CHAPTER 4 Middle Atlantic Bight Zooplankton: Second Year Results and a Discussion of the Two-Year BLM-VIMS Survey G. C. Grant with contributions by J. E. Olney, S. P. Berkowitz, J. E. Price, P. 0. Smyth, M. Vecchione, and C. J. Womack Virginia Institute of Marine Science Gloucester Point, Virginia 23062 Contract AA550-CT6-62 with the Bureau of Land ManagemE!nt July 1979 Special Report in Applied Marine Science and Ocean Engineering No. 192 (Reprinted January 1981) CHAPTER 4 TABLE OF CONTENTS INTRODUCTION • 4-1 METHODS AND MATERIALS 4-2 Sampling Locations 4-2 Shipboard Procedure • 4-2 Subsurface Zooplankton. 4-2 Surface Zooplankton (Neuston) 4-4 Laboratory Procedure 4-5 Frozen Collections • 4-5 Biomass Measurements • 4-5 Sorting of Preserved Samples • 4-5 Data Analysis 4-6 Data Cards and Storage • 4-6 Diversity Measurements 4-6 Cluster and Nodal Analyses • 4-6 RESULTS 4-7 Fall 1976 Cruise No. BLMOSW. 4-7 Summary of Collections • 4-7 Biomass 4-7 Fauna! Description. 4-9 Diel Cycles of Dominant Neustonts 4-20 Station Ll. 4-20 Station 12. 4-20 Station L4. 4-20 Station 16. 4-24 Station Cl. 4-24 Station E3. 4-24 Station J 1. 4-24 Station BS. 4-24 Station A2. 4-30 Community Analysis • 4-30 Frequency of Occurrence and Abundance • 4-30 Diversity. • • • . 4-30 Cluster Analysis • • 4-38 Synopsis of Cruise BLM05W 4-50 Winter 1977 Cruise No. BLM06W. 4-50 Summary of Collections. 4-50 Biomass 4-51 Fauna! Description. • • • 4-51 Diel Cycles of Dominant Neustonts 4-61 Station Ll. • ••• 4-61 Station 12. 4-61 Station L4. 4-61 Station L6. • . 4-61 Station Cl. 4-66 Station E3. • . 4-66 Station J 1. • • . 4-66 Station BS. 4-66 Station A2. 4-66 Community Analysis . 4-72 Frequency of Occurrence and Abundance . 4-72 Diversity . • . 4-72 Cluster Analyses. 4-79 Synopsis of Cruise BLM06W . 4-90 Spring 1977 Cruise No. BLM07W . 4-91 Summary of Col lee tions . 4-91 Biomass 4-91 Fauna! Description . 4-93 Diel Cycles of Dominant Neustonts . 4-102 Station Ll. 4-102 Station L4. 4-102 Station L6. 4-102 Station Cl. 4-102 Station E3. 4-108 Station J 1. 4-108 Station BS. • • 4-108 Station A2. 4-108 Community Analysis . 4-113 Frequency of Occurrence and Abundance . 4-113 Diversity . 4-113 Cluster Analyses. 4-113 Synopsis of Cruise BLM07 w . 4-131 Summer 1977 Cruise No. BLM08W . 4-132 Summary of Collections . 4-132 Biomass 4-132 Faunal Description . 4-134 Diel Cycles of Dominant Neustonts 4-144 Station Ll. 4-144 Station L2. • • • . 4-144 Station L4. • . 4-144 Station L6. • . 4-148 Station Cl. • • . • . 4-148 Station E3. • . 4-148 Station Jl. 4-148 Station BS. • • . 4-148 Station A2. • . • . 4-154 Community Analysis . 4-154 Frequency of Occurrence and Abundance . 4-154 Diversity . • . • 4-154 Cluster Analysis. • • . • . 4-162 Synopsis of Cruise BLM08W . • . • . 4-174 Replication of Bongo Sampling . • . 4-175 Biomass • • • • • • • • • • • • • • • • • 4-175 Replication and Species Dominance ••••••• 4-178 Species Abundance ••••••••••••••• 4-178 DISCUSSION ••••••• . 4-183 Seasonal Succession of Zooplankton Communities ••••• 4-183 Subsurface Zooplankton • • • ••• 4-189 The Neuston •••••••••••••••••••• 4-196 Station Cl ••••••••••••••••••• 4-196 Station E3. • • • • • • • • • • • • • ••• 4-200 Station Jl •••••••••••••••••• • 4-205 Stations Sampled Only in Second Year • ••••••• 4-210 Northern Stations BS and A2 •••••••••• 4-211 Southern Stations Ll and 12 •••••••••• 4-211 Offshore Southern Stations ••••••••••• 4-211 Zooplankton and Hydrography •••• 4-211 Water Types and Neuston •••••••••• 4-211 Indicators of Communities ••••••••••••• 4-214 Coastal Boundary Layer ••••••••••••• 4-215 Central Shelf Fauna • • • • • • • • • • • • • • 4-215 Shelf-break and Slope Fauna ••• 4-218 Factors Affecting Distribution of Zooplankton ••• 4-221 Biomass • • • • • • • • • • • • • • • • • • 4-221 February Biomass 4-222 May Biomass . 4-222 Diversity ••••••••••••••••• 4-223 Middle Atlantic Bight Neuston ••• 4-224 LITERATURE CITED •• . 4-233 CHAPTER 4 MIDDLE ATLANTIC BIGHT ZOOPLANKTON: SECOND YEAR RESULTS AND A DISCUSSION OF THE TWO-YEAR BLM-VIMS SURVEY G. C. Grant INTRODUCTION A baseline survey of zooplankton in Middle Atlantic Bight waters subject to impact from development of oil and gas resources was initiated in the fall of 1975. Sampling in the first year was conducted quarterly along a transect of six stations extending from near the coast of southern New Jersey to the continental shelf edge. Location of this initial transect was chosen to pass through an area of the outer shelf expected to be of high interest to the leasing oil corporations. Results of the first year's study (Grant 1977a) demonstrated that Middle Atlantic Bight zooplankton has been much neglected and is, therefore, poorly described. Findings also confirmed our suspicions that the neustonic, or surface layer, habitat is a critically important one for early developmental stages of many fishes and decapod crustaceans in continental shelf waters. Community analyses of zooplankton collections revealed the continual presence of a coastal assemblage of species, presumably associated with the Coastal Boundary Layer, a flow-trapped