The coral reefs of the Florida Keys and Dry Tortugas

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1 The coral reefs of the Florida Keys and Dry Tortugas Florida is the only state in the continental United States to have extensive shallow coral reef formations near its coasts. Coral reefs create specialized habitats that provide shelter, food and breeding sites for numerous plants and animals, including spiny lobster, snapper and other commercial and recreational species. Coral reefs lay the foundation of a dynamic ecosystem with tremendous biodiversity. The Florida Reef Tract (FRT) stretches 358 miles from the Dry Tortugas National Park off of the Florida Keys to the St. Lucie Inlet in Martin County and includes 1700 islands.roughly two thirds of the Florida Reef Tract lies within the Florida Keys National Marine Sanctuary (FKNMS), a marine protected area that surrounds the Florida Keys island chain. It is the largest marine protected area in the USA. These resources are the basis for the economically important commercial fishing and tourism located in south Florida, which attracts more than 4 million visitors who spend in excess of 14 million visitor-days per year. The Dry Tortugas are a small group of islands, located at the end of the Florida Keys, about 100km west of Key West. Still further west is the Tortugas Bank, which is completely submerged. The Tortugas are the only barrier reef in North America. The first Europeans who discovered the islands were the Spanish under the lead of explorer Juan Ponce de León in Tortuga is the spanish word for turtle and the Spanish called them Dry, because there is no fresh water on the islands. Its lush sea grass meadows are still a safe feeding areas for hundreds of endangered sea turtles. Furthermore this is ecosystem provides refuge to over 280 species of fish. Development of the Florida reefs: Florida's coral reefs came into existence 5,000 to 7,000 years ago when sea levels rose following the last Ice Age. Reef growth is relatively slow; an individual colony may grow one-half inch to 7 inches a year, depending on the species. All coral reefs are in a constant state of flux. While expanding with new polyps (the living tissue) on the outer surface, they are simultaneously being ground into sand by storms and animals. During long periods of favorable conditions, the reefs may reach awe-inspiring heights and diversity. The tropical coral (warm water corals) reefs of Florida are one of the most northern reefs in the world. More northern are only the reefs of the Bermuda islands. The Florida reefs tract region is warmed by the Florida Current flowing from the Caribbean and the Loop Current from the Gulf of Mexico, enabling major reef building corals and reef species to inhabit such northern latitudes. The net flow of seawater of the Florida Current is from the Gulf of Mexico and the Caribbean along the Florida Keys. (GCRMN 2005 p.52) 23

2 Coral reefs are often used to define the limits of the tropical marine environment. Coral reefs are unique among marine associations or communities in that they are built up entirely by biological activity. Reefs are essentially massive deposits of calcium carbonate that had been primarily produced by corals. Although corals are found throughout the oceans of the world in polar and temperate waters as well as in the tropics, it is only in the tropics that reefs in shallow waters are developed. This is because there are two different groups of corals: hermatypic and ahermatypic. Ahermatypic are distributed worldwide, hermatypic only in the tropics. The distinguishing feature between the two is that most of the hermatypic corals have in their tissue small symbiotic living plant cells, called zooxanthellae. Limiting factors for warm water corals - Temperature: No reefs are developed where the annual mean minimum water temperature is below 18 C. Optimal reef development occurs in waters of C annual mean water temperature. The maximum temperature should not exceed 36 C, although some corals tolerate up to 40 C - Depth /solar radiation: Develop not in water deeper than 50 70m. Most reefs grow in depth of 25m or less the hermatypic corals require light. It is most important factor limiting coral reefs necessary for the symbiotic zooxanthellae - salinity: corals and many other species are intolerant of salinities deviating significantly from normal seawater ( %). Were the discharge of rivers is significant, reefs are absent. Increasing discharge is threatening the corals - Sedimentation: often correlated with the freshwater discharge. Sediment, both in the water and settling out on the corals has an adverse effect, although corals have a cleaning mechanism coral growth is greater in areas with wave action. The strong skeleton can withstand the power of the waves, and the waves are cleaning the corals from sediment and are responsible for renewing the plankton which serves as food. - limited in upward direction by emergence into the air Abundant secretion of mucus prevent dehydration for a short time (1 hour or two), most corals are killed by long exposure to air limiting growth to the lowest tide level Types of Reefs and Corals The three major types of coral reefs around the world are atolls, fringing reefs and barrier reefs. Florida's coral reef system most closely resembles a barrier reef, however, the reefs are closer to shore and they lack the shallow inshore lagoons found on most barrier reefs so it is more aptly named a bank reef. Florida also has patch reefs, which grow between the reef tract and the land in shallower waters. Patch reefs are typically small (the size of your back yard or a small home). Compared to other areas in the world, especially to the coral triangle of SE-Asia, the biodiversity is rather poor. Only 45 species of stony corals and 37 species of octocorals are found along the 24

