We gratefully acknowledge the very able assistance provided by the Officers, Crew, and Marine
Technician of the R/V ENDEAVOR. Their professional expertise and willingness to apply it to
special problems that arose during the cruise, made it possible to accomplish nearly all of our
research goals and objectives.
This report was prepared by Cabell Davis, Bob Campbell, Dian Gifford, Stephan Plourde, and
Jeff Van Keuren with assistance from others in the scientific party. This cruise was sponsored by
the National Science Foundation with additional support for supplies from the NOAA, NURP
program.
1. Introduction
1.1 Purpose of the Cruise 4
1.2 Cruise Overview 5
2. Cruise Narrative 6
3. Individual Reports 12
3.1 Copepod development, growth, and vertical distribution:
Zooplankton Abundance, Physiological Condition, and Growth Rates
(E. Durbin, A. Durbin, R. Campbell, J. Gibson, and M. Wagner) 12
3.2 Copepod feeding:
Ingestion of Phytoplankton, Nanozooplankton and Microzooplankton by Calanus finmarchicus (D. Gifford and M. Seiracki) 14
3.3 Copepod egg production:
Egg production of dominant copepods species on Georges Bank.
(J.A. Runge and S. Plourde) 16
3.4 Copepod behavior and micro-mesoscale distributions of plankton:
Video Plankton Recorder Sampling of plankton behavior and micro-mesoscale distributions (C. Davis and S. Gallager) 17
Appendix I Personnel List 21
Appendix II Event Log 22
1. Introduction
1.1 Purpose of the Cruise
The overall goal of the U.S. GLOBEC Georges Bank Program is to determine how population dynamics interacts with physical processes in controlling the abundance of key animal species on the bank, namely cod and haddock and the dominant spring copepods Calanus and Pseudocalanus. The program consists of several components including field and laboratory studies for estimating population structure and vital rates as well as modeling and retrospective analyses to synthesize the empirical information. The field program is in its first major sampling year and is focussing on how the development of vernal physical stratification affects the population dynamics of the target species. The field program involves process cruises to experimentally measure the vital rates and fine-scale vertical migration behaviors in relation to the physical properties of the water column, and broad-scale cruises to map the distribution of physical and biological properties of the Bank. The process cruises were further divided into those focusing on the larval cod and haddock and those focusing primarily on Calanus and Pseudocalanus.
The present cruise aboard the R/V ENDEAVOR was the last in a series of five zooplankton process cruises spaced at roughly monthly intervals.
The two main objectives of the second leg of this cruise were:
1) to determine the vital rates and vertical migration behaviors of Calanus and Pseudocalanus in relation to local circulation and hydrography, and
2) to measure, in three dimensions (using the VPR system mounted on the ROV JASON), the swimming behaviors of Calanus and Pseudocalanus together with the physical microturbulence in order to determine the mechanisms of aggregation of these copepods at the pycnocline.
The first objective was the same as that for all other process cruises, while the second objective was specific to the second leg of this cruise.
The vital rate and behavioral information provided by our process cruises together with the larger-scale context of population distribution provided by the broadscale cruises will be incorporated into models of biological-physical processes controlling population dynamics of these species.
Our specific objectives were:
(1) to measure vital rates including feeding, birth, development, and growth rates of Calanus finmarchicus and Pseudocalanus spp. while following a drogue in the stratified and well mixed areas of the bank.
(2) to measure the fine-scale (cm) vertical and horizontal distributions of these species in relation to hydrography and other planktonic and particulate matter.
(3) to measure the three-dimensional swimming paths of Calanus finmarchicus and Pseudocalanus spp. together with 3-D paths of passive particles.
(4) to conduct a hydrographic and plankton survey using the VPR in the vicinity of the Great South Channel to determine the location of dense patches of Calanus finmarchicus in relation to hydrography and to measure the physical turbulence and swimming behaviors of C. finmarchicus in these patches.
(5) a final engineering objective was to determine the feasibility of using intermediate sized UNOLS vessels for JASON operations.
1.2 Cruise overview
During this cruise, the work during the daylight morning hours involved the usual station-keeping near a drifter with the usual CTD, zooplankton pump, and net sampling. In the afternoon, VPR/JASON operations were conducted to measure in situ swimming behaviors and microturbulence in 3-D. The ship's ADCP unit was used to make continuous measurements of the water current profile under the ship, in order to construct the local current fields at each site. These data will be used to help in the interpretation of all the other observations made on the cruise.
