Florida Coral Reef Research Articles

Population dynamics of giant barrel sponges on Florida coral reefs

The structure of coral reef benthic communities has changed significantly in recent decades and will likely continue to change with the increasing frequency and scale of disturbances. Reef-building corals and macroalgae have been regularly included in assessments of coral reef communities, however very little is known about the long-term dynamics of sponge populations. The giant barrel sponge Xestospongia muta is a dominant component of Caribbean coral reef communities, and it was previously reported that populations significantly increased in the Florida Keys over 2000–2006. Using surveys of sponges from the same permanent plots on reefs off Key Largo, Florida, USA, this study extended the investigation of the population dynamics of X. muta for 2000–2012 at three depths (15, 20, 30m). Over 12years, the density of X. muta significantly increased by a mean of 122% (range=53–336%) on Conch Reef and by a mean of 44% on Pickles Reef. Both the cover and volume of X. muta concomitantly increased at all sites and increases in both metrics were greater over 2006–2012 relative to 2000–2006 due to decreased mortality of the largest sponges in the population over time. Population growth accelerated at all sites on Conch Reef due to a significant increase in recruitment and sponge survival, and was greater at deeper relative to shallow depths; on Pickles Reef, recruitment decreased, but survival increased and population growth remained constant over time. Despite mortality due to putative pathogenesis, and in contrast to the persistent decline of reef-building corals, these results suggest that conditions on Florida coral reefs have been increasingly favorable for the growth of barrel sponge populations. Given the long lifespan of X. muta, it remains to be seen whether these results represent a persistent change with broad geographic relevance, or stochastic variation in local demographics.

Perilous proximity: Does the Janzen–Connell hypothesis explain the distribution of giant barrel sponges on a Florida coral reef?

One popular concept used to explain the high biodiversity of some ecosystems is the Janzen–Connell hypothesis, which states that the distribution of conspecifics is controlled by species-specific pathogens or predators that are attracted to adults or to their reproductive output. The distribution of the affected species would then display a distinct pattern, with survivorship increasing at greater distance from the conspecific adult (negative density dependence), leaving a vacant area around the adult where other species can survive. The giant barrel sponge, Xestospongia muta, is an abundant and long-lived sponge on Caribbean coral reefs that is actively grazed by sponge-eating fishes and is susceptible to disease. We tested the Janzen–Connell hypothesis on barrel sponges on Conch Reef, Florida, by examining their distribution as a function of size using spatial point pattern analyses. Clark and Evans tests and a series of Ripley’s K function analyses revealed no consistent distribution pattern, with most analyses resulting in a random pattern of sponge distribution. While predation by sponge-eating fishes has recently been discovered to structure sponge communities on reefs across the Caribbean, these top-down effects do not translate to spatial distributions of X. muta that support Janzen–Connell predictions.

Climate change projected effects on coastal foundation communities of the Greater Everglades using a 2060 scenario: need for a new management paradigm.

Rising sea levels and temperature will be dominant drivers of coastal Everglades' foundation communities (i.e., mangrove forests, seagrass/macroalgae, and coral reefs) by 2060 based on a climate change scenario of +1.5 °C temperature, +1.5 foot (46 cm) in sea level, ±10 % in precipitation and 490 ppm CO2. Current mangrove forest soil elevation change in South Florida ranges from 0.9 to 2.5 mm year(-1) and would have to increase twofold to fourfold in order to accommodate a 2060 sea level rise rate. No evidence is available to indicate that coastal mangroves from South Florida and the wider Caribbean can keep pace with a rapid rate of sea level rise. Thus, particles and nutrients from destabilized coastlines could be mobilized and impact benthic habitats of southern Florida. Uncertainties in regional geomorphology and coastal current changes under higher sea levels make this prediction tentative without further research. The 2060 higher temperature scenario would compromise Florida's coral reefs that are already degraded. We suggest that a new paradigm is needed for resource management under climate change that manages coastlines for resilience to marine transgression and promotes active ecosystem management. In the case of the Everglades, greater freshwater flows could maximize mangrove peat accumulation, stabilize coastlines, and limit saltwater intrusion, while specific coral species may require propagation. Further, we suggest that regional climate drivers and oceanographic processes be incorporated into Everglades and South Florida management plans, as they are likely to impact coastal ecosystems, interior freshwater wetlands and urban coastlines over the next few decades.

