Abstract:The Mediterranean is one of the most overfished seas of the world where mesopredators are severely threatened. The trophic strategies of four pelagic species that inhabit the Adriatic Sea (Scomber spp. and Trachurus spp.) were investigated through an integrated approach of stomach contents and stable isotopes analyses. Our study demonstrated that Scomber colias feeds mainly on strictly pelagic prey, with fish larvae as a secondary prey in the Southern Adriatic Sea, while S. scombrus feeds on prey belonging to … Show more
“…The food web of the Adriatic Sea seemed to be better represented by a continuum of trophic levels rather than discrete ones (see Fig. 7 ) with “ancillary” small pelagics 29 , located at the TP 4, followed by small tunnids 34 , and potentially preyed by large pelagic species such as the swordfish, Xiphias gladius (authors’ unpublished data), and the bottlenose dolphin, Tursiops truncatus , the apex predators of the pelagic food web of the Western Adriatic Sea 35 . Figure 7 Scatterplot of isotopic data for zooplankton, sprat, sardine, anchovy, large pelagic fish and bottlenose dolphin.…”
Section: Resultsmentioning
confidence: 99%
“…and Scomber spp. 29 . Such food web structure could drastically change in a climate change scenario with persistent high level of fishing pressures 64 .…”
Section: Discussionmentioning
confidence: 99%
“…Stable isotope analyses give a time-integrated picture of fish diet and allow to evaluate the relative contribution of various food sources in consumer’s diet, intraspecific trophic relationships as a response to ontogeny, neighboring-linked connectivity, migration, reproduction, and changes in environmental features 26 – 28 . However, SIA alone also fails to differentiate between two food sources with overlapping isotope values and among ecological niches of species that have the same isotopic niche 29 . This can be partially solved through Bayesian mixing models to estimate errors concerning turnover rates and isotope ratios of putative food sources 30 .…”
The Adriatic Sea is one of the largest areas of occurrence of shared small pelagic stocks and the most fished area of the Mediterranean Sea, which is in turn one of the most exploited basins of the world. The variations in the stable isotope contents (δ15N and δ13C) were determined for three small pelagic fishes (i.e., Engraulis encrasicolus, Sardina pilchardus, and Sprattus sprattus, respectively known as anchovies, sardines and sprats) collected across the western side of the basin. Our data allowed to determine the width and features of their trophic niches, to assess potential overlap or resource partitioning among them, and likely anticipate species adaptation to future climate change scenarios. Moreover, variations in stable isotope contents were correlated to both resource availability (i.e., mesozooplankton) and environmental variables. The high productivity and in turn the high resource availability of the basin, especially in the northern part, resulted in favor of the resource partitioning that occurs in each sub-area of the Adriatic Sea among the three species. Medium-sized specimens of the three species mostly fed on small zooplankton, while adult sprats relied on large copepods and those of sardines and anchovies also consumed large portion of phytoplankton, confirming the high trophic plasticity of these two dominants small pelagic species. However, considering that anchovies have the greatest degree of trophic diversity compared with the other two species, they could be the most adapted to changing feeding conditions. The increase in sea temperatures that are reducing primary production and in turn zooplankton abundances, coupled with even more frequent extreme meteorologic events could exacerbate the competition for trophic resources among pelagic mesopredators, and could lead to more notable stocks’ fluctuations and unpredictable wasp-waist effects.
