Reef Zones Research Articles

Gorgonian octocoral community at Varadero coral reef in the Colombian Caribbean: diversity and spatial distribution

Varadero reef has unique ecological characteristics and faces the risk of disappearing because of the dredging for an access channel of large vessels to the Cartagena port in Colombia. In this ecosystem, the sessile benthic community, such as gorgonian octocorals and associated fauna, will be impacted. We examined the diversity and spatial distribution of gorgonians from seven sites located in the mixed coral reef zone. These organisms are generally found in depths between 6 and 10 m in the area. The richness of the gorgoniansspecies is lower than that recorded in other areas of the Caribbean. The low values of abundance and richness species are due to the characteristics of reef setoff and sedimentation processes existing in Cartagena bay.

Collapsing Complexity: Quantifying Multiscale Properties of Reef Topography

AbstractSeafloor topography affects a wide range of physical and biological processes; therefore, collapsing the three‐dimensional structure of the bottom to roughness metrics is a common challenge in studies of marine systems. Here we assessed the properties captured by metrics previously proposed for the seafloor, as well as metrics developed to characterize other types of rough surfaces. We considered three classes of metrics: properties of the bottom elevation distribution (e.g., standard deviation), length scale ratios (e.g., rugosity), and metrics that describe how topography varies with spatial scale (e.g., Hölder exponents). The metrics were assessed using idealized topography and natural seafloor topography data from airborne lidar measurements of a coral reef. We illustrate that common roughness metrics (e.g., rugosity) can have the same value for topographies that are geometrically very different, limiting their utility. Application of the wavelet leaders technique to the reef data set demonstrates that the topography has a power law scaling behavior, but it is multifractal so a distribution of Hölder exponents is needed to describe its scaling behavior. Using principal component analysis, we identify three dominant modes of topographic variability, or ways metrics covary, among and within reef zones. Collectively, the results presented here show that coral reef topography is both multiscale and multifractal. While individual metrics that capture specific topography properties relevant to a given process may be suitable for some studies, many applications will require a set of metrics that includes statistics that capture how topography varies with spatial scale.

A Low‐Sulfidation Epithermal Mineralization in the River Reef Zone, the Poboya Prospect, Central Sulawesi, Indonesia: Vein Textures, Ore Mineralogy, and Fluid Inclusions

AbstractThe Poboya Prospect lies along the North Northwest ‐ South Southeast Palu‐Koro Fault Zone in the central part of the West Sulawesi Arc. The geology of the area consists of the Palu Metamorphic Complex overlain by the Paleogene‐Neogene Tinombo Formation of volcanosedimentary rocks, the Celebes Molasse sediment, and Late Cenozoic granitic rocks. Petrography, scanning electron microscope with energy‐dispersive spectrometry (SEM‐EDS), electron probe microanalyzer (EPMA), and fluid inclusion microthermometry were carried out to examine vein textures, ore mineralogy, and characteristics of the ore‐forming fluid responsible for mineralization in the River Reef Zone, the Poboya Prospect. Textures of quartz‐carbonate veins in the River Reef Zone include massive micro‐comb, moss, colloform, crustiform, mosaic, feathery, flamboyant, lattice bladed, ghost bladed, parallel bladed, and saccharoidal textures representing primary growth, recrystallization, and replacement. The homogenization temperature and fluid salinity are 240–250°C and 0.3–0.7 wt% NaCl eq., respectively. Ore minerals precipitated in the early stage consist of electrum, naumannite‐aguilarite, chalcopyrite, pyrite, marcasite, sphalerite, and pyrrhotite. Apart from pyrrhotite, these ore minerals were also precipitated in the late stage along with selenopolybasite, freibergite, argyrodite, pyrargyrite, and galena. Selenium more preferably occurs as the crystallographic replacement of sulfur in naumannite‐aguilarite, argyrodite, pyrargyrite, selenopolybasite, and freibergite instead of as independent selenide minerals. The low‐sulfidation epithermal deposit in the River Reef Zone, the Poboya Prospect, illustrates the potential of the West Sulawesi Arc, particularly along the Palu‐Koro Fault Zone, to host epithermal gold mineralization.

