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“Proceedings in Marine Biology” is an international journal publishing original research by graduate students on all aspects of marine biology. Subjects covered include: ecological surveys and population studies of oceanic, coastal and shore communities; physiology and experimental biology; taxonomy, morphology and life history of marine animals and plants. Papers are also published on techniques employed at sea for sampling, recording, capture and observation of marine organisms. This volume deals exlusively with the results of the research field trip of the Humboldt-Universität zu Berlin to the AWI - Biologische Anstalt Helgoland (Germany) from 26.09. - 05.10.2023, Peer Reviewed

Appendicularia comprises 70 marine, invertebrate, chordate species. Appendicularians play important ecological and evolutionary roles, yet their morphological disparity remains understudied. Most appendicularians are small, develop rapidly, and with a stereotyped cell lineage, leading to the hypothesis that Appendicularia derived progenetically from an ascidian-like ancestor. Here, we describe the detailed anatomy of the central nervous system of Bathochordaeus stygius, a giant appendicularian from the mesopelagic. We show that the brain consists of a forebrain with on average smaller and more uniform cells and a hindbrain, in which cell shapes and sizes vary to a greater extent. Cell count for the brain was 102. We demonstrate the presence of three paired brain nerves. Brain nerve 1 traces into the epidermis of the upper lip region and consists of several fibers with some supportive bulb cells in its course. Brain nerve 2 innervates oral sensory organs and brain nerve 3 innervates the ciliary ring of the gill slits and lateral epidermis. Brain nerve 3 is asymmetric, with the right nerve consisting of two neurites originating posterior to the left one that contains three neurites. Similarities and differences to the anatomy of the brain of the model species Oikopleura dioica are discussed. We interpret the small number of cells in the brain of B. stygius as an evolutionary trace of miniaturization and conclude that giant appendicularians evolved from a small, progenetic ancestor that secondarily increased in size within Appendicularia., Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659, David and Lucile Packard Foundation http://dx.doi.org/10.13039/100000008, Peer Reviewed

The Australasian Barnacle Austrominius modestus possesses a great number of chemical receptors and is able to discriminate between chemical mixtures based on their single compounds. Prior studies showed that related barnacles (Semibalanus balanoides) have the ability to memorize chemical cues and connect them with specific reactions. The aim of the present study was to confirm this capacity in barnacles and further investigate whether it lasts over a longer period of time or decreases with time. For this the Australasian Barnacle Austrominius modestus was used as a model organism. The results of the previous study could be reproduced in this species as well and showed that barnacles can be conditioned with a neutral stimulus. Furthermore, the study demonstrated that this conditioning lasts at least 3 hours with a slight decrease over time. The ability to learn is of great advantage for the barnacles in a continuously changing environment., Die Australische Seepocke Austrominius modestus besitzt eine große Anzahl an chemischen Rezeptoren und ist in der Lage chemische Gemische aufgrund ihrer Teilstoffe zu unterscheiden. Bereits vorangegangene Veröffentlichungen zeigten außerdem die Fähigkeit einer verwandten Seepockenart (Semibalanus balanoides) sich chemische Reize zu merken und diese mit spezifischen Reaktionen zu verknüpfen. Ziel dieser Studie war es, die Fähigkeit des Lernens und Verknüpfens bei Seepocken zu bestätigen und weiterhinzu untersuchen, inwieweit diese Fähigkeit über längere Zeit anhält bzw. abnimmt. Dazu wurde die Australische Seepocke Austrominius modestus als Versuchtier ausgewählt. Die Daten konnten die Ergebnisse der vorherigen Studie auch bei dieser Art reproduzieren und zeigen, dass Seepocken auf einen neutralen Stimulus konditioniert werden können. Desweitern wurde herausgefunden, dass diese Konditionierung über mindestens 3 Stunden anhält, wobei ein leichter abnehmender Trend nach dieser Zeit erkannt wurde. Die Fähigkeit zu Lernen ist in der sich ständig ändernden natürlichen Umgebung der Seepocken von großem Vorteil., Peer Reviewed

Hemigrapsus sanguineus and Hemigrapsus takanoi are invasive shore crabs in the German Wadden Sea. The monitoring is an important task to evaluate their impact on the ecosystem. This paper analyzes the preference of Hemigrapsus sp. for different bait types. The results of the chi square test based on Pearson shows a preference for Mytilus edulis as bait. M. edulis is the superior bait type for Hemigrapsus sp., Peer Reviewed

