Comparative population biology and reproduction of two sympatric crabs (Grapsidae) on Azores cobble beaches

ABSTRACT

Population biology of the intertidal crabs Pachygrapsus marmoratus Fabricius, 1787 and P. maurus (Lucas 1846) was investigated at cobble beaches with different levels of wave exposure. Surveys were taken monthly over 1.5 years at three intertidal levels. The growth rate of both species was similar, although P. marmoratus reached larger sizes. This species was more abundant on the mid-littoral zone of sheltered beaches, whereas P. maurus was more abundant on more exposed ones. The sex ratio was male biased in both species, particularly for the smaller and larger size classes. Both species showed an extended reproductive season, coinciding with the rising temperatures of spring and summer, with ovigerous females being found from June to September for P. marmoratus and from May to August for P. maurus. The present study indicates that both could develop adaptive strategies allowing them to coexist in the Azores littoral. The greater size of P. marmoratus seems to be an advantage on the competition for refuges with P. maurus, which results in its higher abundance and general dominance in the higher shore levels and in less exposed shores. However, P. maurus seems to be more fitted to live in the higher hydrodynamic habitats.

KEYWORDS:

• Population biology
• mottled shore crabs
• animal reproduction
• sex ratio
• age and growth

Acknowledgments

Authors thank the valuable collaboration of Dr Susana Alves and Mr Durval Costa from the Azores Regional Veterinary Laboratory and of Dr Ricardo Camarinho from Centre for Volcanology and Evaluation of Geological Risks, Ponta Delgada, Portugal for their help in the histology procedures. The contribution of two anonymous referees helped improved the manuscript.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This research was partially supported by the European Regional Development Fund (ERDF) through the COMPETE – Operational Competitiveness Programme and national funds through FCT – Foundation for Science and Technology, under the project ‘PEst-C/MAR/LA0015/2013’, by the Strategic Funding UID/Multi/04423/2013 through national funds provided by FCT – Foundation for Science and Technology and European Regional Development Fund (ERDF), in the framework of the program PT2020 and by cE3c funding (Ref: UID/BIA/00329/2013). Project development also benefited from CIRN support. Tarso de M. M. Costa was funded by CNPq-Brazil (203255/2014-3). Nuno V. Álvaro was funded by Fundo Regional para a Ciência e a Tecnologia (M3.1.2/F/015/2011).