Planktonic copepod community of a reef zone in the southern Gulf of Mexico

ABSTRACTIn this study, the variation of seasonal and inter-annual density and diversity of the copepod community in the Parque Nacional Sistema Arrecifal Veracruzano (PNSAV) was analysed. Samples were collected under nortes, rainy and dry weather conditions in 2011, as well as under nortes and dry weather conditions in 2012 and 2013 in four transects. Surface trawls with 330-μm conical nets were made. The temperature, salinity and dissolved oxygen were measured in situ. The values obtained were 23.07 ± 0.53 to 29.29 ± 0.27°C for temperature, 33.43 ± 0.49 to 35.91 ± 0.09 for salinity, and 2.52 ± 0.08 to 6.56 ± 0.08 mg l−1 for dissolved oxygen. The copepods collected belonged to 19 families, 28 genera and 62 species. Copepods represented between 69.74% and 76.79% of the abundance of crustaceans present in zooplankton. The highest number of copepods occurred under nortes weather conditions in 2011 with 401,885 ± 28,092 copepods/100 m3 of the species Temora stylifera. In 2012, 256,325 ± 76,872 copepods/100 m3 of the species Paracalanus aculeatus were obtained and in 2013, 311,526 ± 76,872 copepods/100 m3 of the species T. turbinata. The highest specific richness was found in the southern zone with 28 species. In 2013 the highest density was found in the northern zone with 100,323 ± 28,888 copepods/100 m3. The highest diversity was found under dry weather conditions in 2011 with 3.71 bits/individual. In the 3 years of study, 24 species were dominant; 12 of these, appeared in the 3 years of sampling: T. stylifera, T. turbinata, Labidocera scotti, P. aculeatus, O. latus, Pontellopsis villosa, Centropages velificatus, Parvocalanus crassirostris, Corycaeus speciosus, Undinula vulgaris, Oithona plumifera, and Farranula gracilis. Canonical correlation analysis showed the formation of five groups explained by the neritic or oceanic affinity of the species and their tolerance to changes in salinity or temperature.

Marine heatwaves reveal coral reef zones susceptible to bleaching in the Red Sea.

As the Earth's temperature continues to rise, coral bleaching events become more frequent. Some of the most affected reef ecosystems are located in poorly monitored waters, and thus, the extent of the damage is unknown. We propose the use of marine heatwaves (MHWs) as a new approach for detecting coral reef zones susceptible to bleaching, using the Red Sea as a model system. Red Sea corals are exceptionally heat-resistant, yet bleaching events have increased in frequency. By applying a strict definition of MHWs on >30 year satellite-derived sea surface temperature observations (1985-2015), we provide an atlas of MHW hotspots over the Red Sea coral reef zones, which includes all MHWs that caused major coral bleaching. We found that: (a) if tuned to a specific set of conditions, MHWs identify all areas where coral bleaching has previously been reported; (b) those conditions extended farther and occurred more often than bleaching was reported; and (c) an emergent pattern of extreme warming events is evident in the northern Red Sea (since 1998), a region until now thought to be a thermal refuge for corals. We argue that bleaching in the Red Sea may be vastly underrepresented. Additionally, although northern Red Sea corals exhibit remarkably high thermal resistance, the rapidly rising incidence of MHWs of high intensity indicates this region may not remain a thermal refuge much longer. As our regionally tuned MHW algorithm was capable of isolating all extreme warming events that have led to documented coral bleaching in the Red Sea, we propose that this approach could be used to reveal bleaching-prone regions in other data-limited tropical regions. It may thus prove a highly valuable tool for policymakers to optimize the sustainable management of coastal economic zones.

Identity of coral reef herbivores drives variation in ecological processes over multiple spatial scales.

