Isidella elongata 

Scope: Mediterranean
Language: English

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Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Cnidaria Anthozoa Alcyonacea Isididae

Scientific Name: Isidella elongata (Esper, 1788)
Isis elongata Esper, 1788
Taxonomic Source(s): WoRMS Editorial Board. 2015. World Register of Marine Species. Available at: http://www.marinespecies.org. (Accessed: 16 April 2015).
Taxonomic Notes:

Isidella elongata represents the only member of the Family Isididae (bamboo corals) of the Mediterranean Sea and it is easily recognized thanks to the typical alternation of white carbonatic internodes and brown organic nodes along the ramifications (Carpine and Grasshoff 1975). It is a large-sized alcyonacean, that may reach 70 cm high giving rise to a candelabrum-shaped colony with a 45° inclination among the branches (Carpine and Grasshoff 1975, Cartes et al. 2013). Polyps, arranged on two rows, are 3 mm tall and are surrounded by a crown of long sclerites. Shape of the colony, arrangement and shape of the sclerites are the taxonomic features that separate this species from the Atlantic cogeneric Isidella lofotensis and Acanella arbuscula (Carpine and Grasshoff 1975).

Assessment Information [top]

Red List Category & Criteria: Critically Endangered A2bc+4bc (Regional assessment) ver 3.1
Year Published: 2015
Date Assessed: 2014-10-01
Assessor(s): Bo, M., Cerrano, C., Antoniadou, C., Garcia, S. & Orejas, C.
Reviewer(s): Kružić, P., Otero Villanueva, M. & Numa, C.

Isidella elongata is listed as Critically Endangered. This species meets Criterion A2bc+4bc because the declining trend of the population is inferred to be around 80% over 100 years (probably less than 3 generations due to very slow growth rates), on the basis of a reduction in the quality of habitat and on the available past and present bycatch data. The latter suggest a dramatic effect of trawling activity on the majority of the known Isidella grounds of the Mediterranean Sea in a period comprehended between present and the beginning of intensive, industrial fishing activities (around 1960s). Specific surveys conducted in the Catalan area suggest that the decline may locally show very rapid trends, with approximately 15 years as a critical lapse of time to extinguish a population (Cartes et al. 2013). The causes of the reduction at present have not ceased, and, even if the species is geographically widespread thanks to a supposedly large EOO (all muddy bathyal seafloors), it seems that surviving forests thrive only in certain areas appearing less suitable for fishing activities (shallow enclaves protected by hardgrounds or below 1,000 m where trawling is forbidden) (Bo et al. 2015). The recovery ability of this species is very low, due to extremely slow growth rates, low dispersal ability, and a very long life span. The destruction of these coral gardens is accompanied by a great ecosystemic and biodiversity loss in consideration of all those species, pelagic or demersal, that gravitate around these habitats.

The Mediterranean population probably represents the great majority of the global population, with very few Atlantic records, such that the species is considered nearly-endemic. Therefore, the regional sub-populations are probably not dependent on Atlantic larvae immigration for long-term survival, and, since Atlantic populations are not as common as the regional ones, a rescue effect is less plausible. Moreover, as for most of the deep arborescent anthozoans, also in this case it is important to take into consideration the low dispersal ability of the larvae. The threats acting at a regional level are significant given the highly urbanized Mediterranean coastline and the major fishing activity carried out in this basin, as well as a substantial lack of specific management plans (with few exceptions). However, a major management plan of specific high biodiversity hotspots and the inclusion of this species in International Conventions may greatly reduce the population reduction. 

Geographic Range [top]

Range Description:

Isidella elongata is a near-endemic species to the Mediterranean Sea, reaching as far as the adjacent Atlantic waters of Gulf of Cadiz and North Morocco (Grasshoff 1988, 1989). The bathymetric range of this species goes from 115 m in Sardinia (Bo et al. submitted) to 1500 m in the Atlantic Ocean, whether deeper records, down to about 4000 m do exist (Grasshoff 1989). In the Mediterranean Sea, this species was known to inhabit the bathyal muds from 200 to 1200 m depth with vast meadows of closely located colonies especially deeper than 500 m depth (Pérès and Picard 1964, Carpine and Grasshoff 1975).

