A Close Up View of a Florida Reef Ecosystem
A Close Up View of a Florida Reef Ecosystem
By Jonathan Lowrie SeaMuskrat@aol.com
We all think of the reef as just a collection of corals, rocks, algaes, fish and invertebrate life. This definition can be somewhat misleading and very limiting. The typical coral reef in nature is a part of a larger biome of related habitats. I would like to take you on a journey through some of these biomes. What follows is a compilation of many months of observation of these natural systems, at the Looe Key National Marine Sanctuary. This is a representative reef of the Florida Coast, and the Northern Caribbean. Reefs in the Pacific Ocean are also part of larger ecosystems, but of a different nature. All of these observations were compiled from field notes and observations made from September 6, 1992 to December 13,1992. Multiple visits per day were made to these reefs, and associated biomes, and the species were cataloged and monitored. What follows is the compilation of these observations.
We already know that coral reefs provide underwater housing for an amazing diversity of animals including fish, crustaceans, sponges, worms, and mollusks by offering food and shelter for these marine organisms. The reef communities provide important breeding and nursery grounds for economically important species like lobster, shrimp, grouper and snapper. But a coral reef community is just one part of a complex coastal ecosystem. Each part of this hammock- mangrove- seagrass- coral reef ecosystem depends on the other, like links in a living chain. Every component is essential- alter one and it affects all the others. We can trace a ‘water drop’ through this eco-system eventually passing the coral reef, and ending in the open ocean.
Most reefs are very close to a land mass. This is crucial as the tropical Hardwood Hammock is a vital habitat for reefs. Take a typical Florida Reef Ecosystem: A hardwood hammock would be a few hundred meters from the waters edge. They are commonly found at slightly higher elevations to prevent any risk of seawater flooding. The dense hardwood tropical trees and a myriad of tropical plants that flourish in this habitat, create a cool refuge hospitable to many types of wildlife. These regions can look like miniature rainforests, both in terms of animal and plant diversity and by appearance. The Arawak Indians used the word ‘hamaca’ to describe this region. They also considered the sea and nearby resources to be almost sacred- and they made every effort to care for the lands.
In this habitat you would commonly find the Poisonwood tree ( Metopium toxiferum ), the Gumbo Limbo Tree ( Bursea simaruba ), the Silver Palm ( Cocothrinax argentata ), Torchwood tree ( Amyris elemifera ) and the Wild Coffee Bush ( Psychotria undata ). All of these trees are firmly rooted in dirt, and cannot tolerate any seawater flooding. Many types of mammals, birds, lizards, and amphibians would take advantage of this vegetation. Woodrats ( Neotona floridana ) are found , and the pygmy keys deer ( Odocoileus virginianus clavium ) among the thickets of brush. Making webs with the broad leaves of the Pine Bromiliad ( Tillandsia ultriculata ) would be the Golden Orb Spider ( Nephila clavipes ). Further up in the vines the common green anole ( Anolis carolinesis ) catches insects, and harasses the green tree frog ( Hyla regina ). Along the layers of decaying leaves, lives the Black racer ( Coluber constrictor ) which feeds on the rats, and Land Crabs ( Cardisoma guanhumi ).
Moving further towards to reef, we encounter the nearshore Hardbottom and mangrove habitats. This habitat is not as clearly defined. It can vary form a few meters to almost 30 from shore. Because of the dense growth of mangrove trees, in some areas, this habitat can extend many meters into the sea.. Mangroves seem to be the ever popular buzzword of the late 1990’s in the reef hobby. These seawater loving trees have been considered the next revolution in filtration, or just a ‘tree with pretty leaves’. In reality, the mangrove trees do act as a natural filtration system between land and water. They filter the ground water and run off water from land, the dense root structure acts as a sieve, and the growth on the rhizomes act as chemical filters. Much like the salt marshes of New England, mangroves of the Southern United States are a crucial habitat in the ecosystem. The submerged branches and nearby seagrass communities provide shelter, food, and nursery grounds for many reef dwelling creatures that begin their life near shore.
The most common mangrove tree at this habitat is the red mangrove ( Rhizophora mangle ). Many animals from the nearby seagrass beds intermingle within the huge roots of the mangrove community . Within their roots would be Silversides ( Menidia penninsulae ), Mangrove Snappers ( Lutjanus griseus ), Highhats, ( Equetus acuminatus ), Damselfish species ( Pomacentrus spp.), and even Four Eye butterfly fish ( Chaetodon capistratus ). Also within the mangrove roots would be Florida Spiny Lobster ( Panulirus argus ), Chicken liver sponges ( Chondrilla nucula ), and Loggerhead sponges ( Spheciospongia vesparium ) on the roots themselves. All of this is surrounded by tufts of Calupera , and Halimeda macroalgaes, as well as Penicillus and Udotea . Further out, away from the roots, Snook ( Centropomus undecimalis ) congregate hoping to make a meal of the smaller fish that venture from the shelter of the reef. Along the mud/sand bottom live the Coon Oyster ( Isognomon alatus ) and the Mangrove Jellyfish ( Cassioppea xamachana ). Out in the more direct light, even hard corals abound. Sidastrea and Diploria and Favia are plentiful. And turning your head skyward, Green-backed Herons ( Butirides sriatus ) and Pelicans ( Pelacanus occidentalis ) can be seen in abundance.
