Distribution of viral abundance in the reef environment of Key Largo, Florida.

The distribution of viral and microbial abundance in the Key Largo, Fla., reef environment was measured. Viral abundance was measured by transmission electron microscope direct counts and plaque titer on specific bacterial hosts in water and sediment samples from Florida Bay (Blackwater Sound) and along a transect from Key Largo to the outer edge of the reef tract in Key Largo Sanctuary. Water column viral direct counts were highest in Blackwater Sound of Florida Bay (1.2 x 10(7) viruses per ml), decreased to the shelf break (1.7 x 10(6) viruses per ml), and were inversely correlated with salinity (r = -0.97). Viral direct counts in sediment samples ranged from 1.35 x 10(8) to 5.3 x 10(8)/cm(3) of sediment and averaged nearly 2 orders of magnitude greater than counts in the water column. Viral direct counts (both sediment and water column measurements) exceeded plaque titers on marine bacterial hosts (Vibrio natriegens and others) by 7 to 8 orders of magnitude. Water column viral abundance did not correlate with bacterial direct counts or chlorophyll a measurements, and sediment viral parameters did not correlate with water column microbial, viral, or salinity data. Coliphage, which are indicators of fecal pollution, were detected in two water column samples and most sediment samples, yet their concentrations were relatively low (<2 to 15/liter for water column samples, and <2 to 108/cm(3) of sediment). Our findings indicate that viruses are abundant in the Key Largo environment, particularly on the Florida Bay side of Key Largo, and that processes governing their distribution in the water column (i.e., salinity and freshwater input) are independent of those governing their distribution in the sediment environment.     

Growth of Pleistocene massive corals in south Florida: low skeletal extension-rates and possible ENSO,decadal, and multi-decadal cyclicities

Skeletal extension-rates and their variability are significantly lower in Pleistocene massive reef-building corals (Montastraea annularis group) in south Florida as compared with modern corals of the same taxa in the same study area. We analyzed 1,429 annual increments in 18 cores of Montastraea colonies from Windley Key and the Key Largo Waterway in the late Pleistocene Key Largo Limestone, which was deposited during marine isotope stage 5e (ca. 125 kyrs BP). The average extension-rate is 5.2 mm/year, which is about half the value known for modern Montastraea in shallow water reef environments. With an average standard deviation (SD) of 1.01, the variability of extension-rates is at the lower range limit of modern Montastraea in south Florida (SD = 1–3.6). Due to the higher sea level, the Pleistocene Key Largo patch reef trend was located on a large carbonate platform. Unlike today, the island chain of the Florida Keys, which function as a shelter for the Florida Reef Tract from inimical bank water, was not in existence. Corals probably grew under higher-than-present sea surface temperatures, which resulted in comparably low skeletal extension-rates. The detection of 3–7 year, decadal, and multi-decadal cyclicities in extension-rate time series suggests that the major modes of modern tropical climate variability such as the El Niño-Southern Oscillation (ENSO) and possibly the Atlantic Multidecadal Oscillation (AMO) were in effect during the last interglacial.     

Middle Ordovician reefs of Norway

The Middle Ordovician reefs of Norway were the first to develop in the western part of the Balto-scandian epicontinental sea and are the earliest coral-stromatoporoid reefs so far reported in Europe. Small patch reefs in the Steinvika Limestone, Langesund-Skien district, consist mainly of algae, echinoderms, corals and stromatoporoids. Bryozoans, molluscs, arthropods and brachiopods are also present. The reefs developed on pelmatozoan-rich substrates and are organically zoned, consisting of a pioneer community of stemmed echinoderms and sheet algae, a high-diversity intermediate community dominated by fasciculate corals and a low diversity climax community of massive corals and stromatoporoids. These communities are interpreted as the seral stages of an autogenic ecological succession. Small patch reefs are also present in the laterally equivalent Mjøsa Limestone, Toten and Nes-Hamar districts. These are organically very similar to those in the Steinvika Limestone and developed in an identical way. A large complex, consisting of several reefs, is also present in the Mjøsa Limestone. Unlike the reefs elsewhere, which developed within shallow inshore areas, this complex developed at the outer edge of the inshore shelf. The outstanding feature of the complex is the main reef forming the offshore limit which is totally dominated by stromatoporoids and lacks a sequential development. This is due to the influence of the harsher environment at the shelf edge.     

