Growing up is hard to do: a demographic model of survival and growth of Caribbean octocoral recruits

PeerJ. 2022 Nov 18:10:e14386. doi: 10.7717/peerj.14386. eCollection 2022.

Abstract

Background: Among species with size structured demography, population structure is determined by size specific survival and growth rates. This interplay is particularly important among recently settled colonial invertebrates for which survival is low and growth is the only way of escaping the high mortality that small colonies are subject to. Gorgonian corals settling on reefs can grow into colonies of millions of polyps and can be meters tall. However, all colonies start their benthic lives as single polyps, which are subject to high mortality rates. Annual survival among these species increases with size, reflecting the ability of colonies to increasingly survive partial mortality as they grow larger.

Methods: Data on survival and growth of gorgonian recruits in the genera Eunicea and Pseudoplexaura at two sites on the southern coast of St John, US Virgin Islands were used to generate a stage structured model that characterizes growth of recruits from 0.3 cm until they reach 5 cm height. The model used the frequency distributions of colony growth rates to incorporate variability into the model.

Results: High probabilities of zero and negative growth increase the time necessary to reach 5 cm and extends the demographic bottleneck caused by high mortality to multiple years. Only 5% of the recruits in the model survived and reached 5 cm height and, on average, recruits required 3 y to reach 5 cm height. Field measurements of recruitment rates often use colony height to differentiate recruits from older colonies, but height cannot unambiguously identify recruits due to the highly variable nature of colony growth. Our model shows how recruitment rates based on height average recruitment and survival across more than a single year, but size-based definitions of recruitment if consistently used can characterize the role of supply and early survival in the population dynamics of species.

Keywords: Colony growth; Coral reef; Gorgonian; Matrix model; Partial mortality; Recruitment; Survival.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Anthozoa*
  • Caribbean Region
  • Population Dynamics
  • United States Virgin Islands

Grants and funding

This research has been funded by grants from the US National Science Foundation to Howard R. Lasker (OCE1756381 and OCE1801475), and by funding awarded to Ángela Martínez-Quintana by the Mark Diamond Research Fund (Graduate Student Association at the University at Buffalo). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.