Spatial Variability in a Symbiont-Diverse Marine Host and the Use of Observational Data to Assess Ecological Interactions

Edwin Cruz-Rivera,Mohy-El-Din Sherif,Thomas Lombardi,Salma El-Sahhar

doi:10.3390/d14030197

Edwin Cruz-Rivera, Mohy-El-Din Sherif + Show 2 more

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https://doi.org/10.3390/d14030197

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Abstract

Despite a rich taxonomic literature on the symbionts of ascidians, the nature of these symbioses remains poorly understood. In the Egyptian Red Sea, the solitary ascidian Phallusia nigra hosted a symbiotic amphipod and four copepod species, with densities as high as 68 mixed symbionts per host. Correlation analyses suggested no competition or antagonism between symbionts. Ascidian mass, ash-free dry mass per wet mass (AFDM/WM), and both symbiont density and diversity per host, differed significantly among three reefs from El Gouna, Egypt. However, there was no correlation between amphipod, total copepod, or total symbiont densities and host mass or AFDM/WM. A host condition index based on body to tunic mass ratio was significantly related to symbiont density overall, but this positive pattern was only strong at a single site studied. Despite assumptions based on the habit of some of the symbiont groups, our analyses detected little effect of symbionts on host health, suggesting a commensal relationship.

Highlights

Many marine symbioses are poorly understood and have been often classified based on the taxonomy of the animals involved rather than on quantification of costs and benefits [1–3]
By comparing animals from three reefs in the Red Sea, we evaluate the role of spatial variation in symbiont–host interactions
Total ash-free dry mass per wet mass (AFDM/WM) of the ascidian hosts was significantly lower at Abu Tig than at Zeytouna Beach, this difference was

Summary

Introduction

Many marine symbioses are poorly understood and have been often classified based on the taxonomy of the animals involved rather than on quantification of costs and benefits [1–3]. While taxon-based inferences have been informative and often correct, they can obscure fundamental differences in the nature of interactions within a clade and the context dependence of symbioses within a parasitism to mutualism continuum [4–8]. A manipulative approach in which hosts and symbionts are grown independently from one another, and together, could offer an ideal method to quantify fitness effects for each interacting species. This is not feasible in most cases of obligate symbioses and is difficult to achieve when life cycles require multiple hosts or when endosymbiont presence cannot be confirmed without sacrificing the host

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