Have you ever been snorkelling and seen something absolutely fascinating, but you can’t tell anyone you saw it because you don’t know what it’s called? It’s important to not only know the defining characteristics of types of fishes, but also of types of corals in order to fully understand a coral reef ecosystem.
Even if you don’t recall the actual name of a species, you can narrow down the category it must fit in to. Before I go in to explaining the multitudes of diverse species Bermudian reefs support, I’ll first explain the types of reef our island houses since these determine what kind of species live there.
Patch/Lagoonal reef: A rim of coral surrounds a bed of sediment, often supporting seagrass beds in or around the reefs. Visibility is often poor due to concentration of sediment and too much sediment in the water column can harm corals. These reefs usually occur in shallow water and support a great diversity of corals due to their relatively low wave energy. Soft corals, sponges and branching corals (which are resistant to sediment accumulation due to their growth structure) are all abundant.
Example: Church Bay reef systems.
Rim reef: Reefs which have high wave energy due to their position in the ocean. These reefs generally have wonderful visibility. Because of their exposure, large, boulder-shaped hard corals, like brain and star corals, dominate the reef.
Example: North Rock reef.
Terrace reef / fore reef slope: The reef farthest from the shore in deep water, these reefs operate differently than inshore reefs. They have high wave energy and low sediment concentration, allowing for brilliant visibility, but supporting mostly hard, flat corals which grow on top of each other.
Corals obviously form the basis of all reef ecosystems, and their versatility allows them to adapt to a variety of marine conditions. What appears to be a single head of coral to us is actually a colony of thousands of small coral polyps. These polyps use cnidocytes on their tentacles to catch zooplankton and extract calcium carbonate from the seawater to make their skeletons – the part of coral we are able to collect when dead.
However, relying only on zooplankton for nourishment is not sufficient for corals. They partner with photosynthetic algae called zooxanthellae, and these unicellular organism provide them with most of their energy and nutrients while the corals provide them with a surface to grow on which is exposed to a good light source. Zooxanthellae are also the reason for pigmentation in corals. When corals are stressed (due to temperature or visibility conditions), their zooxanthellae are expelled which results in what is called “coral bleaching”. Without the colorful algae, the corals will die unless their environment returns to stable enough conditions for zooxanthellae to return.
Now for the identification part. Corals fall in to two categories: soft and hard (stony) corals.
Hard corals belong to the order scleractinia, and their polyps have six tentacles. Polyps synthesize calcium carbonate to create a hard, sturdy skeleton. Examples of hard corals include brain corals (boulder shape), star corals (flatter shape) and branching corals (branching shape). Soft corals belong to the order gorgonia and their polyps have eight tentacles. Instead of a hard skeleton, these corals flow with the water with a flexible gorgonin skeleton. Examples include the common sea fan (one of the sturdiest members of this group) , sea rods and sea feathers.
If it sways with the current, it’s a gorgonian. If it resists the current and is made of a hard skeleton, it’s ascleractinian . Within these categories, further differentiations can be observed. The two types of brain coral found in Bermuda, for example, are relatively easy to be told apart when next to one another. Strigosa is the text-book brain coral, pictured below. Notice that its ridges are thin and its grooves are not uniform. The ridges of labyrinthiformis, on the other hand, appear to be raised islands among the surrounding grooves.
If a ridge on brain coral is surrounded by a groove on both sides, it’s strigosa. If it’s folded back on itself with another groove on one side, it’s labyrinthiformis.
Star and starlet corals are also found in Bermuda, which are given the genus name montastr. These corals are characterized by their many cheerio shaped polyps (which are larger than most corals). Star corals found in Bermuda include greater and lesser star coral.
Finger corals make up another percentage of hard corals in Bermuda and are given the genus name porites. They are a small polyp coral which usually occur in a finger-like morphology. Examples include dead finger coral and mustard hill coral.
Acropora is the genus name given to branching hard corals, the most prominent of which (in Bermuda) is branching fire coral which can deliver a nasty sting. All corals have stinging cells in order to capture prey, but fire coral is particularly potent in this regard.
