Prof. Dr. Stefan Herlitze, Dr. Mareike Huhn, Til Böttner
Benthic invertebrates are continuously exposed to a wide range of environmental stressors, both natural and anthropogenic, making them valuable models for understanding ecosystem resilience and change. Among these organisms, ascidians represent an extremely diverse yet often overlooked group with a key evolutionary link to vertebrates. Their free-swimming larvae possess a notochord and tail, while adults are sessile filter feeders enclosed in a cellulose-rich tunic. Their ability to rapidly contract and expel water when disturbed reflects a highly responsive physiology that can be leveraged to study stress perception.
We focus on ascidians as model organisms to investigate how benthic invertebrates perceive and respond to environmental stress, with particular emphasis on marine noise as an emerging and underexplored stressor. Increasing underwater noise from shipping, coastal development, and tourism introduces persistent acoustic and vibrational disturbances into marine habitats. We study how ascidians detect and process these signals, aiming to uncover the sensory mechanisms underlying noise perception. By analyzing behavioral responses such as contraction dynamics, as well as physiological and molecular indicators, we seek to understand how noise affects organismal performance and stress tolerance.
In addition to marine noise, we examine how multiple stressors - including rising sea temperatures and sedimentation - interact to shape the resilience of benthic invertebrates. Given their ecological flexibility and tolerance to fluctuating conditions, ascidians provide a useful system for identifying measurable physiological parameters and species-specific sensitivities that can serve as bioindicators of environmental disturbance.
Our work is closely integrated with the CORDAP-funded COSMARINDO (Coral Spawning and Awareness for Restoration Network Indonesia) project, which addresses environmental stressors in reef-building corals from a complementary perspective. Within this initiative, we collaborate with Indonesian partners to train students from six universities in monitoring coral spawning events and supporting coral larvae propagation as a restoration strategy. By enhancing the supply of genetically diverse coral larvae to degraded reefs, this approach aims to improve the natural resilience of restored populations to ongoing and future environmental stress.
Our research connects mechanistic insights from ascidian stress ecology with applied efforts in coral reef restoration. By addressing how different benthic invertebrates respond to shared stressors, we contribute to a more integrated understanding of ecosystem-level resilience and support the development of sustainable, biodiversity-based mitigation strategies.
COSMARINDO:
International collaborations:
Opportunities for students:
⇒ Please contact me for more information
In order for the egg and sperm cells of corals from different colonies to intermingle, the individuals of one species must spawn at the same time. But how do they manage to synchronise it?
Mareike Huhn during one of her dives.
With the help of a magnifying glass, she tries to identify the coral species more closely.
Didemnum molle
Damage caused by anchors or dynamite fishing can be the trigger for spreading of non-native fouling organisms, such as Didemnum molle
The high biodiversity in Indo-Pacific coral reef habitats challenges the identification of causes and consequences of climate change and anthropogenic pressure on the ecosystems. During yearly dive excursions, students can get a first impression of the incredible diversity found in these habitats.
This blue Clavelina sp. belongs to the only ascidian genus known to be bioluminescent, so far.
Aplidium elegans, a colonial ascidian found in the Mediterranean Sea. Halocynthia papillosa, a common solitary ascidian in the Mediterranean Sea and bioindicator for negative impacts of scuba diving.
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Last update: Apr 28, 2026