Acknowledgements

The scientific party thanks the captain and crew of the R/V Endeavor, the Marine Technician David Nelson, and the URI Marine Office and Marine Technical personnel for all of their efforts to help make the cruise a success. Satellite images were made available during the cruise by Jim Bisagni's group and John Ryan.

This report was prepared by Karen Wishner and Dawn Outram, with contributions from the various investigators on the cruise.

Table of Contents

Purpose and Objectives of the Cruise 3

Cruise Narrative: EN301 4

Reports from Scientific Investigators 8

Copepod Naupliar Grazing Experiments and

Distribution of Chlorophyll, Micro-, and Nanoplankton 8

Distributions and Stomach Contents of Micronekton and

Macrozooplankton: 10-meter MOCNESS Sampling 9

Inputs and Losses of Zooplankton in Episodic Features and

Associations with Hydrography and Bio-optically Defined

Water Masses: 1 m^2 MOCNESS Sampling 9

Sources to and Losses of Invertebrate Predators from Georges

Bank, and In Situ Feeding Rates of Selected Predators 14

Gut Passage Time Experiments 15

Blue-water Dive Operations 17

Studies of the Ctenophore Bolinopsis (Ph. D. Research) 18

Solar Ultraviolet Radiation and Marine Planktonic Ciliate

Survival on Georges Bank (Ph. D. Research) 19

Undergraduate Training Report 20

Outreach Educational Activities 20

Figure 1. Map and Cruise Track 21

Figure 2. Satellite Image 22

Figure 3. Detrainment Feature Survey Track 23

Figure 4 a - h. 10-meter MOCNESS Data 24

Personnel List 32

Appendix I: Summary of Measurements and Samples Taken 33

Appendix II: Event Log 34

Purpose of the Cruise

This was the third of a three-part series of 1997 GLOBEC Vital Rates cruises. These cruises, part of Phase II of the U.S. GLOBEC Georges Bank program, studied aspects of the distributions and feeding of zooplankton (especially the copepod Calanus finmarchicus) and their predators in the context of the physical environment and seasonal cycle. The special focus of projects during Phase II of the Georges Bank program was Source, Retention, and Loss of populations of target species on the Bank. The first two cruises of this series were in March (EN296, Chief Scientist Dian Gifford) and April 1997 (EN298, Chief Scientist Larry Madin). During EN301, six stations were occupied on and near Georges Bank (Great South Channel, Crest, Georges Basin, Northeast Peak, Cold Plume, South Flank), similar to the first two cruises, and a survey of a detrainment feature (water being drawn off the southern flank of the Bank by a warm core ring) was also done (Fig. 1).

The major objectives of this cruise were to:

(1) determine quantitatively the contribution of small-sized prey to recruitment of copepod populations on Georges Bank (Gifford / Sieracki). Experiments (shipboard incubations) were conducted at paired off-Bank / on-Bank stations to investigate ingestion rates and diet of the nauplii of Calanus finmarchicus. Both laboratory-reared and wild nauplii were used along with the natural plankton prey assemblages collected from each station. The hydrography and the abundance and distribution of potential food items available to the copepods (micro- and nanoplankton) were determined from water column profiles with a CTD and rosette with Go-flo bottles.

(2) determine the diversity and abundance of predatory species on and off the Bank and estimate feeding rates, gut passage times, and diets of selected species (Bollens / Madin / B. Sullivan / Klein-MacPhee). Distributions were determined from day and night vertically-stratified collections with a 10 m^2 MOCNESS at the six stations. Predators from the 1 m^2 MOCNESS samples will also be analyzed (B. Sullivan). Live animals were collected by divers (Horgan / Coverdale) for behavioral observations and experiments on gut passage times (Butler / Bollens / B. Sullivan). Ring net tows were taken for quick collections of selected species to compare their gut contents with animals from the longer MOCNESS tows (B. Sullivan).

(3) determine the role of episodic advective features in the input and loss of zooplankton on the Bank and the association of zooplankton with optically-defined water masses (Wishner / Donaghay). Zooplankton distributions and water mass associations were determined from day and night vertically-stratified collections with a 1 m^2 MOCNESS at the six stations. A WETlabs SaFire multispectral fluorometer and AC9 were incorporated into the MOCNESS sensor array to obtain optical data (Donaghay / J. Sullivan). The Cold Plume of water from the Scotian Shelf was located and sampled on this cruise, as well as on the two previous cruises in this series. The detrainment feature drawing water off the southern flank was surveyed with CTD and MOCNESS transects (as well as the ship's ADCP) to quantify the role of these features in the loss of zooplankton from Georges Bank (Wishner / Sieracki / J. Sullivan / B. Sullivan and most of scientific party)

Ancillary objectives of the cruise were to:

(4) determine the effects of exposure to UV light on microzooplankton (especially ciliates) in deck incubations and the vertical profile of UV in the water column with a radiometer (thesis work of Martin).

(5) determine aspects of the biology of the ctenophore Bolinopsis infundibulum (thesis work of Coverdale).

(6) find and sample the layer of the diatom Chaetoceros socialis previously seen on the southern flank at this time of year (Sieracki / Gifford).

(7) collect live animals for workers onshore.

(8) collect ADCP data (Flagg)

(9) collect water for optics experiments onshore (thesis work of Twardowski)

(10) conduct training and educational exercises for the 5 undergraduates participating in the cruise.

(11) provide material for outreach educational activities, including a cruise video for elementary school children and e-mail communication with a fourth grade teacher for real time use in class (B. Sullivan)

Cruise Narrative

The cruise got underway at 1025 on 23 May 1997 from Narragansett. In contrast to the two earlier cruises which began with the Georges Basin station on the northeastern part of the Bank, we decided to do the Gifford / Sieracki stations clockwise starting with the Great South Channel station in order to leave time at the end of the cruise for extra work in the southern flank area (Fig. 1). Satellite images at the start of the cruise showed a strong detrainment feature in the south of water apparently being drawn off the Bank by a warm core ring (Fig. 2), and all participants agreed that this would be an interesting phenomenon to investigate. Also in contrast to the earlier cruises, the weather was excellent up until the last few days, which allowed for very efficient use of shiptime, a high degree of success for all projects, and time for a survey at the end of the cruise of the detrainment feature.

