Coping with potential bi-parental inbreeding: limited pollen and seed dispersal and large genets in the dioecious marine angiosperm Thalassia testudinum

The high prevalence of dioecy in marine angiosperms or seagrasses (>50% of all species) is thought to enforce cross-fertilization. However, seagrasses are clonal plants, and they may still be subject to sibling-mating or bi-parental inbreeding if the genetic neighborhood is smaller than the size of the genets. We tested this by determining the genetic neighborhoods of the dioecious seagrass Thalassia testudinum at two sites (Back-Reef and Mid-Lagoon) in Puerto Morelos Reef Lagoon, Mexico, by measuring dispersal of pollen and seeds in situ, and by finescale spatial autocorrelation analysis with eight polymorphic microsatellite DNA markers. Prevalence of inbreeding was verified by estimating pairwise kinship coefficients; and by analysing the genotypes of seedlings grown from seeds in mesocosms. Average dispersal of pollen was 0.3–1.6 m (max. 4.8 m) and of seeds was 0.3–0.4 m (max. 1.8 m), resulting in a neighborhood area of 7.4 m² (range 3.4–11.4 m²) at Back-Reef and 1.9 (range 1.87–1.92 m²) at Mid-Lagoon. Neighborhood area (Na) derived from spatial autocorrelation was 0.1–20.5 m² at Back-Reef and 0.1–16.9 m² at Mid-Lagoon. Maximal extensions of the genets, in 19 9 30 m plots, were 19.2 m (median 7.5 m) and 10.8 m (median 4.8 m) at Back-Reef and Mid-Lagoon. There was no indication of deficit or excess of heterozygotes nor were coefficients of inbreeding (Fis) significant. The seedlings did not show statistically significant deficit of heterozygotes (except for 1 locus at Back-Reef). Contrary to our expectations, we did not find evidence of bi-parental inbreeding in this dioecious seagrass with large genets but small genetic neighborhoods. Proposed mechanisms to avoid bi-parental inbreeding are possible selection against homozygotes during fecundation or ovule development. Additionally, the genets grew highly dispersed (aggregation index Ac was 0.09 and 0.10 for Back-Reef and Mid-Lagoon, respectively); such highly dispersed guerrilla-like clonal growth form likely increases the probability of crossing between different potentially unrelated genets.Brigitta Ine Van Tussenbroek, Tania Valdivia-Carrillo, Irene Teresa Rodríguez-Virgen, Sylvia Nashieli Marisela Sanabria-Alcaraz, Karina Jiménez-Duran, Kor Jent Van Dijk, Guadalupe Judith Marquez-Guzmá

Tropical biogeomorphic seagrass landscapes for coastal protection:Persistence and wave attenuation during major storms events

The intensity of major storm events generated within the Atlantic Basin is projected to rise with the warming of the oceans, which is likely to exacerbate coastal erosion. Nature-based flood defence has been proposed as a sustainable and effective solution to protect coastlines. However, the ability of natural ecosystems to withstand major storms like tropical hurricanes has yet to be thoroughly tested. Seagrass meadows both stabilise sediment and attenuate waves, providing effective coastal protection services for sandy beaches. To examine the tolerance of Caribbean seagrass meadows to extreme storm events, and to investigate the extent of protection they deliver to beaches, we employed a combination of field surveys, biomechanical measurements and wave modelling simulations. Field surveys of sea- grass meadows before and after a direct hit by the category 5 Hurricane Irma documented that estab- lished seagrass meadows of Thalassia testudinum re- mained unaltered after the extreme storm event. The flexible leaves and thalli of seagrass and calci- fying macroalgae inhabiting the meadows were shown to sustain the wave forces that they are likely to experience during hurricanes. In addition, the seagrass canopy and the complex biogeomorphic landscape built by the seagrass meadows combine to significantly dissipate extreme wave forces, ensuring that erosion is minimised within sandy beach fore- shores. The persistence of the Caribbean seagrass meadows and their coastal protection services dur- ing extreme storm events ensures that a stable coastal ecosystem and beach foreshore is maintained in tropical regions

Caribbean-Wide, Long-Term Study of Seagrass Beds Reveals Local Variations, Shifts in Community Structure and Occasional Collapse

