Life history of Porphyra hollenbergii Dawson (Bangiales, Rhodophyta) from the Gulf of California, Mexico

The life history of Porphyra hollenbergii Dawson, a species endemic to the Gulf of California (Mexico), was investigated in relation to temperature, photoperiod and photon fluence rates. The hypothesis was that its life history is controlled by extremes of temperature (< 10 degrees C to > 30 degrees C), photoperiod (short/neutral/long) and photon fluence levels (low/high light). Culture experiments were set up using a factorial 5 x 5 x 3 design with five photon fluence levels (10, 20, 40, 60 and 80) mu mol photons m(-2) s(-1)), five temperatures (10, 15, 20, 25 and 30 degrees C) and three photoperiods [8:16, 12:12 and 16:8 light:dark (L:D)]. For the gametophyte phase, the optimal release of zygotospores was at 15 degrees C, with photon fluence level of 60 mu mol photons m(-2) s(-1) and long photoperiod 16:8 L:D. Germination was best at 20 degrees C, a photon fluence level of 60 mu mol photons m(-2) s(-1) and under a long photoperiod 16:8 L:D. The abundance of archeospores differed significantly at temperatures of 25 and 30 degrees C. The number of archeospores mm(-2) of the conchocelis tufts was significantly different in the long photoperiod 16:8 L:D when compared with the neutral 12:12 and short 8:16 L.:D. The abundance of conchosporangia at temperatures of 15, 25 and 30 degrees C were different and differed from the other conditions. In addition, abundance of conchosporangia mm(-2) were significantly different in all photoperiod treatments. Conchospores were released after 6 weeks at 10 degrees C, 20 mu mol photons m(-2) s(-1) at 8:16 L:D. On the basis of our results, we found that water temperatures were the limiting factor for conchocelis growth. However, it is the combination of photoperiod and high water temperatures that are the environmental conditions that appear to control the development of archeospores and conchospores. Porphyra hollenbergii life history is controlled by an array of factors at each stage, strongly suggesting the environmental influence of the habitat on this species.