Wochenbericht L17-18

01.11.-08.11.201

Wochenbericht L16-20

14.11. – 18.11.201

Wochenbericht L18-01

02.01. – 09.01.201

Wochenbericht L17-04

Wochenbericht L17-04 03.04. – 06.04.201

Limitations of Boulder Detection in Shallow Water Habitats Using High-Resolution Sidescan Sonar Images

Stones and boulders in shallow waters (0–10 m water depth) form complex geo-habitats, serving as a hardground for many benthic species, and are important contributors to coastal biodiversity and high benthic production. This study focuses on limitations in stone and boulder detection using high-resolution sidescan sonar images in shallow water environments of the southwestern Baltic Sea. Observations were carried out using sidescan sonars operating with frequencies from 450 kHz up to 1 MHz to identify individual stones and boulders within different levels of resolution. In addition, sidescan sonar images were generated using varying survey directions for an assessment of range effects. The comparison of images of different resolutions reveals considerable discrepancies in the numbers of detectable stones and boulders, and in their distribution patterns. Results on the detection of individual stones and boulders at approximately 0.04 m/pixel resolution were compared to common discretizations: it was shown that image resolutions of 0.2 m/pixel may underestimate available hard-ground settlement space by up to 42%. If methodological constraints are known and considered, detailed information about individual stones and boulders, and potential settlement space for marine organisms, can be derived

Dynamics of Stone Habitats in Coastal Waters of the Southwestern Baltic Sea (Hohwacht Bay)

Cobbles and boulders on the seafloor are of high ecological value in their function as habitats for a variety of benthic species, contributing to biodiversity and productivity in marine environments. We investigate the origin, physical shape, and structure of habitat-forming cobbles and boulders and reflect on their dynamics in coastal environments of the southwestern Baltic Sea. Stone habitats are not limited to lag deposits and cannot be sufficiently described as static environments, as different dynamic processes lead to changes within the physical habitat structure and create new habitats in spatially disparate areas. Dynamic processes such as (a) ongoing exposure of cobbles and boulders from glacial till, (b) continuous overturning of cobbles, and (c) the migration of cobbles need to be considered. A distinction between allochthonous and autochthonous habitats is suggested. The genesis of sediment types indicates that stone habitats are restricted to their source (glacial till), but hydrodynamic processes induce a redistribution of individual cobbles, leading to the development of new coastal habitats. Thus, coastal stone habitats need to be regarded as dynamic and are changing on a large bandwidth of timescales. In general, wave-induced processes changing the physical structure of these habitats do not occur separately but rather act simultaneously, leading to a dynamic type of habitat

Circular structures on the seabed: differentiating between natural and anthropogenic origins—Examples from the Southwestern Baltic sea

Hydroacoustic observations of shallow marine environments reveal a variety of seafloor structures–both of natural and anthropogenic origin. Natural processes can result in features with circular geometries on the seafloor, such as kettles, sinkholes or iceberg pits, but human activities such as dredging, dumping, or detonating explosives can also cause similar shapes. Explaining the origin of these features is difficult if there are only few observations or if competing natural and anthropogenic processes have acted in the same area. Even though the location of dredging and dumping operations and munition blasting may be well documented in many parts of the global coastal ocean today, little information might be available about human practices in the past. In this study, more than 3,000 circular features were identified in side-scan sonar (SSS) datasets covering 1,549 km2 of shallow waters in the southwestern Baltic Sea. Additional data obtained by multibeam echosounder (MBES), sub-bottom profiler (SBP), and different SSS was considered in the analysis of 205 circular features that were characterized based on their sedimentology, morphology, SSS and SBP acoustic signatures. Characteristic differences between the structures allow their classification into six classes, which provide insight into their formation mechanisms. The obtained parameters (morphology, MBES and SSS acoustic backscatter, SBP characteristics and spatial distribution) allow the classification to be applied to the entire SSS dataset, resulting in the classification of 2,903 features. The mapped circular features have diameters between 6 and 77 m and correspond to pockmarks, dumping spots and explosion craters in water depths ranging from 8 m up to 25 m. Despite this rather multi-methodological approach, the origin of some observed features still cannot be explained with certainty, leaving room for further investigations of natural processes and human impacts on the seafloor

(Micro)evolutionary changes and the evolutionary potential of bird migration

Seasonal migration is the yearly long-distance movement of individuals between their breeding and wintering grounds. Individuals from nearly every animal group exhibit this behavior, but probably the most iconic migration is carried out by birds, from the classic V-shape formation of geese on migration to the amazing nonstop long-distance flights undertaken by Arctic Terns Sterna paradisaea. In this chapter, we discuss how seasonal migration has shaped the field of evolution. First, this behavior is known to turn on and off quite rapidly, but controversy remains concerning where this behavior first evolved geographically and whether the ancestral state was sedentary or migratory (Fig. 7.1d, e). We review recent work using new analytical techniques to provide insight into this topic. Second, it is widely accepted that there is a large genetic basis to this trait, especially in groups like songbirds that migrate alone and at night precluding any opportunity for learning. Key hypotheses on this topic include shared genetic variation used by different populations to migrate and only few genes being involved in its control. We summarize recent work using new techniques for both phenotype and genotype characterization to evaluate and challenge these hypotheses. Finally, one topic that has received less attention is the role these differences in migratory phenotype could play in the process of speciation. Specifically, many populations breed next to one another but take drastically different routes on migration (Fig. 7.2). This difference could play an important role in reducing gene flow between populations, but our inability to track most birds on migration has so far precluded evaluations of this hypothesis. The advent of new tracking techniques means we can track many more birds with increasing accuracy on migration, and this work has provided important insight into migration's role in speciation that we will review here