Stabilised Coal Ash Studies in Italy

The ENEL Ash Research Centre - (Brindisi, Italy) - has started a research programme on the use of coal ash derived from its thermoelectric power plants as a component of blocks for artificial habitats. After preliminary laboratory tests, systematic physical, chemical, and biological tests were carried out in an experimental installation constructed in the area of the Torrevaldaliga power plant (80 km NW of Rome).

Two reef models - each made by assembling pyramids of 225 20 × 20 × 20 cm blocks - were submerged in two tanks (10 × 2 × 1.5 m) with running sea water (water flow: 3-5 cm s-1). the ash blocks were composed of fly ash (52.1%), bottom ash (26.1%), hydrated lime (5.2%) and water 16.6%, while concrete blocks were made of pozzolanic cement, sand and gravel. After two years, ash based blocks showed no weathering, volume variation or swelling; marked compressive strength and sonic velocity increases have, on the contrary, been recorded. No significant leaching of chemical elements of environmental concern was found. the biotic settlement on the ash blocks proved greater in quantity and better in quality than that on the concrete blocks; on ash blocks 62 species were found, compared to 54 on concrete. Ash-based materials seem to be more suitable for the settlement of the macrobenthos.     

Stabilized Coal Ash Artificial Reef Studies

In 1989, an experimental stabilized coal ash reef was deployed in Poole Bay off the southern coast of the UK. Three different mixtures of pulverised fuel ash, gypsum, flue gas desulphurisation sludge and cement were used along with concrete controls. the aim was to study the environmental compatibility of the reef materials through heavy metal analyses of the blocks to determine if any leaching or changes were occurring. at the same time, reef encrusting and associated biota have been analyzed together with material from concrete control and natural reefs to determine if there was any evidence for excess bioaccumulation.

This paper presents the results from studies of sectioned reef blocks immersed for 3 and 4 years. No significant change in levels of heavy metals (Cd, Cr, Cu, Mn, Ni, Pb, Zn) has been detected. Surface loss of calcium, presumably associated with the gypsum component, is confirmed with evidence of replacement by magnesium. Trends in data suggest initial surface changes which slow with time.

Epibiota have been analyzed for heavy metal content. the variety of reef-associated organisms has been extended to include mobile, resident species which are higher in the food chain: molluscs, crustaceans and territorial fish. No consistent evidence of bioaccumulation of a range of heavy metals (above those levels found in organisms associated with control reefs) has been detected. Monitoring of the encrusting species range and densities shows little difference between colonisation of the concrete and ash mixture blocks.     

Stability of a Coal Waste Artificial Reef

The feasibility of using U.K. coal-fired power station waste materials for artificial reef production is being examined. in June, 1989, an experimental artificial reef was constructed in Poole Bay, off the central south coast of the U.K., using three different mixtures of pulverised fuel ash (PFA), flue gas desulphurisation (FGD) gypsum and slurry, stabilized with cement and formed into blocks. Fifty tonnes of 40 × 20 × 20 cm blocks were formed into eight conical reef units replicating three different PFA/gypsum mixtures and one concrete control. the reef structure is 10m below chart datum on a flat sandy sea-bed.

Combustion of coal concentrates the heavy metal content in the resultant ash. the purpose of stabilization of the ash as blocks is twofold: to immobilize heavy metals (or other components) and to provide hard substratum for the attachment of organisms. to examine the effectiveness of this stabilization and hence the environmental compatibility of the block materials, heavy metal (Cd, Cr, Cu, Pb, Mn, Ni, Zn) content of the blocks has been monitored routinely over two years, to determine leaching rates. Sectional profiles indicate partial replacement of calcium content by magnesium. Associated with this there has also been some redistribution of heavy metals. Only in the case of cadmium has there been a detectable loss from the surface of blocks. Chromium and manganese concentrations appear to have increased. the metal content of the reef epibiota (including ascidians, Ascidia mentula; hydroids, Halecium spp.; bryozoans, Bugula spp. and red algae) growing on the ash blocks has been compared to that of epibiota attached to the concrete controls and surrounding sea-bed. to date no evidence of excess bioaccumulation of metals has been detected.

The physical integrity of the ash reef blocks has been maintained. There is evidence that the blocks are increasing in compressive strength.

An indication of the fishery enhancement potential of the experimental structure is given by the presence of eight commercially fished species (crustaceans and molluscs) including lobsters (Homarus gammarus).     

