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| Titel |
Characterisation of hard-substrate habitats in the German Bight (SE North Sea) from video observation |
| VerfasserIn |
Rune Michaelis, Finn Mielck, Svenja Papenmeier, Lasse Sander, H. Christian Hass |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250153743
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| Publikation (Nr.) |
 EGU/EGU2017-18759.pdf |
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| Zusammenfassung |
| Accumulations of cobble- to boulder-sized material provide important habitat functions for
many plant and animal species in the marine environment. These include nursery for fish,
anchor point for sessile marine species and feeding ground for many different organisms.
Detailed knowledge of such reef habitats and their properties is thus crucial for the
determination of marine protected areas and consequently also for the management of the
North Sea. As stones and boulders usually cannot be recovered from the seafloor to be
investigated in the lab most analyses have to rely on non-invasive methods like e.g.
underwater video- and diver-observation data. Due to these limitations these habitats are not
well understood with regard to their spatial distribution, temporal development and ecology.
Furthermore, there is no standardized way to assess the structure and cover of biological
communities on such hard-substrates, which discourages comparison of data between
different regions.
We here present a standardized workflow to analyse underwater videos of hard-substrate
habitats recorded in different areas of the North Sea. The idea is to combine these detailed
information with an area-wide habitat classification based on sidescan sonar data. For
image-based evaluation, the videos are transformed into single frames, extracted every five
seconds of video running time and imported into a self-developed image analysis script. This
script allows the user to select and count different descriptors in numerical categories. These
include amongst others the different size classes of stones, the areal coverage of sessile
marine organisms, the surrounding sediment properties or the presence of grazers. These
semi-quantitative data are subsequently statistically analysed to produce a set of standardized
characteristics of the hard-substrate habitats and the controlling factors of their current state
and development.
Preliminary results show that boulders in sandy environments are predominantly covered by
sessile invertebrate organisms (e.g. the soft coral Alcyonium digitatum and the sea-anemone
Metridium senile), while cobbles are largely uncovered. In muddy areas, however, even
cobbles show a higher amount of sessile coverage though at an earlier or reduced state of
development.
The proposed method allows to obtain detailed data on the distribution, kind and composition
of marine sessile organisms populating hard-substrate habitats in the North Sea.
Already at this stage, the practical assumption of many investigations that stones
are all and always inhabited by the typical organisms, which is utilized in many
investigations can hardly be supported. Our research further shows the need to develop
methodologies to upscale these observations to be able to assess spatial patterns between
and within larger reef complexes. The video analysis presents a valuable first step
towards a full-scale characterization of hard-substrate habitats under difficult survey
conditions. |
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