Most of the bottom of the Gulf of Mexico is a flat sandy/muddy plain providing little to no food or cover. Historically there were some large naturally occurring reefs that covered 1.6% of the bottom that provide habitat for adult fish. That high relief reef is still there. Additionally, there was low relief nursery reef that also comprised the bottom of the food chain made up of organically cemented sandstone, friable caliche lumps, clay balls, and the little humps and bumps that were on the coastal plain, drowned over the last 40,000 years as sea level rose. That low relief reef is essentially gone except in a very few places. We still find it’s remnants near high relief reef where it has been protected from trawl fishing.
From the 1960s to the late 90’s the Texas shrimping fleet drug a net with a chain across the front of the net over 1million acres of the bottom every night. This abraded the low relief reef into nothing.
Juvenile reef fish, including Red Snapper, need cover to survive. A rock or a hole provides a place to get out of the unceasing current, rest, and convert food into body mass. That rock also provides a place to out-turn a faster straight-line speed predator. It also gives the fish an address, a neighborhood that it can learn where the better feeding is, a starting place for foraging trips. If the cover has some flat areas and a sharp corner, vortices are created in the water, disorienting prey. Those vortices also pull organics out of the passing water column, creating just enough matter on the bottom to feed microbes, the food of marine invertebrates, crustaceans, and filter-feeding clams, bivalves, mollusks, and barnacles.
Friends of RGV Reef makes extensive use of donated recycled concrete material, accumulated on our site donated by the Port of Brownsville that has deep water dock frontage and a rail siding. We use broken concrete, donated by local construction firms like Foremost paving, and purchased cinder blocks, but primary RGV Reef has been built with recycled concrete railroad ties donated by the BNSF Railroad. Concrete railroad ties make an absolutely fabulous reef. Tangled on the bottom like pick up sticks they provide an exceptionally complex structure that is scalable from providing the foundation of nursery reef all the way up to high relief reef.
Cinder Blocks make excellent nursery reef but deployed on their own sink into the bottom over a period of a few years. During our January – MArch 2020 deployment Friends initiated their “Durable Nursery Reef Patches” designed to last for decades. In the new 400 acres CCA Nursery, 84 sandwiches of material were built with a foundation of either 50 or 100 tons of ties as a base. To provide small cracks and holes, 20 tons of concrete rubble was deployed on top of the ties, and 350 cinder blocks on top of that. This yields a nursery patch from 90 to 120 ‘ in diameter, one or two feet tall, with thousands of individual cracks, crevasses, and holes.
RGV Reef also has 300 prefabricated reefing pyramids, which make fine medium relief reef for adult fish. The problem with reefing pyramids is that elsewhere on the Gulf Coast reefs are populated exclusively with pyramids. These monocultures only provide habitat for adult fish grown and attracted from elsewhere, and elsewhere is short of fish.
RGV Reef’s managers are the only reef builders in the Gulf that actually pay attention to marine research, the fish biology, the biologist’s conclusions, and then actually build what’s right for the fish. We use Red Snapper research primarily, as that is the largest body of knowledge. Interestingly, when you follow research’s best practices, you wind up with something that is very much like the most productive natural reefs. Large, patchy, varied, complex reef with differing heights. Happily, all the fish living on the continental shelf evolved to do best either living on or visiting reefs. So when you make it right for one, it’s right for all.