preliminary report of ecomers 2011 field · pdf fileecosystems are generally able to...

Preliminary report of ECOMERS’ 2011 field campaigns

Biodiversity assessment in three alternate stable states of

the biocenosis of photophilic macroalgae of Infralittoral Mediterranean rocky reefs:

Cystoseira forest, Dictyotales- and/or Sphacelariales- dominated assemblages and barren-grounds

Scientists attached to the laboratory Ecosystèmes Marins Côtiers et Réponses aux Stress (ECOMERS)

from the University of Nice Sophia-Antipolis conducted two field campaigns in May and July 2011,

respectively in Corsica and Menorca. The aim was to describe flora and fauna in three different habitats

recognized as alternate stable states of the biocenosis of photophilic macroalgae of Mediterranean rocky

reefs: Cystoseira forest, Dictyotales- and/or Sphacelariales- dominated assemblages and barren-grounds.

Within each habitat, several underwater sampling methods by scuba diving were used for assessing

assemblage structure of (i) sedentary necto-benthic fishes, (ii) cryptic fishes, (iii) vagile macro-invertebrates,

(iv) sessile macro-invertebrates, (v) erect macro-algae and (vi) encrusting macro-algae.

The sampling design included two bioregions (Corsica and Menorca) in order to take into account

natural spatial variability at the scale of the North-Western Mediterranean Basin. In each bioregion, two

localities having all the three different habitats were selected. In Corsica, sampling was done in a protected

locality, “Réserve Naturelle de Scandola”, from 2011 May 7th to 14th

, and in an unprotected locality, “Baie

de Calvi”, from 2011 May 15th

to 21th

. In Menorca, a protected locality, “Reserva Norte de Menorca”, and

an unprotected locality, “Punta Grossa”, were sampled simultaneously from 2011 July 2nd

to 17th

.

This report describes the scientific framework of these field campaigns, the sampling

designs and methods used. Also, it acknowledges the people and organizations who made

these field campaigns possible.

Preliminary report of ECOMERS’s 2011 field campaigns – [email protected] 2/11

Teams and partners involved

In Corsica, the ECOMERS‟ team was composed of Hazel ARCEO, Adrien

CHEMINEE, Jean-Michel COTTALORDA and Pierre THIRIET. They started at the Marine

Protected Area “Réserve Naturelle de Scandola” which is part of the “Parc Naturel Régional

de Corse”. The park management team headed by Jean Marie DOMINICI kindly hosted the

ECOMERS‟ team. Then, for sampling in “Baie de Calvi”, the ECOMERS‟ team settled at

“Station de Recherches Océanographiques et sous-marines (STARESO)” which is a private

marine station headed by Pierre LEJEUNE. Both the local teams of “Réserve Naturelle de

Scandola” and STARESO provided all logistic support: accommodation, boat and driver,

compressor etc. Moreover, their knowledge was really helpful in choosing the study sites and

appropriately managing weather forecast windows.

In Menorca the ECOMERS‟ team was composed of Adrien CHEMINEE and Pierre

THIRIET and was strengthened by three members of the NGO “Septentrion Environnement”:

Solène BASTHARD-BOGAIN, Médéric BEZELGUES and its director Olivier

BIANCHIMANI. They provided priceless help all throughout the mission, a testament to their

skills, professionalism and involvement into environmental conservation issues. The team was

kindly hosted at the “Estación de Investigación Jaume Ferrer” headed by Joan MORANTA.

This marine station is a branch of the “Instituto Español de Oceanografia”. They provided

boat and accommodation. Moreover, Joan MORANTA and Marta SALES helped in selecting

the study sites through discussions and by accompanying the team during the first field days.

Sampling in the Marine Protected Area “Reserva Norte de Menorca” was allowed by the

“Govern de les illes Balears”.

These field campaigns are part of Pierre THIRIET„s PhD thesis (ECOMERS, 2010-

2013). He is co-supervised by Patrice FRANCOUR and Luisa MANGIALAJO.

