Environmental controls of life cycles of seaweeds and seagrasses

Little is known on the environmental controls of life cycles of dominant estuarine ecosystem engineers as seaweeds and seagrasses. Here we will specifically investigate the effects of light, temperature (global change!), nutrient availability and hydrodynamics forces on the sexual reproduction of native North Sea and SW Delta brown seaweeds Laminaria digitata and Saccharina latissima, as well as seagrasses Zostera marina and Z. noltii.

Scope

The project aims to relate to the recently developed concept of Windows of Opportunity, thereby integrating across scientists within the department Estuarine and Delta Systems (EDS, NIOZ-Yerseke). Sexual reproduction in brown seaweed sporophytes is via zoospores produced in sori, developing to gametophytes that produce gametes, resulting (after fertilisation) in young sporophytes. There is only sparse knowledge on the environmental controls in the induction of sori and development of the gametophytes. Light and/or light sensing is deemed important as for cultivation purposes red light is used to refrain gametophytes from forming gametes, whereas blue light induces gametes. Similarly, it can be inferred that other environmental variables as temperature, nutrient availability as well as hydrodynamic forces will influence the sexual reproduction of brown seaweeds.

Whereas seed dispersal is a widely used method of restoration, environmental controls of sexual reproduction in seagrasses are still poorly known. This is important to gain more knowledge about, as the reproductive output of marine hydrophilous plants is generally low. Recent work showed that pollen limitation can be an important factor in limiting fruit-set, if flowering-spathe densities become too low. Flowering spathe densities were found to be lower in warmer regions along a latitudinal gradient. These findings raise questions about the effects of climate change on the reproductive output of seagrasses. Similar effects of other abiotic factors such as e.g. hydrodynamics may be expected

The fundamental knowledge gained on environmental controls over life cycles in seaweeds and seagrasses is poor at best. Gaining such understanding will enable numerous applications from having young sporophytes available year-round for mariculture to improving estuarine ecosystem restoration possibilities that depend on seed. Most importantly, it provides an interesting scientific context, varying from organism comparisons (algae versus seagrass) and broadening the current WoO theory with questioning if there might also be WoO’s for sexual reproduction.

Experimental plan

Native North Sea and SW Delta brown seaweeds Laminaria digitata and Saccharina latissima, as well as seagrasses Zostera marina and Z. noltii will be subjected under controlled experimental conditions to different light regimes (quality and quantity), different dissolved nutrient regimes (N and P, concentration and ratio), varying temperature regimes and varying hydrodynamic forces, as to determine the effects of these environmental factors on the growth and sexual reproduction. In addition to manipulative experiments, we will also explore latitudinal gradients, which learned us so much about the seagrasses. The PhD will initially start with focusing on seaweeds, as they tend to be easier to grow than seagrasses.

Relation with research at EDS, NIOZ, UU and other universities: This project will benefit from the experimental work done on seagrasses by Tjeerd Bouma, and seaweeds by Klaas Timmermans, the latter in close cooperation with the SME Hortimare. Application of the knowledge on seaweed sexual reproduction will be valuable for Hortimare. The project will enable cooperation with the Department of Ecophysiology at U. Utrecht (prof Pierik) on plant photobiology (and Utrecht programme of Future Food). Link with HZ University of Applied Sciences Vlissingen, Building with Nature projects, Mariculture initiatives in Delta and North Sea.

Relation with current EDS/NIOZ infrastructure and planned investments: in 2018 new incubation tanks for seaweed cultivation (outside mesocosms) are realized in Yerseke, moreover the incubation tanks of the SeaweedCentre Texel will be available. Inside climate chambers are available at Yerseke, as well as possibilities for flume studies, plant shakers, and dissolved nutrient analyses.