Higher Order Consumers Research Articles

Can polycentric cities provide more and higher-order consumer amenities? Evidence from shopping malls in China

It remains unclear whether a polycentric city can support more and higher-order consumer amenities. This paper presents new evidence from shopping malls in China and includes the effect of urban spatial structure on the order of consumer amenities and the moderating effect of transportation infrastructure, both of which have been neglected in previous empirical studies. We find that a monocentric city can provide a greater number and higher order of shopping malls than a polycentric city. Additionally, better transportation infrastructure can compensate for the disadvantage of polycentricity in the provision of low-order shopping malls, while it reinforces the merit of monocentricity in higher-order shopping malls. The findings advance the understanding of the relationship between polycentricity and the quantity and quality of consumer amenities and provide insights into polycentric structure policies.

Spatiotemporal stressors, not secondary structures or small temperature increases, control rapid facilitation of intertidal epifauna

Small animals (epifauna) are ubiquitous in marine systems. Epifauna have high secondary production and provide trophic linkages between primary producers and higher-order consumers, like fish. Despite their importance, little is known about how these animals respond to warming or how their communities vary across spatiotemporal gradients. Here we use mimics of turf seaweed and invasive kelp holdfast to test, in a 5-factorial field experiment, whether intertidal epifauna are facilitated by different habitat structures, temperature conditions, and along cooccurring spatiotemporal gradients. We found that facilitation of epifauna by intertidal turf seaweed peaked in summer, at low elevation, in older habitats and at a less wave-exposed site. However, epifauna were not affected by the presence of a secondary structure like kelp holdfast mimics or small temperature increases from passive solar heating of black and white mimics. There were many significant two-way, but few higher order interactions, showing stronger facilitation under specific environmental conditions, like at low elevation in summer, or low elevation in old habitats. These results highlight that turf-associated epifauna are controlled by vertical elevation, season, hydrodynamics, and habitat age, and appear to be resilient to small temperature increases. Findings are important to better understand linkages between primary producers and higher order consumers and system-wide productivity, and because fast growing turf, facilitated by global warming and eutrophication, are increasingly outcompeting slower growing large perennial canopy forming seaweeds, like kelp and rockweeds.

Biosynthetic constraints on amino acid synthesis at the base of the food chain may determine their use in higher-order consumer genomes.

Dietary nutrient composition is essential for shaping important fitness traits and behaviours. Many organisms are protein limited, and for Drosophila melanogaster this limitation manifests at the level of the single most limiting essential Amino Acid (AA) in the diet. The identity of this AA and its effects on female fecundity is readily predictable by a procedure called exome matching in which the sum of AAs encoded by a consumer's exome is used to predict the relative proportion of AAs required in its diet. However, the exome matching calculation does not weight AA contributions to the overall profile by protein size or expression. Here, we update the exome matching calculation to include these weightings. Surprisingly, although nearly half of the transcriptome is differentially expressed when comparing male and female flies, we found that creating transcriptome-weighted exome matched diets for each sex did not enhance their fecundity over that supported by exome matching alone. These data indicate that while organisms may require different amounts of dietary protein across conditions, the relative proportion of the constituent AAs remains constant. Interestingly, we also found that exome matched AA profiles are generally conserved across taxa and that the composition of these profiles might be explained by energetic and elemental limitations on microbial AA synthesis. Thus, it appears that ecological constraints amongst autotrophs shape the relative proportion of AAs that are available across trophic levels and that this constrains biomass composition.

Relating absolute abundance of an estuarine fish to habitat area in an urbanizing environment

Organisms that rely on salt marsh habitat are an important trophic link, helping to maintain estuarine ecosystem productivity. We used GIS to quantify intertidal (assumed salt marsh) area from aerial photographs taken in 1939 and from software-supplied satellite imagery taken in 2021 for tidal creeks in North Carolina (USA) that have experienced minor (<20%), moderate (20-60%), or substantial (>60%) losses of intertidal habitat over the 8 decades. The current (2022) absolute abundance of adult Fundulus heteroclitus, a trophically important resident fish in US Atlantic estuaries, was estimated over each season in each creek by fitting a Lincoln-Petersen model to tag-recapture data. Current abundances of F. heteroclitus were lowest in creeks with the lowest intertidal area. The median and 2.5/97.5 credible intervals of the posterior probability distribution for the slope of a regression model relating current fish abundance to current intertidal area were positive, demonstrating that intertidal area was a meaningful covariate of abundance. Loss of intertidal area in the creeks between 1939 and 2021 ranged from 8 to 93%. The correlation between current intertidal area and historical loss of this habitat was negative and significant (Pearson r = -0.91, p = 0.012). Parameters from the regression relating current abundance to intertidal area were used to estimate historic F. heteroclitus abundances in each creek using GIS-derived estimates of historic intertidal area. Historic abundances were predicted to have been on average (across study creeks) 7.5 times greater in 1939 than in 2022. Reduced abundances, and thus reduced trophic relay by F. heteroclitus to higher-order consumers, can be expected in estuaries that have lost salt marsh due to inter-decadal development.

Lipid dynamics in the southern hemisphere: a 30-year meta-analysis of marine consumers

Assessing the total lipid content (TLC, expressed as % wet weight, WW) and constituent fatty acid (FA) composition (expressed as % of total FA) in marine organisms provides vital knowledge about the transfer of energy and essential nutrients from primary producers to higher-order consumers, including humans. To obtain a broad understanding of marine lipid dynamics, we used information from more than 470 species of Australian and Southern Ocean marine consumers spanning across the food web, from secondary to apex predators, sampled over a 30 yr period (1989 to 2019). Taxa group, trophic guild, and collection period were found to be the most influential drivers of variability in 4 key variables (TLC, docosahexaenoic acid [DHA, 22:6n-3], eicosapentaenoic acid [EPA, 20:5n-3] and arachidonic acid [ARA, 20:4n-6]). Highest TLC was observed in marine mammals and mid-trophic consumers, highest DHA occurred in fish and apex predators, highest EPA occurred in krill and other lower-level consumers, and highest ARA was present in rays and other apex predators. Horizontal habitat type was also an important driver with significantly higher TLC, EPA, and DHA found in samples from oceanic and pelagic habitat types, whilst coastal habitat samples had significantly higher ARA. Generalised additive mixed models determined that there were regional spatial patterns and interannual trends for all variables over the 30 yr period across all taxa groups. This study provides new understanding of the spatial distribution, temporal trends, and drivers of lipid and essential fatty acids (EFA) in marine ecosystems in the southern hemisphere.

Diet and isotopic niche dimensions of predatory fish in two estuaries with different degrees of anthropogenic disturbances: a case study of Wami and Pangani Tanzanian coastal estuaries

Diverse anthropogenic activities including alteration of hydrological regime and agricultural development in the upstream of the river catchments modify the structural components and ecological roles of the species in estuarine ecosystems. The present study compared the diet, carbon (δ13C) and nitrogen (δ15N) isotopic signals, trophic niches and metrics of trophic redundancy of predatory fish and their potential phytodetritivore prey-fish between two estuaries with different degrees of anthropogenic disturbances. The δ13C and δ15N signals, Bayesian mixing models and stomach content analyses were adopted. It was revealed that the diet among the predators Arius africanus, Epinephelus coioides, Sillago sihama and Pomadasys argenteus and their isotopic signals including their phytodetritivore-prey, Valamugil buchanani were significantly different between Wami and Pangani estuaries (PERMANOVA, Pseudo –F ≥ 3.1, p = 0.05). The total isotopic niche area between estuaries accounted by the comparable Bayesian standard ellipse area (SEAb) was significantly smaller in Wami than that of Pangani (t-test, t = 4.3, p < .001). The ANOVA test further confirmed significant variation in SEAb among fish populations in two estuaries (F = 27.84, p < 0.001). The Layman metric indices of trophic diversity and redundancy of Wami estuary were substantially smaller than those observed at Pangani estuary. These findings mean that despite Wami estuary being under conservation status, the extent of disturbances in the upstream is high enough to induce the ecological changes at the base of the food web, subsequently cascading its effect up to the higher-order consumers of the ecosystem. As a result, the ecological redundancy and ecosystem complexity of Wami is somewhat compromised relative to that of Pangani estuary. Therefore, the degree of anthropogenic disturbances in river catchments affect differently the trophic niches of predatory and phytodetritivore fish and hence overall food web structures, trophic redundancy and complexity of estuarine ecosystems.

The effects of hydrology on macroinvertebrate traits in river channel and wetland habitats

AbstractIncreased need for freshwater for human uses from the mid-1900s has severely impacted rivers and floodplain wetlands so that they are some of the most seriously degraded environments in the world. Research and monitoring in this area to date has focused on understanding ‘flow-ecology’ relationships, without investigating the mechanisms underlying them. The use of species traits offers a tool for defining mechanistic connections between biotic responses and environmental conditions. We examined nine macroinvertebrate trait categories in both wetlands and channels to determine whether their profiles responded to hydrology in the Gwydir River system in the northern Murray-Darling Basin, Australia. Trait responses were shown for the wetlands but not the river channels. Twelve traits showed positive relationships with the time the wetlands were connected to their river channels. It is unclear the reason(s) why the river channel invertebrate traits did not respond to hydrology. However, the use of environmental flows in the river systems may be important to other aspects of macroinvertebrate assemblages such as their role in food webs to support higher-order consumers.

Trophic Structure and Sources of Variation Influencing the Stable Isotope Signatures of Meso- and Bathypelagic Micronekton Fishes

To better understand spatiotemporal variation in the trophic structure of deep-pelagic species, we examined the isotope values of particulate organic matter (POM) (isotopic baseline) and seven deep-pelagic fishes with similar diet compositions but contrasting vertical distributions across mesoscale features in the Gulf of Mexico (GOM) using stable isotope and amino acid compound-specific isotope analyses. Species examined included four migratory (Benthosema suborbitale, Lepidophanes guentheri, Melamphaes simus, Sigmops elongatus) and three non-migratory zooplanktivorous fishes (Argyropelecus hemigymnus, Cyclothone obscura, Sternoptyx pseudobscura). Isotopic values of POM increased with depth, with meso- and bathypelagic samples characterized by higher δ13C and δ15N values relative to epipelagic samples. Despite similar diet compositions, mean δ15N values of fishes spanned 3.43‰ resulting in mean trophic position estimates among species varying by 1.09 trophic levels. Interspecific differences in δ15N were driven by higher δ15N values in the non-migratory and deepest dwelling C. obscura (10.61‰) and lower δ15N values in the migratory and shallowest dwelling L. guentheri (7.18‰) and B. suborbitale (8.11‰). Similarly, fish δ15NsourceAA values were correlated with depth, with values found to be lowest in the migratory L. guentheri and B. suborbitale and highest in the non-migratory C. obscura. Our data suggests that depth-related trends in fish δ15N and δ15NsourceAA values are driven by shallower dwelling species feeding within epipelagic food webs supported by POM with lower δ15N values, while deeper dwelling, non-migratory species increasingly use food webs at depth supported by POM with elevated δ15N values. Horizontal isotopic variation was observed across a large mesoscale oceanographic feature (Loop Current) for POM and migratory and non-migratory species which were characterized by higher δ13C and lower δ15N values in the anticyclonic Loop Current relative to surrounding water masses. Our results demonstrate that isotopic values of POM can vary significantly over relatively small horizontal and vertical scales, and that baseline variation can be conserved in the signatures of higher-order consumers. By gaining a more thorough understanding of the sources contributing to isotopic variation of deep-pelagic fishes, this paper will inform the design and interpretation of future feeding studies in the pelagic realm and advances our knowledge of deep-pelagic food web structure.

Planktonic Protists of the Eastern Nordic Seas and the Fram Strait: Spatial Changes Related to Hydrography During Early Summer

