Prey In Food Webs Research Articles

Otolith Shape Indices of Japanese Threadfin Bream (Nemipterus japonicus, Bloch 1791) from the Makassar Strait, Indonesia

Japanese threadfin bream (Nemipterus japonicus) is a demersal fish that plays a very important role in maintaining ecosystem stability related to webs and food chains. This fish often becomes prey for predatory fish. In efforts to reveal the relationship between predators and prey in food webs and food chains, there is still limited information due to the difficulty of identifying digested food. In connection with this, this study aims to identify the morphology shape index value otolith of Japanese threadfin bream. Sampling was carried out at the Labuang Maros Fish Landing Site with 150 samples and morphometric data were collected from 150 pairs of otoliths in April and May 2023. The calculation of the shape index uses six descriptors, which include form factor (FF), roundness (RO), circularity or compactness (C), rectangularity (Rt), ellipticity (E), and aspect ratio (AR). The results showed that there was no significant difference in the otolith morphometry of the right and left otoliths (P>0.05). Based on the shape index value obtained, it explains that the morphometric shape of the otolith of Japanese threadfin bream tends to be oval, elongated, and has an irregular surface.

Dietary metabarcoding of keystone sardine species reveals the importance of their ichthyoplankton prey in food webs of the Southern Brazilian Bight fisheries

AbstractClupeiform fishes are ecologically and economically important species contributing to industrial and artisanal fisheries worldwide. They represent key links in food webs, influencing the dynamic between trophic levels. The dietary interactions of these species are poorly studied in many regions, yet essential for fisheries management. To elucidate the role of these species in food webs of the Southern Brazilian Bight pelagic fisheries, we used metabarcoding analysis of fish stomach contents of Clupeiformes and possible predators. Onboard sampling from March to September 2016 allowed for processing of 87 stomach samples representing 31 species (including 12 samples representing three species of Clupeiformes). Links between trophic levels showed the predominance of Sardinella brasiliensis and Engraulis anchoita as important dietary items of a large range of fishes (28 species belonging to 18 families) and representing the majority of the total prey read abundance assigned to clupeiform fishes (~46% and ~32%, respectively). Opisthonema oglinum contributed to the diet of 16 species in 13 families and ~18% of total read abundance of clupeiform fishes as prey. The appearance of multiple clupeiform taxa in the diet of predators that are not commonly associated with pelagic prey indicates that ecosystem‐based fisheries management should not be separated between pelagic and demersal fisheries. The diet of Clupeiformes revealed an unexpectedly large diversity of fish species and a low proportion of invertebrates (<5% of clupeiform prey reads). This was likely due to a combination of both a limitation of the metabarcoding method (primer bias and low success of invertebrate taxonomic identification) as well as a contribution of early life stages (ichthyoplankton) to the diet of these fishes. The potential role of clupeiform fish populations as a constraint to the recruitment from the ichthyoplanktonic phase of other ecologically or commercially important fishes should be considered as an important direction for future studies.

Forage fish fisheries management requires a tailored approach to balance trade‐offs

AbstractEcosystem‐based fishery management requires considering the effects of actions on social, natural and economic systems. These considerations are important for forage fish fisheries, because these species provide ecosystem services as a key prey in food webs and support valuable commercial fisheries. Forage fish stocks fluctuate naturally, and fishing may make these fluctuations more pronounced, yet harvest strategies intended to ameliorate these effects might adversely affect fisheries and communities. Here, we evaluate trade‐offs among a diverse suite of management objectives by simulating outcomes from several harvest strategies on forage fish species. We demonstrate that some trade‐offs (like those between catches and minimizing collapse length) were universal among forage species and could not be eliminated by the use of different control rules. We also demonstrate that trade‐offs vary among forage fish species, with strong trade‐offs between stable, high catches and high‐biomass periods (“bonanzas”) for menhaden‐ and anchovy‐like fish, and counterintuitive trade‐offs for sardine‐like fish between shorter collapses and longer bonanzas. We find that harvest strategies designed to maintain stability in catches will result in more severe collapses. Finally, we show that the ability of assessments to detect rapid changes in population status greatly affects control rule performance and the degree and type of trade‐offs, increasing the risk and severity of collapses and reducing catches. Together, these results demonstrate that while default harvest strategies are useful in data‐poor situations, management strategy evaluations that are tailored to specific forage fish may better balance trade‐offs.

Eastern rockhopper penguins Eudyptes filholi as biological samplers of juvenile and sub-adult cephalopods around Campbell Island, New Zealand

Early life-history stages of cephalopods are known to play an important role as prey in food webs of the Southern Ocean, but little information is available about their biology and availability to predators. Top predators, such as penguins, are known to feed regularly on coastal juvenile/sub-adult cephalopods. Using eastern rockhopper penguins Eudyptes filholi as coastal biological samplers, we examined in detail the cephalopod component of their diet in Campbell Island (New Zealand) during two consecutive breeding seasons in order to evaluate (1) the relative importance of cephalopods (by frequency of occurrence, by number and by mass) to the diet of both adult and chick penguins, (2) the habitat and trophic levels of the cephalopods in the region and (3) the status of the juvenile/sub-adult cephalopod community in the waters around Campbell Island. Our results show that eastern rockhopper penguins feed on eight species of juvenile and sub-adult cephalopods, with Onykia ingens, Martialia hyadesi and Octopus campbelli being the most important species by frequency of occurrence, number and mass. Differences between the diets of adult and chick penguins and between breeding seasons were found. Habitat (δ13C) and trophic level (δ15N) information also showed that all cephalopod species (and all studied stages) occupy similar habitat on the Campbell shelf, with M. hyadesi showing lower δ15N values than O. ingens and O. campbelli. This study indicates that eastern rockhopper penguins can be valuable biological samplers of local juvenile/sub-adult cephalopods (including poorly known cephalopod species) around Campbell Island when breeding, that these cephalopods were likely to be caught naturally (not from fisheries), providing relevant information for the conservation of these penguins.

The role of a water bug,Sigara striata, in freshwater food webs

Freshwater food webs are dominated by aquatic invertebrates whose trophic relationships are often poorly known. Here, I used laboratory experiments to study the role of a water bug, Sigara striata, as a potential predator and prey in food webs of stagnant waters. Multiple-choice predation experiment revealed that Sigara, which had been considered mostly herbivorous, also consumed larvae of Chironomus midges. Because they often occur in high densities and are among the most ubiquitous aquatic insects, Sigara water bugs may be important predators in fresh waters. A second experiment tested the role of Sigara as a potential prey for 13 common invertebrate predators. Mortality of Sigara inflicted by different predators varied widely, especially depending on body mass, foraging mode (ambush/searching) and feeding mode (chewing/suctorial) of the predators. Sigara was highly vulnerable to ambush predators, while searching predators caused on average 8.1 times lower mortality of Sigara. Additionally, suctorial predators consumed on average 6.6 times more Sigara individuals than chewing predators, which supports previous results hinting on potentially different predation pressures of these two types of predators on prey populations. The importance of these two foraging-related traits demonstrates the need to move from body mass based to multiple trait based descriptions of food web structure. Overall, the results suggests that detailed experimental studies of common but insufficiently known species can significantly enhance our understanding of food web structure.

Long-term changes in the composition and diversity of deep-slope megabenthos and trophic webs off Catalonia (western Mediterranean): Are trends related to climatic oscillations?

