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

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

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

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

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

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

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

Path of Scanfish 10 Pressure 20 30 40 5 10 15 20 25 30 35 10 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)

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

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)

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)

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)

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)

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

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 2004 - H

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

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

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)

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

TIES TRANSECT – 310 KM LONG

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

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

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?

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

Mean Fish Biomass 1995-1999

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?

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.