Abundance Of Benthos Research Articles

Study of water quality in ex-mining pits for fish cultivation in Gunung Mas regency, Central Kalimantan

Ex-mining pit is a wide expanse, often becomes a problem, especially for the environment. Lack of information about the use of mining pits for fishing activities, especially for the studies on the quality of mining pits to support the growth of cultivated fish. This research was conducted in the village of Tanjung Riu, Gunung Mas Regency, Central Kalimantan Province, using two ex-mining ponds belonging to the community. The results show that the water quality for both mine pits with water parameters for: dissolved oxygen (DO) on average 6.09 mg/l – 7.45 mg/l, pH 2.94 – 3.54, Biological Oxygen Demand (BOD) 4.78 mg/L, temperature 30 -32 oC, turbidity 51.7-53.5 NTU, value of Total Dissolved Solids (TDS) 0.003 – 0.017 gr/L, mercury (Hg) content of 0.000247 mg/l - 0.000359 mg/l, the depth of the pool is 1.7 m – 2.74 m. The abundance of plankton is between 869 - 1106 cells/L, and abundance of benthos is between 264 - 352 ind/m2. The range of pond water quality based on second-class national water quality standards, which is suitable for fish cultivation with moderate abundance of plankton.

Effects of a realistic pesticide spraying sequence for apple crop on stream communities in mesocosms: negligible or notable?

BackgroundSeveral large-scale studies revealed impacts and risks for aquatic communities of small rural lakes and streams due to pesticides in agricultural landscapes. It appears that pesticide risk assessment based on single products does not offer sufficient protection for non-target organisms, which are exposed repeatedly to pesticide mixtures in the environment. Therefore, a comprehensive stream mesocosm study was conducted in order to investigate the potential effects of a realistic spraying sequence for conventional orchard farmed apples on a stream community using pesticides at their regulatory acceptable concentrations (RACs). Eight 74-m-long stream mesocosms were established with water, sand, sediment, macrophytes, plankton and benthic macroinvertebrates. In total, nine fungicidal, four herbicidal and four insecticidal pesticides were applied in four of the eight stream mesocosms on 19 spraying event days in the period from April to July while the remaining four stream mesocosms served as controls. The community composition, the abundance of benthos, periphyton and macrophytes, the emergence of insects, physico-chemical water parameters, and drift measurements of aquatic invertebrates were measured.ResultsThe pesticide spraying sequence induced significant effects on invertebrates, periphyton, and macrophytes as well as on the water ion composition especially in the second half of the experiment. It was not possible to relate the observed effects on the community to specific pesticides applied at certain time points and their associated toxic pressure using the toxic unit approach. The most striking result was the statistically significant increase in variation of population response parameters of some taxa in the treated mesocosms compared to the controls. This inter-individual variation can be seen as a general disturbance measure for the ecosystem.ConclusionsThe pesticide spraying sequence simulated by using RAC values had notable effects on the aquatic stream community in the conducted mesocosm study. The results indicate that the current risk assessment for pesticides may not ensure a sufficient level of protection to the field communities facing multiple pesticide entries due to spraying sequences and other combined stress. Hence, there is still room for improvement regarding the prospective risk assessment of pesticides to further reduce negative effects on the environment.

Benthic Macroinvertebrates Assemblages in the Fish Pond

Overall, small holder of fish farmers in Kelantan in particular does not monitor their pond water quality to maintain fish health due to tedious and expensive work. Hence, this study was proposed to identify the assemblages of benthic macroinvertebrates at the fish pond for potential as a tool for water quality assessment via biological indicator. The study area was in one of the small holder fish pond at Gua Musang, Kelantan, Malaysia. Benthic macroinvertebrates were collected monthly from March to August 2021. Benthic macroinvertebrates were collected by using a heavy-duty D-frame dip net combined with a bag-shaped. The ecological indices were calculated (Shannon diversity index, Margelef’s richness index, Pielou’s evenness index, and Simpson’s dominance index). Results showed a total of 356 individuals from 27 taxa of aquatic insects were collected. Corixidea (Hemiptera) recorded high abundance in July 2021. Even though there were differences in the abundance of benthos for monthly sampling, the season was only a part of the factors that might contribute, however the other factors cannot be neglected such as food availability, water quality and substrates composition conditions. Hopefully the findings could be used by the small holders to assess their pond water quality effectively with minimum cost.

