Projected Rapid Habitat Expansion of Tropical Seagrass Species in the Mediterranean Sea as Climate Change Progresses

Abstract

During the last 150 years, the tropical seagrass species Halophila stipulacea has established itself in the southern and eastern parts of the Mediterranean Sea. More recently (2018), Halophila decipiens was observed for the first time in the eastern Mediterranean, and was described as the second non-native seagrass species in the Mediterranean Sea. We implemented a species distribution model (SDM) approach to (1) hindcast the habitat suitability of H. stipulacea over the last 100 years in the Mediterranean basin, and (2) to model the increase in the potential habitat suitability of H. stipulacea and H. decipiens during the current century under two very different climate scenarios, RCP 2.6 (lowest carbon emission scenario) and RCP 8.5 (highest carbon emission scenario). In addition, a principal component analysis (PCA) and k -means cluster based on temperature and salinity drivers were applied to visualize the distance and relatedness between the native and invasive H. stipulacea and H. decipiens populations. Results from this PCA suggest that the H. stipulacea populations of the Mediterranean and Red Sea are likely to be similar. In contrast, H. decipiens from the Mediterranean is more related to the Atlantic populations rather than to the Red Sea populations. The hindcast model suggests that the expansion of H. stipulacea was related to the increases in seawater temperatures in the Mediterranean over the last 100 years. The SDMs predict that more suitable habitat will become available for both tropical species during this century. The habitat suitability for H. stipulacea will keep expanding westward and northward as the Mediterranean continues to become saltier and warmer. In comparison, the SDMs built for H. decipiens forecast a restricted habitat suitability in the south-eastern Mediterranean Sea at the present environmental conditions and predicts a progressive expansion with a potential increase in habitat suitability along 85% of the Mediterranean coastline. The predicted rapid expansion of non-native seagrass species could alter the Mediterranean’s seagrass community and may entail massive impacts on associated ecosystem functions and services, impacts that have severe socio-economic consequences.

Dietary analysis of two sympatric marine turtle species in the eastern Mediterranean

“…The nutritional quality of C. nodosa has been demonstrated to exceed that of P. oceanica in dietary preference studies of other Mediterranean herbivores, through both the higher quality of its leaves as well as its epiphytic community (Marco-Méndez et al 2015). Considering C. nodosa was generally not a preferred dietary species in the current study and with H. stipulacea (Beca-Carretero et al 2020) and P. oceanica (Telesca et al 2015) both widespread off Cyprus, this may suggest they are more prevalent than C. nodosa, with prey availability driving dietary preferences. This is consistent with other studies noting local availability of resources as a key determining factor (Cardona et al 2010;Reisser et al 2013;Campos and Cardona 2020) where some green turtles primarily consume macroalgae instead in regions where seagrasses are scarce (e.g., Carrión-Cortez et al 2010;Reisser et al 2013;Vélez-Rubio et al 2016).…”

Seagrass (Halophila stipulacea) invasion enhances carbon sequestration in the Mediterranean Sea

“…At present, H. stipulacea is distributed in the Eastern and Central Mediterranean Basin, where the minimum seawater temperature exceeds the lower thermal tolerance limit for species growth in the Mediterranean Sea (14°C, Wesselmann et al, 2020), and it is expected to expand its distribution into the Western Mediterranean basin and improve its performance during this century with future warming as the Mediterranean Sea warms up (Beca‐Carretero et al, 2020; Wesselmann et al, 2020). The upper thermal tolerance of H. stipulacea is higher (Wesselmann et al, 2020) than those of the native seagrasses, particularly P. oceanica (Savva et al, 2018).…”

Unusually Warm Summer Temperatures Exacerbate Population and Plant Level Response of Posidonia oceanica to Anthropogenic Nutrient Stress

“…Posidonia oceanica meadows might tolerate further heat waves in the Mediterranean, but are likely to experience substantial cutbacks in their photosynthetic performance as well as in their carbohydrate allocation for storage and growth. This weakens the plant ability to compete with other macrophytes, that are not only able to survive, but also to photosynthesize and grow within a wider range of temperatures ( Klein and Verlaque, 2008 ; Boudouresque et al, 2009 ; Rotini et al, 2017 ; Marín-Guirao et al, 2018 ; Beca-Carretero et al, 2020 ). Additionally, further increases in ambient nutrient concentrations as well as the rising input of ammonium due to the growing demand for agriculture and mariculture off the Mediterranean coasts ( Karakassis and Hatziyanni, 2000 ; Pusceddu et al, 2007 ), pose a threat to the growth and survival of P. oceanica meadows.…”

“…P. oceanica is an extremely slow growing plant with shoots living for several decades and limited sexual reproduction ( Marbà et al, 1996 ; Marbà et al, 2004 ; Díaz-Almela et al, 2009 ). Therefore, P. oceanica meadows need a long time to recover from these mortality events ( Marbà and Duarte, 2010 ), and early successional seagrass species, invasive species, or macroalgae can colonize the free space if given the chance ( McGlathery, 2001 ; Nowicki et al, 2017 ; Beca-Carretero et al, 2020 ).…”