Amorphous Detritus Research Articles

Dietary composition and fatty acid content of giant salmonflies ( Pteronarcys californica ) in two Rocky Mountain rivers

AbstractMany aquatic invertebrates are declining or facing extinction from stressors that compromise physiology, resource consumption, reproduction, and phenology. However, the influence of these common stressors specifically on consumer–resource interactions for aquatic invertebrate consumers is only beginning to be understood. We conducted a field study to investigate Pteronarcys californica (i.e., the “giant salmonfly”), a large‐bodied insect that is ecologically and culturally significant to rivers throughout the western United States. We sampled gut contents and polyunsaturated fatty acid composition of salmonflies to compare resource consumption across river (Madison or Gallatin, Montana), sex (male or female), and habitat (rock or woody debris). We found that allochthonous detritus comprised the majority of salmonfly diets in the Gallatin and Madison Rivers, making up 68% of the gut contents on average, followed by amorphous detritus, diatoms, and filamentous algae. Diets showed little variation across river, sex, or length. Minor differences in diets were detected by habitat type, with a higher proportion of diatoms in the diets of salmonflies collected from rocky habitat compared to woody debris. Fatty acid composition generally supported the results of gut content analysis but highlighted the importance of primary producers. The presence of eicosapentaenoic acid (20:5n‐3) and alpha linolenic acid (18:3n‐3) indicated consumption of diatoms and filamentous green algae, respectively. Our research underscores the importance of a healthy riparian zone that provides allochthonous detritus for invertebrate nutrition as well as the role of algae as an important source of fatty acids.

Serum markers for immunological response to metal alloys of endoprostheses

A study of solid-phase structures of blood serum using wedge-shaped and marginal dehydration methods (Litos system technology) was conducted in order to find out the causes of an inflammatory reaction followed by fibrosis in the second operated joint in a patient with bilateral knee arthritis. The study was aimed at identifying specific morphological markers that characterize the bodys response to the endoprosthesis material. Its solid-phase structures indicated the activation of a hyperergic reaction with daily incubation of blood serum with an alloy of titanium, aluminum, and vanadium. On the contrary, the immunological activity of blood serum can be suppressed and the structures present in it can be transformed into amorphous detritus with the incubation of an alloy of cobalt, chromium, and molybdenum. It was observed from the study that the nature of the immunological reaction of a sensitized organism depends on the type of metals that are part of the endoprosthesis. The immune response causes inflammation of the periarticular tissue, followed by its fibrosation and the formation of a scar demarcation shell that separates the periarticular tissue from the endoprosthesis and performs the function of an immunological barrier on the alloy of titanium, aluminum, and vanadium. On the other hand, an immunological reaction causes the destruction of inflamed periarticular tissue, followed by gradual destruction of the articular bag on the alloy of cobalt, chromium, and molybdenum.

Trophic basis of production in tropical headwater streams, Puerto Rico: an assessment of the importance of allochthonous resources in fueling food webs

The relative importance of allochthonous and autochthonous resources in fueling tropical headwater streams remains an open topic. We combined estimates of secondary production and assessment of its trophic basis to determine which resources were responsible for animal production. We studied benthic insect assemblages in two streams in the Luquillo Experimental Forest, Puerto Rico. Habitat-weighted production estimates were similar in both streams (528.5 and 591.5 mg m−2 year−1), but production was over twice as high in pool versus riffle habitats. The mayfly Neohagenulus (Leptophlebiidae) was a major contributor to total production (259.1 and 352.2 mg m−2 year−1). All taxa relied heavily on amorphous detritus and plant tissue. Aquatic insect production was similar to that reported for shrimp assemblages in the same study area, but low relative to temperate region estimates. The trophic basis of production appears to be allochthonous organic matter, which agrees with the small size and closed canopy cover over the study streams. This is the first study quantifying the production and trophic basis of the non-shrimp macroinvertebrate assemblage in tropical island streams. We also provide support for the importance of riparian vegetation as the main energy sources for stream tropical stream food webs.