Human-Induced Sharp Salinity Changes in the World’s Largest Hypersaline Lagoon Bay Sivash (Crimea) and Their Effects on the Ecosystem

Lakes and lagoons play an important role worldwide, and salinity fluctuations significantly affect their ecosystems. Bay Sivash, the world’s largest hypersaline water body, underwent a sharp change in salinity, induced by the closing of the North Crimean Canal. To monitor a shift in the ecosystem, a study was carried out from 2014 to 2020 at 15 sites of the lagoon. Since the closure of the canal, the average salinity increased from 22 g L−1 (2013) to 94 g L−1 (2020). Suspended solids and dissolved organic matter also increased. When salinity increased above 50 g L−1, the number of taxa significantly decreased; this was a negative linear relation. The increase in salinity significantly changed the structure of zooplankton and benthos. The most dramatic changes occurred with the salinity increase from 25 to 70 g L−1. Chironomidae larvae numbers began to increase greatly in the ecosystem of the bay, and since 2014, they have rapidly increased their contribution to the abundance of benthos and plankton. The concentration of benthic–planktonic species increased in plankton, in particular, in Harpacticoida and Chironomidae. At salinity above 80–90 g L−1, nauplii and adult brine shrimp appeared to become abundant in plankton and benthos. The transit of the ecosystem to a new alternative state occurred.

МАКРОБЕНТОС ОЗЕР ВОЖЕ И ЛАЧА

The taxonomic composition of macrozoobenthos in lakes Vozhe and Lacha and in some sections in the Svid and Onega rivers is presented. The dominant complex in the lakes was formed by representatives of chironomids. Two species of oligochaetes and a gastropod were dominant in the rivers. The index of faunal similarity of macrobenthos between the lakes was rather high and amounted to 70%, while the similarity between the river and lake benthos was less than 30%. In the lakes, only two taxonomic groups were recorded, oligochaetes and chironomids that formed the basis of the benthos abundance: 87–93% of the average abundance and 92–95% of the average biomass in the lake. Oligochaetes and mollusks played a significant role in the river communities; in total, they formed 76% of the total abundance and 98% of the biomass. The trophic structure of macrobenthos in the lakes was almost similar, except the appearance of the group of phytodetritophages- filter-feeders in Lake Lacha. Detritophages-swallowers dominated in the river communities. In the previous studies of the lakes, the species richness of benthos both in Lake Vozhe and Lake Lacha was much higher. A decrease in the number of taxonomic groups and decrease in their abundance were observed in Lake Vozhe. At the same time, the role of chironomids in the formation of benthos in the lake was still significant. In general, changes in the taxonomic structure and abundance of benthos in lakes Vozhe and Lacha may be caused by a complex effect of environmental factors and long-term and intra-annual dynamics of dominant (cenose-forming) representatives of the main groups of macrobenthos. The simplification of the structure of the bottom communities, the inclusion of species with wide ecological spectra, the predominance of eurybionts among the dominants, may indicate pollution, eutrophication, and contamination of water bodies. According to the indicator species both lakes may be regarded as mesosaprobic water bodies.

Benthic Communities of Coastal Water Bodies at Different Stages of Isolation from the White Sea in the Vicinity of the White Sea Biological Station, Moscow State University, Kandalaksha Bay, White Sea

