Florida Coral Research Articles

Low reservoir ages for the surface ocean from mid‐Holocene Florida corals

The 14C reservoir age of the surface ocean was determined for two Holocene periods (4908–4955 and 3008–3066 calendar (cal) B.P.) using U/Th‐dated corals from Biscayne National Park, Florida, United States. We found that the average reservoir ages for these two time periods (294 ± 33 and 291 ± 27 years, respectively) were lower than the average value between A.D. 1600 and 1900 (390 ± 60 years) from corals. It appears that the surface ocean was closer to isotopic equilibrium with CO2 in the atmosphere during these two time periods than it was during recent times. Seasonal δ18O measurements from the younger coral are similar to modern values, suggesting that mixing with open ocean waters was indeed occurring during this coral's lifetime. Likely explanations for the lower reservoir age include increased stratification of the surface ocean or increased Δ14C values of subsurface waters that mix into the surface. Our results imply that a more correct reservoir age correction for radiocarbon measurements of marine samples in this location from the time periods ∼3040 and ∼4930 cal years B.P. is ∼292 ± 30 years, less than the canonical value of 404 ± 20 years.

Macroalgal blooms on southeast Florida coral reefs: I. Nutrient stoichiometry of the invasive green alga Codium isthmocladum in the wider Caribbean indicates nutrient enrichment

Invasive blooms of the siphonaceous green algae Codium spp. have been considered a symptom of coastal eutrophication but, to date, only limited biochemical evidence supports a linkage to land-based nutrient pollution. Beginning in the summer of 1990, spectacular blooms of unattached Codium isthmocladum developed on deep coral reef habitats in southern Palm Beach County and northern Broward County, and in subsequent years, attached populations formed on reefs in northern Palm Beach County. To better understand the nutrition of these HABs, we collected C. isthmocladum and other reef macroalgae from various locations in southeast Florida as well as the wider Caribbean region for tissue C:N:P analysis in order to gauge variability in the type and degree of N- and/or P-limited growth. Widespread nutrient enrichment in floridian C. isthmocladum populations was evidenced by significantly higher tissue P (0.06% versus 0.04% of dry weight) and lower C:N (12 versus 19), C:P (425 versus 980), and N:P (35 versus 50) ratios compared to more nutrient-depleted Caribbean populations. To determine nutrient availability on southeast Florida's reefs, we sampled near-bottom waters at a variety of locations for DIN ( NH 4 + + NO 3 − + NO 2 −) and SRP analysis. In general, concentrations of NH 4 +, NO 3 − and SRP were all high on southeast Florida's reefs compared to values reported for Caribbean coral reefs. Although summertime upwelling provides episodic NO 3 − and SRP enrichment to reefs in southeast Florida, these transient nutrient pulses have not historically supported C. isthmocladum blooms. We suggest that the widespread P enrichment of C. isthmocladum tissue and water column DIN:SRP ratios <16:1 in southeast Florida drive this system toward N limitation where low level NH 4 + enrichment becomes of paramount importance. Hence, the recent C. isthmocladum blooms appear to be supported by increasing land-based nutrient pollution, particularly, sewage that is enriched in NH 4 + and SRP at a low N:P ratio (<10:1) critical to sustaining balanced growth during bloom formation.

Macroalgal blooms on southeast Florida coral reefs: II. Cross-shelf discrimination of nitrogen sources indicates widespread assimilation of sewage nitrogen

Since 1990, coral reefs off southeast Florida have experienced an unprecedented succession of macroalgal blooms and invasions. To determine if anthropogenic land-based nitrogen (N) sources support these HABs, we collected macroalgal tissue for stable nitrogen isotope (δ 15N) analysis at three spatially distinct depths ranging from the shallow subtidal to the shelf break (∼43 m) along seven transects from Jupiter to Deerfield Beach, Florida, USA. This sampling was initiated during a historically significant drought in the spring of 2001 when rainfall, stormwater runoff, and upwelling were at a minimum. The sampling was repeated in the summer wet season following significant stormwater runoff and during a strong upwelling event. Despite significant seasonal changes in N source availability, δ 15N values did not vary between samplings. Collectively, δ 15N values were significantly higher on inshore shallow reefs (+8.1‰) compared to mid (+6.1‰) and deep reefs (+6.7‰). Values were also elevated in the southern portion of the study area (e.g., Boca Raton, +8.5‰) where nearly 1.5 billion l/day of secondarily treated wastewater is discharged into the ocean via coastal outfalls. Codium isthmocladum, a macroalga that assimilates its nutrients entirely from the water column, was the dominant bloom species in the southern study area, where tissue δ 15N values matched source values of nearby sewage outfalls. The northern study area was dominated by species of the genus Caulerpa, particularly the invasive Pacific native C. brachypus var. parvifolia, which are capable of accessing benthic nutrient sources (e.g., submarine groundwater discharge, SGD) by means of root-like rhizoids. The northern area does not have sewage outfalls but features a highly transmissive geologic zone where SGD may be enriched with septic tank leachate and effluent from municipal deep injection wells. Multiple lines of evidence supported the hypothesis that land-based sewage N was more important than upwelling as a N source to these HABs: (1) δ 15N values were highest on shallow reefs and decreased with increasing depth, indicating land-based sources of enrichment; (2) elevated δ 15N values occurred in these HABs during the dry season, prior to the onset of the summer upwelling; (3) elevated NH 4 + concentrations occur on these reefs during both upwelling and non-upwelling periods and are kinetically preferred by macroalgae compared to upwelled NO 3 −. These findings provide a case study of a coupling between increasing anthropogenic activities and the development of macroalgal HABs, including invasive species that threaten economically important reef resources in southeast Florida.

