Food web characterization based on δ15N and δ13C reveals isotopic niche partitioning between fish and jellyfish in a relatively pristine ecosystem

Abstract

Human-induced stresses on the marine environment seem to favor some jellyfish species to the detriment of other competitors such as planktivorous fishes. In pristine ecosystems, trophic relationships among these consumers are poorly understood. We determined stable carbon and nitrogen isotope signatures of representative consumers in the relatively pristine ecosystem of the Cananéia Estuary, Brazil, in order to understand the food web structure. We described isotopic niche breadth, position, and overlaps between fish and jellyfish (including comb jelly) species. Most of the δ 13 C values suggest that phytoplankton is the major carbon source, especially for pelagic consumers. Sessile benthic invertebrates had enriched δ 13 C values, suggesting a contribution of microphytobenthic algae. Seasonal variation of values was significant only for 13 C, with different patterns for pelagic and benthic organisms. Isotopic niche breadth of some jellyfishes was wider than those of fish species of the same trophic group, possibly as a consequence of their broad diets. Isotopic niche overlaps of fish and jellyfish species were related to: (1) trophic diversity, since planktivorous species occupied niches distinct from macroinvertebrate/fish feeders; and (2) life stages, since isotopic niche partitioning pattern can change during species ontogeny. Replacement of declining populations of fish by jellyfish competitors probably depends on the pool of other compensatory species, as well as on reproductive, growth, and feeding performance of other consumers. Description of isotopic niches provides a general picture of trophic roles, interactions and the degree of functional redundancy among species, allowing an evaluation of possible directions of community shifts resulting from the removal or proliferation of keystone consumers.

Stable isotope‐based location in a shelf sea setting: accuracy and precision are comparable to light‐based location methods

“…Between-individual variances in jellyfish isotope compositions were estimated from jellyfish sampled both in 2011 (MacKenzie et al 2014) and in 2015 as 1Á69& and 1Á04& for d 13 C cor and d 15 N values, respectively. These between-individual variance estimates are similar to those provided for gelatinous zooplankton by Fleming et al (2015) and Nagata et al (2015), particularly when accounting for the marked effect of size on isotopic variance in the Fleming et al (2015) data. Total uncertainty in the assignment isoscape was given by: r 2 isoðx;yÞ ¼ r 2 k:isoðx;yÞ þ r 2 m:isoðx;yÞ þ r 2 bi:isoðx;yÞ eqn 2 where r 2 isoðx;yÞ is the pooled variance associated with the isoscape prediction, r 2 k:isoðx;yÞ is the variance associated with the spatial interpolation model, r 2 m:isoðx;yÞ is the variance associated with measurement error and r 2 bi:isoðx;yÞ is the variance associated with in situ between-individual variation.…”

Ontogenetic and sexual characterization of the feeding habits of franciscanas, Pontoporia blainvillei, based on tooth dentin carbon and nitrogen stable isotopes

“…These shifts will most likely put them at different trophic levels, i.e ., larger prey sizes would occupy higher trophic positions (Nagata et al . ), which in turn would result in variations in the δ 15 N values among different length categories. Therefore, it is worth emphasizing the importance of collecting the prey species within the size range consumed by franciscanas in each age category; hence, the importance of integrating previous information on the species feeding habits instead of relying exclusively on the model's outcome.…”

“…, Nagata et al . ), prey samples were collected taking into account the average prey size consumed by the dolphins, according to Bassoi (). Prey samples were stored at −20°C until preparation for isotope analysis.…”

Trophic relationships in tidepool fish assemblages of the tropical Southwestern Atlantic

“…However, ontogenetic changes in diet, such as in omnivorous species shifting to herbivory in adulthood, also lead to changes in trophic guilds throughout life (Muñoz & Ojeda, 1998, 2000 and induce temporal variations at both guild and community structure levels (Wilson & Sheaves, 2001). In this respect, stable isotope and fatty acid analyses are promising approaches to characterize complex trophic interactions and define trophic niches (Hielscher et al, 2015) through the integration of spatial and temporal information of the trophic relationships within communities (Nagata et al, 2015).…”