Vafidis D et al. (2021), Abundance and population characteristics of the...

ECB-ART-49166

J Biol Res (Thessalon) 2021 May 21;281:11. doi: 10.1186/s40709-021-00142-9.

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Abundance and population characteristics of the invasive sea urchin Diadema setosum (Leske, 1778) in the south Aegean Sea (eastern Mediterranean).

Vafidis D , Antoniadou C , Voulgaris K , Varkoulis A , Apostologamvrou C .

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BACKGROUND: The Indo-Pacific sea urchin Diadema setosum has invaded the Mediterranean Sea and has spread along many locations in the southeastern part of the basin, where established populations exist on the shallow subtidal rocky shore. Diadema setosum is a ubiquitous species, of particular ecological importance due to the high levels of grazing pressure it imposes on benthic communities. Its biology, however, is not adequately studied, especially along its introduced range of distribution. The present study examines the population status of D. setosum outside its native range, in the Dodecanese island complex, south Aegean Sea. Thirty-four stations located across 16 islands were surveyed by scientific SCUBA-diving (up to a depth of 10 m) in December 2019 and June-July 2020. Samplings included: (i) visual census along transects to estimate relative abundance and population density, and (ii) random collection of specimens from densely populated stations to assess biometry and reproductive condition (histological examination of gonads) of D. setosum. RESULTS: Diadema setosum was found in 21 out of the 34 surveyed stations. The species had sparse populations of well-hidden individuals in rocky crevices, but with dense localized patches in Agathonisi, Leros, Kalymnos, Pserimos, Symi, Alimia and Chalki islands. In those seven islands, mean population density was 2.5 ± 1.48 individuals m-2. Diadema setosum had denser populations in shallower depths but larger dimensions in deeper; these results suggest segregated density and size patterns along a depth gradient. The size structure, according to the size frequency distribution of the test diameter, was unimodal with a fitted mode at 4.0-4.5 and 6.5-7.0 cm in shallow and deep populations, respectively. The examined morphometric relationships followed negative allometry, as previously suggested for the species within its native range of distribution, and test diameter appeared to be a good predictor of biomass. Diadema setosum specimens had immature gonads in winter and mature in summer, suggesting a synchronous reproductive pattern. These results conform to previous data from temperate populations of the species. CONCLUSIONS: Differences in local environmental conditions, e.g. hydrodynamics and habitat type, together with biotic interactions, e.g. recruitment and competition, probably shape D. setosum population in the south Aegean distributional range. The establishment of D. setosum has severe implications on benthic communities and local sea urchin populations demanding management measures to prevent the forecasted further expansion of this invasive species.

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References [+] :

Abdelkarem, Diadema setosum: isolation of bioactive secondary metabolites with cytotoxic activity toward human cervical cancer. 2022, Pubmed, Echinobase

	Fig. 1. Sampling stations and relative abundance of Diadema setosum in the marine area of the Dodecanese island complex. A abundant, F frequent, O occasional, R rare, P present, NP no present
	Fig. 2. Mean population density ± Fisher LSD of Diadema setosum in the densely populated (A, C or F relative abundance grade) islands (left) and in the two depth zones (right) surveyed
	Fig. 3. Mean size (Ht = test height, Dt = test diameter) and biomass (tW = total weight) ± Fisher LSD of Diadema setosum in the densely populated (A, C or F relative abundance grade) islands (left) and in the two depth zones (right) surveyed
	Fig. 4. Mean size (Ht = test height, Dt = test diameter) and biomass (tW = total weight) ± Fisher LSD of Diadema setosum in the densely populated (A, C or F relative abundance grade) islands in the shallower (left) and lower (right) depth distribution of the species
	Fig. 5. Size (Dt = test diameter)—frequency distribution of the studied Diadema setosum population per depth distribution zones surveyed (data were pooled over stations and islands)
	Fig. 6. Size (Dt = test diameter)—frequency distribution of the studied Diadema setosum population per island, in the shallower (top graph) and deeper (lower graph) depth distributional zone of the species
	Fig. 7. Morphometric relationships, weight/test diameter (tW/Dt), weight/test height (tW/Ht) and test height/test diameter (Ht/Dt) of the studied Diadema setosum population (data were pooled over islands and surveyed depths)
	Fig. 8. Reproductive stages according to Bronstein et al. [11] of the studied Diadema setosum population in Dodecanese island complex, observed in December 2019 and July 2020 samplings. A Stage II (recovering): clusters of previtellogenic oocytes formed in the ovarian germinal epithelium which may also occupy the central space of the female gametes. B, C Stage IV (mature): Ovaries (B) and testicular lumen (C) packed with mature ova and spermatozoa, respectively. Oocytes at different maturation stages are distinguished in the germinal epithelium. Ge germinal epithelium, Co coelom, NP nutritive phagocytes, Po previtellogenetic oocytes, Ov ova, Sz spermatozoa, Sc spermatocyte