Ricardo Haroun

Spatial variation in the structural parameters of Cymodocea nodosa seagrass meadows in the Canary Islands: a multiscaled approach

Abstract Meadows of the seagrass Cymodocea nodosa (legislated as an endangered species) are the dominant vegetated communities in shallow soft bottoms throughout the Canary Islands (central east Atlantic Ocean). We provide baseline ecological information for this key species for the whole Canarian Archipelago by describing the spatial distribution patterns of structural parameters (percent coverage and shoot density) at different hierarchical spatial scales (from tens of meters to hundreds of kilometers). The coverage values varied between 42.5 and 100% (mean±SE=76.7±2.5%, N=80) and the mean shoot density per location ranged between 164 and 710 shoots m−2 (mean±SE=403.6±17.0 shoots m−2, N=160). We observed a strong variability at small- to medium-spatial scales (locations within islands separated by tens of kilometres and sites hundreds of meters apart within locations) in contrast to a lack of inter-island variability. Additionally, the structural parameters respond differentially to different sets of ecological and physical processes operating at these scales.

Can one species determine the structure of the benthic community on a temperate rocky reef? The case of the long-spined sea-urchin Diadema antillarum (Echinodermata: Echinoidea) in the eastern Atlantic

We sampled 36 coastal rocky reefs throughout the overall Canarian Archipelago and consider (1) the daily macroalgal consumption of the long-spined sea urchin Diadema antillarum and (2) the daily net production of macroalgae along temperate rocky-substrates, to provide evidence that Diadema antillarum plays an important role in the structure of the shallow benthic environment of the eastern Atlantic. D. antillarum was found to be the main key-herbivore species, as it controls by its own the algal assemblages, with negligible contribution of other grazing species.

Phytogeography of Lusitanian Macaronesia: biogeographic affinities in species richness and assemblage composition

Analysis of biogeographic affinities is a key tool to establish and improve the resolution of hierarchical biogeographic systems. We describe patterns of species richness of the marine macroalgal flora across Lusitanian Macaronesia (Azores, Madeira, the Salvage Islands and the Canary Islands), and test (i) whether such differences are related to differences in proximity to the nearest continental shore and size among islands. We also explore biogeographic affinities in the composition of macroalgal assemblages (= presence/absence of each taxon in multivariate datasets) to determine (ii) whether each archipelago is a biogeographic unit within this ecoregion and (iii) whether patterns in assemblage composition are related to proximity (i.e. distances) among islands. Presence/absence matrices were created to test and visualize multivariate affinities among archipelagos. A total of 872 taxa were compiled. Species richness peaked at the Canary Islands and decreased towards the Azores; the pattern matched a progressive increase in distance from the nearest continental shores, matching the classical island biogeography theory. Intra-archipelago differences in species richness were largely related to variations in island size. Biogeographic similarities among archipelagos were hierarchically structured. Madeira and the Salvage Islands constituted one biogeographic unit. Floras from the Azores, Madeira and the Salvage Islands were barely separable from each other, but were different from those at the Canary Islands. Such biogeographic similarities among islands were negatively correlated with the geographical separation (i.e. distances) among them. Proximity to nearby continental shores, in conjunction with large- and meso-scale oceanographic patterns, seems to interact to create patterns in richness and composition of algal assemblages across Lusitanian Macaronesia.

Coastal Resources Exploitation can Mask Bottom–up Mesoscale Regulation of Intertidal Populations

We describe the spatial distribution patterns of rocky intertidal Patella spp. limpets (heavily collected by shellfishers) and top-shell snails belonging to the genus Osilinus (comparatively slightly harvested) through a multiscaled sampling design spanning five orders of magnitude of spatial variability (from 10s of m to 100s of km) throughout the Canarian Archipelago (eastern Atlantic); where rocky intertidal assemblages on opposite sides of the Archipelago (western vs. eastern islands) are subjected to different regimes of bottom-up effects, as large spatial variation in oceanographic conditions is recorded across an east–west gradient. We tested the hypothesis that the response of rocky intertidal populations to mesoscale oceanographic bottom-up variability (quantified using differences in Chlorophyll-a concentration among islands as an approximation to bottom-up effects) depends on the exploitation status of coastal resources, by means of a correlative approach. Our study represent another case in which mesoscale shore-associated physical processes seem to be correlated to large-scale differences (variability among islands, 10s to 100s of km apart) in the abundance of slightly harvested intertidal grazers (topshell snails). In contrast, we did not observe large-scale spatial differences for heavily collected grazers (limpets). In conclusion, our study suggests that the signal of bottom-up processes in coastal populations may be difficult to demonstrate under intense human exploitation.

Phenotypic plasticity in wild marine fishes associated with fish-cage aquaculture

Two opportunistic fish species associated with fish farms, bogue (Boops boops) and salema (Sarpa salpa), were studied to infer whether changes in their feeding habits may cause a phenotypic response in body and otolith shape. Specimens were collected close to aquaculture cage sites, called ‘wild-farmed fish’, and from control sites far away from these areas, called ‘wild fish’. The fish body shapes were examined with geometric morphometric analysis using 21 landmarks. The otolith contours were analysed using wavelet function, whereas otolith weights were used as indicators of fish growth rates. Statistically significant differences were observed in body shape between wild-farmed fish and wild fish of both species. The wild-farmed fish had a smaller head and eye, and in bogue also a slighter snout curvature and head depth. Otolith shape and weight did not differ between groups in bogue. By contrast, there were significant differences in otolith shape and weight between groups in salema. A complementary study in salema indicated that the wild-farmed fishes grew more in weight and accumulated higher concentrations of ‘terrestrial fatty acids’ (linoleic and alpha-linolenic acids), which are used in fish feeds. Our findings clearly demonstrated an influence of coastal sea cages on metabolism of some wild fishes.

Does Depth and Sedimentation Interact with Sea Urchins to Affect Algal Assemblage Patterns on Eastern Atlantic Reefs

ABSTRACT A range of factors may affect the composition and abundance of macroalgae on subtidal rocky reefs. We experimentally determined the interactive effect of the occurrence of the long-spine sea urchin, Diadema antillarum, depth and sedimentation levels on macroalgal assemblage structure on eastern Atlantic rocky reefs. Specifically, we manipulated sea urchin densities (removal of all individuals vs. untouched controls at natural densities) on rocky reefs devoid of erect vegetation, and predicted (1) that removal of sea urchins would differently affect macroalgal assemblage structure between deep (16–18 m) and shallow (8–9 m) reef strata, and that (2) the effect of sea urchin removal on macroalgae would be altered under different scenarios of sedimentation (ambient vs. enhanced). Experimental circular plots (2 m in diameter) were set up at 3 locations at Gran Canaria (Canarian Archipelago), and were maintained and monitored every 4 wk for 1 y. At the end of the experimental period, the structure of the algal assemblages differed between urchin treatments and depth strata, with a larger cover of turf and bushlike algae where urchins were removed and at the shallow reef stratum. More important, differences in algal assemblage structure between urchin treatments were irrespective of sedimentation levels, but shifted from the shallow to the deep stratum. This interactive effect was, in turn, observed for bushlike algae, as a result of a larger magnitude of response (i.e., larger cover) in the shallow stratum relative to the deep stratum, but was not detected for either turf or crustose coralline algae. These results highlight the importance of some physical conditions (here, differences in depth) to interact with biotic processes (here, urchin abundance) to create patterns in the organization of subtidal and benthic assemblages.

Spatio-temporal variability in a key herbivore, the long-spined black sea urchin ( Diadema antillarum , Echinodermata: Echinoidea) in the Canary Islands

Spatio-temporal variability in the population structure of long-spined black sea urchin, Diadema antillarum, was investigated at two islands (Gran Canaria and Tenerife) in the Canarian Archipelago over a year. The mean abundance of D. antillarum across all counts was 2.70 � 0.07 ind m 72 (meanSE, N¼1440), while the mean biomass was 105.76 � 3.75 g m 72 (meanSE, N¼1440). Abundances and biomasses of D. antillarum diiered consistently between vegetated and unvegetated bottoms; however, loca- tions within each habitat at each island £uctuated following diierent trends. For the overall study, mean densities and biomasses in the barren locations varied between 3.36^6.97 ind m 72 and 93.76^405.13 g m 72 , respectively; while mean densities and biomasses in the algal stand locations varied between 0^0.33 ind m 72 and 0 ^ 7.34 g m 72 , respectively. Striking diierences existed in the size-structure among locations; however, larger size-classes (test diameter 43.5 cm) were present at all locations, and usually dominated in terms of abundance. The majority of individuals in the algal stands were large-sized, probably as a result of the high abundance of the most palatable food. In contrast, small-sized individuals (test diameter 51.5 cm) only occurred in the barren habitat, suggesting that recruitment of D. antillarum could be favoured by the presence of high densities of congeners, as a way to decrease the risk of predation.

