Mangroves, The Marls, Abaco, Bahamas (Keith Salvesen, Rolling Harbour)


For some time now, there has been understandable concern about the increasing evidence of mangrove die-back in the Abaco Marls and elsewhere in Abaco waters. Scientific investigations are ongoing and you will find some of the survey results so far on the excellent Abaco Scientist interactive map HERE. You’ll find other relevant and authoritative mangrove material if you check out the BLOG menu of the website.
Abaco - The Marls

The ‘200 sq. miles’ in my map is debatable, depending what one includes. Other estimates are of 300 or even 400 sq. miles. Whichever, the Marls cover a massive area of mangroves, islets, flats, channels and wonderfully diverse wildlife. A large proportion of the many species – fish, birds, turtles etc – depend on the complex ecology of the mangroves for food, shelter and breeding. Depletion of the mangroves from whatever cause will have a direct effect on the creatures of the Marls.

Stingrays Abaco Marls 6

Ryann Rossi, a PhD student with North Carolina State University, has been researching the worrying phenomenon of mangrove die-back in the Marls this summer. She has written an interesting and informative  account (conveniently in the RH ‘Facts about…’ style) that was published in Abaco Scientist last week. The blue links will take you to the ABSCI site for further information on each topic. I’m grateful to Ryann and ABSCI for permission to use the material.

Five Things to Know About the Mangrove Die-back in The Marls (at this point, anyway)

1. This die-back appears to be the result of multiple stressors acting together. Think of it in the sense of our own body – when our immune system is down, we are often more susceptible to getting sick. The same thing is likely happening to the mangroves.Mangrove Die-back 1 (Abaco Scientist : Ryann Rossi)

2. It appears as though a fungal disease may be taking advantage of already stressed mangroves and causing die-back. We did preliminary surveys across Abaco and found fungal lesions nearly everywhere. However, the fungus was present in different densities in different areas. In the die-back area nearly all the leaves remaining on trees have lesions. We think that this pathogen capitalized on the mangroves being weakened by other stressors such as hurricanes, which cause extensive leaf drop, change in the movement of water, change in sedimentation and erosion.

Mangrove Die-back 2 (Abaco Scientist : Ryann Rossi) jpg

3. We are still working on identifying the pathogen associated with the lesions we’ve found. We are confident that it is a fungus and are currently growing fungal cultures in the lab to examine defining morphological characteristics in addition to using DNA sequencing to identify the culprit.

4. We have documented the presence of the Robust Bush Cricket (Tafalisca eleuthera) in the die-back areas as well as other areas with high densities of lesions. These crickets are documented to consume Red and White mangrove leaves. As such, we were concerned about their potential role in die-back. We set out a caging experiment to exclude the crickets from certain dwarf Red mangrove trees to see just how much grazing they may be doing in the die-back area. This experiment is ongoing.

Mangrove Die-back 3 (Abaco Scientist : Ryann Rossi) jpg

5. The take home: there is likely more than one causal agent of the die-back in The Marls. Many factors govern mangrove productivity and functioning: nutrient availability, salinity, sedimentation rate, herbivory, and disease are just a few of the factors that contribute to overall mangrove function making it very difficult to pin point which factors may be driving the die-off. On the bright side, we are confident that we have a lead on the causes and we are working hard in the field and laboratory to fully understand what is going on in The Marls.

By Ryann Rossi|August 26th, 2015|Disease, fungus, Insects, Mangroves and Creeks, The Marls
All pics below taken while fishing on the Marls except Melinda’s shark (I’ve never got a good one)
Hawksbill Turtle, Abaco Marls (Keith Salvesen)Bonefish Abaco Marls 4Shark 4 ©Melinda Riger @ G B Scuba copyOsprey - Abaco Marls 1 Reddish Egret (White Morph), Abaco MarlsRoyal Tern, Abaco, Bahamas (Marls) 3Willet, The Marls, AbacoSouthern Stingray, Abaco Marls (Keith Salvesen 4)
FRIENDS OF THE ENVIRONMENT has also included an article on die-back by Ryann in its latest Newsletter:

Mangrove Die Off on Abaco by Ryann Rossi, NCSU

This summer Stephanie Archer and I continued research efforts focused on determining the cause of the mangrove die-off in The Marls (work funded by the National Science Foundation). Our efforts were predominantly focused on the fungal pathogen we found associated with the die-off site. We created a small citizen science and outreach project to document the presence or absence of the pathogen across Abaco. This project consisted of short surveys and leaf collections. In total, 92 areas were surveyed including locations from Abaco and San Salvador. We also took this outreach project to the annual Bahamas Reef Environment Education Foundation (BREEF) teacher training conference.  There we disseminated survey packets to teachers from islands throughout The Bahamas who will help us collect more data on the presence (or absence) of this pathogen on other Islands.

