Mj. Keough et Pt. Raimondi, RESPONSES OF SETTLING INVERTEBRATE LARVAE TO BIOORGANIC FILMS - EFFECTS OF LARGE-SCALE VARIATION IN FILMS, Journal of experimental marine biology and ecology, 207(1-2), 1996, pp. 59-78
Results of previous studies have shown that at two sites in-southeaste
rn Australia (Williamstown and Mornington), some sessile invertebrate
species recruit at higher densities onto surfaces that have a microbia
l film present, and that some species recruit in proportion to the age
(0-6 days) of that film. Other sessile species, notably colonial asci
dians, do not respond to the presence of these films, and some barnacl
es may avoid the films. We tested whether larvae can detect or respond
to differences in the microbial films that develop in different geogr
aphic localities and on longer time scales. To do this, we first confi
rmed that laboratory-developed microbial films induced higher recruitm
ent of benthic invertebrates at a third site, Queenscliff, in Port Phi
llip Bay, Victoria, Australia. Approximately two-thirds of the sessile
species settling at the time of the experiment were more abundant on
the filmed surfaces. We then allowed microbial films to develop at all
three sites on experimental substrata that were covered with plankton
mesh to exclude larvae. The sites were chosen to represent three diff
erent rates of development of microbial films. After 1 week, we remove
d the plankton meshes and reciprocally transplanted experimental surfa
ces between all three sites. At the same time, we brought a sample fro
m each site back to the laboratory to estimate the number of recruits
passing through plankton meshes. We tested two hypotheses using these
data, first that settling larvae at a particular site respond more str
ongly to locally-developed films than to films originating elsewhere a
nd second, that it is the density of the microbial film, rather than i
ts origin, that determines recruitment. Williamstown appeared to have
the fastest-growing, most luxurious microbial films, followed by Morni
ngton and Queenscliff. Locally-developed films were not significantly
more attractive than foreign films at Mornington or Queenscliff; none
of the 15 taxa tested showed higher recruitment rates to the local tre
atment, and highest recruitment occurred on substrata filmed at Willia
mstown. At Williamstown, there were differences in recruitment rates t
o plates with films of different origin, but in each case, films from
Williamstown received the most recruitment. These latter results could
not separate our two hypotheses, but those from Mornington and Queens
cliff suggest that larvae do not recognize and/or respond to films fro
m their local area, but that more heavily-filmed surfaces may be more
attractive lit settling larvae. The species showing rile strongest res
ponses were polychaetes, encrusting bryozoans. and some solitary ascid
ians. We also compared the attractiveness of laboratory-developed film
s varying in age up to 1 month and round that some species (serpulid p
olychaetes and encrusting bryozoans) recruited onto these surfaces ar
variable rates, while other species, notably ascidians, did not distin
guish between the different substrata.