Sediment Mobility of Maerl Modelling Study

Maerl biogenic gravel beach at Carraroe, County Galway

ResearchBlogging.orgOur new study on “Mobility of maerl-siliciclastic mixtures: impact of waves, currents and storm events,” has just been published (in press) in Estuarine, Coastal and Shelf Science. This is the final part of my PhD in maerl sediment dynamics. Sediment mobility in its simplest form is the percentage of time grains of a particular size are mobile during  a tidal cycle (Idier, 2010). This study focuses on the sediment mobility of maerl in particular, utilising coupled hydrodynamic-wave-sediment transport models to model the oceanography during calm and storm conditions and the resulting sediment transport. Sediment mobility models are another way of quantifying the disturbance of the seafloor as a result of currents, waves and combined wave-currents. This study calculates two sediment mobility indices, the Mobilization Frequency Index (MFI) and the Sediment Mobility Index (SMI), related to the magnitude and frequency of disturbance events (Li, 2015). The residual currents, which are the part of the current remaining after removing the oscillatory tidal component, show that maerl prefers intermediate mobility environments and is often found at the periphery of the residual current gyres. Sediment mobility maps can be used to inform marine spatial planning for the management of both live and dead (fossil) maerl beds, as a result of climate change or anthropogenic activity.

The full research paper, Joshi 2017, can be found here.



Idier, D., Romieu, E., Pedreros, R., & Oliveros, C. (2010). A simple method to analyse non-cohesive sediment mobility in coastal environment Continental Shelf Research, 30(3-4), 365-377 DOI: 10.1016/j.csr.2009.12.006

Joshi, S., Duffy, G., & Brown, C. (2017). Mobility of maerl-siliciclastic mixtures: Impact of waves, currents and storm events Estuarine, Coastal and Shelf Science DOI: 10.1016/j.ecss.2017.03.018

Li, M., Hannah, C., Perrie, W., Tang, C., Prescott, R., Greenberg, D., & Rygel, M. (2015). Modelling seabed shear stress, sediment mobility, and sediment transport in the Bay of Fundy Canadian Journal of Earth Sciences, 52 (9), 757-775 DOI:10.1139/cjes-2014-0211

Book Review: Rhodolith/Maërl Beds: A Global Perspective


This new book on Rhodolith/Maërl Beds* has been much anticipated by the rhodolith research community. With over four years in the making, it is a volume tributed to Prof. Rafael Riosmena-Rodríguez, who dedicated 25 years particularly to the study of the taxonony of coralline algae and sadly passed away earlier this year. Prof. Riosmena-Rodríguez will be very much missed by the rhodolith research community and this book is an important tribute.

The book begins with the role of rhodolith/maërl beds in modern oceans, with chapters on natural history and biodiversity around maërl beds, rhodoliths as climatic archives, modern day threats of ocean acidification on maërl and economic importance. The role of rhodolith in historical oceans and the geological significance is explored by the following section, with a particular focus on the Mediterranean area as well as the North Atlantic sedimentary dynamics. The final part of the book covers the conservation status of rhodoliths globally and serves to be an important summary of current state of regional knowledge of rhodoliths in the major geographic areas.

“These marine beds occur worldwide, from the tropics to the poles, ranging in depth from intertidal to deep subtidal habitats and they are also represented in extensive fossil deposits.”

Overall, this is a much needed edition for marine biology libraries around the world and highly recommended for students of one of the four macrophyte dominated benthic communities. I made a blog post about attending the International Rhodolith Workshop in Granada and one of the key conclusions of the 2015 workshop in Costa Rica was that international recognition is needed for rhodolith habitats to ensure their protection. This book is an important step required to make this possible. It serves to be a useful and comprehensive introduction summarizing the multidisciplinary study of global rhodoliths/maërl beds.

*The term maerl originally refers to the branched growth form of Lemoine (1910) and the term rhodolith is sedimentalogical or genetic term for both the nodular and branched growth forms (Basso et. al, 2015).


