Trace metal concentrations in the tropical sponge Spheciospongia vagabunda at a sewage outfall: synchrotron X-ray imaging reveals the micron-scale distribution of accumulated metals

Major and trace elements were measured in sponges, seawater and sediment in Darwin Harbour (Australia) to test the hypothesis that metals are elevated in sponges closer to a sewage outfall compared with unimpacted sites. Seawater and sediment at the sewage discharge site contained high, but localised, concentrations of phosphorus (P), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), arsenic (As) and lead (Pb) compared with background sites. Metal concentrations in the sponge Spheciospongia vagabunda were highly elevated compared with other sponges and, although site specific, high metal concentrations were unrelated to the presence of sewage effluent. X-ray fluorescence microprobe imaging was used to investigate the metal distribution pattern in S. vagabunda. High Fe, Ni and Zn concentrations were either localised in circular patches (100–200 μm size) near water canals or in the pinacoderm, or scattered in spots (approximately 10 μm) throughout the tissue. This supports a microflora-mediated metal bioaccumulation hypothesis. In contrast, Co and Mn were highly dispersed and probably associated with aluminium- and iron-oxide rich sediment inclusions. Although the lack of association between sewage effluent and metal accumulation precludes the use of S. vagabunda as a biomonitor, the apparent differential mechanisms of metal accumulation warrants further investigation.     

Variation in Patterns of Metal Accumulation in Thallus Parts of Lessonia trabeculata (Laminariales; Phaeophyceae): Implications for Biomonitoring

Seaweeds are well known to concentrate metals from seawater and have been employed as monitors of metal pollution in coastal waters and estuaries. However, research showing that various intrinsic and extrinsic factors can influence metal accumulation, raises doubts about the basis for using seaweeds in biomonitoring programmes. The thallus of brown seaweeds of the order Laminariales (kelps) is morphologically complex but there is limited information about the variation in metal accumulation between the different parts, which might result in erroneous conclusions being drawn if not accounted for in the biomonitoring protocol. To assess patterns of individual metals in the differentiated parts of the thallus (blade, stipe, holdfast), concentrations of a wide range of essential and non-essential metals (Fe, Cr, Cu, Zn, Mn, Pb, Cd, Ni and Al) were measured in the kelp Lessonia trabeculata. Seaweeds were collected from three sampling stations located at 5, 30 and 60 m from an illegal sewage outfall close to Ventanas, Chile and from a pristine location at Faro Curaumilla. For the majority of metals the highest concentrations in bottom sediment and seaweed samples were found at the site closest to the outfall, with concentrations decreasing with distance from the outfall and at control stations; the exception was Cd, concentrations of which were higher at control stations. The patterns of metal concentrations in different thallus parts were metal specific and independent of sampling station. These results and the available literature suggest that biomonitoring of metals using seaweeds must take account of differences in the accumulation of metals in thallus parts of complex seaweeds.     

Temporal variations of trace metals in aquatic insects

1. Temporal fluctuations were measured in the concentrations of the trace metals cadmium (Cd), copper (Cu) and zinc (Zn) in six insect taxa collected from the same sites in a temperate zone lake over a 14-month period. The consequences of temporal changes in insect contaminant concentrations for biomonitoring studies are assessed. 2. Significant temporal fluctuations in the concentrations of the three metals were measured in almost all of the insect taxa studied. In no case was there a greater than sixfold change in the concentration of a trace metal over the course of the year. The extent of the fluctuations was generally greater for CD, a non-essential metal, than for the essential micronutrients Cu or Zn. 3. Temporal fluctuations in CD concentrations appeared to follow a seasonal periodicity for most taxa. Minima were measured during the winter period in the megalopteran Sialis spp. and in the dipteran taxa Chaoborus punctipennis, Glyptotendipes sp., and Procladius spp., whereas a maximum was measured in the mayfly Hexagenia Hmbata during the same season. In general, temporal fluctuations in Cu and Zn concentrations were less seasonal in character than were those of Cd. 4. For some of the taxon—metal combinations studied, temporal fluctuations in metal concentrations could be ignored in biomonitoring studies, whereas in other cases a temporal window of minimum variability should be chosen for the collection of organisms from different sites.     