Significance of <Emphasis Type="Italic">Halimeda</Emphasis> bioherms to the global carbonate budget based on a geological sediment budget for the Northern Great Barrier Reef,Australia

Since the correlation between carbon dioxide (CO₂) levels and global temperatures was established in the ice core records, quantifying the components of the global carbon cycle has become a priority with a view to constraining models of the climate system. The marine carbonate budget is still not adequately constrained and the quantitative significance of the calcareous green alga Halimeda still remains particularly poorly understood. Previously, it has been suggested that Halimeda bioherms on the shelf of the Great Barrier Reef may contain a volume of carbonate equal to or greater than that contained within the shelf edge coral reefs. This study uses published datasets to test this hypothesis in the Northern Great Barrier Reef (NGBR) province. It is estimated that Halimeda bioherms on the outer shelf of the NGBR contain at least as much (and up to four times more) CaCO₃ sediment as the adjacent ribbon reef facies. Globally, if these findings are even only partially applicable, the contribution of shallow water carbonate sediments to the global carbon budget based on coral reefs alone is currently substantially underestimated.     

Mid-Cretaceous shelf carbonates: The Mfamosing Limestone,Lower Benue Trough (Nigeria)

This study focuses on the microfacies and diagenetic development of the mid-Cretaceous Mfamosing Limestone, a carbonate body which was deposited during marine incursions into the Calabar Flank in the eastern Niger delta hinge zone of the Lower Benue Trough. Microfacies and diagenetic criteria indicate that the carbonates are products of one Albian transgressive cycle only with two periods of relatively rapid crustal deepening. The data strongly supports the conclusion that the carbonates were deposited in a shallow shelf characterized by strong lateral facies variations. High energy submarine bar carbonate sands, patch reefs and algal boundstones are well represented. During the deposition of the shelf carbonates an increasing detrital terrestrial input is documented by an increasing amount of quartz, feldspar and clay minerals. Isopachous rim cements indicate a marine phreatic environment. Locally short-time supratidal conditions are documented by granular meniscus cements.     

Late Viséan (MFZ14) foraminifers and algae from the Kirchbach Limestone (Carnic Alps,Austria) and geological implications

The Kirchbach Limestone occurs in the middle part of the early Viséan to Bashkirian Hochwipfel Formation, which was deposited in a flysch basin that formed during an extensional rifting phase in the foreland of the Noric Terrane, was filled with deep-marine synorogenic sediments and closed during the Bashkirian. The Noric Terrane split off from Gondwana and drifted towards the north, closing the flysch basin, which was part of the Paleo-Tethys. The Kirchbach Limestone is composed of bioclastic mudstone and carbonate conglomerate. Microfacies of the limestone clasts include wackestone, packstone, grainstone, and rudstone with diverse fossil assemblages. Bindstone clasts are derived from very shallow, restricted environments. Other clasts are bioclastic mudstone derived from deeper settings. All the foraminifers and algae identified correspond to the upper MFZ14 biozone, after the appearance of Bradyina; in contrast, the markers of the uppermost MFZ14 (Asteroarchaediscus, Loeblichia paraammonoides, and Warnantella) and those of MFZ15 (Janischewskina, Climacammina, and Biseriella) are totally absent. The Kirchbach markers are Cribrospira mikhailovi, Bradyina cf. flosculus, Howchinia bradyana, and Eostaffella parastruvei. Revised local taxa are Mstinia, M. minima n. comb., Consobrinellopsis n. gen., and C. ex gr. consobrina n. comb. The Kirchbach Limestone is derived from a shelf area displaying various shallow-water environments from which the clasts were transported into deeper-marine environments as sediment gravity flows. Limestone clasts of the Kirchbach Limestone indicate the presence of a shallow carbonate shelf along the northern margin of the Hochwipfel flysch basin. The late Asbian (MFZ14) limestone clasts derived from this carbonate shelf were probably subaerially exposed prior to their reworking and redeposition within the flysch sediments, which are late Brigantian (MFZ15) in age. Fossiliferous carbonate shelf sediments of Viséan–Serpukhovian (Namurian) age in the Veitsch Nappe of the eastern Graywacke Zone may be remnants of this shelf. Similar trilobite faunas of Nötsch and Veitsch indicate that they were originally adjacent and probably connected to this shelf north of the flysch basin. These data confirm that the Carnic Alps were located in the Viséan Mediterranean subprovince.     

