Catch organism assemblages along artificial reefs area and adjacent waters in Haizhou Bay

To better understand the community patterns mediated by connectivity in artificial reefs of coastal areas, it is necessary to understand the distribution and coexistence of organisms with artificial reefs area and adjacent waters. This study was conducted to examine main catches assemblages collected by trawls in Haizhou Bay,which included five habitats: the artificial reef area(AR), aquaculture area(AA), natural area(NA), estuary area(EA) and comprehensive effect area(CEA). The result shows that the total abundances of species in the five habitats were highly different(univariate PERMANOVA: P = 0.001, n = 24), but some species were also unique in their habitat(e.g. Scapharca subcrenata and Glossaulax didyma in AA). The body size distribution of specific species between habitats are different. For Collichthys lucidus, their body size in AR(14.63 cm ± 1.64 cm) and EA(14.3 cm ± 0.85 cm) is higher than that in NA(10.65 cm ± 1.64 cm), CEA(11.28 cm ± 1.85 cm) and AA(12.1 cm ±0.43 cm), which indicates the potential connection from AR to EA mediated by their adult population. We concluded that artificial reefs in AR can be considered key components that have the ability to support species assemblages in adjacent habitats. This study has implications for the conservation and monitoring of species assemblages in coastal areas in terms of that artificial reefs can be applied in different stages of habitat protection implementation and in different combinations of scenarios.

The Variation of Plankton Community Structure in Artificial Reef Area and Adjacent Waters in Haizhou Bay

Plankton are an important component of marine protected areas(MPAs),and its communities would require much smaller interpatch distances to ensure connection among MPAs.According to the survey from MPAs dominated by artificial reefs and adjacent waters(estuary area(EA),aquaculture area(AA),artificial reef area(ARA),natural area(NA)and comprehensive effect area(CEA))in Haizhou Bay in spring and autumn,we analyzed phyto-zooplankton composition,abundance and biomass,and correlation with hydrologic variables to gain information about the forces that structure the plankton.The results showed that the dominant zooplankton were copepods(spring,98.9%;autumn,94.2%),while the phytoplankton were mainly composed of Bacillariophyta(spring,61.8%;autumn,95.6%).The RDA results showed that temperature,salinity and depth highly associated with the distribution and composition of plankton species among the habitats than other factors in spring;temperature,Chla and DO had the strongest influence in autumn.The zooplankton in the ARA and AA ecosystems basically contained the same species as those in other habitats,and each habitat also exhibited a relatively unique combination of plankton species.The structures of the EA zooplankton in spring and the EA phytoplankton in both seasons were much different than other habitats,which may have been caused by factors such as currents and tides.We concluded that there exists similarity of the plankton community between artificial reef area and adjacent waters,whereas the EAs may be relatively independent systems.Therefore,these interaction between plankton community should be considered when designing MPA networks,and ocean circulations should be considered more than the environmental factors.

Flow Field Characteristics of Multi-Trophic Artificial Reef Based on Computation Fluid Dynamics

On the basis of computational fluid dynamics,the flow field characteristics of multi-trophic artificial reefs,including the flow field distribution features of a single reef under three different velocities and the effect of spacing between reefs on flow scale and the flow state,were analyzed.Results indicate upwelling,slow flow,and eddy around a single reef.Maximum velocity,height,and volume of upwelling in front of a single reef were positively correlated with inflow velocity.The length and volume of slow flow increased with the increase in inflow velocity.Eddies were present both inside and backward,and vorticity was positively correlated with inflow velocity.Space between reefs had a minor influence on the maximum velocity and height of upwelling.With the increase in space from 0.5 L to 1.5 L(L is the reef lehgth),the length of slow flow in the front and back of the combined reefs increased slightly.When the space was 2.0 L,the length of the slow flow decreased.In four different spaces,eddies were present inside and at the back of each reef.The maximum vorticity was negatively correlated with space from 0.5 L to 1.5 L,but under 2.0 L space,the maximum vorticity was close to the vorticity of a single reef under the same inflow velocity.

