Ocean warming is the key filter for successful colonization of the migrant octocoral Melithaea erythraea (Ehrenberg, 1834) in the Eastern Mediterranean Sea.

Michal Grossowicz,Eli Shemesh,Or M Bialik,Guy Sisma-Ventura,Hubert B Vonhof,Dan Tchernov

doi:10.7717/peerj.9355

Abstract

Climate, which sets broad limits for migrating species, is considered a key filter to species migration between contrasting marine environments. The Southeast Mediterranean Sea (SEMS) is one of the regions where ocean temperatures are rising the fastest under recent climate change. Also, it is the most vulnerable marine region to species introductions. Here, we explore the factors which enabled the colonization of the endemic Red Sea octocoral Melithaea erythraea (Ehrenberg, 1834) along the SEMS coast, using sclerite oxygen and carbon stable isotope composition (δ18OSC and δ13CSC), morphology, and crystallography. The unique conditions presented by the SEMS include a greater temperature range (∼15 °C) and ultra-oligotrophy, and these are reflected by the lower δ13CSCvalues. This is indicative of a larger metabolic carbon intake during calcification, as well as an increase in crystal size, a decrease of octocoral wart density and thickness of the migrating octocoral sclerites compared to the Red Sea samples. This suggests increased stress conditions, affecting sclerite deposition of the SEMS migrating octocoral. The δ18Osc range of the migrating M. erythraea indicates a preference for warm water sclerite deposition, similar to the native depositional temperature range of 21–28 °C. These findings are associated with the observed increase of minimum temperatures in winter for this region, at a rate of 0.35 ± 0.27 °C decade−1 over the last 30 years, and thus the region is becoming more hospitable to the Indo-Pacific M. erythraea. This study shows a clear case study of “tropicalization” of the Mediterranean Sea due to recent warming.

Highlights

Increasing global temperatures caused by recent climate change may impose a dramatic effect on the structure and function of ecosystems worldwide (Lejeusne et al, 2009; Burrows et al, 2011)
The sclerites captured in the scanned electron microscopy (SEM) were mostly spindle shaped, a shape found in all samples
The Red Sea sclerites looked thicker than the Mediterranean ones, and their wart density appear to be higher

Summary

Introduction

Increasing global temperatures caused by recent climate change may impose a dramatic effect on the structure and function of ecosystems worldwide (Lejeusne et al, 2009; Burrows et al, 2011). Temperature, as a function of climate, is considered a key filter that could determine the success of introduced marine species (Theoharides & Dukes, 2007). Under the right environmental conditions and ecosystem fragility, an introduced species may become invasive, i.e., a pest in its new location, which spreads by natural means (Ehrenfeld, 2010). Understanding how these long-term fluctuations in environmental conditions facilitate the introduction and successful colonization is of prime importance for developing better predictions regarding the ecological effects of future climate change

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Discussion

Conclusion