Marine Atlas: Maximizing Benefits for Tonga

TRAVELLERS OR HOMEBODIES: MARINE SPECIES RICHNESS Tonga’s marine environment hosts two types of animals: pelagic species and benthic species, both of which are im- portant and biologically interconnected.

Pelagic species are those that live in the water column away from the sea floor and coast. Often these species migrate across vast areas of ocean, driven by oceanic conditions and sea- sonal food availability (see also chapter “Go with the flow”). On the other hand, benthic species are those that live on or close to the sea floor. Unlike pelagic species, which migrate large distances, benthic species are often associated with specific sea-floor features and are either attached to the substrate or very site-specific. Both pelagic and benthic species contribute to Tonga’s rich marine biodiversity, are part of complex food chains and form important habi- tats. Furthermore, many commercially important species of both types are found in Tonga’s waters. According to Tonga’s National Biodiversity Strate- gy and Action Plan, there are 38 identified pelag- ic fish, 12 species of whales and six species of

turtles found within Tonga’s waters. Commercially important pelagic species include several spe- cies of tuna, such as albacore ( Thunnus alalunga ), bigeye ( Thunnus obesus ) and yellowfin ( Thunnus albacares ) tuna, and several important commer- cial billfish species, such as blue marlin ( Makaira nigricans ), black marlin ( Makaira indica ), striped marlin ( Kajikia audax ) and swordfish ( Xiphias gla- dius ). There are also some pelagic shark species. including the blue shark ( Prionace glauca ), oceanic whitetip ( Carcharhinus longimanus ), shortfin mako shark ( Isurus oxyrinchus ) and silky shark ( Carchar- hinus falciformis ). Tonga is also one of a handful of places in the world where tourists can dive with humpback whales ( Megaptera novaeangliae ), which attract countless dive tourists and revenue to Tonga (see also chapter “Beyond the beach”). Pelagic species also include the smaller species that support these

Pelagic or benthic?

Some marine species move from one place to another, while others tend to stay in the same location. These species are described as either “pelagic” or “benthic” (see also chapter “Still waters run deep”).

large, commercially important species (see also chapter “Fishing in the dark”). The routes these species take to migrate, and thus the connectivity of their habitats, are an important consideration for marine management and conservation planning. As for Tonga’s numerous benthic species, many invertebrates (those without a backbone) are found in soft sediment habitats. According to its National Biodiversity Strategy and Action Plan, Tonga has numerous marine invertebrates, including 192 species of hard corals, 150 species of molluscs, including bivalves (such as oysters and mussels) and gastropods (such as snails and slugs), 26 crustaceans (such as crabs, lobsters and shrimps) and 33 echinoderm species (including starfish, sea urchins and sea cucumbers). Many benthic species form habitats in Tonga’s shallow waters, including corals, seagrass, mangroves and algae (see also chapter “Home, sweet home”). In general, species richness can be used as an indicator of conservation significance. It does not, however, provide information on species compo-

14°S

176°W

172°W

PELAGIC MARINE SPECIES RICHNESS (number of species)

6 - 19 20 - 33 34 - 46 47 - 59 60 - 73 74 - 86 87 - 99

100 - 113 114 - 126

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

30