CORALCHANGE · Effects of global warming and alien species invasions on high diverse communities of NW Mediterranean Sea

Effects of global warming and alien species invasions on high diverse communities of NW Mediterranean Sea

Publishable Summary Europe's marine biodiversity constitutes a vast but fragile resource of great cultural and economic importance to its people. Many marine species of the Mediterranean Sea are presently endangered and some are probably prone to extinction. The degradation of marine Mediterranean ecosystems began centuries ago, but there is no global summary of the magnitude of this change. This project aimed the direct and combined effects of global warming and invasive species on high-diverse coralligenous communities. The highly-diverse coralligenous communities support social and economic development in several European regions. Therefore, their protection is an imperative socioeconomic and environmental need. My research is therefore useful to provide information on the future impacts, allowing managers to anticipate ecosystem decline through an understanding of the sequences of species and habitat loss. A summary description of the project objectives and of the work performed: Factors that favour the spreading of the invasive species Womersleyella setacea and Caulerpa racemosa: The aim of this objective has been first, to elucidate abiotic conditions influencing invasive species biology and growth. In this line, we have monitored and studied Caulerpa racemosa and Womersleyella setacea populations in situ, besides to experimentally study effects of different temperature and irradiance conditions in the laboratory. On the other hand, I have also studied how biotic interactions with the native hosting assemblages can influence macroalgae invasions in the Mediterranean Sea. Response of calcareous algae and gorgonian populations face the warming trend and the invasive species Womersleyella setacea and Caulerpa racemosa: In order to assess the thermotolerance thresholds of gorgonian I set up an experiment submitting the target species to different temperature treatments. Furthermore, in order to evaluate the potential adaptation of different populations dwelling with different environmental conditions and genetic origin, the experiment was carried out with two different populations developing in contrasting abiotic conditions. On the other hand and thanks to the expertise of my scientific in charge we have set up several experiments in the laboratory in order to elucidate temperature and irradiance requirements and tolerance of the most important calcareous species thriving in the Mediterranean coralligenous. Impacts of positive thermal events and invasive species on coralligenous communities: Both invasive species had a strong and consistent negative effect on P. clavata fitness, demonstrated by the lower survivorship, higher necrosis rates and lower biomass of the colonies submitted to the invasive algae overgrowth. Furthermore, considering that the persistence of P. clavata populations affected by mass mortality outbreaks mainly depends on the recovery of small colonies, the most susceptible to the invasive species overgrowth, our results provided new insights into the additional negative effect of invasive species on the recovery of P. clavata populations already affected by mass mortality outbreaks. Clearly significant results Temporal and spatial variability of the invasive Caulerpa racemosa var. Cylindracea: The invasive green alga Caulerpa racemosa var. cylindracea represents an important threat to the diversity of Mediterranean benthic coastal ecosystems by interfering with native species and modifying benthic assemblages. The present study deals for the first time with temporal and spatial variability on biomass and phenology of Caulerpa racemosa, considering both deep and shallow-water populations. Two sampling depths (30 and 10 m) were sampled at three different rocky bottom sites every three months in the Archipelago of Cabrera National Park (western Mediterranean). All morphometric variables analysed showed a spatial variation and temporal patterns depending on depth. Within depths, Caulerpa racemosa biomass, stolon length, number of fronds and frond length were usually significantly higher at deep water populations, suggesting that Caulerpa racemosa grows better in deep-waters. Moreover, deep and shallow-water populations displayed a high temporal variation although no evidence of seasonal patterns was found, in contrast with what has been reported by other authors. The sources of this variability are still unknown but probably both physical factors and differential herbivory pressures display a key role. Cebrian E, Ballesteros E (2009) Temporal and spatial variability in shallow and deep-water populations of the invasive Caulerpa