1. Spatial and Temporal Variability of Zooplankton in the Northern Gulf of Mexico: Effects of Low Oxygen Bottom Waters
Mike Roman, Dave Kimmel, Jamie Pierson,
Krista Hozyash, Bill Boicourt and Xinsheng Zhang
ACKNOWLEDGE CO-AUTHORS
FUNDED BY NOAA-COASTAL OCEAN PROGRAM
Horn Point Laboratory
University of Maryland Center for Environmental Science
Cambridge, Maryland

2. NGOMEX 2006 – Spatially-explicit, High-resolution Mapping and Modeling to Quantify Hypoxia Effects on the Living Resources of the Northern Gulf of Mexico
PROJECT OBJECTIVES:
1. Conduct high resolution mapping of NGOMEX pelagic food web in relation of hypoxia.
2. Integrate our ecosystem measurements through a variety of models designed to assess the effects of hypoxia on pelagic food webs and production.
3. Quantify habitat suitability for economically important fishes.
4. Provide tools to forecast food-web interactions, habitat suitability and fish production in relation to hypoxia.
OVERALL PROPOSAL TITLE AND OBJECTIVES
HIGH RESOLUTION MEASUREMENTS OF BACTERIA, PROTOZOA, PHYTOPLANKTON, ZOOPLANKTON AND FISH
MENTION NANCY’S WORK – ALSO NECOP
ECOPATH MODELS TO ASSESS IMPACTS OF HYPOXIA ON FOOD WEB
BIOENERGETIC AND IBM MODELS TO ASSESS EFFECTS OF HYPOXIA ON FISH

3. NGOMEX ZOOPLANKTON RESEARCH
Possible Effects of Hypoxia on Zooplankton
Decrease/Increase Biomass/Abundance
Change Vertical Distribution
Change Size Distribution
Change Species Composition
THE FOCUS OF OUR ZOOPLANKTON RESEARCH
I WILL FOCUS ON POSSIBLE EFFECTS ON BIOMASS AND VERTICAL DISTRIBUTION
KIMMEL ON SIZE DISTRIBUTION
SPECIES COUNTS STILL BEING COMPLETED

4. AREA OF BOTTOM HYPOXIA – RABALAIS
VOLUME IMPORTANT TO PELAGIC ORGANISMS
GIVE EXAMPLE IN ROOM – HYPOXIA A FOOT OFF THE FLOOR VS HALF-WAY TO CEILING

5. HYPOXIA IS VARIABLE IN SPACE AND TIME
AVHRR OF SUSPENDED SEDIMENTS (RIVERINE INPUTS)
INPUTS FROM MISSISSIPPI AND ARCHAFALA

6. Mississippi River/Gulf of Mexico
PLUME POSITION (AND ORGANIC INPUTS LEADING TO HYPOXIA) CAN CHANGE WITH FW DISCHARGE AND WINDS
MOVES LIKE A FIRE HOSE

7. SCANFISH SAMPLING
HIGH-RESOLUTION UNDERWAY MEASUREMENTS (7KTS)
SENSORS – T, S%, O2, CHL, OPC
OPC TECHNOLOGY – 256 LIGHT BEAMS - COUNTS PARTICLE > 250 ESD
REMEMBER THAT IT IS AN OPTICAL PARTICLE COUNTER – SOMETIMES PARTICLES ARE NOT ZOOPLANKTON
WE ALSO SAMPLED ZOOPLANKTON WITH A HIGH VOLUME PUMP – AND HIGH FREQUENCY ACOUSTICS

8. Path of Scanfish 10 Pressure 20 30 40 5 10 15 20 25 30 3510
Pressure 20
WHAT YOU SACRIFICE IN ACCURACY – YOU GAIN IN SPATIAL RESOLUTION
PATH OF SCANFISH OSCILLATION
DATA BINNED 0.5 M VERTICAL, HORIZONTAL RESOLUTION DEPENDS ON DEPTH – AVERAGE 7 OSCILLATIONS PER KM
MISS TOP AND BOTTOM 1-2 M – DEPENDING ON SEA STATE 30 40 5 10 15 20 25 30 35
Transect Distance (km)

