Cabbage palm, Photo by Mmcknight4, Wikimedia Commons
(Click on the following link to listen to an audio version of this blog … Palm trees and seagrass
There are twelve species of palm trees that are native to Florida. Notable on this “palm tree-dozen” list are cabbage palm (Sabal palmetto) (the official state tree of Florida), needle palm (Rhepidophyllum hystrix), royal palm (Raystonea regia) and silver palm (Coccothrinax argentata). Worldwide there are 2500 species of palm trees and, probably, most of them would grow in the subtropical lushness of Florida.
A good estimate, though, is that there are about fifty species of “exotic” palms growing in some abundance in Florida, possibly at the expense of several of the native species.
The palm tree that has taken on an iconic role in the visual mythology of Florida, though, is an alien, exotic species that only arrived in the state 140 or so year ago. This is the palm tree that graces so many of the Florida picture postcards that winter visitors to the state send back home to their ice-and-snow-bound friends and neighbors. This is the palm tree that grew in abundance around our rented beach house when we went to the Florida Keys in early December and set the tropical tone for our stay in the Keys. This palm is the coconut palm (Cocos nucifera).
Coconut palms. Photo by M. Hamilton
The coconut palm is native to the tropical islands of the western Pacific. It has spread widely throughout Oceania and, eventually, throughout the world first due its buoyant, water-tight seeds (the coconuts, of course) and then due to some long distant human-assisted transport. The coconut palm plays a key role in the cultures of many of the native peoples of the Pacific islands. It is a source of food, fuel, medicines and building materials. It is tightly woven into the histories and mythologies of many island cultures.
The coconut palm came to Florida very recently. The wreck of a Spanish sailing ship carrying a load of coconuts from Cuba to Spain in 1878 spilled its cargo onto the Florida shore. Some coconuts germinated where they washed ashore and others were carried off by people to other spots and planted. I am sure, though, that many more coconuts followed!
Coconut palms are large trees with long, curving trunks covered with smooth, grayish-brown bark. They can grow up to 100 feet tall. They form an apical mass of pinnate leaves that are each 13 to 20 feet long, and each leaf has pinna that are 2 to 3 feet long. A mature coconut palm can make 75 coconuts a year. It usually takes 6 to 10 years for coconut production to begin, and another 15 or 20 years to reach maximum productivity. Coconut palms are productive for 60 to 100 years. They are referred to as “three generation” trees. A person who plants a coconut palm can expect to eat the coconuts from it as can their children and their grandchildren!
Palm trees at sunset. Photo by D. Silllman
Coconut palms are held in place by broad, fibrous root systems. They do not make stabilizing tap roots but instead rely on their flexibility and relatively narrow profiles to withstand winds that would topple most other types of trees.
There is something calming about a coconut palm tree. Its arching, “slouchy” trunk. Its messy, mussed up “head” of leaves, and its ability to deliver delicious coconuts for food and beverages. They are the tropics, indeed!
Much more important than palm trees to the ecosystems of Florida, though, even they are much less visual and much less photogenic, are seagrasses.
Seagrass meadow. Photo by NOAA,. Public Domain.
Seagrasses are true plants not seaweeds. The evolution of plants some 500 million years ago involved a variety of structural and physiological changes from the seaweeds that enabled these new, photosynthetic organisms to live on land. Stems, complex leaves, vascular systems, flowers, seeds, fruit and nutrient and water gathering roots all played vital roles in the origin and then the diversification of plants. About 100 million years ago, well after plants had attain incredible domination of the Earth’s landmasses, some of these terrestrial plant species returned to the sea! These new plants, the seagrasses, colonized shallow, sunlit coastal habitats and established extremely productive, complex biological communities all around the world.
Turtlegrass. Photo by J. St. John. Wikimedia Commons
There are between 50 and 72 distinct species of seagrass (experts differ in the delineation of specific species designations). Seven of these species are found in Florida: turtle grass (Thalassia testudinum), shoal grass (Halodule wrightii), manatee grass (Syningodium filiforum), widgeon grass (Ruppia maritima), stargrass (Halophila englemanni), paddlegrass (H. decipiens), and Johnson’s seagrass (H. johnsonii). Turtle grass, manatee grass and shoal grass are Forida’s most abundant seagrasses.
