Rocky Shore Monitoring in Taranaki
Comprehensive environmental monitoring of Taranaki's rocky shore ecosystems from 1994-2024, tracking biodiversity, species richness, and ecological health across six representative reef sites.
Executive Summary
30 Years of Coastal Monitoring
The Taranaki Regional Council has monitored rocky shore communities since 1994 as part of its State of the Environment programme. Six representative reef sites are surveyed twice yearly using fixed transect and random quadrat methods, tracking changes in species richness, diversity, and community composition.
Monitoring Period
1994-2024: Three decades of comprehensive ecological data collection
Survey Sites
Six reef locations spanning the Taranaki coastline from Motunui to Hāwera
Survey Frequency
Biannual surveys conducted in spring and summer seasons
Key Findings: Species Diversity Trends
Mānihi Road Reef consistently demonstrated the highest species richness and diversity, with a mean of 20.16 species per quadrat and Shannon-Wiener index of 1.05. This reflects optimal conditions including low sand supply and stable pool environments.
Waihi Reef showed the lowest diversity (11.46 species per quadrat, index 0.84), likely due to high wave energy and unstable habitat conditions.
20.16
Mānihi Reef
Highest mean species richness
11.46
Waihi Reef
Lowest mean species richness
Monitoring Locations
Six Representative Reef Sites
The monitoring programme encompasses six strategically selected sites representing different coastal conditions across Taranaki. Each site experiences unique environmental pressures including varying wave exposure, sand deposition, and habitat complexity.
01
Tūrangi Reef (Motunui)
Northernmost site, 7km east of Waitara River mouth
02
Orapa Reef (Waitara)
1.5km west of Waitara River, extensive reef platform
03
Mangati Reef (Bell Block)
North of New Plymouth, 3km from Waiwhakairoa River
04
Greenwood Road Reef (Ōkato)
West of New Plymouth, 8km from Hangatāhua River
05
Mānihi Road Reef (Rahotu)
Western-most site, 10km south of Cape Egmont
06
Waihi Reef (Hāwera)
Southernmost site, high-energy wave environment
The Taranaki Rocky Shore Environment
Rocky reefs dominate Taranaki's intertidal zone, formed primarily from volcanic lahar materials containing andesite cobbles and boulders. Selective erosion creates extensive platform reefs extending up to five kilometers offshore near Waitara.
The region experiences high-energy wave and wind conditions from the Tasman Sea. Prevailing southwesterly winds and dominant westerly waves create significant sand movement along the coast, resulting in turbid nearshore conditions.
Reef Formation
Volcanic lahar materials with andesite cobbles and boulders
Wave Climate
High-energy conditions from Tasman Sea
Cultural Significance
The reefs of Taranaki provide valuable kaimoana (seafood) for Māori communities, holding significant cultural value beyond food provision. This resource maintains tribal mana and standing, representing deep connections between iwi and the coastal environment.
Iwi Associations
Te Atiawa, Ngāti Tama, Ngāti Mutunga, Taranaki, Ngāruahine, and Ngāti Ruanui maintain traditional connections to these reef systems
Kaimoana Resources
Pāua, kina, and kuku (mussels) represent important traditional food sources
Customary Protection
Rāhui established December 2022-2026 protecting shellfish, seaweed, and other species along western Taranaki coast
Methodology
Survey Methods and Data Collection
Each site is monitored using a standardized fixed transect and random quadrat survey design. A 50-meter transect is laid parallel to shore at approximately 0.6m above chart datum. Five blocks are established along the transect, with five random 0.5m² quadrats per block, totaling 25 quadrats per site.
Percentage cover of algae and encrusting animals is estimated using grids. Mobile animals larger than 3mm are counted and identified to the lowest taxonomic level possible, including under-boulder biota where rocks can be easily overturned.
1
Transect Setup
50m parallel to shore, 0.6m above chart datum
2
Quadrat Sampling
25 random 0.5m² quadrats per site
3
Species Recording
Cover estimates and individual counts
Ecological Indices: Measuring Biodiversity
Two key ecological indices are calculated from survey data to assess community health and resilience. Species richness measures the mean number of species per quadrat, while the Shannon-Wiener diversity index accounts for both species number and relative abundance.
Species Richness
Mean number of species recorded per quadrat, indicating overall biodiversity
Shannon-Wiener Index
Diversity measure incorporating species number and evenness of distribution
Community Resilience
Higher diversity indicates greater resilience to environmental stressors
Species Composition: Key Findings 2019-2024
Encrusting algae Corallina sp. (paint) and Ralfsia sp. were the most widespread primary producers. The barnacle Chamaesipho columna and tube worms Neosabellaria kaiparaensis and Spirobranchus cariniferus dominated filter-feeding communities.