3 Florida Reef Tract. (In the coral triangle: more than 700 species). Each kind lives in a separate colony that is shaped differently. The colonies take on the various hues of the algae that live within them. Corals can generally be divided into two main categories: stony corals and octocorals (sea fans and other soft corals). Marine sponges are also very important within the coral reef community and over 70 species can be found along the Florida Reef Tract. Stony corals are the major reef architects. Polyps, the living portion of corals, extract calcium from seawater and combine it with carbon dioxide to construct the elaborate limestone skeletons that form the reef backbone. Florida's most common reef-building corals are brain, star, elkhorn and staghorn. Along the northern extension of the Florida Reef Tract, the reefs generally occur in a series of one to three discontinuous reef lines (terraces) that parallel the shoreline, extending north from Miami- Dade County to Martin County. Different reef organisms characterize the type of habitats found along Florida reefs, typically transitioning from a cover of algae and small octocorals nearshore to numerous octocorals and varied hard coral populations at the outer reefs. The various reef architectural and compositional components create an environment that is ecologically diverse and productive, one that supports many other aquatic plants and animals that make southeast Florida reefs their home. Some typical stony corals (photos: Elkhorn Coral (Acropora palmata ) Common brain coral (Diploria strigosa) Massive starlet coral (Siderastrea sidereal) Staghorn Coral Great Star coral Mustard Hill coral (Acropora cervicornis) (Montastraea cavernosa) (Porites asteroides) 25

4 Importance of the coral reefs Coral reefs deliver ecosystem services to tourism, fisheries and shoreline protection. In Florida they play an important role for hurricane protection. The annual global economic value of coral reefs has been estimated at $US375 billion. However, coral reefs are fragile ecosystems, partly because they are very sensitive to water temperature. Florida reefs are not as rich in biodiversity as other reefs in the world related to the location at the boundary of occurence Threats: Coral reefs worldwide are under threat from climate change, ocean acidification, blast fishing, cyanide fishing for aquarium fish, overuse of reef resources, and harmful land-use practices, including urban and agricultural runoff and water pollution, which can harm reefs by encouraging excess algae growth. All coral reefs of the US are under protection, thus threats related to overfishing or destructive fishing could be diminished. Threats to coral reefs world wide Natural threats: - the rising SST causes stress to corals which are already living close to their max.temperature bleaching and death - Meteorological disturbanices: Hurricanes - pest outbreaks massive occurrence of organisms that have- due to their high abundance- directly or indirectly harmful effects on the ecosystem. Organisms involved are either native or introduced. Examples: harmful algae bloom (HAB). This is not secured that it is only natural. Man-caused changes in the ecosystem due to fishing are meant to cause the problem Anthropogenic threats: - Marine pollution: sewage oil Eutrophication and sedimentation: chlorinated hydrocarbons (DDT, PCB), inorganic chemicals, suspended solid waste, discharge of waste heat Increase of agricultural use in the catchment and changing freshwater input eutrophication - Increase of the water temperature due to global warming stress situation for the corals bleaching - Overexploitation: disturbance of the ecosystem. Mainly due to boating and diving tourism Sever problems due to anchoring - Dynamite and cyanide fishing - Coastal construction and pollution - physical destruction of aquatic habits Tourism: boating and walking; - Ocean acidification: Increase of carbondioxid in the atmosphere: the oceans are a sink getting more acidic. The development and deposition of calciumcarbonate in the oceans decreased since 1850 by 6-11%. 58% of reefs worldwide are endangered by human activity. 26

