TMAP Monitoring Handbook

1 Introduction

In the Wadden Sea two seagrass species area found: the small and very narrow-leaved Zostera noltii is the most common. It grows in the intertidal and is usually perennial. It is often accompanied by a mostly annual, narrow leaved small morph of the large Z. marina particularly in puddles filled with water during low tide. Around low water line and deeper beds of large and perennial Z. marina once occurred in the Wadden Sea. In the course of the wasting-phenomenon in the 1930s these beds vanished and never came back. Under brackish conditions the related wigeon grass Ruppia maritima occurs in the Wadden Sea.

Seagrass beds have an important ecological function for coastal ecosystems. They provide habitats for several species such as fish, juvenile bivalves, crustaceans and a diverse range of other organisms. Zostera beds constitute a food for birds such as brent geese and wigeon. With their dense growth, they also protect the sediment against erosion and facilitate deposition.

Both species Z. marina and Z. noltii show considerable interannual fluctuations in size and shape of local beds. Salinity and nutrient loading, separately and in combination, are important environmental factors for seagrass development. Local runoff of freshwater is considered advantageous for seagrass growth; these runoff points have been diminished by sea dike strengthening. Eutrophication, turbidity and hydrodynamics seem to be the major factors determining the distribution of seagrasses in the Wadden Sea, while shellfish fishery and land claim have negative effects on a more local scale (Reise et al., 2005).

In the southern and central Wadden Sea, a decline of seagrass was observed between the 1950s and 1990s, which seems to have come to a halt, and some recovery is evident. In 2002/2003, intertidal seagrass beds were distributed rather unevenly. More than 80% of the beds occur in the northern Wadden Sea between Eiderstedt and Skallingen (Reise et al., 2005).

Due to divergent methods of assessment, the total area of seagrass in the Wadden Sea is considered to be a rough estimate.

2 Objectives

Trilateral policy and management aims “to achieve, as far as possible, a natural and sustainable ecosystem in which natural processes proceed in an undisturbed way” (Guiding Principle).

With respect to the “Tidal Area” (intertidal and subtidal), the following Target applies (Wadden Sea Plan) to seagrass:

• An increased area of, and a more natural distribution and development of … Zostera fields.

The monitoring of seagrass is carried out to support trilateral policy and management. It should

• assess changes in the distribution of seagrass,
• assess changes in species composition and abundance of Zostera and related aquatic phanerogames such as Ruppia,
• contribute to causal analysis of changes,
• enable an estimation of potential carrying capacity in the Wadden Sea for seagrass and assess deviation from it,
• prepare recommendations for management.

3 Monitoring requirements

Wadden Sea Plan (WSP)

Targets on “Tidal Area”

• A natural dynamic situation in the tidal area.
• An increased area of geomorphologically and biologically undisturbed tidal flats and subtidal areas.
• A natural size, distribution and development of natural mussel beds, Sabellaria reefs and Zostera fields.

EC Habitats Directive (HD)

HD

Article 11 Monitoring of habitat types
Seagrass is a characteristic feature of habitat types 1140 ”Mudflats and sandflats” and 1160 “Large shallow inlets and bays”.

Water framework directive (WFD)

Annex 5, chapter 1.2.4 and Article 4

Annex 5, chapter 1.2.4
Article 4: No deterioration, good status by 2015, reduction of pollutants, achievement of objectives set for protected areas in EC legislation.
Good ecological status of surface water: biological quality element “Angiosperms”

Oslo Paris convention (OSPAR)

Biological Diversity and Ecosystems Strategy, Annex V and Appendix 3

Initial OSPAR List of Threatened and/or Declining Species and Habitats (Ref-Nr. 2004-06): Zostera beds.
EcoQO Issue 8 “threatened and/or declining habitats”: presence and extent of habitats in the North Sea as shown on the initial OSPAR List: “Zostera beds”

4 Definitions

Seagrass bed

Seagrass beds in the Wadden Sea comprise submerged phanerogame plants belonging to the genera Zostera (Z. noltii and Z. marina) and Ruppia maritima.