Among 51 mollusc species identified, top shells Lunella smaragda and Diloma aethiops were the most widespread mobile grazers. Twenty-four crustacean species were recorded, with porcelain crab Petrolisthes elongatus being most common.
51
Mollusc Species
Most diverse animal phylum
24
Crustacean Species
Second highest diversity
Sand Cover: A Critical Environmental Factor
Sand deposition profoundly affects intertidal communities in Taranaki. Orapa Reef showed the highest average sand cover at 23.5%, followed by Tūrangi (13%), Mangati (10.8%), and Greenwood Road (3.7%). Mānihi Reef maintained the lowest coverage at less than 1%.
1
1998 Erosion Event
Hangatāhua River headwater scarp collapse initiated major sand influx
2
2008 Second Event
Additional significant erosion increased coastal sand supply
3
Ongoing Transport
Black sand transported northeast along coast, affecting reef communities
Long-term trend analyses found highly likely increasing sand cover at Tūrangi (5.83% annual change), Orapa (3.63%), and Greenwood (11.9%), with very likely increases at Mangati (1.76%).
Sand Impact on Species Diversity
Heavy sand inundation results in dramatic short-term declines in species richness and diversity. Encrusting and non-motile organisms are particularly susceptible to smothering and burial, often resulting in death.
Motile organisms demonstrate better coping mechanisms. Gastropods aggregate on protruding rocks above sand levels, while pāua escape to deeper waters. Reefs typically recover within one to two years if sand accumulation doesn't persist.
23.5%
Average sand cover at Orapa Reef (highest)
1%
Average sand cover at Mānihi Reef (lowest)
Seagrass and Sandy Tube Worms
Certain species thrive with increased sediment availability. Seagrass Zostera capricorni was recorded only at Orapa Reef during 2019-2024, requiring optimal sediment for root mat formation. The sandy tube worm Neosabellaria kaiparaensis showed significantly higher coverage at Orapa than any other site.
Seagrass Habitat
Dense patches at Orapa Reef indicate suitable sediment conditions
Tube Worm Colonies
Large N. kaiparaensis colonies utilize sediment for tube construction
Long-Term Trends
Species Richness Trends 1994-2024
Long-term trend analyses revealed significant patterns across sites. When adjusting for sand cover, mean species richness was highly likely increasing at Orapa (0.81% annual), Mangati (0.63%), and Mānihi (0.96%). Tūrangi and Greenwood showed likely increases, while Waihi demonstrated a likely decrease.
Mānihi Reef
Highly likely increasing: one species every 5 years
Orapa Reef
Highly likely increasing: one species every 8 years
Mangati Reef
Highly likely increasing: one species every 11 years
Waihi Reef
Likely decreasing: one species every 77 years
Shannon-Wiener Diversity Trends
Diversity index trends showed highly likely increases at Orapa (0.38% annual), Mangati (0.35%), and Mānihi (0.27%). Conversely, highly likely decreases occurred at Greenwood (0.19%) and Waihi (0.23%), with a likely decrease at Tūrangi (0.17%).
0.38%
Orapa Increase
Highest diversity growth rate
0.35%
Mangati Increase
Strong positive trend
0.27%
Mānihi Increase
Consistent improvement
Despite statistical significance, rates of change were very low at three sites. The most meaningful trends were increases in species richness and diversity at Mānihi, Orapa, and Mangati Reefs, suggesting improving environmental conditions at these locations.
Wave Exposure Effects
Wave exposure dramatically influences species composition on Taranaki's rocky shores. Wave energy is generally higher in western Taranaki, decreasing northeast toward New Plymouth and southeast toward Hāwera. Reef morphology, including slope angle and seaward extent, also affects exposure levels.
Waihi Reef: High Exposure
Steep gradient and direct wave approach create most exposed conditions. Large boulders shift position between surveys. Lower species richness reflects harsh environment.
Orapa Reef: Lower Exposure
Extensive seaward reef platform dissipates wave energy. Sheltered conditions support seagrass growth, typically found in protected environments.
Habitat Complexity and Geomorphology
Habitat complexity significantly influences diversity differences between sites. At Tūrangi, Orapa, and Mangati, substrates can become cemented with sand and rubble, reducing under-boulder habitat availability.
Mānihi Reef's geomorphology comprises minimal cemented reef and diverse substrate sizes, providing heterogeneous habitat including stable pools, under-boulder spaces, and rock crevices.
