Epilithic diatom communities from areas of invasive Caulerpa species (Caulerpa taxifolia and Caulerpa cylindracea) in the Adriatic Sea, NE Mediterranean

Abstract

Epilithic diatom community structures are compared among three locations of the eastern Adriatic Sea coast (Croatia), in the presence of two different invasive Caulerpa species, C. taxifolia and C. cylindracea, which have spread rapidly in the Mediterranean in the last decades. Forty samples were taken seasonally at three sites (island of Hvar, island of Mljet, and Dubrovnik) between November 2008 and October 2010. Light and electron microscopy examinations were used for qualitative analysis. Altogether 310 epilithic taxa belonging to 65 genera were identified. The highest number of these taxa belonged to Mastogloia (48) and Amphora (32), followed by Diploneis (24), Nitzschia (23), Navicula (22), and Cocconeis (19). A similar seasonal shift in growth form structure was observed for epilithic communities at the three sampling sites, where the number of erect group diatoms doubled (Hvar, Mljet) and tripled (Dubrovnik) in spring. Apart from erect forms, Dubrovnik and Mljet were characterised by adnate forms, while Hvar was characterised by tube-dwelling forms. The highest values of the Shannon-Wiener Diversity Index were recorded in autumn and ranged from 5.26 to 5.34. ANOSIM tests performed on species relative abundance data confirmed that the diatom communities differed significantly between the sampling sites, and that the differences were correlated with the presence of the two species of invasive macroalgae (Hvar – area of C. taxifolia; Mljet and Dubrovnik – areas of C. cylindracea). As revealed by SIMPER analyses, the group of taxa contributing the most to variance between diatom assemblages from sites of different invasive alga included Cocconeis scutellum var. scutellum, Rhopalodia pacifica, Navicula ramosissima, and Berkeleya rutilans. Although the spatial variation in communities may also reflect the effects of unmeasured environmental variables, the results suggest the possible influence of invasive seaweeds of the genus Caulerpa which may affect the habitat by competing with autochthonous algae. This study contributes to the knowledge of diatom diversity both at regional and at broader scales in these challenged environments.

The Contribution of Scientific and Historical Data to the Conservation and Management of the Island of Lokrum Marine Area

“…A necessity of monitoring Posidonia oceanica beds in the Lokrum marine area is specially accentuated in the Protocol on Posidonia oceanica monitoring [68] which is well illustrated in the papers pointing out the threats of allochthonous red alga Womersleyella setacea (Hollenberg) R.E. Norris, 1992 [62] and green alga Caulerpa racemosa (Forsskål) J. Agardh, 1873 [64,31]. In response to these pressures related to scientific research, the appropriate guidelines are pointed in the paper ( Table 2).…”

“…The collections from the Dubrovnik Natural History Museum weren't available to the public at that time, so Kršinić published paper suggesting the need for establishing a new museum which should exhibit the existing collections systematically presented, as well as establishing new collections which should be presented in line with the ecological principles covering the themes of the protected areas of Dubrovnik among which a special place should be reserved for the special reserve Lokrum [51]. [64,31,62,57,46,32,68,27]. This confirms the requirement of following these guidelines to propose concrete measures in the management acts in order to manage the marine ecological network more efficiently in accordance with the legal requirements.…”

“…Recent studies include the disappearance and vulnerability of certain species in this area [43], as well as new records of the species whose appearance in the Adriatic sea has rarely been reported [28]. Allochthonous species, one of the main threats to biodiversity, have been studied as well as their interaction with autochthonous species [64,31,62,57]. There have also been studies on other anthropogenic threats to the Lokrum area, such as the influence of the increasing number of anchoring vessels in front of the island [32,27].…”

Indonesian coral reef habitats reveal exceptionally high species richness and biodiversity of diatom assemblages

“…This is especially the case when the data are compared to the equivalent biodiversity estimates on temperate diatom assemblages from coastal sediments (e.g. Hendey, 1977;Underwood, 1994;Weckströ;m & Juggins, 2005;Ulanova and Snoeijs, 2006;Çolak Sabanci, 2011;Dalu, 2016), tropical rocky substrates (Siqueiros-Beltrones and Romero, 2004), mangrove roots (Siqueiros-Beltrones et al, 2005) and seaweeds and sediments (Car et al, 2019). Most studies exploring diatom assemblage biodiversity preferred to use H′ and E H , whereas Gottschalk et al (2007) applied the Bulla Evenness Index (Bulla, 1994), which makes a direct comparison to our results somewhat problematic.…”

Ocorrência e distribuição do gênero Caulerpa J.V. Lamour. (Bryopsidales - Chlorophyta) no Estado de Alagoas, Nordeste Brasileiro

“…Algumas espécies de Caulerpa têm despertado muita atenção e preocupação de diversos pesquisadores e órgãos governamentais por estarem envolvidas em eventos de bioinvasão. Fato este verificado no mar Mediterrâneo desde a década de 70, que vêm sofrendo os efeitos ambientais desastrosos envolvendo pelo menos, duas espécies, C. racemosa e C. taxifolia (Jousson et al 1998, Meinesz et al 2001, Velarque et al 2003, Bulleri 2010, Car et al 2019. Evidenciam-se também interesses farmacológicos acerca deste gênero, por ser fonte de vitaminas e sais minerais, bem como por possuir princípios bioativos (Trono Jr. 1999).…”