FLORIDA BAY
Florida Bay is a shallow, shelf-lagoon, encompassing a triangular area of over 1,100 square miles enclosed by the graceful arc of the Florida Keys on the south and the Everglades to the north. The rich mix of marine and freshwater environments, shallow, crystal-clear water, and abundant sunlight provide a perfect environment for a complex web of marine life including marine plants, and a host of organisms from tiny foraminifera to manatees, dolphins, giant tarpon, sharks, rays and even twelve-foot long prehistoric sawfish. The calcareous bottom mud provides a substrate for turtle grass and manatee grass which carpet the bottom and provide both food and cover for many other forms of life. As in other estuaries, fresh water mixes with sea water to provide a wide range of salinities to which many different species are adapted. The Everglades, just to the north, are the source of fresh water which flows southward to mix with seawater from the Gulf. Thus the salinity of the Bay increases toward the south providing a variety of salinity concentrations suitable for many different life forms. In summer, when the sun heats and evaporates Bay water salinity tends to increase from normal sea water levels (@33 parts per thousand) to concentrations sometimes two or three times that level. On the other hand, during periods of heavy rainfall, salt concentration in some parts of the Bay may fall to well below normal. The plants and animals associated with the Bay are mostly adapted to these fluctuations and thrive in the area.
Because of its shallow depth, one sees a great deal of bay-bottom. The view is a fleeting as one skims and bounces over the surface at 35 miles per hour, your skiff driven by big twin outboards, pushing up a white rooster tail and making a wide wake. But even in passing it is apparent how shallow the Bay is and what it is like. Here and there where boat props gouge into its surface one can see that it is composed of a white lime mud. My sources say that mud may be tens of feet thick, and thicker in the west than in the east. The mud banks have been cut and filled by currents and are somewhat controlled by the limestone bedrock underneath the mud. There are shallow ridges and deeper basins. In places, storms scour coarse lime-sand and mud from one place and pile it in another. When that happens the mud banks might be high enough for Mangroves to grow on them, once they take root on the banks…that’s how the islands form.
The Bay's shallow water protected it from incursion. Were it deeper it would have been exploited for its fish and open space long ago, and would not be the isolated, pristine place it is now. The fact is that its shallow depth has prevented human occupation and incursion of criss-crosssing, pollution-spewing big boats which can not navigate in the Bay. Even the small-draft Florida Bay skiffs, which draw only a foot or more, can become trapped in the shallows. The skiffs and the fishing guides navigate the Bay by keeeping a mental map of each of the many channels and deeps using that knowledge to get from one place to another. There is no straight-line course through the Bay--one must follow the complex maze of channels and "lakes" to safely get from one place to another..that's one reason why one needs a knowlegeable guide to fish there.
Another factor is the tide which compounds the depth problem. In the Bay itself, between the banks and flats are basins. “We call ‘em “lakes,” says Jim Wilcox our Florida Bay Fishing Guide. “The water in the lakes can be six feet deep at low tide. More than once, when fishin’ was so good I didn’t pay attention to the falling tide, I actually got trapped in Rabbit Basin and had to wait till the tide came up before I could navigate out of there.”
FLORIDA BAY KEYS
Jim Wilcox our guide remarked that it was the Mangrove roots, especially Red Mangrove, which act to trap wave-and-current-washed mud and sand. This builds up around the roots and as time goes by, the plants may form a living ring around the sand bank on the ridge. High tides and storm surges wash sediment into the mangrove ring. Mangrove roots act to trap sediment and cause the outer rim of the island to grow upward. The process tends to produce islands with more a less a “dish” or “platter” cross section--high on the edges and shallower in the interior. But in time, the interior fills up too. Different plants take up residences as the mud and sand accumulates. Black Mangrove prefers slightly higher or less inundated soils, and White Mangrove prefers to have its roots dry out once each day. So in time a natural sequence of Red mangrove, Black Mangrove and White Mangrove slowly form to completely or nearly occupy much of the area of the islet or key.”
Following up on what Jim said, I did some research and discovered the following about mangroves.
The Red Mangrove (Rhizophora mangle) has a reddish bark and can grow to 50 feet, but is most often a shrub. It grows closest to open water. And is sometimes called the “walking tree,” since it has multiple “prop” roots, that help to stabilize the tree in soft mud and which encourage sediment to settle around its roots. These aerial roots also help provide oxygen to the roots, which are either totally underwater or if in mud are often growing in anoxic conditions. In addition, these roots filter out salt from the salt-water environment they most often grow in. This is one of the few trees that has its seeds (propagules) actually germinate while on the tree. See this site:
http://www.dep.state.fl.us/coastal/habitats/mangroves.htmThe Black Mangrove (Avicennia germinans) is taller than the former species, growing to 60 feet in height (but often less in Florida Bay). It is also more likely to be growing higher above sea level, or further inland where its roots are in dry or semi-dry substrate at least at low tide. It has a dark-gray or dark brown to black bark and no prop roots, but it does have tube-like structures called pneumatophores which the plant sends up vertically from the roots and into the air, and which serve to provide air to roots which are constantly wet and in water with little or no oxygen. The Black Mangrove has hairs on its under-leaf- sides which excrete excess salt. Crystals of salt can often be seen collecting there. The salt is pure sea-salt and this “mangrove salt” was harvested by early Florida colonists as an important source of edible salt. The Black Mangrove also has seeds which germinate while still on the trees.
