Giant Kelp: Complex Life Cycles and Complex Relationships

Imagine you are walking along the beach and you see something washed up on shore. When you take a closer look you think that it might be a plant but as you pick it up it doesn’t feel like a normal plant. The leaves are brown and rubbery and you realize maybe this isn’t a plant at all. And you would be correct: what you found is a type of algae that lives in the ocean called giant kelp. Algae are both distantly related to animals and plants. There are three main types of algae: red, green, and brown. Algae comes in lots of different shapes and sizes. Giant kelp is a type of brown algae that is native to the California coast. 

An Underwater Forest 

Giant kelp form underwater forests that are home to many different species including sea urchin, many fish, and even sea otters. In these underwater forests there are also many microscopic creatures living alongside them. Along with the sea creatures we can see, there are many bacteria also living in the ocean. These bacteria play important roles in the nutrient cycling of the oceans. They can also form relationships with the larger creatures such as living in coral and producing food for them. In giant kelp forests, there are bacteria that live directly on their blades. This bacteria helps protect the giant kelp from harmful diseases. 

Due to climate change, these giant kelp forests are in danger. Giant kelp are very sensitive and are not able to grow when the water they live in becomes too warm. Giant kelp forests are important homes for many animals in the oceans and we need to understand how to protect these habitats.

How does the giant kelp become so giant? 

The life stage that we see most often is the adult stage of giant kelp’s complex life cycle. Unlike you and me giant kelp do not grow from two adult stage parents. The life cycle begins when the adult blades release single-celled spores into the surrounding water. These spores grow into small puff balls called gametophytes. The gametophytes only contain half of their genetic information. These puff balls can be male or female. They settle onto the seafloor; they come back together to mate and begin to reproduce. Together they grow into baby giant kelps that rapidly increase in size. Eventually they grow into the giant kelp you find on the beach. 

The gametophytes are the seeds of the giant kelp. This life stage is very important for the giant kelp forests being able to grow every year. This small life stage must successfully develop into adult giant kelp that can grow into healthy forests. Reproduction is a sensitive process. It depends on environmental cues such as temperature and light. These cues need to fit into an ideal range for reproduction to occur. Due to increasing temperatures of ocean waters, giant kelp may not be able to successfully reproduce.

This is where my research comes in. My work focuses on how bacteria are interacting with the gametophytes as they grow and develop. 

I want to answer these questions:

• Are there symbiotic relationships between bacteria and giant kelp gametophytes during development?
• How do bacteria affect the timing of development of kelp gametophytes?

These relationships could be helpful in understanding how we could make giant kelp more resilient to warming waters. 

What does symbiosis mean? 

Before I explain how I am answering these questions, let’s dive into what symbiosis is. Symbiosis has many different definitions. The definition I follow is that it’s a continuous relationship between two different organisms for all or part of their life cycles.

There are many types of symbiotic relationships that can occur. Two common types are mutualism and parasitism. Mutualism is where both partners benefit from the relationship. For example, bacteria that live in the roots of soybean plants provide food for the plants and the plants provide a home for the bacteria. Parasitism is where one partner is taking advantage of the other and causing harm. An example of parasitism is ticks needing to feed on a host to reproduce. In giant kelp, the adults have bacterial partners living on their blades. The bacteria provide disease protection and the giant kelp provides a food source. While we know about the adult giant kelp and bacteria we know very little the relationships with the gametophytes. Any of these types of symbiosis could be occurring between the giant kelp gametophyte and the bacteria that live in the water around them. We need to investigate what the cost and benefits of the bacteria are to the gametophytes. 

My Summer Research

To begin investigating this I will use giant kelp gametophytes we grow in the lab and seawater collected from Catalina Island. The seawater will be used to introduce the bacteria living in the ocean to the gametophytes. Thanks to the Bertics Summer Graduate Fellowship, I have gotten to travel to the Wrigley Marine Science Center (WMSC) on Catalina Island to collect water samples for my experiments this summer. 

This summer, I travelled to Catalina Island once a month to collect seawater from the giant kelp forests near the WMSC. This seawater contains the bacteria that are living in the giant kelp forests. My goal is to understand how these bacteria form their relationship with the giant kelp. I will be using seawater that is full of the bacteria found in the ocean to bring it to our kelp we keep in our lab.   

To introduce the bacteria I will use our lab’s gametophytes and place them in the seawater to grow. Using a microscope I watch the growth and development of the gametophytes. This includes looking for any growth of eggs or small giant kelp blades. We will also use DNA sequencing to understand what bacteria are living in the water.

Zoey Papka is supported by the Bertics Summer Graduate Fellowship.