Coral Reef Systems Research Articles

Variations in the abundance and structural diversity of microbes forming biofilms in a thermally stressed coral reef system

Little information is known about biofilm formation in the thermally stressed coral reef systems north of the Arabian Gulf. The current study investigates the abundance and diversity of marine microbes involved in biofilm formation and their succession over a period of 14weeks (May–August 2007) at temperatures exceeding 32°C. The results showed variations in microbial numbers and the development of more stable biofilm communities as the biofilms aged. The culture-dependent technique and microscopic examination of the developed biofilms showed the dominance of key species known for their role in precipitating CaCO3 such as Vibrio and in facilitating coral larvae settlement and metamorphosis such as Pseudoalteromonas, Bacillariophyceae and Rhodophyceae. The results revealed biofilm formations with microbial diversities that have the potential to support the larval settlement and metamorphism of marine organisms and to consolidate and stabilize biofilms via the process of calcification in the thermally stressed coral reef system considered herein.

A gonad-stimulating peptide of the crown-of-thorns starfish, Acanthaster planci

The crown-of thorns starfish, Acanthaster planci, has been blamed for coral mortality in a large number of coral reef systems in the Indo-Pacific region. Because population outbreaks of A. planci are closely related to reproduction, it is important to examine the mechanism of reproductive control in this starfish. Previously, a relaxin-like gonad-stimulating peptide (RGP) in starfish Asterina pectinifera has been identified as the gonadotropin responsible for final gamete maturation. On the basis of homology research on RGP cDNAs from several species, this study was carried out to identify gonadotropin in A. planci. The cDNA sequence of RGP was determined using a RACE product of mRNA from the radial nerves of A. planci. The coding DNA sequence consisted of 351 base pairs with an open reading frame encoding a peptide of 116 amino acids (aa), including a signal peptide (29 aa), B-chain (19 aa), C-peptide (44 aa), and A-chain (24 aa). The chemical structure of A. planci RGP was exactly the same as that of A. pectinifera RGP. Furthermore, synthetic RGP could induce gamete spawning and oocyte maturation in the ovarian fragments of A. planci. This strongly suggested that the RGP is a gonadotropin in A. planci.

Taxonomy of reproductive Nereididae (Annelida) in multispecies swarms at Ambon Island, Indonesia.

Multispecies, or mass, spawning of different invertebrate species is well known for coral reef systems; however, incidences involving polychaetes are poorly documented. In this study we report on mass swarming, prior to spawning, of Nereididae at Ambon Island, Maluku, on three occasions: in 1866, inferred from an historical sample deposited in Naturalis, Leiden, and in March, 2009 and 2014, based on newly collected samples. The 2009 and 2014 events co-occurred with spawning of other polychaetes, known locally as wawo and including the widespread Indo-Pacific eunicid, Palola viridis (Gray in Stair). Ten species of reproductive Nereididae are described, including Composetia marmorata (Horst) new combination, formerly Ceratonereis marmorata; epitokous modifications are described for both sexes of each species including taxonomically important features such as body colour and number of pre-natatory chaetigers. Three distinct types of natatory region morphologies are recognized, which appear to characterise groups of genera. The ten new records brings to 13 the total number of nereidid species known to undergo mass swarming at Ambon Island; a key to the 13 species is provided. Species composition varies slightly between the three time periods: four species were common between all three periods, five species were in common between 1866 and 2014, and four species were in common between 1995 and 2009/14. Two species of Neanthes and one of Nereis are identified as potentially new and will be described in subsequent papers.