Occurrence of fecal indicator bacteria in surface waters and the subsurface aquifer in Key Largo, Florida.

Sewage waste disposal facilities in the Florida Keys include septic tanks and individual package plants in place of municipal collection facilities in most locations. In Key Largo, both facilities discharge into the extremely porous Key Largo limestone. To determine whether there was potential contamination of the subsurface aquifer and nearby coastal surface waters by such waste disposal practices, we examined the presence of microbial indicators commonly found in sewage (fecal coliforms, Clostridium perfringens, and enterococci) and aquatic microbial parameters (viral direct counts, bacterial direct counts, chlorophyll a, and marine vibriophage) in injection well effluent, monitoring wells that followed a transect from onshore to offshore, and surface waters above these wells in two separate locations in Key Largo in August 1993 and March 1994. Effluent and waters from onshore shallow monitoring wells (1.8- to 3.7-m depth) contained two or all three of the fecal indicators in all three samples taken, whereas deeper wells (10.7- to 12.2-m depth) at these same sites contained few or none. The presence of fecal indicators was found in two of five nearshore wells (i.e., those that were < or = 1.8 miles [< or = 2.9 km] from shore), whereas offshore wells (> or = 2.1 to 5.7 miles [< or = 3.4 to 9.2 km] from shore) showed little sign of contamination. Indicators were also found in surface waters in a canal in Key Largo and in offshore surface waters in March but not in August. Collectively, these results suggest that fecal contamination of the shallow onshore aquifer, parts of the nearshore aquifer, and certain surface waters has occurred.(ABSTRACT TRUNCATED AT 250 WORDS)     

Carbonate Production by Benthic Communities on Shallow Coralgal Reefs of Abrolhos Bank,Brazil

The abundance of reef builders, non-builders and the calcium carbonate produced by communities established in Calcification Accretion Units (CAUs) were determined in three Abrolhos Bank shallow reefs during the period from 2012 to 2014. In addition, the seawater temperature, the irradiance, and the amount and composition of the sediments were determined. The inner and outer reef arcs were compared. CAUs located on the inner reef shelf were under the influence of terrigenous sediments. On the outer reefs, the sediments were composed primarily of marine biogenic carbonates. The mean carbonate production in shallow reefs of Abrolhos was 579 ± 98 g m^-2 y^-1. The builder community was dominated by crustose coralline algae, while the non-builder community was dominated by turf. A marine heat wave was detected during the summer of 2013–2014, and the number of consecutive days with a temperature above or below the summer mean was positively correlated with the turf cover increase. The mean carbonate production of the shallow reefs of Abrolhos Bank was greater than the estimated carbonate production measured for artificial structures on several other shallow reefs of the world. The calcimass was higher than the non-calcareous mass, suggesting that the Abrolhos reefs are still in a positive carbonate production balance. Given that marine heat waves produce an increase of turf cover on the shallow reefs of the Abrolhos, a decrease in the cover represented by reef builders and shifting carbonate production are expected in the near future.     

