Ecology of marine landscapes and habitats:

Report of field work in Ria de Formosa

Ines Haberle

EMBC 2012/2013

June, 2013

1

Introduction

Habitat mapping is a multidisciplinary approach for addressing spatial distribution of

habitats and projecting it on a 2D map. It generally combines geophysical and biological data,

used to map not only the physical environment but also the associated community types. The

limitation of this approach is that it cannot be used for extensive areas since biological data

are generally lacking at a large scale.

To overcome this problem, Roff and Taylor (2000) developed the concept of marine

landscapes which allows to map habitats relatively fast without using biological data. The

concept is based on the assumption that there is a link between abiotic and biotic elements

and that geophysical data can be used as a proxy for biological data. Because the approach

serves as an alternative for habitat mapping, the defined marine landscapes must assure that

they are biologically relevant, i.e. they have to be supported with biological information. This

biological data is usually derived from real biological samples on the one hand and from

sediment parameters on the other hand.

Another important term of addressing biotic-abiotic connection was first introduced

in 1908 by Frederik Dahl as "the biotope of a biocenosis". During the last 20 years, its meaning

has evolved in several directions. Nowadays, biotope is recognised as a fundamental

organizational unit of coastal ecosystems, consisting of two main components: physical

'habitat' and its biological 'community‘. The first component is defined by the environmental

factors and has three structural parameters - heterogeneity, complexity, and the definition

scale. The second component refers to species composition which depends on their access to

the habitat and on other biological requirements. But not only living organisms themselves

can be considered as biological features. Rather, these include also the signs of any biological

activity such as empty shells, faecal pellets, burrows, or traces (Olenin and Ducrotoy 2006).

In this study, the biotope approach was used to address habitat composition of a

sandy muddy tidal flat in Ria Formosa. The most important abiotic factor was sediment type,

followed by wetness and slope. For the biotic component seagrass and shell coverage were

observed, along with presence of algae.

2

Study area

Ria de Formosa is a lagoon system in south of Portugal, placed along the eastern

coast of the Algarve Region. It streches from from Faro in the west to Tavira in the east,

covering the area of around 110 km2 (Figure 1a). This large mesotidal multi-inlet barrier

system has average depth of 4 meters and is characterized by sand and mudflats that are

exposed during low, and submerged during high tide. Tides play an important role in

functioning of this system. Tidal dynamics is highly connected with sediment dynamics,

controlling inflow of the sediments in and out of the lagoon. The representative constituent of

tides in Ria Formosa is principal lunar semi-diurnal (M2) constituent, resulting in two high and

two low waters each day. (Dias and Sousa 2009)

Figure 1 The Ria Formosa Lagoon (a) and location of our study area (b). Letter T indicates the position

of the transect. (Adapted from: (a) Dias and Sousa 2009; (b) Google Maps)

Our study site is located on the western part of Ria Formosa, nearby the Faro Airport (Figure

1b). It is a sandy muddy tidal flat sized about 100 meters is lenght. Towards the water there is

a slight slope, making the upper sandy part of the flat dryer than the lower muddy part. The

study site is partially covered by terrestrial grass that appears in two patches, one large and

one small. Our observing and sampling took place on 18th of April from 13h to 15h, during low

tide.

3

Materials and methods

During the field work few different techniques were used in order to determine

present biotopes. They can be divided in two main groups: Sampling and Describing.

Sampling. The sampling strategy was a transect. The choice of transect direction and length

was random, but was based on quick pre-observation of the study area, in order to enable

addressing the gradient of biotopes. Selected transect was oriented from the upper part of the

tidal flat (high tide line) towards the water level during the low tide. The length of the transect

was about 12 meters and the sampling was done on 5 sites along it, approximately every 3

meters (Figure 2). The first (0th meter) and the last three (6th, 9th, 12th m) sampling sites

corresponded with potential biotopes. One additional sampling was made on 3rd meter (noted

as Sample 2), as it looked like an intermediate biotope (Appendix, Sampling site 2 figures). At

each site, two random photo shoots were taken, using a 50 cm ruler as a scale. Also,

organisms from those areas were sampled in a plastic bag, separately for each sampling site.

Next day, organisms were identified in the lab using different identification guides/keys and

with generous help and contribution of the University staff. The list of sampled organisms is

presented in Table 1.

Figure 2 Transect overview. White horizontal lines correspond to specific sampling sites.

0m

3m

6m

9m

12m

4

Biotope Description. During the sampling, extra notes about geophysical and biological

characteristics of sampling sites were taken. Along with this notes, photo shoots were used to

describe coverage in more details. For organism assemblage comparison, the presence of each

species at different sites was taken into account. The species data was analysed with PRIMER

software, providing similarity matrix, cluster and multidimensional scaling plot. All before

mentioned results helped in identifying individual biotopes. The sampling site was considered

as a separate biotope if the scale of unique feature (e.g. shell gravel, algal mats) was 2x2m

area at least.