Thermal niche diversity and trophic redundancy drive neutral effects of warming on energy flux through a stream food web.

Climate warming is predicted to alter routing and flows of energy through food webs because of the critical and varied effects of temperature on physiological rates, community structure, and trophic dynamics. Few studies, however, have experimentally assessed the net effect of warming on energy flux and food web dynamics in natural intact communities. Here, we test how warming affects energy flux and the trophic basis of production in a natural invertebrate food web by experimentally heating a stream reach in southwest Iceland by ~4°C for 2yr and comparing its response to an unheated reference stream. Previous results from this experiment showed that warming led to shifts in the structure of the invertebrate assemblage, with estimated increases in total metabolic demand but no change in annual secondary production. We hypothesized that elevated metabolic demand and invariant secondary production would combine to increase total consumption of organic matter in the food web, if diet composition did not change appreciably with warming. Dietary composition of primary consumers indeed varied little between streams and among years, with gut contents primarily consisting of diatoms (72.9%) and amorphous detritus (19.5%). Diatoms dominated the trophic basis of production of primary consumers in both study streams, contributing 79-86% to secondary production. Although warming increased the flux of filamentous algae within the food web, total resource consumption did not increase as predicted. The neutral net effect of warming on total energy flow through the food web was a result of taxon-level variation in responses to warming, a neutral effect on total invertebrate production, and strong trophic redundancy within the invertebrate assemblage. Thus, food webs characterized by a high degree of trophic redundancy may be more resistant to the effects of climate warming than those with more diverse and specialized consumers.

Spatial and Temporal Trends in Diet for Pinfish (Lagodon rhomboides) from Turtle Grass (Thalassia testudinum) Beds with Contrasting Environmental Regimes in the Lower Laguna Madre, Texas

Seagrass meadows in far South Texas are dominated by turtle grass (Thalassia testudinum), and juvenile pinfish (Lagodon rhomboides) are abundant grazers of seagrass epifauna. As they grow, pinfish exhibit an ontogenetic dietary shift and begin consuming increasing amounts of plant material. In this study, contrasting environmental regimes in two seagrass meadows were examined to identify how they might affect pinfish diets, diet shifts, and growth across the growing season. The eastern site was sheltered from prevailing southeasterly winds by a barrier island, while the western site was shallower and subjected to higher wind energy and turbidity. Gut contents from 290 pinfish were quantified from May through October 2016 and multivariate analyses showed strong but overlapping separation of diets and temporal change in feeding habits. Although there were spatial and temporal differences between the two sites, a site by time interaction indicated different temporal trends. Nonetheless, ooze (amorphous detritus) and aquatic invertebrates (primarily amphipods) were the primary diet items consumed at both localities across time. Pinfish at both sites consumed seagrass, which increased in importance as the growing season progressed, although volume and consumption rate did not differ between sites. Growth rates of pinfish were similar at both sites, but pinfish from the western site were larger and fewer in number across the study. Although pinfish diets differed under different environmental regimes, they were generalist consumers in South Texas seagrass meadows with high diet variability that trended towards herbivory in late summer and fall.

A tropical eastern Pacific invasive brittle star species (Echinodermata: Ophiuroidea) reaches southeastern Florida.