The European Arctic is rapidly changing where increasing water temperatures and rapid loss of sea-ice will likely influence the structure and functioning of the entire ecosystem. This study aimed to describe the taxonomic composition and spatial distribution of early summer (2015-2016) nano- and microplanktonic protists in the Nordic (Norwegian, Greenland) Seas and the Fram Strait (70.99°N to 78.84°N; 1.52°E to 19.90°E) and to determine the distribution patterns of the communities from the aspect of hydrography, as deduced from in situ measurements. Here we identify some generalized regularity in the protistan distribution, indicating the two separated domains at the 6 °C threshold. While Phaeocystis seemed to be a fairly conservative representative of the colder area ( 6 °C) may vary significantly between successive summers: from mostly Bacillariophyceae-dominated communities in 2015 to flagellate-dominated in 2016. Based on our results, we hypothesised that the more intense phototrophs development in the area, as deduced from higher remotely sensed chlorophyll a concentrations in 2016, i.e., record warm year in the observational period, could lead to faster depletion of nutrients, and thus, an earlier shift into the post-bloom community stage. Taking into account the possible phenological shift towards early summer domination of flagellates in a warmer year, as well as a higher number of heterotrophic protists associated with the warmer domain in two evaluated summers, it is highly likely that climatic warming of this region will have an impact on energy transfer to higher trophic levels. Although generalized patterns could be elucidated, more information is needed to predict and understand how the changing Arctic will alter protistan communities, and thus, higher-order consumers.

Toward a goal-oriented view of customer journeys

PurposeCustomer experience research predominantly anchors the customer journey on a specific offering, implying an inherently firm-centric perspective. Attending calls for a more customer-centric approach, this study aims to develop a goal-oriented view of customer journeys.Design/methodology/approachThis study interprets the results of a phenomenological study of a transformative journey toward a sober life with the self-regulation model of behavior to advance understanding of customer journeys.FindingsThe consumer's journey toward a higher-order goal encompasses various customer journeys toward subordinate goals, through which consumers engage in iterative cognitive and behavioral processes to adjust or maintain their experienced situation vis-à-vis the goal. Experiences drive behavior toward the goal. It follows that negative experiences may contribute to goal attainment.Research limitations/implicationsThis study highlights the importance of looking at the consumers' higher-order goals to obtain a more holistic understanding of the customer journey.Practical implicationsCompanies and organizations should extend their view beyond the immediate goals of their customers to identify relevant touchpoints and other customer journeys that affect the customer experience.Originality/valueThis study proposes conceptualization of the customer journey, comprising goal-oriented processes at different hierarchical levels, and it demonstrates how positive and negative customer experiences spur behaviors toward the higher-order consumer goal. This conceptualization enables a more customer-centric perspective on journeys.

A Comparative Analysis of the Mouthpart Structures of Two Epischura Species (Copepoda, Calanoida) from Lakes Differing in their Trophic Status

Planktonic copepods, being a connecting link between primary production and higher order consumers, are often a key component of the food net in limnetic ecosystems. Many studies indicate a strong relationship between feeding mode and the structure of the mouthparts of copepods. Early studies attributed members of the genus Epischura to different groups according to their feeding mode and assumed that the species inhabiting the territory of Asia were only adapted to feeding on phytoplankton. We compared the fine morphology of the mouthparts of the Asian species, Epischura baikalensis and E. chankensis, living in different environments. The measurements were made using electron and light microscopy. The mesh sizes of the food capture net formed by the setae and setules ranged between 3.2 μm for E. chankensis and 9.1 μm for E. baikalensis. The area presumably covered by the first maxillae was 13215 μm2 and 66470 μm2, respectively. The resistance force of one seta is ten times higher for E. baikalensis than for E. chankensis. According to the results of calculations of hydrodynamic characteristics based on Reynolds number, these species are unable to filter food particles, but they capture them by drawing them into the mouth. The significant difference in the length of the oral appendages indicates that E. baikalensis is better adapted to living in an oligotrophic lake. For feeding on small particles at low concentrations, it is more beneficial to have long oral appendages even at high energy costs

Sargassum epifaunal communities vary with canopy size, predator biomass and seascape setting within a fringing coral reef ecosystem

Tropical seascapes are comprised of a range of patch habitat types, yet we have only a partial understanding of how local patch condition and seascape position may influence patterns of marine biodiversity, particularly for invertebrate taxa. We investigated how the epifaunal abundance and biomass of tropical Sargassum varied with canopy size (volume, total length and dry weight), local patch conditions (macroalgal composition, canopy structure and invertivorous fish biomass) and seascape setting (nearshore, lagoon and back reef) within the Ningaloo fringing reef ecosystem, Australia. A total of 49431 epifauna, dominated by crustaceans and molluscs, were extracted from the thalli of 81 tropical Sargassum polycystum individuals. Epifaunal abundance and biomass were most strongly correlated with host Sargassum canopy volume and dry weight, respectively. Epifaunal abundance and biomass also varied significantly among separate Sargassum meadow patches, with a significant interaction between canopy size and seascape position. Considerable site-level variations in epifaunal biomass density (mg per g Sargassum dry weight) were best predicted by either seascape context or local invertivorous fish biomass. Sargassum within meadows furthest from the back reef tended to have the highest epifaunal biomass (dominated by molluscs), while meadows closest to the back reef were dominated by crustacea. Sargassum within meadows with a high local abundance of invertivorous labrids and serranids tended to have the lowest epifaunal biomass. Strong Sargassum canopy size-epifauna relationships indicate that even small differences in canopy extent have major flow-on effects for the trophic function of tropical marine ecosystems by affecting the epifaunal secondary productivity available to higher-order consumers, such as fishes.

