ArticlePublisher preview available

Lake trophic status and hydrological connectivity modify mechanisms underlying mollusc assemblage structuring

January 2023
Hydrobiologia 850(4):1-14

DOI:10.1007/s10750-022-05125-y

Authors:

Erika Šlachtová

Masaryk University

Jindřiška Bojková

Masaryk University

Eliska Marsalkova

The Czech Academy of Sciences

Jan Sychra

Masaryk University

Show all 5 authorsHide

Species distribution and assemblage structuring are influenced by a combination of species dispersal mode and the dispersal routes used. Habitat connectivity is particularly important for passively dispersing taxa such as freshwater molluscs. In addition, current anthropogenic eutrophication affects the structure of assemblages by reducing native fauna and promoting the spread of generalist species. Here, we examined mollusc assemblages in two systems of small lakes differing in hydrological connectivity. The assemblages of 22 isolated lakes in Albania were mainly controlled by the distance between the lakes with a lower contribution of environmental conditions and lake area. In contrast, assemblages of 52 interconnected lakes in Czechia were driven primarily by environmental conditions. However, as lake trophic status increased, the assemblages in Czechia became more homogeneous in species composition as high trophic status filtered out all species except generalists. These assemblages from 33 eutrophic lakes were strongly determined by environmental variables, whereas the remaining assemblages from 19 low trophic lakes were structured by a combination of spatial and environmental variables. We conclude that hydrological connectivity between lakes is crucial for the distribution of molluscs, but eutrophication may influence the importance of individual mechanisms structuring mollusc assemblages.

Study regions with the position of 54 lakes in Czechia and 58 study lakes in Albania. Classification of sites: black/green/blue dots, molluscs were recorded; white dot, no mollusc recorded; cross, both no mollusc recorded and environmental variables not measured. Czechia: green dots, low trophic (mesotrophic/oligotrophic) lakes; black dots, high trophic (eutrophic/hypertrophic) lakes. Albania: blue dots, low trophic (oligotrophic) lakes; black dots, high trophic (mesotrophic/eutrophic) lakes (see Methods). The lake numbers correspond to the numbers in Table A.1 and A.2 in the Online Resource

…

Percentage of explained adjusted variation (Adj.R²) in 22 aquatic mollusc assemblages from Albania (A) and 52 from Czechia (B). To make the explained variation comparable between regions, the proportions were rescaled to the same totals and therefore presented as percentages of the total explained variation for each region (C, D). Pure and shared percentages of the explained variation were partitioned among environmental (light-grey circle; ENV), geographic (grey circle; GEG), and spatial (dark-grey circle; SPA) variables using the forward selection procedure in RDA (Table 2). While Table 2 provides gross variation of each variable, the values here show their pure fractions. Significance of these pure fractions was tested by pRDA with Monte Carlo permutation test and is indicated by asterisks (*P < 0.05; **P < 0.01; ***P < 0.001; ns, not significant)

…

Density histogram of chlorophyll-a concentrations in Albanian (black curve) and Czech (dashed curve) study lakes. Vertical lines represent the threshold values of water trophic status according to Vollenweider (1968). The solid and dashed vertical lines define the threshold in the Albanian and Czech lakes, respectively, to categorize the lakes into low or high trophic status. The median distance to the centroid of each group of lakes is shown below the number of lakes in the groups. The shorter the distance from the centroid, the more homogeneous the species composition of the lakes. Differences were significant only for the Czech lakes (TukeyHSD, P = 0.013)

…

Percentage of explained adjusted variation (Adj.R²) in aquatic mollusc assemblages from A 33 high trophic lakes (eutrophic/hypertrophic lakes < 25 µl/l of chlorophyll-a) and B 19 low trophic (oligotrophic/mesotrophic lakes ≥ 25 µl/l) from Czechia. Pure and shared percentages of the explained variation were partitioned among environmental (light-grey circle), geographic (grey circle), and spatial variables (dark-grey circle) using the forward selection procedure in RDA (Table A.7 in the Online Resource). Significance of pure fractions was tested by pRDA with Monte Carlo permutation test and is indicated by asterisks (*P < 0.05; **P < 0.01; ***P < 0.001; ns, not significant)

…

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Hydrobiologia (2023) 850:793–806

https://doi.org/10.1007/s10750-022-05125-y

PRIMARY RESEARCH PAPER

Lake trophic status andhydrological connectivity modify

mechanisms underlying mollusc assemblage structuring

ErikaŠlachtová · JindřiškaBojková ·

EliškaMaršálková · JanSychra·

MichalHorsák

Received: 10 February 2022 / Revised: 5 December 2022 / Accepted: 19 December 2022 / Published online: 18 January 2023

Abstract Species distribution and assemblage

structuring are inﬂuenced by a combination of spe-

cies dispersal mode and the dispersal routes used.

Habitat connectivity is particularly important for pas-

sively dispersing taxa such as freshwater molluscs. In

addition, current anthropogenic eutrophication aﬀects

the structure of assemblages by reducing native fauna

and promoting the spread of generalist species. Here,

we examined mollusc assemblages in two systems

of small lakes diﬀering in hydrological connectivity.

The assemblages of 22 isolated lakes in Albania were

mainly controlled by the distance between the lakes

with a lower contribution of environmental condi-

tions and lake area. In contrast, assemblages of 52

interconnected lakes in Czechia were driven primar-

ily by environmental conditions. However, as lake

trophic status increased, the assemblages in Czechia

became more homogeneous in species composition as

high trophic status ﬁltered out all species except gen-

eralists. These assemblages from 33 eutrophic lakes

were strongly determined by environmental vari-

ables, whereas the remaining assemblages from 19

low trophic lakes were structured by a combination of

spatial and environmental variables. We conclude that

hydrological connectivity between lakes is crucial for

the distribution of molluscs, but eutrophication may

inﬂuence the importance of individual mechanisms

structuring mollusc assemblages.

Keywords Eutrophication· Homogeneity· Biotic

ﬁlters· Distribution· Molluscs· Small lakes

Introduction

Freshwater habitats are more isolated compared to

marine or terrestrial habitats and are therefore consid-

ered to be at higher risk, whether from habitat pollu-

tion, eutrophication, and/or invasion by exotic species

(Stendera & Johnson, 2005; Dudgeon etal., 2006).

This seems to be particularly true for ponds and lakes,

Handling editor: Luis Mauricio Bini

Supplementary Information The online version

contains supplementary material available at https:// doi.

org/ 10. 1007/ s10750- 022- 05125-y

E.Šlachtová(*)· J.Bojková· J.Sychra· M.Horsák

Department ofBotany andZoology, Faculty ofScience,

Masaryk University, Brno, CzechRepublic

e-mail: erikalorencova@mail.muni.cz

J. Bojková

e-mail: bojkova@sci.muni.cz

J. Sychra

e-mail: honzas@mail.muni.cz

M. Horsák

e-mail: horsak@sci.muni.cz

E.Maršálková

Department ofExperimental Phycology

andEcotoxicology, Institute ofBotany oftheCzech

Academy ofSciences, Brno, CzechRepublic

e-mail: eliska.marsalkova@ibot.cas.cz

Content courtesy of Springer Nature, terms of use apply. Rights reserved.

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