Recruitment of mud clam Polymesoda erosa (Solander, 1876) in a mangrove habitat of Chorao island, Goa

Abstracts

Habitat-specific settlement success results either from active habitat selection or differential mortality after non-selective settlement. The mud clam Polymesoda erosa (Solander, 1876) is an ecologically and economically important benthic invertebrate with high abundance in the mangrove forests of Chorao Island, Goa, India. A one-year study (Jul 2004-Jul 2005) was conducted to characterize the patterns of post-larval settlement and survival of P. erosa in the mangrove habitat. The mean density of settling post-larvae was 28 no.m-2 with a majority of settlers during Sept 04. The density of adult clams in the landward zone ranged from 7-12 no.m-2 (mean: 9 ± 6 sd; n=122). In the seaward region, adults were completely absent at the low tide level. Higher densities of juveniles observed at the low- and mid-tide levels were assumed to be due to frequent inundation which allowed the young individuals to feed adequately and attain the critical sizes at which vulnerability to physical and biological constraints is substantially reduced, whereas, at high-tide level, increased desiccation may account for the mortality of settlers. It is speculated that initially the settlers settle according to the hydrodynamic conditions for sedimentation; however, adult survival is affected by their recruitment in a suitable habitat (e.g. substrates near Avicennia sp.). Thus, habitat dependent viability during the post-settlement phase could be the best explanation for the non-random, patchy distribution of P. erosa observed in the Chorao mangrove swamp.

Cages; Abundance; Mortality; Juveniles; Chorao island; Goa

Um assentamento larval bem sucedido resulta da seleção ativa do habitat pelas larvas ou da mortalidade diferencial destas após o assentamento não seletivo. Nos manguezais da ilha Chorao, Goa, India, a ostra do lodo Polymesoda erosa (Solander, 1876) é um invertebrado muito abundante e de importância econômica. O presente trabalho, realizado durante um ano (julho de 2004 a julho de 2005), visou caracterizar os padrões de assentamento pós-larval e a sobrevivência de P. erosa no ambiente do mangue. Os resultados mostraram que a densidade de larvas pós-assentadas foi de 28 indiv.m-2, com a maioria dos assentamentos ocorrendo em setembro de 2004. A densidade de adultos fixados no lado terrestre variou de 7 a 12 indiv.m-2 (média: 9 ± 6 dp; n = 122). Na região voltada ao mar, os adultos estiveram ausentes no nível da maré baixa. As altas densidades de juvenis observadas nos níveis de maré baixa e média estão provavelmente relacionadas à inundação frequente da área, o que permite aos indivíduos jovens alimentarem-se adequadamente e atingirem os tamanhos críticos em que a vulnerabilidade aos estresses físicos e biológicos são substancialmente reduzidos. Além disso, na maré alta, o aumento da dissecação pode favorecer a mortalidade dos indivíduos recém-assentados. É lançada a hipótese de que o assentamento ocorre inicialmente devido às condições hidrodinâmicas da sedimentação, mas a sobrevivência do adulto é afetada pelo recrutamento em ambiente favorável (p. ex., em substratos próximos a Avicenia sp.). Desta forma, a viabilidade do habitat durante o período pós-assentamento pode ser a melhor explicação para a distribuição não randômica, em manchas, observada para P. erosa no manguezal da ilha Chorao.

Gaiolas; Abundância; Mortalidade; Juvenis; Ilha Chorao; Goa

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Publication Dates

• Publication in this collection
  11 Oct 2011
• Date of issue
  June 2011

History

• Accepted
  21 Feb 2011
• Reviewed
  03 Aug 2010
• Received
  14 Oct 2009