Within-island differentiation and between-island homogeneity: non-equilibrium population structure in the seaweed Cladophoropsis membranacea (Chlorophyta) in the Canary Islands

The seaweed Cladophoropsis membranacea forms extensive mats of coalesced thalli on coral reefs and along rocky coastlines throughout the tropics and subtropics. In a previous study on Gran Canaria, small-scale dispersal distances were found to be limited to < 5 m and significant differentiation (F ST) was detectable at distances as small as 5 km. Such strong, small- scale differentiation led to the prediction that strong isolation by distance (IBD) would be found under a stepping stone model at larger spatial scales. In the present survey, 23 sites were sampled in the Canary Islands and one in the Cape Verde Islands. Using eight microsatellite loci analysed in an AMOVA framework, we determined that approximately 75% of the variation occurred within sites and approximately 25% between sites separated by 1–125 km. In a three-level AMOVA, only 6% of the variation was accounted for between islands (≈100–300 km). Moderately strong IBD was found within islands and Mantel tests revealed significant correlation for Gran Canaria and Tenerife but not for Fuerteventura. In contrast, there was no detectable IBD among the Canary Islands regardless of how geographic distances were computed. Only when the Canary Islands were compared with the Cape Verde Islands was strong IBD detected. Our seemingly paradoxical results of strong differentiation and IBD at small distances and weak to absent IBD at large distances reflect non-equilibrium conditions. In addition, the wide scatter of points we observed over all degrees of geographic separation is consistent with isolation in which drift dominates over gene flow. The lack of equilibrium in present-day populations of C. membranacea is probably mainly due to the fact that they are only thousands or even hundreds of years old. Therefore, population structure should be interpreted in terms of history rather than gene flow.

Monitoring a Massive Escape of European Sea Bass (Dicentrarchus Labrax) at an Oceanic Island: Potential Species Establishment

The post-escape behavior of aquaculture escapees is a growing topic of research. We monitored a massive escape event of the European sea bass, Dicentrarchus labrax, which occurred at a sea-cage fish farm off the oceanic island of La Palma, Canary Islands, eastern Atlantic. Stomach contents and gonadal development of escapees were analyzed from two islands (Gran Canaria and La Palma) in order to assess the degree of postescape establishment,. We also tested (at both islands), the suitability of fatty acid profiles as biomarkers of aquaculture escapes, processing recaptured escaped fish at a range of distances away from aquaculture facilities. Escaped European sea bass concentrated within breakwaters and decreased in abundance through time after the massive escape at La Palma. Decapod crustaceans (particularly Percnon gibbesi and Rhynchocinetes sp) were the main diet constituents of escapees, followed by fishes (mainly the parrotfish, Sparisoma cretense). Only one spawner male was found. Crude lipid, oleic acid, linoleic acid, linolenic acid, eicosapentaenoic acid, Σn-9 fatty acids and Σmonounsatured fatty acids showed higher values in cultured or escaped individuals near cages relative to fish far away from farms. Arachidonic acid, docosahexaenoic acid, Σn-3, satured fatty acids, Σn-3/Σn-6 ratio and Palmitic acid showed the opposite pattern. Our data showed that escaped European sea bass is able to exploit natural recourses, altering their fatty acid profiles relative to farmed conspecifics. The usefulness of fatty acids as biomarkers is, however, limited to a short period of time after escape events.

Variabilidad espacial en la estructura de la ictiofauna asociada a praderas de Cymodocea nodosa en las Islas Canarias, Atlántico nororiental subtropical

A description of the patterns in spatial variability of fish assemblages is particularly relevant to guarantee an adequate management of these marine resources. Thirty six trawls were considered on six seagrass meadows (10 km apart) in three islands (100 km apart) of the Canary Islands to (i) analyze the spatial variability in the structure (richness, abundance and diversity) of fish assemblages associated with Cymodocea nodosa seagrass meadows, and to (ii) assess how the structural complexity of this habitat affects fish assemblage structure. A total of 3,616 fishes were captured, belonging to 30 species and 15 families. The total length of ca. 95% of individuals was < 10 cm, and ca. 90% of individuals were juveniles. Spatial variability in fish assemblage structure was larger when considering the scale of meadows than the scale of islands (27.28% vs. 6.64% respectively, in the amount of explained total variability); the smallest spatial scale (i.e., the variability among replicated trawls within each seagrass meadow) accumulated the largest amount of variability (66.07%). Differences in fish assemblage structure were largely driven by changes in the abundance of a few species, including Diplodus annularis, Spondyliosoma cantharus, Mullus surmuletus and Symphodus trutta. These species recruited into seagrass meadows, and confirmed the nursery role of this habitat in the canarian coastal waters. Mean shoot density and variation of the seagrass canopy height were the descriptors that accounted for the most variability when explaining patterns in fish assemblage structure.