Sediment Organic Content Research Articles

The influence of deposit-feeding organisms on sediment stability and community trophic structure

Deposit-feeding and suspension-feeding benthos in Buzzards Bay, Massachusetts, show marked spatial separation; suspension feeders are largely confined to sandy or firm mud bottoms while deposit feeders attain high densities on soft muddy substrata. Food source and bottom stability have been investigated as potential factors effecting this trophic-group separation. Between October 4, 1967 and August 22, 1969, observations were made at 11 stations in Buzzards Bay, Massachusetts, along two widely separated transects over bottoms ranging in texture from silt to fine and medium sand. Water depths at these stations ranged from 3 m to 20 m. Scuba divers made many of the field observations and collected most of the samples. This study included sampling of benthic macrofauna, taking bottom photographs, analyzing sedimentary structures, texture, organic content and water content of the sediments, and measuring both water currents and suspended sediment above the bottom. Laboratory experiments were also carried out to determine differential resuspension between burrowed and unburrowed muds. Intensive reworking of the upper few centimeters of a mud bottom by deposit feeders produces a fluid fecal-rich surface that is easily resuspended by low-velocity tidal currents. We suggest that the physical instability of this fecal surface tends to: (i) clog the filtering structures of suspension-feeding organisms, (ii) bury newly settled larvae or discourage the settling of suspension-feeding larvae, and (iii) prevent sessile epifauna from attaching to an unstable mud bottom. Thus suspension feeders are unable to successfully populate all areas of the bottom where a suspended food source is available, especially in areas where mud bottoms are intensively reworked by deposit feeders. Modification of the benthic environment by deposit feeders, resulting in the exclusion of many suspension feeders and sessile epifauna, is an example of trophic group amensalism. This biotic relationship appears to be important in shaping trophic-group distributions in embayments and basins on continental shelves.

Species Density and Lead (Pb) Pollution in Mangrove Ecosystem, South Kalimantan

Its crucial to get information about lead (Pb) heavy metal pollution from mining and oil palm plantation on species density in mangrove ecosystem, to anticipate its impacts. This study aimed is to compare the types and densities of vegetation in mangrove ecosystems allegedly due to mining in Setarap village, Tanah Bumbu Regency and oil palm plantations in Kuala Tambangan Village, Tanah Laut Regency. We also analysis the condition of waters (TDS, pH and DO) and organic content in sediments to acquire data from the South Kalimantan mangrove ecosystems. The results showed there were four species of true mangroves (Avicennia alba, Acanthus ebracteatus, Nypa fruticans and Rhizophora apiculate) could live well in the environment affected by mining or oil palm plantations. The species density for trees was low (933 ind/ha) for mangroves affected by coal mines, while those affected by oil palm plantations had higher densities (1,067 ind/ha). pH value of waters in affected area by coal mining showed more acidic value (pH 5.76) especially at the back, while those by palm oil plantations are more acidic (pH 6) in the estuary. Organic matter content in sediments affected by coal mines was in the range of 0.61-6.59%, while those affected by oil palm plantations showed higher values (0.12-2.19%). Lead heavy metal content (Pb) in waters affected by coal mines was 0.031-0.056 mg/L, while the area affected by oil palm plantations was of higher value (0.110-0.128 mg/L). Lead (Pb) levels in sediments indicate higher values than waters, which reach 3.512-6.046 mg/Kg (affected by coal mines), and in areas affected by oil palm plantations reaching 6.658-6.66 mg/Kg. The general conclusion is that vegetation densities in areas affected by coal mines are lower than oil palm plantations. The level of lead (Pb) pollution in the sediments is higher than in the waters.

