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- Restoration techniques for Macrocystis pyrifera (Phaeophyceae) populations at the southern limit of their distribution in Mexico,
- Following the 1982-83 El Nino, Macrocystis pyrifera (L.) C. Agardh, forests disappeared throughout their range in Baja California. The giant kelp forests subsequently recovered within this range except at their extreme southern 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 these forests: juvenile transplantation and seeding with sporophylls. For transplanting, juvenile M. pyrifera sporophytes were attached to Eisenia arborea stumps seasonally over a two-year period. Average survival of transplants 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 surface fronds from 0 to 34 per plant. Average frond growth rate of the transplants ranged from 8.1 cm day -1 in summer to 10.8 cm day -1 in winter. No significant 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 day -1) and lower in summer (4.4 cm day -1). The seeding technique was tested in a fully orthogonal-block design with three factors with two levels (factors: ± sporophylls addition, ± Eisenia arborea and ± understory algae). 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 with Eisenia arborea. This results suggest that a lack of spores and the presence of understory algae were the main factors inhibiting Macrocystis pyrifera recruitment in the area. Lower sea water temperatures and high nutrient concentrations occurred in spring and high temperatures and low nutrients in summer suggesting, as in southern California, an inverse relationship between these two factors. The results suggest a combined approach of transplanting juveniles and seeding during spring would be most effective for restoring the M. pyrifera forests., Cited By (since 1996):22, CODEN: BOTNA, ,
- Hernández-Carmona, García, Robledo, Foster
- Diversity and natural history of a Lithothamnion muelleri-Sargassum horridum community in the Gulf of California
- We quantitatively assessed the relative contribution of the rhodolith form of Lithothamnion muelleri, a likely foundation species, to macroorganism diversity in a community also inhabited by the large fucalean Sargassum horridum at a site near Cabo Los Machos at the mouth of Bahía Concepción, Baja California Sur, Mexico. The composition and abundance of seaweeds, epibenthic invertebrates, and fish were estimated in March and October 2003, and invertebrates within rhodoliths (cryptofauna) in March 2003. Rhodoliths and Sargassum horridum had the highest cover of all organisms within the 0.5-km 2, 2-8-m-deep cobble-sand site. A total of 29 species of seaweeds, 40 taxa of benthic invertebrates, and 33 species of fish were sampled in transects and quadrats. Macroalgal and fish diversity were similar between sampling times as a result of loss and replacement of taxa, but benthic invertebrate diversity declined without replacement from March to October. Rhodolith cover was similar at both sampling times. The cover and density of S. horridum were highly seasonal, and the non-rhodolith flora changed from abundant S. horridum (35% cover) in March to abundant red algal turf in October (22% cover). The sea urchin Arbacia incisa, tunicates, and polychaetes were the most abundant epibenthic invertebrates in March, but declined by October, the former to zero. Grunts (Haemulon maculicauda) and porgies (Calamus brachysomus) were the most abundant fish at both sampling times, but there were large temporal changes in some other species, especially schooling fishes. Rhodolith density in March was 24 ind m -2, with numerous individuals >8 cm diameter. Fifteen rhodoliths from a range of size classes contained 114 cryptofaunal taxa with an average of 40 taxa /individual in the largest rhodoliths. These results show the importance of rhodolith habitat to diversity, the large temporal changes in some assemblages, and the exceptionally high diversity of this subtropical community.
- Foster, McConnico, Lundsten, Wadsworth, Kimball, Brooks, Medina-López, Riosmena-Rodríguez, Hernández-Carmona, Vásquez-Elizondo, Johnson, Steller