Are land plants good or bad for coral reefs?

Coral reefs are under threat, and not for the first time in Earth history. Here we ask whether plants are a good thing for coral reefs because they trap mud on land. The student will test this idea by looking at fossil corals and the rock record.

Recent studies show that the first land plants with roots and fungi dramatically changed Earth surface environments, apparently trapping and binding huge amounts of mud on land. Mud kills corals, so early plants may have had a much bigger effect on coral reefs than has so far been realised.

The student will here test the evidence that the amount of mud, nutrients and organic carbon transported into shallow marine environments changed through Palaeozoic time as plants evolved. Second, we will look to see whether the shallow marine carbon isotope record ever shows the effects of these hypothesised changing volumes of terrestrially derived nutrient inputs to carbonate environments (thereby influencing organic carbon production and burial), either locally or globally? Third, have changes in the amount of mud and nutrients in coastal waters through time had any effects on the types of organisms (e.g. photoautotrophs vs heterotrophs) inhabiting shallow marine environments in proximity to coasts and rivers?

These questions are geologically interesting but also directly relevant to the modern world because many endangered shallow marine species including reef-building corals are thought to be threatened by inputs of mud, silt and anthropogenic waste to their coastal habitats (Gattuso et al., 2014).

In summary, the student will develop and test a hypothesis that from the Ordovician Period onwards land plants dramatically reduced the export of mud and nutrients to shallow marine environments, helping coral reefs. The student will search for trends in global and local shallow marine carbon isotope records, tied to volumes of terrigenous mud vs sand and/or limestone that may be deduced from examination of Earth's sedimentary rock record. They will explore the rock record for changes in types and lifestyles of organisms that might have been related to variations in mud exported to shallow marine environments through the Phanerozoic.

The student will use a proven combination of field and laboratory studies to explore the ancient rock record, beginning with construction of a database from a literature search, and then using this to select appropriate and exciting field sites for further sedimentological, petrographic (advanced microscopy) and stable isotope geochemical investigations. Trends identified from this search will be verified using statistical and computer modelling techniques.