Lagoons: a model habitat to explore

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1 WHAT is a lagoon? A lagoon is a body of shallow sea water or brackish water separated from the sea by some form of barrier shallow or exposed barrier beach, sandbank of marine origin, coral reef, or similar feature (Reid, 1961).

2 WHAT does a lagoon differs from an estuary? Estuaries are transition zones between rivers and the sea, which differ from both in abiotic and biotic conditions McLusky and Elliot (2004).

3 WHY lagoons are important? 1. The most significant lagoons and the sedimentary barriers that enclose them are incorporated into nature reserves (primarily to protect the visiting birds or the flora of the shingle). 2. More than half of the larger lagoons along the Mediterranean coast are used for fishing and aquaculture (both for fish and shellfish). 3. Semi-enclosed systems, easy to access and sample. 4. Naturally disturbed systems with severely fluctuating environmental and ecological gradients along the sea-land axis. 5. Annual ecological cycle from an ecological friendly state with diverse fauna and flora to the anoxic crisis, almost azoic.

4 Main theory for the microtidal lagoons: Confinement. water circulation is the main environmental driver...which has some parallels with the organic enrichment gradients, or the P-R model (Pearson & Rosenberg, 1978).

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6 The concept: The concept of the paralic domain and its zonation along the marine-freshwater axis was introduced by Guelorget and Perthuisot (1983). It has been proposed that six zones can be defined along this axis, each hosting a particular combination of species which originate from three domains: marine, lagoonal or freshwater. According to this theory, confinement (referring to the time of renewal of the components of marine origin) is the factor controlling the organization of the communities (Guelorget and Perthuisot 1992).

7 Benthic species categories: The brackish-water zoobenthos is represented primarily by four groups of species: (i) a group of marine species, commonly found in coastal semi-enclosed areas which prefer low hydrodynamic environments such as bays or harbours; (ii) a group of so-called opportunistic species with high ecological tolerance, known to be abundant in organically enriched environments; (iii) a group of typical euryhaline brackish-water species which are often used to characterize the brackish-water zones; (iv) a group of freshwater species.

8 The environmental character: The severely fluctuating hydrologic and trophic conditions (marine influence and inputs of continental origin) of these shallow, coastal and, inherently organically enriched environments, often cause abrupt seasonal variations in their physical-chemical water and sediments variables. The extremes of these results are, at times, severe hypoxic/anoxic (known also as dystrophic) crises which subsequently result in massive mortality events.

9 The anoxic crisis - mechanism: Increased of organic material and temperature Increased microbial activity Reduced oxygen in the water column and in the sediments Mass mortality event

10 The anoxic crisis - results: Nilsson & Rosenberg (2000)

11 The anoxic crisis - results:

12 Ways of scientific research: Multivariate methods A plethora of approaches (e.g. Cluster, nmds); advantages over the afore-mentioned methods

13 Ways of scientific research: Multivariate methods: CCA (ter Brack, 1987)

14 Ways of scientific research: Multivariate methods: Linking patterns to the environment

15 and ecosystems.. (Gaston & Spicer, 2004) Ways of scientific research: Biodiversity: a term referring to the variety of life the variability among living organisms from all sources including inter-alia, terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are part (CBD). includes diversity within species between species

16 Ways of scientific research:

17 Ways of scientific research:

18 Ways of scientific research: Hierarchical-response response-to-stress hypothesis hypothesis (Pearson & Rosenberg, 1978):

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20 Ways of scientific research: Variation in Taxonomic Distinctness (VarTD, Λ + ) explores the eveness of the distribution of taxa across the tree: