G. Hernandez-carmona et al., Restoration techniques for Macrocystis pyrifera (Phaeophyceae) populationsat the southern limit of their distribution in Mexico, BOTAN MARIN, 43(3), 2000, pp. 273-284
Following the 1982-83 Fl Nino, Macrocystis pyrifera (L.) C. Agardh, forests
disappeared throughout their range in Baja California. The giant kelp fore
sts subsequently recovered within this range except at their extreme southe
rn limit, a region encompassing 50 km of coastline with a former giant kelp
standing stock of 28,000 wet tons. Two techniques were tested to restore t
hese forests: juvenile transplantation and seeding with sporophylls. For tr
ansplanting, juvenile M. pyrifera sporophytes were attached to Eisenia arbo
rea stumps seasonally over a two-year period. Average survival of transplan
ts ranged from 7% in spring to 41% in winter. After two years, the average
number of basal fronds per plant increased from 2 to 64 per plant and surfa
ce fronds from 0 to 34 per plant. Average frond growth rate of the transpla
nts ranged from 8.1 cm day(-1) in summer to 10.8 cm day(-1) in winter. No s
ignificant differences in growth rate were found among treatments (seasons)
for the transplants, but control plants showed a seasonal variation, with
higher frond growth rates in winter (13.3 cm day(-1)) and spring (9.3 cm da
y(-1)) and lower in summer (4.4 cm day(-1)). The seeding technique was test
ed in a fully orthogonal-block design with three factors with two levels (f
actors: + sporophylls addition, +/- Eisenia arborea and +/- understory alga
e). Macrocystis pyrifera recruitment occurred only in treatments with added
sporophylls. The highest recruitment occurred where all algae were removed
from the bottom, followed by the treatments without understory algae but w
ith Eisenia arborea. This results suggest that a lack of spores and the pre
sence of understory algae were the main factors inhibiting Macrocystis pyri
fera recruitment in the area. Lower sea water temperatures and high nutrien
t concentrations occurred in spring and high temperatures and low nutrients
in summer suggesting, as in southern California, an inverse relationship b
etween these two factors. The results suggest a combined approach of transp
lanting juveniles and seeding during spring would be most effective for res
toring the M. pyrifera forests.