9. K J M H I A AA F G CC E D DD TRANSECTS OF NANCY RABLAIS SUMMER SURVEY
WE DID IN 2003 AND 2004
2006 – REPEATED TIME SERIES OF SELECTED TRANSECTS TO STUDY DIEL CHANGES IN SPATIAL DISTRIBUTION OF PELAGIC FOOD-WEB
TODAY FOCUS ON COMPARISONS OF C, H AND I – POINT OUT TRANSECTS

10. Transect C (Day) 2003 Depth (m) Latitude (deg) Salinity
Chlorophyll (ug/L)
Transect C (Day)
2003
Depth (m)
Dissolved Oxygen (mg/L)
SALINITY/CHLOROPHYLL/DO/OPC ZOOPLANKTON
2003 C TRANSECT – DAY
IF ZOOPLANKTON MIGRATE – SHOULD SHOW INTERACTIONS OF HYPOXIA AND ZOOPLANKTON
CHLOROPHYLL HIGHEST IN LOW SALINITY WATER – SOME HIGHER CHL LOOKS LIKE IT IS MOVING OFFSHORE AT DEPTH
THIS LAYER CORRESPONDS TO LOWER CXYGEN WATERS
ZOOPLANKTON HIGHEST AT SURFACE AND 10 M
Total Zooplankton Biovolume (ml/m^3)
Latitude (deg)

11. Transect C (Day) 2004 Depth (m) Latitude (deg) Salinity
Chlorophyll (ug/L)
Transect C (Day)
2004
Depth (m)
Dissolved Oxygen (mg/L)
SALINITY/CHLOROPHYLL/DO/OPC ZOOPLANKTON
2004 C TRANSECT – DAY
GREATER AMOUNT OF FRESH WATER
CHL VALUES < 1
GREATER EXTENT OF LOW OXYGEN BOTTOM WATER
NOT MUCH ZOOPLANKTON IN LOW OXYGEN BOTTOM WATERS
LOWER AMOUNTS OF ZOOPLANKTON BIOMASS – PEAKS AT BASE OF HALOCLINE
Total Zooplankton Biovolume (ml/m^3)
Latitude (deg)

12. Transect C (Day) 2006 Depth (m) Latitude (deg) Salinity
Chlorophyll (ug/L)
Depth (m)
Dissolved Oxygen (mg/L)
SALINITY/CHLOROPHYLL/DO/OPC ZOOPLANKTON
2006 C TRANSECT – DAY
HIGHER SALINITY SURFACE WATERS AS COMPARED TO 2004
ISOPYCNAL TRANSPORT – CHL, OXYGEN, ZOOPLANKTON
ZOOPLANKTON APPEAR TO AVOID LOWEST OXYGEN WATERS
Total Zooplankton Biovolume (ml/m^3)
Latitude (deg)

13. Dissolved Oxygen (mg/L) Total Zooplankton Biovolume (ml/m^3)
2003
2003
Depth (m)
2004
2004
COMPARISON OF TRANSECT C – DAY
SHOWS RELATIONSHIP BETWEEN LOW OXYGEN WATERS AND ZOOPLANKTON
SUGGESTIONS THAT LOWEST OXYGEN WATERS HAVE LOWER ZOOPLANKTON BIOMASS
CONSIDERABLE VARIABILITY DUE TO DIFFERENT WATER MASS MOVEMENT
2006
2006
Latitude (deg)
Latitude (deg)

