Microscopic organisms that penetrate calcareous structures by actively dissolving the carbonate matrix, namely microendoliths, have an important influence on the breakdown of marine carbonates. The study of these microorganisms and the bioerosion traces they produce is crucial for understanding the impact of their bioeroding activity on the carbonate recycling in environments under global climate change. Traditionally, either the extracted microendoliths were studied by conventional microscopy or their traces were investigated using scanning electron microscopy (SEM) of epoxy resin casts. A visualisation of the microendoliths in situ, that is within their complex microbioerosion structures, was previously limited to the laborious and time-consuming double-inclusion cast-embedding technique. Here, we assess the applicability of various fluorescence staining methods in combination with confocal laser scanning microscopy (CLSM) for the study of fungal microendoliths in situ in partly translucent mollusc shells. Among the tested methods, specific staining with dyes against the DNA (nuclei) of the trace making organisms turned out to be a useful and reproducible approach. Bright and clearly delineated fluorescence signals of microendolithic nuclei allow, for instance, a differentiation between abandoned and still populated microborings. Furthermore, infiltrating the microborings with fluorescently stained resin seems to be of great capability for the visualisation and quantification of microbioerosion structures in their original spatial orientation. Potential fields of application are rapid assessments of endolithic bio-and ichnodiversity and the quantification of the impact of microendoliths on the overall calcium carbonate turnover. The method can be applied after CLSM of the stained microendoliths and retains the opportunity for a subsequentThis is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.

<p>Beach wrack is defined as any material washed ashore by wind and wave actions plays a vital part in coastal ecosystems: it fosters dune formation and prevents beach erosion at land, provides food and shelter to beach fauna, both in and off the water. Nevertheless, it is often seen as nuisance and therefore removed at recreational beaches. So far, no complex data has been retrieved regarding the decay of beach wrack when left at the beach and in the shallow water.<br>To gain insight into the decomposition processes of beach wrack local seagrass of the species Zostera marina was chosen as prime example species and vital part of beach wrack at the southwestern German Baltic Sea coast at the island of Poel. In different seasonal experiments, seagrass was filled into white and black litterbags. In another experiment, seagrass in white litterbags was left in the shallow water until total disintegration of biomass. Sampling was conducted in regular intervals. The seasonal experiments were moved from water to land and land to water every week to mimic the movement between these interfaces in tidal seas for a period of six weeks. Constant exposure to the shallow water lasted for between 140 and 210 days. With every sampling, the biofilm was scratched off the decaying leaves of seagrass. The development of its microbial community as well as biomass loss were investigated. C/N-ratio was measured with the respective changes over time. The influence of abiotic parameters like light, salinity and temperature for the microbial community during the decay were then evaluated. <br>In respect to decomposition processes at micro-tidal coasts, these studies provide an important insight into seagrass decay, at land and in the shallow water. Beach management processes at recreational beaches, and the possibilities of nutrient back-flow, need to be implemented into nature-compatible approaches. A corresponding system based on this research results can be promoted for leading to a balanced coexistence between man and nature.  </p>

<p>Beach wrack, defined as material washed ashore by wind, waves and tides, is a natural phenomenon observed at all coasts worldwide. Often seen as a nuisance and being removed at recreational beaches, it is an important component for dune vegetation succession and habitat for beach faunal components both being negatively impacted by beach management practices. In order to balance the conflicting interests of tourism and nature protection, sound data about amounts, seasonality and composition of beach wrack washed ashore as well as residence time and decomposition kinetics are required, but not available yet for microtidal Seas as the Baltic.</p><p>The decay of beach wrack at the beach and under controlled and dry conditions was investigated in the past several times. In this work, the decay of beach wrack, and i.e. seagrass of the genus <em>Zostera marina</em> was documented under natural conditions. Therefore, litterbags of fine mesh were sewed and filled with a defined amount of freshly detached seagrass from the local shore. Altogether six experiments were carried out: first two experiments starting in summer or winter, respectively, with constant wet conditions in appx. 1 m water depth. The remaining four experiments were conducted throughout the four seasons. Here, the litterbags were put into water, removed onto land, and vice versa for a total time period of six weeks. The experiments were run in the shallow water at the island of Poel completely submerged and, for a comparison with changing conditions between water and land, at the beach of Warnemünde. Additionally, the experiments were split between light and dark conditions by the use of different mesh colors.</p><p>Data about degradation rate through loss of biomass have been retrieved, as well as abiotic parameters influencing the rate of decomposition. For additional insights into the decay of seagrass each sampling time the biofilm was removed, DNA extracted and analyzes of the microbial biofilm are at an initial stage. This work will give valuable information on the degrading community, the influence of seasons, temperature, light availability and the continued change when beach wrack is washed ashore and retrieved back by the sea for many times through all decomposition stages.</p>