The invasive brittle star Ophiothela mirabilis (family Ophiotrichidae), a tropical Indo-Pacific endemic species, first reported in Atlantic waters off southern Brazil in 2000, has extended its range northward to the Caribbean Sea, to the Lesser Antilles in 2011, and was first reported in south Florida in January 2019. Its occurrence in southeast Florida extends along nearly 70km of coastline, from near the Port of Miami, Miami-Dade County, northward to Deerfield Beach, Broward County. It occurs abundantly as an epizoite on octocorals, attaining population densities of 25 individuals and more per 10-cm long octocoral stem. The surface texture of octocoral hosts (rough, smooth) did not affect the densities of the ophiuroid epizoites, and there were significantly greater abundances on octocorals during two winter sampling periods than in the summer. Beige and orange-coloured morphs are sometimes present on the same octocoral stem. Gut content analysis supported a suspension feeding mode, revealing essentially identical ingested items in both colour morphs with a preponderance of amorphous detritus and filamentous algae. Molecular genetic evidence (COI & 16s) has established the identity of O. mirabilis and its relationship to invasive Brazilian populations. The orange and beige morphs form two distinct, but closely related lineages that may represent two separate introductions. The orange morph shares haplotypes with Brazilian and Caribbean specimens suggesting a further range expansion of the 'original' invasion. The beige morph, however, shares haplotypes with specimens from the Mexican Pacific and Peru and potentially represents a secondary introduction. Traits promoting dispersal and establishment of this species in new habitats are manifold: vagility and ability to cling tightly to diverse host taxa (e.g. sponges, cnidarians, bryozoans, and echinoderms), frequent asexual reproduction (fissiparity), suspension feeding, including a wide range of dietary items, possession of integument-covered ossicles and arm spines offering protection from predators, and an effective competitive edge over associated microbiota for substrate space.

River food webs: an integrative approach to bottom-up flow webs, top-down impact webs, and trophic position.

The majority of food web studies are based on connectivity, top-down impacts, bottom-up flows, or trophic position (TP), and ecologists have argued for decades which is best. Rarely have any two been considered simultaneously. The present study uses a procedure that integrates the last three approaches based on taxon-specific secondary production and gut analyses. Ingestion flows are quantified to create a flow web and the same data are used to quantify TP for all taxa. An individual predator's impacts also are estimated using the ratio of its ingestion (I) of each prey to prey production (P) to create an I/P web. This procedure was applied to 41 invertebrate taxa inhabiting submerged woody habitat in a southeastern U.S. river. A complex flow web starting with five basal food resources had 462 flows >1mg·m-2 ·yr-1 , providing far more information than a connectivity web. Total flows from basal resources to primary consumers/omnivores were dominated by allochthonous amorphous detritus and ranged from 1 to >50,000mg·m-2 ·yr-1 . Most predator-prey flows were much lower (<50mg·m-2 ·yr-1 ), but some were >1,000 mg·m-2 ·yr-1 . The I/P web showed that 83% of individual predator impacts were weak (<10%), whereas total predator impacts were often strong (e.g., 35% of prey sustained an impact >90%). Quantitative estimates of TP ranged from 2 to 3.7, contrasting sharply with seven integer-based trophic levels based on longest feeding chain. Traditional omnivores (TP=2.4-2.9) played an important role by consuming more prey and exerting higher impacts on primary consumers than strict predators (TP ≥ 3). This study illustrates how simultaneous quantification of flow pathways, predator impacts, and TP together provide an integrated characterization of natural food webs.

Trophic dynamics of macroinvertebrate communities of a subtropical river in China

This study was the first attempt to resolve both spatial and temporal patterns of macroinvertebrate trophic dynamics in a Chinese subtropical river continuum, the Shengli River, from 1st to 4th order. Gut content analysis was adopted to assess the trophic basis and consumption rates of communities. Furthermore, annual energy flow food webs were constructed. Trophic basis analyses showed that 34–79% of the diet of macrozoobenthos in the Shengli River and its tributaries was amorphous detritus. Leaf litter was the second most important food source, followed by animal material. Filamentous algae, diatoms, and fungi served only as subsidies, contributing no more than 5% to total consumption. The macroinvertebrates in 1st and 3rd order streams appeared to show seasonal consumption patterns of different food types, while the communities in 2nd and 4th order streams had the same diet composition throughout the year. Total consumption rates of the communities increased from 1st to 3rd order streams, and declined in 4th order streams. The energy flow food web of 1st order streams was simpler than those of higher‐order streams. With increasing stream order, the food webs increased in complexity until 3rd order, and became simpler again in 4th order streams.