Effect of diagenetic variation on the static and dynamic mechanical behavior of coral reef limestone

Coral reef limestone at different depositional depths and facies differ remarkably on the textural and mineralogical characteristics,owing to the complex sedimentary diagenesis.To explore the effects of pore structure and mineral composition associated with diagenetic variation on the mechanical behavior of reef limestone,a series of quasi-static and dynamic compression tests along with microscopic examinations were performed on the reef limestone at shallow and deep burial depths.It is revealed that the shallow reef limestone(SRL)is classified as a porous aragonite-type carbonate rock with high porosity(55.3±3.2)%and pore connectivity.In comparison,the deep reef limestone(DRL)is mainly composed of dense calcite-type calcium carbonate with low porosity(4.9±1.6)%and pore connectivity.The DRL strengthened and stiffened by the tight grain framework consistently displays much higher values of the dynamic compressive strength,elastic modulus,brittleness index,and specific energy absorption than those of the SRL.The gap between two types of limestone further increases with an increase in strain rate.It appears that the failure pattern of SRL is dominated by the inherent defects like weak bonding interfaces and growth lines,revealed by the intricate fracturing network and mixed failure.Likewise,although the preexisting megapores in DRL may affect the crack propagation on pore tips to a certain distance,it hardly alters the axial splitting failure of DRL under impacts.The stress wave propagation and attenuation in SRL is primarily controlled by the reflection and diffusion caused by plenty mesopores,as well as an energy dissipation in layer-wise pore collapse and adjacent grain crushing,while the stress wave in DRL is highly hinged on the insulation and diffraction induced by the isolated megapores.This process is accompanied by the energy dissipation behavior of inelastic deformation resulted from the pore-emanated microcracking.

A machine learning-based strategy for predicting the mechanical strength of coral reef limestone using X-ray computed tomography

Different sedimentary zones in coral reefs lead to significant anisotropy in the pore structure of coral reef limestone(CRL),making it difficult to study mechanical behaviors.With X-ray computed tomography(CT),112 CRL samples were utilized for training the support vector machine(SVM)-,random forest(RF)-,and back propagation neural network(BPNN)-based models,respectively.Simultaneously,the machine learning model was embedded into genetic algorithm(GA)for parameter optimization to effectively predict uniaxial compressive strength(UCS)of CRL.Results indicate that the BPNN model with five hidden layers presents the best training effect in the data set of CRL.The SVM-based model shows a tendency to overfitting in the training set and poor generalization ability in the testing set.The RF-based model is suitable for training CRL samples with large data.Analysis of Pearson correlation coefficient matrix and the percentage increment method of performance metrics shows that the dry density,pore structure,and porosity of CRL are strongly correlated to UCS.However,the P-wave velocity is almost uncorrelated to the UCS,which is significantly distinct from the law for homogenous geomaterials.In addition,the pore tensor proposed in this paper can effectively reflect the pore structure of coral framework limestone(CFL)and coral boulder limestone(CBL),realizing the quantitative characterization of the heterogeneity and anisotropy of pore.The pore tensor provides a feasible idea to establish the relationship between pore structure and mechanical behavior of CRL.

Paleogene and Early Neogene Lacustrine Reefs in the Western Qaidam Basin, China

Typical reefs in the Paleogene and early Neogene strata of the Qaidam Basin, Tibetan Plateau, China, reveal their internal structures and sedimentation environments and consist mainly of algal reef, stromatolite reef and thrombolite reef with distinct reef structures, fore-reef, back-reef and reef-plateau. The fore-reef is characterized by a combination of pinnacle reef, thrombolite and algal reef. The back reef is composed of stromatolite reef and algal reef. The pinnacle reefs (micro-atoll), most of which are several tens of centimeters in diameter (whereas some exceptionally big ones are over 200 cm in diameter), and several tens of centimeter to 2 m in height, are situated on the far front-edge of the reef; the pinnacle reef is also often of recumbent form with a gravel-filled circular hole in the center. The algal reef is in the form of dome and irregular beds, and filled with algal detritus, ostracodes, spirorbis fossils, ooid and terrigenous debris, and worm traces; cavities and scour marks are often developed. The algal reef is gray commonly when fresh and weathers to a brown color. The lacustrine thrombolite in the Qaidam Basin is light gray or deep gray when fresh, white-gray or brown when weathered, dense and homogeneous with abundant pores filled by oil and bitumen. Observed under the microscope, the thrombolite consists mainly of brown or brown-black clots with a little algal debris, ooid, pellet, ostracodes, spirorbis fossils and terrigenous debris, in some cases, terrigenous debris, even gravel, is abundant. Many features of the thrombolite suggest that it is formed in a high-energy envkonment. The stromatolite reefs developed on the lacustrine algal reef in the Qaidam Basin are very complex whether in shape or in internal structure. The simplest ones form laminated layers and the most complex ones have intensely branching structures. The size is also variable.