White Mangrove (Laguncularia racemosa) is smaller than the other trees and grow in areas which are flooded less frequently. This species lives where the substrate drys out every day. The trunks and branches are often twisted and misshapen. This characteristic is often attributed to the poorer soils and more variable soil-moisture and salinity concentrations where it grows, as well as its exposure to strong winds. The petiole of its leaves have two small glands near the base of each leaf (called nectaries) which excrete salt. Salt crystals may be seen near them and on the base of the leaf. It typically has no prop-roots or pneumatophores but it does have many lenticles or breathing pores on the lower surface of the trunk to provide needed oxygen when water levels are high.
Jim described the Bay bottom topography this way. “It’s like the rough skin of an old ‘gator’ or salt-water ‘croc’ with long ridges, and spines and low places in between. And the whole ‘gator skin’ is carpeted with a thick layer of lime-mud. So’s all the ridges and hollows and swales are smoothed out a bit to make the average depth about three feet while the deep basins are me’be nine or ten feet. If it warn’t fer the mud, you guys could walk out here ta fish.” He giggled at that, adding, “But the mud’s a lot deeper than the water..so don’t try that.”
THE STUFF BELOW THE MUD
I found Jim to be correct about the bottom being like a “gator skin”--see above. The mud has its own ups and downs but it also sits on top of an even more corrugated surface of basement rock. Geologists tell us that Florida Bay has a rock basement of limestone which can be traced to a depth of 20,000 feet or more. They have termed the top-most stratum, the ‘Miami Limestone’. This layer was deposited during the last ice age (Pleistocene Epoch) when sea level rose and fell in the region by as much as 200 feet. During that time there were long periods when some of the beds that would be the Miami Limestone were exposed to aerial erosion and chemical alteration. As in all such places where limestone sits exposed to the air, naturally acidic rainwater and humic acids (from decayed vegetation) can dissolve the calcreous surface rock and permit acid water to seep downward through naturally occurring joints and cracks. In the process, the flow of water may hollow out deep holes, or create large solution cavities. We will recogize these features elsewhere as subterranean caves and caverns. Often the rroofs of these caves collapse as a result of the weight of the overlying rock The result is to create an irregular surface with ridges and hollows known as “karst” topography. These processes affected Florida Bay to create that "gator skin" texture Jim, our guide spoke of. That surface was finally inundated in the last several thousand years and marine lime-mud carpeted the entire area. The underlying karst topography is the factor which controls the locations of the two-hundred or so “keys” or mud islands in the Bay and the intervening deep basins or “lakes”. The keys are generally located on the resistant higher ridges and the solution cavities or depressions in the underlying Miami limestone (of Late Pleistocene) control the locations of the deep holes and basins. Another interesting fact is that the underlying Pleistocene Epoch, Miami Limestone slopes gently from east to west, as a consequence, the mud deposits are thicker in the west than in the east.
When I mentioned that fact to Jim on one of our forays out into central Florida Bay near Rabbit Basin, he pushed his long billed fishing cap off the side of his head for a good scratch, then without a response went back to “anchoring” the skiff in the shallow water near a small “fishin’ hole” using the long boat push-pole. All of the Florida Bay skiffs carry these boat-long push-poles secured to their side decks. I noticed Jim was easily able to poke the near 20 foot skiff-pole down a good ten feet in soft mud in the shallows around Rabbit Basin and elsewhere. The Florida Bay fishing skiffs can be rendered stationary by stabbing the long, boat pole, into the deep mud at a 60 degree angle. After Jim set the pole deep enough, he secured it to the stern, with a length of rope. Then our guide finallly turned to make a leisuely response to my comment.
“Damned if I care how deep the bay-mud is, as long as this ##@$###’ pole, holds us steady on the edge of my 'secret fishin' hole' where we’ll ketch fish.”
It did. And at each cast, our hooks, baited with fresh grass shrimp, attracted ravenous fish which gobbled our baits. Both Bob and I netted us each several nice-size fish. We pulled at least ten keeper-size Red Fish, Speckled Trout or Snapper out of that spot (but we put only one each in the ice chest). Oh…you ask, “Where is that hole?” Sorry, I was sworn to secrecy.