Seepage rate variability in Florida Bay driven by Atlantic tidal height

Atlantic tidal fluctuations drive pressure head variations in shallow offshore wells drilled into the limestone subsurface on both the Florida Bay and Atlantic sides of Key Largo, Florida, USA. We tested the hypothesis that these pressure head variations influence groundwater flow and that flux rate variability is associated with tidal variability. We used an automated Rn monitor to make continuous measurements of ²²²Rn, a natural tracer of groundwater discharge, in Florida Bay waters. We also deployed three types of seepage meters, including an automated heat pulse meter to collect a continuous record of seepage from the sediments. Drum type seepage meters inserted into soft sediments and fiberglass meters cemented to the rocky bay floor were utilized with pre-filled 4-l bag collectors, and monitored on an hourly basis. Maximum Rn inventories in Florida Bay waters were associated with high tide on the Atlantic side of the island. Modeling of the Rn variation indicated variable groundwater discharge rates with maximum flux occurring at high Atlantic tide. Seepage meter results in Florida Bay were consistent with ²²²Rn modeling. Florida Bay seepage meter rates showed positive correlation with Atlantic tide, meter 1, r?=?0.63, n?=?12, p?<?0.025 and meter 2, r?=?0.67, n?=?12, p?<?0.025. A seepage meter offshore of the Atlantic side of Key Largo exhibited rates that were inversely correlated with Atlantic tide (r?=?0.87, n?=?9, p?<?0.005) showing negative rates when the tide was high, and positive rates when the tide was low. Overall, our results are consistent with the hypothesis of Reich et al. (2002), that pressure head variations driven by Atlantic tide influence groundwater seepage rate variability in Florida Bay off Key Largo. Effectively, as proposed by Reich et al. (2002), Key Largo functions as a semi-permeable dam separating Florida Bay and the Atlantic Ocean.     

Fitness consequences of habitat variability,trophic position,and energy allocation across the depth distribution of a coral-reef fish

Environmental clines such as latitude and depth that limit species’ distributions may be associated with gradients in habitat suitability that can affect the fitness of an organism. With the global loss of shallow-water photosynthetic coral reefs, mesophotic coral ecosystems (~30–150 m) may be buffered from some environmental stressors, thereby serving as refuges for a range of organisms including mobile obligate reef dwellers. Yet habitat suitability may be diminished at the depth boundary of photosynthetic coral reefs. We assessed the suitability of coral-reef habitats across the majority of the depth distribution of a common demersal reef fish (Stegastes partitus) ranging from shallow shelf (SS, <10 m) and deep shelf (DS, 20–30 m) habitats in the Florida Keys to mesophotic depths (MP, 60–70 m) at Pulley Ridge on the west Florida Shelf. Diet, behavior, and potential energetic trade-offs differed across study sites, but did not always have a monotonic relationship with depth, suggesting that some drivers of habitat suitability are decoupled from depth and may be linked with geographic location or the local environment. Feeding and diet composition differed among depths with the highest consumption of annelids, lowest ingestion of appendicularians, and the lowest gut fullness in DS habitats where predator densities were highest and fish exhibited risk-averse behavior that may restrict foraging. Fish in MP environments had a broader diet niche, higher trophic position, and higher muscle C:N ratios compared to shallower environments. High C:N ratios suggest increased tissue lipid content in fish in MP habitats that coincided with higher investment in reproduction based on gonado-somatic index. These results suggest that peripheral MP reefs are suitable habitats for demersal reef fish and may be important refuges for organisms common on declining shallow coral reefs.

     

Papers of interest in other journals

Abstract

Nonlithified, dome‐shaped deep‐water stromatolite analogs grow at a depth of 36 m and a light intensity of 100 Es^?1m^?2 off French Reef in the Key Largo National Marine Sanctuary. The only other modern deep‐water stromatolite analogs known to occur in the world are in antarctic freshwater lakes and these structures exist at light levels ≤ 1% of surface values (<1.0 Es^?1m^?2). Even though the two habitats are very dissimilar, they share the commonality of nonlithified, laminated stromatolite analogs growing in low‐light environments. The Key Largo formations exist on a carbonate sand substrate and have a low chlorophyll a:biomass ratio in comparison to the antarctic stromatolite analogs. The dominant cyanobacteria in the majority of antarctic habitats and in the Key Largo habitat are members of the genus Phormidium. The cyanobacterium in the Key Largo stromatolite analogs has been tentatively identified as Phormidium nov. sp. Reasons for the ability of the Key Largo structures to exist in areas of potential metazoan bioturbation present a biological enigma that remains to be explained.     

