Appendix A. Description of S. compressa’s life history and methods used to culture embryos.
Life history: S. compressa individuals are iteroparous and relatively long-lived (4–8 years; Gunnill, 1980). On the central California coast, peak reproduction typically occurs November through May. Although reproductive individuals can be found throughout most of the year, recruitment to macroscopic stages is low and sporadic (Johnson and Brawley 1998; personal observation). Mortality of S. compressa zygotes and germlings in natural populations is extremely high, and previous work has demonstrated the vulnerability of early post-settlement stages to abiotic stresses associated with exposure to the air at low tide (Brawley and Johnson 1991, Davison et al. 1993, Johnson and Brawley 1998).
Terminology and culturing of embryos: I use the terminology recommended by Brawley and Johnson (1991) to describe early development in S. compressa: a fertilized egg is a zygote until germination or formation of the rhizoid (approximately 12–14 h post-fertilization), after which time the individual is considered an embryo. S. compressa embryos were obtained by collecting either (1) mature receptacles clipped from individuals in the field or (2) entire individuals (e.g., for the lab desiccation trials, described below). Receptacles were maintained in the dark at 4 degrees C for 48–72 hours before gamete release was induced using standard methods (Jaffee 1954): fronds were placed in beakers or Nalgene tubs under bright sunlight or florescent lights for 3–5 hours, until the accumulation of air bubbles on the surface of the thallus was visible. Each individual was then placed in a separate beaker with freshly filtered seawater in the dark for approximately 15 minutes, during which gamete release and subsequent self-fertilization of eggs occurred.
LITERATURE CITED
Brawley, S. H., and L. E. Johnson. 1991. Survival of fucoid embryos in the intertidal zone depends upon developmental stage and microhabitat. Journal of Phycology 27(2):179–186.
Davison, I. R., Johnson, L. E., and S. H. Brawley. 1993. Sublethal stress in the intertidal zone: tidal emersion inhibits photosynthesis and retards development in embryos of the brown alga Pelvetia fastigiata. Oecologia 96(4):483–492.
Gunnill, F. C. 1980. Demography of the intertidal brown alga Pelvetia fastigiata in Southern California USA. Marine Biology 59(3):169–180.
Jaffe, L. F. 1954. Stimulation of the discharge of gametangia from a brown alga by change from light to darkness. Nature 174:743.
Johnson, L. E., and S. H. Brawley. 1998. Dispersal and recruitment of a canopy-forming intertidal alga: the relative roles of propagule availability and post-settlement processes. Oecologia 117(4):517–526.