Seagrass Monitoring Report

East Pass Seagrass Study

Prepared by Linda Fitzhugh

The St. Andrew Bay Resource Management Association

May 2003

Abstract

The St. Andrew Bay Resource Management Association (RMA) studied the impact of opening East Pass on the seagrass beds in the St. Andrew Bay system, Panama City, Florida, over the summer of 2002. East Pass was dredged in December 2001, and RMA was assigned the duties of mapping the seagrass beds post-construction and collecting qualitative and quantitative data within the seagrass beds.

The seagrass mapping schedule consisted of surveying the edge of the seagrass beds that lie within 1000’ of the northern limits of East Pass. An original pre-construction (baseline) map was created by Bay County in May of 2000. Fifty-seven GPS coordinates were collected and a map was created by Coastal Tech showing the deep edges of the seagrass beds. Using these original coordinates, RMA volunteers surveyed the seagrass beds approximately 14 months after the pass was opened.

To determine if the health of the seagrass beds was influenced by the opening of East Pass, RMA volunteers set up two transects (Sites 11 and 12) within the boundaries of these seagrass beds in May 2002. Once each month, volunteers visited these two sites and collected the following data: overall percent cover, percent cover by species, species height, and water depth. A diver then swam along the length of the transect and shot video. This video was used to determine the relative density of the seagrass and to record any changes in water clarity.

Two other transects (Sites 9 and 10) that lie outside the seagrass beds near East Pass were visited almost every month so that any changes in seagrass health due to the opening of East Pass could be determined. RMA volunteers have been monitoring the health of the seagrass at Sites 9 and 10 since the fall of 2000.

Results show that seagrass coverage near East Pass has declined since May 2000. However, the seagrasses that remain appear to be very healthy. Near East Pass, three different species of seagrasses are present whereas other parts of the bay system only support two species of seagrasses. Furthermore, the seagrasses near East Pass have longer and wider blades than those in other parts of the bay. Although not quantified in this report, the clarity of the water near East Pass is much greater than that in other parts of the bay.

Introduction

Study Sites

Entry into the St. Andrew Bay system is through one of two passes. West Pass, the man-made pass adjacent to Grand Lagoon and St. Andrews State Park, was initially dredged in 1938 to a depth of 32 feet. Since then, maintenance dredging occurs every 2-3 years with the latest dredging in February 2003. Because of its depth, most of the water enters and exits the bay at West Pass. Using Bay County data, RMA volunteers have estimated that less than 5% of the water flowing into and out of the bay travels through East Pass. Because of this, East Pass closed in 1998. In December 2001, Bay County dredged East Pass to a depth of 10 feet to restore the flushing of St. Andrews Bay. East Pass was open to boat traffic for approximately 17 months; by May 2003 it was barely navigable.

In the summer of 2000, RMA volunteers set up seagrass monitoring stations in West Bay and St. Andrews Bay. The focus of this report will be on the health of the seagrasses near East Pass in St. Andrews Bay.

Figure 1: Overall view of the St. Andrew Bay system, Panama City, Florida

Figure 1 shows the four bay systems (West Bay, North Bay, East Bay, and St. Andrews Bay) and the location of the seagrass monitoring stations behind Shell Island and in Grand Lagoon (blue dots). The yellow dots represent the seagrass beds located within 1000 feet of East Pass.

Figure 2: Close up of the seagrass monitoring stations behind Shell Island and in Grand Lagoon.

Figure 2 shows the location of the East Pass seagrass beds (yellow dots) to the seagrass monitoring stations (blue dots) that have been monitored since the fall of 2000. Sites 9 and 10 are approximately ½ nautical mile from Sites 11 and 12 which lie within the East Pass seagrass beds.

Background Information on Seagrasses in St. Andrew Bay

Seagrasses are underwater flowering plants that can reproduce sexually by producing pollen and flowers and asexually by producing underground rhizomes, or horizontal stems, that expand outward from the parent plant. Seagrasses require sunlight to grow, so if water clarity is poor, then seagrass will die. Water clarity if often reduced by excessive nutrients in the water which promote the growth of phytoplankton and by sediments that are suspended in the water column. Nutrients can come from stormwater runoff or point-source discharges such as waste-water treatment plants. Sediments can enter the bay through stormwater runoff, or they can be continually resuspended through wave action. The presence of seagrasses reduces the resuspension of sediment as the roots hold the sediment in place.