Two principal sites were occupied (both were drifter sites), one in the stratified southern flank and one in the mixed area (Figure 1). Station #1 was chosen based on information from the first leg and previous broadscale cruise which found higher concentrations of Calanus and gadoid larvae in this area of the bank. It was also upstream of the Eulerian sampling site occupied by Neil Oakey on the R/V Seward Johnson. This station was chosen as the best location to deploy our first ARGOS/GPS drifter since it was within the stratified region but far enough away from the bank edge that the drifter would not be carried off the bank. A large warm-core ring was observed in satellite images of the bank and appeared to be pulling bank water out into the Slope Water (Figure 2). Station #2 was chosen, as usual, in the mixed area next to the long-term crest mooring site. After sampling was completed at the stratified and crest sites, a VPR towyo transect was made from the stratified region toward the Slope Water and, as it turned out, through a shelf water streamer being pulled off the bank by the ring (Figure 3). VPR/JASON deployments were made in all of these areas: mixed region, stratified site, streamer and Slope Water. A fourth region sampled was the western edge of the bank and Gulf of Maine just north of the Great South channel. A VPR survey was made in this region together with a transect in which a Right Whale (feeds primarily on Calanus) was followed while towyoing the VPR. A dense layer of Calanus was found near the bottom (from 80 m down to 10 m off the bottom which was at 160 m).
A priority was assigned to each of the major cruise activities so that in event of worse-than-expected weather, the most relevant work could be completed. The highest priority was given to station #1, where the gadoid eggs were observed, followed in terms of priority by station #2, the VPR Slope Water transect, and the Great South Channel region. Weather limitations during the last day two days of the cruise made it impossible to sample using the VPR/JASON system, so that no behavioral information inside the deep Calanus patch could be obtained.
In general, all of the major cruise objectives listed above were achieved, except for the last part of (4) which as just stated was impossible to achieve due to bad weather. Although we obtained some useful behavioral information from the VPR/JASON system, a considerable amount of cumbersome maneuvering was required resulting in useful data being obtained only about 10 % of the time or less. It was concluded that a ship with dynamic positioning and a reasonably powerful bow-thruster is essential for positioning the ship relative to JASON. A large amount of time was wasted trying to position the ship manually using the Endeavor's weak bow-thruster to obtain slack in the tether between JASON and the clump weight MEDIA (the latter hung directly down from the crane boom off the starboard aft quarter). Thus, most of the time was spent dragging JASON by its tether during which no useful data were obtained. The short periods of slack tether, however, enabled us to use the VPR/JASON system as a maneuverable underwater microscope (which was its intended use) and excellent video of motions of small plankton and passive particles was obtained for the first time in the open sea, and, likewise, micro-turbulence was observed and documented directly using the video.
A list of personnel is given in Appendix I, and a formal log of the sampling events (with correct times and locations) is given in Appendix II.
2. Cruise Narrative
Day 1 (Thursday 6/8/1995)
Departed Woods Hole at 0815. We were delayed leaving by a day to avoid bad weather on Georges Bank (remnants of Hurricane Alison).
Day 2 (Friday 6/9/1995)
We arrived at the Beardsley hydroline station 4 (40 59.6 N 67 39.6 W) at 0327 and began towing the VPR (VPR-1) towards the northeast to locate a patch of Calanus. The VPR tow ended at 0604 at 41 01.8 N 67 28.3 W. A few Calanus were observed along the tow path, but no large concentrations were found. At 0630 we transferred new MOCNESS nets to R/V Albatross IV and then made surface and vertical net tows at 0748 (41 00 N 67 29 W) to determine the species composition of the zooplankton. Pseudocalanus was dominant and several Calanus were observed together with other copepods.
We then steamed southeast about 3 miles to find more Calanus and made a net tow at 0851 (40 57.02 N 67 26.92 W). The species composition was the same as at the previous station. A CTD cast was made to check for intrusion of Slope Water, and none was found. So it was decided that the site was adequate for launching the GPS/ARGOS drifter.
The ARGOS/GPS drifter (drogued at 5 m) was launched at 0949 at 40 57 N 67 27 W, and the following general daily sampling routine began and was used for the rest of the time at this drifter station with the exception that a MOCNESS tow and a night pump cast were not made on the first day due to time constraints of the Durbin group.
Daily Schedule:
0000-0400 Towed-VPR
1000 Zooplankton Pump
1100 CTD/Hydro
1200 Live zooplankton net tows
1300-2030 VPR/JASON deployment
2200 CTD
2230 Zooplankton Pump
See event log (Appendix II) for exact times of these daily operations.
From 1400-1720, practice maneuvering was done using the Endeavor's bow thruster, since the
main screw was not used during JASON deployments. At 1745, we returned to the drifter and
made a test deployment of JASON/VPR (VPR-2J) while keeping JASON on its deployment
rope. Electrical problems were found with the VPR system on JASON and the rest of the
evening was spent trouble-shooting the system, so that no night VPR sled tow was made.
Day 3 (Saturday 6/10/1995)
A CTD component was transferred to the R/V Oceanus at 0630. A diaphragm pump cast (at
1140) was added to the daily morning schedule. A test launch of JASON/VPR (VPR-3J) was
made at 1425 followed by a full launch from 1510-2032. The ship's mates tried to maneuver the
ship to keep slack in JASON's tether using only the bow thruster, and after some practice we
were able to obtain some useful data.