structure best known from physical studies (Csanady 1976), and a Central Shelf community. Offshore or shelf-break species were less well-defined, except in the fall of 1975, when a distinct community of oceanic species occurred at the shelf-break and slope stations. These results and a better definition of the localities that were of prime interest to oil companies dictated an expansion of zooplankton sampling in the second year. The original transect was again included in the sampling plan, although with a reduction in 24-hour neuston collections, two new stations were added to the north of that transect, and a transect of four stations extending from the coast of Virginia to the shelf-edge near Norfolk Canyon was also added. Biomass estimates and replication of bongo tows were further implementations. This report presents the results of the second year of seasonal zooplankton sampling in Middle Atlantic Bight waters, obtained from four seasonal cruises starting in November 1976 and ending in September 1977, and discusses conclusions based on data from both sampling years. ~1 METHODS AND MATERIALS Sampling Locations Twelve stations were occupied each quarter for sampling of surface and subsurface zooplankton (Figure 4-1). These stations extended from the coasts of New Jersey and Virginia to the continental shelf edge and from south of Hudson Canyon to the vicinity of Norfolk Canyon. Sampling regimes at these stations were of three types as indicated on Figure 4-1 and detailed below. Shipboard Procedure Subsurface Zooplankton Double-oblique tows, from surface to near-bottom and back to surface, were made at ench of the 12 stations with 60 cm opening-closing bongo systems (McGowan and Brown 1966), first with paired 202 µm nets, then with SOS µm nets. The track of tows followed a broad arc, except in heavy weather when w~ves were quartered. All tows were taken using a 1/4-inch stainless steel cable, towed at a vessel speed of approximately 1.5 knots. To avoid surface contaminants, samples were submerged in closed position, opened below the surface, then re-closed before retrieval through the surface layer. Flowmeters (General Oceanics, Inc.) were excluded from the net utilized for chemical analysis. Precautions against contamination of collections for chemical analysis also included minimizing contact between nets and ship surfaces, through use of a bongo rigging stand (Ocean Instruments, Inc.) and sailbags to contain nets not in active use. Collections for analysis of trace metals and hydrocarbons were emptied into stainless steel buckets before net wash-down to avoid contamination from the ship's seawater system. These collections were then concentrated on 110 µm netting, split into two roughly equal portions (one each for hydrocarbons and trace metals), then transferred with teflon-coated utensils into acid-washed glass jars. Jars were sealed with teflon-lined caps and immediately frozen. At quality control stations (one randomly-selected station in each quarterly cruise), each collection for chemistry was doubly split to provide extra samples for a SLM-designated laboratory. Samples collected in the metered half of bongo net pairs and reserved for taxonomy were washed down with the ship's seawater system into collecting buckets, concentrated on 110 µm netting, transferred to glass jars and preserved in 5-8 percent buffered formaldehyde in seawater. 4-2 \ / ,, ,, . ,.·/ / ..... ----~--/" - -:-c- l:'\ ,,~ ..... - ::, - --, '"-- _,..,,, c- - -..... / - - J '- --:::. -::::. ,- ' \ '1 ' / A211 1 • I I I i I I I / ,,, / I/ ) S \ / .,.) I') I \ ~.., ,,, .,., / \ "' \ , , ; ,,,,,--;. r .J c.... \ ,' ..... C. \ I 1· /.:., I \ j/~'-) \ )f ~ r I .,.,.-\" I r ) \ I (~ / ) \ ,ii , JI ' },JI* < ~ DI I ,W i ' F2 1 l~ ; ' • . )'- ~} ' /\ ,\ . \ / ) N3• I ~-') \ ...'i , E3l t I , , , /~ I 1 • I )t i ,:.,· C \ / Su / I I _I ) \ ff' - :'I; \ )'r ,) \ ,• ... ,'/~//I \ /'( c..... ( \ .._-' -· ' \ '\ \' -, L \ \ I\ ,- ,,," \ \ l 1 r ..... c..,- \ ,\ \ ( / \ _c". If r1 \ .J I l \ \ I"'" Figure 4-1. Sampling locations for subsurface and surface (neuston) zooplankton in the Middle Atlantic Bight, 1976-1977. Routine collections of 202 µm and 505 µm bongo nets and an accompanying neuston tow were augmented as indicated: *24-hr neuston station, **24-hr neuston plus 3 replicate bongo tows. 4-3 Additional bongo collections were made at stations A2, BS and E3 on each cruise to provide replicate samples for statistical purposes. At these stations the initial two bongo tows (202 µ m and 505 µ m nets) were followed in succession by three additional tows. The latter utilized an array of two 60 cm bongo samplers and a time-depth recorder. Efficient operation of the messenger-actuated, opening-closing device on the bongo systems was possible only with the uppermost system, due to the necessary close spacing of bongo systems on the towing wire. Bongos were fitted with paired 202.µm and 505 µm nets, the upper pair closed on descent for chemistry samples and unmetered, the lower pair open on descent and with both sides metered for taxonomy and biomass collections.