Changes in the benthic fauna and flora after application of temephos to a stream on Mt. Tsukuba

A dose of 2 ppm of temephos in emulsifiable formulation was applied to a mountain stream to observe its effects on the zoobenthos and the subsequent changes in benthic algae. Most zoobenthos in the treated region drifted but there were slight differences among taxa. Ephemeroptera and Plecoptera disappeared but some Trichoptera and Diptera survived. Chironomids recolonized earlier than other invertebrates and reached a higher density level than before the treatment. A bloom of benthic algae occurred following the destruction of fauna. The increase in the standing crop of algae was accompanied by an increase in the number of species. Among these, Achnanthes lanceolata, Meridion circulare and Tetraspora gelatinosa were predominant. The end of the bloom began with the recovery of the zoobenthos population.     

Importance of foraminifera for the formation and maintenance of a coral sand cay: Green Island, Australia

 CaCO₃ production by reef-building organisms on Green Island Reef in the Great Barrier Reef of Australia is estimated and compared with the contribution of benthic foraminifera to the sediment mass of the vegetated sand cay. Major constituents of the cay are benthic foraminifera (mainly Amphistegina lessonii, Baculogypsina sphaerulata, and Calcarina hispida), calcareous algae (Halimeda and coralline algae), hermatypic corals, and molluscs. Among these reef-building organisms, benthic foraminifera are the single most important contributor to the sediment mass of the island (ca. 30% of total sediments), although their production of CaCO₃ is smaller than other reef-building organisms. Water current measurements and sediment traps indicate that the velocity of the current around Green Island is suitable for transportation and deposition of foraminiferal tests. Abundant foraminifera presently live in association with algal turf on the shallow exposed reef flat, whose tests were accumulated by waves resulting in the formation and maintenance of the coral sand cay. Accepted: 30 June 1999     

The ecology of ruffe,Gymnocephalus cernuus (Pisces: Percidae) introduced to Mildevatn,western Norway

Synopsis Diet, habitat use, diel and seasonal activity and a number of population parameters were studied on ruffe,Gymnocephalus cernuus, introduced to Mildevatn, western Norway. This lake is sited outside the natural range of the ruffe and has a lower fish diversity and a different fish species composition than within its native range. From June through September the ruffe was planktivorous and mainly caught at 4 to 6 m depth in the benthic zone. At other times of year ruffe was feeding on zoobenthos and caught deeper in the benthic zone. Ruffe was mainly day active. Zooplankton feeding during summer is the clearest difference compared to ruffe populations living within its natural range. Presence of large zooplankton organisms available for ruffe is suggested as the main reason for the difference found in food choice. The availability of large zooplankton is probably due to community structure caused by a predator and lack of interspecific competition for zooplankton in the deeper parts of the lake. Piscivorous brown trout.Salmo trutta, restrict the habitat of threespined stickleback,Gasterosteus aculeatus, to the zone of littoral vegetation, allowing high densities of larger zooplankton species likeBythotrephes longimanus to be present in the lake. Brown trout is present only in the upper light and well oxygenated parts of the lake, leaving a refuge for the ruffe, where they can feed on the rich zooplankton community.     

The role of zoobenthos in energy flow in two shallow lakes

Net production of zoobenthos in two shallow and eutrophic lakes, i.e. the S-basin of Mývatn, Iceland (maximum depth 4.2 m, mean depth 2.3 m) and Hjarbæk Fjord, Denmark (maximum depth 6.5 m, mean depth 1.9 m) were calculated as 878 and 1093 kJ m^-2 yr^-1, respectively. The zoobenthos in both lakes was dominated by Chironomidae (Diptera) living partly as filtrators feeding on suspended particles (phytoplankton) and partly as surface feeders foraging on benthic algae and/or seston. Respiration and consumption were estimated from the literature. Net production efficiency averaged 0.41 and 0.48 in Hjarbæk Fjord and Mývatn, respectively. Ingestion was dominated by herbivorous chironomids, while detritivorous tubificids were insignificant. Zoobenthic production made up 86% of total secondary production (zooplankton plus zoobenthos) in both lakes. The trophic efficiency between net primary production and benthic net secondary production was 8% and 11% in Hjarbæk Fjord and Lake Mývatn S-basin, respectively.     

