CONTROL OF GAMETE RELEASE IN FUCOID ALGAE - SENSING HYDRODYNAMIC CONDITIONS VIA CARBON ACQUISITION

We investigated the environmental factors providing signals for gamete re lease in fucoid algae, with a particular focus on the inhibitory e ffect of water motion. The release of gametes by Focus distichus occur red in still water under high light and was associated with the deplet ion of dissolved inorganic carbon (DIC) in tide pools isolated from th e ocean during daytime low tides. Diurnal patterns of gamete release t hat lasted for 2-3 d, as in natural populations, were found in recepta cles cultured in a 12 h light:12 h dark photoperiod under calm conditi ons or in a simulated tidal regime. Constant light disrupted the diurn al component of release, however, suggesting that an endogenous circad ian periodicity was absent. The effects of increased [DIC] on cultured receptacles under calm conditions were similar to the inhibitory effe cts of high water motion; both conditions reduced release in several s pecies from both tide pool and intertidal habitats. Bicarbonate concen tration, rather than carbon dioxide, or carbonate, was shown to be the component of the DIC system most closely correlated (inversely) with gamete release in the intertidal fucoid Pelvetia compressa. The hypoth esis that gamete release is triggered by DIC depletion in the unstirre d boundary layer during periods of low water motion in the light was f urther supported by experiments with P. compressa. These showed that g amete release was not inhibited by high water motion when DIC was abse nt. In the same experiments, high water motion inhibited release at 2 and 20 mmol/L DIC, confirming that the sensitivity of gamete release t o water motion is DIC dependent. The ability of fucoid algae to couple physiological processes (e.g., photosynthesis) with life history even ts (gamete release) allows external fertilization to occur under favor able hydrodynamic conditions, and may contribute greatly to reproducti ve success in organisms inhabiting periodically turbulent environments .