Allochthonous vs. autochthonous energy resources for aquatic insects in cloud forest streams, Veracruz, Mexico

Background. Recent tropical studies question the assumption that forested headwater streams rely on allochthonous resources as their main energy source, suggesting that autochthonous resources are more important. Goals. Here, we characterized the energy base, as gut contents, of cloud forest streams with contrasting riparian vegetation cover in Veracruz, Mexico, during dry, rainy and “nortes” (e.g., less dry and cold) seasons. Methods. Two first-order streams were selected for the study - one flowing through forest and the other through pasture with sparse riparian vegetation. Gut content analyses showed aquatic insect diets composed of diatoms, green algae, fungi, plant tissue, and amorphous detritus. Results. The forest stream had taxa with gut contents composed of 31 to 99% allochthonous material, while the pasture stream reached a maximum of 82% during “nortes”. Diatoms accounted for most of the autochthonous material in guts, especially in the pasture stream during the dry season. A significant proportion of ingested allochthonous material was fungi, mainly in the forest stream during the rainy season. Conclusions. Overall, our study supports the view that in forested tropical streams autochthonous material is an important food resource. However, allochthonous material was found to be an important food item, even in pasture streams with limited riparian cover.

&lt;p class="HeadingRunIn"&gt;&lt;strong&gt;Biology of &lt;em&gt;Anisocentropus pallidus &lt;/em&gt;(Martynov) (Trichoptera, Calamoceratidae): Laboratory and field observations&lt;/strong&gt;&lt;/p&gt;

The biology of the East Asian caddisfly Anisocentropus pallidus (Martynov 1935), Calamoceratidae, was studied in both the laboratory and field in Hokkaido, northern Japan. The egg and early instar larva are newly described. The larvae are abundant in dense accumulations of plant detritus and eat the detritus in littoral areas of ponds in marshes. Their cases are flat, oval and made of two leaf pieces with anteromesal slits, posterior concavities and interior silken chambers. Just after eclosion, a temporary cylindrical tubular case is made of amorphous detritus. The pupal case is also a flattened oval with small anterior and posterior openings on dorsal valves and attached on hard leaves and stems. The prepupal + pupal stage requires 15–19 days at 15–17˚C. Adults appear from June to September with peak emergence during mid June. Females have mature ovaries at emergence. A one− or two-year life cycle is suggested by seasonal changes of instar frequency and larval weight.

Habitats and Foraging Movements of Larvae of Molanna uniophila Vorhies (Trichoptera: Molannidae) in Pratt Lake, Michigan, USA

Habitats and foraging movements of larvae of Molanna uniophila Vorhies (Trichoptera: Molannidae) were studied during four summers in Pratt Lake, Michigan. Larvae lived and fed in shallow (&lt;10 cm), sand-bottomed lake margins, where macrophyte densities ranged from 86 to 452 stems/m2. Average densities of larvae varied fivefold between years (2.7 versus 13.6 individuals/m2), but larval densities did not vary significantly between habitat patches with low (120 stems/m2) and high (360 stems/m2) macrophyte densities. Larvae and their cases exhibited strong patterns of simple, linear growth. Diets of larvae were dominated by amorphous detritus, plant debris, diatoms, and filamentous algae, but midges, cladocerans, and other microscopic aquatic animals also were consumed. Larvae shifted their bodies and cases forward across the surface sediments up to 4 times/minute while foraging, moving as much as 2.5 m/hour. Movements and distances traveled while feeding increased significantly with increased water temperatures, peaking during midafternoon hours. Distances moved by feeding larvae did not differ between habitats with low versus high macrophyte densities. Larvae foraged most actively during daylight hours and did not selectively utilize macrophyte beds as partial refugia from potential predators while feeding.

High secondary production in a Coastal Plain river is dominated by snag invertebrates and fuelled mainly by amorphous detritus

Summary The 2‐years production dynamics of major taxa (family/order) and functional feeding groups was synthesised from detailed production analyses previously published for all major invertebrate species/genera (retained by a 100 μm sieve) found on snags (submerged wood) in a sixth‐order south‐eastern U.S. Coastal Plain river. The trophic basis of this production and annual consumption of six food types were quantified. Invertebrate production (148 and 203 g dry mass m−2 year−1 of snag surfaces for the 2 years) was among the highest ever measured for a specific habitat in non‐polluted or unregulated rivers and was still relatively high when converted to overall area of the river bed (48 and 70 g m−2 year−1). Snag production constituted 73% of total main‐channel production (production from snag and river bed combined). Chironomidae (40–44% over the 2 years), Ephemeroptera (14–21%) and Trichoptera (25–31%) together represented the majority (88–93%) of the putative production of primary consumers on snags. Functional group analysis showed that fine filterers (26–36% over the 2 years), gatherers (36–44%) and macro‐filterers (21–25%) represented the majority of total invertebrate production. Production of predaceous insects (mostly Plecoptera, Odonata and Megaloptera) represented only 5–7% of the total. Production of the three major taxa and three major functional groups was remarkably consistent over 2 years of monthly sampling, despite strong seasonal variation in discharge/light/temperature and production of individual genera and families. Seventy‐nine per cent of production by primary consumers was supported by microbially enriched amorphous detritus, the major component of seston originating primarily from floodplain forests. Invertebrates consumed ˜357 g AFDM m−2 (river bed) year−1 of seston, 325 g m−2 year−1 of amorphous detritus and 20 g m−2 year−1 of diatoms. Dividing seston consumption by seston transport indicated that ˜67% of seston was consumed over 100 km of river length. Consumption was higher than autochthonous net primary production, supporting other evidence that terrestrially derived dissolved organic matter, incorporated via the microbial loop, is the main trophic basis of this riverine food web. Macro‐filtering hydropsychid caddisflies were omnivorous with &gt; half their production from carnivory. Snag predators, including hydropsychids, consumed ˜60% (29 g m−2 year−1 of river bed) of invertebrate production (assumed to be from snags), leaving the remainder for emergence, downstream transport and consumption by fish.

High Diet Overlap between Native Small‐Bodied Fishes and Nonnative Fathead Minnow in the Colorado River, Grand Canyon, Arizona

AbstractRiver regulation may mediate the interactions among native and nonnative species, potentially favoring nonnative species and contributing to the decline of native populations. We examined food resource use and diet overlap among small‐bodied fishes in the Grand Canyon section of the Colorado River as a first step in evaluating potential resource competition. We compared the diets of the predominant small‐bodied fishes (native Speckled Dace Rhinichthys osculus, juvenile Flannelmouth Sucker Catostomus latipinnis, and juvenile Bluehead Sucker C. discobolus, and nonnative Fathead Minnow Pimephales promelas) across seasons at four sites downstream of Glen Canyon Dam using nonmetric multidimensional scaling and Schoener's similarity index. The diets of these fishes included diatoms, amorphous detritus, aquatic invertebrates (especially simuliid and chironomid larvae), terrestrial invertebrates, and terrestrial vegetation. Diets varied with season and were affected by high turbidity. Fish consumed more amorphous detritus and terrestrial vegetation during the summer monsoon season (July–September), when turbidity was higher. The diets of all species overlapped, but there was large variation in the degree of overlap. The diets of juvenile suckers and Fathead Minnows were most similar, while Speckled Dace had relatively distinct diets. The differences took the form of higher proportions of diatoms and amorphous detritus in the diets of Bluehead Suckers and Fathead Minnows and higher proportions of simuliids and chironomids in those of Speckled Dace. If food resources are or become limiting, diet overlap suggests that competition may occur among native and nonnative species, which could have implications for the population dynamics of these fishes and for the management of the Colorado River ecosystem in Grand Canyon.Received September 4, 2013; accepted February 11, 2014

Dietary overlap of invertivorous fishes and macroinvertebrates in the Gila River, New Mexico