Substrate Diversity
Range of rock and cobble sizes creates multiple ecological niches
Pool Habitats
Stable pools provide refuge and consistent environmental conditions
Under-Boulder Spaces
Critical habitat for chitons, crabs, and other cryptic species
Tube Worm Impact on Diversity
Large colonies of sandy tube worm Neosabellaria kaiparaensis can significantly reduce habitat diversity at Orapa Reef. When tube worm mounds build up, they decrease availability of under-boulder, above-boulder, and pool habitats.
1
Low Tube Worm Cover
High diversity: multiple habitat types available for colonization
2
Increasing Coverage
Gradual reduction in habitat complexity as mounds expand
3
High Coverage
Pronounced diversity decline: tube worm mounds dominate substrate
Recent years showed pronounced, contrasting changes in species diversity corresponding to fluctuations in tube worm cover, demonstrating their significant influence on community structure.
Anthropogenic Factors
Human Impacts and Wastewater Discharges
Natural physical factors largely drive diversity and composition at SoE sites, making subtle anthropogenic changes difficult to detect. However, noticeable impacts can be evident. Prior to 1997, dairy factory wastewater discharged near Hāwera significantly affected local intertidal communities.
Pre-1997
Nearshore outfall caused detectable adverse effects on intertidal communities
1997 Improvement
Long outfall installed, discharging 2km offshore
Post-1997
Stepwise improvement in species richness and diversity at affected sites
Orapa and Mangati sites are located near wastewater outfalls. Norovirus analysis indicates previous shoreline contact with wastewater, resulting in microbial contamination of shellfish. However, adverse impacts on species richness and diversity have not been detected through compliance monitoring.
Sediment Loads and Land Erosion
Land development since European settlement has increased erosion in some catchments, resulting in two to six times higher sediment loads in Taranaki's larger rivers compared to natural conditions. This sediment affects coastal water quality and nearshore reef communities.
Soil Conservation Gains
Riparian fencing, planting, and scrub reversion achieved 29% reduction in sediment loads by 2018
Future Challenges
Climate change may increase storm intensity and mass erosion event frequency
Regional Variation
Steep hill country generates higher sediment loads than volcanic ring plain catchments
Coastal Turbidity Gradient
A turbidity gradient exists in North Taranaki coastal waters, increasing from Cape Egmont toward Waitara/Motunui. This pattern is largely attributed to high suspended sediment loads delivered by the Waitara River.
SedNetNZ modeling demonstrates how sediment loads vary by catchment characteristics. When standardized by area, steep erosion-prone hill country catchments generate substantially higher sediment loads than volcanic ring plain catchments.
Planned soil conservation works offer potential for further sediment load reductions, though climate change projections suggest increased challenges ahead.
Recreational Impacts and Rock Turning
Humans can have localized impacts when exploring rock pools and collecting kaimoana. Intertidal communities are adversely affected when rocks and boulders are overturned but not returned to their original position.
Top Surface
Algae require light for photosynthesis, growing on upper rock surfaces
Bottom Surface
Invertebrates shelter underneath rocks to avoid predation and desiccation
Impact
Failure to return rocks causes mortality of both algae and invertebrates
While not associated with SoE monitoring sites, this issue has been observed at various Taranaki locations, typically lower in the intertidal zone where pāua and kina are gathered.
Customary Rāhui Protection
Following concerns from mana whenua and public consultation, a customary rāhui under section 186A of the Fisheries Act 1996 was established in December 2022, extended until December 2026. The rāhui spans from Herekawae Stream (New Plymouth) to Taungatarata Stream (Ōpunake).
Protected Species
Temporary closure to shellfish take (excluding rock lobster), seaweed (except beach cast), sea anemones, stingrays, and two conger eel species
Coverage Area
Greenwood Road and Mānihi Road SoE monitoring sites located within rāhui boundaries
Monitoring Value
Long-term data sets could reveal potential effects of rāhui on species richness and diversity
Climate Change
Climate Change Impacts on Rocky Shores
Climate change impacts on intertidal rocky reef habitats are likely to increase. Some impacts may exacerbate existing processes, while others will have selective effects on community composition.
Increased Erosion
More frequent intense rainfall accelerating erosion in river headwaters, introducing more sand to coast
Temperature Stress
Species resilient to heat and desiccation better suited to cope with rising ocean and atmospheric temperatures
Ocean Acidification
Increased dissolved CO₂ potentially benefiting seaweeds while hindering shell-forming molluscs
Sea Level Rise
Permanent reduction or elimination of intertidal habitat where hard structures prevent landward migration
Site Comparison: Diversity Patterns
Statistical analyses revealed significant differences in species richness and diversity across reef locations. Mānihi consistently showed higher diversity than all other sites, while Waihi demonstrated lower diversity compared to remaining locations.