14. ANOTHER WAY TO MAKE SENSE OF TRANSECT DAY TO EXAMINE OXYGEN AND ZOOPLANKTON IN SIMILAR WATER MASSES
PLOT OF OXYGEN VALUES IN “T – S SPACE” FOR C, H AND I TRANSECTS
MORE LOW OXYGEN IN 2004 – MORE FRESH WATER (AND PRESUMABLY ORGANIC INPUT) – OTHER YEARS HAVE TRUNCATED PLOTS WITH NO WATER < 25PSU
ALL YEARS – LOW OXYGEN WATERS TEND TO OCCUR IN LOWER-RIGHT HAND PORTIONS OF GRAPH (LOWER TEMP/HIGHER SALINITY) – BUT NOT ALL RECALL WELL DEVELOPED HYPOXIA MID-SHELF IN 2004

15. ZOOPLANKTON IN “T-S SPACE” FOR C, H AND I DAY TRANSECTS
RELATIVE ZOOPLANKTON BIOMASS CALCULATED BY DIVIDING ALL THE BIOMASS DATA FOR EACH TRANSECT BY THE MAXIMUM VALUE ON THE PARTICULAR TRANSECT. VALUES RANGE FROM 0 TO 1.
NOTE FOR THE MOST PART, HIGHEST RELATIVE ZOOPLANKTON BIOMASS DOES NOT OCCUR IN LOWER-RIGHT HAND PORTION (LOWER T, HIGHER S) OF GRAPHS
ZOOPLANKTON USUALLY HIGHEST IN LOWER SALINITY WATERS
SOME OVERLAP WITH LOW OXYGEN WATERS IN H

16. MEDIAN DEPTH = DEPTH BELOW WHICH 50% OF THE ZOOPLANKTON BIOMASS IS FOUND
UPPER AND LOWER LIMITS OF BOXES REPRESENT INER QUARTILE RANGES
WHISKERS ON EACH BOX REPRESENT THE RANGE OF DATA
C, TRANSECTS; YELLOW = DAY; BLUE = NIGHT
NORMOXIC VS HYPOXIC (< 2 MG/L) WATERS
LARGER DAY/NIGHT DIFFERENCE IN NORMOXIC WATERS AS COMPARED TO HYPOXIC
DAYTIME DEPTHS IN HYPOXIC WATERS – SHALLOWER THAN NORMOXIC AND MORE CONCENTRATION – CHOW LINE?
WHY LESS DAY/NIGHT VARIATION IN HYPOXIC WATERS – FISH SUPPRESSING OR SMALLER COPEPODS (LARGER ONES GET EATEN) – WHICH DO NOT MIGRATE

17. PUT ON YOUR SPECIAL 3-D GLASSES
TEASER FOR KIMMEL’S TALK
MEDIAN DEPTH VS TIME VS OPC SIZE CLASS –C TRANSECTS
AS HAS BEEN SHOWN FOR ZOOPLANKTON POPULATIONS AND COMMUNITIES USING TRADITIONAL NET TOWS:
LARGER SIZE CLASSES (PRESUMABLY BECAUSE THEY ARE MORE VUNERABLE TO PREDATION) EXHIBIT GREATER DIEL CHANGES IN DEPTH THAN SMALLER SIZES
THIS IS REFLECTED BY CHANGES IN MEDIAN DEPTH OVER TIME
SOME VARIATION DUE TO DIFFERENT WATER MASSES

18. Total Zooplankton Biovolume
(ml/m^3)
Dissolved Oxygen (mg/L)
Fish (dB)
2003
2003
Fish (dB)
2003
2004
2004
-110
-50
-70
-90
-30
2004
Depth (m)
C TRANSECT DURING THE DAY – 2003, 2004, 2006
DO, OPC-ZOOPLANKTON AND ACOUSTIC ESTIMATES OF FISH BIOMASS (dB) – LUDSON/BRANDT
NOTE DIFFERENT DEPTH SCALES FOR FISH
FISH KEEP OUT OF LOW OXYGEN WATERS
CONSIDERBLE COINCIDENCE BETWEEN MAX CONCENTRATIONS OF ZOOPLANKTON AND FISH
FISH MAY FOCUS THEIR FEEDING EFFORTS ON CHOW-LINE CREATED BY HYPOXIC BOTTOM WATERS
2006
2006
2006
2006
Latitude (deg)
Latitude (deg)
Latitude (deg)

