Alderdice Bank

Color bathymetric map of Alderdice Bank
Alderdice Bank is an oval salt dome about 100 miles northeast of East Flower Garden Bank.

Bottom Depth Range: 165-240 feet (50-73 meters)

Alderice Bank is located about 52.5 km (32.5 mi) southeast of Sonnier Bank, about 60 km (37 mi) west northwest of McGrail Bank, and 157 km (97 mi) east northeast of East Flower Garden Bank. The bank is an oval lying in an east-west direction, and covers an area of about 16 km2 (10 mi2).

Three spectacular basalt spires of Late Cretaceous origin (~77 million years old) are found at Alderdice Bank. These are the oldest known exposed rocks on the continental shelf off of Texas and Louisiana, and unique geologic features for this region. The outcroppings crest at about 50 m (165 ft), with their bases at about 73 m (240 ft).

An underwater peak with fish swarming around it
A basalt spire at Alderdice Bank

Rich fish assemblages swarm around the outcroppings. Benthic invertebrates, such as basket stars, are conspicuous inhabitants of the basalt blocks, in addition to sea whips, sponges and branching bryozoan colonies.

Habitat below the spires is dominated by black corals, gorgonians, fish, sponges, algae and invertebrates. Because of these extensive deep coral communities, Alderdice Bank is a Habitat Area of Particular Concern (HAPC).

Alderdice Bank was named after Robert Alderdice, founder of the Flower Garden Ocean Research Center (FGORC).

Rocky sea floor covered in algae and brigth orange encrusting sponge with branching orange gorgonians standing to the left and top
Basalt blocks at Alderdice Bank are covered in gorgonians, encrusting sponges and algae
Leafy green algae, bushy black corals and skinny white sea whips cover the sea floor along with a few sponges. Small reef fish school just above.
An anchor chain (top left corner) draped through a field of algae, sponges and black corals at Alderdice Bank

Video

The following video is a compilation of footage taken during ROV (remotely operated vehicle) and manned submersible explorations at Alderdice Bank.

0:00 A bathymetric map of Alderdice Bank followed by a second map showing the actual tracks the ROV traveled to acquire the following footage in the area around the unique basalt spires of this bank at 160 to 220 feet deep (49-67 meters).

0:27 Nurse shark, various black corals and gorgonians, sea urchins, spotfin hogfish, creolefish, trumpetfish, ocean triggerfish, gray snapper, scamp grouper, various other fishes and black coral.

1:38 A bathymetric map showing a different set of ROV tracks at Alderdice Bank. Footage shows the southeast sponge/algal mound at 160 to 235 feet deep (49-72 meters).

1:47 Close-up view of spiny lobster scratching its eye with its leg.

1:58 Sponges, marbled grouper, gray snapper, rock beauties, angelfish, amberjacks, whitespotted filefish, blue angelfish, algae/sponge area, yellowtail reeffish, cherubfish, crinoid, black corals, damsels, wrasse bass, squirrelfish, southern stingray, and a variety of other fishes and gorgonians. A sponge with a yellowtail reeffish and a juvenile bluehead wrasse swimming nearby.

Video Length: 3:14

Credit: FGBNMS