Influence of Anthropogenic Pressures on the Bioactivity Potential of Sponges and Soft Corals in the Coral Reef Environment

The wealth of marine sponges and soft corals in Indonesian waters represents a rich source of natural products. However, anthropogenic pressures potentially decrease diversity in coral reefs. Presented here are trends for tropical sponge and soft coral biodiversity and their bioactivity potential under the influence of increasing anthropogenic pressures. Samples were collected along transects (near, mid, and far) at Karimunjawa and Seribu Islands Marine National Parks and environmental parameters (salinity, pH, dissolved oxygen (DO), phosphate, nitrate, and ammonia), sponge and soft coral biodiversity, and the bioactivity potential of those organisms (50% Growth Inhibition (GI50) of cancer cell lines H460-Lung, MCF7-Breast, and SF268-CNS) are compared. The environmental conditions and biodiversity were found to be significantly different between groups of sampling sites (P<0.05). Canonical Discriminant Analysis (CDA) revealed DO was the discriminant factor driving the separation between groups (90.1%). Diversity tended to be higher in the Far group with strong and significant relation to DO (R= 0.611, P<0.05) and ammonia (R = -0.812, P<0.05). The CDA also showed that an increase in bioactivity (low % GI50) of sponge and soft coral extracts was related to a canonical function (57.21%) consisting of high DO, high pH, and low nutrients. These findings indicate the production of bioactive compounds is related to diversity and complexity of coral reef systems. Therefore, strategies for marine protection by mitigating the impacts of anthropogenic pressures needs to be optimized in order to conserve the overall environment and sustain its natural bioactivity potential indefinitely.

Isolation by resistance across a complex coral reef seascape.

A detailed understanding of the genetic structure of populations and an accurate interpretation of processes driving contemporary patterns of gene flow are fundamental to successful spatial conservation management. The field of seascape genetics seeks to incorporate environmental variables and processes into analyses of population genetic data to improve our understanding of forces driving genetic divergence in the marine environment. Information about barriers to gene flow (such as ocean currents) is used to define a resistance surface to predict the spatial genetic structure of populations and explain deviations from the widely applied isolation-by-distance model. The majority of seascape approaches to date have been applied to linear coastal systems or at large spatial scales (more than 250 km), with very few applied to complex systems at regional spatial scales (less than 100 km). Here, we apply a seascape genetics approach to a peripheral population of the broadcast-spawning coral Acropora spicifera across the Houtman Abrolhos Islands, a high-latitude complex coral reef system off the central coast of Western Australia. We coupled population genetic data from a panel of microsatellite DNA markers with a biophysical dispersal model to test whether oceanographic processes could explain patterns of genetic divergence. We identified significant variation in allele frequencies over distances of less than 10 km, with significant differentiation occurring between adjacent sites but not between the most geographically distant ones. Recruitment probabilities between sites based on simulated larval dispersal were projected into a measure of resistance to connectivity that was significantly correlated with patterns of genetic divergence, demonstrating that patterns of spatial genetic structure are a function of restrictions to gene flow imposed by oceanographic currents. This study advances our understanding of the role of larval dispersal on the fine-scale genetic structure of coral populations across a complex island system and applies a methodological framework that can be tailored to suit a variety of marine organisms with a range of life-history characteristics.

Development in a warm future ocean may enhance performance in some species

Understanding the capacity of organisms to cope with projected global warming through acclimation and adaptation is critical to predicting their likely future persistence. The vast majority of research on tropical species suggests they will be substantially negatively affected by future warming and have limited capacity to acclimate to changes. This study tested whether the spine cheek anemonefish, Premnas biaculeatus, has the capacity for developmental thermal acclimation of metabolic attributes and critical thermal maximum (CTmax) to increasing sea water temperature. Juveniles of P. biaculeatus exhibited high capacity for developmental thermal acclimation of aerobic physiology. Fish reared at +1.5°C and +3.0°C above present-day mean temperatures possessed enhanced performance across all testing temperatures (28.5°C to 31.5°C), i.e. overcompensation. Specifically, this occurred through increases in maximum oxygen consumption (MO2Maximum) that resulted in elevations in both net and factorial aerobic scope. In addition, fish reared at +1.5°C also exhibited a partial increase in critical thermal maximum (CTmax) by 0.5°C, however no increase was observed in fish reared at +3.0°C. Fish reared at +3.0°C were significantly longer, heavier and in better condition than +0.0°C present-day fish, suggesting that alterations to aerobic physiology correspond to enhancement of growth and condition as would be predicted with the oxygen and capacity limited thermal tolerance hypothesis. These results indicate that the acclimation to future warming may produce overall enhanced performance in some species. It also suggests that the developmental acclimation ability varies substantially between species within the same family and a greater understanding of promoted or reduced acclimation capacity will be critically important to predicting the impacts of climate change on coral reef systems.

