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Due to specific geomorphologic characteristics of the Dalmatian coast type, formed primarily from karst limestone, Eastern Adriatic coast shows great diversity of habitats. This diversity is also influenced by the position of the Adriatic Basin, stretching from northwest to southeast, climatic differences along its length, and the direction of sea currents. Habitats in the submerged karst characteristic for the Croatian side of the Adriatic Sea are anchihaline caves, sea caves, cold sea caves and pits with bathyal elements, vruljas, karst estuaries, submerged river canyons, submerged tuffa barriers, marine lakes, and bare karst in the sea. Though sea caves, vruljas, coralligen, marine lakes, and Posidonia beds are today threatened by direct and indirect anthropogenic influences (pollution, eutrophication, tourism, nautical tourism, coastal development, aquaculture), only a few of these habitats have been declared as areas of special interest for conservation or as threatened habitats under the relevant international conventions. There are still too few targeted studies that could contribute to better understanding of these habitats and their levels of threat. Therefore, some of these specific and valuable habitats are in danger to be destroyed before they can be investigated (1). Sea caves, vruljas, and coralligen are quite inaccessible and, therefore, there is insufficient information on the organisms living there. The mechanisms how deep-sea organisms settle into cold-water sea caves and how they survive and reproduce in these caves are insufficiently investigated. All the ecological factors which result in such a large diversity of sponges in the semi-dark cave communities are also unknown. Preliminary research of anchihaline caves shows that it might be possible that karstification processes occur just beneath the sea surface (2). Marine lakes, ecologically separate from the surrounding sea due to limited contact, are very rare at the eastern Adriatic coast and, therefore, very threatened. The benthos of these lakes includes a small number of organisms that have very large populations, which is contrary to what we find in the surrounding sea. All the preliminary research has proven these habitats to be very interesting.

The sponges Oopsacas minuta (Hexactinellida) and Asbestopluma hypogea (Demospongiae, Cladorhizidae) belong to groups that are typical of deep water, but both species have already been recorded from the shallow water Trois Pepes cave at La Ciotat (Marseille area). We here report on subsequent findings of A. hypogea in two other littoral caves: one at Garmenjak Island in the Middle Adriatic (Croatia), the other at Jarre Island (Marseille, France). The maximum temperatures experienced in situ by these populations are significantly higher than those from the deep Mediterranean Sea, but they are also up to 6°C higher than those reported for the Trois Pepes cave population, up to 23.1 °C in July 2002 for Garmenjak population and 22.8 °C in August 2004 for Jarre population (exposures from a few hours to a few days). The average summer temperature inside both caves remains several degrees lower than the outside temperature at the same depth. Long time survival of A. hypogea populations at the relatively high summer/autumn temperatures in both Jarre cave (4 years monitoring) and Garmenjak cave (5 years monitoring) indicates that the species can successfully colonise such shallow habitats in spite of its presumed deep-water origin. We also report of additional cave records of O. minuta from the Middle Adriatic (Croatia): at Hvar Island in the marine part of the Živa Voda anchialine cave, and from the marine caves at Iski Mrtovnjak, Lastovo and Fraskeric Islands. The wide distribution of this species in the deep Mediterranean is substantiated by a record on Santa Lucia Bank north of Corsica (303 m) and photographs taken by the submersible Cyana in the Central Tyrrhenian Sea (2912 m, 2845 m) and the Ionian Sea (2447 m). Possible colonisation patterns of littoral caves by both sponges are discussed.

The Croatian coastal karst abounds in submerged caves that host a variety of environmental conditions depending on the geomorphology, depth and submarine groundwater discharge. One example is the Y-Cave, a shallow, mostly submerged, horizontal cave on Dugi Otok Island, on the eastern Adriatic coast. This study was aimed at examining the temporal and spatial variability of the marine cave environment, including temperature, salinity, light intensity, cave morphology and hydrodynamism, along with the dissolutional effect caused by the mixing of sea and freshwater. The general distribution of organisms in the Y-Cave was positively correlated to the light gradient and reduced water circulation, thus the highest species diversity and abundance were recorded in the front part of the cave. The phylum Porifera was the most dominant group, and the poriferan species diversity in the cave ranks among the ten highest in the Mediterranean. The middle part of the cave, although completely dark, hosts an abundant population of the gastropod Homalopoma sanguineum and clusters of the gregarious brachiopod Novocrania anomala, whose presence could be connected to tidal hydrodynamics. The absence/scarcity of sessile marine organisms and pronounced corrosion marks at shallow depths inside the cave suggest a freshwater impact in the upper layers of the water column. A year long experiment with carbonate tablets revealed three different, independent ongoing processes affected by the position in the cave: bioaccumulation, dissolution and mechanical erosion. The results of long-term temperature readings also revealed water column stratification within the cave, which was not disturbed by either tidal or wave action. The shallow, partly submerged and relatively small Y-Cave is characterised by a suite of complex environmental conditions, which, together with the resulting distribution of organisms, are unique to this cave.