Quantitative Evaluation of the Sea-level Drop at the End-Permian: Based on Reefs

The amplitude of pre-Quaternary sea level drop, H, can be calculated by usingthe formula H = D + To, where To is the original thickness from the top of the tidal deposits onthe reef core to the bottom of the tidal deposits on the reef front, or to the bottom of the ancientmeteoric vadose zone, or to the edge of the mixed-water dolostone zone. The identity and similaritybetween the sea-level drop amplitudes calculated from different reefs far away from each otherindicates that such sea-level changes are eustatic rather than relative changes. Evidence of anend-Permian sea-level drop has been found on the Changxingian (i.e. the end of the Palaeofusulinazone) reefs at Ziyun in South China, including algal laminated deposits, sabkha-related dolostone,desiccation cracks, dissolution collapse breccia. According to calculation based on the meteoricdissolution zone of the reef-core sequence at Ziyun, Guizhou province, the amplitude of thesea-level drop at the end-Permian is about 89.3 m. Calculation via the dolomitized upper part of theChangxingian reef in Lichuan, Hubei Province, yields an 88.9 m amplitude of the sea-level drop atthe end-Permian. Comparison shows that the sea-level drop recorded in the two distantly locatedreefs may be of eustatic type. So the amplitude of the sea level drop of the Tethys Sea at theend-Permian might be at least 89.3 m.

Studies on Factors Influencing Hydrodynamic Characteristics of Plates Used in Artificial Reefs

As a simplified model of artificial reefs, a series of plate models punched with square or circular openings are designed to investigate the effects of openings on the hydrodynamic characteristics of artificial reefs. The models are grouped by various opening numbers and opening-area ratios. They are physically tested in a water flume or used in the numerical simulation to obtain the drag force in the uniform flow with different speeds. The simulation results are found in good agreement with the experimental measurements. By the non-dimensional analysis, the drag coefficient specified to each model is achieved and the effects of openings are examined. It is found that the key factor affecting the drag coefficient is the open-area ratio. Generally, the drag coefficient is a linear function of the open area ratio with a minus slope. The empirical formulae for the square and circular openings respectively are deduced by means of the multiple regression analysis based on the measured and numerical data. They will be good references for the design of new artificial reefs. As a result of numerical simulation, the vorticity contours and pressure distribution are also presented in this work to better understand the hydrodynamic characteristics of different models.

Post-Rifting Magmatism and the Drowned Reefs in the Xisha Archipelago Domain

Fourteen isolated drowned reefs have been identified around the Xisha Uplift by multibeam and seismic data. The drowning processes of these reefs can be divided into three different stages, which correspond to three different accelerated tectonic subsidence periods. The drowning of the Xisha reefs is the result of the combined action of tectonic subsidence and sea level fluctuations, and the tectonic subsidence rate had to remain above 0.2 mm yr^(-1 )for a long time. Three abrupt accelerated tectonic subsidence events that occurred in the late Miocene, Pliocene and early Quaternary in the Xisha Uplift were closely related to the thermal subsidence processes after three stages of post-rifting magmatism. The magmatism of the middle Miocene and the following thermal subsidence resulted in the drowning of reefs in the northwestern Xisha uplift(Zone A). During the early Pliocene, massive magmatic intrusions and volcanic eruptions occurred in the Xisha Uplift. Then, the subsequent thermal subsidence started the drowning process of reefs in the northeastern and western regions of the Xisha Uplift(Zone B and C). During the early Quaternary, large-scale magmatism also occurred in the Xisha Uplift. The subsequent thermal subsidence resulted in a new rapid tectonic subsidence, which caused the reefs in the southern and southeastern regions of the Xisha Uplift to drown(Zone D and E).

