Download Florida`s Mangroves: An Overview - Miami

Florida’s Mangroves: An Overview Biology Mangroves are a specialized group of trees and shrubs that reside in the intertidal areas on the edge of the land and sea. While they are found in the subtropics and trop‐
ics their distribution is dependent on four major factors including: climate, salt water, tidal fluctuation, and soil type. The mangrove’s tidal environment is harsh with an‐
aerobic sediments (no oxygen), fluctuating water levels, and high salt content. Mangroves favor these conditions not because they can’t live in fresh water, but because fewer species are able to live in this environment so there is less ecological competition. Unlike these fresh water plants, mangroves thrive in their habitat because of evolved adaptations in root structure, reproductive strate‐
gies, and the ability to maintain a salt balance. Surpris‐
ingly, individual species have evolved different solutions to deal with the same challenges. Worldwide, there are more than 50 species of mangroves. In Florida, three true species of mangroves comprise the mangrove forests, the red mangrove (Rhizophora mangle), the black mangrove (Avecennia germinans), and the white mangrove (Laguncularia racemosa). There is also a man‐
grove associate species, the Buttonwood (Conocarpus erectus) which is found further upland. Distribution of each species in the mangrove forest is dependent on their level salt tolerance. tree, the propagule floats in the water for up to a year where it is eventually washed ashore, develops roots, and establishes itself as a mangrove plant. The black mangrove (Avicennia germinans) occupies slightly higher elevation than the red mangroves where it can be reached only by high tides. However, salt deposits readily in these soils so black mangroves must excrete more salt than any other of the mangrove trees. They do this by excreting salt through specialized glands on the leaf surface. You can actually see salt crystals on the underside of most black mangrove leaves. Black mangroves are most eas‐
ily recognized by their pencil‐
like roots, called pneumato‐
phores. These pneumatopho‐
res grow vertically up through the sediment and provide oxy‐
gen to the underground root system. Like the red mangrove, black mangroves utilize vivipary and propagule dispersal. The clusters of white flowers produce a smaller, lima‐bean shaped propagule that splits once germinated on the parent tree. Establish‐
ment of new mangrove seedlings is limited to the area above the low tide water mark. Red mangroves (Rhizophora mangle) are found closest to White mangroves (Laguncularia ra‐
the water and are the most recognizable mangrove trees cemosa) are found further inshore and due to their “walking” prop roots. These prop roots not can have either pneumatophores or only provide support and stability for the tree, but they prop roots depending on habitat condi‐
also have pores (called lenticels) which supply oxygen to tions, although they may have neither. the buried roots. Red mangroves, unlike the black and While the white mangroves are the white mangrove species, are salt excluders and obtain smallest of Florida’s mangroves, they fresh water from the salt water by blocking the absorption are best identified by their rounded of salt at the roots. Due to the red mangrove’s location leaves which have two small nodules at along the water’s edge, the species undergoes a special the leaf stalk that excrete sugar. White form of reproduction known as vivipary. The trees pro‐
mangroves also excrete salt through duce yellow flowers and after pollination, a yellow fruit their leaves and exhibit similar repro‐
and propagule is formed. This propagule is an embryo ductive strategies as the black man‐
which germinates and develops while still attached to the grove. tree (vivipary). Once it’s mature and breaks away from the Florida’s Mangroves An Overview The buttonwood or button mangrove (Conocarpus erec‐
tus) is related to the white mangrove but is only consid‐
ered a mangrove associate. It is usually an upland spe‐
cies, although it my grow intertidally. Button woods also have glands on their leaf stalks, but the arrangement of leaves differs from the three other mangrove species. But‐
ton mangrove leaves are arranged alternately, whereas the other species have leaves located opposite one an‐
other. Importance The mangrove community plays an important physical and biological role in the tropical and subtropical regions. Mangrove forests protect the coastline from strong winds and waves. The trees provide a buffer zone that minimizes coastal damage from storms and hurricanes. They also provide protection and stabilization for coastal lands. By trapping sediments that are deposited with the tides and those washed downstream, the mangroves help to in‐
crease the soil around them. This stabilization is critical for preventing shoreline erosion. Mangroves can also fil‐
ter and remove runoff, debris, and pollutants from adja‐
cent uplands. This prevents the pollutants from contami‐
nating waters and helps to maintain and improve water quality, as well as protecting the offshore seagrass and coral reef communities. In addition to protective services, mangroves provide essential feed‐
ing, breeding, and nursery habitat for marine organisms, and are an integral part of coastal and estua‐
rine food webs. Mangrove forests produce 3.6 tons/acre of leaf litter per year. This decomposed detri‐
tus forms the foundation of the mangrove food web. The branches and root system of the mangroves provide protected nursery areas for shellfish, crustaceans, and fish. They also provide food for a num‐
ber of marine species including oysters and shrimp, snook, snapper, tarpon, jack, sheepshead, and red drum. So much so, that an estimated 75% of game fish and 90% of the commercial species in south Florida depend on the mangrove ecosystem at some point in their life history. The mangrove branches also serve as rookeries (nesting areas) for a diversity of diving and wading birds. Threats While storms and hurricanes can damage mangroves, hu‐
man destruction of mangrove habitat by shoreline devel‐
opment is their greatest threat. Between 1943 and 1970, nearly 500,000 acres of mangroves were removed in the state of Florida. Removal of these trees can increase coastal erosion, change waterfront runoff patterns, and impact biodiversity; resulting in large economic impacts especially in the fisheries realm. As a result, the removal of mangroves is now regulated by state and local laws. Sources: http://www.sfrc.ufl.edu/Extension/pubtxt/for43.htm http://www.dep.state.fl.us/coastal/habitats/mangroves.htm Lisa Krimsky Miami‐Dade County Sea Grant Extension Agent 305‐421‐4017 [email protected] The Institute of Food and Agricultural Sciences (IFAS) is an Equal Employment Opportunity – Affirmative Action Employer authorized to provide
research, educational information and other services only to individuals and institutions that function without regard to race, color, sex, age,
handicap or national origin. U.S. DEPARTMENT OF AGRICULTURE, COOPERATIVE EXTENSION SERVICE, UNIVERSITY OF
FLORIDA, IFAS, FLORIDA A. & M. UNIVERSITY COOPERATIVE EXTENSION PROGRAM AND BOARDS OF COUNTY
COMMISSIONERS COOPERATING.