3 men on a skiff, Abaco Marls (Keith Salvesen : Rolling Harbour)

Three men on a skiff – Abaco Marls

On Abaco, we constructed an experiment to investigate the role of grazing and the presence of fungal lesions on Red mangroves. We simulated grazing using crafting scissors to cut small sections on 600 leaves in 4 different mangrove creeks. We observed the leaves for 28 days to determine if cutting leaves predisposed leaves to fungal infection. At these sites we also trapped for insects to gain an idea of what kind of grazers may be chewing on the leaves. We also did a series of disease incidence surveys that will be routinely monitored for disease progress over the next 2 years. These surveys will allow us to systematically track the progress of the disease. In addition to our field work, we spent many hours in the laboratory isolating fungi from leaves to grow in culture. These cultures were brought back to North Carolina State University and will be sequenced in order to help us identify the fungal pathogen responsible for making the lesions on the mangrove leaves.

Mangroves, Abaco Marls (Keith Salvesen)

Credits: Source material Ryann Rossi; Abaco Scientist; all photos © Keith Salvesen @ Rolling Harbour except those by Ryann / ABSCI in the main article and Melinda Riger’s cool shark


Hawksbill Turtle © Melinda Riger @ G B Scuba


The Bahamas has breeding populations of 5 of the world’s 7 sea turtle species – Green, Loggerhead, Hawksbill, Leatherback and Kemp’s Ridley turtles (the other two are Olive Ridley – occasionally found in the Bahamas – and Flatback turtles). All are endangered. There’s no getting away from the fact that Man and Man’s activities are now the primary threats. The IUCN ratings below make for sad reading. To see some of the problems, check out THREATS TO SEA TURTLES

Admire the photos here of Hawksbill Turtles Eretmochelys imbricata while you can – the species is IUCN red-listed and I can’t improve on this explanatory display…Hawksbill Turtle Eretmochelys imbricata (IUCN Red List)


(thanks as ever to Melinda Riger of Grand Bahama Scuba, but for whom etc)Hawksbill Turtle ©Melinda Riger @ G B Scuba Hawksbill Turtle ©Melinda Riger @ G B Scuba copy Hawksbill  Turtle ©Melinda Riger @ Grand Bahama Scuba copyHawksbill Turtle ©Melinda Riger @ GB Scuba copy

I did ask myself whether including this shot might show a lack of sensitivity for the essential dignity of a fine species, infringing its Testudinal rights. But overall, I feel the public interest is best  served by showing it. Anyway, it has plainly discovered something very tasty to get stuck into, so it won’t be unduly bothered. The pair of French Angelfish aren’t going to get a look-in…Hawksbill Turtle ©Melinda Riger @ G B Scuba copy 3

 The SEA TURTLE CONSERVANCY has produced an outstanding series of posters similar to the LOXAHATCHEE posters about corals, conchs, sea grass, bonefish etc. Here is their Hawksbill one, with illustrations by artist DAWN WITHERINGTON. Click the link to reach her website and see her excellent scientific drawings and a lot more besides. This excellent poster contains pretty much all the details you need to hold your own in any hawksbill-related conversation. You can enlarge it by doing that thing with 2 fingers on your track pad thingy.


I rather like this video from Andros, with the turtle’s gentle tolerance while being approached by a photographer until at last  it decides to move slowly off. The music’s a bit annoying though – it doesn’t really fit the scene IMO. 

Credits: IUCN, Melinda for the fab photos, Sea Turtle Conservancy


Hawksbill Turtle © Melinda Riger @ G B ScubaDCB GBG Cover Logo dolphin


The Bahamas has breeding populations of 5 of the world’s 7 sea turtle species – Green, Loggerhead, Hawksbill, Leatherback and Kemp’s Ridley turtles (the other two are Olive Ridley – occasionally found in the Bahamas – and Flatback turtles). All are endangered. There’s no getting away from the fact that Man and Man’s activities are now the primary threats. The IUCN ratings below make for sad reading.

GREEN TURTLE  (Chelonia mydas)

.Photo of turtle swimming towards surface with diver in background

HAWKSBILL TURTLE (Eretmochelys imbricata)

Hunted almost to extinction for their shells

Photo of swimming turtle

LOGGERHEAD TURTLE (Caretta caretta)

A loggerhead sea turtle in an aquarium tank swims overhead.  The underside is visible. Photo of a loggerhead swimming above a reef.

LEATHERBACK TURTLE  (Dermochelys coriacea)

The largest sea turtle

A leatherback sea turtle digging in the sand

KEMP’S RIDLEY TURTLE (Lepidochelys kempii)

The smallest sea turtle


A helpful source of information about sea turtles and their protection is the BAHAMAS SEA TURTLE CONSERVATION GROUP Their excellent summary of the multiple threats to these creatures (below) puts the critical situation very well. Anyone who has watched a TV program about sea turtles and their breeding will be familiar with the vulnerability of turtle nests and hatchlings to predation – and that’s before they ever get to the sea. Despite that, all the species managed to flourish until human intervention (direct or indirect) tipped the balance of survival much further against them. So if we lose one or more of these wonderful species, at least we’ll know who to blame.

