Download Susan Mullane

Additional northern range extension of Rhizophora
mangle
(Red Mangrove) in Northeastern Florida, United States
Kayla Tennant, Jessica Canas, Suzey Mullane & Raleigh
Clarke
Rhizophora mangle
Abstract
The northernmost range of Rhizophora mangle, commonly known as Red Mangrove, has
been previously documented at Fort Matanzas National Monument in St. Johns County, Florida
in 2006 (N29 54.897 W81 18.489). Further research has shown that R.mangle has been growing
north of that location in northern parts of St. Johns County, and may have been for some time.
The research was designed to test the hypothesis that climate change affects the distribution of
Rhizophora mangle in northeastern parts of Florida.
Introduction
Rhizophora mangle can grow up to 5-20 m in deep organic soils and are commonly
found in salt water marshes or mangrove swamps. Red mangroves grow in salt marshes in low
marsh tidal zones similar to the habitats where we conducted field research (see figure 1)
(Tiner, 1193, p. 10-14). Red mangrove populations are primarily located in southern parts of
Florida with the exception of extreme northern distributions in Cedar Key and north of the
Ponce de Leon Inlet (Sprung, 1999, p.2-3). Along with the red mangroves, there are two other
species of mangroves that inhabit the southeastern coast range, black mangrove (Avencennia
germinans) and white mangrove (Languncularia racemosa).
R.mangle has very distinct characteristics that distinguish them from other mangroves;
such as aerial prop roots and reddish bark. The leaves are evergreen, thick and leathery. The
tops are glossy and green and the underside is yellow-green with black dots and no visible
veination. The propped roots of the plant come from the stem and function in stabilizing the
plant. They also facilitate gas exchange for respiration when they are completely submerged in
water (Mehlig & Hill, 2007).
R. mangle is generally found in subtropical to tropical coastal regions: fringe, riverine,
over wash, basin and super tidal flats. The plants can live completely submerged in water or
where the tide fluctuates along the coasts. R. mangle lives in salinity levels between 0-90ppt
and temperatures that average around 76 degrees Fahrenheit. The plants act as a natural
barrier for coastlines, acting as a storm buffer. Its surrounding vegetation includes Avicennia
germinans (Black Mangrove), Batis maritima (Salt Wart), Juncus roemerianus (Black Rush),
Ditichlis spicata (Seashore Salt grass), Iva frutescens (Marsh Elder), and Borrichia frutescens
(Sea Oxeye) (Florida Division of Forestry, 1979, p. 24-29). These associations create a unique
environment and an extremely diverse yet crucial habitat for marine and estuarine
invertebrates and fish, as well as a nesting site for wading birds, creating an extremely diverse
habitat.
We attempted to test whether climate change might have contributed to the
distribution of R. mangle growth in the north eastern coast of Florida. Before our fieldwork
began we knew that the northern most point of red mangrove last documented was located at
Fort Matanzas National park, although through the semester we have surpassed that last
location by 17.8 miles north of that location. We documented the most recent, northern extent
located at Camachee Cove Yacht Harbor in St. Augustine.
Materials and Methods
The search for the northernmost point of R.mangle was centered in St John’s County, St.
Augustine, Florida. This work took place from January 2010 until April 2010. The starting point
was determined utilizing the location of the previously documented northernmost point, 29°
42’N, 81° 14’W 29° (Zomlefer, Judd & Giannasi, 2006, p.239-244). The vegetation surrounding
the original plant was identified as the Batis maritima (saltwort), Avicennia germinans (black
mangrove), Salicornia europaea (glasswort), Iva frutescens (marsh elder), Lycium carolinanum
(Christmas berry),and Juncus roemerianus (needle rush). GIS data waypoints were taken at this
location with the use of a hand held Garmin GPS 76Cx. A measuring tape was used to document
the heights of the saplings in SI units (m). The morphology of the saplings was identified as
R.mangle through the use of Peterson Field Guides (Petrides & Wehr, 1998, p. 214-216), and
photographs taken previously at Fort Matanzas. The access to Google Earth and aerial
photographs obtained from the St. Johns River Water Management District provided insight
into potential areas with populations of R.mangle.
