SEASCAPE-BASED MODELING OF BENTHIC HABITATS SPATIAL DISTRIBUTION. CASE STUDY: AVREN PLATEAU...

12th Int. Conference on Marine Science and Technology "Black Sea" 2014

Varna, Bulgaria pp. 175-182., ISSN 1314-0958

1 Eng. Bogdan Prodanov, PhD Student, Institute of Oceanology – Bulgarian Academy of Sciences (IO-

BAS) E-mail: [email protected] 2Iliyan Kotsev, Research Assistant, Institute of Oceanology – Bulgarian Academy of Sciences (IO-BAS)

E-mail: [email protected] 3Assoc. Prof. Eng. Lyubomir Dimitrov, Institute of Oceanology – Bulgarian Academy of Sciences (IO-

BAS) E-mail: [email protected]

SEASCAPE-BASED MODELING OF BENTHIC HABITATS SPATIAL

DISTRIBUTION. CASE STUDY: AVREN PLATEAU SUBLITTORAL

ZONE, BULGARIAN BLACK SEA

Bogdan PRODANOV1, Iliyan KOTSEV

2, Lyubomir DIMITROV

3

ABSTRACT

The study examines the present-day submarine landscape structure of the Avren Plateau

sublittoral zone and its benthic habitat diversity. It is accompanied by GIS-aided landscape

mapping and cartography carried out at scale 1: 50, 000 as well as by analysis of the geo-

components forming the contemporary seabed spatial pattern. Special attention is paid to the

national biotopes related to the lowest taxonomic rank of the underwater landscape

hierarchy, namely the landscape kind.

Keywords: submarine landscape complexes, seabed biotopes, seascape morphologic pattern

1. INTRODUCTION

The seascape approach to studying the

nature of the seafloor is an innovative

interdisciplinary concept in modern-day

marine ecological studies. According to this

notion, the landscape of the seabed comprises

a complex mosaic of habitats (biotopes) that

are interlinked and consistently found

together and thereby forming its spatial

morphologic pattern [1]. Hence, the cited

concept considers the submarine landscape as

a natural complex [2; 3; 4 etc.] that combines

the physical benthic environment and the

contiguous group of floristic, epi- and

infaunal organisms that inhabit the seafloor

[5; 6]. Furthermore, some authors describe the

benthic habitats (biotopes) as the essential

morphologic components of the underwater

landscape complex [7], which implies for the

hierarchic organization of the submarine

nature’s elements into a coherent geo-

ecosystem [8; 9; 10 etc.].

2. DESCRIPTION OF THE STUDY

AREA

The study site encompasses the shallow

sublittoral zone adjacent to the Avren Plateau

coastal area, Bulgarian Black Sea. It stretches

between the southern portion of Varna Bay

near “Karantinata” locality on north and cape

Ilandzhik on south in the vicinity of Kamchia

Depression, reaching maximum depth of 24-

25m. The medio- and sublittoral landscape

complexes within the investigated sector are in

paragenetic relations with the subaereal terrestrial

landscapes of the coastal zone, thereby having

similar lithologic varieties presented by

unconsolidated and solid sedimentary rocks with

Neogenic age, e.g. sandstones, conglomerates,

heterogeneous sands, silts etc. The loose seabed

substrates are additionally diversified by the

presence of gravels with terrestrial origin and

organic debris, e.g. whole and disintegrated shells

of marine invertebrates. The topography of the

seabed comprises abrasive, abrasive-landslide,

structural-abrasive, and structural-accumulative

geomorphic elements with Neogenic and

Quaternary age. Finally, the benthic biota is

presented by floristic, epi- and infaunal coenoses

typical for the Black Sea basin, e.g. algal, mussel

and clam communities, burrowing thalassinids

etc.

3. DATA AND METHODS

Several data sources were used for the

purpose of the present study, e.g. scanned

lithologic, bathymetric and geomorphologic maps

of the seabed adjacent to the Avren Plateau

coastal area, geo-data sets on benthic substrates,

archive bathymetric contours, point ESRI shape

files on benthic biota etc. All these were

integrated, processed and subsequently analyzed

in Arc GIS 9.3.1 environment.


