Abstract

Seamounts and knolls are ‘undersea mountains’, the former rising more than 1000 m from the seafloor. These features provide important habitats for aquatic predators, demersal deep-sea fish and benthic invertebrates. However most seamounts have not been surveyed and their numbers and locations are not well known. Previous efforts to locate and quantify seamounts have used relatively coarse bathymetry grids. Here we use global bathymetric data at 30 arc-sec resolution to identify seamounts and knolls. We identify 33,452 seamounts and 138,412 knolls, representing the largest global set of identified seamounts and knolls to date. We compare estimated seamount numbers, locations, and depths with validation sets of seamount data from New Zealand and Azores. This comparison indicates the method we apply finds 94% of seamounts, but may overestimate seamount numbers along ridges and in areas where faulting and seafloor spreading creates highly complex topography. The seamounts and knolls identified herein are significantly geographically biased towards areas surveyed with ship-based soundings. As only 6.5% of the ocean floor has been surveyed with soundings it is likely that new seamounts will be uncovered as surveying improves. Seamount habitats constitute approximately 4.7% of the ocean floor, whilst knolls cover 16.3%. Regional distribution of these features is examined, and we find a disproportionate number of productive knolls, with a summit depth of<1.5 km, located in the Southern Ocean. Less than 2% of seamounts are within marine protected areas and the majority of these are located within exclusive economic zones with few on the High Seas. The database of seamounts and knolls resulting from this study will be a useful resource for researchers and conservation planners.

Research highlights

? The identification of 33,452 seamounts and 138,412 knolls. ? Global seamount habitats represent 4.7% of the ocean floor. ? Knoll habitat covers 16.3% of the ocean floor. ? Seamounts on the high seas are in need of protection

Over centuries, the ocean has been studied from outside, either on the coast or on board. The latest development in marine technology has enabled longterm observations inside the ocean. The paper briefly discusses how the systems of seafloor observatories and mobile observing platforms offer unprecedented opportunities for all fields of ocean researchers. To this new trend, China has to pay its closest attention to the course of developing ocean science in the country.

几百年来，人类总是从海洋外面——在船上或者岸上研究海洋。随着技术的最新发展，人类现在可以从海洋内部来研究海洋。简要讨论了海底观测系统和活动观测平台为各领域的海洋研究提供的空前机遇，并指出中国发展海洋科学必须对这一新趋势给予密切注意。

Abstract

We studied in a deep-sea megafaunal community the relationship of different trophic variables to the depth ranges inhabited by and depth zonation of species, after the ordination of fish and decapod crustaceans in feeding guilds. The variables studied included trophic level of species, food sources exploited, mean weight of predators and prey, feeding intensity and dietary diversity of species. We compiled data on the diets of 18 species of fish and 14 species of decapod crustaceans distributed between 862 and 2261 m in the Catalano-Balearic Basin (Western Mediterranean). Feeding guilds were identified for fish and decapods separately and at two depth strata (862–1400 and 1400–2261 m). The zonation rates (degree of depth overlap) between species within each trophic guild differed by guild and taxon (fish and decapods). The three guilds (G1, G2 and G3) of decapod crustaceans showed quite significantly distinct overlap. G1 (plankton feeders) showed the widest overlap (1326–1381 m) and G3 (benthos feeders) the narrowest (330–476 m). Among the four guilds established for fish, G1, comprising larger predators such as sharks, showed the lowest overlap (between 194 and 382 m). Macrourids overlap ranged between 122 and 553 m, the rest of benthopelagic feeders ranged between 423 and 970 m, and G3 (benthos feeders) gave overlaps between 867 and 1067 m. Significant differences were detected between the depth overlap of most feeding guilds excluding the paired comparisons between G1/macrourids, and G2/G3. Among decapods higher zonation rates (=lower depth overlap) were identified in those guilds occupying higher trophic levels (TL), with a similar, though not as general, trend among fish. In the ordination of species in feeding guilds, TL as indicated byδ¹⁵N measurements, was significantly correlated with Dimension 1 (D1) of ordination—MDS-analysis, both in fish and decapods at 862–1400 m. However, deeper (at 1400–2261 m), D1 was not significantly correlated with TL but with the mean weight of predator and prey in fish. In general, TL was again the main explanatory variable (accumulated variances,r², explained by multi-linear regression—MLR-models between 0.54 and 0.69) both of the zonation rates and the depth ranges occupied by megafauna (fish and decapods together) throughout all the depth range studied. Possible relationships between zonation rates/depth distributions and other biological variables (i.e. egg size, fecundity) are also discussed.

Abstract

The cold-water scleractinian coralsLophelia pertusa andMadrepora oculata form mound structures on the continental shelf and slope in the NE Atlantic. This study is the first to compare the taxonomic biodiversity and ecological composition of the macrobenthos between on- and off-mound habitats. Seven box cores from the summits of three mounds and four cores from an adjacent off-mound area in the Belgica Mound Province in the Porcupine Seabight yielded 349 species, including 10 undescribed species. On-mound habitat was three times more speciose, and was richer with higher evenness and significantly greater Shannon's diversity than off-mound. Species composition differed significantly between habitats and the four best discriminating species werePliobothrus symmetricus (more frequent off-mound),Crisia nov. sp,Aphrocallistes bocagei andLophelia pertusa (all more frequent on-mound). Filter/suspension feeders were significantly more abundant on-mound, while deposit feeders were significantly more abundant off-mound. Species composition did not significantly differ between mounds, but similarity within replicates decreased from Galway Mound

