From exotic to invasive in record time: The extreme impact of Rugulopteryx okamurae (Dictyotales, Ochrophyta) in the strait of Gibraltar.

In 2015, the exotic seaweed Rugulopteryx okamurae was detected for the first time on the south side of the Strait of Gibraltar, in Ceuta (northern Africa). This highly sensitive area is ideal for monitoring local environmental impacts arising from global warming, as well as the intrusion of alien species. Within one year, R. okamurae became an invasive species with an overflowing competitive capacity and growth. In 2015, more than 5000 tons of upstream biomass was extracted from beaches in Ceuta, and it has since spread irrepressibly on rocky illuminated bottoms of the subtidal zone to a maximum observed depth of 40 m. The highest coverage (80-90%) of R. okamurae in Ceuta was observed between 10 and 20 m depth in illuminated habitats, where it was having a severe impact on local benthic communities which were displaced. Between 5 and 30 m depth, coverage of R. okamurae exceeded 70% over a wide variety of substrate types. A submarine sentinel sessile bioindicators permanent quadrats (SBPQ) station installed in 2013 on poorly lit, vertical, and shady substrate in the El Estrecho Natural Park, on the north side of the Strait of Gibraltar (Tarifa), detected the presence of R. okamurae in July 2016 and recorded the subsequent increase in coverage. These findings reveal the useful role of this type of monitoring SBPQ sentinel station for the detection of impacts and exotic species in marine protected areas, and for the monitoring of global warming based on indicator species. We conclude that the catastrophic bloom of R. okamurae exhibited an initial geographical expansion (2015-2017) to the northern coastal area of the Strait of Gibraltar (Tarifa-Gibraltar) and subsequent extension in the south of the Iberian Peninsula, towards the Atlantic coast (2018) and the Mediterranean coast (2019). This bloom could have been associated with the temperature peak in July 2015 and was thus possibly linked to global warming.

Benthic assemblages, biodiversity and invasiveness in marinas and commercial harbours: an investigation using a bioindicator group.

Fouling communities on artificial marine structures are generally different from benthic communities in natural rocky habitats. However, they may also differ among different types of artificial structures. Two artificial structures in direct contact with arriving vessels were compared: floating pontoons within recreational marinas, and sea-walls within commercial harbours. Natural rocky habitats were used as a reference, and the genus Eudendrium (Cnidaria, Hydrozoa) was chosen as a bioindicator. The assemblages were different among the three types of habitat studied, with different species characterising each habitat. The probability of finding an invasive Eudendrium species was significantly higher on pontoons. Diversity was the lowest on pontoons, but it was not significantly different between sea-walls and natural rocks. In general, a barrier to the spread of exotic species exists between harbours and natural rocky habitats. Floating pontoons seem to be a less suitable habitat for native fauna and a key element in marine biological invasions.

GROWTH DYNAMICS OF ULVA ROTUNDATA (CHLOROPHYTA) IN A FISH FARM: IMPLICATIONS FOR BIOMITIGATION AT A LARGE SCALE(1).

Changes in biomass of several macroalgae [Ulva rotundata Bliding; Gracilariopsis longissima (S. G. Gmel.) Steentoft, L. M. Irvine et Farnham; Ulva intestinalis L.; and Cladophora sp.] and marine plants (Zostera noltii and Ruppia cirrhosa) growing naturally in earthen ponds of a fish farm (Acuinova, San Fernando, Southern Spain) were recorded during a year. The farm is mainly devoted to the culture of gilthered seabream (Sparus aurata). The most conspicuous algal species thriving in the ponds was U. rotundata, which reached densities up to 600 g dry mass · m(-2) and produced up to 20.45 g C · m(-2) · d(-1) . Dissolved nutrients (phosphate and ammonium), tissue nutrient content, and growth rates of this species were estimated during 2001 and 2002. Evidence of natural biomitigation by U. rotundata when water circulates throughout the fish farm is presented. Due to the fish cultivation, both phosphate and ammonium increased as water circulated from the preculture ponds to the postculture ponds. As a consequence, U. rotundata tissue nitrogen (N) and phosphorus (P) increased from algae growing in preculture ponds to algae growing in the outflow channel, so that mean C:N:P ratio varied from 773:57:1 in preculture ponds to 567:64:1 in the outflow channel. Phosphorus limited growth of U. rotundata during the spring. As growth rates increased as a function of tissue P, data were fitted to the Droop equation. From this equation, the estimated maximal growth rate was 0.295 ± 0.041 d(-1) , the subsistence quota was 0.05 ± 0.01% P of dry mass, and the critical quota was 0.215% P of dry mass. The results suggest that management of the fish farm based on a large-scale integrated mariculture system of fish and macroalgae may increase the total ecological and economic benefits, both for the farm and for the environment.