Three categories can be recognized based on occurrence of seagrass and the methods applied for their assessment:
1. Areas within the Wadden Sea may be entirely devoid of seagrass or may have a few isolated plants with coverage <5%.
2. Areas may show growth of scattered seagrass plants when at peak vegetation period average cover is between 5 and 20%.
3. In addition or instead, areas may show seagrass beds with >20% cover at peak vegetation period.

Beds have either a coherent coverage of >20% or are composed of clusters of patches (with >20% coverage) less than 25 m apart.
In ground surveys, area is preferably measured in a spatial resolution of 10x10 m and in airborne surveys in a spatial resolution of 100x100 m.
The area is given as gross area belonging to category 2 and/or 3 and, if available, also the seagrass net area by multiplying gross area with coverage (0.05 to 0.2 or >0.2 to1).

Coverage categories

The available coverage data (ranges) will be combined for the TMAP as follows:

TMAP Category	TMAP Density	Coverage %
1	Devoid or scarce	<5
2	Scattered	5-20
3	Beds	>20

More detailed coverage categories should be applied equally for sub-regions in the Wadden Sea if data are available.

Peak vegetation period

Time between mid of July to mid September.

Coverage

The average amount of living seagrass plants covering the bottom of the sea at low tide exposure during peak vegetation period from mid July to mid September.
At permanently submerged bottoms the coverage is measured as the shadow of seagrass plants cast onto the bottom when light shines vertically from above.

Ephemeral areas

Areas with occasional occurrence of seagrass within a period of about 10 years.

Permanent areas

Areas which are known as covered or can be assumed to have been covered with seagrass over 10 or more consecutive years.

Potential area of intertidal seagrass in the Wadden Sea

Surface area of intertidal seagrass beds which may be reached under the current conditions (e.g. continued decrease of nutrient inputs, maintenance of the present dike lines, no land claim or other mechanical disturbance) and the existing hydro-morphological regime (derived from historical data and expert knowledge. It may change with sea level rise, shifts in tidal range and with restoration measures.

Species composition

	Type of seagrass bed	Species composition
1	Z. noltii bed	Consists of >75% Zostera noltii
2	Z. marina bed	Consists of >75% Zostera marina
3	Mixed Zostera bed	Percentage of Z. noltii or Z. marina between 25-75%
4	Ruppia bed	Consits of >75% Ruppia maritima

5 TMAP Monitoring Strategy

A draft TMAP guideline with common definitions and a classification of seagrass beds was developed in 2006 which allows a common interpretation of monitoring results of the entire Wadden Sea. Because of the extreme uneven distribution of intertidal seagrass, different monitoring methods are in use.

In the marine and brackish coastal waters of the Wadden Sea, the aquatic phanerogames comprise two genetically highly diverse seagrasses (Z. marina, Z. noltii) and restricted to brackish conditions the wigeon grass Ruppia maritima.

Seagrass should be monitored covering all potential intertidal flats for seagrass in the entire Wadden Sea. Within the Wadden Sea regional assessments and analyses of spatial distribution should be carried out to fulfill the reporting commitments of the relevant EC Directives.

Selected monitoring sites should be assigned which are representative for a larger part of the Wadden Sea and where field surveys can be carried out with a high frequency. This should also include potential seagrass sites.
Additional surveys should be considered to include suitable subtidal areas for Zostera marina and brackish transitional water bodies for Ruppia spp.

The following strategy should be followed (see Table 5.1):

Complete mapping (see A.) of the entire tidal flats is done every year in areas with dense seagrass beds (which can easily be identified by airborne surveys). In areas with sparse coverage, annual monitoring is done in field survey on transects; a complete mapping of the entire tidal flats is done at least every 6 years.

In both cases detailed monitoring (see B.) is carried out at selected sites to monitor further characteristics of the bed (as required by WFD and HD), these parameters are optional for the TMAP.

(Table 5.1) Parameters with monitoring locations and frequencies and the relation to the other monitoring requirements.

