Effects of Macroalgal Chemical Extracts on Spore Behavior of the Antarctic Epiphyte Elachista antarctica Phaeophyceae

Abstract

Most macroalgal species along the Western Antarctic Peninsula (WAP) are defended against predation, many using chemical defenses. These subtidal communities are also mostly devoid of free living filamentous algae. However, one endo/epiphyte, Elachista antarctica, is found growing exclusively out of the palatable rhodophyte Palmaria decipiens. To understand this unusual and exclusive epiphytization, we tested whether macroalgal secondary metabolites such as those responsible for deterring sympatric grazers, affect the behaviors of the epiphyte's spores. Settlement, germination, and swimming behaviors of the epiphyte's motile spores were quantified in the presence of fractionated lipophilic and hydrophilic extracts of host P. decipiens and other rhodophytes from the shallow subtidal. Host P. decipiens was the only alga tested that did not inhibit spore settlement or germination. We also examined whether extracts from these chemically rich algae affect spore swimming behaviors and found spores to be chemotactically attracted to seawater soluble extract fractions of host P. decipiens. These results indicate that chemosensory behaviors of the epiphyte's spores to metabolites associated with these chemically defended macrophytes can explain this exclusive epiphyte-host interaction.

The influence of species, density, and diversity of macroalgal aggregations on microphytobenthic settlement

“…Results show that the environmental modifications driven by the macroalgae appear to play a significant role in promoting distinct temporal and spatial patchiness in the microphytobenthos. However, we cannot disregard a biological response based on species specificity, as other factors such as chemical cues or deterrents may also influence microphytobenthic settlement and development (Lam et al 2008, Bucolo et al 2012.…”

Endophyte presence as a potential stressor on growth and survival in Antarctic macroalgal hosts

“…Host defenses against endophyte infection may be present in Antarctic algae but are not thoroughly characterized. For instance, settlement of the filamentous epi/endophyte E. antárctica is inhibited by extracts of most sympatric macroalgae save its one known host P. decipiens (Bucolo et al 2012). Although the present study focuses on filamentous algal endophytes, fungal endophytes have also been reported in three species of Antarctic macroalgae (Loque et al 2010).…”

Crustose coralline algae and associated microbial biofilms deter seaweed settlement on coral reefs

“…only develop the protective cell wall upon settlement (Braten 1971). On the other hand, since algal spores can be repelled by a number of chemical stimuli (Bucolo et al 2012), the CCA's inhibitory component can act as a negative cue, preventing spore settlement until death ensues (Egan et al 2001b). There are only few studies regarding CCA allelopathy against seaweed spores, most of them on temperate CCA; our results are similar to those found in temperate studies (Table 4).…”