Ecological characteristics of the Mljet Islands seawater lakes (South Adriatic Sea) with special reference to their resident populations of medusae

Abstract

SUMMARY: Ecological properties and distribution and abundance of medusae were studied over an 18-month period in the Mljet Island seawater lakes, south-east Croatia. Strong stratification during the summer differentiates these lakes from the oligotrophic South Adriatic ecosystem. The lakes are designated as a moderately eutrophicated ecosystem. Very small numbers of hydromedusae were noted, representing only the Anthomedusae and Leptomedusae. A new species of the genus Tima was found in considerable numbers of individuals. High abundance of the scyphomedusa Aurelia sp. was observed throughout the year. This species differs in terms of genetic divergence from Aurelia aurita found elsewhere in the Mediterranean and could be attributed to the boreal origin.

Hypoxia in deep waters of moderately eutrophic marine lakes, Island of Mljet, eastern Adriatic Sea

“…2B, C). A similar finding was reported by Benović et al (2000). The only water that is denser than the near-bottom water of BL in October (σ T 28.81 kg m -3 , depth ≥43 m) was situated below the depth of 44 m in G (σ Tmax 28.83 kg m -3 , depth of 49 m) in March (Fig.…”

“…Anoxia below 39 m in BL in the period 26-28 August 1996 (Benović et al 2000) did not last for long and wintertime cooling homogenized the entire water column. Quiescent or slowly moving speciemens within a swarm of Aurelia sp.…”

“…The arrangement of data concerning the mixing and stratification periods and water column division was adjusted to be comparable to the recent report on WRT in the MLs (Cuculić et al 2012), while offering an extension to parts of the research that revealed an anoxic event in deep water of BL more than a decade ago (Benović et al 2000). Anoxia in the water of the MLs was not detected after August 1996 and vertical homogenization has been noted to occur regularly since 2003 (Vilibić et al 2010).…”

Population study of the fan shell <i>Pinna nobilis</i> L. in Malo and Veliko Jezero of the Mljet National Park (Adriatic Sea)

“…It also has a more restricted exchange of water with the open sea and therefore a higher water residence time. According to Benović et al (2000), zooplankton densities were constantly higher in Malo Jezero than in Veliko Jezero, especially during the spring and summer. The factors described above point to potentially more food sources for P. nobilis in Malo Jezero than in Veliko Jezero and this could be a factor influencing the difference in densities.…”

“…Malo Jezero is connected with Veliko Jezero through a shallow and narrow channel, which is in turn connected to the surrounding open sea through a somewhat deeper and wider channel. Detailed descriptions of the environmental conditions in these two inlets are given in Benović et al (2000).…”