Effect of temperature on an alga‐grazer trophic transfer: A dual stable isotope (¹³C, ¹⁵N) labeling experiment

Abstract

In this study, we examined the impact of temperature on the carbon and nitrogen trophic transfers from a macroalga to a macro‐grazer by the use of dual 13C‐ and 15N‐labeling. Using an experimental approach in mesocosms, individuals of the urchin Psammechinus miliaris were maintained for 1 month at 17°C (mean summer temperature in the Bay of Brest) and at 20°C (maximum summer temperature) and fed with 13C‐ and 15N‐labeled Solieria chordalis. The results showed that the urchins’ 13C uptake was 0.30 µg13C g dry weight (DW)−1 at 17°C and 0.14 µg13C g DW−1 at 20°C at the end of the experiment. The lower uptake at the higher temperature may be attributed to a decrease in metabolic activity at 20°C, involving lower feeding and/or respiration rates. Conversely, no significant effect of temperature was detected on 15N uptake. At the end of the experiment, the urchins’ 15N uptake was 0.04 µg15N g DW−1 at 17°C and 0.03 µg15N g DW−1 at 20°C. This suggests that temperature may affect carbon and nitrogen trophic fluxes differently. The use of dual isotope labeling offers interesting prospects and needs to be further extended in order to better understand trophic interactions in marine communities and the consequences of current environmental changes, such as global warming.

Isotopic labeling of cultured macroalgae and isolation of 13C-labeled cell wall polysaccharides for trophic investigations

“…Experiments based on the 13 C-labelled red macroalga Gracilaria spp (9 At% 13 C) under decomposition in sediments revealed transfers of isotopic label to bacterial biomass through the 13 C enrichment of specific bacterial amino acids or fatty acids (Hardison et al, 2010). Recently, a dual stable isotope labelling experiment was performed on adult specimens of the red alga Solieria chordalis using both H 13 CO 3 and 15 NH 4 additions to investigate the uptake of whole algal tissues by the sea urchin Psammechinus miliaris under different temperature regimes (Legrand et al, 2018). However, stable isotope labelling studies considering macroalgae as a bulk biomass do not inform on (1) the labelling of different molecular fractions of the algae,…”

“…In the present study, stable isotope labelling was performed on actively growing juvenile brown algae for 3 months, contrasting with the shorter incubation periods (1-2 weeks) previously used on red algae (Hardison et al, 2010;Legrand et al, 2018). This was required to ensure incorporation of 13 C-label into cell wall polysaccharides, which can have a long turnover time compared to smaller compounds (Macler, 1986).…”

“…Few studies have implemented stable isotope labelling techniques on adult specimens of the red algae Gracilaria spp. and Solieria chordalis to assess their fate in benthic systems (Hardison, Canuel, Anderson, & Veuger, 2010;Legrand, Martin, Leroux, & Riera, 2018).…”

Meiofauna versus macrofauna as a food resource in a tropical intertidal mudflat

“…This approach has been used to evaluate the ingestion of bacteria and microphytobenthos by meiofauna (Moodley et al 2002, Pascal et al 2008b, Pascal et al 2008c), macrofauna (Pascal et al 2008a, Leroy et al 2012) and fishes (Como et al 2018). A similar approach has also been used to measure the consumption of macroalgae (Pascal & Fleeger 2013, Legrand et al 2018. However, to our knowledge, this approach has never been used to assess the ingestion of meiofauna and macrofauna by predators.…”