Overexploitation of key species can negatively impact ecosystem processes, so understanding the ecological roles of individual species is critical for improving ecosystem management. Here, we use coral reefs and the process of herbivory as a model to examine how species identity of consumers influence ecosystem processes to inform management of these consumers. Herbivorous fishes can facilitate the recruitment, growth, and recovery of corals by controlling the fast-growing algae that can outcompete corals for space. However, herbivorous fish guilds are species rich with important differences among species in diet, movement, and habitat preferences. Yet, we lack a general understanding of (1) how these species-specific differences in feeding and behavior scale up to reef-wide rates of ecosystem processes and (2) how species identity and diversity impact these processes. To address these knowledge gaps, we used field observations to derive key species- and size-specific foraging parameters for nine herbivorous parrotfish species on coral reefs in the Florida Keys, USA. We then combined these foraging parameters with fish survey data spanning multiple spatial scales to estimate the rates of three ecosystem processes: area of reef grazed, amount of macroalgae removed, and rate of bioerosion. We found that predicted rates of ecological processes varied dramatically among habitats and among reef zones within habitats, driven primarily by variation in abundance among species with different foraging behaviors. In some cases, assemblages with similar levels of total biomass had different rates of ecological processes, and in others, assemblages with different biomass had similar rates of ecological processes. Importantly, our models of herbivory using species-specific parameters differed from those using genus-level parameters by up to 300% in rates of ecological processes, highlighting the importance of herbivore identity in this system. Our results indicate that there may be little overlap in the roles species play, suggesting that some systems may be vulnerable to loss of ecological function with the reduction or loss of just a few species. This work provides a framework that can be applied across the region to predict how changes in management may affect the ecological impact of these important herbivores.

Differential disease incidence and mortality of inner and outer reef corals of the upper Florida Keys in association with a white syndrome outbreak

The Florida Keys Reef Tract has suffered extraordinary losses in live coral cover over the past four decades and is now battling an unprecedented coral disease outbreak. Here, colonies of Siderastrea siderea (Ellis and Solander, 1786) and Pseudodiploria strigosa (Dana, 1846) were tracked over 3 yrs (2015–2017) across two pairs of inner and outer reef sites in the upper keys, offering a unique perspective into the distribution of disease throughout the reef tract. We found that outer reef colonies of both coral species exhibited greater disease incidence and mortality associated with this ongoing epidemic, while inner patch reef colonies remained largely unaffected. These findings suggest that ecological or biological factors that differentiate coral populations across these reef zones may play an important role in susceptibility to disease.

Effect of increased CO2 concentration on the growth rate of Isopora palifera and Acropora hyacinthus from different cross-shelf reef zones

The rise in atmospheric carbon dioxide (CO2) concentration due to emissions associated with economic development is altering ocean chemistry, a process known as ocean acidification. The resultant decrease in oceanic pH will affect marine organisms, in particular those which build their skeletons through calcification such as scleractinian corals. The aim of this research was to analyse the likely impact of changing CO2 concentrations and thus seawater pH on the growth rate of two common corals, Isopora palifera and Acropora hyacinthus. This research was conducted at the Marine, Coastal and Small Island Research Centre, Universitas Hasanuddin, Indonesia. Samples of Isopora palifera and Acropora hyacinthus were collected along an inshore-offshore cross-shelf gradient from 3 sites: Pulau Karanrang (inner zone), Pulau Badi (intermediate zone), and Pulau Kapoposang (outer zone). A fully randomised research design was used with three replicates for each of three CO2 treatments: 390 ppm (control), 550 ppm (2030 prediction), 1000 ppm (2050 prediction). The samples were weighed weekly for 1 month (digital balance, accuracy 0.1 mg). ANOVA analysis with post hoc Tukey Test showed a significant (p < 0.05) between treatment difference in growth rate for both Isopora palifera and Acropora hyacinthus (P<0,05). The corals from all three zones exhibited positive growth at 390 ppm CO2, and negative growth at CO2 concentrations of 550 ppm and 1000 ppm.

Hydrodynamic conditions that favor the settlement of Diadema antillarum to a western Caribbean coral reef

The reduction in the Diadema antillarum Philippi, 1845 population across the Caribbean region in the 1980s had adverse ecological consequences, including coral-algal phase-shifts. Reduced larval supply, and subsequent low recruitment success, has hampered population recovery. To examine larval density and the influence of hydrodynamics on settlement of D. antillarum, monthly plankton tows were conducted from May 2014 to April 2015 in the lagoon and fore reef zones of a western Caribbean coral reef (Xcalak, Mexico). A moored Nortek acoustic waves and currents (AWAC-Nortek) oceanographic instrument recorded wave height, wave velocity, and suspended particles in the water column. To assess settlement of D. antillarum, collectors were placed along the lagoon and fore reef, and inspected monthly. Monthly samples had a mean density of 0.06 larvae per 15 m3 from June to August corresponding to two developmental stages. Five settlers with test diameter approximately 1 mm were collected from August to December. During August, Doppler profiles recorded via the AWAC-Nortek instrument showed the lowest wave height values (<0.3 m) and a low bottom shear stress of <0.15 N m–1. Acoustic signals indicated that the particle displacement was driven primarily by wave action and that currents played a secondary role. During settlement of D. antillarum, wave orbital velocity (Uw ) was below the threshold of motion (Uwr ), allowing deposition of particles at the seabed. These hydrodynamic conditions suggest a window of opportunity for larval transport and benthic settlement. Ours is the first field study documenting the mechanisms that link hydrodynamics to the settlement of D. antillarum to a Caribbean reef.

