text: biscayne national park biscayne national park is a u.s. national park located in southern florida , south of miami . the park preserves biscayne bay and its offshore barrier reefs . ninety - five percent of the park is water , and the shore of the bay is the location of an extensive mangrove forest . the park covers 172 , 971 acres ( 69 , 999 ha ) and includes elliott key , the park 's largest island and first of the true florida keys , formed from fossilized coral reef . the islands farther north in the park are transitional islands of coral and sand . the offshore portion of the park includes the northernmost region of the florida reef , one of the largest coral reefs in the world . biscayne national park protects four distinct ecosystems : the shoreline mangrove swamp , the shallow waters of biscayne bay , the coral limestone keys and the offshore florida reef . the shoreline swamps of the mainland and island margins provide a nursery for larval and juvenile fish , molluscs and crustaceans . the bay waters harbor immature and adult fish , seagrass beds , sponges , soft corals , and manatees . the keys are covered with tropical vegetation including endangered cacti and palms , and their beaches provide nesting grounds for endangered sea turtles . offshore reefs and waters harbor more than 200 species of fish , pelagic birds , whales and hard corals . sixteen endangered species including schaus ' swallowtail butterflies , smalltooth sawfish , manatees , and green and hawksbill sea turtles may be observed in the park . biscayne also has a small population of threatened american crocodiles and a few american alligators . the people of the glades culture inhabited the biscayne bay region as early as 10 , 000 years ago before rising sea levels filled the bay . the tequesta people occupied the islands and shoreline from about 4 , 000 years before the present to the 16th century , when the spanish took possession of florida . reefs claimed ships from spanish times through the 20th century , with more than 40 documented wrecks within the park 's boundaries . while the park 's islands were farmed during the 19th and early 20th centuries , their rocky soil and periodic hurricanes made agriculture difficult to sustain . in the early 20th century the islands became secluded destinations for wealthy who built getaway homes and social clubs . mark c. honeywell 's guesthouse on boca chita key was the area 's most elaborate private retreat , featuring a mock lighthouse . the cocolobo cay club was at various times owned by miami developer carl g. fisher , yachtsman garfield wood , and president richard nixon 's friend bebe rebozo , and was visited by four united states presidents . the amphibious community of stiltsville was established in the 1930s in the shoals of northern biscayne bay , taking advantage of its remoteness from land to offer offshore gambling and alcohol during prohibition . following the cuban revolution of 1959 , elliott key was used as a training ground for infiltrators into fidel castro 's cuba by the central intelligence agency and by cuban exile groups . originally proposed for inclusion in everglades national park , biscayne bay was cut from the proposed park to ensure everglades ' establishment . it remained undeveloped until the 1960s , when a series of proposals were made to develop the keys in the manner of miami beach , and to construct a deepwater seaport for bulk cargo , along with refinery and petrochemical facilities on the mainland shore of biscayne bay . through the 1960s and 1970s , two fossil - fueled power plants and two nuclear power plants were built on the bay shores . a backlash against development led to the 1968 designation of biscayne national monument . the preserved area was expanded by its 1980 re - designation as biscayne national park . the park is heavily used by boaters , and apart from the park 's visitor center on the mainland , its land and sea areas are accessible only by boat . geography biscayne national park comprises 172 , 971 acres ( 69 , 999 ha ) in miami - dade county in southeast florida . extending from just south of key biscayne southward to just north of key largo , the park includes soldier key , the ragged keys , sands key , elliott key , totten key and old rhodes key , as well as smaller islands that form the northernmost extension of the florida keys . a wide shallow opening in the island chain , located between the ragged keys and key biscayne just north of the park 's boundary , is called the safety valve , as it allows storm surge water to flow out of the bay after the passage of tropical storms . the park 's eastern boundary is the ten - fathom line ( 60 - foot ; 18 m ) of water depth in the atlantic ocean on the florida reef . the park 's western boundary is a fringe of property on the mainland , extending a few hundred meters inland between cutler ridge and mangrove point . the only direct mainland access to the park is at the convoy point visitor center , adjacent to the park headquarters . the southwestern boundary adjoins the turkey point nuclear generating station and its system of cooling canals . the southern portion of biscayne bay extends between elliott key and the mainland , transited by the intracoastal waterway . the park abuts the florida keys national marine sanctuary on the east and south sides of the park and john pennekamp coral reef state park to the south . only 9 , 075 acres ( 3 , 673 ha ) of the park 's area are on land , with the offshore keys comprising 4 , 250 acres ( 1 , 720 ha ) and mainland mangrove swamps account for the remaining 4 , 825 acres ( 1 , 953 ha ) . as an extension of the everglades ecosystem , much of the park was originally proposed to be included in everglades national park , but was excluded in order to obtain a consensus for the establishment of the everglades park in 1947 . geology biscayne bay marks the southernmost extent of the atlantic barrier islands , represented by key biscayne , and the northernmost extent of the florida keys at elliott key . the keys are distinguished from the barrier