Trophic ecology of sea urchins in coral-rocky reef systems, Ecuador

Abstract

Sea urchins are important grazers and influence reef development in the Eastern Tropical Pacific (ETP). Diadema mexicanum and Eucidaris thouarsii are the most important sea urchins on the Ecuadorian coastal reefs. This study provided a trophic scenario for these two species of echinoids in the coral-rocky reef bottoms of the Ecuadorian coast, using stable isotopes. We evaluated the relative proportion of algal resources assimilated, and trophic niche of the two sea urchins in the most southern coral-rocky reefs of the ETP in two sites with different disturbance level. Bayesian models were used to estimate the contribution of algal sources, niche breadth, and trophic overlap between the two species. The sea urchins behaved as opportunistic feeders, although they showed differential resource assimilation. Eucidaris thouarsii is the dominant species in disturbed environments; likewise, their niche amplitude was broader than that of D. mexicanum when conditions were not optimal. However, there was no niche overlap between the species. The Stable Isotope Analysis in R (SIAR) indicated that both sea urchins shared limiting resources in the disturbed area, mainly Dictyota spp. (contributions of up to 85% for D. mexicanum and up to 75% for E. thouarsii). The Stable Isotope Bayesian Ellipses in R (SIBER) analysis results indicated less interspecific competition in the undisturbed site. Our results suggested a trophic niche partitioning between sympatric sea urchin species in coastal areas of the ETP, but the limitation of resources could lead to trophic overlap and stronger habitat degradation.

DNA metabarcoding unveils niche overlapping and competition among Caribbean sea urchins

“…The lack of overlapping diets has been observed in sea urchin populations before, supporting a more omnivorous feeding strategy, as proposed by Rodríguez-Barreras et al (2015). We could also interpret our results in terms of habitat preservation, mainly due to differences in food resources consumption (see Cabanillas-Terán et al 2016).…”

Sargassumblooms in the Caribbean alter the trophic structure of the sea urchinDiadema antillarum

“…The rank found for D. antillarum in this study is consistent with the study conducted by Rodríguez-Barreras et al (2015) in Puerto Rico where microinvertebrates were used as source of organic matter by the sea urchin. Finally, TL values support the premise that echinoids are able to modify their foraging behaviour depending on the availability of resources (Randall, Schroeder & Starck, 1964; Muthiga & McClanahan, 2007), and in this case under Sargassum blooms condition was not only determined by macroalgae availability, but for unusual conditions that caused a shift in the ecosystem (Cabanillas-Terán et al, 2016).…”

“…This procedure supplied accurate information about the contribution of algal species to the sea urchin tissues, as it provided the proportion for every source and recognized the main sources as important components of the diet (Peterson, 1999; Fry, 2006; Wing et al, 2008) at three different sites, and under and without Sargassum effect. To run the model, the isotopic discrimination factor values used were 2.4 ± 1.6‰ (mean ± SD) for δ 15 N, and 0.4 ± 1.3‰ (mean ± SD) for δ 13 C (Minagawa & Wada, 1984; Fry & Sherr, 1989; Moore & Semmens, 2008; Cabanillas-Terán et al, 2016).…”

In Situ Observation on the Mass Aggregation of Edible Sea Urchin Stomopneustes variolaris in Shingle Island, Gulf of Mannar

“…Distributional records of echinoids in Gulf of Mannar was mainly carried out from the fish landing centre. Despite of several studies concentrated on commercial important of sea urchin, very few research studies were carried out on sea urchin ecology and aggregation patterns in coral reef environment [9][10][11]. Therefore, the present study aimed to report photographic evidence of mass aggregation of S. variolaris in Shingle Island of Gulf of Mannar and provide information on the favorable habitat of sea urchin S.variolaris aggregation.…”