Response of meiofaunal community with special reference to nematodes upon deployment of artificial reefs and cessation of bottom trawling in subtropical waters, Hong Kong

The response of meiofaunal communities, especially nematodes, upon the deployment of artificial reefs and cessation of bottom trawling at a designated Marine Protected Area (MPA) in Hong Kong was studied through comparison of meiofaunal samples collected inside and outside the MPA. Total organic carbon (TOC), total Kjeldahl nitrogen (TKN), total phosphorus (TP), water content and silt-clay fraction in sediments were also analyzed. The level of TOC and TKN, and total meiofaunal and nematode abundance were significantly lower inside than that outside the MPA. Multivariate analysis also indicated differences in community structure. Biological traits analysis revealed that the proportions of nematodes with a clavate tail shape, longer adult length, stout body shape and k-strategy life history were higher inside than that outside the MPA. Such changes in nematode community structure could be a result of the presence of the artificial reefs and closure of the MPA from bottom trawling.     

Meiofaunal community structure in Thermaikos Gulf: Response to intense trawling pressure

Among the most important impacts of trawling is the disturbance of the benthic environment as well as the mortality of the larger benthic organisms, which is caused by the passage of the fishing gear. Meiofauna, which are among the smallest benthic organisms, may be more resistant to disturbance by trawling since they are likely to be re-suspended rather than killed by trawls. Their short generation times allow populations to withstand elevated mortality. In this study, we determined the effect of trawling disturbance, season and sediment type on the structure of meiofaunal communities in a commercial fishing ground in Thermaikos Gulf, north Aegean Sea, Greece. The trawling season is limited to 8 months between October and May. A grid of five nearshore stations was chosen along a north–south productivity gradient and an additional offshore station was included as a reference point. Sediment chemistry and meiofaunal community structure were studied before the trawling season started, as well as 1 and 4 months after the initiation of the fishing period. Results showed that there were no short term (30 days) trawling impacts on meiofauna in terms of abundance and community structure but that there were recognizable effects on the community structure of nematodes and the abundance of polychaetes. In contrast, most meiofaunal taxa displayed significant seasonal variability, 4 months after the initiation of the fishing period; however, other closely related factors such as temperature, sediment particle size and primary productivity are more likely to be responsible for the observed patterns.     

Marine meiobenthic and nematode community structure in Victoria Harbour,Hong Kong upon recovery from sewage pollution

Sediment quality, meiofaunal and nematode communities were monitored across six time points at two inside-harbour and three outside-harbour sites over a three-year period in Victoria Harbour, Hong Kong, after the implementation of a sewage treatment project. Twenty-one meiofaunal groups comprising mainly free-living nematodes and harpacticoid copepods and 188 species of free-living nematodes were identified. The outside-harbour area had a more diverse and significantly different nematode community structure as compared to that in the inside-harbour area. Such spatial difference was highly correlated with the total Kjeldahl nitrogen content of the sediments. Over the study period, there was no significant improvement in sediment quality within the harbour. However, in the last sampling time, an increase in meiofaunal abundance and a closer similarity in nematode composition between one of the inside- and outside-harbour sites suggested signs of recovery of the meiofauna as a response to abatement of sewage pollution.     

Marine meiobenthic and nematode community structure in Victoria Harbour, Hong Kong upon recovery from sewage pollution

Sediment quality, meiofaunal and nematode communities were monitored across six time points at two inside-harbour and three outside-harbour sites over a three-year period in Victoria Harbour, Hong Kong, after the implementation of a sewage treatment project. Twenty-one meiofaunal groups comprising mainly free-living nematodes and harpacticoid copepods and 188 species of free-living nematodes were identified. The outside-harbour area had a more diverse and significantly different nematode community structure as compared to that in the inside-harbour area. Such spatial difference was highly correlated with the total Kjeldahl nitrogen content of the sediments. Over the study period, there was no significant improvement in sediment quality within the harbour. However, in the last sampling time, an increase in meiofaunal abundance and a closer similarity in nematode composition between one of the inside- and outside-harbour sites suggested signs of recovery of the meiofauna as a response to abatement of sewage pollution.     