Seagrasses make flowers just like terrestrial grasses, and they reproduce sexually by pollination of their flowers. The pollen is transferred from male flowers to female flowers by water movement and also by small crustaceans that carry the sticky pollen on their bodies from flower to flower (these little crustaceans are sometimes called “sea bees!”). Seagrasses also spread by clonal reproduction and grow extensive numbers of new shoots from spreading rhizomes. Often, large areas of seagrass are actually a single organism sprouting off of extensive, common rhizomes buried in the sediment. One of the largest, if not the largest, organisms in the world is a clonal patch of sea grass off the coast of Western Australia that covers 77 square miles! Also, one of the oldest, if, indeed, not the oldest, organisms on Earth is also a seagrass: a patch of Posidium ocenica in the Mediterranean Sea estimated to be over 200,000 years old!
Manateegrass. Photo by J. St. John. Wikimedia Commons
Seagrasses grow in the photic zone of shallow coastal habitats both in salty and brackish water. One acre of seagrass can, according to the University of Miami, produce over 10 million tons of biomass each year! A single acre of seagrass supports over 40,000 fish and 500,000,000 invertebrates! The seagrass roots stabilize the underlying sediments and the stems and leaves provide shelter for fish, crustaceans and shellfish, protecting them against predators, tides, strong currents and storms. Large herbivores like sea turtles and manatees rely on seagrasses for food and through their grazing stimulate the growth and vitality of the seagrass beds. Seagrasses also help to maintain water clarity by filtering out fine sediments from water.
Human activity has had massive, negative impacts on seagrass. Direct disruption of seagrass by trawling and by the careless dragging of boat motor propellers across the seagrass plains can leave extensive bare spots that may take decades (or longer) to repair. Even more seriously, pollutants pouring into the coastal seagrass zones from land-based sources (pesticides, herbicides and fertilizers from farms, phosphates and nitrates from urban sources and oil and industrial pollutants from refineries and factories) can directly kill the seagrass or, more insidiously, stimulate the growth of algae that leads to a Harmful Algae Blooms (HAB’s). A HAB can then tie up most of the oxygen in the coastal waters and lead to the widespread death of the seagrasses and also many of the other organisms that live in the seagrass ecosystem. Worldwide, 1.2% of all existing seagrass areas are being destroyed each year!
Seagrass on shore near our beach house (plus one iguana!). Photo by M. Hamilton
At the beach near our rental house in order to get into the water, we had to walk over a two foot wide and one foot high mass of dead seagrass (I think that it was turtle grass) that had washed ashore. We watched a four-man cleanup crew work for two hours with rakes and a front loader gathering up and removing this layer of dead of seagrass. As the crew left you could see new, dead leaves of seagrass washing up on shore. Within an hour the pile was back along the length of the beach. Off shore, the turtle grass was dying!
Florida Bay was just to the north of our Gulf-side beach house. It is a large estuary off of the tip of the Florida Penninsula. The health of the seagrass in the Bay is reflective of the ongoing problems all across the Florida coasts. Florida Bay is sheltered by the upper Keys to the east, and connects to the Gulf of Mexico to the west. Water movement, though, out of the Bay is very slow primarily because of the abundance of seagrass. Freshwater from two rivers that drain the Everglades is constantly delivered into the Bay. High levels of pollutants in these waters (especially agricultural pollutants) has caused massive seagrass-killing HAB’s. Also, drought has increased the salinity of the Bay which has caused more die-offs of seagrass. Since 2015, 40,000 acres of seagrass have been lost in Florida Bay.
Manatee. Photo by USFWS. Public Domain
Seagrass is dying all through coastal Florida. Animals that depend on seagrass for food (like manatees and sea turtles) are starving. The costal ecosystems that depend on seagrass for food, shelter and stability are also declining in productivity and diversity. This loss of seagrass, considering its very slow rates of recovery and repair, is a major, long-term ecological catastrophe.