Reefs in peril
spacer Reefs in peril
Proximal causes of decline in health of coral reefs hot buttons for peril part of BIOLOGY OF CARIBBEAN CORAL REEFS overfishing/reef collecting on Caribbean coral reefs disease on Caribbean coral reefs SCUBA/snorkeling recreation on Caribbean coral reefs future of Caribbean coral reefs pollution on Caribbean coral reefs eutrophication of Caribbean coral reefs hot button for bleaching part of Biology of Caribbean Coral Reefs
There are several major proximal causes for reef decline. The topic of pollution is dealt with here, while other topics are accessible via the "hot" buttons.
subtitle button for "pollution" section of BIOLOGY OF CARIBBEAN CORAL REEFS website Pollution

Pollution of coral reefs comes from many sources, including release of sewage into reef areas directly or via rivers, seepage from septic fields or discharge of septic tanks from tourist hotels, and industrial wastes. Once they are outside of the 12-mile limit from Caribbean islands, cruise boats release "black", "brown", and "gray" water without restriction into the ocean. Sedimentation from excessive land clearing could also be considered a kind of pollution, although its main effect would likely be smothering.

Chronic effects of gasoline and oil spills around marinas, and throughout heavily trafficked recreation areas tend to create sterile areas.  

NOTE black water is bilge water, often with oil contamination; brown water is toilet sewage; and gray water is anything with soap in it, such as laundry, kitchen, bath, and sink water

seahorse cartoon for "reefs in peril" section of BIOLOGY OF CARIBBEAN CORAL REEFS photograph of an old cannon taken from a video

"This old cannon may be just be a plant for the tourist SCUBA divers in the Cayman Islands, but many genuine ones exist throughout Caribbean reefs. It’s ironic to think that reef contamination and destruction started, no matter how innocuously, with its first visitors." - Little Cayman Island 2002


Coral reefs are especially susceptible to oil contamination, both acute, from wrecks, and chronic, from natural oil seeps and offshore dumping of ballast waters from ships. various forms of oil pollution on reefs



photograph of octopus with tin can around its denAlthough junk such as old bottles, tin cans, and other debris deposited around Caribbean reefs is mostly biologically harmless, its presence may be associated photograph of beer bottle with fire coral growing on itwith a more insidious lack of environmental awareness and an ignorance of what are the serious threats to survival of coral reefs.

Fire coral Millepora sp. grows on a beer
bottle in St. Kitts


An octopus Octopus sp. has collected some shiny stuff for its
den in the Bahamas
. Photo courtesy Anne Dupont, Florida

  photograph of running shoe with attached goose barnacles Lepas anatifera
Floating shoe with attached goose barnacles Lepas anatifera in Aruba
photograph of beach debris in Little Cayman Island
Beach debris on Little Cayman Island

photograph of surfer within a cresting wave of garbageIf you've ever felt angry standing on the deck of a dive boat and seeing endless numbers of plastic bags passing by, think of how you would feel about surfing or diving in this debris-laden water off the coast of Java. Millions of tons of plastics are dumped into the world's oceans every year. The big stuff is bad enough when eaten by sea turtles, birds, fishes, and other organisms, but the worst and most insidious is the fine particulate matter that plastic becomes when it degrades through exposure to UV light and wave action. These particles are microscopic in size and permeate all ocean waters. Their debilitating effect on fishes and suspension-feeding invertebrates is to clog gill filaments and feeding structures, affecting gas exchange and food intake, sometimes fatally. Photograph courtesy Zac Noyle and
National Geographic Magazine


A surfer in Java has a close view of ocean "garbage" as it passes by overhead.


schematic drawing showing Great Pacific Garbage Patch in colours representing relative plastics concentrationsmap of Pacific Ocean showing sources of contamination that form the Great Pacific Garbage PatchMuch of the floating plastic debris in the Pacific Ocean has aggregated in a large gyre midway between California and Hawai’i known as the Great Pacific Garbage Patch. Originally estimated to contain between 4-12 thousand tonnes in an area of about 1 million km2, recent developments in monitoring technology now increases these figures to 80 thousand tonnes in an area of 1.6 million km2. About half the mass is estimated to be made up of fishing nets (many possibly still fishing), and the remainder of microplastics and larger bits. The scientists, a consortium of 16 from several European countries and New Zealand, estimate that the Patch is increasing in size exponentially. New assessment techniques include aerial imagery from aircraft and bag/net trawlings from ships. Models of pathways leading to the Patch include environmental forces of currents, waves, and winds with numerous estimates of sources from coastal-population “hotspots”, river discharge, and fishing, aquaculture, and shipping activities (see map of origins on Right). About 15% of the debris input is estimated to have come from a single source, the 2011 Tohoku tsunami. Of the forces noted above, wind is found to be the least influential, mainly owing to the fact that only a tiny component of the debris sticks out of the water; most is submerged. The authors are not able at this time to estimate time-spans for degradation, only that inflow of plastics is much greater than outflow. The study is a tour de force of international cooperation and is much to be admired. The data are mind-boggling and present a frightening glimpse of what the future holds for the world’s oceans. Lebreton et al. 2018 Nature Sci Reports 8: 4666.

NOTE these <4.75mm-sized particles count in the trillions globally, but in the Patch make up only about 13% of the total floating mass

NOTE although plastic makes up the bulk of floating material (99.9% by numerical contribution), other components are glass, paraffin, tar, rubber, wood, pumice, and seeds. Wherever possible manufacturer names and sources are ascertained and recorded. One-third of items so identified are found to be from Japan, 1/3 from China, and the remainder from 9 other countries. On the map above Right, yellow indicates origins and transit of plastics in the gyre