Cromer Shoal Chalk Beds MCZ Report

In 2021, Seasearch was commissioned by Natural England to report on the distribution and biodiversity of seabed habitats in the Cromer Shoal Chalk Beds Marine Conservation Zone (CSCB MCZ). Marine Conservation Zones are areas set up to protect a range of nationally important, rare or threatened habitats and species. The CSCB MCZ was designated in 2016 and is valued for large areas of chalk reef. Outcrops of chalk within a larger area of sandy seabed provide relatively stable surfaces on which many species depend. Because chalk is not very hard, it can erode into a wide variety of shapes and structures, thereby providing habitat for a diverse set of species, including those of economic value. The softness of chalk does, however, mean that it can be damaged by human activity.

Gully walls of steep chalk covered in floral and faunal turf, contrasting with sediment on the gully floor.

Natural England, as a statutory conservation agency, is obliged to monitor the marine environment, and to assess the condition of protected species and habitats. Making such condition assessments is challenging, time-consuming and expensive, so there is a clear need to explore options that support this process. One possibility is to use data from citizen science (like Seasearch).

The work was based on records of species and habitats collected by Seasearch since 2005 and augmented by the enormous experience and knowledge of Seasearch staff in East Anglia. Although Seasearch volunteers have already collected a large amount of data from the MCZ, as yet, little interpretation of these records has been made and the ecology of subtidal chalk habitat is not well understood. If Natural England is to make sensible recommendations about the ongoing management of the MCZ, we need to improve our understanding of the distribution and character of chalk features, and of any associations between species and these features. Only then can implications of change or damage be evaluated and managed.

Galathea strigosa shelter in crevices or holes in the chalk.

The report improves our understanding in three areas: 

1. Where different habitats (eg chalk, clay, sand) and particular structural features (like gullies and arches) occur within the MCZ;
2. How biodiversity varies between different habitats; and
3. Whether there are any particular associations between species and structural features (eg the tube-dwelling worm Polydora ciliata is found predominantly on vertical or overhanging chalk).

Maps were created for distributions of different habitats, i.e. different types of rock and chalk with different degrees of ruggedness (how smooth or irregular the surface was). The analytical methods used to explore the biodiversity living in different habitats were industry-standard and well established from other applications of Seasearch data.  Local expertise was collated for observed associations between structural features and particular seaweeds or animals.

Cromer Shoal Chalk Beds MCZ supports a diverse range of habitats and species, within a relatively small area. Different habitats are not spread evenly across the MCZ. For example, chalk seabed typically gets more irregular with increasing distance from shore. Chalky seabeds supported much greater diversity than did clay seabeds. Seabeds with an irregular surface (eg with gullies and cobbles) supported more biodiversity than did less complex habitats.

The full report describing the methods and results in detail is available from Natural England.

Boulders and cobbles are the perfect place for small crustacea to live.

This information and new understanding are massively dependent on the efforts of our volunteers and could not have been generated from any other source or in any other way. Such information is needed so we can understand which areas are more vulnerable, sensitive or resistant to disturbance, which may influence how the area is managed. It also provides a ‘baseline’ against which any future change might be assessed and identifies directions for useful work in the future.

All photographs by Dawn Watson and Rob Spray - Seasearch East.

AUTHOR

Dr Angus Jackson
Seasearch Data Officer

Angus joined the Marine Conservation Society in 2018 as the data officer for Seasearch. Much of his working week is spent delving around the large project databases containing records of species and habitats on the seabed around the British Isles.