Biology Reference
In-Depth Information
Galil 2007). In southeastern Australia, total numbers of fishes were similar when
Caulerpa
and native seagrass beds were observed (York et al. 2006). However, spe-
cies richness was significantly reduced in
Caulerpa
patches with high proportions
of gobiid fishes and limited numbers of syngnathid and monacanthid fish species
(York et al. 2006). In NSW, Gollan and Wright (2006) found that there were only
four herbivores that co-occurred with
C. taxifolia
. The fish
Girella tricuspidata
, the
sea hare
Aplysia dactylomela,
and two mesograzers, the amphipod
Cymadusa
setosa
and the polychaete
Platynereis dumerilii antipoda,
all preferentially fed on
other food sources in lab and field trials. Pinnegar and Polunin (2000) examined
C. taxifolia
impacts on the labrid fish
Coris julis
, which has limited migration and
dispersal. Oxidative stress was examined for foraging
C. julis
in three habitat types:
meadows of
C. taxifolia
,
C. prolifera
, and
P. oceanica
in waters surrounding
Mallorca Island, Spain. Increased activity of liver antioxidant enzymes in
Caulerpa
meadows suggested ongoing detoxification of caulerpenyne by
C. julis
if algal
blades or organisms that previously have consumed
Caulerpa
blades were ingested
(Pinnegar and Polunin 2000). Even humans have suffered ill effects from cauler-
penyne. Patients have been diagnosed with food poisoning after consuming
Sarpa
salpa
, a fish that consumes
C. taxifolia
in the Mediterranean; doctors also docu-
mented neurological disorders such as amnesia, vertigo, and hallucinations associ-
ated with caulerpenyne consumption (DeHaro et al. 1993).
Predators have been documented to be negatively impacted by
C. taxifolia
in
ways not related directly to caulerpeyne. For example,
Caulerpa's
dense clumps of
rhizomes and stolons can form obstructions to fish trying to feed on benthic inver-
tebrates (Fig. 15.2). Levi and Francour (2004) documented obstructions with the
striped red mullet
Mullus surmuletus
. Longpierre et al. (2005) additionally found
that the mullet's foraging effort increased with increased
density of C. taxifolia
with
significantly fewer large individuals in
Caulerpa
meadows (1.2%) vs. 27.8% in
Posidonia
seagrass beds. The number of individuals of the bivalve
Anadara trape-
zia
increased in areas of
C. taxifolia
relative to unvegetated controls in Australian
waters (Gribben and Wright 2006), possibly the result of increased structural com-
plexity. However, delayed reproductive development, changes in timing of spawn-
ing, and fewer oocytes and sperm were all associated with
Caulerpa
beds relative
to controls (Gribben and Wright 2006).
15.3.7
Other Characteristics that Promote Invasiveness
Other aspects of the life history of the genus
Caulerpa
that promote “invasiness”
include (1) ability to survive burial in sediment, and (2) ability to extract nutrients
from multiple sources. Typically, unicellular species such as
Caulerpa
can translo-
cate chloroplasts away from portions of the thallus if buried or held in darkness.
Glasby et al. (2005b) documented that partial burial of
Caulerpa
in sediment had
very limited impacts on individuals, while total burial for 17 days resulted in only
35% survival. While many seagrasses obtain a large fraction of nutrients from the