Decadal changes in the structure of Cymodocea nodosa seagrass meadows: Natural vs. human influences

Abstract

Keywords: seagrass water quality decline human-mediated impact Canary Islands a b s t r a c t Seagrass meadows are deteriorating worldwide. However, numerous declines are still unreported, which avoid accurate evaluations of seagrass global trends. This is particularly relevant for the western African coast and nearby oceanic archipelagos in the eastern Atlantic. The seagrass Cymodocea nodosa is an 'ecological engineer' on shallow soft bottoms of the Canary Islands. A comparative decadal study was conducted in 21 C. nodosa seagrass meadows at Gran Canaria Island to compare the structure (shoot density, leaf length and cover) between 2003 and 2012. Overall, 11 meadows exhibited a severe regression, while 10 remained relatively stable. 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; the rate of seagrass erosion between 2003 and 2012 was significantly predicted by the number of human-mediated impacts around each meadow. This result highlights promoting management actions to conserve meadows of C. nodosa at the study region through efficient management of local impacts.

Population structure of the pearly razorfish, <em>Xyrichtys novacula</em> (Actinopterygii: Labridae), in sand-seagrass mosaics: spatial variation according to habitat features and sampling techniques

“…There is no significant variation in oceanographic conditions (e.g. seawater temperature, salinity and chlorophyll a concentrations) at the coast between the southeastern and southwestern side of the island (Tuya et al 2014a), and the pool of fish species is the same on both sides of the island (Espino et al 2011a). The oceanographic conditions are characterized by the northeastern trade winds and the Canary current, which flows towards the southwest.…”

“…The area covered by these seagrass meadows ranges between 98417 and 261550 m 2 at 10-18 m depth ( Table 1, Tuya et al 2014a). Each location was visited seasonally four times through an entire annual cycle: in February 2011, May 2011, August 2011and November 2011.…”

The structure of a nearshore fish assemblage at an oceanic island: insight from small scale fisheries through bottom traps at Gran Canary Island (Canary Islands, eastern Atlantic)

“…The shallow subtidal platforms around each island are not continuous except between the islands of Lanzarote and Fuerteventura, and as a result each island has its own independent shallow benthic populations (Sangil et al 2013). Sediments and rocky reefs mainly compose nearshore bottoms, with a high variability in the distribution and complexity of these habitats, which can be colonized by a range of canopy-forming species (Tuya and Haroun 2006;Tuya et al 2014). By taken advantage of a published marine cartography for the entire island (GRAFCAN 2008), we grouped the bottom types in three categories: hard (i.e.…”

Photo-physiological performance and short-term acclimation of two coexisting macrophytes (<em>Cymodocea nodosa</em> and <em>Caulerpa prolifera</em>) with depth

“…Sea surface temperature typically varies between 18°C in winter and 24ºC in summer (Tuya et al 2014). Vegetative fragments of C. nodosa (horizontal rhizomes ca.…”

“…This alga has a prostrate axis (stolon) with rhizoids and upright axes (fronds) that are potentially independent units; the whole plant can regenerate after a frond or stolon is lost (Collado-Vides 2002). In the Canary Islands, the presence of C. nodosa has decreased in the last two decades, particularly in certain areas, correlating with a significant increase in the abundance of C. prolifera (Tuya et al 2013a, Tuya et al 2014. In this region, C. nodosa typically inhabits shallower waters than C. prolifera, though the two macrophytes can be found intermixed (Tuya et al 2013a).…”