2.4a Macrofaunal Ecology Report - Marcus, Metaxas, Tunnicliffe
NEMO 2000 was a very successful cruise for the macrobiology collections and observations. Dive coordination and ROV configuration plans allowed us to retrieve a large number of varied samples (see attached list) for numerous projects. The fauna are directly linked to geological, hydrological and microbial dynamics. In that sense, the interdisciplinary nature of the NEMO program is essential to understanding the setting of the Axial community and the response to the 1998 eruption. Three of the major studies in this program include: Time-series on the new lavas - Temporal change of community composition on the new lavas is the subject of Jean Marcus' PhD dissertation. This third year of collection has been vital to the sequence, especially as the tubeworm is establishing in all sites. She was able to replicate eight sites from 1999 and six from 1998. While the numbers remain a statistical challenge, it is the first time anyone has examined the complete faunal sequence of new vents. Corresponding information from water chemistry, temperature records and microbial dynamics will form a uniquely complete picture.
We had the opportunity to sample not only the tubeworms but the peripheral zonation of one vent. It is possible that spatial displacement of some taxa may occur with time. The time-lapse camera was recovered from Marker 33 after a second year-long deployment at this site. We will have 550 images over the two years to examine faunal changes.
We will continue to examine conditions of optimal growth and recruitment of tubeworms. The 1998 samples from Nascent/N41 showed very large numbers of recruits appearing but high mortality (likely grazing). Repeat sampling from 1999 and 2000 will allow us to follow the growth of cohorts and changing recruit abundance as water chemistry shifts.
Larval Dynamics - One of the missing pieces to the puzzle of community development at vents is the role of larval supply. Our long-term goal (3 years) is to examine spatial variability in larval supply and recruitment among vents with different histories. A series of plankton collections were done using different sampling devices, to obtain a preliminary synoptic view of larval abundance in different areas of Axial Seamount. Net tows over the South Pillow Mound and near Bag City showed greater larval abundance near the vents than over SPM. We collected several samples with a pump, over South Pillow Mound, while transiting between vents (Bag City to Joystick), and at Cloud vent, where we found the greatest larval abundance. Additionally, we deployed passive larval traps at ASHES and Mkr 33 for 10 and 13 days, respectively. Preliminary examination of the samples indicates that gastropods and polychaetes were the most abundant larvae, using all collection methods. Copepods, ostracods and foraminiferans were the most abundant taxa in the samples. We will use this year's data to design a more detailed sampling scheme for next year.
Gastropod Ecology - The most abundant animals on Juan de Fuca Ridge vents are two species of gastropods (the limpet and glob snail). Nothing is known of their ecology, requirements or interactions. A new student's thesis will be built on this theme. The extant sample suites will be examined for population characteristics and interactions of these two species. Some fine close-up video will augment habitat information, as will the time-lapse images. We were able to collection these and several other gastropod species for physiological analysis by a Washington State colleague. He (Ray Lee) will meet the ship to retrieve live specimens for respiration measurements.
New Lava Communities - There are notable changes in the community composition at vents on the new lavas over the 30 months since the January 1998 eruption. While only a small sample could be analyzed on the ship the table below gives an impression of the marked shift in animal representation that has occurred. Some polychaete groups predominated at the initial phases, then pandora and palmworms moved in but the numbers of snails and limpets increased to predominate the current sample.
Marker 33, Southeast Rift Zone: suction samples from the venting crack.
|Snails and limpets
New Species - It is always exciting to find new species - in the past, some new vent species have represented major finds for systematists. While we cannot know what we have until the specialists see them, there are three animals that warrant close attention. On the new lavas, a small golden snail has appeared in several samples. It is unusual as it is always associated with tiny attached juveniles as if it is brooding its young. Secondly, two specimens of a high spired limpet were found near Castle - sampling outside the immediate vent are often turns up overlooked species. Thirdly, and most interesting, is the blueberry mat seen at Oldworms, Marker 113 and other locations. Its coverage resembled a known single-celled protozoan but it is clearly a metazoan with haemoglobin. Observed closely in video, the anterior end extends far from the tube and synchronized retraction is observed. Lastly, the new scaleworm (Bathybahamas sp. nov.) that was so common on the new lavas was rarely observed this year.
New Approaches - The biggest failure in the cruise was a timed pumping system to be deployed for a year to gather larvae and particulates. It failed on the deck. However, we had the loan of a filtration system on the submersible for large volume samples. Hundreds of litres were pumped through meshes fine enough to capture larvae. Secondly, two plankton tows with a small net in the submersible arm gave excellent returns. Thirdly, coordinated visual observations during Imagenex runs will allow us to document larger animals in the waters above the vents. And lastly, the cruise allows the first experimental deployment of collecting tubes for settling larvae. All these techniques together will allow us to develop a project to examine the dispersal of vent organisms through larval stages and their interaction with the overlying zooplankton.
Macrobiology Sample List - NeMO 2000
Investigators: J. Marcus, A. Metaxas, V. Tunnicliffe
This listing includes samples targeted for us, samples shared with others and subsamples from other types of samples
South Rift Zone, Axial Seamount
Tube worm grabs
McLane pump plankton samples
Plankton net samples
R543-21: Mkr 33, time lapse camera recovered after year-long deployment
ASHES, Axial Seamount