Fine‐scale structure among mesophotic populations of the great star coral Montastraea cavernosa revealed by SNP genotyping

Mesophotic reefs (30‐150 m) have been proposed as potential refugia that facilitate the recovery of degraded shallow reefs following acute disturbances such as coral bleaching and disease. However, because of the technical difficulty of collecting samples, the connectivity of adjacent mesophotic reefs is relatively unknown compared with shallower counterparts. We used genotyping by sequencing to assess fine‐scale genetic structure of Montastraea cavernosa at two sites at Pulley Ridge, a mesophotic coral reef ecosystem in the Gulf of Mexico, and downstream sites along the Florida Reef Tract. We found differentiation between reefs at Pulley Ridge (~68 m) and corals at downstream upper mesophotic depths in the Dry Tortugas (28–36 m) and shallow reefs in the northern Florida Keys (Key Biscayne, ~5 m). The spatial endpoints of our study were distinct, with the Dry Tortugas as a genetic intermediate. Most striking were differences in population structure among northern and southern sites at Pulley Ridge that were separated by just 12km. Unique patterns of clonality and outlier loci allele frequency support these sites as different populations and suggest that the long‐distance horizontal connectivity typical of shallow‐water corals may not be typical for mesophotic systems in Florida and the Gulf of Mexico. We hypothesize that this may be due to the spawning of buoyant gametes, which commits propagules to the surface, resulting in greater dispersal and lower connectivity than typically found between nearby shallow sites. Differences in population structure over small spatial scales suggest that demographic constraints and/or environmental disturbances may be more variable in space and time on mesophotic reefs compared with their shallow‐water counterparts.     

Paleocurrent and paleoslope — A case study

The relationship between the paleocurrent pattern and the paleoslope in several continental and marine environments has been reviewed. This relationship in shelf sediment is not adequately established, and appears to be more complex than is now understood. The paleocurrent pattern of the Mississippian Loyalhanna—Trough Creek Limestone (a shelf calcarenite) is presented here as a case study. The study shows that the sediment dispersal system and the current pattern are independent of the paleoslope, and that the vector orientation is polymodal. It is, however, argued that before a precise paleocurrent model for shelf carbonate is formulated, more investigation in recent and ancient rocks is necessary.     

Controls on reef development and the terrigenous-carbonate interface on a shallow shelf,Nicaragua (Central America)

Marine geology and physical oceanographic data collected during two field projects (∼4 months) on the Caribbean shelf of Nicaragua indicate a surprising dominance of carbonate deposition and reef growth on a shelf that is receiving an abnormally large volume of terrigenous sediments. High rainfall rates (∼400–500 cm/year), coupled with a warm tropical climate, encourage rapid denudation of the country’s central volcanic highland and transport of large volumes of terrigenous sediment and fresh water to the coast. Estimates suggest that three times more fresh water and fifteen times more sediment are introduced per unit length of coastline than on the east coast of the United States. Distribution of the terrigenous facies, development of carbonate sediment suites, and the location and quality of viable reefs are strongly controlled by the dynamic interaction near the coasts of highly turbid fresh to brackish water effluents from thirteen rivers with clear marine waters of the shelf. Oceanic water from the central Caribbean drift current intersects the shelf and moves slowely in a dominant northwest direction toward the Yucatan Channel. A sluggish secondary gyre moves to the south toward Costa Rica. In contrast, the turbid coastal water is deflected to the south in response to density gradients, surface water slopes, and momentum supplied by the steady northeast trade winds. A distinct two-layered flow is commonly present in the sediment-rich coastal boundary zone, which is typically 10–20 km wide. The low-salinity upper layer is frictionally uncoupled from the ambient shelf water and therefore can expand out of the normally coherent coastal boundary zone during periods of abnormal flooding or times when instability is introduced into the northeast trades. Reef distribution, abruptness of the terrigenous-carbonate interface, and general shelf morphology reflect the long-term dynamic structure of the shelf waters. A smooth-bottomed ramp of siliciclastic sands to silts and clays mantles the inner shelf floor in a linear belt paralleling the coast. This belt generally corresponds to the western flank of the coastal boundary zone. Occurrence of reefs is generally confined to areas outside this zone. Terrigenous clays and silts of the inner shelf are abruptly (<20 km from the coast) replaced byHalimeda-rich sediment of the middle and outer shelf. Within the carbonate facies belt, reef complexes thrive as small, isolated masses; large, reef-capped platforms; reef fringes around islands; and shelfedge structures with vertical relief that can exceed 25 m. In general, the frequency and proliferation of reefs increase away from the turbid coastal boundary layer and toward the cooler and saltier water that upwells at the shelf margin.     