FLORIDA'S LONG AND INTERESTING GEOLOGICAL HISTORY
Geologically, Florida (and its extreme southern tip, Florida Bay) is a most recent addition to the North American continent. Florida became a part of North America only late in the continent’s history, during the early Mesozoic Era, about 200 million years ago (mya), when dinosaurs roamed the earth. That was a time when all the earth’s continental slabs had been swept together into one great supercontinent known as “Pangaea.” The upper surface layer of the earth, or “crust” is able to slip around on the deeper and heavier mantle surface, as you might shift and slide the pieces of a Rubic’s Cube. This process of coalescence and spreading of continental slabs has occurred several times in the past over the earth’s long 4.5 billion year history. The cyclical process includes a phase in which the lighter continental slabs slide over the surface to combine into one large world continent, forming mountain chains at the line of collision, then, after a period of quiescence, they fracture and separate apart again. The continents, composed of lighter, low-density rocks (called sial) were formed by the chemical and physical alteration of the primordial heavy, dark-colored basalt rock from the earth’s mantle. Sial is formed from mantle rock when it is extruded onto the surface of the earth where it interacts with the atmosphere and hydrosphere to produce a relatively lighter and light-colored frothy rock we know as sialic rock or granite. The process of creating supercontinents and taking them apart again has been going on for nearly as long as the earth has been around. Geologists have documented several past sequences. But in the most recent phase, (in what is known as the Mesozoic Era, or Age of Dinosaurs occurring from 250 mya to 65 mya), North America, Africa, Eurasia, Australia and Antarctica were sutured together (if you can imagine that) along a line which ran down the east coast of North America. This great suture-line was puckered up along its length to form the ancient Appalachian Mountain chain. To the east was the vast continent of Africa, and to the west that of North America. The process of continent collision had begun hundreds of millions of years earlier in the Paleozoic Era (about 460 mya) with the process being completed to form Pangaea, about 250 mya.
The great mountain chain running from Georgia to Maine had been undergoing erosion for some time when our Florida story begins, but it even then it resembled more the present-day Himalayas than our Appalachians of today.
Our story of Florida begins after the supercontinent of Pangaea had been formed and was in place for about 20 million years (early in the Mesozoic Era (Dinosaur Age) about 180 million years ago). At that time (180mya), the southern end of Pangaea just east of where the Appalachian Mountains ended began to fray apart at a “rift” zone between what would be today the North American and African continents. The source of the rifting or spreading was both slow persistent currents in the mantle and the intrusion of thin layers of molten rock into the overlying crust. Molten rock from the earth’s mantle, heated by nuclear fission, squeezed and melted its way upward through elongate cracks and fractures in the brittle, upper-crust. Thin slivers of molten mantle-rock (basalt) penetrated the crust and cooled. The process continued at a steady rate, causing the crust to bulge upward slightly and press the two sides of the rift apart. The combined effects actually push and spread continents apart, in this case driving the giant slabs of North America and Africa apart from each other. The area formed by the fracture zone, known as a “rift valley” (like the one in east Africa today), comprised of heavy rock sagged and was soon filled with sea-water as spreading continued. This newly created arm of the sea, between North America and Africa was, of course, the primordial Atlantic Ocean and the spreading center (pushing the continents apart at the rate at which human finger nails grow) would create a low, elongate bulge on the bottom of the Atlantic Ocean about half-way between Africa and North America eventually known as the Mid-Atlantic Ridge.
But back to Florida’s history! As North America spread away from Africa, an accessory rift in this location isolated a large rectangular chunk of the African continent, and left it stranded near the southern end of present-day Georgia as Africa slid away. That piece of African basement-rock which remained behind would eventually become what geologists call the ‘Florida Platform’ or the base upon which other more modern sediments accumulated to form what we know as the State of Florida.
The Florida Platform has a distinct pattern of two different rock types, basalt rock in the northern end, granite in the center, and basalt in the southern end. Geologists working in western Africa can point today to the place where these rocks were rifted away from that continent, so very long ago. A closer look at the Platform reveals a central portion which is comprised of lighter rock and which tended to be buoyed-upward while the northern end and southern ends are of heavier rock which sagged downward. This pattern of basement rock orientation continued to control geological processes on the peninsula as we will see below.
Initially, the whole of the primordial Florida peninsula was buoyant enough to rise up above sea level. A shallow ocean, much like what we see in present day Florida Bay covered the entire peninsula of those days, with perhaps small portions of the central corridor rising up as low islands. At this time, due to the sag in the northern end of the peninsula (where the rocks were denser), a “trough” formed which permitted the ancient Gulf Stream to meander its way across the northern end of early Florida near where present-day Jacksonville is now situated. Though erosion was actively wearing down the steep Appalachian mountains just north of Florida and producing copious clastic (continental or sialic) sediments two features, the Florida Trough, and the Gulf Stream current prevented the accumulation of these from reaching peninsula Florida. As it is today in Florida Bay the sources of water bring little or no clastic sediment and the water remains clear. Only marine derived lime sediment from the mechanical break-down of marine shell is found in Florida Bay. That is very much what all of peninsula Florida looked like in those days.
Thus, for millions of years the bottom of the shallow seas which washed over Florida accumulated only marine-derived sediments such as coral-and-shell-derived-lime-mud. Continental clastic (i.e. mud and sand ) sediments such as quartz or sialic-mineral sands were excluded. The early seas would have looked much like modern day Florida Bay where the natural processes of growth and decay of corals, shell-fish, crustaceans and tiny marine organisms which live in the warm tropical and clear waters creates the sediments, as they do today in Grand Bahamas Banks.
North of Florida on the mainland, near the end of the Mesozoic Era, parts of the Appalachian chain were uplifted and a new flood of continental sediments (made up of weathered and broken siliceous rocks such as granite) were carried down from Georgia’s highlands and eventually filled in the Gulf Trough.
