Large colonies of the bryozoan Pentapora fascialis (Pallas, 1766) growing inside the plume of submarine freshwater springs (vruljas) have been surveyed. In the Velebit Channel, P. fascialis grows only under the influence of a vrulja's outflow, at depths from 1 m to 35 m. We have investigated the water chemical composition and temperature of each vrulja's plume. The amount of nutrients, carbonates, and temperature of the vruljas' plumes were measured during three different seasons in 2002 and 2003. All measured nutrients had considerably higher concentrations inside the vruljas than in the seawater (9.185 ± 7.111 mmol/m 3NO 3 - in vruljas and 1.109 ± 0.949mmol/m 3NO 3 - in the seawater; 7.911 ± 8.316mmol/m 3SiO 4 in vruljas and 1.643 ± 1.330mmol/m 3SiO 4 in the seawater; 1.757 ± 1.496mmol/m 3NH 4 + in vruljas and 1.141 ± 1.299mmol/m 3NH 4 + in the seawater; 0.116 ± 0.119mmol/m 3NO 2 - in vruljas and 0.105 ± 0.106mmol/m 3NO 2 - in the seawater and 0.102 ± 0.189mmol/m 3PO 4 3- in vruljas and 0.025 ± 0.013mmol/m 3PO 4 3- in the seawater). Furthermore, the amount of total CO 2, HCO 3 - and dissolved CO 2 was higher inside the plume (2.570 ± 0.436mmol/l total CO 2 in vruljas and 2.270 ± 0.441 mmol/l total CO 2 in the seawater; 2.431 ± 0.479mmol/l HCO 3 - in vruljas and 2.003 ± 0.549mmol/l HCO 3 - in the seawater and 0.044 ± 0.034mmol/l dissolved CO 2 in vruljas and 0.017 ± 0.012mmol/l dissolved CO 2 in the seawater), while CO 3 2- had lower values inside vruljas' plumes than in the seawater (0.098 ± 0.075 mmol/l CO 3 2- in vruljas and 0.202 ± 0.081 mmol/l CO 3 2- in the seawater). The temperature of the vruljas' outflow was low and constant throughout the year and varied between 9.76 and 14.02°C, while the seawater temperature at 23 m varied between 8.22 and 23.52°C. The period of vruljas' inactivity was only 5.6 days per year which means that P. fascialis must be permanently adapted to grow in the conditions of fluctuating, lower salinity. © 2005 Taylor & Francis Group.