Mapping subtidal estuarine habitats with a remotely operated underwater vehicle (ROV):
- Wasserman, J, Claassens, Louw, Adams, Janine B
- Authors: Wasserman, J , Claassens, Louw , Adams, Janine B
- Date: 2020
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/150163 , vital:38945 , DOI: 10.2989/1814232X.2020.1731598
- Description: Subtidal habitats have not yet been accounted for in habitat maps of South African estuaries. In this study, a novel method for mapping subtidal estuarine habitats, using a remotely operated underwater vehicle (ROV) piloted from a boat, was developed and tested in the Knysna Estuary. Video footage was recorded along 48 transects across the width of the estuary, and then reviewed to identify, classify and map habitats. Using the method developed in this study, 21 hours of footage was recorded over 15 days of sampling, and about 30 hours of post-processing was carried out to map an area exceeding 850 ha. This study has produced the first baseline dataset of subtidal habitats for a South African estuary. Additionally, the study revealed the previously unknown distribution of the invasive red seaweed Asparagopsis taxiformis, and the underestimation in previous studies of the estuary of area cover of eelgrass Zostera capensis by 130 ha.
- Full Text:
- Date Issued: 2020
- Authors: Wasserman, J , Claassens, Louw , Adams, Janine B
- Date: 2020
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/150163 , vital:38945 , DOI: 10.2989/1814232X.2020.1731598
- Description: Subtidal habitats have not yet been accounted for in habitat maps of South African estuaries. In this study, a novel method for mapping subtidal estuarine habitats, using a remotely operated underwater vehicle (ROV) piloted from a boat, was developed and tested in the Knysna Estuary. Video footage was recorded along 48 transects across the width of the estuary, and then reviewed to identify, classify and map habitats. Using the method developed in this study, 21 hours of footage was recorded over 15 days of sampling, and about 30 hours of post-processing was carried out to map an area exceeding 850 ha. This study has produced the first baseline dataset of subtidal habitats for a South African estuary. Additionally, the study revealed the previously unknown distribution of the invasive red seaweed Asparagopsis taxiformis, and the underestimation in previous studies of the estuary of area cover of eelgrass Zostera capensis by 130 ha.
- Full Text:
- Date Issued: 2020
UN Decade on Ecosystem Restoration 2021–2030: what chance for success in restoring coastal ecosystems?
- Waltham, Nathan J, Elliott, Michael, Lee, Shing Yip, Lovelock, Catherine, Duarte, Carlos M, Buelow, Christina, Simenstad, Charles, Nagelkerken, Ivan, Claassens, Louw, Wen, Colin K-C, Barletta, Mario, Connolly, Rod M, Gillies, Chris, Mitsch, William J, Ogburn, Matthew B, Purandare, Jemma, Possingham, Hugh, Sheaves, Marcus
- Authors: Waltham, Nathan J , Elliott, Michael , Lee, Shing Yip , Lovelock, Catherine , Duarte, Carlos M , Buelow, Christina , Simenstad, Charles , Nagelkerken, Ivan , Claassens, Louw , Wen, Colin K-C , Barletta, Mario , Connolly, Rod M , Gillies, Chris , Mitsch, William J , Ogburn, Matthew B , Purandare, Jemma , Possingham, Hugh , Sheaves, Marcus
- Date: 2020
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/149836 , vital:38887 , https://doi.org/10.3389/fmars.2020.00071
- Description: On 1 March 2019, the United Nations (UN) General Assembly (New York) declared 2021–2030 the “UN Decade on Ecosystem Restoration.” This call to action has the purpose of recognizing the need to massively accelerate global restoration of degraded ecosystems, to fight the climate heating crisis, enhance food security, provide clean water and protect biodiversity on the planet. The scale of restoration will be key; for example, the Bonn Challenge has the goal to restore 350 million km2 (almost the size of India) of degraded terrestrial ecosystems by 2030. However, international support for restoration of “blue” coastal ecosystems, which provide an impressive array of benefits to people, has lagged. Only the Global Mangrove Alliance (https://mangrovealliance.org/) comes close to the Bonn Challenge, with the aim of increasing the global area of mangroves by 20% by 2030. However, mangrove scientists have reservations about this target, voicing concerns that it is unrealistic and may prompt inappropriate practices in attempting to reach this target (Lee et al., 2019). The decade of ecosystem restoration declaration also coincides with the UN Decade of Ocean Science for Sustainable Development, which aims to reverse deterioration in ocean health. If executed in a holistic and coordinated manner, signatory nations could stand to deliver on both these UN calls to action.
