{"id":10519,"date":"2016-11-15T00:05:51","date_gmt":"2016-11-15T00:05:51","guid":{"rendered":"http:\/\/www.ocean4future.org\/savetheocean\/?p=10519"},"modified":"2026-04-27T15:12:10","modified_gmt":"2026-04-27T13:12:10","slug":"part-ii","status":"publish","type":"post","link":"https:\/\/www.ocean4future.org\/savetheocean\/archives\/10519","title":{"rendered":"Laminaria rodriguezii, a Mediterranean deep-water kelp is in danger in the Adriatic Sea – part II"},"content":{"rendered":"tempo di lettura: <\/span> 14<\/span> minuti<\/span><\/span>

.<\/span><\/p>\n

livello medio<\/span><\/a>
\n.<\/span>
\nARGOMENTO: BIOLOGIA MARINA<\/span><\/strong>
\nPERIODO: XXI SECOLO<\/span><\/strong>
\nAREA: MAR MEDITERRANEO<\/span><\/strong>
\nparole chiave: alga.<\/span><\/p>\n

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Fishery and biocenology expeditions in 1950s and early 1960s<\/span>
\n<\/strong><\/span>A fishery expedition in the area of Bi\u0161evo in 1953 detected a shallower (93\u201365\u00a0m) community, \u201cdensely overgrown\u201d with L. rodriguezii<\/em> (Grubi\u0161i\u0107 and Gospodneti\u0107 1955<\/a><\/span>; Table\u00a01<\/a><\/span>). During the biocenology expeditions performed in 1957\u20131961, the occurrence of L. rodriguezii<\/em> was confirmed in Jabuka at 5 out of 6 locations where it had been found during the Hvar expedition, and collected at one new location at Jabuka (Fig.\u00a01<\/a><\/span>a; Table\u00a01<\/a><\/span>). During these expeditions, L. rodriguezii<\/em> was categorized in the lowest abundance category with an average number of specimens of less than 10 per transect.<\/p>\n<\/section>\n

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Unpublished records and expeditions MEDITS from 1998 to 2014
\n<\/strong><\/span>In 1998 a thallus of L. rodriguezii<\/em> was collected near Palagru\u017ea Island by a grab at 118\u00a0m depth. Since 2002, during 14 annual MEDITS fisheries expeditions (including data from 2015) with more than 225 transects inside the documented historical distribution range of L. rodriguezii<\/em>, the alga was collected on a total of seven occasions during bottom trawling transects between 155 and 200\u00a0m, all in the area of Palagru\u017ea (Fig.\u00a01<\/a><\/span>b; Table\u00a02<\/a><\/span>). On these seven occasions, L.<\/em>\u00a0rodriguezii<\/em> was very rare and present only in fragments (Fig. S1B). MEDITS expeditions (Bertrand et al. 2002<\/a><\/span>) have covered 835 transects in Croatian waters since 2002.<\/p>\n

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\"Questa<\/p>\n

Table 2\u00a0<\/span><\/span><\/strong>Recent records of Laminaria rodriguezii<\/em> in the Adriatic Sea (1998 \u20132013) <\/span><\/span><\/strong>All were in the Palagru\u017ea area. Prevailing sediment type on MEDITS locations is defined indirectly on the basis of collected benthic invertebrates. Depths recorded by MEDITS expeditions must be considered with caution as these findings might represent drift material from shallower areas<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/section>\n

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Sampling by ROV
\n<\/strong><\/span>During a total of 14 ROV diving hours on coralligenous and detritic substrata between 60 and 130\u00a0m in the areas of Jabuka, Bi\u0161evo and Palagru\u017ea in 2010, we encountered two thalli of L. rodriguezii<\/em>, both close to Palagru\u017ea island at around 90\u00a0m depth (Figs.\u00a01<\/a><\/span>c, S1C, D; Table\u00a03<\/a><\/span>).<\/p>\n

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Oceanographic parameters determined in the bottom layer (100\u00a0m) of the water column collected at oceanographic station CJ011 (Fig.\u00a01c; bottom depth at 102\u00a0m) during 1994\u20132013<\/span><\/strong><\/p>\n

