Spatial diet overlap and food resource in two congeneric mullet species revealed by stable isotopes and stomach content analyses

Abstract

Food partitioning among coexisting species in different habitats remains an important research topic in trophic ecology. In this work, we combined carbon and nitrogen stable isotope ratios and stomach content analyses to investigate differences in diet and niche overlap of two congeneric juvenile mullet species (Mugil curema and Mugil liza) coexisting in a marine surf-zone and an estuarine zone in southern Brazil (29 o S). These habitats have contrasting levels of food availability, especially in terms of prey diversity, with higher microalgae diversity in the estuary than in the marine surf-zone. In these contrasting conditions, we predicted that both mullet species will have (a) higher niche overlap and smaller niche breadth at the marine surf-zone due to the common exploration of highly abundant surf-zone diatoms and (b) lower niche overlap and higher niche breadth inside the estuary due to selective feeding on more diverse food resources. Isotope niche areas (measured as standard ellipse areas) were higher in the estuary (6.10 and 6.18) than in the marine surf-zone (3.68 and 3.37) for both M. curema and M. liza, respectively. We observed an overlap of 52% in isotopic niches of both species in the marine surf-zone and none in the estuary. We also found contrasting patterns in the diet composition between species according to the habitat. At the marine surfzone, diatoms of the classes Bacillariophyceae and Coscinodiscophyceae dominated (> 99%) the food content of both mullet species. In contrast, green algae, cyanobacteria, dinoflagellates and flagellates comprised the diet of both species in the estuary. These results could be explained by spatial differences in food availability (especially regarding diversity of microalgae) between both habitats. At the marine site, both species explored the most abundant microalgae available (mostly the surf-zone diatom Asterionellopsis cf. guyunusae and fragments of Coscinodiscus), whereas in the estuary both species shifted their diets to explore the greater diversity of microalgae resources. Overall, our findings revealed that niche partitioning theory could not fully predict changes in breadth and overlap of food niches of estuarine dependent fish species with complex life cycles encompassing marine to estuarine systems with contrasting food availabilities.

Consumption of benthic cyanobacterial mats on a Caribbean coral reef

“…Cyanobacteria, in general, are known to be targeted by fishes in both marine 29–33 and freshwater 27,28 systems as important nutritional sources 29,34 . This includes other members of the genus Acanthurus , specifically on coral reefs in the Indian Ocean and Red Sea 31,32 .…”

“…However, the role of top-down control by grazing in regulating the abundance and distribution of coral reef benthic cyanobacterial mats remains equivocal. Cyanobacteria, in general, are known to be targeted and consumed by numerous species of both freshwater 27,28 and marine fishes 29–33 , and can be important nutritional sources for consumers 29,34 . Feeding on mat-forming cyanobacteria, however, has rarely been documented.…”

Niche overlap and diet composition of three sympatric coastal dolphin species in the southwest Atlantic Ocean

“…Although prey sources used for mixing models differ among delphinid species, it is important to note that both Guiana and the bottlenose dolphin are primarily consuming mullet species along the southern Brazilian coast (Daura‐Jorge et al, 2011; Milmann et al, 2016). Mugil curema and M. liza are common dolphin prey that consume a mixed diet of macroalgae, microphytobenthos, and small benthic invertebrates and thus likely occupy a lower trophic level than more pelagic prey (Cardona, 2001; Garcia et al, 2018; Drake, Arias, & Gállego, 1984). Consumption of these omnivorous prey could contribute to the similar and lower δ 15 N values of Guiana and the bottlenose dolphin relative to franciscana.…”

Long-Term Spatiotemporal Variation in the Juvenile Fish Assemblage of the Tramandaí River Estuary (29°S) and Adjacent Coast in Southern Brazil

“…They spawn during the winter and adults occur in higher numbers south of TRE (Vieira, 1991). It is possible that, in addition to the reproductive period, ecological processes related to feeding and to habitat use influence spatial patterns of juveniles of these two species (Garcia et al, 2018a).…”