Over 30% of the Antarctic continental shelf is permanently covered by floating ice shelves, providing aphotic conditions for a depauperate fauna sustained by laterally advected food. In much of the remaining Antarctic shallows (<300 m depth), seasonal sea-ice melting allows a patchy primary production supporting rich megabenthic communities dominated by glass sponges (Porifera, Hexactinellida). The catastrophic collapse of ice shelves due to rapid regional warming along the Antarctic Peninsula in recent decades has exposed over 23,000 km(2) of seafloor to local primary production. The response of the benthos to this unprecedented flux of food is, however, still unknown. In 2007, 12 years after disintegration of the Larsen A ice shelf, a first biological survey interpreted the presence of hexactinellids as remnants of a former under-ice fauna with deep-sea characteristics. Four years later, we revisited the original transect, finding 2- and 3-fold increases in glass sponge biomass and abundance, respectively, after only two favorable growth periods. Our findings, along with other long-term studies, suggest that Antarctic hexactinellids, locked in arrested growth for decades, may undergo boom-and-bust cycles, allowing them to quickly colonize new habitats. The cues triggering growth and reproduction in Antarctic glass sponges remain enigmatic.

The trophic response of the scleractinian coral Pocillopora meandrina (Dana, 1846) to large amplitude internal waves (LAIW) was investigated in the Andaman Sea. Corals living on the western sides of the Similan Islands (Thailand) exposed to LAIW showed significantly higher biomass and protein content than sheltered corals on the eastern sides. LAIW-exposed corals were also more heterotrophic, displaying lower δ 13 C ratios in their tissues and higher rates of survival in artificial darkness compared to sheltered counterparts. Heterotrophic nutrition in concert with photosynthesis leads to higher energy reserves in corals from LAIW-exposed reefs, making them more resilient to disturbance. As these differences in trophic status are due to LAIW-enhanced fluxes of organic matter, LAIW may play an important role in supporting coral metabolism and survival in these monsoon beaten reefs.KEY WORDS: Large amplitude internal waves · Corals · Heterotrophic plasticity · Current regime · Pocillopora meandrina · Andaman Sea Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 412: [113][114][115][116][117][118][119][120][121][122][123][124][125][126][127][128] 2010 solved organic materials (Muscatine et al. 1989, Grottoli 2002.Along with photosynthesis, heterotrophy enhances skeletal (Houlbrèque et al. 2003) and tissue growth by building up energy stores including lipids (Anthony 2006, Treignier et al. 2008 and proteins , Houlbrèque et al. 2003. Heterotrophy has been shown to support coral photosynthesis (Grottoli 2002, Borell et al. 2008) and resilience to stresses such as turbidity (Anthony 2006), warming (Borell et al. 2008) and bleaching , Palardy et al. 2008. Although active feeding does not generally constitute the dominant carbon source for zooxanthellate corals, it may reduce temporary energy deficits (Anthony 2000) so that corals with a high capability to heterotrophically assimilate carbon may be more effective in surviving multiple bleaching events and become dominant in future reefs .The relative proportion of heterotrophy in coral metabolism may vary markedly between species , and has been documented in several studies. For example, Wellington (1982) observed that the branching coral Pocillopora damicornis grew independent of zooplankton supply, and was more markedly affected by shading than the massive coral Pavona clavus. Sebens & Johnson (1991) documented higher zooplankton capture rates by Madracis decactis with increasing current strength, but not by Meandrina meandrites. showed that the δ 13 C ratios of Montipora capitata host tissue decreased when bleached because of increased heterotrophic feeding, while Porites compressa did not alter its nutrition. Moreover, Palardy et al. (2008) observed that the feeding response to one disturbance may vary significantly between different coral species.The importance of heterotrophic feeding in coral metabolism may further vary between environments (Palardy et al. 2005). Decreasing light and photosynthesis (Mus...

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Cold-water corals provide an important habitat for a rich fauna along the continental margins and slopes. Although these azooxanthellate corals are considered particularly sensitive to ocean acidification, their responses to natural variations in pH and aragonite saturation are largely unknown due to the difficulty of studying their ecology in deep waters. Previous SCUBA investigations have shown an exceptionally shallow population of the cold-water coral Desmophyllum dianthus in near-surface waters of Comau Fjord, a stratified 480 m deep basin in northern Chilean Patagonia with suboxic deep waters. Here, we use a remotely operated vehicle to quantitatively investigate the distribution of D. dianthus and its physico-chemical drivers in so far uncharted naturally acidified waters. Remarkably, D. dianthus was ubiquitous throughout the fjord, but particularly abundant between 20 and 280 m depth in a pH range of 8.4 to 7.4. The persistence of individuals in aragonite-undersaturated waters suggests that present-day D. dianthus in Comau Fjord may show pre-acclimation or pre-adaptation to conditions of ocean acidification predicted to reach over 70% of the known deep-sea coral locations by the end of the century.

Underwater video transects have become a common tool for quantitative analysis of the seafloor. However a major difficulty remains in the accurate determination of the area surveyed as underwater navigation can be unreliable and image scaling does not always compensate for distortions due to perspective and topography. Depending on the camera setup and available instruments, different methods of surface measurement are applied which make it difficult to compare data obtained by different vehicles. 3-D modelling of the seafloor based on 2-D video data and a reference scale can be used to compute subtransects dimensions. Focussing on the length of the subtransect, the data obtained from 3-D models created with the software PhotoModeler Scanner are compared with those determined from underwater acoustic positioning (Ultra-Short BaseLine – USBL) and bottom tracking (Doppler Velocity Log – DVL). 3-D models building and scaling was successfully conducted on all three tested setups while the distortion of the reference scales due to substrate roughness was identified as the main source of imprecision. Acoustic positioning was generally inaccurate and DVL unreliable on rough terrain. Subtransect lengths assessed with PhotoModeler were on average 20% longer than those derived from the USBL due to the higher spatial resolution and the inclusion of slope. On a high relief wall, DVL and 3-D modelling yielded similar results. At present, 3-D modelling is the most powerful, albeit the most time-consuming, method for the accurate determination of video subtransect dimensions