The diets of stoneflies (Perlodidae) and hellgrammites (Corydalidae) from the Gila River, New Mexico, were quantified and compared to diets of three native fishes that also occupy riffle habitats along with stoneflies and hellgrammites: speckled dace (Rhinichthys osculus); longfin dace (Agosia chrysogaster); desert sucker (Catostomus clarkii). The highest overlap occurred among corydalids, desert sucker, and longfin dace, which had diets dominated by amorphous detritus. Speckled dace and perlodids consumed less amorphous detritus, with nymphs of mayflies and larval black flies dominating their respective diets. Our results suggest moderate to high overlap of resources among invertivorous fishes and invertebrates. Although we found high dietary overlap between corydalids and two fishes, it is unclear whether amorphous detritus is a limiting resource that drives competitive interactions.

Annual production, trophic basis and ingestion currency of dominant caddisfly (&lt;i&gt;Hydropsyche&lt;/i&gt; sp.) in Shengli River, Bahe catchment, the middle reach of the Yangtze River basin

为了加强长江中游地区大型无脊椎底栖动物的研究工作,2009年3月至2010年3月,对长江中游巴河支流的胜利河毛翅目优势种的生产力和营养基础进行了为期一年的调查研究.结果表明,胜利河中主要毛翅目优势种纹石蛾的生活史为一年3代.一至四级河流中,其生物量周年平均值分别为1.77、7.80、44.82、51.55 mg/m².采用体长频率法测算的年均生产量为7.72 mg/m²,P/B系数为13.21.利用肠内含物分析法研究了胜利河中纹石蛾的营养结构.比较一至四级河流的营养基础发现,无形态碎屑为纹石蛾最常见的食物,占肠内含物的45.22%~62.92%;而对生产量贡献率最高的多是动物组织,达52.86%~68.58%.各季节的营养基础状况也有差异,春季无形态碎屑所占比例和对生产量的贡献率较高,而夏、秋和冬季动物组织则有更高的生产量贡献率.一至四级河流的年均物质通量分别为11.83、34.76、237.52和273.17g/(m²·a).由此可见,该优势种在河流生态系统中发挥着重要作用.;In order to enrich the knowledge on the benthic macroinvertebrates in the middle reach of Yangtze River, a one-year investigation from March 2009 to March 2010 on secondary production and trophic basis of the dominant caddisfly in Shengli River (Shengli Town, Luotian County, Hubei Province), Bahe catchment, the middle reach of the Yangtze River Basin, was conducted. The result showed that the dominant caddisfly Hydropsyche sp. was trivoltinism. From the 1st to 4th rivers, the annual average biomasses of this species are 1.77, 7.80, 44.82 and 51.55 mg/m², respectively. Its annual production and P/B calculated with size (instar) -frequency method is 7.71 g/m2 and 13.21, respectively. Foregut content analysis showed that amorphous detritus was the dominant food of Hydropsyche sp., constituting 45.22%-62.92%, while the animal material usually gave the biggest contribution to secondary production, up to 52.86%-68.58%. In spring, amorphous detritus occupied the largest proportion and contributed most production, while in summer, autumn and winter animal material contributed the largest part of production. The annual ingestion currency of the species in different order rivers was 11.83 g/(m2 ·a) for 1st, 34.76 g/(m2 ·a) for 2nd, 237.52 g/(m²·a) for 3rd, and 273.17 g/(m²·a) for 4th, respectively. The study indicated that this caddisfly played an important role in the material cycling and energy flow of the Shengli River ecosystem.

