Warming Threatens to Propel the Expansion of the Exotic Seagrass Halophila stipulacea

The spread of exotic species to new areas can be magnified when favored by future climatic conditions. Forecasting future ranges using species distribution models (SDMs) could be improved by considering physiological thresholds, because models solely based on occurrence data cannot account for plasticity due to acclimation of individuals to local conditions over their life-time or to adaptation due to selection within local populations. This is particularly relevant for the exotic seagrass Halophila stipulacea, which colonized the Mediterranean Sea a century ago and shifted its thermal niche, coping with a colder regime. Here, we used two hybrid models combining correlative SDMs with the thermal limits for growth of native and exotic H. stipulacea populations to predict the distribution of the species in its native (Indian Ocean and Red Sea) and exotic ranges (Mediterranean Sea and Caribbean Sea) under two scenarios forecasting limited (RCP 2.6) and severe (RCP 8.5) future climate changes by 2050 and 2100. Then, we assessed the differences between hybrid models based on native Red Sea thermal limits (niche conservatism: 17–36°C) and on exotic Mediterranean thermal limits (local adaptation: 14–36°C). At the Mediterranean exotic range, the local adaptation hybrid model accurately agreed with the present distribution of the species while the niche conservatism-based hybrid model failed to predict 87% of the current occurrences of the species. By contrast, both hybrid models predicted similar species distributions for the native range and exotic Caribbean range at present and projected that H. stipulacea will maintain its current worldwide under all future greenhouse gas emission scenarios. The hybrid model based on Mediterranean thermal limits projected the expansion of H. stipulacea through the western Mediterranean basin (except the gulf of Leon) under the most severe scenario (RCP 8.5) by 2100, increasing its distribution by 50% in the Mediterranean. The future expansion of H. stipulacea is related to its capacity to cope with warm waters and it may become a relevant species in the future, particularly under the projected decline of native Mediterranean seagrasses, resulting in important shifts in seagrass communities and overall ecosystem functions.

A comparative study of Seagrasses Species in Regional Seas and QMZ

Seagrasses are flowering monocot green plants that have adapted to marine life, and remain completely immersed in seawater and are primary producers of food for numerous marine animals. Seagrasses are of worldwide distribution and it was earlier estimated that there are approximately 60-72 known species of seagrasses. It is now evident that the number of seagrasses species is almost 200, comprising 25 genera and 5 families, namely Cymodoceaceae, Hydrocharitaceae, Posidoniaceae, Zosteraceae and Ruppiaceae, covering a global area of 300,000-600,000 km2. It is also estimated that they have declined in area by 29%. The Western Indo-Pacific realm encompasses 13 species in two families; the Cymodoceacae with 4 genera and the Hydrocharitaceae with 3 genera. Twelve species extend into the Red Sea, 4 occur in the Arabian/Persian Gulf and 4 in the Arabian Sea. The total area of Qatar marine zone (EEZ) is approximately 35,000km2 and three species of seagrasses are known to occur in this zone. These are Halophila stipulacea, Halophila ovalis and Halodule uninervisis, the most common one. It is established that seagrasses consolidate and stabilize bottom sediments, create and maintain good water quality (clarity), produce oxygen, provide food, nursery ground for many animals and have been proven to be very important in GHG emissions.

Teasing apart the host-related, nutrient-related and temperature-related effects shaping the phenology and microbiome of the tropical seagrass Halophila stipulacea

Background: Halophila stipulacea seagrass meadows are an ecologically important and threatened component of the ecosystem in the Gulf of Aqaba. Recent studies have demonstrated correlated geographic patterns for leaf endophytic community composition and leaf morphology, also coinciding with different levels of water turbidity and nutrient concentrations. Based on these observations, workers have suggested an environmental microbial fingerprint, which may reflect various environmental stress factors seagrasses have experienced, and may add a holobiont level of plasticity to seagrasses, assisting their acclimation to changing environments and through range expansion. However, it is difficult to tease apart environmental effects from host-diversity dependent effects, which have covaried in field studies, although this is required in order to establish that differences in microbial community compositions among sites are driven by environmental conditions rather than by features governed by the host. Results: In this study we carried out a mesocosm experiment, in which we studied the effects of warming and nutrient stress on the composition of epiphytic bacterial communities and on some phenological traits. We studied H. stipulacea collected from two different meadows in the Gulf of Aqaba, representing differences in the host and the environment alike. We found that the source site from which seagrasses were collected was the major factor governing seagrass phenology, although heat increased shoot mortality and nutrient loading delayed new shoot emergence. Bacterial diversity, however, mostly depended on the environmental conditions. The most prominent pattern was the increase in Rhodobacteraceae under nutrient stress without heat stress, along with an increase in Microtrichaceae. Together, the two taxa have the potential to maintain nitrate reduction followed by an anammox process, which can together buffer the increase in nutrient concentrations across the leaf surface. Conclusions: Our results thus corroborate the existence of environmental microbial fingerprints, which are independent from the host diversity, and support the notion of a holobiont level plasticity, both important to understand and monitor H. stipulacea ecology under the changing climate.