islands by the coral limestone that extends to the islands ' surface under a thin veneer of topsoil , while the barrier islands are dominated by wave - deposited sands that cover most of the limestones . biscayne bay lies between low ridges of oolitic miami limestone on the west , forming cutler ridge , and the coral - based key largo limestone that underlies elliott key and the keys to the south . the miami limestone was deposited in turbulent lagoon waters . the key largo limestone is a fossilized coral reef and was formed during the sangamonian interglacial period of about 75 , 000 to 125 , 000 years ago . the miami formation achieved its present form somewhat later , during a glacial period in which the lagoon deposits were consolidated and cemented by fresh water . the key largo limestone is a coarse stone formed from stony corals , between 69 and 200 ft ( 21 and 61 m ) in thickness . as a consequence of their origins as reefs , the beaches of elliott key and old rhodes key are rocky . significant sandy beaches are found only at sands key . hydrology biscayne bay is a shallow semi - enclosed lagoon which averages 10 ft ( 3 . 0 m ) in depth . both its mainland margins and the keys are covered by mangrove forest . the park includes the southern portion of biscayne bay , with areas of thin sediment called " " , and vegetated seagrass meadows supporting and shoal grass . as a result of efforts to control water resources in florida and projects to drain the everglades during the early and mid - 20th century , water flow into biscayne bay has been altered by the construction of canals . these canals channel water from portions of the southeastern everglades now used for agriculture into the bay . prior to canal construction , most fresh water inflow came from rain and groundwater , but the canals are now altering the salinity profile of the bay , conveying sediment and pollutants and leading to saltwater intrusion into the biscayne aquifer . the comprehensive everglades restoration plan ( cerp ) was established in 2000 to mitigate the effects of human intervention into the natural water flow of the everglades . primarily aimed at the restoration of historical patterns of water flow into everglades national park , the project will also deal with issues arising from the diversion of water out of the southern everglades into biscayne bay . the biscayne bay coastal wetlands project ( ) is a cerp component specifically intended to redistribute water flow so that fresh water is introduced gradually through creeks and marshes rather than short , heavy discharges through drainage canals . human history native people native americans were present in lower florida 10 , 000 years ago , when ocean levels were low and biscayne bay was comparatively empty of water . water levels rose from about 4000 years ago and inundated the bay . archeologists believe that any traces left by the peoples of that era are now submerged ; none now exist on dry lands in the park . the cutler fossil site , just to the west of the park , has yielded evidence of human occupation extending to at least 10000 years before the present . the earliest evidence of human presence in biscayne dates to about 2500 years before the present , with piles of conch and whelk shells left by the glades culture . the glades culture was followed by the tequesta people , who occupied the shores of biscayne bay . the tequesta were a sedentary community living on fish and other sea life , with no significant agricultural activity . a site on sands key has yielded potsherds , worked shells and other artifacts indicating occupation from at latest 1000 ad to about 1650 , after contact was made with europeans . a total of fifty significant archaeological sites have been identified in the park . exploration juan ponce de león explored the area in 1513 , discovering the florida keys and encountering the tequesta on the mainland . other spanish explorers arrived later in the 16th century and florida came under spanish rule . the tequesta were resettled by the then - spanish government in the florida keys , and the south florida mainland was depopulated . ponce de león referred to the bay as " chequescha " after its inhabitants , becoming " tequesta " by the time of spanish governor pedro menéndez de avilés later in the century . the present name has been attributed to a shipwrecked basque sailor known as the " " or " " who lived in the area for a time , or to a more general allusion to the bay of biscay . spanish treasure fleets regularly sailed past the florida keys and were often caught in hurricanes . there are 44 documented shipwrecks in the park from the 16th through the 20th centuries . at least two 18th - century spanish ships were wrecked in the park area . the spanish galleon nuestra del popolo is believed to have been wrecked in park waters in 1733 , though the site has not been found . hms fowey was wrecked in 1748 in what is now anchorage , at some distance from the fowey rocks . the discovery of the ship in 1975 resulted in a landmark court case that established the wreck as an archaeological site rather than a salvage site . 43 wrecks are included on the national register of historic places in the offshore reefs archeological district , which extends for 30 mi ( 48 km ) along the seaward side of the biscayne national park keys . during the 18th century , elliott key was the reputed base of two different pirates , both of whom were called black caesar , commemorated by caesar 's creek between elliott and old rhodes key . settlement and pre - park use the first permanent european settlers in the miami area did not come until the early 19th century . the first settlements around biscayne bay were small farms on elliott key growing crops like key limes and pineapples . john james audubon visited elliott key in 1832 . colonel robert e. lee surveyed the area around biscayne bay for potential fortification sites in 1849 . at the end of the american civil war in 1865 , a number of confederates passed through the area as they were attempting to escape to cuba . elliott key