Filander, Z.N., Sink, K.J., Kitahara, M.V., Cairns, S. D. & A.T. Lombard. Diversity patterns of the South African azooxanthellate scleractinians (Cnidaria: Anthozoa), with considerations of environmental correlates. PLoS ONE, 8, e0296188 (08 August 2024). 10.1371/journal.pone.0296188.
Shallow water corals in tropical reefs, like the Great Barrier Reef, harbor microscopic plant-like organisms in their flesh. Those organisms, called photosynthetic symbionts, get protection from predators inside the coral, while the corals get food from the organisms they house. But, what about cold water corals, that live well below the layer of the ocean in which light can support plants and plant-like organisms?
Cold water corals (CWCs) are azooxanthellate corals, which are corals that live below 50 m (about 164 ft), but predominantly in the deep sea below 250 m (about 820 ft). CWCs lack photosynthetic symbionts as a food source, instead catching food out of the water, commonly referred to as filter feeding.
Studying the deep sea is difficult because it is challenging to get to and expensive to collect data from. Scientists are still learning where CWC species are, why they live there, and how diverse they are (i.e how many different species there are within a given area). CWC diversity and distribution is related to a number of factors, such as temperature, salinity, and seafloor type. Exploring these factors will lay the groundwork to understanding the competition for food and space in the deep-sea. Some areas, such as South Africa, are harshly understudied, and remain with more questions than answers.
To answer the question of why CWC species live in South African waters, Filander and her team used historical surveys of South African coral dating back to the late 1800s through the late 1900s. This breadth of data required some deep cleaning in order to be utilized. For example, to verify the data locations the team cross referenced historical depth records and coordinates with modern seafloor depth maps. They also had to verify and correct species identifications because of modern discoveries and updates to the evolutionary tree.
The diversity was then compared to two variables: longitude (how east or west the CWCs are located) and depth in the water. These two variables could be used to infer other factors, such as, water temperature and salinity. However, Filander and the team did not consider the seafloor type as a variable for purposes of this study, due to lack of information in the historical records.
From their analysis of biodiversity, longitude and depth, the team confidently determined there are two distinct groups of CWCs in the South African waters, that they refer to as Group A and Group B. Group A, to the East, has the highest overall biodiversity of all groups, meaning there were the most species present. Group B, to the West, has lower biodiversity overall; the team theorized this might be due to the different currents present, and different seafloor type, though they lacked confirmed seafloor data.
However, both Group A and B have peaks in biodiversity at 50 m depth and 1000 m, which lays groundwork for understanding where to look for CWCs in South Africa in the future. Additionally, both Group A and B had exclusivity in species present, meaning some species were only present in Group A or Group B, but not both.
The work Filander and the researchers did is an early examination of the biodiversity of CWCs in South Africa. This is essential in building the understanding of why CWCs are where they are. Not only this, but understanding the biodiversity of the deep sea is key to understanding changes to this remote ecosystem in the future. Additionally, this is the first study to utilize corrected and confirmed historical data to understand biodiversity in the deep sea. This is a potential way to continue to study the deep sea, without needing to collect new data, which can be costly and time consuming. Finally, this project helps build a preliminary understanding of the biodiversity of CWCs in this region of the oceans, which will be crucial in future studies and research regarding CWCs in this area.
I am a PhD student in Biological Oceanography at the University of Rhode Island, Graduate School of Oceanography. I completed my M.Res in Ocean Science at the University of Southampton, and completed my B.S. in Biology at Florida State University. I study deep sea coral communities and hydrothermal vent communities, especially with a focus on how physical and geological variable drive organism distribution, diversity, and change over time. When I’m not focused on school, I work with reptiles, and spend a lot of time making art for my friends and family!
