Reefs in peril
 
Reefs in Peril
 
 
Proximal causes of decline in health of coral reefs hot buttons for peril part of BIOLOGY OF CARIBBEAN CORAL REEFS
There are several major proximal causes for reef decline. The topics of overfishing/reef collection/invasions are dealt with here in 3 sections, while other topics are accessible via the "hot" buttons.
hot button for bleaching part of Biology of Caribbean Coral Reefs
 
 
title button for overfishing section of BIOLOGY OF CARIBBEAN CORAL REEFS website

Overfishing

The topic of overfishing is considered here, while those on REEF COLLECTION and INVASIONS can be found by scrolling down or clicking on the highlighted headings

 
 

graph showing historical fishing patterns in the Caribbean Sea in relation to reef integrity and microbial abundance
Overfishing started early in the Caribbean area.  Reconstructions of historical fishing activities disclose that countess millions of large fishes, sharks, sea turtles, and manatees were killed throughout the 17th-19th centuries (see graph).  The studies suggest that the absence of these large consumers may have played as much a role in reef collapse as have more recent changes in climate, eutrophication, and disease outbreaks.  Jackson 2001 Proc Nat Acad Sci USA 98: 5411.

  graph showing historical fishing records from several Caribbean islandsEstimates of original live masses of snappers, parrotfishes, and seabasses from bones found at archeological sites in 5 Caribbean islands shows that even in historic times catch-sizes were declining. Although the data are limited, there seems to be marked decreases in catch sizes in at least 3 of the 5 island sites sampled (see graph). Wing & Wing 2001 Coral Reefs 20: 1.
 

photograph of Nassau grouper Epinephalus striatusIn Belize and elsewhere Nassau groupers Epinephelus striatus seasonally aggregate for spawning at sites characterised by sand floors or spurs with sand-channel grooves, in close proximity to drop-offs.  A report based on a national survey of these spawning sites in 2001 concludes that several of the major sites, still being fished at the time, are critically threatened with extinction.  The fisheries in Belize is small, worth only about $8000 annually (2001 estimate) from local market sales, yet is nonetheless critical for the fishers involved.  Is a single “tame” grouper worth more than $8000 per year as a tourist-type attraction for SCUBA-divers and snorkellers?  If so, would tourism viewing of groupers at these sites offer a viable economic alternative to fishing?  The authors think not, at least not at comparatively remote and less-visited sites on the Belizian coast, but it could be a different story in other, more frequently dived, Caribbean locationsPaz & Grimshaw 2001 Status report on Nassau groupers for Belize.  Green Reef Envir Inst, Beliz.

NOTE Roatan has a thriving SCUBA industry, and the reefs around the island used by the divers are mostly or all enclosed within the Roatan Marine Park. Roatan also supports successful and well-managed fisheries for deep-water snapper and shrimps but, at the same time permits fisheries near well-dived reef sites for predatory fishes such as barracudas and tunas. Now, barracudas are highly desireable for viewing and photographing by SCUBA-divers, and one would think that a single living barracuda on the reef must have greater tourist value than one caught and eaten by a tourist fisher. Is it naive to think that the many dozens of SCUBA shops on the island not get together to disallow sports-fishing for this priceless resource? And what about groupers that are virtually absent from Roatanian dive sites? Could these not similarly be protected (thinking naively), perhaps by some type of "no-fish" subsidy?

 
 
drawing of seahorse with video camera indicating a video to be shown in BIOLOGY OF CARIBBEAN CORAL REEFS photograph of a Nassau grouper Epinephalus striatus

"It's always a thrill to see a big grouper, especially a Nassau grouper. They were once an important market-fish throughout the Caribbean, but overfishing has greatly reduced their numbers." - Turneffe Island, Belize
Video courtesy Andy Stockbridge, Belize.

