Marine Biology (1996) 125:189-197 9 Springer-Verlag 1996 S. Reizopoulou 9M. Thessalou-Legaki 9A. Nicolaidou Assessment of disturbance in Mediterranean lagoons: an evaluation of methods Received: 28 September 1995/Accepted: 26 October 1995 Abstract A number of methods were applied to assess disturbance in macrozoobenthic communities in three Mediterranean lagoons with different levels of stress. Tsopeli, Ionian Sea, with no obvious source of stress, harbours a fauna typical of brackish-water lagoons. Vivari, Aegean Sea, also without apparent source of disturbance, is characterised by a few typical lagoonal species and some species characteristic of perturbation. Goro lagoon, in the northern Adriatic, is much larger and more open to the sea. At the centre of the lagoon, where anoxia is known to occur in the summer ("Goro polluted"), the fauna is dominated by species typical of disturbance and a few lagoonal species. A dredged area closer to the sea ("Goro dredged") is totally dominated by species characteristic of disturbance. The species diversity in all lagoons ranges from low to very low. According to the distribution of individuals in geomet- ric abundance classes, all the lagoons are characterised as stressed. The distribution of individuals in geometric size classes shows dominance of larger specimens in the least disturbed Tsopeli and exclusively small sizes in the greatly disturbed dredged area of Goro. The abun- dance/biomass comparison curves characterise Tsopeli as undisturbed, Vivari and Goro polluted stations as moderately disturbed and Goro dredged station as disturbed. The last two methods agree with the charac- terisation derived by examining the dominant species. It is concluded that methods based on size changes of the fauna are more sensitive than those based on rela- tive abundance in assessing disturbance in coastal brackish-water lagoons. Communicated by O. Kinne, Oldendorf/Luhe S. Reizopoulou 9 M. Thessalou-Legaki- A. Nicolaidou ( ~ ) Zoological Laboratory, University of Athens, Panepistimiopolis, GR- 15784 Athens, Greece Introduction Mediterranean coastal lagoons are relatively enclosed water bodies. Situated between the land and the sea, they are under the influence of both the marine and the terrestrial environment. Among the main character- istics of coastal lagoons is their shallowness, the shelter from currents and waves, the soft substratum and the well mixed water column due to wind action (Barnes 1980). Lagoons are often nutrient rich (Fiala 1973; Mee 1978) both as a result of input of nutrients by rivers and by recycling between sediment and water mass, facili- tated by their shallowness (Murphy and Kremer 1985; Nowicki and Nixon 1985). Thus, coastal lagoons are organically enriched areas where high biomass and productivities are attained (Barnes 1980). As opposed to high abundance, however, diversity is low. This is of particular importance in the oligotrophic eastern Mediterranean which is generally characterised by low abundance and high diversity (Bellan-Santini 1985). Environmental conditions in coastal lagoons are very changeable due to their confinement from the open sea and to their shallowness. In this sense they could be considered a stressed environment. Further- more, being close to land, they are vulnerable to human disturbance (Bellan 1972; Stora and Arnoux 1983) Correlation between organic enrichment and com- munity characteristics over the years has led to a series of empirical models which describe the impact of or- ganic disturbance on benthic communities (Pearson and Rosenberg 1978; Gray 1989). It is generally be- lieved that increased organic enrichment will result in (a) a decrease in the species richness and an increase in the number of individuals, as a result of high densities of few opportunistic species, and (b) a reduction of biomass, except for a small increase at the peak of opportunists. Based on these principles a great number of methods have been proposed in order to describe and quantify the effects of pollution (Warwick 1986;