In order to narrow down the search for the distribution of R.mangle, the team targeted
areas most populated with vegetation commonly found in R.mangle habitat. They were the
following: the site at East side of Fort Matanzas National Monument Park, Camachee Cove
Yacht Harbor, the Castillo de San Marcos, the Fountain of Youth, the Guana Tolomato Matanzas
Research Reserve, and Fishers Island near the 312 Bridge. Fort Matanzas, the Guana Tolomato
Matanzas Estuarine Research Reserve, and Fishers Island were explored by foot and a kayak
(see Figure 1). The kayak was utilized to explore the intracoastal waterway unreachable by foot.
Results
The goal was to observe and document the northernmost occurrence R.mangle during
the months of January, February, and March 2010 and compare the findings to climate factors.
We documented that R.mangle has been growing further north of the previously-documented
northernmost range at Fort Matanzas National Monument. Our search began at Fort Matanzas
National Monument, Rattlesnake Island, 29⁰42’N, 81⁰14’W, where previously documented
R.mangle still remains after four years.
After making observations and analyzing the morphology, the search continued along
the eastern shoreline of the Matanzas River where 15 plants were discovered (See Figure 1).
The plants were found in different stages of growth; including a propagule and a hypocotyl,
several seedlings, (indicating recruitment) and several adult plants ranging from .6096-1.8288
(m) were also found in the same area.
The red mangroves found along the eastern shoreline of the Matanzas River were green
and alive, with many signs of new growth. The red mangroves found at this point of interest
were growing along the muddy banks and shell beds along the Matanzas River, which was an
ideal place for R.mangle to propagate. Furthermore, the surrounding common vegetation
indicated that this was a suitable habitat for the mangroves (Florida Division of Forestry, 1979,
pg. 24-29). Next, we selected potential sites by analyzing aerial photographs (St. Johns River
Water Management District, 2007-2010) . By analyzing this imagery, we could identify the
locations of dense black mangroves and possibly the location of red mangroves; therefore, the
next point of interest was North of the 312 Bridge at Fishers Island Marina (N29 52.227 W81
18.186). After hiking through thick black mangroves, we discovered three red mangroves that
measured 2.19 (m), 2.96 (m), and 3.048 (m). It was clear that R.mangle had been growing for
some time, making Fishers Island the most northern point of red mangrove distribution at this
point in our explorations. Fishers Island is an appropriate habitat due to its low energy
shorelines accumulated with organic mud and protected shell beds (Sprung, 1999, p.2).
At Camachee Cove Yacht harbor (N29 54.897 W81 18.489) we found one red mangrove
measuring 1.25 (m). The tree was leafless; however, the roots were moist and a new plumule
was emerging, showing signs of new growth. We determined that this plant was an outlier,
because there was no evidence of R.mangle in the surrounding areas. The propagation of this
particular plant was located in dense Spartina alterniflora (Smooth cordgrass); exposed to
higher wave action and higher current velocities when compared to the other documented
location at Fisher Island. Higher wave energy environments make it difficult for the R.mangle
to propagate. Furthermore, this area was more susceptible to temperature stress; including
high winds and frosts due to the lack of protection from surrounding vegetation in comparison
to other R.mangle habitats (Sprung, 1999, p.1).
Discussion
The historic range for red mangroves have been reported as far north as Cedar Key on
the west coast of Florida and north of the Ponce de Leon Inlet on the east coast of Florida: both
of these extremes lie at approximately 29⁰10’ N. The R.mangle species ranges have fluctuated
over the past several centuries due to short-term climate change (Odum, McIvor, & Smith,
1982, p.2). R.mangle is most prevalent in south Florida, particularly the Florida Keys and in the
Everglades (Alexander, 1954, p.209)
Our attempts to document new, more northern locations of the red mangrove started
where it was last documented in 2006, Fort Matanzas. Starting where we knew R.mangle was
already present gave us insight to the living environment of R.mangle. R.mangle does not
develop adequately in regions where the annual average temperature is below 66 Degrees
Fahrenheit (Odum, McIvor, & Smith, 1982, p.1). The average temperature in St. Augustine
(www.srh.noaa.gov,2010) from 2006-2009 was 71.79 Degrees Fahrenheit, with the current
average of January-March 2010 being 51.35 Degrees Fahrenheit. The higher than normal
average temperature patterns for the last several years have likely allowed for R.mangle to
grow in more northern parts of Florida. On the other hand, recent freezes (dates?)have a
tremendous affect on the growth and distribution of the mangroves by decreasing tree height
and decreasing leaf size (Lugo and Zucca, 1997).