Underwater laboratory

To understand better why seaweed grows abundantly around Florida's coral to the coral's detriment, scientists have set up a laboratory at the bottom of the ocean floor. Aquarius is an 80-ton steel and glass underwater laboratory off Key Largo (FL, USA) that acts as home base for researchers who plan on spending eight to ten hours a day in the water, trying to understand the outgrowth of seaweed. Kevin Beach (University of Tampa, FL, USA), part of the six-member team, told reporters ‘when you see a reef that's 70% seaweed, it's a problem. We're going to look at what's fertilizing the seaweed and promoting its growth’. [Loft, K. (2001) The Tampa Tribune 30 July, Metro p. 1] TS

Predicting high-frequency upwelling: Spatial and temporal patterns of temperature anomalies on a Florida coral reef

High-frequency measurements reveal a rapidly changing, highly variable temperature regime on the slope of Conch Reef, a coral reef in the upper Florida Keys, USA. Water temperatures 1 m above the reef were measured at 20 min intervals at 21 and 33 m depths from 1992 through 1997, for all of 1992 at 7 m depth and 1997 at 10 m. While the annual variation in dailyaveraged temperatures was approximately 10°C in most years (Winter lows near 20°C to Summer highs near 30°C), temperature fluctuations as large as 6 to 10°C were recorded within individual days. Temperature variation is concentrated at semi-diurnal internal tidal frequencies, with a variety of mechanisms including internal tides, internal tidal bores, and cold water intrusions most likely related to variability of the Florida Current influencing high-frequency upwelling at this site. An analysis of extreme values in the long-term temperature records is used to predict return times for cold water upwelling events at depths of 7, 21, and 33 m. This analysis provides quantitative, seasonal estimates for among-depth differences in the extent of cool water pulsing. Return times for cooling events are shorter in May through September than in October through April, and decrease markedly with increasing depth on the reef slope. In Summer, the predicted median return times for a -3°C temperature anomaly are 136, 14, and 7 days at 7, 21, and 33 m depths, respectively. Predictable physical forcing arising from upwelling of cool water may be an important source of externally derived nutrients and suspended particles for this coral reef. The methods and results presented here should be applicable to a range of studies of temperature variation and nutrient dynamics in the Florida Keys and other regions.

Breaking internal waves on a Florida (USA) coral reef:a plankton pump at work?

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 166:83-97 (1998) - doi:10.3354/meps166083 Breaking internal waves on a Florida (USA) coral reef: a plankton pump at work? James J. Leichter1,*, Gregory Shellenbarger2, Salvatore J. Genovese3, Stephen R. Wing4 1Woods Hole Oceanographic Institution, Department of Biology, MS #34, Woods Hole, Massachusetts 02543, USA 21 Lincoln Street, Marblehead, Massachusetts 01945, USA 3Northeastern University, Marine Science Center, Nahant, Massachusetts 01908, USA 4Department of Marine Science, University of Otago, 304 Castle Street, Dunedin, New Zealand *E-mail: jleichter@whoi.edu Temperature, salinity, flow speeds, and plankton concentrations can be highly variable on the slope of Conch Reef, Florida Keys (USA), as warm surface water is mixed with cool, subsurface water forced onshore by broken internal waves. In August 1995 the water column seaward of the reef exhibited strong temperature and density stratification with a sharp pycnocline and associated subsurface chlorophyll a maximum layer at 45 to 60 m depth. On the reef slope, near-bottom zooplankton sampling at 22 to 28 m showed high concentrations of calanoid copepods, crab zoea, and fish larvae associated with upslope flow of cool, chlorophyll-rich water. In contrast to these periods of high concentrations, zooplankton concentrations were low during periods of long-shore and offshore flow of warm surface waters. Both the frequency of internal bore arrival and the mean duration of cool water events increase with increasing depth on the reef slope. Delivery of zooplankton to the reef is, therefore, also expected to increase with depth. A short-term settlement experiment showed increased settlement of serpulid worms at 20 and 30 m depth compared with 15 m, and a 15.5 mo transplant experiment showed significantly enhanced growth rates of the suspension-feeding coral Madracis mirabilis (Scleractinia: Pocilloporidae) at 30 m depth relative to growth at 15 or 20 m. Internal tidal bores appear to be a predictable, periodic source of cross-shelf transport to Florida coral reefs and an important influence on the spatial and temporal heterogeneity of suspended food particles and larval delivery to the benthos. Internal waves · Internal bores · Zooplankton · Transport Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 166. Publication date: May 28, 1998 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1998 Inter-Research.