Salicornia spp. as a biomonitor of Cu and Zn in salt marsh sediments

Macroalgae in estuarine and coastal waters, in contrast to vascular salt marsh plants, have previously been utilised as biomonitors of sediment-held metals. The colonising halophyte Salicornia spp., however, occurs in both mudflats alongside macroalgae, as well as in association with salt marsh vascular plants. The present research aims to determine the relationships between fluctuations in sediment-held metals and those in Salicornia spp. over the course of a growing season. Samples of the species and corresponding underlying sediment were collected from the metal mine-polluted Restronguet Creek of the Fal Estuary, Cornwall on a monthly basis between March and November, 2000. Oven-dried sediment and vegetation samples were analysed for total Fe, Cu, Zn and Mn. Significant correlations with both the roots and aerial portion of the plant were found with sediment Cu and Zn concentrations. Significant relationships with either Mn or Fe were not observed. Thus, Salicornia spp. would appear to be a suitable tool for biomonitoring Zn and, particularly, Cu. Hyperaccumulation of Zn in the aerial portion during initial growth also indicates that Salicornia spp. may be useful for alleviating metal contamination through phytoextraction, whilst Cu in the roots is proposed as having potential for phytostabilization.     

Fractionation and ecological risk assessment of trace metals in surface sediment from the Huaihe River,Anhui, China

Abstract

The Huaihe River has suffered increasing pressure from pollutants including metals from anthropogenic activities. In this study, enrichment and fractionation behavior of trace metals were analyzed in sediment samples obtained from fish spawning area of the Huaihe River (Anhui Section) to evaluate the potential ecological risk of trace metals to aquatic organisms. Geochemical indices including enrichment factor and geo-accumulation index as well as mean probable effect concentration quotient and risk assessment code were adopted to assess the contamination degree and potential ecological toxicity. Results showed that the total contents of Cu, Pb, Zn, Cr, Cd, As, and Hg in sediment were 23.1?±?6.4, 32.3?±?11.1, 76.8?±?14.2, 84.6?±?17.2, 0.2?±?0.1, 9.0?±?3.0, and 0.031?±?0.010?mg/kg, respectively. The indexes EF and I_geo revealed slight accumulation for Pb, Zn, Cr, Cd, and As in some sampling sites. The result of Q_m-PEC demonstrated that trace metals in sediment were not toxic to aquatic organisms. Most trace metals appeared to mainly associate with the residual form suggesting lower mobility whereas Cd presented a relative higher exchangeable fraction indicating a great degree of bioavailability. The result of risk assessment code (RAC) evaluation revealed that Cd poses a medium ecological risk for aquatic organisms whereas most of the other trace metals pose low risks.     

再生水补水对河道底泥细菌群落结构的影响

以北京市永定河麻峪湿地再生水补水口附近河道底泥为研究对象,应用末端限制性片段长度多态性(Terminal Restriction Fragment Length Polymorphism,T-RFLP)技术探究再生水补水口附近底泥细菌群落结构的空间差异特征以及环境因子所产生的影响,并借助典范对应分析(Canonical Correspondence Analysis,CCA)方法分析麻峪湿地底泥细菌群落结构空间差异特征的形成原因。分析结果表明:河道底泥微生物群落对再生水的净化主要发生在距补水口1200m的范围内,随着再生水与上游来水径向混合净化渐变过程,在补水口2000m处河道底泥微生物群落结构与河道再生水补水口上游趋于相似。基于样点聚类结果的群落结构多样性分析表明随着再生水净化过程的实现微生物综合多样性指数呈现下降的趋势,从均匀度指数的变化趋势看,再生水补水口具有最高均匀度指数,补水口下游1200米处由于非优势菌群所占相对丰度最低以及偶见菌群缺失,导致群落结构比较单一、群落多样性和均匀度指数都最低。CCA方面分析结果表明再生水补水口上游细菌群落与因累积效应形成的重金属有密切关系,补水口出口底泥细菌群落则主要受到总磷和总有机碳的影响较大,而再生水补水与上游来水汇水径向渐变过程可能与氨氮净化具密切关系。研究区的主要优势菌种为假单胞菌属、贪食菌属和芽孢杆菌属,是与再生水中有机碳、氮降解具有密切关系的菌属。     

