Distribution of the epiphytic organisms on Posidonia australis and P. sinuosa, two seagrasses with differing leaf morphology

Abstract

The distribution of epiphytic algae and sesslle invertebrates on the leaves of the seagrasses Posidonla australis Hooker f. and P, sinuosa Cambridge and Kuo is not random. Epiphyte load on the leaves of both species increases with increasmg distance away from the basal meristem There are approximately 3 times as many epiphytic algal species as invertebrate species, and many of these epiphytes grow at distinct locations on the leaves. Epiphytic invertebrates were found primarily on the basal sections of the leaves, whereas algae were most abundant near the leaf apex. Distribution of epiphyte load across the leaf surface was also non-random, with initial settlement of epiphyte propagules occurring at the marqns of the leaves. The structure of the epiphytic community is strongly correlated with leaf age, with a greater abundance of epiphytic species occurring on the older leaves It is clear that leaf morphology also plays a significant role in the distribution of the epiphytes. There is no apparent difference m the epiphytic community between the sides of the flat P. australis leaf whereas, in P. sinuosa, the concave side of the curved leaf supports a more diverse epiphytic community than the convex side. Similar patterns in the distribution of epiphytic organisms were observed on artificial seagrass leaves, indicating that, although a temporal component is involved, epiphyte distribution is influenced mainly by the relative position upon the leaf surface as well as leaf morphology, which affects the water flow pattern over the leaf.

Variability patterns of epibenthic microalgae in eastern Tunisian coasts

“…Moreover, the epiphytic species zonation on leaves of Posidonia was reported to be related to the concentration of phenolic compounds produced in abundant quantities, depending on the state of stress caused by environmental conditions (Dumay et al 2004). However, the use of artificial leaves made of plastic tape showed the same apico-basal distribution of epiphytic algae (Trautman and Borowitzka 1999), supporting the hypothesis that epiphyte settlement was unlikely to be the result of changes in the surface chemistry of the leaves (Borowitzka et al 2006). These variations were likely due to differences in hydrodynamic or light intensity related to the shape and orientation of the leaves.…”

“…This result had already been reported in previous studies (Alcoverro et al 2004) and explained by the fact that the apical part of the leaves, and to a lesser degree the middle part, expose their epiphytes to high light intensities and water movement. This would promote photosynthetic organisms such as epiphytic macroalgae, which increase the nutrient intake from water and remove inhibitory substances (Trautman and Borowitzka 1999). Moreover, the epiphytic species zonation on leaves of Posidonia was reported to be related to the concentration of phenolic compounds produced in abundant quantities, depending on the state of stress caused by environmental conditions (Dumay et al 2004).…”

Nitrate reductase activity in macroalgae and its vertical distribution in macroalgal epiphytes of seagrasses

“…The current study did not include detailed analyses of species composition and there are few comparative studies of the epiphyte assemblages on different seagrasses. However, previous work has shown a significant variation in the composition of epiphytes among seagrass species (Trautman & Borowitzka 1999, Lavery & Vanderklift 2002. It is possible, therefore, that some of the differences in mass-specific NR activity between A. antarctica and P. sinuosa epiphytes were due to differences in the species composition.…”

“…For seagrasses with strap-like leaves, such as Posidonia sinuosa, the diversity, as well as biomass, of epiphytic algae is highest on the leaf apex (Trautman & Borowitzka 1999). P. sinuosa leaves have an average longevity of 245 d (Marbà & Walker 1999) and grow from the base, with the oldest part of the leaf at the top of the canopy where the greatest epiphyte biomass was observed (Table 2; Trautman & Borowitzka 1999). This 'conveyer belt' of P. sinuosa leaf growth means that algae recruited to the younger leaf surface that remain attached to the leaf will be more mature when they reach the top of the leaf, a factor which may influence NO 3 -metabolism.…”

Evolutionary history of the seagrass genus Posidonia

“…australis') (Cambridge & Kuo 1979). The species that gives the name to this complex has the widest distribution among Australian Posidonia species and is found from western Australia (from Shark Bay), around the southern and southeastern coastlines and along the northern coast of Tasmania (Cambridge & Kuo 1979, Kuo & Cambridge 1984, Trautman & Borowitzka 1999 Fig. B1A).…”