5 Threats to the Florida coral reefs: The coral reef community of the Florida Keys is vulnerable to both natural and anthropogenic impacts, including: extreme changes in sea surface temperatures; coral diseases; increased sedimentation; tropical storms and hurricanes; exposure to pollution from the land; habitat degradation and loss resulting from coastal development; over-fishing; and excessive visitor use. However, the overwhelming threats to the coral reefs have been coral diseases and increasing sea surface temperatures (SSTs) over the past 28 years. This thermal stress has been exacerbated by other anthropogenic pressures on the ecosystem. All the coral reef threats above occur along the coastline of Florida. Coastal development and pollution from the large and growing human population in southern Florida probably constitute the most significant stressors to the nearshore marine environment. Impacts associated with coastal construction, dredging for navigation, beach nourishment and infrastructure installation can reduce water quality and increase the damage to coral reefs and hard bottom communities. One of the biggest threats are the wastewater effluents. Compared to Europe the USA are a developing country concerning wastewater treatment. Up to now, wastewater effluents are pumped into the ocean near the reefs via 6 outfalls that discharge 1100 mio l/day!!! of minimal(!) treated wastewater. A law requiring effective sewage treatment in SE Florida passed legislation 2008, but higher treatment levels have to be reached only by 2018 and achieving at least 60% recycling of wastewater by The first treatment plant was set up in 2010(!). In comparison: In Germany, the Netherlands and Scandinavia these regulations were set up in 1980! In Italy and in France in 1990, and even in Spain in Status of the coral reefs of Florida: Southeast Florida: The reefs of SE Florida generally have low stony coral species richness and high cover of octocorals, sponges and macroalgae. The most common octocorals in Florida are sea fans and sea whips. Sea fans are pale lavender or green fan-shaped corals. Their fans flutter in the ocean current like lace curtains. Sea whips have long feathery branches that spread in all directions. They can be orange, lilac, purple, yellow, brown or buff. They are all poisonous and can sting seriously if touched! In recent years, corals in Florida have experienced declines due to a combination of factors, including bleaching, coral disease, resource extraction and damage from hurricanes. There is a trend towards reduced coral species richness to the north with having Broward County 24 species, but Martin County has only 8 species. The most common corals in the reefs of SE Florida are Monastraea cavernosa (Great Star Coral), Siderastrea siderea (Massive starlet coral) and Porites asteroides (Mustard Hill Coral). Octocoralia consistently contribute most to the bottom biota. Total stony coral cover is generally between 0.5% and 2.5%, however, some small sites have more than 15% cover. Florida Keys: Coral reef resources have been degrades by resource extraction as well as habitat loss and damage since the Europeans discovered the area. These caused long-term changes to the reefs which are still noticeable, although today most of the reefs are protected. 27