By about 45 mya in the early Cenozoic, the Gulf Stream was directed further south around this build-up of continental sand and clay sediment on the Florida Platform. More clastic deposits such as land-derived silt, clay and sand poured down onto the peninsula, washing south to create the uplands and flatlands of northern and north-central Florida. More of these materials were found along the west and east coasts than in the interior, as a consequence a shallow topographic trough developed in this central region. During this time, the southern end of the peninsula, from Lake Okeechobee south, remained isolated from these events and the southern region continued to be partially inundated by shallow seas.
In the most recent periods of geologic history, the Pleistocene and Holocene Epochs, this fragile area experienced several periods when sea levels receded and the land was exposed, and other times when high stands of the sea washed in and covered it again. During the latter periods more deposits of lime-mud accumulated, building up thick deposits of limestone as the basement rock for most of southern Florida. In the former times when the limestone basement was exposed to aerial erosion the limestone became weakened and eroded, exposed joints in rock widened and let mildly acid rain water and groundwater seep downward. In some places, solution cavities and limestone caverns formed beneath the surface. Over time the solution cavities enlarged and the caverns collapsed to create an uneven and checkered surface called karst topography.
LAKE OKEECHOBEE AND FLORIDA BAY
Lake Okeechobee (with an area of more than 700 square miles, an average depth of nine feet deep, and with a capacity of more than a trillion gallons of fresh water) sits at the northern end of a long shallow topographic depression which occupies the central portion of the southern half of the Florida peninsula and dips toward the south. The trough formed when the clay which underlies the center of the peninsula compacted more than the sand and limestone deposits found along both coasts. The region was once dry land, but with increased rainfall and rising ground water tables it became a marshy, low-lying zone where from about 6000 to 4000 years ago peat bogs developed. With increasing rainfall and rising water levels the bogs flooded, forming a shallow lake. As result of the high stand of the water table much of the vegetation in the central area of the lake died. The southward flow of surface water tended to carry decayed materials and nutrients in that direction where it accumulated in drifts along the south shore of the lake. In these regions, the rate of growth of the peat-forming vegetation along the south bank was enhanced and the rate of peat formation increased. Eventually, peat deposits built up, rising to a level of about 13 feet, a height sufficient to dam the water flow and create a permanent, but shallow lake behind it. Seasonally, during the spring and fall, water levels in the lake would reach levels high enough to rise up and top the dam. These overflow waters flow south into the Everglades where it slowly drifts further south and eventually seeps into Florida Bay. This southward seepage was critical for the health of the freshwater Everglades (The River of Grass) and as well for the vegetation and creatures of the estuarine lagoons of Biscayne Bay and Florida Bay, many of which (such as Turtle Grass and Mangrove ) are dependent upon a modulated level of salinity to survive and reproduce. Evaporation of the sea water in the shallow Florida Bay during the summer months and during drought periods sometimes causes salinity to rise to more than twice (or in some cases three times) the concentration of sea water. Those levels can kill or stunt the growth of some plant species were it not for the steady flow of fresh water from the Everglades.
Finally, in the last fifty (50) million years, the earth cooled and ice built up in northern regions forming continental glaciers on North America (where their farthest extent south on the east coast was at Long Island, New York) and elsewhere in the world, as a result causing world-wide sea levels to fall. Sea level fell so low (nearly 300 feet) causing nearly the entire Florida Platform at one time to be exposed to the air, becoming over three hundred (300) miles wide at the latitude of Lake Okeechobee rather than the present day 135 miles wide. Then, slowly, as the glaciers melted and retreated, about 10-15,000 years ago in the north, they added meltwaters back into the sea (and the climate warmed) causing sea-level to rise slowly at a rate of about (since 1932, sea levels have been rising at a rate of 1 foot (0.30 m) per 100 years) ----cm per year.
CORAL REEFS AND THE HISTORY OF THE KEYS
During the last 10,000 years coral reefs formed along the southern end of peninsula on the steep edge of the original basement rock one the edge of the Florida Platform. Corals can live and thrive only in clear, warm, agitated seawater, and only within 200 feet of the surface. They are almost exclusively found in tropical or near tropical waters. The southern end of Florida, where the basement rocks dropped off into abyssal depths, and the Gulf Stream carries silt-free, warm, sea water–is a place where corals can thrive. Here along the southern edge of the peninsula, grew underwater “forests” of brain coral, fan coral, shelf coral, and staghorn corals. In the process of growing and expanding, the corals produced vast quantities of coral-rock which filled in the spaces around the living corals and create environments for other creatures, such as mollusks, crustaceans, bryozoans, foraminifera, and some forms of algae all of which remove calcium from sea water and create calcium carbonate.
As sea levels rose, the corals grew upward to keep within the well-lit or photic zone (@ upper two hundred feet (sixty meters) of the surface where there was sufficient sunlight for the living algae which live symbiotically within the body of the coral polyps and carry on photosynthesis. These algae, which like plants, come in many different colors, are termed zooxanthelle (they are a form of “green” algae which live within the coral polyps bodies in a symbiotic relationship and which produce the majority (90%) of energy the coral polyps need to thrive.)
