The availability of colonizable substrate is an important driver of the temporal dynamics of sessile invertebrates on coral reefs. Increased dominance of algae and, in some cases, sponges has been documented on many coral reefs around the world, but how these organisms benefit from non-colonized substrate on the reef is unclear. In this study, we described the temporal dynamics of benthic organisms on an Indonesian coral reef across two time periods between 2006 and 2017 (2006–2008 and 2014–2017), and investigated the effects of colonizable substrate on benthic cover of coral reef organisms at subsequent sampling events. In contrast with other Indonesian reefs where corals have been declining, corals were dominant and stable over time at this location (mean ± SE percentage cover 42.7 ± 1.9%). Percentage cover of turf algae and sponges showed larger interannual variability than corals and crustose coralline algae (CCA) (P < 0.001), indicating that these groups are more dynamic over short temporal scales. Bare substrate was a good predictor of turf cover in the following year (mean effect 0.2, 95% CI: 0–0.4). Algal cover combined with bare space was a good predictor of CCA cover the following year generally, and of sponge cover the following year but only at one of the three sites. These results indicate that turf algae on some Indonesian reefs can rapidly occupy free space when this becomes available, and that other benthic groups are probably not limited by the availability of bare substrate, but may overgrow already fouled substrates.

Mixing in Ellis Fjord, Vestfold Hills, East Antarctica, is controlled by processes which are influenced by the extent of ice formation. A study of water temperature and salinity at a site near the middle of the fjord was undertaken from May 1994 to February 1995 after a summer (1993–94) in which the ice cover of the fjord was largely retained. Vertical mixing resulting from the exclusion of salt during the limited winter formation of ice was insufficient to mix completely the non-meromictic basins of the fjord. In contrast, a previous study during a winter with far more ice production recorded much stronger vertical mixing throughout the fjord. Warming and freshening of the fjord during the 1994–95 summer, when the ice again did not melt significantly, was attributable to the flow of warmer, less saline water along the fjord. This process was probably related to the formation of tidal jets at the narrow and shallow entrance to the fjord, and was thus influenced by the ice conditions around the entrance. These jets would also have introduced significant amounts of extra-fjord water (along with any resident biota) into the fjord.