“…The food web of the Adriatic Sea seemed to be better represented by a continuum of trophic levels rather than discrete ones (see Fig. 7 ) with “ancillary” small pelagics 29 , located at the TP 4, followed by small tunnids 34 , and potentially preyed by large pelagic species such as the swordfish, Xiphias gladius (authors’ unpublished data), and the bottlenose dolphin, Tursiops truncatus , the apex predators of the pelagic food web of the Western Adriatic Sea 35 . Figure 7 Scatterplot of isotopic data for zooplankton, sprat, sardine, anchovy, large pelagic fish and bottlenose dolphin.…”
Section: Resultsmentioning
confidence: 99%
“…and Scomber spp. 29 . Such food web structure could drastically change in a climate change scenario with persistent high level of fishing pressures 64 .…”
Section: Discussionmentioning
confidence: 99%
“…Stable isotope analyses give a time-integrated picture of fish diet and allow to evaluate the relative contribution of various food sources in consumer’s diet, intraspecific trophic relationships as a response to ontogeny, neighboring-linked connectivity, migration, reproduction, and changes in environmental features 26 – 28 . However, SIA alone also fails to differentiate between two food sources with overlapping isotope values and among ecological niches of species that have the same isotopic niche 29 . This can be partially solved through Bayesian mixing models to estimate errors concerning turnover rates and isotope ratios of putative food sources 30 .…”
The Adriatic Sea is one of the largest areas of occurrence of shared small pelagic stocks and the most fished area of the Mediterranean Sea, which is in turn one of the most exploited basins of the world. The variations in the stable isotope contents (δ15N and δ13C) were determined for three small pelagic fishes (i.e., Engraulis encrasicolus, Sardina pilchardus, and Sprattus sprattus, respectively known as anchovies, sardines and sprats) collected across the western side of the basin. Our data allowed to determine the width and features of their trophic niches, to assess potential overlap or resource partitioning among them, and likely anticipate species adaptation to future climate change scenarios. Moreover, variations in stable isotope contents were correlated to both resource availability (i.e., mesozooplankton) and environmental variables. The high productivity and in turn the high resource availability of the basin, especially in the northern part, resulted in favor of the resource partitioning that occurs in each sub-area of the Adriatic Sea among the three species. Medium-sized specimens of the three species mostly fed on small zooplankton, while adult sprats relied on large copepods and those of sardines and anchovies also consumed large portion of phytoplankton, confirming the high trophic plasticity of these two dominants small pelagic species. However, considering that anchovies have the greatest degree of trophic diversity compared with the other two species, they could be the most adapted to changing feeding conditions. The increase in sea temperatures that are reducing primary production and in turn zooplankton abundances, coupled with even more frequent extreme meteorologic events could exacerbate the competition for trophic resources among pelagic mesopredators, and could lead to more notable stocks’ fluctuations and unpredictable wasp-waist effects.
“…Moreover, a large proportion of these thaliaceans are not consumed and usually sink to the bottom, together with their fecal pellets, where they can fuel the rich benthic community of the Northern Adriatic [82][83][84]. On the other hand, copepods and cladocerans, which increased in 2022, might have had a key role in the pelagic trophic web, as they are known to be the preferred food of many important pelagic species like sardine, sprat, Atlantic horse mackerel, and Mediterranean horse mackerel [5,85,86].…”
Zooplankton are a pivotal component of the pelagic community, and their abundance and distribution are often strongly dependent on environmental conditions at sea. However, climate change can pose significant challenges to planktonic organisms. Therefore, in this study, we tried to address the possible effect of short-term climatic anomalies on the zooplankton community in the North Adriatic Sea, comparing mesozooplankton composition in June between two years with very different temperature and rainfall levels, i.e., 2019 and 2022. Environmental conditions at sea were significantly different, since 2022 faced rising temperatures in the northern part of the area and higher salinity and lower chlorophyll values in coastal samples. Our data unveiled a community shift, from a Noctiluca-dominated community to a crustacean-dominated one, and revealed that even offshore areas can be subject to changes, despite having quite stable environmental parameters. Our findings confirmed the influence of river inputs and temperature on the Adriatic community’s distribution and composition, highlighting how climate-driven changes could have unpredictable effects on the whole Adriatic ecosystem. Indeed, each species has its own role in ecosystem functioning and climatic anomalies could uncouple the fine-scale connections that make up the pelagic trophic web.
“…and Scomber spp. 20 . Therefore, such food web structure could drastically change in a climate change scenario with persistent level of shing pressures 51 .…”
Small pelagic fishes play a crucial role in pelagic food webs as both top-down and bottom-up controllers. Their role as predators could also exert a wasp-waist flow control. The Adriatic basin is one of the largest areas of occurrence of small pelagic shared stocks and the most exploited basin of the Mediterranean Sea. Here, we analyzed the ontogenetic and spatial variations in the stable isotope composition of three small pelagic fishes (i.e., Engraulis encrasicolus, Sardina pilchardus, and Sprattus sprattus) collected throughout the western side of the basin and relate such differences to both resource availability and environmental variables. Medium-sized specimens of the three species mostly fed on small zooplankton, while adult sprats relied on large copepods and those of sardine and anchovy seemed to shift on phytoplankton, confirming the high trophic plasticity of these two dominants small pelagic species. Resource partitioning occurred at each size and in each sub-area, also favored by the high productivity and in turn high resource availability of the basin, especially in the northern part. These small pelagic fish were located at different, but very close, trophic position with other small pelagic species, and thus competition might occur in the future driven by modified feeding conditions as consequence of increasing sea temperatures.
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