Study of the Spatiotemporal Variability of Oceanographic Parameters and Their Relationship to <i>Holothuria</i> Species Abundance in a Marine Protected Area of the Mediterranean Using Satellite Imagery

Marine protected areas (MPAs) are designated to protect marine ecosystems and, among other things, to monitor climate variability, which in turn affects aquatic species. The aim of this study is to examine the contribution of remotely sensed data as an indication of Holothuria abundance, by investigating the spatiotemporal variability of physicochemical parameters. The study area is in the National Marine Park of Alonissos Northern Sporades, which is included in the NATURA 2000 network. Firstly, the abundance of Holothuria species was measured by scuba diving. At the same time, depth profiles of five physicochemical parameters (temperature, salinity, pH, dissolved oxygen and Chl-a) were recorded by CTD (conductivity, temperature, depth), a primary instrument used to determine the essential physical and chemicals properties of seawater column profiles in the coastal zone. The physicochemical variables examined are the most common environmental parameters with the highest impact on growth, reproduction, productivity and survival rate of sea cucumber species, affecting the availability of food sources. Analysis of this data allows us to identify parameters which are essential for their existence. The analysis showed that only temperature and Chlorophyll-a (Chl-a) could be useful for identifying the abundance. These two parameters are readily available from satellite data. Additionally, particulate organic carbon (POC) is essential for Holothuria’s existence. Consequently, a time series of satellite data products from Terra/MODIS sensor were utilized from 2000 to 2020 for sea surface temperature (SST), Chl-a and POC. The monthly temporal trend shows that the abundance could be justified in areas where the Holothuria presence has been established. Monthly spatiotemporal analysis shows that SST, Chl-a and POC availability, could be an indication of the differences in abundance recorded

Population Characteristics of the Mid-Littoral Chthamalid Barnacle C. stellatus (Poli, 1791) in Eastern Mediterranean (Central Greece)

Barnacles are key space-occupiers in rocky shore communities on European coasts. Barnacles of the species Chthamalus stellatus (Poli, 1791) were collected between June 2014 and May 2015 from two sites, two stations per each site with varying degree of exposure to wave action and anthropogenic pressure (trampling), in the Eastern Mediterranean (Pagasitikos Gulf, Central Greece). This study addresses a knowledge gap in population characteristics of C. stellatus populations in the Eastern Mediterranean, assessing population structure and allometric relationships. Patterns of distribution and abundance (density and percentage cover) were studied both temporally (seasonally) and spatially (water level and site). Morphometric characteristics exhibited spatiotemporal variation. Population density was significantly higher at the site with higher wave exposure. The population cover exhibited high levels of similarity among shore levels, both spatially and temporally. Spatial distribution exhibited a clumped pattern of dispersion in autumn, winter, and spring, mainly in the sheltered site. Six dominant age groups were identified, with the dominant cohort in the third-year class. Significant negative allometric relationships were exhibited between all morphometric characteristics. Differences in growth patterns among populations were indicated, with a higher rate of growth at the site of lower wave exposure

Population Characteristics of the Upper Infralittoral Sea Urchin Arbacia lixula (Linnaeus, 1758) in Eastern Mediterranean (Central Greece): An Indicator Species for Coastal Water Quality

The black sea urchin (Arbacia lixula, Linnaeus, 1758) is a non-edible marine echinoderm of high ecological importance with the potential to affect marine ecological communities. A. lixula were sampled monthly for one year from the supralittoral fringe at two locations in the Pagasitikos Gulf, in the north-western Aegean Sea. Morphometric characteristics exhibited significant spatiotemporal variation. The population in closer proximity to treated sewage effluent outflow exhibited significantly higher biometric relationships resulting in possible improved physiological conditions. Spatial distribution exhibited a clumped pattern of dispersion, consisting of predominantly six age classes. The dominant cohort was the four-year age class, comprising 31.2% of the total population. Significant negative allometric relationships were exhibited between all morphometric characteristics. The maximum approximate age of the total A. lixula population was estimated at 15.27 years. The von Bertalanffy growth equation for the entire population was estimated as: test diameter = 62.881&times;1&minus;e&minus;0.196&times;Age+1.147. The gonadosomatic index indicated a seasonal cycle with a peak in late spring. The approximate age of sexual maturity was estimated at 4.45 years. We observed a significantly higher number of females than expected at the site in closer proximity to the treated sewage effluents (32% of total female number)

Population dynamics and reproduction of Holothuria tubulosa (Holothuroidea: Echinodermata) in the Aegean Sea

The Atlanto-Mediterranean holothurian Holothuria tubulosa is among the conspicuous benthic invertebrates in the shallow sublittoral zone. It is an edible species, harvested at the Aegean Sea and utilized as fishing bait. Considering the lack of information for the Aegean populations, a one-year survey, based on monthly or semimonthly samples, was carried out focusing on population structure, allometric relationships and reproductive status of H. tubulosa stocks in Pagasitikos Gulf Population density varied around 9.93 individuals/100 m(2). This value was rather low compared with other studied Mediterranean populations of the species, possibly due to the scarcity of seagrass meadows in the area studied. All measured biometric characters showed high plasticity, and all the examined morphometric relationships followed negative allometry indicating a change to the shape of the animal's body as it grows. Holothurians' length was a moderate predictor of biomass since r values reached 60%; in contrast a very strong relation was observed between drained and gutted weight. Size-frequency distribution analysis was unimodal with the exception of spring where a second mode of larger sized individuals appeared. The gonadosomatic index showed a single spawning season per year, in late summer; accordingly the reproductive cycle of the species showed a clear annual pattern which was highly correlated with the seasonal variations of temperature

Mussel farming impacts on trophic status and benthic community structure in Maliakos Gulf (Eastern Mediterranean)

The impact of shellfish farming on the water column nutrient concentration and the benthic community structure was investigated seasonally at a mussel farm (Mytilus galloprovincialis L.) of Maliakos Gulf (Eastern Mediterranean). In most cases concentration of nutrients and chl a at the farm site was lower than those observed at the control sites. Statistical analysis in concentration of all nutrients and chl a indicated significant interactions between sites and seasons, which in all cases were temporal. Furthermore, no significant interactions were found between sites and seasons for all sediment and benthic community parameters, except for Shannon-Wiener diversity index and species richness. The significant interactions detected in the biotic data were temporal. Analysis of similarity and similarity percentages analysis revealed a certain fluctuation of benthic macrofaunal community during the overall sampling year mainly due to temporal rather than spatial effects. Cluster analysis and multidimensional scaling ordination plot indicated the clearly separation of the farm site and the control sites in most of the seasons. K-dominance curves showed small difference in elevation and overlap indicating minimal difference in biological stress between the farm site and the control sites. All the above indicates that probably the farming of mussels was beneficial for the trophic status of Maliakos Gulf and that there was a minimal environmental stress caused by the shellfish farming for the surrounding benthic environment