This species has been mainly reported as accidental bycatch during experimental or professional fishing surveys, however, more recently, some populations have been investigated by means of ROV. I. elongata is found in various localities of the Alboran Sea (Ocaña et al. 2000, Pardo et al. 2011), along the Balearic islands (Marín et al. 2011), Catalan coasts (Sardà et al. 1994; Cartes et al. 2009, 2013; Maynou and Cartes 2012), Gulf of Lion (Dieuzeide 1960; Bas 196; Maurin 1962, 1968; Vaissiere and Carpine 1964; Vaissiere and Fredj 1964; Carpine 1970; Fabri et al. 2014), Ligurian Sea (Relini-Orsi and Relini 1972, Relini-Orsi and Wurtz 1977, Relini, 1981, Relini et al. 1986, Mori and Manconi, 1990), Corsica, Tuscan Archipelago, south-western coasts of Sardinia (Bo et al. submitted), Gulf of Naples (Von Koch 1887), Messina Strait and Sicily (including Aceste Seamount) (Aguilar et al. 2013), Sicily Channel (Greenpeace 2009), Apulia and Otranto Strait, Adriatic Sea (Broch 1953, Pax and Muller 1962), Tunisia, Algeria and Morocco (Carpine and Grasshoff 1975), at 150 m depth in the Aegean Sea (Vafidis et al. 1994) and in the Eastern Ionian Sea up to Crete (Bory de Saint Vincent 1834, Steindachner 1891, Vafidis et al. 2006, Smith et al. 2009, Mytilineou et al. 2013). It seems absent in the extreme Levantine basin (Peres and Picard 1958). 

Countries occurrence:
Algeria; Croatia; France (Corsica, France (mainland)); Gibraltar; Greece (East Aegean Is., Greece (mainland), Kriti); Italy (Italy (mainland), Sardegna, Sicilia); Malta; Morocco; Portugal (Portugal (mainland)); Spain (Baleares, Spain (mainland)); Tunisia
FAO Marine Fishing Areas:
Atlantic – eastern central; Mediterranean and Black Sea
Additional data:
Continuing decline in area of occupancy (AOO):Yes
Estimated extent of occurrence (EOO) - km2:
Continuing decline in extent of occurrence (EOO):Yes
Lower depth limit (metres):4000
Upper depth limit (metres):115
Range Map:50012256-3

Population [top]


Isidella elongata is known to form wide meadows (ca. 255 colonies ha-1, with an distance of 4-5 m among colonies) on flat or sloping muddy bottoms (Cartes et al. 2013). As with the majority of deep sea coral, also this species shows slow growth rates (Andrews et al. 2009) and a long life span (400 years) (Sherwood et al. 2009). 14C data suggested longevities of 75-126 years for Alaskan isidids (Roark et al. 2005) and radial growths of 110 mm yr-1 for a Tasmanian Isidella sp. (Sherwood et al. 2009).

Little is known about important life history aspects of Isididae, such as reproduction, dispersal and colonization patterns (Cartes et al. 2013).

Current Population Trend:Decreasing
Additional data:
Continuing decline of mature individuals:Yes
Population severely fragmented:No
Continuing decline in subpopulations:Yes

Habitat and Ecology [top]

Habitat and Ecology:

Isidella elongata is one of the few alcyonaceans able to live on flat or sloping (5%) soft bottoms (Peres 1967, Laubier and Emig 1993, Oceana 2011). In fact, similarly to Spinimuricea klavareni, it uses a large, basal root of anchorage penetrating the mud and unconsolidated substrate.

The I. elongata bathyal facies (Maurin 1962, Peres and Picard 1964, Carpine 1970, Bellan-Santini et al. 1985) are often associated with populations of deep shrimps such as Aristeus antennatus, Aristemorpha foliacea, Nephros norvegicus and Plesionika spp. which has also been considered in the past as triggering the occurrence of the corals thanks to their mud movimentation (Vaissiere and Fredj 1964, Carpine and Grasshoff 1975, Maynou and Cartes 2012). The biocoenosis is also well identified from the hydrological point of view being located at the limit of the zone of intermediate waters (Carpine and Grasshoff 1975) which is also rich in near-bottom zooplankton (Cartes et al. 2009). High densities of bamboo corals have been observed in the oxygen mimimum zone in the Northeast Pacific Ocean (Baco 2007).