The effect of benthic algae on phosphorus exchange between sediment and overlying water in shallow lakes: a microcosm study using 32P as a tracer

Sediments are of key importance in determining the nutrient levels of water in shallow lakes as they can act as either source or sink for phosphorus (P) depending on environmental conditions, sediment characteristics, and external nutrient loading. We examined the role of benthic algae in the P cycling between sediment and overlying water in experiments using ³²P as a tracer. Sediment and water samples were collected from Huizhou West Lake, a shallow, eutrophic waterbody located in Huizhou City, South China. Laboratory cultured benthic algae were transferred to cover the sediment core in tubes. When ³²P was added to the water in experimental tubes containing sediment cores with and without benthic algae, ³²P activity after 48 h was significantly lower in the tubes with algae, indicating that benthic algae removed P from the overlying water. When the tracer was injected into the sediment, ³²P activity in the water overlying sediment with benthic algae was substantially lower than in tubes with naked sediment, suggesting that benthic algae reduce the release of sediment P. Oxygen levels were significantly higher in the upper 3 mm of the sediments covered by benthic algae; thus, we hypothesized that oxygen produced by the algae helps inhibit the release of P from the sediment. Our study demonstrates that benthic algae are capable of reducing P levels in water overlying the sediment, suggesting that loss of benthic algae during eutrophication triggered by impoverished light conditions may accelerate the shift in shallow lakes from a clear water to a turbid state.     

Day‐Night Vertical Distribution and Feeding Patterns of Fourth Instar ofChaoborus Larvae in a Neotropical Reservoir (Socuy Reservoir,Venezuela)

The day‐night vertical distribution, diel feeding activity and diet of fourth instar of Chaoborus larvae were analyzed in lacustrine zone of a neotropical reservoir which shows seasonally contrasting hypolimnetic oxygen conditions. Larvae stayed in sediment and water bottom during day and ascended to surface during night. Results indicate that feeding activity is limited mainly to the plankton population. Phytoplankton, rotifers or remains of Chaoborus larvae were not found in crops. With the exception of ostracods, all crustacean prey available in the zooplankton occurred in the guts. Ceriodaphnia cornuta and Moina micrura were the most frequent food items (about 75% of occurrence frequency) and were positively selected. The remainder crustacean zooplankton taxa were negatively selected by larvae. The most intense feeding activity in larvae occurred near midnight and sunrise, in dates when the hypolimnion was anoxic. When oxygen was available on the bottom, a higher and not changing diel feeding activity was detected. Our results indicate that vertical migration may promote a spatial separation between larvae and zooplankton, and feeding activity of larvae occurred only when both overlapped. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Consumer movement dynamics as hidden drivers of stream habitat structure: suckers as ecosystem engineers on the night shift

Ecosystem engineering can control the spatial and temporal distribution of resources and movement by engineering organisms within an ecosystem can mobilize resources across boundaries and distribute engineering effects. Movement patterns of fishes can cause physical changes to aquatic habitats though nesting or feeding, both of which often vary in space and time. Here we present evidence of ecosystem engineering by the Sonora sucker Catostomus insignis, a dominant fish in streams of the southwestern United States, and show how cryptic nocturnal movement patterns and bioturbation activities control heterogeneity in benthic substrates, and in sediment and carbon export. Sonora suckers exhibit distinct diel movement patterns, spending daylight hours in refuge habitats (typically deep pools) while moving into shallow habitats at night to feed. Feeding by suckers creates substantial disturbance in soft sediments that are patchy in space and time. These disturbances moved up to 2.4 × 10⁴ cm³ of sediment per square meter per week in locations that are up to hundreds of meters away from sucker daytime refuges. The diel cycles in feeding activity (i.e. nocturnal digging in benthic substrates) caused nighttime pulses in suspended sediment that comprised up to 32% of the daily suspended load and organic matter transport of a stream reach. During the daytime, this particulate transport settles in habitats beyond the location of the initial disturbance, thus redistributing both sediment and organic matter. Our data indicate that cryptic movement by ecosystem engineers can distribute their effects in space and time generating heterogeneity in resources and suggest that habitat modifications restricting consumer movement may alter the impact of engineering activities.     

Distribution of Antarctic benthic foraminifers settling on the pecten Adamussium colbecki

Summary Some benthic foraminifers in Explorers Cove, Antarctica, occur both in the sediment and on hard objects such as rocks and invertebrates. The abundances of four of these foraminiferal species have been measured from sediment samples and from the upper valve of the pecten Adamussium colbecki. The two calcareous species, Cibicides refulgens and Rosalina globularis were more abundant on the pecten shells than the sediment: the agglutinated species, Trochammina ochracea and T. malovensis were more abundant in the sediment. A zone of low foraminiferal density was observed around the outer margin of each shell, but no evidence of an influence of pecten feeding currents on the foraminiferal distributions was found. The size of the pecten shell influenced the density of epizoic foraminifers colonizing it; large shells (area >43 cm²) supported much higher densities than smaller ones.     

