Epibenthic Feeding Research Articles

Seasonal Variation in the Epibenthic Feeding Habits of Hilsa Shad (Tenualosa ilisha) in the Upper Meghna River Estuary, Bangladesh

Seasonal changes in feeding habits of hilsa (Tenualosa ilisha) were studied monthly in 2019 in the upper Meghna estuary, Bangladesh, through gut content analyses. Tychoplanktonic diatoms followed by copepods were abundant in all months and size groups of hilsa. The inverse relationship between niche breadth and relative length of the gut revealed hilsa consume a variety of food at their early stages while their feeding habit changes towards diatoms during the adult stage with the development of gill rakers. Young hilsas prefer mostly tychoplanktonic diatoms (Aulacoseira sp., Triceratium sp., Nitzschia sp., Synedra sp., and Coscinodiscus sp.) and copepods (Pseudodiaptomus sp.). However, adult hilsas rejected Aulacoseira sp. during their spawning season. Ingested sand grains correlated with tychoplankton, revealing their food value from epipelic microalgae and bacteria clinging to them and epibenthic foraging by young hilsas. Thus, this study revealed that young hilsas primarily feed on tychoplanktonic diatoms and copepods from water and near bottom of the upper Meghna estuary during January to June while later stages with the development of gill rakers allow hilsas to feed on planktonic diatoms. Epibenthic feeding needs to be considered more fully in evaluating the biology of hilsa and, perhaps, other clupeids, and in evaluating possible human impacts on this foraging habitat.

Habitat Heterogeneity and Spatio-Temporal Distribution of Macrobenthos in in a Tropical Estuarine Mangrove Ecosystem

This paper deals with spatio-temporal distribution of macrobenthos and their relationship with physico-chemical environment and sediment properties in estuarine mangrove ecosystem of Chorao, Goa. The complex mangrove habitats provide nutrient and play vital role in the establishment of healthy mangrove fauna. The mangrove of Chorao is inhabited by 14 species of mangrove and associated flora in different substrata. The macrofaunal density in the four study stations varied significantly. Total numerical count was 7960 at C1, 3300 at C2, 6705 at C3 and 7075 at C4. The wet weight biomass was 27.18 at C1, 17. 62 at C2, 15.85 at C3 and 24.30 at C4. There was strong seasonality in the occurrence of fauna in the study area. The average macrofaunaltaxa was dominated by polychaeta (55%), crustacea (26%) and mollusca (14%). The other groups like nematode, echiurida and nemertenea was insignificant. The epibenthic feeding forms of polychaetes and scavengers/browsers of crustacean were more common in the sandy substratum, while deposit feeders were common in muddy substratum at Chorao mangrove. The result of the present study suggests that mangrove ecosystem with different substrata and physico-chemical parameters supports varied fauna and had different effect on the benthic community.

Prediction of suitable feeding habitat for fishes in a stream using physical habitat simulations

This study presented the suitable feeding habitat for target fish species using physical habitat simulations for both fishes and macroinvertebrates. The suitable feeding habitat is a novel concept for the fish habitat that guarantees a certain level of feeding condition as well as the suitability of the physical habitat. The study site is a 0.9 km long reach of the Gongneung-cheon Stream, which is a tributary of the Han-gang River in Korea. Three dominant fish species were selected as target fishes such as Rhinogobius brunneus, Zacco platypus, and Pseudogobio esocinus. In order to consider the feeding condition of these fishes, Hydropsyche kozhantschikovi, Chironomidae, Baetis fuscatus, and Cheumatopsyche brevilineata were selected as target macroinvertebrates. Physical habitat simulations were carried out for both fishes and macroinvertebrates, and the distributions of the suitable feeding habitat for the target fishes were provided. It was shown that the suitable feeding habitat properly represents the quality of the target fishes’ habitats. Then, the Weighted Usable Area (WUA) and Weighted epi-Benthic Feeding Area (WBFA) for target fishes were compared, and the results indicated that WBFA predicts fish abundance better than WUA.