Laboratoire Ecosystèmes Marins Côtiers et Réponses aux Stress (ECOMERS)

Pierre THIRIET ([email protected]) & Patrice FRANCOUR (dir. , [email protected])

Université de Nice Sophia-Antipolis, 06108 NICE Cedex 2, France

Association Septentrion Environnement

Olivier BIANCHIMANI (Président, [email protected] )

Maison de la Mer, Anse du Prophète, 244 Corniche Kennedy 13007 Marseille , France

Réserve naturelle de Scandola - Parc naturel régional de Corse

Jean-Marie DOMINICI (Conservateur, [email protected] )

2 rue major Lambroschini BP417 20184 Ajaccio Cedex, France

Station de Recherches Océanographiques et sous-marines (STARESO)

Pierre LEJEUNE (Directeur, [email protected] )

Pointe de la Revellata, BP33 20260 Calvi, France

Estación de Investigación Jaume Ferrer

Joan MORANTA (Coordinador scientifico, [email protected] )

La Mola, Maó, Menorca, Illes Balears, España

Direcció General de Medi Rural i Marí (managing the MPA “Reserva Norte de Menorca”)

Oliver NAVARRO (Coordinador de medio marítimo , [email protected] )

C/ dels Foners, 10 - 07006 Palma, Mallorca, Illes Balears, España

mailto:[email protected]








Scientific framework

Human impacts affect benthic communities in direct (e.g. pollution or habitat degradation)

or indirect ways (e.g. overfishing which can potentially induce trophic cascades and related

habitat shift). Coastal rocky shores are among the most threatened ecosystems, as they are

subjected to both land and sea-based impacts. Unfortunately, biodiversity and functioning of

rocky shores ecosystems in the Mediterranean Sea are still very poorly known, and dramatic

changes are happening without us being able to understand or even notice them.

In Infralittoral rocky reefs of the North-Western Mediterranean, areas preserved from

human impact present a biocenosis of photophilic macroalgae characterized by Cystoseira

forests. Cystoseira species are large brown algae that can thrive and reach high densities from

the surface to the limit of the euphotic zone. They are habitat formers and represent an

important habitat for diversified assemblages of associated macroalgae (e.g., sciaphilic

marcoalgae species), invertebrates and fishes. Cystoseira species are very sensitive to direct

and indirect human impacts and their regression has been recorded in several areas of the

Mediterranean Sea.

Indeed, in areas with degraded water quality (e.g. increase in turbidity, waste waters, other

pollutant), Cystoseira forests disappear and are replaced by Dictyotales- , Sphacelariales-

and/or articulated Corallinales- dominated assemblages (forming bush-land). In areas where

date-mussel fishery and/or overfishing (especially of the sea breams) are occuring, they are

replaced by barren grounds, generally characterized by high abundances of herbivores (sea-

urchins). Such barren grounds are almost lacking in primary producers (except encrusting

Corallinales) and can be compared to desertified areas. These new states of marine

ecosystems are generally able to self-maintain and are therefore considered as alternate stable

states.

Macroalgae are primary producers. Moreover, macroalgal assemblages affect the

structural attributes that define a habitat at a fine spatial-scale. These shifts of alternate stable

states (from forests to bush-lands or deserts) may strongly affect biodiversity and ecosystem

functioning. For instance, the structure of macroalgal assemblages affects benthic invertebrate

assemblages, which occupy intermediate trophic levels between primary producers and fish.

Furthemore, more structurally complex habitats may generally provide more shelter for small-

sized fishes reducing their mortality due to predation.

The “trophic” and the “shelter” roles of macroalgae concertedly determine (along with

many others processes such as settlement/recruitment) the patterns of fish distribution and

abundance that are observed in the field. Therefore, in order to disentangle the respective

contribution of these two functions to the whole ecosystem functioning, the necessary

approach appears to be the complementary use of (1) field survey assessing

abundances/biomasses of every trophic level related to each alternate stable states, (2)

stomach contents and isotopic ratios analysis for assessing energy fluxes, and (3) in situ

experiments where conditions are controlled (especially habitat architecture and predation).


Aim of the present study

As the first step in approaching the research problem, the present study is a field survey

aiming to characterize the different alternate stable states in terms of biological and functional

diversity. Specifically, assemblage structures of (i) sedentary necto-benthic fishes, (ii) cryptic

fishes, (iii) vagile macro-invertebrates, (iv) sessile macro-invertebrates, (v) erect macro-algae

and (vi) encrusting macro-algae were assessed.

Definition of the three alternate stable states

(in the framework of the present study)

At the local scale (10m), habitats are characterized by their abiotic features (e.g. depth,

substrate, slope) and biotic features (e.g. macrophytobenthos). In the framework of the present

study which aim to assess macroalgal effect on fish assemblages, abiotic features were fixed.

Each “habitat unit” sampled covered an area of at least 7m in length and 4.5m in width.

The depth was between -4m and -8m. Substrate of the whole area was monolithic rock (as

opposed to blocks, pebbles etc.). Because substrate rugosity is quite difficult to estimate and

therefore to control, steps and crevasses were avoided. Slope was characterized as gentle

(between 0° and 30°). The cover of the habitat unit (7 x 4.5 m²) may appear small but larger

areas fulfilling all these criteria are usually difficult to find because of the small scale

heterogeneity of seascape (fragmentation) in Infralittoral Mediterranean rocky reefs.

