Personal Project, 2020

Advisor: Lisa Marks

Seaweaver

Seaweaver is an ongoing personal project inspired to explore solutions to problems concerning Earth’s oceans ecosystems. Human activity has greatly harmed oceanic habitats and biodiversity, and continues to do so. There are countless aspects of this to address, but there are 3 major factors that I feel are particularly severe in harming ocean wildlife.

What are the most significant threats toward ocean ecosystems?

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2

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Rising Ocean Temperatures

Marine plants and animals had specific temperature windows at which they can survive. If an ecosystem temperature increases beyond this window, a species will die and can no longer contribute to their ecosystem. This is impactful to all marine ecosystems, not just the colder polar oceans.

Ocean Acidification

The burning of fossil fuels has released a huge amount of carbon into the atmosphere, and this carbon finds its way into oceans. This change in water quality is hazardous to all marine life, but is especially harmful toward plankton and algae who are foundational to all marine ecosystems.

Depletion of Fish Population

Technology has increased our ability to locate and capture ocean life at huge scales, and as a result we have been overfishing the ocean to dangerously low levels. In addition to overfishing, practices such as bottom trawling destroy ecosystems as they harvest from them.

So where to start with solving this? Given the scale of the situation, it is daunting to begin to consider how these problems might be solved. It is not realistic to attempt to come up with an invention which can accomplish cooling the ocean, improving its water quality, and bringing back lost populations and habitats. Rather that try to create something that does these things, we must consider the ways that these processes occur in the natural world, and explore how we can encourage and employ these natural processes at scale.

These factors affect organisms at all levels, from the largest marine mammals to microscopic plankton and algae. Plankton are the primary producers of the open ocean ecosystem, and coral depend on algae in a symbiotic relationship. If the plankton and algae die in an area, their entire ecosystem can collapse.

Plants & Algae

Plants perform these functions in their natural processes. On land, trees oxygenate the air, provide shade, and are themselves the environment for entire ecosystems. Seaweed and algae, the cousins of land plants, perform similar roles in aquatic environments. Sunlight powers their photosynthesis, rather than warming the water. They improve water quality and intake carbon, in many cases at a higher rate than terrestrial trees. Seaweed forests are also entire ecosystems, supporting far more life than bare patches of ocean.

 

As living things, trees and seaweed want to grow and thrive, and will do so as long as they have what they need.

Employing plants as a solution:

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Cools Local Environment

2

 

Improves Water Quality

3

 

Creates

 Ecosystems

What does seaweed need in order to grow?

Similar to terrestrial plants, seaweed requires water, nutrients, sunlight, and a structure to affix itself to. There is no shortage of water in the ocean, and almost everywhere in the ocean has sufficiently nutritious water to support seaweed growth. Photosynthesis requires sunlight, which confines seaweed to the euphotic zone, within 100m of water depth. The real limiting factor is a structure in the right location from which the seaweed can grow.  Sand does not provide an adequate hold for most seaweeds to withstand currents and tides, so seaweed generally must grow from rocks or other structures resting at the lowest level of the water table, known as the Benthic Zone. Here is a visualization of these requirements:

Euphotic Zone

sunlight available for photosysnthesis

Aphotic Zones

insufficient sunlight for photosysnthesis

Benthic Zone (any depth)

The seafloor and structures there

sunlight , but no structure

both sunlight &

structure insufficient

structure, but no sunlight

seaweed

can grow here

In other words, seaweed can grow only where fixed structures, bound to the Benthic zone, overlap with the Euphotic zone. To present this more abstractly, we can draw a Venn Diagram:

Euphotic Zone

sunlight available for photosysnthesis

Sandy seafloor within photic zone

To encourage the growth of seaweed, and therefore to scale its effects of local cooling, carbon sequestration, and habitat-building, we must expand this area of overlap highlighted in greenwhich are the environments where seaweed readily grows

Benthic Zone

Fixed structures rest on ocean floor

Structures below photic zone

Seaweed can

grow here

Defining "Structure"

As stated above, the structure from which seaweed naturally grows is rocks within the photic zone. However, seaweed readily grows on anything fixed inside the Euphotic zone. Shipwrecks that lie within this zone function as artificial reefs, and have an afterlife serving as the structure from which seaweed and coral, and an entire ecosystem, grows. Artificial reefs are even sometimes intentionally created for this purpose: Redbird Reef is a site 25 km off the coast of Delaware where hundreds of retired subway cars and military vehicles have been dumped, and is now a large attraction for marine biodiversity, recreational diving, and sport fishing.

This much structure is excessive, however. Modern seaweed farming uses little more than a rope held taught across a body of water as the structure from which to grow.

© Atlantic Sea Farms

Location

Seaweed is naturally confined to structures in the Euphotic-Benthic overlapping areas. The most direct place to begin seaweed forestry is bare sandy areas of Euphotic-Benthic overlap which have no structures for seaweed to grow from. A structure could be suspended there, byuoyant and wanting to float, but tethered outward at angles to prevent movement in any direction. Given the proximity to the seafloor, structures tethered in this area would require little material to remain fixed in place. 

Euphotic-Benthic Overlap

Continental Shelf

Continental Slope

Suspending the structure in this way can be controlled to specific depths. The depth of the ocean floor varies across the world, but in many of the world's seas there are vast stretches where the continental shelf is below the photic zone, but yet with still relatively short distances to anchoring elements on the floor. This bathymetric map highlights in red areas where ocean depth is less than 250 meters, requiring little tethering material to reach up to Euphotic depths.