Diet of the freshwater crab Bottiella niceforei (Schmitt & Pretzmann, 1968) (Decapoda: Trichodactylidae) and its relationship with organic matter processing in an intermittent stream of northwestern Venezuela

In order to study the role of the freshwater crab Bottiella niceforei in processing the organic matter in an intermittent stream of northwestern of Venezuela, we studied its natural diet by analyzing the gut contents during the period between June 2009 and February 2010. The abundance was determined based upon the proportion of individuals captured by traps throughout all the sampling period and on each pool. The highest crab densities occurred in September (2.7 ind trap-1), followed by June (2.3 ind trap-1) and July (2.1 ind trap-1); while the lowest were obtained in November and February, possibly due to the erosive effect of the current during the rainy season. No significant differences in the abundance and diet between pools were found. During the period from June to November it was found that the most abundant item in the crab diet was the plant detritus, with an average of 68%, followed by animal matter (fish remains), 50% on the average, and amorphous vegetal detritus with 14%. These results demonstrate the important participation of B. niceforei on the leaf litter processing in the pools of cano Carichuano.

Diet and functional feeding groups of Chironomidae (Diptera) in the Middle Paraná River floodplain (Argentina)

The gut contents of nine genera of benthic Chironominae and Tanypodinae from the Middle Paraná River floodplain habitats (a lake and a secondary channel) were analyzed to determine their feeding patterns and functional feeding groups. Amorphous detritus, animal and vegetal tissues, and mineral materials (predominantly sand) were observed in the larval guts. Amorphous detritus were the main food item found for Polypedilum (Tripodura) sp., Chironomus gr. decorus sp., Endotribelos sp., Phaenopsectra sp., Cladopelma sp., and Pelomus sp. (Chironominae), while animal tissues (mainly oligochaetes) were the most important food item found for Ablabesmyia (Karelia) sp., Coelotanypus sp., and Procladius sp. (Tanypodinae). Dietary overlap was calculated for all pairs of genera. Within predators, the highest overlap was obtained between Coelotanypus sp. and Ablabesmyia (Karelia) sp., while within detritivores the highest niche overlap was obtained between Endotribelos sp. and Phaenopsectra sp.

Succession and fate of the spring diatom bloom in Disko Bay, western Greenland

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 419:11-29 (2010) - DOI: https://doi.org/10.3354/meps08813 Succession and fate of the spring diatom bloom in Disko Bay, western Greenland Michael Dünweber1,4, Rasmus Swalethorp1,4, Sanne Kjellerup1,4, Torkel Gissel Nielsen1,4,*, Kristine Engel Arendt2, Morten Hjorth1, Kajsa Tönnesson3, Eva Friis Møller1 1National Environmental Research Institute, Department of Marine Ecology, University of Aarhus, Frederiksborgvej 399, 4000 Roskilde, Denmark 2Greenland Climate Research Centre, Greenland Institute of Natural Resources, Kivioq 3, Po Box 570, 3900 Nuuk, Greenland 3Department of Marine Ecology—Göteborg, University of Gothenburg, Box 461, 405 30 Göteborg, Sweden 4Section for Oceanecology and Climate, National Institute of Aquatic Resources, Technical University of Denmark, Kavalergården 6, 2920 Charlottenlund, Denmark *Corresponding author. Email: tgin@aqua.dtu.dk ABSTRACT: Phytoplankton and copepod succession was investigated in Disko Bay, western Greenland from February to July 2008. The spring phytoplankton bloom developed immediately after the breakup of sea ice and reached a peak concentration of 24 mg chl a m–3 2 wk later. The bloom was analyzed during 3 phases: the developing, the decaying, and the post-bloom phases. Grazing impact by the copepod community was assessed by 4 methods; gut fluorescence, in situ faecal pellet production, and egg and faecal pellet production from bottle incubations. Calanus spp. dominated the mesozooplankton community. They were present from the initiation of the bloom but only had a small grazing impact on the phytoplankton. Consequently, there was a close coupling between the spring phytoplankton bloom and sedimentation of particulate organic carbon (POC). Out of 1836 ± 180 mg C m–2 d–1 leaving the upper 50 m, 60% was phytoplankton based carbon (PPC). The composition and quality of the sedimenting material changed throughout the bloom succession from PPC dominance in the initial phase with a POC/PON ratio close to 6.6 to a dominance of amorphous detritus with a higher POC/PON ratio (>10) in the post-bloom phase. The succession and fate of the phytoplankton spring bloom was controlled by nitrogen limitation and subsequent sedimentation, while grazing-mediated flux by the Calanus-dominated copepod community played a minor role in the termination of the spring bloom of Disko Bay. KEY WORDS: Spring bloom · Calanus spp. · Grazing · Faecal pellets · Sedimentation · Arctic · Greenland Full text in pdf format PreviousNextCite this article as: Dünweber M, Swalethorp R, Kjellerup S, Nielsen TG and others (2010) Succession and fate of the spring diatom bloom in Disko Bay, western Greenland. Mar Ecol Prog Ser 419:11-29. https://doi.org/10.3354/meps08813 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 419. Online publication date: November 30, 2010 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2010 Inter-Research.

