Trophic cascades of waterbirds on benthic microalgal communities in coastal wetlands in the Yangtze estuary

doi:10.17521/cjpe.2024.0170

Abstract

Abstract:

Aims Benthic microalgae are one of the primary producers in coastal wetlands, providing basic energy and material to the food web of coastal wetlands and playing an important role in maintaining the stability of coastal wetland ecosystems. Previous studies have focused on the effects of environmental factors, vascular plants and herbivores on benthic microalgae, neglecting the trophic cascade effects of predators.
Methods We investigated the trophic cascade effects of waterbirds on benthic microalgae in a manipulative field experiment in a coastal wetland in the Chang Jiang (Yangtze) estuary, where we measured the biomass of benthic microalgae monthly and their species composition quarterly for a year.
Important findings Results showed that: (1) benthic microalgal biomass was significantly decreased in waterbird exclusion treatments. In waterbird exclusion treatments, although the lack of direct consumption by waterbirds facilitated benthic microalgae, increases in the abundance of crabs feeding on microalgae suppressed benthic microalgae more strongly. (2) Crab exclusion treatments (simulating intense predation by waterbirds) also significantly reduced benthic microalgal biomass. In crab exclusion treatments, the abundance of snail feeding on microalgae increased substantially. (3) Waterbird and crab exclusion treatments both significantly reduced the abundance of the dominant microalgal taxa, diatoms, and increased the diversity of benthic microalgal communities. This study demonstrates that waterbirds in coastal wetlands can exert strong top-down effects on benthic microalgal communities through multiple direct or indirect processes, and enriches our understanding of the mechanisms controlling microalgal communities in coastal wetlands.

Key words: coastal wetlands, trophic cascade, animal consumers, benthic microalgae, community diversity

LIU Ying-Lin, LI Chun-Ming, WANG Hao, WU Chang-Lu, HE Qiang. Trophic cascades of waterbirds on benthic microalgal communities in coastal wetlands in the Yangtze estuary[J]. Chin J Plant Ecol, 2025, 49(3): 367-378.

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URL: https://www.plant-ecology.com/EN/10.17521/cjpe.2024.0170

https://www.plant-ecology.com/EN/Y2025/V49/I3/367

Figures/Tables 7

Fig. 1 Biomass (given as chlorophyll a content) of benthic microalgae in different experimental treatments (mean ± SE). Within a month, different lowercase letters indicate statistical differences between different treatments (p < 0.05). Seasons are separated by shadings of different colors.

Table 1 Abundances of waterbird tracks, crab burrows, and snails in different experimental treatments (mean ± SE)

响应变量 Response variable	种植+水鸟去除 Planting + waterbird exclusion	种植+蟹类去除 Planting + crab exclusion	种植 Planting	空白对照 Control	p (Tr)	p (Ti)	p (Tr × Ti)
水鸟足迹 Waterbird tracks	3.50 ± 2.17^b	0.17 ± 0.33^c	170.17 ± 45.24^a	165.63 ± 49.42^a	<0.000 1	<0.000 1	<0.000 1
蟹洞 Crab burrows	26.80 ± 2.98^a	0.38 ± 0.32^c	13.54 ± 1.77^b	13.25 ± 1.53^b	<0.000 1	0.000 3	0.220 0
拟沼螺 Assiminea sp.	4.92 ± 1.49^b	30.25 ± 6.89^a	2.79 ± 0.82^b	3.50 ± 1.40^b	<0.000 1	0.008 5	0.001 6
拟蟹守螺 Cerithidea sp.	3.42 ± 1.21^b	17.54 ± 5.81^a	2.00 ± 0.58^b	2.38 ± 0.83^b	<0.000 1	<0.000 1	0.015 6

Fig. 2 Relationships between the biomass of benthic microalgae (given as chlorophyll a content) and the abundances of different animal consumers. A, Waterbird tracks (the inset shows the results without planting + waterbird exclusion and planting + crab exclusion treatments). B, Crabs (the inset shows the results without planting + crab exclusion treatments). C, Assiminea sp. D, Cerithidea sp. p indicates the statistical significance of a linear mixed-effects model, and R2 is the proportion of variation in the dependent variable explained by the model, the gray areas are 95% confidence intervals.

Fig. 3 Structural equation modeling of the effects of waterbirds on the biomass of benthic microalgae. A, Hypothetical model. B, Statistical model. The numbers corresponding to paths are path coefficients; *, p < 0.05; **, p < 0.01; ***, p < 0.001; R2 is the fit of the path.

Fig. 4 Differences in the mean relative abundance (%) of benthic microalgae among different experimental treatments (mean ± SE). A, Phylum level. B, Genus level (only for phyla and genera with an abundance percentage greater than 1%; those < 1% are shown as others). Within a phylum or genus, different lowercase letters indicate significant differences between treatments (p < 0.05).

Fig. 5 Non-metric multidimensional scaling (NMDS) analysis for the genus-level composition of benthic microalgal communities in different experimental treatments. Ellipses indicate 95% confidence limit. Stress indicates the difference between the relative distances of samples in the lower-dimensional space and those in the original high-dimensional data; when stress is <0.2, it is generally considered that the model fit is acceptable.

Fig. 6 Diversity indices of benthic microalgae communities in different experimental treatments in different seasons (mean ± SE). Within a season, different lowercase letters indicate significant differences between treatments (p < 0.05).

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