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- Environmental factors influencing distribution and morphology of rhodoliths in Bahia Concepcion, B.C.S., Mexico
- Aerial and SCUBA diving observations revealed numerous, dense concentrations of free living, branched, nongeniculate coralline algae (rhodoliths) at depths of 3–12 m in Bahía Concepción, B.C.S., México. Plants were up to 10 cm in size, and commonly occurred at high densities forming a near continuous layer overlying a mixture of calcareous fragments and sediment. In contrast to other geographic regions, rhodolith shape remained spherical along depth-related gradients of water motion and sedimentation. Branch density and size, however, generally decreased with increasing depth. Surveys, as well as transplant and movement experiments, suggested that broad scale (east vs. west shore) and depth distribution of rhodolith beds within the bay are controlled by water motion and sedimentation. Additional experimental and taxonomic studies are needed to understand the smaller scale distribution patterns, and among and within bed variation in plant size and branch density. Such studies will allow a more rigorous interpretation of paleoenvironments based on the morphology of fossil rhodoliths.
- Steller, 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