Eukaryote diversity in the neuston: Fungi and protists are important too!

The sea surface microlayer (SML) occupies a large portion of Earth’s surface, roughly about 70%. Organisms found within this neustonic layer have an important role in the functioning of this ecosystem, yet little is known about the diversity and abundance of many of the groups found within it. A paper by Taylor and Cunliffe (2014) uses new techniques to look at the diversity of eukaryotes, in particular protists and fungi, within the SML or bacterioneuston before and during the spring bloom. This is the most thorough study to date of these groups within this habitat, using newer techniques than employed in previous studies that measured microbial diversity within the SML. It is also the first study of fungal diversity within the SML.

Methods:

Seawater samples were collected during February and April from the L4 water sampling station in the Western English Channel, using a mesh screen sampler to measure assemblages to a depth of 400 μm. Plankton samples were taken from a depth of 2 m using a sampling bottle and all samples were filtered before analysis. Protist and fungal diversity was measured using denaturing gradient gel electrophoresis (DGGE) and high-throughput 18S rRNA gene sequencing. These are methods for looking particular genes to identify organisms within a microbial community.

Findings:

This study, using 18S rRNA gene diversity assessment, indicated that many groups were more abundant and diverse in the SML, particularly during the spring blooms. Fungi were more abundant and diverse in the neuston layer compared to the underlying water. The authors acknowledge that some of the fungi may be terrestrial in origin, which is one of the issues associated with studying marine fungi. Most of the fungal groups, however, have been previously identified in other studies looking at fungal diversity at the L4 station. The diversity of many protist groups was higher in the SML than the plankton. Protist diversity also showed temporal changes, with higher diversity pre-spring bloom, compared to April, during the spring bloom. Some protist groups in the neuston layer, such as diatoms, were distinct from assemblages in the plankton. Many groups of fungi and protists dominated the SML in February and April, coinciding with the spring bloom. This links in with previous work at the L4 station which showed that major groups of phytoplankton followed a seasonal cycle of abundance.

This study is a valuable addition to work concerning fungal and protist diversity in other regions around the world. Still little is known about the diversity of these groups in marine habitats, their seasonal fluctuations or their impact upon biogeochemical cycles. One criticism I would have is that this paper isn’t divided into sections such as methods, introduction, discussion etc. which makes it difficult to read, though this may be the publisher’s requirement. An extension to this study could include a more extensive look at how the abundance of protist and fungal groups changes throughout the year to provide a more complete picture of how these change seasonally.

Taylor, J.D. and Cunliffe, M. (2014) High-throughput sequencing reveals neustonic and planktonic microbial eukaryote diversity in coastal waters, Phycological Society of America, 50, 960-965.

http://onlinelibrary.wiley.com/doi/10.1111/jpy.12228/full