Communities of macrozoobenthos in the White Sea coastal water bodies that have partially or completely lost connection with the sea as a result of postglacial land uplift, are studied. As the degree of isolation from the sea increases, stable vertical stratification with a tendency to meromixis and gradual dilution of seawater provide the conditions for the formation of an unusual composition of macrofauna and succession, from a normal or slightly depleted marine biome to a completely freshwater ecosystem. Data collected in the years 2012–2017 present the macrozoobenthos community of five marine lagoons and four meromictic lakes in comparison with the marine communities of Kislaya Inlet, which connects the two water bodies studied, and with the freshwater lakes of the Kindo Peninsula. The typology of the water bodies was carried out according to the degree of isolation, taking into account the hydrological regime and differences in fauna lists. A naturally determined change in bottom communities occurs as the degree of isolation of the water body from the sea increases. In marine lagoons, regularly flooded by tides, there is a community of Macoma balthica (L. 1758)–Pontonema vulgare (Bastian 1865) Filipjev 1916, widespread in the marine littoral. In more isolated lagoon-type water bodies with a similar set of species, Mytilus edulis L. 1758 and Mya arenaria L. 1758 make up a significant share in biomass in addition to M. balthica. The populations of the gastropod mollusk Hydrobia ulvae (Pennant 1777) are much developed here. Even at this stage, the fauna comprises more littoral eurybionts (H. ulvae, M. balthica, M. arenaria, M. edulis, Arenicola marina (L. 1758), Tubificoides benedeni (d’Udekem 1855), chironomids, etc.) and less sublittoral stenohaline forms. At the next stage, H. ulvae dominates by biomass, and the share of the chironomid Chironomus gr. salinarius and oligochaete T. benedeni increases as well. Insects and their larvae (beetles, chironomids, and other dipterans) settle in shallow areas. In meromictic lakes, where a salt aerobic layer is preserved under the pycnocline, the fauna of the mixolimnion mainly comprises insect larvae, while only a few euryhaline forms remain from the marine fauna, namely, the amphipod Gammarus duebeni Lilljeborg 1852 and the chironomid Ch. gr. salinarius. At the stage of complete isolation from the sea, conditions are anaerobic below the pycnocline and, despite the suitable salinity, there is no marine fauna. In such water bodies, the benthos is represented exclusively by freshwater forms, mainly insects and mollusks. In completely freshwater bodies, chironomids make up the majority of the biomass; each lake has its own set of species, which changes from year to year. In the fresh water of Nizhnee Ershovskoe Lake, the population of G. duebeni remains in the part of the lake closest to the sea. The species diversity decreases as the water body is isolated from the sea; the maximum number of species was found in marine lagoons near Sonostrov Island (23–34 species); in Kislo-Sladkoe Lake, 10–15 species are found per survey. In Bol’shie Khruslomeny Lake, the aerobic part of the monimolimnion has a critical salinity and the species diversity is minimal (6–10 species). The number of species increases again after a stable fresh layer appears in the water body. The quantitative characteristics of the macrobenthos change in a similar way. The maximum abundance were noted in marine lagoons; in Kislo-Sladkoe Lake, the average abundance is significantly lower. In the meromictic water bodies with a fresh mixolimnion, the maxima of abundance and biomass are observed in the upper 0.5-m water layer, while in marine lagoons the maxima are located in the depth range of 1.0–2.5 m; in addition, in less isolated water bodies, the maximum biodiversity is observed in deeper layers than in more isolated ones. This layer is characterized by the highest content of dissolved oxygen, and often by supersaturation. The benthos abundance varies greatly in freshwater bodies.

Where does the salt marsh start? Field-based evidence for the lack of a transitional area between a gradually sloping intertidal flat and salt marsh

Salt marshes are vegetated ecosystems between land and sea, hosting unique plant and animal communities, contributing to crucial habitats for birds and providing numerous other ecosystem services. They form a sustainable nature-based coastal protection, and its protective value increases with the width of the system. Salt marshes and their adjoining tidal flats are often studied separately. At present, there is a lack of studies that describe the features of these two systems in unison and in relation to each other. This study descriptively assesses an array of abiotic and biotic variables that potentially affect successful vegetation establishment. Unfavourable soil conditions may limit establishment as well as bioturbation of infauna. This is related to the marsh expansion potential and could aid in salt marsh restoration and marsh growth stimulation projects. In a naturally developing salt marsh, we sampled the elevation gradient from the tidal flat to the low marsh for benthic species composition, plant seed availability and abiotic variables. The abundance of benthos was highest landwards of the transition zone, in the pioneer zone. Distinct meiobenthic groups occurred in the different zones along the tidal flat to low marsh gradient, but macrobenthos was largely absent from the muddy soil. In the sparsely vegetated transition zone, the abundance of salt-marsh seeds was low, similar to the tidal flat. It suggests that, even though a seed source was in proximity, seed availability in spring was insufficient to achieve lateral marsh expansion. Clustering and nMDS analyses showed that an identifiable transition zone was lacking. The transition zone resembled the bare tidal flat in terms of its abiotic and biotic conditions. This was mainly driven by significant changes in soil oxygenation and seed availability.