Feeding dynamics,nitrogen budgets,and ecosystem role of a desert stream omnivore,Agosia chrysogaster (Pisces: Cyprinidae)

Synopsis Feeding habits, diel periodicity and total daily ingestion, and nitrogen budgets of longfin dace (Agosia chrysogaster) were examined on two occasions when food quality, but not quantity, differed. Agosia chrysogaster was found to be an opportunistic omnivore, consuming primarily insects when the preferred taxon (baetid mayflies) was abundant in the environment, but consuming primarily algae when mayfly abundance was low. Ingestion provided a better measure of diel feeding periodicity than gut fullness; feeding was diurnal on both sample dates, but more markedly so when the primary food was algae. Mean nitrogen content of algal foods was low, and A. chrysogaster apparently compensated for this by increasing its daily ingestion rate when algae were the major food. A reduction in nitrogen content of food during digestion from 4–6% (of dry mass) to less than 1% (in feces) suggested a high assimilation efficiency for nitrogen (nitrogen assimilated/nitrogen consumed = 72–78%). Populations of this abundant and successful cyprinid in Sonoran Desert streams may play an important role in ecosystem nitrogen dynamics. Nitrogen stored in fish biomass comprised 3–6% of the total nitrogen stored in Sycamore Creek, and excretion of ammonia by the fish represented 5–10% of total nitrogen uptake by algae. Such rapid recycling of usable nitrogen to primary producers is significant in this nitrogen limited stream ecosystem.     

The omnivorous triggerfish Melichthys niger is a functional herbivore on an isolated Atlantic oceanic island

This study evaluated the functional role of the highly generalist omnivore Melichthys niger in the remote St. Peter and St Paul's Archipelago (SPSPA), Brazil, where grazing herbivorous fishes are very scarce. We analysed patterns of distribution from zero to 30 m deep during three time intervals during the day and sampled different aspects of their feeding behaviour, including diel feeding rate, feeding substrate and diet. The density of M. niger increased with depth (26–30 m) and decreased by the end of the day. Although M. niger did not present a typical herbivore diel feeding pattern, they targeted the epilithic algal matrix as their primary feeding substrate, ingesting predominantly algae and detritus. The characteristic Caulerpa racemosa var. peltata from SPSPA was ingested only as detached fronds. We suggest that in the isolated SPSPA, the single species M. niger may perform a unique role as a link between benthic primary production and higher levels. Further studies on the trophic ecology of omnivorous species are necessary to better understand their roles in a reef system, especially in impoverished areas where they are likely to play a crucial role.     

Depth‐specific variation in carbon isotopes demonstrates resource partitioning among the littoral zoobenthos

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Altered sediment biota and lagoon habitat carbonate dynamics due to sea cucumber bioturbation in a high‐pCO2 environment

The effects of global change on biological systems and functioning are already measurable, but how ecological interactions are being altered is poorly understood. Ecosystem resilience is strengthened by ecological functionality, which depends on trophic interactions between key species and resilience generated through biogenic buffering. Climate‐driven alterations to coral reef metabolism, structural complexity and biodiversity are well documented, but the feedbacks between ocean change and trophic interactions of non‐coral invertebrates are understudied. Sea cucumbers, some of the largest benthic inhabitants of tropical lagoon systems, can influence diel changes in reef carbonate dynamics. Whether they have the potential to exacerbate or buffer ocean acidification over diel cycles depends on their relative production of total alkalinity (A_T) through the dissolution of ingested calcium carbonate (CaCO₃) sediments and release of dissolved inorganic carbon (C_T) through respiration and trophic interactions. In this study, the potential for the sea cucumber, Stichopus herrmanni, a bêche‐de‐mer (fished) species listed as vulnerable to extinction, to buffer the impacts of ocean acidification on reef carbonate chemistry was investigated in lagoon sediment mesocosms across diel cycles. Stichopus herrmanni directly reduced the abundance of meiofauna and benthic primary producers through its deposit‐feeding activity under present‐day and near‐future pCO₂. These changes in benthic community structure, as well as A_T (sediment dissolution) and C_T (respiration) production by S. herrmanni, played a significant role in modifying seawater carbonate dynamics night and day. This previously unappreciated role of tropical sea cucumbers, in support of ecosystem resilience in the face of global change, is an important consideration with respect to the bêche‐de‐mer trade to ensure sea cucumber populations are sustained in a future ocean.     