Carbon Isotopic Fractionation in Organic Matter Production Consistent With Benthic Community Composition Across a Coral Reef Flat

Carbon fluxes on coral reefs (net community production and net community calcification) aggregate the collective activity of all coral reef community members. This integrated approach provides powerful community-level insights, but is unable to resolve the finer-scale contributions of different reef functional groups to the community-scale rates. Tools are required to disaggregate the community-scale approaches and evaluate the performance of co-existing reef functional groups. Such assessments are necessary to improve forecasts of coral reef responses to global and local environmental change. We present results from a coral reef field study on One Tree Island reef in the Great Barrier Reef in September-October 2016 where we combined observations of total alkalinity, dissolved inorganic carbon (DIC), and the stable isotopic composition of dissolved inorganic carbon ($\delta^{13}C_{DIC}$) to estimate carbon isotopic fractionation during organic matter formation. Portions of the reef with greater abundance of non-calcifying algae fractionated DIC ~5 $\text{\textperthousand}$ more (stronger preference for $^{12}\text{C}$) during organic metabolism than did portions of the reef with a greater abundance of calcifiers. These results were consistent across a wide range of assumed isotopic fractionation factors for net calcification. We attribute the observed differences in carbon isotopic fractionation to the metabolic activities of the ecological community underlying each section of the reef, not to environmental factors such as light availability or water temperature. The patterns in carbon isotopic fractionation were generally consistent with inferred ratios of calcification to primary production in each reef zone, giving further confidence to our inference that differences in carbon isotopic fractionation can be related to differences in the ecological community on small spatial scales.

Age and growth of gray triggerfish (Balistes capriscus) from a north-central Gulf of Mexico artificial reef zone

The overexploitation of many traditionally targeted reef fishes, such as red snapper, Lutjanus campechanus (Poey, 1860), alongside the implementation of increasingly restrictive management measures on those species, has led to increased targeting of conventionally discarded Gulf of Mexico gray triggerfish, Balistes capriscus Gmelin, 1789, commercially and recreationally. The goal of this study was to assess age and growth of gray triggerfish from the Alabama Artificial Reef Zone in the north-central Gulf of Mexico. Gray triggerfish (n = 1135) were collected predominantly from artificial habitat during 1999–2017. Specimens were sexed macroscopically and ages were assigned by counting translucent increments in sections of the first dorsal spine. Fish ranged in size from 22 to 617 mm fork length. The oldest female was assigned an age of 9 yrs; the oldest male, 10 yrs. A suite of growth models was tested to develop combined and sex-specific models. The von Bertalanffy growth function best fit the combined data with parameters L∞ = 488.63 (SE 5.19), k = 0.57 (SE 0.02), and t 0= –0.27 (SE 0.03). Mean size-at-age differed between sexes for six of the eight ages which possessed sample sizes large enough to make comparisons. Growth differed between sexes, and the best-fitting version of the von Bertalanffy growth function permitted L∞ to vary by sex [female L∞ = 480.26 (SE 7.99); male L∞ = 532.89 (SE 8.95); k = 0.44 (SE 0.04); t 0 = –0.78 (SE 0.16)]. These findings enhance our knowledge of the age and growth of Gulf of Mexico gray

Stable isotope analysis reveals trophic diversity and partitioning in territorial damselfishes on a low-latitude coral reef

