Multiple Approaches to the Trophic Role of Mesopelagic Fish around the Iberian Peninsula

Animals : an Open Access Journal from MDPI · 3 authors, 2 centres

AI SUMMARY

FIDELITY 92%

POPULATION29 species of mesopelagic fish (Myctophiformes and Stomiiformes) collected around the Iberian Peninsula (western Mediterranean Sea and northeastern Atlantic Ocean)

INTERVENTIONNot applicable (observational dietary study)

COMPARISONDiet composition compared across five geographic zones (Balearic Sea, Alboran Sea, Gulf of Cadiz, Lisbon, Galicia), between migratory behaviors (migrant, partial migrant, non-migrant), and between developmental stages (transformation vs. juvenile/adult)

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AGENT 01 · STRUCTURED SUMMARY

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TL;DR

This study analyzed the stomach contents of 29 mesopelagic fish species around the Iberian Peninsula to characterize their feeding ecology. The researchers found that copepods were the primary prey for most species, but feeding strategies varied widely—from generalist zooplanktivores to specialist piscivores—with diet composition influenced by geographic zone, migratory behavior, body size, and developmental stage. These findings provide essential baseline data for understanding the ecological role of mesopelagic fish and the potential impacts of their future commercial exploitation on marine food webs and fisheries sustainability.

Full summary

4,212 CHARS

**Background:** Mesopelagic fishes (myctophids and stomiiforms) constitute the largest fish biomass in the oceans and play a critical role as intermediates in marine food webs, consuming zooplankton and serving as prey for top predators. Many species perform diel vertical migrations (DVMs), transporting organic matter from surface waters to depth and contributing to the biological carbon pump (estimated at 8–40% of deep carbon flux). Despite their ecological importance, there is limited information on their feeding strategies, particularly at the community level. The potential commercial exploitation of mesopelagic fish (e.g., Norway's trial fisheries for *Benthosema glaciale* and *Maurolicus muelleri*) makes understanding their trophic role urgent for assessing impacts on marine ecosystems and fisheries sustainability.

**Methods:** Fish samples were collected during the SUMMER survey (30 September–18 October 2020) aboard the R/V Sarmiento de Gamboa across five zones around the Iberian Peninsula: Balearic Sea, Alboran Sea (western Mediterranean), Gulf of Cadiz, Lisbon, and Galicia (northeastern Atlantic). A total of 349 specimens from 29 species were dissected for stomach content analysis. Prey items were identified to the lowest taxonomic level, counted, measured, and their carbon mass estimated using published length-weight algorithms. Diet composition was expressed using percentage frequency of occurrence (%F), percentage numerical abundance (%N), percentage carbon mass (%C), and two standardized Indexes of Relative Importance (%IRI and %IRIC). Statistical analyses included non-metric multidimensional scaling (NMDS), PERMANOVA, SIMPER, cluster analysis with SIMPROF, and canonical correspondence analysis (CCA) relating diet to environmental variables (sea surface temperature, temperature at 450 m depth, and integrated fluorescence).

**Key Results:** Empty stomachs occurred in 16% of fish (56/349). A total of 19,136 prey items were identified across 42 prey categories. Copepods were present in 63% of fish stomachs and constituted 19 of the 42 identified categories. Calanoid copepods were the most common prey among myctophids but nearly absent in *Chauliodus* spp. PERMANOVA showed significant differences in prey abundance among fish species (Pseudo-F = 4.667, p = 0.001), and for species depending on zone (Pseudo-F = 2.503, p = 0.001), developmental stage (Pseudo-F = 3.9033, p = 0.001), and migratory behavior (Pseudo-F = 1.887, p = 0.02). Significant diet differences between zones were detected in *Argyropelecus hemigymnus*, *Valenciennellus tripunctulatus*, *Cyclothone braueri*, *Ceratoscopelus maderensis*, *Diaphus holti*, *Hygophum benoiti*, *Lobianchia dofleini*, and *Myctophum punctatum*. Ontogenetic differences were significant only for *A. hemigymnus* (p = 0.045) and *H. benoiti* (p = 0.010). Migrant and non-migrant species differed significantly (t = 1.32, p = 0.007), with ~85% dissimilarity. CCA explained 26% of total variance; temperature at 450 m (12.6%) and sea surface temperature (11.3%) were significant predictors, while fluorescence was not. The mean number of prey items was significantly higher in myctophids (29.9 ± 12.4) than stomiiforms (22.3 ± 7.32) (Kruskal–Wallis chi-squared = 16.06, df = 1, p = 6.137 × 10⁻⁵). Six feeding guilds were delineated: zooplanktivorous-mixed crustacean feeders, generalists, micronektivorous, copepod feeders (myctophids), and zooplanktivorous and micronektivorous (stomiiforms). Plastic fragments were found in 3 individuals (*Lampanyctus pusillus* and *Photostomias guernei*).