The fields of I. elongata are not only accompanied by a rich invertebrate commercial fauna, but also by a rich fish fauna (Carpine 1970, Carpine and Grasshoff 1975). A study conducted in the Ionian Sea revealed that I. elongata seemed to have more close relationships with some species of the fish assemblage (Galeus melastomus, Helicolenus dactylopterus) (Mytilineou et al. 2013). ROV observations revealed that H. dactylopterus is mostly resting, almost immobile on muddy bottoms (Smith et al. 2010). No clear relationship for diet or reproduction was detected between this species and the bamboo corals, and therefore it was hypothesized only a protection advantage for the fish (Mytilineou et al. 2013). Additionally, only few fish juveniles (Phycis blennoides) live in the Isidella facies, while the majority of the fish are adult (Cartes et al. 2013). Buhl‐Mortensen and Mortensen (2005) found that fish species richness and abundance are significantly correlated with the coral morphology (e.g. branches, weight, percent of exposed skeleton), for example, arborescent black corals are associated with a higher number of fish species, probably related to the more complex structure of this coral (Mytilineou et al. 2013).

Similarly, I. elongata was found associated  to a Merlucius merlucius nursery and with Plesionika spp. populations in the Alboran Sea (Pardo et al. 2011). This species often shares the habitat with other soft bottom species such as Kophobelemnon stelliferum and Funiculina quadrangularis (Pardo et al. 2011) or may form small aggregations in the sandy patches among rocky elevations or dead coral mounds (Bo et al. submitted, Pardo et al. 2011).

The epibiontic fauna of this species includes numerous sessile invertebrates such as hydroids, actinians, barnacles and vagile fauna, such as polychaetes and crabs whether not with species-specific relationships (Arena and LiGreci 1973, Carpine and Grasshoff 1975, Guerao and Abello 1996, Cartes et al. 2013). Various cephalopods and sharks may use the coral ramifications to lay the eggs (Carpine and Grasshoff 1975, Cuccu et al. 2007).

Despite many studies supporting the biological importance of Isidella facies in enhancing high biodiversity and fishery production (Maynou and Cartes 2012), it must be taken into consideration that a recent study pointed out that a severe impact on some Balearic Isidella facies hardly altered fish and invertebrate composition, suggesting a low capacity of this species to form a proper structured habitat for megafauna, which instead may only share common bathymetric ranges and ecological conditions with the coral (Cartes et al. 2009). For example, I. elongata and some macrurid fish and pandalid shrimps may both benefit from wide soft bottoms and high food quality of sediment and zooplankton aggregations enhanced by the slope geomorphological features (Cartes et al. 2009).

Occasionally this species can form tanatocoenosis composed of dead fragments, as those located in the Santa Maria di Leuca deep-water coral province or along the Balearic slope (Rosso et al. 2010, Maynou and Cartes 2012), and that may be used as an indicator of past occurrence of a coral facies (Hawkes and Scott 2005).

Continuing decline in area, extent and/or quality of habitat:Yes
Generation Length (years):35-400

Use and Trade [top]

Use and Trade:

No uses are known for this species. Local artisanal jewellery is reported in Italy with the occasional bycatch.

Threats [top]

Major Threat(s):

Three main categories of threat can be recognised for Isidella elongata:

Trawling activities

Bathyal meadows of I. elongata are now considered very rare (D’Onghia et al. 2003, Sardà et al. 1994), but in the 70-80s there were already some indications (on a few decades scale) of a great decline based on the great reduction of coral bycatch, as in the case of the Ligurian or Sicilian trawling grounds (Peres and Picard 1964, Arena and LiGreci 1973, Relini 1986, Bellan-Santini et al. 2002). Similarly, in the French canyons, I. elongata was very abundant in the past but, at present, this species is encountered at very low abundances probably swept away by repeated trawlings (Fabri et al. 2014). In the Catalan area, the colonies were usually found where no trawling scars were detected on the bottom, but in general along the Balearic slope this species is considered highly disturbed (Maynou and Cartes 2012, Cartes et al. 2013). In the Sardinian area, small enclaves of colonies have been found in refuge areas protected by hardgrounds which were avoided by trawlers (Bo et al. submitted).

