Hard-substrate habitats in the German Bight (South-Eastern North Sea) observed using drift videos

Michaelis, Rune; Hass, H Christian; Mielck, Finn; Papenmeier, Svenja; Sander, Lasse; Ebbe, Brigitte; Gutow, Lars; Wiltshire, Karen Helen

doi:10.1016/j.seares.2018.11.009

Cited by 39 publications

(33 citation statements)

References 24 publications

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“…Video tows were effected by either allowing the vessel to drift with wind and tide, or by steaming into the direction of drift to effect a speed over the ground of ≤ 0.25 ms −1 ; at any greater speed images were blurred and not usable for data extraction. This is consistent with contemporary practise for remote image-based sampling in deep water (e.g., Cánovas-Molina et al, 2016;Michaelis et al, 2019).…”

Section: Macro-epibenthos Surveyssupporting

confidence: 88%

“…The primary sampling technique was visual sampling using video and still images from sensors mounted on a towed benthic imaging sled, a technique now widely used for benthic habitat classification and mapping (Barker et al, 1999;Stevens and Connolly, 2005), and for monitoring of ecosystem changes over time (Sheehan et al, 2013;Stevens et al, 2014). Image-based underwater sampling has the advantage of being able to sample very large areas cost-effectively (Michaelis et al, 2019), and including sites beyond the practical reach of diver-based surveys (Enrichetti et al, 2019). The imagery also allows examination of the relationship between structural elements of the benthos in situ.…”

Section: Macro-epibenthos Surveysmentioning

confidence: 99%

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Partial Recovery of Macro-Epibenthic Assemblages on the North-West Shelf of the Black Sea

et al. 2019

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The northwest shelf of the Black Sea has suffered well-documented declines in biodiversity since the 1960s, and by the 1990s was considered a dead zone with virtually no sign of macroscopic epibenthic life. It was characterised by high levels of anthropogenic input, massive phytoplankton blooms, and periodically hypoxic to anoxic bottom waters. An important contributor to primary production on the northwest shelf is the red alga Phyllophora spp. growing in waters to 70 m depth. Phyllophora is a habitat forming taxon supporting complex assemblages of bivalves, sponges, and ascidians, with an associated rich fish fauna. From 1990 on, nutrient loads entering the system plummeted and the severity of algal blooms decreased. Changes to benthic communities, however, were far less rapid, and the trajectory and rate of any recovery of the dead zone, in particular Zernov's Phyllophora Field, is far from certain. This study used towed underwater video imagery from research cruises in summer 2006 and spring 2008 to classify and map macro-epibenthic assemblage structure, and related this to putative physical, chemical and spatial drivers. Distinct and relatively stable benthic communities were in evidence across the northwest shelf at that time. These communities were largely structured by substrate type and depth, but there is some evidence that nutrients continued to play a role. Phyllophora spp. was present across much, but not all, of its former range, but at far lower percent cover than previously. The pattern of abundance of Phyllophora in 2006-2008 did not correlate with the documented pre-eutrophication pattern from 1966. There is some evidence that fastergrowing opportunistic species have hindered recovery. We conclude that while there was evidence of sustained recovery, by 2008 the macro-epibenthic communities of the northwest shelf of the Black Sea were far from their pre-eutrophication state.

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Section: Macro-epibenthos Surveyssupporting

confidence: 88%

Section: Macro-epibenthos Surveysmentioning

confidence: 99%

Partial Recovery of Macro-Epibenthic Assemblages on the North-West Shelf of the Black Sea

et al. 2019

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“…These stones do not show a recognizable shadow as a consequence of either too low mosaic pixel resolution or because they are located too close to the nadir. Michaelis et al [9] have shown that the number of cobbles (6.3-20 cm) is approx. 25-fold larger than the number of boulders (20-63 cm) in the SOR.…”

