Dietary variation and food selection by an algivorous loach (Pseudogastromyzon myersi: Balitoridae) in Hong Kong streams

Yang, Grace Y.; Dudgeon, David

doi:10.1071/mf09032

Cited by 11 publications

(19 citation statements)

References 37 publications

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“…As predicted, neither insect abundance nor rates of leaf‐litter breakdown were affected by the removal of algivorous fishes, as long as predatory macroconsumers remained present. However, the lack of any significant effect of fish removal on periphyton accumulation or silt accrual on cobbles was unexpected, given that periphytic FPOM makes up approximately one‐quarter of the diet of P. myersi (Yang & Dudgeon, ). Small balitorids evidently did not exert the bioturbating effects associated with relatively large‐bodied loricariids, parodontids and prochilodontids in the Neotropics (Flecker, ; Flecker & Taylor, ), nor the Asian cyprinid Acrossocheilus paradoxus that resuspend silt while grazing (Wang, ).…”

Section: Discussionmentioning

confidence: 99%

Are high densities of fishes and shrimp associated with top‐down control of tropical benthic communities? A test in three Hong Kong streams

Dudgeon

2015

Freshwater Biology

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Summary Top‐down control of benthic communities by fishes in temperate and Neotropical streams has received considerable attention, yet relatively little is known about the occurrence or strength of such top‐down control in tropical Asian streams. We undertook pool‐scale removals of an entire macroconsumer assemblage of fishes and predatory shrimp, as well as its component guilds (algivores versus predators), in three Hong Kong streams during the dry season and monitored the responses of periphyton, benthic macroinvertebrates (predominantly insects) and leaf‐litter breakdown. Pools supported high densities and biomass of predatory macroconsumers. Algivorous balitorid fishes had a mean density of 30.1 indiv m−2 (range: 1.5–58.2 indiv m−2) and a wet‐weight biomass of 20.9 g m−2 (range: 1.6–34.2 g m−2); values for predatory fishes (mainly a nemacheilid and a goby) were 9.4 indiv m−2 (range: 7.3–11.1 indiv m−2) and 29.7 g m−2 (range: 24.1–38.0 g m−2). Densities of predatory palaemonid shrimp were likewise high (mean: 14.0 indiv m−2; range: 8.9–19.0 indiv m−2). Despite high macroconsumer standing stocks, there was little evidence of top‐down control of benthic communities. The removal of algivorous fishes had no effects on algal biomass, periphyton accumulation, silt accrual or abundance of benthic insects. The removal of all predators (fishes and shrimp), as well as the removal of all macroconsumers, was associated with a small increase in the density of insect scrapers (especially baetid mayflies), although no such effect was evident when predatory fishes (but not shrimp) were removed. Apparently, shrimp substituted for the role of predatory fishes by cropping any excess prey. However, the removal of the entire predatory guild or all macroconsumers produced no additional changes in macroinvertebrate assemblages, nor any influence on periphyton or leaf‐litter breakdown. The pool‐scale approach used in this investigation, combined with the inclusion of three study streams, should have provided a realistic picture of the significance of top‐down control of benthic communities by macroconsumers. Statistical power may have been limited by logistical constraints on the number of replicate pools. Localised nutrient limitation caused by the removal of macroconsumers might have contributed to the apparent weakness of top‐down control of benthic communities. However, given the high standing stocks of fishes and shrimps, it is remarkable that experimental manipulations resulted in generally small or negligible effect sizes.

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Section: Discussionmentioning

confidence: 99%

Are high densities of fishes and shrimp associated with top‐down control of tropical benthic communities? A test in three Hong Kong streams

Dudgeon

2015

Freshwater Biology

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“…Gomphonema, which was generally abundant, was least numerous in NTC, and its erect, stalked growth form makes it vulnerable to grazers (Wellnitz et al, 1996;Wellnitz & Rader, 2003). Since Gomphonema is a major food of Pseudogastromyzon myersi (Yang & Dudgeon, 2009b), high fish densities at NTC might account for its scarcity. Fishes, by removing Gomphonema, may have facilitated the growth of competitors such as the short, filamentous cyanobacteria Homoeothrix which was conspicuously abundant at NTC.…”