NOTE Epinephelus striatus

 
 

small fish caught in gill netFishing in reef areas has biological and political ramifications which cannot be solved separately.  Long-term survival of reefs in the Caribbean will, at the very least, require that they be divided into areas of dedicated usage, such as fishing, recreation, and protected preserves as done for other marine parks such as the Great Barrier Reef Marine Park flying-fish fleet on the east coast of Barbadosin Australia.

 

Creole wrasse Clepticus parraecaught in fixed
gill-net in
St. Lucia

 

 

Barbados flying-fish fishing fleet in the halcyon fishing
days of the 1960s. Even nowadays, flying fish represent
the largest of 8 recognised fisheries on the island

 
 

photograph of green turtle courtesy Anne Dupont, Florida
Decline in numbers of green turtles in the Caribbean from estimates of 30-40 million in Columbus’ time to virtual extinction today has had profound influences on seagrass-bed ecology. Photograph courtesy Anne Dupont, Florida.

 

 

 

Green sea turtle Chelonia midas



 

graph showing effective of long-term absence of green turtles on health of seagrass beds in the Caribbean
When green turtles are not eating their fill of seagrasses, the blades grow longer, shade more, become more enfouled and weakened, and break off more in storms to create more sedimentation.  More sediment leads to smothering, buildup of anoxic sulphides, increased infection of the fronds from slime moulds, and ultimately to poor health of the seagrass bed.   Jackson 2001 Proc Nat Acad Sci USA 98: 5411.

NOTE lit. “without oxygen”


 

  The photo series below depicts the changes in an eelgrass bed in the absence of turtle cropping:
 
photograph of healthy unshaded eelgrass blades
Healthy eelgrass when turtles are abundant
photograph of eelgrass when few or no green turtles are present
With few or no turtles, eelgrass blades lengthen
photograph of heavily shaded and unhealthy eelgrass blades when turtles are fewer in number
Lower blades become more shaded & unhealthy
photograph of unhealthy, overgrown, and eroded eelgrass blade in absence of cropping by green turtles
Blade tips become fouled, die, and break off
photograph of eelgrass bed with increased sedimentation & fouling in the absence of cropping by green turtles
Sediments in the bed deepen & become anoxic

photograph of sedimented, unhealthy eelgrass bed in the absence of green turtles
The eelgrass bed becomes generally unhealthy

 
 

photos showing various uses and applications of conch shells in the Caribbean It has been said that queen conchs are as “Caribbean” as rum punches.  They are eaten as chowders, seviches, and fritters; their shells are used for jewellry and for adorning pathways and flowerbeds; and their icons appear on flags, currency, and stamps.  Extensive overfishing in many parts of the Caribbean has led to active programmes of hatchery-rearing and restocking in Belize, Florida, Turks & Caicos, and Bahama Islands. Creswell & Davis 1991 World Aquacult 22: 28. 
















 

photograph showing diver with lobsters
In the absence of properly organised and enforced guidelines for population management of spiny lobsters Panulirus argus in most Caribbean islands, they are becoming more scarce.

 

 

 

 

 

Diver collects lobsters
Panulirus argus in Tobago








 
 
title button for reef collecting section of BIOLOGY OF CARIBBEAN CORAL REEFS website Reef collecting
 
  Collection and commercial sale of living fishes and other reef creatures occur on every reef in the world, but most particularly those in the Philippines, Indonesia, and other Indo-Pacific islands. Fishes for aquarium display are hand-netted or anaesthetised with chemicals, such as Rotenone. Not only is there mortality associated with collection, and local handling and storage, but large losses occur during transport.
 
photo composite showing shells being sold as art in tourist shops

 
photograph of a red "coral" necklace
Necklace of “red coral” is actually a type of gorgonian, Corallium sp., found in the Mediterranean Sea
photograph of shark jaws for sale
Shark jaws for sale in a tourist shop in Corpus Christi, Texas
corals, shells, and related items for sale in a tourist shop in Port Aransas, Texas
This tourist shop in Port Aransas, Texas features shells & coral-reef items from all over the world
   
