Sunday, April 29, 2012

Florida’s Mangroves: A Cross-family Comparison

By Lily Everson and Kara Cecil

This post is one of a series from professor Nisse Goldberg's Plant Taxonomy students at Jacksonville University. FNPS blogger Laurie Sheldon assisted the students with their initial drafts, providing suggestions for editing and content development.

Overview
Mangroves are tropical trees that can grow well in both fresh and brackish water. There are four main species of mangroves in Florida: the red mangrove (Rhizophora mangle, Fig. 2), the black mangrove (Avicennia germinans, Fig. 3), the white mangrove (Laguncularia racemosa, Fig. 4), and buttonwood (Conocarpus erectus). This article will focus on the red, black, and white mangrove species.

Figure 1. Mangrove zonation.
Mangroves are traditionally found on the coasts of Florida as far north as St. Augustine. With the warming of temperatures, the mangroves have been spreading northward into salt marsh habitats dominated by Spartina alterniflora. This has become a topic of interest due to the ecological consequences of such a major habitat shift.

The red mangrove, a member of the Rhizophoraceae family, is common to Florida’s coastal peninsula.  This family of mangroves dominates the waterline of Florida’s southern estuaries (Fig. 1) and is easily identified by its prop roots (Fig. 2), big shiny leaves, and long, pencil-like fruits, which can be seen floating in the water.


The family that the black mangrove (Fig. 3) belongs to is actually up for debate. Some consider it a member of the Avicenniaceae, Acanthaceae, or even the Verbenaceae. It is found further up in the intertidal zone, and between the bands of red and white mangroves (Fig. 1). The black mangrove has narrow, elliptical leaves that are typically encrusted with salt. Their cable-like roots radiate out from the tree and have finger-like projections or pneumatophores that extend out the soil.  These structures are used to provide oxygen to the roots.

The white mangrove (Fig. 4), a part of the Combretaceae family, dominates the upper intertidal zone along the coasts of Florida (Fig. 1). It has oval-shaped leaves that appear silvery with a green-yellow tint. The nectary glands are found on the stem at the base of the leaf and are used by the plant to attract ants, which in turn protect the plant from herbivorous insects.

Figure 5.  Mangrove propagules. Photo credit:
Marine Resources Council of East Florida.
Mangroves spread their offspring as propagules (Fig. 5). The propagules mature on the parent plant and then float with the currents before they settle. They each require a certain amount of time floating in the water before they can successfully take root. Look for the propagules that may wash up on your beach! 

Florida State Law protects mangroves as they help prevent erosion of our beaches by stabilizing the sand and dampening the impact of waves. They are also very important to the food chain because they are a major habitat source for juveniles of many species.

References
Judd, WS, Campbell, SC, Kellogg, EA, Stevens, PF, and Donoghue, ML. 2008. Plant systematics: A phylogenetic approach. Sinauer Associates, Inc. Massachusetts, USA.
http://www.florida.plantatlas.usf.edu/
http://flenvirothon.com/Studyguides/enviro_aquatic.pdf
http://www.sms.si.edu/irlspec/Mangroves.htm
http://www.sms.si.edu/irlspec/Rhizop_mangle.htm
http://www.sms.si.edu/irlspec/Avicen_germin.htmhttp://www.sms.si.edu/irlspec/Lagunc_racemo.htm  

Image Sources
Figure 4. http://www.flmnh.ufl.edu/Fish/southflorida/mangrove/zonation.html
Figure 1. http://florida.plantatlas.usf.edu/Photo.aspx?id=2934
Figure 2. http://florida.plantatlas.usf.edu/Photo.aspx?id=11538
Figure 3. http://www.sms.si.edu/irlspec/Lagunc_racemo.htm
Figure 5. http://www.mrcirl.org/marker/marker1703/0503.html

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