Experiments were done to determine if ammonium, phosphate and feeding on Artemia nauplii affected the population density of symbiotic algae (zooxanthellae) in the Red Sea coral Stylophora pistillata . Corals were incubated for 14 days under natural sunlight at reduced intensity in running seawater aquaria. The seawater was continuously spiked to give final concentrations of either 20 μM ammonium or 2 μM phosphate, or both. A second set of similarly treated corals was also fed Artemia nauplii daily. Population density of zooxanthellae in corals spiked with ammonium, or ammonium plus phosphate, approximately doubled, and the ratio of zooxanthellae carbon: nitrogen decreased. Phosphate supplementation alone had no effect. The increase in zooxanthellae numbers was linearly proportional to the increase in protein in zooxanthellae, suggesting that availability of inorganic nitrogen leads to increased protein synthesis in zooxanthellae. Feeding on Artemia alone or together with phosphate had no effect on the population density of zooxanthellae. Feeding on Artemia and ammonium produced a small increase in population density but it was not statistically significant. The small effect could be due to insufficient influx of ammonium in fed animals, or growth of both animal and algae resulting in little or no net change in the population density of zooxanthellae. The results are consistent with the hypothesis that the growth of zooxanthellae in S. pistillata from the Red Sea is nitrogen limited.

We review the status of marine shellfish ecosystems formed primarily by bivalves in Australia, including: identifying ecosystem-forming species, assessing their historical and current extent, causes for decline and past and present management. Fourteen species of bivalves were identified as developing complex, three-dimensional reef or bed ecosystems in intertidal and subtidal areas across tropical, subtropical and temperate Australia. A dramatic decline in the extent and condition of Australia’s two most common shellfish ecosystems, developed by Saccostrea glomerata and Ostrea angasi oysters, occurred during the mid-1800s to early 1900s in concurrence with extensive harvesting for food and lime production, ecosystem modification, disease outbreaks and a decline in water quality. Out of 118 historical locations containing O. angasi-developed ecosystems, only one location still contains the ecosystem whilst only six locations are known to still contain S. glomerata-developed ecosystems out of 60 historical locations. Ecosystems developed by the introduced oyster Crasostrea gigas are likely to be increasing in extent, whilst data on the remaining 11 ecosystem-forming species are limited, preventing a detailed assessment of their current ecosystem-forming status. Our analysis identifies that current knowledge on extent, physical characteristics, biodiversity and ecosystem services of Australian shellfish ecosystems is extremely limited. Despite the limited information on shellfish ecosystems, a number of restoration projects have recently been initiated across Australia and we propose a number of existing government policies and conservation mechanisms, if enacted, would readily serve to support the future conservation and recovery of Australia’s shellfish ecosystems.

The representation of the Northern Hemisphere (NH) storm tracks and jet streams and their response to climate change have been evaluated in climate model simulations from Phases 3, 5, and 6 of the Coupled Model Intercomparison Project (CMIP3, CMIP5, and CMIP6, respectively). The spatial patterns of the multimodel biases in CMIP3, CMIP5, and CMIP6 are similar; however, the magnitudes of the biases in the CMIP6 models are substantially lower. For instance, the multimodel mean RMSE of the North Atlantic storm track for the CMIP6 models (as measured by time-filtered sea-level pressure variance) is over 50% smaller than that of the CMIP3 models in both winter and summer, and over 40% smaller for the North Pacific. The magnitude of the jet stream biases is also reduced in CMIP6, but by a lesser extent. Despite this improved representation of the current climate, the spatial patterns of the climate change response of the NH storm tracks and jet streams remain similar in the CMIP3, CMIP5, and CMIP6 models. The SSP2-4.5 scenario responses in the CMIP6 models are substantially larger than in the RCP4.5 CMIP5 models, which is consistent with the larger climate sensitivities of the CMIP6 models compared to CMIP5.

No abstract