Parasitism and branchitis in various fish species from 4 Cook County,Illinois inland freshwater lakes,5-year survey,2017–2021

Materials and methods

Histologic analysis

Formalin-fixed tissues were processed routinely, sectioned at 5 µm, and stained with H&E for light microscopic evaluation. Histologic sections were reviewed by 2 of the investigators (Jennifer A. Landolfi, Michael J. Kinsel), American College of Veterinary Pathologists (ACVP)-boarded pathologists with extensive experience in fish pathology. All tissues were examined for histologic evidence of damage or disease. Gills were subjectively assessed for the presence or absence of branchitis. Branchitis was indicated by alterations in secondary lamellar epithelium including hypertrophy and hyperplasia, as well as the presence of inflammatory cells in the branchial interstitium. Distribution of branchitis was noted (diffuse vs. multifocal or regional), and branchitis was scored as absent (0), mild (1), moderate (2), or severe (3; Fig. 1). Any branchial parasites noted cytologically or in histologic sections were recorded, and distinctive morphologic features of organisms were described, including size and microanatomic structures. Specifically for downstream statistical analyses, branchial monogeneans were documented as either present or absent. Coelomic tissues were assessed for endoparasitic burden. Endoparasites included both encysted visceral metazoan and protozoan organisms as well as alimentary tract luminal parasites. Affected tissues were assessed for associated reactive changes including damage (degeneration, necrosis), inflammation, and repair (hyperplasia, fibrosis). A subjective assessment of overall parasite burden was assigned to each case (0 = none, 1 = mild, 2 = moderate, 3 = severe). Factors influencing parasite burden score included distribution and proportion of tissue affected and estimated number and diversity of individual parasites. For all endoparasites, distinctive morphologic features, including size and microanatomic structures, were described and recorded to allow for identification to phylum or class level.

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Figure 1.

Branchitis in bullheads from Cook County inland lakes. A. In cases of mild branchitis, interlamellar spaces and the basal up to 20% of secondary lamellae are covered by 3–5 layers of polygonal epithelial cells (hyperplasia). Epithelial cells are separated by scant colorless space (intercellular edema) and a few scattered intraepithelial leukocytes. B. In cases of moderate branchitis, interlamellar spaces and the basal up to 50% of secondary lamellae are covered by hyperplastic epithelium with intercellular edema and a few scattered intraepithelial and interstitial leukocytes. C. In cases of severe branchitis, interlamellar spaces and the basal >50% of secondary lamellae are covered by hyperplastic epithelium with intercellular edema and a few scattered intraepithelial and interstitial leukocytes. H&E.

Results

We examined 429 fish (Table 1). Data from all Ameiurus spp. were combined. Sufficient numbers of each bullhead species from each lake were not obtained to justify separate analysis.

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Table 1.

Total fish collected from Cook County inland lakes, 2017–2021.

	Busse			Powderhorn			Tampier			Axehead			Total per species
	Spr	Sum	Fall	Spr	Sum	Fall	Spr	Sum	Fall	Spr	Sum	Fall
Largemouth bass	10	10	10	10	10	10	10	10	10	10	8	10	118
Bluegill	9	10	10	9	10	9	10	10	9	10	8	10	114
Bullhead	10	10	9	8	8	9	10	10	10	8	4	2	98
Carp	10	10	10	10	10	10	10	10	10	7	0	2	99
Total per lake	118			113			119			79			429

Spr = spring; Sum = summer.

All fish were in good body condition with adequate skeletal musculature and coelomic adipose stores. No lesions considered to pose a risk for human consumption were detected in any fish species, from any lake, at any time during the survey. In all examined fish, skeletal muscle (flesh) was free of inflammation and other tissue damage.

Lesions of possible significance to fish health were detected in every sampling year and included branchitis and endoparasitism. Some degree of branchitis was detected in 261 of 429 (60.8%) cases. Severity was mild in 189 of 261 (72.4%) cases, moderate in 60 of 261 (23%) cases, and severe in 12 of 261 (4.6%) cases. Distribution of branchitis was most often diffuse, and branchial parasites were detected in 175 of 261 (67%) branchitis cases. Observed branchial parasites included monogeneans (244 of 254; 96%), copepods (17 of 429; 4%), and ciliates (3 of 429; 0.07%), and were detected in cases (254 of 429; 59.2%) both with and without branchitis. Monogeneans were monopisthocotyleans based on their hook-bearing haptors. Morphologic features evident in wet-mount cytologic preparations including size, anterior margin (head) shape, and presence or absence of eyespots, were most consistent with families Gyrodactylidae or Dactylogyridae (Fig. 2).^10,22,27 The mean branchitis scores of fish with and without monogeneans were similar (with monogeneans = 0.807; without monogeneans = 0.800). The Kruskal–Wallis test showed no significant difference in branchitis severity score between fish with and without monogeneans (p = 0.484). Copepods had ergasiliform morphologic features, including a cephalothorax, abdomen, anterior grasping antennae, and, in females, paired egg sacs (Figs. 3, 4). Ciliates were morphologically similar in all cases affected. Organisms were round and ~40-µm diameter with uniform, circumferential cilia, and an oral disc with refractile hook-like denticles; features were consistent with Trichodina spp. (Fig. 5).^10,22

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Figures 2–5.

Branchial parasitism of various fish from Cook County inland lakes. Figure 2. Wet mount, gill clip cytologic preparation from a common carp. The branchial secondary lamellus has a monogenean with a scalloped anterior margin, 4 eye spots, and posterior haptor-bearing refractile hooks, consistent with a dactylogyrid. Figure 3. Wet mount, gill clip cytologic preparation from a largemouth bass containing a branchial copepod. The copepod is ergasiliform with anterior grasping antennae, cephalothorax, abdomen, and paired egg sacs. Figure 4. Photomicrograph of gill from a largemouth bass containing a branchial copepod. Histologically, copepods had features consistent with arthropods including a chitinous exoskeleton and bands of striated muscle. H&E. Figure 5. Wet mount, gill clip cytologic preparation from a largemouth bass containing a round protozoan with uniform, circumferential cilia and an oral disk with refractile, hook-like denticles, consistent with Trichodina spp.

Using generalized ordered logistic regression to determine which variables influenced branchitis severity, fish species was found to be a significant predictor (p < 0.001). Most of the cases with high branchitis severity scores were bullheads (10 of 12; 83%). In contrast, common carp had the fewest cases of branchitis (44 of 99; 44%) and, when present in this species, branchitis was most often mild (37 of 44; 84%). The interaction of lake and alkalinity was also found to be a significant predictor of branchitis severity (p < 0.001; Fig. 6). Alkalinity and branchitis severity were lowest in Axehead Lake (Table 2). The most severe cases of branchitis were observed in fish from Busse, Powderhorn, and Tampier lakes when total alkalinity was at its highest. The interaction of water temperature and season was also found to be a significant predictor of branchitis severity (p < 0.001; Fig. 7). Cases with the most severe branchitis were mostly documented in the fall and when water temperatures were lower (Table 2). This association was observed only in bullhead, carp, and bluegills.

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Figure 6.

Branchitis severity by lake, species, season, and alkalinity. Most cases of severe branchitis occurred in bullheads. When branchitis was detected in carp, it was mild. Alkalinity and branchitis were lowest in Axehead Lake, and the most severe cases of branchitis occurred when total alkalinity was at its highest for other lakes.

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Table 2.

Summary of Cook County inland lake water chemistry parameters, 2017–2021.

	Busse			Powderhorn			Tampier			Axehead
	Spr	Sum	Fall	Spr	Sum	Fall	Spr	Sum	Fall	Spr	Sum	Fall
Average temperature, °C	19.0	24.3	11.1	20.8	25.9	14.7	21.1	25.8	12.5	19.5	25.8	14.9
Average dissolved oxygen, mg/L	5.87	4.29	9.18	5.17	8.99	8.73	5.71	7.77	10.3	9.13	9.49	6.94
Average alkalinity, mg/L	135	126	138	147	130	134	97.4	116	112	108	81.9	115
Average chloride, mg/L	230	176	121	35.7	43.7	53.4	45.6	54.6	56	561	560	594
Average color, APC	181	130	145	53.7	43.9	65.2	97	143	107	30.6	31.6	40.5
Average turbidity, FTU	47	39	40.4	17.1	13.3	19.6	29.4	43	31.2	11.9	9.05	12.1
Average nitrate, mg/L	3.32	3.62	2.61	2.61	2.36	2.17	3.26	3.74	3.46	1.55	1.45	18.1
Average phosphorus, mg/L	0.64	0.35	0.33	0.43	0.35	0.17	0.59	0.60	0.15	0.97	0.15	0.14
Average ammonia, mg/L	0.69	0.63	0.54	0.52	0.38	0.65	0.74	0.93	0.62	0.30	0.30	0.69
Average pH	7.53	7.84	7.73	8.42	8.50	8.21	7.98	8.13	7.99	7.94	8.60	7.87

Spr = spring; Sum = summer.

