Recovery processes of the brown alga Fucus gardneri following the 'Exxon Valdez' oil spill: settlement and recruitment

The 1989 'Exxon Valdez' oil spill and subsequent cleanup efforts left many shorelines in Prince William Sound (Alaska, USA), especially in the higher tidal zones, mostly devoid of the dominant intertidal alga Fucus gardneri. Settlement and recruitment processes of F. gardneri were studied to determine the factors that can limit F. gardneri recolonization. Zygote settlement rates were initially lower at oiled sites relative to unoiled sites, but increased to values similar to those for unoiled sites in the lower intertidal zones after 3 yr. In the upper intertidal, settlement rates after 3 yr had not yet converged with those at unoiled sites. The low settlement rates of F. gardneri at oiled sites were probably due to low densities of reproductive plants and limited egg dispersal. Settlement was also negatively correlated to net flow of water. The effect of substrate rugosity on settlement was investigated by using grooved ceramic tiles. We found that grooves enhance survival and recruitment of germlings in the high intertidal zone. Germlings survived best initially in deep, narrow grooves. After 2 yr there were more recruits in medium width, deep grooves. Manipulation of F. gardneri canopy over tiles revealed that F. gardneri canopy ameliorated heat and desiccation stress, but a whiplash effect dislodged small plants. Overall the positive effects of canopy were stronger than the negative effects. There were no significant herbivore effects on germling survival, but both recruitment and average thallus size were increased in the absence of herbivores.