NURP Project Summary


	Deep East - A Voyage of Discovery: Exploring Deep Sea Coral Communities (Year 1 of 1) Project Number: NAGL-01-04A Principle Investigators: Watling, L. E., P. J. Auster, I. G. Babb, K. J. Eckelbarger, S. C. France, and B. Hecker Region(s): Georges Bank Submarine Canyons

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Introduction:

To most people, the concept of a deep-water coral is an oxymoron. Until the recent legislation banning trawling in deep coral beds off the coast of Norway, the existence of these species was known only to a handful of scientists and a large number of fishermen. In North America there is little knowledge of their existence in the minds of the general public as well as the broader scientific community (Breeze et al. 1997), although a recent symposium (1st International Deep-Sea Coral Symposium, Halifax, 31 July- 3 August, 2000) dealing with the subject may help to bring the issue to attention of the general public.

Along the American east coast deep-water corals have been known since at least 1862 when Verrill notes the presence of a Primnoa on Georges Bank (Verrill 1862). One of the most important deep-water corals, from both general biological as well as ecological perspectives is the gorgonian, Paragorgia arborea (Tendal 1992). In the Atlantic it is found from the tip of Georges Bank, Greenland, Iceland, and the Faeroes to northern Norway. Grasshoff (1979) showed this species to be bipolar in its distribution, being found in the colder and deeper waters of the southern hemisphere as well as in the north Atlantic and Pacific oceans. Hecker (1990) used a camera sled to record several species of both hard corals and octocorals as dominants of the upper and middle slope faunas in the canyons south of Georges Bank.

Given that the existence of these remarkable species has been known for more than a century, it is striking that almost nothing is known about their biology, population status, the role they play in enhancing local species diversity, and their role as habitat for deep water fishes, including those species targeted in recent exploratory fisheries. It is not known whether any of the species, other than perhaps the octocoral, Primnoa resedaeformis, occurs in what could be called "thickets," and no information exists about their reproductive, and therefore, recolonization capability. Recent studies have shown individual octocorals to be hundreds to thousands of years old (Druffel et al. 1995, Risk et al. 2000); consequently there is a critical need to understand the very basic aspects of their biology, such as reproduction and recruitment, and estimates of growth and population size distributions. There is virtually no information about what other species are commonly associated with the octocorals (a careful scan of Verrill's papers reveals the names of a few associates), or whether they offer important refuge space for juvenile fish and associated species as do other areas where reef-forming corals have created a strongly three-dimensional habitat (e.g., Fosså et al. 2000). The rarity of encounters with octocorals over 15 years of submersible dives across the shelf of the northeast U.S. suggests that the distribution of these species has significantly contracted since the time of the surveys conducted by Wigley, Theroux and others (Theroux and Grosslein, 1987; Wigley, 1968). The very existence of these species may now be threatened as trawling with roller gear has allowed larger and heavier gear into the areas where these corals occur(ed), perhaps completing the destruction of populations that were under long term threat as a result of various fixed gear fisheries.

The proposed expedition will provide the basis for the Principal Investigators to conduct future studies on deep sea (continental slope and seamount) and continental shelf octocoral communities. Future studies will compare slope communities with inshore octocoral communities in the Gulf of Maine (funded by NURC NA&GL and utilizing their ROV systems). The remaining inshore coral communities seem to have been missed by the mobile fishing gear because of the roughness of the bottom areas where they occur, while the deep sea coral communities have been generally protected, at least until recently, by depth.

Exploration Objectives:

The overall goal of this project is the characterization of deep-water octocoral communities along the continental slope and on seamounts off the northeastern United States. Due to the difficulty associated with studying these animals, scientists have only recently begun to understand their potential importance to benthic ecosystems, their rarity in the underwater landscape, and their sensitivity to human caused disturbances. The proposed Alvin cruise will focus on the deep-water communities of the Georges Bank Canyons and on Bear Seamount.

Objective 1. Characterize the diversity of coral communities in different canyon habitats, on Bear Seamount, and in the Gulf of Maine.

