TITLE:
Competing for Space: Factors That Lead to Sponge Overgrowth When Interacting with Octocoral
AUTHORS:
Elizabeth L. Mclean, Klaus Rützler, Penelope S. Pooler
KEYWORDS:
Porifera, Gorgonacea, Interactions, Attachment, Overgrowth
JOURNAL NAME:
Open Journal of Marine Science,
Vol.5 No.1,
January
13,
2015
ABSTRACT: The overgrowth of
octocorals by sponges is generally disadvantageous for the octocorals. When the
growth of octocoral populations increases the reefs’ structural complexity,
more substrate space becomes available for epibionts to grow. One of these
epibionts is the sponge Desmapsamma
anchorata, known to grow
exponentially faster than other sponges, and for its ability to overwhelm the
substrate over which it grows. Our objective in this study is to determine if
the overgrowth of branching octocorals by varying sponges is defined only by
species-specific interactions, or
if some physical attributes make this octocoral more susceptible to being
overgrown than others. To
determine this, on a reef south of Carrie Bow Cay, Belize, we monitored the
attachment of various demosponges to branching octocorals in a series of
experiments to assess the response effect of the interactions and properties
leading to attachment and subsequent sponge overgrowth on branching octocorals.
Substrate effects, species-specific reactions, and time of exposure were
considered. Additionally, following successful-attachment, preliminary growth
rates of two sponge species epizoic on two octocoral species were monitored.
Differences in the observed interaction between species and treatments were
analyzed with a multinomial response model to isolate a species-specific effect
from other interacting effects of the properties tested. Results indicate that
time of exposure of a sponge in direct contact with the octocoral fragment
significantly affects the outcome of the interaction; secondly, physical
properties and species-specific interactions also influence the attachment.
Following the successful attachment to an octocoral, the growth of the sponge
varies as a function of the sponge’s differential growth rate and the substrate
species over which it grows. In the context of species successions,
understanding interactions between coralreef organisms is important as these
interactions explain species composition and diversity, and provide a basis for
the prediction of future changes in complex reef communities.