No abstract

Submarine lava flows on the leeward flank of the Island of Hawai'i, USA, were examined by submersible and remotely operated vehicles to understand the structure and development of deep-water coral communities. Three sites were selected where historically documented lava flows crossed older prehistoric flows, providing 3 pairs of lava substrates of different ages (61/ 400 yr, 134/2000 yr, 143/2330 yr) to compare and contrast with a nearby older coral community (15 000 yr) growing on fossil carbonate. The number of coral taxa, abundance, and colony size increased with substrate age on the 3 historical lava flows and fossil carbonate site, but not on the prehistoric flows. The faster-growing Coralliidae were the dominant taxa forming patches on the peaks of ridged terrain, while the slower-growing Antipatharia and Isididae were less abundant except at the fossil site where the community was dominated by the slowest-growing corals (including Kulamanamana haumeaae). A multivariate analysis of similarity of coral communities on lava flows found site, rather than substrate age, to be a better explanation for why paired flows were ecologically the same despite considerable age differences. The data suggest that hot, turbid, mineral-rich water from the more recent historical lava event re-initialized the community succession of the adjacent prehistoric lava substrate. Coral mortality would be greatest close to the edge of the historical flow with the expectation that survivorship would increase with distance from the impact. The survey transects were too short to detect a significant increase in the total coral community, but an increase was evident for the Coralliidae.

Little is known about effects of large storm systems on mesophotic reefs. This study reports on how Typhoon 17 (Jelawat) affected Ryugu Reef on Okinawa-jima, Japan in September 2012. Benthic communities were surveyed before and after the typhoon using line intercept transect method. Comparison of the benthic assemblages showed highly significant differences in coral coverage at depths of 25-32 m before and after Typhoon 17. A large deep stand of Pachyseris foliosa was apparently less resistant to the storm than the shallower high diversity area of this reef. Contradictory to common perception, this research shows that large foliose corals at deeper depths are just as susceptible to typhoon damage as shallower branching corals. However, descriptive functional group analyses resulted in only minor changes after the disturbance, suggesting the high likelihood of recovery and the high resilience capacity of this mesophotic reef.