Marine intertidal hard substrates provide an ecologically important habitat for many sessile or semi-sessile organisms. As shelter, food source, nursery or living space, they are of central importance in marine ecosy- stems worldwide (Bellan-Santini et al., 1994). Particularly in the Wadden Sea, dominated by soft substrates and extensive tidal flats, the few hard substrates are essential to many sessile organisms. Therefore, such habitats require special protection. During the last forty years, the pacific oyster became more dominant in the North Sea. While it appears to be in compe- tition with the blue mussel, it could provide potential new niches for sessile organisms, on the other side (Dietrich, 2005). This study aims to make a comparative investigation of the biodiversity on the different types of hard substrates in the intertidal zone of the North Sea on Sylt Island. In total, 53 species belonging to three different ecological guilds (algae, sessile and mobile animals) could be documented on four dif- ferent substrates under two conditions. Besides the attached species’ list, different ecological parameters were calculated, including species abundance, Evenness, and the Shannon-Wiener Index (H). The latter was highest for rocks from the rock-blue mussel reef and lowest in detached rocks taken from the mudflat. In bivalves, the observed biodiversity in sessile organisms was higher in pacific oysters than it was on blue mussels. The opposite is true for mobile organisms, which showed a higher biodiversity on blue mussels found in reef than on isolated oysters. This study has shown that the isolated oysters provide a comparable biodiverse habitat for species living on hard substrate in the Wadden Sea, showing a comparable biodiversity. The native blue mussel as well as the rock reefs shows a great abundance of species, being a shelter for specialist taxa like the hydrozoans. In contrast to the expectations, the oysters offer living space for many native taxa. Th, Peer Reviewed

The hermit crab Pagurus bernhardus, which is native to the Wadden Sea, is permanently exposed to water level and associated temperature fluctuations due to the strong tides there. Closely related species, including P. longicarpus, also occur in warmer regions such as Texas. To determine the light and temperature tolerance of P. bernhardus and how the species responds to light stress and an increase in temperature in terms of activity, we studied them at increased light intensity and temperatures between 20 and 25 degrees Celsius. In this study, we did not find significant differences in behavior in relation to light and temperature stress, so we assume that P. bernhardus is a generalist with respect to the constantly changing environmental con- ditions of the Wadden Sea., Der Einsiedlerkrebs Pagurus bernhardus, welcher im Wattenmeer beheimatet ist, ist aufgrund der dort stark ausgeprägten Gezeiten permanent Wasserstands- und damit verbundenen Temperaturschwankungen ausgesetzt. Nah verwandte Arten, darunter P. longicarpus, kommen auch in wärmeren Regionen wie beispielsweise in Texas vor. Um herauszufinden, wie hoch die Licht- und Temperaturtoleranz von P. bernhardus ist und wie die Art auf Lichtstress und einen Temperaturanstieg in Bezug auf ihre Aktivität reagiert, untersuchten wir diese bei erhöhter Lichtintensität und Temperaturen zwischen 20 und 25 Grad Celsius. In dieser Studie konnten wir keine signifikanten Unterschiede im Verhalten in Bezug auf Licht- und Temperaturstress feststellen, weshalb wir davon ausgehen, dass P. bernhardus ein Generalist bezüglich der sich ständig ändernden Umweltbedingungen des Wattenmeeres ist., Peer Reviewed

Anthropogenic action has introduced many non-native species to different environments around the world. In northern Germany, the shores of the Island of Sylt in the Wadden Sea are no exception. Many alien species have been reported there, among them the barnacle Austrominius modestus, whose population appears to have surpassed that of the native barnacles Semibalanus balanoides and Balanus crenatus over the past 15 years. In this study we analyze and compare the barnacle populations in the Intertidal and upper subtidal zone near List in the North of Sylt. It is known that previously (until 2001) S. balanoides was the most frequent barnacle species in the Intertidal zone and B. crenatus in the Subtidal zone, with only a few Austrominius modestus scattered in between. Furthermore, it was also investigated whether the three species of barnacles showed a preference for which mussel they would colonize, the native blue mussel Mytilus edulis or the neozoan Pacific oyster Magallana gigas. In our analysis, we found that the invasive species A. modestus dominated both Intertidal and upper Subtidal and outnumbers both S. balanoides and B. crenatus, which suggests that it is more competitive than the native species. Neither the native barnacles nor A. modestus showed a preference regarding the substrate., Durch menschliche Eingriffe wurden weltweit viele nicht heimische Arten in verschiedene Lebensräume eingeführt. In Norddeutschland bilden die Küsten der Insel Sylt im Wattenmeer keine Ausnahme. Viele gebietsfremde Arten wurden dort verzeichnet, darunter die Seepocke Austrominius modestus, deren Population in den letzten 15 Jahren die der einheimischen Seepocken Semibalanus balanoides und Balanus crenatus übertroffen zu haben scheint. In dieser Studie analysieren und vergleichen wir die Seepockenpopulationen in der Gezeitenzone bei List im Norden von Sylt. Es ist bekannt, dass früher (bis 2001) S. balanoides die häufigste Seepockenart im Eulitoral und B. crenatus im obersten Sublitoral war, mit nur wenigen verstreut vorkommenden Austrominius modestus. Außerdem wurde untersucht, ob die drei Seepockenarten eine Vorliebe für eine bestimmte Muschelart als Substrat zeigten, ob sie häufiger auf der einheimischen Miesmuschel Mytilus edulis oder der neozoischen Pazifischen Auster Magallana gigas siedelten. Unsere Analyse ergab, dass die invasive Art A. modestus sowohl im Eulitoral als auch im obersten Sublitoral dominiert und sowohl S. balanoides als auch B. crenatus zahlenmässig übertrifft, was darauf schließen lässt, dass sie konkurrenzfähiger ist als die einheimische Art. Weder die einheimischen Seepocken noch A. modestus zeigten eine Präferenz für eines der beiden Substrate., Peer Reviewed

