The importance of grazing intensity and frequency for physiological responses of the tropical seagrass Thalassia hemprichii |
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| Authors: | J.S. Ekl f, M. Gullstr m, M. Bj rk, M.E. Asplund, L. Hammar, A. Dahlgren,M.C.
hman |
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| Affiliation: | aDepartment of Systems Ecology, Stockholm University, SE-106 91 Stockholm, Sweden;bDepartment of Zoology, Stockholm University, SE-106 91 Stockholm, Sweden;cDepartment of Botany, Stockholm University, SE-106 91 Stockholm, Sweden;dDepartment of Marine Ecology, Göteborg University, Kristineberg Marine Research Station, SE-450 34 Fiskebäckskil, Sweden |
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| Abstract: | Seagrass grazing is an intrinsic disturbance in primarily tropical and subtropical areas. While there is a general parabolic response in seagrass growth to grazing intensity, there is less knowledge on the role of grazing frequency, as well as potential interactions between grazing intensity and frequency. This study experimentally investigated physiological responses in Thalassia hemprichii to simulated (leaf cutting) grazing regimes with different intensities (25% vs. 75%) and frequencies (1 times vs. 3 times) over 35 days in Chwaka Bay (Zanzibar, Tanzania). The results showed that the two high-intensity treatments (75% removal) had 37–41% lower growth rate than the low-intensity/low-frequency treatment, and rhizome sugar and starch content were both affected in a similar way. A 36% lower starch content in the simulated low-intensity/high-frequency regime (25% × 3) compared to the one of low-intensity/low-frequency (25% × 1) also shows an interaction between grazing intensity and frequency. This suggests that high-intensity (and to some extent frequency) grazing regimes, in comparison to low-intensity regimes, could negatively affect T. hemprichii growth, energy reserves, and thereby the ability to deal with additional stress like light limitation or grazing. |
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| Keywords: | Disturbance regime Grazing Herbivory Seagrass Carbohydrate Thalassia hemprichii |
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