In time, coral reefs along Florida’s south coast developed and expanded into an elongate arc of approximately two-hundred miles long. The arc of coral reefs begin in the east, off shore from Virginia Key near Miami, and extend south and west all the way to the Dry Tortugas some 230 miles distant to the west. Protected from wave action and erosion by the reef line, is a quiet area of sea water where there is little of no sediment from land and where calcium carbonate-debris produced by corals, bryozans, foraminifera, mollusks, crustaceans and other sea life accumulates as a lime-mud sediment. The shallow lagoons we know as Biscayne Bay and Florida Bay as well as the sandy banks which make up the lower keys are composed of this waste by-product of coral growth as well as other animals and some plants which remove carbon-dioxide from the water and combine it with calcium ions in sea water to produce calcium carbonate (though not in that order). Thus corals and other marine organisms help to remove and sequester carbon dioxide from the atmosphere. In that way they help to cleanse the atmosphere of excess carbon dioxide. They are indeed “green” organisms. The lime-mud produced by corals and other animals carpets the sea-floor, and like other sediments is carried by currents to settle in areas of quiet water. The lagoon environment landward of the Florida Keys was and remains such an environment--where carbonate mud accumulates. In some places the fine grained deposits are reworked by currents and waves to form small oval particles (1-2 mm in diameter) called “ooids” (“oo oids”) when this material becomes compacted it forms what is known as oolitic limestone. The lower Keys and Key West are composed of this form of limestone.
FLORIDA BAY AS A LAGOON SYSTEM
The Florida Bay lagoon is a shallow warm-water tropical, sea. The lagoons are carpeted in a thick carbonate mud upon which the Turtle Grass and Manatee Grass grow. It is noteworthy that these plants are not “seaweeds” or “real grass”, but actual flowering plants which only remotely resemble seaweed. They have true flowers and produce fruits as well. The “grasses” of the lagoons are an integral element of the overall ecology of the Bay.
The lime-mud and sand sediment which carpets Biscayne and Florida Bays is derived from fragments of living corals, algae, sea grasses, shellfish-- such as oysters and clams, and mostly the vast numbers of minute animals with calcareous shells which live on the sea grasses and algae and within the sediments of this environment.
Florida Bay, Biscayne Bay, parts of the western keys and the Marquesea Islands and the Dry Tortugas are all part of the lagoon-system protected from the sea by the arc of reefs we know as the Florida Keys.
All about corals at”
http://en.wikipedia.org/wiki/Coral_reefAs we cast our lines into the quiet waters near Carl Ross Key and watched the rod tips for that tell tale bobbing action of a feeding fish, I asked, Jim what’s it like on that island?”
“It’s all jest lime mud or stuff the geologists call “ooliths”. He pulled down the bandana he used to protect his face from the sun to mouth out the word precisely.
“Yeah oo..oo..liths,” he said.
“The basement of the islands of the upper Keys are made up of stony corals and stuff that breaks off the corals and gets crushed up by fish like parrot fish which actually eat coral,” said Jim.
We often think of only the hard skeleton when we hear the word “coral”, however, the actual hard, stony coral is, in life, covered by a thin film of living matter from which, in a regular pattern, spring tiny sac-like animals with a ring of tentacles around their mouth and known as “colonial coelenterates”. The word coelenterate, signifies an animal which has a “coelenteron” or an empty sac which communicates with the outside sea water through a manubrium or mouthlike structure. Some of the “sac-bearing animals” form colonies which secrete calcium carbonate to support their soft bodies. Each individual looks like a tiny sea anemone, another coelenterate. Like that creature, it has tentacles arranged around a central mouth and a coelenteron (a sac-like structure). The tentacles are armed with stinging cells (scientists call them “cnidoblasts”) which are designed to immobilize and entangle small floating prey-animals. Once immobilized, the tentacles move the prey to the manubrium (mouth) and then into the coelenteron where digestion takes place. Unlike anemones, corals can lay down a solid film of sturdy calcium carbonate just below its base to anchor it and to help support their soft bodies. The colony of corals can produce calcite forms of great variety which can grow to great size as each season a new layer of calcite is added on top of the old layer. Like plants, corals tend to grow toward the light. So, if they live on a slowly subsiding sea-bottom they can maintain their preferred location, close to the surface, by adding new growth at a rate that keeps up with the subsidence. However, when sea levels fall, and they are exposed to the air, they die and their calcite skeletons break up and become part of the sea sediment.
As a consequence of their great potential for exuberant growth, corals and the complexes they form called “reefs” are sometimes referred to as “the marine equivalent of the tropical forest” or the tropical forests of the oceans. The individual animals (of the colony) or these are referred to as “polyps”, each have colorful zooxanthelle (single-celled “green” plants) which live symbiotically within the animals’s clear tissues, and as a result live corals are often very brightly colored. The chlorophyll in these cells may have various colors. Corals thus exhibit symbiosis-- a mutually beneficial relationship between two different species. The zooxanthelle living within the polyp’s tissues use sunlight to photosynthesize carbon dioxide and water into simple sugars which are then used by the coral animals (and the zooxanthelle) as a major part of their nutrient supply. Like all green plants the zooxanthelle produce oxygen which is used by the coral polyps. While the benefit to the zooxanthelle is that they have a safe place to live (inside of the coral polyp) where they are well-supplied with carbon dioxide resulting from the metabolism of the coral animal, and, as well, have free access to water and sunlight.
