the gills of the mussel Dreissena polymorpha [40]. Compound 2 came to the fore of
invasion biology especially when the commercial fish Diplodus sargus was noticed
to have changed its alimentary habits in the Mediterranean Sea, consuming large
amounts of the alga C. cylindracea. D. sargus is a native fish of high commercial
relevance, also playing a major ecological role in controlling the abundance of
keystone benthic herbivores in the Mediterranean [41, 42]. The novel “exotic diet”
of the fish attracted the attention of researchers especially because the red pigment 2
was found to enter the food chain accumulating in the fish tissues. The levels of 2 in
the fish were thus correlated with general biological condition markers associated
with fish health and reproductive development, suggesting a possible detrimental
effect of the dietary exposure to C. cylindracea on D. sargus [43]. The level of 2 in
the fish tissues was also used as an indicator of the trophic exposure to the invasive
pest and related to observed cellular and physiological alterations, including the
activation of some enzymatic pathways (catalase, glutathione peroxidases, glutathione S-transferases, total glutathione and the total oxyradical scavenging capacity,
and 7-ethoxy resorufin O-deethylase), and the inhibition of others (acetylcholinesterase and acylCoA oxidase), along with an increase of hepatosomatic index and
decrease of gonadosomatic index [44]. The observed alterations supported a detrimental health status and altered behaviors in D. sargus, potentially preventing the
reproductive success of fish populations, because of the Caulerpa-based diet.
Subsequent biomarkers analyses of fish exposed to C. cylindracea revealed
limited alterations of the main antioxidant defenses, increased activities of cytochrome P450, glutathione S-transferases, and acyl CoA oxidase, as well as enhanced
gene transcription for peroxisome proliferator-activated receptor alpha, cytochrome
P4501A, and vitellogenin 1 [45].
In further study, the trophic exposure of D. sargus to C. cylindracea was related
with a significant reduction in the amounts of essential fatty acids, suggesting that
the novel diet affects the nutritional value of the fish flesh [46]. All above findings
suggested that bioactive metabolites from C. cylindracea could modulate lipid
metabolism in D. sargus. This hypothesis was then confirmed by feeding experiment
followed by spectroscopic and multivariate analysis that provided the evidence of
a direct effect of 2 on fish flesh lipid metabolic profile, with a significant loss of
polyunsaturated fatty acids in fish fed with a caulerpin-enriched diet [47].
However, the macromolecular targets responsible for the observed effects
remained unclear. The problem assumed wider proportions when it was discovered
that other native Mediterranean sparid species feed on C. cylindracea, among
which Spondyliosoma cantharus and Sarpa salpa accumulate caulerpin (2) in their
tissues [48].
A first evidence of behavioral changes induced in D. sargus as an effect of 2 has
been provided by experiments both on groups and on single fish under different
doses of dietary 2, showing that the aggressiveness of the fish decreases with the
administration of 2. It was thus demonstrated that not only a Caulerpa-based diet but
also the purified metabolite 2 alone is able to alter the behavior on native species,
with possible consequences on fish growth and population dynamics [49]. More
light on neural mechanisms behind the altered behavior of D. sargus has been shed
6 Molecular Interactions as Drivers of Changes in Marine Ecosystems
125
invasion biology especially when the commercial fish Diplodus sargus was noticed
to have changed its alimentary habits in the Mediterranean Sea, consuming large
amounts of the alga C. cylindracea. D. sargus is a native fish of high commercial
relevance, also playing a major ecological role in controlling the abundance of
keystone benthic herbivores in the Mediterranean [41, 42]. The novel “exotic diet”
of the fish attracted the attention of researchers especially because the red pigment 2
was found to enter the food chain accumulating in the fish tissues. The levels of 2 in
the fish were thus correlated with general biological condition markers associated
with fish health and reproductive development, suggesting a possible detrimental
effect of the dietary exposure to C. cylindracea on D. sargus [43]. The level of 2 in
the fish tissues was also used as an indicator of the trophic exposure to the invasive
pest and related to observed cellular and physiological alterations, including the
activation of some enzymatic pathways (catalase, glutathione peroxidases, glutathione S-transferases, total glutathione and the total oxyradical scavenging capacity,
and 7-ethoxy resorufin O-deethylase), and the inhibition of others (acetylcholinesterase and acylCoA oxidase), along with an increase of hepatosomatic index and
decrease of gonadosomatic index [44]. The observed alterations supported a detrimental health status and altered behaviors in D. sargus, potentially preventing the
reproductive success of fish populations, because of the Caulerpa-based diet.
Subsequent biomarkers analyses of fish exposed to C. cylindracea revealed
limited alterations of the main antioxidant defenses, increased activities of cytochrome P450, glutathione S-transferases, and acyl CoA oxidase, as well as enhanced
gene transcription for peroxisome proliferator-activated receptor alpha, cytochrome
P4501A, and vitellogenin 1 [45].
In further study, the trophic exposure of D. sargus to C. cylindracea was related
with a significant reduction in the amounts of essential fatty acids, suggesting that
the novel diet affects the nutritional value of the fish flesh [46]. All above findings
suggested that bioactive metabolites from C. cylindracea could modulate lipid
metabolism in D. sargus. This hypothesis was then confirmed by feeding experiment
followed by spectroscopic and multivariate analysis that provided the evidence of
a direct effect of 2 on fish flesh lipid metabolic profile, with a significant loss of
polyunsaturated fatty acids in fish fed with a caulerpin-enriched diet [47].
However, the macromolecular targets responsible for the observed effects
remained unclear. The problem assumed wider proportions when it was discovered
that other native Mediterranean sparid species feed on C. cylindracea, among
which Spondyliosoma cantharus and Sarpa salpa accumulate caulerpin (2) in their
tissues [48].
A first evidence of behavioral changes induced in D. sargus as an effect of 2 has
been provided by experiments both on groups and on single fish under different
doses of dietary 2, showing that the aggressiveness of the fish decreases with the
administration of 2. It was thus demonstrated that not only a Caulerpa-based diet but
also the purified metabolite 2 alone is able to alter the behavior on native species,
with possible consequences on fish growth and population dynamics [49]. More
light on neural mechanisms behind the altered behavior of D. sargus has been shed
6 Molecular Interactions as Drivers of Changes in Marine Ecosystems
125