Section: Discussionmentioning

confidence: 97%

“…The sediment composition of the seafloor has a strong influence on the availability of such substrates. In environments with high sediment mobility, e.g., shallow shelf seas affected by waves and tides, hard substrates might become temporarily buried while previously buried ones might become exposed [9,10]. As yet, the spatial detection of underwater objects can only be achieved using hydroacoustic remote-sensing devices such as side-scan sonars (SSS), multibeam echo sounders (MBES), and parametric sediment echo sounders (pSES) (e.g., [11][12][13]).…”

Section: Introductionmentioning

confidence: 99%

Automated Stone Detection on Side-Scan Sonar Mosaics Using Haar-Like Features

et al. 2019

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Stony grounds form important habitats in the marine environment, especially for sessile benthic organisms. For the purpose of habitat demarcation and monitoring, knowledge of the position and abundance of individual stones is necessary. This is especially the case in areas with a scattered occurrence of stones in an environment which is otherwise characterized by relatively mobile sandy sediments. Exposed stones can be detected using side-scan sonar (SSS) data. However, apart from laborious manual identification, there is as yet no automated or semi-automated method available for a fast and spatially resolved detection of stones. In this study, a Haar-like feature detector was trained to identify individual stones on an SSS mosaic (~12 km2) showing heterogeneous sediment distribution. The results of this method were compared with those of manually derived stones. Our study shows that the Haar-like feature detector was able to detect up to 62% of the overall occurrence of stones within the study area. Even though the sheer number of correctly identified stones was influenced by, e.g., the type of sediments and the number of grey values of the mosaic, Haar-like feature detectors provide a relatively easy and fast method to identify stones on SSS mosaics when compared to the manual investigation.

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“…These are -as well as the coarse sand -natural relicts of Pleistocene moraines (Köster, 1979;Zeiler et al, 2008) highly unlikely to be transported by tidal currents. However, they provide the only natural hard substrates in a soft-sediment environment, giving a habitat to some sessile species and serving as steppingstones in the dispersal of others (Sheehan et al, 2015;Michaelis et al, 2019). During sand mining, stones >10 cm are filtered out and remain on the seafloor (LKN-SH, pers.…”

Section: Discussionmentioning

confidence: 99%

Persistent effects of sand extraction on habitats and associated benthic communities in the German Bight

Mielck¹,

Michaelis²,

Hass³

et al. 2020

Preprint

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Abstract. Sea-level rise demands for protection measures of endangered coastlines crucial for the local population. At the island of Sylt in the SE North Sea, shoreline erosion is compensated by replenishment with sand dredged from an offshore excavation site. We studied the long-term effects of sand extraction on bathymetry, geomorphology, habitats, and benthic fauna. Hydroacoustic surveys revealed that changes of bathymetry and habitat characteristics caused by sand extraction can be still detected after > 35 years while the investigation of grab samples revealed persistent changes in sediment composition and benthic faunal composition. The comparison of recently dredged areas ( 10 years ago) and undisturbed sites exposed significant differences in the number of individuals and species of macrozoobenthic organisms as well as in the mud content, indicating a persistent successional stage of the communities in the dredged areas. The slow backfill of the dredging pits results from low ambient sediment availability and relatively calm hydrodynamic conditions, despite high wave energy during storms. Based on current sedimentation rates, we conclude that a complete backfill of the deep excavation sites and re-establishment of the benthic communities is likely to take centuries in this area. Since re-establishment of the benthic communities depends on previous re-establishment of habitat characteristics, habitat mapping with remote sensing techniques is suggested as a cost-effective means to monitor the state of regeneration.

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Hard-substrate habitats in the German Bight (South-Eastern North Sea) observed using drift videos

Cited by 39 publications

References 24 publications

Partial Recovery of Macro-Epibenthic Assemblages on the North-West Shelf of the Black Sea

Partial Recovery of Macro-Epibenthic Assemblages on the North-West Shelf of the Black Sea

Automated Stone Detection on Side-Scan Sonar Mosaics Using Haar-Like Features

Persistent effects of sand extraction on habitats and associated benthic communities in the German Bight

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