The pivotal role of mesograzers in modulating the impact of ocean warming on Fucus

Transcription

1 The pivotal role of mesograzers in modulating the impact of ocean warming on Fucus The actors: 1. Structural, prennial macroalgae: Fucus serratus and Fucus vesiculosus 2. Shading filamentous epiphytes 3. Mesograzers: Idotea balthica, Gammarus spp. 4. Fishes: stickleback Bioc students Background: OW favors filamentous algae which may be controlled by mesograzers. Mesograzers are favoured by moderate and inhibited by strong OW Fish reduce the abundance (and size?) of mesograzers Fucus are negatively impacted by epiphytes (and OW) Hypotheses: Fv and Fs are differently impacted by epiphytes Fish impair Fucus by suppressing mesograzer control of epiphytes OW impact on Fucus will be mitigated by mesograzers OW impact on Fucus enhanced by fish Benthocosm Experiment 17 1

2 The infrastructure: Kiel Outdoor Benthocosms Bioacid II: Seasonal response patterns Benthocosm Experiment 17 2

3 acroepiphyte bm [g DW] acroepiphyte bm [g DW] Fucus bm [g FW] Fucus bm [g FW] Fucus bm [gfw] Microepiphyte bm [pgc] Microepiphyte bm [pgc] Microepiphyte bm [pgc] Fucus bm [gfw] Fucus bm [g FW] Fucus bm [g FW] Macroepiphyte bm [g DW] Mi 18 g AFDW] Macroepiphyte bm [g DW] Indirect effects of warming on epiphytes and F. vesiculosus were mediated by grazers 118 g AFDW] x1 4x1 8x1 OW x Grazer ab ambient temperature high temperature Grazer ab 1 F. Werner B. Matthiessen GEOMAR r=-.69 p<.5 x1 2x1 7 4x1 7 Microepiphyte bm [pgc] Microepiphyte bm [pgc] 4x1 7 3x1 7 2x x1 r=-.72 p= Grazer ab 4x1 7 3x1 7 2x x Grazer bm [g Grazer AFDW] ab Benthocosm 5 Experiment r=.6 p<.5 Grazer ab Controlled by warming, grazers may reduce epiphytes and thereby favour Fucus M

4 Example: Warming Grazing Epibiosis - Fucus Ecosystem services (structure, C & N binding, O2 ) Benthocosm Experiment 17 4

5 Summer Nutrient enrichment Epibiotic biofilms Performance items: D = defense production G = growth P = photosynthesis R = reproduction enhancement reduction P Fucus modulation Warming D G R Epiphytism Acidification Grazing rates Grazer abundance Fish Benthocosm Experiment 17 5

6 Growth Repro Defense Burning ember for the fate of a Fucus community Spring Summer Winter Autumn Very high risk High risk Low risk Beneficial effect F u c u s v e s i c u l o s u s

7 Micro Macro Amphi Iso Burning ember for the fate of a Fucus community Spring Summer Winter Autumn Very high risk High risk Low risk Beneficial effect E p i p h y t e s M e s o g r a z e r s

8 Balanus Mytilus Asterias Burning ember for the fate of a Fucus community Spring Summer Winter Autumn Very high risk High risk Low risk Beneficial effect F i l t e r f e e d e r s P r e d a t o r s

9 The beneficial (cleaning) or detrimental (consumption) role of gammarid mesograzers under present and future temperature conditions on two important Fucus species Set-up x T ambient x T 5 C Benthocosm Experiment 17 9

10 July June May April Tasks Set-up Continuous logging of ph, salinity, O2 Fish (y/n), mesograzers (y/n), F. vesiculosus & serratus Set-up in mid-march Fucus Fucus WW, C/N, epibiosis, performance (O2 prod) Ecosystem 24h monitoring (O2, ph, DIC, TA, plankt. CHl a) x T ambient Structural Fucus WW and length growth, C/N, epibiosis, performance (O2 prod), abundance & size mesograzers Functional 24h monitoring (O2, ph, DIC, TA, nutrients, plankt. CHl a), Fucus performance (O2 prod), feeding rates of mesograzers Structural Functional Fucus WW and length growth, C/N, epibiosis, performance (O2 prod), abundance & size mesograzers 24h monitoring (O2, ph, DIC, TA, nutrients, plankt. CHl a), Fucus performance (O2 prod), feeding rates of mesograzers... x T 5 C Structural Functional Trophic structure Fucus WW and length growth, C/N, epibiosis, performance (O2 prod), abundance & size mesograzers 24h monitoring (O2, ph, DIC, TA, nutrients, plankt. CHl a), Fucus performance (O2 prod), feeding rates of mesograzers... stable isotopes of all components Benthocosm Experiment 17 1

11 Possible project topics (to be done alone, in student pairs, or in collaboration with a scientist) Effect of OW on population growth of gamarids Effect of temperature on consumption rates of gammarids Effect of OW on palatability of Fucus vesiculosus and Fucus serratus Do the two Fucus species differ in their responses to OW (reg. photosynthesis, growth, palatability)? Effect of OW on filamentous epiphytes on Fucus Control of epiphytism by mesograzers und ambient and warmed conditions Changes of ecosystem functions in repsonse to OW and/or grazing... Benthocosm Experiment 17 11

12 ANOVA REGRESSION (regular) REGRESSION (random) T Benthocosm Experiment 17 12

13 W a r m i n g Small swimming crustaceans: amphipods, isopods The tiny engineers of Global Change Warming -> Grazer response -> Macroalgal response -> Ecosystem response today No grazing -> explosion of epiphytes Fucus Intense grazing -> Fucus Moderate grazing -> epiphytes Fucus X X All year round Fucus contributes to a healthy environment provides shelter for juvenile fish habitat for numerous species supplies oxygen binds CO2 mitigates ocean acidification What you see: tanks with and without grazers and with warming between and 5 C (from light to dark shades) N (left) S (right) Expectation: with increasing warming the ecologically important macroalga Fucus will first suffer from excessive grazing, then from excessive overgrowth and may finally disappear Responsible: Prof. Dr. Martin Wahl (GEOMAR), more infos: