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Increased atmospheric carbon dioxide leads to ocean acidification and carbon dioxide (CO.sub.2) enrichment of seawater. Given the important ecological functions of seagrass meadows, understanding their responses to CO.sub.2 will be critical for the management of coastal ecosystems. This study examined the physiological responses of three tropical seagrasses to a range of seawater pCO.sub.2 levels in a laboratory. Cymodocea serrulata, Halodule uninervis and Thalassia hemprichii were exposed to four different pCO.sub.2 treatments (442-1204 μatm) for 2 weeks, approximating the range of end-of-century emission scenarios. Photosynthetic responses were quantified using optode-based oxygen flux measurements. Across all three species, net productivity and energetic surplus (P.sub.G:R) significantly increased with a rise in pCO.sub.2 (linear models, P < 0.05). Photosynthesis-irradiance curve-derived photosynthetic parameters-maximum photosynthetic rates (P.sub.max) and efficiency (α)-also increased as pCO.sub.2 increased (linear models, P < 0.05). The response for productivity measures was similar across species, i.e. similar slopes in linear models. A decrease in compensation light requirement (E.sub.c) with increasing pCO.sub.2 was evident in C. serrulata and H. uninervis, but not in T. hemprichii. Despite higher productivity with pCO.sub.2 enrichment, leaf growth rates in C. serrulata did not increase, while those in H. uninervis and T. hemprichii significantly increased with increasing pCO.sub.2 levels. While seagrasses can be carbon-limited and productivity can respond positively to CO.sub.2 enrichment, varying carbon allocation strategies amongst species suggest differential growth response between species. Thus, future increase in seawater CO.sub.2 concentration may lead to an overall increase in seagrass biomass and productivity, as well as community changes in seagrass meadows., Author(s): Y. X. Ow[sup.1] [sup.2] , C. J. Collier[sup.1] [sup.3] , S. Uthicke[sup.2] Author Affiliations: (1) College of Marine and Environmental Science, James Cook University, 4811, Townsville, QLD, Australia (2) [...]

Effects of acclimation to projected near-future ocean acidification (OA) conditions on physiology, reproduction and development were investigated in the tropical sea urchin Echinometra mathaei. Following 6 weeks in control or one of the three elevated pC[O.sub.2] ([pH.sub.NIST] 7.5-8.1; pC[O.sub.2] ~ 485-1,770 µatm) conditions, adult urchins exhibited a slight decline of growth in low pH treatments and moderately reduced respiration at intermediate levels. At 7 weeks, gametes from adults were used to produce larvae that were reared in their respective parental treatments. To assess whether larvae from acclimated parents are more resilient to elevated pC[O.sub.2] than those not acclimated, larvae from control animals were also reared in the elevated pC[O.sub.2] treatments. There was no difference in female 'spawnability' and oocyte size between treatments, but male spawning ability was reduced in increased pC[O.sub.2] conditions. In elevated pC[O.sub.2] treatments, the percentage of normal larvae and larval size decreased in the progeny of control- and elevated pC[O.sub.2]-acclimated parents, and arm asymmetry increased. Thus, acclimation of the parents did not make the progeny more resilient or sensitive to OA effects. Negative effects of increased pC[O.sub.2] on reproduction and development may impact on recruitment and population maintenance of this species., Introduction Present-day atmospheric C[O.sub.2] concentrations are over 30% higher than the maximum observed in the previous 2 Mil years (Honisch et al. 2009). A large percentage of C[O.sub.2] is absorbed [...]

The seasonality of asexual reproduction in Holothuria atra and Stichopus chloronotus was examined through calculation of fission rate and population densities on the Great Barrier Reef. High fission rates were obtained during the winter season with peak values occurring between May and July. Several factors such as water temperature, physical disturbance, population density and nutrient supply influence the periodicity of reproduction.

Summary: Foraminifera host diverse microbial communities that can shift in response to changing environmental conditions. To characterize climate change impacts on the foraminifera microbiome across life stages, we exposed adult Marginopora vertebralis (Large Benthic Foraminifera) to pCO2 and temperature scenarios representing present‐day, 2050 and 2100 levels and raised juveniles under present‐day and 2050 conditions. While treatment condition had no significant effect on the seawater microbial communities, exposure to future scenarios significantly altered both adult and juvenile microbiomes. In adults, divergence between present‐day and 2050 or 2100 conditions was primarily driven by a reduced relative abundance of Oxyphotobacteria under elevated temperature and pCO2. In juveniles, the microbial shift predominantly resulted from changes in the proportion of Proteobacteria. Indicator species analysis identified numerous treatment‐specific indicator taxa, most of which were indicative of present‐day conditions. Oxyphotobacteria, previously reported as putative symbionts of foraminifera, were indicative of present‐day and 2050 conditions in adults, but of present‐day conditions only in juveniles. Overall, we show that the sensitivity of the M. vertebralis microbiome to climate change scenarios extends to both life stages and primarily correlates with declines in Oxyphotobacteria and shifts in Proteobacteria under elevated temperature and pCO2. [ABSTRACT FROM AUTHOR]