Amelioration of marine farming impact on the benthic environment using artificial reefs as biofilters

An in situ monitoring of the sediment characteristics and macrobenthic communities was undertaken at a marine fish culture site in subtropical waters of Hong Kong before and after the deployment of biofilters which were made of cement concrete artificial reef (AR) structures. According to the distance to the boundary of the fish cages, 6 points were selected as sampling stations: 2 at the fish cages, 2 near the boundary of the fish culture area, and 2 reference sites further away from the culture area. Bimonthly sediment samples were collected for analysis of silt-clay fraction (SCF), moisture content (MC), total organic carbon (TOC), total Kjeldahl nitrogen (TKN) and total phosphorus (TP). The macrobenthos (>0.5 mm) present in the sediment were sorted, identified and enumerated. TOC, TKN and TP levels at the fish cage stations were consistently higher than those at the reference stations over the 1-year pre-AR and 2-year post-AR deployment monitoring period. The diversity of macrofauna was significantly reduced at the fish cage stations relative to the reference sites. The intermediary stations near the fish culture area showed a transitional state of disturbance. Over the 2-year post-AR deployment period, TOC, TKN and TP showed a decreasing trend at the fish cage and intermediary stations. More diverse macrofaunal communities were recorded at the fish cage stations, with species diversity H′increasing from 0–1 at the beginning of the AR deployment to H′ > 2 at the end of the study. The present results demonstrated that artificial reefs can improve the benthic abiotic environment and biotic conditions beneath fish rafts which are deteriorated due to farming activities.     

Amelioration of marine farming impact on the benthic environment using artificial reefs as biofilters

An in situ monitoring of the sediment characteristics and macrobenthic communities was undertaken at a marine fish culture site in subtropical waters of Hong Kong before and after the deployment of biofilters which were made of cement concrete artificial reef (AR) structures. According to the distance to the boundary of the fish cages, 6 points were selected as sampling stations: 2 at the fish cages, 2 near the boundary of the fish culture area, and 2 reference sites further away from the culture area. Bimonthly sediment samples were collected for analysis of silt-clay fraction (SCF), moisture content (MC), total organic carbon (TOC), total Kjeldahl nitrogen (TKN) and total phosphorus (TP). The macrobenthos (>0.5mm) present in the sediment were sorted, identified and enumerated. TOC, TKN and TP levels at the fish cage stations were consistently higher than those at the reference stations over the 1-year pre-AR and 2-year post-AR deployment monitoring period. The diversity of macrofauna was significantly reduced at the fish cage stations relative to the reference sites. The intermediary stations near the fish culture area showed a transitional state of disturbance. Over the 2-year post-AR deployment period, TOC, TKN and TP showed a decreasing trend at the fish cage and intermediary stations. More diverse macrofaunal communities were recorded at the fish cage stations, with species diversity H'increasing from 0-1 at the beginning of the AR deployment to H'>2 at the end of the study. The present results demonstrated that artificial reefs can improve the benthic abiotic environment and biotic conditions beneath fish rafts which are deteriorated due to farming activities.     

Spatio-temporal changes of marine macrobenthic community in sub-tropical waters upon recovery from eutrophication. I. Sediment quality and community structure

