Proceedings of the Second Mediterranean Symposium on Marine
Proceedings of the Second Mediterranean Symposium on Marine
Proceedings of the Second Mediterranean Symposium on Marine
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PROCEEDINGS OF THE SECOND MEDITERRANEAN SYMPOSIUM ON MARINE VEGETATION (ATHENS, 12-13 DECEMBER 2003)<br />
238<br />
SEAGRASS ECOSYSTEMS AS BIOLOGICAL INDICATORS.<br />
A COMPARISON OF TWO APPROACHES: LEAF EPIPHYTE TAXONOMY<br />
AND A COMBINED SET OF BIOLOGICAL DESCRIPTORS<br />
Begoña MARTINEZ, Adriana VERGÉS TRAMULLAS, Patricia PRADO, Javier ROMERO and<br />
Teresa ALCOVERRO.<br />
ABSTRACT<br />
The main objective <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> present study is <str<strong>on</strong>g>the</str<strong>on</strong>g> comparis<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> two separate approaches<br />
to <str<strong>on</strong>g>the</str<strong>on</strong>g> use <str<strong>on</strong>g>of</str<strong>on</strong>g> P. oceanica meadows as biological indicators <str<strong>on</strong>g>of</str<strong>on</strong>g> water quality. One is based<br />
<strong>on</strong> <str<strong>on</strong>g>the</str<strong>on</strong>g> use <str<strong>on</strong>g>of</str<strong>on</strong>g> a combined set <str<strong>on</strong>g>of</str<strong>on</strong>g> biological descriptors (physiological, morphological,<br />
structural, communal and envir<strong>on</strong>mental) and <str<strong>on</strong>g>the</str<strong>on</strong>g> o<str<strong>on</strong>g>the</str<strong>on</strong>g>r is based <strong>on</strong> <str<strong>on</strong>g>the</str<strong>on</strong>g> tax<strong>on</strong>omy <str<strong>on</strong>g>of</str<strong>on</strong>g> leaf<br />
epiphytes. Both sets <str<strong>on</strong>g>of</str<strong>on</strong>g> descriptors were measured in 12 locati<strong>on</strong>s, eight <str<strong>on</strong>g>of</str<strong>on</strong>g> which were<br />
deep (15 m) and four <str<strong>on</strong>g>of</str<strong>on</strong>g> which were shallow (5 m). The selecti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g>se locati<strong>on</strong>s was<br />
based <strong>on</strong> a previous four-year seagrass m<strong>on</strong>itoring study and was aimed at <str<strong>on</strong>g>the</str<strong>on</strong>g><br />
homogenous cover <str<strong>on</strong>g>of</str<strong>on</strong>g> a wide range <str<strong>on</strong>g>of</str<strong>on</strong>g> water qualities, from poor to quasi-pristine<br />
c<strong>on</strong>diti<strong>on</strong>s. Principal comp<strong>on</strong>ent analysis (PCA) applied to a set <str<strong>on</strong>g>of</str<strong>on</strong>g> biological descriptors<br />
resulted in two principal comp<strong>on</strong>ents which explained 46% <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> variance. Comp<strong>on</strong>ent<br />
I appears to be related to c<strong>on</strong>diti<strong>on</strong>s <str<strong>on</strong>g>of</str<strong>on</strong>g> eutrophia and metallic c<strong>on</strong>taminati<strong>on</strong> and<br />
explains 28.8% <str<strong>on</strong>g>of</str<strong>on</strong>g> variance. Comp<strong>on</strong>ent II explains 17.2% <str<strong>on</strong>g>of</str<strong>on</strong>g> variance and seems to be<br />
related to herbivory, which is c<strong>on</strong>siderably more intense in shallow locati<strong>on</strong>s.<br />
Corresp<strong>on</strong>dance analysis applied to leaf epiphyte tax<strong>on</strong>omy <str<strong>on</strong>g>of</str<strong>on</strong>g> axis I and II explain 22%<br />
and 17.1% <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> variance respectively. Axis I provide an ordering <str<strong>on</strong>g>of</str<strong>on</strong>g> locati<strong>on</strong>s that is<br />
related to existing water quality data, whilst axis II again seems to be related to herbivory.<br />
The two approaches are coherent with <strong>on</strong>e ano<str<strong>on</strong>g>the</str<strong>on</strong>g>r, and <str<strong>on</strong>g>the</str<strong>on</strong>g>y both provide a good<br />
indicati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> water quality. The ordering <str<strong>on</strong>g>of</str<strong>on</strong>g> locati<strong>on</strong>s provided by both sets <str<strong>on</strong>g>of</str<strong>on</strong>g> descriptors<br />
is coherent with existing water quality data from <str<strong>on</strong>g>the</str<strong>on</strong>g> regi<strong>on</strong>. Even though <str<strong>on</strong>g>the</str<strong>on</strong>g> two<br />
approaches provide remarkably similar results, <str<strong>on</strong>g>the</str<strong>on</strong>g> combined set <str<strong>on</strong>g>of</str<strong>on</strong>g> biological indicators<br />
<str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> Posid<strong>on</strong>ia oceanica ecosystem appears as a more powerful tool in <str<strong>on</strong>g>the</str<strong>on</strong>g><br />
discriminati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> medium-to-good water qualities. Meadows found in shallow waters are<br />
clearly influenced by internal forcings such as herbivory, which are in no apparent way<br />
related to water quality. For that reas<strong>on</strong>, deeper meadows are recommended for use in<br />
any future m<strong>on</strong>itoring studies.