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

Abstract

Lampreys have a complex life cycle which includes a multi‐year infaunal larval stage (ammocoete). Gut content analysis has generally identified detritus (i.e., unidentifiable organic matter) as the major dietary component to ammocoetes, though algae can also be important. However, gut content preserves only a snapshot of the animal's diet and does not reflect assimilated material. In order to better characterise the nutritional sources supporting ammocoete growth, we analysed ammocoete body tissue and potential dietary sources at two streams using natural Δ14C and δ15N to estimate time‐integrated nutritional support. Bayesian isotope mixing models revealed differences in the importance of sources supporting ammocoetes between sites. Ammocoetes from a stream in a mixed land usage area (~50% agriculture, ~40% forest and ~10% developed) were primarily supported (mean: ~50%) by fresh terrestrial organic matter but were also supported by substantial contributions (mean: ~30%) by aged organic matter (AOM) and autochthonous material (algae; mean ~20%). In a predominantly forested (~90%) headwater stream, different modelling scenarios (uninformed or informed priors) suggested that algal support of ammocoete nutrition ranged from 7% to 45%. However, the model relying on informed priors developed from gut content analysis produced the low estimates, suggesting these were more reliable. When algae were a minor component of the nutrition at the forested site, ammocoetes were highly dependent on AOM (83 ± 26%; mean ± SD). Based on these findings, ammocoete growth and development are predicted to be strongly influenced by both land use and the availability of allochthonous and autochthonous materials of varying ages within streams.

Fruit of the forest ‐ larval sea lamprey Petromyzon marinus are fuelled by allochthonous resources

“…We performed lipid treatment a priori and included hydrogen isotope analysis in our study in an attempt to overcome this, which may account for the difference in results between studies. A subsequent re‐analysis of the systems tested by Evans and Bauer () which accounted for potential lipid effects and also included radiocarbon as an additional tracer indicated that the earlier study may have overestimated the contribution of autochthonous materials to larval P. marinus (Evans et al ., ), lending further weight to our conclusions.…”

Salvage using electrofishing methods caused minimal mortality of burrowed and emerged larval lampreys in dewatered habitats

“…Lampreys exhibit a multiyear larval stage, which is thought to be biologically and ecologically similar among species (Dawson et al 2015; Docker and Potter 2019). Biologically, all species of lamprey burrow in substrates of freshwater environments and they filter‐feed on algae, bacteria, and organic detritus of aquatic and terrestrial origin during the larval life stage (Dawson et al 2015; Evans et al 2019). As a result of burrowing and feeding activities, larval lampreys are ecologically similar among species in that they can alter the physical and chemical environment of the benthos (Shirakawa et al 2013; Boeker and Geist 2016; Nika et al 2021), leading Shirakawa et al (2013) to suggest that declines in abundance and distribution of larval lampreys in freshwater habitats could diminish overall ecosystem function.…”

Structure and seasonal variability in fish food webs in a small macrotidal estuary (Canche estuary, Eastern English Channel) based on stable carbon and nitrogen isotope analysis

“…In estuarine ecosystems, organic matter of terrestrial origin is a major contributor to allochthonous organic matter (Duan et al, 2014;Lu et al, 2013). Analysis of the carbon and nitrogen stable isotopic compositions of estuarine organic matter can identify their contributions to the food web (Darnaude et al, 2004;Evans et al, 2019). Generally, POM in estuaries is composed of river POM (mixture of terrestrial POM and freshwater phytoplankton), estuarine-produced and marine phytoplankton, resuspended microphytobenthos and diverse detritus (e.g.…”