Monitoring the genetic diversity in holothurian populations from the Italian coasts with mitochondrial DNA sequences.

Sea cucumbers are deposit feeding members of marine benthic communities. The over-exploitation of sea cucumber natural stocks, especially in the Mediterranean basin, is having negative impacts on the marine ecosystem. This concerns had led the Italian government to take legal actions to preserve these important marine resources. The aim of this study was to evaluate the level of genetic diversity and population structures within two sympatric Holothuria sea cucumber species, H. polii and H. tubulosa, across ten Mediterranean areas along Italy. A 323 bp portion of the COI mitochondrial gene was sequenced in a total of 441 holothurians (251 H. polii, 177 H. tubulosa and 13 from other species). Genetic diversity analyses and analysis of molecular variance (AMOVA) suggest that H. polii and H. tubulosa species are distinct, but within and among populations are homogeneous, indicating active gene flows across the Mediterranean areas investigated. H. polii showed a lower genetic diversity than H. tubulosa, probably related to differences in life history traits. Phylogenetic analyses showed a clear differentiation between the two species, even if six specimens morphologically assigned to a species clustered within the other species, indicating a possible occurrence of hybridization events. These data will be useful in implementing conservation actions for these holothurian genetic resources.

Evaluating sea cucumbers as extractive species for benthic bioremediation in mussel farms.

Filter-feeding mussels blend suspended particles into faeces and pseudo-faeces enhancing organic matter flows between the water column and the bottom, and strengthening benthic-pelagic coupling. Inside operating farms, high bivalve densities in relatively confined areas result in an elevated rate of organic sinking to the seabed, which may cause a localized impact in the immediate surrounding. Deposit-feeding sea cucumbers are potentially optimal candidates to bioremediate mussel organic waste, due to their ability to process organic-enriched sediments impacted by aquaculture waste. However, although the feasibility of this polyculture has been investigated for a few Indo-Pacific species, little is known about Atlanto-Mediterranean species. Hence, for the first time, in the present study, we conducted a comparative investigation on the suitability of different Mediterranean sea cucumber species, to be reared in Integrated Multitrophic Aquaculture (IMTA) with mussels. A pilot-scale experiment was accomplished operating within a mussel farm where two sea cucumbers species, Holothuria tubulosa and Holothuria polii, were caged beneath the long-line mussel farm of Mytilus galloprovincialis. After four months, H. tubulosa showed high survivorship (94%) and positive somatic growth (6.07%); conversely H. polii showed negative growth (- 25.37%), although 92% of specimens survived. Furthermore, sea cucumber growth was size-dependent. In fact, smaller individuals, independently from the species, grew significantly faster than larger ones. These results evidenced a clear difference in the suitability of the two sea cucumber species for IMTA with M. galloprovincialis, probably due to their different trophic ecology (feeding specialization on different microhabitats, i.e. different sediment layers). Specifically, H. tubulosa seems to be an optimal candidate as extractive species both for polycultures production and waste bioremediation in M. galloprovincialis operating farms.

Population status, distribution and trophic implications of Pinna nobilis along the South-eastern Italian coast.

The dramatic Mass Mortality Event, MME, of Pinna nobilis populations initially detected in the western Mediterranean basin, has also spread rapidly to the central and eastern basin. Unfortunately, there is still a significant lack of information on the status and health of P. nobilis, since only a fragmentary picture of the mortality rate affecting these populations is available. Regarding the Italian coast, several surveys have given only localized or point-like views on the distribution of species and the effect of the MME. Therefore, for the first time, this study investigated P. nobilis density of individuals, distribution and mortality throughout 161 surveys along 800 km of coastline in the Apulia region (South-east of Italy). The geographical scale of this investigation made it the largest ever conducted in Italy, and this was achieved through a rapid and standardized protocol. During this monitoring campaign, 90 km of linear underwater transects were surveyed, along which no live individuals were observed. This result allowed to estimate that the P. nobilis populations had totally collapsed, with a mortality rate of 100% in Apulia. The distributional pattern of the species showed a strong overlap with seagrass meadows on meso- and macro-geographical scale, however this was not the case on a micro-scale. This result evidenced that relationships between P. nobilis and seagrass meadows are not limited to the habitat patch, but cross the boundaries of seagrass leading us to suggest that the distribution of P. nobilis hold a trophic link through the cross-boundary subsidy occurring from seagrass meadows to the nearby habitat, by means of the refractory detrital pathway.