The Barrier Reef sediment apron: Tobacco Reef,Belize

Sedimentological and biological surveys of the back-reef sediment apron of Tobacco Reef, a continuous segment of the Belizean Barrier Reef, reveal five distinct biogeological zones: (1) coralline-coral-Dictyota pavement, (2) Turbinaria-Sargassum rubble, (3) Laurencia-Acanthophora sand and gravel, (4) bare sand and 95 Thalassia sand. These zones parallel the entire 9-km reef. The distribution of these zones is related to the spatial patterns of fish herbivory, the size of bottom sediments, and the stability of the substrate. Sedimentological and hydrodynamic studies indicate that most of the sediments in this area are transported from the reef crest and fore reef during periods of storm or hurricane activity and that their size distribution is largely the result of differential transport by high bottom-water velocities during those periods.     

Empirical and dynamical models of production and biomass of benthic algae in lakes

This work presents new empirical and dynamical models for benthic algae in lakes. The models were developed within the framework of a more comprehensive lake ecosystem model, LakeWeb, which also accounts for phytoplankton, bacterioplankton, two types of zooplankton (herbivorous and predatory), macrophytes, prey fish and predatory fish. The new dynamic model provides seasonal variations (the calculation time is 1 week). It is meant to account for all factors regulating the production and biomass of benthic algae for lakes in general. This work also presents and uses a new data-base established by us from published sources. Many of the lakes included in this study are situated in the former Soviet Union. They were investigated during the Soviet period and the data and results have up until now been largely unknown in the West. We present empirical models for benthic algae, and show that the biomass of benthic algae in whole lakes can be estimated from the ratio between the lake area above the Secchi depth to the total lake area and the primary production of phytoplankton. We also present several critical tests of the dynamical model. The dynamical and empirical models give corresponding results over a wide limnological domain. We provide algorithms for (1) the production rate of benthic algae (2) the elimination rate (related to the turnover time of benthic algae), (3) the rate of benthic algae consumption by zoobenthos, and (4) the rate of physical erosion of benthic algae. Our results indicate that the production of benthic algae is highly dependent on lake morphometry and sediment character, as well as water clarity, and less dependent on nutrient (phosphorus) concentrations in water and sediments. This work provides new quantitative support to such conclusions and also a useful model for predictions of production and biomass of benthic algae.     

Comparative feeding ecology of two herbivorous damselfishes (Pomacentridae: Teleostei) from the Gulf of California,Mexico

Two species of benthic damselfishes from the Gulf of California, Mexico, use contrasting behaviors when feeding on benthic algal communities. The small (±70 g) Cortez damselfish, Eupomacentrus rectifraenum (Gill, 1862), feeds selectively from a multi-species algal mat, eats fleshy red and green algae and ignores brown and calcareous algae. The giant blue damselfish, Microspathodon dorsalis (Gill, 1862), is a large (±450 g), lethargic, nonselective feeder which grazes on a near monoculture of a fleshy red alga, Polysiphonia sp. Feeding activity for both species is low in the morning peaks during late afternoon, and drops sharply as night approaches. Based on feeding rates, gut-filling times, and weights of gut contents, Cortez damselfish process six to eight full guts of food and giant blue damselfish three full guts of food per day. The algal mat exhibits high standing crops (291–618 g dry wt · m^?2) and low productivity, but the preferred food of the Cortez damselfish (Ulva) appears to colonize the mat frequently and grow rapidly. The Polysiphonia dominated community on giant blue damselfish territories exhibits low standing crops (23 g · m^?2) and high productivity (34–47 times that of the mat per gram algae). Even though the feeding behaviors and resources used by the two damselfishes differ, both species eat similar food (delicate red and green fleshy algae, and depend on rapid colonization and/or high productivity to maintain their primary foods in the grazed algal community.     

A Study on the Macro-Zoobenthos and the Physico-chemical Characteristics of the Bottom of Bakhira Lake,Uttar Pradesh,India

Bakhira Lake is the largest man-made lake of Eastern Uttar Pradesh. It is utilized for Boro (coarse paddy) cultivation, irrigation and fishing by poor village farmers. Hydrographical features, qualitative and quantitative composition of the macro-zoobenthos, and the physico-chemical characteristics of the bottom water and sediment were studied from October 1976 to April 1977. Molluscs, insects, ostracods, annelids, nematodes and crustaceans are the main groups of zoobenthos. Molluscs together with insects dominate the benthic fauna (95.2 to 96.4% of numbers). The benthic density varied from 273 to 517 individuals/m². Average density of macro-zoobenthos is more or less inversely related to the total alkalinity of the bottom water. Molluscs showed a positive correlation to temperature and a negative correlation to insect density.     