The four bay systems surrounding Panama City: St. Andrew Bay, East Bay, North Bay, and West Bay, cover approximately 69,000 acres or 105 square miles. Seagrass coverage within these four bay systems is extensive; however, the coverage may be continuous or patchy. By comparing aerial photos taken by the U.S. Geological Service in 1953, 1964, 1980, and 1992, we can see that thousands of acres of seagrass beds have been lost in the entire bay system.

Table 1: Seagrass coverage totals (in acres) for all four of the bay systems.

Coverage	1953	1964	1980	1992
Continuous	3,773	5,395	5,689	4,225
Patchy	8,070	6,234	4,501	5,607
Total	11,843	11,629	10,190	9,832

Table 1 shows that seagrass coverage in the entire bay system decreased 17% from 1953 to 1992.

Table 2: Seagrass coverage totals (in acres) for the St. Andrews Bay system.

Coverage	1953	1964	1980	1992
Continuous	1,214	1,404	1,713	1,324
Patchy	1,344	1,433	1,026	1,258
Total	2,558	2,837	2,739	2,582

Table 2 shows that seagrass coverage in St. Andrews Bay decreased 9% from 1964 to 1992. This part of the bay system is open to the Gulf of Mexico at both East Pass and West Pass. (Tables 1 and 2 were taken from a letter written by Mike Brim, U.S. Fish and Wildlife Service, on the extent of seagrass loss in the bay system. The USFWS was responsible for obtaining the aerial surveys used to map the seagrasses in the entire bay system.)

It must be noted that over 50% of the seagrass beds within the four bay systems show signs of prop scars (Sargent, 1994). Props on boats traveling in water that is too shallow to accommodate the drafts of their boats tear up seagrasses at their roots and rhizomes. This creates a bare strip within the seagrass bed. Seagrasses at the edge of the prop scar must grow horizontally to fill in this gap. Although prop scar recovery can occur within ten years in the Florida Keys if the scar is not too deep, no one knows exactly how long it takes for prop scars in Northwest Florida to heal.

Methods

Seagrass Mapping

A post-construction survey was completed by RMA volunteers 14 months after East Pass was dredged. The original GPS coordinates collected by Bay County in May 2000 were used to navigate the boat. Since many of the coordinates were not over seagrass, volunteers navigated the boat so that it followed the deep edge of the seagrass beds and new GPS coordinates were determined. A map was then created in ArcView 3.1 using both sets of GPS coordinates.

Seagrass Health

RMA volunteers set up two sites, Sites 11 and 12, in the East Pass seagrass bed in May 2002. Sites 9 and 10 already existed. Volunteers collected overall percent cover, percent cover by species, seagrass height, and water depth at the following sites as weather and time permitted.

Table 3: Sampling schedule for the East Pass study, Summer 2002

Site	May	June	July	Aug	Sept	Oct
9		Ö	Ö	Ö		Ö
10		Ö	Ö		Ö	Ö
11	Ö	Ö	Ö	Ö	Ö	Ö
12	Ö	Ö	Ö	Ö	Ö	Ö

Data Collection

Volunteers followed the protocols for seagrass monitoring that were determined by the Florida Department of Environmental Protection and the St. John’s River Water Management District. To collect data, volunteers set up a transect using weighted ropes that were marked every 10 meters with duct tape. One end of the rope was fastened to the submerged PVC pipe at the deep edge of the seagrass bed, and another submerged PVC pipe at the midpoint as well as a compass bearing were used to place the rope in its correct location. Each transect ran perpendicular to the shoreline. Volunteers collected data every 10 meters as they swam along the transect.

Overall percent cover was measured by placing a 1m² quadrat that had been divided into 100 cells over the seagrass. The number of cells that contained seagrass was the overall percent cover. To determine percent cover by species, the number of cells that contained a particular species of seagrass was counted.

Seagrass height was measured to the nearest centimeter using a ruler. Five seagrass blades of each species were measured and the data averaged. A PVC pole with markings in decimeters was used to measure the water depth.

Volunteers noted the presence of drift algae and prop scars, and they made qualitative observations regarding water clarity as they swam along the transect. Before each transect was removed, a videographer swam along the transect and shot video. Later, the video was displayed on a TV screen and the relative density of the seagrasses as the videographer swam along the transect was determined.

Results

Seagrass Mapping

Figure 3: Seagrass coverage within 1000 feet of East Pass, May 2000 to February 2003.

