Seasonal dependence on seagrass detritus and trophic niche partitioning in four copepod eco-morphotypes

Abstract

Benthic copepods dominate meiofaunal communities from marine phytodetritus, both in terms of numerical abundance and species diversity. Nevertheless, ecological factors driving copepod co-existence and population dynamics are still largely unknown. Here, we aimed to explore feeding habits of four copepod species commonly found in Mediterranean seagrass detritus accumulations, representing distinct eco-morphotypes (planktonic, phytal, epibenthic and mesopsammic). Joint use of fatty acid and stable isotope trophic markers showed that co-occurring harpacticoid copepods have diversified diets. Contrary to what was expected, microphytobenthos does not serve as their main food source. Instead, we found evidence from both techniques that major food items include heterotrophic biomass, macro-epiphytes and, depending on eco-morphology and season, of seagrass detritus-derived organic matter. Isotopic niches suggested that eco-morphotypes showed resource segregation. This segregation varies temporally, and partial overlap occurs between niches of phytal and epibenthic eco-morphotypes in some seasons. Our results highlight that, contrary to what is often assumed for meiofaunal consumers, considerable trophic diversity exists among copepod assemblages. They also indicate that, through multiple non-exclusive possible mechanisms, copepods could constitute a major link between seagrass detritus and associated biomass and higher trophic levels (namely macroinvertebrates and juvenile fish).

Seagrass organic matter transfer in Posidonia oceanica macrophytodetritus accumulations

“…δ 15 N. Isotopic data from harpacticoid copepods composing the "meiofauna" food source (hereafter, "COP") are fromMascart et al (2018).SIAR modellingTheBayesian mixing model SIAR (Stable Isotope Analysis in R; Inger et al, 2010; Parnell et al, 2010) was used to give estimations of the contribution of every potential food source to the diet of the invertebrate consumers. The SIAR 4.2.2 package was fitted in R 3.3.2 (R Development Core Team, 2016), using the isotopic composition of each individual, the potential food sources (mean ± SD), and the trophic enrichment factors (hereafter, TEFs; expressed as mean ± SD).…”

“…animals with a body size between 38 µm and 1 mm) as an intermediary step in this trophic web(Mascart et al, 2015). In addition, meiofauna may also assimilate seagrass organic matter in these EMAs(Mascart et al, 2018) increasing the potential amount of seagrass organic material transmitted to upper trophiclevels. The third trophic level was composed of 3 large carnivorous decapods: Palaemon xiphias, Processa edulis, and Liocarcinus navigator.…”

Meiofauna is an important, yet neglected, component of biodiversity ofPosidonia oceanica

“…We sorted 18 ecological studies (Table S2) that addressed the variation in taxonomic richness, species composition, and abundance of meiofaunal communities at regional (i.e., between localities, generally kilometres away; in nine studies) and local spatial scales (i.e., between samples within the same habitat in a given locality; in 13 studies). Only three of these studies incorporated functional metrics (Novak, 1989;Mirto et al, 2014;Guilini et al, 2017), and a single paper investigated diet preferences (Mascart et al, 2018). Nematodes and copepods were the preferred groups (six studies at specific level), whereas other groups were often recorded at the taxonomic rank of phylum or class.…”

“…These drastic annual changes in the plant structure affect how the hydrodynamic forces impact P. oceanica, since the habitats become increasingly complex and sheltered as the meadow develops (Folkard, 2005). At the same time, densely aggregated leaves foster many epiphytes, offering new and more abundant food sources to the meiofauna (Velimirov & Walenta-Simon, 1993;Mascart et al, 2018; but see Lebreton et al, 2012 on Zostera noltii). Indeed, all studies addressing temporal variation in P. oceanica found substantial differences over time, not only in taxa composition and abundance (Novak, 1989;Villora-Moreno et al, 1991;Losi et al, 2012;Cvitković et al, 2017;Polese et al, 2018), but also in species' dietary preferences (Mascart et al, 2018).…”

“…Food availability within each habitat, finally, drives the presence of different species not only depending on the amount of food (Mirto et al, 2010(Mirto et al, , 2014Castejón Silvo, 2011;Losi et al, 2012;Mascart et al, 2013;Cvitković et al, 2017;Polese et al, 2018) but also upon the presence of specific food sources. In fact, it has been shown that even closely related meiofaunal species may prefer different food sources (Mascart et al, 2018).…”