Davide Seveso

Global-scale relationships between colonization ability and range size in marine and freshwater fish

Although fish range sizes are expected to be associated with species dispersal ability, several studies failed to find a clear relationship between range size and duration of larval stage as a measure of dispersal potential. We investigated how six characteristics of the adult phase of fishes (maximum body length, growth rate, age at first maturity, life span, trophic level and frequency of occurrence) possibly associated with colonization ability correlate with range size in both freshwater and marine species at global scale. We used more than 12 million point records to estimate range size of 1829 freshwater species and 10068 marine species. As measures of range size we used both area of occupancy and extent of occurrence. Relationships between range size and species traits were assessed using Canonical Correlation Analysis. We found that frequency of occurrence and maximum body length had a strong influence on range size measures, which is consistent with patterns previously found (at smaller scales) in several other taxa. Freshwater and marine fishes showed striking similarities, suggesting the existence of common mechanisms regulating fish biogeography in the marine and freshwater realms.

Mushroom corals as newly recorded hosts of the hydrozoan symbiont Zanclea sp.

Abstract Mushroom corals (Anthozoa: Scleractinia: Fungiidae) have been well documented as hosts of a rich associated fauna, but no records involving the symbiotic hydrozoan genus Zanclea (Hydrozoa: Capitata: Zancleidae) are known. These small (~1 mm long), coral-associated hydroids have only been reported from associations involving 23 non-fungiid scleractinian host species in the Indo-Pacific. Since both groups, Fungiidae and coral-dwelling Zanclea hydroids, are known to occur on Indo-Pacific coral reefs, it was unclear why no mushroom coral hosts were known. Therefore, a survey in the Maldives was performed aiming at the discovery of Zanclea–Fungiidae associations. Subsequently, 10 new host species were discovered and the number of recorded coral host genera increased from 17 to 24, taking recent taxonomic revisions into account. These findings indicate that the coral-associated biodiversity is still insufficiently explored.

First report of coral diseases in the Republic of Maldives

Little is known about coral diseases in the Indian Ocean region, especially in the Republic of Maldives. This study aimed at documenting the presence of coral diseases in the archipelago of the Maldives. Surveys for lesions in scleractinians conducted at 8 sites around Magoodhoo Island (Faafu Atoll) in October and November 2010 led to the identification of 5 coral diseases and 1 anomalous pigmentation response affecting 8 hard coral genera. White syndrome, skeleton-eroding band disease, black band disease, and Porites dark discoloration response were the most commonly observed conditions. In contrast with several reports of other reef systems, the overall observed prevalence of coral diseases was rather low (<2%), with individual prevalence ranging from 0.7% for skeleton-eroding band to 0.18% for Porites dark discoloration response. These data represent the first report of coral diseases for the Republic of Maldives.

Zanclea–coral association: new records from Maldives

To date, few hydroids have been observed to be associated with anthozoans, and only three Pacific Zanclea species are known to live in symbiosis with scleractinian corals, namely Zanclea gilii, Z. margaritae, and Z. sango (Boero et al. 2000; Pantos and Bythell 2010; Hirose and Hirose 2011). Here, we report the first evidence of this kind of association in the Indian Ocean. During recent expeditions to Magoodhoo Island (3 04¢N; 72 57¢E, Faafu Atoll, Republic of Maldives), numerous Zanclea spp. colonies wereobserved to live in symbiosis with scleractinians up to about 10 m depth. Specimens belonging to Zanclea spp. were found not only on Acropora muricata and Pavona sp., which are scleractinians previously known to be involved in this association, but also on coral colonies belonging to Favia favus, Favites halicora, Leptastrea purpurea, Montipora sp., Porites cylindrica, and Symphyllia sp. (Fig. 1a–f). Thus, our results extend the geographic distribution and the host range of this symbiosis, strongly suggesting that associations between hydroids and scleractinians could be much more widespread than previously thought, which is consistent with the scenarios depicted by recent molecular studies (Fontana et al. 2012). The benefits and costs of this symbiosis are still not clear. Although trophic and/or protection mutualism seems a plausible explanation of the relationship, a possible relationship between the occurrence of hydroids and coral diseases has also been proposed (Pantos and Bythell 2010). The potential implications of the hydroid–scleractinian symbiosis for coral health, its wide distribution, and the number of species it involves indicate urgent need for further investigations.

