THE MICROBIAL FOOD WEB OF THE COASTAL SOUTHERN BALTIC SEA AS INFLUENCED BY WIND-INDUCED SEDIMENT RESUSPENSION I n a u g u r a l - D i s s e r t a t i o n zur Erlangung des Doktorgrades der Mathematisch-Naturwissenschaftlichen Fakultät der Universität zu Köln vorgelegt von TOBIAS GARSTECKI aus Magdeburg Köln, 2001 Berichterstatter: Prof. Dr. STEPHEN A. WICKHAM Prof. Dr. HARTMUT ARNDT Tag der letzten mündlichen Prüfung: 29.06.2001 Inhaltsverzeichnis Angabe von verwendeten Fremddaten .............................................. 5 Abkürzungsverzeichnis ..................................................................... 6 1. Einleitung ........................................................................................................ 7 1.1. Begründung der Fragestellung ......................................................... 7 1.2. Herangehensweise ..................................................................... 11 2. A comparison of benthic and planktonic heterotrophic protistan community structure in shallow inlets of the Southern Baltic Sea ........… 13 2.1. Summary ................... ........................................................................ 13 2.2. Introduction ................................................................................. 14 2.3. Materials and Methods ..................................................................... 15 2.3.1. Study sites ..................................................................... 15 2.3.2. Sampling design ......................................................... 17 2.3.3. Sampling procedure ......................................................… 18 2.3.4. Identification and enumeration of protists ....................... 19 2.3.5. Statistical analysis ......................................................... 20 2.4. Results ............................................................................................ 20 2.4.1. General trends ..................................................................... 20 2.4.2. Distribution and taxonomic composition of ciliates ........... 24 2.4.3. Distribution and taxonomic composition of rhizopods .....… 30 2.4.4. Distribution and taxonomic composition of flagellates .....… 30 2.4.5. Relationships between layers and between pelagic protists, seston, and chlorophyll a concentrations ........... 31 2.5. Discussion ................................................................................. 32 2.5.1. Quantitative importance of heterotrophic protists ........... 32 2.5.2. General trends of heterotrophic protistan community structure ........................................................... 33 2.5.3. Contribution of taxonomic groups .................................. 34 2.5.4. Methodology ..................................................................... 37 2.5.5. Significance of benthic-pelagic coupling ....................... 37 Tobias Garstecki 3. Seasonal abundances and community structure of benthic rhizopods in a shallow lagoon of the Southern Baltic Sea ........................................ 39 3.1. Summary ................................................................................ ........ 39 3.2. Introduction ..................................................................................... 39 3.3. Materials and Methods ..................................................................... 41 3.3.1. Study area ....................................................................... 41 3.3.2. Sampling ........................................................................ 42 3.3.3. Determination of the taxonomic composition of the rhizopod community ................................................…......... 42 3.3.4. Enumeration of rhizopods ............................................... 43 3.3.5. Methodological investigations .......................................... 44 3.4. Results ............................................................................................ 45 3.4.1. Abundance and biovolume totals at station Bäk .................. 45 3.4.2. Taxonomic composition of the rhizopod fauna ................. 46 3.4.3. Contribution of taxonomic groups...................................….. 46 3.4.4. Applicability of the liquid aliquot method ....................... 50 3.5. Discussion ................................................................................. 52 3.5.1. Quantitative importance and distribution of rhizopods .....… 52 3.5.2. Rhizopod community structure .......................................…. 53 3.5.3. Methodology ..................................................................... 56 4. Effects of experimental sediment resuspension on a coastal planktonic microbial food web ................................................................................ 58 4.1. Summary ................................................................................. 58 4.2. Introduction ..................................................................... 58 4.3. Materials and Methods ......................................................... 60 4.3.1. Study site ..................................................................... 60 4.3.2. Experimental design .............................................. 60 4.3.3. Abiotic parameters and chlorophyll a ....................... 61 4.3.4. Microbial community structure …............................... 62 4.3.5. Statistical analysis ......................................................... 62 4.4. Results ............................................................................................ 63 4.4.1. Abiotic parameters ......................................................... 63 4.4.2. Autotrophs ..................................................................... 65 4.4.3. Bacteria and heterotrophic protists .................................. 68 4.4.4. Microbial food web interactions .................................. 71 2 Inhaltsverzeichnis 4.5. Discussion ................................................................................. 72 4.5.1. Effectiveness of experimental design .................................. 72 4.5.2. Direct transport effects of resuspension .............................. 72 4.5.3. Indirect effects of resuspension on autotrophic organisms .. 74 4.5.4. Indirect effects of resuspension on heterotrophic organisms 76 4.5.5. Significance of resuspension for the microbial food web of the study area ............................................................... 77 5. The response of a benthic rhizopod community to experimental sediment disturbance does not support the intermediate disturbance hypothesis ................................................................................ 79 5.1. Summary ............................................................................................ 79 5.2. Introduction ................................................................................. 79 5.3. Materials and Methods ..................................................................... 81 5.3.1. Reference site ..................................................................... 81 5.3.2. Experimental design ......................................................... 82 5.3.3. Sampling and sample analysis .................................. 83 5.4. Results ............................................................................................ 84 5.4.1. Intensity experiment ......................................................... 84 5.4.2. Frequency experiment ......................................................... 88 5.5. Discussion ................................................................................. 88 6. Effects of resuspension and mixing on population dynamics and trophic interactions in a model benthic microbial food web ............ 92 6.1. Summary ................................................................................. 92 6.2. Introduction ................................................................................. 93 6.3. Materials and Methods ..................................................................... 93 6.3.1. Model community ......................................................... 93 6.3.2. Experimental design ......................................................... 95 6.3.3. Inoculation and incubation .............................................. 96 6.3.4. Sampling and sample analysis .................................. 97 6.3.5. Statistical analysis ......................................................... 98 3 Tobias Garstecki 6.4. Results ............................................................................................ 98 6.4.1. Whole-community experiment ............................................ 98 6.4.2. Community subset experiment .................................. 100 6.4.3. Particulate enrichment experiment .................................. 103 6.5. Discussion ................................................................................. 107 6.5.1. Food web structure ......................................................... 107 6.5.2. Resuspension effects on Amphora coffeaeformis and bacteria ........................................................................ 108 6.5.3. Resuspension effects on protistan population dynamics … 109 6.5.4. Significance under field conditions and possible mechanisms 111 7. Zusammenfassung ........................................................................................ 113 7.1. Vergleich des benthischen und des planktischen mikrobiellen Nahrungsgewebes der Boddengewässer