Diversity and Disturbances in the Antarctic Megabenthos: Feasible versus Theoretical Disturbance Ranges Karin Johst, 1 * Julian Gutt, 2 Christian Wissel, 1 and Volker Grimm 1 1 UFZ Centre for Environmental Research, Department of Ecological Modeling, P.O. Box 500136, D-04301, Leipzig, Germany; and 2 Alfred Wegener Institute for Polar and Marine Research, D-27568, Columbusstrasse, Bremerhaven, Germany ABSTRACT The intermediate disturbance hypothesis (IDH) predicts a hump-shaped relationship between re- gional diversity and the disturbance rate. We tested the IDH for the megabenthos inhabiting the Ant- arctic sea floor, which is disturbed by iceberg scouring. We used models based on the empirical knowledge of succession to calculate the IDH curve for this system and to extrapolate the presently observable range of the IDH curve to higher and lower disturbance rates. Although the hump- shaped relationship has been found for a purely theoretical (extremely large) disturbance range, within the feasible disturbance range (assumed as realistic in the Antarctic region under climate change), the regional diversity of successional stages due to iceberg scouring strongly decreases with lower disturbance rates but levels off only slowly with higher disturbance rates. The reason is the unevenness in the lifetimes of the successional stages, in that early stages are short-lived whereas late stages are long-lived. With such unevenness, increasing disturbances support the early stages without jeopardizing the later ones. Additionally, we converted this regional diversity of stages to the regional diversity of taxa using a transformation formula based on empirical knowledge of the number and mean abundance of taxa in the par- ticular stages. Our results suggest that a decrease in iceberg scouring due to climate change would be more detrimental to the diversity of the Antarctic megabenthos than an increase. Key words: disturbance; diversity; intermediate disturbance hypothesis; succession; iceberg scouring; climate change; Antartic. INTRODUCTION The intermediate disturbance hypothesis (IDH) predicts that too much disturbance reduces the abundance of late successional stages, whereas too little disturbance does not allow pioneer stages to persist (Connell 1978; Huston 1994; Wilson 1994; Collins and Glenn 1997; Tilman 1999; Hubbell and others 1999; Levin 2000; Roxburgh and others 2004). Thus, diversity should be maximal with intermediate disturbances, a hypothesis that has been studied in the aquatic realm by field studies (for example, Sousa 1979; Flo ¨ der and Sommer 1999; Barnes 1999; Maughan and Barnes 2000; Brown and others 2004; Conlan and Kvitek 2005) and laboratory investigations (for example, Gaed- eke and Sommer 1986; Sommer 1995; Buckling and others 2000). In this study, we investigated the impact of disturbances in the form of iceberg scouring on the regional diversity of the Antarctic mega-epibenthos (larger than 5 mm). We com- Received 15 April 2005; accepted 9 January 2006; published online 17 November 2006. *Corresponding author; e-mail: karin.johst@ufz.de Ecosystems (2006) 9: 1145–1155 DOI: 10.1007/s10021-006-0054-9 1145