Health assessment of marine environments: Parasites of the evileye blaasop, Amblyrhynchote honckenii (Bloch), as bioindicators

Abstract

Marine parasitology in South Africa remains a largely neglected field, with few comprehensive studies available to inform understanding of parasite diversity, host-parasite interactions, and the influence of anthropogenic stressors on these relationships. Notably, parasites are increasingly recognised as sensitive bioindicators of environmental change, reflecting pollution levels and habitat disturbances with great fidelity. Integrating parasites into environmental monitoring can thus provide early-warning signs of ecosystem degradation that traditional measures might overlook. This research adopted an environmental parasitology framework, integrating parasitology with ecotoxicology, to investigate the parasite communities of the evileye blaasop, Amblyrhynchote honckenii (Bloch), along the coast of South Africa. The project aimed to fill critical knowledge gaps in the taxonomy, ecology, and environmental sensitivity of marine parasites in the region. Field sampling was conducted at five localities located inside, near, and outside marine protected areas (MPAs) to assess spatial variation in parasite diversity and community composition. A total of 10-15 A. honckenii specimens were collected per locality and subjected to thorough parasitological screening, targeting all major parasitic taxa, including ecto- and endoparasites. Parasites were identified and documented, with notes on prevalence, intensity, and site specificity. This provided baseline data on parasite biodiversity, host associations, and life cycle characteristics within this poorly studied host species. Furthermore, host tissues (muscle and liver) were sampled for contaminant analysis to quantify concentrations of element contaminants (e.g., As, Cd, Cu, Mn, Ni, Pb, Se, and Zn) and persistent organic pollutants (including organochlorine pesticides, OCPs, and polychlorinated biphenyls, PCBs). Chemical analyses were conducted using standard, well-established protocols to ensure reliable quantification and comparison across localities. These data allowed for the assessment of pollution loads in fish hosts and their potential correlation with parasite community structure, richness, and infection patterns. Moreover, this study also explored the potential role of MPAs in conserving parasite biodiversity and mitigating contaminant-related impacts on fish health. In addition to field-based assessments, a short-term laboratory exposure experiment was conducted to evaluate copper (Cu) accumulation in both the hosts and their ectoparasites, Cinusa tetrodontis Schjödte & Meinert, 1884. Twenty A. honckenii individuals were exposed to Cu concentrations for 24 hours. The accumulation of Cu was measured in various tissues of all fish, as well as in Cin. tetrodontis (when present). Comparisons were made between parasitised and non-parasitised fish to assess differences in metal accumulation potentially linked to parasite presence. Furthermore, biomarker analyses were conducted on liver and muscle tissue to quantify metallothionein (MT) levels as indicators of metal exposure and physiological stress. By integrating parasitological, toxicological, and biomarker data, this study provides novel insights into how anthropogenic pollution influences host-parasite interactions in coastal marine systems. Across five coastal localities, a remarkably diverse assemblage of metazoan parasites was recorded, including several taxa that represent new host and geographic records. These findings provide the first comprehensive baseline of parasite biodiversity in this species, highlighting its role as a reservoir for both specialist and generalist parasites. Parasite assemblages varied strongly with environmental conditions. In and near MPAs, parasite communities were species-rich and included complex multi-host taxa, whereas communities from more degraded, urbanised localities were simplified and dominated by tolerant, direct-cycle species. This clear pattern demonstrates the sensitivity of parasite biodiversity to habitat quality and the broader conservation value of MPAs. Element analyses revealed that the isopod parasite, Cin. tetrodontis, accumulated elements at concentrations far higher than those found in the host, establishing this species as an effective biological accumulator for local metal pollution. Analyses of host tissues showed that persistent organic pollutants such as OCPs and PCBs were highest in non-protected urban localities and lowest in protected or lightly impacted areas, directly linking contaminant burdens to land use and management regimes. The controlled Cu exposure experiment confirmed that Cin. tetrodontis alters the host-pollutant relationship by sequestering the metal, thereby reducing metal loads and lessening the need for detoxification responses in its host. The parasite exhibited strong metal accumulation and metallothionein induction, with female isopods showing particularly high metal uptake. These findings reveal a dual role for this abundant parasite: it acts as a sensitive sentinel of local contamination and alleviates the physiological burden of pollution on its host. Comparisons between localities revealed the potential role of MPAs not only in conserving fish populations but also in maintaining parasite diversity, which is often overlooked despite its ecological importance. This study highlights the value of using parasites as bioindicators of environmental change and anthropogenic stress and demonstrates the need to include parasitic taxa in marine conservation and monitoring frameworks.