Submerged fossil reefs discovered beyond the limit of modern reef growth in the Pacific Ocean

Balls Pyramid is the southernmost island in a linear island chain in the southwest Pacific Ocean, 24km south of the limit of known coral reef formation at Lord Howe Island. This paper describes the geomorphometric structure of the shelf surrounding Balls Pyramid through the application of remote sensing data to create a high-resolution digital elevation model of the shelf (5m cell size) and seafloor feature classification. Seafloor features were delineated using the bathymetry model together with slope, backscatter and sub-bottom profile data. The average depth of the 260.6km2 shelf was 55m (±21m), with the majority of shelf area (77%) within 30–60m water depth. Dominating the shelf is an extensive, mid-shelf reef at 30–50m depth, dissected by basin and channel features. Outer-shelf reef and platform features surround the mid shelf, with terrace sequences marking the seaward outer-shelf rim in 65–100m depth. Sub-bottom profiles and backscatter data demonstrate substantial accumulation (up to 16.5m) of unconsolidated sediments within basin and channel features. The submerged mid-shelf reefs of Balls Pyramid are similar to the fossil coral reef system discovered on the Lord Howe Island shelf, implying origins as a drowned coral reef system. This paper reveals complex shelf topography with extensive submerged reefs on what was previously considered to be a planated volcanic shelf outside of reef-forming seas.

Shelf morphology as an indicator of sedimentary regimes: A synthesis from a mixed siliciclastic–carbonate shelf on the eastern Brazilian margin

Modern shelf morphology is the result of the interplay between short and long term sedimentary processes. The relation between rates of sediment supply/carbonate growth and accommodation space creation will not only control coastal transgression and regression, but will also define the shelf sedimentary regimes acting to shape the seabed. Herein, shelf morphology and sedimentology are investigated in order to discuss how these characteristics can be representative of distinct sedimentary regimes. The study area is the eastern Brazilian shelf where coastal transgression and regression coexist with the most important coral reef system of the South Atlantic. A compilation of existing published and unpublished data was carried out in order to produce morphological and faciological maps and compare the mapped features with high-resolution seismic and sonographic data. The results show three major regions or morphological compartments: Abrolhos Shelf, Doce River Shelf and the Paleovalleys Shelf. In terms of shelf sedimentary domain, rhodolith beds predominate over the outer shelf along the entire area, coralline reefs are present along the northern Abrolhos inner shelf and a significant terrigenous mud deposit is observed associated to the Doce River adjacent inner shelf beds. The rest of the shelf is composed by bioclastic or terrigenous mud sand and gravel. Terrigenous sedimentation is always restricted to the shoreface or inner shelf shallower areas and carbonate sands and gravels are predominant elsewhere. The Abrolhos shelf shows two distinct sectors; the northern area is a typical mixed sediment environment that has a supply regime along the coast/shoreface, mainly due to longshore transport and a carbonate regime along the inner and outer shelf. The southern shelf morphology and sedimentation are controlled by the antecedent topography and is typically a accommodation regime shelf with associated rhodolith beds. The Doce river shelf is a supply regime environment with the formation of a 5–8 m thick regressive deposit with downlapping clinoforms. Southward from the Doce river shelf, a significant shift in sedimentary regime is observed as the morphology becomes very irregular with associated hardbottoms and unfilled paleovalleys. This sector of the shelf (Paleovalley shelf) is characterized by an accommodation regime. The interpretation shows that the entire study area can be defined as a mixed sedimentation shelf, showing supply and accommodation regimes. Shelf morphology worked as an indicator of these changes. Carbonate/terrigenous deposition during a highstand/regressive phase coeval along the eastern Brazilian shelf, either laterally and across shelf. This lateral/along coast variation in sediment supply and carbonate production leads to distinct lateral facies and geometry. These spatial changes in morphology and facies, with coexistence of carbonate and siliciclastic sedimentation, are very important for the correlation and interpretation of the geological record, especially stratigraphic surfaces and sequence units.

Recent dynamics and condition of coral reefs in the Colombian Caribbean

Long-term monitoring data provide a basis to recognize changes in coral reef communities and to implement appropriate management strategies. Unfortunately, coral reef dynamics have been poorly documented at any temporal scale in the Southern Caribbean. Through the "National Monitoring System of Coral Reefs in Colombia" (Spanish acronym: SIMAC), we assessed 32 permanent plots at different depth levels in six reefs areas of the Colombian Caribbean from 1998 to 2004. Temporal trends in coral and algal cover were evaluated by repeated measures ANOVA. The model included the effect of depth levels (a fixed effect), monitoring plots (a random effect) as a nested factor within depths, and time (repeated factor). We found high spatial variability in major benthic components. Overall means indicated that algae were the most abundant biotic component in nearly all areas, ranging from 30.3% at Rosario to 53.3% at San Andrés. Live coral cover varied considerably from 10.1% at Santa Marta up to 43.5% at Urabá. Coral and algae cover per se are not always accurate reef indicators and therefore they need supplementary information. Temporal analyses suggested relative stability of coral and algal cover along the study but the causes for the observed trends were rarely identified. A significant decrease (p = 0.042) in coral cover was only identified for some monitoring plots in Tayrona-time x plot (depth level) interaction, and importantly, few coral species explained this trend. Significant increase (p = 0.005) in algal cover was observed over time for most plots in Rosario. Temporal trajectories in algal cover were influenced by depth-significant time x depth interaction-in San Andrés (increase, p = 0.004) and Urabá (decrease, p = 0.027). Algae trends were mainly explained by changes in algal turfs. Monitoring programs must focus on the mechanisms mediating the changes, in particular those concerning coral recovery and reef resilience in the current context of climate change.

SIMAC: Development and implementation of a coral reef monitoring network in Colombia

Significant coral reef decline has been observed in Colombia during the last three decades. However, due to the lack of monitoring activities, most of the information about health and changes was fragmentary or inadequate. To develop an expanded nation-wide reef-monitoring program, in 1998 INVEMAR (Instituto de Investigaciones Marinas y Costeras: "Colombian Institute of Marine and Coastal Research") designed and implemented SIMAC (Sistema Nacional de Monitorco de Arrecifes Coralinos en Colombia: "National Monitoring System of Coral Reefs in Colombia") with the participation of other institutions. By the end of 2003 the SIMAC network reached more than twice its initial size, covering ten reef areas (seven in the Caribbean and three in the Pacific), 63 reef sites and 263 permanent transects. SIMAC monitoring continued without interruption until 2008 and should persist in the long-term. The SIMAC has a large database and consists basically of water quality measurements (temperature, salinity, turbidity) and a yearly estimation of benthic reef cover, coral disease prevalence, gorgonian density, abundance of important mobile invertebrates, fish diversity and abundance of important fish species. A methods manual is available in the Internet. Data and results of SIMAC have been widely circulated through a summary report published annually since 2000 for the Colombian environmental agencies and the general public, as well as numerous national and international scientific papers and presentations at meetings. SIMAC information has contributed to support regional and global reef monitoring networks and databases (i.e. CARICOMP, GCRMN, ReefBase).

Pervasive genetic structure at different geographic scales in the coral-excavating sponge Cliona vermifera (Hancock, 1867) in the Mexican Pacific