A two-year study was conducted in the vicinity of a harbour in sub-tropical Hong Kong, to examine the progress of improvement in sediment quality and recovery of macrobenthic community upon cessation of organic pollution caused by sewage discharge. Median sediment particle diameter (Mdphi) and levels of total organic carbon (TOC), total Kjeldahl nitrogen (TKN), ammonia-nitrogen (NH(3)-N) and total phosphorus (TP), as well as macrobenthic species composition and abundance were determined bi-monthly at three inside-harbour and two outside-harbour locations. At the two inside-harbour locations, significantly higher levels of TOC, TKN, NH(3)-N and TP in sediments were observed than the outside-harbour locations. However, no significant temporal change of nutrient levels was detected at all sampling locations during the two-year study, except a significant decrease in TKN and NH(3)-N levels at one outside-harbour location and a decline in NH(3)-N content at another outside-harbour location. Spatially, the highest in mean total species number, individual number, species diversity H' and lowest evenness J was found at one outside-harbour location, whereas the other four locations had relatively similar values. H' was negatively correlated with TOC, TKN, NH(3)-N and TP content in sediments while J was positively correlated with MDphi. Across the study period, the patterns of macrobenthic community were significantly different among all samplings and that the spatial difference of benthic community was best correlated with MDphi, TOC, TKN and water depth. A weak sign of recovery in macrobenthic community structure was detected at inside-harbour locations, with replacement of opportunistic by ubiquitous species over the two-year study. The slow recovery of macrobenthic community was related to sediment characteristics. Results of a larval settlement bioassay using the polychaete Capitella sp. I also demonstrated that the inside-harbour sediments were still unfavourable for colonization and larval settlement of species sensitive to pollution. The slow biodegradation of the organic pollutants and continuous presence of heavy metals in the sediment may hinder settlement and colonization of benthic animals. However, increases of H' and J were observed in a longer time scale when comparing the present data with those obtained four years ago. This suggested that a detectable recovery of benthic community in the harbour may take at least three years and a complete recovery may even take longer duration.     

Influence of the ornamental red cherry shrimp Neocaridina davidi (Bouvier, 1904) on freshwater meiofaunal assemblages

Meiofauna serves as a link between microbial production and higher trophic levels, such as macroinvertebrates and juvenile fish. However, the role of meiofauna in the freshwater food web has not been accurately evaluated, and the influence of shrimp predation on freshwater meiofaunal assemblages is unknown. In this study, the predation effects of Neocaridina davidi, an ornamental freshwater shrimp native to inland water bodies in Asia, on meiofaunal density, biomass, structure, and secondary production were examined using model ecosystems (microcosms) that were sampled repeatedly over 42 days. Shrimp predation altered the structure of the meiofaunal community over the course of the experiment, in particular the density, biomass, and secondary production of nematodes, microcrustaceans, and oligochaetes. An analysis of the stomach contents of N. davidi indicated a high degree of omnivory and the frequent consumption of meiofaunal organisms. The results indicated that predation by the freshwater shrimp N. davidi depresses the overall abundance, biomass, and secondary production of meiofaunal assemblages. Moreover, they also provide insights into food-web ecology and the first evidence of freshwater shrimp predation on meiofaunal assemblages.     

Fatty acid profiles of benthic environment associated with artificial reefs in subtropical Hong Kong

Artificial reefs can enhance habitat heterogeneity, especially in seabed degraded by bottom-dredging and trawling. However, the trophodynamics of such reef systems are not well understood. This study provided baseline data on trophic relationships in the benthic environment associated with artificial reefs in late spring and mid summer of subtropical Hong Kong, using fatty acid profiles as an indicator. Data from sediments collected at the reef base, materials from sediment traps deployed on top and bottom of the reefs, total particulate matter from the water column and oyster tissues from reef surface were subjected to principal component analysis. Results showed variations of fatty acid profiles in the total particulate matter, upper sediment trap and oyster tissue samples collected in the two samplings, indicating seasonal, trophodynamic changes within the reef system. The wastes produced by fish aggregating at the reefs can also contribute a source of biodeposits to the nearby benthic environment.     

Nematode/copepod ratios for monitoring pollution: A rebuttal

The nematode/copepod ratio recently proposed by Raffaelli & Mason is not a valid tool for assessing pollution. We found many discrepancies in the original paper and felt obliged to point them out. There was no quantitative assessment of contagion; and seasonal variation was great, two factors which could alter the ratio. We partitioned the original data into Raffaelli & Mason's and others and found that the ratio was not significantly correlated with grainsize when using the literature values. There are several exceptions to their statement that nematodes dominate in organically enriched sites and that there are not copepods in deep water samples. We do not believe that reducing the very complex meiofaunal community structure to a single ratio is appropriate and are concerned that those not familiar with the meiofaunal literature will try to use this ratio method as a panacea for assessing pollution before its validity is fully known.     

