Title:
Chemical defense in the seaweed Dictyopteris delicatula: differential effects against reef fishes and amphipods
Chemical defense in the seaweed Dictyopteris delicatula: differential effects against reef fishes and amphipods
Author(s)
Hay, Mark E.
Duffy, J. Emmett
Fenical, William
Gustafson, Kirk
Duffy, J. Emmett
Fenical, William
Gustafson, Kirk
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Abstract
Many seaweeds produce chemicals that deter feedlng by fishes and sea urchins. A
growing body of evidence suggests that small, relatively immobile herbivores (mesograzers) such as
amphpods, polychaetes, and ascoglossan gastropods are often unaffected by these compounds and
may preferentially consume seaweeds that are chemically defended from fishes. We tested this
hypothesis by examining the responses of reef fishes and amphipods to a mutture of 2 C,, hydrocarbons,
&ctyopterenes A and B, produced by the Canbbean brown alga D~ctyopteris delicatula. This alga was
intermediate in preference for reef fishes, and the dictyopterenes reduced fish grazing by a significant
40 %. In contrast, D. delicatula was highly preferred by a muted-species group of amphipods and the
dlctyopterenes had no effect on their feeding Despite the tendency for mesograzers to selectively
consume some seaweeds that are chemically deterrent to fishes, true specialization by these or other
marine herbivores appears to be rare in companson with terrestnal systems. Plant-dwelling amphipods
at our study site in the Grenadine Islands were found on, and consumed a variety of, macrophytes; they
were not restrict~velys pecialized to D. delicatula. Many terrestnal insects are very specialized feeders,
sequester toxins from theu food plants, and use these as duect defenses against predation. In contrast,
sequestenng of seaweed toxlns by marine mesograzers appears to be relahvely rare. However, the
indirect advantage of llving on seaweeds that are not eaten by fishes may be considerable. We
hypothesize that mesograzers living on plants chemically defended from fishes wlll experience less
predation than those living on plants preferred by fishes.
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Date Issued
1988-09-21
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