19. CHESAPEAKE BAY – OLD DOGMA WHY ESTUARIES ARE PRODUCTIVE
HIGH NUTRIENT INPUTS; ALLOCTHONOUS ORGANIC INPUTS FROM WATERSHEDS; EFFECTIVE TIDAL MIXING AND 2-LAYERED FLOWS WHICH TRAP NUTRIENTS
HAVE ALL BEEN SUGGESTED AS POTENTIAL MECHANISMS FOR EFFICIENT TROPHIC TRANSFER IN ESTUARIES
LESS ATTENTION HAS BEEN GIVEN TO THE PHYSICAL MECHANISMS WHICH MAY CONCENTRATE FOOD AND ENHANCE TROPHIC EFFICIENCIES
ESTUARIES ARE RICH WITH PHYSICAL DISCONTINUITIES FORCED BY FRESHWATER-SALTWATER INTERFACES, COMPLEX BATHYMETRIES, PERIODIC
TIDAL FORCING AND OPEN FETCH TO WIND SHEAR.
THE FRONTS AND CIRCULATION PATTERNS ASSOCIATED WITH THESE FEATURES CAN RESULT IN ENHANCED CONCENTRATIONS OF ZOOPLANKTON AND FISH

20. TIES TRANSECT – 310 KM LONG

21. TIES DATA
POINT OUT AXIS
ANNUAL DIFFERENCES IN HYPOXIA AND ZOOPLANKTON
BLUE HOLES IN ZOOPLANKTON MATCHUP WITH YELLOW BLOBS IN OXYGEN

22. RELATIVE ZOOPLANKTON CENTER OF MASS VS NORMALIZED % OF WC THAT IS HYPOXIC
POINT OUT 1:1 LINE
THE MORE HYPOXIC WATER – THE SHALLOWER THE MEDIAN DEPTH (CLOSER TO SURFACE) – EXCEPT TRANSECT H
CHESAPEAKE BAY HAS MORE HYPOXIA THAN THE GULF – BLACK LINE SHIFTED TO RIGHT
GOM == 10 to 40% of WC hypoxic – but in CB 40 to 60%
COMPARE TO CELING HEIGHT
BOTH DAY AT NIGHT
TIES JULY 2000

23. TIES DATA – JULY 2000 JUST DEEP PORTION
ZOOPLANKTON MEDIAN DEPTH CLOSER TO SURFACE AT NIGHT
ZOOPLANKTON DISTRIBUTION SQUEEZED IN HYPOXIC WATER IN GOM
CHESAPEAKE VERTICAL DISTRIBUTION DATA MORE VARIABLE – ACCLIMATE TO HYPOXIA?

24. July 1996 WT YEAR – MORE HYPOXIA DRY YEAR – LESS HYPOXIA
FOCUS ON ZOOPLANKTON
1996 – BLUE HOLE IN MID-BAY – LOW ZOOPLANKTON IN WC WITH HYPOXIC BOTTOM WATERS

25. Mean Fish Biomass

26. LESS COPEPODS IN HYPOXIC WATER
HYPOXIA REFUGE OR FALSE BOTTOM
JELLYFISH VS FISH PREDATORS IN LOW OXYGEN WATER
IS HYPOXIA A SOURCE OF MORTALITY FOR COPEPOD EGGS?

27. Conclusions
The distribution of Scanfish-OPC zooplankton estimates show the same spatial structure as traditional net tow measurements and make sense in relation to measured hydrographic variables and fish distributions.
Zooplankton biomass appears to be lower in hypoxic waters.
Chesapeake Bay zooplankton appear to occur in hypoxic bottom water more than GOM zooplankton.
Hypoxic bottom waters may result in shallower daytime depths of larger zooplankton, making them more vulnerable to predation by visual feeders.