Invasive behaviour of the marine Rhodophyta Sphaerococcus coronopifolius Stackhouse, in a hypereutrophic...

Area of Science:

• Marine Biology
• Algology
• Lagoon Ecology

Background:

• Sphaerococcus coronopifolius blooms occurred in a specific area of the Orbetello lagoon.
• This area received effluents from two land-based fish farms.
• The species was absent in areas further from the fish farm effluents.

Purpose of the Study:

• To investigate the factors contributing to the dense mat development of Sphaerococcus coronopifolius.
• To compare the environmental conditions in bloom areas with non-bloom areas.
• To understand the ecological role of Sphaerococcus coronopifolius in response to nutrient enrichment.

Main Methods:

• Field monitoring of sediment labile organic matter, water column physico-chemical parameters, and nutrient content (2017-2022).
• Analysis of biomass and Carbon (C), Nitrogen (N), Phosphorus (P), and Sulfur (S) content in Sphaerococcus coronopifolius.
• Microcosm experiments to simulate lagoon conditions and assess species response.

Main Results:

• Sphaerococcus coronopifolius developed dense and extensive mats in areas with high orthophosphate and nitrate nitrogen concentrations.
• The physico-chemical and nutrient content of the water column differed significantly between the bloom and non-bloom areas.
• Biomass and elemental composition (C, N, P, S) of the alga were correlated with nutrient levels.

Conclusions:

• High concentrations of orthophosphate and nitrate nitrogen ions promote the development of Sphaerococcus coronopifolius vegetative blooms.
• Sphaerococcus coronopifolius acts as an opportunistic species, rapidly colonizing and forming mats in response to nutrient enrichment.
• Fish farm effluents are a likely source of the nutrient enrichment driving these algal blooms in the Orbetello lagoon.