The Last Interglacial Stage: Definitions and marine highstand, North America and Eurasia

Delineation of the boundary between the Last Interglacial (LIG) and the last (Wisconsinan) Glacial Stage in North America represents a critical, yet unresolved issue. Subdivisions of the late Pleistocene are based on oxygen isotope, ice cover, and pollen stratigraphic data. Boundaries defined by isotope chronology hinge on complex interrelationships between δ18O in foraminifer tests, ice volumes stored on land, and coeval sea-level position. In the absence of adequate pollen-stratigraphic documentation, Pleistocene subdivision boundaries were harder to establish in North America than in Europe. Time-transgressive pollen zones revealed increased lengths of the climatically-floristically defined LIG from the European subarctic to the Mediterranean. Conflicting definitions of “Sangamon,” as representing only the last interglacial of minimum ice cover and higher temperatures or broadly defined, “sensu lato,” also incorporating early part of the Last (Wisconsinan) Glacial Stage persist in the North American literature. The exclusively interglacial age of the Sangamon Geosol, originally used in dating the Sangamonian Stage proved untenable. Designation of an “Eowisconsinan” interval corresponding to Susbtages MIS 5d-a also lacks merit. Despite climate- and vegetation-related discrepancies, pollen- and coastal deposit-based comparisons between Europe and North America during MIS 5 and the Holocene are useful in establishing the climate history of the North American Sangamonian and subsequent early Wisconsinan substages. An overarching MIS 5 cooling trend represented by scattered subarctic and high-mountain ice accumulation events followed the MIS 5e Eemian–Sangamonian temperature peak. Adoption of the general European practice that asymmetrically splits MIS 5 into a short MIS 5e interglacial and a long early Wisconsinan Glacial (MIS 5d-a) interval is preferred in North America as well. Subdivisions in the normalized δ18O curve that serve as the chronological framework and the wealth of European pollen data support this approach. While multiple pre-Sangamon Pleistocene marine-paralic intervals do occur on the NW Gulf coast, all pre-Sangamon Pleistocene marine and brackish-inshore deposits had been removed by erosion in the NE coastal plain. A single inshore-nearshore marine sediment and highstand interval is well-documented in this region. The LIG highstand sequence correlates with varied Eemian marine and paralic MIS 5e deposits encountered along northern and western European, Siberian, and additional shores. Apart from reliably dated Sangamonian S Florida coral reefs, identification and dating of LIG highstand deposits remain highly problematical in SE Atlantic shore terraces.

Indicators for assessing the ecological dynamics and sustainability of southern Florida's coral reef and coastal fisheries

Commercial and recreational fisheries target hundreds of fish and shellfish species across the seascape of southern Florida including inshore coastal bays, the flats of barrier islands, coral reefs and offshore pelagic waters. The ecological dynamics and economic sustainability of these valuable fishery resources are key conservation concerns. This study examined two ecological indicators of fishing impacts on exploited populations: (1) the more traditional metric catch per unit of fishing effort (CPUE); and (2) the non-traditional metric average length (L¯) in the exploited life stage of a population. We show that both indicators were closely related to stock productivity via fisheries population dynamics theory, and that either indicator could be used to estimate fishing mortality rates (F). Data requirements are much less stringent for estimating F from the L¯ indicator than CPUE, making it more practical for data-poor situations common to tropical marine fisheries. Using indicator-based estimates of Fˆ within a population dynamic modeling framework enabled an evaluation of fishing impacts on sustainability at both the species and community levels, an important step toward ecosystem-based fisheries assessment and management. A comparison of these approaches applied to the assessment of southern Florida coral reef fisheries suggested that fishing has fundamentally altered the ecological structure of the fish community by depleting the biomass of higher-trophic level carnivores to the extent that the stocks are unsustainable.

Approaching a functional measure of vulnerability in marine ecosystems

Ecosystem vulnerability is a major concern for management purposes, especially when directed toward conservation and sustainable exploitation. We estimate the relative vulnerability of selected marine-ecosystems in the Gulf of Mexico through simulation experiments based on trophic models. The same perturbation pattern was applied to different functional groups at different trophic levels. Perturbation consisted of increasing biomass extraction for a single group up to 98% at a constant rate over 50 years. The ratio Ascendency to Capacity of Development, A/C, was estimated as a measure of ecosystem order. The maximum negative difference respect to the initial A/C represents the gain of entropy. The slope of the relationship between entropy gained and the trophic level provides an estimate of the relative vulnerability of the ecosystem. This was applied to five ecosystems in the Gulf of Mexico: Florida coral reef; Mexican coastal lagoon, Terminos Lagoon; and three continental shelves, the northern Gulf of Mexico, USA; Yucatan and the Campeche Sound, Mexico. The pattern of vulnerability among ecosystems is related to ecosystem complexity. The coral reef exhibited a lower slope, corresponding to higher vulnerability, which is related to higher connectivity, production efficiency, and net ecosystem production. Increasingly higher slopes, corresponding to lower vulnerability, followed a gradient from the coral reef to the continental shelves to the least vulnerable system, the coastal lagoon. Middle trophic levels contribute to higher vulnerability. This interpretation is supported by the concept of energy flows within trophic networks. The relevance of these findings for management is discussed.

