Download IN126 Are Mutualistic Relationships the Norm? An evolutionary

IN126 Are Mutualistic Relationships the Norm?
An evolutionary strategy for many species existing within mega biodiversity hotspots such as those
of the coral triangle is to form mutualistic relationships with other species. Mutualism occurs when
two species interact in such a way as to increase the fitness of each other and several examples have
been being well-defined on coral reefs. Perhaps the best known example is the relationship
that exists between anemones and their inhabiting anemonefish species and also the relationship
between many species of fish and their cleaners such as the blue streaked cleaner fish (Labroides
dimidiatus) or cleaner shrimps (eg Periclimenes koroensis and Periclimenes pedersoni) common to
the Indo-Pacific. However evidence suggests that mutualism, or at least commensalism (where one
species benefit with no effect on the other), is common but not fully explored. Tight associations
between species appear common place and inter-dependency between species is one of the main
reasons relatively small areas can harbour such high levels of species richness. There are many
different ways to explore mutualism on reef systems and this dissertation topic is designed for
students to explore their interests, to challenge scientific knowledge and to add to our growing
understand of what drives biodiversity and the consequences of biodiversity loss that could beyond
a single species. Within this extended summary we outline three main approaches.
The first approach could be focused on increasing our scientific our understanding of the
interactions between species that have been documented to have defined relationships with other
species but where questions still remain, for example what drives these relationships and whether
they remain stable overtime. Recent research has demonstrated that different species of
anemonefish on the coral reefs surrounding Hoga cohabit the same anemone “host” species (see De
Bawer et al 2015) . Cohabitation on the reefs is greater than any other reef in the world (see Camp
et al 2016). Although research has been completed addressing why this may be so there still remains
many unanswered questions. What advantages does cohabitation bring and how does this balance
against the disadvantages of having to share an anemone host with potentially increased conflict
between cohabiting species? Are there local conditions, such as host limitation or high abundance of
potential predators, that favours cohabitation as a strategy amongst cohabiting anemonefish? If this
is a successful strategy then why is cohabitation only seen amongst certain species and not all? Such
questions can be addressed by close examination of cohabitation patterns, adjacent fish community
surveys and detailed behavioural studies.
Cleanerfish studies are numerous within the literature and tend to focus on a single cleaner.
However we do know that several different taxa are involved in the functional cleaning of fish clients
(ie the cleanerfish and also cleaner shrimps, see Floeter et al 2007). However we are yet to
understand what controls the relative frequency of occurrence of cleaner fish stations as compared
to cleaner shrimps. The presence of both may be competitive so which taxa has most success? Is the
client base different and the quality of services provides varied amongst the taxa? Are some species
more likely to be cleaned by fish rather than shrimps or is it more opportunistic? Are their controls
on the abundance of cleaner fish as compared to cleaner shrimps and which predominates on reefs
of different conditions? Numerous hypothesis-led questions could be considered that would help us
understand the drivers of functional biodiversity and the role different species they play within the
system.
The second approach that could be used under this research area could be to explore previously
under-investigated relationships for which there is mounting anecdotal evidence but very limited
published research. Thus this research would be amongst the first carried out to explore unique
relationships between reef fish species. Apart from the well-documented mutualistic relationships
there is substantial evidence that leads us to be believe that mutualism or at least commensalism
are commonplace on reefs. For example several species of fish (small Wrasse and juvenile Goatfish)
can be found to be associated with adult Goatfish (eg Parupeneus barberinus) that feed within sandy
sediments. Several species of Goatfish are invertebrate feeders and sift through sand and soft
sediments by using their barbels to locate their prey. In doing so they bioturbate the substratum and
potentially expose invertebrate infauna that would not otherwise be available to fish species that do
not have barbels or the ability to locate and capture buried invertebrates. Our research teams have
previously noted that some fish species appear to utilise this disturbance to feed in the small craters
made by Goatfish but we do not know how common this behaviour is, whether it is predominantly a
single species or several, or whether the benefiting species utilises different feeding strategies in
different reef environments. We also do not know whether this is truly a mutualistic relationship
(where both species benefit eg through enhanced bioturbation and increased exposure of
invertebrates fed upon by both species) or whether it represents a more commensalistic relationship
(with only the one species benefiting but at no cost to the Goatfish).