The Dredging Impact on the Lake Manzherok (Republic of Altay) Hydro/biological and Sanitary/micro/biological Characteristics

The article assesses ecological status of the Lake Manzherok (Republic of Altay Mayminsk Rayon) by its hydro/biological and sanitary/micro/biological characteristics after completion of dredging works. To estimate the bio/ceonosis dynamics we used the archive data of 2007–2015 and references. The aquatic communities demonstrated low indicators of development, phytoplankton – 26 taxons, abundance did not exceed 1.3·103 thousand cells/m3, biomass did not exceed 64.0·10-3 mg/m3. In water we found the sapropel vegetative pigments with the chlorophyll a of 237 mg/m3. We identified 16 species of zooplankton with 3. 5 –18.2 t housa nd pieces/m3 abu nda nce w it h 23.4 –97. 3 mg/m3 biomass. In comparison with 2015 the filtering zooplankton organisms’ abundance and biomass were 10–15 times lower. In contrast with 14–15 species in previous years we identified 5 species of macrophytes. The benthos abundance was not more than 1.48 thousand pieces/m2, the biomass did not exceed 1.56 g/m2, that is lower than in 2007. Such low indicators of the aquatic communities’ development with high concentration of organic matter argue the temporal state of anthropogenic metabolic regress. The Lake Manzherok water quality by its sanitary/micro/biological characteristics did not agree with the requirements to recreational water bodies. The whole content of coliform bacteria in the off-shore zone 25 times exceeded the norm, while the content of thermo/tolerant coliform bacteria in the center of the lake and in the macrophytes tangle 2.3 times exceeded the norm.

Studies on the Physicochemical Properties of Ebonyi River in Ebonyi State, Nigeria and on the Abundance of Benthic Fauna during the Rainy Season

The study of physicochemical parameters have been documented, however little may still be known on how those parameters determine the abundance and composition of benthic fauna. We investigated, from May to August, 2018 the relationship between physicochemical parameters and the abundance of some benthic fauna found in Ebonyi River. Using a scoop-net, we collected samples ranging from vertebrates and invertebrates. Four sampling stations were chosen so as to encompass as a wide range of physical conditions. The mean values of dissolved oxygen (10.56 ± 0.6 mg/L), alkalinity (25.5 ± 0.3 mg/L) and hardness (15.3 ± 0.4 mg/L) were determined. We found out that the abundance of benthos was influenced by physicochemical quality of the water, habitat, and immediate substrate of occupation, tropic condition, resource partitioning and predation. Six classes of both vertebrates and invertebrates were recorded of which the class Insecta was dominant. The genera of Coenagrion nymph, Sympetrum, and Chironomus negatively correlated to the depth and velocity of water. However, we found a positive relationship between the water temperature and Belostoma genus. The negative relationships may be as a result of pollutants acquired through anthropogenic activities. However, the positive relationship between temperature and Belostoma genus may be as a result of essential resources e.g. food and mating season.

Macro benthic fauna in relation to limnological variables in a migratory bird visiting lake at Jahangirnagar University, Bangladesh

The abundance of macro benthic organisms was observed from a migratory bird visiting lake in Jahangirnagar University, Savar for a period from July 2016 to June 2017. A total of 22 species belonging to three phyla (viz. Mollusca, Annelida and Arthropoda) and 14 families was recorded with maximum abundance in summer season and minimum in winter season. Molluscan population (37%) was dominant in benthos, followed by Annelida (31%) and Arthropoda (28%). Average values of water temperature, dissolved oxygen and water pH were within standard permissible ranges in the aquatic habitats of the country. Water and soil parameters were in suitable ranges for the growth and abundance of benthos. Correlation indicated that Mollusca and Annelida were closely dependent on water temperature, water pH, water depth, soil organic carbon and soil organic matters, whereas Arthropoda had less dependency on them. In the present study lower Shanon-Wiener diversity index (2.55-2.92) and low species richness (18-24) clearly demonstrated that the lake is moderately polluted.
 J. Biodivers. Conserv. Bioresour. Manag. 2018, 4(2): 99-106

Complex relationships between shallow muddy benthic assemblages, sediment chemistry and toxicity in estuaries in southern New South Wales, Australia

Synoptic sediment quality triad (contaminants, benthic assemblages, toxicity testing) data were collected for sites in Sydney estuary, adjacent Cooks River and five less-modified southern estuaries. Matching data tested relationships between contaminants and benthic assemblages, correlations with specific contaminants, and the ability of sediment quality guidelines to predict the risk of adverse effects.Significant but weak relationships occurred in complex patterns between assemblages, contaminant concentrations and environmental variables. Maximum benthos abundance occurred where sediment contamination was high and was dominated by polychaetes. Spionidae (polychaete) and Galeommatidae (mollusc) abundances were strongly correlated with site environmental characteristics and with varying mixtures of metals and organic contaminants.The risk of adverse effects on benthic assemblage structure increased with increasing sediment toxicity except for areas of very high contamination and for non-bioavailable anthropogenic chemicals. The overall weight-of-evidence scores differentiated the highly modified sites from less-contaminated southern estuaries, where toxicity scores were higher than predicted.