Ontogenetic diet shift, feeding rhythm, and daily ration of juvenile yellowfin goby Acanthogobius flavimanus on a tidal mudflat in the Tama River estuary, central Japan

To ascertain the feeding habits of benthic juvenile yellowfin goby Acanthogobius flavimanus, the gut contents of 599 specimens (15–41 mm in standard length, SL), collected on a tidal mudflat in the Tama River estuary throughout the diel cycle, were examined. The major prey items changed from harpacticoid copepods to errant and sedentary polychaetes at ca. 20 mm SL. Prey width increased with fish size. Fish of 26–28 mm SL fed mainly from sunset to morning, with highest feeding intensity during twilight hours and/or high tide. Based on the gut evacuation rate estimated from a forced feeding experiment in the laboratory and data for the diel change of mean gut-content volume in the field, the daily ration of juvenile yellowfin goby (26–28 mm SL) was calculated to be 13.8 mm³ fish⁻¹ day⁻¹. This volume is approximately equivalent to 3.9 individuals of the errant polychaete Ceratonereis erythraeensis (9.7 mm in body length, BL) or 8.1 individuals of the sedentary polychaete Prionospio japonica (14.8 mm BL), both species occurring abundantly on the mudflat during the study.     

Diel variation in use of cover and feeding activity of a benthic freshwater fish in response to olfactory cues of a diurnal predator

Some fish recognize the threat of predatory fish through chemical cues, which may result in variation in diel activity. However, there is little experimental evidence of diel shifts in activity of prey fish in response to the diel activity of a predator. We compared the total prey consumed and the use of cover by common bullies (Gobiomorphus cotidianus), a native benthic feeding eleotrid, when exposed to the odour of an exotic predator, European perch (Perca fluviatilis), over a 12-h period. Our results showed no significant effect of perch odour on feeding activity, but a significant increase in the use of cover at night and a decrease in the use of cover by day. While common bullies may recognize the presence of a predator through chemical cues, dark conditions may inhibit this and other sensory mechanisms, affecting their ability to recognize the proximity of a predator. For example, during the daytime they may rely on visual cues to initiate cover-seeking behavior, but in the dark, vision is impaired giving them less warning of predators, thus potentially making them more vulnerable.     

Food consumption of five deep‐sea fishes in the Balearic Basin (western Mediterranean Sea): are there daily feeding rhythms in fishes living below 1000 m?

Predation and food consumption of five deep‐sea fish species living below 1000 m depth in the western Mediterranean Sea were analysed to identify the feeding patterns and food requirements of a deep‐sea fish assemblage. A feeding rhythm was observed for Risso's smooth‐head Alepocephalus rostratus, Mediterranean grenadier Coryphaenoides mediterraeus and Mediterranean codling Lepidion lepidion. Differences in the patterns of the prey consumed suggest that feeding rhythms at such depths are linked with prey availability. The diets of those predators with feeding rhythms are based principally on active‐swimmer prey, including pelagic prey known to perform vertical migrations. The diets of Günther's grenadier Coryphaenoides guentheri and smallmouth spiny eel Polyacanthonotus rissoanus, which did not show any rhythm in their feeding patterns, are based mainly on benthic prey. Food consumption estimates were low (<1% of body wet mass day^?1). Pelagic feeding species showing diel feeding rhythms consumed more food than benthic feeding species with no feeding rhythms.     

Shifts in the food of Nile tilapia, Oreochromis niloticus (L.) in Lake Victoria, Kenya

Studies of the food of introduced Nile tilapia, Oreochromis niloticus (L.) with respect to size, habitat and season were conducted between November 1998 and October 2000 in Kenyan waters of Lake Victoria. Stomach contents of 1980 specimens collected by demersal trawl and seining were analysed. Nile tilapia originally known to be herbivorous, feeding mostly on algae has diversified its diet to include insects, fish, algae and plant materials. The major diet of fish <5 cm total length was zooplankton whereas bigger fish included a wider range of food items in their diet. There was spatial variation in diet with insects and algae dominating in the gulf and open water habitats respectively. There was no seasonal variation in the food items ingested and diel feeding regime indicated that O. niloticus is a diurnal feeder. The shift in diet could be due to ecological and environmental changes in Lake Victoria, which have been associated with changes in composition and diversity of fish and invertebrate fauna, emergence and dominance of different flora including water hyacinth Eichhornia crassipes (Mart.) Solms‐Laub., and algae communities. The feeding habit of O. niloticus is discussed in the context of changes occurring in the lake.