The GIS procedures carried out with

reference to the present study at scale 1:50,

000 involved georeferencing of the scanned

map materials, digitizing of the necessary

map elements and subsequent creation of

graphic ESRI polyline/polygon shape files,

with the accompanying descriptive

information embedded in the attribute tables

etc. These procedures are described more in

detail by Kotsev [11]. Final result of the

activities carried out in GIS environment is

the production of a digital map of the benthic

landscape complexes, whose legend

represents logical hierarchic organization of

the identified submarine landscape complexes

into 4 taxa, namely class, type, genus and

kind, as described by Kotsev [12] and

provided in Figure 1.

The following stage of the study

represents the creation of a geo-dataset of the

seabed habitats using the descriptive data on

benthic substrates and biota embedded in the

attribute table of the already available

submarine landscape-complex dataset. A

correlation among depth, substrate type and

biotic components was performed in Arc GIS

and visualized under the form of a digital

map, provided in Figure 2. The legend of the

map produced was compiled according to the

classification system of the national benthic

biotopes, proposed by Todorova et al. [13].

4. RESULTS

The contemporary submarine landscape

morphologic pattern of the investigated area

comprises 22 landscape kinds (Figure 1),

hierarchically united in 6 genera, 4 types and

2 classes as described by Kotsev [12]. The

area calculations reveal that the greatest

percentage, approximately 70%, of the

investigated sublittoral sector is occupied by

accumulative landscapes in the weakly active

and inactive portions of the sublittoral zone,

while these in the active mediolittoral and

shallow sublittoral sectors encompass less

than 10%.

The benthic habitat diversity includes 10

biotope types, united in 3 groups on the basis of

the underlying substrates (Figure 2). Greatest

areas are occupied by the deeper sublittoral soft-

bottom biotopes, while these of the geogenic reefs

are with much smaller spatial extent. Additional

elements of the seabed represent artificially

created spatial elements, such as areals of

stationary pound nets and mussel farms, which

are of insignificant total area.

5. DISCUSSION AND CONCLUSIONS

The investigation herein represents the first

attempt in Bulgarian marine studies to correlate

the morphologic submarine landscape pattern

with the associated habitats that build-up the

benthic environment. However, due to

imperfections of the geo-data used, which come

as a consequence from the coarse spatial

resolution and the insufficient geographic

coverage, especially when discussing the data

available on seabed biological communities, the

biotopes identified are mainly of predictive nature

and poorly backed by in situ investigations.

Besides, as can be noticed from the map in Figure

2, the submarine landscape complexes usually

contain several biotopes at a time. Therefore, for

correct investigations of the benthic habitat

diversity much finer mapping procedures are

needed at scale 1:5,000 or 1:10,000. Nevertheless,

the proposed seascape-based approach represents

an innovative and effective method for

identification and subsequent hierarchic

classification of the benthic biotopes in the

Bulgarian sector of the Black Sea

ACKNOWLEDGEMENTS

All authors have contributed equally for the

current report, thus our given names are arranged

in alphabetical order.

We would like to express our gratitude to the

colleagues from Department “Biology and

ecology of the sea” at IO-BAS for the provided

point data on benthic biotic diversity.


Figure 1


Figure 2


I. Sandy-bottom biotopes; II. Biotopes with

silty sands and sandy silts; III. Hard-bottom

biotopes; a - Sands with Chamelea gallina; b

- Fine and medium sands with Lentidium

mediterraneum; c - Coarse and medium

mediolittoral sands, exposed to wave activity

with Donacilla cornea and Ophelia bicornis;

d - Infralittoral rocks overgrown by Mytilus

galloprovincialis and Mytilaster lineatus; e -

Coarse and medium shallow sands with

Donax trunculus; f - Shelly sands and gravels

with Modiolus adriaticus и Gouldia minima;

g - Silty sands and sandy silts with Upogebia

pusilla; h - Sands and silty sands with

Chamelea gallina; i - Infralittoral rocks

overgrown by Cystoseira sp.; j - Infralittoral

rocks overgrown by annual communities of

green and red algae;

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