Existing data from around the world suggests that deep-sea coral communities vary with depth, substrate and between areas on scales of kms to 1000's of kms. Depending on such factors as larval duration (which includes time to reach competence as well as time to settlement) it is possible that local populations are the result of larval delivery from upstream sources. Community composition may be an initial indicator of connectivity among coral communities (i.e., similar compositions are indicative of general connectivity while different coral communities may be mediated by either or both local processes and larval supply).

Objective 2. Determine whether coral populations are capable of reproduction through histological analysis of the polyps.

The information from this part of the study will help to determine the capability of these species to recolonize marine protected areas that might be designated as a means of restoring deep-water communities that have been subject to heavy fishing pressure. Assuming that shallower coral communities have been greatly reduced in size and number, it is possible that the some coral species are living under conditions that would not allow reproduction. On the other hand, inflow from other sources (deeper or upstream from unimpacted sites) could deliver recruits from remote populations.

Objective 3. Determine the size class distribution of octocoral populations.

The size class distribution of a population can be used to make inferences about recruitment events and growth rate of individuals. Few, if any, young gorgonian colonies have been seen on natural substrates. Exactly why this is so is difficult to determine, but first it must be established that young (small) gorgonians are, in fact, rare in areas where there are larger colonies. An estimate of the number of successful recruitment events can be obtained by examining the size classes of gorgonians found in each of the areas of investigation.

Objective 4. Characterize patterns of coral habitat use by associated fauna.

There has been considerable discussion about whether cold-water coral beds provide critical nursery habitat for juvenile fish. The only area so far investigated with a high density of deep-water gorgonians is the Gulf of Alaska (Krieger 2000). In this area, submersible investigations showed high numbers of rockfish, but the other components of the fauna, such as the infaunal and epifaunal smaller invertebrates were not studied. The present study will determine the role that deepwater octocorals play in enhancing local patterns of biological diversity by collecting samples of infauna and epifauna as well as video transects of vagile species, in and out of coral habitats.

Objective 5. Verify the taxonomy and genetic similarity of octocoral species from the continental slope off Georges Bank with gorgonians on Bear Seamount.

To date gorgonians in deeper cold waters have been identified solely on the basis of morphological characters (Deichmann 1936). Larval transport patterns, reproductive timing, severe population declines, and variable habitat conditions can serve to isolate populations. This cruise provides an opportunity to verify taxonomic identifications of octocorals within the U.S. waters and determine relationships between populations. Strong ecological inferences are best made on the basis of careful taxonomic identifications. Comparisons of canyon and seamount specimens will be made using both morphological and molecular genetic criteria. There is a strong presumption that many of the species will exist in common between the two areas since much of the fauna found by Hecker (1990) in the canyons is also known from the New England seamounts.

A. results.

Preliminary Scientific Results (from 9/15/01 Quick Look Report): Two dives were made in the submersible Alvin. One found corals on rock outcrops in Oceanographer Canyon; the other did not find corals, but instead found high numbers of deep sea red crabs and flounders on mud slopes in Hydrographer Canyon. The presence of mud at Hydrographer Canyon apparently precludes the presence of corals. However, we also did not see other octocorals, such as the umbellulids, that also favor muddy bottoms.

Objective 1. Characterize coral diversity: Four species of gorgonian octocorals were obtained from two collection sites in Oceanographer Canyon. These have tentatively been identified as belonging to the genera Thouarella sp. (probably a new species according to Dr. F.M. Bayer, Smithsonian Institution), Paramuricea sp., and, Anthothella grandiflora. One specimen of Paramuricea was also severely overgrown by the colonial anemone Amphianthus sp.cf. mirabilis. Specimens of the octocorals were sent to the Smithsonian Institution for verification. A piece of the colonial anemone will be sent to John Ryland for verification. In the videos it appears that a substantial fraction of the Paramuricea are overgrown by Amphianthus. We intend to investigate whether we can use color differences to determine which polyps are present on the Paramuricea-shaped skeletons.

Objective 2. Coral polyp reproductive state: All coral and colonial anemone specimens were fixed aboard ship for electron microscopy. On return to the lab these specimens were embedded in plastic and await micro-sectioning. One problem needing solving, and thus holding up further processing of this material has to do with the fact that the gorgonians have numerous calcareous spicules embedded in their tissue. In some cases, as in Thouarella sp., the spicules are large and form an nearly continuous “exoskeleton”. We are currently researching decalcification techniques that could be applied to these colonies without ruining the biological tissues.