Work began in the Great South Channel at 0530 on 24 May with zooplankton tows (to collect nauplii) and CTD casts (to obtain water for experimental incubations and profiles). Two MOC 1 tows and two MOC 10 tows during the daytime, a CTD cast at dusk, and two more MOC 1 tows and MOC 10 tows at night were then done. This became the basic routine for most of the stations. Occasional work was interspersed between these activities at the different stations. In the Great South Channel, a light cast at noon was taken for the UV experiments. The station was completed about 0400 on 25 May, and the ship departed for the Crest Station.

A similar plan was followed at the Crest, but since this station was so shallow (about 40 m), the MOCNESS "replicates" could be done within a single tow which went down and up twice. The CTD cast for experimental water began at 0900 on 25 May. Single MOC 1 and MOC 10 tows were done day and night. Vertical hauls with a small ring net were done between the MOCNESS tows during the day and in the evening between the CTD and MOCNESS tow series to collect animals for gut content studies. Work was completed at about midnight.

The ship then steamed for about 9 hours to Georges Basin. Work at Georges Basin began at 0844 on 26 May with zooplankton tows and a CTD cast for the incubations, followed by the MOC 1 and MOC 10 tow series day and night. Because of the high swell, the second nighttime MOC 10 tow was cancelled, but was made up on 28 May when we returned to this station for this purpose. Vertical ring net tows were done in the morning along with the zooplankton tows for the experiments and at night between the two MOC 1 tows. A dusk CTD also was done. Work was completed just after 0200 on 27 May.

We then proceeded to the Northeast Peak station just a few hours away. Work began at 0810 on 27 May with the zooplankton tows, CTD cast, and daytime ring net tows. The day and night MOCNESS series followed. A light cast was done around 1100 between the daytime MOC 1 tows, and vertical net tows were done between the nighttime MOC 1 tows. An afternoon CTD and two dives (one during the afternoon of 27 May and one the next morning) were also completed.

Because we had decided to return to the Georges Basin station to obtain the replicate for the nighttime MOC 10 series, we had some extra time during the day of 28 May. There were five undergraduates on board, two from URI, two working for the summer at WHOI, and one from SFSU. Because they were working with different groups and at different hours on the ship, they had not been able to interact with each other much and had not had a chance to learn about some of the standard gear or to actually direct operations. They were given a few hours of time at the northeast peak station and back at the Georges Basin station to design a small undergraduate project and to operate the CTD and ring nets by themselves (with help from the Marine Technician). They developed some hypotheses, collected water samples and zooplankton, and coalesced into an enthusiastic group, much more aware of the big picture and eager to ask questions of all the scientists on board.

Work at the Northeast Peak ended at about 1030 on 28 May, and we returned to the Georges Basin station primarily to do the missing MOC 10 replicate. Day and night MOC 10 tows were completed. The undergraduates had some time for a CTD and ring net tow. Work was completed at this station by about 2230 on 28 May.

We then set out to locate the Cold Plume feature, cold low salinity water coming from the Scotian Shelf area, that had been prominent on the northeast peak of Georges Bank since early spring . This feature was apparent in satellite images (Fig. 2) and could be identified from shipboard on the basis of sea surface temperature (ideally about 3°C) and salinity (< 32%o). Work on the two previous cruises showed that it was a surface layer, sometimes up to about 20 m thick but often just a few meters thick, and that the location of its edge changed over time, possibly with the tidal cycles. The satellite image from near the start of the cruise indicated that this water was still present, but was warming up as the weather continued calm and sunny. We directed the ship to steam from the Georges Basin station to a waypoint (41°52'N 66°20'W) just east of the Northeast Peak station and then to steam due east to intercept the feature. Running plots of sea surface temperature and salinity were monitored in the lab to detect the sharp decrease in temperature and salinity characteristic of the feature. The edge of the feature (salinity < 32%o) was found at 0518 on 29 May at 41°52.00'N 66°06.12'W. A nominal sampling station was established (at 0555) slightly farther into the feature at 41°52'N 65° 54'W, where the sea surface salinity was 31.66%o and the temperature was 6.88°C. The temperature had obviously warmed up over time, but was still cooler than outside the feature (about 8.12°C in Georges Basin for example). Over the course of the station, the sampling site changed to about 41°48'N 65°50'W to stay within the feature during the MOCNESS tows.

Sampling at the Cold Plume station began at 0607 on 29 May with CTD casts (to check the thickness of the Cold Plume layer and for incubation water) and zooplankton net tows for the incubation experiments. The second CTD cast also obtained water in the Cold Plume for J. Sullivan (for Twardowski's optics experiments at URI as part of his Ph.D. thesis). Two MOC 10 tows followed (1 failed because of a dead battery), then two MOC 1 tows, then another MOC 10 tow in the afternoon to make up for the earlier missing tow. An evening CTD (also used to obtain water below the Cold Plume for J. Sullivan and Twardowski) was followed by two night MOC 10 tows and two MOC 1 tows. The order of the MOC 10 and 1 tows was switched at this station (midcruise) to even out the late night burden on the two MOCNESS teams, similar to the arrangement on the previous cruise. Work at the Cold Plume station ended at 0300 on 30 May, and we steamed for about 9 hours to the South Flank station.

Work at the South Flank station began at 1340 on 30 May with the CTD cast and zooplankton tows for the incubation experiments. A dive was done in the afternoon. After an evening CTD, one MOC 10 tow was done. A problem with the ship's crane used to deploy the MOC 10 occurred during recovery. After about 15 harrowing minutes at the stern, the crane finally operated enough to enable the MOC 10 to be brought onboard (at 2230). The second MOC 10 tow was cancelled until the crane could be fixed the next morning in daylight. Two MOC 1 tows were then done at night, with short vertical net tows for B. Sullivan's work between them. The morning (31 May) began with two CTD casts, in part to sample the Chaetoceros socialis (diatom) subsurface layer that was found at this station, similar to the 1995 work in this area. Incubation experiments with water from this layer were begun. Two MOC 1 tows followed. The order of MOCs was switched to allow time for repairs to the crane, which was successfully fixed in a few hours after a lot of hard work by all the ship's engineers. The problem involved a faulty seal in the hydraulic system. The two daytime MOC 10 tows were then successfully accomplished in the afternoon. The crane problem highlighted the vulnerability to equipment failure of the MOC 10 launch and recovery procedures on the Endeavor, and for the remainder of the cruise, the captain required even calmer conditions than previously for MOC 10 operations (although bad weather had not been an obvious factor in the crane failure). An afternoon dive successfully obtained many Bolinopsis specimens for Coverdale's thesis work and samples of Chaetoceros socialis colonies for Sieracki and Merrell to do direct counts of concentration and colony size distributions. A short net tow to collect food for the live specimens completed the afternoon and station (at about 1607 on 31 May).

We then steamed south for about 5 hours to the detrainment feature, which had been visible in AVHRR satellite images since before the start of the cruise (Fig. 2). This feature, a filament of cold water emanating south from Georges Bank, apparently was being drawn around the eastern edge of a warm core ring. This seemed like an ideal feature to document and quantify aspects of zooplankton loss from Georges Bank, as part of the Phase II focus on Source, Retention, and Loss. The plan was to do a CTD survey consisting of 3 transects perpendicular to the axis of the feature, followed by day and night MOC 1 and MOC 10 tows at 3 locations along one of the transects. This would allow us to document the dimensions of the feature (from CTDs and satellite images), its transport (from ADCP data and dimensions), and the association of zooplankton and predators from the Georges Bank ecosystem with the feature.

The ring had moved westward during the first part of the cruise and our most recent satellite image was from 29 May, so the first priority was to locate and survey the feature. Salinity of 34%o was considered the approximate boundary condition, with water of lower salinity part of the feature and water of higher salinity outside the feature (thanks to advice from Dave Mountain via radio from the Albatross). The marine tech Dave Nelson consolidated data displays for optimal real time decision making: at the command center of the lab, we had computer displays of the latest satellite image, bathymetry from the CHIRP sonar, a graphical display of the ship's course from the bridge's computer, running plots of sea surface temperature and salinity, and the usual numerical screen display of GPS position and underway data. The strategy was to steam south across the southern edge of Georges Bank, find the boundary of the feature, and then cross the feature with the CTD transects. However, the salinity remained low during the transit south, and we finally realized that we were probably steaming within the feature (it had moved west more than anticipated). At 2050 on 31 May, we decided to begin the CTD survey in order to get three transects into the allotted 24 hrs; we assumed that we would find the feature edges during the survey.

The CTD survey consisted of CTDs to 200 m at 2 nm spacing along three 20 nm lines that were 10 nm apart and oriented at 67° and 247° T (Fig. 3). Mate Steve Vetra calculated exact station locations (to the hundredths digit) for each CTD with the bridge's navigation software, a service much appreciated by both the scientists and officers. The Go-Flo bottles were removed from the rosette and replaced with several Niskin bottles (for salinity calibrations) to reduce time spent cocking bottles. Three watches were established (Sieracki, Martin, and J. Sullivan operating the computer; volunteer techs and students on deck) to undertake the survey nonstop for 24 hours. We started on the southern line (heading northeast); we assumed that the feature would be most sharply defined and narrowest in the south versus the broad neck region in the north nearest the Bank. We also assumed that the eastern edge would be a gradual boundary into the slope water while the western edge would be a sharp transition into the ring. During the survey we had to extend the second and third lines to the west (and drop the easternmost stations on the third line) to cross the feature edge. The survey lasted until 1835 on 1 June (CTDs #18 - 56).

We then steamed to the middle transect (the most well-defined crossing) and started the MOCNESS series. The original plan was to alternate MOC 1 and MOC 10 tows over the course of 2 days to obtain day and night tows at 3 locations along the transect to document the community structure across the feature. This plan was unacceptable to ship personnel, however, because it did not allow sufficient time for rest between tow operations. (The MOC 10 deck operations required 3 extra crew members in addition to the regular watch, and there was concern about sleep schedules). Therefore, we decided to spend the first 24 hours doing the MOC 1 transect operation and the next 24 hours doing the MOC 10 series, a plan that was acceptable to all. The plan was that each MOC series would consist of 3 tows during the day at 3 stations along the transect (east, core of the feature, west; waypoint numbers 62, 78, 83 respectively--see Fig. 3) followed by 3 tows at night at the same locations, with the steaming time between stations (an hour or less) occurring while the nets were being washed from the previous tow and cocked for the next tow. This would also provide the most synoptic means of surveying a dynamic feature, within the constraints of MOCNESS operations. Station locations were selected on the basis of the hydrographic results from the CTD survey to represent the three regions of the feature, with locations modified as necessary in real time based on sea surface temperature and salinity. CTDs with Go-flo bottles were scheduled before each MOCNESS tow to document location within the feature and to obtain profiles of chlorophyll, nano-, and microplankton.

We completed the nighttime MOC 1 and CTD series on 1 - 2 June and started on the daytime set. The weather turned bad during the first of the 3 daytime tows (east side), and the ship hove to from about 1048 on 2 June until 0932 on 3 June. At that time a slight break in the weather occurred. We were able to re-find the low salinity signature of the feature despite storm mixing, and the daytime CTD at the mid-feature station was done under rough conditions. The seas were still too rough for towing, however, so we hove to again until the afternoon when another slight break allowed the MOC 1 tow at the feature core station (slightly southwest of the nighttime tow location) to be done under marginal conditions. A short (wet) ring net tow to obtain live animals for researchers ashore was also done, and then the ship hove to until the evening weather forecast. Bad weather continued, and the radio weather forecast at 1800 was for gale force winds and high seas to continue beyond our originally scheduled departure time (0600) the next day. It was highly unlikely that conditions would improve enough for MOC 10 use or even for less demanding operations, so we departed for Narragansett on 3 June about 1830. The ship arrived in port about 1812 on 4 June.

Reports from Scientific Investigators

Copepod Naupliar Grazing Experiments and Distributions of Chlorophyll, Micro-, and Nanoplankton

Jeff Merrell (URI), Mike Sieracki (Bigelow), Kellie Merrell (URI), and Elena Martin (URI)

Our primary objectives for EN301 were to: 1) conduct grazing experiments using laboratory-reared and wild nauplii of the copepod Calanus finmarchicus and natural plankton prey assemblages collected from each station; and 2) to utilize the CTD / Go-flo rosette bottle samples to characterize the hydrography and micro- and nanoplankton of the water column at each station.

Laboratory nauplii were reared from adult Calanus that were collected from ring net tows during an earlier cruise, EN298. At each EN301 station, we began our activities with a vertical net tow in order to obtain wild Calanus nauplii (if present). We were successful in obtaining wild nauplii at stations 1 (Great South Channel), 3 (Georges Basin), 4 (NE Peak), 5 (Cold Plume), and 6 (Southern Flank). A net tow was not taken at station 2 (Crest) because of time constraints and the probable paucity of nauplii there. Immediately following the ring net tow, a CTD cast was made to obtain necessary profiles of temperature, salinity, fluorescence, and light transmission and to collect water with the Go-flo rosette. Water samples from various depths were fixed in acid Lugol's solution for microzooplankton and phytoplankton counts. Samples were also taken for nanoplankton analysis by flow and imaging cytometry, and to determine total chlorophyll a concentrations (in g/L). At each station several Go-flo bottles were reserved for collecting water and prey from the mixed layer (generally ~ 10 m) for use in the naupliar grazing experiments. Control bottles and experimental bottles containing either wild or lab-reared nauplii were incubated for 24 h in rotating flow through incubators on deck. Experiments were also conducted at each station with laboratory-reared naupliar cohorts in order to estimate naupliar growth over a 48 h period.

At the southern flank station (#6), we located a dense patch of Chaetoceros socialis. An experiment was conducted to investigate grazing by adult female Calanus on the C. socialis colonies. Preliminary chlorophyll results suggest that the adults grazed on the larger than 20 m size fraction, which was dominated by the colonies. This confirms the results of a similar experiment conducted on the southern flank in 1995. Samples of the C. sociales colonies were collected by divers at 3 m intervals through the layer for direct counts and colony size distribution measurements.

We participated in an extensive CTD survey aimed at locating a detrainment feature associated with a warm core ring, potentially pulling water off Georges Bank. Approximately 41 CTD casts were made to 200 m along 3 transects across the expected location of the feature. An additional four CTD / Go-flo casts were made prior to MOC 1 tows at selected locations near the edges and center of the feature. Samples were taken from the Go-flos during these 4 casts for chlorophyll, nano- and microplankton analyses.

Distributions and Stomach Contents of Micronekton and Macrozooplankton: 10-meter MOCNESS Sampling

Steve Bollens (SFSU), Erich Horgan (WHOI), Mari Butler (SFSU), Becky Coverdale (WHOI), Steve Lowe (SFSU), Heather Macrellis (WHOI), and Erica Estrada (WHOI).

Objectives: 1) To determine the distribution and abundance of micronekton and macrozooplankton at key stations on and around Georges Bank; 2) Collect specimens of invertebrate and vertebrate predators for subsequent determination of stomach contents back in the laboratory, using both microscopical and immunological techniques.

Methods: We used the 10-meter MOCNESS to sample at six stations in the Georges Bank region: the Great South Channel; the Crest (or central, shoal region); Georges Basin; the Northeast Peak; a "cold water" plume of Scotian Shelf water near the Northeast Peak; and the Southeastern Flank. We were unable to sample the warm-core ring feature that was of primary interest to us because of bad weather and wire-time limitations. Duplicate daytime and nighttime vertical series of samples were collected at each of the six stations, with the exception of the Southeast Flank, for which the nighttime sampling consisted of only a single series. Four depth strata were sampled on each deployment of the net, the exact dimensions of which varied between stations depending on hydrography and our previous choice of sampling depths during our earlier GLOBEC cruise in April, 1997 (EN298). Depth strata were, however, held constant between tows at each station to aid in the subsequent application of standard statistical techniques. Immediately following retrieval of the 10-m MOCNESS on to the deck, each net was rinsed down and the contents examined in the wet lab for identification and "quick counts" of all organisms present. Catches were then preseved in 5% formalin-seawater solution, usually within 10 minutes of being brought aboard.

Results: The figures on the eight pages following the text represent the results of our shipboard "quick counts" of the dominant eight taxa of micronekton and macrozooplankton (Fig. 4a-h). Another ca. 50 taxa were identified and counted, but were too rare to warrant presentation here. These results should be considered as preliminary only; more careful, precise counts and identifications, as well as the stomach content analyses, will be performed in our laboratories in San Francisco and Woods Hole.

Inputs and Losses of Zooplankton in Episodic Features and Associations with Hydrography and Bio-optically-defined Water Masses: 1 m^2 MOCNESS Sampling

Karen Wishner, Jim Sullivan, Dawn Outram, Barbara Sullivan, Summer Nelson, and Jen Schadlick (all at URI)

Our focus on this cruise, as on EN296 and EN298, was to measure inputs and losses of zooplankton associated with episodic features and to determine the associations of zooplankton with different water masses (described hydrographically and bio-optically) on and near Georges Bank. We interfaced a MOCNESS 1 m^2 net system (153 m mesh) with 2 bio-optical instruments, a WETlabs SaFire and AC9, using a WETlabs MODAPS as a central data acquisition and archiving system. The SaFire measures 2-D spectral DOM fluorescence at a subset of wavelengths within the total 96 excitation/emission pairs, and the AC9 measures spectral total absorption and attenuation, or DOM absorption when a prefilter is attached to the intake. The combination of these optical signatures allows us to identify water types with a high degree of differentiation and to track subtle features over time. We sampled with the MOCNESS / SaFire / AC9 system day and night at locations just off Georges Bank, on the Bank itself, and within episodic features of opportunity.

A total of 27 1-m^2 MOCNESS tows were taken (Table 1), 22 of them at the 6 Gifford / Sieracki experimental stations and 5 of them along transects of a detrainment feature (water being drawn southward off the Bank around a warm core ring). Tows were usually done during the same day or night as the 10 m^2 MOCNESS tows (Bollens group), and tow depths were coordinated between the two groups. Eight vertically-stratified samples were usually obtained from each 1 m^2 MOCNESS tow. Depth strata varied with the station depth; broader intervals were usually used for deep samples and 10 m depth intervals were used near the surface. Some day and night tows used standard depth strata; others used depth strata modified on the basis of the bio-optical and hydrographic signatures. Satellite imagery (courtesy of Jim Bisagni's group and John Ryan) and underway measurements of sea surface temperature and salinity were used to locate the Cold Plume and the south flank detrainment feature (see the Cruise Narrative for the description of the feature-chasing procedures). The detrainment feature was studied with a 24 h hydrographic (CTD) survey along 3 transects, followed by night and day MOCNESS tows along 1 of the transects. Stormy weather mixed the water column between the night and day tows in the feature, which provided some interesting contrasts. Shipboard ADCP data (Flagg) will be used to help interpret flow in these features. Sampling of the detrainment feature was cut short by bad weather.

Table 1 Summary of 1 m^2 MOCNESS tows

Station # day tows # night tows

1 Great South Channel 2 2

2 Crest 1 1

3 Georges Basin 2 2

4 Northeast Peak 2 2

5 Cold Plume 2 2

6 Southern Flank 2 2

7 Detrainment Feature 2 3

MOC 1 Zooplankton Results (Karen Wishner)

The following notes are based on visual observations of whole samples fresh from the nets and will obviously be modified by direct counts later in the lab. In contrast to the previous two cruises, clogging of the zooplankton nets by phytoplankton was usually not a problem, since blooms of the large cells had ended at most locations.

The Great South Channel station (bottom depth about 170 m) was highly structured hydrographically. There was a mixed layer in the upper 10 m, a broad depth zone of stepped decreases in temperature to about 70 m, a zone of intermediate water to about 110 m, and a bottom layer below that. Calanus and Limacina occurred in the upper 20 m, including a particularly dense patch of Limacina and Clione in the upper 10 m in one of the two night tows. Copepods and euphausiids were found at depth day and night; the euphausiids were also found throughout most of the water column at night.

The Crest station (44 m depth) was well mixed to the bottom. A mixture of copepods, small amphipods, and sand were found in samples during the day and night; night samples also had some isopods, fish, and a polychaete. Some hydroids and chaetognaths also were found.

Georges Basin (about 365 m) had warm low salinity water at the surface, a temperature minimum at about 60 m, and warm high salinity water from about 190 m to the bottom. During the day, concentrated raspberry-colored Calanus occurred from 10 - 50 m. Calanus and amphipods were found throughout the water column day and night, and euphausiids occurred at depth during the day and in the upper nets at night. Large shrimp were also caught at night and Pleurobrachia were caught in the upper 20 m. Some Coscinodiscus occurred from 50 - 100 m.

The Northeast Peak station (about 80 m) was well mixed to the bottom, although some small-scale variability was evident. Small copepods were common at all depths day and night. Pleurobrachia were common during the day from 10 - 40 m. Isopods were evident at night at all depths. Chaetognaths and amphipods also occurred.

The Cold Plume (134 m depth) had low salinity in the surface water (the 32%o isoline occurred from about 24 - 36 m during the different tows). The temperature at the surface showed the effects of solar warming, and the temperature minimum was about 60 m. Temperature and salinity increased with depth below that. Abundant Calanus and amphipods occurred throughout the water column day and night. During the day, small amphipods occurred deeper than the large ones. Pleurobrachia and Bolinopsis were found mostly in the upper 10 m, except for one of the night tows when they occurred to 50 m.

The South Flank station (about 110 m) had relatively warm low salinity water at the surface, a temperature minimum at about 40 m, and a very warm salty bottom layer below about 80 m. The Chaetoceros layer was a thin feature at about 20 m (see Optical results), and Coscinodiscus was also found in many of the plankton nets (as well as in bottle samples). Chaetognaths, gelatinous organisms, and copepods occurred in the deeper nets day and night. Copepods, tiny amphipods, and some large amphipods were common in the upper nets day and night.

The core of the detrainment feature was very narrow and was marked by a thin layer of Georges Bank water (cold, low salinity) overlying warmer saltier water. The maximum thickness of the surface layer was about 20 - 40 m in the center of the feature, but it thinned out rapidly within a few km. A large portion of the area shown as cold water in the satellite image had only a thin surface veneer (10 m thick or less) of the cold Georges Bank water. Below about 60 m, the water column was isothermal to 200 m, the limit of our sampling. At the "feature core" station during the night MOC 1 tow, the sea surface temperature was 11.86°C and the sea surface salinity was 31.99%o. At the east and west stations just a few km away, sea surface temperature was 15.9 - 16.1°C and sea surface salinity was 33.18 - 34.07%o. During the night tow in the core of the feature before the storm, much layering was visible optically (see below) and in the samples, both for phytoplankton and zooplankton. The zooplankton in the cold water nets included copepods and large amphipods and resembled the Georges Bank fauna. In the warmer water below and outside the feature, a variety of oceanic species occurred including pyrosomes, myctophids, and copepods. Phytoplankton layers (Coscinodicus, Ceratium, Chaetoceros) in the cold feature had distinct optical signatures and depths (see below). The daytime tow during the storm after over 24 h of 30 - 40 kt winds showed no layering near the surface, although the sea surface low temperature and low salinity signatures were still evident. The

phytoplankton layers were gone, presumably mixed into the water column. Calanus occurred primarily from 20 - 50 m. Oceanic and Bank species were mixed in the surface waters.

MOC 1 Optics Results (Jim Sullivan)

General Comments:

The cruise was very successful with 27 MOCNESS casts completed and no instrument failures of any kind. DOM spectral fluorescence and DOM spectral absorption were measured using a WETlabs SaFire and an AC9 mounted onto the MOCNESS. The spectral peak in DOM fluorescence was at the EX:EM pair of 265:490 throughout the water column. Occasionally the EX:EM pair 265:540 would be greater than the 265:490 pair in the near-surface water. This was most likely due to increased scattering in this layer. The SaFire depth sensor was recalibrated (from a depth offset of 15.5 m to a depth offset of 26.5 m) and was probably giving accurate depths to +/- 2 m. The SaFire pressure sensor was used to target the MOCNESS sampling depths because the MOCNESS pressure sensor had a variable offset of 23 - over 30 m. At deep water stations (>250 m), the MOCNESS tows did not exceed 220 m in depth because the pressure ratings for the SaFire and the AC9 were approximately 200 m maximum depth.

Station 1 - Great South Channel (5-24-97)

During the daytime vertical profiles there was a large core of water from ca. 20-130 meters that had a nearly uniform DOM fluorescence value of ca. 24-25 units. At both the near-surface (0-20 m) and near-bottom (140-160 m), there was a slight decrease in DOM fluorescence to a value of ca. 21-23 units. The nighttime vertical profiles were similar to the daytime casts except that there appeared to be a small peak in DOM fluorescence at ca. 120 m with a value of ca. 27-28 units. This was similar to the results found during the April cruise where DOM fluorescence did not closely mimic the hydrography.

Station 2 - Crest (5-25-97)

This was a shallow water station (ca. 40 meters) that was hydrographically uniform from the surface to the bottom (well mixed). The DOM fluorescence was also uniform with depth at a value of ca. 23-24 units. There was no difference between the daytime and nighttime vertical profiles.

Station 3 - Georges Basin (5-26-97)

During the daytime vertical profiles, DOM fluorescence increased between 0 and 30 m from ca. 20-22 units to 22-24 units respectively. There was a peak in the DOM fluorescence at ca. 50 m with a value of 24-26 units. The DOM fluorescence slowly decreased with increasing depth until ca. 200 m, where it reached a low value of 16-17 units. DOM absorption showed the same trend as DOM fluorescence throughout the profile. Both seemed to be inversely correlated with the temperature profile. Nighttime vertical profiles were similar to the daytime profiles; however, the peak in DOM fluorescence varied between ca. 75 m and 30 m on the up and down cast respectively.

Station 4 - Northeast Peak (5-27-97)

This was another relatively shallow station (ca. 80 m depth). CTD hydrography showed no structure with depth (well mixed). DOM fluorescence was similar to hydrography and was uniform with depth at a value of ca. 23-25 units. There was no difference between daytime and nighttime vertical tows.

Station 5 - Cold Plume (5-29-97 to 5-30-97)

This station was characterized by a near-surface intrusion of cold plume water onto the Bank. This water had a temperature of ca. 6.5°C, a salinity of 31.7 ppt, and was restricted to the upper 20 m of the water column. DOM fluorescence profiles were fairly uniform with depth at a value of 23-25 units; however, both the daytime and nighttime vertical profiles had small peaks in DOM fluorescence between 30-50 m at a value of ca. 25-27 units. There appeared to be a unique DOM fluorescence signature to the cold plume of water that was characterized by an increase in the 540 EM:265 EX relative to 490 EM:265 EX. It also seemed more pronounced on the downcasts.

Sterile filtered water was collected at 10 and 100 m at this station from Go-flo bottles on CTD casts for SaFire laboratory experiments onshore investigating the changes in DOM fluorescence due to photic processes (thesis work of Mike Twardowski).

Station 6 - South Flank (5-31-97 to 6-1-97)

This station had a large DOM fluorescence signal associated with a cold pool of water at a depth of ca. 30-50 m. This broad peak reached a value of 25-27 units. The DOM fluorescence signal decreased in the upper 20 m to a value of ca. 23-24 units and to a value of 19-21 units at ca. 90 m. This station was also characterized by a strong peak in chlorophyll fluorescence at ca. 20 m which was created by large numbers of Chaetoceros socialis (diatom) colonies. This "thin layer" was targeted with the MOCNESS using the SaFire chlorophyll fluorescence trace.

Station 7 - Ring "streamer" (6-1-97 to 6-3-97)

This feature was first mapped by a 24 h CTD transect to find its spatial boundaries. Three stations were assigned to be sampled, one on the eastern edge of the streamer, one in the center of the streamer, and one in the western edge of the streamer. During the nighttime vertical profiles all 3 stations were sampled. During the daytime vertical profiles only the eastern and central stations were sampled (weather forced an end to deck operations). The eastern and western stations were characterized by warm surface water (ca. 16.5°C) and very low DOM fluorescence values (16-17 units), while the central station had cool surface water (ca. 11.5°C) and DOM fluorescence values more like that of Georges Bank (20-22 units). The central station had a chlorophyll fluorescence peak at 20 m similar to that seen at the South Flank station of Georges Bank. The phytoplankton found in this cool surface water were also the same species seen at the South Flank station on Georges Bank.

This combined data set should provide some interesting and alternative methods for interpreting macrozooplankton distributions. DOM fluorescence and absorption values sometimes behave as non-conservative water mass tracers which are changed by in-situ biological, chemical, and photic processes. How zooplankton distributions correlate to these changes will be an exciting result of this field work.

Sources to and Losses of Invertebrate Predators from Georges Bank, and In Situ Feeding Rates of Selected Predators

Barbara K. Sullivan (URI and Predation Group)

Major Objectives:

1) Investigate sources to and losses of invertebrate predators from the Georges Bank ecosystem.

2) Determine in situ feeding rates of selected abundant invertebrate predators on target species with the ultimate objective of defining site-specific mortality due to predation by invertebrates.

Methods:

1) Describe abundance and diel vertical distribution of invertebrate predators in MOC 1 tows collected at sites on and off the bank as well as in physical features that may be sources or sinks of predators (e.g. Scotian shelf water, waters adjacent to Gulf Stream ring).

2) Improve estimates of in situ predator feeding (per individual) rates begun in GLOBEC Phase I. On this cruise I concentrated on feeding rate estimates of the ctenophore, Pleurobrachia sp. and the chaetognath, Sagitta elegans.

Sagitta elegans

Sagitta elegans was one of the most abundant predators in MOC 1 samples during Phase I. At stations sampled on this cruise S. elegans was apparently less abundant than in 1994-1995. Hydroids may also have been less abundant . If this was true bankwide, then this could provide an opportunity to examine the response of prey to a "low" predation year, at least predation by these two predators.

In situ feeding rates per chaetognath are being determined from gut content analysis of individuals from MOC 1 net tows. Gut evacuation rates are already well established but data on number and type of prey per chaetognath at different stations is still being collected. To ensure most accurate rates from this analysis, I collected 14 additional tows designed to minimize artifacts introduced by net collection (such as cod end feeding, egestion of gut contents during long tows or long processing time of MOC 1 collections). The 14 tows were short ( 8-10 min) vertical tows with a coarse ( 0.4 mm) mesh net, preserved immediately. These tows were made immediately before or after MOC 1 collections to allow direct comparison between rates obtained from each net type. Any difference in number of prey per gut or prey types in the gut will be used to correct rates obtained from analysis of MOC 1 tows, with the assumption that short tows in coarse mesh nets provide the most accurate data.

Pleurobrachia sp.

Five experiments were run to determine gut evacuation rates of Pleurobrachia. These rates will be used with numbers of prey per ctenophore from gut content analysis to calculate feeding rates on target species. Number of prey per ctenophore will be obtained from both diver-collected ctenophores preserved immediately after being brought on board the ship and from individuals collected in MOC 10 net tows. A total of 31 ctenophores were collected by divers from 2 stations (Northeast Peak and South Flank) and 5-6 were used for each experiment. Three experiments estimated gut evacuation rates of ctenophores immediately after collection and two other experiments determined digestion rates of ctenophores fed 2-6 Calanus females (Table 2).

Table 2. RESULTS OF GUT EVACUATION EXPERIMENTS (Sullivan)

Prey ingested in situ included 19 large copepods (a mix of Calanus and Centropages), 10 "small copepods", 3 crab zoea and 1 Limacina.

Egg production: It was noted that all individuals from the South Flank laid many (>400) eggs per individual during overnight incubations, whereas only a single individual from the NE Peak laid eggs.

Gut Passage Time Experiments

Mari Butler (WHOI), Steve Bollens (SFSU), Steve Lowe (SFSU), Heather Macrellis (WHOI), and Erica Estrada (WHOI)

We attempted to measure gut passage times on two of the more abundant animals that were captured in the 10 meter MOCNESS hauls. The euphausiid Meganyctiphanes norvegica was a dominant taxon caught in the Great South Channel, and the amphipod Themisto gaudichaudii was a dominant taxon caught at most of the other stations especially in one tow taken in the cold plume. Therefore, we chose to look at these two taxa.

Two experiments were run where 10 M. norvegica were allowed to feed on carmine-dyed Calanus finmarchicus for 30 min after which time the euphausiids were each put in individual 1-liter jars containing 30 mm filtered sea water. Hourly observations of presence or absence of fecal material provided estimates of the amount of time it took for prey to pass through M. norvegica 's guts (Table 3). The average gut passage time for M. norvegica was estimated to be 2.10 h with estimates ranging from 1.28 h to 3.63 h.

Four similar experiments were conducted feeding T. gaudichaudii C. finmarchicus (Table 4). The estimates for T. gaudichaudii ranged from 2.00 h to 7.00 h with an average gut passage time of 3.81 h. These estimates are higher than the few estimates we made on EN298 in April 1997 where the average gut passage time was 8.7 h. Although our estimates made on EN301 are higher than those made on EN298, the temperature at which the EN298 experiments were run ranged from 3-7°C while the temperature at which the EN301 experiments were run ranged from 10-14°C. In addition, different prey types such as fish larvae were used during EN298, while only C. finmarchicus were used during EN301. Other data (Sheader and Evans, 1975) agree with our estimates made at the warmer temperatures (10-14°C) but differ greatly at the lower temperatures (3-7°C). At

5°C, they estimate gut passage times of nearly 72 h compared to our estimate of 9 h. At 10-14°C, they estimate gut passage times of about 2- 12 h, which is within our range of estimates.

Sheader, M amd F. Evans, 1975. Feeding and gut structure of Parathemisto gaudichaudii (Guerin) (Amphipoda, Hyperiidea). J. mar. biol. Ass. U.K. 55:641-656.

Table 3.

MEGANYCTIPHANES NORVEGICA GUT PASSAGE TIMES

Table 4.

THEMISTO GAUDICHAUDII GUT PASSAGE TIMES

Blue-water Dive Operations

Erich Horgan (WHOI)

We completed four dives during EN301 in order to evaluate in situ feeding by gelatinous predators and to collect those animals for shipboard determination of gut clearance rates, accurate identification, and feeding studies.

Our first dive was at the Northeast Peak, 41°51.2'N 66°29.8'W. Water temperature was 7.5°C. This was the only dive during this cruise during which both ctenophore species Pleurobrachia pileus and Bolinopsis sp. were seen together. Eleven Pleurobrachia were collected ranging from 1.5 -3.0 cm oral-aboral length. Bolinopsis (n=5) were found only near the surface. Beroe sp. was frequent, with 1 collected (1.5 cm). Hydroids, both Obelia sp. and Clytia gracilis,were very common, with actively feeding hydranths. The Obelia colonies were isolated and brought back to Woods Hole for culturing. In situ observations of Pleurobrachia noted individuals (with tentacles retracted and adorned with prey items) spinning at ca. 1 revolution per second; the guts of these individuals (n=4) were packed with prey.

The second dive was in Georges Basin, at 41°48.9'N 66°30'W. Water temperature was 7.5° C. Pleurobrachia was very abundant, but only below 50 ft. depth, where they were estimated to be 0.3-1 individual / m3. Eight were collected, between 2-3 cm diam. Other gelatinous animals collected included Cyanea sp. (9 cm), a bryozoan colony, and 5 hydroid colonies (Obelia type)

The third and fourth dives were on the Southeast Flank of Georges Bank: both dives revealed a nearly identical water column. Pre-dive CTDs showed a fluorescence peak near 20 m. Surface water temperature was 11.5°C. Position of the first dive was 40°34.7'N 67° 34.8'W, the second was at 40°34.6'N 67°55.6'W. The water column was very calm during both dives. A water sample was collected in a jar at 60 ft. The flocculant material most abundant at this depth reminded the collector of a Chinese calligrapher's brush strokes ("The water looked like tapioca"). Mike Sieracki was given this jar of Chaetoceros socialis for Calanus grazing experiments. Pleurobrachia was abundant (> 1 / m3) from the surface down to 15 ft. Eleven individuals collected ranged from 1.5-2.5 cm diameter. One individual collected had three large Themisto gaudichaudii feeding upon its ctenes; several of the other individuals had small (0.8 mm) amphipods attached to (feeding upon?) their ctenes. A tentative identification is Hyperia galba. A single Physophora hydrostatica (physonect siphonophore) and a Staurophora sp. were collected; shipboard video was taken of the siphonophore.

During the fourth dive, Bolinopsis were abundant from the surface down to 100 ft (1-2 / m3). These animals ranged from 1 cm to over 30 cm. Individuals (n=10) were brought aboard for videotaping and 35 mm photomicrography. Water samples were taken at 55, 65, 75, and 85 ft depth for size frequency determination and abundance of Chaetoceros socialis. A large hydromedusae, possibly Dipleurosoma or Halopsis, was frequent below 50 ft. One individual measuring 5 cm was collected.

Studies of the Ctenophore Bolinopsis (Ph.D research)

Becky Coverdale (WHOI)

My main objective during the cruise was to obtain ctenophores (Bolinopsis infundibulum) for thesis research. I scuba dove with dive buddy Erich Horgan on four occasions to collect animals. The dive dates, locations, and animals collected are listed below.