was a brief stopping point for john c. breckinridge during his flight to cuba . the former united states vice president , confederate general and confederate secretary of war spent two nights in biscayne bay on his journey . few people lived in the park area until 1897 , when israel lafayette jones , an african - american property manager , bought porgy key for $ 300 us . the next year jones bought the adjoining old rhodes key and moved his family there , clearing land to grow limes and pineapples . in 1911 jones bought 212 - acre ( 86 ha ) totten key , which had been used as a pineapple plantation , for a dollar an acre , selling in 1925 for $ 250 , 000 . before israel jones ' death in 1932 the jones plantations were for a while among the largest lime producers on the florida east coast . carl g. fisher , who was responsible for much of the development of miami beach , bought adams key , once known as cocolobo key , in 1916 and built the cocolobo cay club in 1922 . the two - story club building had ten guest rooms , a dining room , and a separate recreation lodge . patrons included warren g. harding , albert fall , t. coleman du pont , harvey firestone , jack dempsey , charles f. kettering , will rogers and frank . israel jones ' sons lancelot and arthur dropped out of the lime - growing business after competition from mexican limes made their business less profitable , and after a series of devastating hurricanes in 1938 they became full - time fishing guides at the cocolobo club . the club had declined with the crash of 1929 which cost fisher his fortune , but was revived by garfield wood in 1934 . among the joneses ' clients was avid fisherman herbert hoover and his family . the joneses also provided the club with fish , lobster and crabs . arthur and lancelot jones were the second largest landowners and the only permanent residents of the lower biscayne bay keys during the 1960s . wood sold the cocolobo cay club to a group of investors led by miami banker bebe rebozo in 1954 , who renamed it the coco lobo fishing club . clients guided by the joneses included then - senators john f. kennedy , lyndon johnson , richard nixon , herman talmadge and george smathers through the 1940s and 1950s . during the cold war the future park area was used as a training ground for cuban exiles training for missions in fidel castro 's cuba . elliott key in particular was used by the central intelligence agency as a training area in the early 1960s in preparation for bay of pigs invasion . the largest facility was ledbury lodge , the only hotel ever built on the key . as late as 1988 a group of cuban exiles were arrested when they tried to use the key for a mock landing . farther north , exiled venezuelan president marcos pérez jiménez kept a house on soldier key until he was extradited in 1963 . proposed development as modern communities continued growing in and around miami , developers looked to southern dade county for new projects . the undeveloped keys south of key biscayne were viewed as prime development territory . beginning in the 1890s local interests promoted the construction of a causeway to the mainland . one proposal included building a highway linking the biscayne bay keys to the overseas highway at key largo and to the developed barrier islands to the north . at the same time , pressure built to accommodate industrial development in south florida . this led to competing priorities between those who wished to develop for residential and leisure use and those in favor of industrial and infrastructure development . on december 6 , 1960 , 12 of the 18 area landowners who favored development voted to create the city of islandia on elliott key . the town was incorporated to encourage dade county to improve access to elliott key in particular , which landowners viewed as a potential rival to miami beach . the new city lobbied for causeway access and formed a negotiating bloc to attract potential developers . in 1962 an industrial seaport was proposed for the mainland shores of biscayne bay , to be known as seadade . seadade , supported by billionaire shipping magnate daniel k. ludwig , would have included an oil refinery . in addition to the physical structures , it would have been necessary to dredge a 40 - foot - deep ( 12 m ) channel through the bay for large ships to access the refinery . the channel would have also required cutting through the coral reef to get to the deep water . in 1963 florida power and light ( fp & l ) announced plans for two new 400 - megawatt oil - fired power plants on undeveloped land at turkey point . many local residents and politicians supported seadade because it would have created additional jobs , but a group of early environmentalists thought the costs were too high . they fought against development of the bay and formed the safe progress association . led by lloyd miller , the president of the local chapter of the izaak walton league , miami herald reporter juanita greene , and art marshall , the opponents of industrialization proposed the creation of a national park unit that would protect the reefs , islands and bay . after initial skepticism , the park proposal obtained the support of miami herald editors , as well as florida congressman dante fascell and florida governor claude r. kirk , jr . , and were supported by lobbying efforts by sympathetic businessmen including herbert hoover , jr . one vision of islandia , supported by land owners , would have connected the northern florida keys – from key biscayne to key largo – with bridges and created new islands using the fill from the seadade channel . although ludwig 's seadade plans were not supported by miami - area politicians or the state of florida , islandia 's supporters continued to lobby for development support . in 1968 , when it appeared the area was about to become a national monument , islandia supporters bulldozed a highway six lanes wide right down the center of the island , destroying the forest for 7 miles ( 11 km ) . islandia landowners called it elliott key boulevard , but called it " spite highway " privately . it was hoped that since there was so much environmental damage , no one would want it for a national monument . over time in the near - tropical climate , the forest grew back and now the only significant hiking trail on elliott key now follows the path of elliott key boulevard . the oil - fired turkey point power stations were completed in 1967 – 68 and experienced immediate problems from the discharge of hot cooling water into biscayne bay , where the heat killed marine grasses . in 1964 fp & l announced plans for two 693 mw nuclear reactors at the site , which were expected to compound the cooling water problem . because of the shallowness of biscayne bay , the power stations were projected to consume a significant proportion of the bay 's waters each day for cooling . after extensive negotiations and litigation with both the state and with ludwig , who owned lands needed for cooling water canals , a closed - loop canal system was built south of the power plants and the nuclear units became operational in the early 1970s . portions of the present park were used for recreation prior to the park 's establishment . homestead bayfront park , still operated by miami - dade county just south of convoy point , established a " blacks - only " segregated beach for african - americans at the present site of the dante fascell visitor center . the segregated beach operated through the 1950s into the early 1960s before segregated public facilities were abolished . park establishment and history the earliest proposals for the protection of biscayne bay were included in proposals by everglades national park advocate ernest f. coe , whose proposed everglades park boundaries included biscayne bay , its keys , interior country including what are now homestead and florida city , and key largo . biscayne bay , key largo and the adjoining inland extensions were cut from everglades national park before its establishment in 1947 . when proposals to develop elliott key surfaced in 1960 , lloyd miller asked secretary of the interior stewart udall to send a park service reconnaissance team to review the biscayne bay area for inclusion in the national park system . a favorable report ensued , and with financial help from herbert hoover , jr . , political support was solicited , most notably from congressman fascell . a 90 - acre ( 36 ha ) area of elliott key was by this time a part of the dade county park system . the 1966 report noted that the proposed park contained the best remaining areas of tropical forest in florida and a rare combination of " terrestrial , marine and amphibious life , " as well as significant recreational value . the report found that the most significant virtues of the potential park were " the clear , sparkling waters , marine life , and the submerged lands of biscayne bay and the atlantic ocean . here in shallow water is a veritable wonderland . " president lyndon b. johnson signed public law 90 - 606 to create biscayne national monument on october 18 , 1968 . the monument was expanded in 1974 under public law 93 - 477 and expanded again when the monument was redesignated a national park by an act of congress through public law 96 - 287 , effective june 28 , 1980 . the 1980 expansion extended the park almost to key biscayne and included boca chita key , the ragged keys and the safety valve shoal region , together with the corresponding offshore reefs and a substantial portion of central biscayne bay the first islandia property owner to sell land to the national park service was lancelot jones , together with katherine jones , arthur 's widow . they sold their lands for $ 1 , 272 , 500 , about a third of the potential development value . jones was given a life estate on 3 acres ( 1 . 2 ha ) at the age of 70 . he visited with park rangers stationed at the former cocolobo club , which eventually burned down in 1975 . the other life estate in the park was held by virginia tannehill , the widow of eastern airlines executive paul tannehill . jones ' house built by lancelot , his father and his brother , burned down in 1982 . he lived in a two - room shack for the next ten years , riding out hurricanes on porgy key , but left his home permanently just before hurricane andrew in 1992 . the house was destroyed and jones remained in miami until his death in 1997 at 99 years . deprived of a rationale for existence by the national monument 's establishment , islandia languished . the hiring of a police chief in 1989 prompted questions from the national park service to the dade county state attorney 's office , headed by janet reno . in 1990 reno 's office determined after investigation that all of the town 's elections were invalid , since the elections were restricted only to landowners , not residents . the town was finally abolished by the miami - dade board of county commissioners in march 2012 . the impact of hurricane andrew on neighboring homestead air force base caused the air force to consider closing the base and conveying it to miami - dade county , which was interested in using the base for commercial air traffic as an alternative to miami international airport . an environmental impact study concluded that the resulting flight paths over the bay , only 2 mi ( 3 . 