Investigating the niche overlap of ecologically similar species can reveal the mechanisms that drive spatial partitioning in high-diversity systems. Understanding how food resources are used and whether the diets of neighboring species are different are particularly important when considering the coexistence and functional role of species. Territorial damselfish on coral reefs are considered to be herbivores that defend algal mats from other food competitors. However, this guild contains numerous small species whose functional role and dietary diversification is poorly understood. Here, the relationships between diet and spatial distribution of seven intermediate-sized territorial damselfishes at Kimbe Bay, Papua New Guinea (5°30′S, 150°05′E) were investigated. These species partition habitat across three reef zones with distinct patterns of fine-scale distribution. It was predicted that neighboring species partition food resources with minimal dietary overlap. Examination of isotope ratios of carbon and nitrogen delineated three distinct feeding strategies: pelagic, reef-based, and an intermediate group feeding on both prey types. None of the species appear to be strict herbivores. Adjacent species exhibited high–intermediate trophic niche partitioning when examining pelagic versus reef-based production sources, with two species previously described as benthic herbivores exhibiting pelagic feeding. The study demonstrates that diet reinforces the patterns of spatial partitioning and coexistence among ecologically similar damselfishes. These findings add to a growing view that interspecific differences among similar species are lost when categorizing species into broad functional classifications, and that previous studies suggesting that territorial damselfish are strictly reef-based feeders may not be applicable in all systems or for all species.

Structure and depositional environment of the Valanginian-Hauterivian sections in the middle reaches of the Bodrak River (South-Western Crimea)

The materials, collected during the description of 17 outcrops of Karatlykh formation (Lower Valanginian) and Karaghach formation (Lower Hauterivian) in the Bodrak River middle course (South-Western Crimea), are analyzed. The results of microscopic descriptions of thin sections, computed micro-tomography of samples, carbonate content detection, and particle-size analysis of insoluble residue are presented, the remains of scleractinian corals and cartilaginous fish are studied. Descriptions and sedimentological interpretation of 8 lithological-genetic types of layers are also presented in this article. During Karatlykh time and regressive phases of Karaghach time, terrigenous sedimentation prevailed. From the coast to the center of the basin there were pebble-sandy beaches, sandy ripples, detrital ripples with sandy depressions, detrital ripples of the far part of the shallow-water shelf. During transgressive phases of the Karaghach time, there was a shortage of terrigenous sedimentary material and carbonate sedimentation dominated. The area with solitary corals was formed along the coast and separated from the sea by patch reefs zone, detritus and coral bioherms were located on the fore reef zone. Deeper there were detrital ripples with sandy depressions, detrital rippleswith single bioherms and detrital ripples with rare biostromes. According to bed’s vertical sequences, transgressive-regressive sedimentation cycles are established. It became the basis for a detailed correlation of sections. Paleogeographic schemes for the short range of geological time corresponding to transgressive and regressive maxima are compiled. It is shown that in the paleobasin there were two types of lateral sequences of accumulative landscapes. As a result, we demonstrate that in Lower Valanginian and Lower Hauterivian the studied territory represented a shallow offshore part of the sea, washed the land southeastward. This land represented the main terrigenous provenance for the basin.

Late glacial to deglacial variation of coralgal assemblages in the Great Barrier Reef, Australia

Abstract Integrated Ocean Drilling Program (IODP) Expedition 325 cored submerged reefs along the shelf edge of the Great Barrier Reef (GBR) to study sea-level and environmental changes and their impacts on reef communities and reef growth since the Last Glacial Maximum (LGM). Previous work defined five reef sequences (Reef 1–5) that span the last 30,000 years. Here we examined the variation in coralgal assemblages and their paleoenvironmental settings in late glacial to deglacial sequences from 23 holes cored seaward of the modern GBR in water depths from 46 to 131 m along four transects at three localities: Hydrographers Passage (HYD-01C and HYD-02A), Noggin Pass (NOG 01B), and Ribbon Reef (RIB-02A). We identified three coralline algal assemblages and eight coral assemblages indicating a broad range of reef settings from the shallow reef crest (0–5 m) to the deep forereef slope (>20 m). We document in detail for the first time the distribution and composition of reef communities that grew in the GBR during the LGM from 22,000–19,000 years ago. They included coral taxa that are major reef builders today: Isopora, Acropora gr. humilis, Dipsastraea gr. pallida, Porites, and Montipora. Prior to the fall in sea level to the maximum extent of the LGM, late glacial reef communities developed more proximally (landward) to the modern GBR along the shelf edge. Their distribution and composition reflect influences of the older Pleistocene basement depth and possible terrigenous sediment inputs. Post-LGM deglacial reef growth was vigorous in proximal sites and characterized by the accretion of a very shallow high-energy coralgal assemblage composed of medium to robustly branching Acropora, including A. gr. humilis, and thick algal crusts of Porolithon gr. onkodes associated with vermetid gastropods. More distally, reef growth was variably impacted by terrigenous input following deglacial reflooding of antecedent reef terraces. The coralgal succession and sedimentary facies in Noggin Pass indicate that an early drowning trend was linked to increased turbidity that was likely controlled by shelf morphology (narrow shelf, steep slope) and/or proximity to a paleo-river mouth. The deglacial succession in Ribbon Reef lacks typical shallow-water indicators, which may reflect influences of the particularly steep slope of the northern GBR shelf edge on reef zonation. A major sea-level jump at the onset of the Younger Dryas displaced reef habitats further upslope, forming a barrier reef system mainly composed of robustly branching acroporids distinct from the more distal sites. Our results highlight the importance of sedimentation and shelf morphology in addition to relative sea-level changes in controlling variations in reef community over centennial to millennial timescales.

