Macrobenthic molluscs from a marine - lagoonal environmental transition in Lesvos Island (Greece)

Abstract Background This paper describes an occurence dataset, also including numerical abundance and biomass data, pertaining to the macrobenthic molluscan assemblages from a marine - lagoonal environmental transition. The study system was the soft-substrate benthoscape of the area of the Kalloni solar saltworks (Lesvos Island, Greece). Specifically, the study area extended from the infralittoral zone of the inner Kalloni Gulf (marine habitat) to the bottoms of the first two evaporation ponds of the Kalloni solar saltworks (lagoonal habitat). Bottom sediment samples (3 replicates) were collected with a Van Veen grab sampler (0.1 m2) at four sampling sites, along a 1.5 km long line transect that spanned the marine - lagoonal environmental transition. A total of four surveys were carried out seasonally in 2004. A total of 39,345 molluscan individuals were sorted out of the sediment samples and were identified to 71 species, belonging to the Gastropoda (36), Bivalvia (34) and Scaphopoda (1) classes. Numerical abundance and wet biomass (with shells) data are included in the dataset. New information The dataset described in the present paper partially fills a significant gap in the scientific literature: Because ecological research of coastal lagoons has seldom explicitly considered the marine - lagoonal habitats interface, there are no openly accessible datasets pertaining to the particular structural component of the transitional waters benthoscapes of the Mediterranean Sea. Such datasets could prove valuable in the research of the structure and functioning of transitional waters benthoscapes. The present dataset is available as a supplementary file (Suppl. material 1) and can also be accessed at http://ipt.medobis.eu/resource?r=kalloni_saltworks_phd.


Introduction
Transitional waters (e.g. estuaries, coastal lagoons) may be considered as "ecotone ecosystems" that structurally and functionally link marine, continental and freshwater ecosystems along the coastline (Levin et al. 2001, Basset et al. 2012. Their existence along the interface between the sea and the land determines their abiotic environment, which is characterized by complex spatial gradients in structural features and pronounced temporal variability (Little 2000). The often extreme in magnitude and variability abiotic factors control the composition and spatial distribution of the biota (Barnes 1980, Guelorget and Perthuisot 1992, Barnes 1994. Macrobenthic invertebrates are considered as a key group among the biota in all coastal aquatic ecosystems (Levin et al. 2001). Molluscs are an important component of the macrobenthic fauna of coastal lagoons (Barnes 1994). Their abundance and diversity are also important in the lower salinity ponds of solar saltworks (e.g. Britton and Johnson 1987, Pavlova et al. 1998, Vieira and Amat 1996, where the habitat is considered to be essentially lagoonal. The response of molluscan communities to the environmental stress gradients has been extensively studied in coastal lagoons (e.g. Guelorget and Perthuisot 1992, Koutsoubas et al. 2000, Reizopoulou and Nicolaidou 2004, Rossi et al. 2006, as well as in the lower salinity ponds of solar saltworks (e.g. Evagelopoulos and. Ecological research of coastal lagoons has seldom explicitly considered the marine -lagoonal habitats interface (but see de Wit 2011). However, the interfaces between habitat patches are considered to be among the primary structural and functional components of landscapes (Turner and Gardner 2015). Their importance lies in the fact that they may modulate flows of materials, energy, organisms or information across the landscape, potentially also affecting processes inside the interacting habitat patches (Pickett andCadenasso 1995, Wiens et al. 1985).
This paper describes an occurence dataset, also including numerical abundance and biomass data, pertaining to the macrobenthic molluscan assemblages from the marine -lagoonal environmental transition at the area of Kalloni solar saltworks (Lesvos Island, Greece). The present dataset paper partially fills a significant gap in the scientific literature, as no openly accessible datasets from case studies of marine -lagoonal habitats interfaces have been published thus far and such datasets could prove valuable in the research of the structure and functioning of transitional waters benthoscapes.

General description
Purpose: This dataset was assembled in the framework of the PhD thesis of Dr. Athanasios Evagelopoulos (Department of Marine Sciences, University of the Aegean, Greece) (Evagelopoulos 2008).

Project description
Title: Macrobenthic molluscs from the marine-lagoonal environmental transition at the area of Kalloni saltworks (Lesvos Island, Greece).