Abstract

Long-term (?1-year) records obtained by seabed observatories (BOBO) and repeated (24-h) CTD casts show the presence of a highly energetic environment in and around two cold-water carbonate-mound provinces, on the Southwest and Southeast Rockall Trough (SW and SE RT) margin. Carbonate mounds, covered with a thriving coral cover, are embedded mainly in the Eastern North Atlantic Water (ENAW) and are observed in a confined bathymetric zone between 600 and 1000 m water depth. Cold-water corals seem to be restricted in their growth by temperature and food availability. The presence of living corals on top of the carbonate mounds appears linked to the presence of internal waves and tidal currents in the water column, and consequently carbonate mound structures are shaped by the local hydrodynamic regime. Mound clusters have an elongated shape perpendicular to the regional contours and corresponding to the direction of the highest current speeds. On the SW RT margin temperature, salinity and current speed reflect a diurnal tidal pattern, causing maximum temperature variations at 900 m depth of more than 3 °C. Current speeds up to 45 cm s⁻¹ occur, and a residual current of 10 cm s⁻¹ is directed along the slope to the southwest. At the SE RT margin the temperature of the bottom water fluctuates more than 1 °C with a semi-diurnal tidal cyclicity. Amplitudes of average and peak current speeds here are comparable with those measured on the southwest margin, but the residual current in this area is directed to the northeast. Tidal currents and internal waves at both margins force the formation of intermediate and bottom nepheloid layers and bring fresh food particles with increased velocity to the mounds. The distribution of corals in both mound areas is considered directly related to the presence of enhanced turbidity. An increase in temperature can be directly related to an increase in the amount of particles in the water column. Current velocity increases when a transition occurs from cold to warm waters. High current velocities prevent local sedimentation but provide sufficient food particles to the corals, so that the corals thrive at the mound summits.

Abstract

Seamounts, knolls, pinnacles and other “seamount-like” features are prominent and widely distributed features of the New Zealand marine environment, and also the focus of important commercial fisheries and some exploratory mineral mining. There is considerable debate about the effects of such activities on the benthic habitat of deep-water seamounts. In 2001 a study was undertaken of eight seamount-features on the Chatham Rise, an area that has been heavily trawled for orange roughy since the early 1990s. Half of the study seamounts were considered unfished and the other half fished. Benthic macro-invertebrate assemblages of each seamount were sampled using epibenthic sleds, whilst the presence of habitat-forming fauna (e.g., live corals), substrate type and indications of trawling (e.g., trawl door marks) were determined using a towed underwater camera. Fisheries catch-effort data were examined to determine the amount and distribution of bottom trawling effort on the seamounts. Analyses of camera data revealed that unfished seamounts possessed a relatively large amount of stony coral habitat comprising liveSolenosmilia variabilis andMadrepora oculata (predominantly on the seamount peaks) whereas fished seamounts had relatively little coral habitat. Indications of trawling were observed over six times more frequently on seabed images from fished as opposed to unfished seamounts, and appeared related to the amount of fishing effort on individual seamounts. Multivariate analyses of sled data revealed a significant difference in macro-invertebrate assemblage composition between fished and unfished seamounts. The variability observed in assemblage composition between seamounts can in part be explained by the relative fishing pressure measured by a fishing effects index. The results of the study are discussed with respect to management of seamount habitat, and the need for ongoing monitoring and research to derive conservation practices that allow for sustainable seamount fisheries.

Western Pacific is definitely the place one has to pass through when China implements the national ocean strategy from shallow water to deep sea. From the view of national demands, western Pacific is rich in the sea bottom resources and the marine environment there is quite complicated, so it would be the focus to safeguard national interests and one of the barriers in national security; From the view of scientific frontier, western Pacific has the particular trench-arc-basin tectonics, backarc basin hydrothermal systems, the remains of oceanic plate motion and lots of seamount ecosystems, and there also has the cold/warm water conversion zone of the thermohaline ocean circulation. Launching the western Pacific deep sea scientific research with wellplanned strategy for about 10 years exploration and research, the breakthrough in China′s deep sea research will be surely achieved.

西太平洋是我国实施由浅海向深海发展战略的必经之地。从国家需求的角度来看，西太平洋海底资源丰富、海洋环境复杂，是维护国家权益的焦点、保障国防安全的屏障；从科学前沿的角度来看，西太平洋发育有独特的沟弧盆构造体系和弧后盆地热液系统，存有海底板块运动的遗迹和众多海山生态系统，更是“大洋传送带”冷暖水系的转换区。科学有序地进入西太平洋深海研究领域，通过10年左右的探索与研究，实现我国深海科学研究的突破。

This paper is a brief review of the development of marine science and technology over the past century. A number of examples, including the deepwater sampling and deep-sea drilling, remote sensing and underwater monitoring, moored long-term continuous observation and “Autonomous and Lagrangian Platforms and Sensors”, deep-water diving and sea-floor cabled observation network, are discussed to show how scientific imagination stimulates new technological innovation, and how major improvements in tool capabilities lead to leaps in scientific understanding. The paper is an attempt to convince the Chinese research community and administration that marine science and technology have to develop in a coupled way, not in separation, and their close coupling is prerequisite to science and technology innovation.

简单回顾百余年来现代海洋科学的发展历程，并用一系列的实例，如深海取样和深海钻探, 遥测遥感和水下观测，锚碇长期连续测量和智能水下活动平台，深潜技术和海底观测网等，说明科学的想像能促进技术的创新，而工具的重大改进能导致科学理解的跃进。文章的目的是向我国学术界和管理部门说明：科学和技术必须协同、而不是分头发展，只有两者的结合发展才是科学技术的创新之道。