Influence of biotic and abiotic factors of seagrass Posidonia oceanica recruitment: Identifying suitable microsites.

The period between seed germination and successful seedling establishment is considered the most vulnerable phase for plant development. To better predict recruitment patterns within plant communities, it is essential to identify the abiotic constrains and biotic interactions that allow for the colonization of substrates by plant species. We evaluated which combination of factors are associated with successful survival and development of seedlings of the seagrass Posidonia oceanica in order to identify the most important microsite features acting together on recruitment success. Our results show that P. oceanica seedlings are rather specific in their environmental requirements during their first 18 months of life, when their development and survival are favored in microsites of consolidated substratum (solid rock, and to a lesser extent P. oceanica matte) covered by macroalgae (mainly crustose algae) and located in sheltered locations (with energy flux values not exceeding 7 × 105 kg s-2 m s-1). After this phase, their probability of surviving becomes more independent from external conditions.

Negative effects of warming on seagrass seedlings are not exacerbated by invasive algae.

The observed and projected rise in sea surface temperature challenges marine biodiversity worldwide, and particularly in temperate ecosystems dealing with the arrival of novel species of tropical provenance. When the impacted biota are early life stages of ecosystem engineers, the effects of those impacts are of major concern for ecologists and coastal managers. We experimentally examined the individual and potential additive effects of seawater warming and the presence of the invasive algae on the development of seedlings of the seagrass Posidonia oceanica in a three-month mesocosm experiment. Whereas the presence of the invasive algae (Caulerpa cylindracea and Lophocladia lallemandii) did not result in detrimental effects on seedlings, warming negatively affected seedling development. Interestingly, the presence of both invasive algae may ameliorate the negative effects of warming.

Field transplantation of seagrass (Posidonia oceanica) seedlings: Effects of invasive algae and nutrients.

Seedlings are a key life stage in seagrasses, providing genetic diversity and being a useful tool for restoration. We examined the influence of increased sediment nutrients and the presence of the invasive macroalga Caulerpa cylindracea on the success of in situ transplanting Posidonia oceanica seedlings in a six-month experiment. Our results indicate that one-year old seedlings successfully survive in the field and their survival and growth are positively affected by the presence of C. cylindracea. Furthermore, nutrient addition in the sediment had positive effects on both C. cylindracea (increasing its cover) and seedlings (increasing leaf development), and the increased C. cylindracea cover did not result in detrimental effects on seedlings. Therefore, biological invasions and nutrient addition do not reinforce each other in the short term to negatively impact transplanted seedlings, which highlights facilitative interactions between invasive algae and native seagrass and provides useful information for successful strategies of seagrass restoration.

Fatty acid composition and chilling resistance in the green alga Caulerpa prolifera (Forrskal) Lamouroux (Chlorophyta, Caulerpales).

Plant resistance to chilling injury depends on the maintenance of membrane functions. An increase in the degree of unsaturation of membrane fatty acids can help maintain membrane function at low temperatures by reducing the temperature at which deleterious membrane phase-transitions occur. The fatty acid composition of membranes of the chlorophycean Caulerpa prolifera was determined in summer and winter in the Mar Menor coastal Lagoon (SE Spain). In January the percentage of polyunsaturated fatty acids was higher than in August. Membrane content of mono- and diunsaturated fatty acids was similar in the two seasons. The unsaturation index of membranes changed from 76.15 +/- 1.80 (mean +/- standard error) in August to 128.05 +/- 0.32 in January. It is suggested that this increase in the degree of unsaturation might be important to allow C. prolifera to decrease its lower threshold of survival temperature and acclimate net photosynthesis and dark respiration rates to winter temperatures in the Mar Menor.