The “habitat unit” may belong to any of the three types of habitat defined by biotic

features, i.e. the three alternate stables states:

Forest: at least 80% covered by

Cystoseira spp. (except C.

compressa) forming a canopy that

is quite continuous.


Bush-land: at least 80% covered

by erect macroalgae belonging to

the order Dictyotales (sometimes,

a high component of

Sphacelariaceae family were

considered as acceptable).

Barren-grounds: rock usually

covered by encrusting

macroalgae (mostly Corralinales)

and/or sponges. Cover of erect

macroalgae (usually recruits)

must not exceed 25%.


Sampling design

To describe and compare the three alternate stable states, the sampling design included the

orthogonal fixed factor “Habitat type” encompassing three levels: Cystoseira forest, bush-land

and barren grounds.

To take into account natural spatial variability, the sampling design encompassed 3 nested

spatial scales. At the spatial scale of the North-Western Mediterranean, Corsica and Menorca

(Balearic Islands) were choosen as two bioregions. Within each bioregion two localities were

identified, and within each locality two sites were sampled for all the three types of habitat

(Fig. 1).

Because it could be difficult to find study sites with barren-grounds within No-Take-

Zones (NTZs) and inversely it could be difficult to find study sites with Cystoseira forest

outside NTZs, for each bioregion one locality was sampled within a NTZ (even if it does not

encompass barren-grounds) and the other locality was sampled within a non-protected area

(even if it does not encompas Cystoseira forest). Even if this design might induce a potential

confounding effect between the habitat-type effect and the fishing ban effect, it appeared to be

the only way for achieving comparison of the three habitats. Since this study did not attempt

to assess fishing ban effect (i.e. effectiveness of the NTZ), the non balanced presence of

forest/barren-grounds in NTZ and outside should not be determinant for the interpretation of

results. The factor locality was therefore kept as a random and nested factor within bioregion.


Sampling methods

Five different methods were used for sampling (a) sedentary necto-benthic fishes, (b)

cryptic fishes, (c) vagile macroinvertebrates, (d) erect-macroalgae, and (e) encrusting

macroalgae and sessile macroinvertebrates. Within each habitat unit, one replicate for each

sampling method was performed (See numbers of replicat in Fig. 1).

(a) Sedentary necto-benthic fishes

Highly mobile fish species were not included

because we consider that they are not strongly

associated with any habitat type. They rather

opportunistically exploit resources of habitats they

cross during their daily movement.

Sedentary species assemblages were evaluated

using point count method within a half-disk (9.4m²).

This area was centered within the 7m x 4.5m “habitat

unit” in order to avoid edge effect (Fig. 2). This

method was preferred to transect method because, at

the spatial scale of a standard transect size (25m x

5m), the seascape is usually heterogeneous (multiple

habitats).

One visual census was carried out for each

suitable “habitat unit” (see section above). The diver

kneeled on the floor and waited 1 minute for the fish

to get used to his presence. Then, as fast as possible,

he estimated body size (total length to the nearest cm)

and species of every fish individuals that were present

within the half-disk when estimation started. Data

were recorded using pen and slate. This task usually

lasted less than 3 minutes. The diver then swam

around the sampled area to look for potentially hidden

fish individuals. He also measured the height of the

canopy (if any) in 6 points randomly chosen.

Finally, he put a 1-meter rope on the floor to be

used as a scale when an orthogonal picture of the

whole sampled area was taken. At the laboratory,

macroalgal cover was estimated from the picture (Fig.

3) at the scale of the habitat unit (despite covers are

already ranged by definition of the habitat type, see

section above).

Fig. 2: Position of the diver performing

visual census. The sample area is 9.4m²

and is centered within the habitat unit.

Fig 3. an orthogonal picture

(scaled) of the area sampled.


(b) Cryptic fishes

Visual census methods are not suitable for cryptic fishes as blennioidea. This is especially

true in highly structured habitats such as Cystoseira forests because small fishes may be

hidden within the canopy. One suitable method for sampling cryptic fishes is the use of an

“enclosed quinaldine station”.

In order to delineate the sample area and to prevent fish from escaping, a mesh-fence was

used. It was a cylinder 112.8cm in diameter (1m²) and 100cm in height, top- and bottom-less.

It was laid vertically on the seafloor (Fig. 4a). Quinaldine was sprayed through the canopy to

put fish to sleep (Fig. 4b). Fish were then collected using an airlift pump (Figure 4c).

All fish gathered

in the net bag of the

airlift pump were

fixed in 70%

alcoholic solution.

