Twilight Zone… the Expedition

100 m deep on Flower Garden Banks. Photo credit FGBNMS/NURC.

Like many marine protected areas around the world, most of the seafloor in the Flower Garden Banks National Marine Sanctuary (FGBNMS) is deeper than the depth limit for recreational and scientific diving (50 m). We call this the “twilight zone“, a poorly known depth zone considered too deep for divers, and too shallow for manned submersibles. Some marine biologists call this a new frontier. So, four years ago, I asked myself…why not make a dissertation out of it?

Join the HRI Biodiversity and Conservation Laboratory as we embark on the Benthic Assemblages in the Twilight Zone (BATZ) Expedition to characterize mesophotic benthic assemblages 50-200 m deep in the Gulf of Mexico August 25 – September 2nd, 2008. We will be using the Phantom II remotely operated vehicle (ROV) to collect samples on a few banks (uplifted salt dome features) along the continental shelf break.

I’ll compare gorgonian diversity and abundance on and off a dozen small mound features of different depth and relief with my advisor Dr. Tom Shirley. My colleagues Doug Weaver, Morgan Kilgour, and Dr. Fabio Moretzsohn will study the fish, crabs, and mollusks associated with gorgonian assemblages . Dr. Ian MacDonald will deploy his famous panoramic time lapse camera.

We will try to post events daily from the RV Nancy Foster via the FGBNMS Expedition Website. Come aboard! More fascinating background information is provided below to pique your interest. Please join us if you can.

UPDATE: Cruise delayed due to generator trouble on the RV Nancy Foster.

Manned submersible expeditions using the Diaphus sub first characterized these habitats in the mid 70’s. But, ROV surveys since 2001 confirm that hard bottom features 100 m deep are characterized by antipatharians (aka black corals) and gorgonians (aka sea fans). Deep-water sea fans provide important habitat to associated species of fish, crustaceans, echinoderms, and mollusks, so we will focus research effort on these assemblages.

An important aspect of this cruise is the timing of the season. Shallow reef corals at FGBNMS spawn annually in synchrony with the new moon. This is a fairly well-documented phenomenon. Now, scientific divers are finding barrel sponges (Xestospongia sp.) spawning in deep-water. How deeply does this phenomenon occur? We can’t say for sure. Scientists on this cruise will examine reproductive condition of FGBNMS deep-water gorgonians and crabs for the first time.

The primary research tool for BATZ is the National Undersea Research Center’s Phantom SII ROV, a small tethered unit equipped with a manipulator arm, two lasers, a temperature logger, a still camera, and a video camera. The Phantom SII is capable of diving 300m. We will use the robot to collect samples and perform video transects across mounds inside and outside FGBNMS boundaries. Stay tuned for more!