Evaluation of hydropeaking impacts on the food web in alpine streams based on modelling of fish- and macroinvertebrate habitats

Hydropeaking as a result of peak-load electricity production has been identified as one of the most significant pressures in alpine streams. Scouring of macroinvertebrates leads to downstream transport of aquatic organisms (catastrophic drift). Additionally, invertebrates are affected by periodic drying of wetted area during the dewatering of gravel bars and exposed areas along the banks. Even though fish are physiologically better adapted to switch to suitable habitats, artificial flow fluctuations may be followed by lethal stranding and quick alteration in habitat quantity and quality. Nevertheless, the interactions between pressures on fish and macroinvertebrates in terms of hydropeaking have not been investigated so far. The aim of this paper is to evaluate effects of flow fluctuations on potential epibenthic feeding grounds. Therefore, we evaluated changes in habitat distribution resulting from rapid flow fluctuations in river reaches with different river morphological characteristics, for five different macroinvertebrate taxa. Additionally, microhabitats for brown trout at two different life stages were calculated using representative peaking events (seasonal analysis) based on mid- to long term times series. Moreover, GIS-analysis allowed the evaluation of hydropeaking impacts (interaction) on both, macroinvertebrates and fish. In this study, it could be documented that feeding from the benthos for juvenile and subadult brown trout is inhibited during peak flow and is therefore reduced to times of base flow. Moreover, potential benthic feeding areas occurring at base flow have been found to increase with the level of morphological heterogeneity within analyzed river reaches. Likewise, hydrological sensitivity testing in terms of reducing ∆Q at different levels was performed and revealed that possible positive effects required heterogeneous river morphology as a precondition. However, this approach might be applied for estimating the impacts of hydrological mitigation measures in hydropeaked rivers concerning physical condition and/or growth rate of salmonids considering the river morphology of the investigated stream.

Assessing sediment toxicity: Past, present, and future

Assessing sediment toxicity: Past, present, and future

Colour, confusion, and crossing: resolution of species problems inBohadschia(Echinodermata: Holothuroidea)

Sea cucumbers of the genus Bohadschia (Holothuroidea: Echinodermata) are among the larger and more common echinoderms on tropical coral reefs. While the genus is easy to identify and has been recognized for some time, the number and status of species have varied substantially for over a century. The species problem in Bohadschia is the result of high intra-specific variability and little inter-specific divergence in the principal, traditional taxonomic characters, the shape and size of microscopic dermal ossicles. We re-evaluate Bohadschia primarily based on colour pattern of living animals and mitochondrial sequence data. The character sets are congruent, and both cleanly delineate 11 species and one common hybrid form. The vexing Bohadschia marmorata complex is resolved into four species, all of which have available names, although two have not been recognized correctly since their description. A fairly common colour form intermediate between B. argus and B. vitiensis has mtDNA sequences matching either one or the other species and is interpreted as a hybrid form. Several species occur sympatrically at most locations; however, the most closely related species show evidence of allopatric divergence. Character state reconstructions suggest that the prevalent diurnal burrowing and nocturnal epibenthic feeding behaviour among Bohadschia evolved early in the history of the genus. Ossicle shape and size were found to perform poorly in distinguishing species, while colour pattern is diagnostic.

Using aerial photography to investigate evidence of feeding by bowhead whales

AbstractAerial photographs were analyzed to investigate the feeding habits of the Bering‐Chukchi‐Beaufort (BCB) population of bowhead whales (Balaena mysticetus), particularly epibenthic feeding near Barrow, Alaska. Evidence of epibenthic feeding was based on mud visible on the dorsal surface of whales, resulting from feeding near the seafloor. Other cues used to assess feeding were an open mouth or the presence of feces in photographs. Over 3,600 photographs were analyzed including photos from surveys in spring and late summer and in both the western and eastern Beaufort Sea. Of all the photographs analyzed, 64% were scored as definitively muddy. In spring, ratios ranged from a low of 27% in 2003 to a high of 76% in 2004. When all May sample sets off Barrow were combined (1985, 1986, 2003, 2004), there was a significant difference (t‐test, P < 0.004) between the proportion of muddy juveniles to the proportion of muddy adults, with muddy adults being more common. The Barrow area was a commonly used feeding ground during migrations in both the spring (61% of the sample were feeding; 55% epibenthically) and autumn (99% of the sample; 97% epibenthically). Bowheads both migrate and feed through areas where petroleum extraction is underway and anticipated; hence, exposure to oil after a spill is of considerable concern to Native communities and management agencies.

Effects of turbidity on the ability of juvenile rainbow trout, Oncorhynchus mykiss, to feed on limnetic and benthic prey in laboratory tanks

The feeding rate of juvenile rainbow trout, Oncorhynchus mykiss Richardson, 1836, on small (1–2 mm diam.) Daphnia spp. in laboratory tanks was not reduced by turbidity levels up to 160 Nephelometric Turbidity Units (NTU). Furthermore, the high feeding rates on larger, benthic prey (viz. Deleatidium spp. and chironomid larvae) in clear water (0 NTU) were maintained at turbidities up to 160 NTU. Therefore, any impairment of vision by increased turbidity did not affect the ability of trout to feed on these prey, and non‐visual senses may be used for the capture of such prey in turbid waters. Although trout were strongly size‐selective for both large chironomid and Deleatidium larvae in clear water, turbidities over 20 and 160 NTU, respectively, reduced size‐selection. Vision is therefore needed by trout to select larger prey. However, chironomid larvae were consumed by trout in the complete absence of light, so their ability to capture these prey in tanks was not dependent on visual cues. It is apparent that trout do use other senses such as the lateral line system to detect and capture such prey when turbidity levels are high and when light levels or water clarity are low. This ability is expected to offset any reduction in visual feeding caused by increased turbidity, and it helps explain the increased emphasis on epibenthic feeding by trout in turbid waters.

