Northeast U.S. Canyons Exploration - EX 1304 Leg 2

From July 31 to August 16, the Northeast U.S. Canyons 2013 Expedition continued exploration of the geomorphology and benthic ecology of deep-sea canyons and Mytilus Seamount along the Northeast US Atlantic margin. During Leg 2 of this mission, ROV Deep Discoverer (D2) surveyed the area extending between Alvin and Block canyons in the west and Heezen Canyon (eastern limit of the EEZ) to the east. Fifteen dives, ranging in depth from 490 to 3300 m were completed at five named canyons (Nygren, Heezen, Oceanographer, Lydonia, and Welker), one minor canyon (unnamed near Shallop Canyon), two intercanyon sites, two USGS geohazards targets, and Mytilus Seamount.

Submarine Canyons

Many of the ROV dives conducted represented the first exploration and visual examination of this region. Submarine canyons investigated were diverse and dramatic environments, with no two canyons appearing to be exactly alike, in terms of lithology or biology. Overall, we expanded our understanding of the spatial distributions, both geographic and bathymetric, of species along the continental margin and slope, including observations of species not previously known from the region and species once considered rare.

While the canyons explored on Leg 1 were mostly Eocene/Cretaceous in origin, with heavily eroded carbonates, canyons visited on Leg 2 were composed of a high diversity of lithologies. Some rock surfaces were heavily encrusted with manganese-iron coating that it was difficult to obtain a complete description of rock composition. Lydonia Canyon was composed of a chalky material, but confirmation of rock type would require a physical sample. Heezen Canyon was composed mostly of mudstone. Given the presence of numerous large colonies of Paragorgia arborea and other octocorals, it is apparent that the slope stability of Heezen Canyon is high, at least approximately several hundred years. However, the presence of large, displaced blocks indicates this area experiences long-term erosional processes. The extensive manganese coating on the rock features observed at Nygren Canyon suggest that the steep features observed here have longer-term strength and stability. In contrast, Oceanographer Canyon contained an extensive debris apron, talus slopes, indicating this area likely experiences continuous shedding, making it a less suitable habitat for slow-growing encrusting fauna. While numerous species of corals were observed in Oceanographer Canyon, most individuals were of similar size, suggesting periodic recruitment events follow shedding episodes. However, further examination of the dive video, in concert with known age estimates for the deep-sea corals, are needed to advance our understanding of the slope stability and frequency of shedding events for this region.

Overall, preliminary observations indicate that this region supports a high diversity of fauna and habitat types. Initial estimates of species include at least 40 species of corals and 40 species of fishes. Additionally, numerous species of sponges (glass, demosponges, and encrusting types), crustaceans (squat lobsters, crabs [Chaceon sp., Cancer sp.], shrimps, euphausiids, hermit crabs, amphipods, barnacles), cephalopods (squid: Brachioteuthis, Chirotheuthis, Illex, Mastigoteuthis, bobtail squid, and various octopuses), echinoderms (seastars: brisingids, Hymenaster, Pythonaster, Evolplosoma, Pteraster, Chondraster giganteus; various ophiuroids, crinoids, urchins, and holothurians), and other invertebrates (e.g., salps, siphonophores, aplacophorans, bivalves), were observed throughout the dives. Large unicellular xenophyophores were documented both on the sedimented seafloor and on the steep walls of Mytilus Seamount. Overall, exploration of this region advanced our understanding of species distributions and occurrences, including expanded ranges for certain species. But many questions remain. For example, little is known about connectivity of species found among the canyons examined.

Seep Discovery

Of particular note was the discovery of a seep in Nygren Canyon. Although discovery of other newly documented seeps along the coast of the northeastern US were predicted from unique backscatter and multibeam data, no such data suggested the presence of this seep. This area was characterized by extensive exposed carbonate rock and patches of bacterial mat. Nestled within cracks in the rock were chemosynthetic Bathymodiolus mussels, Serpulidae and Polynoidae polychaetes, and various gastropods. Light, white fluffy material was easily disturbed from the site. Similar material, possibly microbial in origin, also was observed at the seeps explored near Veatch and Nantucket canyons. Further comparisons of all recently discovered seep communities will enable better understanding of the biodiversity and ecology of chemosynthetic environments found along the Atlantic margin.