It is axiomatic that corals occur in warm, clear, low-nutrient, tropical waters, typically described as “blue water”. Blue water is encountered far off-shore (or in enclosed seas like the Mediterranean which is surrounded largely by dry or desert lands) or places far away from land where sediment is scarce(terrestrial environments shed sediment via rivers and streams). These areas also are source of minerals such as phosphates, and nitrates, plant nutrients, which cause blooms of algae. The deep blue color of “blue water” is a sign of low nutrient load and low suspended (sediment)matter. The blue color is generally a good indicator of a water column of low fertility. The blue itself is the result of the fact that the sun’s rays are able to penetrate to depth where the red and yellow wavelengths are absorbed and reflect back only the short-wave blue and violet part of the spectrum which are of a wave length which interact (or scatter) with the water molecules themselves, scattering them and sending those wavelengths back into our eyes. The blue color indicates that light is not coming in contact with suspended matter—such as sediment and plankton--indicating very low nutrient load. Since corals can produce their own food, they can survive in these low-nutrient environments. But since corals can live only in the photic (well-lighted) zone, they die when they are too deep (over 200 feet) where sunlight can-not penetrate, or also where they are too cold, preferring water around 20-27 degrees C (i.e., close to room temperature), or in poorly oxygenated or murky sediment-laden water—or water that is too acid.
When corals are stressed by one or more of these conditions they might void their zooxanthelle (or digest them) and thus turn colorless. “Bleached corals” are corals that are being environmentally stressed. Thus, it is easy to understand why corals are threatened worldwide. Along the well-visited Florida Keys where 82,000 inhabitants make their homes (and an equal or greater number of tourists make visits each year) there are obvious major disturbances. These are caused by the physical presence of motor boats, by the dumping of fuels, by disposal of sewage and human wastes rich in nitrogen and phosphorous. The latter substances can cause algae blooms, as well as the alteration of the acid-base level or pH of sea-water, which is normally well-buffered, but in many places now shows signs of increasing acidification as a result of burning fossil fuels—you know-- global warming.
Jim Wilcox, our well-informed guide, pointed out that though corals inhabit only less than one-tenth of one-percent of the earth’s ocean surface…they provide a home to twenty-five percent of the oceans marine species. Jim ticked off a list of fish, mollusks, worms, crustaceans, echinoderms, tunicates that live in or around coral reefs.
“That’s what a ‘paradox’ is,” said Jim, as he focused his eyes, partly obscured by his thin face mask (a protection against the sun) on the gentle but regular bobbing of the last ferrule on the tip of the heavy rod, baited with a big chunk of a Ladyfish.
“What’s that?” asked Bob, rising from a bit of mid-day sun-induced lethargy.
“Probably a crab or a small catfish nibblin’ on that bait,” said Jim.
“No, I mean what’s the ‘paradox’?” said Bob.
“Oh, the paradox is that these coral critters thrive so well as to produce all this here mud in the Bay, by livin’ only in waters that are so poor in nutrients. They are like them nitrogen-fixing plants—the legumes-- of the land-plant world--they also can produce their own food—ya know, by them nodules on their roots,” he added, stopping to reel in a bit of slack on the heavy rod. Then he turned and faced Bob “and that’s how they create such a rich environment for all these other critters…..” But at that point Jim suddenly stopped speaking, as he turned to the stern of the skiff where the rod tip bounced hard in its holder and the braided 100 lb test whirred out over the restraint of a tight star-drag…”and even these big-mouth Tarpon out here”, grunted Jim, as he pulled the rod from its holder and jabbed at the blue sky with a vicious hook-setting strike.
The heavy rod tip, bent into a sharp curve.
Jim yelled excitedly. “He’s on!”
He violently pumped in a few yards of line as the rod bent into a bow-shape, it's tip bending down over the gunwhale to dance just above the water.
“He’s a big’un,” he said, his arms straining as he as he moved aft to pass the tense rod over to Bob.
“What’s on?"Bob and I yelled in unison.
“Dunno, but it's a big unnnnnnnn!" grunted Jim through clenoched teeth, as the rod jerked downward sharply, twisting our fish guide around and pulling him toward the gunwale.
Then--- "Auuuuu…shit!” cursed Jim' as the line suddenly went slack.
“Lost im,” said Jim, disconsolately, as he reeled the loose wavy line in over the boat side.
Then he turned optimistic again, continuing."It would be a horrible mistake if we stupidly let something bad happen to these coral critters,” opined Jim as he rummaged in his well stocked orderly fishing box to replace the lost hook and leader.