Identification of in situ Canadian Arctic bivalves using underwater photographs and diver observation

Summary In situ bivalves in the Barrow Strait region of the Canadian Arctic can be identified accurately to genus from siphon characteristics or general appearance. Identification characteristics are described for seven taxa found in the area including Mya truncata, Serripes groenlandicus, Hiatella arctica, Musculus spp., Astarte spp., Macoma spp. and Delectopecten greenlandicus. Contribution No. 15 from the Resolute Marine Laboratory     

Evaluation of trace metals in sediment,water, and fish (Mugil cephalus) of the central Black Sea coast of Turkey

In this study, concentrations of trace metals such as As, Cd, Cu, Cr, Fe, Pb, Ni, Sn, Se, and Zn were determined in sediments, water, and a kind of fish (Mugil cephalus) of the central Black Sea coasts by employing Inductively Coupled Plasma Mass Spectrometry and microwave digestion technique. Gill, muscle, liver, and other tissues were analyzed separately for each sample. The accuracy of the results were checked by using a certified reference material (DORM-4). In water samples, the metal determined at highest concentrations was Cu (1645.44 µg/L). In sediment samples, the metal determined at highest concentrations was Fe (12223.50 mg/kg). The levels of trace metals found in the different parts of the fish were: Zn in muscle tissue (30393.28 mg/kg), Sn in gill tissue (5140.08 mg/kg), and Cu in liver tissue (289.31 mg/kg). These results were also compared with various relevant guidelines and literature.     

The Lusitanian toadfish as bioindicator of estuarine sediment metal burden: The influence of gender and reproductive metabolism

Early diagenetic processes and anthropogenic activities are responsible for metal enrichment in estuarine sediments. The Tagus estuary (Portugal) is no exception, and as a result of past and present pressures, surface sediment contamination is still an issue in some areas. Since such metal loads may be incorporated by benthic organisms, this study analyzed the accumulation of trace metals in the Lusitanian toadfish (Halobatrachus didactylus) in the Tagus estuary. In order to determine the role played by the seasonal reproductive cycle of the Lusitanian toadfish in the bioaccumulation process of trace metals in its tissues, the concentrations of Cd, Co, Cr, Cu, Ni, Pb and Zn were determined in the liver of male and female specimens captured during reproductive and non-reproductive periods. The results showed that metal accumulation in the liver was related simultaneously with gender and season, with females having higher levels of Cd, Cu and Zn during the reproductive period. The metabolic roles of Cu and Zn in embryonic development may explain such results, as both metals accumulated in the female liver to be transported to the gonads later on. Cd, on the other hand, does not have a metabolic role, and the higher concentrations of this metal found in spawning females could be related to the high affinity of Cd to vitellogenin, which is produced in the liver. To assess the species’ potential as an indicator of metal contamination, the concentrations of the seven elements were compared in the muscle tissue of adult, type I males (age ≥5), from two areas with distinct sediment metal loads. Non-essential metals in the muscle reflected the same differences between areas that were found in the sediment samples, evidencing H. didactylus as a potential indicator of those elements bioavailability from the sediment. The results showed that the muscle tissue of adult specimens of a relatively sedentary species such as H. didactylus is a useful indicator of long term accumulation of trace metals. On the contrary, liver concentrations of trace metals showed variation according to the reproductive status, which could lead to overestimate of the environmental status concerning trace metals bioavailability. Spawning season and liver tissue should thus be avoided in biomonitoring studies targeting this benthic fish.     