QUATERNARY AND RECENT OSTRACODES OF THE TYRRHENIAN AND RED SEAS PART 1: BAIRDIIDAE, BYTHOCYPRIDIDAE, CYTHERELLIDAE

Систематичне вивчення четвертинних і рецентних остракод Тиренського моря (шельф, глибоководна западина) та Червоного моря (прибережна зона коралових рифів) містить систематичний опис 14 видів остракод рядів Podocopida (родини Bairdiidae, Bythocyprididae) і Platycopida (родина Cytherellidae). Для видів, визначених у номенклатурі sp.nov. (3 види), sp. (2 види), aff. (1 вид), окрім синоніміки, розмірів, місцезнаходження, стратиграфічного положення й географічного поширення, надано голотип і діагноз. Зображення зовнішньої і внутрішньої будови черепашки зроблено на SEM JEOL JSM-6490 LV (6 фототаблиць).

Estimating Exploitation Rates in the Alabama Red Snapper Fishery Using a High‐Reward Tag–Recapture Approach

AbstractAccurate estimates of exploitation are essential to managing an exploited fishery. However, these estimates are often dependent on the area and vulnerable sizes of fish considered in a study. High‐reward tagging studies offer a simple and direct approach to estimating exploitation rates at these various scales and in examining how model parameters impact exploitation rate estimates. These methods can ultimately provide a better understanding of the spatial dynamics of exploitation at smaller local and regional scales within a fishery—a measure often needed for more site‐attached species, such as the Red Snapper Lutjanus campechanus. We used this approach to tag 724 Red Snapper during 2016 in the Alabama Artificial Reef Zone within the northern Gulf of Mexico to estimate recreational exploitation rates in Alabama waters. We fitted a series of tag return models, analyzed using maximum likelihood, to examine how release depth, movement between depth strata, fish length, and the rate at which anglers released fish impacted estimates of exploitation rate under a range of assumed natural and tagging mortality rates. Our model results suggested higher fishing mortality in the shallower depth stratum than in the deep stratum, constant movement rates with release depth, and constant release rates across fish lengths. Exploitation rate for the aggregate tagged population across the entire sample area was estimated at 0.14. Exploitation rates estimated for each depth stratum were 0.20 (shallow stratum: &lt;36.5 m) and 0.06 (deep stratum: 36.5–61.0 m). In addition, length‐based vulnerability to harvest was dome‐shaped, with peak exploitation rates of 0.37 (shallow stratum) and 0.12 (deep stratum) occurring at 600–700 mm TL. Although previous studies have suggested higher exploitation rates in shallower waters compared to deeper waters, few estimates exist at these smaller spatial scales.

Functional reef fish groups of the Mexican Caribbean: implications of habitat complexity

The Caribbean Sea is considered a unique biogeographic region and is among the top 5 world hotspots of marine biodiversity. Yet, over the last years it is among the regions where the most serious declines in terms of reef area, health, and productivity is occurring. In this study, the coral reef fish community of the Mexican Caribbean was analyzed and classified into functional groups. The aims of this study were: 1) determine the functional relationships of the fish community based on diet and morphology, and 2) determine the extent of the influence of habitat complexity and the protection of the Sian-Ka'an reserve on the fish richness and functional diversity of the ecosystem. Eleven reef localities of the Yucatan Peninsula and 160 species were analyzed. Twenty-eight functional groups were described for both ecological and morphological variables. Our results indicate that variation in habitat complexity was a significant factor related to fish richness and functional diversity; however, the protection of the reserve does not show a relationship with any of the response variables. On the other hand, the slope is the reef zone with the highest fish richness in all localities, creating a belt of richness and connectivity in the whole area.