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Figure 7.

Branchitis severity by lake, species, season, and water temperature. More cases with severe branchitis were documented in the fall and when water temperatures were lower.

Endoparasitism was detected in 312 of 429 (72.7%) fish. Encysted larval trematodes (metacercaria) were most common and detected in 240 of 429 (55.9%) fish; the vast majority were in bluegills or largemouth bass (228 of 240; 95%). Metacercariae were identified in squash preparations of coelomic viscera including liver, spleen, and kidney. Cytologic evaluation of intact, whole organisms revealed an elongate body with rounded ends and anterior and posterior regions delimited by a lateral constriction. The anterior aspect of the body was gradually tapered; the posterior aspect was more bulbous. At the anterior pole, an oral sucker was evident and communicated with a short esophagus that split into paired and branching intestinal ceca. A ventral sucker was evident at the level of the mid-body. The large muscular and circular Brande organ was just anterior to the lateral body constriction (Fig. 8). Described features were consistent with published descriptions of trematode metacercariae. Morphology was most supportive of diplostomoid trematodes (Neodiplostomidae).^3,23 In histologic sections, metacercaria were evident as 200–300-µm wide metazoans with a smooth eosinophilic cuticle, parenchymatous body, oral/ventral suckers, Brande organ, and paired, branching intestinal ceca with smudged, pale basophilic, mucinous material (Fig. 9). Sequence analysis of DNA amplified from hepatic metacercaria (277 bp) was most consistent with Posthodiplostomum centrarchi (100% identity). Metacercaria were situated in a discrete round cystic structure with a thin wall of eosinophilic, hyalinized, slightly refractile matrix (parasitic cyst). In bluegill, parasitic cysts generally lacked histologic evidence of surrounding inflammation or tissue reaction. In the largemouth bass, these parasitic cysts were often encompassed by a couple to a few layers of flattened or epithelioid macrophages and hypocellular, collagen-rich, dense fibrous tissue to form a quiescent granuloma.

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Figures 8–11.

Parasitism of various organs of fish from Cook County inland lakes. Figure 8. Wet mount, squash cytologic preparation of liver from a bluegill. Organisms consistent with trematode metacercaria have an elongate body with a tapered anterior and bulbous posterior region delimited by a lateral constriction. The anterior aspect of the organism has an oral sucker and short esophagus that splits into paired and branching intestinal ceca. The ventral sucker is evident at the level of the mid-body. The large muscular and circular Brande organ is just anterior to the lateral body constriction. Figure 9. Caudal kidney from a bluegill with a parasitic cyst containing a larval trematode (metacercaria). The metazoan parasite has a narrow tapered anterior aspect and wide bulbous posterior margin, smooth eosinophilic cuticle, parenchymatous body, oral/ventral suckers, Brande organ, and paired, branching intestinal ceca with smudged, pale basophilic, mucinous material. The parasite is surrounded by a thin layer of eosinophilic, hyalinized matrix; inflammation is absent. H&E. Figure 10. Intestinal perforation with intralesional acanthocephalan in a bluegill. The intestinal wall is focally discontinuous, and the mural defect contains a metazoan with a smooth eosinophilic cuticle, thick hypodermis with lemnisci, circular and longitudinal muscle layers, and body cavity containing some ova. The parasite is surrounded by small amounts of hypereosinophilic, smudged necrotic debris and several concentric layers of flattened epithelioid macrophages. Along the serosal aspect, the defect is delimited by several layers of moderately cellular and collagenous and dense fibrous tissue that extend into the bordering mesentery. The adjacent intestinal lumen has an additional cross-section of a similar metazoan. H&E. Figure 11. Biliary myxosporidiosis in a bluegill. The gall bladder mucosa is overlain by a thin-walled cystic structure (plasmodium) containing several round basophilic immature myxospores and fewer ovoid, slightly refractile mature myxospores with internal polar capsules (Chloromyxum sp., presumed). H&E.