Distribution and assessment of heavy metals in the aquatic environment of Lake Manzala,Egypt

Analysis of trace metals from sediment and fish collected from eight locations in Lake Manzala, Egypt, during May, June and July of 2011, indicated anthropogenic impacts. The highest concentrations of metals, except Mn and Sr, were detected at Bahr Al-Baqar (S1) which drains from Cairo. At the other sampling locations, the concentrations of selected trace metals fall below the levels of concern while the geo-accumulation index (I_geo) suggests unpolluted conditions for the majority of the studied metals at most sites. However, near the Bahr Al-Baqar (S1) drain concentrations of Ag, Hg and Zn fall above the Long and Morgan's (1990) effects range low (ERL) while Pb was above their effects range median (ERM). I_geo values suggest unpolluted to moderately polluted condition for As and Sn, moderately polluted conditions for Zn, moderate to extremely polluted conditions for Ag, and severely to extremely polluted conditions for Pb at Bahr Al-Baqar. Two sites (Legan, S5, and Al-Ginka, S8) were indicated by I_geo as moderately polluted for Ag while two other sites (West of Bashar, S3, and Al Dehdy, S6) were indicated as unpolluted to moderately polluted for Ag. The Legan and Al-Ginka sites were also indicated as being moderately polluted for Zn. Similar to the sediments, the highest concentrations of metals in fish tissue were from Bahr Al-Baqar (S1). Al concentrations at all sites were comparable to concentrations known to cause lesions in fish. At all sites concentrations of selected trace metals in fish tissue were below the limits set by the FAO.     

Geochemical distribution and fractionation of heavy metals in sediments of a freshwater reservoir of India

Abstract

Sediments of a polluted reservoir were evaluated for total contents of Cd, Cr, Cu, Ni, Pb and Zn along with their different geochemical forms (exchangeable, carbonate, Fe–Mn, organic matter and residual). Mineralogy of the sediments and physico-chemical parameters i.e. pH, OC and percentage of sand, silt and clay were also evaluated to see the dependency of heavy metals concentration on these parameters. The total concentration of heavy metals in the sediments varied according to sites and seasons. Except for station H1 which had moderately higher concentration of Cu (45.5 mg kg^-1), concentrations of all other metals at all the sites under study were below the standard shale value. Maximum proportions of all metals were associated with the carbonate and residual fractions. The Risk Assessment Code showed a low risk for Cr, Ni and Zn, and a medium risk for Cu at station H3 and H4. On the basis of freshwater sediment quality guidelines, there is a strong possibility of Cr and Cu toxicity for aquatic biota of the reservoir. The data were further processed using Pearson’s correlation and factor analysis to obtain more accurate information about the behaviour of these metals. A positive relationship among the metals confirmed the anthropogenic sources of pollution in the reservoir. Significant positive relationships of heavy metals with the texture of the sediment were also obtained.     

Chemometric Methods for Studying the Relationships Between Trace Elements in Laryngeal Cancer and Healthy Tissues

A quick and reliable method for the evaluation and classification of two types of tissues is presented. Several chemometric methods were applied to evaluate multivariate data of the tissue samples with respect to the content of trace elements. The content of Pb, Al, Zn, Cd, Cu, Ni and Co was determined in samples of healthy and cancerous tissue obtained from 26 patients. Determination was done at milligram/kilogram level with inductively coupled plasma optical emission spectrometry (ICP-OES) and atomic absorption spectroscopy (AAS) techniques. Contents of trace metals in studied tissues are not normally distributed; however, normal distribution was confirmed for log values. There is a statistically significant difference in the content of Zn, Cd, Cu and Al (p?<?0.01) and Ni and Co (p?<?0.05) when healthy tissue is compared to cancerous one. Correlation between contents of trace elements for studied tissues was positive; the highest was found between Zn and Cu. A chemometric methodology seems to be a promising tool for classifications of the tissue samples.     