2 km ) to the east , would result in degradation of the park . in 1999 the air force prohibited major commercial development at homestead as a result . the park 's popularity as a destination for boaters has led to a high rate of accidents , some of them fatal . the columbus day weekend has been cited as the " most dangerous weekend of the year . " an annual boating regatta in its 57th year in 2012 resulted in six deaths between 2002 and 2011 , with damage to seabeds from vessel groundings and littering . although official regatta activities take place outside the park , the area of elliott key has become a popular destination for some participants . a fifth generating unit fueled by natural gas and oil was added to the turkey point generating station in 2007 . in 2009 , turkey point was proposed as the site of two new 1117 mw nuclear reactors , to be designated turkey point 6 and 7 . if built , the new reactors would make turkey point one of the largest generating sites in the united states . other neighboring influences on the bay are the agricultural lands of south miami - dade county , a sewage treatment facility on the park boundary at black point , and its neighbor , the south miami - dade landfill . activities biscayne national park operates year - round . camping is most practical in winter months , when mosquitoes are less troublesome on the keys . private provide full day tours in the park that include snorkeling , hiking , paddling and sailing from the park headquarters . boat excursions to boca chita and adams key are also available . recreation access to the park from the mainland is limited to the immediate vicinity of the dante fascell visitor center at convoy point . all other portions of the park are reachable only by private or boats . activities include boating , fishing , kayaking , windsurfing , snorkeling and scuba diving . miami - dade county operates four marina parks near the park . homestead bayfront park is directly adjacent to the park headquarters at convoy point . farther south black point park provides access to adams and elliott keys . matheson hammock park is near the north end of the park , and crandon park is on key biscayne . although it is a federally designated park , fishing within biscayne is governed by the state of florida . anglers in biscayne are required to have a florida recreational saltwater fishing license . fishing is limited to designated sport fish , spiny lobster , stone crab , blue crab and shrimp . tropical reef fish may not be collected , nor may sharks , conch , sea urchins and other marine life . reef life species such as coral and sponges are also protected from collecting by visitors . additionally , is prohibited in the biscayne bay - card sound lobster sanctuary , administered by the state of florida to protect spiny lobster breeding areas , which overlaps much of biscayne bay . a private provides tours from the park headquarters into the bay and to the keys . most tours are operated during the peak winter season from january to april . personal watercraft are prohibited in biscayne and most other national parks , but other private powerboats and sailboats are permitted . island facilities most of biscayne 's permanent facilities are on the offshore keys . a seasonally staffed ranger station is located on elliott key , as well as a campground and 36 boat slips . a single loop trail runs from the harbor to the oceanfront , and a path following the spite highway runs the length of the island . adams key is a day - use - only area for visitors , although two park service residences are on the island . boca chita key is the most - visited island , with a campground and picnic areas . the boca chita lighthouse is occasionally open to visitors when staffing permits . and diving and scuba diving on the offshore reefs are popular activities . the reefs have been the cause of many shipwrecks . a selection of wrecks have been the subjects of ranger - led snorkeling tours and have been organized as the maritime heritage trail , the only underwater archaeological trail in the national park service system . the wrecks of the ( sank 1878 ) , erl king ( 1891 ) , alicia ( 1905 ) , lugano ( 1913 ) and mandalay ( 1966 ) are on the trail together with an unknown wreck from the 1800s and the fowey rocks lighthouse . the alicia , erl king and lugano are relatively deep wrecks , best suited for scuba dives . the mandalay is at a shallower depth and is especially popular for snorkeling . historical structures although most of biscayne national park 's area is water , the islands have a number of protected historical structures and districts . shipwrecks are also protected within the park , and the park 's offshore waters are a protected historic district . stiltsville stiltsville was established by eddie " crawfish " walker in the 1930s as a small community of shacks built on pilings in a shallow section of biscayne bay , not far from key biscayne . comprising 27 structures at its height in the 1960s , stiltsville lost shacks to fires and hurricanes , with only seven surviving in 2012 , none of them dating to the 1960s or earlier . the site was incorporated into biscayne national park in 1985 , when the park service agreed to honor existing leases until july 1 , 1999 . hurricane andrew destroyed most of stiltsville in 1992 . the park service has undertaken to preserve the community , which is now unoccupied . the community is to be administered by a trust and used as accommodation for overnight camping , educational facilities and researchers . other structures biscayne national park includes a number of navigational aids , as well as an ornamental structure built to resemble a lighthouse . the fowey rocks light is a skeleton - frame cast iron structure built in 1878 . already included within the boundaries of the park , the light was acquired by the park service on october 2 , 2012 . the unmanned pacific reef light is about three miles offshore from elliott key . the original 1921 structure was replaced in 2000 and its lantern was placed on display in a park in islamorada . industrialist mark c. honeywell was a cocolobo club member who bought boca chita key in 1937 , expanding the facilities to include a small lighthouse . boca chita key was developed with several structures including an imitation lighthouse , built using coral rock and topped with a wire cage resembling a lighthouse lantern , and the end of a jetty on the north side of the key . the key was owned by honeywell until 1945 . mark and olive honeywell also built a chapel , a guesthouse , seawalls and utility buildings on the island . the boca chita key structures are administered as a cultural landscape , interpreting the area 's use as a retreat for the rich . more modest homesteads include the now - abandoned plantations developed by israel jones and his sons , and the sweeting homestead on elliott key . the frame structures associated with these