The brown shrimp Crangon crangon is an opportunistic feeder that is widely distributed in the Atlantic Ocean. It has a large pray spectrum and uses ambush tactics while hunting. To explore the possibility of memory and learning in this species, we attempted to condition specimens to a light stimulus using food (Mytilus edulis) as a reward. After starving the specimens for 32 hours prior to the experiment, several conditioning rounds (20 s light stimulus followed by 60 s of feeding) were absolved on four consecutive days. After conducting short-term experiments with four replicates as well as a long-term experiment (same group for all four trial days) we could not document a successful conditioning with the chosen experiment set up as there were no significant trends in the development of the specimens‘ behavior. We accredit the lack of conditioning mainly to unfavorable management of holding conditions, feeding management and stimulus application but cannot exclude the possibility of memory or learning in the brown shrimp Crangon crangon., Peer Reviewed

Pollution of the oceans by anthropogenic influences is a serious problem that will continue to progress in the coming years. The aim of this study was to investigate whether harbour water, which is presumably affected by increased ship traffic or water mixed with sunscreen has an influence on the hiding and feeding behaviour of Carcinus maenas. The crab is frequently found in the shallow water zones of the Wadden Sea and is therefore used as a model organism. The results of our short-term study showed no significant response of the crabs to the pollution used. However, in order to be able to make a clear statement, the sample size must be significantly increased in future experiments., Die Verschmutzung der Meere durch anthropogene Einflüsse ist ein schwerwiegendes Problem, welches in den kommenden Jahren noch weiter fortschreiten wird. In dieser Studie sollte untersucht werden, ob Hafenwasser, welches vermutlich durch das erhöhte Schiffsaufkommen beeinträchtigt ist oder mit Sonnencreme versetztes Wasser einen Einfluss auf das Versteck- und Fressverhalten von Carcinus maenas hat. Die Strandkrabbe kommt unter anderem häufig in den Flachwasserzonen des Wattenmeeres vor und wird daher als Modellorganismus verwendet. Die Ergebnisse unserer Kurzzeitstudie zeigen keine signifikanten Verhaltensänderungen der Krabben auf die verwendeten Verschmutzungen. Um jedoch eine eindeutige Aussage treffen zu können, muss die Stichprobengröße in zukünftigen Versuchen deutlich erhöht werden., Peer Reviewed

First evidence demonstrating associative learning in the sessile invertebrate barnacle Semibalanus balanoides., In this study we investigated the ability to associate chemosensory cues with a stressful event in the common acorn barnacle (Semibalanus balanoides). The ecological benefit of associative learning relies on accurate assessment of predictive cues. There are no reports available on experience-dependent behavioral changes in adult barnacles’ autonomic responses. We demonstrated that repetitive aversive conditioning elicited a significant increase in the retraction rate of the cirrus and closure of the operculum after presentation of a cue. These results indicate that adult acorn barnacles are able to anticipate an aversive event through associative learning., Peer Reviewed

Anthropogenic disturbance is known to be highly influential on ecosystems. Sensitive systems with a high ratio of specialized Fauna and Flora are often more affected than those inhabited with generalists. An example of a sensitive ecosystem is the mudflats located off List on the island of Sylt. To investigate the anthropogenic disturbance of the mudflats, we examined populations of Peringia ulvae and Corophium volutator. In this article we show that already a one-time disturbance of the mudflats leads to a significant reduction of density of P. ulvae. No significant difference could be observed between the area disturbed multiple times and the zone that was disturbed only once, indicating that a single disturbance has drastic effects on the ecosystem. Total numbers of C. volutator increased in zones that were disturbed compared to the control area. While organic mass did not significantly differ between disturbed and control area, disturbance, even a single one, resulted in a visual alteration and a decrease of net animal count., Peer Reviewed