Sediment toxicity and heavy metals in the Kattegat and Skaggerak

Superficial (0 to 2 cm) sediments were sampled from 62 sites in Kattegat and Skagerrak during autumn 1989 and spring 1990, tested for toxicity to Daphnia magna and Nitocra spinipes (Crustacea) and analyzed for heavy metals (Cd, Cr, Cu, Hg, N, Pb, Zn), nutrients (N and P) and organic carbon. Whole sediment toxicity to Nitocra spinipes, expressed as 96-h LC50, ranged from 1.8 to > > 32 percent sediment (wet wt), which is equivalent to 0.63 to 53 percent dry wt. Sediment total metal concentrations (mg kg^-1 dry wt) ranged from 0.01 to 0.32 for Cd, 8 to 57 for Cr, 3 to 40 for Cu, 0.03 to 0.86 for Hg, 3 to 43 for Ni, 6 to 37 for Pb and 21 to 156 for Zn. Analyzed concentrations of heavy metals were tested for correlation with whole sediment toxicity normalized to dry wt, and significant correlations (Spearman p<0.05) were found for Cd, Cr, Cu, Hg, and Ni. However, the analyzed concentrations of these metals were below the spiked sediment toxicity of these heavy metals to N. spinipes, except for Cr and Zn for which analyzed maximum concentrations approached the 96-h spiked sediment LC50s. There was no improvement in correlation between the sum of heavy metal concentrations normalized to their spiked toxic concentrations (Toxic Unit approach) and the whole sediment toxicity. Calculated heavy-metal-derived toxicity based on toxic units and whole sediment toxicity ranged from 0.1 to 24 (mean value 2.3 and SD 4.2). Theoretically, a value of 1.0 would explain whole sediment toxicity from measured metal concentrations using this approach. Thus, in spite of the fact that the total concentrations of the heavy metals were sufficient to cause toxicity based on an additive model for most of these sediments, the observed toxicity of the sediments from Kattegat and Skagerrak could not exclusively be explained by the concentrations of heavy metals, except for Cr and Zn at their maximum concentrations. Therefore, other pollutants than these heavy metals must also be considered as possible sediment toxicants.     

Assessment of nutrient availability and limitation using macroalgae

Discs of the macroalga,Ulva lactuca L., were transplanted around an ocean outfall and at a reference site in Køge Bay, Denmark, to assess the influence of the outfall on the nutrient availability. At 2-wk intervals, samples were collected and analyzed for growth, nitrogen, and phosphorus content.The tissue concentrations of nitrogen and phosphorus decreased with distance to the outfall, showing that the tissue concentrations are suitable for monitoring nutrient availability in coastal areas and provide a time-integrated measure of the nutrient availability. The lowest tissue concentrations of nitrogen were recorded at the reference station, where the internal concentrations generally were below the critical concentration level, showing that nitrogen limited the growth. At the station located close to the outfall, the flux of nitrogen was sufficient to maintain the maximum growth rate. The tissue concentrations of phosphorus were only below the critical concentration level on one occasion, and the result showed a net uptake throughout the study period.It was concluded that in the Køge Bay, nitrogen was the main limiting factor for macroalgae growth during the summer. The applicability of tissue concentrations for assessment of nutrient availability is discussed and it is considered that the method, when evaluated against established critical concentrations, provides a valuable tool for assessing ecosystem health with regard to eutrophication.     

Freshwater amphipods as biomonitors of metal pollution in surface and interstitial aquatic systems

1. The relationships between levels of metals (Zn, Cu) in the environment (water, sediment) and in the tissues of three species of amphipod crustaceans were investigated in superficial and interstitial ecosystems of the Rivers Rhone and Ain, France. 2. Epigean and hypogean amphipods differed in their ability to accumulate Zn and Cu. At all sites, Gammarus fossarum (epigean) showed lower Zn or Cu body concentrations than Niphargus of, rhenorhodanensis or Niphargopsis casparyi (hypogean). Differences were also observed between the two interstitial taxa. 3. A significant difference among sites was observed for metal concentrations in sediment. In contrast, no significant inter-site differences were found for metal concentrations in organisms. 4. No significant correlation was found between metal concentrations in the three taxa and quantities of metals in the water. A positive correlation was observed between Zn and Cu body content in Gammarus fossarum and metal level in the sediment. No relationships were found between interstitial amphipods and metal concentrations in the sediment. 5. Differences in accumulation rates among the three amphipod species suggest their potential use as biological indicators for monitoring metal pollution.     

