ABSTRACT1. Rhodolith beds, unattached coralline reefs, support a high diversity and abundance of marine species from both hard and soft benthos. We used surveys in multiple shallow (3-20 m) beds in the Gulf of California to (1) examine seasonal patterns in associated floral and faunal diversity and abundance, (2) compare differences in faunal associations between rhodolith beds and adjacent sedimentary habitats, (3) examine the importance of complexity of rhodolith structure to community structure, and (4) estimate the impact of anthropogenic disturbance on rhodoliths and associated species.2. Macroalgal richness was seasonal, and beds supported higher richness in winter (to 36 species) than summer (6-7 species), primarily due to foliose red algae. Strong seasonal variation in the abundance of dominant cover organisms was due to a shift from macroalgae and mat-forming colonial invertebrate species to microalgae.3. The community in a rhodolith bed of high-density thalli (El Coyote average $11000 thalli/ m À2 ) had higher richness (52 versus 30 species) and abundance of epibenthic and crypto-and infaunal species compared with an adjacent sand community. Species diversity and abundance was particularly high for unique cryptofaunal organisms associated with rhodolith interstices. Cryptofauna reached average densities of 14.4 organisms/ cm À3 rhodolith, the majority of which were crustaceans, polychaetes and cnidarians along with rhodolith-specific chitons.4. Results from sampling across a range of rhodolith morphs in the El Requeson bed (with lower average cryptofaunal densities of 2.3 organisms/ cm À3 ) revealed that the total organisms supported by a rhodolith significantly increased with both complexity (branching density) and space available (thallus volume). These data suggest that reducing the population size structure, structural complexity and cover of living rhodoliths could decrease species richness and abundance.5. While disturbance is a natural feature of these free-living beds, increased anthropogenic disturbance from trawling, anchoring and changes in water quality can directly impact the bed community through substrate alteration. Commercial fishing threatens rhodolith beds in the Gulf of California by decreasing rhodolith size and increasing sedimentation and burial rates. In addition to

Seagrasses, although well adapted for submerged existence, are C0,-limited and photosynthetically inefficient in seawater. This leads to high light requirements for growth and survival and makes seagrasses vulnerable to light limitation. We explored the long-term impact of increased CO, availability on light requirements, productivity, and C allocation in eelgrass (Zostera marina 1.1. Enrichment of seawater CO, increased photosynthesis 3-fold, but had no longterm impact on respiration. By tripling the rate of light-saturated photosynthesis, CO, enrichment reduced the daily period of irradiance-saturated photosynthesis (Hsat) that is required for the maintenance of positive whole-plant C balance from 7 to 2.7 h,

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Efecto de la temperatura sobre las tasas de fotosíntesis, crecimiento y calcificación del alga coralina de vida libre Lithophyllum margaritae