Macrofaunal diversity and community structure of the DeSoto Canyon and adjacent slope

Northern Gulf of Mexico canyons are centers of organic matter accumulation and biodiversity, but studies of their finer-scale (sub-100 km) ecological patterns are scarce. Detailed sampling of macrofauna within the DeSoto Canyon was undertaken along 3 depth transects on the canyon wall, axis, and adjacent slope. Sediment, terrain, and water mass parameters were also compiled for the same stations. Within the canyon, macrofaunal abundance decreased, evenness increased, and richness followed the expected parabolic curve with depth, peaking at 1100 m. Cluster analysis identified 3 canyon depth groups that conformed to established bathymetric boundaries for the non-canyon Gulf of Mexico slope: Group I at <500 m, Group II at 669-1834 m, and Group III at >2000 m. Explanatory environmental models indicate that canyon community structure was strongly correlated with oxygen concentration and fluorescence, with a weaker potential influence from any of salinity, particulate organic carbon, sediment organic carbon, or slope. Comparisons of the habitats indicated that abundances were highest on the canyon wall. Slope community structure differed from that of either of the canyon habitats. Environmental models consisted of single variables including oxygen concentration, sediment organic carbon, slope, and temperature with similar explanatory values. Community differences within the canyon and between the canyon and adjoining slope contradict previous findings of a single faunal zone for the whole study area. Factors that may contribute to inter-habitat heterogeneity include potential hydrocarbon seepage, organically enriched sediment deposits along channels, or remnant influence from the Deepwater Horizon spill, warranting more research into this dynamic ecosystem.

Macrofaunal Diversity and Community Structure of the DeSoto Canyon and Adjacent Slope

Macrofauna within the DeSoto Canyon, northern Gulf of Mexico (GOM), along the canyon wall and axis, and on the adjacent slope, were sampled along with sediment, terrain, and water mass parameters. Within the canyon, abundance and species richness decreased with depth, while evenness increased. Cluster analysis identified three depth-related groups within the canyon that conformed to previously established bathymetric boundaries: stations at 464 – 485 m, 669 – 1834 m, and > 2000 m. Abundance differed between depth groups. Species richness was lowest for the deepest group and evenness was lowest for the shallowest. Community structure within the canyon most related to fluorometry and oxygen saturation, combined with any of salinity, particulate organic carbon, sediment organic carbon, or slope.Canyon wall abundances were higher than the canyon axis or adjacent slope. Community structure differed between all three habitat types. Ordination of community structure suggests a longitudinal pattern that potentially tracks with increasing sea-surface chlorophyll that occurs in the eastward direction across the northern GOM. Canyon and slope differences may result from seasonal water masses entrained by canyon topography characterized by high salinity, oxygen saturation, fluorometry, and turbidity. Higher fluorescence and turbidity in the canyon did not translate into higher sediment organic matter. Flushing along canyon wall channels and the canyon axis may explain the low organic matter. Differences in abundance and structure between the canyon wall and axis may result from microhabitat heterogeneity due to potential hydrocarbon seepage, organically enriched sediment deposits along channels, or remnant influence from the Deepwater Horizon blowout.

Fear: The Maze in Canyonlands and John of the Cross

It’s one thing to wake up in the middle of the night to an imagined terror. It’s another thing to be wide awake and feel the hand of fear creeping up your spine. Camping alone one winter night above Ghost Ranch in New Mexico, I heard (or did I dream I heard?) scratching on the wall of the tent and the heavy breathing of an animal outside in the snow. I was so frightened I couldn’t voice the scream stifled in my throat. Or was it in my dream that I wasn’t able to make any sound? On waking I wasn’t sure what had or hadn’t happened—or whether it was all in my mind. An even more uncanny experience came on another moonlit night in the depths of the Maze in Canyonlands National Park in southeast Utah. A friend and I had walked a mile down the canyon from our campsite, under the shadow of the towering walls within that vast winding labyrinth. Hiking in the light of a full moon without flashlights, we felt a sense of wild, animal abandonment. With reckless exuberance we’d been howling like wolves at the moon. But then we found ourselves standing before a canyon wall covered with ancient figures painted by archaic artists some two thousand years ago. These were spirit beings standing vigil—long, ethereal shadows hovering on the surface of the rock. Whether they were guarding, witnessing, or offering protection, I didn’t know. But in the hollowed-out world of moonlight and shadow that formed the Maze, I sensed the presence of something I couldn’t name. It’s a place about as far away from other people as you can get in the lower forty-eight, yet for an instant I had an uncanny awareness of a finger lightly touching me on the back of the neck. I’d been taken into a profoundly deeper meaning of fear. Three days earlier we had driven seven hours from the Hite Marina on Lake Powell along a tortuous dirt road, part of the old Flint Trail. It was a belly-scraping, wheel-spinning, bronco-twisting ride, with hairpin turns around huge boulders and narrow rocky ledges.