Feeding ecology in five shrimp species (Decapoda, Caridea) from an Arctic fjord (Isfjorden, Svalbard), with emphasis on Sclerocrangon boreas (Phipps, 1774)

Analyses of stomach contents indicate diet specificity in the species of shrimps investigated. Eualus gaimardii displayed a mostly pelagic feeding habit by preying mainly on copepods and amphipods. However, high loads of sediment in the stomachs of E. gaimardii indicate that feeding also occurred in the vicinity of the sea floor. More epibenthic feeding behaviour was found in Lebbeus polaris, in which large amount of hydrozoans and amphipods were recorded in the stomach. Spirontocaris spinus showed the strongest affinity to foraminiferans and hydrozoans as prey items. In Sclerocrangon boreas, eight out of ten prey categories were recorded, which makes this the most opportunistic among the species considered. Male S. boreas were generally found at shallower depths than females. Females fed more on infaunal organisms, while males used epibenthic organisms as a food source. When dissimilarities in diet are considered at the two shallowest stations, there is a stronger effect of depth than of sex, indicating that faunal changes at different depths are more important for diet composition than the sex of an individual.

A stable isotope (δ13C, δ15N) model for the North Water food web: implications for evaluating trophodynamics and the flow of energy and contaminants

The North Water Polynya is an area of high biological activity that supports large numbers of higher trophic-level organisms such as seabirds and marine mammals. An overall objective of the Upper Trophic-Level Group of the International North Water Polynya Study (NOW) was to evaluate carbon and contaminant flux through these high trophic-level (TL) consumers. Crucial to an evaluation of the role of such consumers, however, was the establishment of primary trophic linkages within the North Water food web. We used δ15N values of food web components from particulate organic matter (POM) through polar bears (Ursus maritimus) to create a trophic-level model based on the assumptions that Calanus hyperboreus occupies TL 2.0 and there is a 2.4‰ trophic enrichment in 15N between birds and their diets, and a 3.8‰ trophic enrichment for all other components. This model placed the planktivorous dovekie (Alle alle) at TL 3.3, ringed seal (Phoca hispida) at TL 4.5, and polar bear at TL 5.5. The copepods C. hyperboreus, Chiridius glacialis and Euchaeta glacialis formed a trophic continuum (TL 2.0–3.0) from primary herbivore through omnivore to primary carnivore. Invertebrates were generally sorted according to planktonic, benthic and epibenthic feeding groups. Seabirds formed three trophic groups, with dovekie occupying the lowest, black-legged kittiwake (Rissa tridactyla), northern fulmar (Fulmarus glacialis), thick-billed murre (Uria aalge), and ivory gull (Pagophilia eburnea) intermediate (TL 3.9–4.0), and glaucous gull (Larus hyperboreus) the highest (TL 4.6) trophic positions. Among marine mammals, walrus (Odobenus rosmarus) occupied the lowest (TL 3.2) and bearded seal (Erignathus barbatus), ringed seal, beluga whale (Delphinapterus leucas), and narwhal (Monodon monoceros) intermediate positions (TL 4.1–4.6). In addition to arctic cod (Boreogadus saida), we suggest that lower trophic-level prey, in particular the amphipod Themisto libellula, contribute fundamentally in transferring energy and carbon flux to higher trophic-level seabirds and marine mammals. We measured PCB 153 among selected organisms to investigate the behavior of bioaccumulating contaminants within the food web. Our isotopic model confirmed the trophic magnification of PCB 153 in this high-Arctic food web due to a strong correlation between contaminant concentration and organism δ15N values, demonstrating the utility of combining isotopic and contaminant approaches to food-web studies. Stable-carbon isotope analysis confirmed an enrichment in 13C between POM and ice algae (–22.3 vs. –17.7‰). Benthic organisms were generally enriched in 13C compared to pelagic species. We discuss individual species isotopic data and the general utility of our stable isotope model for defining carbon flux and contaminant flow through the North Water food web.