Table\u00a03
\n<\/span><\/strong><\/span><\/p>\n

This station is within the present distribution area of <\/span>Laminaria rodriguezii<\/em><\/p>\n<\/div>\n<\/div>\n<\/div>\n

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Table\u00a04<\/span><\/strong><\/p>\n

Accessions of sequences, with new sequences in bold face<\/p>\n<\/div>\n<\/div>\n

\n\n<\/colgroup>\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n
\n

Sample<\/span><\/p>\n<\/th>\n

\n

ITS<\/span><\/p>\n<\/th>\n

\n

Rubisco spacer<\/span><\/p>\n<\/th>\n

\n

5\u2032-COI<\/span><\/p>\n<\/th>\n<\/tr>\n<\/thead>\n

\n

Laminaria rodriguezii<\/em> Croatia<\/strong><\/p>\n<\/td>\n

\n

LN896341<\/strong><\/p>\n<\/td>\n

\n

LN896348<\/strong><\/p>\n<\/td>\n

\n

LN896336<\/strong><\/p>\n<\/td>\n<\/tr>\n

\n

Laminaria rodriguezii<\/em> Hecate<\/strong><\/p>\n<\/td>\n

\n

LN896342<\/strong><\/p>\n<\/td>\n

\n

LN896349<\/strong><\/p>\n<\/td>\n

\n

ND<\/strong><\/p>\n<\/td>\n<\/tr>\n

\n

Laminaria abyssalis<\/em> L\u00fc1291<\/strong><\/p>\n<\/td>\n

\n

LN896343<\/strong><\/p>\n<\/td>\n

\n

LN896350<\/strong><\/p>\n<\/td>\n

\n

LN896337<\/strong><\/p>\n<\/td>\n<\/tr>\n

\n

Laminaria ochroleuca<\/em> BR93<\/strong><\/p>\n<\/td>\n

\n

LN896344<\/strong><\/p>\n<\/td>\n

\n

LN896351<\/strong><\/p>\n<\/td>\n

\n

LN896338<\/strong><\/p>\n<\/td>\n<\/tr>\n

\n

Laminaria ochroleuca<\/em> GAL98<\/strong><\/p>\n<\/td>\n

\n

LN896345<\/strong><\/p>\n<\/td>\n

\n

LN896352<\/strong><\/p>\n<\/td>\n

\n

LN896339<\/strong><\/p>\n<\/td>\n<\/tr>\n

\n

Laminaria pallida<\/em> NAM93<\/strong><\/p>\n<\/td>\n

\n

LN896346<\/strong><\/p>\n<\/td>\n

\n

LN896353<\/strong><\/p>\n<\/td>\n

\n

LN896340<\/strong><\/p>\n<\/td>\n<\/tr>\n

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Laminaria pallida<\/em> SAF01<\/strong><\/p>\n<\/td>\n

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LN896347<\/strong><\/p>\n<\/td>\n

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LN896354<\/strong><\/p>\n<\/td>\n

\n

ND<\/strong><\/p>\n<\/td>\n<\/tr>\n

\n

Laminaria digitata<\/em><\/strong><\/p>\n<\/td>\n

\n

FJ042772<\/strong><\/p>\n<\/td>\n

\n

AY851559<\/strong><\/p>\n<\/td>\n

\n

AJ344328<\/strong><\/p>\n<\/td>\n<\/tr>\n

\n

Laminaria digitata<\/em><\/strong><\/p>\n<\/td>\n

\n

AF319014<\/strong><\/p>\n<\/td>\n

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AF318971<\/strong><\/p>\n<\/td>\n

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JN099683<\/strong><\/p>\n<\/td>\n<\/tr>\n

\n

Laminaria hyperborea<\/em><\/strong><\/p>\n<\/td>\n

\n

AY441771<\/strong><\/p>\n<\/td>\n

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AF318972<\/strong><\/p>\n<\/td>\n

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FJ409154<\/strong><\/p>\n<\/td>\n<\/tr>\n

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Laminaria setchellii<\/em> Silva<\/strong><\/p>\n<\/td>\n

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AF319016<\/strong><\/p>\n<\/td>\n

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AF318973<\/strong><\/p>\n<\/td>\n

\n

GU097710<\/strong><\/p>\n<\/td>\n<\/tr>\n

\n

Laminaria sinclairii<\/em><\/strong><\/p>\n<\/td>\n

\n

AF319017<\/strong><\/p>\n<\/td>\n

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AY851558<\/strong><\/p>\n<\/td>\n

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KJ960264<\/strong><\/p>\n<\/td>\n<\/tr>\n

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Laminaria ephemera<\/em> Setchell<\/strong><\/p>\n<\/td>\n

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FJ042733<\/strong><\/p>\n<\/td>\n

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AY851557<\/strong><\/p>\n<\/td>\n

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FJ409152<\/strong><\/p>\n<\/td>\n<\/tr>\n

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Laminaria solidungula<\/em> J. Agardh<\/strong><\/p>\n<\/td>\n

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FJ042757<\/strong><\/p>\n<\/td>\n

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AY851556<\/strong><\/p>\n<\/td>\n

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FJ409161<\/strong><\/p>\n<\/td>\n<\/tr>\n

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Laminaria yezoensis<\/em> Miyabe<\/strong><\/p>\n<\/td>\n

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FJ042749<\/strong><\/p>\n<\/td>\n

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AY851555<\/strong><\/p>\n<\/td>\n

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FJ409167<\/strong><\/p>\n<\/td>\n<\/tr>\n

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Saccharina japonica<\/em> (Areschoug) Lane, Mayes, Druehl & Saunders<\/strong><\/p>\n<\/td>\n

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DQ143070<\/strong><\/p>\n<\/td>\n

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DQ143101<\/strong><\/p>\n<\/td>\n

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AP011493<\/strong><\/p>\n<\/td>\n<\/tr>\n

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Saccharina sessilis<\/em> (C. Agardh) Kuntze<\/strong><\/p>\n<\/td>\n

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FJ042748<\/strong><\/p>\n<\/td>\n

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AY851553<\/strong><\/p>\n<\/td>\n

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FJ409207<\/strong><\/p>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

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The data for the different markers in the new sequences are from the same sample, whereas in the published sequences they are usually from different specimens of the same species – ND<\/em> no data<\/span><\/strong><\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/section>\n

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Information from fishermen
\n<\/strong><\/span>Professional fishermen from the island of Lastovo, who perform trammel net fishing, provided personal accounts in 2011. They regularly collected L. <\/em>rodriguezii<\/em> as by catch near Palagru\u017ea Island (Fig. 1<\/a><\/span>c; Table\u00a02<\/a><\/span>) at depths between 90 and 110\u00a0m. Our confidence in these communications is high as the fishermen described L. <\/em>rodriguezii<\/em> as a \u201cflat brown seaweed with characteristic roots which firmly entangle into the net<\/span><\/strong>\u201d.<\/em> Contrary to this, fishermen from trawling boats operating in the area of Jabuka and Bi\u0161evo did not report any findings of L. rodriguezii<\/em>.<\/p>\n<\/section>\n<\/div>\n<\/section>\n

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Oceanographic characteristics of the Palagru\u017ea area
\n<\/strong><\/span>Long-term data on oceanographic parameters are summarized in Table\u00a03<\/a><\/span> and Fig. S4. The high-resolution temperature time series recorded by the ADCP at 163\u00a0m, less than 1\u00a0m above the sea bottom (Fig. S5) showed temperature oscillations between 10.67 (March 2012) and 14.63\u00a0\u00b0C (end of October 2012), which is in accordance with the long-term measurements (Fig. S4). The distribution of near-bottom current speeds and directions at the ADCP station is shown as a rose plot in Fig. S6. Current direction was stable, the direction of the flow was in >65\u00a0% between east and southeast, indicating predominant outflow across the Palagru\u017ea Sill, towards the South Adriatic Pit. The strongest currents were also measured for these directions, with maximum speeds reaching 44\u00a0cm\/s. Generally, near-bottom currents were relatively strong, with speeds larger than 10 and 20\u00a0cm\/s encompassing more than 40 and 11\u00a0% of all measurements, respectively. They were particularly energetic between March and July 2012 (Fig. S7), when the dense water outflow was the strongest. The average bottom current speed during 9\u00a0months was 10.1\u00a0cm\/s.<\/p>\n<\/section>\n

