Life in marine driftwood: The case of driftwood specialist talitrids

Once marine driftwood begins to decay, it undergoes a specific succession. Firstly, it is colonized by salt tolerant, wood degrading fungi and bacteria, along with a few invertebrates able to digest wood by producing native wood degrading enzymes. The latter include gribbles (isopods) and chelurid amphipods.

Driftwood hoppers (talitrids), as well as isopods, chilopods, insect larvae, some ants and termites, comprize the secondary colonizers. They are all characterized by their inability to utilize driftwood directly. Instead, they rely on symbiotic microflora for digestive purposes.

Within all talitrids, the driftwood hoppers count as few as seven species, most likely because they are extremely difficult to locate and, therefore, discover and describe. Apart from living in tiny burrows, they measure between 13 and <6 mm, which makes the latter the smallest known talitrid.

Having reviewed the driftwood specialized talitrids, Dr. David Wildish of the St. Andrews Biological Station, Canada, concludes that all seven known species demonstrate dwarfism based on slow metabolism and growth. Their sexual development begins earlier compared to faster growing related species. All of them are also characterized with reduced eye size and absence of dorsal pigment patterns.

In his review article published in the open access journal Zoosystematics and Evolution, the scientist confirms that dwarfism in driftwood hoppers has evolved due to poor diet, in turn resulting in slowed metabolism and growth. A further adaptive challenge is the empty gribble burrow size occupied by talitrids (burrow diameter between 0.6 to 5 mm) with the smaller ones being more widespread. Larger talitrids can only complete their life cycle in the larger burrows.

"The size gradient in gribble burrow diameter provides a satisfactory explanation for serial dwarfism within the driftwood talitrids and is why each species becomes successively smaller," explains the researcher.

Responsibility for first establishing the driftwood talitrid ecological grouping was made during graduate studies by David Wildish, London University, U.K., and Laura Pavesi, University of Rome, Italy. The two criteria for inclusion of a talitrid in the driftwood grouping was: behavioral fidelity to the occupied driftwood and that the food source was solely rotting driftwood (see references).

The larger talitrid family are small/medium in body length (< 30 mm) crustaceans with more than 400 species described in the world list. Ecological groupings within the family include marine/estuarine supralittoral wrack generalists, sand-burrowing, marsh-living and driftwood specialists. A few freshwater and many terrestrial species are also known.