Cliona vermifera is one of the most abundant excavating sponges in Mexican coral reefs, and represents a potential threat to their health. It appears to have limited dispersal potential, but, paradoxically, it is widespread over much of the 2000 km of Mexican Pacific waters, suggesting mechanisms of long-distance dissemination. Despite its ecological importance, nothing is known about its patterns of genetic structure and connectivity in space and time. In this study, we assess levels of genetic structure and test the hypothesis of limited dispersal and isolation by distance among coral reef systems in the Mexican Pacific. Genetic diversity levels were consistently low in DNA sequences from two mitochondrial genes and one nuclear gene; however, they revealed strong and significant genetic differentiation throughout the study region. Patterns of genetic differentiation from the slow-evolving mitochondrial, but not the nuclear, genes were geographic scale dependent. We found higher mitochondrial genetic similarity among localities at 10–100s km than at larger scales (100–1000s km). However, all samples were genetically differentiated at the nuclear locus, which is inconsistent with frequent long-distance dispersal. Significant isolation by distance is consistent with life history traits shared by boring sponges: a short larval period and larval philopatric behavior. The patterns of genetic differentiation in C. vermifera concur with those found in other sympatric coral species, and suggest the influence of community-wide ecological and genetic mechanisms on the genetic makeup of coral reef species in the Mexican Pacific. Fixed genetic differences suggest that the southern population of Oaxaca may be experiencing incipient speciation.

Changes in coral reef communities across a natural gradient in seawater pH.

Ocean acidification threatens the survival of coral reef ecosystems worldwide. The negative effects of ocean acidification observed in many laboratory experiments have been seen in studies of naturally low-pH reefs, with little evidence to date for adaptation. Recently, we reported initial data suggesting that low-pH coral communities of the Palau Rock Islands appear healthy despite the extreme conditions in which they live. Here, we build on that observation with a comprehensive statistical analysis of benthic communities across Palau's natural acidification gradient. Our analysis revealed a shift in coral community composition but no impact of acidification on coral richness, coralline algae abundance, macroalgae cover, coral calcification, or skeletal density. However, coral bioerosion increased 11-fold as pH decreased from the barrier reefs to the Rock Island bays. Indeed, a comparison of the naturally low-pH coral reef systems studied so far revealed increased bioerosion to be the only consistent feature among them, as responses varied across other indices of ecosystem health. Our results imply that whereas community responses may vary, escalation of coral reef bioerosion and acceleration of a shift from net accreting to net eroding reef structures will likely be a global signature of ocean acidification.

Mercury (Hg) speciation in coral reef systems of remote Oceania: Implications for the artisanal fisheries of Tutuila, Samoa Islands

We investigated Hg in muscle tissue of fish species from three trophic levels on fringing reefs of Tutuila (14°S, 171°W), plus water, sediment and turf alga. Accumulation of total Hg in the herbivore Acanthurus lineatus (Acanthuridae, lined surgeonfish, (n=40)) was negligible at 1.05 (±0.04) ngg−1 wet-weight, (∼65% occurring as methyl Hg). The mid-level carnivore Parupeneus spp. (Mullidae, goatfishes (n=10)) had total Hg 29.8 (±4.5) ngg−1 wet-weight (∼99% as methyl Hg). Neither A. lineatus or Parupeneus spp. showed a propensity to accumulate Hg based on body size. Both groups were assigned a status of “un-restricted” for monthly consumption limits for non-carcinogenic health endpoints for methyl Hg. The top-level carnivore Sphyraena qenie (Sphyraenidae, blackfin barracuda, n=3) had muscle tissue residues of 105, 650 and 741ngg−1 wet-weight (100% methyl Hg, with increasing concentration with body mass, suggesting that S. qenie >15kg would have a recommendation of “no consumption”.

Bottom-Up Factors for Algal Productivity Outweigh No-Fishing Marine Protected Area Effects in a Marginal Coral Reef System