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Molecular systematic analyses<\/span><\/strong>
\nA total of 6000-bp DNA sequences for six markers (see \u201cMethods<\/a><\/span>\u201d section; Table S3) were produced from the L. rodriguezii<\/em> field specimen from Croatia. From the herbarium specimen of L. rodriguezii<\/em> from the western Mediterranean, we generated a short sequence of 129 bp in the highly variable first part of ITS1. It was identical to the sequence from Croatia confirming con-specificity of the two samples. For the western Mediterranean specimen, also a Rubisco spacer sequence was produced which resembled the sequence from Croatia except for two substitutions. In addition, sequences of the highly variable \u201cbarcode\u201d markers ITS, Rubisco spacer and 5\u2032-COI were generated for L. ochroleuca, L. pallida<\/em> and L. abyssalis<\/em>. In the last species, the ITS sequence generated for our gametophyte culture was highly similar to four sequences recently published for field specimens from Brazil (Marins et al. 2012<\/a><\/span>).<\/p>\n

\n
In the sensitive, variable markers ITS and Rubisco spacer, L. rodriguezii<\/em> showed most similarity with a cluster formed by L.<\/em>\u00a0ochroleuca<\/em>, L. pallida<\/em> and L. abyssalis<\/em> (henceforth OPA clade), followed by L.<\/em>\u00a0digitata<\/em> (Hudson) Lamouroux and L. hyperborea<\/em> (Gunnerus) Foslie (Table S3). In the mitochondrial marker (5\u2032-COI), genetic distances within the OPA cluster were\u00a0\u2264\u00a01.6\u00a0%, and L.<\/em>\u00a0rodriguezii<\/em> was as divergent from the OPA clade (3.3\u20134.4\u00a0%) as from L. digitata<\/em> (0.44\u00a0%) and L.<\/em>\u00a0hyperborea<\/em> (0.39\u00a0%). Analyses of the combined dataset of ITS, Rubisco spacer and COI consistently placed L.<\/em>\u00a0rodriguezii<\/em> in a highly supported clade together with the OPA clade (Fig.\u00a02<\/a><\/span>). In the more conservative rbc<\/em>L and SSU, many species from the Laminariales showed highly similar sequences but phylogenetic analyses were not performed because sequences of the OPA clade were unavailable.<\/span><\/div>\n
<\/div>\n
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\"tassonomia-lamin-med\"<\/a><\/p>\n

Fig. 2 Phylogenetic tree of Laminaria spp. based on a neighbour-joining analysis of Kimura-2-parameter distances of concatenated entire ITS (763 bp), Rubisco spacer (553 bp) and 5\u2032-COI (658 bp) sequences. Two species of Saccharina served as outgroup (Lane et al. 2006). Parsimony and maximum likelihood analyses of the same dataset, as well as analyses of data of the single markers, gave similar results, in most cases placing L. rodriguezii in a highly supported clade together with L. ochroleuca, L. pallida and L. abyssalis. Numbers at nodes indicate bootstrap support from 1000 resamplings for distance, parsimony and likelihood analyses, respectively. Accessions of sequences are provided in Table 4<\/span><\/strong><\/p>\n<\/div>\n<\/div>\n<\/section>\n<\/div>\n<\/section>\n

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Discussion<\/span>
\n<\/strong><\/span>Historical data from herbarium samples collected from ca. 1896 until 1963 and from fishery expeditions (1949\u20131961) (Tables 1 and S2) indicated that Laminaria rodriguezii<\/em> had three principal areas of distribution in the Adriatic Sea: Jabuka Pit and around the islands of Bi\u0161evo and Palagru\u017ea, all of which are located in the central part of the Adriatic Sea (Fig.\u00a01<\/a><\/span>a). Fisheries expeditions from the 1960s until the early 2000s did not pay attention to L.<\/em>\u00a0rodriguezii.<\/em> In the same period, commercial trawling effort increased, undoubtedly with consequences for benthic communities (Mannini and Massa 2000<\/a><\/span>; Jukic-Peladic et al. 2001<\/a><\/span>; Mannini et al. 2005<\/a><\/span>). We thus consider the data on the distribution of L. rodriguezii<\/em> in the Adriatic Sea until the early 1960s as historical range or zero state<\/em>, similar to the zero state<\/em> for bottom trawling of commercial fish species (Jukic-Peladic et al. 2001<\/a><\/span>). Recent data on the distribution of L. rodriguezii<\/em> in the Adriatic Sea reveal that the distribution range of the species has drastically declined within the last 40\u00a0years (Fig.\u00a01<\/a><\/span>). Since 2000, the MEDITS project has surveyed almost the same transects on which L. rodriguezii<\/em> was collected during the Hvar expedition in the late 1940s. Even though L.<\/em>\u00a0rodriguezii<\/em> was one of the target species, the alga was recorded only at Palagru\u017ea. In the last 50\u00a0years, it has not been officially recorded in the area of Jabuka Pit where it was repeatedly found in the late 1940s and 1950s. Taking into account that the areas of Jabuka and Bi\u0161evo have been well investigated recently through fisheries surveys, but also in particular during the deep-water brown algal expeditions using ROVs, it can be said with high confidence that L. rodriguezii<\/em> is no longer present at Jabuka and Bi\u0161evo. Consequently, the extent of occurrence (as defined by IUCN 2012<\/a><\/span>) of this alga within the Adriatic Sea has shrunk by more than 85\u00a0%, from 8700\u00a0km2<\/sup> (area covering all records) to 1200\u00a0km2<\/sup> (historical and recent records in the Palagru\u017ea Island area).
\nThere is no information about historical or recent population densities of L. rodriguezii<\/em> around Palagru\u017ea Island. The latest information provided by fishermen operating in the area suggests that certain dense and healthy populations still exist in a spatially reduced area SE of Palagru\u017ea Island, while in the wider area of Palagru\u017ea the species is rare. Low abundance in a wider area of Palagru\u017ea is indicated by sporadic bycatch of the alga during the MEDITS project, with just a few fragments collected in the last 14\u00a0years (Fig.\u00a01<\/a><\/span>b, c; Table\u00a02<\/a><\/span>). Additional underwater ROV surveys would be required for more precise information on the condition of the populations at the sites suggested by fishermen.<\/p>\n

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As Jabuka Pit is one of the most important trawling areas in the Adriatic (UNEP\/CBD\/EBSA\/WS 2014<\/a><\/span>), the disappearance of L. rodriguezii<\/em> is likely a result of bottom trawling activities. Mechanisms of impact would be direct, by removal of algae as bycatch, and indirect by stirring up sediments (Jones 1992<\/a><\/span>; Palanques et al. 2001<\/a><\/span>). In the Jabuka Pit, a layer of dense bottom water can in some years persist over longer periods (Artegiani et al. 2001<\/a><\/span>). Resuspended sediments, which circulate inside the enclosed water mass within the depression, would possibly decrease light intensity under the light compensation point of the algae. It was pointed out in other parts of the Mediterranean that frequent trawling might influence L. rodriguezii<\/em> (UNEP\/IUCN\/GIS Posidonie 1990<\/a><\/span>; Joher et al. 2012<\/a><\/span>), but the disappearance of L.<\/em>\u00a0rodriguezii<\/em> from Jabuka and Bi\u0161evo is up to now the greatest reported decline of this species. The area of Palagru\u017ea is not an intensive trawling area like Jabuka (IOF, unpublished data) but still has important commercial fishing activity. Moreover, the locations where L.<\/em>\u00a0rodriguezii<\/em>was recently reported by fishermen, observed and collected by ROV and grab (Fig.\u00a01<\/a><\/span>c), correspond to an area where trawling is not allowed (minimum 2 nautical miles from the Island) and only small scale fishing like trammel nets is performed. In addition, strong bottom currents in the Palagru\u017ea may allow fast removal of fine sediment dispersed in bottom water due to bottom trawling, and possibly also clean the surface of thalli from deposited sediments. The historical records of L. rodriguezii<\/em> at Jabuka, at 150\u2013260\u00a0m depth, were the deepest of that species in the entire Mediterranean. Such a depth is in the range of the deepest records of seaweeds worldwide (Littler et al. 1985<\/a><\/span>; Markager and Sand-Jensen 1992<\/a><\/span>). Sporadic findings of the alga in the Palagru\u017ea area during MEDITS surveys during the last 14 years were also in the depth range between 170 and 200 m. Collected specimens did not have hold-fasts, thus it is not possible to conclude with certainty whether they were attached or just dispersed fragments. Bottom currents of 50 cm s\u22121<\/sup> might be sufficient for proper fragment drifting. However, according to data provided from ADCP, bottom currents with E\u2013SSE directions (Fig. S6) could not transport fragments from Palagru\u017ea Island to locations where L. rodiguezi<\/em> was collected during MEDITS campaigns (Fig.\u00a01<\/a><\/span>b; 10\u201330\u00a0km in N\u2013NE direction). Anyway, depths reported by earlier studies based on bottom trawling surveys must be considered with a certain caution. Without direct observation by ROV, exact data on light intensity on the bottom and ideally supporting, ecophysiological experiments, we cannot be sure that L. rodriguezii<\/em> can develop at such extreme depth. The lower depth limits for kelp is assumed to be at 1\u00a0% of surface irradiance (L\u00fcning and Dring 1979<\/a><\/span>); however, this may not apply for L.<\/em>\u00a0rodriguezii<\/em>. Secchi values measured in the last 15\u00a0years were around 20\u00a0m, with a maximum of 30\u00a0m. Such surface values of transparency only might be indicative and indeed reveal no information about the light intensity reaching the bottom. Giaccone (Giaccone 1967<\/a><\/span>) noted how Secchi disks were visible up to 35\u00a0m near the island of Ustica (Italy) where L. rodriguezii<\/em> populations occurred between 45 and 85\u00a0m depth. At 85\u00a0m, the seabed at Ustica was too steep and formed an environment with low luminosity that did not allow life of photosynthetic organisms. The locations where the alga was collected near Palagru\u017ea and historically at Jabuka are mostly flat, and therefore probably allow development of the alga at greater depth (no shading effect) even if the transparency is equal. Similar to the Palagru\u017ea site, costal detritic bottoms occur in Spain, where L. rodriguezii<\/em> has been mainly reported between 70 and 80\u00a0m, with a maximum at 95\u00a0m (Joher et al. 2012<\/a><\/span>; Sergi Joher Sais pers. comm.).<\/p>\n

There is not much information on oceanographic conditions prevailing in the locations of other populations of L. rodriguezii<\/em> in the Mediterranean. However, most reports suggest that favourable conditions include a hard coralligenous or rhodolithic substratum, dim light, highly transparent open sea water due to very low abundance of suspended particles, water temperatures permanently below 15\u00a0\u00b0C, and constant, mostly unidirectional weak to strong currents (Ercegovi\u0107 1960<\/a><\/span>; Giaccone 1967<\/a><\/span>; UNEP\/IUCN\/GIS Posidonie 1990<\/a><\/span>; Bellan-Santini et al. 2002<\/a><\/span>). This study presents for the first time precise long-term measurements of temperature, currents, salinity and nutrients in the bottom seawater in the documented distribution range of L.<\/em>\u00a0rodriguezii<\/em>. Seawater temperature is almost constantly around 14\u00a0\u00b0C with temperature extremes slightly above 15\u00a0\u00b0C and below 12\u00a0\u00b0C being a very rare occurrence over 60\u00a0years of seasonal measurements (Fig. S4). Current measurements from the ADCP station close to Palagru\u017ea showed that bottom currents were relatively strong and very stable. The strong bottom current in the area is the result of formation and sinking of cold and dense North Adriatic Dense Water (NAdDW) formed in the North Adriatic shelf and coastal area (Mihanovi\u0107 et al. 2013<\/a><\/span>). One of the two major pathways of the NAdDW from the shallow northern Adriatic shelf and Jabuka Pit to the deep South Adriatic Pit is located to the north of Palagru\u017ea (Vilibi\u0107 et al. 2004<\/a><\/span>; Janekovi\u0107 et al. 2014<\/a><\/span>). Predominant flow directions measured at the ADCP station were between east and southeast, corresponding to the northern pathway of the NAdDW outflow across the Palagru\u017ea Sill. The NAdDW formation event that occurred in January\/February 2012 was exceptional and bottom density currents between March and June 2012 were particularly intense. Still, even after that period, weaker but persistent bottom currents, flowing mostly towards E\u2013SE were observed in the area, till the end of measurements in December 2012 (Fig. S7). Both current and temperature measurements corroborate the global perception how persistent and stable currents and low temperatures play important roles in the formation of favourable condition for the development of L. rodriguezii<\/em>. Therefore, NAdDW outflow with both strong currents and low and relatively stable temperatures is probably essential for the development of L.<\/em>\u00a0rodriguezii<\/em> in the Central Adriatic. It thus appears that presence of L. rodriguezii<\/em> in the Adriatic Sea coincides with oceanographic conditions that differ from the upwelling of cold waters at deep water kelp sites in tropical regions (Graham et al. 2007<\/a><\/span>).<\/p>\n

