Hydroid gardens of Nemertesia ramosa (Lamarck, 1816) in the central North Atlantic
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- Gomes-Pereira, J.N. & Tempera, F. Mar Biodiv (2016) 46: 85. doi:10.1007/s12526-015-0325-9
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Nemertesia ramosa (Lamarck, 1816) is a large eurybathic hydrozoan species. Its habitat and spatial distribution in the Azores archipelago (central North Atlantic) are described based on 22 new records collected in situ by scuba diving and by observations using a drop-down camera and remote operated vehicles (ROVs) between 2004 and 2011. N. ramosa grows on hard substrates in mono and multi-specific assemblages. In the Azores it is well known in the sublittoral at 15–158 m depth in the central group of islands, but historical records exist from seamounts down to bathyal grounds of nearly 1000 m. Scuba diving surveys generally reveal N. ramosa as an occasionally occurring and rare species in the infralittoral (1–9 colonies 10−3 m−2), although it may also be common and even abundant at some sites. A circalittoral aggregation was assessed in detail exhibiting densities of up to 2.82 colonies m−2 on rocky substrate and one order of magnitude lower on mixed bottom (0.25–0.55 colonies m−2). An aggregated spatial distribution is described, with aggregations being considered hydroid gardens (>1–9 10−1 m−2). Colonies measured on ROV imagery averaged 23.5 cm in height (STD = 4.1). Taller colonies (max = 36.7 cm) were registered on rocky outcrops protruding more than 15 cm. N. ramosa co-occurred mainly with brown and red algae, bryozoans, polychaetes, and other hydroids. A diverse ichthyofauna was associated to these habitats. Circalittoral communities of N. ramosa included hydrozoans, sponges, and fish.