Competitive interactions among zoanthids (cnidaria: zoanthidae) in an intertidal zone of northeastern Brazil

Sessile organisms that live in consolidated substrates frequently compete for space. Coral species have many strategies to face this competition, including harming their opponents or hindering their growth. In the present study, the competitive interactions between three species of zoanthids were investigated in the intertidal zone of a sandstone reef environment in northeastern Brazil. The competitive abilities of the three species were evaluated by periodic observation of the natural fringes of contact and experimental evaluation of their growth rate through removal of 100 cm2 of colonies of each species. Palythoa caribaeorum and Zoanthus sociatus had similar growth rates, and both species grew faster than Protopalythoa variabilis. The recolonization strategy seems to differ among species. The contact fringes between P. caribaeorum and Z. sociatus remained unchanged over time, without any type of aggressive interaction between them, suggesting that stand-off was the strategy used by these organisms. Palythoa caribaeorum and Z. sociatus grew among the polyps of P. variabilis, often killing its colonies. The coexistence of zoanthids reveals a capacity for survival in the face of competition for limited resources such as free substrate, which led to the colonization and establishment of zoanthids in intertidal environments. A competi o por espa o é comum em organismos sésseis que vivem em substrato consolidado. Os corais apresentam muitas estratégias para competi o por espa o, incluindo danos ao oponente ou inibi o do crescimento. No presente estudo, as intera es competitivas entre três espécies de zoantídeos foram investigadas em um ambiente de recifes de arenito no nordeste brasileiro. As habilidades competitivas dos zoantídeos foram analisadas por observa es periódicas das margens de contato entre as col nias em ambiente natural e avalia o experimental da taxa de crescimento, através da remo o de uma área de 100 cm2 de col nias de cada espécie. Palythoa caribaeorum e Zoanthus sociatus apresentaram taxa de crescimento similar, crescendo mais rápido que Protopalythoa variabilis. A estratégia de coloniza o parece ser diferente entre as espécies. As margens de contato entre P. caribaeorum e Z. sociatus permaneceram inalteradas ao longo do tempo, sem qualquer intera o agressiva entre as col nias, sugerindo que a inibi o do crescimento foi a estratégia utilizada. Palythoa caribaeorum e Z. sociatus cresceram entre os pólipos de P. variabilis, muitas vezes sufocando e matando suas col nias. A coexistência entre os zoantídeos revela uma capacidade de