Mesophotic Coral Ecosystems

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MESOPHOTIC CORAL ECOSYSTEMS – A LIFEBOAT FOR CORAL REEFS? 69
The shallow reef fishery in La Parguera, Puerto Rico, is an important
activity shaping the ecosystem. It has a direct impact on species,
stocks and habitats present in the region (Valdés-Pizzini and
Schärer-Umpierre 2014). Many commercially-important species
thathistoricallysupportedaproductivefisheryhavesignificantly
decreased over the last 50 years. For example, fishing pressure
has resulted in the loss of large-bodied species and spawning
aggregations (Kimmel 1985), the depletion of some species
and reductions in body size (Kimmel 1985, Pittman et al. 2010).
Keystone commercial species, such as the rainbow ( Scarus
guacamaia) and midnight (S. coelestinus) parrotfish and Nassau
( Epinephelus striatus; Figure 6.1) and tiger (Mycteroperca tigris)
groupers are no longer found in the area. Other commercially-
important reef fish are less frequently observed (e.g. red hind, E.
guttatus), and only the smaller grouper species are still common
in shallow areas (e.g. graysby, Cephalopholis cruentata; Pittman
et al. 2010). The low number of predators and the poor state
of herbivores suggests that overfishing has impacted the food
web (Guénette and Hill 2009, Pittman et al. 2010).
A recent study assessing the fish associated with MCEs off La
Parguera found thatmanyof these formally abundant species on
the shelf are now only found, or are only present in abundance,
off the steep insular slope at a depth of 60–70 m (Bejarano
Commercially-important mesophotic fish in La Parguera, southwest Puerto Rico
et al. 2014). Some examples include the goliath grouper (E.
itajara), black grouper (M. bonaci; Figure 6.2), yellowfin grouper
(M. venenosa), rainbow parrotfish (S. guacamaia), nurse shark
(Ginglymostoma cirratum), dog snapper (Lutjanus jocu), cubera
snapper (L. cyanopterus) and Caribbean reef shark (Carcharhinus
perezii). The more structurally complex MCEs have greater
abundances of these species, as fish can shelter under steep
overhangs and in caves and crevices.
The presence of many common shallow reef species at
mesophotic depths (76 per cent of 103 species), the variability in
fish assemblage composition, relative abundance and specific
fish life stages suggest that connectivity occurs between
shallow and mesophotic reefs via multiple mechanisms such
as swimming, larval dispersal and ontogenetic and spawning
migrations. Although shelf-edge MCEs support a richer and
more diverse fishery resource than nearshore habitats, these
areas are subject to a lower impact from fisheries due to their
distance from the coast (10 km), steep sloping environment,
narrow area and prevailing onshore winds and currents. The
connectivity between the less-impacted MCEs and the shallow
reefs of La Parguera may help to support the conservation of
commercially fished species, by providing a refuge from the
heavily exploited shallow-water areas.
Figure 6.1. Nassau grouper, Epinephelus striatus, on an MCE in
La Parguera, Puerto Rico (photo Héctor Ruiz).
Figure 6.2. Black grouper, Mycteroperca bonaci, on an MCE in La
Parguera, Puerto Rico at 62 m in depth. Many such large-bodied
grouper species are now only found in high abundance on MCEs,
due to overfishing on shallow reefs (photo Héctor Ruiz).
Koenig et al. 2005, Reed et al. 2007). The Oculina reefs were
first discovered in the 1970s, with high coral cover and high
densities of grouper spawning aggregations (Koenig et al.
2000). A small portion was set aside as a marine protected
area in 1984, but the remaining reefs were left unprotected
and open to trawling for rock shrimp. Chains were dragged
through the reefs to provide tracks for the rock shrimp
trawls. Submersible surveys showed the devastation caused
by the trawls as the unprotected coral was crushed to rubble
(Figure 6.3; Reed et al. 2007). Live coral areas have over 70
species of fish, while the dead coral areas are virtually devoid
of fish, with the few recorded being smaller bodied groups
of low commercial value, such as damsels and butterflyfish
(Koenig et al. 2000, 2005). This information led to the
enactment of new legislation in 2015 that doubled the size
of the Oculina marine protected area to approximately 600
nmi2 and prohibits all bottom-tending gear, such as trawls,
longlines and traps.