MASTERARBEIT / MASTER’S THESIS Titel der Masterarbeit / Title of the Master‘s Thesis „Drilled gastropods: temporal and spatial variabilities of predation pressure in the Northern Adriatic Sea“ verfasst von / submitted by Markus Dengg, BSc angestrebter akademischer Grad / in partial fulfilment of the requirements for the degree of Master of Science (MSc) Wien, 2017 / Vienna 2017 Studienkennzahl lt. Studienblatt / A 066 833 degree programme code as it appears on the student record sheet: Studienrichtung lt. Studienblatt / Masterstudium Ecology and Ecosystems degree programme as it appears on the student record sheet: Betreut von / Supervisor: Univ. Prof. Mag. Dr. Zuschin Martin Inhalt 1 Abstract ........................................................................................................................................... 4 2 Zusammenfassung ........................................................................................................................... 6 3 Introduction ..................................................................................................................................... 8 4 Sampling Area .................................................................................................................................. 9 5 Material and Methods ................................................................................................................... 10 7 Results ........................................................................................................................................... 12 7.1 Grain size analysis .................................................................................................................. 12 7.2 DF, IDF, MDF .......................................................................................................................... 13 7.2.1 Venice ............................................................................................................................ 14 7.2.2 Panzano ......................................................................................................................... 15 7.2.3 Po ................................................................................................................................... 17 7.2.4 Brijuni ............................................................................................................................ 19 7.2.5 Piran ............................................................................................................................... 21 7.3 PE ........................................................................................................................................... 25 7.3.1 Venice ............................................................................................................................ 25 7.3.2 Panzano ......................................................................................................................... 26 7.3.3 Brijuni ............................................................................................................................ 27 7.3.4 Piran ............................................................................................................................... 27 7.4 DF per taxonomic Level ......................................................................................................... 29 7.4.1 Venice ............................................................................................................................ 29 7.4.2 Panzano ......................................................................................................................... 30 7.4.3 Po ................................................................................................................................... 33 7.4.4 Brijuni ............................................................................................................................ 36 7.4.5 Piran ............................................................................................................................... 38 7.5 Life Habits .............................................................................................................................. 41 7.5.1 Ecotypes ........................................................................................................................ 41 7.5.2 Feeding Guilds ............................................................................................................... 47 8 Discussion ...................................................................................................................................... 54 8.1 Higher DF in nutrient-rich areas ............................................................................................ 54 8.2 DF is linked to life habits ....................................................................................................... 54 8.3 High diversity increases DF´s ................................................................................................. 56 8.4 DF in the Northern Adriatic is at an pre-Cenozoic level ........................................................ 57 8.5 DFs over time are stronger influenced by changes in abiotic factors than by biotic interactions. ....................................................................................................................................... 58 9 Conclusion ..................................................................................................................................... 59 2 10 Acknowledgements ................................................................................................................... 60 11 References ................................................................................................................................. 61 12 Appendix .................................................................................................................................... 65 3 1 Abstract Drilling predation is known to control species composition and biodiversity in molluscan benthic assemblages. This study focuses on changes in drilling frequency (DF) on a temporal (up to 5000 years) and spatial (from west to east coast) scale in the Northern Adriatic Sea. We used sediment cores do perform deep time and spatial analysis of predation. A total of 44393 gastropods were distinguished, counted and checked for drill holes. The median DF across all samples was 16.93%. The highest values were found in Piran (31.23%) and the lowest at the Po Delta (7.50%). On the family level Turritellidae (up to 58.96%) and Crithiidae (up to 39.27%) showed the highest values in DF. Cerithiidae was the most abundant family with a total of 13208 individuals and occured in nearly every sample, except Panzano. Turritellidae were found to be much lower in abundance with a total of 2652 individuals. No members of the family were found in the core of Venice, whereas they make up to one third of total species abundance in the cores of the Po delta. DF changes over time are diverging between cores. In the cores of Piran and Panzano DF increase towards modern layers. This trend can also be found in the core of Brijuni, but here DF shows a total collapse (from around 40% to 0%) in the most modern layer (0-2 cm depth). The core of Venice shows strong fluctuating DFs all through the core. However, beginning from the middle of the core, DF was found to be lower than in older layers. Cores from the Po-delta show drilling in oldest layers but none at most modern. Epifaunal living gastropods showed the highest values of DF (28.90%). DF of infaunal living filter- feeders (23.76%) and epibiontic (organisms living attached to others, without any kind of mutualistic interaction) living gastropods (21.30%) were high despite their cryptic lifestyle. It seems to be that more mobile species (e.g., predators and scavengers) were affected by lower predation pressure. This might be the case because molluscivorous predators in the Northern Adriatic Sea consume a wide variety of prey organisms. While naticids prey on infaunal organisms, muricids prey on epifaunal and shallow buried molluscs. The species Octopus vulgaris is also known to prey on a wide range of molluscs. We found that species composition and biodiversity do not correlate with DFs in our cores from the Northern Adriatic Sea. Differences were found for the abundance of prey organisms. It seems to be that more abundant species (e.g., T. communis at the cores of the PO) are affected by a higher predation risk. Moreover, it seems to be the case that nutrient and freshwater input, sedimentation rates and anthropogenic impacts shape the gastropod communities at this marine basin. We also found strong varying intensities in these factors between our sampling sites, which might explain some of the trends. While at the stations from the Po-delta, freshwater and sedimentation rates probably had a big influence on DFs, in Venice the benthic assemblages might suffer from the severe human dredging activities. In other cores were anthropogenic impact and abiotic factors are minimized (e.g., Brijuni) DFs do positively correlate with biodiversity. 4 The predation rates found in this study show values typical for Cenozoic basins, but differ strongly between sites in the Northern Adriatic Sea. As for trends in DF along cores, we found that abiotic factors like freshwater input (overall low DF along the core) and the strong anthropogenic impact in some
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