Study area description:
A detailed description of the study area is provided by  and can be summarized as follows: The study area is characterised by a shallow water column (approx. 0.5 m deep), a softsubstrate bottom and a benthic vegetation of macroalgae and phanerogams (e.g. Cladophora sp., Enteromorpha sp., Gracilaria sp., Ruppia sp.). The habitat types according to the environment ontology of EnvO (Buttigieg et al. 2013, Buttigieg et al. 2016) occuring in the study area included the "neritic sub-littoral zone" (sampling site 1), the "artificial channels" (site 2) and the "lagoons" (sites 3 & 4). Macroalgal mats were developed at the inlet and in the ponds during the late spring -early summer of 2004. Wind forcing together with the shallow depth of the water column were the main factors involved in the recurrent bottom sediment resuspension and the high water turbidity that wereoften observed in the study area. The bottom sediment at the inlet and the ponds was anoxic near its surface, due to the high productivity of the ecosystem. Macroalgal growth led to a dystrophic crisis incident in the study area in the summer of 2004.
Funding: This dataset was assembled in the framework of the PhD thesis of Dr. Athanasios Evagelopoulos, which was supported by a PhD scholarship from HERACLITUS: Research scholarships with priority in basic research (2nd Operational Programme for Education and Initial Vocational Training, 3rd CSF) that was funded by the Greek Ministry of Education and co-funded by the ESF (EU).
Authoring of the present data paper and data management and upload to the MedOBIS IPT were supported by the LifeWatchGreece infrastructure (MIS 384676), funded by the Greek Government under the General Secretariat of Research and Technology (GSRT), National Strategic Reference Framework (NSRF).

Sampling methods
Study extent: The study area ( Fig. 1) consisted of the soft-substrate benthoscape of the area of the Kalloni solar saltworks (Lesvos Island, Greece). It extended from the infralitoral zone of the inner Kalloni Gulf (marine habitat) to the bottoms of the inlet and the first two evaporation ponds of the Kalloni solar saltworks (lagoonal habitat). The spatial extent of the study was thus approximatelly 1.5 km long, whereas its temporal extent was one year. The geographic coordinates of the sampling sites are given in Table 1.

Sampling site
Site description Latitude (DD) Longitude (DD) Sampling description: The field and laboratory methodology used followed the one described by Eleftheriou and Moore (2005). Bottom sediment samples (3 replicates) were collected with a Van Veen grab sediment sampler (0.1 m sampling surface area) at four sampling sites that were located along a line transect that spanned the marine-lagoonal environmental transition. The sampling sites ( Fig. 1) were located at the infralittoral zone of the inner Kalloni Gulf (site 1), at the inlet channel of the saltworks (site 2) and at the first two evaporation ponds of the saltworks (sites 3 and 4, respectively). The surveys were seasonal and carried out in February, May, September and November of 2004.
Geographic coordinates of the sampling sites.

Quality control:
• Species identification was reviewed by a molluscan taxonomy expert (Prof. Drosos Koutsoubas) and the species names were checked using the Taxon Match tool of the World Register of Marine Species (http://www.marinespecies.org/ aphia.php?p=match). Dimitra Mavraki and Matina Nikolopoulou of the LifeWatchGreece Core Team assisted in the management of data and the upload of the dataset to the MedOBIS IPT according to the DarwinCore schema (DwC).
Step description: After their collection, the sediment samples were washed onsite through a 0.5 mm mesh sieve and subsequently fixed with 5% formalin and stained with Rose Bengal. In the laboratory, the macrobenthic invertebrates were sorted out of the sediment, and classified first into families and then into species. The individuals of each species in each sample were enumerated and their total wet weight (with shells) was measured with a high precision (0.1 mg) balance. During the data management process, the species names were checked with WoRMS, the dataset was prepared according to the Darwin Core standard and, finally, the data were uploaded to the MedOBIS IPT.

Geographic coverage
Description: The geographic coverage of the dataset extends from the part of the inner Kalloni Gulf that is adjacent to the Kalloni solar saltworks to the first two evaporation ponds of the saltworks. A map of the study area is given in Fig. 1   A map of the study area, indicating the sampling stations.

Taxonomic coverage
Description: The taxonomic coverage of the dataset is limited to the molluscan assemblages of the study area. Specifically, the dataset includes gastropod, bivalve and scaphopod species. A list of the species included in the dataset, also indicating their taxonomic classification, is given in Table 2.  The distribution of species number in the bivalve and gastropod families is presented in Fig. 2 and Fig. 3 respectively. Fustiaria rubescens (Deshayes, 1825), which belongs to the Fustiariidae family, is the only species of tusk shells included in the dataset.   Description: The dataset includes two files: Events and Occurences. The former contains the information on the sampling design, whereas the latter contains primarily the species abundance, biomass and taxonomy information.