Stability of a Coal Waste Artificial Reef

The feasibility of using U.K. coal-fired power station waste materials for artificial reef production is being examined. in June, 1989, an experimental artificial reef was constructed in Poole Bay, off the central south coast of the U.K., using three different mixtures of pulverised fuel ash (PFA), flue gas desulphurisation (FGD) gypsum and slurry, stabilized with cement and formed into blocks. Fifty tonnes of 40 × 20 × 20 cm blocks were formed into eight conical reef units replicating three different PFA/gypsum mixtures and one concrete control. the reef structure is 10m below chart datum on a flat sandy sea-bed.

Combustion of coal concentrates the heavy metal content in the resultant ash. the purpose of stabilization of the ash as blocks is twofold: to immobilize heavy metals (or other components) and to provide hard substratum for the attachment of organisms. to examine the effectiveness of this stabilization and hence the environmental compatibility of the block materials, heavy metal (Cd, Cr, Cu, Pb, Mn, Ni, Zn) content of the blocks has been monitored routinely over two years, to determine leaching rates. Sectional profiles indicate partial replacement of calcium content by magnesium. Associated with this there has also been some redistribution of heavy metals. Only in the case of cadmium has there been a detectable loss from the surface of blocks. Chromium and manganese concentrations appear to have increased. the metal content of the reef epibiota (including ascidians, Ascidia mentula; hydroids, Halecium spp.; bryozoans, Bugula spp. and red algae) growing on the ash blocks has been compared to that of epibiota attached to the concrete controls and surrounding sea-bed. to date no evidence of excess bioaccumulation of metals has been detected.

The physical integrity of the ash reef blocks has been maintained. There is evidence that the blocks are increasing in compressive strength.

An indication of the fishery enhancement potential of the experimental structure is given by the presence of eight commercially fished species (crustaceans and molluscs) including lobsters (Homarus gammarus).     

Possible Use of Ash Residues for the Construction of Artificial Reefs at Sea

Utilization of ash residues, including coal ash, oil ash, and municipal solid waste combustion ash, for the construction of artificial reefs at sea has been investigated by many researchers throughout the world for nearly 20 years. Both laboratory and field studies have shown that an artificial reef made of stabillized ash-concrete (SAC) has had no adverse effect on the marine environment. Indeed, published studies have shown that fish counts increase around SAC reefs owing to an abundance of colonizing organisms and to protection provided by cavities within the reef structures. However, public and regulatory resistance to the use of SAC for artificial reef construction at sea is still very strong in certain countries due to concern for possible negative environmental impacts, primarily in the area of bioaccumulation of elements or compounds originating from the ash component of SAC.

In this paper, technological feasibility of using ash residues for artificial reef construction is presented, based on the available 20 years of scientific data, including engineering workability, physical integrity, chemical leaching potential and biological effects. More important, we also identify conceptual barriers for the acceptance of using SAC for the construction of ocean reefs and suggest approaches to overcome these barriers.     

Possible Use of Ash Residues for the Construction of Artificial Reefs at Sea

Utilization of ash residues, including coal ash, oil ash, and municipal solid waste combustion ash, for the construction of artificial reefs at sea has been investigated by many researchers throughout the world for nearly 20 years. Both laboratory and field studies have shown that an artificial reef made of stabillized ash-concrete (SAC) has had no adverse effect on the marine environment. Indeed, published studies have shown that fish counts increase around SAC reefs owing to an abundance of colonizing organisms and to protection provided by cavities within the reef structures. However, public and regulatory resistance to the use of SAC for artificial reef construction at sea is still very strong in certain countries due to concern for possible negative environmental impacts, primarily in the area of bioaccumulation of elements or compounds originating from the ash component of SAC.

In this paper, technological feasibility of using ash residues for artificial reef construction is presented, based on the available 20 years of scientific data, including engineering workability, physical integrity, chemical leaching potential and biological effects. More important, we also identify conceptual barriers for the acceptance of using SAC for the construction of ocean reefs and suggest approaches to overcome these barriers.     

