Marine Atlas: Maximizing Benefits for Tonga

sition, nor does it identify whether there are rare or priority species in an area. Further, areas with similar species richness may have very different species present, which would affect the conserva- tion and management measures required. Globally, pelagic fish are generally more abundant in tropical waters and decrease as latitude increas- es. As the map shows, within Tonga’s waters, there is a trend for higher species richness around the islands and to the west of the islands. Lower spe- cies richness to the east of the islands may reflect the different sea-floor complexity, with the deep, relatively featureless sea floor to the east resulting in less upwelling (see also chapter “Voyage to the bottom of the sea”). Large geographic features that rise off the sea floor, such as the Tonga Ridge, interact with currents and create upwellings (see also chapter “Go with the flow”). Pelagic fish abun- dance and biomass can, therefore, peak deep in the water column in association with abrupt bathy- metric features such as seamounts and mid-ocean ridges (Sutton et al., 2010). Furthermore, migrating species, including whales, frequently pause over seamounts and other shallow geographical fea- tures (Garrigue et al., 2015). Similarly, tropical waters tend to have a higher benthic species richness than waters at higher latitudes. Again, in Tonga’s waters, there is a trend for higher species richness around the islands. Benthic species richness is higher in shallow water compared with deep water, both in Tonga and glob- ally. The highest benthic species richness is found around Tonga’s main islands and extending south along the Tonga Ridge. Benthic species richness is particularly low to the east of the main islands, where the sea floor is more than 5,000 metres deep.

The Zebra shark is found throughout the tropical Pacific, but listed as endangered species.

14°S

176°W

172°W

BENTHIC MARINE SPECIES RICHNESS (number of species)

2 - 106 107 - 209 210 - 313 314 - 416 417 - 520 521 - 623 624 - 727 728 - 830 831 - 934

75 150 km

Sources : Becker et al, 2009; Claus et al, 2016; Kaschner et al, 2016; Smith and Sandwell, 1997. Copyright © MACBIO Map produced by GRID-Arendal

18°S

22°S

26°S

MAXIMIZING BENEFITS FOR TONGA

HABITAT VALUES

31