Sponges form symbiotic relationships with various organisms, including mutualisms with photosynthetic bacteria/plant cells and with swimming scallops and crabs, and parasitisms with molluscs.

NOTE “symbiosis” is a general term used in North America for any two organisms living together.  There are several categories of symbiosis described in the scientific literature, but the one most commonly used, commensalism (one partner benefits while the other is unaffected) assumes information about the participants that is most often unavailable. The two symbioses of clearest definition (and most interest) are mutualism, where both partners benefit, and parasitism, where one partner benefits and the other is harmed

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Research study 1

Several west-coast sponges house single-celled plants known as zoochlorellae. The relationship is thought to be mutualistic in that the plants provide products of photosynthesis (glycerol, glucose, amino acids) to the host in return for a place to stay, and the host provides carbon dioxide and ammonia nutrients required for photosynthesis. A common host for zoochlorellae is the “crumb-of-bread” sponge Halichondria panicea which has two growth forms. One is a flat, tough open-coast form that often contains so many zoochlorellae that it appears greenish in colour. For some reason, the green open-coast symbiotic Halichondria often has a bad smell. Whether this has something to do with its algal symbionts, or with the presence of defensive chemicals, is not known. The other non-symbiotic form is often found on docks in quiet water conditions, although may occur in open-coast situations. It has a softer consistency and mostly lacks symbionts.

NOTE thought to be similar to green plant cells found in west-coast sea anemones. These are discussed elsewhere in the ODYSSEY: SEA ANEMONES: SYMBIONTS

photograph of open-coast variant of Halichondria panicea that contains zoochlorellae symbiontsOpen-coast Halichondria panicea with zoochlorellae symbionts 0.7X photograph of non-symbiont form of sponge Halichondria panicea courtesy Sally Leys, Univ AlbertaNon-symbiont form of H. panicea 0.4X Photo courtesy Sally Leys, Univ Alberta
Research study 2

photograph of a nudibranch Doris montereyensis nestled in a bed of its prey sponge Halichondria paniceaStudies in Alaska on trophic relationship between the sponge Halichondria panicea and its nudibranch predator Doris montereyensis show that it is not just the sponge that benefits from the zoochlorellae. Over a 21d experimental period, Doris that eat sponges containing symbiotic zoochlorellae feed more, grow faster, and produce more eggs than ones eating sponge with zoochlorellae removed. Knowlton & Highsmith 2005 J Exper Mar Biol Ecol 327: 36.

histogram showing feeding rates of nudibranchs Doris montereyensis on Halichondria sponges with and without symbiotic zoochlorellaeNOTE the zoochlorellae are removed by shading the sponges for 2-3wk

Nudibranch Doris montereyensis
in its feeding excavation in the sponge Halichondria panicea 0.7X

Live masses of sponge eaten ("Feeding"), tissue produced ("Growth"), and egg ribbon
deposited ("Egg ribbon") by the nudibranch Doris montereyensis on diets of sponge
Halichondria panicea
with zoochlorellae intact (green bars) or with zoochlorellae
removed (yellow bars). All pairs of bars differ significantly


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What is the explanation for the enhanced growth performance of the nudibranch? Select the best idea from the list below and then CLICK HERE to see explanations of the answers. Ideas from Knowlton & Highsmith 2005 J Exper Mar Biol Ecol 327: 36.

Nudibranchs eat more of the zoochlorella-containing sponge.

The symbionts increase the density of the sponge tissue; hence, providing more tissue per bite for the nudibranch.

The symbionts increase the nutritional content of the food.

Research study 3
photograph of a hermit crab Pagurus sp. with a covering growth of sponge Suberites sp. covering its body

Certain hermit crabs place bits of sponge Suberites sp. onto their shells. The sponge bits, now given a clean place to grow free from competitors, soon overgrow the shell. This provides the crab with camouflaging and likely chemical protection. Eventually, the shell becomes completely etched away, but the sponge continues to surround its host. As the hermit crab grows, there is no further need to replace its shell with a larger one because the sponge grows in pace with the growth of the crab.

Hermit crab Pagurus sp. with an enveloping growth of sponge 1X

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photograph of a hermit crab Pagurus sp. with a "shell" of sponge Suberites sp. taken from a video

CLICK HERE to see a video of a Pagurus sp. hermit crab bearing a "shell" of sponge Suberites sp.

NOTE the video replays automatically

NOTE there appears to be little or no work done on this symbiotic relationship in west-coast species

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Research study 4
  photograph of a scallop Chlamys sp. with a growth of sponge Myxill sp. on its shellSponges Myxilla spp. grow on the shells of swimming scallops Chlamys spp. As it is the scallop that benefits most from the relationship, this symbiosis is considered in more detail elsewhere in the ODYSSEY: LEARN ABOUT SCALLOPS: PREDATORS & DEFENSE
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Research study 1

By secreting special shell-dissolving enzymes, boring sponges are able to break down the calcareous shells of living and dead molluscs, and the calcareous plates of barnacles. From the outside the sponge Cliona californiana appears as small yellow blobs (these are the chimneys) but, inside, the shell is hollowed into interconnected galleries in which the sponge lives.


Giant rock-scallop Crassadoma gigantea with sponge, hydroid, and
coralline algal epibionts. Chimneys of the boring sponge Cliona
are visible along the edge of the lower valve 0.5X


Research study 2

drawing of an amoebocyte of a boring sponge Cliona sp. breaking apart the crystalline structure of calcium carbonate in the shell of a scallop that the sponge is occupyingThe “boring” is actually an etching and is done by specialised amoebocyte cells. The cells crawl to spots on the shell and, by extending “noose-like” protoplasmic strands between and around the calcium-carbonate crystals making up the shell, each cell eventually frees up a chip of shell by secretion of a shell-dissociating enzyme. The enzyme appears to be carbonic anhydrase, possibly released from granules located in the cytoplasm surrounding the nucleus in each amoebocyte. No acid appears to be involved. Cobb 1969 Am Zool 9: 783; Hatch 1980 Biol Bull 159: 135.

NOTE lit. “change” "cell" G., referring to the changing shape of this type of cell through cytoplasmic streaming. Many different types of specialised cells make up the body of a sponge, including different amoebocytes

Amoebocyte of Cliona extending its noose-like strands
around a single crystal of calcium carbonate 7000X



Research study 3
Boring sponges can be serious pests to oyster-growers. If the boreholes penetrate too deeply, the oyster expends energy in repairing its shell - energy that would otherwise go into production of edible flesh or gametes for reproduction. Excavations in the shells of living abalones are repaired by secretion of nacreous material, sometimes producing beautiful iridescent “blister pearls”. Some mollusc shells with infestations, such as large scallops, may be 5 times thicker than ones without. Hansen 1970 Veliger 13:90.
photograph of the inner nacreous layer of an abalone Haliotis sp. showing nacre secreted in the form of blister pearls to repair damage caused by borin sponges and other pestsInterior view of the shell of an abalone Haliotis sp. showing nacreous shell-secretions in the form of rough blister pearls 0.5X Shell valves of dead giant scallop Crassadoma gigantea showing past infestation of boring sponge Cliona. It appears as if the sponge has left enough original shell to maintain its integrity (i.e., stop it falling apart), but in reality it is the scallop that has reinforced its shell from the inside. Shells of Crassadoma can become grossly thickened from this cause 0.4X
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