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

Abstract

The 1989 'Exxon Valdez' oil spill and subsequent cleanup efforts left many shorelines in Prince Willlam Sound (Alaska, USA), especially In the higher tidal zones, mostly devoid of the domlnant intertidal alga FLICUS gardneri. Settlement and recruitment processes of F. gardnel-j were studied to determine the factors that can limit F. gardneri recolonizat~on Zygote settlement rates wel-e ~nitially lower a t oiled sites relative to unoiled sites, but increased to values similar to those for uno~led 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 limitcd e g g dispersal. Settlement wds also negatively correlated to net flow of water The effect of substrate rugos~ty on settlement was investigated by using grooved ceramlc 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 recrults in medium width, deep grooves. Manipulation of F. gardneri canopy over tiles revealed that F, gal-dneri canopy ameliorated heat and desiccation stress, but a whiplash effect dislodged small plants. Overall the posltive effects of canopy were stronger than the negative effects. There were no significant herbivore effects on gerrnling survival, but both recruitment and average thallus size were increased in the absence of herbivores.

Recovery of the brown alga Fucus gardneri following a range of removal intensities

“…We have shown that substrate temperatures are considerably higher on bare rock than under intact Fucus canopies. The amelioration of physical stress by adults often improves Fucus germling survival Johnson, 1991, 1993;van Tamelen et al, 1997). Furthermore, reproductive adults are an important source of local recruits in species with short-distance dispersal such as Fucus (Ang, 1991a).…”

“…Canopy-forming algae have also been shown to enhance (McCook and Chapman, 1991;Albrecht and Reise, 1994) or suppress (Dethier and Duggins, 1988) herbivore abundance, and thus may indirectly influence recovery rates, but herbivore abundances in our experiment did not differ between treatments. Similarly, the removal of Fucus canopies often leads to blooms of other algal species (Southward and Southward, 1978;van Tamelen et al, 1997), which may suppress recovery. Ephemeral algal cover was weakly, if at all, correlated with the initial disturbance intensity in our experiment.…”

“…Studies to date have focused on the effect of presence versus absence of adult cover, but generally have not examined the effect of a range of adult cover densities on recovery. However, limited evidence suggests the effect of these processes may not necessarily be linear over a range of adult densities; in the absence of adult canopy, Fucus germling survivorship decreased non-linearly with increasing microclimate desiccation stress (van Tamelen et al, 1997). Here, we test the net effect of a range of disturbance intensities, manifested as experimental canopy reductions, on the recovery of F. gardneri.…”

Exxon Valdez oil spill: impacts and recovery in the soft-bottom benthic community in and adjacent to eelgrass beds

“…These included reductions in the abundance and Cover by the dominant intertidal alga Fucus gardnen and reductions to a suite of intertidal infauna and epifauna (e.g. De Vogelaere & Foster 1994, Gilfillan et al 1995, Highsrnith et al 1996, van Tamelen et al 1997. Assemblages of infauna from oiled mixed-soft beaches and epifauna from oiled sheltered rocky shores were essentially recovered by the Summer of 1991; sites subjected to high-pressure hot-water washing remained in early stages of recovery for both infauna and epifauna by the summer 1992 .…”

Disturbance and subsequent recovery of mid-shore assemblages on seasonal, tropical, rocky shores

“…Several studies of colonisation and subsequent recovery, the stage at which assemblage structure in disturbed areas reaches the same state as adjacent undisturbed areas, of newly created free space have focused on the events that result in space being made available, including scouring of the substrate (Shanks & Wright 1986, McQuaid & Dower 1990, McCook & Chapman 1993, van Tamelen 1996, periods of high heat stress (Isaac 1933, Menge & Sutherland 1987, storm damage (Dayton 1971, Alvarado et al 2001) and oil spills (Stirling 1977, Southward & Southward 1978, van Tamelen et al 1997. The unpredictable nature of disturbance events, however, often makes it difficult to follow an assemblage from its pre-disturbance phase to its re-colonisation and subsequent recovery.…”