A CTD and zooplankton pump cast were made at 2204 and 2225 respectively.
Day 4 (Sunday 6/11/1995)
A VPR sled towyo (VPR 4) was made around the drifter 0022-0407. An attempt was made to
follow a grid around the drifter using another GPS drifter on the ship, the GONIO receiver, and a
MATLAB program. The error and delays in the GPS data made this approach not useful, so we
decided to simply move around the drifter using the program's display as a rough guide. The fog
made it impossible to see the drifter during this period. The drifter moved towards the ST1 array
and became too close to follow, so we decided to simply move around the array and the R/V
Seward Johnson.
The morning sampling routine was followed as scheduled, and an afternoon/evening
VPR-JASON (VPR-5J) deployment was highly successful due to calm wind and glassy seas.
JASON was retrieved at 2024, followed by a CTD cast (no pump cast was made).
Day 5 (Monday 6/12/1995)
A VPR/JASON deployment (VPR-6J) was made from 0055-0154, but the wind (12-15 knots)
caused the ship to drift through the water faster than JASON was able to move toward it. Thus
JASON was dragged through the water, and we could not get any slack in the tether. A. Bowen
decided it was too risky to try to maneuver with the bow thruster at night, so the tow was aborted.
A VPR sled towyo (VPR 7) was made from 0215-0415 about 12 km to the east, ending
north-northeast the R/V Seward Johnson. The ship then steamed back to the drifter. A dense
Chaetoceros socialis patch was observed in the southeast corner of the triangle.
The morning sampling was done according to schedule except that no zooplankton pump cast
was made. The VPR sled (VPR-8) was deployed at 1344 in a triangular transect starting about a
mile from the drifter to about 1 mile northwest of the Seward Johnson, then south for 4 miles at a
distance of about 1 mile from the Seward Johnson, then back to and around the drifter (~1 nm
radius) about 2115.
CTD and zooplankton pump casts were made from 2200-2300.
Day 6 (Tuesday 6/13/1995)
A VPR transect (VPR-9) from the drifter to the south (about 12 nm) was made from 0012-0417.
A dense Chaetoceros socialis patch was found at the southern end of this transect. We then
steamed back to the drifter.
We then stayed by the drifter until the sampling began. The morning sampling went according to schedule, (pump, CTD, net tows) except that the drifter was retrieved just before the net tows were made at 1231.
We then steamed to a location (40 42 N 67 42 W) just north of where we had seen the
Chaetoceros socialis patch and made a VPR tow (VPR-10) toward the south from 1524-1758
looking for the patch. A CTD cast was made at 1818 followed by a pump cast at 1910.
We steamed to Beardsley hydroline station #4 to begin a VPR transect (VPR-11) across the tidal
mixing front toward the crest mooring. At this station, the Durbin group first made a net haul for
RNA/DNA at 2142, then the VPR was deployed at 2208. During the transect, near the middle of
the front (41 03.39 N 67 36.37), the ship was slowed to 1-2 knots, and a second net tow was
made at 2300 while the VPR remained in the water.
Day 7 (Wednesday 6/14/1995)
The VPR tow ended at 0005 in the well-mixed water north of the front (41 07.7 N 67 36.57 W),
and a third net tow was made.
We steamed about 3 nm back into the front (41 05.47 N 67 36.21 W) and made a VPR-JASON
deployment (VPR-12J) from 0105-0348.
We then steamed to the crest mooring and launched the drifter at 0735 at 41 23.8 N 67 33.6 W.
An exploratory net tow for species composition was made at 0752 followed by a pump cast at
0847, CTD at 0925, and net tows at 0946. A VPR transect (VPR-13) to the north from the drifter
was made from 1049-1322. The ship remained by the drifter until night sampling with nets
(2136), CTD (2202), and pump (2212).
Day 8 (Thursday 6/15/1995)
The VPR was towed in a 1-2 nm "box" pattern (VPR-14) around the drifter from 0016-0407, and
the ship stood by the drifter until morning sampling which included a pump cast (1004), CTD
(1059), and net tows (1210).
The drifter was retrieved at 1548, and we steamed to a "Chaetoceros socialis" station at 40 40.0
N 67 42.0 W. A CTD cast was made but no fluorescence maximum was found, indicating no
Chaetoceros were present. We steamed a few miles to the west to 40 40.0 N 67 22.43 W, where
we found the Chaetoceros patch. CTD and net tows were made at 2217 and 2251, respectively.
Day 9 (Friday 6/16/1995)
Plans for a VPR-JASON launch were aborted during pre-deployment test where a fiber was
found to be broken.