In late summer and early autumn of 1989 benthic mortality in the upper part of Krka estuary extended from the Skradinski buk waterfalls to approximately 5 km downstream. Dead benthic organisms were found on the bottom at depths of up to 4.5 m. During August, a freshwater phytoplankton bloom was recorded in Visovac lake (which supplies the Skradinski buk waterfalls). The green tide in the lake was composed of up to 11.9 million cells. 1--1, predominantly of Synedra acus and Dinobtyon sertularia. At that time the maximal total inflow of phytoplankton cells through the waterfalls was approx. 0.41 S-I (38000 1. d-1). Cells of these two species died after reaching the salt wedge and the cummulative effect of their decomposition apparently caused an oxygen demand sufficient enough to trigger the benthic mortality. Due to the water mass dynamics, the spreading of mortality downstream was slow (from August to October, approx. 5 km). Certain benthic fishes (like Gobius sp.) were observed on the bottom of the affected area in mid-October 1989.

The Adriatic Sea can be considered as a large, mostly shallow embayment of the Mediterranean Sea. The latitudinal SE-NW extension of the Adriatic results in considerable climate differences along its coast. In this work we compiled the listof sponges from classes Demospongiae and Homoscleromorpha recorded in the Adriatic up to now: we performed a thor-ough literature check and we added the results of our decade long research with a special emphasis on sponge fauna inmarine caves. All the records were assigned to the North, Middle or South Adriatic according to their geographic location,and the analysis showed a very high similarity among the sponge fauna of the 3 areas. The likeness between the N. andthe M. Adriatic is over 83 %, between the M. and the S. Adriatic over 76 % and between the N. and the S. Adriatic over66 %. Altogether 283 species of sponges from these two classes (our field data and literature survey) have been recordedin the whole Adriatic up to now, which is a considerably higher number than in previous reviews. Among the 125 speciesthat we found so far in our research along the Croatian coast, 77 were found in marine caves. We are still discovering spe-cies not previously found in the Adriatic Sea (especially from cryptic habitats) and here we report 15 new records for the Adriatic Sea, 9 of which were noted only in caves.

This study examined the impact of fish farming on foraminiferal communities in the Adriatic coastal zone. Samples were taken directly beneath the farm, near the edge of the farm, and at a reference station away from the farm. The foraminiferal community near the farm is characterized by Epistominella exigua, Globocassidulina subglobosa, Haynesina germanica and the genera Elphidium, Bulimina and Brizalina. These foraminiferal species are less abundant seaward. Asterigerinata mamilla, Neoconorbina terquemi and genus Cibicides are almost absent below the cages. Total phosphorus (TP) and total nitrogen (TN) in the sediments decrease with distance from the cages. The abundances of E. exigua, G. subglobosa, H. germanica and the genera Elphidium, Bulimina and Brizalina are correlated with TP and TN, indicating their dependence on nutrient input. The absence of A. mamilla, N. terquemi and the genus Cibicides below the cages is a due to a degraded Posidonia community. According to our study, foraminiferal community composition can be used as indicator of organic enrichment caused by fish farm activities.

With the intention of reconstructing Late Pleistocene – Holocene sea-level changes along the Eastern Adriatic coast, a series of speleothems were collected from several submerged caves and pits, in order to constrain periods of their deposition and ceased growth related to sea-level fluctuations. For that purpose, stalagmites provide more reliable records than stalactites, due to their successive layers deposited perpendicularly to the growth direction. Therefore, stalagmites have been collected preferably. But, two of 17 speleothems displayed unexpected interior morphology – speleothem L-1 collected at the depth of 1.5 m in Medvjeđa spilja Cave on Losinj Island, and speleothem M-25 from Pit near Iski Mrtovnjak Islet collected at the depth of 25 m. Both of the samples were taken from the cave floor, in the growth position of the stalagmite. But the insight into the perpendicular cut with evident central tube revealed their true (stalactitic) origin and additional confirmations were obtained by longitudinal cut and U-Th and 14C dating. Just as the causes of their breakdowns were probably different, so were their falls; speleothem M 25 (together with several other speleothems around it) stuck in the marine sediment in its primary position, while L-1 turned upside-down and even continued crystallizing during the lower sea level. These events are possible in the continental caves, as well. Evidently, it is much easier to recognize and avoid these problems in air-filled caves than in the submarine ones where the speleothems are almost always covered with marine overgrowth, which disguises their outer morphology. Additionally, the bases of the stalagmites are also sometimes covered with marine sediment, which makes correct estimation rather difficult.