We are resuming our Diadema re-locations after spending two years collecting lionfish for NOAA. We now know we can be successful as long as we clean the algae off the area where we intend to re-locate the Diadema.
We stopped at Up Jumped the Devil to check the Diadema that had been re-located the previous August. We were shocked to see a yacht had dropped their anchor just upwind from the re-location spot. The anchor had gotten stuck on a coral head which was broken loose from the bottom, the anchor then drifted into the coral head at our re-location spot smashing it, before hitting several more coral heads. We found 3 piles of Diadema shells & spines. They had no sentiment on them indicating they had died recently. An examination of one of the coral that had been knocked loose and was resting upside down showed that the coral was bleached but still alive indicating it had happened recently. This led us to believe that at least 3 Diadema had survived for 4 months.
The Diadema cages were checked and 15 Diadema were still in them.
15 Diadema were re-located to Up Jumped the Devil, a wall in the Exumas. Prior to the re-location a 10' by 10' area was cleaned of algae and the Diadema re-located there.
This same trip we checked the Diadema that had been re-introduced from the lab. A total of 15 were found. It is believed that the previous summer's death of 25 Diadema was from the toxins in the algae that was added to the cage in the belief that the Diadema needed more algae then was available in the cage.
A survey of dive sites where we had done re-locations showed that most had not been successful. The two exceptions being Exumas dive sites Close Mon Reef and Pillar Wall. Blackbeard's Cruises has just moved its base of operations to a house in Freeport, Grand Bahama. The seawall there is covered with algae, so we moved 15 Diadema from another canal that had Diadema to the seawall at our dock. We were able to observe them daily at this location, something we couldn't do in the Exumas or Bimini. Everything was fine until 9 to 10 days after the re-location. At that time they became lethargic and started losing spines. Several were collected and frozen. The others died. We were unsure about the reason for the deaths but had these theories.
- Pollution in the canal.
- Overeating by Diadema coming from an area with little algae.
- Something in the algae that was killing them.
We decided to clean off two 10' lengths of seawall and re-locate another 15. This was done and we had no die-off of Diadema until 8 months later when the warm water caused the algae to grow quickly shrinking the area available for the Diadema to eat. Some were seen eating mature algae. A total of 7 died in August/September but the remaining 8 survived the rest of the year. Algae experts said the likely cause was dinoflagellates. These organisms are known to create the toxin that causes ciguatera and red tide.
Cat Ppalu July 23, 2005 trip
We began our Diadema re-location efforts in April of 2004. During that first spring we re-located over 1,000 Diadema from shallow areas to the deeper reefs offshore. We then planned to evaluate our efforts in September, 2004. There are two ways to measure the success of this effort.
1) Counting the Diadema at night. Unfortunately since we have begun, seas have prevented us from making night dives at most of the sites.
2) Comparing algae cover between the coral ridges where Diadema were released with nearby coral ridges. It takes 2-4 months for Diadema to make much of a difference in the algae cover, so we planned to evaluate these areas in the fall of 2004. Unfortunately the Exumas were hit by two hurricanes before we could evaluate these sites. Not only did the hurricanes kill a large percentage of the Diadema, but they sand blasted many of the reefs, removing most algae. This made algae cover comparisons impossible.
Because of these problems we had to start over this year. So far this year we have re-located 254 Diadema. We were then lucky to have beautiful, calm seas during our July 23-29, 2005 Diadema trip. What we found was that our efforts had been rewarded with very successful results at some sites while at others we found no positive results. We now need to try and determine why there was a difference betweens sites. The following is what we discovered this trip.
1)During 2004 we relocated 85 Diadema to the coral ridge near the Pillar Wall mooring. Earlier this year we discovered that many Diadema had moved to a ridge just to the south that was 20' higher. We were able to make a night dive on Pillar Wall and discovered that over 60 of the Diadema from 2004 were still there. We then relocated 53 more. The next day Dr Tom Wood of George Mason University and I made several algae/coral cover measurements. Pillar Wall is a dive site where we have been documenting the coral/algae cover measurements for since 2003. We found that algae had decrease by 50% while coral had increased by 23%.
| ||Coral Cover||Algae Cover
2)During our April, 2005 Diadema trip we re-located 25 Diadema to 5 coral heads around the Dog Rocks mooring. The coral heads were marked with small floats. During a night dive we were only able to find 2 Diadema. We did not see obvious reason for the decline.
3)During a May trip led by Dr Tom Wood of George Mason University, 40 lab raised Diadema from the University of Miami program monitored by Tom Capo were flown to Nassau and transported by the Cat Ppalu. The next day, May 23, they were placed in 3 cages at Barracuda Shoals dive site. Two cages measuring one meter square each held thirteen lab raised Diadema. Fourteen were placed in a slightly smaller cage. The smaller cage also held 4 juvenile Diadema that were collected from the wild. Two weeks later the cages were inspected and all the Diadema were still alive. A large amount of network algae was added to the cages at this time. I believe that I probably added too much as it made a layer 4" thick at the bottom of the cage. On July 27 we did another dive to check their status. We found 20 of the lab raised and all 4 of the wild Diadema were still alive. We also found 2 young juveniles that had settled this spring. I think that it is probable that many of the lab raised Diadema died due to the quantity of algae that was added. Regardless, we view the results as a huge success. In the event of another die-off of Diadema, we will need to be able to re-introduce lab-raised back into the wild to create breeding colonies.
4)A survey of Close Mon reef revealed that the Diadema re-introduction here continues to be successful. The area of the reef where they were re-introduced is maintaining its algae free state while the other areas are almost completely covered with algae.
