Succession in megafaunal assemblages of an artificial reef during a three-year monitoring in the Eastern Mediterranean basin
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1
Institute of Fisheries Research, Greece
Introduction: Artificial reefs (AR) are comprehended as a type of refugium which is constructed in the marine environment in the context of species conservation and biocoenose’s productivity. In the Eastern Mediterranean Sea more than 11 structures have been developed with well-established macrofaunal communities (Fabi et al., 2011). Eastern Mediterranean has been characterized as one of the most important sub-basins of the Mediterranean Sea in the framework of species’ invasions, of new colonizations of habitats and of biological impacts on the macrofaunal communities (Giakoumi et al., 2013). The so called tropicalization of the basin, due to the increase of the mean water temperature, has been produced significant changes to the fishes’ and invertebrates’ assemblages and generally to the fisheries’ dynamics and economics. Although the scientific interest for these assemblages is increasing, the relevant information remains poor and dispersed, while long-term monitoring on ARs fish assemblages are little or lacking at all. The aim of the present study is to record the profile of the area, the succession and the bathymetric changes in megafaunal assemblages of an artificial reef during a three-year monitoring, in order to highlight possible faunal dissimilarities.
Material and Methods: The study area includes the AR of Kitros which is located at the marine area of Kitros Pierias at 1.5 n.m. distance from the shore (NW Aegean Sea). It is deployed at 15-18 m depth and occupies an area of 0.044 km2. This area is characterized by hard substratum, whereas the bottom of the protected surroundings (4.4 km2) is consisted mainly by sandy mud. The area is subjected under the influence of three rivers (Aliakmonas River, Axios River and Loudias River), outflowing 15 km north of the AR. Νine field expeditions were conducted for the AR monitoring from summer 2015 to autumn 2017 with a trawlnet, at three different depth ranges: 26.5-29.5m, 30-32.5m και 32-33m. Total catches were identified in species level, and the basic gravimetric parameters were measured in situ from three 30 minutes hauls. Water’s physical parameters were measured in the entire water column at 16 stations with the use of a SBE 19plus CTD. Additionally, water samples were collected from multiple depths at four stations for chlorophyll-a (Chl-a) analysis. Abundance (S), Margalef Divesity Index (d), Brillouin Index, Fisher's α, Pielou Regularity Index (J'), Shannon-Wiener (H') Simpson's Variety (1-Lambda) were calculated for different hauls, depths, seasons and years (PRIMER 6 software).
Results: Freshwater parcels arrived from the north and in most of the cases were detected at the surface water layer up to 7m depth (Fig. 1). The strongest freshwater presence found during spring (Salinity= 26.9-28.39). The salinity is increased to the south as the freshwater progressively mixed with the ambient seawater. Water temperature is following the typical seasonal trend, however is also depends on the degree of the freshwater presence. Thermal stratification begins during late spring-early summer months, becomes more intense during summer and maximizes during fall. The thermocline depth varied between 6 and 30 m and it is depended by seasonality (early summer and fall months, respectively). Regarding chlorophyll-α (chl-α) concentrations, peak values measured at the surface layer of the AR northern part during spring, which coincides with the surface salinity minima and thus can be related to the increased freshwater runoff (chl-α = 7.7-10.4 μg/L). Elevated concentrations were also found at the same area during summer and early autumn (chl-α = 6.2-7.7 μg/L). On the contrary, the deeper layer near to the bottom of southern part is characterized by lower chl-α values (0.1-2 μg/L).
During the three-year observation from the total of the 27 hauls (3 years x 3 seasons x 3 depth zones) 79 species were identified and the Holothuridae taxon. Permutational MANOVA analysis (PERMANOVA) showed strong interaction between season and year as selected factors [P(perm)=0.001<0.05], which means that the seasonal catches depend on the year. This could be attributed to the differences in temperature among the seasons and years. Principal Component Analysis (PCA) showed that the 95.8% of the initial variability can be explained by PC1 (explains the 52.5%) and PC2 (explains 43.3%) whose eigenvalues ranged between 3.68 and 3.03, respectively. Figure 2 shows that stations to the left of PC1 demonstrate higher evenness (equal distribution of abundances) compared to those on the right. With respect to the PC2 axis, the stations on the left of the axis exhibit higher richness while evenness found lower.
Main Conclusions: This study showed that Kitros AR is influenced by the freshwater inputs of the three rivers, whereas its megafaunal assemblage is determined temporally by season and year rather than bathymetrically. Seasonal changes in fish and invertebrate assemblages are depending on how early the temperature rise and therefore the stratification of water, occurs. Temperature is a factor that affects distribution and biological circles of the species at different depths. This variation from year to year, even for short periods of time, explains the measured heterogeneity of our samples.
Acknowledgements
Authors would like to thank the captain and the crew of "Agios Andreas" trawl for the technical support on board and the Artificial Reefs' research team of the Fisheries Research Institute for the processing of the collected material. Funding was provided by the Operational Programme Fisheries 2007-2013 / 2014-2020.
References
Fabi G, Spagnolo A, Bellan-Santini D, Charbonnel E, Çiçek BA, et al. (2011) Overview on Artificial Reefs in Europe. Brazilian Journal of Oceanography, 59 (special issue CARAH): 155-166.
Giakoumi S, Sini M, Gerovasileiou V, Mazor T, Beher J, et al. (2013) Ecoregion-Based Conservation Planning in the Mediterranean: Dealing with Large-Scale Heterogeneity. PLoS ONE 8(10): e76449.
Keywords:
Megafauna,
diversity,
abundance,
Eastern Mediterranean,
artificial reefs
Conference:
XVI European Congress of Ichthyology, Lausanne, Switzerland, 2 Sep - 6 Sep, 2019.
Presentation Type:
Poster
Topic:
ECOLOGY AND LIFE CYCLES
Citation:
Anastasiadou
C,
Kamidis
N,
Vidoris
P,
Kallianiotis
A and
Kallianiotis
A
(2019). Succession in megafaunal assemblages of an artificial reef during a three-year monitoring in the Eastern Mediterranean basin.
Front. Mar. Sci.
Conference Abstract:
XVI European Congress of Ichthyology.
doi: 10.3389/conf.fmars.2019.07.00026
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Received:
04 Jun 2019;
Published Online:
14 Aug 2019.
*
Correspondence:
Dr. Chryssa Anastasiadou, Institute of Fisheries Research, Kavala, Greece, anastasiadou@inale.gr