Damselfish, alongside clownfish, are both members of the family Pomacentridae, and are two of the most abundant reef-dwelling fish. They often live in and around coral reefs or sheltered sandy lagoons; however, some species have been recorded to live up to depths exceeding 100m. Primarily herbivores known for cultivating algae ‘gardens’, they may eat some small invertebrates and anemones, but these typically form a small part of their diet. These fish are most well known for their territorial nature and nesting behaviours; unlike most families of pelagic fish, the damsel fish lay their eggs attached to a substrate (a solid object such as coral, rock, and other debris).

It is this nesting behaviour that is open to disruption by anthropogenic (human produced) debris such as plastic bottles, tires, and wooden boat parts, as often these fish use such debris as nesting materials in absence of anemones and healthy reef. The purpose of the surveys conducted was to determine the knock-on effects of removing certain pieces of debris from the ocean floor, particular focus was put on plastic bottles. It is vital that plastic bottles are removed from the ocean, this is because they are made of Polyethylene terephthalate (PET). PET is easily fragmented by the mechanical and chemical processes in water into microplastics, the effects of microplastics in the marine ecosystem are widespread and devastating: bleaching coral (Tang et al., 2021) and poisoning large fish through bioaccumulation (Wang et al.,2020).

Therefore, two types of surveys were undertaken to help better understand how the removal of debris affects the damsel fish. The first type was a general survey to assess how a variety of organisms were using debris. These were undertaken over 3 days with 6 dives in total at 5 different dive sites. The second type looked only at nesting behaviours in damsel fish¸ with the type of debris being noted. These were undertaken at Hin Wong Bay (a dive site that is relatively high in single use plastic pollution) and the ‘Junkyard’ artificial reef. The results were then processed into the following pie chart showing the proportion of nesting damselfish using each type of debris to lay their eggs. The ‘other’ category consisted of gravel filled sacks that were presumably dumped into the ocean, as well as ceramic toilets sunk as part of an artificial reef project.

As the graph shows, the proportion of damsel fish using plastic bottles for nesting is very low; in fact, only 3 were recorded to be doing so. With the other (which consisted of discarded gravel and ceramic) and metal categories making up over 55% of the debris used for nesting, it could be suggested that damsel fish prefer harder, sturdier surfaces that are not prone to moving due to wave action. I concluded from this study that damsel fish are very unlikely to be negatively affected through the removal of single use plastics from the ocean, as they only tend to use them as temporary hiding places rather than for more permanent nesting.

Written by Thomas Burman, Marine Ecology and Conservation internship student at the Roctopus Ecotrust.

Bibliography:

Tang, J., Wu, Z., Wan, L., Cai, W., Chen, S., Wang, X., Luo, J., Zhou, Z., Zhao, J. and Lin, S., 2021. Differential enrichment and physiological impacts of ingested microplastics in scleractinian corals in situ. Journal of Hazardous Materials, 404, p.124205.

Wang, W., Ge, J. and Yu, X., 2020. Bioavailability and toxicity of microplastics to fish species: a review. Ecotoxicology and environmental safety, 189, p.109913.