5)In April we re-introduced 15 Diadema to a Danger Reef coral head just east of the mooring. This coral head was about 10 meters square. The coral head was marked by small buoys. While we didn't have time to make a night dive here we did do coral/algae cover measurements on the coral head and a adjoining coral head. The coral head with the Diadema had an algae cover of 16.9%, while the one without Diadema had an algae cover of 25.3%, thus the reduction of 67% was recorded.
6)It is impossible to re-locate enough Diadema for them to clean the massive walls we have in the Exumas. The idea behind the re-location is for them to clean enough area to allow new Diadema to settle. Diadema will only settle if the bottom is very clean. Gerry Fleming from Blackbeard's Cruises came up with the idea of pressure cleaning the bottom. To try this out, we took a pressure cleaner along. On Danger reef we tried it out. It was very effective, but would still be very time consuming. We have come up with another idea that we will try this winter. Network algae (Microdictyon marinum), that has taken over much of the Bahamas, has a leaf that grows to over 6" in diameter by late fall. This leaf shades everything under it creating a bare area. It is very easy to break this leaf off exposing the clean area underneath. The main time of the year for Diadema to settle is the winter. We plan to operate some trips this winter to clean algae off parts of the reef. The cooler water temperatures at this time will slow its re-growth. We should be able to clean large parts of the reef.
7)Dr Ken Hintz from George Mason University took water sample at most at most of the sites we dove during the week of July 23, 2005. This data will be analyzed by his son Dr Chris Hintz to see if there are differences in water quality between reefs with Diadema and those without. He also collected spines from the Diadema we collected and those in the cages. These will be also be analyzed to see if there are any chemical differences.
8)Barracuda Shoals was the first of our monitored dive sites to experience an increase Diadema population. It has been almost completely clear of algae, but the hurricanes killed many of the Diadema on it. While it is still mostly algae free, there are areas where the algae is returning. This should be temporary as more Diadema settle and continue to consume and control the new growth.
9)When we dove Up Jumped the Devil we saw what happens when there aren't any Diadema. We had one algae measurement of 75%. We re-introduced 35 Diadema to the area around the mooring. Hopefully this will be a site where they are successful.
10)On the return to Nassau, we stopped at a coral head on the Yellow Bank. Despite a water temperature of 90, the reef was almost completely clean of algae and the coral looked healthy.
The hurricanes last year made it very difficult to determine how well the relocated Diadema fared. We do know that on some reefs many of the Diadema died, but the increased wave action did not affect all reefs the same. On two reefs: Close Mon & Pillar Wall, the relocated Diadema have made an impact on the algae. The sea urchins on this reef have been busy as the coral coverage is increasing and there were new clean spots where algae have been devoured. Pillar Wall was exciting because we have been doing coral & algae cover surveys there for several years. This will give us a base line to measure progress later this summer.
Based on our observations from last year, we have changed our collection & relocation techniques. We were able to track 15 Diadema that we relocated to Danger Reef. All 15 survived the first 24 hours.
Later this month we will place 30 lab raised Diadema in cages in the Bahamas. Lab Raised Diadema will be crucial to the overall health of the reef if there is another die off in the future. If they are able to survive in the wild, this will show that we can place breeding colonies in the ocean in the event of another die-off.
On May 28, 2005 Bruce Purdy from Blackbeards Cruises and Tom Capo from the University of Miami transported 40 juvenile lab raised Diadema from Miami to Nassau. They were then transported from Nassau to the Exumas by a group of students from George Mason University. They were led by Dr. Tom Wood. Phil Gillette, one of Tom Capos graduate students, also assisted with the transportation. Once in the Exumas they were put in 3 cages at Barracuda Shoals reef. 13 each in two cages that were 4 meters square. The remaining 14 were put in a cage that was 1 meter square. The smaller cage already had 4 wild juvenile Diadema in it. The oxygen and salinity were checked frequently during the transportation. They were put in the cages the morning of May 29. They were checked again on June 2. All were still alive and appeared to be doing well.
While Bruce Purdy was accompanying a Cat Ppalu private charter, he stopped at Barracuda Shoals on June 12, 2005. He checked the cages and found all 44 Diadema to be still alive. They appeared to be doing well. This is the longest that lab raised Diadema have survived in the wild. He then added a large net full of algae to each cage. Most of the algae was Network algae (Microdictyon marinum), the most common algae in the Exumas. This particular reef was the first to have Diadema naturally settle on it. These Diadema have now been there for 4 years. They had reduced the algae cover to less then 5%. During a quick swim over the reef after checking the cages, there were a number of areas noted where algae cover was increasing. The 2004 hurricanes killed many of the Diadema in the Northern Exumas. This is probably the reason for the algae increase. Hopefully the winter settlement of juveniles will stop the increase by late summer.
During a stop at Pillar Wall on June 13, a quick 5 minute survey was done of the ridge where 30 Diadema were release in April. During the survey 8 Diadema were found. This coral ridge is over 25' high, with most of the hiding spots not visible to a diver, so only a late night survey would let you know how many are there.
On June 14 a night dive was done at Danger Reef. In April 15 Diadema were put on one coral head during the afternoon. They were checked that night and the next morning and both times all were found. During this dive only 3 were found on the first check about 30 minutes after sunset. A check about 1 1/4 hours after sunset found 7, but several of these were just starting to come out of deep hiding spots. On the return to the boat one more Diadema was found on a coral head to the one where they were released. These coral heads were separated by 20' of sand, so it may or may not be one that was released in April, although no Diadema were seen on this coral head in April.