The invasive mud crab enforces a major shift in a rocky littoral invertebrate community of the Baltic Sea
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In rocky littoral communities, intense herbivory allows for the occurrence of trophic cascades where higher trophic levels influence producer communities. Invasive predators can be especially effective in imposing trophic cascades. The North American mud crab Rhithropanopeus harrisii is a recent invader in the Baltic Sea, with an expanding distribution range. Here, we document the effects of mud crab on the native invertebrate community associated with the key foundation species Fucus vesiculosus. During the initial 3 years of invasion, mud crab abundance in F. vesiculosus increased from 2 % to about 25 % of the algae being inhabited by crabs. Simultaneously, the invertebrate community underwent a major transition: Species richness and diversity dropped as a consequence of decreasing abundance and the loss of certain taxa. The abundance of gastropods decreased by 99 % and that of crustaceans by 75 %, while chironomids completely disappeared. Consequently, the community dominated earlier by herbivorous and periphyton-grazing gastropods and crustaceans shifted to a mussel dominated community with overall low abundances of herbivores. At the same time filamentous epiphytic algae prospered and the growth rate of F. vesiculosus decreased. We suggest that this shift in the invertebrate community may have far reaching consequences on ecosystem functioning. These arise through changes in the strength of producer–herbivore interaction, caused by mud crab predation on the dominating grazer taxa. This interaction is a major determinant of ecological function of ecosystems, i.e. productivity and energy flow to higher trophic levels. Therefore, the decrease in herbivory can be expected to have a major structuring role in producer communities of the rocky littoral macroalgal assemblages.
KeywordsMud crab Baltic Sea Predation Herbivory Ecosystem function
We are grateful to Tiina Piltti, Juho Yli-Rosti, Luca Rugiu, Tiina Salo and Anneli Asplund for help in setting up, maintaining and sampling the bladderwrack common garden, and to the Archipelago Research Institute of the University of Turku for facilities and logistic help. The study was funded by the Academy of Finland (Project #251102) and the BONUS, the EU joint Baltic Sea research and development program, project BAMBI.
- Estes JA, Terborgh J, Brashares JS, Power ME, Berger J, Bond WJ, Carpenter SR, Essington TE, Holt RD, Jackson JBC, Marquis RJ, Oksanen L, Oksanen T, Paine RT, Pikitch EK, Ripple WJ, Sandin SA, Scheffer M, Schoener TW, Shurin JB, Sinclair ARE, Soule ME, Virtanen R, Wardle DA (2011) Trophic downgrading of planet earth. Science 333:301–306CrossRefPubMedGoogle Scholar
- Gotelli NJ, Colwell RK (2011) Estimating species richness. In: Magurran AE, Mcgill BJ (eds) Biological diversity. Oxford University Press, New York, pp 39–65Google Scholar
- Haahtela I (1984) A hypothesis of the decline of the bladderwrack (Fucus vesiculosus L.) in SW Finland in 1975–1981. Limnologica 15:345–350Google Scholar
- Kangas P, Autio H, Hällfors G, Luther H, Niemi Å, Salemaa H (1982) A general model of the decline of Fucus vesiculosus at Tvärminne, south coast of Finland in 1977–81. Acta Bot Fenn 118:1–27Google Scholar
- Rönnberg O, Lehto J, Haahtela I (1985) Recent changes in the occurrence of Fucus vesiculosus in the Archipelago Sea, SW Finland. Ann Bot Fenn 22:231–244Google Scholar
- SAS Institute Inc (2008) SAS/STAT® 9.2 user’s guide. SAS Institute Inc, CaryGoogle Scholar