Seagrasses versus seaweeds

We are all aware that seagrass meadows deliver essential functions and services to coastal ecosystems and human welfare. In many places of the globe, however, seagrasses have replaced by seaweeds. The implications of habitat shifts for ecosystem attributes and processes and the services they deliver remain poorly known. We have just published a paper comparing ecosystem structure and function between Cymodocea nodosa seagrass meadows and bottoms dominated by Caulerpa prolifera, a green, native, rhizophytic seaweed, through 5 ecological proxies: (i) primary production (via community metabolism), (ii) composition and abundance of epifauna (a proxy for provision of habitat for epifauna), composition and abundance of (iii) small-sized (juvenile) and (iv) large-sized (adult) fishes (proxies for provision of habitat for fishes), and (v) sediment retention (a proxy for sediment stabilization). Our results suggest that ecosystem structure and function differ if seagrasses are replaced by green rhizophytic seaweeds. Importantly, ecosystem functions may not be appropriate surrogates for one another. As a result, assessments of ecosystem services associated with ecosystem functions cannot be based on exclusively one service that is expected to benefit other services. The full reference is: F. Tuya, Png-Gonzalez, L., Riera, R., Haroun, R., Espino, F. 2014. Ecological structure and function differs between habitats dominated by seagrasses and green seaweeds. Marine Environmental Research 98: 1-13. Feel free to download the paper from the “articles” section of this blog.

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More about sea cucumbers…

Holothurians, our beloved sea cucumbers, are quite interesting organisms, rather amenable for subtidal experimentation. A recent PhD student from the lab (Pablo G. Navarro) has just published an extra chapter from his Thesis, where we tested whether the abundance, particulate organic matter (POM) consumption and displacement of a particular sea cucumber species, Holothuria arguinensis in this case, differed between two adjacent, vegetated, habitats (macroalgal dominated beds and seagrass meadows formed by Cymodocea nodosa). This study sums up to a previous study with Holothuria santori, and provides empirical evidence of a clear connection between the movement an selectivity for POM of sea cucumbers: non selective species ‘travel’ more distance on the seabed than selective species, which tend to remain within particular areas.  Check out the results by downloading the paper from the articles section of this webpage.

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Temperature effects of kelp physiology

Kelp are canopy-forming seaweeds that provide a myriad of resources for associated creatures. Yet, warming events, including global warming, may negatively affect kelp performance. Under the umbrella of the OCEANKELP project that aims to unravel the effect of a range of environmental and biotic processes on the distribution of kelps across continental Portugal, we tested the ability of juvenile sporophytes of two coexisting kelps, Laminaria ochroleuca and Saccorhiza polyschides, to adjust their photosynthesis and respiration to increasing seawater temperatures. L. ochroleuca showed a reduced ability to acclimatize to changing conditions, whereas S. polyschides demonstrated a larger physiological flexibility. These findings are connected with the life-history traits of these species. Additionally, optimum temperatures for the primary production of kelps were assessed, indicating higher values for inter- than subtidal S. polyschides. Our results suggests that, under a warming climate scenario, responses can significantly vary for each species, and that L. ochroleuca is more susceptible to ocean warming than S. polyschides, due to larger acclimatization capacity of the latter. Download the paper from the articles section.

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Implications of the submarine eruption off El Hierro on seaweed performance

At the end of 2012, a submarine eruption started south offshore El Hierro Island (eastern Canary Islands). Despite the large social concern that the eruption caused, it has provided us scientists with an incredible opportunity to work out the effects of such singular events on the performance of a range of organisms. In our case, we studied anatomical and physiological responses by two conspicuous seaweeds (Lobophora variegata and Padina pavonica) living in the intertidal. Our results demonstrated a large resilience of both seaweeds to the event despite large temporal affections for the anatomy and the photobiology of both seaweeds during the eruptive phase. The reference is: S. Betancor, Tuya, F., Gil-Díaz, T., Figueroa, F.L., Haroun, R. 2014. Effects of a submarine eruption on the performance of two brown seaweeds. Journal of Sea Research 87: 68–78. Feel free to download the paper from the “articles” section.

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Decadal changes in the structure of Cymodocea nodosa seagrass at Gran Canaria

We all are aware of the paramount role that seagrasses play along nearshore enviroments. Yet, declines trends in the presence of seagrasses have been worldwide described, what suppose a threat to the services these habitats provide. We performed a comparative decadal study in 21 Cymodocea nodosa seagrass meadows at Gran Canaria Island to compare the demographic structure between 2003 and 2012. In particular, we aimed at determining whether temporal trends would be predicted by a range of natural versus anthropogenic sources. We demonstrate that during this period, natural influences (sea surface temperature, Chlorophyll-a concentration and PAR light, as well as the number of storm episodes detaching seagrasses) had a low predictive power on temporal patterns in seagrass structure. In contrast, proximity from a range of human-mediated influences (e.g. the number of outfalls and ports) seem to be related to the loss of seagrass. This result highlights promoting management actions to conserve meadows of C. nodosa at the study region through efficient management of local impacts. Feel free to download the paper from the “articles” section.

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