Effects of wave surge on growth and nutrient uptake in the green seaweed Ulva pertusa were measured in small tanks fed natural seawater via a dump bucket that could be either locked in place to deliver water continuously, or set to tip at particular volumes. Rates of bulk water flow through the tanks were low (<13 mm s -1 ), as may be typical of highly sheltered marine and estuarine environments. At the maximum bulk flow rates tested, wave surge increased growth in wet mass 1.6-fold. Wave surge increased the rate of ammonium uptake 1.5-fold over the full range of bulk flow rates tested (0.2 to 2.9 mm s -1 ). In winter, when light probably limited U. pertusa in our outdoor cultures, growth in wet mass was relatively unaffected by wave surge and completely unaffected by the experimental addition of nutrients (N and P). However, in summer, when ambient nutrients probably limited growth, wave surge increased growth in wet mass at low (0.21 mm s -1 ) and high (4.06 mm s -1 ) bulk flow rates, and nutrients increased growth rates at low but not high bulk flow rates. Together, these results indicate that the effect of wave surge on U. pertusa at low bulk flow rates (ca. < 2 mm s -1 ) is to enhance the seaweed's access to nutrients. However, at higher bulk flow rates wave surge has a different effect, which we speculate is due either to provision of a micronutrient or removal of an inhibitory substance from the concentration boundary layer. Our work demonstrates how the lack of small-scale water movement in sheltered habitats can constrain seaweed growth.

Total amounts and patterns of bromoisoxazoline alkaloids of Aplysina sponges from Croatia (Mediterranean Sea) were analyzed along an underwater slope ranging from 1.8 to 38.5 m. Total amounts of alkaloids varied from sample to sample and showed no correlation with depth. In contrast, striking differences of alkaloid patterns were found between sponges from shallow sites (1.8 - 11.8 m) and those collected from deeper sites (11.8 - 38.5 m). Sponges from shallow depths consistently exhibited alkaloid patterns typical for Aplysina aerophoba with aerophobin-2 (2) and isofistularin-3 (3) as main constituents. Sponges from deeper sites (below 11.8 m) resembled Aplysina cavernicola with aerothionin (4) and aplysinamisin- 1 (1) as major compounds. The typical A. cavernicola pigment 3,4-dihydroxyquinoline- 2-carboxylic acid (6), however, could not be detected in A. aerophoba sponges but was replaced by the A. aerophoba pigment uranidine (5) which appeared to be present in all sponge samples analyzed. During transplantation experiments sponges from sites below 30 m featuring the A. cavernicola chemotype of bromoisoxazoline alkaloids were translocated to shallower habitats (10 m). The alkaloid patterns in transplanted sponges were found to be stable over a period of 12 months and unaffected by this change in depth. In a further experiment, clones of Aplysina sponges from shallow depths of 5 - 6 m resembling the A. aerophoba chemotype were either kept in situ under natural light conditions or artificially shaded by excluding photosynthetically active radiation (PAR). Neither 4 nor 1 were detected in artificially shaded sponges over an observation period of 12 months. In summary, two chemically distinct types of Aplysina sponges were discovered in this study that proved to be remarkably stable with regard to the bromoisoxazoline patterns and unaffected either by changing the light conditions or depth. It is not clear presently whether the Aplysina sponges collected from depths < 11.8 m represent a new chemotype of A. cavernicola lacking the pigment 6 or whether we have incidentally come across a so far undescribed species of the genus Aplysina.