Column label Column description
eventID An identifier for the set of information associated with an Event (something that occurs at a place and time).
samplingProtocol The name of, reference to, or description of the method or protocol used during an Event.
sampleSizeValue A numeric value for a measurement of the size (time duration, length, area, or volume) of a sample in a sampling event. sampleSizeUnit The unit of measurement of the size (time duration, length, area, or volume) of a sample in a sampling event.
eventDate The date-time or interval during which an Event occurred. year The four-digit year in which the Event occurred, according to the Common Era Calendar.
month The ordinal month in which the Event occurred. day The integer day of the month on which the Event occurred.
habitat A category or description of the habitat in which the Event occurred.
fieldNumber An identifier given to the event in the field.
locationID An identifier for the set of location information. locality The specific description of the place.

minimumDepthInMeters
The lesser depth of a range of depth below the local surface, in meters.

maximumDepthInMeters
The greater depth of a range of depth below the local surface, in meters.

locationRemarks
Comments or notes about the Location.

Abundance and biomass variability
The contributions of the most important species in the mean total abundance (ind./sample) for each site and seasonal survey are given in Fig. 4 .
The most important species in terms of abundanceduring all surveys, were the cerithiid gastropod Bittium reticulatum at site 2 and the mud snail Hydrobia acuta at sites 3 and 4.
The contributions of the most important species in the mean total biomass (g/sample) for each site and seasonal survey are presented in Fig. 5. The most important species in terms of abundance were selected as the ones contributing in at least 10% of the total mean abundance in a dataset sample.
In terms of biomass, the most important species at site 2 was, during all surveys, the cerithiid gastropod Bittium reticulatum, whereas the most important species at sites 3 and 4 were, during all surveys, the bivalves Abra segmentum and Cerastoderma glaucum and the gastropods Cyclope neritea and Potamides conicus.

Observed species diversity variability
The spatial variability of the observed species diversity and eveness during each seasonal survey are given in Figs 6, 7, 8, 9. Contributions of the most important species in the mean total biomass (g/sample) for each site (1, 2, 3, 4) and seasonal survey (WI: winter, SP: spring, SU: summer, AU: autumn) .
The most important species in terms of biomass were selected as the ones contributing in at least 10% of the total mean biomass in a dataset sample. Variability of the observed species diversity and eveness along the sites (1, 2, 3, 4) transect during the winter (WI) survey. Diversity was measured using the Hill numbers N0, N1 and N2, whereas eveness was measured with the F2/1 index.
Observed species diversity was measured with the Hill numbers (Hill 1973 ) N0 (= species richness), N1 (= the exponential form of the Shannon-Wiener entropy index) and N2 (= the Figure 7. Variability of the observed species diversity and eveness along the sites (1, 2, 3, 4) transect during the spring (SP) survey. Diversity was measured using the Hill numbers N0, N1 and N2, whereas eveness was measured with the F2/1 index.

Figure 8.
Variability of the observed species diversity and eveness along the sites (1, 2, 3, 4) transect during the summer (SU) survey. Diversity was measured using the Hill numbers N0, N1 and N2, whereas eveness was measured with the F2/1 index. Figure 9.
Variability of the observed species diversity and eveness along the sites (1, 2, 3, 4) transect during the autumn (AU) survey. Diversity was measured using the Hill numbers N0, N1 and N2, whereas eveness was measured with the F2/1 index. reciprocal form of the Simpson concentration index), whereas eveness was measured using the F2/1 eveness index (Alatalo 1981), a transformation of the N2/1 eveness index of Hill (Hill 1973). All the aforementioned indices have several desirable properties and are preferable to the classic diversity (e.g. the Shannon-Wiener index) and eveness (e.g. the Pielou index) indices (Jost 2006, Tuomisto 2010, Tuomisto 2012. The maximum observed species richness (N0 index) was measured either at site 1, 2 or 3, depending on the season, whereas the minimum was invariably measured at site 4. The minimum observed diversity (N1, N2 indices) was invariably recorded at site 2, due to the minimum of eveness measured therein (F2/1 index).