As for soft corals, there are three main categories; sea fans, sea feathers and sea rods. The common or purple sea fan is the most commonly occurring sea fan in Bermuda with its characteristic netting shape. Sea rods occur in single stem and branching stem variations which are difficult to tell apart at a glance, and sea feathers occur in feather-like shapes with what appears to be a central “stem” accompanied by many feathery projections.
Corals can succumb to disease due to a disruption in their rich exterior mucus layer which is populated by bacteria. Environmental changes, such as temperature, sediment, or the presence of sewage in water can cause the normally healthy bacteria to become pathogenic. This causes either black or yellow band disease.
Fish are easier to tell apart than corals in some respects, since they occur in a wide variety of shapes, sizes and colours, thought they can be more difficult due to the fact that they move, and also that the same species can occur in dramatically different variations according to physical maturity or sex.
Major fish categories include surgeonfish, butterflyfish, silvery fish, damselfish, parrotfish and wrasse. Parrotfish are incredibly important to the reef because they eat algae – cleaning it off of the reef surface and allowing coral to be exposed to sunlight to maintain their symbiosis with zooxanthellae. Wrasse are also important as cleaner fish to other fish; eating parasites off of larger fish’s skin.
Surgeonfish are characterized by a common oval body shape with large, sloping, anal and dorsal fins. This group includes surgeonfish, doctor fish and blue tang (don’t confuse them with damselfish!). In addition, these fish have a razor sharp barb located at the base of their tails. This is only used for defensive purposes, however, as all surgeonfish are algae eaters.
Damselfish are generally smaller than surgeonfish. They are very agressive fish despite their size, defending their algae gardens and egg nests. They occur in a variety of colours which may change throughout their lives. Notable species from this group include the cocoa damselfish, yellowtail damselfish, sergeant major (cow polly) and blue chromis. Blue chromis do not share the rounder shape that many damselfish possess, instead appearing more tapered. There is recent evidence to suggest that Bermuda may be home to a native species of the fish, distinct from species occurring elsewhere due to its yellow fins.
Butterflyfish are not to be confused with damselfish. This group is more diminutive, and often travel in pairs. Butterflyfish sport confusing patterns in order to confuse their larger predators. The classic example of this is the foureye butterflyfish which has an eye-like marking on the back of its body to confuse predators. Other notable butterflyfishes include the spotfin, reef and banded varieties.
Silvery fish tend to be pelagic, but many can still be seen on reefs. Bermuda bream (which are our only endemic fish) and chub are frequent reef dwellers, as well as the formidable barracuda. These fish, which can grow up to 72 inches long, are no danger to humans – but are quite curious fish. It is not uncommon to turn around while snorkeling to find one following you silently.
Parrotfish occur in a wide variety of species in Bermuda’s waters. We have nine species altogether, but to the untrained eye we can appear to have many more. Parrotfish have both dramatic differences in colouration due to sex and stage of physical maturation. The male and female stoplight parrotfish, for example, may appear to be different species entirely, and their juvenile phase is also drastically different. All parrotfish share a common mouth – one which looks somewhat like a parrots beak and which they use to scrape off algae from rocks and produce sand.
Wrasses are the cleaner fish of the reef for the most part, however this group includes larger fishes such as the hogfish and puddingwife. The bluehead wrasse has the ability to change sex during its lifetime, should the need arise. One male, with the characteristic blue head, commands a harem of smaller, yellow females. If the dominant male dies, a strong female from the harem will transition in to masculinity and take charge of the harem.
Other miscellaneous sea creatures can also be frequently observed on reefs such as octopuses, squid, eels, lobsters, jellyfish, and even sometimes turtles, rays and sharks. In particular, eels are sometimes observed hunting in pairs with a coney, a small grouper. The best way to find marine life is to look in unusual places – under rocky overhangs and in caves, or follow other fish.
I hope this blog post gave you some insight in to identifying a small portion of Bermuda’s marine life. For the sake of word count many more organisms are omitted. A wonderful book about Bermudian fish is Bermuda Reef Portraits by Ron Lucas. I am yet to find a guide for Bermudian corals.