Percent recent mortality (PRM) of stony corals as an ecological indicator of coral reef condition

The reef communities of the Florida coral reef tract play a major role in supporting the regional economy but are threatened by increased exploitation and environmental factors. Coral reef ecosystem services are vital to the economy of SE Florida where revenue and jobs depend on the status of reef resources. Here, we used an extensive, reef monitoring database collected by the Florida Reef Resilience (FRRP, 2003–2011) and the Atlantic and Gulf Rapid Reef Assessment (AGRRA, 1997–2011) programs to evaluate percent recent mortality (PRM) as a robust ecological indicator of coral colony and coral reef status. PRM, the proportion of a coral colony that has experienced recent tissue mortality so that corallite structures in the non-living parts of the coral are still intact and identifiable to species, can be attributed to disturbances taking place within days to a few months preceding the surveys.Based on data from >50,000 colonies from 11 coral species and nearly 1400 sites, we propose a benchmark level of <1% PRM and <5% prevalence of partial mortality for Florida reefs during periods of background, low-stress environmental conditions. PRM levels >1.0% and prevalence levels >5% can be used as early warning indicators of degrading conditions. Average PRM values >2% are indicative of increasingly stressful conditions as those experienced during temperature anomalies and major hurricanes. Finally, PRM values considerably >2% are reflective of significantly stressful conditions and warning signals of potential major coral mortality as evidenced by mean PRM levels of >10% recorded in Florida as a consequence of the 2010 extreme cold-water event. PRM and prevalence values from Florida reefs compared favorably with those recorded in the Caribbean and the Mesoamerican region where a benchmark of 2% for background levels of PRM under low-level, chronic stress was proposed. The status of this indicator can be easily communicated to stakeholders and will benefit managers by providing: (1) a baseline to assess the status of coral populations; and (2) early-warning indicators of unfavorable conditions that may trigger management actions such as temporary closures or the establishment of more permanent protection such as MPAs.

Recreational diving impacts and the use of pre-dive briefings as a management strategy on Florida coral reefs

Ecotourism often is promoted as an ecologically sustainable activity, but some ecotourism activities negative- ly impact coastal ecosystems. Impacts of intensive diving tourism on coral reefs remain poorly understood, especially in the Florida Keys. We determined patterns of recreational dive frequency, diver behaviour, and coral damage on reefs near Key Largo, and assessed how pre-dive briefings and other factors affect these damage rates. Recreational divers contacted live stony corals ~ 18 times per scuba dive; most contacts deposited sediment onto corals, but also caused abrasion to coral tissues and fracture of coral skeletons. Divers who received pre-dive ecological briefings caused significantly less coral damage than those who did not, and divers with cameras and/or gloves caused the most damage. The proportion of damaged corals increased significantly with the estimated rate of recreational diving on each reef, and the percent cover of live corals decreased. We conclude that current rates of recreational diving in Key Largo are unsustainable, resulting in damage to >80 % of coral colo- nies and reduction of live coral cover to <11 % at heavily- dived sites. We recommend that dive tour operators admin- ister pre-dive ecological briefings to all recreational divers, provide extra briefings to camera and glove users, and employ underwater dive guides who intervene when divers inadvertently damage live stony corals. This study provides a scientific basis to support management of intensive eco- tourism on Florida coral reefs.

Multispecies survey design for assessing reef-fish stocks, spatially explicit management performance, and ecosystem condition

Principles of statistical sampling design were used to guide refinement of a 30-year multispecies fishery-independent diver visual survey of population abundance and size structure of more than 250 exploited and non-target fishes in the Florida coral reef ecosystem. Reef habitat features and no-take marine reserves (NTMRs) were used to partition the 885 km 2 sampling domain into sub-areas (or strata) to control the variation of fish density. For the period 1999–2008, survey precision of population density and abundance (CV, coefficient of variation, ratio of standard error to mean) ranged from 7% to 20% for the majority of 13 primary exploited species in the Florida Keys and Dry Tortugas regions. Population sustainability metrics like species average length in the exploited life stage were comparable between our fishery-independent survey and fishery-dependent catch-sampling. The survey design also performed well for non-target fishes, yielding CVs between 6% and 15% for population density for the majority of 36 species. Sampling efficiency was improved over time via an iterative learning process by which past survey data was used to refine the stratification and allocation schemes of future surveys. We show how survey data are used to support multispecies stock assessments, evaluate the effectiveness of NTMRs, and assess ecosystem condition for the reef fish community.