Trace Metal Bioaccumulation in Epibenthic Macroinvertebrates (EMI) from the San Pedro Shelf,California

Trace metal/metalloid (As, Ag, Cd, Cr, Cu, Hg, Ni, Pb, Se, Zn) bioaccumulation was measured over a period of ten years (1985–1995) in five species of epibenthic macroinvertebrates (EMI) from the San Pedro Shelf, California. Four of the species are numerical dominants in the Southern California Bight (SCB) and two species are commercially harvested. Among three echinoderms, a predatory sea star yielded highest tissue concentrations compared to a sea cucumber and a sea urchin, and concentrations measured in a mantid shrimp exceeded those from a prawn. Comparison of trace metal bioaccumulation from the study area, including the ocean outfall, and elsewhere indicated that bioaccumulation in local EMI was generally low. Measurements from an outfall station and two reference stations were used to evaluate the spatial and temporal relationship between trace metal bioaccumulation and the wastewater discharge. It was concluded that there was no spatial or temporal relationship between EMI trace metal bioaccumulation and the discharge.     

Sediment toxicity in lakes along the river Kolbäcksån,central Sweden

The River Kolbäcksån system is located in a historical mining and steel works district of central Sweden. Ten years ago, intensive limnological studies indicated that the sediments in many of the lakes of this system were contaminated with metals and oil (grease). More recently a very high toxicity was found in the sediments from some of these lakes in tests with Daphnia magna and Tubifex tubifex. The objective of this study was to determine the toxicity to Daphnia magna of surficial sediments from representative locations (N = 39) within this system of lakes and to look for possible correlations with concentrations of metals (Cd, Cr, Cu, Hg, Ni, Pb, Zn) and oil (total) analysed in parallel samples. These results were also compared with spiked sediment toxicity data generated for these metals and with the bottom fauna at 8 of the 39 locations. Among the metals analyzed, only Cd, Pb and Zn were correlated with whole sediment toxicity. Only for Zn and Cr did the maximum concentrations approach those that were toxic in the spiked sediments. Correlations using single and combined metal contamination and toxicity (additive models) explained 16% of the sediment toxicity (r ² = 0.16; N = 39). Significant correlations with the bottom fauna in situ (gross abundance, biomass and species richness) were found for whole sediment toxicity, but not for metal contamination (N = 8). The use of the sediment quality triad approach for assessment of sediment quality is exemplified with a numerical normalization procedure for the latter 8 sites.     

Consumer versus resource control and the importance of habitat heterogeneity for estuarine bivalves

The relative influence of consumers (top down) and resources (bottom up) on the distribution and abundance of organisms remains a key question in ecology. We examined the relationships between consumer and resource variables along a productivity gradient for a dominant predator–prey interaction in a marine soft‐sediment system. We 1) quantified density and size of the clam Macoma balthica (prey species) in six replicate sites at each of four habitat types (shallow mud, deep mud, muddy sand and detrital mud) in the Rhode River, Chesapeake Bay. We selected one habitat type of high food availability and clam density (shallow mud) and another of low food availability and clam density (muddy sand) for manipulative experiments. Then, we 2) measured M. balthica survival and growth through transplants, 3) measured food availability as sedimentary organic carbon content, 4) quantified predator density, and 5) calculated predator foraging efficiency in the two habitat types. Clam density in the four habitat types differed and was related to sedimentary carbon availability and predator density. One of the habitats, detrital mud, appeared to be a population sink because it only held juvenile Macoma that never survived to reproductive age. Macoma size and growth, and predator (mainly blue crab Callinectes sapidus) densities were positively correlated with productivity and were higher in shallow mud than muddy sand. In contrast, Macoma mortality, local ‘interaction strength’, and predator foraging efficiency were lower in the productive habitat (shallow mud). Thus, predation intensity was inversely correlated with productivity (food availability); consumer and resource effects differed by habitat type; and, at a relatively small spatial scale, consumer and resource forces jointly determined population dynamics in this soft‐sediment marine system.     