Paleoecology of Early Ordovician Reefs in the Yichang Area,Hubei:a Correlation of Organic Reefs Between Early Ordovician and Jurassic

The Early Ordovician System is composed mainly of a series of carbonate platform deposits interbedded with shale and is especially characterized by a large number of organic reefs or buildups that occur widely in the research area.The reefs have different thicknesses ranging from 0.5 m to 11.5 m and lengths varying from 1 m to 130 m.The reef-building organisms include Archaeoscyphia, Recepthaculitids,Batostoma,Cyanobacteria and Pulchrilamina.Through the research of characteristics of the reef-bearing strata of the Early Ordovician in the Yichang area,four sorts of biofacies are recognized,which are(1) shelly biofacies:containing Tritoechia-Pelmatozans community and Tritoechia-Pomatotrema community;(2) reef biofacies:including the Batostoma,Calathium-Archaeoscyphia, Pelmatozoa-Batostoma,Archeoscyphia and Calathium-Cyanobacteria communities; (3) standing-water biofacies:including the Acanthograptus-Dendrogptus and Yichangopora communities;and(4) allochthonous biofacies:containing Nanorthis-Psilocephlina taphocoense community.The analysis of sea-level changes indicates that there are four cycles of sea-level changes during the period when reef-bearing strata were formed in this area,and the development of reefs is obviously controlled by the velocity of sea-level changes and the growth of accommodation space.The authors hold that reefs were mostly formed in the high sea level periods.Because of the development of several subordinate cycles during the sea-level rising,the reefs are characterized by great quantity, wide distribution,thin thickness and small scale,which are similar to that of Juassic reefs in northern Tibet.The research on the evolution of communities shows that succession and replacement are the main forms.The former is favorable to the development of reefs and the latter indicates the disappearance of reefs.

Underwater topography detection of Shuangzi Reefs with SAR images acquired in different time

Imaging mechanism of underwater topography by SAR and a underwater topography SAR detection model built on the theory of underwater topography detection with SAR image presented by Yuan Yeli are used to detect the underwater topography of Shuangzi Reefs in the Nansha Islands with three scenes of SAR images acquired in different time. Detection results of three SAR images are compared with the chart topography and the detection errors are analyzed. Underwater topography detection experiments of Shuangzi Reefs show that the detection model is practicable. The detection results indicate that SAR images acquired in different time also can be used to detect the underwater topography, and the detection results are affected by the ocean conditions in the SAR acquiring time.

Survey of reefs based on Landsat 8 operational land imager(OLI)images in the Nansha Islands, South China Sea

A detailed survey of the reefs in the Nansha Islands＇ sea that are of strategic importance is conducive to their future development. In this study, a total of 50 Landsat 8 operational land imager（OLI） images were used to analyze the geological features and spectral characteristics of the Nansha reefs. The exposed islands/sandbanks,reef flats and sub-tidal reefs were identified with the near-infrared band, the red and green bands, and the blue band, respectively. Based on the relationships among various characteristics and bands illustrated in the OLI images, the maximum between-cluster variance threshold algorithm（OTSU method） and the mathematical morphology were employed to extract characteristic parameters of the spatial geometry of the reefs from top to bottom, which were subsequently operated by a series of post-processing methods such as vectorization,simplification and topological analysis. Among the 132 standalone reefs and 16 atolls that are identified in the study, four reefs have yet to be named in the Standard Names of Various Islands in the South China Sea and the website Nansha Islands Online（http：//www.nansha.org/）. Another 24 ones are exposed to the atmosphere even during high tides. Taiping Island with an area of 0.57 km^2 represents the largest exposed geological feature. This study demonstrated the applicability of medium-resolution satellite images to derive the coral reef information effectively and thus provided information for the related departments that are responsible to manage the coast.An improved resolution of multispectral bands with the panchromatic band in higher spatial resolution（15 m for OLI image） is expected to provide an optimum satellite based approach to map marine habitats.

Formation and evolution of the tertiary carbonate reefs in the Madura Strait Basin of Indonesia