- Full Text:
- Date Issued: 2020
- Authors: Waltham, Nathan J , Elliott, Michael , Lee, Shing Yip , Lovelock, Catherine , Duarte, Carlos M , Buelow, Christina , Simenstad, Charles , Nagelkerken, Ivan , Claassens, Louw , Wen, Colin K-C , Barletta, Mario , Connolly, Rod M , Gillies, Chris , Mitsch, William J , Ogburn, Matthew B , Purandare, Jemma , Possingham, Hugh , Sheaves, Marcus
- Date: 2020
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/149836 , vital:38887 , https://doi.org/10.3389/fmars.2020.00071
- Description: On 1 March 2019, the United Nations (UN) General Assembly (New York) declared 2021–2030 the “UN Decade on Ecosystem Restoration.” This call to action has the purpose of recognizing the need to massively accelerate global restoration of degraded ecosystems, to fight the climate heating crisis, enhance food security, provide clean water and protect biodiversity on the planet. The scale of restoration will be key; for example, the Bonn Challenge has the goal to restore 350 million km2 (almost the size of India) of degraded terrestrial ecosystems by 2030. However, international support for restoration of “blue” coastal ecosystems, which provide an impressive array of benefits to people, has lagged. Only the Global Mangrove Alliance (https://mangrovealliance.org/) comes close to the Bonn Challenge, with the aim of increasing the global area of mangroves by 20% by 2030. However, mangrove scientists have reservations about this target, voicing concerns that it is unrealistic and may prompt inappropriate practices in attempting to reach this target (Lee et al., 2019). The decade of ecosystem restoration declaration also coincides with the UN Decade of Ocean Science for Sustainable Development, which aims to reverse deterioration in ocean health. If executed in a holistic and coordinated manner, signatory nations could stand to deliver on both these UN calls to action.
- Full Text:
- Date Issued: 2020
Bait collecting by subsistence and recreational fishers in Knysna Estuary may impact management and conservation
- Simon, C, du Toit, A N, Smith, M K S, Claassens, Louw, Smith, F, Smith, P
- Authors: Simon, C , du Toit, A N , Smith, M K S , Claassens, Louw , Smith, F , Smith, P
- Date: 2019
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/447056 , vital:74581 , https://hdl.handle.net/10520/EJC-1d75666653
- Description: To facilitate development of tailored management strategies for bait species within Knysna Estuary (South Africa), demand for bait, harvesting activity and perceptions around conservation among recreational and subsistence bait fishers were investigated. In 2015 and 2016, bait collectors were interviewed (n = 84) and observed (n = 167) during low tides at six sites during peak and off-peak holiday periods. Significant associations among subsistence and recreational fishers and their favoured bait species, collecting spots and method, frequency of collection, views on regulations and desired daily limit for mudprawns suggest differences that may warrant different management strategies. Furthermore, observed methods and duration of bait collecting differed according to site, suggesting spatial variation in baiting pressures. Subsistence fishers potentially collect more mudprawns more frequently than do recreational fishers and consequently have a greater impact on mudprawn populations. By contrast, recreational fishers collect more polychaete worms, but because they are mainly active during holidays, their impact on these species may be localised and not yet critical. Most subsistence fishers would like increased daily bag limits, to sell bait and would welcome a rotational zonation scheme to replace the current permanent exclusion zone. The merits and disadvantages of these management options and suggestions are discussed.
