Trophic ecology of the octocoral Carijoa riisei from littoral of Pernambuco, Brazil. I. Composition and spatio-temporal variation of the diet

Abstract

Octocorals are common components of sublittoral benthic communities in temperate, tropical and polar areas. However, their natural diets and feeding rates are poorly known. The aim of this study was to determine qualitatively–quantitatively the diet of the octocoral Carijoa riisei (snowflake coral) and analyse the distribution and diet composition throughout a whole year at two different depths of the same environment. Hence, 30 colonies were haphazardly sampled for gastric content analysis from 2 and 6 m deep (surface and bottom) at Porto de Galinhas beach, Pernambuco, Brazil, in January, June and October 2006, and March 2007. Relative and absolute abundance, richness and occurrence frequency per gastric cavity were assessed. Shannon–Wiener index (H′) and evenness were also calculated. Items were classified according to the occurrence frequency. The biovolume of preys was estimated from meristic data, and from the biovolume were then estimated wet weight, dry weight and organic carbon. Weighed biovolume (WBV), which relates biomass and abundance, was assessed to estimate the real contribution of preys to octocoral diet. Results attested the presence of 102 phytoplankton and 25 zooplankton taxa. Mean prey size was 112.7 µm. Diatoms showed the greater richness with 88 morphotypes. Only cyanophytes and diatoms, from phytoplankton, were very common (>70%). As a whole, phytoplankton was also the most abundant group (83%), followed by crustacean fragments (5%). Thus, although having low biovolume (<0.09 mm3×10−3), the phytoplankton showed the highest WBV (44.5%). Feeding items richness was homogeneous throughout the study year and in both depths, while abundance showed significant seasonal and bathymetric fluctuation. The t-test (Hutchinson) found significant differences for prey item diversity related to depth and season. From the analysis, it is possible to conclude that the C. riisei population of the Brazilian north-eastern coast is polyphagous, but shows preference for phytoplanktonic elements and small prey. Therefore, the species behaves as a passive suspensivorous feeder with equitable biomass contribution from phytoplankton and zooplankton.

Chemical and biological aspects of octocorals from the Brazilian coast

“…Almost all utilize symbiotic photosynthetic zooxanthella as a major energy source. However, most will readily eat, as passive suspensivorous feeders, any free-floating food, such as phytoplankton and zooplankton out of the water column (Lira et al, 2009;Gomes et al, 2012). They are integral members of the reef ecosystem and provide a habitat for fish, snails, algae and other marine species.…”

Trophic ecology of the zoanthidPalythoa caribaeorum(Cnidaria: Anthozoa) on tropical reefs

“…Most of the studies, however, were undertaken in temperate regions, while tropical coral reef ecosystems have distinct dynamics and high productivity even in oligotrophic waters (Lewis, 1977;Rougerie et al, 1992), with the reef fauna rapidly removing planktonic biomass (Erez, 1990). Studies investigating the diets of benthic cnidarians in these environments have demonstrated the great importance of phytoplanktonic prey (Coma et al, 1999;Lira et al, 2009, Gomes et al, 2012 with a pattern different from temperate species and similar to the diet of P. caribaeorum in northeastern Brazil. The diet of P. caribaeorum seems to be similar in the two beaches studied, without significant variations in their richness or abundance between the dry and rainy seasons.…”

“…Prey items were classified into higher taxonomic groups and assigned to six categories according to their frequency of occurrence: very common (present in more than 70% of the total samples); common (in 30 -69% of the samples); present (in 10 -29% of the samples); scarce (in 5-9% of the samples); rare (in 1-4% of the samples); and unusual (in less than 1% of the samples) (Lira et al, 2009).…”

Prey selectivity of the octocoral Carijoa riisei at Pernambuco, Brazil

“…A previous study on the trophic ecology of C. riisei from Porto de Galinhas beach (Pernambuco, Northeast Brazil) concluded that the species is polyphagous, but with a numerical dominance of phytoplanktonic elements with equitable biomass contribution from phyto and zooplankton (Lira et al 2009). This study focused only on diet composition without considering the availability of prey in the plankton.…”