Section: Wet Season Cyanobacteria Filamentousmentioning

confidence: 99%

“…Information on seasonal changes in grazing intensity might help to resolve this matter, but gut content analyses indicate that Pseudogastromyzon myersi feeds intensively throughout the year (Yang & Dudgeon, 2009b).…”

Section: Wet Season Cyanobacteria Filamentousmentioning

confidence: 99%

Spatial and seasonal variations in benthic algal assemblages in streams in monsoonal Hong Kong

2009

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Samples from stone surfaces were collected in pools within four unpolluted hillstreams (two shaded and two unshaded) in monsoonal Hong Kong (lat. 23°N) to elucidate the extent of spatial (within and among streams) and temporal (seasonal) variations in algal biomass and assemblage composition. Sampling continued for over 12 months, incorporating the dry season when streams were at baseflow, and the wet season when spates were frequent. We anticipated that algal biomass would be lower in shaded streams and during the wet season, with associated seasonal differences in assemblage composition or relative abundance of different growth forms (e.g. erect versus prostrate). Benthic chlorophyll a (a proxy for algal biomass) varied among streams from an annual mean of 11.0-22.3 mg m -2. Dry-season standing stocks were 18% higher than during the wet season when spate-induced disturbance reduced algal standing stocks. Algal biomass varied significantly at the stream scale, but not at the pool scale, and was lower in unshaded streams, where standing stocks may have been limited by high densities of algivorous balitorid loaches (mainly Pseudogastromyzon myersi). An overriding effect of grazers on algal biomass could also have reduced variations resulting from spateinduced disturbance. Significant differences in assemblage composition among streams, which were dominated by diatoms and cyanobacteria (totally 82 taxa) were not systematically related to shading conditions. Seasonal variations in algal assemblages were statistically significant but rather minor, and did not involve major shifts in composition or growth form caused by spate-induced disturbance. The abundance of filamentous cyanobacteria in all the streams may have been due to 'gardening' by balitorid loaches that removed erect or stalked diatoms and favoured cyanobacteria that persist through basal regeneration of filaments. This explanation requires validation through manipulative experiments.

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“…In each reach, epibenthic algae were collected from three randomly selected stones of 10-15 cm diameter (Stewart et al, 2005;Yang & Dudgeon, 2010a;Niu & Dudgeon, 2011a). Each stone was brushed vigorously with a brass-bristled brush to remove all attached periphyton, and the three perpendicular parameters measured to the nearest in order to estimate surface area.…”

Section: Sampling and Laboratory Procedures For Epibenthic Algaementioning

confidence: 99%

Responses of epibenthic algal assemblages to water abstraction in Hong Kong streams

2012

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We studied the effects of flow reduction on epibenthic algal assemblages by comparing up-and down-stream reaches of ten Hong Kong streams subject to different degrees of water abstraction during [2007][2008]. Downstream discharge declined by 71 and 54% during the wet and dry seasons, respectively. Algal responses varied seasonally and according to morphological guild and reflecting reductions in discharge and current velocity, or changes in total nitrogen and phosphate, or their combined effects. Significant inter-reach assemblage differences were observed during the both seasons, but wet-season assemblage structure was not directly influenced by any flow-related variable. During the dry season, scouring-tolerant prostrate/adnate diatoms (especially Achnanthes, Cocconeis) were relatively abundant upstream, whereas intolerant stalked (Eunotia, Gomphonema) and mobile diatoms were more numerous downstream. Both low-and high-profile (erect diatoms, Chamaesiphon, Calothrix) guilds were sensitive to changes in nutrients. Low-flow conditions downstream, surprisingly, enhanced algal diversity, and richness. Based on the linear response of Cocconeis (mainly C. placentula) to discharge reduction, we recommend that[65% of dry-season discharge should be maintained in downstream reaches in order to sustain near-natural algal assemblages; 32% of discharge is required to avoid substantial alterations in assemblage structure.

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Dietary variation and food selection by an algivorous loach (Pseudogastromyzon myersi: Balitoridae) in Hong Kong streams

Cited by 11 publications

References 37 publications

Are high densities of fishes and shrimp associated with top‐down control of tropical benthic communities? A test in three Hong Kong streams

Are high densities of fishes and shrimp associated with top‐down control of tropical benthic communities? A test in three Hong Kong streams

Spatial and seasonal variations in benthic algal assemblages in streams in monsoonal Hong Kong

Responses of epibenthic algal assemblages to water abstraction in Hong Kong streams

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