Population dynamics of giant kelp Macrocystis pyrifera along a wave exposure gradient

摘要: Sporophyte recrultment, holclfast growth and mortality of giant kelp Macrocyst~spynfera were measured seasonally on permanent transects at 3 sltes [protected Intermediate exposed) along a wave exposure gradient the Monterey Peninsula, c e n t ~ l Cal~fornia (USA) between 1988 1991 The constant presence cold, nutnent-nch water relative absence o h kelps large grazers allowed dynanucs M pynfera populations to be examined under conditions in which was highly vanable ~nfluences other abiotlc biotic factors minimized Recovery fiom decreased adult density (presumably due stormlnduced mortality, negatively correlated with storm activity) 2-stage process requiring establishment luvenile condit~ons uitable for ]uvenile size recrultment canopy cover, thus appeared related irradiance Recruitment low continuous temporally stable pyrifera protected slte At intermediate exposed sites, cover more variable, loss greater, durdt~ons longer than site resulting episodic sporophyte recruitment These distinct patterns lecruitment resulted In intermittent luvenlle sites Growth luveniles required additional i r rad~ance probably gleater light requirements We observed that grew slze when adults below threshold denslty estimated -10 plants 100 m 2 , but ~uveni les also occasionally following periods only Ep~sodic coincidence recovery stages, dens~t ies often piior time, by return densities above equal time lag occurrence stages therefore greatest Compansons central southern Cal~tornia pyl~fera populat~ons suggest altering variable frequency magnitude disturbance may result different periodlclties population cycles K E Y WORDS. Glant ke lp . Macrocyst~spyr~fera Wave exposure. Demography. Recruitment. INTRODUCTION motion, temperature, nutrients, light) ( .g competition, grazing, self-shading) facRecent investigations dynamics tors life history species Macrocystispyrjfera (hereafter Macrocystis) (Foster 1982, Dayton et al. 1984, 1992, Foster & Schiel have addressed effects various abiotic (e.g. 1985, Dean Jacobsen 1986, Deysher 1989, Reed 1990). Most these studies, however, been done regions where several 'Present addressUn~versity California San Diego, Scripps Institution Oceanography 0208, La Jo]la, limiting naturally CO-vary. For example, tern92093, USA. E-mail mgraham@ucsd edu perature nutrient levels CO-vary Cali"Addressee reprints. E-mail: charroId@mbayaq.org fornia (Jackson 1977, Zimmerman Robertson 1985), O Inter-Research 1997 Resale full t~c not pe rm~t ed Mar Ecol Prog Ser 148: 269-279, their Macrocystis during El Nifio events are confounded increased (Tegner 1987). Under such circumstances, it impossible isolate individual or interactions populations. Although many studies effect macroalgal populations, most so qualitative estimates Quantitative provide both an unbiased assessment among-site differences exposure, as well accurate temporal record activity (i.e. storms). Seymour (1989) first quantify estimating waves. They horizontal orbital velocities corresponded California. Along is thought strong role regulating community structure Kimura Harrold 1988), quantification spatial variability good correlative test nearshore environment Peninsula offers unique setting study motion Macrocystis. Large occurs frequently California; some experience high (large, waves) much year. This sharp contrast disturbances described (Seymour 1989). Furthermore, upwelling tidal flushing from submarine canyons nutrient-rich throughout year (Traganza 1981, Breaker Broenkow 1994). Temperatures rarely exceed those detrimental reproduction (Deysher 1986), juvenile (Kopczak 1991), (Zimmerman 1985). Also, since re-establishment sea otter this coast late 1960s, urchin grazing has minimal isolated, last documented episode occurring 1986 (Watanabe 1991). Finally, (1988) understory stipitate Pterygophora californica, common competitor space (Dayton 1984), sparsely distributed north Peninsula. context, intra-specific competition remain primary region (Kimura 1988). Our objectives (1) examine relationship comparing recruitment, holdfast growth, its macroscopic California, (2) response recovery) popula ion~ density. Lastly, we compared our results previous work offer potential explanation divergent among