Invasive plant Arundo donax alters habitat use by carnivores

Invasive plants can have significant negative interactions with native flora and fauna, often decreasing the abundance and diversity of native plants and invertebrate and vertebrate herbivores. Less is known, however, about how invasive plants influence higher-order consumers, such as carnivores. Arundo donax is a globally distributed invasive grass that forms dense monotypic stands in the habitats where it successfully establishes. This study investigated the influence of Arundo invasion on mammal assemblages in California’s Santa Clara River Valley. Specifically, we aimed to determine whether Arundo alters habitat use for carnivores, and if so, assess the possible mechanisms driving these differences. We used remote cameras to evaluate carnivore habitat use and model occupancy, and live traps and remote cameras to assay abundance of small mammals, common prey of these larger predators. We found that detections of all carnivores were significantly lower in Arundo-dominated habitat patches, suggesting decreased preference for Arundo habitat. This was reflected in the occupancy model, which found the highest probability of coyote and bobcat habitat use in native patches and lowest in Arundo; however, habitat did not seem to be as important of a predictor as in the pooled species results. Small mammal abundance was similar if not higher in Arundo, suggesting the possibility of Arundo acting as a refuge for prey species and altered predator–prey dynamics in Arundo-dominated patches. This study improves our knowledge of the often-complex ways that invasive plants, like Arundo, influence the ecology and behavior of faunal communities in invaded ecosystems.

The basal food sources for Murray cod (Maccullochella peelii) in wetland mesocosms

The use of freshwater for human consumption and agriculture has resulted in many wetland ecosystems being some of the most seriously impacted ecosystems in the world. In attempts to rehabilitate wetland ecosystems environmental flows are used to restore parts of the hydrological regime altered by human water use. The use of environmental water intends to improve ecosystem health, but frequently aims to have specific outcomes for populations of higher-order consumers such as iconic fish and bird species. To date, research and monitoring has mainly focused on understanding ‘flow-ecology’ relationships, without investigating the mechanisms underlying them. We sought to understand the importance of different basal food sources to the growth of the endangered Murray cod in temporary wetland systems using fatty acid biomarkers. We flooded replicate mesocosms with two different wetland soils to produce sufficient zooplankton prey to sustain and grow Murray cod larvae for approximately 2 weeks. The fatty acid profiles of Murray cod and percentages of different biomarkers were compared at the start and finish of the experiment and our results suggest that the most important basal food source is green algae. However, the biomarkers of diatoms, cyanobacteria and bacteria also increased and differed between wetlands with different hydrological regimes. It is unclear if our results can be extended to other wetland systems and we encourage further research both into the relationship between length of wetland flooding and invertebrate densities in other systems. We also encourage research into the mechanistic pathways in which green algae carbon is transferred through food webs to higher order consumers in wetland systems to help generalise our results to other wetlands and support the management of wetlands through the timing and duration of flooding from environmental water.

