Knowledge and implications of global change in the oceans for biology, ecology, and ecosystem services - Ocean Sustainability in the 21st Century - page 141

4.3.5 Kelp forests
Kelp forests occur along the majority of the world's temperate coastlines, and are among the
mostphyletically diverseandproductivesystemsintheocean(Steneck et al., 2002 ).Climat-
ic variables such as temperature and precipitation play an important role in controlling local
and regional scale differences in population dynamics and species distributions. In many
coastal areas where humans have altered chemical and biological conditions, however, kelp
forests have been replaced by mats of turf-forming algae (Airoldi and Beck, 2007 ). While
kelp canopies inhibit turfs (Russell, 2007 ), developing theory explains shifts from canopy to
turf domination as a function of reduced water quality which enables the cover of turf to ex-
pand spatially and persist beyond its seasonal limits (Gorman et al., 2009 ) , subsequently in-
hibiting the recruitment of kelp and regeneration of kelp forests. Connell and Russell ( 2010 )
reveal that kelp loss may be exacerbated, on human-dominated coasts, by the positive ef-
fects of increasing CO 2 and temperature on kelp inhibitors. Altering global (i.e. CO 2 ) and
local (i.e. eutrophication) stressors in combination can allow turfs to expand to more rapidly
to occupy space made available due to the reduction of kelp forests (Russell et al., 2009 ). As
algal turfs can inhibit kelp recruitment (Connell and Russell, 2010 ), any phenological shift
that allows turfs to persist through periods of kelp recruitment is likely to reduce the resi-
lience of kelp forests to disturbance. When the canopy is lost, there are profound changes
to local environmental conditions, with cascading effects on the ecosystem diversity and
functioning. Recently, Wernberg and collaborators ( 2010 ) revealed that a successful mitiga-
tion of negative effects of global warming is strictly related to an understanding of the link
between physiological and ecological responses of kelp species. Metabolic adjustment may
assist Australasian kelp beds to persist and maintain abundance in warmer waters, while it is
evident that there is a reduction in the physiological responsiveness of kelps to perturbation
and of canopy recovery from disturbances by reducing the ecological performance of kelp
recruits.