A VPR transect (VPR-15) across the shelf/slope front was made from 40 41.0 N 67 48.30 W to
40 18.1 N 67 22.43 W. A CTD cast was made at 1019 but was terminated early due to a problem
with the traction head. At 1116 a deep MOCNESS tow was made.
A successful VPR-JASON deployment (VPR-16J) was made at the Slope Water station from
1309-1507.
After the JASON was aboard, we began steaming toward the Great South Channel station at 41
16 N 68 48 W and stopped in the Shelf/Slope front at the southern end of the Chaetoceros patch
(40 27 N 67 30.5 W) to make net tows. A CTD cast was made at 1803 but no fluorescence
maximum was observed, so we continued along the GSC line about 5 nm to 40 34.2 N 67 40.2
W, where a second CTD cast was made at 1946 and Chaetoceros were found.
A VPR-JASON deployment (VPR-17J) was made at 2126 at the same location and excellent
observations were made in the Chaetoceros patch.
Day 10 (Saturday 6/17/1995)
JASON was retrieved at 0106 and we steamed to the GSC location.
We reached the GSC around 0830 and began looking for right whales as a sign of Calanus
patches. We steamed northeast along the 50 fathom line, and began a zigzag VPR transect
(VPR-18) along the western bank back and forth across the 100 m isobath to map hydrography
and Calanus distributions.
Day 11 (Sunday 6/18/1995)
The main part of the VPR transect ended at 0910 and we continued to towyo to the northeast
toward the first turn in the transect (end of leg 1). Right whales were observed, and we turned
and followed one of them while towyoing the VPR. A dense patch of Calanus was found
between 80 m and the bottom at 140 m. At 1256 the VPR tow ended, and we steamed back a
few miles to where the Calanus layer was dense (41 27.8 N 68 32.03 W). A MOCNESS, net
tow, CTD-light cast, and CTD cast were made from 1325-1540. A net tow was made to collect
Calanus for Wagner and Van Keuren. No VPR/JASON deployment in the patch could be made
due to strong winds.
A VPR towyo (VPR-19) was made across the Great South Channel starting at 2246.
Day 12 (Monday 6/19/1995)
The VPR tow ended at 0405, and we steamed for Woods Hole at 0415.
We docked at Woods Hole at 1630.
3. Individual Reports
3.1 Copepod development, growth, and vertical distribution:
Zooplankton Abundance, Physiological Condition, and Growth Rates
(E. Durbin, A. Durbin, R. Campbell, J. Gibson, and M. Wagner)
Objectives:
(1) To determine the abundance and stage composition of the target zooplankton
species (Calanus finmarchicus and Pseudocalanus spp.) at the proposed drifter locations
on Georges Bank and at several off-bank stations.
(2) To determine the size (length, carbon, and nitrogen) and condition (condition
factor and RNA/DNA ratio) of Calanus finmarchicus over different regions of the bank.
(3) To correlate growth and development rates of Calanus finmarchicus copepodite
stages and egg production rates of adult females with RNA/DNA ratios in ship board
incubations, and compare these results with the RNA/DNA ratios of field collected
copepods to estimate growth rate in the field.
(4) To determine if growth and development rates of Calanus finmarchicus
copepodite stages are food limited on Georges Bank.
(5) To estimate the development rates of the naupliar stages of the target copepod
species at the drifter locations in ship board incubations.
Zooplankton were collected twice each day at the drifter locations. A zooplankton pump equipped with 50 µm mesh nets, that quantitatively retains all of the nauplii of the target copepod species, was used as our primary sampling tool, and sampled the following depth intervals: bottom-40m, 40-15m, and 15m-surface. In addition, a 1 m2 MOCNESS equipped with 150 µm mesh nets, and towed over the same depth intervals as the pump, was also used to sample the larger zooplankton and rarer species that might not be quantitatively sampled by the pump.
The first drifter deployment for the second leg was located on the southern flank at station 7. The dominant copepod appeared to be Pseudocalanus spp. Centropages typicus and Temora longicornis were also numerous. Calanus finmarchicus was less abundant with younger stages (nauplii to C3) being most prevalent. By the second day at this site older stages of Calanus (C3 through adult) were more abundant, but younger stages were still present and this pattern continued for the remainder of the station. Most of the Calanus were found above and within the thermocline day and night. Higher proportions of Pseudocalanus as well as decaying phytoplankton were found in the bottom layer.
At the second drifter station (station 12) on the crest, Centropages hamatus was by far the most numerous copepod. Older stages of Calanus were present, but in very low abundance. Stage C5 was the dominant Calanus stage, while adults and C4s were difficult to find. There were very few copepod naupliar stages of any species present at this station.