Future research suggestions would entail the use of access permits to expand searches
into more potential areas, and of kayaksuse Kayaks would provide access to areas that
traveling by foot would not allow and would serve as a means of transportation to observe
areas closer to the coast and the banks of rivers and the Intracoastal waterway. With this
knowledge a team may be able to have a better understanding of the plants distribution.
Summary
The hypothesis at the beginning of our research stated: how climate change contributed
to the distribution of R.mangle growth on the north eastern coast of Florida. We documented a
northern range extension by 17 miles, however it is impossible for us to assert that climate
change is the sole reason for the extended distribution of red mangroves. Any change in overall
climatic averages, including more frequent extremes in winter temperatures, may limit the
growth and reproduction of R.mangle. However, our documented northern range extension
may contribute to the scientific body of information indicating any changes in species
distributions. The four major factors that appear to limit the growth of R.mangle and determine
the extent of mangrove ecosystem development includes, (1) climate, (2)salt water, (3) tidal
fluctuation, and (4) wave energy (Odum, McIvor, & Smith, 1982, p.1). Therefore, climate
change, with its attendant increased warmer temperatures, longer summers and rising water
levels may also affect the distribution of R. mangle (Sprung, 1999, p.1-9). Other factors that
contribute to the range of R. mangle include: seeds travel north primarily through oceanic
currents, river currents, and wind. These three factors may provide an alternate explanation to
climate change as the primary cause of this range extension, although these factors may also be
affected by weather patterns.
Acknowledgements
We thank Professor Barbara Blonder and Dr. Terri Seron for creating an intriguing
Environmental Science program and being environmental mentors. We also wish to thank
Guana Tolomato Matanzas Research Reserve for partnering and supporting research efforts
with Flagler College’s Science department. We thank Eric Revuelta from the St. Johns River
Water Management District, for guiding us in the field and providing expertise in botany
identification. We are grateful for Hugh for permitting us to conduct research at Fishers Island
Marina, along the Matanzas River.
1 R.mangle present/outlier
Camachee Cove Yacht Harbor.
Accessed by wading.
3 R.mangle present at Fisher Island.
Accessed by kayak.
15 R.mangle present on the East side
Matanzas River across from Fort
Matanzas National Monument.
Accessed by hiking.
(Figure 1: Most southern point previously documented at Fort Matanzas National Monument.
Northern point at Fisher Island is the most consistent documentation of R.mangle. The most
northern point is a single plant, which is labeled an outlier, because there was no evidence of
further R.mangle distribution.
Two most northern
points of R.mangle
(Figure 2: Fort Matanzas Monument where previously documented R.mangle is shown, along
with 15 new plants that were discovered along the east side of the Matanzas River)
(Figure 3: 15 R.mangle discovered slightly north east of previous documentation in 2006)
Literature Cited
Alexander, T. R. (2005). Trees Against The Sea. In T. E. Lodge, The Everglades Handbook:
Understanding The Ecosystem (pp. 207-209). Boca Raton: CRC Press LLC.
Forestry, F. D. (1979). Marsh/Mangrove Zone. In Coastal Plants of Florida-A Key To Good Land
Management (pp. 24-29). Tallahasse: Florida Dept. of Agriculture and Consumer Services,
Division of Forestry .
Mehlig, U, & Hill, K. (2007). Rizophora mangle (aquatic plant, tree, shrub).
Sprung, J. (1999). Ecology and Care of Mangroves. Retrieved April 2010, from Magnificent
Mangroves: http://www.twolittlefishies.com/images/mangrove_manual.pdf
Tiner, R. W. (1993). Field Guide To Coastal Wetland Plants Of The Southeastern United States.
In R. W. Tiner. Thomson-Shore, Inc.
Wehr, G. A. (1998). Peterson Field Guides: Eastern Trees. New York City: Houghton Mifflin
Company.
www.srh.noaa.gov. (1973-2010). Retrieved March 13, 210, from ST AUGUSTINE WFOY,
FLORIDA : http://www.sercc.com/cgi-bin/sercc/cliMAIN.pl?fl7826
Zomlefer, W. B. (2006). Northernmost Limit of Rhizophora mangle (Red Mangrove;
Rhizophoraceae) in St. Johns County, Florida. Castanea , 239-244.