Using stable isotopes and C:N ratios to examine the life‐history strategies and nutritional sources of larval lampreys

Abstract

Natural abundance stable-isotope analysis (δ(13)C and δ(15)N) and C:N ratios were used to study the ammocoete phase of two common non-parasitic lamprey species (least brook lamprey Lampetra aepyptera and American brook lamprey Lethenteron appendix) in two tributaries of the Ohio River (U.S.A.). The C:N ratios suggest that each species employs different lipid accumulation strategies to support its metamorphosis and recruitment into an adult animal. Ammocoete δ(13)C values generally increased with increasing C:N values. In contrast to δ(13)C, ammocoete δ(15)N values were weakly related to the total length (LT) in L. aepyptera, but positively correlated to both LT and C:N ratios in L. appendix. In L. appendix, C:N also correlated positively with LT, and presumably age. A Bayesian mixing model using δ(13)C and δ(15)N was used to estimate nutritional subsidies of different potential food resources to ammocoetes at each site. The models suggested that although nutritional subsidies to ammocoetes varied as a function of site, ammocoetes were generally reliant on large contributions (42-62% at three sites) from aquatic plants. Contributions from aquatic sediment organic matter were also important at all sites (32-63%) for ammocoetes, with terrestrially derived plant materials contributing smaller amounts (4-33%). These findings provide important insights into the feeding ecology and nutrition of two species of lampreys. They also suggest that similar and other quantitative approaches are required to (1) fully understand how the observed stable-isotopes ratios are established in ammocoetes and (2) better assess ammocoete nutritional subsidies in different natal streams.

Mercury concentrations in Pacific lamprey (Entosphenus tridentatus) and sediments in the Columbia River basin

“…More recently, wet weight concentrations of Hg in larval Pacific lamprey in the Willamette and Yakima tributaries of the Columbia River were also found to be 20 to 30 times higher than dry weight concentrations in the corresponding sediments . Although the tissue concentrations reported in these studies are for THg, the present study's findings show that as with most species of fish the dominant form of Hg in ammocoetes is also MeHg, despite the fact that as filter feeders ammocoetes forage at the base of the food chain , where MeHg concentrations are generally lowest .…”

Radioisotope and stable isotope ratios (Δ14C, δ15N) suggest larval lamprey growth is dependent on both fresh and aged organic matter in streams

“…However, previous work by our group has shown that ammocoete δ 13 C values are a complex function of diet and fractionation that may occur during synthesis of tissues (Evans & Bauer, 2016a, 2016b. However, previous work by our group has shown that ammocoete δ 13 C values are a complex function of diet and fractionation that may occur during synthesis of tissues (Evans & Bauer, 2016a, 2016b.…”

“…Traditionally, it is assumed that the lipid content of tissues causes tissue δ 13 C to decrease because of a higher preference for 12 C in lipid synthesis (Post et al, 2007). Since the positive correlation between δ 13 C and C:N ratios in those studies was novel in the literature for a presumed lipid effect, δ 13 C was used in the models without correction (Evans & Bauer, 2016a, 2016b. Since the positive correlation between δ 13 C and C:N ratios in those studies was novel in the literature for a presumed lipid effect, δ 13 C was used in the models without correction (Evans & Bauer, 2016a, 2016b.…”

“…The δ 13 C values of aquatic organisms are often used to decipher their potential dietary and nutritional resources. However, previous work by our group has shown that ammocoete δ 13 C values are a complex function of diet and fractionation that may occur during synthesis of tissues (Evans & Bauer, 2016a, 2016b. Thus, the δ 13 C values of ammocoetes are not used in the present study, except in the correction of the Δ 14 C values.…”

“…Prior work using stable isotope ratios (δ 13 C, δ 15 N) has suggested that ammocoetes increasingly rely on algal sources (and hence autochthony) as they increased in size (Evans & Bauer, 2016a, 2016b.…”