Trophic ecology of a nonnative population of suckermouth catfish (Hypostomus plecostomus) in a central Texas spring-fed stream

Introduced suckermouth catfishes (Family Loricariidae) are now established in a number of spring-influenced streams in North America but their impacts on native biota are not well documented. Purposes of this study were to quantify gut contents of the loricariid Hypostomus plecostomus from the San Marcos River in central Texas and to evaluate the role of H. plecostomus in the San Marcos River food web using stable isotope analysis. Gut content analysis indicated that H. plecostomus (N=36) pri- marily consumed amorphous detritus (87% in bio- volume), filamentous red algae (5.4%), and picoplankton (4.1%). Macrophytes, macroinverte- brates, and fish eggs were not found in gut contents. Stable isotopes demonstrate that H. plecostomus occupies a trophic position indicative of an herbivore and likely utilizes detritus of algal origin. The results from our study suggest that large populations of H. plecostomus in the San Marcos River may directly compete with several native herbivorous fishes and may be disrupting trophic flows and nutrient cycling in spring-influenced streams of central and west Texas.

Beaver invasion alters terrestrial subsidies to subantarctic stream food webs

North American beavers (Castor canadensis) were introduced to Tierra del Fuego Island in 1946 for their fur, and have since spread across the archipelago and onto the South American mainland. We assessed the impact of invasive beavers on streams of these forested watersheds by quantifying the trophic basis of production (TBP) and consumptive organic matter flows of benthic macroinvertebrate assemblages. TBP was determined in two streams: clear- and black-water. Stable isotopes were used across four streams to further elucidate food web structure and dominant pathways. TBP and stable isotopes showed that terrestrially derived organic matter (amorphous detritus, leaves, and wood) supported a majority of secondary production in the benthic food webs at all sites (forested reaches, beaver ponds, and sections downstream of ponds with foraged riparian zones). The magnitude of these flows was enhanced in beaver-modified sites compared with forested habitats (4.0–5.3× increase g AFDM m−2 year−1 in pond habitats, 1.1–2.1× increase in downstream habitats). Diatoms were the only autochthonous resource identified in macroinvertebrate guts, but their contribution to secondary production was small. Consumptive flows mirrored trends in TBP (i.e., dominance of terrestrial sources and greater magnitude in beaver ponds). Collector–gatherer consumption of amorphous detrital material dominated food web flows in all habitats, but was higher in beaver ponds relative to other habitats. Food web structure was simplified in beaver ponds; only two of the five possible functional groups contributed >1% of total organic matter flow in ponds (collector–gatherers and predators). Consumptive flows to predators increased in ponds, and stable isotopes of nitrogen and carbon (δ15N and δ13C) corroborated a relatively greater importance of predators (greater trophic distance), as well as less diversity of basal resources (less variation in δ13C) in ponds. Our findings indicate that invasive beaver’s engineering activities resulted in greater flows of terrestrial organic matter subsidies to in-stream food webs, which had a relatively greater change in the clear-water than in the black-water stream. Owing to the fact that these streams were naturally dependent on allochthonous resources for a majority of production and material flows, changes wrought by beavers to streams in forested environments are probably less than in watersheds with inherently greater dependence on autochthonous production such as the adjacent steppe biome.