Herbivory, together with seasonal variations in temperature, light and nutrient concentration regulate macroalgal populations on coral reefs. Individual management interventions can influence this balance by altering some, but not all of these potential drivers. For example, no-take marine protected areas (MPAs) on coral reefs can increase herbivorous fish abundance, thereby decreasing macroalgal coverage, but have limited influence on water quality and other vagile drivers. We compared the relative influence of seven abiotic water quality variables to that of MPA status on macroalgal coverage in 14 sites (5 of which are within no-take MPAs) over four consecutive seasons (summer through to spring) within the marginal coral reef habitats of Moreton Bay, Australia. Algal cover was quantified by taking 100 photo quadrats per site per sampling with the relative importance of our eight factors determined statistically by generalised additive models. Overall, temporal variations in total macroalgal cover and four out of five important macroalgal genera correlated with factors other than marine protection, especially water temperature, salinity, water clarity (Secchi disc) and nutrient concentration (nitrogen and phosphorus). However, seasonal variations in cover of individual macroalgal genera did not follow strong temporal trends and were not consistent with total macroalgal cover, meaning that different factors were significant for different algal genera. Consequently, we advocate for caution in determining the influence of impact gradients by exclusively measuring total macroalgal cover. This study highlights the importance of considering local impact gradients and habitat recovery processes in the design of protected area networks.

Fish herbivory as key ecological function in a heavily degraded coral reef system

AbstractLocalized impacts, such as eutrophication and overfishing, have been identified as major threats to reefs worldwide, resulting in changes in coral reef community composition, from coral‐dominance to algal‐dominance. Herbivory by fishes is frequently cited as a key process structuring benthic community response to stressors. Here, we experimentally tested the capacity of herbivorous fishes to remove macroalgae along an onshore–offshore spatial gradient in the Spermonde Archipelago, Indonesia; a coral reef system exposed to long‐term anthropogenic disturbances. Bioassays of Sargassum and Padina spp. were collected from the reef flat and transplanted onto the reef slope at five islands varying in distance (1–55 km) from the coastline and city of Makassar, South Sulawesi. Supplementary underwater video deployment and fish surveys were used to identify species‐specific differences in herbivore communities and rates of algal removal. Over a 24 h period, Padina was almost completely removed from the two outermost islands, but removal declined toward shore. With the exception of the site closest to Makassar, more than 50% of all transplanted macroalgae were removed. Species diversity of algal‐consuming fishes and total bites increased toward off‐shore, with only one species, Siganus virgatus (Siganidae), feeding at all sites. These changes in herbivore communities underline the capacity for functional resilience under varying levels of reef degradation. Our results exemplify the complexities of ecological functioning along environmental gradients.

Analysis of Ocean Current Observations in the Northern Veracruz Coral Reef System, Mexico: 2007–12

ABSTRACT Allende-Arandia, M.E.; Zavala-Hidalgo, J.; Romero-Centeno, R.; Mateos-Jasso, A.; Vargas-Hernandez, J.M., and Zamudio, L., 2016. Analysis of ocean current observations in the northern Veracruz Coral Reef System, Mexico: 2007–12. The Veracruz Coral Reef System (VCRS) is a marine protected area located on the continental shelf of Veracruz, in the SW Gulf of Mexico, that is formed by two reef conglomerates: one to the north, in front of the Port of Veracruz, and one to the south, in front of the Anton Lizardo tip. To characterize the currents and their variability for the northern reefs of the VCRS, ocean currents, meteorological parameters, and sea-level observations for the period 2007–12 were analyzed. The temporal variability of the currents was dominated by 2- to 10-day lasting events associated with the atmospheric synoptic conditions through the forcing of the along-coast wind-stress component over the Tamaulipas-Veracruz shelf. During autumn–winter, strong episodic southeastward currents prev...

Water quality assessment in the Mexican Caribbean: Impacts on the coastal ecosystem

Coastal zones are dominated by economically important ecosystems, and excessive urban, industrial, agricultural, and tourism activities can lead to rapid degradation of those habitats and resources. Groundwater in the Eastern Yucatan Peninsula coastal aquifer discharges directly into the coastal ocean affecting the coral reefs, which are part of the Mesoamerican Coral Reef System. The composition and impacts of groundwater were studied at different coastal environments around Akumal (SE Yucatan Peninsula). Radium isotopes and salinity were used to quantify fresh groundwater and recirculated seawater contributions to the coastal zone. Excess Ra distribution suggests spatially variable discharge rates of submarine groundwater. High NO3− levels and high coliform bacteria densities indicate that groundwater is polluted at some sites. Dissolved phosphorous content is elevated in the winter and during the high tourism season, likely released from untreated sewage discharge and from aquifer sediments under reducing conditions.