 
Yield of shells from an afternoon of
snorkeling in Barbados. None of
these shells, however, was alive
at the time of collection 0.15X
photograph showing a collection of snail shells made during an afternoon's snorkeling in Barbados
 
 
 
title button for invasions section of BIOLOGY OF CARIBBEAN CORAL REEFS website Invasions
 
 

There have been many introductions of non-indigenous species into the Caribbean region, but none so potentially threatening as that of lionfishes Pterois spp. This happened about 3 decades ago, possibly from unthinking home-aquarists but also, as one story goes, through accidental loss from a commercial aquarium in Biscayne Bay, Florida in 1992. Initially discovered in North Carolina in 2000, they are now widely distributed, from Rhode Island in the north to Florida in the south, and throughout the Gulf of Mexico and Caribbean Sea. Like other members of the Family Scorpionidae, lionfishes have toxic spines both on the dorsal and anal fins. Although they are visually obvious and float about slowly and serenely, local predatory fishes generally tend to leave them alone. Along with another unwelcome invader, the Indo-Pacific crown-of-thorn sea star, their presence in the Caribbean is cause for great concern.

NOTE 2 species exist in the Caribbean region, Pterois volitans and P. miles. Apparently, they can't be distinguished by eye, and require genetic analysis to identify them to species

 
 

The rate of spread of lionfishes Pterois in in the Caribbean basin has been astonishing. In certain parts of New Providence, Bahamas, for example, researchers from Simon Fraser University, British Columbia in 2009 report densities 5 times greater than recorded in the species’ natural Red-Sea habitats. And this is after only one decade from their first spottings on the North Carolina-Florida coasts. The authors remark, with calm scientist demeanor, that given what they have seen in the Bahamas, “the impacts of lionfish on natural reefs are expected to be extreme.” Green & Cote 2009 Coral Reefs 28: 107; photographs courtesy Richard Carey.

 

 

 

 

Lionfishes Pterois volitans on reefs
in New Providence, Bahamas

photographs of lionfishes Pterois volitans on reefs in New Providence, Bahamas
   
 

But are they really so bad? A conservationist's hackles rise at the thought of introduction of any non-indigenous species into an area, but consider this. In Roatan and other areas of the Caribbean there are organised hunts to kill lionfishes. In Roatan, to join in, an individual needs to apply and pay for a license. Along with the license comes a mandatory field test of one's proficiency at using a speargun and in moving quickly up and down in the water column with SCUBA gear without becoming embolised. Lionfishes are bony, but quite tasty, and most or all kills find their way to local restaurants where chefs compete for the best-tasting lionfish cuisine. The spearfishers are paid a small amount for their efforts, in 2014 something like $3 per pound of cleaned fillets. Spines are discarded before cooking and any residual venom is deactivated by cooking. However, on the basis that spearfishing and tourist-divers make for a potentially unsafe mix on a dive boat, combined with the potential risk to divers in chasing potential prey lionfishes up and down in shallow water, many Roatan SCUBA-operators ban the practise. This is smart. One dive-operator in Roatan describes one of their divers being attacked and bitten on the hand by a moray eel attracted to dead lionfishes being carried by the diver. Other kinds of predatory fishes, most notably groupers, snappers, and sharks similarly have been known to attack and eat freshly killed lionfishes. This suggests that concerns by conservationists that lionfishes would be too-well protected for naive Caribbean reef-predators to eat them may be unfounded. Governmental bounties would seem like a good option, but are unlikely to be effective in reducing numbers of lionfishes except perhaps in limited areas. Although data are still being gathered, lionfishes may be here to stay. Photograph onphotograph of a lionfish Pterois volitansLeft courtesy Antonio Busiello.photograph of a lionfish being eaten by a shark

In Roatan sharks are being trained to eat dead lionfishes, in the hope that they will include
living ones in their diets

 





Lionfishes Pterois spp. eat various molluscs and crustaceans, but it is
their love of fishes, especially juveniles of some of the larger species,
such as groupers and snappers, that give them such a bad reputation 0.5X

 
 

photograph of a fishing catch: a Nassau grouper Epinehelus striatus with a dead lionfish Pterois volitans in its gutAs noted above, a chief concern of Caribbean environmentalists is whether invasive lionfishes Pterois volitans will encounter natural predators in the Caribbean region. This concern is at least partly assuaged with the observation in 2008 of predation of lionfishes by several Nassau groupers Epinephelus striatus in areas of the Bahamas. Maljkovic & Van Leeuwen 2008 Coral Reefs 27: 501. Photograph courtesy the authors.