On June 15 and 16 three stations were occupied along a transect line from the crest into slope water. At the two shallow stations, located near the tidal mixing front and the shelf - slope front, Calanus was dominant with all stages present. In this region a peak in fluorescence was found at the base of the thermocline located on top of a cold pool of water. This fluorescence peak was due to a thin layer of Chaetoceros socialis colonies. A zooplankton pump sample found high concentrations of all stages of Calanus within and above this layer, although the naupliar stages appeared to be more abundant within the layer. At the deep station, located in 1600 meters of water, a MOCNESS tow to 400 meters did not find any significant numbers of Calanus.
A MOCNESS tow was also taken in the Great South Channel in the region where right whales were observed. A layer of Calanus was found deep, between the bottom and 80 meters, while very little biomass was observed above 40 meters.
At the drifter stations, as well as at several other locations on and off the bank, Calanus finmarchicus N6 through adult were routinely collected with live net hauls (150 and 335 um) for size (length, carbon, and nitrogen) and condition (condition factor and RNA/DNA ratio) measurements. Copepods, under anesthetic (MS222), were sorted from the net haul using a dissecting microscope, their images recorded with a video system for later length measurements, and then placed in either a tin boat and dried over desiccant for carbon and nitrogen analysis or put into cryotubes and frozen in liquid nitrogen for RNA/DNA determinations.
Experiments were conducted on board ship to determine the relationships between RNA/DNA ratio and growth, and RNA/DNA ratio and development rate of Calanus finmarchicus copepodites, and whether growth and/or development rate were food limited. These experiments will be used to estimate growth and development rates from the RNA/DNA ratios of the field collected copepods. Copepodites of a specific stage were sorted (unanesthetized) from a live net tow under a dissecting microscope, incubated in 8 l polycarbonate bottles filled with ambient surface water or ambient water enriched with phytoplankton cultures (Tetraselmis sp. and Heterocapsa triquetra) and placed in a water bath (temperature controlled with circulating chilled sea water). Measurements were taken for initial size and condition, and final measurements of size and condition (noting any molting that had occurred) were made after a two day incubation.
In addition, development rates of Calanus and Pseudocalanus naupliar stages
were determined in 100 liter mesocosms. Artificial cohorts were created by sieving a 150
um net sample through a 200 um sieve. The artificial cohort (150 to 200 um) was then
added to the mesocosms (20 copepods / liter) that had been filled by a diaphragm pump
with 100 um filtered water pumped from the chlorophyll maximum layer. The
mesocosms were temperature controlled with circulating chilled sea water. The
mesocosms were sampled once a day for three days with a 150 um sieve towed from the
bottom to the surface of the tanks. The samples were preserved in 4% formaldehyde for
later enumeration and stage determination for calculation of development rates.
3.2 Copepod feeding:
Ingestion of Phytoplankton, Nanozooplankton and Microzooplankton by Calanus
finmarchicus (D. Gifford and M. Seiracki)
The objective of our research is to define the diet of Calanus finmarchicus, with
particular attention to ingestion of nano- and microzooplankton. Specifically, we (1)
measure ingestion rates of all copepodid stages of C. finmarchicus in controlled
experiments and (2) characterize the potential prey field of C. finmarchicus by measuring
the vertical distributions of size fractionated chlorophyll a, nanozooplankton and
microzooplankton.
At the stratified site on the southern flank, approximately 50% of the chlorophyll was <5
µm, 75% was <20 µm, and 29% was >20 µm. Preliminary analysis of epifluorescence
samples confirmed that the phytoplankton was dominated by cells <20 µm in size,
including prymnesiophytes, cryptophytes, and small diatoms. Phototrophic
dinoflagellates were not abundant, although Ceratium spp. were present. The nano- and
microzooplankton was dominated by small flagellates, with relatively high numerical
abundances of heterotrophic dinoflagellates (up to 300/ml), mixotrophic ciliates including
Laboea strobila and Tontonia spp., and Mesodinium rubra. At the mixed station on the
bank crest, 45% of the chlorophyll was <5 µm, 88% was <20 µm, and 12% was >20 µm.
Microscopic analysis revealed that the phytoplankton at this station was dominated by
chain colonies of Pseudonitzschia spp., cyanobacteria, and cryptophytes. Heterotrophic
dinoflagellates and ciliates dominated the microzooplankton.
During EN267, we performed our 51st feeding experiment with Calanus finmarchicus on
Georges Bank. We measured clearance and ingestion rates of copepodid stages C4, C5,
and adult females at two drifter stations, Station 9, located on the southern flank, and
Station 12, located on the bank crest. Experiments done on the southern flank, where the
water column was strongly stratified, measured ingestion rates of C. finmarchicus on prey
assemblages collected from the middle of the mixed layer, from the chlorophyll
maximum at 25m, and from below the chlorophyll maximum at 50m. Experiments done
on the bank crest, where the water column was well mixed, measured ingestion rates of
C. finmarchicus on prey assemblages collected from the middle of the water column at
approximately 15m. Preliminary examination of the chlorophyll data indicates that the
copepods' grazing activity on chlorophyll at both drifter stations was low, but where
present, was focused on particles >5 µm, particularly particles 5-20 µm in size.