Effect of volcanism on environmental conditions and fauna in rivers of Eastern Kamchatka (using the example of watercourses flowing from Kikhpinych Volcano)

The effect of local factors, including the input of pyroclastic rocks and juvenile volcanic waters, on the structure and abundance of zoobenthos and fish in small watercourses of the eastern volcanic belt of Kamchatka has been studied in the summer period. Streams subjected to the minimal effect of the volcano are characterized by a high diversity and abundance of benthos, aggregations of juveniles in low-water season, and spawning accumulations of fish. Water turbidity, pollution with toxicants, and drying up degrade communities. The rise in water temperature results in an increase in abundance and biomass due to some species of chironomids and caddis flies.

When does fishing lead to more fish? Community consequences of bottom trawl fisheries in demersal food webs

Bottom trawls are a globally used fishing gear that physically disturb the seabed and kill non-target organisms, including those that are food for the targeted fish species. There are indications that ensuing changes to the benthic invertebrate community may increase the availability of food and promote growth and even fisheries yield of target fish species. If and how this occurs is the subject of ongoing debate, with evidence both in favour and against. We model the effects of trawling on a simple ecosystem of benthivorous fish and two food populations (benthos), susceptible and resistant to trawling. We show that the ecosystem response to trawling depends on whether the abundance of benthos is top-down or bottom-up controlled. Fishing may result in higher fish abundance, higher (maximum sustainable) yield and increased persistence of fish when the benthos which is the best-quality fish food is also more resistant to trawling. These positive effects occur in bottom-up controlled systems and systems with limited impact of fish feeding on benthos, resembling bottom-up control. Fishing leads to lower yields and fish persistence in all configurations where susceptible benthos are more profitable prey. Our results highlight the importance of mechanistic ecosystem knowledge as a requirement for successful management.

Changes in the macrobenthic communities of the Gudauta Oyster Bank

Twenty-nine benthic invertebrate species were registered for the Gudauta Bank in the depth range of 8–32 m in 1990. The shallow-water biocenose was defined for the depths of less than 10 m, the biocenoses of Anadara inaequivalvis and A. inaequivalvis-Upogebia pusilla occupied the depths of 10–30 m; and the biocenosis of Pitar rudis was found for the depths of more than 30 m. The highest biodiversity and abundance of benthos was registered for the Anadara biocenoses, while the lowest, for the shallow-water ones. It was found that significant changes in the benthic communities took place in the forty years after the predator gastropod Rapana venosa was introduced into the Black Sea. The oysters became extinct on Gudauta Bank, and the species composition of the benthic community has been significantly depleted. Alien species of Anadara and Rapana became the most abundant by biomass, comprising more than 80% of the total biomass of the benthos. The population density of Rapana constituted 12 ind./m2 and was the highest ever registered for the studied areas of the Black Sea. Insufficient nutrition preconditioned the small size of the mollusks.

Distribution of benthic communities affected by human activities in the west coast of Alexandria, Mediterranean Sea, Egypt

