Zooplankton community structure in the northern Gulf of Mexico: Implications for ecosystem management

Transcription

1 Zooplankton community structure in the northern Gulf of Mexico: Implications for ecosystem management By Andrew F. Millett Dauphin Island Sea Lab University of South Alabama W. Monty Graham, Glenn A. Zapfe, Joanne Lyczkowski-Shultz, and Frank J. Hernandez Jr.

2 Large Marine Ecosystems Large areas of ocean space 200,000 km 2 or greater 64 LME s responsible for over 95% of annual global fisheries biomass Defined by four ecological, rather than political or economic, criteria: Bathymetry Hydrography Productivity Trophic Relationships

3 Large Marine Ecosystems 5 Module Assessment: Productivity Zooplankton Fish and Fisheries Pollution and Health Socioeconomic conditions Governance protocols Used for long-term, ecosystem based management

4 Gulf of Mexico LME Home to several commercially important fisheries Zooplankton provide important forage base for fisheries Mid-trophic species Larval forms of higher trophic species Any changes in plankton communities may drastically alter higher trophic levels Little is known about zooplankton on a Gulf-wide scale GOM varies in geography and physical parameters

5 Objectives Synoptically assess zooplankton communities in the northern GOM Establish biological and abiotic factors structuring zooplankton communities Bottom-up vs. Top-Down Temperature, Salinity, Primary Production, Water Depth, Presence of Gelatinous Predators(Aurelia sp.)

6 NOAA SEAMAP Data collected on the NOAA Ship Gordon Gunter during Fall 2007 and 2008 Plankton Survey Coastal Texas to the FL Keys Bongo and Neuston at stations 30nm apart jellyfish presence/absence Fluoro-thermosalinograph flow through system Zooplankton data collected using CUFES

7 Continuous Underway Fish Egg Sampler (Checkley et al. 1997) Samples at ~3m Samples collected between stations 30min transects High Spatial Resolution 2007: n= : n=386 Identified to lowest practical taxonomic level

8 Cluster Analysis Based off Bray-Curtis Similarity Created branches at different resemblance levels Branches were then mapped to examine spatial distribution

9 Zooplankton Spatial Distribution

10 Zooplankton Spatial Distribution

11 Zooplankton Spatial Distribution

12 Bottom-up Processes PC1 + Salinity - Fluorescence 2007 Cruise PC2 - Depth (Distance from shore) No effect from temp A2 and B: offshore, higher salinity, lower fluoro A4 and A5: inshore, low salinity, high fluoro, highest abundance A3c: shallowest PC A2 A3c A4 A5 B E PC1

13 Zooplankton Spatial Distribution

14 Zooplankton Spatial Distribution

15 Bottom-up Processes PC1 - Depth - Salinity 2008 Cruise PC2 + Temp No Fluoro data A2 and B: shallower, inshore, lower salinity A7 and A8: offshore, higher salinity, cooler temp Branch C: Time of Day? PC A2 A6 A7 A8 B C PC1

16 Gelatinous Predators Aggregations do not correspond to different communities Compared zooplankton community within and outside of each aggregation Results variable Decreases recorded in all 2008 aggregations Greatest decrease recorded in Aurelia aggregation Limited jellyfish data Predation effects communities on a localized scale

17 Zooplankton Communities Biggest differences seen between inshore/offshore Driven by meroplanktonic organisms (crab zoea, echinoderms, etc.) Inshore communities differed in salinity and fluorescence levels Fresh Water Discharge Both years exhibited differences between western and eastern GOM

18 Variation in the northern GOM Clear division in salinity between West and East ~88 Longitude (Mobile Bay) Lower salinity is likely from increased fresh water discharge Higher nutrient concentrations Higher Primary Production Higher Zooplankton abundances Salinity Salinity Longitude 2007 Cruise

19 Gulf Coast Diversity Shannon-Weiner: West: H = 1.23 East: H = 2.60 Higher diversity due to greater taxonomic evenness West dominated by calanoid copepods Proportional Abundance Proportional Abundance 1e+0 1e-1 1e-2 1e-3 1e-4 1e-5 1e-6 Western GOM Eastern GOM Rank 2007 Cruise

20 Conclusions Northern GOM consists of several spatially distinct zooplankton communities Differentiated largely by a series of interconnected bottom-up processes: Salinity, primary production, distance from shore Fresh water discharge resulted in a more abundant, less diverse zooplankton community in the western GOM Likely affects higher trophic levels Should be considered for future management and modeling

21 Acknowledgements NOAA NMFS Lab (Pascagoula, MS) Dave Griffith (NOAA/NMFS/SWFSC in La Jolla) FOCAL Sorting Lab Graham Lab Crew of the Gordon Gunter

22 Questions?