Nutrient History Affects the Response and Resilience of the Tropical Seagrass Halophila stipulacea to Further Enrichment in Its Native Habitat

Eutrophication is one of the main threats to seagrass meadows, but there is limited knowledge on the interactive effects of nutrients under a changing climate, particularly for tropical seagrass species. This study aimed to detect the onset of stress in the tropical seagrass, Halophila stipulacea, by investigating the effect of in situ nutrient addition during an unusually warm summer over a 6-month period. We measured a suite of different morphological and biochemical community metrics and individual plant traits from two different sites with contrasting levels of eutrophication history before and after in situ fertilization in the Gulf of Aqaba. Nutrient stress combined with summer temperatures that surpassed the threshold for optimal growth negatively affected seagrass plants from South Beach (SB), an oligotrophic marine protected area, while H. stipulacea populations from North Beach (NB), a eutrophic and anthropogenically impacted area, benefited from the additional nutrient input. Lower aboveground (AG) and belowground (BG) biomass, reduced Leaf Area Index (LAI), smaller internodal distances, high sexual reproductive effort and the increasing occurrence of apical shoots in seagrasses from SB sites indicated that the plants were under stress and not growing under optimal conditions. Moreover, AG and BG biomass and internodal distances decreased further with the addition of fertilizer in SB sites. Results presented here highlight the fact that H. stipulacea is one of the most tolerant and plastic seagrass species. Our study further demonstrates that the effects of fertilization differ significantly between meadows that are growing exposed to different levels of anthropogenic pressures. Thus, the meadow’s “history” affects it resilience and response to further stress. Our results suggest that monitoring efforts on H. stipulacea populations in its native range should focus especially on carbohydrate reserves in leaves and rhizomes, LAI, internodal length and percentage of apical shoots as suitable warning indicators for nutrient stress in this seagrass species to minimize future impacts on these valuable ecosystems.

Fine-tuned method to extract high purified proteins from the seagrass Halophila stipulacea to be used for proteome analyses

The non-indigenous to the Mediterranean tropical seagrass Halophila stipulacea has the possibility to become more prevalent in the Mediterranean basin, exacerbated by the rapid increase of water temperature. Molecular profiling appears a promising tool to study the traits that render H. stipulacea tolerant and resilient and facilitate its rapid and vast geographical spread. Taking advantage from recent seagrass genomes sequencing, proteomics specialty has been applied to several seagrasses giving new insight on the biology and physiology of this group of angiosperms. Thus, it could be of interest to apply proteomics to H. stipulacea that it could be considered as a possible plant model species to study marine biological invasion. The first step to achieve this goal is to obtain high quality proteins from plant tissue. Tissue fixation and protein extraction protocol are the most challenging steps in proteomics . Here we report a fine-tuned procedure obtained by comparing protein yield from H. stipulacea plants frozen in liquid nitrogen or preserved in RNAlater and processed following two different extraction protocols. Higher protein yield have been extracted from the procedure that use the RNA later preserved plants, extracted with trichloroacetic acid in water followed by trichloroacetic acid in acetone, compared to those obtained from all other procedures. Protein purity of these samples have been tested by the separation in SDS-PAGE comfirming a better resolved profile of peptide bands suitable for a gel-based proteomics. Then, to assess the quality of proteins the m HPLC-ESI-MS/MS mass spectrometry analyses and bioinformatics have been performed. Hundreds proteins have been identified against several seagrass genomic resources available at UniProt, NCBI, SeagrassDB and transcriptomic datasets, which were merged to form the first customized dataset useful for H. stipulacea proteomic investigations.