High-resolution fisheries data reveal effects of bivalve dredging on benthic communities in stressed coastal systems

Commercial dredging for blue mussels (Mytilus edulis) and oysters (Ostrea edulis,Crassostrea gigas) constitute the main bivalve fisheries in Denmark. These activities predominantly take place in Limfjorden, a large microtidal sound, and in the Inner Danish waters. Both areas are shallow, estuarine, receive high nutrient inputs from agriculture, and are of nature conservation interest (Natura 2000 sites), thus presenting challenges for an ecosystem approach to fisheries management. Using high-resolution fisheries data (~10 m), we investigated the effects of bivalve dredging on benthic communities at both local (Natura 2000 site) and regional (fishery-wide) scales. Regionally, our results showed that dredging intensity correlated with shifts in species composition and reduced community biomass. We were, however, unable to detect an effect of dredging on community density, trait richness, and trait composition. These metrics were significantly related to other environmental drivers, such as sediment organic content (negative) and mussel bed biomass (positive). At the local scale, the observed relationships between dredging, biomass, and species composition varied significantly. This occurred as dredging impacts were greater in areas that contained suitable reference conditions and experienced relatively low levels of disturbance. By contrast, communities which experienced high nutrient loading, regular anoxic events, and high natural variability were relatively unaffected by dredging. Our results therefore highlight the importance of spatial scales in fishing impact estimations. Furthermore, we demonstrate how targeted sampling, high-resolution fisheries data, and suitable reference areas can be used to detect fishery effects in coastal areas that are highly stressed by eutrophication.

Characteristics of Phosphorus Adsorption and Release in Different Types of Sediments

Taking different types of sediments as the research object, this research studied the adsorption and release characteristics of phosphorus under different conditions of different temperatures, coexisting heavy metal ion system, organic matter content and sediment particle size. Through used correlation analysis and principal component analysis, it discussed the influence of various factors on the adsorption and release of phosphorus in sediments. The results show that the adsorption of phosphorus by five different types of sediments from different sources reached saturation equilibrium in about 10 hours, and the increasing rates of 0 ℃, 15 ℃ and 30 ℃ are 17.5% ~ 23.7% and 18.2% ~ 38.3%, respectively. The addition of coexisting heavy metal ion solution accelerated the adsorption of phosphorus in the sediment and reduced the total amount of phosphorus adsorption, that is, heavy metal ions inhibited the adsorption of phosphorus in the sediment; the presence of organic matter in the sediment would reduce its adsorption of phosphorus , Taihu farm and wetland sampling points have the largest sediment organic matter content. Compared with the other three points, the adsorption of phosphorus of these two points accounted for 20.6% and 22.1%; the adsorption and release of phosphorus by sediment increased with the decrease of particle size. The maximum release rate was 5.216mg/kg-1·h-1. The result of principal component analysis shows that the order of influence on the adsorption and release of phosphorus by sediments is temperature> disturbance> organic matter content> heavy metal ion influence> particle size of sediments.

A quantitative assessment of organic carbon content as a regional sediment-condition indicator

Organic carbon content of sediments, whether directly or indirectly assessed, has often been used as an indicator of marine benthic community condition both in site-specific and regional scale condition assessment studies. The conceptual framework underlying use of this indicator was developed based primarily on site-specific studies. A quantitative analysis of literature data on sediment organic matter impacts in marine systems was conducted to determine whether biotic metrics respond to abiotic indicators of sediment organic content, as predicted by conceptual models, at larger spatial scales. The ability to detect predicted decreases in community metrics (abundance, species richness, species diversity index H', biomass) varied among metrics, with best performance by species richness and H'. There was significant added variation both between and within analytical approaches (loss on ignition, total organic carbon methods), emphasizing the need for careful cross calibration and quality control in studies with multiple laboratory partners. High levels of variability for biotic metrics versus organic carbon metrics appear typical for large scale studies, and organic matter source, site depth, and individual estuarine system differences were important sources of variation. Covariation of organic matter content with percent fine sediments is another known source of variation, but various normalization methods may be inadequate due to inherent sources of variation at estuary level. While likely still useful for point-source studies, multiple major sources of variation appear to limit the usefulness of sediment organic content as a benthic condition indicator at larger spatial scales.

Mapping the estuarine ecosystem service of pollutant removal using empirically validated boosted regression tree models.