Nematodes were the next most frequently detected type of endoparasite (175 of 429; 40.8%), and infection was overrepresented in largemouth bass (97 of 175; 55.4%). Nematodes were detected in the intestinal lumen, gastric wall, and coelomic mesentery. Most nematodes observed in histologic sections lacked mature reproductive tract structures and thus were interpreted to be larvae. Nematodes varied widely in size. Larval organisms within the gastric wall were ~100-µm diameter. Intestinal luminal and mesenteric organisms were 600–1,000-µm diameter. Sequence analysis of DNA (442 bp) amplified from mesenteric nematodes collected at the time of autopsy was most consistent with Contracaecum spp. with 99.5% identity to C. multipapillatum. Intestinal luminal nematodes were not associated with appreciable inflammation or tissue damage. Nematodes within the gastric wall and coelomic mesentery were often surrounded by mild-to-moderate granulomatous inflammation.

Other endoparasites detected in histologic sections with some frequency included cestodes (90 of 429; 21.0%), acanthocephalans (65 of 429; 15.2%), myxosporidia (91 of 429; 21.2%), adult trematodes (37 of 118; 31.4% [largemouth bass only]), and microsporidia (11 of 429; 2.6%). Cestodes included both intestinal luminal adult and visceral encysted larval (plerocercoid) organisms. All species of fish were affected, although largemouth bass and bluegill were overrepresented (61 of 90; 67.8%). Intestinal luminal cestodes were not associated with appreciable inflammation or tissue damage. Cestode plerocercoids were typically surrounded by scant-to-mild granulomatous inflammation. Acanthocephalans were overrepresented in largemouth bass (54 of 65; 83%) followed by bluegill (10 of 65; 15%). A single carp was infected, and acanthocephalans were not detected in bullheads. Acanthocephalans were present in the intestinal lumen and characterized histologically as 200–400-µm diameter metazoans with a smooth eosinophilic cuticle, thick hypodermis with lemnisci, circular and longitudinal muscle layers, and body cavity that often contained ova. The anterior portion of parasites was frequently embedded in the intestinal mucosa or wall with occasional transmural disruption (perforation) of the intestine. At sites of parasite attachment, the mucosa was ulcerated, and parasites were surrounded by granulomatous inflammation (Fig. 10). Sequence analysis of DNA (2 non-overlapping sequences, 607 bp [5′-end] and 633 bp [3′-end], respectively) amplified from intestinal acanthocephalans collected at the time of autopsy was most consistent with Neoechinorhynchus cylindratus (99–100% identity). Myxosporidia were overrepresented (73 of 91; 80%) in bluegill and largemouth bass. In bluegill, coelozoic forms within gall bladder and bile ductules were most common. Histologically, biliary or gall bladder epithelium was overlain by thin-walled plasmodia with several internal round basophilic vegetative bodies and fewer 3–5-μm, ovoid-to-pyriform, slightly refractile mature myxospores with ≥2 polar capsules (Fig. 11). Given location and morphology, Chloromyxum sp. was presumed.^10,18,23 Specific identification was not pursued. No evidence of associated tissue damage or inflammation was detected. In largemouth bass, the renal interstitium contained few-to-several histozoic myxosporidial plasmodia that were up to 300-μm diameter with a thin wall and containing one-to-multiple peripheral layers of clumped vegetative nuclei and myriad central 10–12-µm diameter round myxospores with 2 polar capsules (Fig. 12). Some plasmodia were surrounded by low-to-moderate numbers of lymphocytes and plasma cells. Given morphology, Myxobolus sp. was a differential; however, specific identification was not pursued.^1,10,17,23 Adult trematodes were detected in the pyloric ceca of largemouth bass with no evidence of associated tissue reaction. Gastrointestinal trematodes were only rarely detected in other fish species and were not further characterized. Small microsporidial cysts were detected in a variety of tissues and in all examined fish species without associated tissue reaction.

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Figure 12.

Renal myxosporidiosis in a largemouth bass. The renal interstitium has a thin-walled cystic structure (plasmodium) containing a few peripheral layers of clumped vegetative nuclei (immature myxospores) and myriad central, round mature myxospores with 2 polar capsules. The plasmodium is surrounded by low numbers of lymphocytes and plasma cells. H&E.