Total inorganic nitrogen, orthophosphate and orthosilicate concentrations in the bottom layer (Table\u00a03<\/a><\/span>) were generally higher than in the surface or middle layer of the water column (Vilibi\u0107 et al. 2012<\/a><\/span>), due to remineralization processes from the sediment or to advective mixing of water masses from the Mediterranean. Increased TIN concentrations are particularly expressed during the summer season (Bari\u0107 et al. 2002<\/a><\/span>), as a consequence of more intensive nitrogen flux from sediment that can be an additional source of nutrients facilitating algal growth.\u00a0Laminaria rodriguezii<\/em> has a disjunct distribution within the Mediterranean Sea. The population in the Adriatic Sea, although genetically similar according to ITS sequences (see below), does not seem to be connected to the populations in the Western Mediterranean, since there are no intermediate populations known. Long distances from the next populations and adverse water mass circulation probably inhibit transport of any reproductive phase. Natural reintroduction in the case of total regional extinction in the Adriatic Sea is therefore not possible. The IUCN Red List criteria are commonly used for evaluating the extinction risk of species (IUCN 2012<\/a><\/span>). However, applying these to macroalgae is not simple and there are only a few seaweed species in the world on which they have been applied (Brodie et al. 2009<\/a><\/span>; Phillips and Blackshaw 2011<\/a><\/span>), basically due to lack of information on historical and recent distributions and the species\u2019 biology and ecology. Except for the present comparison of historical and recent records, this also applies to L. rodriguezii<\/em> in the Adriatic. There is still limited knowledge on its biology, population density and exact distribution as well as changes of the last two over exact periods of time, which are relevant criteria for IUCN evaluation. However, such data are clearly very difficult to obtain for such a relatively inaccessible species. In the light of the drastic decline of more than 85\u00a0% of the extent of occurrence in the Adriatic, which is estimated to be nowadays around 1200\u00a0km2<\/sup>, and its disappearance in two of three historical distribution areas (Jabuka Pit and Bi\u0161evo Island area), as well as still ongoing, strong bottom trawling activities (UNEP\/CBD\/EBSA\/WS 2014<\/a><\/span>), we propose that L.<\/em>\u00a0rodriguezii<\/em> should be classified as \u201cEndangered\u201d under IUCN criteria B1ab(i,iii,iv), ver 3.1.in the Adriatic Sea.
\nA management plan should therefore be developed in order to enable maintenance of L.<\/em>\u00a0rodriguezii<\/em> in the area of Palagru\u017ea Island, its last refuge within the Adriatic. Similar measures were proposed for an area with L. rodriguezii<\/em> populations in the Menorca Channel (Barbera et al. 2012<\/a><\/span>). The decline of canopy-forming species, especially those in shallow waters, is an expanding, worldwide trend, largely due to different human activities while only sporadic local actions are taken to remedy this situation (e.g. Thibaut et al. 2015<\/a><\/span>; Yesson et al. 2015<\/a><\/span>, and references therein). Further ROV expeditions should be organized with the objective of not destructively quantifying the abundance of L.<\/em>\u00a0rodriguezii<\/em> and to establish detailed parameters for a further monitoring program. The greatest risk for the species appears to consist in continued bottom trawling. Temperature increases in Mediterranean deep water may represent another threat. The distribution of shallow water kelp species was reported to react rapidly to small changes in seawater temperatures, possibly due to temperature requirements for reproduction (Bartsch et al. 2013<\/a><\/span>). On the other side, Yesson et al. (2015<\/a><\/span>) showed that temperature alone can not account for long-term increases and decreases in abundance of the large brown seaweeds observed around the British Isles and suggested a combination of both physical and biological factors as drivers of these changes. Therefore, the possible future impact of seawater temperature increase on deep water L. rodriguezii<\/em> must remain speculative, as there are no ecophysiological data on growth and reproduction of this species. So far, long-term measurements of sea bottom water in the Palagru\u017ea area have not shown any statistically significant temperature increase (Vilibi\u0107 et al. 2012<\/a><\/span>).<\/p>\n

