The Functional Morphology of Turf-Forming Seaweeds: Persistence in Stressful Marine Habitats

Abstract

Many seaweeds that occur in physically stressful habitats or habitats subject to moderate herbivory grow as colonial turfs rather than as spatially separated individuals. The turf growth form is energetically expensive (the net production per gram ash free dry mass of turfs being 33-61% lower than that of individuals), but turfs suffer less physiological damage during desiccating low tides and lose less biomass to herbivores. The upper portions of turf-forming species show significantly greater rates of apparent photosynthesis and dark respiration than do the lower portions. This spatial partitioning of photosynthetic activity decreases the energetic cost of the turf arrangement and may allow basal portions to function as persistent resting stages during periods of adverse conditions when uprights cannot be maintained. Turf-forming species are specialized for areas that are subject to moderate grazing pressure and physical stresses. They are dependent upon these factors to prevent their competitive exclusion by more productive, but less resistant, seaweeds. Damage to apical portions causes increased branching that results in a more tightly compacted turf. Algae that regenerate in this way can adjust their growth form in accordance with varying levels of disturbance encountered in different habitats and thus incur the minimal cost consistent with survival in that area.For seaweeds occurring in stressful habitats, selection has favored characteristics that increase persistence in space and time even though these involve considerable losses in competitive ability and productivity.

Sediments and herbivory as sensitive indicators of coral reef degradation

“…Any reductions in grazing can lead to the development of long, unpalatable algal turfs (Goatley and Bellwood 2013). Although the absolute length increases we observed may seem small (2.7-4.6 mm increases on the crest and flat), EAMs are often the most abundant benthic cover on coral reefs (Vroom 2011, Bruno et al 2014) and are often highly stable (Hay 1981, Airoldi and Virgilio 1998, Goatley and Bellwood 2013. Even small changes in their composition can thus have widespread impacts on ecosystem function (Goatley and Bellwood 2012, 2013, Clausing et al 2014.…”

Variable modes of facilitation in the upper intertidal: goose barnacles and mussels

“…acorn barnacles: Bertness 1989; mussels: Bell & Gosline 1997, Helmuth 1998; sea anemone : Ottaway 1979, Pineda & Escofet 1989algae: Dayton 1975, Hay 1981, Bertness et al 1999; marsh grasses: Leonard & Luther 1995, Bruno 2000seagrasses: Orth et al 1984, Irlandi & Peterson 1991large polychaete tubes: Woodin 1978). In the present case, an aggregation of Capitulum mitella shielded the rock surface from irradiation so that it remained cooler than areas without C. mitella.…”

Effects of monsoon-driven wave action on coral reefs of Guam and implications for coral recruitment

“…Yet, the role of other potentially important factors, such as substrate availability, interspecific competition, and wave action, in structuring algal communities have received less attention (Shulman and Robertson 1996;Aronson and Precht 1997;Blanchon and Perry 2004). Wave action can have significant effects on coral reef community structure (Rosen 1975;Adey and Burke 1977;Dollar 1982;Dollar and Tribble 1993;Cheroske et al 2000) affecting not only species composition, but also the morphology of sessile organisms (Hay 1981;Palumbi 1984;Palumbi 1986). Wave action can also drastically alter benthic algal communities by either enhancing algal growth by bringing in nutrient-rich water and removing waste (Kingsbury 1962) or reducing cyanobacteria and macroalgal abundances by the mechanical effects of waves on the algal community and substrate (FitzGerald 1978;Dudgeon and Johnson 1992;Cheroske et al 2000).…”