Biology subjects

Riekenberg, P. M.

Publications and source records attributed to Riekenberg, P. M..

5 recordsLinked to original sources

bioRxiv2023

Hot spots drive uptake and short-term processing of organic and inorganic carbon and nitrogen in intertidal sediments

This study uses dual-labelled (13C and 15N) stable isotope applications to examine uptake and short-term processing of carbon (C) and nitrogen (N) by microbial communities in intertidal sediment from three subtropical estuarine sites. We examine differences in microbial uptake and retention that arise due to domination of microbial processing by either microphytobenthos or heterotrophic bacteria. We compare amino acids and algal dissolved organic matter (Algal DOM) and glucose and NH4+ versus newly fixed microphytobenthos C (MPB-C) and NH4+ using in situ applications across 24 h to identify uptake into the microbial community and sediment OM. Algal DOM had preferential C uptake and more retention across 24 h indicating precursors incorporated into biosynthetic pathways for biomass. Conversely, amino acid C was not incorporated or rapidly respired to DIC but displayed clear preferential uptake and retention of 15N. Short-term (24 h) retention of glucose was higher than MPB-C, while uptake of 15N from NH4+ was similar between treatments, potentially indicating glucose-stimulated export of 15N via coupled nitrification-dentrification. Despite careful selection of similar sites and sediment types, we found substantial variability between replicates and sites in the uptake and processing of labeled substrate that challenged traditional statistical analysis due to non-homogenous variance. Uptake variability across orders of magnitude is likely due to disproportionate processing of substrates occurring in hotspots of microbial processing within sediment. Development of analytical techniques to provide robust strategies to handle variability caused by abiotic and biotic factors will allow greater clarity surrounding in situ biogeochemical processing in intertidal environments.

ecology↗

bioRxiv2022

Compound specific stable isotope analysis of amino acid nitrogen reveals detrital support of microphytobenthos in the Dutch Wadden Sea benthic food web

The Wadden Sea is the worlds largest intertidal ecosystem and provides vital food resources for a large number of migratory bird and fish species during seasonal stopovers. Previous work using bulk stable isotope analysis of carbon found that microphytobenthos was the dominant resource use fueling the food web with particulate organic matter making up the remainder. However, this work was unable to account for the trophic structure of the food web or the considerable increase in {delta}15N values of bulk tissue throughout the benthic food web occurring in the Eastern regions of the Dutch Wadden Sea. Here, we combine compound specific and bulk analytical stable isotope techniques to further resolve the trophic structure and resource use throughout the benthic food web in the Wadden Sea. Analysis of {delta}15N for trophic and source amino acids allowed for better identification of trophic relationships due to the integration of underlying variation in the nitrogen resources supporting the food web. Baseline integrated trophic position estimates using glutamic acid (Glu) and phenylalanine (Phe) allow for disentanglement of baseline variations in underlying {delta}15N sources supporting the ecosystem and trophic shifts resulting from changes in ecological relationships. Through this application we further confirmed dominant ecosystem support by microphytobenthos derived resources, although to a lesser extent than previously estimated. In addition to phytoplankton derived particulate organic matter and microphytobenthos supported from nutrients from the overlying water column there appears to be an additional resource supporting the benthic community. From the stable isotope mixing models, a subset of species appears to focus on microphytobenthos supported off recycled (porewater) N and/or detrital organic matter mainly driven by increased phenylalanine {delta}15N values. This additional resource within microphytobenthos may play a role in subsidizing the exceptional benthic productivity observed within the Wadden Sea ecosystem and reflect division in microphytobenthos support along green (herbivory) and brown (recycled/detrital) food web pathways.

ecology↗

bioRxiv2021

Stable nitrogen isotope analysis of amino acids as a new tool to clarify complex parasite-host interactions within marine food webs