The CARICOMP monitoring network gathered standardized data from 52 seagrass sampling stations at 22 sites (mostly Thalassia testudinum-dominated beds in reef systems) across the Wider Caribbean twice a year over the period 1993 to 2007 (and in some cases up to 2012). Wide variations in community total biomass (285 to >2000 g dry m−2) and annual foliar productivity of the dominant seagrass T. testudinum (2000 g dry m−2) were found among sites. Solar-cycle related intra-annual variations in T. testudinum leaf productivity were detected at latitudes > 16°N. Hurricanes had little to no long-term effects on these well-developed seagrass communities, except for 1 station, where the vegetation was lost by burial below ∼1 m sand. At two sites (5 stations), the seagrass beds collapsed due to excessive grazing by turtles or sea-urchins (the latter in combination with human impact and storms). The low-cost methods of this regional-scale monitoring program were sufficient to detect long-term shifts in the communities, and fifteen (43%) out of 35 long-term monitoring stations (at 17 sites) showed trends in seagrass communities consistent with expected changes under environmental deterioration.UCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias Básicas::Centro de Investigación en Ciencias del Mar y Limnología (CIMAR

Climate drives the geography of marine consumption by changing predator communities

Este artículo contiene 7 páginas, 3 figuras, 1 tabla.The global distribution of primary production and consumption by humans (fisheries) is well-documented, but we have no map linking the central ecological process of consumption within food webs to temperature and other ecological drivers. Using standardized assays that span 105° of latitude on four continents, we show that rates of bait consumption by generalist predators in shallow marine ecosystems are tightly linked to both temperature and the composition of consumer assemblages. Unexpectedly, rates of consumption peaked at midlatitudes (25 to 35°) in both Northern and Southern Hemispheres across both seagrass and unvegetated sediment habitats. This pattern contrasts with terrestrial systems, where biotic interactions reportedly weaken away from the equator, but it parallels an emerging pattern of a subtropical peak in marine biodiversity. The higher consumption at midlatitudes was closely related to the type of consumers present, which explained rates of consumption better than consumer density, biomass, species diversity, or habitat. Indeed, the apparent effect of temperature on consumption was mostly driven by temperature-associated turnover in consumer community composition. Our findings reinforce the key influence of climate warming on altered species composition and highlight its implications for the functioning of Earth’s ecosystems.We acknowledge funding from the Smithsonian Institution and the Tula Foundation.Peer reviewe

The foundations of the Nieuwe Kerk Tower in Amsterdam (1645-52)

In 1645, the Amsterdam mayors planned to build a tower onto the Nieuwe Kerk (New Church), which was to become the tallest in the Dutch Republic. Although this structure was never completed, construction started in 1646. The urban location forced the builders to dam the water of the canal, into which the new tower was to be partly built. Thanks to the discovery of detailed data, such as written sources, drawings and wooden models, it is possible to analyze how the tower was planned. Combined with information about foundation technology, materials used, the number of people involved in construction, etc., a detailed insight into the construction process has been obtained and the foundation technique—a combination between old fashioned and modern practices—can be analyzed

Effects of seagrass Thalassia testudinum on sediment redox

The redox conditions were compared in vegetated versus unvegetated sediments across a range of contrasting Thalassia testudinum (sometimes mixed with Syringodium filiforme) meadows at Puerto Morelos Mexico reef lagoon. Moreover, the role of seagrass photosynthetic activity in affecting the redox conditions was tested in one of the meadows by experimentally reducing seagrass photosynthesis through shading. The seagrass rhizosphere extended 26 to 40 cm into the sediment, and accounted for 23 to 504 g DW m-2 of root material, mostly contributed by T. testudinum. T. testudinum placed 50% (i.e. centroidal depth) and 95% of its root biomass within 12.6 ± 0.58 and 54.4 ± 2.53 cm of the sediment surface, respectively; while S. filiforme placed 50 and 95% of its root biomass within 8.0 ± 0.87 and 34.7 ± 3.8 cm of the sediment surface, respectively. Vegetated sediments presented 50% of positive redox potential anomaly (i.e. redox potential in vegetated sediments - redox potential in adjacent bare sediments), remarkably similar (t-test, p > 0.5) to depths to the centroidal depth of the seagrass roots in the sediments. The shading experiment conducted in situ for 5 d demonstrated that the positive redox anomaly found at depth in vegetated sediments was derived from seagrass photosynthetic activity. The sediments around seagrass rhizosphere in the shaded plots were progressively reduced to reach an average decline of the redox conditions by about 45 mV by Day 5. The results presented show that seagrasses contribute to modify sediment redox conditions around their rhizosphere.This project was funded with an academic exchange grant from the Universidad Nacional Autó- noma de Mexico (UNAM, Mexico) and the Consejo Superior de Investigaciones Científicas (CSIC, Spain).Peer Reviewe