The destructive potential of trawling is very high as demonstrated by the removal rate of colonies from a pristine forest found in 1994 off Catalonian coasts which almost disappeared after approx. 15 years of fishing effort (the coral field was reduced to isolated colonies with a density of 0.9 colonies ha-1) (Cartes et al. 2013).

Differently from these areas, it seems that the population of A. antennatus off Algeria, hence the associated soft bottom cnidarians, are not subject to a high fishing pressure (Mouffok et al. 2008).

The possible alteration of trophic webs by trawling on Isidella facies would plausibly increase prey availability after damaging and would cause habitat alteration; on a long scale trawling would reduce benthos production (Maynou and Cartes 2012).

Bottom line fishing

Long lining is a high impact fishing practice in the Mediterranean Sea, since it is generally practised in deeper waters than trawling, or in untrawlable areas that are good habitats for cold water corals, which increases the probability of coral bycatch (Edinger et al. 2007).

Experimental long-line seabream fishing carried out between 500-600 m depth in the eastern Ionian Sea demonstrated that corals occurred in 72% of the long lines and most of the colonies were entire and alive, while others showed already signs of damages as fractures (Mytilineou et al. 2013). I. elongata was highly abundant in the coral bycatch together with black corals with an estimation of 130 live colonies of I. elongata caught per fisherman per year. They demonstrated also that fish species richness and coral bycatch were dependent on the hook size, being higher with smaller hooks.

Long line coral catches are related to the abundance of the coral species in the area, and also to the catchability of the gear and to the morphological structure of the coral (Mytilineou et al. 2013).

Sampaio et al. (2012) mentioned that Alcyonacea was the principal group caught by long lines in the Azores, followed by Scleractinia and Stylasteridae.

At present this species may be considered almost disappeared in the Mediterranean Sea (Cartes et al. 2013) and its occurrence is limited to the shallowest or deepest ranges of its distribution, respectively in shallow water refuges of muddy bottoms protected by trawling activities (Bo et al. submitted) or to grounds where trawling is forbidden, for example on slope grounds or below 1000 m depth (Sacchi 2008, Cartes et al. 2013).

Pollution and mineral extraction

In addition to fishing impact, pollution and litter dumping on I. elongata facies are other important threats (Relini-Orsi 1974) as well as other human activities, such as mineral extraction (Thiel 2003) that favors, together with trawling activities and alteration of rivers run off, high silting levels. Sedimentation clogs the non-retractile polyps of I. elongata and alters their filtering activity (Cartes et al. 2013).

Conservation Actions [top]

Conservation Actions:

The United Nations and FAO (2009) formulated fisheries management protocols to protect vulnerable ecosystems (VMEs) from destructive fishing activities in international waters, recognizing the importance and value of deep‐sea ecosystems and the biodiversity they contain. VMEs include uniqueness and rarities of species and habitat, their functional significance, fragility and structural complexity, and life histories that limit the probability of recovery (GFCM 2009). Ecosystem-based management would greatly benefit from distribution maps of communities overlapped with human activities and by the creation of Fishery Restricted Areas (FRAs) (de Juan et al. 2012). Compact mud facies with Isidella elongata are are recognized among the VME (together with other soft bottom species such as the pennatulacean Funiculina quadrangularis). They are included in the European Habitats Directive (Council Directive 92/43/EEC) and the Barcelona Convention (Annex II).

The species is included in the Marine Protected Areas network of the Gulf of Lion ("Parc Marin du Golfe du Lion" (decree 2011–1269)) (Fabri et al.2014).

Citation: Bo, M., Cerrano, C., Antoniadou, C., Garcia, S. & Orejas, C. 2015. Isidella elongata. The IUCN Red List of Threatened Species 2015: e.T50012256A50605973. . Downloaded on 19 August 2018.
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