Structure and Trophic Niches in Mobile Epifauna Assemblages Associated With Seaweeds and Habitats of Syngnathid Fishes in Cíes Archipelago (Atlantic Islands Marine National Park, North West Iberia)

Abstract

Syngnathids are vulnerable fishes closely associated with seaweeds and seagrass, which provide shelter and food resources. Even though most syngnathids commonly feed on small crustaceans, the feeding regimes may differ depending on the species and prey availability. This is the first monitoring study to explain syngnathid abundances and dietary regimes within macroalgal beds in Cíes Archipelago (Atlantic Islands Marine National Park, North West Iberian Peninsula). We sampled the epifaunal assemblages in seaweed communities dominated by the canopy-forming macroalgae Gongolaria baccata and Codium spp. seasonally during 2 years. The epifaunal structure was mostly represented by harpacticoid copepods, amphipods (especially gammarids) and gastropods. Epifauna exhibited low plant-host specificity and a higher dominance of amphipods on the more structurally complex macroalgae G. baccata. The epifaunal assemblages and syngnathid specimens were assessed for trophic structure using stable isotopes (δ13C and δ15N). The three syngnathids (Hippocampus guttulatus, Syngnathus acus, and Entelurus aequoreus) inhabiting Cíes Archipelago were sympatric. They occupied highly similar trophic positions (TPs), but differed in niche size, in such a way that the snake pipefish E. aequoreus would likely feed on smaller prey. The assessment of the feeding regime in the dominant great pipefish S. acus revealed that amphipods mostly contributed to bulk diet, followed by isopods, carideans, and copepods, whereas mysidaceans were not highly consumed. Seasonal changes in both epifaunal structure and syngnathids abundance confirmed that syngnathids are seasonal residents in Cíes Archipelago, migrating to other areas in autumn when the seaweed cover is drastically reduced and the epifaunal structure modified. This study showed the importance of Gongolaria assemblages in Cíes Archipelago, providing rich dietary sources and potentially contributing to higher abundances and diversity of syngnathids. Ongoing cover reduction in Gongolaria assemblages in certain regions (e.g., Mediterranean) should be considered a potential ecological concern for syngnathids and accompanying fauna, requiring further investigations.

Ecological Traits and Trophic Plasticity in The Greater Pipefish Syngnathus acus in the NW Iberian Peninsula

“…Simultaneously to fish monitoring, samples of potential prey for S. acus were collected in the same sampling sites of this study for further identification and stable isotope analysis [14].…”

“…Due to the low lipid content in the fin samples conserved in ethanol (<5% lipids, C:N < 3.56) [44,45], normalization for lipid correction in the fin samples was not necessary [37,46]. However, the C:N values in the epifauna indicated that the lipid content was higher than 5%, and specific conversion factors constructed for lipid normalization were applied [14]. Additionally, some epifaunal groups were submitted to acidification before SIA [14] by adding dilute (10%) HCl drop-by-drop, until CO 2 release was no longer observed [47,48].…”

“…The distribution, the habitat preference, and some trophic features in syngnathids inhabiting Cíes Archipelago, on the Atlantic Islands National Park (NW Spain), have been recently assessed, focusing on three sympatric species: the long-snouted seahorse Hippocampus guttulatus, the snake pipefish Entelurus aequoreus, and the great pipefish Syngnathus acus [14,15]. Among them, the latter was the most representative species, with a wider distribution, preferentially on macroalgal beds [16].…”

“…The available data on syngnathid populations in Cíes Archipelago indicate high seasonal and spatial variability in distribution and abundances [14,15]. Such variability seemed to be governed by seasonal changes in temperature, the extension and integrity of macroalgal beds, the structure of epifauna assemblages, and potential migratory events.…”

“…Some of the most interesting topics in marine ecology are the assessment of the trophic web and the inference of feeding regimes of targeted species. In Cíes Archipelago, the former was investigated via an isotopic approach, concluding that the three syngnathids occurring in the area were rather similar in trophic features [14]. Isotopic profiles in animals vary depending on the trophic level occupied, and the dietary regime [20][21][22][23][24][25][26].…”