In nature, sea turtles face a host of life and death obstacles to their survival. Predators such as raccoons, crabs and ants raid eggs and hatchlings still in the nest. Once they emerge, hatchlings make bite-sized meals for birds, crabs and a host of predators in the ocean. After reaching adulthood, sea turtles are relatively immune to predation, except for the occasional shark attack. These natural threats, however, are not the reasons sea turtle populations have plummeted toward extinction. To understand what really threatens sea turtle survival, we must look at the actions of humans.

In many cultures around the world, people still harvest sea turtle eggs for consumption. Most countries forbid the taking of eggs, but enforcement is lax, poaching is rampant, and the eggs can often be found for sale in local markets. In these same areas, adult sea turtles are harvested for their meat. Turtle products, such as jewelry made from hawksbill shells, also create a direct threat to sea turtles. Lack of information about sea turtles leads many Americans to unwittingly support the international trade in these endangered species. Buying and selling turtle products within the U.S. is strictly prohibited by law, but turtle shell jewelry and souvenirs are the most frequent contraband seized by customs officials from tourists returning from the Caribbean. Indirect threats are harder to quantify, but they are likely causing the greatest harm to sea turtle survival.

Illegal turtle shells (IUCN)IUCN: illegal turtle shells

The waters of the Gulf of Mexico and west Atlantic coast are a major habitat for turtles, but are also the main shrimping grounds in the U.S. Each year, thousands of turtles become entangled in fishing nets and drown. Worldwide, shrimp trawling probably accounts for the incidental death of more juvenile and adult sea turtles than any other source. At one time, as many as 55,000 sea turtles were killed each year in shrimp nets in the southeastern United States alone. Today, all U.S. shrimpers are required to put Turtle Excluder Devices (TEDs) in their trawl nets. Unfortunately, not all fishermen comply with the law, and sea turtles continue to drown in shrimp nets.

Sea turtle entangled in a ghost net

Thousands of sea turtles die from eating or becoming entangled in non-degradable debris each year, including packing bands, balloons, pellets, bottles, vinyl films, tar balls, and styrofoam. Trash, particularly plastic bags thrown overboard from boats or dumped near beaches and swept out to sea, is eaten by turtles and becomes a deadly meal. Leatherbacks especially, cannot distinguish between floating jellyfish — a main component of their diet — and floating plastic bags (my italics).

One sea turtle’s accumulated ingested plastic

Nesting turtles once had no trouble finding a quiet, dark beach on which to nest, but now they must compete with tourists, businesses and coastal residents for use of the beach. U.S. beaches are rapidly being lined with seaside condominiums, houses and hotels. Lights from these developments discourage females from nesting and cause hatchlings to become disoriented and wander inland, where they often die of dehydration or predation.

Florida at night- NASA : ISSS

Coastal armoring includes structures such as sea walls, rock revetments and sandbags that are installed in an attempt to protect beachfront property from erosion. These structures often block female turtles from reaching suitable nesting habitat and accelerate erosion down the beach. Armoring is especially problematic along the east coast of Florida, where beach development is occurring in the very places where sea turtles come to nest by the thousands.


Beach nourishment consists of pumping, trucking or otherwise depositing sand on a beach to replace what has been lost to erosion. While beach nourishment is often preferable to armoring, it can negatively impact sea turtles if the sand is too compacted for turtles to nest in or if the sand imported is drastically different from native beach sediments, thereby potentially affecting nest-site selection, digging behavior, incubation temperature and the moisture content of nests. If renourishment is allowed to proceed during nesting season, nests can also be buried far beneath the surface or run over by heavy machinery.

Beach restoration WIKI

Pollution can have serious impacts on both sea turtles and the food they eat. New research suggests that a disease now killing many sea turtles (fibropapillomas) may be linked to pollution in the oceans and in nearshore waters. When pollution kills aquatic plant and animal life, it also takes away the food sea turtles eat. Oil spills, urban runoff of chemicals, fertilizers and petroleum all contribute to water pollution.
Although the problems of habitat destruction and exploitation seem almost too big to overcome, there are many things within our control that can be changed. Greater public awareness and support for sea turtle conservation is the first priority. By learning more about sea turtles and the threats they face, you can help by alerting decision-makers when various issues need to be addressed.

“Look on thy works, ye Humans, and despair…”  [Gulf of Mexico]Sea Turtle / Oil Pollution / ReutersCredits / Reuters


 Bahamas Sea Turtle Research Logo            BAHAMAS SEA TURTLE RESEARCH


Bahamas National Trust Logo                BAHAMAS NATIONAL TRUST (Factsheets)         SEATURTLE.ORG (image library)

Sea Turtle Conservancy        SEA TURTLE CONSERVANCY


Credits: BSTCG; Wiki (images / IUCN tables); / wiredscience;; Reuters; NASA; STC


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