Lionfish Pterois volitans dissected from the stomach
of a Nassau grouper Epinephelus striatus. By its
orientation in the grouper’s stomach the prey was
swallowed head-first, allowing the toxic spines
to glide more easily through the gullet. Is this a
learned behaviour, do you think?

 
 

Lionfishes Pterois spp. have not only insatiable appetites for small fishes, but on the inner barrier reef in Belize they have zeroed in on an endemic wrasse, the social wrasse Halichoeres socialis, an already threatened species owing to habitat destruction and pollution. The social wrasse makes an photographs of a lionfish Pterois sp. with prey social wrasses Halichoeres socialiseasy target for the lionfish because of its small size and habit of hovering in schools. Lionfishs, like other gulping-type predators, must seem non-threatening to a naive prey. They float in serenely without haste and then, GULP, the prey is gone. Researchers from the California Academy of Sciences and the Smithsonian Institution in Washington conclude from stomach-analysis data that Halichoeres comprises almost half of the lionfish diet in the inner-reef area of Belize. The authors remark that the added lionfish predation makes the social wrasse possibly the most threatened coral-reef fish-species in the world. Rocha et al. 2015 Coral Reefs 34: 803. Photographs courtesy the authors.

NOTE the authors note that while targeted removal programmes for lionfishes exist in many other parts of the Caribbean, none at the time of publication is apparently underway in Belize’s inner barrier reef

Lionfish Pterois sp. with dissected-out stomach contents:
two mature female social wrasses Halichoeres socialis

 
 
header for symposium on Caribbean lionfishes published in a special number of the journal Marine Ecology Progress Series
 

The interest generated by lionfishes P. volitans/miles and their depredatory habits in the Caribbean has resulted in hundreds of scientific publications and at least 9 symposia. One of the last of these was hosted by the Gulf & Caribbean Fisheries Institute at its annual conference in Panama in November 2015. Of the many talks and posters presented, 9 were selected by a board of editors for publication in the journal Marine Ecology Progress Series (Hixon et al. eds. 22016 Vol. 558: 159-279, October 2016) in a special “Theme Section” entitled, Invasion of Atlantic coastal ecosystems by Pacific lionfish. As examples of the general nature of research on lionfishes currently being done, brief summaries of each are presented here:photograph of longspine squirrelfish Holocentrotus adscensionis

Skin bacteria of lionfishes P. volitans/miles show lethal activity against 6 known fish bacterial pathogens, indicating an enhanced disease resistance, and perhaps helping to explain their impressive invasion success. In comparison, similar tests with native longspine squirrelfishes Holocentrus adscensionis yielded only a small fraction with similar antibacterial activity. Stevens et al. 2016 Mar Ecol Progr Ser 558: 167.

DNA analysis of stomach contents of lionfishes P. volitans/milesin Puerto Rico provides a useful method of identifying prey fishes, and results underscore their generalist predatory behaviours. For example, 63 lionfishes collected from inshore and offshore reefs around La Parguera are found to have eaten 39 native fish species from 16 different Families. Data from this type of metabarcoding are much more precise than from traditional visual identification. Harms-Tuohy et al. 2016 Mar Ecol Progr Ser 558: 181.

In comparison, stomach-content analyses of lionfishes P. volitans/miles in Bermuda, at the northern limit of their invasive range, show that fewer species of reef fishes are eaten, and crustaceans actually make up the larger component of their diets. Eddy et al. 2016 Mar Ecol Progr Ser 558: 193.