5-26-97. 17:30. Georges Basin (41°51.2'N 66°29.8'W)

Collected 5 Bolinopsis (relatively few seen). Also collected Pleurobrachia (abundant) and Beroe (few).

5-27-97. 10:00. NE Peak (41°48.9'N 66°30.0'W)

The only ctenophore we saw was Pleurobrachia (collected). These were found at 60 - 70 ft in abundances of 0.5-1 / m³. One Cyanea (scyphomedusa) was collected.

5-30-97. 16:24. S Flank (40°34.7'N 67°34.8'W)

The only ctenophore seen was Pleurobrachia (collected). Many of the these were infested (particularly on comb rows) with hyperiid amphipods, that keyed out to Hyperia galba. Most of the hyperiids I saw appeared to be larvae or juveniles. The water was clouded by diatoms (Chaetocerous socialis), and at 50 - 70 feet we saw a lot of flocculant material in the shape of Chinese brush strokes that, when examined under the scope, appeared to consist mostly of mucus (few cells visible). A siphonophore, Physophora hydrostatica, was collected.

5-31-97. 15:15. S Flank

Bolinopsis was very abundant (1-2 / m³) throughout the water column (max dive depth 90 ft by Erich). Small hyperiids (the size of those seen earlier on Pleurobrachia) were seen on some Bolinopsis. Below about 40 ft the water was soupy with Chaetocerous and flocculent material (described above). Bolinopsis was feeding (lobes outstretched, balloon-like) throughout the water column (even in the soupy stuff!). A hydromedusa, identified as Dipleurosoma or possibly Halopsis, was collected.

(As a side note, a dinner plate-sized Periphylla periphylla (coronate scyphomedusa) was caught in a MOC 10 at about 200 - 300 meters).

Part of my thesis research concerns the feeding ecology of Bolinopsis infundibulum. Bolinopsis collected at the Northeast Peak and the South Flank were photographed using a still camera. I will later use image analysis to determine the surface area of structures used for feeding (lobes and tentacles, etc.) for animals of different sizes. The lobes and tentacles are probably specialized for capturing different types of prey. Thus, the proportion of space devoted to these structures for animals at different developmental stages will ultimately help me to predict how the ctenophore might affect prey populations.

Several animals were also videorecorded with prey (Calanus and smaller zooplankton) in a small tank. Here, I hoped to record particle movement showing flow patterns around the ctenophore's body and feeding structures, and to observe predator-prey interactions. Unfortunately, the ctenophores insisted on remaining in the bottom corners of the tank most of the time, so my efforts were not very successful this time. While diving I observed the animals feeding, and in doing so they expanded the lower half of the lobes (oral end) out in a balloon-like fashion. I think enclosing them in a small tank prevents them from assuming this posture. Several times I observed one swim forward and begin to extend its lobes, then suddenly strike the side of the tank. I hope to resolve this problem by videorecording in situ or in a mesocosm.

Solar Ultraviolet Radiation and Marine Planktonic Ciliate Survival on Georges Bank (Ph.D. Research)

Elena Martin, Al K. Hanson, and Dian Gifford (all at URI)

To test the hypothesis that solar UV radiation decreases survival in marine planktonic ciliates, three UV-Exposure experiments were performed during EN301. The microzooplankton assemblages used in these experiments were collected from depths of 10 to 30 m in Go-Flo bottles from stations 1 (Great South Channel, CTD 02), 4 (NE Peak, CTD 08), and 6 (Southern Flank, CTD 15). Each assemblage was exposed for 2 days to sunlight with and without UV in polyethylene bags in a flow-through incubator on deck at subsurface light levels. Photosynthetically active radiation (PAR: 400-700 nm) and ultraviolet radiation (UVB: 310 nm, 320 nm; UVA: 340, 380 nm) were recorded continuously during the experiments using Biosphericals instruments PUV500 underwater radiometer. One light profile was recorded at station 4. Ciliates and other microzooplankton were preserved in Acid Lugols and prepared for epifluorescent microscopy for later enumeration. Chlorophyll concentrations were also measured.

Undergraduate Training Report

Summer Nelson (URI), Erica Estrada (WHOI), Steve Lowe (SFSU), Heather Macrellis (WHOI), and Jen Schadlick (URI)

On 5/28/97, the undergraduate members of the cruise had the opportunity to work together for the first time. They used this time to familiarize themselves with some of the non-MOCNESS scientific equipment on board and the biota of Georges Bank. With the help of the Marine Tech, the undergraduates took ring net tows (400 m mesh) and CTDs at both the Georges Basin and NE Peak stations. Informally, the data collected from these procedures were used to evaluate the differences that exist between well mixed and stratified water columns.

The ring net tows allowed the undergraduates to observe, first hand, the high degree of species variability on Georges Bank. Their primary foci included a comparison of the zooplankton species found between the stations and an exploration into some of the sources of bioluminescence on the Bank. Through this process, the undergraduates gained an appreciation for the variation of diversity that exists on Georges Bank, as well as a working knowledge of equipment that became helpful in the later days of the cruise.

Outreach Educational Activities

Barbara Sullivan (URI)

A video of cruise activities and the comments and perspectives of the various scientists and crew members on board was recorded. After editing, this is to be used for elementary school science outreach programs. E-mail communications during the cruise were maintained with a fourth grade public school class. Students could ask questions about the cruise and science, and receive replies from the ship. Thanks to all the crew and scientists who helped with this project!

captions

Fig. 1. Cruise track and nominal station locations for EN301. The position listed for the detrainment feature survey is the location of the central feature station on the middle transect, and the black dots represent locations of MOCNESS tows.

Fig. 2. AVHRR satellite image from 29 May 1997 from Jim Bisagni. The Scotian Shelf (Cold Plume--CP) water is visible on the northeast edge of Georges Bank, and the Detrainment Feature (DF) is visible in the lower center of the image.

Fig. 3. Locations of planned CTDs for the Detrainment Feature hydrographic survey (map drawn by Steve Vetra). The small numbers are the bridge's way point identifiers (not the CTD cast numbers). The eastern stations on the north line were not done because we added stations to the west. MOCNESS tows and CTD-Go-flo casts were done at stations 62 (east), 78 (feature center), and 83 (west).

CP

DF