Site 12

Site 11

Figure 3 shows the deep edges of the seagrass beds that were mapped by Bay County personnel in May 2000 (yellow dots) and the deep edges of the same beds in February 2003 (red dots). The blue dots represent the deep edges and midpoints of Sites 11 and 12. The deep edges of Sites 11 and 12 were in the same location two years after the initial mapping. The yellow and red dots that lie below Sites 11 and 12 in Figure 3 represent a separate seagrass bed.

Figure 3 shows that seagrass coverage has declined. The deep edge of the East Pass seagrass bed migrated toward the shore from May 2000 to February 2003. However, seagrass coverage near Sites 11 and 12 did not appear to change much from May 2000 to February 2003. Furthermore, seagrass coverage near East Pass did not appear to change during the duration of the study. When RMA volunteers went out in May 2002 to set up Sites 11 and 12, they chose the widest section of the seagrass bed for their transects. Therefore, even in May 2002, the deep edge of the seagrass bed at Sites 11 and 12 was in the same location as it was in May 2000. However, the deep edge of the seagrasses west of Sites 11 and 12 had already migrated toward shore.

Seagrass Health

Overall Percent Cover

From May 2002 to October 2002, overall percent cover did not change significantly at any of the sites. This is represented in Figure 4 for Site 12. Graphs showing the overall percent cover for each site can be found in Appendix A.

Figure 4: Comparison of overall percent cover at Site 12 from May 2002 to October 2002.

Figure 4 shows that overall percent cover at Site 12 was typically greater than 90%. Although a bare strip of ground ran parallel to the shore and crossed the transects for Sites 11 and 12, the sampling point usually landed just outside this area so this data was not recorded.

Percent Cover by Species and Water Depth

Species composition changed as water depth changed. In general, shoal grass (Halodule wrightii) was present in the shallow water while turtle grass (Thalassia testudinum) and manatee grass (Syringodium filiforme) were present in deeper water. This is represented in Figures 5 and 6 for Site 12. Graphs showing the percent cover by species as well as water depth for each site can be found in Appendix B.

Figure 5: Percent Cover by Species at Site 12 in July 2002.

Figure 6: Average Water Depth at Site 12, October 2002

At Sites 11 and 12, turtle grass and manatee grass were present at depths greater than 0.8 meters. The maximum water depth at Site 11 was approximately 1.1 meters while the maximum water depth at Site 12 was approximately 1.3 meters. At Sites 9 and 10, shoal grass was present at water depths greater than 1 meter and manatee grass was present in water shallower than 1 meter; however, this was more of an anomaly than a trend.

Seagrass Height

On average, manatee grass grew 15-70 cm tall, turtle grass grew 10-60 cm tall, and shoal grass grew 15-50 cm tall. This is represented in Figure 7 for Site 12. Graphs showing seagrass height for each site can be found in Appendix C.

Figure 7: Average Seagrass Height at Site 12, July 2002.

Qualitative Observations

In general, the density of the seagrass beds increased as water depth decreased. At most of the sites, the seagrasses were not only densely packed but they filled the entire quadrat. Another indication that the seagrass beds at each site were healthy was the observation that the turtle grass near East Pass and behind Shell Island had wider leaves than that in other parts of the bay.

In May, the seagrasses at Sites 11 and 12 were covered with drift algae. By the end of June, most of the drift algae was gone. Was this natural or was this caused by the flushing of the bay at East Pass?

In late summer, volunteers noted that sea urchins had invaded Sites 11 and 12 creating a “mowed grass” effect. A lot of the manatee grass near these transects had been “mowed” to a height of 5 cm.

As the summer progressed, more people visited East Pass by boat or wave runner. Volunteers noticed that the number of prop scars also increased over the course of the summer. There were no buoys out to mark the channel through East Pass, and as the tides changed, many shoals near East Pass were observed. In fact, the deep edges of Sites 11 and 12 had water depths less than 1 meter!

Discussion

Seagrass Mapping

Figure 3 showed that seagrass coverage near East Pass declined from May 2000 to February 2003. There are several reasons why we cannot conclude that the opening of East Pass caused a decrease in seagrass coverage. First, the pre-construction GPS coordinates were collected in May 2000 by Bay County personnel yet the pass was not dredged until December 2001. How much of a decline in seagrass coverage occurred from May 2000 to December 2001?

Second, the post-construction GPS coordinates were collected by volunteers from RMA in the winter rather than the summer since they initially had trouble entering the original GPS coordinates into their GPS devices. It is important to note that while seagrasses die back during the winter, their overall coverage does not necessarily decrease. Individual plants die causing the density of the seagrasses within the bed to decrease, but the extent of coverage does not necessarily change. In fact, volunteers have noted that over the past three years, the deep edges of the seagrass beds in the bay system do not change significantly.