A LIST OF CRITTERS I OBSERVED ON THE TRIP
INVERTEBRATES
PORIFERA
Unidentified sponges
INSECTS
Great Southern White Butterfly (Ascia monuste). Food: Sea Rocket and Saltwort
CRUSTACEANS
Horseshoe crab
Blue Crab
FISH
Gafftopsail Catfish
Great Barracuda or “cuda”
Ladyfish
Mangrove Snapper
Mullet
Pinfish
Red Drum
Smalltooth Sawfish (a rare and threatened species) (Pristis pectinata) adults are 9-13’
long, but we saw several three-foot babies in the shallows)
Speckeled Trout
Southern Stingray
Spotfin or Mojarra
Stripped Mullet
Tarpon or “poon”
REPTILES
Atlantic Ridley Turtle
Reef Gecko
American crocodile (Jim spotted a muddy area on a small key he said looked like a “croc mud wallow”. So not seen but reputed to be in the area)
MAMMALS
Bottlenosed Dolphin
BIRDS
Bald Eagle
Black Vulture
Brown Pelican
Common Tern
Caspian Tern
Cormorant-very common..some seen resting on stakes above turtle grass replenishment zones.
Double Crested Cormorant
Frigate Bird
Great Blue Heron (Ardea herodias)—On Carl Ross Island
Great White Egret—(Ardea albus) widespread
Great White Heron
Laughing gull
Magnificent Frigate bird
Osprey (Pandion haliaetus) commonly seen feeding on channel stakes out in Florida Bay
Ring necked Dove
Ringbilled Gull
Roseate Spoonbill—near Car Ross Island Florida Bay
Roseate Tern ?—common on channel marker stakes where they rest and feed
Royal Tern
Showy Egret (Egretta thula) widespread
Distance Note:
From Bud and Mary’s Marina on Matacumba.Key it is thirty miles to the Gulf of Mexico
PLANTS
Grasses
Turtle Grass
http://www.flmnh.ufl.edu/fish/southflorida/seagrass/profiles.htmlManatee Grass
http://www.flmnh.ufl.edu/fish/southflorida/seagrass/profiles.htmlTurtle grass (Thalassia testudinum) is not a sea weed---or a grass. It is a flowering plant which has flowers which produce light green to pink blooms underwater and are pollinated under water. The fruit form and drift away to form new plants. Turtle grass has a horizontal rhizome buried as much as ten inches under the marine mud on which it lives. The plant prefers water of high salinity and protected from wave action. The flat elongate leaves with rounded tips arise from the rhizome and can be as long as 10-12 inches long. The plants expand into new areas by growth of the rhizome at its terminal end. If these are cut they do not re-grow. Cutting rhizomes by mechanical means—such as a boat propeller- can kill the plant and cause vacuae in the beds which may not quickly fill in. Skimming over the surface the “flats” in Jim Wilcox’s skiff at forty-knots we could often clearly see bottom—and the elongate propeller “scars” in the turtle-grass beds where as Jim noted..”some ‘boat cowboys’ ” had “a problem” keeping to the channel at low tide. These scars were quite common on the bay bottom..”too common” remarked Jim.
Many fish feed among the turtle grass beds. Some use the beds to hide from predators, seek shade or shelter or to stalk prey, while many others are fish-herbivores which feed on the grass itself. While fishing for Speckled Trout, Jim threaded a white, rubber-shrimp on a 2-0 lead-head lure for each of his two “sports”. He directed us to cast out and bump the lure back along the bottom. Invariably we would get a sharp strike on the first or second pump of the rod tip. Then we would have a sharp battle with the resistant trout, ladyfish, pinfish or drum to get it to the boat side and into the ice box or bait well on the stern of the boat. On several occasions, missing these first strikes and retrieving the lure closer to the boat, I could watch it clearly through the crystal clear and shallow water as it bounced among the thick turtle grass and patches of dead weed that Capt. Jim called “underwater tumble weed”. On several occasions I watched as a trout or a drum would lurch out of a clump of turtle grass to pounce on the lure.
Manatee Grass is very similar. It grows along the bottom attached to long rhizomes, but the Manatee grass favors slightly deeper water. On our way back to Bud and Mary’s one day, Jim Wilcox stopped the skiff over a deep hole where Manatee grass grew profusely. The leaves on this plant, which were aligned by a strong current, are longer and cylindrical rather than flat as they are in turtle grass. Jim indicated that the rhizomes are not buried as deep in the mud as are those of the former species. So they are more likely cut and damaged by boat properllers. “Maybe that’s why they are only found in these deep holes” suggested Jim. Jim indicated the name “manatee grass” is result of the fact that this species is a preferred food of manatees. But we saw none feeding on it. Though Jim says he is on the lookout for them since they are often found in the Bay but not in the flats. Among the Manatee grass we did find circular open patches bare or grass which were occupied by large “breadloaf” sponges. Indeed to me they did look like large loaves of those artisanal Italian round loaves—I love so much.
