Marine algal (seaweed) flora of Terceira Island, Azores

In order to improve the knowledge of Terceira Island’s macroalgal flora, extensive observations were made in the period between 2000 and 2014, encompassing both collections and presence data recordings, and covering the littoral and sublittoral levels down to approximately 40 m around the island (total area of approximately 49 km2). This paper lists the resulting taxonomic records and provides information on each species’ ecology and occurrence on the island’s littoral.

Located along a WNW-trending strip and spreading over 500 km in the North Atlantic, roughly at 38°43′49″N 27°19′10″W, the Azores archipelago is composed by nine islands and several islets. The islands are surrounded by deep waters due to the absence of a continental shelf, and therefore have a restricted coastal extension, which is subjected to swell and surge most of the year. The tidal range is small (<2 m, see Instituto Hidrográfico 1981) and the shore geomorphology alternates between high cliffs and rocky cobble/boulder beaches (Borges 2004). The climate is temperate oceanic, with regular and abundant rainfall and high levels of relative humidity and persistent winds mainly during winter and autumn (Morton et al. 1998). Terceira, located in the central group, roughly at 38°48′50″N, 27°23′25″W, 150 km northeast of São Miguel, is the third biggest island of the Azores archipelago. It has an elliptical form, 29 km long and 18 km wide, a maximum altitude of 1021 m at the summit of Serra de Santa Bárbara, and a total area of about 397 km2. The coastline has a total length of 112 km and is characterized by cliffs that vary from small to moderate heights, interrupted by small bays. Sandy beaches are limited to Praia da Vitória, located on the more protected eastern part of the island. The northern coast is more exposed and constantly submitted to the wave action (Gomes & Pinto 2004). The intertidal and shallow subtidal rocky-shore communities of Terceira are dominated by macroalgae, similarly to those of the remaining Azorean islands (Neto et al. 2005). The frondose species Fucus spiralis Linnaeus, Ulva rigida C.Agardh and Gelidium microdon Kützing are often present at mid shore levels, growing interspaced with the small chthamalid barnacles. Slightly below this level, the lack of herbivores, resulting from the overexploitation of limpets (Martins et al. 2008, 2011, Faria et al. 2015), favours an almost homogeneous coverage of the shore by algal turfs. These are growth forms of either diminutive algae or diminutive forms of larger species that create a dense, compact mat 20-30 mm thick, either monospecific (mainly composed by Caulacanthus ustulatus (Mertens ex Turner) Kützing or Gymnogongrus spp.), or multispecific and composed by articulate calcareous algae (e.g. Ellisolandia elongata and Jania spp.) and/or soft algae (e.g. Centroceras clavulatum (C.Agardh) Montagne, Chondracanthus spp. and Laurencia spp.). Lower in the shore the erect, corticated macrophytes Ellisolandia elongata (J.Ellis & Solander) K.R.Hind & G.W.Saunders, Cystoseira spp. and Osmundea pinnatifida (Hudson) Stackhouse are commonly found, frequently epiphyting multispecific algal turfs. The shallow subtidal is mainly characterized by associations of two or three frondose macrophytes, predominantly the brown seaweeds Dictyota spp. and Zonaria tournefortii (J.V. Lamouroux) Montagne.

The algae referred to in this paper were sampled during field studies at littoral and sublittoral levels down to approximately 40 m on Terceira Island, covering an area of 49 Km2. Presence recordings and physical collections were made by walking over the shores or by scuba diving. The specimens collected were taken to the laboratory for standard procedures and the resulting vouchers were deposited at the AZB Herbarium Ruy Telles Palhinha, at the Faculty of Sciences and Technology of the University of the Azores.

This study was mainly financed by the following projects/scientific expeditions: • Campaign CAMAG-TER/2008, under the project “CAMAG/TER - Caracterização das massas de água costeira da Ilha Terceira”. 2008 - 2009. The Azores Regional Government; • Project “ACORES-01-0145-FEDER-000072 - AZORES BIOPORTAL – PORBIOTA. Operational Program Azores 2020 (85% ERDF and 15% regional funds); • Portuguese National Funds, through FCT – Fundação para a Ciência e a Tecnologia, within the projects UID/BIA/00329/2013, 2015 - 2018, and UID/BIA/00329/2019 and UID/BIA/00329/2020-2023; • Portuguese Regional Funds, through DRCT – Direção Regional da Ciência e Tecnologia, within several projects, since 2013; • CIRN/DB/UAc (Research Centre for Natural Resources, Universidade dos Açores, Departamento de Biologia); • CIIMAR (Interdisciplinary Centre of Marine and Environmental Research, Porto, Portugal).