The Hidden Diversity of Zanclea Associated with Scleractinians Revealed by Molecular Data

Scleractinian reef corals have recently been acknowledged as the most numerous host group found in association with hydroids belonging to the Zanclea genus. However, knowledge of the molecular phylogenetic relationships among Zanclea species associated with scleractinians is just beginning. This study, using the nuclear 28S rDNA region and the fast-evolving mitochondrial 16S rRNA and COI genes, provides the most comprehensive phylogenetic reconstruction of the genus Zanclea with a particular focus on the genetic diversity among Zanclea specimens associated with 13 scleractinian genera. The monophyly of Zanclea associated with scleractinians was strongly supported in all nuclear and mitochondrial phylogenetic reconstructions. Furthermore, a combined mitochondrial 16S and COI phylogenetic tree revealed a multitude of hidden molecular lineages within this group (Clades I, II, III, V, VI, VII, and VIII), suggesting the existence of both host-generalist and genus-specific lineages of Zanclea associated with scleractinians. In addition to Z. gallii living in association with the genus Acropora, we discovered four well-supported lineages (Clades I, II, III, and VII), each one forming a strict association with a single scleractinian genus, including sequences of Zanclea associated with Montipora from two geographically separated areas (Maldives and Taiwan). Two host-generalist Zanclea lineages were also observed, and one of them was formed by Zanclea specimens symbiotic with seven scleractinian genera (Clade VIII). We also found that the COI gene allows the recognition of separated hidden lineages in agreement with the commonly recommended mitochondrial 16S as a DNA barcoding gene for Hydrozoa and shows reasonable potential for phylogenetic and evolutionary analyses in the genus Zanclea. Finally, as no DNA sequences are available for the majority of the nominal Zanclea species known, we note that they will be necessary to elucidate the diversity of the Zanclea-scleractinian association.

First record of coral-associated Zanclea (Hydrozoa, Zancleidae) from the Red Sea

Although corals are known to host a variety of marine organisms, to date few benthic hydrozoans have been observed to be associated with anthozoans. However, three species belonging to the genus Zanclea have recently been discovered that inhabit reef-building scleractinians. Here we report the first evidence of such Zanclea-coral associations from the Red Sea, extending their known geographical distributions and host range.

Exploring the effect of salinity changes on the levels of Hsp60 in the tropical coral Seriatopora caliendrum.

Osmotic stress represents a limiting physical parameter for marine organisms and especially for sessile scleractinian corals which are known to be basically stenohaline and osmoconformers. The salinity changes may cause important cellular damage since corals lack any developed physiological regulatory system. One mechanism of reaction to deleterious conditions is the rapid increase of the induction of heat shock proteins. This study highlights the modulation of the expression of a mitochondrial heat shock protein, such as the chaperonin Hsp60, in the animal tissues of the scleractinian coral Seriatopora caliendrum under three salinity scenarios (hypersalinity of 45 ppt, hyposalinity of 25 ppt and extreme hyposalinity of 15 ppt). The study was performed during the time course of a 2-day period and accompanied also by the assessment of the coral health condition. For each salinity stress S. caliendrum responds differently at the morphological and cellular levels, since the Hsp60 exhibited specific patterns of expression and the coral showed different tissue appearance. Furthermore, the response reflects the severity and exposure length of the disturbance. However, the results indicate that S. caliendrum seems able to tolerates high salinity better than low salinity. In particular, in extreme hyposalinity conditions, a considerable gradual down-regulation of Hsp60 was detected accompanied by necrosis and degradation of the coral tissues. The study suggests that Hsp60 may be involved in the mechanisms of cellular response to stress caused by exposure to adverse salinity.