Behaviour of Dioxins, Furans and Metals Associated with Stabilized Msw Combustor Ash in Sea Water

This report presents the results of a research programme designed to examine the engineering and environmental acceptability of stabilizing municipal solid waste (MSW) combustor ash for artificial reef construction. Municipal solid waste combustor ash was combined with Portland cement to form solid blocks using conventional construction block making technology. the resultant stabilized combustor ash (SCA) blocks were used to construct an artificial habitat in Conscience Bay, Long Island Sound, New York and compared to identical concrete blocks, fabricated using natural aggregates. Over a 4.5 year period divers periodically returned to the site to monitor the interaction of SCA blocks with the marine environment and compare the performance of these blocks with the concrete control blocks. Results show that the SCA blocks retain their strength after prolonged sea water exposure. Contaminants of environmental concern, including metals, dioxins and furans, were retained within the cementitious matrix of the SCA blocks after prolonged sea water submersion. in addition, organisms growing on the surfaces of the SCA blocks did not accumulate contaminants from the blocks.     

Behaviour of Dioxins,Furans and Metals Associated with Stabilized Msw Combustor Ash in Sea Water

This report presents the results of a research programme designed to examine the engineering and environmental acceptability of stabilizing municipal solid waste (MSW) combustor ash for artificial reef construction. Municipal solid waste combustor ash was combined with Portland cement to form solid blocks using conventional construction block making technology. the resultant stabilized combustor ash (SCA) blocks were used to construct an artificial habitat in Conscience Bay, Long Island Sound, New York and compared to identical concrete blocks, fabricated using natural aggregates. Over a 4.5 year period divers periodically returned to the site to monitor the interaction of SCA blocks with the marine environment and compare the performance of these blocks with the concrete control blocks. Results show that the SCA blocks retain their strength after prolonged sea water exposure. Contaminants of environmental concern, including metals, dioxins and furans, were retained within the cementitious matrix of the SCA blocks after prolonged sea water submersion. in addition, organisms growing on the surfaces of the SCA blocks did not accumulate contaminants from the blocks.     

Fishery Enhancement Reef Building Exercise

The constructive use of coal-fired power station waste products for building artificial reefs is being explored for the first time in the U.K. at present, the practice of sea dumping of raw pulverised fuel ash (PFA) from coal combustion is under review and the use of consolidated PFA blocks offers a possible alternative. the planned fitting of flue gas desulphurisation (FGD) plant in the U.K. will additionally produce large quantities of gypsum. to test the environmental compatability of such materials in marine structures, an experimental reef has been constructed off the central south coast of the U.K. Fifty tonnes of blocks made from different combinations of PFA, gypsum, FGD waste water sludge, cement and gravel using standard concrete as the control material, were deployed. the site selected is remote from prominent sea bed features in an area of flat sand with limited species variety.The preliminary studies leading to the licensing of this project included bioassay experiments with diatom cultures, field trials with test tiles and trace metal bioaccumulation studies the stages of consultation and licensing of the project are outlined.

Colonisation of the reef has been rapid, initially by shoaling fish, particularly by bib (Trisopterus luscus) then, within the first month, by representatives of the commercial crab and lobster species typical of the local natural rocky coast. After three months the epifauna and flora were well established. at this stage some 80 species of flora and fauna have been identified in association with the reef with no differentiation in colonisation apparent between the PFA/gypsum mixtures and the concrete control. the number of species far exceeds that of PFA powder dumping grounds. Analyses for heavy metal ions in the reef blocks after 2 months immersion have not shown any significant difference from the original composition.     

Fishery Enhancement Reef Building Exercise

The constructive use of coal-fired power station waste products for building artificial reefs is being explored for the first time in the U.K. at present, the practice of sea dumping of raw pulverised fuel ash (PFA) from coal combustion is under review and the use of consolidated PFA blocks offers a possible alternative. the planned fitting of flue gas desulphurisation (FGD) plant in the U.K. will additionally produce large quantities of gypsum. to test the environmental compatability of such materials in marine structures, an experimental reef has been constructed off the central south coast of the U.K. Fifty tonnes of blocks made from different combinations of PFA, gypsum, FGD waste water sludge, cement and gravel using standard concrete as the control material, were deployed. the site selected is remote from prominent sea bed features in an area of flat sand with limited species variety.The preliminary studies leading to the licensing of this project included bioassay experiments with diatom cultures, field trials with test tiles and trace metal bioaccumulation studies the stages of consultation and licensing of the project are outlined.

Colonisation of the reef has been rapid, initially by shoaling fish, particularly by bib (Trisopterus luscus) then, within the first month, by representatives of the commercial crab and lobster species typical of the local natural rocky coast. After three months the epifauna and flora were well established. at this stage some 80 species of flora and fauna have been identified in association with the reef with no differentiation in colonisation apparent between the PFA/gypsum mixtures and the concrete control. the number of species far exceeds that of PFA powder dumping grounds. Analyses for heavy metal ions in the reef blocks after 2 months immersion have not shown any significant difference from the original composition.     