Results and Discussion

Transect overview. Looking at the transect from a distance, I could recognize 4 different

zones when moving from the upper part towards the water level. These were the pre-

observed, potential biotopes where sampling was made. As mentioned before, I took one

additional sample between first and second biotope. It looked like an intermediate biotope,

and I wanted to see whether it is a part of adjacent biotope or if it can be considered as a

separate one as well.

Table 1 The list of sampled organisms and their presence/absence at specific sampling sites

Phylum - Class Species Sampling site

1 2 3 4 5

Mollusca - Gastropoda

Gibbula umbilicalis + +

Mesalia varia + +

Monodonta sp. +

Nassarius pfeifferi + + +

Nassarius reticulatus +

Columbella rustica +

Conus ventricosus +

Mollusca - Bivalvia Anomia ephippium +

Cerastoderma edule +

Arthropoda - Crustacea Barnacle +

Chlorophyta

Ulva sp. + + + +

Ulva enteromorpha var. Intestinalis

+ + +

Phaeophyceae Fucus spiralis +

Angiosperms Zostera noltii + + + + +

Terrestrial grass +

5

Biotope identification. To visually identify different biotopes along the transect, sediment

type, colour and wetness were chosen as dominant physical features. Dominant biological

features were seagrass and shell coverage. Secondary features that could help in determining

biotopes were slope as abiotic and presence of algae as biotic factor.

According to before mentioned characteristics, 4 potential biotopes could have been visually

observed, on Sampling sites 1, 3, 4 and 5. These are: muddy sand with shell coverage, muddy

sand with seagrass and algal and coverage, semi-dry mud with terrestrial grass and dry

seagrass and algae, and deep wet mud with seagrass coverage. There is one intermediate

biotope on the Sampling site 2 that has muddy/sandy sediment and both algal and shell

coverage.

Describing sampling sites and biotopes based on species samples and photo shoots.

Here, a more detailed description of each sampling site and potential biotope is provided. It is

based on sampled organisms (Table 1) and photo shoots that can be found in the Appendix at

the end of this report.

Sampling site 1

The first sampling site was located on the upper part of the transect, about 20 meters from

the low tide water line. It is characterized by brownish muddy sand sediment that is drier than

the rest of the transect. The flat sediment is covered with bivalve and gastropod shells and a

bit of gravel. There are few fragments of Zostera noltii leaves, probably delivered during the

high tide. No algae were found on this site. Based on the photo shoots, shells make 50% of the

total coverage.

Sampling site 2 – intermediate biotope

At first look, it seems like this site has the same features as the Sampling site 3. But when

examined in detail, I found that it also shares some physical and biological characteristics with

Sampling site 1. The base is brown coloured mud, but the coverage is transitioning towards

the seagrass and algal dominance with visibly less shell gravel. The statistical analysis of the

samples gives more information on similarity between this intermediate sampling site and its

surrounding ones (Figure 3). This helps to determine whether it can be considered as a

separate biotope or not, which is discussed later.

As seen on the pictures, seagrass coverage takes around 40%, algal 20%, and shells 10% of the

surface. All animal organisms found on this site belong to Gastropod class.

Sampling site 3

Moving closer to the water level, the sediment gets wetter and darker. On the 6th meter of the

transect, the sediment is homogenous, dark brown mud. It is not visible due to thick algal mat

lying on Zostera noltii patch. There are no animal traces on surface, but we could probably

expect infaunal species that are burrowed in the mud.

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80% of the coverage consists of filamentous green algae Ulva enteromorpha var. intestinalis.

The rest is the contribution of Zostera noltii and a different Ulva species (leafy).

No animals or their remains were found and collected at this sampling site.

Sampling site 4

This was visually the most distinct sampling site. The reason was the presence of terrestrial

grass creating an ‘island’ in surrounding muddy sediment. The size of the grass patch was

around 5m2 so I consider it as a separate biotope. The sediment is black mud that is semi-dry

due to a slight flat elevation in comparison to adjacent biotopes. Except terrestrial grass that

makes more than 60% of the coverage, the rest are dried algae fragments: Fucus spiralis

(30%), Zostera noltii (<10%) and Ulva sp. (10%). Only two animal species were found, one of

them being present only in this biotope (Monodonta sp.).

Sampling site 5

The last part of the transect was closest to the water and is highly impacted by water

movement during tide changes. This is probably the reason why not so much algal coverage

was found – it was moved by the water. The sediment here is mud, it is the deepest of all

transect, and its colour is black. 90% of the coverage is Zostera noltii, with the rest being

filamentous and leafy Ulva species. There was one gastropod species found on this site

(Nassarius pfeifferi), probably transported by tidal movement from the upper part of the

transect.