Humans rely on the natural environment and benefit from the goods and services provided by natural ecosystems. Quantification and mapping of ecosystem services (ES) is required to better protect valued ES benefits under pressure from anthropogenic activities. The removal of excess nitrogen, a recognized catchment-derived pollutant, by biota in estuarine soft sediments is an important ES that potentially ameliorates the development of eutrophication symptoms. Here, we quantified estuarine benthic sediment characteristics and denitrification enzyme activity (DEA), a proxy of inorganic N removal, at 109 sites in four estuaries to develop a general ("global") model for predicting DEA. Our initial global model for linking DEA and environmental characteristics had good explanatory power, with sediment mud content having the strongest influence on DEA (60%), followed by sediment organic matter content (≈35%) and sediment chlorophyll a content (≈5%). Predicted and empirically evaluated DEA values in a fifth estuary (Whitford, n=90 validation sites) were positively correlated (r=0.77), and the fit and certainty of the model (based on two types of uncertainty measures) increased further after the validation sites were incorporated into it. The model tended to underpredict DEA at the upper end of its range (at the muddier, more organically enriched sites), and the relative roles of the three environmental predictors differed in Whitford relative to the four previously sampled estuaries (reducing the explained deviance relative to the initial global model). Our detailed quantification of DEA and methodological description for producing empirically validated maps, complete with uncertainty information, represents an important first step in the construction of nutrient pollution removal ES maps for use in coastal marine spatial management. This technique can likely be adapted to map other ecosystem functions and ES proxies worldwide.

Nutrient fluxes from sediments pose management challenges for the Knysna Estuary, South Africa

This study investigated seasonal dynamics of benthic nutrient fluxes using in situ benthic chambers deployed over a 24–hour period at the sediment water interface for four distinct regions of the Knysna Estuary. The sediment in the Upper Estuary, Lagoon and Bay acted as a source of NH4 with a rate of 100–300 µmol m−2 day−1 N, and soluble reactive phosphorus (SRP) with a rate of 15 µmol m−2 day−1 P, whereas that of Ashmead channel exceeded these rates by far. The sediment acted as a sink for NO3− with fluxes of between −200 and 100 µmol m−2 h−1. Benthic nutrient fluxes in the estuary were positively related with sediment organic content and silt. Nutrient fluxes in the Ashmead channel were significantly greater than the other regions because of the anoxic sediment, reduced flushing and a legacy of pollutant and organic matter retention. This condition can only be improved by removing wastewater input and dredging. Such drastic interventions are necessary to improve the health of South Africa’s top ranked estuary in terms of biodiversity importance.

ANALYSIS CONTENT OF ORGANIC MATTER IN SEDIMENT AND ABUNDANCE OF MACROZOOBENTHOS IN TELUK BUO PADANG WEST SUMATERA

This research was conducted in May 2018 in the waters of Teluk Buo, Padang, West Sumatra. The purpose of this study was to determine the environmental quality of the Teluk Buo waters, especially to determine the abundance of macrozoobenthos and determine the relationship between sediment organic matter and abundance of macrozoobenthos. The method used in this study is a survey method. The results of the study note that the waters of the Teluk Buo are included in the medium polluted criteria with a diversity index (H ') ranging from 2.18-3.43, dominance index (C) 0.10-0.32 and uniformity index (e) 0.51-0,78. Abundance ranges from 80-240 ind/m2 with the number of macrozoobenthos species found there are 9 species of gastropods and 5 species of bivalves. The relationship of sediment organic matter content to macrozoobenthos abundance was included in the moderate criteria with a correlation coefficient (r) -0.382.

Species choice in mangrove reforestation may influence the quantity and quality of long-term carbon sequestration and storage