A comparison of stygofauna communities inside and outside groundwater bores

Sampling stygofauna is both time consuming and labour intensive. The challenge is to get samples from as many bores as possible within a limited time. The essential assumption for this is that faunal communities inside bores are comparable and representative of the communities outside.To compare relative abundance, taxonomic richness and community composition of the fauna inside groundwater bores to the fauna of the surrounding aquifer, 20 monitoring bores in Palatinate, southwestern Germany, were sampled twice in 1 month. Initially, a sample of 4 l of water was collected from the bottom of each bore. A further sample of 51 l was collected from the groundwater surrounding the bore using a pneumatic piston pump with double packer sampler.Water chemistry inside and outside the bore was similar, but the relative amounts of sediments within the bores were higher compared to those from outside. Relative abundances of fauna inside the bores were higher than in the aquifer, but taxonomic composition was similar with the exception of the proportions of nematodes and amphipods, which were higher inside. As a result, the proportions of cyclopoids were lower inside. Higher nematode proportions are explained partially by the nearly complete extraction of bore sediment. A “habitat heterogeneity effect” states that in heterogeneous aquifers with few suitable habitats, faunal distribution is supposed to be extremely patchy. Thus, detritus accumulates in bores, attracting animals and providing “habitat islands” in the groundwater. This effect could explain the higher amphipode proportions inside the bores, which were generally more frequently populated than the surrounding groundwater. As a consequence, fauna is thought to be nearly absent from groundwater, where suitable habitats are lacking. In those sparsely populated aquifers, samples representative of the aquifer taxonomic richness and composition can only be collected by removing large volumes of water, or by sampling the bottom of bores. These findings also suggest that the use of unbaited colonisation chambers or traps in the groundwater, which are comparable with bores, would seem to be a promising approach.     

Structural and functional response of meiofauna rocky assemblages to sewage pollution

Despite meiofauna being one of the most popular tool for detecting the ecological effects of different sources of impact, the application of structured experimental designs to this benthic component is typically neglected, especially in subtidal rocky shores. In this study, an asymmetrical design was used to detect hard-bottom meiofaunal abundance and biodiversity response to sewage discharge. Sampling was carried out at a depth of 3-4 m by SCUBA diving, by means of a modified manual corer. Six replicate cores were collected at three sites (80-100 m apart), at each of three locations (one purportedly impacted [I] and two controls [Cs]). A total of 84,994 specimens were collected. The outfall affected meiofaunal assemblages in terms of taxon richness, by determining a significant reduction of the number of taxa in the disturbed location, and community structure, by causing functional changes in terms of a decrease of the abundance of nematodes and an increase of the hydrozoan component. Nematodes and syllid polychaetes showed significant lower average abundance at I. Multivariate analyses showed that both meiofaunal assemblage and syllids were significantly different at I compared with Cs. The sewage outfall also affected patterns of spatial distribution at the scale of site (100 m apart) and of replicate units (centimetres apart), both in syllids and in nematodes. Our results provide evidence that the selection of multiple controls is crucial to prevent the widespread risk of Type II error, highlighting the need of more accurate experimental designs when dealing with meiofauna.     

Effects of nutrient enrichment derived from fish farming activities on macroinvertebrate assemblages in a subtropical region of Hong Kong