In ecological manipulation experiments on reefs in northwest Florida, removal of lionfishes P. volitans/miles (single vs. multiple “sweeps”) from artificial reefs leads to only inconclusive results. While this is contrary to expectation, the authors do note that smaller native fishes are generally diminished in numbers following the lionfish invasion. Dahl et al. 2016 Mar Ecol Progr Ser 558: 207.

NOTE experimental results may have been confounded by effects of oil contamination from the Deepwater Horizon incident that occurred in the Gulf of Mexico at the same time of the study; also, maintaining experimental "cleared" areas was difficult as both juvenile and adult lionfishes quickly recruited to previously cleared areas

photograph of bicolor damselfish Stegastes bipartitusAlong the same lines, removal experiments in the Boco Del Toro province of Panama (but of shorter duration), reveal that lionfishes P. volitans/miles significantly reduce the density of their prey but not their genetic diversity. The specific expectation, with particular attention tobicolour damselfishes Stegastes bipartitus, was that by removing the predator, numbers of bicolour damselfishes would increase and be accompanied by an increase in genetic diversity. Palmer et al. 2016 Mar Ecol Progr Ser 558: 223.

photograph of fairy basslet Gramma loreto





As found in other regions of the Caribbean, lionfishes P. volitans/miles may so severely reduce densities of native prey fishes to cause extinction. This is noted in the area of Cape Eleuthra, Bahamas, where losses of fairy basslets Gramma loreto incurred from predatory activities of lionfishes, when added to those from natural predators, tipped the scales towards extinction for some local populations. Ingeman 2016 Mar Ecol Progr Ser 558: 235.

photograph of graysby Cephalopholis cruentataIn laboratory feeding experiments at the Cape Eleuthera Institute, Bahamas, lionfishes P. volitans/miles are found to prefer fairy basslets Gramma loreto over blackcap basslets G. melacara, whereas native graysby groupers Cephalopholis cruentata prefer blackcaps. photograph of blackcap basslet Gramma melacaraBy preferentially consuming the graysby’s lesser preferred basslet species, lionfishes may be aiding survival of both basslet species, rather than contributing to the demise of one of them. The authors’ findings emphasise how much there is to learn about direct and indirect community interactions revolving around lionfishes. Kindinger & Anderson 2016 Mar Ecol Progr Ser 558: 247; photograph of blackcap basslet courtesy Wolfram Sander COLORS OF THE REEF.



Where densities of lionfishes P. volitans/miles are high in Bahamian patch reefs, their activity levels naturally increase, both temporally and spatially. This leads to the lionfishes expanding their foraging into neighbouring seagrass meadows, and doing so at dusk. This means that native reef fishes that are active at dusk and/or out and about in neighbouring seagrass beds may be more vulnerable to lionfish predation. Benkwitt 2016 Mar Ecol Progr Ser 558: 255.

Finally, in areas of Florida Bay, red groupers Epinephelus morio clean out karst-solution holes in the reef, which they defend. THese holes also photograph of red grouper Epinephelus morioprovide refuges for small reef fishes. Experimental manipulation of numbers of both groupers and lionfishes P. volitans/miles in these holes show that the groupers negatively affect the lionfishes. Thus, relative to holes in which both predatory species are excluded, juvenile reef-fish abundance is much higher when only groupers are present, much lower when only lionfishes are present, and similar when both predators are present. This suggests that presence of the larger-sized groupers in some way inhibits predatory activities of the lionfishes, who instead switch to eating various types of invertebrates as alternative prey. Ellis & Faletti 2016 Mar Ecol Progr Ser 558: 267; photograph courtesy NOAA Ocean Explorer.

NOTE these are pockmarked pits in limestone caused by past freshwater dissolution



The editors sum up their review of the symposium by stating that “the lionfish invasion is unprecedented and potentially catastrophic from multiple perspectives”. They add that given that eradication is currently impossible, the invasion may permanently alter coral-reef ecosystems in the greater Caribbean region, especially ones already threatened by human activities. Hixon et al. 2016 Mar Ecol Progr Ser 558: 161.