Control of foraging behavior of individuals within an ecosystem context: the clam Macoma balthica and interactions between competition and siphon cropping

Macoma balthica (L.) is a common clam of the estuarine seafloor, belonging to an important group of invertebrates possessing the capacity to choose between the two fundamental modes of feeding available, using its siphon to inhale either suspended food particles from the water or food particles deposited on the sediment surface. Field experiments demonstrate that intraspecific competition, effects of other competing benthic invertebrates, and complex interactions between competition and partial predation (siphon cropping by fishes) modify the foraging behavior of Macoma. When protected by caging from siphon nipping by fishes, Macoma demonstrated greater siphon regeneration at lower density, indicating the importance of competition for limited resources. In the absence of siphon croppers, these same clams also exhibited more deposit feeding at the lower density either because of improved ability to deposit-feed with longer siphons or because deposited foods become more rapidly depleted than suspended foods on local spatial scales. Addition of siphon-nipping fishes caused greater reductions in siphon size of clams at lower density, presumably because the intensity of nipping per clam was greater where clam targets were fewer and because deposit feeding, which was more intense at lower densities, confers a greater risk of cropping from greater siphon extension and activity than characterize suspension feeding. Deposit feeding by Macoma was reduced in the presence of siphon croppers at both high and low density of clams, but the intensity of deposit-feeding activity at low density was substantially higher than predicted by additive effects of clam density and cropping. This suggests operation of a balancing strategy in Macoma whereby it is accepting greater risks of partial predation when rewards of greater food harvest are larger. The surprising failure to adopt a risk-averse stratery may be explained by the non-lethal nature of partial predation, which renders siphon loss an energetic penalty replacable through regeneration. The presence of a bed of suspension-feeding Rangia cuneata also altered foraging behavior of Macoma by inducing a switch to more intense deposit feeding, in response either to the documented near-bottom depletion of suspended foods or to likely enhanced biodeposition from feces and pseudofeces. The induction of greater deposit feeding by the presence of this competing suspension feeder led to greater siphon losses during exposure to croppers because Macoma was practicing more risky feeding behavior. This enhanced loss of siphon tissues to croppers in the presence of the suspension-feeding Rangia induced an interaction between the effects of siphon croppers and Rangia, such that Macoma exhibited a larger switch away from deposit feeding in the presence of siphon croppers when Rangia were also present. Clearly, the foraging decisions made by individuals can only be understood in a broad holistic context of population, community, and ecosystem processes.     

Heavy metals distribution in the coral reef ecosystems of the Northern Red Sea

Concentrations of seven heavy metals (Cu, Zn, Pb, Cd, Ni, Co and Fe) were measured in the seawater, sediments, common scleractinian reef-building corals and soft corals (Octocorallia : Alcyonacea) at seven reef sites in the Northern Red Sea: I (Hurghada), II (Ras Za’farana), III (El-Ain Al-Sukhna), IV (El-Tur), V (Sha’b Rashdan), VI (Sharm El-Sheikh) and VII (Dahab). Levels of heavy metals were considerably elevated in seawater, sediments and corals collected from reef sites exposed to increased environmental contamination, as a result of diversified natural and anthropogenic inputs. Soft corals of genera Lithophyton, Sarcophyton and Sinularia showed higher concentrations of Zn, Pb, Cd and Ni than hard coral genera Acropora and Stylophora. Soft coral Sarcophyton trocheliophorum collected from El Ain Al-Suhkna (Gulf of Suez) had greater concentration of Cu, followed by hard corals Acropora pharaonis and Acropora hemprichi. The elevated levels of Zn, Cd and Ni were reported in the dry tissue of soft coral Sinularia spp. On the other hand, the soft coral Lithophyton arboreum displayed the highest concentration of Pb at Sha’b Rashdan (Gulf of Suez) and elevated concentration of Zn at Sharm El-Sheikh. Sediments showed significantly higher concentration of Fe than corals. The higher levels of Fe in hard corals than soft corals reflected the incorporation of Fe into the aragonite and the chelation with the organic matrix of the skeleton. The greater abundance of soft corals in metal-contaminated reef sites and the elevated levels of metals in their tissue suggesting that the soft corals could develop a tolerance mechanism to relatively high concentrations of metals. Although the effects of heavy metals on reef corals were not isolated from the possible effects of other stresses, the percentage cover of dead corals were significantly higher as the concentrations of heavy metals increased.