6 The changes include: (1) loss of the top predators, i.e. the monk seal (2) loss of spawning aggregations and reductions in the abundance of large groupers and snappers (3) loss of habitat structure including mangroves, corals and seagrass beds (4) reduction in conch, lobster and urchin populations (5) loss of ecosystem services provided by the aforementioned flora and fauna History of coral bleaching in the Florida Keys (GCRMN 2007) A combination of stress events, such as cold water stress from winter fronts, brief warm water events, or reduced light penetration during lengthy periods of turbid water, occurred in the 1970s. 1979: The first sign of stress on the outer coral reefs was a die-off of sponges in June-July 1979, with a massive loss of the barrel sponge, Xestospongia muta 1980: In June-July 1980, doldrum-like weather patterns replaced the normal summer trade winds; the skies remained clear and almost cloudless and the seas were very calm for 6 weeks. Within a few weeks, angelfish, surgeonfish, butterflyfish and some other reef fish showed signs of extreme stress; they were respiring heavily and could be collected by hand. Open wounds and disease were commonly seen on the fish and large numbers began dying throughout the Keys : Elevated SSTs continued in the Florida Keys and nearby reefs.(exptemely strong El Nino event in the Pacific). In In July 1983, doldrum-like conditions returned to the Florida Keys at the same time the urchins (Diadema) were dying in what was then the Looe Key National Marine Sanctuary. The corals began turning white after only a couple of weeks of these conditions. This first mass coral bleaching spread along the seaward part of the outer coral reef tract from Big Pine Key to Sand Key Reef off Key West. Coral bleaching was most severe on the shallow fore-reef habitats, and especially on the outer shallow reefs in the lower Florida Keys where there is the greatest exposure to currents from the warmer waters of the Gulf and Florida Bay. 1986: In May and June 1986, there was an alarming outbreak of black-band disease on fore-reef coral colonies at Looe Key Reef. 1987: Similar doldrum-like weather patterns re-occurred in the Florida Keys in June By mid-august, a mass coral bleaching event was occurring on the outer reefs of the entire Florida Reef Tract. 1990: More doldrum-like weather patterns with calm seas returned to the Florida Keys in July Early signs of bleaching were seen Although there was no mass coral bleaching in the Florida Keys between 1990 and 1997, there were wide-spread outbreaks of various diseases that affected both branching corals (Acropora)and boulder corals (Diploria, Montastraea, etc.) : Doldrum-like weather conditions returned to the Florida Keys in July 1997 and by mid-august, a mass coral bleaching event was underway.(1997/98 was again an extreme El Nino year) Once again, the bleaching event was widespread and heavily damaged the inshore corals. Third generation residents raised the alarm and reported to Sanctuary managers that such bleaching was unknown in the Florida Keys in recent history. The 1997 coral bleaching event was extensive and long-lasting, and affected both offshore and inshore corals, with many remaining bleached or mottled well into : Although elevated SSTs occurred in the Florida Keys in 2004 and 2005, there was only minor to patchy coral bleaching. The corals escaped the severe coral bleaching 28

7 that was recorded throughout much of the Wider Caribbean. Both 2004 and 2005 were active hurricane seasons; each tropical storm reduced SSTs, by mixing the surface waters with deeper, cooler waters. In % of the corals in the Dry Tortugas were affected. Although climate change and sea level rise are concerns in Florida, there has been no mass bleaching off southeast Florida between 2004 and There was a moderate bleaching in 2005, but the passage of the hurricanes mixed the surface waters and lowered the SST enough that Florida was buffered from the mass bleaching There are no reports since 2008 available check out for bleaching during the expedition! 2005 a critical year for the Florida corals: a hot year: Up to then, 2005 was the hottest year in the Northern Hemisphere on average since the advent of reliable records in That year exceeded the previous 9 record years, which have all been within the last15 years. But it was even topped by the years 2007, 2008 and Large areas of particularly warm surface waters developed in the Caribbean and Tropical Atlantic during The warm water temperatures caused coral bleaching as a stress response to the excessive water temperatures, but not to the extent of previous years, due to the cooling effect of the hurricanes later in the year. a hurricane year: The 2005 hurricane year broke all records with 26 named storms, including 13 hurricanes. In July, the unusually strong Hurricane Dennis struck Grenada, Cuba and Florida. Hurricane Emily was even stronger, setting a record as the strongest hurricane to strike the Caribbean before August. Hurricane Katrina in August was the most devastating storm to hit the USA. It caused massive damage around New Orleans. Many of these hurricanes caused considerable damage to the reefs via wave action and runoff of muddy, polluted freshwater. But: Although the frequent hurricanes of the season 2005 caused some damages of the coral reefs, it also reduced sea surface temperature to below critical bleaching thresholds. a year of extensive coral mortality and disease: The Florida corals were not influenced so dramatically than these of the Lesser Antilles, West Indies and U.S. Virgin Islands The mean number of observed stony coral species and coral cover declined at permanent patch-, deep-, and shallow-reef sites throughout the Florida Keys since The coral decline is partly due to the loss of major framework building corals, specifically the boulder star coral (Monastraea annularis), staghorn coral (Acropora cervicornis) and elkhorn coral (Acropora palmate).elkhorn coral populations declined by about 50% between 2004 and 2006 primarily from hurricane and disease impact. Staghorn corals occurred at low density (< 1 colony/m²) in about 45% of the habitat types. In 2006, elkhorn and staghorn coral were listed as threatened species under the Endangered Species Act. To restore these corals that were once so abundant, coral nurseries have become established along Florida's coast and in the Florida Keys. Nurseries are growing new colonies and successfully out-planting them to octocorals, some of which are also called gorgonians, look like strange trees and shrubs, although they too are composed of living polyps. Unlike stony corals, 29