Just a few feet from the mangroves the seagrass beds begin. They start as light pockets of growth, but as you travel further from the shore, they become dense thickets of grasses, mush like an underwater field of green. After foraging in the seagrass beds, many animals retreat to the close by patch reefs for safety. These small, scattered reefs usually consist of ‘boulder’ corals, often surrounded by a barren ring of sand created by fish and invertebrates grazing on the surrounding seagrasses.
The water here is deeper, and never is exposed to air in low tides. You will find more pelagic animals like the moon jellyfish ( Aurelia aurita ), Mangrove snapper ( Lutjanus griseus ), Grey Angelfish ( Pomocanthus arccuatus ), and many silversides ( Hypoatherina harringtonesis ). This habitat is hard to distinguish from the seagrass flats- as there is no geological distinction, only the types of animals present. Mainly- as you leave the shore and the water deepens, this habitat begins. The bottom material is mostly a loose sand, and the Southern Sting Ray ( Dastyatis americana ) will often cover itself with a layer of sediment. More corals can be found here, including star corals ( Montasrea annularis ), Brain corals ( Colpolphyllia natans ), and some soft corals like the seafeather ( Pseudopterogorgia acerosa ) and the purple seafan ( Gorgonia ventalina ). Among the rock rubble and corals will be Red Finger sponge ( Haliclona rubens ), long spined urchins ( Diadema antillarum ) and Mermaids Shaving Brush ( Penicillius capitilus ).
The mid channel reef is far enough out to get some cross currents. Corals in the mid channel reef rise up to 15 feet from the bottom to provide an important refuge for fish and invertebrates during different stages of their life cycles. This region is most commonly accessed via snorkeling. In this habitat you can also find more seagrasses and a greater diversity of invertebrate life. At this point in our journey, we are 20 to 30 meters from shore.
Tufts of Manatee grass ( Syringodium filiforme ) abound on the sandy seafoor. Intermingled with the thin blades of manatee grass is Turtle grass ( Thalassia testudinum ). Within the blades of the grass, and grazing off algaes on these blades are various Surgeon fish/tangs ( Pomacanthus spp.). Further out from the sparse grass are some growths of hydrocorals- the Crenelated Fire Coral ( Millepora alcicornis ) and the nearby Vase Sponge ( Ircinia campana ). Along the substrate many furry sea cucumbers ( Astichopus multifidus ) crawl, along with the Slimy Brittle Star ( Ophiomyxa flacissa ). Hovering above the Turtle grass might be a Hawksbill sea turtle ( Eretmochelys imbricata ), or some Snapper ( Lutjanus appodus ). The coral heads are mainly comprised of large specimens of Star coral ( Monstrea annularis ) and Brain corals ( Diplora labryithiformes ). Hiding within crevices of the reef lives the spotted moray eel ( Gymnothorax moringa ), and the Long Spine Squirrel Fish ( Holocentrus rufus ). Here again, the Spiny Lobster ( Panulirus argus ) can be found.
Offshore Patch Reef is a deeper habitat that is still relatively close to shore. It is just a few meters beyond the mid channel reef, and about twice as deep. It has abundant soft coral growth as well as stony coral growth. This is another patch reef- consisting of small outcropping of corals, and plants. It serves as a refuge for smaller fish, and as a feeding zone for larger fish.
The dominant form of coral here are the soft corals. Specifically soft corals with long branches, and many polyps. Plankton and fish larvae are plentiful here as they get swept up by the channel current an remain suspended in the water column. Very large and expansive growths of the Candelabra Soft Corals ( Muricea atlantica , and Eunecia plamtaginea ) can be seen. The seafloor is dotted by many large sponges like the Vase Sponge ( Dasychalina cyanthinia ) and the Pipes of Pan Sponge ( Agelas schmidti ). Many smaller invertebrates also call this region their home like the common sea cucumber ( Holothuria floridana ), the Christmas Tree Worm ( Spirobranchus giganteus ) and various sea stars like the reticulated brittle star ( Ophinoneris reticulata ) and the Bahamian sea star ( Oreaster reticulatus ). More fire coral ( Millepora complanata ) makes its presence know in this region as well, providing shelter to Blue Headed Wrasse ( Thalassoma bifasciatum ).Fishlife includes the Grunt ( Haemulon plumeris ), Gray Angelfish ( Pomacanthus arcuatus ) and the Four Eye Butterfly fish ( Chaetodon capistratus ). One of the most unusual inhabitants of this region is the Porcupine Pufferfish ( Diodon hystrix ), as they dart between branches of the soft corals. Along the seafloor many reef urchins ( Echinometra viridis ) can be seen grazing the algal mats, while the Golden Moray Eel ( Mureana milaris ) hunts for food.