**Clinical Implications:** While not directly clinical, this study provides critical ecological data for fisheries management and conservation. Mesopelagic fish are key prey for commercially important species (e.g., tuna, hake) in the heavily fished Iberian region (Mediterranean GS5 and GS1; FAO subarea 27.9.a). Understanding their feeding ecology is essential for predicting how potential commercial exploitation of mesopelagic fish could impact top predator populations and overall marine ecosystem functioning. The carbon content data also inform models of active carbon transport, relevant to climate change research.

PICO

PPOPULATION

29 species of mesopelagic fish (Myctophiformes and Stomiiformes) collected around the Iberian Peninsula (western Mediterranean Sea and northeastern Atlantic Ocean)

IINTERVENTION

Not applicable (observational dietary study)

OOUTCOME

Diet composition in terms of numerical prey abundance, frequency of occurrence, and estimated carbon content; assignment to feeding guilds; identification of factors driving dietary differences

STUDY TYPE

cross-sectional

SPECIALTY

marine biology

SUMMARISED BY

AI pipeline

FIDELITY CHECK

92% · A

ORIGINAL PAPER

PMC10000212

Multiple Approaches to the Trophic Role of Mesopelagic Fish around the Iberian Peninsula

Animals : an Open Access Journal from MDPI

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ABSTRACT

Simple Summary Mesopelagic fish form the largest fish biomass in the oceans. They are essential intermediates in marine food webs, having an important role as zooplankton consumers and prey for top predators such as pelagic fish or marine mammals, as well as in connecting the surface and more impoverished oceanic depths, since many mesopelagic species perform diel vertical migrations. The collapse of most commercial fisheries has led to the consideration of the future commercial exploitation of these fish, which is highly debated. Unfortunately, we have limited information about their feeding strategies and contribution to the marine carbon pump of mesopelagic fish, due to the difficulty of investigating their habitat, the twilight zone. This study analyzed the diets of mesopelagic fish species around the Iberian Peninsula (Atlantic and Mediterranean areas) in terms of numerical prey abundance and carbon weight, which allowed for their assignment to specific feeding guilds. We found that, despite their great diversity, mesopelagic fish food resource use is partitioned by being spatially segregated, using different feeding strategists (generalist, facultative feeding behavior, and specialized diets), or as a result of their dietary shift from juvenile to adult stages, rather than having different food compositions. The assessment of the trophic role of mesopelagic species will provide baseline data regarding the impacts that their potential exploitation might have on the populations of top predators that also play a key role in regulating marine ecosystems. Abstract Myctophids, commonly vertical migrators, and partial and non-migrant stomiiforms constitute most of the mesopelagic biomass, and transport organic matter throughout the food web from the surface to the ocean’s depths. Both the diet and trophic structure of twenty-nine species of mesopelagic fish collected around the Iberian Peninsula were studied through the analysis of stomach contents, quantifying food items with a high taxonomic resolution. The investigation covered oligotrophic to productive habitats, with sampling stations distributed in five discrete zones of the western Mediterranean Sea and the northeastern Atlantic Ocean. The geographic environmental conditions, migratory behavior, and species-specific body sizes allowed for the identification of some major feeding patterns for these fish communities. The trophic niche of migrant myctophids showed a high overlap, with copepods as the primary prey category. The diet composition of generalist myctophids (e.g., Ceratoscopelus maderensis and Hygophum benoiti ) reflected the distinct zooplanktonic communities between zones. Large stomiiforms ( Chauliodus spp., Sigmops elongatus ) preferred feeding on micronekton, while the smallest stomiiforms (e.g., Argyropelecus spp., Cyclothone spp., Vinciguerria spp.) preyed on copepods and ostracods. Given the relevance of the mesopelagic fish communities for commercially exploited species and, therefore, for maintaining the sustainability of the fisheries’ activity in the zones analyzed, the information provided in the present study is essential for a better understanding of the biology and ecology of these species.

CITATION EXPORT

Ainhoa Bernal, Víctor Manuel Tuset, María Pilar Olivar. Multiple Approaches to the Trophic Role of Mesopelagic Fish around the Iberian Peninsula. Animals : an Open Access Journal from MDPI. (2023). https://doi.org/10.3390/ani13050886

AUTHORS

3 · 2 CENTRES

Ainhoa Bernal, Víctor Manuel Tuset, María Pilar Olivar

1Department of Renewable Marine Resources, Institut de Ciències del Mar (ICM-CSIC), 08003 Barcelona, Spain
2Instituto de Oceanografía y Cambio Global (IOCAG), Universidad de Las Palmas de Gran Canaria (ULPGC), Parque Científico Tecnológico Marino de Taliarte, 35214 Las Palmas de Gran Canaria, Spain

EDITOR / REVIEWER

Clive J. C. Phillips, Pietro Battaglia