Diel feeding periodicity, daily ration and prey selectivity in juvenile brown trout in a subarctic river

Feeding of age‐1 brown trout Salmo trutta in a third‐order river in northern Finland was usually highest in the twilight hours and lowest around midday. Diel periodicity in food intake was less distinct and rarely significant for age‐0 trout. Daily rations declined seasonally, being lowest in October, and highest in June (age‐1 trout) or early August (age‐0 trout). Prey selection did not differ between day and night, but differences between age classes and sampling dates were distinct. Age‐0 trout preferred Ephemerella nymphs in summer and Micrasema larvae later in the season. Age‐1 trout fed selectively on caddis larvae on all sample dates. Aerial insects and Baetis nymphs were avoided by both age classes on most occasions. These patterns of preference are probably explained by a trend towards epibenthic feeding, which may be a predominant foraging mode in some trout populations. Nevertheless, repuscular peaks in feeding periodicity suggest that trout were able to capitalize on the increased availability of drifting prey in the twilight, especially in the early summer months.

Factors affecting the foods and feeding patterns of lake‐dwelling rainbow trout (Salmo gairdnerii)in the North Island of New Zealand

Abstract Differences in feeding between age classes, males and females, and hatchery reared and wild rainbow trout (Salmo gairdnerii) in Lake Rotoma are described. Analysis of results, in conjunction with other published data on trout foods and feeding, showed that there was a summer increase in epibenthic feeding which, in Lake Rotoma, was most apparent in the species of forage fish predated. When trout feeding on forage fish was examined in a variety of lakes, 2 trends emerged. In large, clear, oligotrophic lakes trout fed predominantly on smelt (Retropinna retropinna) which are shoaling, epipelagic fish. Trout in small turbid lakes fed mainly on the solitary, benthic bully (Gobiomorphus cotidianus). These differences in feeding on forage fish were associated with the effects of water temperature and turbidity on trout distribution and foraging behaviour.

Diets and bathymetric distributions of the macrourid fish of the Rockall Trough, northeastern Atlantic Ocean

The Macrouridae are the most common fish caught in demersal trawls on the continental slope and rise of the Rockall Trough. They represented 41% of all fish caught, with Coryphaenoides rupestris amounting to 28% of the catch. No previous study of the trophic interaction of these fish has been made over a wide bathymetric range. Samples were obtained at 250-m intervals of depth between 400 and 2 900 m in the period 1975 to 1981. The stomachs of 5 326 fish belonging to 12 species were examined to define their diets. Eight species are primarily benthopelagic feeders while four are primarily epibenthic feeders. The bathymetric centres of distribution of the populations of the benthopelagic feeding Trachyrhynchus murrayi, Malacocephalus laevis, Coryphaenoides rupestis, C. guentheri, Nematonurus armatus, Chalinura brevibarbis, C. leptolepis and C. mediterranea are different from each other. Similar differences in bathymetric distribution occurred among the epibenthic feeding Nezumia aequalis, Coelorhynchus coelorhynchus, C. occa and Lionurus carapinus. These differences decrease competition among species that exploit similar resources.

Epibenthic Feeding by Rainbow Trout (Salmo gairdneri) in the McCloud River, California

SUMMARY (1) The stomach contents of rainbow trout from the McCloud River, California, were compared with the composition of the epibenthic invertebrate fauna and the composition of the invertebrate drift. The epibenthic fauna was dominated by Ephemeroptera and Plecoptera nymphs and immature Trichoptera and Diptera while the drift was dominated by Baetidae nymphs (Ephemeroptera), larval Simuliidae and Chironomidae (Diptera), and flying adult insects of both terrestrial and aquatic origin. Although the different groups of drifting invertebrates had different patterns and rates of drift, the overall peak in numbers of drifting organisms occurred at night. (2) Rainbow trout fry and juveniles relied predominantly upon drifting benthic invertebrates. During the day these fish consumed very little food. The most abundant organisms in the adult trout stomachs were larvae of Trichoptera (especially Dicosmoecus), Plecoptera, Ephemeroptera, Diptera, and terrestrial insects. Nearly half the stomach contents were undigestible algae, debris and exuviae. Feeding appeared to be continuous throughout the day, with no striking peaks in stomach fullness. The stomach contents showed no apparent relationship with the patterns and rates of drifting. (3) The epibenthic feeding behavior of the adult trout is probably due to the turbidity of the river, which makes drift feeding difficult when light levels are low. Epibenthic feeding, coupled with the high level of intraspecific competition probably present in an unexploited trout population, is probably responsible for the slow growth rates of the McCloud River trout.