Grazing by small crustaceans stimulates growth of Ulva spp. (Chlorophyta) through preferential consumption of epiphytes
Kamermans, P.; Malta, E.-J.; Verschuure, J.M.; Schrijvers, L.; Lentz, L.F.; Lien, A.T.A. [s.d.]. Grazing by small crustaceans stimulates growth of Ulva spp. (Chlorophyta) through preferential consumption of epiphytes. CEME/NIOO: Yerseke. 22 pp.
Eutrophication of shallow coastal waters often leads to blooms of macroalgae. Grazing by small crustaceans, such as amphipods and isopods, can reduce macroalgal biomass accumulation. The role of grazing by small crustaceans on Ulva spp. biomass development was investigated in the Veerse Meer, a brackish lagoon situated in the Southwest Netherlands. Exclusion of grazing in the field did not stimulate Ulva spp. growth. In fact, growth rates were higher in exclosures that allowed grazers to enter. Edibility tests identified the amphipod Gammarus locusta (L.), and the isopods Idotea chelipes (Pallas) and Sphaeroma hookeri Leach (Lejuez) as grazers on Ulva spp. However, when epiphytic diatoms were present on the Ulva spp. thalli, Gammarus and Sphaeroma did not graze on Ulva tissue. Only Idotea continued to graze on Ulva spp. A laboratory growth experiment revealed a positive effect of Gammarus presence on Ulva spp. growth, probably caused by preferential removal of epiphytic diatoms from the Ulva spp. thalli. The growth stimulation by epiphyte removing grazers such as Gammarus may explain the higher growth rates in the presence of grazers observed in the field. When determining the potential role of invertebrate grazers in controlling macroalgal biomass accumulation, it is important to include an assessment of the epiphyte abundance on the macroalgae, as preferential removal of epiphytes may stimulate growth and thus have the opposite effect.
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