Annual and spatial variation in recruitment of labroid fishes among seven reefs in the Capricorn/Bunker Group,Great Barrier Reef

Recruitment of labroid fishes to a lagoonal habitat within each of 7 reefs in the Capricorn/Bunker Group on the Great Barrier Reef was recorded for 2 yr (April 1982–April 1983). The density of recruitment of a species on one reef was not a good indicator of its density on other reefs. There were significant differences in the levels of recruitment between years. For several species, the ranking of reefs according to density of recruitment changed between years and the ranking of the two years changed among reefs. Recruitment varied differently for each species. Southern reefs were ranked more highly than northern reefs overall, but no North-South gradient was apparent. Populations of labroid fishes in the Capricorn/Bunker Group experience unpredictable variations in recruitment.     

Chemical Behaviour of Calcium in Stabilized Oil Ash Reef Blocks After Five Years in the Ocean

Abstract

Reef blocks made from stabilized oil ash were taken from the sea after five years in the ocean to examine the chemical behaviour of calcium. Experiments included (1) determination of the calcium leaching rate and a comparison with the rate for unexposed blocks to test the validity of a diffusion model for predicting long term (5 years) leaching rates, (2) determination of the effect of biological cover (shell) on the leaching rate, (3) determination of the leaching rate of the core of exposed reef blocks, (4) determination of the calcium content in ‘ring areas’ - regions of discoloration observed in sectioned exposed reef blocks, and (5) determination of the leachable fraction of the total calcium in exposed reef blocks. Results showed the presence of a pronounced calcium discontinuity zone located 3–7 cm from the outside surface of the reef blocks. Cumulated calcium release rates ranged from 2.81–3.14 μmol cm^?2 day^?1 for original unexposed reef blocks and the core of exposed (in the ocean for five years) blocks, respectively, to 0.47–0.50 μmol cm^?2 day^?1 for outside (facing sea water) surfaces of exposed reef blocks. Tank leaching studies also showed that the presence or absence of hard biological cover (shells) had little or no effect on the calcium release rate. the diffusion model normally used in modelling the chemical behaviour of calcium cannot be used to predict the long term (five years) leaching of calcium. the core of the exposed blocks released calcium at a rate similar to new, unexposed reef block material. Overall, it appears that the calcium discontinuity zone is probably responsible for restricting the release of calcium and hence the failure of the diffusion model.     

Chemical Behaviour of Calcium in Stabilized Oil Ash Reef Blocks After Five Years in the Ocean

Reef blocks made from stabilized oil ash were taken from the sea after five years in the ocean to examine the chemical behaviour of calcium. Experiments included (1) determination of the calcium leaching rate and a comparison with the rate for unexposed blocks to test the validity of a diffusion model for predicting long term (5 years) leaching rates, (2) determination of the effect of biological cover (shell) on the leaching rate, (3) determination of the leaching rate of the core of exposed reef blocks, (4) determination of the calcium content in 'ring areas' - regions of discoloration observed in sectioned exposed reef blocks, and (5) determination of the leachable fraction of the total calcium in exposed reef blocks. Results showed the presence of a pronounced calcium discontinuity zone located 3-7 cm from the outside surface of the reef blocks. Cumulated calcium release rates ranged from 2.81-3.14 μmol cm^-2 day^-1 for original unexposed reef blocks and the core of exposed (in the ocean for five years) blocks, respectively, to 0.47-0.50 μmol cm^-2 day^-1 for outside (facing sea water) surfaces of exposed reef blocks. Tank leaching studies also showed that the presence or absence of hard biological cover (shells) had little or no effect on the calcium release rate. the diffusion model normally used in modelling the chemical behaviour of calcium cannot be used to predict the long term (five years) leaching of calcium. the core of the exposed blocks released calcium at a rate similar to new, unexposed reef block material. Overall, it appears that the calcium discontinuity zone is probably responsible for restricting the release of calcium and hence the failure of the diffusion model.     

Application of High-Volume Fly Ash Concrete to Marine Structures

A new material with high content of fly ash named ‘Ashcrete’ has been developed. to examine the applicability of Ashcrete to marine structures, strength characteristics, resistance to sea water attack, and safety in the marine environment have been studied. the following results have been obtained:

1) the strength characteristics of high-volume fly ash concrete depend upon the type and proportions of chemical activators as well as curing conditions.