LANDING ON CARL ROSS KEY
Carl Ross Key is located in the northwestern end of Florida Bay, bounding the Gulf of Mexico. It is about 35 miles northwest of Upper Matecumba Key and about an hour’s trip by speeding skiff from the village of Islamorada (Spanish: “Purple Island”). Jim Wilcox our guide landed the skiff there after we successfully fished the near-by channel on a flooding tide. My fishing buddy Bob R. caught a big barracuda in the channel and landed it, while later on, I hooked in to a 'huge' yellow-tipped shark. The shark pulled like a locomotive and bent the stiff, gamefish-pole, threaded with braided, 100 lb test line into an unsustainable “c” curve. The rig was set for tarpon (which have no real teeth) so there was only a two foot monofilament leader attached to a big 2”0” hook. I had the shark on for a good arm-wrenching twenty minutes as it pulled us and the skiff along, while Jim, using the long boat pole, tried to herd the critter, by poling the boat toward shallow water to where we might get a look at it. Finally, it swam into a dead-end channel, and to get out it had to double back past the boat…as I reeled in furiously to take up slack we did get to see the dorsal fin and the long angled-up tail as it swam between the boat and the bank. But the change in direction must have scraped the mono over those sharp triangular teeth and after one more powerful run--the leader parted and the fish was gone.
“Fare thee well Mr. Shark” I called after it, as Jim swore in anger over my shoulder.
“Should’a had a wire-leader on that’un in this channel!”
At this point, we were close to Carl Ross Key and Jim suggested we land there for a bit of exploring. On the way in we cut the engine and drifted over shallows, where we caught a few Mangrove Snappers by casting our lead-head jigs with a white rubber shrimp threaded on to the hook. Jim showed us how to thread the shrimp on so the tail fanned out. “Let’s see that one ‘Dr. Rock’,” he said, which was the name he coined for me…there being two “Bobs” in the skiff that day. “Don’t thread it on to make a “c” shape out of the shrimp..leave that hook tip bare…they’ll catch themselves..those hungry little beggars!”
As Jim slowly poled us up to a sandy landing spot on the key, Bob and I caught five or six nice-size snappers and dumped two of the biggest into the ice-chest to keep for our fish supper. We stowed the poles and stepped off onto Carl Ross Key.
“A few years back…this here little key and that one out there was joined up into one long island”, said Jim, but when Hurricane Emily came through here out of the Gulf it beat the hell out of this key--swept the mangroves clear off and made two keys out of one. This here small key is the remnant of that storm,” said Jim, stepping down into the clear water and pulling the skiff’s bow ashore, onto a cream-colored fine sandy mud. As Jim tied the bow to a thick mangrove branch, Bob and I looked at each other and about sixty years each drifted away as we stepped ashore feeling like little kids living out the fantasy of setting foot on a treasure or desert island. It was my first landing on a real “tropical island.” I was fascinated. Jim, Bob and I took a slow walking tour around the small island in bright hot sunlight. The key was only about two acres in extent, but a world away from our everyday experiences.
I observed that the Black Mangrove formed a ring of growth around the edge of the island. As I strolled around I observed that the sand as I noted above. was all of marine origin, a calcareous deposits of sand and mud. Any pebble-sized materials were shell or shell fragments. The sand that formed the key seemed to have been washed up from the surrounding bay. I envisioned huge waves carrying Bay sediment up through the mangroves and over-washing the island. I was glad I was not there at that time. Jim told of several big mangrove trees which were washed off of Carl Ross Key and ended up in Rabbit Basin far to the east. There the trees sat in deep water with its upper branches just breaking the surface. (Later that day, we fished at those very same Carl Ross Key trees. Each tree acted as a barrier to the currents which swept around them, creating a deep hole or depression in the bay mud. The depression was a great attraction to the local fish and each cast, brought a vicious strike by a big snapper, speckled trout, or drum and we hauled in each one the end of the line.)
Back on Carl Ross Key, I made notes on some of the major plants which had colonized the island. Aside from the Black Mangrove (which was in bloom on the day of the visit May 17, 2011) I observed large areas colonized by the common backyard plant known as portulacca It was common in dry hot and exposed areas. While Day Flower, Commelina virginica (or a related species) appeared to occupy areas more protected from the hot sun. In the center of the key, where the substrate was piled a few feet above sea level were lively clumps of dark green Indian Fig (Opuntia humifosa ?) and scattered among them were a few yucca plants.
PLANTS OBSERVED ON CARL ROSS KEY (May 2011)
Black Mangrove
Red Mangrove
White Mangrove
The Day Flower (Commelina virginica) commonly known as the Virginia day-flower, is a perennial herbaceous plant in the
dayflower family. It is native to the mideastern and southeastern
United States, where it is typical of wet soils. While most members of the genus have thin, fibrous roots, the Virginia dayflower is relatively unique for its genus in having a perennial
rhizome. This rhizome may be able to be uprooted and washed along with storm waves. That may be a way in which this plant may have reached the isolated island.
Yucca species possibly (Yucca flaccida) is native to Florida and is found growing on coastal sands, waste places, beach sands, and similar places in the state. Either its seeds or roots could have been carried to the island by waves or ocean or storm currents.
Indian Fig (Opuntia humifusa?) The Indian Fig is found in dry places from New England to Florida. Its fruit is edible and its “pads” can produce a new plant. It is common onnbeach environments in the south of Florida.
Portulaca or Purslane (Portulaca grandiflora?) which is a common garden plant in south Florida and since its succulent leaves and stems can float it is a good candidate to have arrived by storm waves or floating on a raft of weed stems. It is an edible plant and could have served some cast-away (not