racemosa var. cylindracea in the western Mediterranean. Estuarine and Coastal Shelf Sciences, 83: 469–474. Invasion of L. lallemandii on rocky benthic assemblages: Lophocladia lallemandii (Montagne) F. Schmitz is an invasive red alga which has recently become widespread in the Mediterranean Sea. Temporal variability in biomass of L. lallemandii across a depth gradient (10 to 30 m depth), as well as invasive potential by means of its reproductive output and recruitment abilities were assessed. No variability was found across the depth gradient, suggesting a homogenous pattern of invasion between the sampled depths. In contrast, all variables displayed a clear temporal pattern with higher growth and reproductive output with increasing temperatures, both in shallow and deep populations. The high total and relative biomass values of L. lallemandii confirm the invasive nature of this species. Likely, the high potential reproductive output by means of tetrasporocysts (41.8 ± 9.34 cm-2), together with the high recruitment abilities (352 ind. m-2) explains the great colonisation capacity of L. lallemandii which prevents any kind of manual eradication. Cebrian E, Ballesteros E (2010) Invasion of Mediterranean benthic assemblages by red alga Lophocladia lallemandii (Montagne) F. Schmitz: depth-related temporal variability in biomass and phenology. Aquatic Botany, 92: 81-85. Native herbivores provide resistance to macroalgae marine bioinvasions: Generalist herbivores in marine ecosystems are poorly examined for their potential to serve as a source of biotic resistance against algal invasion. We assessed how one of the main generalist herbivores in Mediterranean rocky reefs (the sea urchin Paracentrotus lividus) affects Lophocladia lallemandii and Caulerpa racemosa, two algal invaders with strong detrimental effects on native benthic communities. In a comparison of sea urchin gut contents to algal community composition, strong preferences were exhibited, leading to no relationship between consumption and availability. Both Caulerpa racemosa and L. lallemandi were abundant in algal assemblages (more than 60% occurrence), but Caulerpa racemosa (20% of diet) was consumed more than L. lallemandi (3.5%). Experimental enclosures of sea urchins (12 sea urchins per m-2) were carried out in locations where L. lallemandii was already established and Caulerpa racemosa was rare (new invasion) or abundant (established invasion). Caulerpa racemosa was negatively affected by sea urchins only when it was rare and no effect was detected when the alga was already abundant. Results for L. lallemandi were exactly opposite: urchins limited seasonal increases in L. lallemandi in highly-invaded areas. Because of the small amount of direct consumption of L. lallemandi, its decrease in abundance may be related to the grazing of native algae where L. lallemandii is attached. Overall, our results show that high densities of native herbivores may reduce invasive algae at low densities, due to a combination of direct and indirect effects, but it has no significant effect in highly-invaded areas. Cebrian E, Ballesteros E, Linares C, Tomas F. Do native herbivores provide resistance to Mediterranean marine bioinvasions? A seaweed example. Biol Inv. DOI 10.1007/s10530-010-9898-1. Differential herbivory of invasive algae by native fish in the Mediterranean Sea: The potential role of generalist herbivores to serve as a source of biotic resistance against algal invasion in marine ecosystems has been poorly examined. The present study investigates the capacity of Mediterranean herbivorous fishes to consume three of the most invasive seaweeds of the western Mediterranean (Caulerpa racemosa, Lophocladia lallemandii and Womersleyella setacea) and examines vertical and temporal variations of such consumption. Our results show that although fish feed throughout the depth gradient examined (5-35 m), they concentrate in shallow waters and can consume high amounts of Caulerpa racemosa. Such high ingestion of Caulerpa racemosa does not appear to be random, since this alga is consistently chosen when offered in pairs with several native species. Conversely, L. lallemandii and Womersleyella setacea are barely eaten by fish even though they can be very abundant in the field throughout the year. Our results suggest that fish could be an important controlling agent that has been overlooked in temperate marine invasions and they may be able to provide certain resistance to Caulerpa racemosa invasion. In contrast, they are unlikely to exert any important control effects on L. lallemandii or Womersleyella setacea. Tomas F, Cebrian E. Ballesteros E. Differential herbivory of invasive algae by native fish in the Mediterranean Sea. Estuarine and Coastal Shelf Sciences, 92: 27–34.

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