Benthic trophic networks of the southern North Sea: contrasting soft-sediment communities share high food web similarity

We examined whether taxonomically distinct benthic communities from contrasting sediments in the German Bight (southern North Sea) also differ in their trophic structure. As a case study, we compared the Amphiura filiformis community (AFC) of silty sands and the Bathyporeia− Tellina community (BTC) of fine sands using a combination of stable isotope analysis and data on trophic interactions. Differences between the food webs were evident in the feeding guild compo� sition of important primary consumers: deposit and interface feeders are the most diverse primary consumer guilds in the AFC, whereas suspension and interface feeders play a major role in the BTC, reflecting differences in physical properties and food availability at the sediment−water interface. While all primary consumer guilds had the same trophic level (TL) in the AFC, deposit feeders of the BTC occupied a trophic position intermediate between other primary and higher� order consumer guilds, likely explained by partially incomplete knowledge of their trophic eco - logy and selective feeding, including the ingestion of meiofauna. Most food web properties, how�ever, were similar between the AFC and BTC: they mainly depend on pelagic primary production, reach TL 4 and are characterized by a prevalence of generalist higher-order consumers. Further� more, both trophic networks had similar linkage densities and high directed connectance, the lat�ter feature suggesting considerable food web robustness. Our findings suggest that although com�munities in the German Bight differ in some aspects of their trophic structure, they share a similar food web topology, indicating a comparable degree of resilience towards natural and anthro�pogenic disturbances.

Correction to: First data on the parasite fauna of daubed shanny Leptoclinus maculatus (Fries 1838) (Actinopterygii, Perciformes: Stichaeidae) in Svalbard waters

The daubed shanny, Leptoclinus maculatus (Fries 1838), is an arctic-boreal fish species and widely distributed in Svalbard waters. The ecological role of L. maculatus is determined by its complex life cycle—adults are bottom-dwelling while the young are pelagic—which indicates its place in the Arctic trophic food webs, both pelagic and benthic. As an intermediate link between lipid-rich copepods on which the young of L. maculatus feed, while juvenile L. maculatus are the prrey of Arctic birds and mammals, the species can be considered as an important reservoir and host for Arctic marine parasites. In the present study, we examined fish for parasites by total necropsy. This paper reports, for the first time, data on the parasite fauna of L. maculatus in the waters around Svalbard. L. maculatus is considered an ecologically significant species in this area, and an important link in the transfer of matter and energy from primary producers to higher-order consumers in the Arctic food chains. Peritrichianciliates Scyphidia sp., adult trematodes Helicometrainsolita Polyansky 1955, encysted metacercariae Neophasis sp., juvenile anisakid nematodes, and dyhyllobothriid larvae were found in L. maculatus. The most frequent findings were Neophasis sp. (64%). The data obtained in this study indicate the involvement of L. maculatus in certain transfers of parasites in Arctic waters, between hosts at the same stage of development and between hosts at different stages of development.

The Effect of Different Habitat Types and Ontogenetic Stages on the Diet Shift of a Critically Endangered Fish Species, Coreius guichenoti (Sauvage and Dabry de Thiersant, 1874).

This study examined the effect of habitat types and ontogenetic stages on the diet shift of Coreius guichenoti (Sauvage and Dabry de Thiersant, 1874), a critically endangered fish species. Based on the stable isotope analysis method, the following was explored: the variations in δ13C and δ15N values, isotopic niche width and four basal food sources (Mollusks, Macrocrustaceans, Aquatic insect larvae and particulate organic matters (POMs)) among three essential habitat types (the spawning ground, natural riverine feeding and nursery area, and Three Gorges Reservoir area) and between two ontogenetic stages (immature and fully mature stages). A diet shift associated with habitat type changes was observed, but there were no obvious differences in diet composition between the two ontogenetic stages. Dietary plasticity and a preference for specific foods were the important determinants of feeding behavior through the life history of this species. POM was important for the survival of this species in the resource-limited spawning ground, but this species fed more heavily on higher-order consumers in resource-abundant areas. This study highlights the importance of maintaining free connectivity among different habitats (particularly spawning grounds) to ensure the long-term sustainability of potamodromous fish species as well as the full investigation of all types of critical habitats for understanding the trophic ecology of a single fish species.

