New published paper from Oriol Mascaró PhD thesis!

After a long journey, the chapter four of the thesis of Oriol has been published in Estuarine, Coastal and Shelf Science. In this paper we report an assessment of shoot demography in the seagrass Cymodocea nodosa at an unprecedented high-resolution temporal level. We attempted to estimate shoot mortality and recruitment rates, that is, the rates at which the units (say “individuals”) of the plant die and born. We found that recruitment (“births”) were strongly correlated to light availability and were partially supported by carbohydrate resources, that is, energy saved from the preceding year. In contrast, mortality was correlated to high temperatures stimulating respiratory demand and to shading among neighboring shoots. In addition to this, the presence of macroalgae in eutrophic areas caused additional mortality of shoots.

As births exceeded deaths from March to August, the number of shoots, and then the density and biomass of the meadows increased during that period. In contrast, as deaths exceeded births from August to November, density and biomass of the meadows decreased during that period.

In summary, the strong seasonality in the number of shoots in these seagrass meadows result from the different controls by environmental factors on births and deaths, and in the seasonal uncoupling between these two factors. 

 

Mascaró, O. Romero, J. Pérez, M., 2014.  Seasonal uncoupling of demographic processes in a marine clonal plant. Estuarine Coastal and Shelf Science, 142: 23-31.

 

 

 

 

 

 

Reproduction of Pinna nobilis

Pinna nobilis in a Cymodocea nodosa meadow.
Northwestern Mediterranean, Delta de l'Ebre.

These images were captured during field work in the summer of 2013.

Conserving ecosystem modifiers: a double-edged sword

Poster presentation at the Megafauna and Ecosystem Function conference. Oxford 17-20th March

Abstract. The drastic decline of megaherbivores from the world’s oceans has contributed to a growing uncertainty of their functional contribution to the dynamics of marine vegetated ecosystems. Conservation efforts have focused on restoring these flagship populations to historically pristine levels, without much understanding of the sometimes-unintended consequences these population increases can have on extant ecosystems. This becomes particularly important given that most megaherbivores are ecosystem engineers. We studied the dominant megaherbivores (the dugong, Dugon dugong, a herbivorous fish, Sarpa salpa and the green turtle, Chelonia mydas) in three seagrass meadow systems in order to understand the functional consequences of their engineering. While the dugong populations we studied were at critically low densities in the Andaman and Nicobar Islands (India), both Sarpa salpa densities in Medes Islands in Catalonia and green turtle populations in the Lakshadweep Archipelago (India) are among the highest recorded, thanks to enhanced protection. At all three locations, we assessed the impacts of these megaherbivores by deploying exclusion cages in seagrass meadows, measuring direct herbivory rates on seagrasses, evaluating seagrass responses to elevated herbivory rates (in terms of production) and assessing the community of seagrass-dwelling fish or invertebrates to test for cascading effects. Our results show that all three herbivorous species are important ecosystem engineers, significantly modifying the density and canopy structure of meadows.  Even at critically low present densities, dugongs were able to overgraze meadows in which they fed, and the high-density populations of fish and turtles (in the Mediterranean and Lakshadweep respectively) had strong effects on grazed meadows including decreased seagrass shoot biomass and production, shifts in dominant seagrass species and lowered habitat structure. Taken together, this suite of habitat changes had serious cascading implications for the entire ecosystem: with increasing structural loss, these ecosystems showed major declines in communities of invertebrates and fish. In addition, in the Mediterranean, we document that megaherbivore fish can trigger complex indirect interactions, modifying predator-prey dynamics by increasing predation rates on other keystone herbivores. Our work across these systems is highlighting the fact that marine megaherbivores are potentially strong interactors capable of producing a cascade of direct and indirect effects on seagrass ecosystems. This has important implications when setting conservation targets for these flagships since it requires a more holistic understanding of the functional consequences of their conservation on entire ecosystems given their present extent and carrying capacity.

You can download the poster in pdf at: https://www.dropbox.com/s/mx8jk8nyolgvwsh/Megafauna_v8OK.pdf