Analysis of 2 D seismic data over 4 500 km in length from the Madura Strait Basin in the East Java Sea reveals seismic re?ection characteristics of reefs and associated sedimentary bodies, including asymmetrical or symmetrical dome re?ections, slope progradational re?ections, chaotic re?ections and discontinuous strong re?ections inside the reef, which onlap the ?ank of the reef. It is concluded that the developmental paleo-environment of most reefs is mainly conducive to shallow marine carbonate platform facies and platform margin facies, based on well core data, variations in seismic facies and strata thickness.The formation and evolution of all reefs are primarily in?uenced by the tectonic framework of the Madura Strait Basin. Platform margin reefs are principally controlled by two types of structures: one is a series of E-W trending Paleogene normal faults, and the other is an E-W trending Neogene inversion structures. In addition, wave actions, tidal currents and other ocean currents play an accelerated role in sorting, rounding and redeposition for the accumulation and evolution of reefs. Tertiary reefs in the MSB can be divided into four types: 1) an open platform coral reef of Late Oligocene to Early Miocene, 2) a platform margin coral reef controlled by normal faults in Late Oligocene to Early Miocene, 3) a platform margin Globigerina moundreef controlled by a "hidden" inversion structure in Early Pliocene, and 4) a platform margin Globigerina mound-reef controlled by thrust faults in the early Pliocene. Patterns of the formation and evolution of reefs are also suggested.

A Comparative Study of Numerical Models for Wave Propagation and Setup on Steep Coral Reefs

Complex factors including steep slopes, intense wave breaking, large bottom friction and remarkable wave setup should be considered while studying wave propagation over coral reefs, and how to simulate wave propagation and setup on coral reefs efficiently has become a primary focus. Several wave models can be used on coral reefs as have been published, but further testing and comparison of the reliability and applicability of these models are needed. A comparative study of four numerical wave models (i.e., FUNWAVE-TVD, Coulwave, NHWAVE and ZZL18) is carried out in this paper. These models’ governing equations and numerical methods are compared and analyzed firstly to obtain their differences and connections;then the simulation effects of the four wave models are tested in four representative laboratory experiments. The results show that all four models can reasonably predict the spectrum transformation. Coulwave, NHWAVE and ZZL18 can predict the wave height variation more accurately;Coulwave and FUNWAVE-TVD tend to underestimate wave setup on the reef top induced by spilling breaker, while NHWAVE and ZZL18 can predict wave setup relatively accurately for all types of breakers;NHWAVE and ZZL18 can predict wave reflection by steep reef slope more accurately. This study can provide evidence for choosing suitable models for practical engineering or establishing new models.

Depositional Architecture and Evolution of Late Permian Reefs in Ziyun County,Southern Guizhou, China

The uppermost Permian reef complex in Ziyun County, southern Guizhou occurs as a third-order depositional sequence developed in the platform marginal break zone during the Late Permian transgressive period This paper deals with the evolution of the third-order sequence and depositional arthitecture of the sequence stratigraphic units with the analysis of outcrop sequence stratigraphy and chemostratigraphy. Thirteen parasequences which belong to four system tracts are recognized. According to their genetic facies features,three growth strategies of reef accrete from the systems tracts during sea level changes are distinguished as keep-up reefs, give-up reefs and catch-up reefs. In combination with an absolute water depth analysis by chemostratigraphic method, we establish an entire sea level curve of the third-order sequence and discuss its evolution and depositional response.

Habitat values for artificial oyster (Crassostrea ariakensis) reefs compared with natural shallow-water habitats in Changjiang River estuary

Oyster reefs have an equivalent, complex 3-dimensional structure to vegetated habitats and may provide similar functions in estuarine environments. Nevertheless, few studies have compared oyster reefs with adjacent natural shallow-water habitats. Here the resident benthic macroinvertebrate communities in an artificial oyster （Crassostrea ariakensis） reef and in adjacent natural estuarine shallow-water habitats （salt marsh, intertidal mudflat, and subtidal soft bottom） in the Changjiang （Yangtze） River estuary were described. The mean total densities and biomass, Margalef＇s species richness, Pielou＇s evenness and Shannon-Weaver biodiversity indices of the resident benthic macroinvertebrate communities differed significantly among the habitats. Significantly higher densities and biomass of benthic macroinvertebrates occurred in the oyster reef compared with the other three habitats. Ordination plots showed a clear separation in benthic macroinvertebrate communities among the four habitat types. The results demonstrated that the artificial oyster reef supported distinct and unique benthic communities, playing an important role in the complex estuarine habitat by supplying prey resources and contributing to biodiversity. In addition, the results suggested that the oyster reef had been restored successfully.