A bryozoan buildup from the Lower Carboniferous of North Wales

A carbonate buildup dominated by trepostome Bryozoa is described from Dinantian (Asbian) strata near Llandudno in North Wales. A three-phase ecological succession is recognised within the buildup: (i) a basal diverse community with fenestrate, ramose, encrusting trepostome and cystoporate bryozoans in a mud rich wackestone; (ii) a bulk facies, dominated by encrusting and foliaceous, trepostome bryozoans in a fine packstone, and (iii) a thin capping phase, dominated by unilaminar, encrusting trepostome bryozoans in a slightly coarser lithology, including skeletal debris derived from the mound top and possible flanking beds. The buildup probably had topographic relief and developed in a shallow marine environment. The internal tripartite zonation reflects the growth of the structure into a shallower, higher energy regime, with the capping beds being deposited just below wave base. The buildup developed to the north of St. George's Land, on a carbonate shelf edge bordering the deeper basinal facies of the Irish Sea Basin. Dinantian, Asbian, buildup, trepostome Bryozoa, Foraminifera, corals, calcareous algae, Carboniferous, North Wales .     

Patch-reef morphology as a proxy for Holocene sea-level variability,Northern Florida Keys,USA

A portion of the northern Florida Keys reef tract was mapped with the NASA Experimental Advanced Airborne Research Lidar (EAARL) and the morphology of patch reefs was related to variations in Holocene sea level. Following creation of a lidar digital elevation model (DEM), geospatial analyses delineated morphologic attributes of 1,034 patch reefs (reef depth, basal area, height, volume, and topographic complexity). Morphometric analysis revealed two morphologically different populations of patch reefs associated with two distinct depth intervals above and below a water depth of 7.7 m. Compared to shallow reefs, the deep reefs were smaller in area and volume and showed no trend in topographic complexity relative to water depth. Shallow reefs were more variable in area and volume and became flatter and less topographically complex with decreasing water depth. The knoll-like morphology of deep reefs was interpreted as consistent with steady and relatively rapidly rising early Holocene sea level that restricted the lateral growth of reefs. The morphology of shallow “pancake-shaped” reefs at the highest platform elevations was interpreted as consistent with fluctuating sea level during the late Holocene. Although the ultimate cause for the morphometric depth trends remains open to interpretation, these interpretations are compatible with a recent eustatic sea-level curve that hindcasts fluctuating late Holocene sea level. Thus it is suggested that the morphologic differences represent two stages of reef accretion that occurred during different sea-level conditions.     

Survey of raccoons on Key Largo, Florida, USA, for Baylisascaris procyonis

Numbers of the endangered Key Largo woodrat (KLWR; Neotoma floridana smalli) have been declining for at least 25 yr. The raccoon (Procyon lotor) roundworm, Baylisascaris procyonis, has been found to have an adverse effect on the survival of Alleghany woodrats (N. magister). High densities of raccoons can exacerbate this problem by increasing the amount of feces containing viable eggs of B. procyonis available to woodrats. In 2002, 64 fecal samples were collected and examined for eggs of B. procyonis from >32 raccoons within the KLWR's known range on Key Largo, Florida, USA. All samples were negative for eggs of B. procyonis. Raccoon density in this area was approximately 0.62 raccoons/ha. Despite this high density of raccoons, B. procyonis does not appear to be a threat to the KLWR population.     