Egg boon fatty acids reveal effects of a climatic event on a marine food web

AbstractFlow of essential fatty acids (EFAs) through food webs is critical for the health of individual animals, populations, and communities. Planktonic eggs may play a central role in marine systems because they are highly concentrated in EFAs, superabundant, and consumed by a variety of species. Previous research suggests that egg fatty acid composition should not be useful for trophodynamic studies because it should be tightly regulated to meet the nutritional needs of embryos. Eight years of sampling the egg boon of the teleost fish red drum (Sciaenops ocellatus) provided the opportunity to test the hypothesis that extreme climatic events differentially alter abundances of prey populations and, ultimately, egg fatty acid composition. Fatty acid composition of eggs varied significantly among years and three major patterns of interannual variation (principal components) paralleled trends in the Palmer Drought Severity Index. Each of the first three principal components was related to abundances of particular prey (blue crabs, filter‐feeding fishes, and brown shrimp, respectively) during the spring and summer. Summer abundances of blue crab and brown shrimp were most strongly correlated with bay salinity 12–14 months earlier. Summer abundances of filter‐feeding fishes were most strongly correlated with bay salinity 0–1 month earlier. The delayed responses of crustacean abundances to variations in bay salinity likely operate through variability in recruitment. The fast connection for filter‐feeding fishes suggests a behavioral response to changing environmental conditions. The analyses revealed changes in trophodynamic flow that were associated with the phases of the climatic event. EFA content of eggs increased during drought years then decreased in the recovery years, indicating the potential for downstream effects on reproductive output, offspring viability, and tissue composition of egg consumers. Generally, nutrients move from intermediate sized consumers to a larger, higher order consumer (adult red drum). Then, trophic flow reverses when the egg boon is exploited by smaller planktivores. The analysis also revealed climate‐related shifts in the degree of benthic‐pelagic coupling and pelagic recycling that were mediated by the egg boons. This study demonstrates that egg boons can be a useful subject for investigations of trophodynamics in marine ecosystems.

Seasonal trophic variation of yellow perch exceeds spatial variation in a large lake basin

Abstract Trophic structuring of complex food webs may vary at multiple spatial and temporal scales, both in terms of direct trophic connections and underlying energy pathways that support production. In large freshwater systems, the prey and primary producers that support individual higher-order consumers may vary across seasons and habitats due to differences in food availability, predator consumption patterns, seasonal succession of organisms at lower trophic levels, and heterogeneous nutrient inputs. We examined spatial and temporal variation in stomach contents, fatty acids, and stable isotopes of yellow perch (Perca flavescens) across seasons and across sites spanning approximately 200 km in Lake Erie's Central Basin (LECB). Stomach contents provided a short-term index of trophic patterns, while biochemical markers (fatty acids and stable isotopes) provided a more temporally integrated description of underlying energy pathways and trophic links. We found limited spatial variation of biochemical indicators and documented seasonal variation for all three trophic indicators, especially fatty acid profiles. Differences in stomach contents were driven by relative chironomid consumption, the most abundant prey resource, while fatty acid profiles were predominantly influenced by seasonal fluctuations in C22:6n-3 (DHA). Seasonal trends were evident in δ13C and δ15N; however, they varied within a narrow range of values. Our findings suggest that adult yellow perch in LECB showed little differentiation in resource use across space in 2014, but their diets and biochemical compositions varied seasonally.

Gene expression and activity of digestive enzymes of Daphnia pulex in response to food quality differences.

Food quality is an important factor influencing organisms' well-being. In freshwater ecosystems, food quality has been studied extensively for the keystone herbivore genus Daphnia, as they form the critical trophic link between primary producers and higher order consumers such as fish. For Daphnia, the edible fraction of phytoplankton in lakes (consisting mostly of unicellular algae and cyanobacteria) is extraordinarily diverse. To be able to digest different food particles, Daphnia possess a set of digestive enzymes that metabolize carbohydrates, lipids and proteins. Recent studies have found a connection between gene expression and activity of single digestive enzyme types of Daphnia, i.e. lipases and proteases, and transcriptome studies have shown that a variety of genes coding for gut enzymes are differentially expressed in response to different food algae. However, never before has a set of digestive enzymes been studied simultaneously both on the gene expression and the enzyme activity level in Daphnia. Here, we investigated several digestive enzymes of Daphnia pulex in a comparison between a high-quality (green algal) and a low-quality (cyanobacterial) diet. Diet significantly affected the expression of all investigated digestive enzyme genes and enzyme activity was altered between treatments. Furthermore, we found that gene expression and enzyme activity were significantly correlated in cellulase, triacylglycerol lipase and β-glucosidase when switched from high to low-quality food. We conclude that one of the factors causing the often observed low biomass and energy transfer efficiency from cyanobacteria to Daphnia is probably the switch to a cost-effective overall increase of gene expression and activity of digestive enzymes of this herbivore.