Figure: Paracentrotus lividus with its faecal pellets used to investigate diet with eukaryotic DNA metabarcoding.
Ocean acidification not only affects the physiology of marine organisms but also profoundly transforms their feeding relationships and may intensify competition between species that previously occupied distinct trophic niches. This is one of the main conclusions of the TROIA project (TROphic Interactions of two echinoderms under ocean Acidification), led by Dr. Vanessa Arranz and Dr. Sara González-Delgado from the Marine Biodiversity and Evolution (MBE) group at the Biodiversity Research Institute (IRBio) of the University of Barcelona, and funded through a PR IRBio 2024 Grant.
The study was carried out in the natural CO₂ vent system of Punta de Fuencaliente, on La Palma (Canary Islands), one of the few naturally acidified environments in the Atlantic. In this area, submarine volcanic emissions generate a pH gradient along the coast that allows researchers to simulate the oceanic conditions projected for the coming decades and to study their long-term effects on real marine communities.
The results, currently under publication, show that under acidification the isotopic niche space of the benthic community is significantly reduced. Basal carbon sources become homogenized and functional trophic diversity decreases. “Acidification simplifies the benthic food web: there is less resource variety and organisms converge towards more similar feeding strategies,” explains Dr. Sara González-Delgado.
Two species, two contrasting responses
The study focuses on two sea urchin species common in the Mediterranean and the Atlantic: Paracentrotus lividus and Arbacia lixula. The results reveal contrasting responses to acidification. While P. lividus maintains a relatively stable diet along the pH gradient, A. lixula undergoes a notable dietary shift, moving from a predominantly carnivorous diet under current conditions (around 79% animal prey) to herbivory in acidified environments. This shift leads to an increase in trophic niche overlap between the two species, rising from 0% under current conditions to more than 27% in the most acidified sites. “Arbacia lixula is highly trophically plastic, but this flexibility comes at a cost: under acidification it begins to compete for the same resources as Paracentrotus lividus,” notes Dr. Vanessa Arranz.
Combining methods to better understand diet
The project combined two complementary methodological approaches: stable isotope analysis (δ¹³C and δ¹⁵N) and eukaryotic DNA metabarcoding from fecal samples. One of the study’s key contributions is the first validation in these species of using feces as a non-invasive sample to study diet through COI gene metabarcoding.
…
Ecological implications in a changing ocean
The results have important implications for predicting changes in marine communities under the acidification scenarios projected by the IPCC. The study highlights the need to go beyond individual physiological effects and also consider how trophic interactions and the ecological roles of species are altered within marine ecosystems.
…
IRBio, 15 April 2026. Full article.
0 Responses to “Ocean acidification simplifies food webs and may intensify competition between sea urchins”