Investigating the contribution of allochthonous subsidies to kelp forests in central California

Transcription

1 Investigating the contribution of allochthonous subsidies to kelp forests in central California melissa m foley UCSC Institute of Marine Science and Center for Ocean Solutions

2 system connectivity rivers nearshore ocean open ocean coral reefs mangroves estuaries forests

3 system connectivity - subsidies seabirds and islands Maron et al salmon, bears, and watersheds Hicks et al watersheds to rivers Power et al. 2004

4 system connectivity - subsidies terrestrial open ocean nearshore ocean

5 system connectivity - subsidies terrestrial open ocean? nearshore ocean

6 system connectivity - subsidies nutrients particulate organic matter nearshore ocean importance of different subsidies depends on * temporal availability * spatial availability * abundance * quality

7 nearshore ecosystems ~ 7% marine habitat ~ 25% primary productivity - disproportionately diverse - valuable ecosystem services - threatened by human activities

8 giant kelp (Macrocystis) forests foundation species support high algal, invert, & fish diversity high productivity and biomass persist year-round life history stages affected by inputs from terrestrial and open ocean systems

9 system connectivity what subsidies are delivered via stream and upwelling sources to giant kelp communities throughout the year? rivers open ocean Macrocystis

10 interdisciplinary approach oceanography ecology biogeochemistry rivers open ocean Macrocystis

11 Big Sur, California San Francisco Bay Monterey Bay Big Sur

12 Big Sur, California stream Big Sur Big Creek Non-River River North Big Creek River South stream N

13 allochthonous subsidies DIC & NO 3 atmospheric input stream input DIC DIC NO 3 NO 3 DIC DIC NO 3 upwelling input

14 allochthonous subsidies -upwelling DIC DIC NO 3 NO 3 DIC DIC NO 3 upwelling input open ocean inputs seasonal upwelling circulation narrow continental shelf

15 allochthonous subsidies - streams stream input DIC DIC NO 3 NO 3 DIC DIC NO 3 terrestrial-derived inputs short, steep watersheds seasonal rainfall episodic inputs

16 Big Creek stream dynamics 30 December January 2006

17 allochthonous subsidy delivery stream input upwelling input

18 allochthonous subsidy delivery upwelling strength m 3 /s/100m Jan Feb 2005 Mar Apr May Jun Jul Aug Sep Oct Nov Dec stream discharge Jan Feb 2006 Mar Apr May Jun Jul Aug Sep month Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec m 3 s Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 5 0 Jun Jul Aug Sep month

19 water sampling nearshore non-river intertidal winter only spring/summer only year round nearshore river north nearshore river south intertidal upstream

20 nitrate & phosphate Nitrate concentration (um) Non-river River Upstream Phosphate concentration (um) Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 2006 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 2007 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Month

21 chlorophyll-a concentration 10 8 Big Creek Non-river River Upstream Chlorophyll Concentration (µg/l) Big Sur Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Month

22 [chlorophyll-a] in context Point Reyes Monterey Bay Big Sur

23 decoupled chl-a & nitrate dynamics concentration concentration time iron replete area time iron limited area chlorophyll nitrate

24 stable isotopes C and N * naturally occurring in unequal abundances * differential uptake caused by increased mass of heavy isotope (light isotope = faster) * predictable change between trophic levels * signature is ratio of heavy:light isotope e.g. higher = more 13 C; lower = more 12 C

25 allochthonous subsidy delivery stream input DIC DIC NO 3 NO 3 upwelling input DIC DIC NO 3 is there temporal and/or spatial variation in Macrocystis isotope values due to seasonal changes in the subsidy source?

26 kelp isotopes and tissue content * blades collected monthly * collected from 5 & 15 meters depth * standardized blade size & condition * analyzed for δ 13 C, δ 15 N, C:N, %C, %N

27 allochthonous subsidies isotope signatures stream UPWELLING Non-River δ 13 C DIC ~ 0 δ 15 N DIN ~ +7 to 8 TERRESTRIAL δ 13 C DIC ~ -15 to -5 δ 15 N DIN ~ -2 to +4 River North River South stream N

28 possible seasonal patterns δ 15 N late summer spring early summer winter early spring δ 13 C

29 seasonal variability 9 8 Macrocystis Late Summer - Winter (Aug-Dec) Spring - Early Summer (Mar-Jul) 5 m δ 15 N m 15 m 5 15 m δ 13 C

