The Marine Macrophytes Study Group (GEMM) blog is a site to share scientific research in marine ecology, formalities aside
...because there are some moments in scientific life for which there are no technical reports, articles, lectures or conferences...
From 6 to 10th of November took place in
Sanya, China, the 11th International Seagrass Biology Workshop (ISBW11)
organized by South China Sea Institute of Oceanology, Chinese Academy of
Science and sponsored by the World Seagrass Association (WSA) among others.
Under the main theme “Declining seagrasses in
a changing world”, experts from all over the world presentedtheir latest works and discussedabout four main questions: 1) Ecosysems
vulnerability and resilience, 2) Biodiversity and ecosystems services, 3)
Management and restoration and 4) Key ecological processes.
Both temperate and tropical seagrasses are
vulnerable to global changes caused by human activities (i.e. eutrophication),
climate change (i.e. temperature increase), and naturalprocesses (i.e. tsunamis). Understanding how
seagrasses respond to these changes is critical for future ecosystem
management.
Our contribution to these conferences was with
two oral presentations. Neus Sanmartí presented the study “Positive interactions
between fan mussel and sea urchins in seagrass meadows: can it increase
herbivory pressure?” This work showed how strong positive interactions between Pinnanobilis and Paracentrotuslividus within a Cymodocea nodosa meadow can
affect indirectly the herbivory pressure on the plant. Aurora M. Ricart followed with her
presentation “The effects of landscape configuration on the exchange of
materials across habitats on marine coastal ecosystems”. This work showed the
effect of landscape configuration on the exchange of materials, an enhanced
export of detrital leaves with reduction on seagrass patch size and a nitrogen
limitation on leaves on reduced seagrass patches.
Aurora and Neus at ISBW11
Besides the excellent conference, we had also
time for a field trip to know the Chinese tropical seagrass species and also to
visit the city of Sanya and enjoy its exotic food.
Marine
landscape has a deep, yet relatively unexplored, influence on ecosystem
functions. We, ecologists, often transmit the biased impression that a given
square meter of an underwater habitat (say, for example, of a seagrass meadow)
follows exactly the same functional pattern, irrespectively of its context.
Landscape ecology tells us that how a square meter of a given habitat works
largely depends on how it is embedded in the mosaic of habitat patches in the
sea bottom. In other words: ecological processes within a given habitat will
depend on which are the habitat neighbors. In this complex scenario, herbivory
plays an important role in population dynamics, composition, distribution,
production and biodiversity of seagrass meadows.
As a part of a large collaborative
research project (“ECOMOS: The influence of landscape mosaics in mediating
functional interactions in marine ecosystems: an experimental approach”), we examined herbivory in Cymodocea nodosa meadows, and compared the herbivory rates in
different contexts, such as meadow edges, frontiers (between Cymodocea nodosa and Posidonia oceanica meadows, between
meadows and rocky reefs) and central areas of large meadows. The study was conducted
in the bay of Fornells in Minorca Island (Balearic Archipelago) in June 2014.
It was a hard underwater work to
mark and measure hundreds of the thin C.
nodosa leaves, which was eased by the outstanding beauty of the island and
its underwater landscapes. Hope that this effort will render nice results in
the next future…
Grazing mosaics: Seascape attributes drive differences in herbivory in seagrass meadows
You can access the full text published in Functional Ecology or the pre-print version through Researchgate. Even the simplest ecosystems exist as a patchwork of connected habitats forming a complex matrix through which animals have to navigate. The configuration of this mosaic can seriously affect both the number of species that can use the landscape, as well as their abundances. Some of these species may themselves be important actors in ecosystem processes, performing critical roles as herbivores or predators. By modifying how these species use the ecosystem, these landscape characteristics could have important implications for ecosystem functioning. In our study, we looked at how differences in seagrass meadow mosaics could influence the way herbivory (a key process in these systems) was distributed across the landscape. Our principal herbivores were a mobile fish and a much less-mobile sea urchin. If these species were being influenced by the configuration of the patchwork, we hypothesised that differences in their interaction with landscape attributes would significantly influence herbivory rates. To do this we measured rates of herbivory in seagrass patches that were embedded either in rocky substrates or on sand (the matrix attribute), close or far from rocky reefs (the distance attribute), and in the interior of meadows or at their edges (the edge attribute). We found that herbivory was higher in patches set in a rocky matrix compared to those on sand, and that the centres of meadows received higher rates of herbivory than their edges. These patterns were not influenced by the distance of the patches to rocky reefs. In itself this shows that landscape configurations can play an important role in determining how vital functions are distributed across the ecosystem. To understand if herbivore numbers or food quality could explain these patterns, we measured herbivore abundances, seagrass production and plant quality in all the studied patches. Interestingly, the patches did not show significant differences in these variables. This suggests that the most likely reason for the patterns we recorded in herbivory lie in behavioural differences between species in their evaluation of risk, movement and food preference in relation to landscape configuration. Our results indicate that species richness and abundance patterns may not be sufficient to predict the impact of key species on the functioning of ecosystems within a mosaic of habitats.
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.
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.
From the
Pleistocene to the Anthropocene. Conference in Oxford
Last week Jordi Pagès
attended the Megafauna and ecosystem function conference in Oxford. It was a
multidisciplinary meeting full of interesting people from different fields. The
conference had three aims: (1) to understand megafaunal extinctions, (2) to become
aware of the great impacts of megafauna on ecosystem functioning (before and now)
and (3) to analyse the possible implications of rewilding.
The main question
during the first day was to try to elucidate the causes of megafaunal
extinctions at the end of the Pleistocene. We listened to several researchers
presenting evidences that at least for the Americas and Australia, the
principal cause of these extinctions was the arrival of Homo sapiens. In Europe, the combined effects of a climate change
plus human arrival were possibly the reasons of the extinction of the mammoth, among other huge mammals.
During the second day,
we were presented with evidences of the great role that megafauna had and has
in spreading nutrients from rivers to floodplains, their role in linking
interaction networks, their importance in determining canopy height across most
biomes, their crucial role in dispersing fruits and seeds, etc. Several researchers
suggested that if we look carefully at European flora, we can still find a
great number of megafauna-adapted species (e.g. to mammoth or rhinos), such as Prunus spinosa (with long hard spines),
or trees such as the birch or the hazel that resprout very easily, etc. The
final talk of the day was by George Monbiot, a biologist and journalist for The
Guardian. The talk was a spectacular introduction to the rewilding debate,
which was the theme of the last day of the conference (find a summary of his talk
clicking the link at the end of this post).
On the third day we focused
on the effects of reintroducing megafauna into the wild, or even on the possibilities of bringing back (de-extinct) species such as
the mammoth. Sergey Zimov and Franz Vera presented their respective long-term
“experiments” on the effects of rewilding megafaunal species. The impacts of
these huge ecosystem engineers in Siberia and The Netherlands respectively are spectacular; they challenge the old-standing hypothesis by Hairston, Smith and
Slobodkin on why the world is green. Indeed, both scientists argued that the world we currently live on might follow the HSS hypothesis (i.e. plants
dominate the world, since herbivores cannot control them thanks to their being
top-down controlled by predators); but this might not be the case in the Pleistocene
world, when megaherbivores dominated the Earth. Very interesting views!
We will write about
our poster presentation in a coming post! Until then, you can find most of the
audios and slides of the conference in this website:
Last week, (4-6 March) a large representation of our group attended to the Final Conference of the Cost Action “Seagrass productivity: from genes to ecosystem management” (posar link) that was held in Olhão, Portugal.
This conference, with the topic Seagrass in Europe: threats, responses and management, was an excellent opportunity to bring together researches and students from several European countries, and also from outside as Israel, Tunisia or Mexico, and to exchange recent findings and advances in our challenging topic.
