Southern California 2013, Leg 2: Molecular Ecology

May 18-24, 2013

Our expedition aims to sample invertebrate animals living on a whale carcass and at hydrocarbon seeps in the Southern California region. It was hypothesized that deep-sea hydrothermal vent fauna can disperse between widely separated sites by exploiting intermediate stepping-stones formed around whale-falls and other chemosynthetic habitats. We suspect that this popular hypothesis is mostly incorrect due to species misidentifications and undersampling of cold-water hydrocarbon seeps along continental margins. Instead, we propose that cold seeps provide the primary habitat for many opportunistic organisms that can also invade nearby habitats such as whale-falls and sedimented hydrothermal vents.

Hydrocarbon seeps found along the western North America margin are primary habitats for a diverse assemblage of vesicomyid clams and other chemosymbiotic animals such as the siboglinid tubeworms, Lamellibrachia barhami and Escarpia spicata. Our ongoing molecular phylogenetic studies strongly support the hypothesis that these animals first evolved in seep-like habitats and more recently invaded organic food-falls and vents. For example, Akebiconcha (=Vesicomya) gigas is a widespread eastern Pacific species that lives in methane seeps from the Oregon coast to the Costa Rica margin. It also occurs in sedimented areas near vents along the Juan de Fuca Ridge and in the Gulf of California. That it also occupies chemosynthetic whale-falls along the California margin is not surprising. The tubeworms, L. barhami and E. spicata, also occupy seeps along this margin, and they are rarely found in sediments near vents and at a whale-fall. These opportunistic worms and clams have never been found on basaltic vent sites of the Northwest pacific ridge systems, the East Pacific Rise, or the Alarcón Rise.

Given the rarity of these species at sedimented vents and whale-falls, it is more likely that these alternative habitats represent demographic sinks rather than sources of dispersing larvae that propagate throughout widely dispersed chemosynthetic systems. New collections on this expedition from a Southern California whale-fall and cold seeps should fill a significant sampling gap between the Northwestern Pacific vents and seeps, Monterey Bay, and the Gulf of California. High-resolution maps from MBARI’s mapping AUV will help us to locate new cold seeps and characterize the sulfide levels that support chemosynthetic microbes and chemosymbiotic invertebrates.

Logbook

Attached to the ROV, this Styrofoam cup, decorated with seep clams, was shrunk down to its small size due to the enormous pressure of the ocean at 1,800 meters (5,900 feet).

High winds

Today, we benefitted again from earlier MBARI efforts that mapped, and then surveyed, the Santa Monica South Canyon.
Shannon Johnson of MBARI's Molecular Ecology Lab directs sampling efforts at one of the dense fields of Ectenagena elongata clams. One great aspect of using ROVs for deep-sea research is that the entire science party can view, interact, and engage during the dive, thus making the entire operation more efficient and successful.

Santa Monica clam and worm reef

Today, we benefitted again from earlier MBARI efforts that mapped, and then surveyed, the Santa Monica South Canyon.
The skull at Pedro’s whale-fall site.

May 20, 2013

We started our day with a dive at Pedro’s whale carcass, discovered by Peter Brewer and his team last week in the North Santa Cruz Basin. We were ordered to recover the vehicle shortly after the start of this dive because a naval operation was planned for this area
Different colors of bacterial mats covering a carbonate outcrop.

Clam dig at a deep seep

We started our day with a remotely operated vehicle (ROV) dive at a methane seep mound visited by Peter Brewer and his team on May 14. We found extensive bacterial mats of different colors...
This is an image from the ROV of the bone camera deployed on the seafloor.

A whale fall community

Our first dive of this series took place 10 miles west of San Diego, California, at a site where, 18 months ago, scientists from the Scripps Institution of Oceanography deployed a whale carcass.