30 what drives seasonal variability? Use environmental variables to estimate the timing and concentration of DIC and DIN delivered to nearshore kelp beds Use statistical tests to determine if any environmental variables explain the variability in seasonal isotope values River discharge (m 3 /s) River discharge Water transport (m 3 /s/100m) Upwelling Index Nitrate Concentration (µm) Nitrate Concentration 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec -40 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

31 upwelling strength & [nitrate] seasonal variability in δ 13 C and δ 15 N driven by upwelling strength DIN (nitrate) concentration Water transport (m 3 /s/100m) Upwelling Index Nitrate Concentration (µm) Nitrate Concentration -40 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

32 upwelling strength & [nitrate] δ 13 C δ 15 N NO 3 (µm) NO 3 (µm) δ 13 C Jul 05 Aug 05 Sep 05 Oct 05 Dec 05 May 06 Jun 06 Jul 06 Oct 06 Nov 06 Sep 06 Mar 07 May 07 Jun 07 Jul 07 Aug 07 Sep Nitrate Concentration (µm) δ 15 N Jul 05 Aug 05 Sep 05 Oct 05 Macrocystis Nitrate Dec 05 May 06 Jun 06 Jul 06 Oct 06 Nov 06 Sep 06 Mar 07 May 07 Jun 07 Jul 07 Aug 07 Sep Nitrate Concentration (µm) date date

33 [nitrate] & isotope values k e l p

34 [nitrate] & isotope values k e l p k e l p kelp = lighter than source

35 [nitrate] & isotope values k e l p kelp = lighter than source k e l p kelp = same as source

36 seasonal variability 9 8 Macrocystis Late Summer - Winter (Aug-Dec) Spring - Early Summer (Mar-Jul) 5 m δ 15 N m 15 m 5 15 m δ 13 C

37 what does this mean for consumers?

38 consumer subsidies terrestrial POM kelp phytoplankton red blades (20%)

39 consumer subsidies terrestrial POM kelp phytoplankton what food source(s) do kelp forest consumers use and does that vary seasonally? red blades (20%)

40 isotope value of resources Macrocystis Phytoplankton Terrestrial POM 10 δ 15 N δ 13 C

41 isotope value of seasonal resources Spring Macro Summer Macro Fall Macro Phytoplankton Terrestrial POM δ 15 N δ 13 C

42 δ 13 C kelp forest consumers filter feeders Spring Summer Fall Bryozoans δ 13 C ~9.5 (Membranipora) δ 15 N ~9.5 δ 15 N Mussels (Mytilus) δ 13 C ~3.5 δ 15 N ~3.6 δ 15 N δ 13 C δ 13 C Sponges (Tethya) δ 13 C ~5.5 δ 15 N ~6.3 δ 15 N

43 seasonal resources & consumers 14 possible scenarios Spring Macro Summer Macro Fall Macro Phytoplankton Terrestrial POM δ 15 N δ 13 C

44 seasonal resources & consumers δ 15 N Spring consumers Summer consumers Fall consumers Spring Macro Summer Macro Fall Macro Phytoplankton Terrestrial POM δ 13 C

45 stable isotope mixing model MixSIR 14 δ 15 N Spring consumers Summer consumers Fall consumers Spring Macro Summer Macro Fall Macro Phytoplankton Terrestrial POM Bayesian approach incorporates uncertainty accommodates multiple isotopes and sources δ 13 C (Moore & Semmens 2008)

46 MixSIR results Macrocystis dominates % contribution to consumer tissue Total kelp Phytoplankton Terrestrial POM Me spr Me sum Me fall My spr 5m My spr 15m My sum 5m My sum 15m My fall 5m Nereocystis luetkeana (30%) My fall 15m Te spr Te sum Te fall Membranipora Mytilus Tethya

47 summary kelp & isotopes terrestrial POM kelp phytoplankton

48 summary kelp & isotopes stream input (iron) kelp upwelling input

49 importance of connectivity climate change wildfire habitat destruction rivers open ocean primary producers consumers

50 altering connectivity wildfire rivers open ocean primary producers consumers

51 altering connectivity

52 altering connectivity increased sediment increased terrestrial material

53 altering connectivity 120 Stream POM 600 Stream total PM 70 Intertidal total PM Concentration (mg/l) pre-fire post-fire Big Creek Big Sur 0 Big Creek Big Sur 0 Big Creek Big Sur increased particulate matter

54 altering connectivity 3.5 Chlorophyll (µg/l) 20 Nitrate (µm) 0.5 Phosphate (µm) Concentration pre-fire post-fire Big Creek Big Sur 0 Big Creek Big Sur 0.0 Big Creek Big Sur increased nutrient concentration

55 altering connectivity?

56 questions?