Despite carbon sequestration being an important service of mangrove ecosystems, many mangrove reforestation projects have little consideration of the carbon sequestration capacity of species to be planted. Species selection is mostly based on growth rate and convenience in planting. In this study, to compare the quantity and quality of carbon stored in soil, four habitats were selected in Haijiang River Estuary, southern China to assess the contribution by different mangrove species to sediment carbon pool. Two 12-year-old mangrove forests of the exotic Sonneratia apetala and native Kandelia obovata, respectively, and the adjacent sandflat and mudflat as unvegetated referencing sites had been studied. The total sedimentary organic carbon and active sedimentary organic content in sediment suggested that after 12 years of growth, (1) mangrove forests significantly increased the organic carbon content of sediment; (2) total organic carbon in the K. obovata forest was higher than that of the S. apetala forest; but (3) the carbon pool of the K. obovata forest was less stable than that of the S. apetala forest. These results corroborated with other studies that the sediment carbon pool of S. apetala forests reached a stable state after 13 years of growth, while that of K. obovata forests gradually stabilised upon long-term (>13 years) growth. Our study confirms that K. obovata is more conducive to capture carbon in long-term mangrove reforestation projects, demonstrating that the provision of this service may not be directly related to apparently relevant plant traits such as growth rate.

Assessment of Sediment and Benthic Macrofauna Distribution at Dar es Salaam Harbour Channel

Sediment and macrobenthic fauna distribution at Dar es Salaam harbour channel were investigated to attest the influence of sediment grain size distribution and total organic carbon contents on benthic macrofauna dominance and diversity. Sampling campaign was conducted from January to April, 2019 in 25 sampling stations along the channel. Sediment grain sizes ranged between 0.7405 and 0.00273 mm with an average of 0.0804 mm classified as medium silt. Sediment distribution showed an onshore-offshore pattern consisting of fine dark clay-silt sediments in the southern part of the harbour close to Mwalimu Nyerere Bridge, medium (sandy) at the harbour and coarse sandy offshore. Five classes of macrofauna were identified with sedentary Polychaetes (Diopatra cuprea) found in tubes and free forms being dominant in most of the sediment types, however more abundant in clay-silt. High species diversity index values were encountered in sediments with medium total organic carbon (TOC) and sediment grain sizes (sand-silt). Apparently, low species similarity indices were observed in all sediment type indicating significant dissimilarities in species composition among sediment grain sizes. Thus, the distribution of benthic macrofauna species along Dar es Salaam harbour channel is strongly influenced by the sediment grain sizes and organic carbon contents in sediments.

Microbial communities of upland peat swamps were no different 1 year after a hazard reduction burn

Fire in wetlands is poorly understood, yet hazard reduction burns are a common management practice and bushfires are becoming increasingly prevalent because of climate change. Fire may have long-lasting implications for the microbial component of these wetland ecosystems that regulate carbon and nutrient cycling. The extremely fire-prone Blue Mountains World Heritage Area in south-eastern Australia contains hundreds of endangered peat-forming upland swamps that regularly experience both bushfires and hazard reduction burns. In a before–after control–­impact study, we surveyed the sediment microbial community of these swamps to test the impact of a low-intensity hazard reduction burn. Along with sediment pH, moisture and organic content, we measured gene abundances including those relating to carbon cycling (quantitative PCR (qPCR) of pmoA, mcrA, bacterial 16S rRNA and archaeal 16S rRNA), and bacteria community fingerprint (terminal restriction fragment length polymorphism (T-RFLP)). One year after the hazard reduction burn, there were no significant differences in the gene abundances or microbial community fingerprint that could be attributed to the fire, suggesting that the hazard reduction burn did not have a long-term impact on these microbial communities.

Changes in the heavy metals and petroleum hydrocarbon contents in seawater and surface sediment in the year following artificial reef construction in the Pearl River Estuary, China.

Marine pollution is an important driver of ocean biodiversity loss, which can be mitigated by the construction of artificial reefs (ARs). Many studies have explored how ARs affect marine organisms, but our understanding of the changes in heavy metals and petroleum hydrocarbons after AR construction is limited. In the current study, we assessed the heavy metal and petroleum hydrocarbon contents of the seawater (surface and bottom seawater) and surface sediment before and after AR construction in AR habitat and in nearby non-reef control habitat in the Pearl River Estuary, China. AR construction tended to decrease the contents of Cu, Pb, Cd, and Hg but tended to increase Zn content in seawater and in surface sediment. Petroleum hydrocarbon content changed irregularly in seawater and surface sediment. Effects of AR construction were similar in the nearby non-reef habitat vs. the AR habitat. Seawater heavy metal and petroleum hydrocarbon contents were correlated with the seawater physicochemical properties (mainly temperature, inorganic nitrogen, chemical oxygen demand, available phosphate, and suspended particulate organic matter), and sediment heavy metal content was correlated with sediment organic matter content. Additional studies over longer time periods and at larger spatial scales are needed to clarify how AR construction affects heavy metal and petroleum hydrocarbon contents in marine environments.

