A biome is a collection of ecosystems containing communities with similar characteristics and structure, typically due to similar climate and environmental conditions. For example, subtropical deserts are defined as regions with high average temperatures and very little annual precipitation. Organisms that live in these harsh conditions have adapted to retain what little water they can find and are tolerant of the high daily temperatures. Although subtropical deserts are prevalent around the world (e.g. the Sahara Desert in Africa, the American Southwest, the Gobi Desert in China, etc.), each desert harbors its own, unique community of organisms that have evolved to thrive under similar conditions. This ecological similarity, a result of a process called convergent evolution, enables us to identify biomes from around the world.
Coastal biomes are classified as those found in shallow water, possibly at the intersection between land and sea. Based on these criteria, many types of environments may be classified as coastal biomes. Some of the more common ones found in and around the Bahamas are outlined here.
Coastal biomes are classified as those found in shallow water, possibly at the intersection between land and sea. Based on these criteria, many types of environments may be classified as coastal biomes. Some of the more common ones found in and around the Bahamas are outlined here.
Coral Reefs
Probably the most well known of coastal biomes, coral reefs are critical centers of marine biodiversity, easily competing with tropical rainforests for the number of species they may harbor. Central to the development to any coral reef is the animal for which the reefs are named. Corals are marine invertebrates closely related to sea anemones (class Anthozoa), that build complex external skeletons out of calcium carbonate, the same material found in clam shells and limestone. As generations go by, coral skeletons continue to build on top of each other until they create complex topographies that makes the environment a 3-dimensional oasis in an otherwise empty ocean "desert". As a result, countless groups of animal life from fish to urchins are able to find refuge in the complex structure, hunt for prey, and gather for reproduction.
Coral reefs are typically found in shallow waters and are frequently located around islands and cays. The carbonate platform upon which the islands of the Bahamas form allows for the development of large reef systems. |
Seagrass Beds
Seagrasses are fully marine angiosperms (flowering plants) that typically inhabit shallow coastal waters. Seagrass "meadows" can be found near sandy beaches, adjacent to coral reefs, or in association with mangrove coasts (see below). With their roots attached to the ocean floor and leaves growing upwards, seagrasses can stabilize sediment and provide animals with protection from wave action and tidal changes. While not as diverse as coral reefs, seagrass beds support rich infaunal (beneath sediment) and pelagic (free-swimming) communities of their own and serve as a food source or nursery for deeper-water organisms.
While corals have a long evolutionary history that spans back to the Cambrian Period (540 million years ago), seagrasses evolved much more recently in the Cretaceous Period (145-66 million years ago), when dinosaurs still walked the Earth. They have since been prominent members of the coastal environments and continue to be widespread throughout the tropics. |
Mangrove Coasts
Mangroves (genus Rhizophora) are trees that grow well along tropical coasts. They are tolerant of both high salinity and low oxygen, allowing them to grow in standing bodies of marine or brackish water. Coastlines with thick mangrove coverage are sometimes referred to as mangal biomes. Beneath the water, many marine organisms take advantage of the coverage and organic input that mangrove roots provide. Mangroves may exist in conjunction with other coastal biomes, such as seagrass beds, depending on the water level at low tide. Because of this coexistence, there can be considerable overlap in community composition between mangrove and seagrass biomes.
Because dense mangrove coasts offer excellent protection, they often serve as nurseries for reef fish and other organisms that typically live in more exposed waters. Therefore, it's not uncommon to find sharks or manatees opting to raise their young in the thickets. |
Sandy Shores
While a shore of white sand sounds perfect to most beach combers on vacation, the wildlife that inhabits the beach can often be overlooked. Terrestrial crabs, burrowing shrimp, iguanas, and shore birds are only a few of the many organisms that live on or near the sandy shores of the Bahamas. Because of wave action and the tide, the boundary between the terrestrial and marine realms is not easily defined. Sea turtles breech onto shore in order to dig holes for incubating eggs while cormorants and other birds of prey hunt for fish that swim in the shallows.
Because of the wide variety of niches that terrestrial and marine organisms occupy within a beach community, sandy shores are diverse and unique biomes where land and sea meet in more ways than one. |
Intertidal Zones
Living in shallow water poses a big risk to marine life. As the tide shifts from high to low, many organisms may find themselves trapped above sea level until the tide comes back in. This elevation range at which sea level naturally rises and falls is called the intertidal zone.
As a coastal biome, the intertidal zone is no place for the weak. Organisms that live here must resist the intense energy of the battering waves, usually by adapting a firm grip to bare rock or other sturdy substrate. Furthermore, a resistance to desiccation and protection of sensitive tissues from the dry terrestrial world are critical. Due to these harsh conditions, intertidal biomes are composed of "extremophiles" and otherwise more tolerant organisms than those in safer, less energetic coastal environments. |
Marine Lakes/Ponds
The carbonate platform that builds the islands of the Bahamas has resulted in the dissolution of exposed limestone into a karst landscape of caves, sinkholes, and inland conduits to the open ocean. Because of these conduits, many islands have inland saline waters in the form of lakes and ponds. During interglacial periods, the ocean rose to levels that allowed marine life to colonize these lake environments before subsequently becoming isolated when sea levels retreated again. Therefore, these marine lakes serve as "islands" of unique biomes likely evolving in response to different environmental conditions.
On San Salvador Island, for example, several marine lakes on the north end of the island are dominated by algae rather than macrophyte vegetation. While many species within inland marine lakes can be found in the open ocean, these lake biomes have a notably low biodiversity compared to the ocean, likely due to an ecological bottleneck resulting from isolation. |
References:
Edwards, D.C. 1996. The inland saline waters of the Bahamas as distinctive scientific resources. In Elliot, N.B., Edwards, D.C., and P.J. Godfrey. Eds. Proceedings of the 6th Symposium on the Natural History of the Bahamas. Bahamian Field Station, San Salvador, Bahamas: 152-162.
Meyer, E., Nilkerd, B., Glover, E.A., and J.D. Taylor. 2008. Ecological importance of chemoautotrophic lucinid bivalves in a peri-mangrove community in eastern Thailand. Raffles Bulletin of Zoology 18: 41-55.
Paulay, G. 1994. Biodiversity on ocean islands: It's origin and extinction. American Zoology 34: 134-144.
Watling, L. 2015. A new genus of bamboo coral (Octocorallia: Isididae) from the Bahamas. Zootaxa 3918 (2): 239-249.
Edwards, D.C. 1996. The inland saline waters of the Bahamas as distinctive scientific resources. In Elliot, N.B., Edwards, D.C., and P.J. Godfrey. Eds. Proceedings of the 6th Symposium on the Natural History of the Bahamas. Bahamian Field Station, San Salvador, Bahamas: 152-162.
Meyer, E., Nilkerd, B., Glover, E.A., and J.D. Taylor. 2008. Ecological importance of chemoautotrophic lucinid bivalves in a peri-mangrove community in eastern Thailand. Raffles Bulletin of Zoology 18: 41-55.
Paulay, G. 1994. Biodiversity on ocean islands: It's origin and extinction. American Zoology 34: 134-144.
Watling, L. 2015. A new genus of bamboo coral (Octocorallia: Isididae) from the Bahamas. Zootaxa 3918 (2): 239-249.