For depths ranging between 650 and 1700 m we have compared recent (2007–2008) to older (from 1988 to 1992) data, searching for long-term changes in the distribution, abundance and composition of deep megafauna (fish and decapods) off the central Catalonian coasts (western Mediterranean). Overall, in the depth interval between 600 and 1100 m, we found higher abundance of fish in 1988–1992 than in 2007, a decrease simultaneous with an increase of decapod crustaceans. Older and more recent haul replicates (after 20 years) had similar assemblage composition in the depth range 1300–1700 m, whereas we found significant changes at 1000 m. Diversity of fish was greater in 1988–1992 than in 2007, while diversity of decapod crustaceans increased between the two periods. Thus, there was a reorganization in benthopelagic communities, rather than a loss of biodiversity. This was in agreement with long-term changes described for diversity of (neritic) zooplankton in the western Mediterranean. We found a dominance of plankton-suprabenthos feeders (e.g. fish such as Lepidion lepidion, Hymenocephalus italicus and Alepocephalus rostratus; the decapods Plesionika spp. and Sergestes arcticus) in 1988–1992. In 2007 by contrast, dominance of plankton-suprabenthos feeders decreased, and assemblages were increasingly composed of benthos-feeding decapods (e.g. Aristeus antennatus, Pontophilus norvegicus and some hermit crabs) preying for instance on polychaetes. These results coincided with low/negative North Atlantic Oscillation index (NAO) in 2007 and in the period immediately before (2004–2006) 2007 (increase of benthos feeders), and with high average NAO in 1988–1992 (decrease of benthos feeders, which in turn may enhance abundance of plankton feeders). The benthic decapod Calocaris macandreae and suprabenthos (small crustaceans, mostly peracarids, living on and just beneath the sediment surface) are key prey in food webs off Catalonian margins, acting as links between surface oceanographic processes and abundance of benthopelagic predators. A conceptual model is presented relating changes in climatic conditions with changes in deep-sea, benthic-suprabenthic food webs. Calocari macandreae was more abundant in 2007, after 3 years of negative NAO. Under negative/low NAO, rainfall and river discharges increase in the NW Mediterranean, which may enhance advective food inputs for macrobenthos. This fits well with the higher abundance of benthos feeders in 2007, as well as with the significant deepening of decapod crustacean assemblages in that same period. Suprabenthos, being short-lived and annual species, were more abundant under positive NAO conditions (1988–1992), probably enhancing the abundance or aggregation of suprabenthic/pelagic feeders.

Body Sizes of Animal Predators and Animal Prey in Food Webs

Summary 1. We measured the body sizes (weights or lengths) of animal species found in the food webs of natural communities. In c. 90% of the feeding links among the animal species with known sizes, a larger predator consumes a smaller prey. 2. Larger predators eat prey with a wider range of body sizes than do smaller predators. The geometric mean predator size increases with the size of prey. The increase in geometric mean predator size is less than proportional to the increase in prey size (i.e. has a slope less than 1 on log-log coordinates). 3. The geometric mean sizes of prey and predators increase as the habitat of webs changes from aquatic to terrestrial to coastal to marine. Within each type of habitat, mean prey sizes are always less than mean predator sizes, and prey and predator sizes are always positively correlated. 4. Feeding relations order the metabolic types of organisms from invertebrate to vertebrate ectotherm to vertebrate endotherm. Organisms commonly eat other organisms with the same or lower metabolic type, but (with very rare exceptions) organisms do not eat other organisms with a higher metabolic type. Mean sizes of prey increase as the metabolic type of prey changes from invertebrate to vertebrate ectotherm to vertebrate endotherm, but the same does not hold true for predators. 5. Prey and predator sizes are positively correlated in links from invertebrate prey to invertebrate predators. In links with other combinations of prey and predator metabolic types, the correlation between prey and predator body sizes is rarely large when it is positive, and in some cases is even negative. 6. Species sizes are roughly log-normally distributed. 7. Body size offers a good (though not perfect) interpretation of the ordering of animal species assumed in the cascade model, a stochastic model of food web structure. When body size is taken as the physical interpretation of the ordering assumed in the cascade model, and when the body sizes of different animal species are taken as log-normally distributed, many of the empirical findings can be explained in terms of the cascade model.