The situation

Connectivity refers to the interconnection of marine populations through larval dispersal, which in turn influence the dynamics of each population.

At present there is very little information on levels of connectivity in coral reef regions, and management in Marine Protected Areas (MPA) depend too much on good luck and “guesstimates”.

Marine populations are interconnected, exchanging individuals - mainly through larval dispersal - and thereby influencing the dynamics of each population.

Most reef species have pelagic larval stages. The dispersal during larval life means that neighbouring populations are connected by the exchange of larvae. This connection is termed “connectivity”.

Measuring connectivity is technically difficult for several reasons including:

  • Long larval lines
  • Larvae are too small to be tagged
  • Larval dispersal – a complex result of passive transport and active movement

Many species are larval for many days or weeks, and potentially able to travel long distances during this time. Their dispersal is strongly influenced by patterns of water movement, but larvae can sense their surroundings, respond to them and swim, sometimes surprisingly well. Larval behaviour also changes as the larvae develop and grow.

The movement of water around complex coral reef topography is itself far from simple.

Measuring connectivity requires field observations that are:

  • Over large regions to encompass the potential extent of larval movement
  • Timed to coincide with critical biological events such as spawning pulses
  • By people with a broad range of skills – physical oceanographers, ecologists, behavioural scientists and others

It also benefits from use of sophisticated laboratory-based sciences including molecular genetics, trace element chemistry and advanced computer modelling. This is not routine monitoring.

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