Objective 3. octocoral size classes: Using the videotape with laser beams for scaling, we will measure the size classes of the gorgonian Paramuricea sp, which seems to be the only species we encountered whose colonies are amenable to such measurement techniques. This has not yet been done but is planned for completion this summer. On the other hand, an undergraduate student at the University of Maine used the video tape from the Hydrographer Canyon dive for her senior project. She measured the size/depth distribution of burrows of the deep-sea red crab Chaceon quinquedens.

Objective 4. Associated fauna: Both Thouarella and Paramuricea colonies had other invertebrates as apparently “obligate” associates. The Thouarella colonies were always inhabited by a polychaetes in the Polynoidae, whereas the Paramuricea or Paramuricea skeletons overgrown by Amphianthus were nearly always inhabited by one large brittle star in the genus Asteronyx. We will use the videotape of the Oceanographer Canyon dive to assess the frequency of Asteronyx colonization of Paramuricea skeletons as well as investigate minimum size of colonization, etc.

In Oceanographer Canyon, 17 species and 180 individuals of fish were identified and counted. From video imagery each fish species was classified according to behavior and substrate. Only 24% of the individuals were actively foraging while 76% exhibited station-keeping/sit-and-wait behaviors (on bottom or in near-bottom water column). This is very different than we would suspect based on other studies. Work by Carbtree et al. and Sulak suggest that North Atlantic deep sea fishes have energetically intensive foraging modes (i.e., active searching). Our observations are consistent with the notion that slopes and canyons may be large scale "edge" habitats where prey are more abundant than in other areas of the deep sea and fish can exhibit conserve energy using sit-and-wait feeding strategies. The video from Hydrographer Canyon will be analyzed by the end of March. This work should result in a short note for a peer-reviewed journal (e.g., Environmental Biology of Fishes).
Objective 5. Coral genetics: Tissue samples from all corals collected were removed and preserved for genetic analysis. Mitochondrial DNA has been extracted and is being analyzed. The sequence data will be kept for reference to the shallow water genetic information to be collected this summer in the Gulf of Maine. Several of the species collected, however, are not known from shallow waters, so their sequences will be compared with Antarctic species sequences obtained from GenBank.

B. Benefits.

Even though we had to contend with a lot of bad weather during the cruise for this project, the two dives accomplished will generate a lot of data about the two canyons we explored. This project had three other components not listed in the objectives above which produced benefits outside the immediate scope of the project. First, we took advantage of the ship’s capabilities for mapping using multibeam sonar and did detailed multibeam bathymetric mapping at the Physalia and Bear seamounts, which will be useful in planning future exploratory cruises. Second, we were accompanied on the cruise by a team of education specialists who produced an updated web page on a daily basis for use by educators on land. Since our cruise was in progress when the events of 11 September transpired, it is difficult to say how much of what was produced actually was used by the land-based component of this educational initiative. Third, we also had on board two artists who are producing artistic renditions of the canyon landscape which will be used for illustrative purposes in articles written for broader audiences.

C. Future Plans.

It is clear that much is not known about life in ocean canyons or about the biology of deep water corals. Our work will help to lay a solid foundation in both those areas. Specifically, however, we see that much more work needs to be done in the deeper areas of the canyons so that coral species distributions and their relationship to water masses can be better determined. Our coral reproductive work is a one-time snapshot and needs to be repeated at different times during the year in order to know whether there is a surface-derived signal, such as phytoplankton bloom fall, that influences time of reproduction and larval strategies. The potential for overgrowth of gorgonian skeletons by colonial anemones was a surprise, even though the phenomenon had been recorded by A.E. Verrill more than 100 years ago. We could see in the videos the extent to which such overgrowth was possible. Much more needs to be investigated on the feeding habits of the canyon inhabiting fish. Specifically, we need to know what the prey items are so that we can better understand why station-keeping feeding strategies are possible in canyon habitats.