Capturing the dynamics in benthic structures: environmental effects on morphology in the macroalgal genera Halimeda and Dictyota

Abstract

Macroalgae are modular organisms that can express different morphologies depending on the environment to which they are exposed. Their growth under varying light, temperature, and nutrient regimes, interacting with disturbance factors such as herbivory and hydrodynamics, leads to particular morphological types. The present study illustrates the potential of using morphological variations of benthic modular and/or clonal organisms as indicators of the factors and processes influencing them in their particular location. The morphogenetic agent-based model SPREAD (spatially explicit reef algae dynamics) was used to determine the range of potential morphological types in 3 dominant macroalgal species (Halimeda tuna, H. opuntia, and a species of Dictyota) in the Florida Reef Tract. Simulations of growth under a range of light, nutrient, and disturbance conditions similarly found at inshore patch and offshore bank reefs led to 6 potential morphological types for H. tuna, 2 for H. opuntia, and 3 for a species of Dictyota. From these potential sets derived from the model, we observed that particular morphological types corresponded to the morphologies found in the 2 reef habitat types. The simulated conditions that led to the formation of these morphologies in the model were similar to the environmental conditions at these sites. In addition to relating combinations of environmental and disturbance factors to macroalgal growth morphologies, the present study provides insights into the differing life-history strategies among the species, and the adaptive value of plasticity expressed by these macroalgae. The morphologies of the successful fragmenters H. opuntia and a generalized species of Dictyota were more influenced by disturbance. On the other hand, the morphology of the less successful fragmenter H. tuna was strongly influenced by the growth factors of light and nutrients.KEY WORDS: Agent-based modeling · Macroalgae · Coral reef · Florida Keys · Morphology · Halimeda spp. · Dictyota Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 411: [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] 2010 gies, similar to many other plants and macroalgae in other systems (Bradshaw 1965, Monro et al. 2007. Their modular construction is one source of their morphological phenotypic plasticity (Halle 1986). A modular organism's body is built up by the iteration of 1 or more distinct units, i.e. modules (Tuomi & Vuorisalo 1989). In terrestrial plants, these modules generally consist of leaves, stems, and roots. It has been shown that these plant modules are able to react, independently of the whole plant, to their local environment (Sutherland & Stillman 1988, de Kroon et al. 2005. Roots, for example can 'forage' for nutrients: in lownutrient patches, the filamentous roots lengthen, whereas under high-nutrient conditions, they branch more in order to exploit the good patch (Lovett-Doust 1981, de Kroon & Hutchings 1995. A continuum of forms can thus be found betwe...

Morphological allometry constrains symmetric shape variation, but not asymmetry, of Halimeda tuna (Bryopsidales, Ulvophyceae) segments

“…Several studies also illustrated that variation of the segments is related to various environmental factors within the marine sublittoral habitats [ 17 – 19 ]. It has been shown that the size of Halimeda segments is often negatively correlated with high irradiation levels typical for shallow habitats close to the sea surface [ 20 , 21 ]. This may lead to large individuals comprising relatively high number of large segments growing in less irradiated, deeper parts of the sublittoral.…”

“…This may lead to large individuals comprising relatively high number of large segments growing in less irradiated, deeper parts of the sublittoral. Conversely, photoinhibition, which occurs in Halimeda populations growing in shallow and highly irradiated locations in the upper sublittoral [ 22 , 23 ], may be coupled with relatively small plants characterized by a compact habitus and small segments [ 17 , 21 ]. These small segments of highly irradiated populations have also been reported as being relatively less calcified than those of populations thriving in shaded habitats [ 17 ].…”

Phenotypic plasticity and morphological adaptation of Halimeda opuntia (Bryopsidales, Chlorophyta) to light intensity

“…The populations in low light levels have loose thalli, small segments and tri-partite segments (Kooistra & Verbruggen 2005). H. opuntia segments from the inshore patch reefs were large, and the thallus form was more upright than that in the population from the offshore spur and groove area (Yñiguez et al 2010). Additionally, in other species, such as H. macroloba, thallus and segment sizes are large in subtidal zones and low light intensity conditions (Pongparadon et al 2015).…”

Morphological and community changes of turf algae in competition with corals

“…The relatively passive role that algae are assumed to play in colonising corals contrasts with their high morphological plasticity in biological interactions. Algal morphology is modified as a response to physical, chemical, and biological factors 8 9 10 11 12 . It has also been suggested that algal phenotypic plasticity may be a key mechanism involved in the occupation of different ecological niches 13 and in the invasion of species 14 , as observed in terrestrial clonal plants.…”