TITLE:
Composition Changes and Movements in Mixed-Species Groups of Algae Grazing Fish in Jamaica and Grand Cayman Island. Part II
AUTHORS:
Andrew Bloch, Layla Al-Shaer, Brandon Baumann, Matthew Draud, M. Itzkowitz
KEYWORDS:
Caribbean, Parrotfish, Scarus, Sparisoma, Surgeonfish, Acanthurus
JOURNAL NAME:
Open Journal of Marine Science,
Vol.11 No.1,
January
8,
2021
ABSTRACT: Although Caribbean mixed-species
herbivorous fish groups are an important component to the reef community by
helping to crop algae that often overgrow and kill corals, little is known of
how they organize their foraging groups. In spite of a highly flexible
membership, the basic structure of these groups consists of a “core species,”
that leads the group and often is either the striped parrotfish (Scarus iserti) or the ocean surgeon (Acanthurus tractus). These species lead their groups to
open areas where they feed largely on low profile turf algae. Other members
prefer macro algae and are termed “associate species,” of which the two common
species we studied were the stoplight parrotfish (Sparisoma viride) and the
redband parrotfish (Sparisoma aurofrenatum). In spite of the large difference
in group sizes between Jamaica and Grand Cayman Islands, the relationships
between movement patterns and compositional changes were largely consistent.
There was no support for the hypothesis that these dramatic and continuous
group changes were related to foraging success. Instead, we speculated that
these group changes perhaps were designed to maintain cohesion among a
membership that was spread over a wide area. We also examined if associates
species may be more than just passive followers of core species but rather
instigated the attracting or the building of core groups. Both associate
species do attract striped parrotfish in open areas and thus appear active in
initiating mixed-species groups. Finally, given that associate species seem to
derive little foraging benefit from following core species, we tested the
hypothesis that associate species joined core groups to gain protection against
predators. Associate species do not selectively join the larger groups of
striped parrotfish but appear to join core species randomly and the groups
they joined resembled the wide assortment of core groups available in the
area. Thus, while associates may be joining core groups for protection, this
protection was not based on sizes of core groups.