Our contribution to the Final Conference was substantial. Teresa Alcoverro with and interesting keynote lecture talked about the seagrass indicators, status and management in Europe and what has been learned from the Action. Guillem Roca followed with an oral session about detecting water quality improvement in the Catalan Coast using seagrass indicators. Aurora M. Ricart presented some results of her PhD research about the importance of landscape configuration and the sources of organic matter into surface sediments of Posidonia oceanica seagrass meadows. Moreover, Jordi Boada presented a poster about his PhD research on the role of habitat complexity in top down and supply side for the Paracentrotus lividus population in NW Mediterranean ecosystems and Neus Sanmartí and Marta Pérez also presented a poster about the importance of root morphology on symbiotic relationship between lucinid bivalves and the seagrass Cymodocea nodosa.
Besides the excellent keynote lectures, communications and posters, there was also plenty of room to share many good times and also to taste the excellent Portuguese cuisine.
Some of us have the opportunity to visit Ria Formosa and see the intertidal meadows of Zostera noltei.
The purple sea urchin Paracentrotus lividus is of the most important herbivores in Mediterranean shallow ecosystems. Seagrass meadows of Posidonia oceanica and macroalgal communities on rocky reefs are the main habitats of this species. As keystone species it can drive ecosystem shifts when the population is out of control, turning a fleshy erect algae system to barrens, characterized to be less productive and diverse. To identify the ecological processes influencing population dynamics of P. lividus is crucial to predict when this outbreaks will occur.
For instance, predation is a community structuring agent in natural ecosystems. In the following video we show predation process and fish predators and scavengers of the sea urchin P. lividus in NW Mediterranean habitats. This is part of the research carried out by one of our team members in Medes Island Marine Protected Area.
The
seagrass (Posidonia oceanica) meadow off
the Medes islands (Marine Protected Area) is among the most studied in the Mediterranean.
The first scientific dive here took place in 1967.
From 1984, scientist
from the Ecology Department at the University of Barcelona and from the Centre
for Advanced Sudies of Blanes (CEAB-CSIC) have been monitoring yearly the
meadow. Data on seagrass cover and density, as well as on accompanying fauna,
are obtained each autumn. The time series is probably the longest in
Mediterranean seagrass meadows.
The 2013
monitoring was delayed for logistic reasons. This represented some extra cold
for the divers, as shown in the video.
Long data
series for understanding natural systems under a larger temporal perspective are
of paramount importance in a changing world.
La pradera de Posidonia
oceanica de las islas Medes, un área marina protegida desde principios de
los ochenta, es posiblemente una de las más estudiadas del Mediterráneo, o al
menos una de las decanas de la investigación submarina, puesto que las primeras
inmersiones para su prospección científica se iniciaron en 1967.
Desde 1984, se mantiene, a cargo de investigadores del
Departament d’Ecologia de la Universitat de Barcelona (y también del Centre d’Estudis
Avançats de Blanes, del CSIC) un programa de vigilancia, gracias al cual se
dispone de la serie de datos más larga que existe sobre praderas mediterráneas.
Cada año, en otoño, se realizan inmersiones para medir
densidad y cobertura de la pradera, así como para seguir la evolución de
estructuras erosivas y comprobar cómo varía la fauna asociada (holoturias,
erizos, Pinna nobilis…). En estas
inmersiones, y a lo largo de los años, han participado ya más de 30 personas, naturalistas,
becarios pre y postdoctorales, investigadores y profesores, cuya contribución
es totalmente altruista.
La campaña de 2013, por contingencias logísticas, se retrasó
hasta diciembre, por lo que los expedicionarios de ese año tuvieron que
aguantar un poco más de frío del que suele ser norma.
Las series largas de datos son ventanas abiertas a una mejor
percepción de los ecosistemas, en escalas de observación que sólo una buena
dosis de paciencia permite aprehender. Estas series largas han ayudado a
entender mejor los sistemas naturales, y también, es de esperar, deberían
ayudar a su gestión y conservación.
Más datos sobre el seguimiento de la pradera de las islas
Medes:
