Tis the season for trees: Christmas trees that is! Christmas trees may not be the first thing that comes to mind when one thinks of the crystal blue waters of the Bahamas, but when looked at closer there is actually more festive flora and fauna than meets the eye. During my time here with the Shark Lab in Bimini, I have been impressed with the sharks and rays, but I was also surprised with how interesting the sessile species found below the waves were. Spirobranchus giganteus or more commonly known as Christmas Tree Worms quickly became some of my favorite animals to spot and as the title of this blog suggests, they are very nice to both look at and to the ecosystems that they inhabit. Later in my internship, I learned about another species with resemblance to Christmas Trees, this one being coastal: Casuarina equisetifolia or the Australian whistling pine tree. While these trees are also quite festive looking, I was surprised to learn that they are an invasive species to the Bahamas, earning them a spot on the naughty list this holiday season. But since these were just my initial impressions, I’ll let you read on and check the list twice:
[Christmas Tree Worms in Bimini. Photo: Sophia Gunther]
On the nice list this season are the Christmas tree worms of Bimini, Spirobranchus giganteus. A tube building polychaete worm, they’re most characteristically noticed because of their festive crowns that resemble Christmas trees. Spirobranchus giganteus are very colorful and are usually either red, yellow, orange, or blue and are around 3.8 cm in length. This marine worm lives in tropical coral reefs ranging from the Caribbean to the Indopacific. Each of the worms have two crowns which come out from its tube-like body, meaning that you’ll usually see two Christmas trees together, making up one worm. These tubes are made of calcium carbonate and the tree like fibers are made up of radioles, which are hair like bristles. These branch-like bristles are composed of chitin called cilia and they help the worm with respiration by collecting oxygen from the currents and predation. The Christmas tree worms are catching things like phytoplankton and microscopic plants with their radioles.
[Christmas Tree Worms in Bimini. Photo: Sophia Gunther]
These tubes can be contracted when danger is sensed because they are sedentary and burrow their tube-like bodies into nearby coral. Once they have their spots within the coral, they stay and settle and can live up to around 40 years! They are external fertilizers and typically have spawning time periods throughout the year. But what makes them nice? Christmas tree worms do not inhibit the coral formations that they are found in and around and even have been linked to healthy coral habitats due to their protection tactics. The Christmas tree’s see the corals as their homes, and since they don’t move, they help defend the coral by deterring predators such as crown of thorn starfish. This protection that they offer, along with being extremely cute has them top of the nice list when talking Christmas trees this year!
[Australian Pine in Bimini. Photo: Sophia Gunther]
On the counterpart of this list is the naughty Casuarina equisetifolia, commonly referred to as the Australian pine. Introduced to the Bahamas in the 1950’s, it has quickly become invasive, over competing native species. Appearance wise Casuarina looks like a pine tree with fruits that resemble cones and pine needle like leaves. Even though it’s been nicknamed Australian pine, Casuarina is actually in the she-oak family and is more closely related to an evergreen tree.
Casuarina is a fast growing (1.5-3m/yr) tree that can grow to a height of 46m. This tree’s growth is most rapid during the first ten years with maximum growth reached in 20 years. The minimum seed-bearing age is 4 to 5 years and reproduction happens at an accelerated rate, making management difficult. Casuarina’s life span maxes out at about 40 to 50 years, being only a bit more long lived than the Christmas tree worms, but doing much more damage within that time.
[Australian Pines in Bimini. Photo: Sophia Gunther]
Concerns about Casuarina out competing native species and inhibiting biodiversity have been growing rapidly as these trees are reproducing and growing at fast rates and are then preventing other species from utilizing the land by producing toxins. Furthermore, casuarina are salt tolerant but have a root system unable to hold the sand, causing beaches to wash away which leads to erosion. Without measures taken from the government, loss of native vegetation would be immense and land washout would continue, leading to millions of dollars in damage. Despite the trees Christmas like appearance, the consequences outweigh and put them on the permanent naughty list in the Bahamas. Conservation efforts have been implemented (which can be found on The Bahamas government page) as well as action to work towards removal of Casuarina, however the road will be long.
[Sophia bringing down and invasive species while bringing Christmas cheer to the Lab!]
One way the lab has worked towards helping fight the invasion of Casuarina is to use one as decoration for the Christmas tree! These trees can also be used for fires this winter as they are slow burners. One by one, these trees will need to be removed and this is both a help to the island and a fun way to decorate this holiday season. Now that you can make the final call of which trees of Bimini are nice and which are naughty, all there’s left to do is have a happy and healthy holiday season - Merry Christmas!
Sources:
“Christmas Tree Worm.” Oceana, 7 Nov. 2021, https://oceana.org/marine-life/christmas-tree-worm/ Accessed 29 November 2021.
“What are Christmas tree worms.” NOAA’s National Ocean Service, 1 June 2013, https://oceanservice.noaa.gov/facts/xmas-tree.html Accessed 29 November 2021.
“What do Christmas Trees have to do with Coral Reefs?” IMA, 9 May 2018, https://www.ima.gov.tt/2018/04/15/what-do-christmas-trees-have-to-do-with-coral-reefs/ Accessed 29 November 2021.
“Invasive Casuarina tree removal underway by ministry of works.” The Government of The Bahamas, 18 June 2020, Kathryn Campbell [Press Release].
“Cost Benefit Analysis of Casuarina Species Management on Eleuthera Island, The Bahamas - Governor's Harbour Airport: A Case Study.” Miller et al. 2012.
“Cauarina.” The Bahamas National Trust, 2010. https://bnt.bs/wp-content/uploads/2019/06/casuarina.pdf Accessed 29 November 2021.