Patterns of variations in C and N stable isotope ratios in size-fractionated zooplankton in the Gulf of Lion, NW Mediterranean Sea

Abstract

Stable isotope ratios for six size fractions of zooplankton (80 to .2000 mm) were analyzed in the Gulf of Lion in spring 2010 and winter 2011. Environmental and plankton community variables were also recorded. The originality of this study is the use of a Lagrangian transport modeling system to determine the origin of the water masses and the assessment of the proportion of detritus in the plankton samples. The highest d 15 N values were observed in the 1000-2000 mm fraction in January and in the 500-1000 mm fraction in May. The largest size class (.2000 mm), dominated by salps, had lower d 15 N values owing to the low isotopic signatures of these organisms. The history of the water masses resulted in two main patterns with different isotopic signatures: the water masses which resided on the shelf and the waters masses carried onto the shelf from off-shelf region by the Northern Current. The d 13 C values varied strongly between January and May, mainly owing to changes in hydrographic conditions. The d 15 N values, plankton size structure and zooplankton feeding activity varied depending on the season, revealing differences in the seasonal trophic structure of the plankton communities. The trophic structure was characterized in January by a high chlorophyl a (Chl-a) concentration, a population dominated by small organisms and herbivores, and in May by patchy Chl-a distribution, higher particulate organic matter concentration, a population dominated by large size organisms and an increase in the number of omnivores.

Trophic niche overlap of sprat and commercial small pelagic teleosts in the Gulf of Lions (NW Mediterranean Sea)

“…Anchovies sampled in 2011 in the eastern region showed higher δ 13 C in the coastal area than on the shelf. This result was not in accord with low δ 13 C observed in particulate organic matter (Harmelin-Vivien et al, 2008) but was in accord with high values of δ 13 C recorded in zooplankton sampled near the Rhône river as this zooplankton previously fed in an offshore area characterised by higher δ 13 C values (Espinasse et al, 2014b). No spatial pattern was found in the Bay of Biscay, indicating high mobility of anchovies in this region (Chouvelon et al, 2014).…”

210 Po and 210 Pb trophic transfer within the phytoplankton–zooplankton–anchovy/sardine food web: a case study from the Gulf of Lion (NW Mediterranean Sea)

“…5), suggesting different origins for the organic matter assimilated by planktonic communities (Fry and Sherr, 1984) in the eastern and western GoL pelagic food webs. Espinasse et al (2014b) demonstrate that the history of the water masses, a couple of weeks before sampling, results in two main patterns with different isotopic signatures of zooplankton, persistent in spring and winter. The water masses sampled in our eastern sites (ST1/ST10, ST2 and ST3) are carried onto the shelf from off-shelf region by the Northern Pradal and Millet (2006).…”

“…Subsamples were acid-dripped with 1% HCl, rinsed and dried, to determine d 13 C (B anaru et al, 2013b;Espinasse et al, 2014b). The remaining untreated sample was used for d 15 N analysis.…”

“…The dominant groups of organisms were determined in each size fraction and the results were compared to those provided by more specific studies performed in the GoL on phytoplankton (Harmelin-Vivien et al, 2008) and zooplankton size-classes (B anaru et al, 2013b;Espinasse et al, 2014b).…”

Seasonal and vertical dynamics in the trophic structure of a temperate zooplankton assemblage

“…). Certainly, seasonal patterns in the stable isotope composition of zooplankton have previously been described (e.g., Rolff ; Matthews and Mazumder ; Kürten et al ; Espinasse et al ), including variations in the relationship between δ 15 N values and size in epipelagic zooplankton (Rolff ). However, ours is the first evidence of seasonal changes in the size‐based trophic structure along a depth gradient.…”