Microscopic analysis of nano- and microplankton samples at our home laboratories will
reveal the extent to which feeding was concentrated on heterotrophic food items.
We did one set of feeding experiments in a 20-m thick subsurface layer of Chaetoceros socialis, located at ~30 m depth on the southern flank (Station 14). Analysis of individual colonies sorted from water collected from the layer revealed that plant pigments consisted of 300 pg ± 100 s.d. chlorophyll a per colony and 800 pg ± 300 s.d. phaeopigment per colony. The dominance of phaeopigment suggested that the layer contained senescent cells at the end of their bloom period. Ancillary samples collected for analysis of major nutrients will assist in evaluating this possibility. Preliminary analysis of the results of experiments done with copepods fed the natural prey assemblage collected from the layer indicated, to our surprise, that C. finmarchicus females consumed the C. socialis colonies. Because C. socialis colonies are nearly as large as the copepods, we hypothesize that this interaction must involve a raptorial feeding mechanism. Preliminary examination of bulk seawater collected from the layer indicated that the layer also contained a diverse protozoan assemblage. Microscopic analyses at our home laboratories will reveal the extent to which the copepods consumed these items.
Ancillary activities included collection of nutrient samples for our GLOBEC colleagues
James Bisagni and Jay O'Reilly, and collection of light data by Jeffrey Van Keuren, a
postdoctoral investigator with the program.
3.3 Copepod egg production:
Egg production of dominant copepods species on Georges Bank.
(J.A. Runge and S. Plourde)
Copepod egg production rates were measured at the six drifter stations, as well as at Sta.
A6 along the hydro line, Sta. 07 and 17 in the Great South Channel and STA16 off the
Southern Flank (140 m deep) Egg laying of Calanus finmarchicus and egg extrusion rates
of Pseudocalanus spp. were observed at drifters stations. Egg production of Centropages
typicus, C. hamatus and Temora longicornis were observed where these species made up
a significant proportion of the total female population.
Although conditions, in terms of extent of stratification and phytoplankton composition,
were clearly different between the southern flank, bank and northeast flank drifter sites,
Calanus egg production rates were consistently high at all stations, except for the Bank
Crest during the second leg and the Great South Channel stations. For other stations,
mean rates ranged between 55 and 75 eggs female-1 d-1, which is equivalent to 6.5-8.5% of
female body weight. This implies that females were able to sustain high, near maximal
egg production rates regardless of the particular environmental conditions. Lower rates
measured at the Crest station during the second leg (c.a. 20 eggs female-1 d-1), due to a low
spawning frequency (c.a. 55%), suggested that population at this site changed between
the 2 legs (c.a. 2 weeks). At the Great South Channel stations, egg laying rates were near
zero. At this point, we attribute this result to life history differences between the Great
South Channel and Georges Banks populations rather than to extensive food limitation.
Incubations for assessment of hatching success of the eggs were conducted. These
samples have been preserved for later analysis. In general, however, the majority of eggs
laid appeared to be viable, with the exception of the second day of drifter Sta. 05, when a
substantial proportion of the eggs appeared to be developing abnormally.
Incubations for Pseudocalanus egg extrusion rates and Centropages and Temora egg
laying rates were preserved for later analysis. Pump samples will be analyzed for the
Pseudocalanus egg ratio. Pump and MOCNESS samples taken at the drifter stations will
be analyzed for female copepod abundance, so that the rate of daily input of eggs into the
water column at each station can be estimated.
3.4 Copepod behavior and micro-mesoscale distributions of plankton:
Video Plankton Recorder Sampling of plankton behavior and micro-mesoscale
distributions (C. Davis and S. Gallager)
The objective of the VPR sampling during the process cruises is two-fold:
1) to measure the distributions of Calanus and Pseudocalanus together with other
plankton and seston in relation to physical properties of the water column over
micro-fine scales (microns to a few kilometers). We are especially interested in
determining whether or not the target species aggregate at the pycnocline during
spring stratification of the water column.
2) to measure the swimming behaviors of these species in three dimensions
together with motions of passive particles to determine how the species'
swimming motions interact with physical microturbulence to form aggregations at
the pycnocline.
Comparative day/night sampling of these variables will provide insights into the diel
swimming behavior of the plankton. These data will help us understand the physical and
biological mechanisms controlling patch formation in plankton, and will provide insights
into the role of vernal stratification in concentrating these organisms, which serve as food
for larval fish (eg. cod and haddock).