Generalized ordered logistic regression was used to determine the statistical significance of variables influencing overall endoparasite burden, fish species, year, and lake chloride content (Table 2). Fish species was found to be a significant predictor of endoparasite load (p < 0.001). The endoparasitism severity in carp and bullhead was consistently low, with none identified at level 2 or 3 (Fig. 13). Endoparasitism severity in largemouth bass and bluegill was consistently high, with most (59.5%) fish having a severity level of 2 or 3. Year, chloride levels, and the interaction of year and chloride levels were also found to be significant predictors of endoparasite burden (p < 0.001, 0.009, and <0.001, respectively). The true impact of chloride levels was uncertain given the discrepancy of the influence of chloride levels between years (Fig. 14).

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Figure 13.

Endoparasitism severity by fish species. Species was found to be a significant predictor of endoparasite load. Endoparasitism severity in carp and bullhead was consistently low, with none identified at level 2 or 3. Endoparasitism severity in largemouth bass and bluegill was consistently high, with most having a severity level of 2 or 3.

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Figure 14.

Probability of endoparasitism severity by year, fish species, and lake chloride levels. Year, chloride levels, and the interaction of year and chloride levels were also found to be significant predictors of endoparasite burden. The influence of chloride levels varied between years; thus, true impact was uncertain.

Aside from branchitis and parasitism, most fish lacked other significant gross and/or histologic lesions. Cases of inflammatory or bacterial infectious disease were identified in rare fish and included chronic granulomatous bacterial endocarditis, and bacterial enteritis in individual carp. A few carp also had mild, focal-to-multifocal gliosis in examined sections of brain. Gliosis was a nonspecific change; no cause was evident, and previous, resolved insult was presumed. Neoplasia was rare and only detected in individual bullheads. One bullhead had a cutaneous chromatophoroma (presumed melanoma), and another bullhead had 4 distinct neoplasms (intrahepatic biliary carcinoma, splenic hemangioma, pancreatic islet cell tumor, intratubular seminoma). Importantly, all fish examined for the study were euthanized and collected in good body condition with no outward signs of disease. All described lesions were well-tolerated and presumed clinically silent at the time of euthanasia.

Discussion

Our results indicate that fish from FPCC inland lakes lack lesions of concern for public health. Examined sections of skeletal muscle had no evidence of damage, disease, or parasitism to preclude recreational sport fishing and/or human consumption of fish flesh. Despite the lack of detectable morphologic or histologic lesions in fish flesh, moderation in human utilization of FPCC fish is still recommended given the likely presence of contaminants (i.e., heavy metals, chemicals) in fish tissues as a consequence of environmental bioaccumulation.^16,35 Currently, all FPCC bodies of water are under state-issued fish consumption advisories because of high levels of tissue toxicants. ¹⁵

Lesions of potential significance to fish health were detected in all species of fish from all FPCC inland lakes that we sampled. Lesions included branchitis and endoparasitism and were present in every sampling year. Although all fish examined were euthanized and collected in good body condition with no outward signs of disease, possible subclinical impacts of these conditions on fitness and long-term population health were considered. Subclinical disease may diminish fish ability to cope with environmental stressors that could become more frequent as ecosystems evolve under the influence of climate change. The understanding of baseline health and disease in the FPCC fish populations provided by our study will provide a foundation for any future investigations. Established data can be a reference for studying outbreaks of clinical disease or die-offs in fish. Results of our baseline health survey may also be useful for informing fisheries management considerations for optimal sustainability of FPCC resources.

Branchitis detected in our study was most often diffuse in distribution and not found to be associated with parasites. Based on findings, environmental parameters were considered most likely contributory to the pathogenesis of gill damage. Influencers of branchitis severity identified by our study included fish species, the interaction of lake and alkalinity, and water temperature and season. Severe branchitis was most common in bullheads. Bullheads are benthic species, and their habitat location in the water column was one hypothesis to account for branchitis severity. Common carp share the benthic niche and generally lack similarly severe gill disease. Thus, benthic habitat alone was unlikely responsible for noted changes. Other unknown species-related factors may account for increased susceptibility to gill damage in bullheads compared with carp. No significant differences were detected between lake types (seepage vs. impoundment); however, severity of branchitis was lower in Axehead Lake compared with other locations. Axehead Lake also had the lowest alkalinity among examined lakes. The influence of alkalinity on branchitis severity was as expected. Optimal fish and gill health in freshwater fish is achieved in a near-neutral pH range of 6.8–7.8. Elevated alkalinity can lead to increases in ammonia (NH₃) and direct gill epithelial toxic damage. Temperature also influences components of total ammonia nitrogen (NH₃ and ammonium [NH₄]); higher temperatures result in greater toxic NH₃ concentrations. Thus, increased alkalinity and elevated temperature are synergistic for elevating environmental NH₃ levels and can be associated with consequent gill damage.^10,21,32