Other relationships observed often relate to protection or predator avoidance. The trumpetfish
(Aulostomus chinensis) for example, especially at the juvenile stage, appears to often be associated
with other reef fish (eg some grouper and rabbit fish species) where they may seek refuge from
potential predators or hide from their potential prey (see Aronson 1983 for an example). The
frequency of occurrence of this relationship, across systems with different biodiversity is unknown
as is the true nature of the relationship. Similarly some species of parrotfish appear to graze in the
presence of rabbit fish (eg Siganus lineatus ) that may afford the more vulnerable parrotfish
protection from predators. Many other examples have been documented where the tight
relationship between two or more species does increase the fitness of both partners and the
frequency of occurrence of direct species interactions can be quantified through direct observations
of a single species and levels of interactions with others species. Damselfish for example play key
ecological roles on many reef flats and crest, and are often very territorial protecting small patches
of reef from unwanted visitors and in doing so may provide a service to other species that utilise the
same reef patch but whose niche (eg food source) does not overlap with the particular damselfish
species. Under such conditions you would hypothesise that the degree of negative / aggressive
interaction between the cohabiting but not competing species would be less than interactions
between possibly competing species. For example (see Robertson and Polunin 1981) the Pygmy
Gregory (Stegastes fasciolatus) feeds on small micro-crustaceans and tend to be located in the
feeding territories of blue-lined surgeonfish (Acanthurus lineatus ) and although there is some
common feeding habitats there isn’t direct overlap, the damselfish may add to the defence of the
surgeonfish territory. It is not known whether the surgeonfish benefits or whether there is simply no
net cost of having damselfish present but it again demonstrates a potential cohabitation and
biological interaction that can exist between fish living in highly competitive environments.
The final approach that could be used within the research area is to examine species interactions
that occur with reef sites rather than to focus on a single species. This approach would enable us to
further explore species-species interactions and the role reef structure plays in enabling high reef
fish biodiversity. Research could closely examine (directly, through video-footage or a combination
of both) defined patches of reef, record community characteristics, and record interactions
between resident and transient fish (eg positive, negative and neutral interactions). This research
could be combined with full characterisation of the physical as well as biological structure of the reef
patches to determine whether reef rugosity and habitat complexity influences the interactions that
occur between the occupying (ie resident and transient) fish species (eg Beukers and Jones 1998).
We expect that reef complexity plays a positive role in enhancing fish biodiversity by providing more
habitat and restricting negative interactions that occur, but as yet this remains fully tested.
Overall this research topic is an exciting and challenging opportunity to further scientific
understanding of the complexity of species-species interactions and the drivers of coral reef
biodiversity. Such knowledge is essential if we are truly to understand the consequences of species
loss and its implications for the functional ecology of reef systems.
References cited and further suggested reading
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Aronson RB (1983). Foraging behaviour of the West Atlantic trumpetfish Aulostomus
maculatus: Use of large herbivorous reef fishes as camouflage. Bulletin of Marin Science. 33:
166-171
Beukers J and Jones G. Oecologia (1998) Habitat complexity modifies the impact of
piscivores on a coral reef fish population. Oecologia. 114: 50 – 59
doi:10.1007/s004420050419.
Bshary R and Wurth M (2011). Cleaner fish Labroides dimidiatus manipulate client reef fish
by providing tactile stimulation. Royal Society of London Proceedings B DOI:
10.1098/rspb.2001.1495
Camp E, Hobbs J, De Brauwer M, Dumbrell A, Smith DJ (2016) Cohabitation promotes high
diversity of anemonefishes in the coral triangle. Royal Society of London Proceedings B. doi:
10.1098/rspb.2016.0277
De Bawer M, Camp E, Jompa J and Smith DJ (2015). High levels of heterospecific
cohabitation among anemonefish around Hoga Island, Indonesia. Mar Biodiv.
DOI10.1007/s12526-015-0343-7
Floeter SR, Vazquez DP and Grutter AS (2007) The macroecology of marine cleaning
mutualisms. Journal of Animal Ecology, 76: 105–111. doi:10.1111/j.1365-2656.2006.01178.x
Grutter AS (1997). Spatiotemporal Variation and Feeding Selectivity in the Diet of the
Cleaner Fish Labroides dimidiatus. Copeia 2: 346-355. DOI: 10.2307/1447754
Robertson DR and Polunin NVC (1981). Coexistence: Symbiotic sharing of feeding territories
and algal food by some coral reef fishes from the Western Indian Ocean. Marine Biology 62:
185-195