- Full Text:
- Date Issued: 2019
- Authors: Simon, C , du Toit, A N , Smith, M K S , Claassens, Louw , Smith, F , Smith, P
- Date: 2019
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/447056 , vital:74581 , https://hdl.handle.net/10520/EJC-1d75666653
- Description: To facilitate development of tailored management strategies for bait species within Knysna Estuary (South Africa), demand for bait, harvesting activity and perceptions around conservation among recreational and subsistence bait fishers were investigated. In 2015 and 2016, bait collectors were interviewed (n = 84) and observed (n = 167) during low tides at six sites during peak and off-peak holiday periods. Significant associations among subsistence and recreational fishers and their favoured bait species, collecting spots and method, frequency of collection, views on regulations and desired daily limit for mudprawns suggest differences that may warrant different management strategies. Furthermore, observed methods and duration of bait collecting differed according to site, suggesting spatial variation in baiting pressures. Subsistence fishers potentially collect more mudprawns more frequently than do recreational fishers and consequently have a greater impact on mudprawn populations. By contrast, recreational fishers collect more polychaete worms, but because they are mainly active during holidays, their impact on these species may be localised and not yet critical. Most subsistence fishers would like increased daily bag limits, to sell bait and would welcome a rotational zonation scheme to replace the current permanent exclusion zone. The merits and disadvantages of these management options and suggestions are discussed.
- Full Text:
- Date Issued: 2019
An endangered seahorse selectively chooses an artificial structure
- Claassens, Louw, Booth, Anthony J, Hodgson, Alan N
- Authors: Claassens, Louw , Booth, Anthony J , Hodgson, Alan N
- Date: 2018
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/123718 , vital:35486 , https://doi.10.1007/s10641-018-0732-4
- Description: The development of a residential marina estate within the Knysna estuary, South Africa, introduced Reno mattresses (horizontal wire cages filled with rocks) as a novel habitat for the endangered Knysna seahorse Hippocampus capensis. Consistently high seahorse densities on these artificial structures, despite the availability of seagrass habitat, begged the question of whether this habitat was chosen by the seahorse in preference to natural vegetation. An in situ habitat choice experiment was conducted which focused on the choice made by adult H. capensis between natural vegetation (Zostera capensis) and artificial (Reno mattress) habitat within a choice chamber. Seahorses were significantly more likely to move away from Z. capensis onto a Reno mattress structure or remain on this structure. This study concludes that higher H. capensis densities on Reno mattresses within Thesen Islands Marina are owing to some positive feature of this habitat and the underlying processes responsible for the choice made by this species (additional food, holdfasts, protection) can now be investigated.
- Full Text:
- Date Issued: 2018
- Authors: Claassens, Louw , Booth, Anthony J , Hodgson, Alan N
- Date: 2018
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/123718 , vital:35486 , https://doi.10.1007/s10641-018-0732-4
- Description: The development of a residential marina estate within the Knysna estuary, South Africa, introduced Reno mattresses (horizontal wire cages filled with rocks) as a novel habitat for the endangered Knysna seahorse Hippocampus capensis. Consistently high seahorse densities on these artificial structures, despite the availability of seagrass habitat, begged the question of whether this habitat was chosen by the seahorse in preference to natural vegetation. An in situ habitat choice experiment was conducted which focused on the choice made by adult H. capensis between natural vegetation (Zostera capensis) and artificial (Reno mattress) habitat within a choice chamber. Seahorses were significantly more likely to move away from Z. capensis onto a Reno mattress structure or remain on this structure. This study concludes that higher H. capensis densities on Reno mattresses within Thesen Islands Marina are owing to some positive feature of this habitat and the underlying processes responsible for the choice made by this species (additional food, holdfasts, protection) can now be investigated.
