Seasonal fluctuation in food sources of herbivorous gastropods in a subtropical seagrass bed estimated by stable isotope analysis

Various herbivorous invertebrates in seagrass beds are considered to be generalists in food use and their diets may temporally fluctuate according to the availability of food sources. We assessed whether food sources of herbivorous gastropods vary in a subtropical seagrass bed in Nagura Bay, Ishigak...

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Bibliographic Details
Published in:Journal of the Marine Biological Association of the United Kingdom 2019-08, Vol.99 (5), p.1119-1125
Main Authors: Nakamoto, Kenta, Hayakawa, Jun, Kawamura, Tomohiko, Ohtsuchi, Naoya, Yamada, Hideaki, Kitagawa, Takashi, Watanabe, Yoshiro
Format: Article
Language:English
Subjects:
Algae
Animal behavior
Aquatic plants
Biomass
Diet
Food
Food availability
Food security
Food sources
Food supply
Gastropoda
Grasses
Herbivores
Invertebrates
Isotope ratios
Marine molluscs
Nitrogen isotopes
Ratios
Sea grasses
Seagrasses
Seasonal variation
Seasonal variations
Seasons
Seaweeds
Spring
Spring (season)
Stable isotopes
Studies
Summer
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Summary:Various herbivorous invertebrates in seagrass beds are considered to be generalists in food use and their diets may temporally fluctuate according to the availability of food sources. We assessed whether food sources of herbivorous gastropods vary in a subtropical seagrass bed in Nagura Bay, Ishigaki Island, where coexisting seaweeds grow densely in spring but minimally in summer. Abundant gastropods and their possible food sources were collected in spring and summer of 2013 and 2015, and their stable carbon and nitrogen isotope ratios were measured. Between the two seasons, each possible food source had similar isotopic values, but all the herbivorous gastropod species in summer were more enriched in 13C than the gastropod samples in spring. The mixing models in SIAR (Stable Isotope Analysis in R) showed that the total contribution rates of seaweeds, i.e. rhodophytes, phaeophytes and chlorophytes, for all herbivorous gastropod species decreased from spring to summer; in contrast, the contribution rate of seagrasses increased. Linear Mixed Models showed that the seasonal variation in δ13C of the herbivorous gastropods was larger than that of the possible food sources, adding further evidence to the seasonal change in food sources of the herbivorous gastropods. This seasonal change in food use appears to correspond to the change in seaweed biomass, suggesting that herbivorous gastropods flexibly change their diets depending on food availability.
ISSN:0025-3154
1469-7769
DOI:10.1017/S0025315418001108