Florida Corals in Bad Shape

Florida Corals in Bad Shape

Water column and sediment nitrogen and phosphorus distribution patterns in the Florida Keys, USA

Measurements of the distribution patterns of nutrients (ammonium, nitrate, orthophosphate, total N and total P) and chlorophyll concentrations were conducted under an interdisciplinary program known as SEAKEYS, initiated because of concern that anthropogenic nutrients may be impacting Florida coral reefs. Samples were collected along transects that extended from passes or canals to 0.5 km offshore of the outermost reefs. Seven of the transects were either in the Biscayne National Park (BNP) and Key Largo (upper keys) or Seven Mile Bridge/Looe Key (upper part of lower keys) areas, which have the best present-day reef development; the two in the middle keys off Long Key were in an area of minimal reef development where passes allow estuarine Florida Bay water to flow onto the Florida reef platform. Off the upper keys, water column concentrations of N and chl a were elevated near marinas and canals (1 μM NO3, 1 μg/l chl a), but returned to oligotrophic levels (e.g., chl a ⩽ 0.25 μg/l; NO3 ⩽ 0.25 μM; NH4 ⩽ 0.10 μM) within 0.5 km of shore. Phosphorus concentrations, however, were often higher offshore ⩾ 0.2 μM PO4). Sediment interstitial nutrient concentrations decreased from inshore to the offshore reef areas (e.g., ⩾ 100 μM NH4 inshore to ⩽ 50 μM NH4 offshore) and were comparable to those of some presumably pristine coastal and reef carbonate sediments. Sediment bulk N was higher nearshore and decreased steeply offshore ( ⩾ 60 μg-at N/gm sediment to ⩽ 20 μg-at N/gm sediment, respectively); bulk P concentrations (⩽ 6 μg- at P/gm sediment) varied little or exhibited the reverse pattern. Sediment N:P ratios were consistently lower offshore (1–10 vs. 20–40 nearshore). Higher offshore P concentrations are attributed to periodic upwelling along the shelf edge. In the middle keys water column nutrients and chl a concentrations were both higher than those in the upper keys, and there was less of an inshore-offshore decrease than that noted in the upper keys. Sediment nutrients were higher also, and nearshore and offshore areas did not differ. Water column and sediment nutrient concentrations and distribution patterns in the upper part of the lower keys were most similar to those measured in the upper keys. Overall, the present data do not support the contention that reef areas in the upper keys are accumulating elevated loads of land-derived nutrients via surface water flow, but does document moderately elevated nutrient and chl a levels in many developed nearshore areas. Most of the anthropogenic and natural nutrients entering the coastal waters from shore appear to be taken up by near shore algal and seagrass communities before they reach patch reef areas. Further work is needed to determine whether nutrient-enriched ground waters reach the reefs, however these would be expected to cause an enrichment of reef sediments, which was not observed.

