Seasonal fluctuations in chemical defenses against macrofouling in Fucus vesiculosus and Fucus serratus from the Baltic Sea

Abstract

Macroalgae, especially perennial species, are exposed to a seasonally variable fouling pressure. It was hypothesized that macroalgae regulate their antifouling defense to fouling pressure. Over one year, the macrofouling pressure and the chemical anti-macrofouling defense strength of the brown algae Fucus vesiculosus and Fucus serratus were assessed with monthly evaluation. The anti-macrofouling defense was assessed by means of surface-extracted Fucus metabolites tested at near-natural concentrations in a novel in situ bioassay. Additionally, the mannitol content of both Fucus species was determined to assess resource availability for defense production. The surface chemistry of both Fucus species exhibited seasonal variability in attractiveness to Amphibalanus improvisus and Mytilus edulis. Of this variability, 50-60% is explained by a sinusoidal model. Only F. vesiculosus extracts originating from the spring and summer significantly deterred settlement of A. improvisus. The strength of macroalgal antifouling defense did not correlate either with in situ macrofouling pressure or with measured mannitol content, which, however, were never depleted.

Seasonal Variations in Surface Metabolite Composition of Fucus vesiculosus and Fucus serratus from the Baltic Sea

“…The nutrient concentrations reached their minimum during the spring/summer months, followed by increasing concentrations in the autumn and winter months. Abiotic parameters are published in [34]. Prokaryotic in situ fouling pressure increased from April onwards and reached peak intensities in August [35].…”

“…Water samples from the same depths were taken weekly and analysed for nitrogen (nitrate + nitrite, ammonium) and phosphate concentrations. These environmental parameters were recorded during a study that ran simultaneously to the one presented here and have previously been published [34]. Data are available at the public data repository 'PANGAEA Data Publisher for Earth & Environmental Science' (doi:10.1594/PANGAEA.858055).…”

“…Data are available at the public data repository 'PANGAEA Data Publisher for Earth & Environmental Science' (doi:10.1594/PANGAEA.858055). For detailed method descriptions see [34]. …”

“…The extraction time was set to 4 s in order to minimize the risk of epidermis damage and extraction of internal metabolites. For details on the extraction procedure see [34]. For the extraction, 3–6 thallus tips (depending on size and branching) were dipped into 100 ml of a constantly stirred n -hexane and methanol (1:1 v/v) emulsion for 4 s. Careful attention was paid to ensure that the cut surface had no contact with the solvents so as to avoid any leaching of internal metabolites.…”

“…serratus and how the metabolite composition relates to the seasonal variations in the environmental factors light, temperature, nutrients and prokaryotic fouling pressure. This study was conducted simultaneously with a study analysing seasonal fluctuations in chemical control against macro- and microfouling, where data on the environmental parameters and prokaryotic fouling data have been published [34, 35]. The following questions structured our project on seasonal variation in surface metabolite composition: (I) Are there significant differences in the surface chemistry composition of Fucus between different seasons?…”