Effects of acidification on carbon and nitrogen stable isotopes of benthic macrofauna from a tropical coral reef

Abstract

Stable isotope analyses are widely used to determine trophic levels in ecological studies. We have investigated the effects of carbonate removal via acidification on the stable carbon and nitrogen isotopic composition of 33 species of tropical benthic macrofauna, and we report guidelines for standardizing this procedure for higher taxa in tropical coral reef ecosystems. Many tropical benthic invertebrates are small in size, and therefore body tissue isolation (separating organic carbon from inorganic structures) is difficult and time-consuming. Literature reviews of invertebrate studies show a lack of consistent procedures and guidelines for preparation techniques, especially for carbonate removal via acidification of whole individuals. We find that acidification decreases the delta(13)C values of samples containing carbonate, with shifts ranging from 0.21 to 3.20 per thousand, which can be related to CaCO(3) content (assessed by a carbonate proxy), justifying acid pre-treatment. Carbonate-containing taxa benefiting from acidification included Amphinomida, Terebellida (Annelida), Anomura, Brachyura, Caridea, Amphipoda, Tanaidacea (Arthropoda) and Edwardsiida (Cnidaria). The delta(13)C shifts of samples containing no carbonate varied up to 0.02 +/- 0.20 per thousand. As this induced delta(13)C shift was lower than the range of an average trophic level shift (0.5 to 1 per thousand), we conclude that acid pre-treatment is unnecessary. Carbonate-free taxa consisted of Eunicida, Phyllodocida (Annelida) and Mollusca. We note minimal impact of acidification on delta(15)N values except for Brachyura, which showed a shift of 0.83 +/- 0.46 per thousand, which is still lower than a single trophic level shift (2.9-3.8 per thousand). We conclude that for trophic level studies, both the delta(13)C and the delta(15)N of carbonate-rich macrofauna can be determined from the same acidified sample.

Effects of demineralization on the stable isotope analysis of bone samples

“…Carbonate content is the other key factor controlling whether or not the δ 13 C values from bioapatite will contribute significantly to the δ 13 C values from whole tissues . Bone carbonate content varies, but averages ~3% by weight .…”

Feeding ecology and ontogenetic dietary shift of yellowstripe goatfish Mulloidichthys flavolineatus (Mullidae) at Reunion Island, SW Indian Ocean

“…POM filters were pretreated and analyzed according to Lorrain et al (2003). Macrofauna samples were analyzed following Kolasinski et al (2008). Lipids were not removed as Mulloidichthys flavolineatus white muscle, macrofauna and STOM have a low lipid content (C/N ratio of all samples were < 4), which does not affect δ 13 C values of these measurements (Post et al 2007).…”

Importance of terrestrial subsidies for estuarine food webs in contrasting East African catchments

“…All samples were collected at ebb tide. Collected material was then filtered through a 500 lm mesh to remove debris and placed in a 200 ml jar where sediment was allowed to settle and zooplankton guts allowed to clear for ;4 h. The top water, containing mostly zooplankton but also some unidentified detrital material, was then carefully collected on a 250 lm sieve, and dried at 608C for 48 h. For d 13 C analysis, samples were acidified in Ag capsules by adding 20-50 lL of 5% HCl drop-by-drop onto the weighed samples to remove carbonates (Jaschinski et al 2008, Kolasinski et al 2008 15 N was measured on untreated samples. Due to the very high suspended sediment load, it was not possible to collect zooplankton from the Betsiboka.…”