8 octocorals are unable to build thick limestone skeletons, but are supported by an internal structure composed of a horn-like substance called gorgonin. An almost continual decline in coral cover in the Florida Keys in all habitats since 1996 ( A statement of Billy Cuasey, the director of the US Marine Sanctuary Program (2007) Coral bleaching has been intensifying over the past 25 years at the local scale in the Florida Keys; this is consistent with other observations at regional and global scales. The pattern and intensity of coral bleaching events has shown a spatial and temporal expansion during this time, with concurrent increases in secondary impacts, such as coral diseases, loss of living tissue and low recruitment on the coral reefs of the Florida Keys. The shallow bank-reef habitats have been most severely affected, probably because they have historically existed in a narrower range of environmental conditions. In contrast, patch reefs, which are regularly exposed to elevated nutrient and sediment levels and broad seasonal fluctuations in water temperature, have been least affected and have retained the highest living coral cover. These corals have probably survived the bleaching episodes because they are better adapted to a broad range of physical conditions, similar to those that occur during doldrum-like weather. The mechanism is unclear; it is possible that natural selection has influenced their genetic composition so that they are able to tolerate greater fluctuations of temperature and nutrient levels, and lower light conditions. Coral reefs of the Florida Keys are affected by the same stresses damaging reefs worldwide: climate change; diseases; land-based sources of pollution; habitat loss and degradation; and overfishing. There is no longer a debate that coral bleaching is linked to global climate change; and a few people debate the causes of global climate change. Irrespective, coral reef scientists and managers need to take every possible immediate action to preserve and conserve the coral reef resources of the world. While such scientific debate is healthy and part of the scientific process, there comes a time when debate seeking second opinion distracts from the obvious, and provides decision-makers with a no-decision option. The suspected causes for the coral loss in the Florida Keys have varied enormously over the years; now there is recognition that elevated SSTs are the primary cause of coral bleaching. A minority viewpoint has focused on land-based sources of pollution as the cause of coral decline. Clearly, both have played a major role in the decline of coral 30

9 reefs on a global scale; research should be focused on unraveling the causes of coral decline at scales from microbial to the ecosystem. In the Caribbean alone, with a decrease of 80% over the last three decades, the coral reef coverage has dramatically changed, causing negative effects on the ecosystem (Gardener, 2003). These declines are directly related to human interferences. The amount of the coral reefs that is estimated to have been impacted by human activities is up to 97% (Lipp, 2002). The two main human impacts in the Florida Keys are the amounts of runoff and wastewater that flow into the Caribbean basin and also the amount of recreational and commercial fishing. Especially in the Keys, human pollution is affecting the coral reefs. Along with being a human health risk and risk to the swimmers, wastewater is an issue impacting the corals. A study at the University of South Florida showed quantitative amounts of wastewater indicators in the coral surface microlayers (CSM). These microlayers are layers of mucus that cover the top few millimeters of the coral. Indicators of human feces bacteria were found in 93.3% of the CSM samples (Lipp, 2002). This is clear evidence that runoff from the local areas is a factor in the reef degradation. Wastewater impacts the coral by reducing the water quality and increasing the algae populations. This wastewater comes from various local sources in the Keys. Most wastewater from the urban cities in Southern Florida seeps into the coastal water from septic system and cesspool effluent (Downs, 2005). In the Florida Keys, coral reef degradation is a problem that needs to be addressed and actions need to be made. Humans are in adversely affecting the coral in various ways such as septic effluent, overfishing, and coastal development. Task: - Discuss the effects of global change on the coral reefs and consequently on the coastal areas. - Discuss the possibilities of protection. - What actions are already done in the area of the Florida Keys, what else can be done. Take the importance of tourism for Florida in consideration! During diving / snorkeling: Can you recognize coral damages (bleaching, physical destruction etc.)? Because there are no status reports about the corals available since 2008, check out for actual symptoms of bleaching and estimate the amount! You can ask the diving instructor Christian for help to recognize bleaching. If the elkhorn/staghorn corals show white tips this is growing, not bleaching. Bleached corals show an irregular pattern of white parts Estimate the coverage with stony corals 31