Parameters	Description	Location	Frequency	Method	WFD	BD/HD	OSPAR	OTHER	Remark
Mandatory TMAP parameters
Area (Seagrass)	size of intertidal seagrass beds (km²)	Entire Area and representative areas	Entire area: at least 6 y, Selected sites: 1/y		X	X	X	-	-
Coverage (seagrass)	Seagrass coverage of the beds (%)	Entire Area and representative areas	Entire area: at least 6 y, Selected sites: 1/y		X	X	X	-	-
Location (seagrass)	coordinates of intertidal seagrass beds (GIS polygon)	Entire Area and representative areas	Entire area: at least 6 y, Selected sites: 1/y		X	X	X	-	-
Optional TMAP parameters
Biomass (seagrass)		Selected sites	1/y		X	X	-	-	Optional for TMAP
Sediment characteristics (seagrass)		Selected sites	1/y		X	X	-	-	Optional for TMAP
Species composition (seagrass)	Zostera marina, Z. noltii, Ruppia maritima, green macroalgae, others	Selected sites	1/y		X	X	-	-	Optional for TMAP

Remarks:

* Seagrass as characteristic feature of habitat types 1140 ”Mudflats and sandflats” and 1160 “Large shallow inlets and bays”.

5.1 Parameters

The parameters currently monitored are sufficient to fulfill the objectives. Further adaptations may be required at a later stage and the comparability of results from different sub-regions should be enhanced.

TMAP Parameters (covering entire intertidal area);

• Area: size of seagrass beds (km²)
• Location: coordinates of seagrass beds (GIS polygon),
• Coverage: Seagrass coverage of the beds (%)

Optional TMAP parameters (if available from ongoing national programs and from selected field sampling sites):

• Species composition (Zostera marina and Z. noltii, Ruppia maritima, green macroalgae, others),
• Biomass,
• Sediment characteristics (such as: presence/absence of fossil clay or peat below sediment surface, accretion/erosion area, presence/absence of mobile sand ridges),
• Other.

5.2 Monitoring locations

Entire Wadden Sea area:

• area and location of seagrass beds (if applicable)
• coverage of seagrass beds (if applicable)

Selected sites (to be specified by the countries):

• area and location of seagrass beds
• coverage of seagrass beds
• species composition (optional)
• biomass (optional)
• sediment characteristics (optional)

6 Methods

No single monitoring method is available to meet all objectives.

1. Remote sensing (RS) provides a good area assessment of aquatic macrophytes in the intertidal zone but cannot separate all taxa sufficiently. In particular, the distinction between seagrass, indicating generally good, and green algae, indicating potentially deteriorating ecological conditions in the Wadden Sea, is at present only possible by using airborne surveys (see b).

Ground surveys provide good taxonomical resolution, but are not feasible where aquatic macrophytes are spread over a very wide tidal area.

2. Seagrass occurrence is extremely uneven in the Wadden Sea. Therefore the achievable accuracy of assessment in the Western Wadden Sea with few seagrass beds cannot be reached in the Northern Wadden Sea with plenty of seagrass beds.

However, this does not preclude consistent data sets from the sub-regions to arrive at reliable estimates of total seagrass area and the respective shares of the taxa, nor does it preclude identifying trends and deviations from the “potential area”.

The following methods may be combined as appropriate in order to reach the objective:

• Application of RS techniques at irregular intervals (such as satellite and airborne sensors / aerial photographs),
• Airborne surveys (visual mapping of extensive occurrences of seagrass and green algae annually),
• Field surveys (all regions: transects, sampling plots, different methods applicable).

6.1 Remote sensing

The selection of the appropriate remote sensing (RS) techniques depends on:

• the overall monitoring strategy in which RS is an integrated part (combination of different methods and/or field surveys),
• the type of information to be delivered by RS (orientation, supporting information for field surveys, preparation of detailed seagrass maps).

There are different remote sensing techniques available which can be applied for monitoring of larger areas in the Wadden Sea.

Table 6.1 Overview Remote Sensing Techniques.