In the framework of marine ecosystem evaluation, this study was carried out where sediment microorganisms were collected bimonthly from 16 sites over one year in the western coast of Alexandria. This area comprises different human activities (urban sewage, agriculture irrigation, industrial wastes, petroleum spill, tourist stress, fishing and commercial navigation). Macrobenthos communities are well indicators of water and sediment quality. Bottom invertebrate’s diversity, comparison of benthos communities at different sampling sites and the biomass were determined as well as the numerical abundance of benthos in comparison to the different environmental parameters. Discharging of chemical pollutants in coastal waters leads to significant degradation in the water quality that altered the macro invertebrates’ diversity indices. The most western sites are less stressed area indicating low diversity rather than the stressed area close to the main sources of pollutants discharge that has relatively high pollution and generally with good diversity. The benthic communities are dominated by few species of pollution tolerance which are used as indicators of polluted sediments such as free-living nematodes and polychaetes. The regional distribution of benthic invertebrate’s communities varied at different sites and over the period of collections that total abundance ranged from 959 to 8444 ind./m 2 with an annual average of 3072 ind./m 2 and seven benthos groups can be sequenced as follows: Nematodes 46% > polychaetes 22% > amphipods 13.8% >cirripedes 4.8% > oligochaetes 4% > gastropods 3.0% > bivalves 1.5%. On the other hand, biomass of benthic structure has an annual average of 155 g/m 2 , where six predomination benthic groups can be ranked in the following sequence: Cirripedes 33.5% > Algae 30.6% > Gastropods 12.7% > Bivalves 9.1% > Sea grass 7.0% > Polychaetes 1.7%. At the different sites, the general structure of species number of benthos groups indicated that Polychaeta was the most common group comprising 27 species of 80 the total number of taxa. The values of species diversity (H`) had relatively moderate diversity (1.3 – 2.02) at most stations and in general the decline in diversity is primarily attributed to the uneven distribution of individuals among the species. On the other hand, the species diversity was only 1.6 at Site 2 though it was the richest that may be attributed to the number of species. Values of the evenness index indicated that sites 1, 8, 9, 10 were highly diverse in benthic communities. The Swartz’s dominance index value indicated less stress with high diversity and number of species. The area located close to the outfall of the two main drains are characterized by having distinct eutrophication level leading to significant increase in the species richness and mean abundance of benthic communities of the tolerant species. Continuous monitoring and assessing of macrobenthic communities is needed to determine the short and long-term changes in the marine ecosystem that are essential for fisheries management along the coastal region.

Rapid and unexpected effects of piscivore introduction on trophic position and diet of perch (Perca flavescens) in lakes recovering from acidification and metal contamination

Summary1. Yellow perch (Perca flavescens) are often the only surviving fish species in acidified lakes. We studied four lakes along a gradient of recovery from acidification and that had different food web complexities. All had abundant yellow perch, two had low piscivore abundance, one had a well‐established piscivore population and one was manipulated by introducing piscivorous smallmouth bass (Micropterus dolomieu). We hypothesised that there would be strong effects on perch abundance, behaviour and diet induced by the presence of piscivores.2. In the manipulated lake, the bass reduced yellow perch abundance by 75% over a 2‐year period. Concomitantly, perch use of the pelagic habitat fell from 48 to 40%.3. In contrast to findings from less disturbed systems, yellow perch in the littoral zone of the manipulated lake did not strongly shift from zooplankton to benthic food sources after the arrival of piscivores. Diet analysis using stable carbon isotopes revealed a strong continued reliance on zooplankton in all lakes, independent of the degree of piscivory. The failure to switch to benthos in the refuge area of the littoral zone is most likely related to the depauperate benthos communities in these formerly acidified lakes.4. Yellow perch in lakes recovering from acidification face a considerable ecological challenge as the necessary switch to benthic diet is hindered by a low abundance of benthos. The arrival of piscivores in these recovering lakes imposes further restrictions on perch access to food items. We infer that future recovery of perch populations (and higher trophic levels) will have to be preceded by the re‐establishment of diverse benthic macroinvertebrate communities in these lakes.

Effects of an anti-salt intrusion dam on tropical fish assemblages

Following the construction of an anti-salt intrusion dam in Pak Panang River, Thailand, changes in the environmental conditions and fish assemblages were monitored both in the estuary and in the river. The present study was conducted during two different phases: when the sluices were open; and when they were closed. Salinity in the estuary declined (P < 0.001), but increased in the river during the open phase (P = 0.002). In the river, the pH increased (P < 0.001) during the closed phase, but was relatively constant in the estuary. No differences were found for water temperatures, chlorophyll a and abundance of phytoplankton. During the closed phase, the abundance of zooplankton was higher in the estuary, but the abundance of benthos in the river declined. Ninety-four fish species were collected. Species richness and the diversity index did not differ in the estuary, but were significantly different in the river; abundance was higher during the open phase. Fish moved between the two systems during the open phase and changes in fish assemblages correlated with salinity gradients and food sources. Sluice regulation to allow fish to move between the river and the estuary is recommended.

