column spacer Primary productivity

Primary productivity: invertebrates

  Information on primary productivity (involving photosynthesis) in snails & clams is considered in this section, while that in SPONGES, GORGONIANS, SEA ANEMONES/JELLYFISHES, and TUNICATES is found in another section.
seahorse dive leader for Biology of Caribbean Coral Reefs website photograph of Elysia crispata taken from a video

"Only a few opisthobranch snails are out and about in the daytime. The frilly Elysia is, because it houses plant-like components within its tissues, which require light for photosynthesis." - Bonaire 2003, Litle Cayman 2001

NOTE Elysia crispata


Primary productivity: invertebrates: snails


photograph of single-celled alga Ventricaria ventricosa
Green coloration in the mantle frills of the opisthobranch Elysia crispata owes to the presence of photosynthesising chloroplasts derived from the animal's algal food. The snail eats several algal types but seems to prefer large single-celled species. It drills a hole with its radula, then sucks out the cell contents, which include the chloroplasts. Photograph of Elysia courtesy Anne Dupont, Florida.

NOTE these are organelles within the plant cells that house the photosynthetic chlorophyll
photograph of opisthobranch Elysia crispata courtesy Anne Dupont, Florida

The marine alga Ventricaria
consists of a single
large cell and may be one of
the foods of Elysia 0.8X



Opisthobranch snail
Elysia crispata

  diagrammatic view of single-cell alga Ventricaria showing chloroplast structureChloroplasts are small structures, or organelles, located within the cells of plants. Within each chloroplast resides a unique system of coiled membranes, known as thylakoid membranes. These contain the photosynthesising chlorophyll.

diagram showing fate of consumed chloroplasts in Elysia crispata
The snail eats large-celled seaweeds such as Ventricaria by piercing them with its muscular proboscis and sucking out the cell contents. The chloroplasts are sucked in and moved into the gut system. They then are diverted into digestive-gland tubules that extend from the gut into the frills on the surface of the snail. The chloroplasts become incorporated into the gastrodermal lining of the digestive-gland tubules, where they continue to photosynthesise and provide nutrients for the snail. Photosynthates, such as glucose and glycerol are thought to diffuse from the chloroplasts, cross the gastrodermal lining of the digestive-gland tubules, and enter the circulatory system.

The extent to which these photosynthates meet the nutrient and energy demands of Elysia has not yet been determined. However, some recent findings by researchers in Germany and The Netherlands suggest that the story of these chloroplasts is far from complete. In brief, these scientists confirm for a related European species of Elysia timida that the chloroplasts do photosynthesise, that carbon-based photosynthates do become incorporated into the hosts' tissues, and that the hosts can survive for long periods without any additional food uptake. This is well and good, but they also state that these same snails can survive several months of starvation in complete darkness without undue weight loss. Under these conditions the chloroplasts apparently are slowly digested and metabolised as food. Thus, photosynthesis in these snails seems not to be required to survive. The authors summarise their findings with the comment that rather than viewing the chloroplasts as "green solar panels", they should actually be viewed as "green food reserves". The work is sure to stimulate renewed interest in the subject. Christa et al 2014 Proc Roy Soc B 281: 20132493.

NOTE researchers at the University of South Florida, Tampa have studied the chloroplasts in a related species Elysia clarki and found that they derive actually from 4 species of green algae in the genera Penicillus and Halimeda, so perhaps the chloroplasts in E. crispata also have multiple sources. The authors note that these 2 species of Elysia are often mixed up because they look so similar, and it is not really clear which species was actually worked on in earlier studies. Curtis et al. 2006 Invert Biol 125 (4): 336; see also Curtis et al. 2005 Microscop Microanal 11 (2): 1194 for information on diets of juvenile Elysia crispata in the Florida area

cartoon 1 of diver conversing with Elysia crispata about its chloroplasts
The interesting sequence shown above is sure to raise questions...
cartoon 1 of diver conversing with Elysia crispata about its chloroplasts cartoon 3 of diver conversing with Elysia crispata about its chloroplasts
cartoon 4 of diver conversing with Elysia crispata about its chloroplasts cartoon 5 of diver conversing with Elysia crispata about its chloroplasts
cartoon 6 of diver conversing with Elysia crispata about its chloroplasts cartoon 7 of diver conversing with Elysia crispata about its chloroplasts

Primary productivity: invertebrates: clams

seahorse dive leader for Biology of Caribbean Coral Reefs website photograph of tunnel through coral reef taken from a video

"Well, we've made quite a jump here, from the Caribbean Sea to the Red Sea, all to get a glimpse of a giant clam. These colorful Tridacna clams have photosynthesising algal symbionts in their gut tissues, of the same or similar type to the ones found in corals." - Red Sea 2003

NOTE Tridacna maxima


photograph of giant clam
Although not found in the Caribbean region, Indo-Pacific giant clams should be familiar to all SCUBA-divers. The clams contain algal symbionts within a finely branched tubular system arising from the stomach and extending into the mantle tissues that are openly exposed to the sun. The symbionts enter and leave the host via its gut system.



The giant clamTridacna gigas can grow to a hundred or more
kilograms in mass 0.1X. The colour of the mantle tissue is
created by differential penetration of light into the tissues,
followed by its absorption and reflection by the symbionts


photograph of giant clams Tridacna maxima in the Red SeaThe photosynthetic symbionts in giant clams include the dinoflagellate Symbiodinium microadriaticum, thought to be the same as found in corals and other cnidarians in the Caribbean region, but may actually be represented by several genetically different populations of zooxanthellae. Their presence contributes to a range of vivid colours in different species of clams and even in different individuals. Carlos et al. 2000 Mar Ecol Prog Ser 195: 93.




These side-by-side individuals of giant
clams Tridacna maxima in the Red Sea
display marked colour variability 0.5X


photograph of giant clams Tridacna maxima being cultured in Palau, MicronesiaMass culture of giant clams Tridacna spp. is as easy as mariculture can ever be. The veliger larvae are short-lived and non-feeding, and inoculation with zooxanthellae occurs during the clam's juvenile stage through entrance of motile Symbiodinium cells from the surrounding seawater. On a sunny day about 85% of the clam's nutrient needs are met from the photosynthetic products of its symbionts.






Because the clams in culture require no additional food
to what is provided in the seawater flowing over them,
they can be raised in densities not possible with other
cultured species. Each of these clams is about 15cm in length


photograph of a bleached giant clam Tradacna maxima courtesy Max Taylor, University of British ColumbiaMaintain a Tridacna clam for an extended period in the dark and the zooxanthellae will die, or leave the host. If the bleached clam is left in the sunlight in normal unfiltered seawater, new symbionts will be attracted to and eaten by the clam, but not digested, and will take up residence in the tubular system of the gut. The mechanics of bleaching in giant clams are similar to that in corals: see CORAL BLEACHING. Photograph courtesy Max Taylor, University of British Columbia.





Giant clam Tridacna maxima after
several weeks in the dark 0.5X


hot button for cyanobacteria part of BCCR hot button for phytoplankton part of BCCR hot button for invertebrates part of BCCR hot button for seaweeds/seagrasses part of BCCR