And lastly, experimental error was increased by using different people and different GPS devices to collect the pre-construction and post-construction GPS coordinates. RMA recommends that the original Bay County personnel who initially mapped the seagrass beds near East Pass go out over the next several years to determine if seagrass coverage continues to change. Seagrass beds do migrate, yet volunteers observed that seagrass coverage near East Pass did not change from May 2002 to October 2002. Mark Fonseca at the National Ocean Service in Beaufort, N.C., estimates that two acres of submerged land are needed to support one acre of seagrass beds. Did the seagrasses die back before East Pass was dredged and now that East Pass is no longer navigable, will the seagrasses decline in coverage?

Seagrass Health

As noted earlier, the seagrasses near East Pass appear to be quite healthy. They produce tall, wide leaves, and they produce many shoots per unit area to create densely packed beds. The biggest problems the volunteers noted were the increased number of prop scars as the summer progressed and the large amount of drift algae present in early summer. Prop scars create bare strips, and no one knows how long it takes for the seagrasses in Northwest Florida to grow back. Drift algae can also kill seagrass since too much drift algae blocks sunlight from reaching the seagrasses.

RMA recommends that Bay County place buoys or channel markers in areas where there are lots of boaters and wave runner operators to keep them from creating prop scars in shallow waters. RMA also recommends the continued financial support of seagrass monitoring. There are more questions than answers.

For example, does drift algae typically build up early in the summer only to be flushed from the system later or did the presence of East Pass help flush out the drift algae last summer? Did the closure of East Pass in 1998 or the opening of East Pass in December 2001 cause the decline in seagrass coverage noted from May 2000 to February 2003 or was this decline a natural fluctuation in seagrass coverage for that area? How does the number of boats and wave runners that visit an area influence the number of prop scars that area receives? Do buoys or channel markers reduce the number of prop scars produced each year? How long does it take for a prop scar in Northwest Florida to heal?

RMA recognizes that long term studies are needed to determine the impact humans have on the bay system. Because there is no baseline data, it is very difficult to determine the impact dredging had on the seagrasses near East Pass. In fact, the closure of East Pass could have had a detrimental effect on the seagrasses; however, because there is no baseline data, even that conclusion cannot be made.

References

Fonseca, M. S., et al. 1998. Guidelines for the Conservation and Restoration of Seagrasses in the United States and Adjacent Waters. NOAA Coastal Ocean Program Decision Analysis Series No. 12. NOAA Coastal Ocean Office, Silver Spring, MD. 222 pp.

Hemminga, M. A. and C. M. Duarte. 2000. Seagrass Ecology. Cambridge University Press. 298 pp.

Keppner, E.J. and L.A. Keppner. 2001. The St. Andrew Bay Ecosystem, Our Environment. A Revision of “A Look to the Future”. St. Andrew Bay Environmental Study Team Publication #0004. vii + 90 pp.

Neckles, H.A. (ed.). 1994. Indicator Development: Seagrass Monitoring and Research in the Gulf of Mexico. U.S. Environmental Protection Agency, Office of Research and Development, Environmental Research Laboratory, Gulf Breeze, FL. EPA/620/R-94/029. 64 pp.

Sargent, F.J., T.J. Leary, D.W. Crewz, and C. R. Kruer. 1995. Scarring of Florida’s seagrasses: assessment and management options. FMRI Tech. Rep. TR-1. Florida Marine Research Institute, St. Petersburg, Florida. 37 pp. plus appendices.

Short, F. T. and R. G. Coles (eds.). 2001. Global Seagrass Research Methods. Elsevier Science B.V., Amsterdam. 473 pp.

Virnstein, R.W. and L.J. Morris. 1996. Seagrass preservation and restoration: a diagnostic plan for the Indian River Lagoon. Technical Memorandum #14. St. Johns River Water Management District, Palatka, Fl. 43 pp.

Appendix A

Overall Percent Cover Charts

Figures A-1 to A-4 show the overall percent cover of seagrass at four sites near East Pass, St. Andrews Bay, Florida. Each graph shows the overall percent cover of the seagrasses during the summer and fall of 2002.

Figure A-1.

Figure A-2.

Figure A-3.

Figure A-4.

Appendix B

Percent Cover by Species Charts

Figures B-1, B-3, B-5, and B-7 show the percent cover by species at four sites near East Pass, St. Andrews Bay, Florida. Figures B-2, B-4, B-6, and B-8 show the average water depth at each site.

Figure B-1