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

Abstract

Sporophyte recrultment, holclfast growth and mortality of giant kelp Macrocyst~spynfera were measured seasonally on permanent transects at 3 sltes [protected Intermediate and exposed) along a wave exposure gradient on the Monterey Peninsula, c e n t~a l Cal~fornia (USA) between 1988 and 1991 The constant presence of cold, nutnent-nch water and the relative absence of o t h e~ kelps and large grazers allowed the dynanucs of M pynfera populations to be examined under conditions in which wave exposure was highly vanable and ~nfluences of other abiotlc and biotic factors were minimized Recovery of M pynfera populations fiom decreased adult density (presumably due to stormlnduced mortality, adult density was negatively correlated with storm activity) was a 2-stage process requiring the establishment of luvenile populations and condit~ons suitable for ]uvenile growth to adult size Sporophyte recrultment was negatively correlated with M pynfera canopy cover, and thus appeared to be related to irradiance Recruitment was low and continuous under a temporally stable M pyrifera canopy at the protected slte At the intermediate and exposed sites, canopy cover was more variable, canopy loss was greater, and durdt~ons of low canopy cover were longer than at the protected site resulting in episodic sporophyte recruitment These distinct patterns in sporophyte lecruitment resulted In continuous luvenile populations at the protected site and intermittent luvenlle populations at the intermediate and exposed sites Growth of luveniles to adult size required additional irrad~ance probably d u e to gleater light requirements for luvenlle growth than for sporophyte recrultment We observed that luveniles grew to adult slze when canopy cover was low and adults were below a threshold denslty estimated at -10 plants 100 m 2 , but ~uveniles also occasionally grew to adult size following periods of low canopy cover only Ep~sodic sporophyte recruitment at the intermediate and exposed sites resulted in decreased coincidence of the 2 recovery stages, adult dens~ties were often decreased below threshold piior to the establishment of luvenile populations Recovery time, that required by populations to return to densities above threshold was equal to the time lag between occurrence of the 2 recovery stages and was therefore greatest at the more exposed sites Compansons between central and southern Cal~tornia M pyl~fera populat~ons suggest that by altering recovery time variable frequency and magnitude of storm disturbance may result in different periodlclties of adult population cycles K E Y WORDS. Glant kelp. Macrocyst~spyr~fera . Wave exposure. Demography. Recruitment. Recovery

Distributional expansion ofCarpophyllum flexuosumonto wave‐exposed reefs in north‐eastern New Zealand

“…This may be a result of bias towards high density sites when making initial site selections. These demographic and morphological trends are similar to those reported for populations of Macrocystis pyrifera across a wave exposure gradient (Graham et al 1997). Predicted mean residence times differed by an order of magnitude between sheltered and exposed populations, but since our tagging study spanned only 12 months it is likely that extreme weather events can play a significant role in the prevention of establishment or eradication of C. flexuosum populations.…”

Organic enrichment of submarine‐canyon and continental‐shelf benthic communities bymacroalgal drift imported from nearshore kelp forests

“…The slopes of both regression equations were significantly different from zero at P < 0.001. All other components were derived from combinations of the above measurements: blade fragments equalled 0.3 of a whole blade; all stipes and fronds were assigned a length of 3 m; all stipe bundles and frond bundles were assigned 20 stipes per bundle (based on stipe and frond counts of living, attached plants from a long-term ecological monitoring program described in Graham et al 1997).…”

“…The diameter of holdfasts counted in the surveys could not be determined from videotapes, so holdfast diameter data from a long-term ecological monitoring program (Graham et al 1997) were used to infer the size of holdfasts in the canyon.…”

A influência da passagem de uma frente meteorológica na distribuição da macrofauna bentônica mesolitoral de uma praia arenosa exposta

“…Deste modo, a zonação das espécies de praias arenosas com características dissipativas parece não estar associada à variação temporal das características do perfil praial. Graham et al (1997) acompanharam um evento meteorológico e concluíram que a alta mortalidade de indivíduos adultos da população de Macrocystis pyrifera durante um período de tormentas está negativamente correlacionada com a densidade da espécie. Nesse caso, a tempestade tem o papel de promover o controle da comunidade (Graham et al 1997).…”

“…Graham et al (1997) acompanharam um evento meteorológico e concluíram que a alta mortalidade de indivíduos adultos da população de Macrocystis pyrifera durante um período de tormentas está negativamente correlacionada com a densidade da espécie. Nesse caso, a tempestade tem o papel de promover o controle da comunidade (Graham et al 1997). Simulando uma situação extrema de alteração das características do sedimento pela pesca de Donax serra, Schoeman et al (2000) removeram artificialmente grandes quantidades de areia, verificando a recuperação da macrofauna bentônica em um período de 7 a 16 dias após o impacto.…”