To measure micro-finescale distributions (including vertical), the sampling design
involved slowly towyoing the VPR in the vicinity of the drifter. In this way, both the
vertical and horizontal distributions of plankton, seston, and hydrography in the vicinity
of the drifter could be determined. The VPR (Davis et al, 1992a,b) was configured with
two cameras set at two different magnifications and viewing concentric volumes. The
high magnification camera had a field of view of 5.8w x 4.8h mm and the low
magnification camera had a field of view of 37w x 27h mm. The video from the
underwater unit was transmitted to the ship via fiber optic cable and was recorded on
board the ship using broadcast quality SONY BETACAM SP Recorders and 90 tapes
(Model 55). The video also was fed into and image processor and SUN workstation to
extract in-focus subimages and store them to disk. The VPR also contained a MOCNESS
sensor package which included SeaBird temperature and conductivity sensors, a pressure
sensor, a SeaTech fluorometer and transmissometer, an angle indicator, and a flowmeter.
These ancillary data were recorded to computer hard disk on shipboard 2 times per
second.
For in situ measurements of zooplankton swimming behaviors and passive particle
motions in three-dimensions, a two-axis VPR system was mounted on a 2 meter square
frame affixed to the front of the ROV JASON. The separation distance between the
cameras and strobes along both axes was 2 m. The cameras were aligned such that the
centers of the two imaged volumes coincided and were nearly orthogonal to each other.
Magnification of both cameras was adjusted to give 6 cm fields of view. One camera was
positioned to provide a top-down view (x,y), while the other was positioned to provide a
side view (y,z). The red-filtered strobes were aligned with the cameras viewing axes but
slightly off axis such that only forward scattered light was imaged. For deployment and
retrieval, the JASON/VPR first was placed off the starboard side using DSL's articulating
Hyab crane. JASON then swam aft of the ship to the end of its tether (50 m) using its own
thrusters. The clump-weight/interface unit, MEDIA, then was lifted over the starboard
side using the main crane boom and the USGS winch. The crane boom remained just off
the starboard side such that the cable down to MEDIA was about 3 m from the side of the
ship. During deployment, operation, and retrieval, the ship's propellers remained
declutched. Once deployed, the ship would attempt to maneuver using only the bow
thruster to keep slack in the tether which ran between JASON and MEDIA. This proved
very difficult, and only during calm periods (<10-15 knot winds) could the system be
used effectively.
The sampling design with the VPR/JASON system involved video taping the plankton for
periods of 0.5-1.0 hours within each layer. Good data were obtained only when the tether
was slack and the VPR/JASON was moving slowly forward and then slowly stopped. In
this way, we knew that only new, undisturbed water was being sampled. This situation
occurred only about 10 % of the time during each sampling period in each layer. The
layers sampled were roughly at 10 m intervals from the surface to 10-20 m off the
bottom.
The chronology of sampling with the towed-VPR and with the VPR/JASON system is
given in the cruise narrative. All VPR deployments are numbered consecutively with
VPR/JASON deployments denoted as VPR-#J.
A total of 19 VPR deployments were made, 7 with the VPR/JASON system and 12 with
the towed VPR. Locations of these deployments are shown in Figure 4. Hydrographic
data plus fluorescence and beam attenuation from the towed system are shown in Figures
5-20. In the stratified region, temperature ranged from near 6.5 0C at the bottom to about
10.5 0C at the surface (eg. Figs. 7-8). In the well mixed area, temperature was 10.3 0C
(Figs. 14-15). Calanus and Pseudocalanus were the principal copepods observed on the
south flank, while Centropages dominated the mixed site. Small medusae (about 2 cm
diameter), which may have been hydroid medusae, were abundant in both the mixed and
stratified areas. During a relatively long towyo (VPR-8) from the south flank drifter
toward the southeast around the R/V Seward Johnson and back around the drifter, a dense
layer of Chaetoceros socialis was found just below the thermocline in the southeastern
region of the towyo (see fluorescence plot in Fig. 10, units = volts). On a later towyo
(VPR-15), we made a transect from the south flank into the Slope Water across the
shelf/slope front and found the Chaetoceros layer extended well off the bank in the shelf
water streamer as did the subsurface "cold band" of bank water (Figs. 3 and 16). Thus,
the front was leaning way over toward the south due to the streamer (Fig. 16). We also
made a towyo transect across the tidal mixing front to map the transition from stratified to
mixed conditions (Fig. 13).
A towyo survey (Fig. 18) was conducted along the western edge of the bank and in the
Gulf of Maine north of the Great South Channel (the former SCOPEX region) to map this
input/output region of the bank and to locate dense patches of Calanus finmarchicus
known to occur in this region. The plan was to locate a patch and use the VPR/JASON
system to measure swimming behaviors of individual Calanus within the patch to
examine mechanisms of patch formation. A program was written in matlab to plot the
number of in-focus images extracted vs time as an index of Calanus abundance (Fig. 19).
This method worked well for the Gulf of Maine where most of the particles were
Calanus, but in the shallower regions on the bank, the particles were largely marine
snow. The survey revealed high concentrations of Calanus at the surface in the Gulf of
Maine along the northern portion of the survey. The Calanus abundance dropped to
undetectable levels (<100 m-3) in the shallower regions up on the bank where marine
snow occurred in huge abundances (>109 m-3).
As we were sampling along this survey track, zig-zagging on and off the bank towards
the southwest, we found that Calanus occurred primarily off bank and in the upper 50 m
of the water column. Upon reaching the cleft in the 100m isobath, which marks the
northern center of the Great South Channel, we began towyoing along a straight transect
back to the starting point of the survey. At this point, we towyoed only in the upper 50 m
since no Calanus had been observed below that depth. Although we were further into the
Gulf of Maine (Fig.18), no Calanus were observed. We then sighted Right whales which
are known to feed on Calanus, so we began following one of the whales and decided to
towyo to the bottom. We found a dense layer of Calanus between 80 m to 10 m off the
bottom at 160 m. These copepods were likely in diapause and rich in lipids. Net samples
of Calanus were collected and frozen for subsequent analysis.
Two daytime VPR/JASON deployments were made at the stratified site on 6/10-11 (VPR-3J and VPR-5J). Excellent video recordings were obtained on the second deployment. Swimming behaviors of Calanus, other copepods, larvaceans and hydroid medusae were recorded at various depths in the water column. Small, circular, swimming patterns of protozoa were also seen. Many Rhizosolenia type diatoms and some Chaetoceros socialis colonies were observed on both deployments.
A nighttime VPR/JASON deployment was made in the tidal mixing front within weakly
stratified waters on 6/12 from 0055-0148, but conditions were marginal and the tow was
terminated. A daytime VPR/JASON deployment was made in the Slope Water at the end
of the VPR-15 transect line across the streamer. Very few plankton were observed at this
station.
The final VPR/JASON deployment (VPR-17J) was made in the Shelf-Slope
front/streamer on 6/16 at 2126. Excellent video of Calanus swimming was obtained
together with video of nauplii, medusae, and ctenophores. Excellent footage was
obtained within the dense Chaetoceros socialis layer. Calanus were observed swimming
within this layer, and appeared to be feeding on the Chaetoceros. D. Gifford and M.
Seiracki then conducted a grazing experiment which confirmed that Calanus did in fact
eat the large Chaetoceros colonies. This last VPR/JASON deployment was the best one,
and several long sequences of undisturbed water were obtained.
In all, the cruise was highly successful in terms of both the towed system as well as the
VPR/JASON system. In situ 3-D swimming behaviors of small plankton were obtained
for the first time in the open sea, and the information gleaned from these data will help
improve our current models of plankton aggregation. The high-resolution towyo data on
Calanus, other plankton and environmental variables will provide new insights into the
mechanisms of fine-mesoscale transport of plankton in the sea.
Scientific
Name Title Organization
1. Cabell Davis Chief Scientist WHOI, Woods Hole, MA
2. Scott Gallager Scientist WHOI, Woods Hole, MA
3. Hidekatsu Yamazaki Scientist Fisheries U. Tokyo, Tokyo
4. Dian Gifford Scientist URI, Narragansett, RI.
5. Bob Campbell Scientist URI, Narragansett, RI.
6. Mike Seiracki Scientist BLOS, Boothbay, ME
7. Andy Bowen Chief JASON Engineer WHOI, Woods Hole, MA
8. Stephan Plourde Research Associate UQAR, Rimouski, Canada
9. Carin Ashjian Posdoc WHOI, Woods Hole, MA
10. Jeff VanKeuren Postdoc URI, Narragansett, RI.
11. Phil Alatalo Research Associate WHOI, Woods Hole, MA
12. Tom Crook JASON Engineer WHOI, Woods Hole, MA
13. Skip Gleason JASON Engineer WHOI, Woods Hole, MA
14. Bob Elder JASON Engineer WHOI, Woods Hole, MA
15. Will Sellers JASON Engineer WHOI, Woods Hole, MA
16. Melissa Wagner Graduate Student URI, Narragansett, RI
17. Jim Gibson Research Assistant URI, Narragansett, RI
18. Bill Fanning Marine Technician URI, Narragansett, RI.
ENDEAVOR Officers and Crew
18. Captain Thomas Tyler Master
19. Everett McMun Chief Mate
20. Steve Vetra Mate
21. Jack Buss Bos'n
22. Jay St. Germain Able-Seaman
23. Glen Prouty Able-Seaman
24. Bijan Emami Able-Seaman
25. Jim Cobleigh Chief Engineer
26. Tim Varney Assistant Engineer
27. Richard Smith Assistant Engineer
28. Daniel Butler Steward/Cook
29. Brian D. Miller Cook/Messman
Appendix II. Cruise Event Log