2) Ashcrete using sodium chloride (NaCI) as a chemical activator shows high initial strength and good strength development with age.

3) Ashcrete containing NaCI activator shows good resistance to sea water from the viewpoint of its strength characteristics, volume changes and microstructurcs.

4) Since 1980 many types of large-scale artificial reefs made of Ashcrete have been installed in the sea. As a result of long-term studies and underwater observations, the Japanese Government has demonstrated the durability of the material, safety in the marine environment and attractiveness to fish.

5) It is therefore proposed that Ashcrete might be used in constructing large-scale sea mounts in deep water for the purpose of generating upwelling.     

Application of High-Volume Fly Ash Concrete to Marine Structures

A new material with high content of fly ash named 'Ashcrete' has been developed. to examine the applicability of Ashcrete to marine structures, strength characteristics, resistance to sea water attack, and safety in the marine environment have been studied. the following results have been obtained:

1) the strength characteristics of high-volume fly ash concrete depend upon the type and proportions of chemical activators as well as curing conditions.

2) Ashcrete using sodium chloride (NaCI) as a chemical activator shows high initial strength and good strength development with age.

3) Ashcrete containing NaCI activator shows good resistance to sea water from the viewpoint of its strength characteristics, volume changes and microstructurcs.

4) Since 1980 many types of large-scale artificial reefs made of Ashcrete have been installed in the sea. As a result of long-term studies and underwater observations, the Japanese Government has demonstrated the durability of the material, safety in the marine environment and attractiveness to fish.

5) It is therefore proposed that Ashcrete might be used in constructing large-scale sea mounts in deep water for the purpose of generating upwelling.     

Quantitative distribution of herbivorous reef fishes in the Gulf of Aqaba (Red Sea)

The distribution of the main herbivorous fishes (Acanthuridae, Scaridae, Siganidae) was studied across a coral reef of the Jordanian coast in the Gulf of Aqaba (Red Sea). Visual counts were realized by diving along transects (200 m long and 5 m wide), parallel to the shore, at 10 stations located from the lagoon to 40 m deep on the outer reef slope. Herbivorous reef fishes reach their highest abundance on the reef front, where 234 fishes were counted per 1,000 m². Their density decreases on the reef flat, with an average of 150 fish 1,000 m^-2, and is lowest on the outer reef slope (69 fish 1,000 m^-2). Surgeonfishes form 63% of the herbivorous ichthyofauna, parrotfishes 35%, and rabbitfishes 2%. Families and species display different distributions according to biota. The Acanthuridae dominate on the reef flat, whereas the Scaridae are more numerous on the outer reef slope. The evolution of the social structure of the main species was observed: the adults generally school in the lagoon and on the reef flat, but are mainly solitary on the reef slope. The distribution of juvenile individuals is more restricted: they are concentrated on the reef front and on the upper part of the reef slope.This study is part of a cooperation programme between the University of Nice (France) and the University of Jordan, to study the ecology of the coral reefs and the surrounding waters of the Jordanian coast (Gulf of Aqaba, Red Sea)     

Demographic plasticity in tropical reef fishes

We use age-based analyses to demonstrate consistent differences in growth, mortality, and longevity of coral reef fishes from similar habitats (exposed reef crests) 20 km apart. On outer-shelf reef crests of the northern Great Barrier Reef (GBR), size in four taxa of reef fishes (Chlorurus sordidus, Scarus frenatus, and S. niger and the acanthurid Acanthurus lineatus) was systematically and significantly smaller when compared with the same taxa on adjacent mid-shelf reef crests. Differences in size could be attributed to differences in growth between habitats (shelf positions). On outer reef crests the species examined had consistently lower size at age profiles and also reduced life spans compared with populations from mid-shelf reefs. To confirm this relationship, two of the most abundant species (C. sordidus and S. frenatus) were selected for more detailed spatial analysis of demographic patterns. Sampling adults of both taxa from reef crests on three mid- and three outer-shelf reefs revealed that most of the variation in growth was explained by shelf position, although C. sordidus also displayed differences in growth among mid-shelf reefs. We conclude that differences in body sizes across the continental shelf of the northern GBR are primarily determined by these trends in growth. Strong spatial patterns also existed in the mean ages of populations and longevity estimates for C. sordidus and S. frenatus between shelf positions. Both species on outer-shelf reefs displayed less variable cohort sizes, significantly reduced mean ages, and foreshortened longevity compared with populations on mid-shelf reefs. Furthermore, differences in these parameters were rare among replicate reefs within mid- and outer-continental-shelf positions. Age-based catch curves suggested that rates of S. frenatus natural mortality on the outer shelf were nearly twice as high as on the mid shelf. Visual surveys indicated that total scarid densities on outer-shelf reef crests are on average fourfold higher than for equivalent mid-shelf habitats. This fact, coupled with significantly reduced growth rates, reduced mean ages, and increased mortality rates, suggests that density-dependent processes may be responsible for observed differences among localities.     