Basso (2015) Monitoring deep Mediterranean rhodolith beds. Aquatic Conservation Marine and Freshwater Ecosystems. 26:3. doi:10.1002/aqc.2586.

Lemoine (1910) Répartition et mode de vie du maërl (Lithothamnium calcareum) aux environs de Concarneau (Finistère). Annales de l’Institut Océanographique. 1: 1–29.

Riosmena-Rodríguez, R., Nelson, W., and Aguirre, J. (Editors) (2016) Rhodolith/Maërl Beds: A Global Perspective, Coastal Research Library 15, VIII, 368pp.DOI: 10.1007/978-3-319-29315-8


Happy Earth Day 2013


As part of Earth Day 2013, Monday 22nd April 2013, Conservation International’s (CI’s) Chairman and CEO Peter Seligmann took part in a Twitter conservation, where followers had the opportunity to send in their own pressing questions about conservation issues important to them! Representing seabed related issues, I decided to ask two questions about rhodoliths and deep sea habitats.

The question on rhodoliths was referring to a recent discovery of the world’s largest rhodolith beds off the coast of Brazil- which cover an estimated 21 000 square km area- an area nearly the size of El Salvador! (Original news article here, with blog post here.)

Rhodolith beds off eastern Brazil
Rhodolith beds off eastern Brazil (© Rodrigo L. de Moura)

Another user asked about the which areas CI will be focusing their conservation efforts in future. A particularly interesting answer to the question was:

Reflecting on Peter’s answer, this coupling between research and education, industry and governments seems to me to be the key to responsible environmental management. Of course this is indeed difficult to do in practice. You can follow more about the organisation’s work on their website, with the full twitter conversation here

Coastlines and Culture in Brazil: Abrolhos Seascape

Conservation International’s (CI) video about their work in the Abrolhos Seascape. Field Chronicles is a series where each episode showcases successful CI programs. This episode presents CI’s work in expanding marine protected areas in Abrolhos, Brazil, home of the greatest concentration of marine life in the South Atlantic. The focus is on the extreme challenges CI’s marine team faced, and how they overcame them through community involvement and amplification. This episode also is a good example of CI’s new mission in action as promoting green economies is key to the CI team’s strategy. Also featured is the discovery of the largest rhodolith beds in the world- an area the size of El Salvador!

Griffith Research Jam Talk


The Griffith Geoscience Programme is administered by the Geological Survey of Ireland (GSI) as part of Ireland’s National Geoscience Strategy and was established by the Department of Communications, Energy and Natural Resources in 2007. The scheme honours the memory of Richard Griffith (1784-1878), the celebrated geologist and engineer. The project uses data obtained as part of the INFOMAR programme, with the use of Ireland’s National research vessels, the Celtic Explorer and the Celtic Voyager. Galway Bay is one of INFOMAR’s 26 selected priority bays, as the INFOMAR project now focuses on mapping Ireland’s shallow water regions.

As part of my PhD research, last week I was invited to speak at the Geological Survey of Ireland in Dublin for the “Griffith Research Jam.” This was an event where researchers and postgraduates funded by the Griffith Geoscience Research Award had the opportunity to present their research and share findings. Researchers came from all four provinces around Ireland including from National University of Ireland, Galway, Queens University Belfast, University College Dublin, University College Cork, Trinity College Dublin and some industry representatives. Here is my presentation entitled “Sediment Mobility Modelling and Benthic Disturbance of Maerl Habitats,” (Siddhi Joshi, Garret Duffy et. al. 2012) The web version of the slides can be accessed below.



Siddhi Joshi, Garret Duffy, Martin White and Colin Brown, 2012, Sediment Mobility Modelling and Benthic Disturbance of Maerl Habitats, Oral Presentation, Griffith Research Jam, Geological Survey of Ireland, Dublin.