MareMundi-Projekt Posidonia – Episode 2

And we are back for episode 2! For those of you who missed the first episode and want to join us on our journey, please follow the link to episode 1.

The author of this article apologizes to those readers who prefer a German version. Besides being reluctant to spending three times as long on the same text, he merely hopes to reach as many interested readers as possible!

As mentioned in episode 1, MareMundi’s research division is currently fully committed to Project Posidonia, an initiative dedicated to the long-term examination of seagrass meadows as an essential marine habitat in the Mediterranean. There is no doubting the importance of this habitat once one observes the tremendous amount of biodiversity found living on as well as within these meadows. Our two master theses have sparked Project Posidonia into motion with the intention of establishing a solid basis for future research collaborations.


What are we’re doing, exactly?

As promised, we intend to shed some light on our slightly cryptic yet fascinating topics:

Alexander Heidenbauer – Anthropogenic effects on the molluscan assemblages of shallow water Posidonia oceanica fields in the Kvarner Bay (Croatia) *


Roberto Piñeyro – Anthropogenic effects on Posidonia oceanica fields in the Kvarner Bay (Croatia) inferred by a live-dead study of seagrass-associated molluscs *

* the scope of our topics may evolve as we deepen our understanding, thus our focus is subject to change *


Posidonia oceanica is known to react sensibly to environmental stress and is thus widely recognized as a good proxy for the health of ecosystems; however, many details behind seagrass associated communities are still unclear and the biodiversity in question is considerable. So what are we doing, exactly? Molluscs (e.g. clams and snails) are the protagonists of our study and are important Posidonia dwellers, whereas some species have stronger associations to seagrass environments than others. Their resistant shells have an excellent potential for preservation and function as bio-geo-archives, small perseverant representatives of past communities. In other words an assemblage of mollusks may, just like fossil records, retain valuable information about the past and the present.


Our intention is to collect -live and dead- mollusks from Posidonia patches and infer information pertaining to their occurrence and distribution; specimen will be collected separately for both the leaves and the rhizomes. This sampling design will help us gather information on the range of local species, their abundances, general community composition and trophic structures. Additionally, we plan to delve into the effects different sources of anthropogenic stress may have on Posidonia meadows, which will help us understand how this stress might have affected past communities, shaping the biodiversity found today.

uebersiht-adria posidonia-meadow-at-stara-baska posidonia-meadow-at-kormat-island

Although both sites are located in the heavily impacted Kvarner bay and are thus under considerable anthropogenic stress, we predict that even comparatively small stretches of cover such as the uninhabited Kormati island can offer enough shelter to positively   influence Posidonia habitats, ultimately promoting higher species richness and abundance in the area. The site on Krk island’s coastline on the other hand is directly affected by Stara Baska, a tourist hot spot, and Krk island’s dominating influence as a popular tourist destination.

Live-Dead Assemblage

It is very important to understand the significance behind the collection of Live Assemblages (LA) and Death Assemblages (DA). All specimen found to be alive fall under the category of LA, whereas all specimen found to be dead (only shells remaining) belong to the DA. One can think of a LA as a ‘snapshot’ of the present population; it is an impression that has a very high temporal resolution.  If we were to find 15 living mollusk species at any given time and location we would retain only a limited impression of the community. However, although it is only a portion of the full story, it is very valuable information. The DA on the other hand represents an accumulation of these snapshots and broadens the scope of the story.

Susan Kidwell is a leading paleontologist who formulated an excellent metaphor to explain what a time-averaged DA is by depicting the floor of a teenager’s bedroom:


At the end of the week, the accumulation of cast-off clothing (mixed by his/her occasional search for a T-shirt to wear again, augmented by items dropped by younger siblings and reduced by items dragged off or destroyed by the family pet) provides a picture of the local clothes-wearer over that interval of time. The time-averaged picture can do an excellent job of capturing the range of temperatures (and relative frequency of temperatures) during the week as well as activities, such as athletics and a formal dinner with grandparents. This kind of data contrasts fundamentally with the picture created by any random snapshot of the teenager running out of the kitchen door; such a photograph has higher temporal and ecological resolution, but a far narrower temporal scope and may be quite atypical of the week.” Original article – by Kidwell (1)

Shifting Baselines Syndrome

This wonderful simplification makes it easier to understand the concept behind our study. Live-Dead analysis has proven to be a valuable tool in paleontology and is gaining importance as we strive to better understand the rapid changes our world is undergoing. By comparing the past to the present we take a step closer to identifying important ecological baseline shifts relevant to our current situation. Past ecological baselines, prior to industrialization and major anthropogenic influence, help us keep in mind the real effect humans have had on the world. We often speak of ‘reference’ conditions to describe current ecosystems that are least impacted by human stress but we also tend to forget that the ecological baseline has shifted almost beyond recognition. For more details on the topic Shifting Baselines Syndrome (2) describes the concept in more depth. This is an important point for conservation biology, which often focuses on the partial recovery of ecosystems based on modern reference conditions, taken from subjective current ecological baseline.


Need a reason to be excited?

The analysis of Live-Dead mollusk assemblages on Posidonia meadows is particularly exciting and important because the method is entirely new to the type of habitat and the Mediterranean. Posidonia meadows play an important role in marine conservation efforts and we hope our study will provide a blueprint for future projects.

(1) Kidwell, S. M. (2013), Time-averaging and fidelity of modern death assemblages: building a taphonomic foundation for conservation palaeobiology. Palaeontology, 56: 487–522. doi:10.1111/pala.12042
(2) Campbell, L. M., N. J. Gray, E. L. Hazen, and J. M. Shackeroff. 2009. Beyond baselines: rethinking priorities for ocean conservation. Ecology and Society 14(1): 14

Bericht: Roberto Piñeyro,
Fotos: MareMundi-Team

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  1. […] geht es weiter mit Teil 3 unseres Projekts Posidonia. Wie in Episode 1 & Episode 2 beschrieben beschäftigen wir uns im Rahmen unserer Masterarbeiten mit den schalentragenden […]

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