Mesophotic Coral Ecosystems

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 nmi 2 and prohibits all bottom-tending gear, such as trawls, longlines and traps.

Commercially-important mesophotic fish in La Parguera, southwest Puerto Rico

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

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).

MESOPHOTIC CORAL ECOSYSTEMS – A LIFEBOAT FOR CORAL REEFS? 69