 
 

An old story from the east coast of North America has oyster culturists attempting to reduce sea-star Asterias spp. predation by collecting them, chopping them up, and tossing the bits back into the ocean. Of course, the remarkable regenerative abilities of the sea stars simply led to their increased numbers and to even greater problems. Despite this history and an awareness of the good regenerative capabilities in asteroids, chopping has still been considered as a possible method of controlling crown-of-thorns sea stars Acanthaster planci on the Great Barrier Reef. However, does chopping kill them or, as with the Asterias example, just exacerbate the problem? Results from uncontrolled field tests in the 1960s were indecisive. More recently, controlled laboratory experiments in Lizard Island Research Station show that when juveniles are cut into halves or 2-third/1-third portions, survival is 75% for all half and 2-third portions, and 0% for all 1-third portions. Although the results are suggestive, the authors recommend that further study be done. Messmer et al. 2013 Coral Reefs 32: 41; photographs courtesy the authors.

 
photograph of crown-of-thorn sea stars Acanthaster planci eating corals on the Great Barrier Reef photograph of a crown-of-thorns sea star Acanthaster planci cut in half
photograph of a half section of a crown-of-thorns sea star mostly regenerated after being cut in half

Left: an infestation of Acanthaster planci on the Great Barrier Reef
Top: Acanthaster cut in half for experiment
Bottom: one of the halves 7wk later

 
 

It is not clear how many, if any, crown-of-thorns sea stars Acanthaster planci are currently within the Caribbean basin, but populations exist on the west coasts of Panama and Costa Rica, and risk of invasion always present. Until recently, current methods of extermination of Acanthaster on the Great Barrier Reef have involved hand-injection of toxic substances by volunteer divers, a time-consuming and risky enterprise, but nonetheless effective on small scale. Recently, however, with the development by researchers at Queensland University of Technology in Brisbane, Australia of COTSbot, a submersible robot with the capability of seeking out and injecting toxic gel into the sea stars remotely, help may be on the way. Trials are currently underway to assess the efficacy and cost of this unique method of control. On the University website the developers/testers note that the device is completely autonomous, searches tirelessly in all kinds of weather, and kills effectively with no error. What is not mentioned is how cost-effective it is, given that it has to be launched from some kind of platform in the ocean, which must be moved around, or how many times it has to be "rescued" and how effective such rescues would be. One envisages it getting tangled up in ropes and seaweeds, or becoming stuck in crevices or under overhangs. If irretrevably lost, it must be expensive to replace. Its kill rate is about 200 during an 8h outing, many fewer than 8 SCUBA-divers could do using hand-injection methods during a 1h period.

NOTE the toxin used is one developed for hand-injection by divers and consists of a mixture of thiosulphate/citrate bile-salts in sucrose agar. Other chemicals used in the past by divers include formalin, vinegar, and sodium bisulphate

 
photograph of robotic submersible crown-of-thorns killer initial search pattern of robotic submersible Acanthaster killer photograph of closer search pattern of robotic submersible seeking out Acanthaster planci to kill
COTSbot is 1.4m in length, is self-propelled, and has
built-in search capabilities
Its image-processing system is programmed to seek out and to identify Acanthaster planci specifically The search is broad-scale at first, then narrows in scope as it zeros in on a subject
narrowly focused search pattern of robotic submersible seeking out Acanthaster planci to kill photograph of robotic submersible COTSbot showing injection apparatus used to kill Acanthaster planci photograph of robotic submersible COTSbot injecting an Acanthaster planci with toxic chemical
Once the presence of an Acanthaster is confirmed, the robot adjusts its own position above it An extensible arm on the robot bears a syringe-like
device that can be thrust into the sea star to inject it
The injection of a toxic gel-like substance is rapid, and death ensues within a day or two
 
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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