plantations , together with those of the cocolobo cay club and frame buildings on boca chita key , have been destroyed by fire and hurricanes . ecology south florida is a transitional zone between the nearctic and neotropical ecozones , resulting in a wide variety of plant and animal life . the intersection of ecozones brings opportunities for visitors to see species , particularly birds , that are not seen elsewhere in north america . the park includes four distinct ecosystems , each supporting its own flora and fauna . mangrove swamp , lagoon , island key and offshore reef habitats provide diversity for many species . in this semi - tropical environment , the seasons are differentiated mainly by rainfall . warm to hot and wet summers bring occasional tropical storms . though only marginally cooler , the winters tend to be relatively drier . bay salinity varies accordingly , with lower salinity levels in the wet summer , trending to more fresh water on the west side where new fresh water flows in . hundreds of species of fish are present in park waters , including more than fifty crustacean species ranging from isopods to giant blue land crabs , about two hundred species of birds and about 27 mammal species , both terrestrial and marine . molluscs include a variety of bivalves , terrestrial and marine snails , sea hares , sea slugs and two cephalopods , the caribbean reef octopus and the caribbean reef squid . the sheltered open waters of the bay and the outlying chain of keys provide resting areas for migrating birds on their way between north american , the caribbean islands , and south america . many southbound land birds stop in the fall at bill baggs cape florida state park , just north of the park on key biscayne , before venturing across the open waters of biscayne bay . northbound spring migrants do likewise on elliott key . most of the small passerine migrants are warblers , with ovenbirds , palm warblers , american redstarts , common , prairie warblers , worm - eating warblers and black - throated blue warblers accounting for the majority . migrant raptors include short - tailed hawks , sharp - shinned hawks , merlins , peregrine falcons and swallow - tailed kites , while bald eagles and ospreys nest in the park . both white - tailed and red - tailed tropicbirds are seen in the park , as are american flamingos , with some of the latter probably escaped captive birds . shoreline and mangrove swamp the mainland shorelines are dominated by a marshy transitional zone chiefly populated by red mangrove and black mangrove growing from the shallow water , with white mangrove growing farther back from the water 's edge . the trees ' aerial root structure provides a sheltered habitat for crabs , fish and wading birds . the brown waters within the mangrove thickets are nurseries for fish , mollusc and crustacean larvae that require a quiet sheltered environment before the immature animals can disperse into open waters . mangroves shed leaves at about 2 to 4 short tons per acre ( 4 . 5 to 9 . 0 t / ha ) per year , providing food for fish , worms and crustaceans . because the carbon in the leaves is sequestered by incorporation into animals , the mangrove swamp is estimated to have two to three times the ability to sequester carbon of terrestrial forests . the mangrove forest on biscayne bay is the longest on florida 's east coast . shoreline and island mangrove swamps , together with the bay , represent a significant nursery for the marine life of southeast florida . the salt - tolerant mangrove margin has expanded inland as freshwater flow into the bay has been channelized , replacing freshwater sawgrass marshes . the l - 31e coastal storm surge levee inland of the park 's western boundary has played a significant role in isolating former freshwater marshlands from their water sources . at the same time , tidal water does not reach the interior of the coastal margin , limiting interchange between salt and freshwater ecosystems . bird life on the shoreline includes yellow - crowned night herons , loggerhead shrikes , prairie warblers and shorebirds . mangrove cuckoos , a notoriously difficult - to - observe species , may be seen at convoy point and black point . biscayne has one of the largest populations of mangrove cuckoos in florida . the park 's margins are habitat for the threatened american crocodile . the construction of miles of cooling water canals in the marl lands close to the shore behind the turkey point power plant , and the canals ' warm waters , have provided a nearly ideal environment for crocodile nesting , making the power plant a nursery for many of those living in the park . although crocodiles and american alligators both occur in extreme southern florida , alligators are uncommon in biscayne , since alligators mainly inhabit fresh waters found farther inland , while crocodiles can live in biscayne 's somewhat saltier estuarine waters . bay waters the open waters are inhabited by fishes , molluscs and crustaceans living on sea grasses or who prey on each other . the shallowness of the lagoon makes it suitable habitat for diving birds such as anhinga , cormorants and diving ducks . the bay also provides habitat for juvenile sea animals that have left the shelter of the mangrove belts . manatees frequent the quiet waters of the bay . the bay has a year - round population of double - crested cormorants . winter residents include northern gannets , american white pelicans and common loons . the bay also has a resident population of common bottlenose dolphins . biscayne bay is a shallow lagoon with little vertical density or salinity gradient due to its lack of depth . instead of a vertical gradient , the bay shows a horizontal density gradient , with fresh water entering from the drainage canals on the west side and seawater entering through gaps in the keys and through the safety valve section of shoals . bay salinity reaches a peak in june . changes in the salinity pattern of the bay have had negative effects on formerly abundant species such as red drum . biscayne bay and florida bay are