Impact of Physical Factors on Periodic Reproduction for Hawaiian Algae Ulva fasciata Delile and Enteromorpha intestinalis (L.) Link

Algae > Volume 11(3); 1996 > Article

Algae 1996;11(3): 325-332.

Hyun-Woung Shin, Celia M. Smith

Department of Botany, University of Hawaii

ABSTRACT

Aspects of the periodicity and fecundity of reproduction for Ulva fasciata and Enteromorpha intestinalis were investigated at two sites. The Kaealawai site was exposed to higher tide levels than the second site, Kahala Beach, although both are geographically closely situated on the southern coast of Oeahu, Hawaiei. At the Ka'alawai site, thalli of Ulva fasciata liberated biflagellate gametes or quadriflagellate spores continuously during the highest tides of the month, and were routinely subjected to tidal exposure through this daily investigation. At the Kahala site, thalli of E. intestinalis and U. fasciata had less predictable patterns of motile cells production. The Kahala site was a shallow subtidal site rarely exposed by low tides. Gametes and spores were occasionally produced by separate thalli on the same day at both sites, indicating some regularity in the life history phases for these populations. The typical ratio of reproductive to vegetative areas was 4.91 for U. fasciata thalli for the ka'ala'wai site. The typical thallus of U. fasciata produced = 4.5 to 5.4 x 10 super(8) motile cells. The n umber of sporulating cells in 1 mm super(2) of tissue was 3315. Each sporulating cells by physical treatments was also investigated to identify some of the important factors leading to cell formation and release for laboratory manipulation. Incubation in a cool temperature (14℃) in the dark consistently induced the highest number of motile cells to be released from tissues of both U. fasciata and E. intestinalis. Dim room light (50 μmol m super(-2) s super(-1)) and cold temperature (-4℃) treatments resulted in fewer cells released than in the 14℃ treatment, but higher numbers than under laboratory desiccation or hyposalinity treatments. In this study, laboratory manipulations confirm that plants respond to cues even if they are not present in the natural environment. Production of numerous spores per plant is clearly an adaptive strategy for ecological success for these weedy algae.

Key words: Enteromorpha intestinalis, gamete, motile cell, physical factors, spore, Ulva fasciata