At the laboratory,

the specimens were

measured (total

length to the nearest

mm) and weighed

(to the nearest g)

(Fig. 5).


(c) Vagile macroinvertebrates

The mesh size of the airlift pump

collector (the bag filtering the output, Fig. 6)

is 1mm. Therefore, vagile macroinvertebrates

were collected at the same when pumping

cryptic fishes. Some macroalgae and some

detritus are also pumped. The same day of the

collection, invertebrates specimens were

extracted from the bag content and were

stored in 70% alcoholic solution. Sample

sorting and quantification will be done in the

next months.

Fig. 6: A diver closing the collector (1mm

mesh-size) as soon as the pump was turned off.

(d) Erect macroalgae

A 625cm² quadrat was randomly positioned.

Every erect macroalgae was scraped using chisel

and hammer. It is worth noting that some

epiphytic-macroinvertebrates (e.g. sponges on

Cystoseira. spp) could be part of the sample.

Sample of erect macroalgae were processed

within the same day of their collection.

Individuals were sorted and weighed (fresh)

according to operational taxonomic units (Fig. 7).

The genus Cystoseira and the order Dictyotales

(eventually also the family Stypocaulaceae) were

identified up to the species level. In case of doubt

about the species, some samples were dried in herbarium for later identification. All other

individuals were pooled into wide operational taxonomic units and weighed. Since the aim of

the study is to characterize biotic features of fish habitat, simple functional groups were

therefore preferred.

(e) Encrusting macroalgae and sessile macroinvertebrates

After collecting erect macroalgae, an orthogonal picture of each quadrat was taken. Cover

of encrusting coralline algae, encrusting non-coralline algae, sponges, other sessile

invertebrates and bare substrate will be estimated later based on the orthogonal picture(Fig. 8)

Fig. 7: Macroalgae pooled in operational

taxonomic units

Fig. 8 : orthogonal

pictures of quadrats after

scraping in Cystoseira

forest, Bush-land and

Barren-grounds (from

left to right).


Summary of data collected and future analysis

For each trophic level, assemblage structure will be compared between habitats using the

different metrics available both in multivariate and univariate contexts. Within each habitat,

correlation between assemblage structure of different trophic level will be explored (e.g. in

Cystoseira forest, correlation between fish density and weight/height/cover of Cystoseira

brachycarpa var. balearica).

Table summarizing all the metrics measured during the study. A total of 24 sites were

sampled. Number of replicat is the number of measures per site.

Trophic level Metrics available

Number

of

replicats

Sedentary

demersal fishes

Body-size and density (indiv./9.4m²) per species

(biomass may be calculated using existing weight-length

relationships)

6

Cryptic fishes Body-size, body-weight and density (indiv./1m²) 3

Vagile

macroinvertebrates

Total weight of specimens (from 625cm²) pooled according

to operational taxonomic units 3

Sessile

macroinvertebrates

Covers (out of 625 cm²) of each operational taxonomic

units (biomass may be calculated using existing weight-

area relationships)

3

Erect macroalgae

Total weight of specimens (from 625cm²) pooled according

to operational taxonomic units 3

Height of the canopy 36

Covers (out of 7 x 4.5 m²) of Cystoseira forest, Bush-land

and barren-grounds 6

Encrusting

macroalgae

Covers (out of 625 cm²) of each operational taxonomic

units (biomass may be calculated using existing weight-

area relationships)

3

Scientific knowledge and management advices expected

The expected results of this study will allow quantifying the loss of

biological and functional diversity due to the regression of Cystoseira forests. At

date, only few studies pointed out Cystoseira spp. as key species. The outcome

of the study might be used as additional argument for establishing more drastic

protection/management measures of the coastal marine environment. Moreover,

analysis of distribution patterns is the first step toward a better understanding of

the mechanisms involved in the self-maintaining of the altered stable states

(Bush-land or Barren-grounds). In perspective, ecological engineering methods

might be designed to facilitate the recovery of Cystoseira forest.


Concluding remarks

Most of data and biological samples collected during these field campaigns

are still to be analyzed. Statistical analyses and ecological interpretation are not

completed. This will be the subject of a second report.

We wish to thank all the scientists, divers and partners cited above who made

these campaigns possible, and especially for making everything go smoothly.

Divers from the ECOMERS‟ team with (a) Jean-Marie DOMINICI on the boat

of Scandolla Reserve, (b) Alexandre VOLPON on the boat of STARESO, and (c)

Marta SALES on the boat of the Estación de Investigación Jaume Ferrer.

preliminary report of ecomers 2011 field · pdf fileecosystems are generally able to...

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