Fragments or propagules? Reproductive tradeoffs among Callyspongia spp. from Florida coral reefs

Fragmentation and propagule formation are alternative reproductive strategies found in both plants and animals, with the latter generally providing greater dispersal capability. When both strategies occur, life history theory predicts that resources should be divided between the two. On coral reefs, both strategies are exhibited by branching corals and sponges, which are broken-up after storm events and rapidly recolonize. In this study, we compared two congeneric Caribbean reef sponges, Callyspongia armigera, which is branched and easily fragmented, and C. vaginalis, which is not, to test whether there is a tradeoff in growth and propagule formation for C. armigera relative to C. vaginalis. Both species were equally abundant on coral reefs off Key Largo, Florida (10.1 3.7 vs 11.9 3.0 per 100 m 2 , respectively), suggesting that they are equally successful relative to two other non-fragmenting congeneric species (C. fallax and C. plicifera) that are much less common. Th e number of substratum attachment points per sponge was signifi cantly higher for C. armigera compared to C. vaginalis (2.31 1.47 vs 1.03 0.18 sponge –1 ), providing further evidence of the reliance of C. armigera on fragmentation, and of C. vaginalis on recruitment from larval settlement and subsequent growth. Growth rates in predator-exclusion experiments were ~4-fold higher for C. armigera compared to C. vaginalis (0.36 0.31 vs 0.08 0.11 % initial mass day –1 ), but C. armigera produced ~13-fold fewer propagules than C. vaginalis (0.04 0.22 vs 0.53 1.08 % tissue area). Our results support a tradeoff between growth and propagule output for C. armigera relative to C. vaginalis, suggesting that these closely related sponge species took diff erent evolutionary trajectories in reconciling their resource constraints.

Importance and Status of Florida Coral Reefs: Questions and Answers

SL-305, a 5-page illustrated fact sheet by Cory J. Krediet, Kim Ritchie, and Max Teplitski, addresses some questions regarding coral reef biology, coral reef health, and the ecological and economic benefits coral reefs provide. Includes references. Published by the UF Department of Soil and Water Sciences, August 2009.

Relationship of Reef Fish Assemblages and Topographic Complexity on Southeastern Florida Coral Reef Habitats

Reef fish assemblage relationships with in situ and lidar topographic measurements across the seascape were analyzed to evaluate the possibility of using lidar metrics as a proxy for prediction models. In situ topographic complexity (i.e., linear rugosity) was measured from 346 point-count fish surveys spanning the reef seascape. Lidar topographic measurements (i.e., surface rugosity, elevation, and volume) were obtained from a high-resolution lidar bathymetric dataset of each survey's footprint. The survey sites were characterized by an independently derived benthic habitat map. Reef fish abundance and species richness appeared to increase with increasing topographic complexity. Although significant, the relationship was weak. Habitat characterization showed that these relationships changed across the seascape. The relationship between topographic complexity and species richness was more pronounced in shallow habitats, whereas, topographic complexity related more closely to abundance in offshore habitats. In situ rugosity measurement yielded the best explanation of fish assemblage structure parameters, but the weaker lidar metric correlations followed similar trends. Accordingly, lidar-measured topographic complexity may be a useful metric for reef fish distributional models. Such predictive models could have many scientific and management applications including: estimating fish stocks, viewing data trends across the seascape, and designing marine protected areas. However, better understanding of the appropriate spatial scale, measurement scale, and fish operational scale is needed, as well as more research on the dynamics of how reef fishes relate to topographic complexity and other ecological factors influencing distributions across the seascape.

Allowing macroalgae growth forms to emerge: Use of an agent-based model to understand the growth and spread of macroalgae in Florida coral reefs, with emphasis on Halimeda tuna

The growth patterns of macroalgae in three-dimensional space can provide important information regarding the environments in which they live, and insights into changes that may occur when those environments change due to anthropogenic and/or natural causes. To decipher these patterns and their attendant mechanisms and influencing factors, a spatially explicit model has been developed. The model SPREAD (SPatially-explicit Reef Algae Dynamics), which incorporates the key morphogenetic characteristics of clonality and morphological plasticity, is used to investigate the influences of light, temperature, nutrients and disturbance on the growth and spatial occupancy of dominant macroalgae in the Florida Reef Tract. The model species, Halimeda and Dictyota spp., are modular organisms, with an “individual” being made up of repeating structures. These species can also propagate asexually through clonal fragmentation. These traits lead to potentially indefinite growth and plastic morphology that can respond to environmental conditions in various ways. The growth of an individual is modeled as the iteration of discrete macroalgal modules whose dynamics are affected by the light, temperature, and nutrient regimes. Fragmentation is included as a source of asexual reproduction and/or mortality. Model outputs are the same metrics that are obtained in the field, thus allowing for easy comparison. The performance of SPREAD was tested through sensitivity analysis and comparison with independent field data from four study sites in the Florida Reef Tract. Halimeda tuna was selected for initial model comparisons because the relatively untangled growth form permits detailed characterization in the field. Differences in the growth patterns of H. tuna were observed among these reefs. SPREAD was able to closely reproduce these variations, and indicate the potential importance of light and nutrient variations in producing these patterns.

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.

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.

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

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.