Sphaeroma

Sphaeroma terebrans, is an ecological engineer that can significantly modify the habitat of free-hanging aerial prop roots of Rhizophora mangle. The wood-boring isopod extensively burrows into red mangrove aerial prop roots for habitat and protection from desiccation and access to phytoplankton. However, the burrows created have major consequences on the mangrove habitat and aerial root inhabitants. It has been suggested that sessile species residing in aerial root communities can either encourage or discourage colonization by S. terebrans. Abiotic factors can affect the distribution and abundance of mangrove forest and are the same factors which determine the composition and abundance of organisms living on the roots. Surveys indicated that burrowing damage was found predominately in the first 20 cm of the root tip. Exploratory Structural Equation Modeling (SEM) was used to test multivariate hypothesized models looking at habitat relationships with S. terebrans in aerial root communities. Temperature and dissolved oxygen were shown to be important drivers in affecting submerged root length of aerial roots. Ultimately, the indirect effects between these parameters proved to be stronger in influencing the barnacle – isopod association, which causes direct negative effects on submerged root length. Colonial tunicates showed weak effects in masking aerial roots from the damaging barnacle – isopod association. Chlorophyll a was used as a proxy for phytoplankton biomass and proved to be less influential than habitat protection for S. terebrans. Results highlight the need for experimentation in addition to modeling in order to determine the mechanisms influencing aerial root community inhabitants and further effects on the habitat.

In Palm Beach County, S. terebrans burrows into grounded roots and
trunks of R. mangle causing collapse. This is contrary to previous studies
suggesting this species burrows only into free-hanging roots. Nutrients and C.
virginica cover may affect S. terebrans abundance and distribution. Surveys
show burrowing significantly varies among sites, but not between free-hanging
and grounded roots. Nutrients vary by site, but neither N nor P was correlated
with burrowing. Nutrient treated roots showed no colonization pattern associated
with N or P. Lignin varied among sites, but didn’t affect burrowing. Finally, C.
virginica limited colonization in the portion of R. mangle tissue it covered. The
location of C. virginica on the seaward/landward side was not predictive of
burrowing. R. mangle height and leaves were not negatively affected by cover
treatment or burrowing. Results highlight the need for additional research to
determine the influence of environmental factors on this species interaction.

Saltwater intrusion is threatening coastal wetlands through alteration of the natural communities leading to native species loss. In southern Florida, the Pond Apple Slough is experiencing tidally driven saltwater intrusion, which is thought to be responsible for the invasion of a marine isopod, Sphaeroma terebrans, into the native, dominant pond apple trees. The isopod appears to be responsible for the death of pond apple trees in the site. The isopod's distribution on trees within the slough appears to be controlled by the period of inundation and distance from the source of saltwater. Restriction of tidal water entering the site may limit the isopod's distribution on the pond apple trees.