Assessment of Egypt’s Red Sea coastal sensitivity to climate change

A coastal sensitivity index (CSI) was developed to assess the response of the Red Sea coast in Egypt to climate change in terms of sea level rise and global warming. Six different variables pertaining to the intrinsic characteristics of the coast that extends to 1200 km were utilized, notably: coastal geomorphology, coastal slope, width of the coastal plain, shoreline exposure, fauna/flora and land use. Data have been extracted, manipulated and presented using remote sensing and GIS analysis. The resulting coastal sensitivity map depicts the susceptibility levels of the Red Sea coastal plain to climate change. The most severely sensitive segments (very high CSI) account for 31 % (365 km) of the coast. They occur across unconsolidated, flat, wide, exposed, ecologically effective and/or inhabited coasts. On the other hand, the least sensitive (low CSI) coastal segments total 245 km (20 %) and are mainly rocky, steep, narrow, barren and/or inaccessible shores. Eustatic sea level rise by 1 m should inundate a coastal area of 106 km2, whereas a sudden tsunami of 5 m height should overwhelm 724 km2, particularly at the southern section near Shalateen. Global warming of seawater should impact the coastal zone between Hurghada and Marsa Alam (270 km long) due to the occurrence of fringing coral reef systems. The coastal sensitivity index provides a synoptic overview that could help prioritize emergency plans and protection strategies to reduce the ramifications of climate change.

Heat balances and thermally driven lagoon‐ocean exchangeson a tropical coral reef system (Moorea, French Polynesia)

AbstractThe role of surface and advective heat fluxes on buoyancy‐driven circulation was examined within a tropical coral reef system. Measurements of local meteorological conditions as well as water temperature and velocity were made at six lagoon locations for 2 months during the austral summer. We found that temperature rather than salinity dominated buoyancy in this system. The data were used to calculate diurnally phase‐averaged thermal balances. A one‐dimensional momentum balance developed for a portion of the lagoon indicates that the diurnal heating pattern and consistent spatial gradients in surface heat fluxes create a baroclinic pressure gradient that is dynamically important in driving the observed circulation. The baroclinic and barotropic pressure gradients make up 90% of the momentum budget in part of the system; thus, when the baroclinic pressure gradient decreases 20% during the day due to changes in temperature gradient, this substantially changes the circulation, with different flow patterns occurring during night and day. Thermal balances computed across the entire lagoon show that the spatial heating patterns and resulting buoyancy‐driven circulation are important in maintaining a persistent advective export of heat from the lagoon and for enhancing ocean‐lagoon exchange.

Marine sponges (Porifera: Demospongiae) from the Gulf of México, new records and redescription of Erylus trisphaerus (de Laubenfels, 1953).

Marine sponges usually constitute the most diverse group of the benthic community in coral reefs. Although they are reasonably well studied at the northern Gulf of Mexico (GMx), the southern GMx is poorly known and lacks records from many major reef systems that lie off the Mexican coast. The present taxonomic study is the first sponge account from Alacranes reef, the largest coral reef system in the GMx, and from the shallow reef banks of Sisal, both in the northwest Yucatan Peninsula. The 19 species herein described represent the first sponge fauna records from these reefs. Among these, seven species represent new record for GMx: Erylus formosus, Cliona flavifodina, Spirastrella aff. mollis, Strongylacidon bermuda, Topsentia bahamensis, Agelas tubulata and Chelonaplysilla aff. erecta. Twelve species are new records for the Southern GMx: Erylus trisphaerus, Cliona amplicavata, Chondrilla caribensis, Halichondria lutea, Hymeniacidon caerulea, Axinella corrugata, Dragmacidon reticulatum, Chalinula molitba, Amphimedon caribica, A. complanata, Hyatella cavernosa and Dysidea variabilis. Additionally, a redescription of Erylus trisphaerus is presented which had not been reviewed since its original description in 1953 off Western Florida, except that it was listed for north La Habana, Cuba.