Intertidal Surveys


This procedural guideline is adapted from Wyn et al. 2001 The technique described here provides a method of sampling 4 different habitat types (sediment biotopes, rock and mixed biotopes, saltmarsh grid points and submerged sample stations) at Phase 1 survey level.

The grid sampling method used allows the following conclusions to be made about the sampled biotope:

  • Distribution of selected biotopes/biotope types throughout the site
  • Relative proportion of selected biotopes/biotope types throughout the site
  • Presence /absence of selected biotopes/biotope types throughout the site

Advantages and disadvantages

The advantages of the methodology outweigh the disadvantages. It allows inexpensive and rapid site monitoring of certain site attributes, without the need for expensive post-survey species identification and data analysis. Results are independent of the accuracy with which biotope boundaries are marked or about the stability of biotope boundaries over time.

Disadvantages include possible inadequate resolution for some monitoring objectives, a lack of reference samples for later re-examination, possible overlooking of some habitats and biotopes and an inability to derive accurate map boundaries from the data.

Personal Safety

Surveyors should always work in pairs due to the inherent dangers of working in a marine environment. The lone worker policy should be followed to provide additional backup should both surveyors be trapped or incapacitated. Risk assessments should be prepared for each location to be surveyed in order to account for local conditions (Wyn et al. 2001). In addition, please read this safety information before carrying out any survey.


The following are required in the field:

  • Clipboard
  • Map of site with grid points and their co-ordinates marked
  • Waterproof survey forms, erasers and sharpener
  • Ordnance Survey map
  • Laminated MNCR biotope manual
  • Collecting equipment for voucher specimens (small pots and labels)
  • Camera (weather-proof)
  • Safety equipment including mobile phone, PPE (including a dry suit), first aid kit and flares
  • Tide tables
  • Spade and 0.5mm mesh sieve for sediment shores differential/non-differential
  • GPS

Further equipment required for post-survey analysis includes simple word-processing and spreadsheet software packages. Minimum staff required are two experienced intertidal surveyors familiar with the application of the biotope classification to the intended survey locality.


Set up an evenly spaced grid of sampling stations across the site from high water springs down to low water springs. Prior to the survey, complete a risk assessment form, gather information on tide times and heights and prepare a map and table of the locations of the grid sample stations. Collate information about access points, land ownership and local site conditions.

Begin the survey at least 2 hours before spring tide low water (daylight permitting). Locate each intended grid sample station using a differential Global Positioning System (GPS) accurate to within 1 metre. Record the sample station number, GPS position, habitat and biotope details on a standard pro forma for each sample station.

Survey the different habitat types as follows:

Sediment biotopes: Take samples within 1 m2 of the grid station and sieve in situ. This involves collecting 2 spade loads of sediment, dug to a depth of 20-25 cm and sieved through a 0.5 mm mesh sieve. Record species presence and abundance. Take specimens of species that are considered important for biotope identification (and which are not initially identified in the field) for later laboratory identification.

Rock and mixed biotopes: Record presence and abundance of species found within 1 m2 of the sample station and assign a biotope code using the Marine Biotope Classification for Britain and Ireland (see references).

Saltmarsh grid points: Gridpoints falling within higher and saltmarsh communities are sampled in one of two ways. If the 1 m2 around the sample stations contains more than 5% cover of saltmarsh plants then it is classed as saltmarsh and the epifaunal/floral species, their abundance and percentage cover are recorded but the sediment infauna are not sampled. However, if the 1 m2 contains less than 5% cover of saltmarsh plants the infauna and surface species are recorded as for other sediment biotopes. Record the abundance and 5 cover of saltmarsh species in all cases. This is necessary to ensure recording consistency across time, ie. that the ‘saltmarsh’ is still the same entity from one monitoring episode to another. Submerged sample stations: Because of the dynamic nature of sites, the channel positions within them may change over time.

Sometimes, sample stations from previous years may be submerged or exposed. Grid sample stations falling within the river channel are not sampled and this must be taken into account during subsequent data analysis. Additional information about more widely dispersed species and habitat details should be recorded from a 5 m radius around each sample station.

Note: Do not monitor sediment sample stations during or immediately after heavy rain, due to loss of surface features. Sieve a sufficiently large volume of sediment to adequately characterise the biotope. Carry out the survey between April and October during periods of spring low tides. Familiarise yourself with all the intertidal and sublittoral fringe biotopes, especially those previously recorded from the site. Some estuary sediments can be unsuitable for biotope identification because of disturbance or instability. Record these as unsuitable. Add additional sample stations if necessary to ensure sufficient numbers of both the major and minor biotopes. If necessary, stratify the sampling to ensure adequate representation of the biotopes to be monitored.

For monitoring sediment biotopes, infaunal species collected in the sieve should be recorded as actual or estimated numbers, not as abundancies. Consider the impact of the sampling strategy. Refill holes at sediment sample stations and be additionally considerate of sensitive and limited habitats e.g. saline lagoons. Use the same version of the national biotope classification to ensure inter-survey consistency. The survey team should clarify the key habitat and species characteristics of each biotope within the specific site, to improve differentiation of biotopes. Notes can be made of variation of the biotope character from the national character.

Use of Collected Data

Data from these surveys will include information about the different proportions of biotopes or biotope types and an account of changes across a time series. These data can inform databases or GIS, according to the monitoring objectives.


1: Wyn, G., Brazier, D. P. and McMath, A. J. (2000). CCW handbook for marine intertidal Phase 1 survey and mapping. CCW Marine Sciences Report: 00/06/01.

2: Connor, D. W., Brazier, D. P. Hill, T.O. and Northern, K.O. (1997) Marine Nature Conservation Review: marine biotope classification for Britain and Ireland. Volume 1. Littoral biotopes. Version 97.06 JNCC Report No. 229.