As the name would suggest, a patch reef is a small reef formation that is isolated and often found in a small area surrounded by water – usually within a small or open body of water, and in some cases even completely submerged underwater.
Sometimes, they also form in the middle of a lagoon or close to barrier reefs and atolls. A few common examples of patch reefs include the reefs occurring off the north coast of St Croix (in the Caribbean) and reefs found on the Florida Reef Tract.
A patch reef has many important qualities that set it apart from most other types of coral reef formations. It is, first of all, important to note that they are most commonly found in shallow waters. Depths of around 3-6 meters (or 10-20 feet) are quite common.
These reefs, in most cases, are also surrounded by a halo of sand that extends to seagrass beds. These are determined by the distance that herbivorous fish decide to forage while keeping in close proximity to the reef, and so each patch reef differs depending on the types of fish and marine creatures that thrive in their generally defined area.
These types of reefs are formed through a unique process set into motion by a coral larva that settles outside the plankton, attaching itself to a harder portion that will later become the center of the reef.
Over time, the larva develops into a moderately sized coral colony that becomes the essential platform for other coral formation after its death. Perishing due to damage caused by either severe storms or predators, the colony leaves behind hardened limestone that is then used as a settlement area by other coral larvae.
Over the course of many hundreds of years, this process continues to repeat itself, as the reef keeps growing and expanding both in height, and later on, in size as well, after it reaches the surface of the water.
Star and brain corals are most prevalent in patch reefs, their majestic and robust structures settling on exposed dead corals to repopulate every little part of the reef with new life.
Other fascinating marine species, large and small, can also be found on these reefs. Sponges, mollusks and various types of worms can commonly be viewed here, excavating the dead corals to create crevices that later provide refuge for small fish and invertebrates.
Reef fish are very prevalent on most types of patch reefs as well, some of the most common varieties of fish species including bluehead, angel fish, redband parrotfish, surgeonfish and damselfish.
You can also commonly observe many other marine creatures thriving in these reefs. These normally include green morays, spiny lobsters, squirrelfish and herbivore fish that find refuge on patch reefs during day time, and feed on the seagrass close by during the night.
Most patch reef formations are safe havens for a variety of other marine creatures as well – especially in the case of reefs formed within lagoons that have been protected by barrier reefs for thousands and even millions of years, allowing marine life in the region to thrive.