First assessment of the potential for coculture of sandfish (Holothuria scabra) with Babylon snail (Babylonia areolata) in Vietnam

AbstractThe potential for the coculture of sandfish, Holothuria scabra and Babylon snail, Babylonia areolata was investigated. Sandfish (weight 1.87 ± 0.41 g) were cultured at low (25 ind/m2; 46.75 g/m2), medium (50 ind/m2; 93.5 g/m2), and high (100 ind/m2; 187 g/m2) densities in monoculture and in coculture with Babylonia at a density of 400 ind/m2 (208 g/m2). In monoculture, sandfish were provided with 1 g m−2 day−1 commercial prawn starter feed. In coculture, trash fish provided for Babylonia (5% total wet weight per day) was the only food input. Sandfish survival over the 84‐day experiment period was reduced in coculture treatments (77.60 vs. 97.22%) but was in line with expected survival rates (80–90%) of commercial sandfish culture. Mean sandfish weight gain and absolute growth rate were around 37% greater in coculture (mean weight gain 13.42 ± 2.90 g vs. 9.77 ± 2.54 g over 84 days). No differences in Babylonia growth rate or survival were evident between sandfish density treatments. Sediment organic matter content did not differ significantly between monoculture (0.43 ± 0.03%) and coculture (0.55 ± 0.06%) treatments, but the latter had elevated concentrations of ammonia. Results provide a basis for further development of land‐based pond coculture systems for sandfish and Babylonia.

Distribution Patterns of Meiofauna Assemblages and Their Relationship With Environmental Factors of Deep Sea Adjacent to the Yap Trench, Western Pacific Ocean

Sediment samples were collected from 23 sites near the Yap Trench in the Western Pacific Ocean with a depth range of 2896 m to 7837 m. The assemblage composition, spatial distribution, and relationship with environmental variables of meiofauna were studied. A total of 17 meiofaunal taxa were identified, including free-living marine nematodes, benthic copepods, nauplii, ostracods, halacarids, kinorhynchs, cumaceans, turbellarians, cladocerans, polychaetes, oligochaetes, isopods, tanaidaceans, amphipods, tardigrades, gastrotrichs, and pycnogonids. The average abundance of meiofauna was (172.88±149.02) ind·10cm-2. Marine nematodes were the most abundant group, with an average abundance of (120.26±102.85) ind·10cm-2, accounting for 69.97% of the total meiofauna, followed by benthic copepods (36.13±48.72) ind·10cm-2, accounting for 21.04%. The horizontal distribution of meiofauna showed that the high values of meiofaunal abundance were mainly distributed in the northwestern part of the study area and correlated with high sediment organic matter content, which possibly was related to the localized topography, food sources, and hydrodynamics within this area. Vertical distribution showed that meiofauna were mainly distributed in the upper and middle sediment layer (0-6cm). Results of BIOENV showed that sediment median diameter and phaeophorbide content were the most important factors affecting meiofauna community structure. This study provides an insight into relationships of deep-sea meiofauna assemblages with environmental factors in the Western Pacific Ocean.

Comparisons Between Laboratory Sediment Toxicity Test Results and Assessment of Benthic Community Changes for a Lake with Mild Metal Contamination.

