Falmouth

Home Laboratory Protocols Offshore Estuary Pontoon Habitat Mapping

Jessica Butland
Bsc Marine Biology with Oceanography

The Fal Estuary is the third largest natural harbour in the world, and is located on the South coast of Cornwall. It is classified as a drowned river valley system, also known as a ria, which was formed during the Holocene at the end of the last glaciation1. The Fal Estuary has a shoreline of 127km; that extends from the estuary mouth at Carrick Roads, to Truro, with a total area of 2500km2 and has 6 major tributaries, consisting of 70% subtidal mudflats, 26% intertidal mudflats and 4% supertidal saltmarshes2. The maximum tidal limit starts at the Carrick Roads and ends 18.1km inland at Tresillian. Carrick Roads has a spring tide range of 5.3m which decreases up the estuary to 3.5m at Truro2.

The Fal is important both economically and recreationally and is one of the county’s busiest harbours that sees between 4000-5000 yachts passing through each year alone3. The Fal is one of the finest sites in Europe for marine wildlife, and is protected as a Special Area of Conservation (SAC) which was designed and implemented by the EU, which aims to protect rare and threatened wildlife both on land and at sea, the Fal Estuary was chosen as it supports a range of habitats outlined within the E.C. Habitat Directive including; saltmarshes, sandbanks, mudflats, eelgrass beds and Maerl. Eelgrass is an important nursing ground for fish and cuttlefish and provides shelter for seahorses and pipefish. Maerl beds are made up of several species of red seaweed with calcified skeletons, which are an important habitat for many different species which live amongst, attached to or beneath the Maerl. Maerl beds are a very fragile habitat and are easily damaged due to aquaculture, trawling, dredging and pollution4. The estuary is also protected under national legislation with two sites within The Fal, listed as Sites of Special Scientific Interest (SSSI), and under English Natures ‘Dodman Point to The Lizard Sensitive Marine Area’ and under county legislation as one of ‘Cornwall Nature Conservation Sites’ which is recognized by the Cornwall Wildlife Trust.

The aim of this study was to investigate the biological, chemical and physical changes within the Fal Estuary, sampling areas from the top of the Fal river to sites offshore. This study was carried out through boat trips offshore, within the estuary and from the King Harry Pontoon. The four survey methods included;

A habitat survey from within the estuary on board MTS Valancia, looking at the seabed habitat communities using a side scan sonar towfish along fixed transects and a using a van veen grab.
An offshore survey on board R.V. Callista, which looked at the extent of stratification from the Black Rock (estuary mouth) towards E1 (an offshore bouy).
An estuarine survey within the Fal estuary onboard R.V. Bill Conway, which looked at estuarine mixing by carrying out horizontal and vertical transects.
A pontoon survey from the King Harry Pontoon, which allowed a time series to be taken over a 3-hour period, looking at the physical properties of the upper estuary.

The Team

The Marine Biologists

The Oceanographers

[1] Stapleton, C. & Pethick, J. (1995) The Fal Estuary: Coastal Processes and Conservation. Report to English Nature, Institute of Estuarine and Coastal Studies, Hull.

[2] Hughes, S. H. (1999). The geochemical and mineralogical record of the impact of historical mining within estuarine sediments from the upper reaches of the Fal Estuary, Cornwall, UK. Fluvial Sedimentology VI. 28, 161-168.

[3] Cornwall County Council , 2006. Environmental: Code of Practice for the ports of Falmouth, Truro & Penryn. Cornwall: Cornwall County Council.

[4] JNCC, 2015. Maerl beds. [Online] Available at: http://jncc.defra.gov.uk/page-6023 [Accessed 29 June 2016].