I start from the huge experience and the many papers published by Dra. Fernández, Dra. Viejo and Dr. Arenas for more than ten years on dynamic, structure and general ecology of Sargassum muticum on the north coast of Spain.

Oli

One of the more surprising results they found was to check that the Gelidium biomass has decreased (at least in one localitie) since the arriving of Sargassum in 1988. An important part of my work will be relationed with this, first of all corroborating it and then trying to know the implicated mechanisms on this decline. On the other hand, I will try to provide more information on the conditions of the native communities for a succesfull invasion of an alien. I will try to study, as well, some aspects on the interactions between Sargassum and native macroalgae.

The main objectives of may work are:

1.- To check the biodiverstiy status on the communities successfully invaded by Sargassum muticum.

2.- To check if there are competency between the invasive species (Sargassum muticum) and any native species (Gelidium latifolium, Bifurcaria bifurcata and Cystoseira tamariscifolia).

3.- To assess if there have been changes on the communities dynamic and structure after the establishment of the invasive algae. If there had any change I would check if these communities have recovery ability after the elimination of the alien.
This chapter will be developed in rocky shores and in tidepools.

4.- To know the features that confer to a community the resistence against an alien.

Íñigo

WORKPLAN

It is divided in three general sections:

1.- Effects of the invasion on community level.

A) ¿Are there changes on the community structure after the invasion?

Hypothesis to check: The arriving of Sargassum muticum on Asturias coasts has introduced changes on the native intermareal algae communities

Workplan: Monthly during one year will be carried out three 50x50 scrape on G. latifolium belt. It will be assess biodiversity at each date and biomass of all the conspicuous species. These data will be compared with data obtained in the same way 25 years ago, when S. muticum was not present yet.

B) Community recovery after invasion:

Hypothesis to check: Exclusion of aliens favor recovery of native species, in mature communities and during the succession.

The experiment will be two years long and will consist in removing of experimental surfaces 50x50 in 1 m2 ( to prevent border effect) all Sargassum muticum plants. This avoid us to determine if the communities can recovery or not after the removing of the alien. The sampling period will be bimonthly and they will consist in the meassure of cover and biomass.

C) Experiments of competency on rocks:

i) Hypothesis to check: Bifurcaria bifurcata and Cystoseira baccata can competitively exclude Sargassum muticum.

It will be done survival and growth experiments with Sargassum embryos on Bifurcaria, Gelidium and Cystoseira belts, under normal coberture and under cleared areas of the dominant algae.

ii) Hypothesis to check: Sargassum is better competitor than Gelidium latifolium.

It will be checked squares with different densities of both species and in these squares it will meassured coverage and biomass of the two species.

100% Sargassum-0% Gelidium
50% Sargassum-50% Gelidium
0% Sargassum-100% Gelidium.

D) Recruitment of Sargassum muticum in areas with different intensities of disturbance:

Hypothesis to check: Sargassum muticum can recruit stronger in areas where it has been a disturbance than areas without disturbance.

It will be installed 6 experimental 50x50 cm area surfaces on the Gelidium latifolium belt for each treatment:

a) Control surfaces (no manipulated)
b) Scraped surgaces six months before the inoculation.
c) Scraped surfaces just before the inoculation. The inoculation will be natural, with the fertile algae of the area of the study.

When the recruits are visible (october-november) it will be made recounts on the experimental surfaces to look for the higher recruitmen conditions.

E) Which is the way S.muticum reduce G latifolium cover?

Hypothesis to check: The shading of S. muticum inhibit G.latifolim growth.

An experiment to contrast the hypothesis will be started in spring 2003.

2.- Effects of the invasion on tidepools.

Hypothesis to check: Removing of an alien induce changes on the structure and biodiversity of the communities.

It will be selected 24 tidepools of two measures (big and small) of the same tide level in three localities of the north spanish coast. Half of the tidepools of each measure will be manipulated scraping all the Sargassum plants. Periodically it will be observed changes in species and abundances.

The study of these tidepools can be used also to clasificate them on number and kind of species related to the measure of the tidepool, situation, substrate, etc.

3.- What are the factors that confer to a community resistance to an invasion?

Hypothesis to check: the fluctuation of resources due to disruption confer to communities lower resistance against invasions.

It will be isntalled experimental surfaces to apply two factors productivity and disruption, with three intensities. Other surfaces will be maintaned without manipulations as controls.