Effects of moderate-to-severe sediment contamination may be readily discernable in both sediment toxicity bioassays and benthic community assessments. However, the impact may be less obvious under conditions of relatively mild contamination and significant variation of natural environmental variables. This study evaluated sediment toxicity and benthic community impacts for a shallow eutrophic lake system with relatively low levels of sediment metal contamination. We evaluated selected sediment physical and chemical properties, as well as benthic community structure, for 50 sites along a sediment Pb contamination gradient in the lake. We tested the toxicity of sediment from 20 of the sites, using a standardized 42-days sediment bioassay with Hyalella azteca survival, reproduction, and growth endpoints. Using principal component and correlation analyses we found negative relationships for both Pb and Cu, between sediment metal concentrations and the diversity and abundance of benthic macroinvertebrates. Taxa known to be metal-sensitive (e.g., Hyalella sp. and Physa sp.) were less abundant at sites with relatively higher Pb and Cu concentrations. However, amphipod performance in the chronic toxicity test was not related to sediment Pb or Cu concentrations (but was influenced by sediment organic content). Our results demonstrate that an assessment of community-level effects may be warranted even when sediment metal concentrations are too low to elicit detectable toxic effects in standardized laboratory tests.

High temperature and crab density reduce atmospheric nitrogen fixation in Red Sea mangrove sediments

Mangrove ecosystems are highly productive and provide important ecosystem services. However, in the Red Sea mangroves are under severe nutrient-limiting conditions, reflected in dwarf plants. The nutrient limitation is especially acute for iron, as verified experimentally, although the low carbon-to-nutrient stoichiometric ratios reported for Red Sea mangrove leaves are indicative of general nutrient depletion. Therefore, atmospheric nitrogen (N2) fixation in mangrove sediments might be particularly important considering the minimal nitrogen inputs from land. Here, we tested the effect of temperature and crab density on sediment N2 fixation rates in mature and juvenile mangrove (Avicennia marina) stands in the central Red Sea. The average N2 fixation rates (from 0.002 ± 0.002 to 0.46 ± 0.12 mg N m−2 d−1) fall in the low range of N2 fixation rates reported in mangroves elsewhere, which is in agreement with the small size of the mangrove plants. Mature mangrove sediments hold higher N2 fixation rates than the juvenile mangrove sediment, related to a higher sediment organic matter and carbon content. We found a detrimental effect of temperature and crab density on sediment N2 fixation rates. Maximum N2 fixation rates were detected at 28 °C with a sharp decrease at 35 °C. Similarly, high crab-density reduced N2 fixation, likely due to the sediment oxygenation or the grazing of cyanobacteria by crabs. This is supported by i) previously reported higher oxygen concentration and redox around burrows compared to undisturbed sediment and ii) lighter sediment carbon isotopic composition in high crab-density than in low crab-density sediments, indicating a higher contribution of microphytobenthos in the mature sediments supporting low crab-density. Our data document temperature and crab density as factors affecting N2 fixation in the Red Sea mangrove sediments.

Retention of microplastics in sediments of urban and highway stormwater retention ponds

Urban and highway surfaces discharge polluted runoff during storm events. To mitigate environmental risks, stormwater retention ponds are commonly constructed to treat the runoff water. This study is the first to quantify the retention of microplastics in the sediments of such ponds. It applied state-of-art FTIR-methods to analyse the composition, size, shape, and mass of microplastics in the range 10–2000 μm. Seven ponds serving four land uses were investigated, and the results are related to catchment characteristics, sediment organic matter content, and hydraulic loading. We have not found a correlation between the microplastics abundance, polymer composition, size distribution and the land use in the catchment, as well as the sediment organic matter content. Both the highest (127,986 items kg−1; 28,732 μg kg−1) and the lowest (1511 items kg−1; 115 μg kg−1) accumulation of microplastics were found in the sediments of ponds serving industrial areas. There was, however, a correlation to the hydraulic loading of the ponds, where the sediments of the highest-loaded ponds held the most microplastics. This study shows that sediments in stormwater retention ponds can trap some of the microplastics and prevent them from being transported downstream. These systems need to be considered when assessing the fate of microplastics from urban and highway areas.

