Comprehensive evaluation of the palatability and chemical defenses of subtidal macroalgae from the Antarctic Peninsula

Abstract

The palatability of 35 non-encrusting, subtidal macroalgal species collected from the vicinity of Palmer Station, Antarctica (64°46' S, 64°03' W), was determined in laboratory bioassays utilizing sympatric sea stars and fish known to consume macroalgae in nature. Overall, 63% of the macroalgal species offered to sea stars and 83% of the macroalgal species offered to fish in thallus bioassays were significantly unpalatable. This included all of the ecologically dominant, overstory brown macroalgae in the region. When organic extracts of unpalatable macroalgal species were incorporated into artificial foods, 76% of the species unpalatable as thallus to sea stars were also unpalatable to them as extract, and 53% of the species unpalatable as thallus to fish were also unpalatable to them as extract. If either sea stars or fish rejected thallus of a macroalgal species, palatability of organic extracts of that species to herbivorous amphipods was determined: 63% of such algal species were unpalatable as extract to the amphipods. It was concluded that antarctic macroalgae are commonly unpalatable to sympatric consumers and that much of this unpalatability is the result of chemical defenses. As a whole, neither thallus toughness nor a variety of nutritional quality parameters appeared to be related to macroalgal palatability. We also tested the hypothesis that nitrogen-containing metabolites should be common in macroalgae from nitrogen-replete, carbon-limited environments such as the coastal waters of Antarctica. Macroalgal acid extracts targeting nitrogenous secondary metabolites were subjected to thin-layer chromatography analysis; no such compounds were detected.

Feeding preference of the sea urchin Lytechinus variegatus (Lamarck, 1816) on seaweeds

“…Among brown seaweeds, those belonging to genus Dictyota are known to produce secondary (ARGANDOÑA et al, 2002;AMSLER et al, 2005;HUANG et al, 2006), including P. brasiliense from the Brazilian coast (PEREIRA et al, 2002). Therefore, the low preference or the reduced consumption of P. brasiliense by L. variegatus may be due to the presence of chemical defenses in this red seaweed.…”

Life strategy, ecophysiology and ecology of seaweeds in polar waters

“…In addition to deterring grazers, organic extracts of all Antarctic macroalgal species tested (2 from McMurdo, 22 from Anvers Island) also were toxic to sympatric diatoms (Amsler et al 2005b). To the best of our knowledge, no comparable information is available on antifouling properties in Arctic seaweeds.…”

Deterrent activities in the crude lipophilic fractions of Antarctic benthic organisms: chemical defences against keystone predators

“…110 m) may have different chemistry due to the variation in depths or the extraction protocol, which yielded unexpected inactivity. Other algae, like Palmaria decipiens, are more preferred as food (though not for our amphipod) but are not preferred as hosts (Amsler et al 2005;Aumack et al 2010;Bucolo et al 2011). Analogous chemical refuges have not been described in Antarctic sponges, yet some defended species host dense amphipod populations ).…”

“…This could be due, in part, to a higher ingestion of algal material by C. femoratus ovigerous females and juveniles during summer (Bregazzi 1972). Hydrophilic deterrents (i.e., phlorotanins), often contributing to asteroid repellence in algae, could have been missed in our analysis (Amsler et al 2005). Antarctic benthic amphipods generally associate with living substrata with no obligate relationships (De Broyer et al 2001), obtaining tri-dimensional habitat and food as well as chemical refuges from prospective enemies, like fish, when hosts are chemically defended Zamzow et al 2010).…”

“…1). Amsler et al (2005) proposed that in second-year D. antarctica mild acidity could assist weak hydrophilic repellents against sea stars, while in first-year algae the lipophilic extract was already effective, suggesting a loss of lipophilic defences with senescence. Glass sponges are readily preyed upon by Odontaster and Acanthaster sea stars (McClintock 1987), and as it turns out, no lipophilic repellents or external defence allocation were shown to assist these sponges in asteroid avoidance (Furrow et al 2003).…”