Transfer of essential lipids from aquatic to terrestrial ecosystems via emerging insects

Abstract

Emerging aquatic insects (EAI) are important vectors through which freshwater-derived organic matter can enter terrestrial food webs. Aquatic-derived dietary energy can support terrestrial consumer fitness, especially via its polyunsaturated fatty acids (PUFA) that are otherwise short in supply from terrestrial diet. Considering qualitative aspects of resource subsidies is thus crucial for understanding energy and nutrient fluxes between ecosystems and for assessing effects on food web processes in recipient habitats. In this context, the objective of this study is to, (1) quantify the export of PUFA from four peri-alpine lakes, (2) evaluate the PUFA transfer from aquatic to terrestrial invertebrate consumers via EAI along an altitudinal lake gradient, and, (3) identify trophic pathways for riparian consumers. We hypothesize that, a) PUFA-flux via EAI will decrease with increasing lake depth, and, b) the effect of aquatic subsidies on terrestrial invertebrate consumers decreases with distance to lakes. To test this assumption, insect biomass and total export of PUFA will be quantified from four lakes at different altitudes. In addition to bulk stable isotopes and fatty acids, compound-specific stable isotopes (d13C and d2H of fatty acids) will be used to assess PUFA export via EAI and the distribution of aquatic PUFA in adjacent terrestrial ecosystems and invertebrate consumers. Laboratory feeding experiments will be conducted to test which aquatic or terrestrial insect prey are preferentially consumed and support the growth of riparian predators (i.e. spiders) more efficiently. This approach will provide novel insight into the potential role of essential nutrients in mediating cross-ecosystem effects.

Full text

Transfer of essential lipids from aquatic to terrestrial
ecosystems via emerging insects
Emerging aquatic insects (EAI) are important trophic vectors through which freshwater-derived organic matter can enter terrestrial food webs (Hoekman et
al.2010; Martin-Creuzburg et al.2017),and support terrestrial consumer fitness, especially via its polyunsaturated fatty acids (PUFA) that are otherwise
short in supply from terrestrial diet (Gladyshev et al.2009).
Considering qualitative aspects of resource subsidies is thus crucial for understanding energy and nutrient fluxes between ecosystems and for assessing
effects on food web processes in recipient habitats (Marcarelli et al. 2011; Twining et al.2016).
Quantify and qualify the transfer of dietary PUFA looking
at both altitudinal and lake depth gradients
Figure 1. Study lakes sampled from June to September 2019, with aquatic traps
presenting a depth gradient from 33 to 1 m.
oTaxa biomass oTotal lipid content
oFA composition
oδ13C of FA
Objective 1
Determine the origin of essential FA for riparian consumers
Figure 2. Map of the sampling sites of the three different ecosystems in Lake Lunz:
lake, stream, and terrestrial.
oBulk Stable Isotopes:
δ13C & δ15N
oδ2H of FA
oInsects & Riparian consumers
Objective 2
Introduction
Figure 3. Relative contribution (%) of different insect groups to
the export of total insect biomass (mg.m-2)at different depths.
Figure 4. Biomass export (mg.m-2)
of Chironomidae and Microsema
insects from different depths
(June 2019).
The effect of aquatic
subsidies on terrestrial
consumers decreases
with distance to lake
PUFA-flux via EAI will decrease
with increasing lake depth and
altitude
Hypotheses
oDifferent taxonomic contribution
as function of lake depth and time
Changes in quantity and quality
of PUFA exports
oBiomass export higher at shallow
lake depths
Transfer of energy varies as
function of sampling sites
Implications
Margaux Mathieu-Resuge1, Tarn Preet PARMAR2, Dominik MARTIN-CREUZBURG2, Hannes H. HAGER1, Martin J. KAINZ1
1 WasserCluster Lunz - Inter-University Centre for Aquatic Ecosystem Research, Lunz am See, Austria
2 Limnological institute, University of Konstanz, Germany
m.mathieuresuge@gmail.com @m_mathieuresuge
https://aquaterr.home.blog/
Preliminary
Results