The Wadden Sea a habitat with extreme variability of abiotic factors. In spring, green gelatinous egg capsules of the polychaete Phyllodoce maculata can be found attached to the sediment, algae or hard substrates. The eggs and the newly hatched larvae have to be resistant against multiple changes of abiotic factors in their habitat. In this study we investigate the influence of changes in the abiotic environment on the early deve- lopmental stages of P. maculata. We tested their reaction to changes in salinity, drought, light conditions, and temperature. We show that the egg capsules and the larvae are resistant against changes in temperature and lighting conditions. The embryos inside the egg capsules and the larvae can tolerate decreased salinity in the sea water of up to 50% for at least 48h. Further decrease in salinity leads to increased lethality of embryos and larvae. In larvae inside the egg capsules, dry conditions lead to further development of the larvae, but the larvae seem to be compromised. For free-swimming larvae, drying out is lethal. Additionally, we show that the early stage trophophora larvae are positively phototactic and prefer open water over sediment., Peer Reviewed

Mussels provide habitat for many organisms – so called epibionts – of the tidal flats by using the shells as a hard substrate for attachment. The abundance of epibionts on mussel shells can vary by location. In this study, the diversity of epibiont species on mussels in the North Sea tidal flats was investigated. For this purpose, mussels and Pacific oysters were collected from three different sites, mixed mudflats, mudflats and mussel beds, and the occurrence of epibiontic species was compared. Epibiontic animal groups identified included Crustacea, Mollusca, Actiniaria, and Bryozoa. The comparison revealed a difference in epibiont diversity on the two bivalve species. The oysters had higher diversity than mussels. The most abundant species include the barnacle species Austrominius modestus. When comparing epibiont diversity among the three sites, an uneven distribution of species was found and the highest diversity was found in the mixed mudflats., Muscheln bieten für viele Organismen – sogenannte Epibionten – des Wattenmeers Lebensraum, indem die Schalen als Hartsubstrat zum Anheften genutzt werden. Das Vorkommen der Epibionten auf den Muschel- schalen kann nach Standort des Watts variieren. In dieser Studie wurde die Diversität der epibiontischen Arten auf Muscheln im Nordsee-Wattenmeer untersucht. Dazu wurden Miesmuscheln und Pazifische Austern aus drei unterschiedlichen Standorten Mischwatt, Schlickwatt und Muschelbank gesammelt und das Artenvorkommen verglichen. Zu den identifizierten epibiontischen Tiergruppen gehören die Crustacea, Mollusca, Actiniaria und Bryozoa. Bei dem Vergleich konnte ein Unterschied in der Epibiontendiversität auf den zwei Muschelarten festgestellt werden, auch wenn gleiche Arten anzutreffen waren. Die Austern wiesen eine höhere Diversität als Miesmuscheln auf. Zu den am häufigsten vorkommenden Arten zählen die Seepockenart Austrominius modestus. Beim Vergleich der Epibiontendiversität zwischen den drei Standorten wurde eine ungleichmäßige Verteilung der Arten festgestellt und die höchste Diversität im Mischwatt festgestellt., Peer Reviewed

The article processing charge was funded by the Open Access Publication Fund of Humboldt-Universität zu Berlin., Background: Appendicularia consists of approximately 70 purely marine species that belong to Tunicata the probable sister taxon to Craniota. Therefore, Appendicularia plays a pivotal role for our understanding of chordate evolution. In addition, appendicularians are an important part of the epipelagic marine plankton. Nevertheless, little is known about appendicularian species, especially from deeper water. Results: Using µCT, scanning electron microscopy, and digital 3D-reconstruction techniques we describe three pairs of complex oral sensory organs in the mesopelagic appendicularian Bathochordaeus stygius. The oral sensory organs are situated at the anterior and lateral margin of the mouth and inside the mouth cavity. A single organ consists of 22–90 secondary receptor cells that project apical cilia through a narrow hole in the epidermis. The receptor cells are innervated by branches of the second brain nerve. Conclusions: Based on position, morphology, and innervation we suggest that the oral sensory organs are homologues of the coronal organs in other tunicates. We discuss the hypothesized homology of coronal organs and the lateral line system of primary aquatic vertebrates. The complex oral sensory organs of B. stygius are unique in tunicates and could be adaptations to the more muffled environment of the mesopelagic., Peer Reviewed