Apparent timing of density banding in the Caribbean coral Siderastrea siderea suggests complex role of key physiological variables

Skeletal growth bands in massive reef-building corals are increasingly used as proxies for environmental records despite an incomplete understanding of their formation. While the bands are known to arise from seasonal changes in light and temperature, conflicting reports about the timing of constituent high- and low-density growth bands have complicated the dating and interpretation of environmental signals recorded in corals’ growth histories. Here, we analyze 35 Siderastrea siderea cores extracted from inshore and offshore reef zones along the Florida Keys Reef Tract to investigate potential drivers of banding variability in this species. A previously proposed model of banding variation is applied to assess its potential to explain band timing in S. siderea. Colony growth characteristics and the timing of band deposition were obtained from the cores via computed tomography and were coupled with tissue thickness measurements and gender identification. Apparent time difference, or the perceived lag in coral growth response to changes in environmental conditions, was quantified for each coral core. Results suggest that linear extension, tissue thickness, and gender together do not fully explain the timing of band formation in S. siderea and therefore do not fully resolve the density patterns observed within this species. This finding suggests that other factors yet to be identified are partially determining the formation and appearance of density bands in S. siderea. The continued characterization of banding variability on scales ranging from the individual colony to entire reef systems will enrich our understanding of both coral growth and the environmental conditions to which corals are exposed.

Soil inorganic carbon in mangroves of tropical China: patterns and implications.

Soil inorganic carbon (IC) is neglected in most blue carbon studies despite the globally significant role of the calcium carbonate cycle in ocean C balance and climate change. We sampled soils to 1 m depth from seven mangrove reserves in Hainan Island, China. Only 45 out of 509 samples were rich in IC (greater than 10 mg cm-3). Most of the IC-rich samples were found at the outer part of Qinglan Bay, which is adjacent to the largest coral reef zone of Hainan Island. Soil IC concentration ranged from 0 to 66 g kg-1 (or 0-67 mg cm-3), accounting for 0-92% of total C. IC concentration increased with soil depth where it was abundant. Soil pH was low (2.36-6.59) in IC-depleted soils, but increased to 5.67-7.99 in IC-rich soils. Soil total C stock and IC stock in mangroves of Hainan amounted to 0.76×106 and 0.12×106 Mg, respectively, with IC accounting for 16% of total C. Our study finds that carbonate concentrations can be high in mangrove soils but their spatial distribution indicates they are largely allochthonous in origin. Evidence of carbonate dissolution in mangroves suggests mangroves may increase total alkalinity to buffer acidification in seawater.

Hydrodynamics and Sediment Mobility Processes Over a Degraded Senile Coral Reef

AbstractCoral reefs can influence hydrodynamics and morphodynamics by dissipating and refracting incident wave energy, modifying circulation patterns, and altering sediment transport pathways. In this study, the sediment and hydrodynamic response of a senile (dead) barrier reef (Crocker Reef, located in the upper portion of the Florida Reef Tract) to storms and quiescent conditions was evaluated using field observations and the Coupled Ocean‐Atmosphere‐Wave‐Sediment Transport model. Waves, circulation, and resultant sediment mobility were modeled across different reef zones. Sediment mobility during quiescent periods and the passage of far‐field storms are driven by nonbreaking waves and, to a lesser degree, regional circulation. Spatial variability in these processes produces the present‐day distribution of sediment grain size at Crocker Reef, wherein finer‐grain material along a shallow central ridge is frequently mobilized (43% to 62% of the time), winnowed away, and deposited along the lower‐energy flanks and in the fore reef where sand mobility occurs less frequently (32% to 43% and 1% to 22% of the time, respectively). Analysis of wave conditions for the period of 2006–2014 supports that wave heights rarely exceed the threshold for breaking (0.1% and 0.3% at the reef crest and at the reef flat, respectively), predominantly during the passage of tropical storms. There is a shift to a wave‐breaking regime during near‐field storms, creating the potential for mobilization of larger material and enhanced reef degradation. Sediment mobility can be enhanced due to wave skewness or the generation of free infragravity waves during periods of depth‐induced wave breaking.