Sequence similarity in a highly variable part of ITS and the Rubisco spacer between our Croatian and Italian samples of L. rodriguezii<\/em> suggested that there may not be much genetic differentiation between individuals from the two sites. The sequences of all markers confirmed that L. rodriguezii<\/em> belongs to the Laminariaceae, which is at present (Guiry and Guiry 2015<\/a><\/span>) understood as a clade formed by the type L. digitata<\/em> and about 20 other species, including all Atlantic kelps with digitate blades, such as L.<\/em>\u00a0hyperborea<\/em>, L.<\/em>\u00a0ochroleuca<\/em>and L.<\/em>\u00a0pallida<\/em>. According to the sequences studied, particularly ITS, L. rodriguezii<\/em> is closely related to a clade formed by L.<\/em>\u00a0ochroleuca, L. pallida<\/em> and L. abyssalis.<\/em> Our sequences suggest that adaptation to deep water in L.<\/em>\u00a0rodriguezii<\/em> and L.<\/em>\u00a0abyssalis<\/em> possibly evolved independently and that the two are different species, which is born out by the fact that the adventive blades characteristic for L.<\/em>\u00a0rodriguezii<\/em> are absent in L.<\/em>\u00a0abyssalis<\/em>. However, these are preliminary data from three markers and few individuals. A more comprehensive phylogeographic hypothesis for L.<\/em>\u00a0rodriguezii<\/em> would require sequences for several markers from replicate individuals from different populations of the two deep-water species as well as of all Atlantic kelp taxa. It is unknown if L. rodriguezii<\/em> can cross with the members of the AOP clade; cross-fertility has been shown experimentally for L. pallida<\/em> and L. abyssalis<\/em> (Dieck and De Oliveira 1993<\/a><\/span>). It is urgent to isolate gametophyte cultures of L.<\/em>\u00a0rodriguezii<\/em> in order to study genetics and physiology of this impressive species.<\/p>\n

\"laminaria-rodriguezii2\"<\/a><\/p>\n<\/div>\n<\/section>\n

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Conclusion<\/span>
\n<\/strong><\/span>Comparison of historical and recent data on the distribution L. rodriguezii<\/em> showed that according to IUCN criteria, the extent of occurrence of this deep water species within the Adriatic Sea has been drastically reduced by more than 85\u00a0% (from 8700 to 1200\u00a0km2<\/sup>). The most probable reasons for its disappearance are direct and indirect impacts of trawling (physical collecting and decrease of water transparency). Taking into account the IUCN criteria, we propose that this species is classified as \u201cEndangered\u201d under IUCN criteria B1ab (i,iii,iv), ver 3.1. in the Adriatic Sea. A management plan should therefore be developed to enable maintenance of L. rodriguezii<\/em> in the area of Palagru\u017ea Island, which according to the data presented here is its last refuge within the Adriatic and the East part of the Mediterranean Sea.<\/p>\n<\/section>\n<\/div>\n

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PAGINA PRINCIPALE - HOME PAGE<\/span><\/a>
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Acknowledgments as in The Mediterranean deep-water kelp Laminaria rodriguezii is an endangered species in the Adriatic Sea | Marine Biology (springer.com)<\/a><\/span><\/strong><\/p>\n

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Supplementary material <\/span><\/strong>227_2016_2821_MOESM1_ESM.pdf<\/a> (1.4 mb)<\/span><\/p>\n<\/section>\n