Underwater habitats of Tremadog Bay

CCW and the Environment Agency recently carried out survey work to chart the underwater habitats of Tremadog Bay. A series of grab samples of sediment were taken at over 30 sites in the bay from the EA Research Vessel Coastal Guardian.
A casual observer swimming over the seabed might well find the sand, mud and gravel areas distinctly uninteresting. But a closer look under a microscope or magnifying glass shows a wealth of creatures with literally hundreds of species to be found.

The waters of Tremadog Bay conceal a diverse and fascinating range of different types of biological communities. These range from kelp forests below the rocky headlands to thick squidgy mud in the central basin of the bay. There are also cobble reefs, seagrass beds, sandy plains, and areas that comprise a mixture of gravel, sand and mud.

Lucy Kay, CCW Marine Conservation Officer said: “The variety and abundance of marine life in Tremadog are why it is part of the Pen Llyn a’r Sarnau Special Area of Conservation. At one site in a small area of sediment only slightly bigger than an A4 size sheet of paper over 1440 animals from 70 different species were found, including worms, small shrimp-like amphipods, small gastropods (relatives of snails), bivalve shells such as mussels and brittlestars, a long-armed relative of the common starfish people are used to seeing on our shores.”

Grab sampling is a technique used to investigate the animals living in sediments like mud and sand. A grab is a device that is lowered to the seabed from a ship and takes a scoop of the sediment, which is then raised back to the surface. The sediment is then sieved so that the animals living in it can be picked out and identified. The amount of sediment taken is small, usually around 5 litres.

CCW will use this data to improve knowledge about the seabed communities within the Bay. This will help with planning future conservation projects and provide a better understanding of the pressures and threats to these submerged habitats. The information will also be useful to compare with data gathered in the future. This will allow more accurate monitoring of this large and fascinating part of Wales’ marine environment.

The EA will use the data to measure the biological health of the water. Some species can survive in polluted waters whilst others are extremely sensitive to changes in conditions so the variety and number of species counted can be used to indicate the condition of the seabed and surrounding environment.

CCW Marine Monitoring Team Leader Bill Sanderson said: “The presence of all these species helps to support those larger species that we are more familiar such as crabs and lobsters. There are also fish such as flatfish and wrasse as well as animals that live above the surface such as scoter ducks and red-throat divers. Other larger species found in Tremadog Bay include seals, dolphins and even occasionally turtles. There are also several rare and unusual species on the floor of Tremadog Bay, including the barbed red seaweed, that hasn’t been found anywhere else in the UK for the last 100 years.”

He added: "The work is part of an ongoing coordinated programme of monitoring work across more than 70% of Welsh waters. This will give us a far better indicator of the condition of important marine habitats like Tremadog Bay".

Mike Best, EA Marine Operations Manager said: “This is part of our on going work to find better ways to assess ecological health for the new Water Framework Directive. We hope to work more with CCW in the near future”