Similarity analysis. With the help of PRIMER software I compared samples from all sampling

sites along the transect. The results of all analyses performed on the collected data are shown

on Figure 3.

As seen from the similarity matrix and clustering, the most similar sampling sites are 3 and 5,

with the similarity over 85%. This results are based on biological features only (presence of

seagrass, algae coverage, no animals), but if we compare the physical features as well –

muddy sediment, wetness, light slope - we could say this two are really the same biotope. The

only difference is the amount of algal coverage, which can be due to transport of algae during

tidal water movement.

Site 2 is as assumed more similar to site 3 than to site 1, due to presence of floral coverage,

but still differs in sampled animals. Although it may be considered as a different biotope, no

appropriate unique EUNIS habitat unit was found.

Sample sites 4 and 1 are the most distinct from all others. Both of them can be considered as

different biotopes, because of terrestrial grass presence, and absence of any plant coverage,

respectively. The MDS plot confirms the given analysis, putting Samples 3 and 5 closer, while

Samples 1 and 4 are far apart.

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Figure 3 Results of PRIMER analyses: similarity matrix (a), cluster (b) and multidimensional scaling plot

(c).

Biotope identification and the relation to EUNIS classification. After samples and photo

shoots were analysed, I concluded that along the chosen transect there are 3 distinct, and one

intermediate biotope. An overview of sampling sites, correspondent biotope, and the nearest

EUNIS habitat classification are presented in Table 2. *

Table 2. Sampling sites, correspondent biotope and its nearest EUNIS habitat type

Site Biotope Nearest EUNIS classification*

1 Muddy sand with bivalve and gastropod shell fragments

A2.242 [Cerastoderma edule] and

polychaetes in littoral muddy sand

2 Mud with combination of Zostera noltii, algal and shell fragments coverage

Intermediate between A2.242 and A.26111

3 Mud with Zostera noltii beds and algal

coverage A2.6111

[Zostera noltii] beds in littoral

muddy sand

4 Terrestrial grass patch with algal and seagrass fragments

A2.5 Coastal saltmarshes and saline

reedbeds

5 Mud with Zostera noltii beds and algal

coverage A2.6111

[Z. noltii] beds in littoral muddy

sand

*Source: European Environment Agency (EEA) - European Nature Information System (EUNIS):

Habitat types. http://eunis.eea.europa.eu/habitats.jsp. Accessed on 4th of May 2013.

b) c)

a)

8

Conclusion

The main goals of the field work in Ria Formosa tidal flat was to get experience in

identification of biotopes, practice how to describe them correctly and improve sampling

methodology.

The sampling strategy was a transect, and notes and samples (biological, photo shoots) were

taken on 5 distances. Integration of lab, computer and descriptive data analysis resulted in

identification of 3 distinct and one intermediate biotopes:

- Muddy sand with bivalve and gastropod shell fragments

- Muddy sand with combination of Zostera noltii, algal and shell fragments coverage

(intermediate biotope)

- Mud with Zostera noltii beds and Ulva coverage

- Terrestrial grass patch with dry algal and Zostera noltii fragments

This results show expected number of biotopes, but their distribution slightly differs from my

initial proposal. I assumed sites 1, 3, 4 and 5 are all different, but the analysis showed that

sites 3 and 5 can be considered as a same biotope. Also, I assumed sampling site 2 was a part

of adjecent biotope, while in fact it can be considered as a separate one.

For all four described biotopes equivalents have been found in EUNIS classification system.

As the biotope identification and description was done by inexperienced person, some

mistakes in process could be found. Nevertheless, the general view on tidal flat biotopes

presented here should be correct and any further work on this specific subject could use this

data as a starting point.

References

Dias J.M., Sousa M. (2009) Numerical modeling of Ria Formosa tidal dynamics. Journal of

Coastal Research, SI56, 1345-1349

European Environment Agency (EEA) (2007) European Nature Information System (EUNIS):

Habitat types. http://eunis.eea.europa.eu/habitats.jsp

Olenin S., Ducrotoy J-P. (2006) The concept of biotope in marine ecology and coastal

management. Marine pollution bulletin, 53, 20-29

Roff J.C., Taylor M.E. (2000) Viewpoint: National frameworks for marine conservation — a

hierarchical geophysical approach. Aquatic conservation and freshwater ecosystems,

10, 209-223

i

Appendix - Sampling site photo shoots (2 per site)

Sampling site 1

ii

Sampling site 2

iii

Sampling site 3

iv

Sampling site 4

v

Sampling site 5