Comparison of deep-water coral reefs and lithoherms off southeastern USA

Two types of deep-water coral bioherms occur off the coast of southeastern United States: Oculina and Lophelia/Enallopsammia. The deep-water Oculina bioherms form an extensive reef system at depths of 70–100 m along the shelf edge off central eastern Florida. These reefs are comprised of numerous pinnacles and ridges, 3–35 m in height. Each pinnacle is a bank of unconsolidated sediment and coral debris that is capped on the slopes and crest with living and dead colonies of Oculina varicosa, the ivory tree coral. In comparison, deep-water reefs of Lophelia pertusa and Enallopsammia profunda corals occur at depths of 500–850 m (maximum 150-m relief) along the base of the Florida-Hatteras slope in the Straits of Florida. On the western edge of the Blake Plateau off South Carolina and Georgia, 54-m high banks of Enallopsammia and Lophelia occur at depths of 490–550 m, whereas on the eastern edge of the plateau the reefs form structures 146 m in height and at depths of 640–869 m. The geomorphology and functional structure of both the Oculina and Lophelia reefs are similar. North of Little Bahama Bank, at depths of 1000–1300 m, a region of bioherms is dominated by the coral Solenosmilia sp.; Lophelia is reportedly absent. This paper summarizes 25 years of submersible studies on the deep-water Oculina reefs, describes submersible reconnaissance of deep-water Lophelia reefs off the southeastern United States, and contrasts these types of bioherms with the deep-water lithoherms in the Straits of Florida west of the Bahamas.     

Abundance and distribution of black band disease on coral reefs in the northern Florida keys

The abundance and distribution of black band disease on the reef building coralsMontastraea annularis, M. cavernosa, Colpophyllia natans, Diploria clivosa, D. labyrinthiformis andD. strigosa were determined at Algae Reef, Grecian Rocks and Key Largo Dry Rocks in the Key Largo National Marine Sanctuary, Florida, USA. During July and November of 1992 and July 1993, surveys of permanently marked sites covering 9424m² of reef tract showed that up to 0.72% of 1397 coral colonies of these species were infected with black band disease. The distribution of the disease among the thirty 20-meter diameter sites was clumped, suggesting that the disease is infectious. Year-round monitoring revealed that seasonal disease patterns varied between reefs. Three seasonal patterns were apparent: some coral colonies were infected year round; several colonies exhibited previously unreported reinfection on a seasonal basis; and some exhibited the widely reported pattern of infection limited to the warmer months of the year (sea water temperatures 25 °C or higher).     

Geographic differences in vertical connectivity in the Caribbean coral Montastraea cavernosa despite high levels of horizontal connectivity at shallow depths

The deep reef refugia hypothesis proposes that deep reefs can act as local recruitment sources for shallow reefs following disturbance. To test this hypothesis, nine polymorphic DNA microsatellite loci were developed and used to assess vertical connectivity in 583 coral colonies of the Caribbean depth‐generalist coral Montastraea cavernosa. Samples were collected from three depth zones (≤10, 15–20 and ≥25 m) at sites in Florida (within the Upper Keys, Lower Keys and Dry Tortugas), Bermuda, and the U.S. Virgin Islands. Migration rates were estimated to determine the probability of coral larval migration from shallow to deep and from deep to shallow. Finally, algal symbiont (Symbiodinium spp.) diversity and distribution were assessed in a subset of corals to test whether symbiont depth zonation might indicate limited vertical connectivity. Overall, analyses revealed significant genetic differentiation by depth in Florida, but not in Bermuda or the U.S. Virgin Islands, despite high levels of horizontal connectivity between these geographic locations at shallow depths. Within Florida, greater vertical connectivity was observed in the Dry Tortugas compared to the Lower or Upper Keys. However, at all sites, and regardless of the extent of vertical connectivity, migration occurred asymmetrically, with greater likelihood of migration from shallow to intermediate/deep habitats. Finally, most colonies hosted a single Symbiodinium type (C3), ruling out symbiont depth zonation of the dominant symbiont type as a structuring factor. Together, these findings suggest that the potential for shallow reefs to recover from deep‐water refugia in M. cavernosa is location‐specific, varying among and within geographic locations likely as a consequence of local hydrology.