Scalability-driven exploration

Seaweed has the desired effect on the water it grows in, and we know right conditions in needs in order to grow. The challenge of utilizing it as a solution is in encouraging its growth at a scale where its desirable effects can be felt in local and larger marine environments. Given the scale of the problem, scalability must drive all aspects of the solution’s design.

  • The sunlight that powers photosynthesis cannot be replicated at scale, which means that the solution must be a structure within the photic zone to utilize the natural abundance of energy.

  • Seaweed requires very little structure to grow; seaweed farms usually use simply a rope in the water, so a scalable structure is one that is the smallest amount of material required to keep a rope in a fixed location.

  • The design of the minimal-structure should minimize the barriers to installation, which may include being made from pieces which are mass-producible, portable and can be assembled on-site.

  • The solution should be an assembly of smaller units, which individually all contain the active elements of the solution. This will allow assemblies of any number of units, and adding additional unit to existing assemblies.

Unit Development: Structural Minimalism

The fundamental element of the solution is the rope from which the seaweed grows. The simplest way to keep a rope taught is an ancient invention: the bow. Bows hold a single rope taught, allowing someone to use it as a tool to fire an arrow, or pull across strings to make music. Seaweed only requires the rope to be there, it does not need it to be accessible in the way that traditional bows are used. Rather than a curved bow which holds just one rope accessibly, we can greatly increase the rope-to-bow ratio by extending the bow all the way into a full circle with rope woven within.

A strand of rope

A bow, holding the rope taught

Bow extended into a full curcle

This circular bow is an efficient way to suspend a large amount of rope using very little material, and the framework naturally allows a variety of different ways to weave the rope.

Tiling

With the circular bow as the rough framework of how an individual unit might be configured, a larger assembly of units covering an area can be thought of as a geometric tiling. For the purpose of scalability, it makes sense to use a single tileable shape for the units. There are three regular polygons which tile a plane with no gaps or overlaps: triangles, squares, and hexagons.

Triangular tiling

Square tiling

Hexagonal tiling

Triangular and square tilings both have a characteristic which is disadvantageous in this setting. The panel edges align into a grid whose lines extend across the entire assembly, highlighted above in red.  The assembly is designed to remain flat, but these straight lines make the assembly geometrically inclined to bend along these ready "crease" lines. Conversely, hexagonal tilings do not have complete through-lines. The geometry of the intersection between hexagonal panels would inherently restrict unwanted bending of the assembly. Additionally, hexagons have less sharp corners than do triangles and squares, which is desirable for structures in an ocean setting. Hexagonal packing closely resemble the most efficient configuration of circular packing, which is why this structure is used by bees in honeycomb. For these reasons, I will be using hexagons for unit shapes from this point forward. 

Rapid prototyping of interlocking hexagonal frames with weaving patterns of varying densities:

Components of Individual Units

We have not yet discussed what size the units should be. Scalability is the goal, so we want them to be large, and we do not want that size to be limited by how large of an intact hexagon we are able to transport. If the frame is able to be broken down into compact components for transportation, this would allow for larger hexagons, more types of vessels able to transport them, and much more compact storage during travel, which would together allow for a much larger application of the solution.

These components should include:

  • 6x edge pieces delineating sides of the hexagon

    • includes features for rope to be woven into​

  • 3x support beams through hexagon center​​​

    • includes features to faster to joint pieces​

  • 7x fastening features where beams intersect​​

  • Rope for weaving.

Support Beams

Edge Pieces

Fasteners

All components are flat and linear

for compact stowing & transportation

The shapes at the ends of the components provide geometry for aligning the components both with one another and with adjacent units. In the earliest model used additional pieces for this, but I found that this geometry has the same benefits while keeping a reduced part count.

Assembly Renderings

Targeted Monoculture vs. Polyculture & Ecosystem Support

Monoculture is the large-scale agricultural production of a single species. We may want to do this because of some particular species’ exceptional ability to sequester carbon, or to mass produce as a food source. In this case, the optimal weaving density for growing that variety should be determined, and ropes installed identically for all units, covering as much area as makes sense for a given location

Examples of feature geometry possibilities which provide large amounts of flat surface areas and internal hiding areas

Polyculture is the cultivation of multiple species together. In addition to focusing on target species in monoculture units, we will also want to be able to provide a foundation for types of ecosystems with much greater biodiversity, to support the greater ocean ecosystem. To this goal, a variety of weaving patterns can be used, providing a variety of densities that more resembles natural environments than the monoculture unit’s common-distance grid weaving.

Natural seaweed forests do not exist in isolation; they grow from the sea floor, and many key species in these seaweed ecosystems are bound to the seafloor. To assist polyculture units to function as  complete ecosystems, the should be a component that provides sanctuary for these organisms. A fitting location for this type of feature could be the fasteners that hold the beams together. Optimizing this geometry for animal dwellings would be another project in and of itself, but it would most likely feature large surface areas and places for animals to hide and feel safe.

Continuation and Future of the Project

There are many angles that I have not yet had the chance to explore. Aiding ocean wildlife is the purpose of the project, so utmost care must be taken to not adversely affect existing ecologies. Material science is also a a huge factor, as the materials used be structural and non-polluting while resisting salt water corrosion. The modular nature of the design could easily allow for additional elements: recreational diving elements, additional structures for multi-trophic aquaculture, and other purposed modules, fitting easily into the hexagon configuration.

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