- Full Text:
- Date Issued: 2018
Aspects of the population ecology, habitat use and behaviour of the endangered Knysna seahorse (Hippocampus capensis Boulenger, 1900) in a residential marina estate, Knysna, South Africa: implications for conservation
- Authors: Claassens, Louw
- Date: 2018
- Subjects: Endangered species -- South Africa -- Knysna , Sea horses -- Behavior -- South Africa -- Knysna , Sea horses -- Habitat -- South Africa -- Knysna , Sea horses -- Ecology -- South Africa -- Knysna
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/54789 , vital:26616
- Description: The Knysna seahorse Hippocampus capensis is South Africa’s only endemic seahorse species, and is found in only three adjacent estuaries along the southern coast. The conservation of this endangered species is important on a national and international level. This study presents the first research on this species within the Knysna estuary since 2001 and specifically focuses on aspects of its ecology within a residential marina estate (Thesen Islands Marina). The physico-chemical and habitat features of the marina were described and the population ecology, habitat use, and behaviour of the Knysna seahorse were investigated. Physico-chemical conditions within the western section of the marina, characterised by high water current velocities, were similar to that of the adjacent estuary. The eastern section of the marina was characterised by lower water current velocities and higher turbidity. Four major habitat types were identified within the marina canals: (I) artificial Reno mattress (wire baskets filled with rocks); (II) Codium tenue beds; (III) mixed vegetation on sediment; and (IV) barren canal floor. Seahorse densities within the marina were significantly higher compared to densities found historically within the estuary. Highest seahorse densities were specifically found within the artificial Reno mattress structures and within the western section of the marina. Seahorse density varied spatially and temporally and the type of habitat was an important predictor for seahorse occurrence. An experimental investigation found that H. capensis chooses artificial Reno mattress habitat over Zostera capensis when given a choice. GoPro cameras were used successfully to investigate daytime seahorse behaviour within the Reno mattress habitat. Seahorses were more active during the morning, spent most of their time (> 80 %) feeding, and morning courting behaviour for this species were confirmed. However, during the summer holiday period (mid-December to mid-January) few seahorses were observed on camera, which suggests that the increase in motor boat activity and the related increase in noise had a negative effect on H. capensis feeding and courting behaviour. The marina development, and in particular the Reno mattresses, created a new habitat for this endangered species within the Knysna estuary. In addition to the protection and restoration of natural habitats in which H. capensis is found, the conservation potential of artificial structures such as Reno mattresses should be realised.
- Full Text:
- Date Issued: 2018
- Authors: Claassens, Louw
- Date: 2018
- Subjects: Endangered species -- South Africa -- Knysna , Sea horses -- Behavior -- South Africa -- Knysna , Sea horses -- Habitat -- South Africa -- Knysna , Sea horses -- Ecology -- South Africa -- Knysna
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/54789 , vital:26616
- Description: The Knysna seahorse Hippocampus capensis is South Africa’s only endemic seahorse species, and is found in only three adjacent estuaries along the southern coast. The conservation of this endangered species is important on a national and international level. This study presents the first research on this species within the Knysna estuary since 2001 and specifically focuses on aspects of its ecology within a residential marina estate (Thesen Islands Marina). The physico-chemical and habitat features of the marina were described and the population ecology, habitat use, and behaviour of the Knysna seahorse were investigated. Physico-chemical conditions within the western section of the marina, characterised by high water current velocities, were similar to that of the adjacent estuary. The eastern section of the marina was characterised by lower water current velocities and higher turbidity. Four major habitat types were identified within the marina canals: (I) artificial Reno mattress (wire baskets filled with rocks); (II) Codium tenue beds; (III) mixed vegetation on sediment; and (IV) barren canal floor. Seahorse densities within the marina were significantly higher compared to densities found historically within the estuary. Highest seahorse densities were specifically found within the artificial Reno mattress structures and within the western section of the marina. Seahorse density varied spatially and temporally and the type of habitat was an important predictor for seahorse occurrence. An experimental investigation found that H. capensis chooses artificial Reno mattress habitat over Zostera capensis when given a choice. GoPro cameras were used successfully to investigate daytime seahorse behaviour within the Reno mattress habitat. Seahorses were more active during the morning, spent most of their time (> 80 %) feeding, and morning courting behaviour for this species were confirmed. However, during the summer holiday period (mid-December to mid-January) few seahorses were observed on camera, which suggests that the increase in motor boat activity and the related increase in noise had a negative effect on H. capensis feeding and courting behaviour. The marina development, and in particular the Reno mattresses, created a new habitat for this endangered species within the Knysna estuary. In addition to the protection and restoration of natural habitats in which H. capensis is found, the conservation potential of artificial structures such as Reno mattresses should be realised.
- Full Text:
- Date Issued: 2018
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