O_LITraditional bulk isotopic analysis is a pivotal tool for mapping consumer-resource interactions in food webs but has largely failed to adequately describe parasite-host relationships. Thus, parasite-host interactions remain largely understudied in food web frameworks despite these relationships increasing linkage density, connectance, and ecosystem biomass. Compound-specific stable isotopes from amino acids provides a promising novel approach that may aid in mapping parasitic interactions in food webs. However, to date it has not been applied to parasitic trophic interactions. C_LIO_LIHere we use a combination of traditional bulk stable isotope analyses and compound-specific isotopic analysis of the nitrogen in amino acids to examine resource use and trophic interactions of five parasites from three hosts from a marine coastal food web (Wadden Sea, European Atlantic). By comparing isotopic compositions of bulk and amino acid nitrogen, we aimed to characterize isotopic fractionation occurring between parasites and their hosts and to clarify the trophic position of the parasites. C_LIO_LIOur results showed that parasitic trophic interactions were more accurately identified when using compound-specific stable isotope analysis due to removal of underlying source isotopic variation for both parasites and hosts, and avoidance of the averaging of amino acid variability in bulk analyses through use of multiple trophic amino acids. The compound-specific method provided clear trophic discrimination factors in comparison to bulk isotope methods, however, those differences varied significantly among parasite species. C_LIO_LIAmino acid compound specific isotope analysis has widely been applied to examine trophic position within food webs, but our analyses suggest that the method is particularly useful for clarifying the feeding strategies for parasitic species. Baseline isotopic information provided by source amino acids allows clear identification of the fractionation occurring due to parasite metabolism by integrating underlying isotopic variations from the host tissues. However, like for bulk isotope analysis, the application of a universal trophic discrimination factor to parasite-host relationships remains inappropriate for compound-specific stable isotope analysis. Despite this limitation, compound-specific stable isotope analysis is and will continue to be a valuable tool to increase our understanding of parasitic interactions in marine food webs. C_LI

ecology↗

bioRxiv2020

Reconstructing the diet, trophic level, and migration pattern of Mysticete whales based on baleen isotopic composition.

Baleen from mysticete whales is a well-preserved proteinaceous material that can be used to identify migrations and feeding habits for species whose migration pathways are unknown. Analysis of {delta}13C and {delta}15N from bulk baleen has been used to infer migration patterns for individuals. However, this approach has fallen short of identifying migrations between regions as it is difficult to determine variations in isotopic shifts without temporal sampling of prey items. Here we apply analysis of {delta}15N values of amino acids to five baleen plates belonging to three species, revealing novel insights on trophic position, metabolic state, and migration between regions. Humpback and minke whales had higher reconstructed trophic levels than fin whales (3.4-3.5 versus 2.7-2.9, respectively) as expected due to different feeding specialization. Isotopic niche areas between baleen minima and maxima were well separated, indicating regional resource use for individuals during migration that aligned with isotopic gradients in Atlantic Ocean particulate organic matter. {delta}15N values from phenylalanine confirmed regional separation between the niche areas for two fin whales as migrations occurred and elevated glycine and threonine {delta}15N values revealed physiological changes due to fasting. Simultaneous resolution of trophic level and physiological changes allow for identification of regional migrations in mysticetes.

ecology↗

bioRxiv2020

Impacts of host phylogeny, feeding styles, and parasite attachment site on isotopic discrimination in helminths infecting coral reef fish hosts.

Stable isotopes of carbon and nitrogen characterize trophic relationships in predator-prey relationships, with clear differences between consumer and diet (discrimination factor, {Delta}13C, {Delta}15N). However, parasite-host isotopic relationships remain unclear, with {Delta}13C and {Delta}15N remaining incompletely characterized, especially for helminths. In this study, we used stable isotopes to determine discrimination factors for 13 parasite-host pairings of helminths in coral reef fish. {Delta}15N differences grouped according to phylogeny and attachment site on the hosts: {Delta}15N was positive for trematodes and nematodes from the digestive tract and varied for cestodes and nematodes from the general cavity. {Delta}13C showed more complex patterns with no effect of phylogeny or attachment site. A negative relationship was observed between {Delta}15N and host {delta}15N value among different host-parasite pairings as well as within 7 out of the 13 parings, indicating that host metabolic processing affects host-parasite discrimination values. In contrast, no relationships were observed for {Delta}13C. Our results indicate that host phylogeny, attachment site and host stable isotope value drive {Delta}15N of helminths in coral reef fish while {Delta}13C is more idiosyncratic. These results call for use of taxon- or species-specific and scaled framework for bulk stable isotopes in the trophic ecology of parasites.

ecology↗