1.05
Mānihi Reef
Highest Shannon-Wiener index
0.90
Mid-Range Sites
Greenwood, Mangati, Orapa, Tūrangi
0.84
Waihi Reef
Lowest Shannon-Wiener index
Paired Wilcoxon tests identified highly significant differences between most site pairs. No significant differences were found between Orapa and Mangati, or between Tūrangi and Greenwood Road, suggesting similar community structures at these paired locations.
Recent Trends: 2019-2024 Period
The most recent five-year monitoring period showed increases in both median species richness and diversity at all sites compared to previous periods. This represents a notable shift from historical patterns.
1994-1999
Baseline period establishing initial diversity levels
2004-2009
Mid-period showing variable trends across sites
2014-2019
Previous reporting period with mixed results
2019-2024
Current period showing improvements at all sites
Mānihi Reef showed the highest mean species richness (24.71 per quadrat) and diversity index (1.15) during 2019-2024. Orapa demonstrated notable increases in both richness (18.76) and diversity (1.03), while Waihi remained least diverse despite marginal improvements.
Sand-Adjusted vs. Unadjusted Trends
Comparing sand-adjusted and unadjusted trend analyses revealed that observed sand cover did not strongly influence current long-term trends at most sites. Similar results were generally observed across both datasets, with one notable exception.
At Greenwood Road, the mean number of species showed a likely increasing trend based on sand-adjusted data, but a likely decreasing trend based on unadjusted data. This suggests periodic sand inundation events are influencing long-term species richness trends at this site.
Most Sites
Sand adjustment did not change trend direction or significance
Greenwood Road
Only site where sand adjustment reversed trend direction
Recommendations
Future Monitoring and Research
Based on 30 years of monitoring data and observed trends, three key recommendations are proposed to enhance understanding of Taranaki's rocky shore ecosystems and improve management effectiveness.
01
Habitat Mapping Extension
Extend monitoring to include habitat mapping techniques gathering broad-scale information on reef topography, sand coverage, seagrass, and other key habitat-forming species
02
Trend Driver Investigation
Undertake further work investigating drivers behind observed trends in species richness and diversity, particularly at sites showing declining trends
03
Seagrass Monitoring
Survey seagrass at Orapa Reef regularly using methods recommended by Shanahan et al. (2023) to detect early changes in extent and condition
Key Species Recorded 2019-2024
During the most recent monitoring period, diverse species assemblages were recorded across all sites. Molluscs dominated with 51 species, followed by 24 crustacean species, reflecting the rich biodiversity of Taranaki's rocky shores.
Molluscs
Top shells Lunella smaragda (1,157 records) and Diloma aethiops (1,273 records) most abundant grazers
Crustaceans
Barnacle Chamaesipho columna (1,099 records) and porcelain crab Petrolisthes elongatus (808 records) widespread
Algae
Coralline paint (1,474 records) and turf (1,399 records) dominated primary producers
Tube Worms
Sandy tube worm N. kaiparaensis (1,248 records) and calcareous S. cariniferus (1,140 records) abundant filter feeders
Overall Summary: 30 Years of Insights
Rocky shore communities at six Taranaki locations have remained relatively stable over 30 years of monitoring, with short-term influences from occasional sand inundation events. Statistical evidence shows both increasing and decreasing long-term trends in species richness and diversity at all sites.
Most Meaningful Trends
Increases in species richness and diversity at Mānihi, Orapa, and Mangati Reefs represent the most ecologically significant changes
Natural Drivers Dominate
Sand cover, wave exposure, and habitat complexity remain primary factors influencing community structure
No Major Anthropogenic Impacts
No noticeable human-caused impacts detected at SoE sites, though subtle changes may be masked by natural variability
Conclusion
Protecting Taranaki's Rocky Shore Future
Three decades of comprehensive monitoring have established a robust baseline for understanding Taranaki's rocky shore ecosystems. This long-term dataset enables effective assessment of natural processes and provides the foundation for mitigating human impacts on the coastal environment.
Ongoing monitoring and management remain critical as climate change, land use pressures, and other factors continue to influence these important habitats. The data collected through this programme guides decision-making and ensures the protection of culturally and ecologically significant reef communities.
With many factors potentially affecting these habitats, continued vigilance and adaptive management will be essential for their long-term conservation and the maintenance of ecosystem services they provide to both people and wildlife.
Robust Monitoring
30-year dataset provides strong foundation for future management decisions
Adaptive Management
Ongoing assessment enables responsive protection strategies
Cultural & Ecological Value
Protecting resources important to both iwi and regional biodiversity