Ante ŽULJEVIĆ, CVITKOVIĆ I., LUČIĆ P., DESPALATOVIĆ M., NEJAŠMIĆ J.
Institute of Oceanography and Fisheries, I. Meštrovića 63, 21000 Split, Croatia
E-mail: zuljevic@izor.hr
THE TOP THREE ALIEN MACROALGAE INVADERS IN CROATIA IN 2022
Abstract
Based on regular monitoring of benthic non-native species, we discuss the three most invasive
macroalgae in the Croatian part of the Adriatic Sea in 2022. Our assessment is based on the algae’s
spreading dynamics, opportunistic behavior, impact on native species and habitats, and on expert
judgment regarding the species’ potential for further expansion and global influence. As the most
invasive alga, we nominate Caulerpa cylindracea Sonder, 1845, which is a species with an exceptional
and demonstrated impact on native benthic species and habitats. This is a fast-spreading alga present
almost everywhere in the Croatian sea and developing on all types of bottoms between 0 and 55 m
depth. The second most invasive species is Acrothamnion preissii (Sonder) E. M. Wollaston, 1968. This
alga is recorded in two distinct areas. Around Dubrovnik (south Adriatic), it affects almost every
rhizome of Posidonia oceanica (Linnaeus) Delile, 1813, forming dense cotton-like coverage and
probably drastically displacing native epiphytic species. The third most invasive alga is Stypopodium
schimperi (Kützing) Verlaque & Boudouresque, 1991. It was recorded for the first time in 2020, but in
two years it has demonstrated an exceptional increase in coverage, tending to affect 100% of the rocky
bottom between 5 and 15 m depth with total displacement of native erect species. Based on its
expansion and impact in just two years, we believe that this alga might soon become the no. 1 invader.
Key-words: Caulerpa cylindracea, Acrothamnion preissii, Stypopodium schimperi, Adriatic
Sea, invasive species.
Introduction
The Croatian part of the Adriatic Sea has its biological and ecological specificity, which
has consequences not only in its native benthic assemblages but also in the spread and
impact of alien species. Approximately 20 non-native macroalgae have been recorded in
Croatia (Tsiamis et al., 2019). Some of them (e.g., Caulerpa taxifolia) declined after
rapid expansion (Žuljević et al., 2019). Based on extensive fieldwork, we present the
three most invasive alien macroalgae in Croatia in 2022.
Materials and methods
To identify the three most invasive non-native algae in 2022, we consider the most current
information collected from the field during monitoring for the MSFD D2 and Benthic NIS
scientific projects. Field monitoring was done through scuba diving and drop-down
cameras. This assessment was based on spreading dynamics, opportunistic behavior, impact
on species and habitats, and expert judgment regarding the species’ potential for further
expansion and global influence.
Results and discussion
On the basis of collected information, Caulerpa cylindracea resulted to be the most invasive
macroalgae in Croatia. First recorded in 2000, this species is now present almost everywhere.
It develops dense settlements that might cover 100% of the different types of sea bottoms, from
a depth of 0 to a maximum of 55 m, in pristine and eutrophic areas. This alga can develop more
2nd Mediterranean Symposium on the Non-Indigenous Species (Genoa, Italy, 22-23 September 2022)
129
Institute of Oceanography and Fisheries, I. Meštrovića 63, 21000 Split, Croatia
E-mail: zuljevic@izor.hr
THE TOP THREE ALIEN MACROALGAE INVADERS IN CROATIA IN 2022
Abstract
Based on regular monitoring of benthic non-native species, we discuss the three most invasive
macroalgae in the Croatian part of the Adriatic Sea in 2022. Our assessment is based on the algae’s
spreading dynamics, opportunistic behavior, impact on native species and habitats, and on expert
judgment regarding the species’ potential for further expansion and global influence. As the most
invasive alga, we nominate Caulerpa cylindracea Sonder, 1845, which is a species with an exceptional
and demonstrated impact on native benthic species and habitats. This is a fast-spreading alga present
almost everywhere in the Croatian sea and developing on all types of bottoms between 0 and 55 m
depth. The second most invasive species is Acrothamnion preissii (Sonder) E. M. Wollaston, 1968. This
alga is recorded in two distinct areas. Around Dubrovnik (south Adriatic), it affects almost every
rhizome of Posidonia oceanica (Linnaeus) Delile, 1813, forming dense cotton-like coverage and
probably drastically displacing native epiphytic species. The third most invasive alga is Stypopodium
schimperi (Kützing) Verlaque & Boudouresque, 1991. It was recorded for the first time in 2020, but in
two years it has demonstrated an exceptional increase in coverage, tending to affect 100% of the rocky
bottom between 5 and 15 m depth with total displacement of native erect species. Based on its
expansion and impact in just two years, we believe that this alga might soon become the no. 1 invader.
Key-words: Caulerpa cylindracea, Acrothamnion preissii, Stypopodium schimperi, Adriatic
Sea, invasive species.
Introduction
The Croatian part of the Adriatic Sea has its biological and ecological specificity, which
has consequences not only in its native benthic assemblages but also in the spread and
impact of alien species. Approximately 20 non-native macroalgae have been recorded in
Croatia (Tsiamis et al., 2019). Some of them (e.g., Caulerpa taxifolia) declined after
rapid expansion (Žuljević et al., 2019). Based on extensive fieldwork, we present the
three most invasive alien macroalgae in Croatia in 2022.
Materials and methods
To identify the three most invasive non-native algae in 2022, we consider the most current
information collected from the field during monitoring for the MSFD D2 and Benthic NIS
scientific projects. Field monitoring was done through scuba diving and drop-down
cameras. This assessment was based on spreading dynamics, opportunistic behavior, impact
on species and habitats, and expert judgment regarding the species’ potential for further
expansion and global influence.
Results and discussion
On the basis of collected information, Caulerpa cylindracea resulted to be the most invasive
macroalgae in Croatia. First recorded in 2000, this species is now present almost everywhere.
It develops dense settlements that might cover 100% of the different types of sea bottoms, from
a depth of 0 to a maximum of 55 m, in pristine and eutrophic areas. This alga can develop more
2nd Mediterranean Symposium on the Non-Indigenous Species (Genoa, Italy, 22-23 September 2022)
129