Melanie Bergmann & Ingo Schewe
Alfred Wegener Institute – Helmholtz Centre for Polar and Marine Research(INDP)
Figure 1: The towed ocean floor observation system (OFOS) on the sea floor
Benthic biota, the organisms living at the bottom of the sea, play an important role in the global carbon cycle through the continuous redistribution of organic matter, oxygen and other nutrients in superficial sediments by breaking down organic matter into its simplest inorganic forms (a process called remineralisation), reworking soils and sediments (bioturbation) and burial of sunken matter. The organisms that inhabit the sediment–water interface at the bottom of the sea and have dimensions larger than 1 cm are called epibenthic megafauna. They contribute considerably to respiration at the sea floor and have a strong effect on the physical and biogeochemical environment at micro scales. These organisms create pits, mounds and traces that enhance habitat heterogeneity and thus diversity of smaller sediment-inhabiting organisms in otherwise apparently homogenous environments. Erect biota, the organisms growing vertically such as sponges or corals, enhance three-dimensional habitat complexity and provide shelter from predation. They may alter the small-scale flow regime on the seafloor affecting the distribution of smaller-sized organisms. Furthermore, megafaunal predators control the population of their prey and therefore shape benthic food webs and community structure. An understanding of megafaunal dynamics is therefore vital to understand of the fate of carbon at the deep seafloor, the Earth’s greatest carbon reservoir.
Recent technological progress has driven the development of camera-based monitoring methods from various platforms (towed systems, remotely operated vehicles, autonomous underwater vehicles, and stationary platforms such as benthic landers) which have increasingly been used to characterise epibenthic communities and habitats on the seafloor. Such methods are less invasive than trawls and enable largescale distribution assessments allowing the description of larger habitats. Recently, such tools have also been used to quantify pollution on the deep seafloor.
Inevitably, such methods generate ‘big data’, often inaccessible to researchers from other institutes or to the general public and can therefore not be used to their full potential. As part of FixO3 Service Activity 1.2 ‘Fram Strait, Arctic: time series on megafauna density and diversity’ we developed a tool to access photographs from the HAUSGARTEN observatory along with geographic information and scientific data products. The seafloor of selected stations of the HAUSGARTEN observatory is surveyed regularly by the towed Ocean Floor Observation System (OFOS; Fig. 1). The vertically facing camera system is used to assess large-scale distribution patterns of megafaunal organisms and other objects on the deep seafloor (e.g. dropstones, garbage). The system is lowered to approximately 1.5 m above the sea floor using a fibre optical cable for data, video and energy transfer, and then towed along a set transect at a speed of 0.5 knots.
Figure 2: Screenshot of the AWI OFOS-Viewer; seafloor picture with associated data from image-analyses
Images and data of these observations are stored in the scientific database PANGAEA. However, relevant information might be difficult to retrieve in such data repository, especially by the general public. A new GISbased web-viewer (Fig. 2) was developed to facilitate access to the collected images and data. The tool also shows the locations on a map where the images were taken and provides data for organism abundances, which are based on scientific image analysis. This product gives the users the extremely rare opportunity to get an idea of how benthic communities inhabiting the deep Arctic seafloor look like and evolved during the years of investigation. The data can also be used to calculate benthic biomass (the total quantity of organic matter on an area of the sea floor) as a baseline to assess the impact of global warming and anthropogenic threats to the Arctic ecosystem such as fishing, litter pollution, cruise tourism and shipping.