Larval dispersal

Understanding how plankton can inform inshore fisheries management

Principal Investigator: Dr Francesca Porri (SAIAB)

The coastal waters along our shores serve as an important habitat for several microscopic marine species. Collectively known as plankton, a drop of seawater can consist of diatoms, protozoans, small crustaceans, and the eggs and larval stages of larger fishes and invertebrates. Many animals are adapted to feed on plankton, especially by filtering the water, such as certain whale and fish species. The successful development and growth of organisms in their early stages is largely determined by the characteristics of the water in which they are found. If we can describe larval distribution at fine scales in different places along the coast, we can find out important information about their position in the food chain, how widely and where they are found, their survival and how they group together. To do this, a research project has been undertaken within the NRF-SAEON Algoa Bay Sentinel Site, Eastern Cape.

The project has a novel tri-disciplinary link incorporating ecological, oceanographic and molecular techniques to unlock larval transport of invertebrates and fishes. By integrating physical and biological processes in larval ecology, we can therefore account for dispersal and settlement and ultimately understand how and why the adults occur where they do. This approach provides essential yet challenging information that will further clarify the links between early life stages and adult population sizes and distribution. The key to understanding what drives the marine coastal populations, is determining the mechanisms and scales of larval connectivity and dispersal. However, how marine larvae are transported in the water column is still poorly understood. This is because of the complex dynamics of the physical environment in which microscopic larvae exist. In the face of global change, eco-physiology studies play a major role in assessing the effect of climate change on the distribution of marine organisms based on an organism’s physiological limits. A central argument to this research is that without the understanding of the role of early life stages in the maintenance of adult populations, most coastal marine resources cannot be safely managed. This project has therefore fundamental potential implications for marine policy and management of coastal inshore fisheries.