Nutrient addition increases consumption rates of tropical algae with different initial palatabilities

Abstract

While nutrient enrichment increases herbivory rates on highly palatable species of tropical algae, it is unclear how nutrient enrichment affects species with differing initial palatabilities. We determined that there was a wide range in relative palatability among 5 perennial and common species of Caribbean coral reef algae in a cafeteria-style choice experiment, with overall preference for Acanthophora spicifera the highest, Dictyota dichotoma and Caulerpa sertularioides intermediate, and Turbinaria turbinata and Sargassum polyceratium the lowest, although there were significant differences in grazing rates among algal species between the 2 fringing reef sites tested. We then tested the hypothesis that increased nutrient content in algae increases palatability using choice experiments between enriched and ambient algal samples for each of 3 species along this palatability gradient: A. spicifera, D. dichotoma, and S. polyceratium. For all species, herbivores selected enriched over ambient samples across the 2 sites despite contrasting herbivore guilds (i.e. dominated by sea urchin Diadema antillarum versus herbivorous fishes). However, despite increased palatability of enriched S. polyceratium, overall herbivory on this species was still relatively low compared to other studies, suggesting that S. polyceratium in this system may have stronger chemical defenses, or that a specialist herbivore guild may be missing on this Caribbean reef. Regardless of the mechanism, our study implies that anthropogenic or natural events that result in high supplies of nutrients in coral reef seawater will increase overall seaweed palatability, even of unpalatable species.KEY WORDS: Tropical marine algae · Dictyota dichotoma · Sargassum polyceratium · Acanthophora spicifera · Herbivory · Nutrient enrichment Resale or republication not permitted without written consent of the publisher

Induced defence to grazing by vertebrate herbivores: uncommon or under-investigated?

“…In this study we investigated (1) whether herbivorous fishes preferentially fed on Sargassum polycystum fronds collected from areas with few herbivorous fishes versus areas with many, (2) whether the difference in palatability we observed could result from an induced response to fish grazing, and (3) whether differential tissue toughness or nutritional value were associated with feeding preference, as has been demonstrated in some studies of insects, marine invertebrates, or fishes (Littler & Littler 1980, Coley 1983, Burkepile & Hay 2009, Chan et al 2012). …”

Combined Effects of Temperature and Nutrient Enrichment on Palatability of the Brown Alga Sargassum yezoense (Yamada) Yoshida & T. Konno

“…Nitrogen concentration is another important factor that affects the palatability of brown algae [13]. Nutrient enrichment is known to result in increased palatability [14], decreased phlorotannin concentration [11], and increased nitrogen concentration [15]. However, it is unclear whether decreased phlorotannin concentration or increased nitrogen concentration is responsible for increased palatability caused by nutrient enrichment.…”

The Individual and Interactive Effects of Nitrogen and Phosphorus Enrichment on Coral Reefs

“…Selective removal of enriched resources has been documented in numerous studies (e.g., Boyer et al 2004;Chan et al 2012; but to this point it has remained unclear whether N versus P drives this pattern. We found that N-enriched algae is preferentially consumed by parrotfishes but that P-enrichment had little effect on parrotfish foraging.…”

“…As a result, animals are often N and P-limited and selectively forage on resources rich in these nutrients (Mattson 1980;; Lemoine et al 2013). Indeed, experiments comparing the consumption of nutrient enriched algae to controls often document higher rates of grazing and biomass removal of algae enriched with N and P (e.g., Boyer et al 2004;Chan et al 2012). However, as of yet no studies have differentiated the effects of N versus P on reef fish foraging, nor clarified the responses of different fish taxa to these enrichments.…”

“…Indeed, consumption rates of N and P enriched algae are often greater than those of algae that has not experienced nutrient enrichment (e.g. Boyer et al 2004;Chan et al 2012). However, it remains unclear how N vs. P may affect the intensity of herbivory, or whether different herbivore species respond differently to these nutrients.…”