Larry Madin, et al.Topics discusssed at the Broad-scale Survey Meeting included interannual variations in hydrography, mesozooplankton results from the MOC-1, abundances of larger organisms from the MOC-10, sampling for gelatinous animals and continuing use of the MOC-10 on BSS cruise.
1. Hydrography (Mountain)
The changes on hydrography that were presented in the Decadal Session were reviewed. The major features were a progressive decrease in salinity and in fluorescence from 1995 through 1998. An important point of interest is whether these types of changes were evident at higher trophic levels in the sytem.
2. Mesozooplankton data. (Durbin)
Data for the distribution and abundance of the copepdite stages of Calanus finmarchicus for the months of February and March were presented These plots indicated advective transport onto the Bank in February and substantial growth of the population by March. Also presented were abundance values for the copepodite and adult stages of Calanus plotted as a time-series for various sectors on the Bank using the data from the broad-scale cruises in 1995 and 1996. There were substantial differences in the timing of development in the early part of the year with delayed development of the population in 1996 compared to 1995. However, the abundance levels at the peak of the production was ~50% higher in 1996 than 1995. For both years, there was fairly high coherence in the seasonal abundance patterns between the various sectors.
3. Macrozooplankton and micronekton.
Steve Bollens presented a progress report from the Predation Group on the sample analysis and data analysis for the MOC-10 macrozooplankton and micronekton samples. All of the 1995 and 1996 samples, and a small proportion of the 1997 and 1998 samples, have been analyzed, including identification and enumeration of all specimens, and measurement for length of up to 50 individuals of each species per net. Bankwide seasonal abundance patterns during 1995 and 1996 were presented for fishes (e.g., cod and herring), larger crustaceans (e.g., shrimps), and gelationous macrozooplankton (e.g., salps). Of a total of approximately 5,000 fishes collected in 1995 and 1996, almost 1,000 were cod, a surprising result given that cod larvae and juveniles were thought to be removed from the catches on ship-board prior to preservation in formalin. It was agreed that closer coordination between the predation group and the Sandy Hook NMFS lab was necessary to assess these data. Length-frequency data were also presented on a range of representative taxa from a variety of seasons and stations. These data included both fish (herring, sandlance) and crustaceans (Pasiphaea, Dichelopandalus) in the 40-100 mm size range. A smaller amount of data were presented on spatial distributions of these organisms on Georges Bank.
4. Gelatinous zooplankton sampling.
Ted Durbin raised the issue of the adequacy of sampling for gelatinous animals like medusae and ctenophores. He noted that they were very abundant on the June, 1998 cruise, but felt that the existing nets did not sample them well. His suggestion was to add a vertical tow with a specialized net, perhaps similar to the design that Pat Kremer used previously in Narragansett Bay to collect Mnemiopsis. A similar attempt had been made in 1997 on the BSS cruises, at the request of the Predation Group. A 1 m² Reeve net was used on two cruises, but was found to be too awkward to handle in rough conditions, and was discontinued. Durbin's proposal was for a shallow, large mesh net with no solid cod end, which could be fished in a short vertical tow at each station. Madin discussed net design with Kremer by phone after the meeting, and the design and protocol were discussed further by the Predation group.
It was generally agreed that a sampling effort directed at jellies was worthwhile and could probably be accommodated within the BS schedule, since a similar procedure had been done previously. An important consideration is the ability of someone on the cruise to examine the jelly catch immediately, before preservation, since ctenophores do not preserve. MOC-10 samples could also be inspected immediately for jellies. The Predation group offered to try to provide one or two people for BS cruises in 1999 to perform this function, as well as participating in normal watch duties. Durbin expressed the opinion that the additional time required for these tows would have to be made up by eliminating the MOC-10 hauls, but it was agreed by others that there should be sufficient time in the schedule for both. The Predation group agreed to present a plan for jelly sampling for the next Broad-scale meeting, sometime later in the fall.
5. Continuing use of the MOC-10 on Broad Scale cruises.
Ted Durbin again brought up the question of the value of MOC-10 trawls on the BSS cruises. His argument was that the trawl didn't appear to catch anything that wasn't also caught by the MOC-1, and was an inordinate amount of work and frustration for the BS science party and crew. This issue first surfaced at the July 1998 EXCO meeting, and it was decided then that a comparison should be made of catch data for selected taxa from the MOC-1 and MOC-10, to see if there were differences in numbers or size categories of organisms collected. That comparison was to be made during the SI Workshop. Durbin and Bollens exchanged lists of taxa to compare, and Bollens provided data on numbers and size frequency of these taxa in selected BS MOC-10 hauls. It has become evident that it will take considerably more effort to produce length frequency data for all categories of predators in MOC-1 samples than was recognized at the July EXCO meeting, and it may be necessary to revisit the issue of whether such a comparison can be made in time to use the information for planning braodscale data collection in 1999.
The discussion of the costs and benefits of the MOC-10 trawls touched on several points. Bollens and Madin reiterated their appreciation for the efforts of Durbin and others in undertaking the MOC-10 sampling. Bollens also reviewed several points in support of continued MOC-10 sampling on the Broadscale cruises, including: 1) collection of cod and haddock, two of the target species, in March-July (data presented as described above); 2) collection of larger (40-100 mm) organisms which are thought to be important predators on adult copepods, and especially larval fish; 3) collection of a sufficient number of these rarer, more dilute predators to obtain an adequate sample size (e.g., 50 individuals), based purely on the larger sampling volume of the MOC-10; 4) continuation of an existing time series (1995-1998) for the MOC-10, and the extreme difficulty of analyzing retrospectively the MOC-1 samples for these larger predators; and 5) the general importance of macrozooplankton and micronekton as components of the pelagic community, especially in the context of GLOBEC's interest in climate variability and potential ecosystem change.
Mountain and Wiebe agreed about the importance of maintaining continuity in the Broadscale sampling program. The MOC-10 was always included in the thinking about the Broadscale protocols (in particular for the collection of larger gadid larvae), and was part of the responsibilities for those participating on the Broadscale cruises in terms of collecting samples at sea as originally proposed by Wiebe and Miller, and subsequently taken on by Durbin and his group at URI. Durbin responded [after the meeting] ”... that when I agreed to take on the Moc1 zooplankton sampling and counting at URI it was with a considerably scaled down tech group compared with what was originally proposed. It was never my intention that this scaled down group of techs at URI would be responsible for other sampling requirements such as the MOC10.”
Mountain and Wiebe both felt that dropping the MOC-10 in the last year of a five year series would compromise the data set and make interannual comparison of larger organisms incomplete. Mountain argued as well that the Broadscale cruises usually were completed on time, or early, and that the time required for MOC-10 sampling generally has not been a limiting factor in completing the surveys. While a consensus was not achieved, the majority view appeared to be for continuation of the MOC-10 sampling on Broad Scale cruises in 1999, provided a protocol could be added to sample the gelatinous predators. It was agreed that the question should be discussed again at the fall Broadscale meeting.
One general issue that came out of the discussions was the need to develop a common set of geographical sectors on the bank that could be used by various investigators to integrate their data into. This would facilitate the intercomparison of the various data sets now being developed. In reply to this point Ted Durbin added [after the meeting]:
The locations of several stations have been changed in subsequent years and we have modified the groups using the above depth criteria. The idea is to pool stations where we may expect responses of animals to be similar for the analysis of population age structure trends and day-night differences in depth distribution. We would welcome any comments.”