Remote Sensing	Technique	Application	Remarks	Operation
Aerial photographs	IR ortho photographs (e.g. resolution 1:10,000)	Monitoring of distinct smaller areas	Seagrass beds with low coverage may be overlooked, discrimination between different Zostera species is difficult or not possible High costs	operational in NL (annually), applied also in Lower Saxony and Denmark for distinct years)
Other airborne sensors	Digital high resolution sensors e.g. HyMap	Synchronous monitoring of a large area	Objective automated analysis possible High costs	Not yet operational (see OFEW project)
Satellites	Various optical sensors (by Landsat or Aster)	Synchronous monitoring of a large area	Objective automated analysis possible.Green macroalgae may not be discriminated from Zostera (see above). Limited data availability Low costs	not yet operational (see OFEW project)
Airborne surveys	visual mapping of seagrass beds	Monitoring of larger areas with high frequency	Seagrass may by overlooked. For seagrass beds >20% coverage. Discrimination between Zostera species is not possible but can mostly be separated from green macroalgae Low costs	operational in SH(annually, during peak season), applied also in Lower Saxony for distinct years)

OFEW = Operationalisierung Fernerkundungsmethoden für das Wattenmeer (Bockmann Consult, 2005-06)

6.2 Field surveys

Field surveys should be carried out

• as ground truth in conjunction with remote sensing.
• to get more detailed information (quantitative and qualitative) to be able to characterize the ecological status of the seagrass beds.
• to monitor areas with scattered occurrence of seagrass (<20% coverage) including potential seagrass areas.

It is recommended to carry out these surveys at seagrass sites which are representative for a selected region during the peak vegetation period (e.g. water bodies according to WFD).

7 Parameter

The parameters currently monitored are sufficient to fulfill the objectives. Further adaptations may be required at a later stage and the comparability of results from different sub-regions should be enhanced.

8 Frequency and time

The monitoring frequency has to be adapted to the situation in the sub-regions:

• NL: annual, biannual and every six years (selected sites)
• Nds: total area every 6 years, selected sites annually
• SH: every year aerial mapping / selected sites annually
• DK: every year aerial mapping / at selected sites biannually

The surveys should be carried out during peak vegetation period (mid of July to mid September).

For details see [Table 5.1].

9 Assessment

For an appropriate seagrass monitoring strategy it is necessary to assess to which extent the trilateral Target “An increased area of, and a more natural distribution and development of … Zostera fields” has already been reached and to which extent the current status relates to the “potential area” where seagrass could grow in the absence of anthropogenic disturbance.

This would be an expert estimation to compare the current situation with the maximum surface area of intertidal seagrass beds which could be reached under high quality conditions. This may give an indication whether the current situation has reached, is below or even far below the potential area (see chapter: Definitions).

For the Netherlands, the current surface area of seagrass beds was regarded as more or less the maximum which can be expected in the intertidal area. Only by intensive effort, esp. In the Groningen salt marsh works, a significant increase in area might be possible.

In Lower Saxony, the intertidal seagrass area is still at least 5 times lower compared to the situation in the 1950s/70s and is regarded as clearly below a potential which may be estimated to about at least 35 km².

In Schleswig-Holstein, the potential area of seagrass beds possible under no land claim and other mechanical disturbances, and continued decrease of nutrient input would be about 1 – 5% coverage in the Dithmarschen area (today 0.3%) and about 20% in the North Frisian Wadden Sea (today 10%), which includes a more or less continuous belt of seagrass along the mainland coast.

Table 9.1 Surface area of seagrass beds (% coverage of intertidal area): Current situation and potential area.
Explanatory note: Areas with less than 5% coverage (Category 1) are not included. For Schleswig-Holstein, only areas with >20% coverage are given; the potential area has to be defined taking into account the 3 different categories of seagrass beds; n.d. = no data.

Region	Current situation (2006)	Current situation (2006)	Potential area	Potential area
Seagrass bed category (% seagrass coverage)	Cat. 2(5-20%)	Cat. 3 (>20%)	Cat. 2 (5-20%)	Cat. 3 (>20%)
Denmark			not defined	not defined
SH-Nordfriesland	n.d.	10%	n.d.	20%
SH-Dithmarschen	n.d.	0.3%	n.d.	1-5%
Niedersachsen		[7.5 km²]*		[about 35 km²]*
Netherlands	[1 km²]*	[0.2 km²]*	[1 km²]*	[0.2 km²]*

* to be converted into % and to be differentiated into category 2 (5-20%) and 3 (>20%)]
[Intertidal area: NL=1240 km², Nds=1440 km² (QSR 2004)]

[to be included: WFD / HD assessment criteria]

Fig. 9.1 Sea grass beds in the Wadden Sea

10 Reporting

All data obtained from aerial and field surveys should be transferred to a geographical information system (GIS) for the analysis and assessment of the data (spatial and temporal development) and in combination with other GIS based information.