ESR DATING OF CORAL REEFS IN THE SOUTH CHINA SEA

ESR dating of aragonitic and calcitic corals , eolianite , calcrete , and corallineae from coral reefs in the South China Sea was applied to study of Quaternary reef geology . The ESR ages of calcitic corals correlated with the biostratigraphy , lithostratigraphy and geochemistry of Well Xi-Chen-1 and the oxygen-isotope stratigraphy of deep sea sediments, were reliable and up to 1.26 Ma. The selection of signals for dating and other related problems are discussed .

Distribution Characteristics of Fat Greenling(Hexagrammos otakii) Inhabiting Artificial Reefs Around Qiansandao Island, Haizhou Bay, China

Chinese government has provided vigorous financial supports to artificial reef(AR)projects to repair marine ecosystem.Qiansandao AR,an important AR project of Fishery Resource Restoration Program in Shandong Province,was built during 2002 to 2007.It has enhanced the local fishery harvest and generated positive economic benefits.Fat greenling(Hexagrammos otakii)is a major commercial reef fish in Qiansandao with high economic values.Its distribution characteristics need to be further studied.In this research,we studied the potential influence of environmental variables and distance from ARs on catch per unit effort(CPUE)and body length of fat greenlings.The results showed that the average body length of fat greenlings distributed within 10 m from ARs was longer than that of fat greenlings distributed more than 600 m away from ARs.Body length also increased with the increased salinity,while it declined as temperature increased.The probability of the presence of fat greenling increased when temperature was below 20℃,then it slightly decreased.CPUE decreased as the distance increased.Our results elucidate the potential effects of environmental variables and distance from ARs on the distribution of fat greenling,which may also be helpful to the distribution research of other reef fish species.

Analysis on coral reefs mapping using SPOT5 data at the Dongsha Atoll

Coral reefs are an sensitive-to-environment complex marine ecosystem. The ecosystem of corals is rich in biodiversity. Remote sensing offers a powerful tool for categorizing coral reefs and is the most cost - effective approach for the large - scale reef survey. The Dongsha Atoll, more than 300 km2 with an average depth of 10 m, is located at the northern continental margin of the South China Sea. It has been abused by destructive fishing during recent decades. Three satellite imageries （Quickbird2, ETM ＋ and SPOTS） are used to evaluate the capabilities of SPOT5 imagery to provide data that are useful for categorizing the current distribution of coral reefs therein. During the data processing, unsupervised classification functions are adopted for ETM ＋ and SPOT5 data, while the supervised classification method is used for Quickbird2. The classes are （or not） merged into coral reef, and then will be operated by vectorization, simplification, and topological analysis. There are 1 331 coral reefs larger than 100 m2 with a detection limit of 3 × 3 pixels at the multi - band data of Quickbird2, which is taken as the comparison baseline. The results extracted from SPOT5 and ETM images are less in number and area than those from the Quickbird2 image, whereas the results from SPOT5 data are better than those of ETM data at the silty lagoon due to its higher resolution. SPOT5 XS band 2 fails to distinguish the deep substrate inside the atoll compared with ETM data because of its poor penetration capability. Only SPOT XS band 1 cannot be used to differentiate coral reef from sand bottom. Merging the SPOT5 multi - bands data with the spatial resolution of SPOT5 pan - data and referring to ETM imagery are expected to provide an optimal satellite - based approach for mapping of coral reefs.

Numerical Simulation and Experimental Study of the Effects of Disposal Space on the Flow Field Around the Combined Three-Tube Reefs

The artificial reefs placed on the seabed with different layouts and disposal spaces will produce variational flow field. The intensity and scale of the combined three-tube artificial reefs with different layouts at five Reynolds numbers（Re） are numerically investigated by use of the RNG k-ε turbulent model and SIMPLEC algorithm. A stationary no-slip boundary condition is used on the models and the bottoms, and the free surface is treated as a ＂moving wall＂ with zero shear force and the same velocity with inflow. In order to validate the simulation results, a particle image velocimetry（PIV） experiment is carried out to analyze the flow field. The numerical simulation results are consistent with the data obtained from experiment. The corresponding errors are all below 20%. Based on the validation, the effects of disposal space on flow field are simulated and analyzed. According to the simulation, in a parallel combination, a better artificial reef effect is obtained when the disposal space between two parallel reefs is 1.0L（L is the length of the combined three-tube reef model）. In a vertical combination, when the disposal space between two vertical reefs is 1.0L to 2.0L, the artificial reef effect is better.