Effects of a mixed culture of common carp, Cyprinus carpio L., and Nile tilapia, Oreochromis niloticus (L.), on terrestrial arthropod population, benthic fauna, and weed biomass in rice fields in Bangladesh

Abstract A field experiment was conducted in order to assess the potential of common carp, Cyprinus carpio L., and Nile tilapia, Oreochromis niloticus (L.) to control arthropod population, benthos, and weeds in rice fields in Bangladesh. The two species of fish were stocked in mixed culture and provided with different inputs: regular urea fertilization, low feeding level, and higher feeding level. Rice only with regular fertilization was kept as a control. Fish significantly reduced the number of dipteran insects sampled by a vacuum suction device in rice fields, from an average of 6.6 m −2 to only 0.8, 1.0, and 1.0 m −2 in the three rice–fish treatments, respectively. No significant effects were found on the other species of insects identified. Benthos analysis revealed significant effects of fish on the abundance of molluscs, oligochaete worms and chironomid larvae. The effect of fish on total benthos abundance was somewhat weaker when fish where provided with a high feeding level, indicating that the supply of supplementary feed reduced the ingestion of natural feed in rice–fish culture. Fish were found to control the weeds in a rice field efficiently. Significant reduction of the weed biomass was observed in all three rice–fish treatments. Compared to rice grown alone, the weed biomass was reduced by 86% in rice–fish with urea fertilization, 85% in rice–fish with a low feeding rate, and 82% in rice–fish with a high feeding rate. In conclusion, fish can play a vital role in integrated pest management of insects and weeds.

Disturbance, biological legacies and community development in stream mesocosms

Disturbances reduce the biota in stream ecosystems, and leave biological legacies, including remnant species, which potentially influence post-disturbance community development but are poorly understood. We investigated whether three remnant species, the snail Radix peregra, the mayfly Serratella ignita and the freshwater shrimp Gammarus pulex, affected community development in mesocosms that mimicked disturbed habitat patches in streams. Following 21 days of colonisation, we found that the occurrence of legacy effects depended on the identity of the remnant species. Radix had the strongest effect. By bulldozing epilithon, the snails acted as ecological engineers that promoted settlement of filter feeders (Simuliidae) and invertebrate predators (especially Pentaneura and Aphelocheirus) and strongly deterred settlement of non-predatory chironomids (e.g. Heterotrissocladius and Microtendipes). Gammarus increased in density (by 665%) where remnant, probably through rapid reproduction. Baetis and Pentaneura were scarce, and Asellus absent, in remnant Gammarus treatments, as a consequence of interference and/or predation by the amphipods. In contrast, Serratella tolerated the colonisation of immigrant species and did not affect the structure of the developing benthic community. Despite the observed effects on the presence and abundance of benthos, remnant fauna had no significant effect on assemblage taxon richness, or that of any specific trophic group. The contrasting effects of remnant species on immigrant colonisation echoed differences in their life-history traits and foraging behaviours. Our results indicate that biota can generate spatial patchiness of epilithon and benthic invertebrates in stream ecosystems.

Coral Reef Benthic Video Surveys Facilitate Long-Term Monitoring in the Commonwealth of the Northern Mariana Islands: Toward an Optimal Sampling Strategy

This study describes a step-by-step process used to design an effective benthic video survey component of the Commonwealth of the Northern Mariana Islands long-term monitoring program. Documenting abundance of major benthic groups at relatively large spatial scales, at the appropriate localities, can empower monitoring programs with the capacity to detect changes over time and assess whether management practices are working. Most pertinent to any long-term monitoring program is the overriding question: do we have enough information, or statistical power, to detect changes if changes occur? To assess the power of our benthic video surveys to detect change in coral cover and diversity we varied (1) transect lengths, (2) number of transects, (3) number of frames per transect, and (4) number of data points per frame. Five replicated 50-m transects yielded the most consistent estimates with the highest statistical power, compared with more numerous replicates of shorter (35-m and 15-m) transects. Increasing the number of frames analyzed per 50-m transect yielded greater power than increasing the number of data points per frame, but increasing the number of data points was more effective at estimating species richness. The greatest power of detecting a change in the benthos at each site, within a feasible sampling period, was evident using 5 by 50 m random transects, extracting 60 frames per transect, and analyzing five data points on each frame. This optimal sampling strategy was tested at 23 other long-term monitoring sites and yielded 90% power to detect a 20–30% relative change in dominant benthos abundance estimates (benthos >20% coverage). Our study addresses the sampling unit, accuracy, and ways to improve estimates, but this does not remove the onus of concisely stated questions for monitoring programs pertaining to management.