The next region to be encountered is the reef flat or back reef. It’s a rise in the seafloor coming closer to the surface. The back reef may be anywhere from 50 to 100 meters from shore. This refuge from waves and wind is protected by a ridge of coral rubble on the seaward side. Shallow seagrasses, sand patches, and scattered coral outcroppings provide habitat for many organisms that prefer this sheltered environment.
Depending on the season, the reef flat will be abundant with reef squid ( Sepioteuthis sepiodea ). And of course, the Great Barracuda ( Sphyraena barracuda ) won’t be far behind, looking for a good meal. The waves are gentle enough that a Portuguese man ‘o’ war ( Physalia physalis ) can survive without being thrashed about in the surf. Along the seafloor the graceful movements of the Queen Conch ( Strombus gugas ) can be seen, along with the comical movements of the Arrow Crab ( Stenoryhnchus seticornis ). Doted along the floor like small carnations are the Atlantic anemones ( condylactis gigantus ). Closer to the sea, great expanses of Purple seafans ( Gorgonia ventalina ) provide some break to the current, along with yellow seawhip ( Pterogorgia citrina ). Upon close examination one may be able to spot a Flamigo tongue snail ( Cyphoma gibbosum ) meandering along the coral branches. There are some outcroppings of stony corals in large clumps. These Staghorn ( Acropora cervicornis ) and Elkhorn ( Acopora palmata ) corals provide the majority of the energy absorbing ability of this habitat. As they waves crash into the thick and densely branched arms of these corals- the wave energy is dispersed, and weakened. Many smaller fish like the Seargeant Major ( Abudefduf saxatilis ) and the Beaugregory ( Pmocentrus leucostitus ) will dart in and out of the branches and surges. This is also a habitat for huge shoals of Blue Tangs ( Acanthurus coeruleus ) to pass by and graze algaes from the dead coral skeletons broken by waves and wind.
The fore reef provides much of the energy absorbing structure that protects the in shore habitats. It includes the reef crest- where the waves first hit, and a very shallow one frequently exposed to low tide or breaking waves. This zone has many deep grooves, and sand channels and the strong surges cause spur and groove formations of the coral growth. The depth of this region is relatively shallow, as the waves are breaking here. Also, there is substantial coral rubble littering the seafloor beneath.
Again the Elkhorn ( Acropora palmata ) and Staghorn ( Acropora cervicornis ) dominate this region. Other large corals include the Pillar coral ( Dendrogyra cylindrus ) and the Cavern Coral (Montastrea cavernosa). Both of these provide the bulk of the reef, and old skeletons provide substrate for the Acroporas to grow upon. In between the crevices and rocks, one can find many false anemones ( Ricordea florida ) and Sea Mats ( Palythoa carriba ). This region also has a number of fish that enjoy the surges and waves. The Smallmouth grunt ( Hamemulon chrysargyreum ) shoals amongst the coral branches. Parrot fish like the Rainbow ( Scarus guacamaia ) and the Blue ( Scarus ceruleus ) chew away pieces of the coral, and contribute to the piles of crushed and broken fragments littering the seafloor. Buried almost to the top in coral rubble, many types of Porites may be seen, along with many small Yellowtail damsels ( Microspathodon chrysurus ) darting between the pieces. The Queen Angelfish ( Holocanthus ciliaris ) also inhabit this zone while looking for a meal.
The gradually sloping intermediate reef is highly diverse. It’s a low profile spur and groove coral reef system. As the reef abruptly drops off, the deep reef begins. Here we leave behind the common reef organisms and join with more pelagic creatures. The water here is an azure blue, as the depths of 10 to 20 meters effectively block some of the sunlight.
In the shallow side as the reef deepens, the coral outcroppings diminish. Some small pockets of Flower Coral ( Mussa angulosa ), and Brain Coral ( Diploria strigosa ) remain. Purple Finger Sponge ( Haliclona hogarthi ) is very apparent and provides refuge for some Butterfly fish ( Chaetodon spp.) while they nibble at the food source. Lettuce coral ( Agarcia agarites ) provides some overhang for thousands of Blue Chromis ( Chromis cyaneus ) to hide. Within the dead skeletons and rock rubble the common Atlantic Octopus ( Octopus vulgaris ) will be seen. This cunning creature will lure invertebrates to its crevice and then have a grand meal. Other fish like the Rock Beauty ( Holocanthus tricolor ) and the Yellowtail Snapper ( Ocyurus chrysusus ) swim into the depths from the fore reef. Deeper down, the seafloor is littered with crinoids ( Nemaster rubiginosas ) and spiny oysters ( Spondolylus americanus ). Once below 60 feet in the open expanses of the water, spotted eagle rays ( Aetogatus narinari ) swim with a reserved grace. And intricate patterns of the deepwater lace coral ( Iciligorgia schrammi ) break up the barren landscape.
We have now seen the complete ecosystem that helps make a reef such a splendid place. As aquarists we can only hope to capture a small percentage of this diversity in out aquariums. With proper planning, some creativity and good skills with PVC, we can incorporate more of this ecosystem than what may be thought. In the next issue, I will discuss how this relates to the home aquarium system, and whether we are trying to keep mini ecosystems, or just pretty gardens of corals.
Last modified 2006-11-19 02:11