There was no significant effect of day vs. night deployments on tissue nitrogen increase of deployed algae. However, the date and depth of deployment, as well as their interaction, had a significant effect on the change in percent dry weight tissue nitrogen in Ulva during outplant experiments (Table 1). In general, at all depths, the increase in percent tissue nitrogen was significantly lower and similar between depths on the warmer days of August 9 and 10, and
significantly higher and different between depths on the cooler days of August 12, 14, and 15, with deeper outplants showing significantly greater tissue nitrogen increase on cooler days. For example, there was no significant difference in tissue nitrogen with deployment depth for August 9, 10, or 13, when average water temperature was above 16.5 °C at all depths (Figs. 3 and 4). Also, mid-water and surface algae showed no significant increase in tissue nitrogen when
temperatures at both depths remained above a 16.8 °C average (i.e.,on August 11 and 15), while tissue nitrogen of bottom algae on those days significantly increased when water cooled below 15.8 °C during the day and night at the 10 m deployment depth (Figs. 3 and 4).However, when both mid-water and bottom temperatures dropped below 15.8 °C, mid-water algae grouped with the bottom, rather than
the surface, deployments (i.e., on August 12 and 14). Therefore, the
significant depth-date interaction effect on tissue nitrogen of the
deployed algae appeared to be controlled by the mid-water
temperature. If water cooled below 15.8 °C at the mid-water depth
(5 m) along with the bottom (10 m) on that date, then mid-water
algae deployments showed a significant increase in tissue nitrogen
along with bottom deployments. On the other hand, on dates when
mid-water temperatures did not drop below 15.8 °C during the algae
deployment, tissue nitrogen of mid-water deployments was similar to
surface deployments.