major nurseries for red grouper and gray snapper . the bottom of the lagoon hosts sponges and soft corals in places where grasses cannot not grow . three primary species of seagrass are found in the park : , shoal grass and manatee grass . the endangered johnson 's seagrass is also found in small quantities in the bay , which is at the southern end of the grass 's range . roughly 75 percent of the central bay floor is covered by grasses . scarring of seagrass beds by vessel groundings or propellers is a significant problem . about 200 such incidents are documented each year , with full re - growth requiring up to 15 years . the bay is also affected by commercial shrimp trawling , which is permitted in park waters . the passage of roller - frame trawl nets does not harm grasses , but damages soft corals and sponges . keys elliott key is the largest island in the park , measuring 1 , 650 acres ( 670 ha ) and about 8 . 1 mi ( 13 km ) long by 0 . 62 mi ( 1 km ) wide . next largest is old rhodes key at 660 acres ( 270 ha ) , then sands key 420 acres ( 170 ha ) , totten key 380 acres ( 150 ha ) and little totten key at 200 acres ( 81 ha ) , with 37 smaller islands arranged in a north - south line 5 to 8 . 7 mi ( 8 to 14 km ) east of the mainland shoreline . the keys shift from barrier islands with rocky cores in the north to coral rock platforms in the south . all are fringed with mangroves , with subtropical vegetation and hardwood forests in the interiors , including gumbo limbo , mahogany , ironwood , and . insects include schaus ' swallowtail , an endangered species , as well as dense clouds of mosquitoes in the wet season , preyed upon by dragonflies . marsh rabbits and raccoons , together with mice and rats comprise the primary mammalian species . reptiles include rattlesnakes and a variety of lizards , as well as an occasional crocodile . the keys are a transitional area capable of hosting unexpected birds , often caribbean species that have strayed near the mainland . the interior of the keys are frequented by warblers and the hawks that prey on them . coastal zones are habitat for ruddy turnstones and least sandpipers . gulls and terns include royal terns , laughing gulls and ring - billed gulls , with brown pelicans just offshore . wilson 's plovers nest on boca chita key , where nesting zones are closed during breeding season . sea turtles nest on island beaches in the park . park staff actively assist turtle nesting by removing debris from beaches that might pose an obstacle to adults and hatchlings . loggerhead turtles are the most common sea turtle species and account for nearly all of the turtle nests in the park . nest sites are identified by daily morning beach patrols and are protected with mesh screen against the predation by abundant raccoon population . nest protection efforts have reduced predation from 100 % of nests disturbed per year to no disturbed nests in 2007 , with a more usual average of more than 50 % nest disturbance in most years . in 2012 one undisturbed nest was found and protected , five partially disturbed nests were protected , and one nest was destroyed by predators . the threatened eastern indigo snake is also present on the island . rare and endangered plant species on the islands include sargent 's cherry palm and the semaphore prickly - pear cactus ( ) . the cactus , which has been described as " near extinction " , has been reduced to about 20 individuals . a colonial population of 570 cacti were found on one island in biscayne bay in 2001 , making it the largest known population of semaphore prickly - pear cactus in the world . the only natural population of sargent 's palm grows on elliott key . fewer than 50 grew on the key in 1991 . despite efforts to propagate the plant , there are now 16 sargent 's palms on elliott key , with about 123 propagated on long key . two critically endangered butterflies , schaus ' swallowtail ( papilio ) and the miami blue , are found in the park , mostly on elliott key . in 2012 the u.s. fish and wildlife service ( usfws ) authorized a capture and captive breeding program for schaus ' swallowtail after only five of the butterflies were found by surveyors in the park , down from 35 in 2011 , of a total surveyed florida population of 41 . the miami blue was feared to be extinct after hurricane andrew in 1992 , but a population was found in 1999 at bahia honda key . captive breeding produced 25 , 000 miami blues , some of which have been released on elliott key with mixed results . coral reef and offshore waters beyond the keys in the atlantic ocean the seafloor slopes gradually down before rising in an almost continuous coral reef . the reef , composed of living corals , is inhabited by more than 200 species of fish , as well as molluscs , crustaceans and worms . every coral species in park waters is considered protected by either federal or state regulations . coral reefs are estimated to cover about half the area of the park , with about 4000 individual patch reefs and areas of bank - barrier reef . hundreds of species of hard and soft corals , sea anemones and sponges are found in bay and offshore waters . the coral reefs may themselves be subdivided into the outer reef on the edge of the florida carbonate platform , the patch reefs between the outer reef and the keys , and the reefs in the shoals on either side of the keys . the offshore reefs are dominated by elkhorn coral to 10 - meter ( 33 ft ) water depth , and staghorn coral below 10 meters . the landward patch reefs are principally composed of boulder star coral and symmetrical brain coral . the island shoal reefs mainly consist of lesser starlet coral and porites finger corals . reef environments in biscayne national park have seen declines in species richness and diversity across all fish species from 1977 to 1981 to 2006 – 2007 . a sampling program showed declines at all sampling sites . a correlation has been posited between the observed decline in coral reef coverage throughout the florida reef tract and the decline in fish species . declines in populations were noted in both