Documented gill parasites in the FPCC fish represented organisms previously described in these host species.^10,20,22,30 Although branchial parasitism may have resulted in some localized gill damage, our findings did not support parasitism as a significant contributor to noted branchitis. Monogeneans were the most frequently encountered gill parasites and were detected at a similar prevalence in fish with and without branchitis. In our experience, low numbers of branchial monogeneans are commonly detected on gills of freshwater fish from Cook County lakes in the absence of appreciable damage or inflammation. Possibly, at least when monogenean numbers are low, a commensal relationship exists between these organisms and the host fish. The prevalence of branchial protozoal parasites was particularly low in our study population. Given that many of such organisms occur along the gill epithelial surfaces without strong attachment to the host tissues, loss in processing was possible and could have resulted in an underestimation of prevalence.

Increased prevalence and severity of endoparasitism was detected in mid-level (bluegill) and apex predator (largemouth bass) species compared with benthic bullheads and carp. This difference was attributed largely to host diet. Bluegill and largemouth bass are carnivorous species with greater diet diversity. These species would be more likely to consume various parasite intermediate hosts to facilitate infection. Carp are herbivorous, thus less likely to ingest intermediate host species. Bullheads are omnivorous and may consume a variety of aquatic invertebrates as well as algae and plants. Bullheads may also opportunistically hunt smaller fish, so could gain exposure to a variety of parasite intermediate hosts as prey species.^4,28 Overall low levels of endoparasitism in the FPCC bullheads, however, suggest that consumption of parasite intermediate host species was a minimal or lesser component of the diet. Documented endoparasites in the FPCC fish represented organisms previously described in these host species.^10,20,23,30 Parasitism was most often associated with absent to only mild tissue damage and inflammation. Inflammation consisted of granulomas that encapsulated encysted larval metazoans. Aside from mucosal attachment sites of enteric acanthocephalans, alimentary tract luminal parasites were not accompanied by an inflammatory tissue reaction. Tissue reaction to parasites was more common and pronounced in largemouth bass compared to other examined species. The reason for this difference was unknown.

Aside from fish species, year and lake chloride content were found to influence endoparasite burden. No specific cause was identified to account for the effect of collection year. Possibly, various environmental parameters contributed to the recognized effect, and it was beyond the scope of our study to identify and further investigate such variables. Chlorine is well known for its antimicrobial and antiparasitic properties.^2,40 An association between decreasing endoparasite burden and increasing water chloride values documented in our study suggested lake chloride level may have had an antiparasitic effect on resident fish; however, long-term salinization of freshwater lakes can have significant detrimental ecologic consequences and should be avoided. Elevated chloride concentrations can have adverse effects on water quality and aquatic ecosystems with immediate and long-term alterations to community structure, diversity, and productivity.^{6 –9,14,36} Although chloride concentrations in freshwaters can vary cyclically with climatic processes (e.g., drought), elevated lake concentrations often result from agricultural, industrial, and transportation practices.^19,38 Salt application for de-icing roadways represents a major source of chloride to groundwater, streams and rivers, and lakes. Following application, road salt quickly dissolves and accesses rivers and lakes through leaching and runoff.^8,24,25,33 Avoiding excess salination of freshwater bodies is essential to maintenance of drinking water, fisheries, recreation, irrigation, and aquatic habitat. It was also important to note that any possible positive impact of chloride level on fish endoparasite burden remains uncertain given the discrepancy of the influence of chloride levels between years indicated by our data.

Our study highlights the importance of baseline wildlife health monitoring for the benefit of ecosystem and public health. Our results can serve as useful reference data for future studies and inform management decisions impacting valuable natural resources. The FPCC is a treasure of the region, and a greater understanding of the complex interactions impacting the various included ecosystems will be essential to enduring sustainability.