A Dive into the Intricate World of Colony-Forming Animals in the Salish Sea

A Dive into the Intricate World of Colony-Forming Animals in the Salish Sea

by Kayley Johns
On a recent shift, I received a curious question from one of our volunteers, “What are those white things on the kelp, I have seen them everywhere lately… is it hurting the kelp like a parasite?”

While I knew the organism in question was a bryozoan, I was stumped to provide any further information about these animals. This sparked a deep dive to learn all about these tiny animals and to delve even further into the world of colony-forming animals. Here I will share my new understanding of some of the interconnected microscopic worlds living in the Salish Sea.

Colony-forming Organisms

Colony-forming organisms are described as groups of individuals that work closely together to form a larger group and are otherwise unable to live on their own. These individuals, known as zooids, connect to each other through tissue or skeleton to form one larger organism. These zooids can be all one type of identical organism or they can have different specialized forms and functions to complete specific roles within the colony. Coral reefs are a well known example of these colony-forming animals as they are composed of thousands of individual animals, called polyps working together. In the Salish Sea, there are cold water corals as well as other animals that are formed from the joining of thousands of individual zooids such as bryozoans, sea pens, and zoanthids.

Bryozoans

Bryozoans, also known as moss animals, are one of the most diverse of all colony-forming animals with over 5000 living species worldwide and are found in most habitats from the intertidal to the deep ocean. The bryozoan that was queried earlier by our volunteer is known as the kelp-encrusting bryozoan, which is commonly found living on kelp in the Salish Sea. These animals look like a thin silver or white circular crust, typically around 1 mm deep and 20 cm wide, that grows on the surface kelp, rocks and floats. This crust forms a radial pattern from many tiny rectangular zooids, with the oldest found in the middle and the newer growth found on the edges through asexual reproduction. Using chitin, these zooids form a protective shell around themselves and all perform the same functions of feeding, reproducing and defending.

Kelp-encrusting bryozoans are typically found growing on algae, where in summer they can bloom to almost cover the entire host, but once the kelp dies the colony will also die. This relationship does appear to be parasitic as the kelp is unable to receive nutrients and light for photosynthesis on the covered areas. But to answer the question that was asked by our volunteers, kelps are perennials and annuals, so they may not live long enough to be totally affected by the bryozoans.

Sea Pens

Another colony-forming animal found in the Salish Sea is the orange sea pen, known for their unique shape which is similar to a feather or quill. The orange sea pen can grow up to half a meter tall and consists of many individual polyps that are arranged into thick branches which project from the stalk and the base of the stalk is anchored into the sand. These polyps differ from kelp-encrusting bryozoans in that each one has a different function based on their location in the colony. Some of the polyps are responsible for filtering food or producing sperm and eggs, while others will intake and expel water to allow the sea pen to expand and contract. This allows the sea pen to withdraw completely into the sea bottom when they are disturbed. Fun fact: when disturbed they can also become luminescent to startle their predator.

Zoanthids

These small anemone-like animals grow to around 1-2 cm in diameter, and are formed by hundreds of orange-yellow polyps that connect to a base sheet known as a stolon. Zoanthids are very similar to anemones as they are columnar in shape and have a short fringe of tentacles around the oral disc. To keep their structure and add protection, these animals are also able to incorporate sand and other materials into their surface layer. They reproduce both sexually and asexually so they will commonly be seen together in large colonies. 

There we have it, this was my deep dive into the world of some of the colony-forming microorganisms that are found living and working together in the Salish Sea. I am fascinated by how so many of these animals seem so simple at a glance, can actually be home to an intricate microscopic world of thousands of tiny animals all working together in harmony, reminding us that not everything is exactly as we see.