 reading mark, early data suggests that upper Pensacola Bay would not support either turtle nor shoal grass, and would not support bay scallops either.  However, there is no historical data that suggests it ever did.  With several tributaries entering the bay in this area, freshwater run-off is now, and has in the past, kept the salinities lower than 20 ppt.  That said, the data from Bayou Grande suggest that it might support seagrasses and in fact does have beds of shoal and widgeon grass.  Widgeon grass (Ruppia) can tolerate lower salinities and has been found in upper Pensacola Bay, Bayou Texar, and portions of Escambia Bay as well.

 

NOTE

Sea Grant also conducts community volunteer surveys of seagrasses and scallops in these areas.  Those reports will be posted by the end of the year.