Integrating sediment dynamics into habitat mapping approaches using sediment mobility indices and seabed classification in Galway Bay, Ireland.

Sediment dynamics information provide vital insights into the important role of oceanographic forcing factors on habitat distribution; yet remains an under-utilized physical surrogate in marine habitat mapping studies. An integrated oceanographic and geophysical analyses of dynamic processes combining sediment mobility indices, obtained from coupled-hydrodynamic- wave sediment transport models; with seabed classification has been made at Galway Bay, Ireland.

Maerl or rhodolith coralline red algae beds are abundant in Galway Bay and these beds represent more than 65% – 70% of the maerl habitats in Ireland (De Grave and Whitaker, 1999). Maerl beds are particularly affected by hydrodynamics and increased storminess resulting in recurrent disturbance of the benthic habitat patch during winter storms. Live maerl beds are biodiversity rich coastal habitats and form subtidal and intertidal banks and open marine beds. Dead maerl beds of the branched maerl morphotype are considered to be biogenic sediment with form dense biogenic gravel debris beaches.

Sediment mobility modelling is of importance to a range of disciplines including sediment dynamics, marine conservation, coastal engineering, and renewable energy (Harris and Coleman, 1998; Idier et al., 2010; Li et al., 2015, Joshi et al, 2017a, Coughlan et al. 2021). It is based on the fundamental quantity of bed shear stress and the impact of pure currents, wave-only, wave-induced currents or combined wave-current flow on surficial sediments.

Multibeam backscatter from the INFOMAR national seabed mapping program of Ireland have been utilized for seabed classification using the new machine learning and deep learning libraries in ArcGIS Pro and Python.

An integrated interpretation of the dynamic processes happening at the seafloor is made as a result of the combined wave-current induced disturbance regime during storm conditions. Implications for future conservation management of maerl beds impacted by increased storminess and anthropogenic activity are discussed.


Coughlan, M., Guerrini, M., Creane, S., O’Shea, M., Ward, S.L., Van Landeghem, K.J.J., Murphy, J., Doherty, P., 2021. A new seabed mobility index for the Irish Sea: Modelling seabed shear stress and classifying sediment mobilisation to help predict erosion, deposition, and sediment distribution. Continental Shelf Research 229, 104574.

De Grave, S., Whitaker, A., 1999. A census of maerl beds in Irish waters. Aquatic Conservation: Marine and Freshwater Ecosystems 9,303-311.

Harris, P.T., Coleman, R., 1998. Estimating global shelf sediment mobility due to swell waves. Marine Geology 150, 171177.

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, 365–377.

Joshi, S., Duffy, G.P., Brown, C., 2017a. Mobility of maerl-siliciclastic mixtures: Impact of waves, currents and storm events. Estuarine, Coastal and Shelf Science 189, 173–188.

Li, M.Z., Hannah, C.G., Perrie, W.A., Tang, C.C.L., Prescott, R.H., Greenberg, D.A., 2015. Modelling seabed shear stress, sediment mobility, and sediment transport in the Bay of Fundy. Canadian Journal of Earth Science. 52, 757–775.

Cite as:

Joshi, Siddhi. (2022). Integrating sediment dynamics into habitat mapping approaches using sediment mobility indices and seabed classification in Galway Bay, Ireland. GeoHab 2022, Venice.


A StoryMap of this research can be found at the link

GeoHab Conference, Winchester


This year the annual GeoHab international marine habitat mapping conference took place in Winchester, UK. This is an annual conference with over 160 people attending from 24 countries, for the first time in England! Organised by my former department of study at the National Oceanography Centre, it had been a long time since I had been back in the South of England. The Monday started with a workshop on Object Based Image Analysis (OBIA). Seabed classification methods can be based on classifying pixels, whereas these newer OBIA methods are based on classifying a group of similar pixels or “objects” on the seafloor. The conference began on the Tuesday with the key note speaker Dr. Larry Mayer of Center for Coastal & Ocean Mapping/Joint Hydrographic Center. The first session was on “Technological Advances in Habitat Mapping” with presentations on how new hydrographic surveying techniques can be used for habitat mapping. A poster session took place where one minute oral snapshots of posters were given. The following session on “Coastal and shallow water habitats” discussed environments such as tidal inlets, seagrass beds and mangroves and then “Shelf and deep-sea habitats” had rhodolith beds, shelf breaks, deep sea corals, submarine canyons, mud volcanoes and cold seeps. “National mapping programs” session then discussed important issues regarding the seabed mapping programs internationally and within the UK. The following session on “Anthropogenic and natural disturbance effects” then looked at man’s and nature’s impacts on benthic habitat and “Role of oceanography in habitat mapping” looked at the physical processes driving habitat distribution. This was for me one of the most interesting sessions. Following this, was very pleased to introduce a special lunchtime screening of my full one hour documentary- “Maerl:A Rare Seabed Habitat.” Being a firm believer in science communication, marine science documentaries can serve to educate, inform and transform the science and are useful tools for stakeholder management. It was great to be able to share our team’s work with scientists and educators internationally and even had one request to translate into Swedish! The final session was on “Development of standards for classification, confidence and assessment of habitat maps“- an important session to conclude on new methods to quantifying the uncertainty of the habitat map.  The conference concluded with thanking the organising committee and preparing for Geohab next year in Halifax, Canada. Overall, it was my first GeoHab in ten years and I was so inspired by the dedication of the GeoHab community – at home and abroad.

Admiral Nelson at the Naval Museum, Portsmouth Historic Dockyard