化学污染物对珊瑚礁生态系统的影响研究进展

化学污染物是影响珊瑚礁生态系统健康的重要因素之一。近年来,中国沿海地区农业活动、城市工业化以及旅游业发展迅速,珊瑚礁区的环境污染问题日趋严重。珊瑚礁生态系统长期处于化学污染物的联合毒性作用下,生态风险日益增加,已受到国内外研究者的广泛关注。本文综述了该领域的重要研究进展,并从个体、细胞和分子水平重点介绍了化学污染物对珊瑚的影响,主要包括:(1)珊瑚礁对重金属和多环芳烃有明显的富集作用,可以作为该海域化学污染物污染水平的外在反映;(2)化学污染物对珊瑚幼体的影响程度比成体大;(3)抗氧化酶和特定的功能基因可被用作生物标记物(biomarker)来监测珊瑚礁生态系统的健康状况。最后,本文对我国珊瑚礁生态系统未来的研究方向进行了展望,建议在典型的珊瑚礁海域进行长期的生态学监测,并结合室内毒理学实验,筛选出敏感的生物标志物,评价珊瑚礁生态系统可能存在的生态风险,为今后珊瑚礁生态系统的保护和管理提供科学依据。     

Coral recruitment: a spatio-temporal analysis along the coastline of Eilat,northern Red Sea

Recruitment rates of stony corals to artificial substrates were monitored for 2 years at 20 sites along the coast of Eilat, northern Red Sea, to compare with those recorded at other coral reef locations and to assess variation in recruitment at several spatial scales. Coral recruitment was low compared to that observed on the Great Barrier Reef in Australia, but was similar to levels reported from other high-latitude reef locations. Pocilloporids were the most abundant coral recruits in all seasons. Recruitment was twofold higher during the first year than during the second year of study. There was considerable spatial variability, with the largest proportion of variance, apart from the error term, attributable to differences between sites, at a scale of 10² m. Spearmans ranked correlation showed consistency in spatial patterns of recruitment of pocilloporid corals between years, but not of acroporid corals. During spring, when only the brooding pocilloporid coral Stylophora pistillata reproduces at this locality, most coral recruitment occurred at central and southern sites adjacent to well-developed coral reefs. During summer, recruitment patterns varied significantly between years, with wide variation in the recruitment of broadcasting acroporid corals at northern sites located distant from coral reefs. Settlement was low at all sites during autumn and winter. This work is the first detailed analysis of coral recruitment patterns in the Red Sea, and contributes to the understanding of the spatial and temporal scales of variation in this important reef process.Communicated by O. Kinne, Oldendorf/Luhe     

Exploited species impacts on trophic linkages along reef-seagrass interfaces in the Florida Keys

The removal of fish biomass by extensive commercial and recreational fishing has been hypothesized to drastically alter the strength of trophic linkages among adjacent habitats. We evaluated the effects of removing predatory fishes on trophic transfers between coral reefs and adjacent seagrass meadows by comparing fish community structure, grazing intensity, and invertebrate predation potential in predator-rich no-take sites and nearby predator-poor fished sites in the Florida Keys (USA). Exploited fishes were more abundant at the no-take sites than at the fished sites. Most of the exploited fishes were either omnivores or invertivores. More piscivores were recorded at no-take sites, but most (approximately 95%) were moderately fished and unexploited species (barracuda and bar jacks, respectively). Impacts of these consumers on lower trophic levels were modest. Herbivorous and smaller prey fish (< 10 cm total length) densities and seagrass grazing diminished with distance from reefs and were not negatively impacted by the elevated densities of exploited fishes at no-take sites. Predation by reef fishes on most tethered invertebrates was high, but exploited species impacts varied with prey type. The results of the study show that, even though abundances of reef-associated fishes have been reduced at fished sites, there is little evidence that this has produced cascading trophic effects or interrupted cross-habitat energy exchanges between coral reefs and seagrasses.