Responses of turf-forming algae to spatial variations in the deposition of sediments

Abstract

Responses of a turf-forming, filamentous, algal assemblage to spatial variation in the deposition of sediments were investigated from September 1994 to September 1996 on a rocky subtidal reef south of Livorno (Mediterranean Sea) Large-and small-scale spatial differences in the amount and size of sed~ment settling on and accumulating in the turf were investigated over 1 yr in relation to meteorological conditions and to patterns of abundance of the turf. A multifactorial manipulat~on of the deposition of sediment was used to test the hypotheses that (1) different amounts and grain-sizes of settling material affect the cover and biomass of the filamentous algae, (2) any effects of sedimentation are independent of the stage of development of the turf and (3) patterns are consistent at different spatial scales, ranging from a few centimetres to several metres. During the investigation, the reglme of sed~mentation fluctuated greatly over time and among s~t e s The distribution of the turf across diiferent sites was, however, not apparently related to large-scale variations in the deposition of sediment Within sites, accumulation of sediment in the turf was patchy. The results of the experiment indicated that patchiness may affect the local biomass of established turf-forming algae, the abundance of which significantly decreased in quadrats which had higher deposition of sediments. On a scale of centimetres, high accumulation of sediment decreased variability of algal biomass within individual quadrats. The effects of sediment on biomass were also significantly influenced by the stage of development of the turf. No effects were observed on the cover of the filamentous algae. These results suggest that the responses of the turf to variations in the characteristics of the depositional environment may vary with changes in spatial scale and may be dependent on the concomitant action of other physical and biological factors.

Facilitation of the introduced green alga Caulerpa racemosa by resident algal turfs: experimental evaluation of underlying mechanisms

“…The sediment was separated from algal tissues and salts by washing samples with distilled seawater and larger particles entangled in the turfing matrix were removed with tweezers (Airoldi & Virgilio 1998). Samples were dried to constant weight (60°C for 24 h) before weighing on a precision scale (Airoldi & Virgilio 1998). The weight of the sediment collected from quadrats varied between 28.04 and 4.62 g in one patch and between 44.56 and 6.35 g in the other.…”

“…Dispersal of sediment during collection of samples was minimised by delimiting quadrats with a 5 cm high square frame. The sediment was separated from algal tissues and salts by washing samples with distilled seawater and larger particles entangled in the turfing matrix were removed with tweezers (Airoldi & Virgilio 1998). Samples were dried to constant weight (60°C for 24 h) before weighing on a precision scale (Airoldi & Virgilio 1998).…”

“…In order to use the same type of sediment as in algal turfs, the material to be added to barren habitats (either natural or artificial) was collected up the cliff. The sediment was passed through a 2 mm mesh and the fraction not retained, composed of fine particles with a grain size within the range of those trapped by algal turfs (Airoldi & Virgilio 1998), was used for our manipulation. Added sediment was only partially retained in barren habitats, probably due to the limited depths at which we operated and it was therefore necessary to estimate the rate at which sediments were washed away.…”

Structure and temporal dynamic of tropical turf forming macroalgal assemblages of the western coast of Mexico

“…Among the most important physical factors are sedimentation (Airoldi & Virgilio, 1998;Balata et al, 2011), wave patterns (Díez et al, 2003;Wernberg & Connell, 2008;Smale et al, 2011), tides (Metaxas & Scheibling, 1993), and water movement (Cheroske et al, 2000).…”

Can strong consumer and producer effects be reconciled to better forecast ‘catastrophic’ phase-shifts in marine ecosystems?

“…What is increasingly recognised is that sediment and turfs provide positive feedbacks for each other because the life-history and physiology of turfs are better suited to nutrient overloading (Worm et al, 1999;Gorgula and Connell, 2004) and their sediment-trapping morphology enables them to rapidly recruit to and retain space under heavy coastal sedimentation (Airoldi et al, 1998). Turfs, like many fast growing and ephemeral algae, lack the ability to store nutrients and have a growth strategy that allows them to exploit sudden increases in nutrient, but collapse when resources are depleted (Pedersen and Borum, 1996).…”