Prevalence, host range, and spatial distribution of black band disease in the Maldivian Archipelago

Little research has been conducted on diseases affecting reef-building corals in the central Indian Ocean. During 2010 and 2011, we performed a quantitative assessment of black band disease (BBD) in the central Republic of Maldives. Distribution, host range, and prevalence of BBD were investigated at 6 coral islands (Magoodhoo, Adanga, Ihuru, Vabbinfaru, Thudufushi, and Athuruga) belonging to 3 different atolls. BBD was found to be widespread among the atolls. All the islands showed a prevalence lower than 0.5%. Magoodhoo Island showed the highest mean disease prevalence. In the whole surveyed area, shallow sites showed higher overall mean BBD prevalence than deep ones. BBD was recorded from 6 scleractinian families (Acroporidae, Faviidae, Poritidae, Siderastreidae, Agariciidae, Fungiidae) and 13 scleractinian genera. Two of them, Gardineroseris and Sandalolitha, constitute new records for the disease. The siderastreid Psammocora (BBD prevalence: 5.33 ± 1.41%, mean ± SE) was the most affected genus, followed by Goniopora (2.7 ± 1.3%). BBD prevalence was positively correlated to the respective host density in both genera. Favites and Acropora were the less affected genera (both <0.1%). Although we observed an extremely low overall disease prevalence in the surveyed area (<1%), the large number of different scleractinian genera affected and the widespread distribution of BBD indicate a need for further investigation.

The occurrence of an Acanthaster planci outbreak in Ari Atoll, Maldives

The corallivorous crown-of-thorns starfish Acanthaster planci (COTS) is recognized as a major cause of coral reef degradation throughout much of the Indo-Pacific region (Fabricius 2013). In this study, we report a localised outbreak of COTS at Mama Ghiri, Ari Atoll, Republic of Maldives in June 2014 (3°44′40′′ N; 72°49′13′′ E) (Fig. 1a-c). Belt transects (approximately 9×100 m) were used to record COTS density in the shallows (0–5m depth). An average density of 120±51 COTS per transect (mean ± SD; n=6), with a maximum of 222, was recorded around Mama Ghiri. Moreover, coral mortality of approximately 70 % including complete or partial death of nearly 100 % of tabular Acropora (mainly belonging to the species A. cytherea, A. clathrata, and A. hyacinthus), was estimated (Fig. 1c). These data are comparable with those of COTS outbreaks recently reported in other Indo-Pacific regions (Baird et al. 2013). Although A. planci outbreaks were previously observed in the Maldives (Ciarapica and Passeri 1993), this event was more intense in terms of COTS density. As in many other parts of the world, Maldivian reefs are subjected to increasing pressure from natural and direct anthropogenic disturbances (Jaleel 2013). Considering that A. planci outbreaks may represent a significant threat to coral reef health and biodiversity, we stress the urgent need to explore other Maldivian reefs to document the extent of this phenomenon and its effect on corals and their associated fauna.

The cellular stress response of the scleractinian coral Goniopora columna during the progression of the black band disease

Black band disease (BBD) is a widespread coral pathology caused by a microbial consortium dominated by cyanobacteria, which is significantly contributing to the loss of coral cover and diversity worldwide. Since the effects of the BBD pathogens on the physiology and cellular stress response of coral polyps appear almost unknown, the expression of some molecular biomarkers, such as Hsp70, Hsp60, HO-1, and MnSOD, was analyzed in the apparently healthy tissues of Goniopora columna located at different distances from the infection and during two disease development stages. All the biomarkers displayed different levels of expression between healthy and diseased colonies. In the healthy corals, low basal levels were found stable over time in different parts of the same colony. On the contrary, in the diseased colonies, a strong up-regulation of all the biomarkers was observed in all the tissues surrounding the infection, which suffered an oxidative stress probably generated by the alternation, at the progression front of the disease, of conditions of oxygen supersaturation and hypoxia/anoxia, and by the production of the cyanotoxin microcystin by the BBD cyanobacteria. Furthermore, in the infected colonies, the expression of all the biomarkers appeared significantly affected by the development stage of the disease. In conclusion, our approach may constitute a useful diagnostic tool, since the cellular stress response of corals is activated before the pathogens colonize the tissues, and expands the current knowledge of the mechanisms controlling the host responses to infection in corals.