Quantifying Tiering of Marine Animal Forests Through Deep Time

Marine ecosystems are among the most important on planet Earth, and the guiding ecological and evolutionary principles that have shaped their origins are crucial to understand the world we live in today. One example of this are marine animal forests, which are three-dimensional canopies akin to underwater forests that are primarily comprised of invertebrate animals with biomineralized skeletons, like corals and echinoderms. These ecosystems are cradles of biodiversity in modern oceans, and they play an important role in the carbon cycle due to the abundance of calcium carbonate biomineralizers. Despite their significance, however, the macroevolutionary and macroecological processes underlying the origin and diversification of marine animal forests are not well constrained. In particular, tiering, the vertical subdivision of space by organisms within a community, has been proposed as a driver of diversification in marine benthic communities such as marine animal forests, but this has rarely been quantified. This lack of quantification has hampered comparisons of marine animal forests across different spatial and temporal scales, and a unified framework facilitating study of tiering and its effects on extinct and extant marine ecosystems is currently lacking.

In order to understand the origin and evolution of marine animal forests and the role of tiering in structuring these communities, we will devise a quantitative, interdisciplinary approach using cutting-edge statistical methods and computer simulations to investigate tiering in crinoid-dominated marine animal forests. Crinoids are benthic suspension-feeding echinoderms, which have been the poster children for tiering in marine benthic communities since the initial conception of the idea over 40 years ago. They are thus the ideal group with which to tackle this topic.

The development of a quantitative approach to tiering has classically been hindered by the absence of complete crinoid fossils, which are necessary to understand the relationship between growth of skeletal elements of the cup, which house the feeding appendages, and the height of the cup above the seafloor. The recent discovery of a new exceptionally-preserved assemblage of Jurassic fossil crinoids from Wiltshire, UK, housed at the Natural History Museum in London, offers the perfect natural laboratory to develop, test, and benchmark a unified framework for quantifying tiering from partial specimens. Once this has been achieved, we will apply our novel framework to quantify tiering in an older Ordovician palaeocommunity and a modern crinoid-dominated marine animal forest to test and ensure the wider applicability of our approach.

The outcomes of our work will provide insight into the ecological and evolutionary drivers underlying marine animal forests. Our new analytical tools will be widely applicable to marine benthic communities, opening up novel directions of research in the environmental sciences.