Ontogenetic resource utilization and migration reconstruction with δ¹³C values of essential amino acids in the Cynoscion acoupa otolith

Abstract

With the increasing anthropogenic impacts on fish habitats, it has become more important to understand which primary resources sustain fish populations. This resource utilization can differ between fish life stages, and individuals can migrate between habitats in search of resources. Such lifetime information is difficult to obtain due to the large spatial and temporal scales of fish behavior. The otolith organic matrix has the potential to indicate this resource utilization and migration with δ13C values of essential amino acids (EAAs), which are a direct indication of the primary producers. In a proof‐of‐concept study, we selected the Acoupa weakfish, Cynoscion acoupa, as a model fish species with distinct ontogenetic migration patterns. While it inhabits the Brazilian mangrove estuaries during juvenile stages, it moves to the coastal shelf as an adult. Thus, we expected that lifetime resource utilization and migration would be reflected in δ13CEAA patterns and baseline values in C. acoupa otoliths. By analyzing the C. acoupa otolith edges across a size range of 12–119 cm, we found that baseline δ13CEAA values increased with size, which indicated an estuarine to coastal shelf distribution. This trend is highly correlated with inorganic δ13C values. The δ13CEAA patterns showed that estuarine algae rather than mangrove‐derived resources supported the juvenile C. acoupa populations. Around the juvenile size of 40 cm, resource utilization overlapped with those of adults and mean baseline δ13CEAA values increased. This trend was confirmed by comparing otolith core and edges, although with some individuals potentially migrating over longer distances than others. Hence, δ13CEAA patterns and baseline values in otoliths have great potential to reconstruct ontogenetic shifts in resource use and habitats. The insight could aid in predictions on how environmental changes affect fish populations by identifying the controlling factors at the base of the food web.

Reading the biomineralized book of life: expanding otolith biogeochemical research and applications for fisheries and ecosystem-based management

“…However, advances using a persulfate-denitrifier method, allow N isotope measurements from small, individual otoliths (Cheng et al 2018;Lueders-Dumont et al 2018, 2020. For δ 13 C measurements of organics, otoliths are demineralized prior to isotopic analysis, facilitating measurements of organic C without dilution from the inorganic carbonate C that comprises most of the otolith mass (Godiksen et al 2019;Grønkjaer et al 2013;McMahon et al 2011aMcMahon et al , 2011bSirot et al 2017;Vane et al 2018a). Otoliths must be demineralized as the mineral fraction is a tracer of other, non-diet related variables (see Ecophysiology section).…”

“…While the advantage of the persulfate-denitrifier method is the lower mass requirements for N, one of the primary advantages of EA-IRMS methods is that both δ 15 N and δ 13 C can be measured from the same otoliths. Micromill sampling, allowing for discrete analyses from juvenile and adult life history, is emerging for δ 15 N (Lueders-Dumont et al 2022;Vane et al 2018b) and for δ 13 C (Vane et al 2018a) analyses of the organic matrix, with higher resolution sampling tied to continued improvements in instrument sensitivity. δ 34 S values in otoliths have also emerged as a useful marker in freshwater systems to identify individuals who spent their early lives feeding in different aquatic habitats such as floodplains, rivers, and/or aquaculture facilities (Bell-Tilcock et al 2021;Johnson et al 2012;Weber et al 2002).…”

Biology and fishery of Acoupa Weakfish Cynoscion acoupa (Lacepède, 1801): a review

“…The connectivity between the estuary and marine coastal zone provides unique attributes of habitat and important features for this species, serving as a nursery and growth area (Barletta-Bergan et al 2002; Barletta and Saint-Paul 2010), explaining its most common occurrence in estuaries or coastal environments with strong river influences. Vane et al (2018) suggest, from otoliths isotopic analysis studies, the existence of ontogenetic migration between the estuary and the coastal environment besides changes in resource utilization for C. acoupa. Therefore, these authors observed that juveniles and adults gradually use distinct environments (juveniles use estuarine while adults uses the marine coast) and overlap in intermediate stages of life, which may indicate that there is a regular movement between estuarine and coastal environments by C. acoupa juveniles.…”

Bulk tissue and amino acid stable isotope analyses reveal global ontogenetic patterns in ocean sunfish trophic ecology and habitat use

“…Further studies should seek to distinguish this from pelagic microalgae carbon sources, e.g. if AAESS 13 C values differ between benthic and pelagic microalgae (Vane et al 2018). Assessing additional isotopes, such as bulk 34 S may also help to detangle benthic and pelagic sources in future studies (Hobson 1999).…”