Inter fjord variations as a key contributor in the meiobenthic faunal distribution in the Arctic Kongsfjord, Svalbard

The community pattern of meiobenthos in an inner and outer glacial fjord of Kongsfjord was analysed during this study. This study examined the hypothesis that there is a significant difference in the distribution of total meiofauna and the major meiofaunal groups between the inner and outer fjords and it also looked into the effect of environmental variables on their distribution. Meiofaunal abundance and diversity was higher in the inner fjord, indicating that meiofauna can be less sensitive to sediment disturbances caused by glacial activity. Average abundance and biomass of the major meiofaunal groups, namely nematodes (54%) and foraminiferans (37%) were higher in the outer region. 45 species of nematodes representing 20 families were identified during the study, in which Dorylaimopsis sp. (39.55%) and Terschellingia longicaudata (12.53%) had the highest relative abundance. Out of the 56 foraminiferan species belonging to 5 suborders, Nonionellina labradorica (18.30%) and Cassidulina teretis (8.85%) had the highest relative abundance. There are clear and significant changes (ANOSIM) in the assemblage of meiofauna with increasing distance from the glacial front which correlates to environmental variables. Species contributing to differences between inner and outer basins (SIMPER) were also determined. Among nematodes, Chromadorids and Araeolaimids had a tendency to distribute in the inner fjord while Enoplids and Monhysterids were more prevalent in the outer fjord. Sediment organic matter, silt content and pH were the best matching variables (BEST) for the distribution of both nematodes and foraminiferans. The Principal Component Analysis (PCA) revealed that environmental variations have significant patterns in the faunal distribution in Kongsfjord. From this study it can be inferred that the inner fjord has the maximum numerical abundance of meiofauna but the foraminiferans and nematodes were numerically abundant in the outer fjord and there is also significant difference in the distribution of species between the two fjords.

Distribution of sea cucumbers in relation to sediment characteristics in coral reef lagoons and adjacent waters around Ishigaki Island, southern Japan

AbstractTo elucidate which environmental factors affect lagoonal‐scale sea cucumber distributions in Ishigaki Island, Okinawa, Japan, intertidal and subtidal areas of three coral reef lagoons were classified into several ground divisions by bottom characteristics, and sea cucumber densities therein were compared with the composition of sediment cover, grain size and organic content, and coverage of macroalgae, seagrass, and massive corals. Holothuria atra, Holothuria leucospilota, Stichopus chloronotus, and Synapta maculata had highest densities in the nearshore areas but were rare in reef flats, probably because of wave disturbance and low areal cover of sand sediment as potential feeding environments. No relationship was observed between sea cucumber densities and sediment organic content or grain size. Thus, even if these sea cucumbers have selectivity for habitats with a high sediment organic content, the effect of such selectivity on the distribution seems to be limited to relatively small areas. The sea cucumber distributions can be classified by bottom sediment/biota composition into bedrock (H. leucospilota), sand (H. atra), and lagoonal types (St. chloronotus and Sy. maculata). These habitat selections were possibly related to various aspects of sea cucumber ecology such as refuge from predators or turbulence, or settlement and nursery place, which have implications for importance of the complexity of lagoonal‐scale topography and sediment/biota conditions for the coexistence of various holothurian species.

New Zealand estuary benthic health indicators summarised nationally and by estuary type

ABSTRACTEcological data are often collected at small geographic scales. However, analysing data collectively over wider scales can reveal results and patterns not shown in the smaller-scale data. We summarised data for intertidal benthic ecological (physico-chemical and biological) health indicators from New Zealand estuaries and compared the results against thresholds above which ecological impacts are expected to occur. Values for the sediment physico-chemical indicators mud and nutrients (nitrogen and phosphorus collectively) were above thresholds for at least 50% and at 31% of sites measured respectively. Sediment organic content and metal concentrations were generally low, with only maximum values exceeding the thresholds. Scores for biological indicators were within (or better than) the moderate health category for either at least 50%, or at least 75%, of sites. When compared across estuary types (based on a geomorphic classification system) we found statistically significant differences for thirteen of the sixteen indicators. Differences (among mean values) for highly significant results were relatively large compared to the range of values observed nationally for those indicators. However, the differences, except those for mud, were smaller than their respective ecological health threshold values. Our summary provides a reference for future comparisons of estuary indicators nationally and across estuary types.