Mytilus Seamount

During this expedition, we dedicated two dives to the exploration of Mytilus Seamount, the least explored seamount of the New England Seamount chain, thus representing the most comprehensive exploration of this seamount to date. While we did not have the opportunity to explore the top of the seamount, the sediment drape was composed of carbonate material, suggesting the seamount may be capped in limestone. Mytilus Seamount is volcanic in origin, and the dives revealed a steep and rugged topography on the north side, whereas the south slope was gentler and contained a thicker sediment drape, possibly resulting from a landslide. While the areas examined on the north and south sides had very different topography, similar faunal assemblages were observed on both sides of the seamount. The large, smooth basalt rock features were colonized by sponges and corals; holothurians and ophiuroids were present on the sedimented ledges. No scleractinian corals were observed on either dive, but several species of bamboo corals and other octocorals were noted. Overall, few fish were present, including macrourids, ophidiids, synaphobranchids, halosaurs, Antimora, Bathychaunax, and Bathysaurus. Seamounts are reputed to be dynamic and diverse environments for marine fauna. These dives enhanced our understanding of the distribution of species on and among seamounts as well as the faunal relationships between seamounts and submarine canyons.

USGS Marine Geohazard Targets

Two dives were conducted at USGS marine geohazard targets to investigate submarine landslide debris fields and scarps. These areas had not been explored previously and were examined to ascertain the potential for tsunami generation, including assessing the instability of the seafloor and other potential hazards. We anticipated that the age of the landslide material might be estimated, based on the characteristic encrusting minerology and fauna. Examination of the thick sediment drape, in some places > 30 cm thick, and little exposed rock, suggested that the landslides were old, relict features.

Predation

The expedition yielded rare observations of predation, parasitism, and reproduction. Acts of predation included squid eating fish, fish eating squid and fish, fish captured by anemones and corals, and sea stars and sea urchins eating coral polyps. In situ observations of parasitism are very rare, and several different types of crustacean ectoparasites attached to fishes were noted during this expedition. These included copepods and Gnathiidae and Cymothoidae isopods. Lastly, regarding reproduction, squids and red crabs mating, fish egg masses on corals and boulders, coiled pink egg mass (possibly from a nudibranch) on a boulder and shark egg cases attached to octocoral branches were observed.

Summary

Additional activities conducted during the expedition included multibeam mapping, subbottom profiling, and CTD casts during non-ROV operations. These data expanded the seafloor mapping database and our knowledge of the oceanographic conditions in the surrounding environments.

Exploration and data collection during this expedition has greatly enhanced our understanding of the geomorphology, biodiversity and ecology of the Northeast canyons along the northern US Atlantic margin. Specifically, canyons represent dynamic environments, supporting diverse species assemblages the composition of which are a function of depth, slope stability, and location within the canyon. It is apparent that the underlying foundation and geological structure are important factors influencing the faunal composition within the canyons. However, the relationship between canyon geomorophology, the role of intercanyon areas, and faunal biodiversity and ecology are still not fully understood. The observations and information gathered on both legs of the expedition will inspire future interdisciplinary research in the region and elsewhere.

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USGS Hazard 1

Area

Northeast U.S. Canyons

Overview

Date:	August 1, 2013
Max Depth:	784.1 Meters
Bottom Time:	7 Hours 1 Minutes 29 Seconds

Purpose

The purpose of this proposed dive is to investigate small, potentially recent, landslide debris deposits and scarps within a larger landslide scar on the upper continental slope. The scientific rationale for this site is:

1. To determine if these small landslide debris features are relatively young and if they pose a hazard in terms of tsunami generation
2. To evaluate the long term stability of landslide scars and test hypotheses about their evolution
3. To attempt to develop a means of using biologic activity on the scarps and deposits as a means of determining relative ages of the features and the response of bottom communities to catastrophic events

Minor Canyon near Shallop Canyon

Area

Northeast U.S. Canyons

Overview

Date:	August 2, 2013
Max Depth:	1139.8 Meters
Bottom Time:	5 Hours 34 Minutes 25 Seconds

Purpose

The purpose of the dive was to:

1. Characterize the submarine canyon geomorphology and benthic habitats, including possible coral and sponge communities in a minor canyon near Shallop Canyon
2. Groundtruth a model of predicted deep-sea coral occurrence

Oceanographer Canyon 1

Area

Northeast U.S. Canyons

Overview

Date:	August 3, 2013
Max Depth:	1239.3 Meters
Bottom Time:	6 Hours 34 Minutes 59 Seconds

Purpose

The purpose of the dive was to:

1. Characterize the submarine canyon geomorphology and benthic habitats, including possible coral and sponge communities at a depth of ~1200 m in Oceanographer Canyon
2. Groundtruth a model of predicted deep-sea coral occurrence

Mytilus Seamount North

Area

Northeast U.S. Canyons

Overview

Date:	August 4, 2013
Max Depth:	3271.4 Meters
Bottom Time:	6 Hours 25 Minutes 56 Seconds

Purpose

Despite a significant level of past effort, the New England seamounts, a major chain of undersea mountains, remains largely unexplored. Building on previous work, we will conduct the first ecological explorations of the New England seamounts. Of those seamounts within the US EEZ, Mytilus Seamount has yet to be visited in this regard. This dive will explore steep terrain along the north side of the seamount to characterize deep sea coral and sponge communities.

Mytilus Seamount South

Area

Northeast U.S. Canyons

Overview

Date:	August 5, 2013
Max Depth:	3262.3 Meters
Bottom Time:	7 Hours 4 Minutes 29 Seconds

Purpose

Despite a significant level of past effort, the New England seamounts, a major chain of undersea mountains, remains largely unexplored. Building on previous work, we will conduct the first ecological explorations of the New England seamounts. Of those seamounts within the US EEZ, Mytilus Seamount has yet to be visited in this regard. This dive will explore steep terrain along the south side of the seamount to characterize deep sea coral and sponge communities.

Nygren Canyon Mid Deep

Area

Northeast U.S. Canyons

Overview

Date:	August 6, 2013
Max Depth:	1590.4 Meters
Bottom Time:	6 Hours 24 Minutes 57 Seconds

Purpose

The purpose of the dive was to:

1. Characterize the submarine canyon geomorphology and benthic habitats, including possible coral and sponge communities at a depth of ~1300-1600 m on the southwestern wall of Nygren Canyon
2. Groundtruth a model of predicted deep-sea coral occurrence

Heezen Canyon Deep

Area

Northeast U.S. Canyons

Overview

Date:	August 7, 2013
Max Depth:	1723.4 Meters
Bottom Time:	6 Hours 6 Minutes 39 Seconds

Purpose

The purpose of the dive was to:

1. Characterize the submarine canyon geomorphology and benthic habitats, including possible coral and sponge communities at a depth of ~1400-1700 m on the southwestern wall of Heezen Canyon
2. Groundtruth a model of predicted deep-sea coral occurrence

Nygren Canyon Shallow

Area

Northeast U.S. Canyons

Overview

Date:	August 8, 2013
Max Depth:	914.6 Meters
Bottom Time:	7 Hours 18 Minutes 53 Seconds

Purpose

The purpose of the dive was to:

1. Characterize the submarine canyon geomorphology and benthic habitats, including possible coral and sponge communities at a depth of ~900 m on the northeastern wall of Nygren Canyon
2. Groundtruth a model of predicted deep-sea coral occurrence

Heezen Canyon Shallow

Area

Northeast U.S. Canyons

Overview

Date:	August 9, 2013
Max Depth:	925.9 Meters
Bottom Time:	6 Hours 35 Minutes 42 Seconds

Purpose

The purpose of the dive was to:

1. Characterize the submarine canyon geomorphology and benthic habitats, including possible coral and sponge communities at a depth of ~1400-1700 m on the southwestern wall of Heezen Canyon
2. Groundtruth a model of predicted deep-sea coral occurrence

Nygren/Heezen Intercanyon

Area

Northeast U.S. Canyons

Overview

Date:	August 11, 2013
Max Depth:	824.3 Meters
Bottom Time:	7 Hours 13 Minutes 26 Seconds

Purpose

The New England and Mid-Atlantic Fisheries Management Councils are particularly interested in intercanyons to provide more information on depth boundaries for deep-sea coral protection. The purpose of the dive was to:

1. Characterize the submarine canyon geomorphology and benthic habitats, including possible coral and sponge communities
2. Groundtruth a model of predicted deep-sea coral occurrence

Lydonia/Powell Intercanyon

Area

Northeast U.S. Canyons

Overview

Date:	August 12, 2013
Max Depth:	662.8 Meters
Bottom Time:	7 Hours 32 Minutes 7 Seconds

Purpose

The New England and Mid-Atlantic Fisheries Management Councils are particularly interested in intercanyons to provide more information on depth boundaries for deep-sea coral protection. The purpose of the dive was to:

1. Characterize the submarine canyon geomorphology and benthic habitats, including possible coral and sponge communities
2. Groundtruth a model of predicted deep-sea coral occurrence

Lydonia Canyon

Area

Northeast U.S. Canyons

Overview

Date:	August 13, 2013
Max Depth:	1238.9 Meters
Bottom Time:	6 Hours 23 Minutes 59 Seconds

Purpose

The purpose of the dive was to:

1. Characterize the submarine canyon geomorphology and benthic habitats, including possible coral and sponge communities
2. Groundtruth a model of predicted deep-sea coral occurrence

Oceanographer Canyon 2

Area

Northeast U.S. Canyons

Overview

Date:	August 14, 2013
Max Depth:	1247.6 Meters
Bottom Time:	6 Hours 44 Minutes 47 Seconds

Purpose

This dive track is along the approximate location of Alvin dive 1035 from 1980 and 3702 from 2001 and will examine potential changes in the biology and geology of the area over 30+ years. The purpose of the dive was to:

1. Characterize the submarine canyon geomorphology and benthic habitats, including possible coral and sponge communities
2. Groundtruth a model of predicted deep-sea coral occurrence

Welker Canyon

Area

Northeast U.S. Canyons

Overview

Date:	August 15, 2013
Max Depth:	1445.4 Meters
Bottom Time:	5 Hours 8 Minutes 35 Seconds

Purpose

The dive track was chosen based on a combination of regional habitat prediction models for deep sea corals and local identification of high slope features from 20 m multibeam mosaics. Past experience and modeling in this region indicates that deep sea coral habitats are often found in the canyons in areas with slopes > 360.

USGS Hazard 3

Area

Northeast U.S. Canyons

Overview

Date:	August 16, 2013
Max Depth:	899.3 Meters
Bottom Time:	7 Hours 11 Minutes 57 Seconds

Purpose

The purpose of this proposed dive is to investigate small, potentially recent, landslide debris deposits and scarps within a larger landslide scar on the upper continental slope. The scientific rationale for this site is to:

1. Determine if these small landslide debris features are relatively young and if they pose a hazard in terms of tsunami generation
2. Evaluate the long term stability of landslide scars and test hypotheses about their evolution
3. Attempt to develop a means of using biologic activity on the scarps and deposits as a means of determining relative ages of the features and the response of bottom communities to catastrophic events