To study the correlation between nutrient enrichment derived from fish farming activities and changes in macrobenthic assemblages, a one-year field study was conducted in Kau Sai Bay marine fish culture zone of Hong Kong. Bimonthly sediment samples were collected at six stations: two at the fish cages, two near the boundary of the fish culture area, and two reference sites further away from the culture area. Sediment physico-chemical characteristics in terms of silt/clay fraction, moisture content, total organic carbon (TOC), total Kjeldahl nitrogen (TKN) and total phosphorus (TP) were analyzed. The macrobenthos (>0.5 mm) present in the sediment were sorted, identified and enumerated. On average, TOC, TKN and TP levels at the fish cage stations were 82.8%, 128.5% and 1315.7% higher than those at the reference stations, respectively. As a result, the N:P molar ratio was greatly reduced from 8.75 at the reference stations to 1.83 at the fish cage stations. Univariate and multivariate analyses revealed that diversity of macrofauna was significantly reduced and community structure differed at the fish cage stations relative to the reference sites. The intermediary stations near the fish culture area showed a transitional state of disturbance. Faunal diversity was negatively correlated with nutrient level, reflecting the adverse impacts of nutrient enrichment derived from fish farming activities on the benthic assemblages. Whilst in subtropical Asia-Pacific trash fish is the major feed for fish culture resulting in a higher nutrient loading and nutrient ratio accumulated in the sediment beneath the fish rafts, the effects of nutrient enrichment on macrobenthic assemblages are comparable to that in temperate waters owing to relatively high sediment metabolism rate and smaller fish culture scale in Hong Kong.     

The use of meiofauna as an indicator of benthic organic enrichment associated with salmonid aquaculture

Sediment chemistry and meiofaunal samples were collected in the Broughton Archipelago, British Columbia, to examine the relationship between sediment variables and meiofauna diversity across near- and far-field gradients surrounding several finfish aquaculture operations. The sediment variables examined consisted of free sulfide concentrations, redox potential (E(NHE)), organic content, and sediment grain size. A strong trend between sediment texture and organic content was observed across all sampling locations, which reflected a wide range of sediment types (sand-silt) that exist within the Broughton Archipelago. The abundance of certain meiofaunal groups (kinorhynchs, crustaceans, polychaetes) declined in an asymptotic fashion with increasing free sulfide concentrations, an indicator of benthic organic enrichment. Within these relationships, low meiofaunal abundances occurred in fine sediments associated with higher organic contents. Although other groups (nematodes, foraminifera) showed a slight decline in abundance with increasing organic enrichment, a high amount of variability in abundance was observed at high free sulfide concentrations, rendering these groups not suitable as indicators of organic enrichment. This study reports both horizontal and vertical trends in meiofaunal distributions relative to free sulfide concentrations. The abundance of nematode and crustacean taxa decreased with sediment depth as well as increasing sulfide concentration, while polycheate abundance increased with increasing free sulfide concentration. The ratio of nematodes to copepods was also shown to represent the degree of organic loading associated with aquaculture operations and its application as an indicator of benthic impact is discussed.     

Small-scale patterns of meiofauna in a bryophyte covered tufa barrier (Plitvice Lakes,Croatia)

Meiobenthic fauna is complex and essential part of the stream benthos and it is known as intermediaries from bacteria to higher trophic levels. However, the dynamics and mechanisms regulating this community at small-scale largely have been neglected. This study was carried out to determine meiofaunal dynamics in a small scale-patterns influenced by flow velocity and other abiotic and biotic factors. We examined meiofauna within bryophytes on a tufa barrier in Plitvice Lakes National Park using a detailed taxonomic approach of various meiofaunal groups and their feeding guilds. We choose three microhabitats (slow, medium, fast) differing significantly in flow velocity above bryophytes. Bdelloid rotifers were the most abundant group in microhabitat with highest flow velocity, while in other two microhabitats nematodes and monogonont rotifers prevailed in abundance. Data on environmental variables and main meiofaunal taxa and feeding guilds were analyzed using redundancy analysis. This analysis indicated that microfilter feeding guild (e.g. bdelloid rotifers) was strongly affected by interaction of flow velocity and POM fractions. Other feeding guilds were influenced by temperature, oxygen and/or pH and did not prefer high flow velocity. Suction-feeder nematodes and microfilter-feeder rotifers were dominant on temporal and spatial scale, indicating their good adaptations on frequently disturbed conditions that prevailed on bryophyte covered tufa barrier. Our results provide comprehensive survey of diversity, density as well as trophic structure of meiofauna in aquatic bryophytes. Differences in meiofaunal composition and density between three microhabitats suggest that the meiofauna is relevant indicator of environmental changes even at small-scale pattern.     