gamefish and in fish species not exposed to fishing pressure . algal cover has increased as coral has declined , so that coral - dwelling species have decreased while herbivorous fish have increased . increased overall salinity and changing salinity gradients in biscayne bay may also play a role , while polychlorinated biphenyl and mercury contamination have been noted in fish samples . the park 's eastern boundary lies just beyond the rise of the offshore reef at ten - fathom ( 60 - foot ; 18 m ) sea depth . areas farther offshore are protected within the florida keys national marine sanctuary , which extends eastward to a boundary corresponding to a depth of 300 fathoms ( 1 , 800 ft ; 550 m ) . the offshore waters harbor brown pelicans , magnificent frigatebirds , brown boobies , particularly around the offshore lights , and pelagic birds such as shearwaters and petrels . whales in offshore waters are rare , but can include right whales , humpback whales , sperm whales , fin whales and sei whales , all of them endangered . the smalltooth sawfish is similarly rare in park waters and endangered . threatened coral species include elkhorn and staghorn corals , as well as pillar coral , listed as endangered in florida . exotic species more than 50 species of exotic plant have been documented in the park , with almost 20 of those considered to be pest species which may displace native plants and possibly alter the ecological balance . green iguanas , cane toads , black rats , lionfish , fire ants , and brown basilisk lizards are common in the park . the lionfish ( and miles ) is a tropical fish from the indian - pacific ocean area . it is known for its voracious appetite and its ability to establish itself in new waters , rapidly replacing other species . researchers theorized that the introduction of this species in the park occurred during hurricane andrew in 1992 . sightings in biscayne bay at that time were believed to have been from home aquariums that were destroyed during the hurricane , though the researcher who first proposed the theory has since retracted the assertion . more recent lionfish sightings are probably from more established populations in the florida keys to the south of the park . also likely originating from human captivity , burmese pythons have been observed near the park 's boundary along the mainland . exotic plant species which pose the highest risk to native plant communities include brazilian - pepper , torpedo grass , tuberous sword fern , guava and . climate biscayne 's tropical climate reflects its location in extreme south florida . southern miami - dade county is classified as tropical savanna in the köppen - geiger system . seasons may be divided into the november – april dry season and the may – october wet season . dry season temperatures average between 66 and 76 ° f ( 19 and 24 ° c ) with an average monthly rainfall of 2 . 1 inches ( 53 mm ) . wet season temperatures average between 76 and 85 ° f ( 24 and 29 ° c ) with an average monthly rainfall of 5 . 39 inches ( 137 mm ) . the wet season roughly coincides with hurricane season , with frequent thunderstorms . like many locations in southern florida , biscayne national park is affected by hurricanes every few years . most storms require temporary closings and occasional repairs to park facilities . a direct hit by a powerful hurricane can produce severe consequences , primarily by its impact on human interventions in the environment rather than on the natural environment of the park , which is well - adapted to these events . significant hurricanes to strike biscayne include storms in 1835 and 1904 , the 1906 florida keys hurricane , the 1926 miami hurricane , the 1929 bahamas hurricane , the 1935 labor day hurricane , the 1935 yankee hurricane , the 1941 florida hurricane , the 1945 southeast florida hurricane , the 1948 miami hurricane , hurricane king in 1950 , hurricane donna in 1960 , . hurricane cleo in 1964 , and hurricane andrew in 1992 . the park can be affected by wave action from more distant tropical storms such as 2012 's hurricane sandy , which damaged facilities on elliott key . on august 24 , 1992 , hurricane andrew came ashore just south of miami , passing directly across biscayne national park with maximum sustained winds of 141 miles per hour ( 227 km / h ) , with gusts to 169 mph ( 272 km / h ) . the storm surge was up to 17 ft ( 5 . 2 m ) above mean sea level . it was a compact category 5 hurricane on the saffir - simpson hurricane scale . biscayne bay was affected by bottom scouring and turbidity and with damage to its fringes of mangrove forest . leakage from damaged boats and marinas polluted the bay with fuel , with discharges continuing for nearly a month after the hurricane 's passage . a commemorative plaque was placed at the dante fascell visitor center in 2002 to commemorate the human and environmental cost of andrew , and to celebrate the area 's recovery from the storm 's effects . the inscription reads in part : on monday , august 24 , 1992 , at 4 : 30 a.m. , the eye wall of hurricane andrew passed over this point before striking homestead and southern miami - dade county . the fowey rocks light station transmitted weather data with winds peaking at a two - minute wind speed of 127 knots ( 235 km / h ) and a gust to 147 knots ( 272 km / h ) before the station ceased transmitting , presumably due to damage from stronger gusts . the strongest part of the eyewall had not reached fowey rocks when it stopped transmitting . since all park lands are no more than a few feet above sea level , they are vulnerable to rising sea levels . park service studies project that much of the park 's land area will be lost in the next two hundred years . sea level in biscayne bay is projected to rise between 3 and 7 inches ( 8 and 18 cm ) by 2030 , and 9 to 24 inches ( 23 to 61 cm ) by 2060 . a sea level rise of 3 to 6 inches ( 8 to 15 cm ) is projected to increase saltwater intrusion into the biscayne aquifer . higher rises will make the southern everglades a saltwater marsh , altering the ecology of the region .