How do food sources drive meiofauna community structure in soft-bottom coastal food webs?

Abstract

Meiofauna have a strong role in the functioning of coastal ecosystems but how their food sources affect their community structure remains unclear, likely due to the influence of abiotic parameters and the small size of these organisms. The meiofauna and their potential food sources were sampled in several intertidal habitats (i.e. mudflat, seagrass bed, sandflat) of the Marennes-Oléron Bay, France, and the Sylt-Rømø Bight, Germany, to assess the relationships between habitat characteristics and meiofauna community structure. Biomass and quality (carbon/chlorophyll a ratios) of food sources were estimated.Meiofauna community structure based on density and biomass was determined, as well as nematode diversity and feeding types. Meiofauna density and biomass varied highly within habitats and within ecosystems, ranging from 1.7*10 5 ind. m -2 to 3.4*10 6 ind. m -2 and from 0.057 gC m -2 to 1.541 gC m -2 , respectively. Benthic microalgae and sediment organic matter are important drivers in these food webs as the density of two important trophic groups of nematodes, non-selective deposit feeders and epigrowth feeders, varied in accordance with these food sources. No clear relationship was observed between bacterial biomass and selective deposit feeders (i.e. bacterivores) probably due to the high production rate of bacteria. Complementary information about production rates of food source as well as data from trophic markers would provide complimentary information to better understand flows of organic matter in intertidal habitats, particularly for opportunistic species such as non-selective deposit feeders.

Trophic importance of microphytobenthos and bacteria to meiofauna in soft-bottom intertidal habitats: A combined trophic marker approach

“…SOM compositions differed between habitats, with a much higher influence of diatoms in the SOM from the sandflat of the Sylt-Rømø Bight (van der Heijden et al, 2018), as demonstrated by its higher δ 13 C values and higher proportions of diatom FA markers. Isotope compositions of SOM also varied between sediment layers with SOM being more depleted in 13 C in the sub-surface layers, as already observed in the Schelde estuary (Moens et al, 2014).…”

“…The intermediate δ 13 C values of SOM limited determining the contributions of the different primary producers in SOM composition, clearly highlighting the importance of the combination of SI and FA markers. Based on FA analyses, SOM was mostly made up of diatoms and bacteria, with very low contributions of seagrass or terrestrial material, even in seagrass beds where the load of seagrass material in the sediment was high (Lebreton et al, 2011;van der Heijden et al, 2018). Diatoms from the SOM mainly originated from the microphytobenthos, as highlighted by the high δ 13 C values of the diatom marker 20:5(n-3) (i.e.…”

“…Contributions of fresh and detrital seagrass material (Z. noltii) as food sources to nematodes and benthic copepods were very low, as highlighted by the very low proportions of vascular plant FA markers in nematodes and benthic copepods, even in seagrass beds where loads of seagrass material were high (van der Heijden et al, 2018). The low use of seagrass material is much likely related to its poor nutritional value and high lignocellulose content (Vizzini et al, 2002).…”

“…The reliance of meiofauna on microphytobenthos might be related to its high nutritional quality (high proportional nitrogen and phosphorus content, low content in refractory compounds, e.g. lignin, compared to vascular plants), turnover rates (Cebrián, 1999) and constant biomass (Lebreton et al, 2009;van der Heijden et al, 2018). Even if no temporal difference of meiofauna fatty acid compositions was observed between the two sampled seasons, a better understanding of the role of these two food sources (i.e.…”

“…Among consumers relying on these primary food sources, meiofauna has been suggested to play an important role in the carbon fluxes of soft-bottom coastal habitats due to their high biomass (Danovaro et al, 2002;Escaravage et al, 1989;van der Heijden et al, 2018), high secondary production (from 4 to 29 g C m −2 year −1 ) (Chardy and Dauvin, 1992;Danovaro et al, 2002;Escaravage et al, 1989) and high turnover rate (Kuipers et al, 1981), as well as their intermediate position in food webs (Giere, 2009), potentially fueling the higher trophic levels (Coull, 1999;Leguerrier et al, 2003). The large species diversity of meiofauna (Heip et al, 1985) results in different feeding behaviors (Giere, 2009), likely leading to different responses when dealing with changes in food sources.…”