Florida's coral reefs are imperiled: Ward, Fred, 1990 Natn. geogr., 178(1):114–132

Florida's coral reefs are imperiled: Ward, Fred, 1990 Natn. geogr., 178(1):114–132

Anomalous levels of 90Sr and 239,240Pu in Florida corals: Evidence of coastal processes

Strontium-90, a radionuclide whose primary source is fallout from nuclear weapons testing, serves as a tritium-like tracer of ocean circulation. The historical record of 90Sr activities in the annual bands of island corals have been shown by other investigators to reflect the 90Sr concentration in surface waters at those site. Strontium-90 activities measured in annual bands in Montastrea annularis from the Florida Keys are 30–120% higher than those in corresponding peak activity years (1960–1965) of a Bermuda coral ( Diploria). The Bermuda 90Sr activity record reflects the fallout source only, whereas the additional 90Sr activity in the Florida Keys is expected to reflect a coastal runoff source as well as the fallout. The coastal circulation patterns off the northern and western edge of the Florida Current further act to concentrate and prolong the exposure of the runoff 90Sr to the corals. Six measured 239,240Pu activities in the Florida coral are 30% of 239,240Pu activities in island coral records previously reported. Since Pu is expected to be scavenged by particles in coastal waters, this decrease in 239,240Pu substantiates the importance of coastal influences in the Florida 90Sr record. Strontium-90 activities measured in subannual coral bands from 1973 to 1974 reflect seasonal changes in the 90Sr concentrations in the surface layer of the coastal waters. This may reflect Loop Current intrusion events. The seasonal and long-term coral 90Sr data presented in this paper suggests that coastal 90Sr coral time series may be very useful for documenting coastal circulation patterns.

Florida Coral

Florida Coral

Geology and Origin of the Florida Keys

The Florida Keys form a crescentic chain of small limestone islands which extend from near Miami to Key West, a distance of about 150 miles. They are made of two main formations of Pleistocene age—the Key Largo Limestone and the Miami Limestone. The former, named and described by Sanford, is an elevated coral reef rock, and the latter, also described by Sanford, is an oolitic limestone in this area. The Key Largo Limestone is the surface rock of the Upper Keys, and the Miami Limestone covers the Lower Keys. A contact found at Big Pine Key shows that the oolitic limestone overlaps the Key Largo, and core borings show that the Key Largo underlies the oolitic cover for the entire area of the Lower Keys. The Key Largo, therefore, extends for the total length of the Keys. A core placed at Dry Tortugas, 70 miles west of Key West, encountered it at 30 feet below sea level. The Key Largo has a maximum thickness of over 200 feet. The fact that the Keys are located about 5 miles from the seaward edge of the Florida coral reef platform creates an interesting problem. They may be (1) remnants of an ancient outer reef similar to that found today bordering the living coral reef tract, or (2) they may have become established as a line of patch reefs in the back reef zone of a pre-existing platform which extended seaward some distance, possibly as far as the present platform. It is believed that the answer to this problem can be found through an understanding of what was happening seaward and leeward of the old reef at the time its corals were flourishing. Consequently, the composition and structure of the reef platform seaward of the Keys and the geologic history of the rocks of the Florida mainland immediately behind the Keys were studied. Information thus obtained plus observations on the composition, especially the coral content, of the Keys themselves have led the authors to believe that the Keys were formed as a line of patch reefs in a back reef area which was bordered on its seaward edge by an outer reef which has since been lowered, chiefly by erosion, and covered by more recent material.

OXYGEN BALANCE IN SOME REEF CORALS

Oxygen exchange is reported for 14 species of Florida reef corals in the dark and at different light intensities. Oxygen tension was monitored with a recording polarographic electrode. Results are given as grams of carbon fixed per square meter of coral surface per day, and compensation light intensities were given for each species. Maximum ratios of photosynthesis to respiration varied from 1.9 to 5.8. Boring, filamentous green algae living in the skeleton of Dichocoenia stokesii were not observed to change their rate of oxygen consumption from dark conditions up to 5000 footcandles of light. It is concluded that reef corals are among the most productive organisms known and that, in Florida corals, the boring green algae contribute very little indeed to this productivity. Some data are given on the light impinging on Florida reefs and the light penetrating coral skeleton. Reasons for believing boring green algae are of minor importance are given in the discussion.

A Study of the Behavior of Some Tagged South Florida Coral Reef Fishes

Several of the larger species of fishes found on the unique patch reefs of south Florida were trapped and tagged over a one-year period. Many of these were recaptured, some as many as 10 to 41 times, and almost invariably on their home reefs (point of initial capture). In repeated recaptures of the same individual we suspect trap conditioning, but even so we conclude that the species was restricted to its home reef. Transplants of small numbers of white grunts indicated a tendency to home. Tenacity of home reef occupation was also indicated by lack of displacement of tagged fishes by a severe hurricane which occurred during the study. There are indications that entrance of fishes into the traps was sea- sonally affected, with the most activity occurring in the warm months. We do not know if decreased numbers of fishes or a change in behavior, or both, accounted for this seasonality, but in at least one instance (gray angelfish) the species appeared to be relatively abundant during all sea- sons, while in another (white grunt) there appeared to be a decrease in numbers (as determined from another study conducted contempo- raneously).