Extent and frequency of vessel oil spills in US marine protected areas

Little is known about how marine protected areas (MPAs) may be vulnerable to vessel oil spills in the United States. This study investigated individual size, frequency, and total amount of vessel oil spilled in US MPAs, and how characteristics of MPAs and individual spill events influenced spills. Vessel oil spills in US waters (2002-06) and MPA boundaries were mapped. Total number and volume of oil spills inside and outside MPAs were computed. Results show that the presence of a MPA does not seem to prevent vessel oil spills or reduce the amount of oil spilled, and that a variety of MPA attributes (e.g., scale of protection, fishing restrictions, and others) and spill event characteristics (e.g., vessel type, year of spill, and others) affect oil spills inside and outside MPAs. These results can be used to develop MPA rules and marine transportation policies that reduce the vulnerability of sensitive resources to oil spills.     

Is there any seasonal variation in marine nematodes within the sediments of the intertidal zone?

The sediment parameters and nematode assemblages in the intertidal zone of the Hichirippu shallow lagoon, Hokkaido, Japan, were investigated. The objectives of this study were to observe the seasonal variation in the nematodes in the sediment, and to investigate the relationships between the nematodes and environmental factors. Samples were collected bi-monthly from five stations on the tidal flat from April 2003 to February 2004. It was found that the sediment parameters (Chl a concentration, AVS, TOC and TN contents) varied throughout the 10-month study. Fifty-four species of nematodes were found in the study area. The density and biomass of the nematodes varied in accordance with the sediment temperature during the sampling period. In this study, there was a seasonal variation in the nematode assemblage found in the intertidal zone of this shallow lagoon. The important factors affecting this variation were sediment temperature, and food competition among the nematodes themselves. The seasonal variation of the nematode also showed a relationship with the Chl a concentration in the sediment during the sampling period.     

Meiofaunal colonisation on artificial substrates: a tool for biomonitoring the environmental quality on coastal marine systems

The use of artificial substrates for monitoring environmental quality and contaminant impact has been repeatedly suggested, but little information is yet available on the applicability and the sensitivity of this approach. One of the crucial points to be addressed for using artificial substrates, as tools mirroring actual benthic community state, is assessing whether, and how, they reflect in situ conditions characterising natural sediments. In this study we investigated short-term dynamics of meiofaunal colonisation on artificial substrates (bottle brushes) deployed in impacted and "pristine" (control) sites. Meiofaunal colonisation reached a threshold level after 4-6 days in both impacted and control sites but with significantly higher densities in artificial substrates deployed in the control site. Meiofaunal parameters in artificial substrates reflected those of meiofaunal assemblages inhabiting natural sediments where artificial substrates were deployed. Colonised artificial substrates were then transplanted from impacted to control sites. This caused a significant increase of meiofaunal abundance, which after 5 days reached values indistinguishable from the non-impacted control. Given the rapid colonisation time, meiofaunal sensitivity to changing environmental conditions, it can be concluded that artificial substrates can represent an useful tool to be further developed for routine and low-cost monitoring studies aiming at integrating biological indicators of environmental quality.     

Changes in nematode communities at the long-term sand extraction site of the Kwintebank (southern bight of the north sea)

We investigated the long-term effects of sand extraction activities on the nematode communities from the Kwintebank. Although changes in nematode community composition cannot be completely uncoupled from natural processes, we suggest that the morphological changes in the sandbank and physical disturbance associated with the dredging activities indeed affected nematode community composition. Nematode diversity did not change since the start of the extraction activities but nematode community composition changed significantly. The SIMPER routine identified predatory nematodes to be important for the within group similarity at the start of the exploitation, while similarity in 1997 and 2001 was determined by the contribution of deposit feeding nematodes. In addition, long nematodes, vulnerable to physical disturbance became less important. These changes are attributed to long term changes in sediment characteristics in combination with additional short-term disturbances by the creation and filling of dredge furrows which are related to the extraction activities.