The data should be reported as they were measured:

• area of the bed (and/or the single patches within a bed) (km²)
• seagrass coverage of the bed (or single patches) (%)

A description of the applied methods should also be reported. If available the accuracy of the data should be included in reporting.

[NOTE: To be included: a more detailed description of data which have to be delivered to the TMAP Data Units. See also: TMAP Data Handling Manual].

11 Quality assurance

Appropriate monitoring protocols should be developed on national level. Intercalibration exercises should be carried out nationally and in the framework of the TMAP.

[to be included: reference to existing QA procedures and SOP]

12 Monitoring authorities

Denmark

Danmarks Miljøundersøgelser (DMU, NERI)

Miljøministeriet, Miljøcenter Ribe

Germany

Landesbetrieb für Küstenschutz, Nationalpark und Meeresschutz (LKN)

Nationalparkverwaltung Niedersächsisches Wattenmeer (NLPV)

Niedersächsischer Landesbetrieb für Wasserwirtschaft, Küsten- und Naturschutz (NLWKN)

Netherlands

Rijkswaterstaat Waterdienst, Lelystad

13 Literature

Adolph, W., S. Jaklin, M. Meemken & H. Michaelis, 2003: Die Seegrasbestände der niedersächsischen Watten (2000 – 2002), Dienstber. Forschungsstelle Küste 1/2003 -- 1-19 Norderney.

Kastler, T. & H. Michaelis, 1997: Der Rückgang der Seegrasbestände im niedersächsischen Wattenmeer. Ber. Forsch.-Stelle Küste Norderney 41: 119 - 139.

Koppejan, H., A.H. Groeneweg & B.J.M. Jansen, 2001: Standaardvoorschift macrophytobenthos kartiering in de Waddenzee en Oosterschelde. Ministerie von Verkeer en Waterstaat – Meetkundige Dienst, rapport MD-GAE-1002. 24 Juni 2001, 38 pp.

OSPAR, 1997c: JAMP Eutrophication Monitoring Guidelines: Benthos (9/6/97), 12 pp.

Reise, K., 2001: Algen und Seegras: grüne Matten und Wiesen im Watten. In. Wattenmeermonitoirng 2000. Schriftenreihe des Nationalparks Schleswig-Holsteinisches Wattenmeer.

Reise, K., M. van Katwijk, D. de Jong, A. Schanz. & Z. Jager, 2005: Seagrass, In: Essink, K., Dettmann, C., Farke, H., Laursen, K, Lüerßen, G., Marencic, H. & W. Wiersinga (Eds.): Wadden Sea Quality Status Report 2004. Wadden Sea Ecosystem No. 19. Trilateral Monitoring and Assessment Group, Common Wadden Sea Secretariat, Wilhelmshaven, Germany.

Schanz, A., & K. Reise, 2005: Seegras-Monitoring im Schleswig-Holsteinischen Wattenmeer, Forschungsbericht zur Bodenkartierung ausgewählter Seegraswiesen im Schleswig-Holsteinischen Wattenmeer 2003, im Auftrag des Landesamtes für Natur und Umwelt des Landes Schleswig-Holstein, Flintbek, 1-25.

Stelzer, K., Brockmann, C. & J. Geißler, 2007: Abschlussbericht OFEW – Operationalisierung von Fernerkundungsmethoden für das Wattenmeermonitoring. Version 1, Überarbeitungsdatum 10.09.2007.

TMAP ad hoc expert group seagrass monitoring, 2006: Draft TMAP Guidelines.

Wadden Sea Plan 2010.: 18 March 2010, pp.88.